SECTION 7
DESIGN & MANUFACTURING
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ASME District F - Early Career Technical Conference Proceedings
ASME District F - Early Career Technical Conference, ASME District F – ECTC 2013
November 2 – 3, 2013 - Birmingham, Alabama USA
INVESTIGATION INTO THE BENEFITS OF USING ASME BPVC SECTION VIII
DIVISION 2 IN LIEU OF DIVISION 1 FOR PRESSURE VESSEL DESIGN
James William Becker
Burns & McDonnell
Kansas City, Missouri, USA
ABSTRACT
ASME Boiler and Pressure Vessel Code Section VIII
Division 1 [1] is one of the most commonly used pressure
vessel codes in the world. The Division 1 rules were originally
written before the age of computers; they were intended to be
solved by simple hand calculations. This simplification led to
rules with a high safety margin and a conservative technical
basis. In 2007, ASME published a completely rewritten edition
of ASME BPVC Section VIII Division 2 [2], intended to lower
the safety margin by introducing more complex, technically
accurate pressure vessel design rules, and make the Code more
cost-competitive in an international market.
The Division 2 Code saves the user money on materials
with the use of higher allowable stresses and more accurate
design formulas. However, in order to justify the increase in
allowable stress, Division 2 mandates additional NDE and a
Professional Engineer’s stamp, which raise the vessel price. At
a certain thickness, the material savings outweigh the additional
cost, and Division 2 becomes cost-effective. Six years after
publication of the new Division 2, the industry has yet to
identify the thickness at which the transition from Division 1 to
Division 2 becomes cost-competitive. Division 2 is still most
commonly used only for very high pressure, high thickness
applications. This investigation compares Division 2 to
Division 1 to determine a reasonable set of design conditions
by which Division 2 will yield a more cost-effective pressure
vessel, even on some lower pressure applications.
NOMENCLATURE
= weld consumable cross section area
ASME = American Society of Mechanical Engineers
BPVC = Boiler and Pressure Vessel Code
= corrosion allowance
= vessel diameter
= joint efficiency
°F
= degree Fahrenheit
FEA
= finite element analysis
ksi
= 1,000 x psi
MDR = manufacturer’s data report
MT
= magnetic particle testing
NDE
= non-destructive examination
= design pressure
ASME District F - ECTC 2013 Proceedings - Vol. 12
psi
PE
RT
∆
UT
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
pounds per square inch
Professional Engineer
vessel radius
radiographic testing
allowable stress
safety factor on tensile strength
safety factor on yield strength
minimum required thickness
Division 1 calculated minimum thickness
Division 2 calculated minimum thickness
change in thickness due to Division 2
design temperature
allowable tensile stress
minimum tensile strength
ultrasonic testing
minimum cost effective weight
allowable yield stress
minimum yield strength at design temperature
BACKGROUND
Pressure vessels, boilers and other pressurized equipment
can contain an abundance of energy and can be dangerous
should one fail. Prior to pressure vessel and boiler safety laws,
boiler explosions claimed thousands of lives. The single worst
maritime disaster in the history of the United States occurred in
1865 when the boiler on the steamboat Sultana exploded,
killing more than 1,600 of the 2,300 Union prisoners of war on
board. [3] The Sultana explosion was more deadly than the
sinking of the Titanic in 1912. At the beginning of the 20th
century there were over 1,200 deaths caused by more than
1,600 boiler explosions in the United States. [4] In 1905, at the
climax of the boiler explosions, the R.B. Grover & Company
Shoe Factory’s boiler exploded, killing 58 and injuring 150 in
Brockton, Massachusetts. [5] The Commonwealth of
Massachusetts, along with the American Boiler Manufactures
Association, persuaded the American Society of Mechanical
Engineers to start work on a safety code for the construction
and inspection of boilers. [6] This first boiler code was
published in 1914, and an updated edition is still used today,
published as ASME Boiler and Pressure Vessel Code Section I.
After the first boiler code was published, ASME published
the first pressure vessel code in 1925, still updated and
published today as ASME BPVC Section VIII Division 1. Since
225
its inception in the early 20th century, Section VIII Division 1
has contained simple pressure vessel calculations that can
quickly and easily be solved by hand. For simplicity,
conservative assumptions form the technical basis of Division
1; therefore, Division 1 also contains a relatively high factor of
safety. In 1975, ASME BPVC Section VIII Division 2 was first
published as a more accurate, less conservative, pressure vessel
code, with a slightly lower factor of safety. [4]
INTRODUCTION
By the mid-1990s, pressure vessel technology and research
had advanced to a point where neither Division 1 nor Division
2 incorporated the latest research or technological
advancements. Computers and the advent of FEA allowed
engineers to study pressure vessel behavior more in depth and
obtain complex, rigorous results quickly. Division 1 was always
intended to house simple pressure vessel rules that, while
conservative, could be solved easily by hand. The advancement
in pressure vessel technology and computation speed provided
the opportunity for more rigorous and accurate calculations to
be included in the Code; however, since Division 1 was one of
the most commonly used pressure vessel codes in the world, the
decision was made to leave Division 1 as-is, a “simple”
pressure vessel code that the industry could continue to
implement without major change. In 1998, the ASME Boiler
and Pressure Vessel Standards Committee commissioned a
project to rewrite Division 2 that would update the Code with
the latest technology and lower the safety margin to make it
more cost-competitive in an international market. [7]
The new, completely rewritten Division 2 was published by
ASME in 2007, only nine years after it was commissioned. The
current Division 2 is a better defined Code than Division 1 from
a technical viewpoint, with more accurate and rigorous
formulas, a lower factor of safety on tensile strength, and a
more user friendly structure. [7] In general, the lower factor of
safety on tensile strength in Division 2 leads to higher
allowable stress values and, therefore, a reduced cost for the
pressure-retaining materials of construction. Alternately,
Division 2 mandates a Professional Engineer’s stamp and
requires an increase in non-destructive examination that among
other factors contribute as cost adders compared to Division 1.
[2] Due to general uncertainty surrounding the relatively new
Division 2, as well as the conflicting cost implications of higher
allowable stresses versus increased NDE, no clear guideline
exists for when a Division 2 pressure vessel might become
cost-effective over a Division 1 design. This investigation
attempts to analyze the cost implications resulting from
different allowable stress values in the two divisions, as well as
the variable and fixed cost adders for Division 2 as seen by the
vessel fabricator, to propose a set of parameters over which
Division 2 might become the more cost-effective pressure
vessel code. The focus of this investigation is on carbon steel,
ASME material specification SA-516-70 [8], as this is one of
the more commonly used materials in the fabrication of
pressure vessels. Other material specifications may yield
different results, and the decision to use Division 2 is typically
ASME District F - ECTC 2013 Proceedings - Vol. 12
much easier to determine with high cost, high chrome-type
materials. As in any investigation with a focus on cost, factors
such as market fluctuations, labor agreements and material
surcharges can greatly influence the results.
ALLOWABLE STRESS AND MINIMUM THICKNESS
Division 2 is a more accurate and technically complex
Code, therefore the safety factor on tensile strength is reduced
and the allowable stress for each type of material is generally
higher than Division 1. Before the relative thicknesses of a
pressure vessel built to either Division 1 or Division 2 can be
compared, first the calculated allowable stress from each
Division must be understood. ASME BPVC Section II Part D
Tables 1A and 1B list the Division 1 allowable stress values for
each material specification at varying temperatures. [9] Section
II Part D Tables 5A and 5B list the allowable stress values for
Division 2. [9] These allowable stress values are calculated by
applying safety factors to both the minimum tensile strength
and the minimum yield strength and setting the lower of these
two values as the maximum allowable stress at each
temperature, as shown in equations 1 through 3. Table 1
indicates the different safety factors for Division 1 and Division
2, which lead to the different allowable stress values in each
Division.
=
(1)
=
(2)
= minimum
(3)
Table 1 Safety Factors [10]
Division 1
3.5
1.5
Division 2
2.4
1.5
As indicated in Section II Part D Table Y-1, the minimum
yield strength of SA-516-70 decreases as the design
temperature increases [9]. In both Division 1 and Division 2,
, is 1.5. [10] In other
the safety factor on the yield strength,
words, the maximum allowable yield stress, , is two-thirds of
the yield strength, , at the design temperature in both
,
Divisions. The Division 2 safety factor on tensile strength,
is 69% of the Division 1 safety factor, leading to a Division 2
allowable tensile stress, , approximately 1.45 times greater
than Division 1 at room temperature. As indicated in Equation
3, the allowable stress of the material from Section II Part D is
the minimum of the allowable yield stress and allowable tensile
stress. [9]
At a given temperature, a material for which the allowable
yield stress is lower than the allowable tensile stress is
226
considered governed by yield strength and a material for which
the allowable tensile stress is lower than the allowable yield
stress is considered governed by tensile strength. Division 2
provides no general material savings benefit for a yield strength
governed material, such as stainless steel. The greatest benefit
from Division 2 is realized for a material that is tensile
governed up to a relatively high temperature. Figure 1 indicates
the allowable stress values for SA-516-70 for both Division 1
and Division 2 at a variety of temperatures. [9]
Allowable Stress (psi)
30,000
Division 1
Division 2
25,000
20,000
15,000
could be quoted at much different prices from different vessel
fabricators. This investigation studies the pricing of pressure
vessels on a percentage basis, because total cost becomes
arbitrary as the input parameters are changed. Regardless of the
total magnitude of cost savings, Division 2 does become costeffective when the percent difference between the Division 1
and Division 2 costs is zero. In general, as the size and
thickness of a pressure vessel increase, so does the total amount
saved by switching to Division 2; however, the percent
difference in cost may be the same for either large or small
vessels at the same design temperature, regardless of size and
thickness. For small pressure vessels, a 5% cost savings may
only be a few thousand dollars, whereas for very large pressure
vessels, a 5% savings may amount to hundreds of thousands of
dollars. In either case, Division 2 would be more cost-effective,
and the decision to use Division 2 should not be limited by the
total dollar amount saved but by the percentage reduction in the
cost of the pressure vessel when using Division 2. This
investigation analyzes the four cases, provided by Curtis Kelly
Inc. shown in Table 2. [12] The thickness shown is the Division
1 minimum required thickness.
10,000
0
100
200 300 400 500 600 700
Design Temperature (°F)
Figure 1 Allowable Stress vs. Design Temperature for SA-51670 [9]
Below 600°F, carbon steel is governed by tensile strength,
and above 600°F carbon steel is governed by yield strength.
Because the higher allowable stress values in Division 2 result
in the majority of the cost savings, this study focuses on design
temperatures significantly less than 600°F where the margin on
allowable stress between Division 1 and Division 2 is most
prominent. [11] When SA-516-70 becomes governed by yield
strength, the allowable stress values between the two Divisions
are identical and there is no financial incentive to choose
Division 2 over Division 1.
The minimum required thickness of the pressure vessel is
inversely proportional to the allowable stress for the material of
construction. Equations 4 and 5 are the minimum thickness
equations for Division 1 and Division 2, respectively. [1] [2]
While these equations appear vastly different at first glance,
they supply very similar results when using the same input
parameters and allowable stress values.
=
=
− 0.6
2
+
−1 +
(4)
(5)
DIVISION 2 VS. DIVISION 1 PRICING
The pricing of a pressure vessel is dependent on so many
factors that, when competitively bid, the same pressure vessel
ASME District F - ECTC 2013 Proceedings - Vol. 12
Table 2 Division 2 Pricing Data [12]
800
Case
Diam
Length
Thickness
1
2
3
4
10’
10’
8’
11’
80’
60’
64’
100’
3.75”
2.75”
3”
1.5”
% Weight
Savings
21%
18%
12%
6%
% Cost
Savings
12%
10%
6%
2%
These four cases cover a variety of pressure vessel sizes,
thicknesses and volumes. All four of these cases would
probably be considered “large” relative to an average-sized
pressure vessel. Traditionally, Division 2 has only been used for
large, thick pressure vessels, because until the Division 2 Code
was rewritten in 2007, there wasn’t much cost advantage for
anything on the average side of the vessel spectrum. [10] In
Figure 1, the Division 2 allowable stresses were plotted with
respect to the design temperature. The design temperature and
corresponding allowable stress for the four test cases are shown
in Table 3. As the design temperature decreases, the allowable
stress increases and therefore the benefit for using Division 2 in
lieu of Division 1 increases. Figure 2 shows the percent cost
savings as a function of the percent weight savings for each
vessel. In Figure 3, the percent cost and percent weight savings
for each of the four test cases is plotted against the allowable
stress. . Both Figure 2 and 3 apply for “large” pressure vessels,
which are defined as vessels whose material cost savings
greatly outweigh the fixed cost of a calculated Division 2
design, stamped by a PE. It should be noted that Figure 2 was
used in this investigation to determine the maximum costeffective design temperature; however, other factors, such as
market demand, supplier availability and volatile labor costs,
can affect the total cost of both Division 1 and Division 2
pressure vessels.
227
Percent Cost Savings
14
12
10
8
6
4
2
0
0
5
10
15
20
25
Percent Weight Savings
Figure 2 Percent Cost Savings vs. Percent Weight Savings
Percent Savings
25
Cost
20
Weight
15
10
5
0
21
22
23
24
25
26
Allowable Stress (ksi)
Figure 3 Percent Savings vs. Allowable Stress [12] [9]
Table 3 Division 2 Allowable Stress Values [9]
Case 1
Case 2
Case 3
Case 4
Design
100 °F
150 °F
250 °F
350 °F
Temp
Allowable
25.3ksi
23.8 ksi
22.8 ksi
22.1 ksi
Stress
RESULTS
In contrast to the material savings realized by switching to
Division 2 from Division 1, there are also cost adders
associated with Division 2, most notably the cost of a PE’s
design and certification, and the cost of additional NDE. In
order to use Division 2, a PE must prepare the MDR, which is a
fixed cost regardless of the pressure vessel size. In this
investigation, the cost of a PE to prepare and stamp the MDR is
estimated at $2,000 per pressure vessel. [12] There are also
variable costs associated with Division 2, which manifest in
additional NDE requirements. In most cases, Division 2
requires RT, UT and MT, in addition to the minimum
requirements in Division 1.
ASME District F - ECTC 2013 Proceedings - Vol. 12
By extrapolating the cost curve in Figure 3, the allowable
stress when the percent cost savings becomes zero is
approximately 21,800 psi. When the Division 2 allowable stress
is less than 21,800 psi, there is no cost benefit for using
Division 2 in lieu of Division 1, regardless of the pressure
vessel size. At 21,800 psi, there remains a 1,800 psi gap, or an
approximate 3% weight difference, between Division 1 and
Division 2 in which material savings can be realized; however,
the fixed and variable costs of a PE stamp and additional NDE
offset the material savings at that low of an allowable stress.
Even for large pressure vessels, when a 3% weight offset alone
could result in tens of thousands of dollars in material savings,
the amount of additional NDE increases as the vessel size
increases, and the additional savings are absorbed by the
increasing variable cost. As shown in Figure 1, the design
temperature associated with a Division 2 allowable stress of
21,800 psi is 380°F. [9] For conservatism, the highest design
temperature for which Division 2 is cost-effective is
approximated as 350°F, which results in an allowable stress of
22,100 psi. As shown in Figures 2 and 3, for large pressure
vessels, an allowable stress of 22,100 psi will result in an
approximate 6% weight savings and 2% cost savings by
switching to Division 2.
As the size and weight of a pressure vessel decreases, so
does the material required for fabrication, and therefore the
amount of money saved by switching to Division 2 also
decreases. The correlations shown in Figure 3 are only
applicable for relatively large pressure vessels, where the
material cost savings greatly outweigh the fixed cost. This same
curve would not be linear for small pressure vessels, because as
a vessel decreases in size the fixed cost of the PE stamp begins
to overwhelm the cost savings from using less material. For
example, the $2,000 PE stamp does not have much effect on a
large pressure vessel from which tens of thousands of dollars
can be saved by switching to Division 2; however, for a small
pressure vessel, where only a few thousand dollars in material
savings exist, a $2,000 PE stamp takes away a relatively large
percentage of the savings. Carbon steel built to the ASME SA516-70N material specification [9] typically costs
approximately 75 cents per pound. [12] SA-516-70N is one of
the most common pressure vessel material specifications for
thicknesses greater than 1 inch, which is the case for most
Division 2 pressure vessels. [13]
The minimum weight of a pressure vessel for which
Division 2 becomes cost-effective is not as simple as dividing
the fixed cost, $2,000, by 75 cents per pound and then dividing
by the minimum percent weight savings. There are cost
advantages from reducing the material thickness beyond
material savings alone, most notably weld labor time. As shown
in Figure 4, as the thickness of a pressure vessel decreases by
∆ , the amount of consumable material used decreases on the
order of ∆ . This also reduces the amount of weld time on the
order of ∆ .
228
design. As the vessel design moves further above and away
from the curve in Figure 5, the cost savings will approach the
values shown in Figure 2. The curve in Figure 5 represents an
estimated cost savings of 0%, or the break-even point for
Division 2.
Figure 4 Weld Consumable Cross-Section Area
In reality, the fabricated savings of a Division 2 pressure
vessel per pound is greater than the 75 cent material cost, partly
due to the reduction in consumable volume and weld labor
indicated in Figure 4. For large vessels, the fabricated cost of a
pressure vessel is close to $3 per pound, and for small pressure
vessels it can escalate to $6-7 per pound. This investigation
assumes the additional cost for Division 2 NDE requirements
will offset the savings realized from reduced weld consumables
and weld labor hours. To be conservative, a fabricated cost, or
savings, of 75 cents per pound is assumed on the marginal
weight difference between the two Divisions. Also, because the
weight savings percentages shown in Figures 2 and 3 apply to
“large” pressure vessels, as the size of a pressure vessel
decreases, the weight savings percentage by switching to
Division 2 also decreases. A small vessel will have a slightly
lower weight savings percentage at each allowable stress than
indicated in Figure 3. In Equation 6, the minimum weight of a
pressure vessel with a design temperature of 350 F is calculated
with a “small vessel” margin of 2 in order to get into a less
volatile weight savings percentage range. This “small vessel”
margin helps move the curve away from the fixed cost of a PE
stamp. At the maximum cost-effective design temperature of
350°F, the minimum fabricated weight at which Division 2
becomes cost effective is 88,622 pounds, as outlined in
Equation 6.
=
(2)($2,000)
= 88,622
$0.75
(6%)
,
(6)
A pressure vessel large enough or thick enough to weigh
90,000 pounds at a design temperature of 350°F will be
approximately the same cost as either a Division 1 or a Division
2 design. Figure 2 shows a 2% cost benefit at 350°F; however,
90,000 pounds is a small enough pressure vessel at 350°F that
the fixed cost begins to govern and the savings is offset. For
each design temperature within the recommended Division 2
range (-20 to 350°F) there is a minimum required fabricated
weight in order to overcome the fixed cost, as shown in Figure
5. To develop Figure 5, Equation 6 was used and the respective
weight savings percentage for each allowable stress was
substituted into the denominator, shown as 6% in Equation 6
for 350°F. A pressure vessel that falls in the range above the
curve in Figure 5 will be more cost-effective as a Division 2
ASME District F - ECTC 2013 Proceedings - Vol. 12
Figure 5 Division 2 Cost-Effective Range
= 1.1341 − 271.67 + 42842
100
350
= 27016
− 20
100 (7)
The polynomial curve fit equation shown on Figure 5 and
in Equation 7 represents the minimum weight at each design
temperature for which Division 2 may become cost-effective.
The price of any pressure vessel is highly dependent on more
factors than were analyzed in this study, including market
supply, demand, labor rates and material surcharges. The design
temperature is bounded on the low side by -20°F, and bounded
on the high side by 350°F, which is the highest temperature at
which Division 2 remains reasonably cost-effective. If a
pressure vessel design falls within the blue shaded region of
Figure 5 or above, a Division 2 design should be considered. At
design conditions close to the curve, the cost savings may be
minimal or nonexistent due to market fluctuations; however, the
equation shown in Figure 5, Equation 7, provides an easily
identifiable set of design conditions under which Division 2
should be explored for cost-effectiveness.
OTHER DIVISION 2 BENEFITS
The possibility of a lower pressure vessel cost is not the
only benefit of using the new Division 2 for pressure vessel
design. Unlike Division 1, all of the rules in Division 2 have a
strong technical basis. Some of the Division 1 rules were
written to be very conservative, and the technical basis has been
forgotten over the years. These rules, such as the reinforcement
area replacement or the 2-inch nozzle exclusion for
reinforcement continue to be published in Division 1 because
they have been around for almost 100 years. Although there
isn’t a technical basis for these rules, they have been proved
through experience to work, so they continue to be accepted.
Division 2 was written with a strong technical basis for all of
229
the rules, which is one of the reasons the safety factor on tensile
strength is reduced.
Another major benefit from using Division 2 is weight
savings. Some vessel applications, such as offshore oil rigs,
demand the lightest construction possible. In these situations,
Division 2 may be used even when it isn’t necessarily costeffective. Shell thickness is not the only avenue for weight
savings in Division 2. The opening reinforcement produce
smaller reinforcement pads, the external pressure calculations
require fewer stiffener rings, and the elliptical head formulas
generally calculate thinner than Division 1, even at the same
allowable stress values.
Division 2, partly because the line at which it becomes costeffective has been unclear. This investigation — and Equation 7
in particular — serve to better define the boundary at which
Division 2 should be analyzed, with hope that industry will
become more comfortable and confident using Division 2.
CONCLUSION
In response to numerous deaths resulting from boiler
explosions around the turn of the century, ASME published the
first pressure vessel safety code in 1925. This first code was
intended to be simple and conservative to enable the solving of
vessel equations by hand. It continues today in the form of
Division 1. In 2007, ASME published a completely rewritten,
more technically accurate code, known as Division 2. Division
2 is more technically sound, the equations are more rigorous,
and therefore the safety factor is lower than Division 1. The
lower safety factor in Division 2 leads to additional cost
savings by reducing the minimum required thickness of a
pressure vessel. There are also additional costs associated with
Division 2, most notably the cost of a PE stamp and additional
NDE requirements. As the size of a pressure vessel increases,
the material savings begin to outweigh the additional costs.
At higher design temperatures, the Division 2 allowable
stress values decrease and the cost advantage of Division 2 is
diminished. Figure 3 and Table 2 show that the maximum
design temperature at which Division 2 is still cost-effective is
350°F. At a constant design temperature, even as the size of the
pressure vessel increases, the cost savings percentage does not
increase. The variable cost of additional NDE as the size of the
pressure vessel increases is offset by additional variable
savings. The main driving factor that causes Division 2 to be
cost-effective is the raw material savings. Even with the
advantageous Division 2 allowable stress values, a small
pressure vessel may not be cost-effective due to the fixed cost
of a PE stamp. Figure 5 and Equation 7 show the minimum
required fabricated vessel weight in order for Division 2 to be
cost-effective at each design temperature. The cost of a pressure
vessel is dependent on many more parameters than outlined in
this investigation, such as market supply, demand, and labor
rates. Vessel design conditions that fall above the curve
bounded by -20°F, 350°F and Equation 7 should be explored
for Division 2; however, due to the many parameters that affect
the price of a pressure vessel, pressure vessels that fall above
but near the curve should be evaluated for both Division 1 and
Division 2.
Cost benefits are not the only advantage of using the new
ASME BPVC Section VIII Division 2. It is more accurate, has
a stronger technical basis and employs better design principles
than Division 1. Today’s market is slow to adapt to the new
REFERENCES
ASME District F - ECTC 2013 Proceedings - Vol. 12
ACKNOWLEDGMENT
This investigation would not have been possible without
the strong technical and commercial support from Curtis Kelly
Inc. Many thanks are extended to the management team at
Curtis Kelly for their continued support and advice. Curtis
Kelly Inc. is a vessel fabricator in the Houston area.
[1] ASME Boiler and Pressure Vessel Committee on Pressure
Vessels, ASME Boiler and Pressure Vessel Code: Section VIII
Division 1, New York: ASME, 2011.
[2] ASME Boiler and Pressure Vessel Committee on Pressure
Vessels, ASME Boiler and Pressure Vessel Code: Section VIII
Division 2, New York: ASME, 2011.
[3] S. Ambrose, "Remembering Sultana," National Geographic,
1
May
2001.
[Online].
Available:
http://news.nationalgeographic.com/news/2001/05/0501_river5.
html. [Accessed 14 July 2013].
[4] K. Mokhtarian, Participant Workbook - ASME Boiler and
Pressure Vessel Code: Section VIII Division 1, Las Vegas,
Nevada: ASME Training & Development, 2012.
[5] D.H. Cook, "The R.B. Grover & Company Shoe Factory
Boiler Explosion," USGen Web, Brockton, Massachusetts,
2002.
[Online].
Available:
http://plymouthcolony.net/brockton/boiler.html. [Accessed 14
July 2013].
[6] S.F. Harrison, "Development, Relationship of the ASME
Boiler-and-Pressure Vessel Committee and the National Board
of Boiler and Pressure Vessel Inspectors," in International
Compressor Engineering Conference, Paper 73, 1972.
[7] David A. Osage et al, "Section VIII: Division 2 - Alternative
Rules," in Companion Guide to the ASME Boiler & Pressure
Vessel Code, New York, ASME, 2009, p. Chapter 22.
[8] ASME Boiler and Pressure Vessel Committee on Materials,
ASME Boiler & Pressure Vessel Code: Section II Part A, New
York: ASME, 2011.
[9] ASME Boiler and Pressure Vessel Committee on Materials,
ASME Boiler & Pressure Vessel Code: Section II Part D, New
York: ASME, 2011.
[10] K. T. Lau, "A Brief Discussion on ASME Section VIII
Divisions 1 and 2 and the New Division 3," in 3rd Annual
Pressure Industry Conference, Banff, 2000.
[11] The B&PV Taskforce on the new ASME Section VIII
Division 2 Code, "A Proposal for the Use of the New (2007)
ASME Section VIII Division 2 Code in Alberta," 2007.
[12] C. K. Kyle Kotzebue, Interviewee, Division 2 Cost
Comparison. [Interview]. 31 December 2012.
[13] E. F. Megyesy, Pressure Vessel Handbook, Oklahoma City:
PV Publishing Inc., 2008.
230
ASME District F - Early Career Technical Conference Proceedings
ASME District F - Early Career Technical Conference, ASME District F – ECTC 2013
November 2 – 3, 2013 - Birmingham, Alabama USA
STRAIN SENSING PROPERTY OF GLASS MICROBALLOONS/CNF
NANOCOMPOSITE EMBEDDED IN SYNTACTIC FOAM
Ephraim F. Zegeye, Ali Kadkhoda Ghamsari
NextGen Composite CREST Center
Mechanical Engineering Department
Southern University and A & M College
Baton Rouge, LA , USA
ABSTRACT
The strain sensing property of a nanocomposite fabricated
from a free standing structure consisting of glass microballoons
(GMB) and carbon nanofibers (CNF) (GMB-CNF
nanocomposite) has been reported [1]. The strain measurement
was performed by attaching the nanocomposite on the surface
of a tensile specimen. In this study, the GMB-CNF
nanocomposite is embedded in compression test sample
fabricated from syntactic foams to measure internal strain. The
electrical resistance of the nanocomposite when subjected to a
compressive strain is investigated. It is found that the average
change in normalized electrical resistance decreases at lower
strain. After about 6.5 % of strain, a sharp increase in the
average change in normalized resistance is observed. The
possible reasons for these behaviors are explained. Results
provide significant information in the use of the nanocomposite
for determining the onset of microballoons fracture or
indicating the initiation of a crack in syntactic foam structures.
INTRODUCTION
The application of composite materials in aircraft,
spacecraft, marine vessels, and automobile structures has been
increasing in recent years. A structural health monitoring
(SHM) system with the ability to detect and monitor the
changes in the structure of composites used for these
applications is very important in order to improve the reliability
of using composite materials, and to reduce the risks associated
with their failure. SHM basically involves embedding a sensing
element (or a set of sensing elements) into a composite
structure for continuous remote monitoring of damage in the
structure. SHM systems are advantageous over traditional
inspection systems, as they can reduce down-time, eliminate
component tear-down inspections, and potentially prevent
failure during operation [2]. Due to their excellent
piezoresistive properties, carbon nanotubes (CNTs) and carbon
nanofibers (CNFs) may enable a new generation of sensors in
nano or micro scales and can be used to develop novel SHM
systems. Consequently, several studies have been carried out to
investigate the use of CNTs and CNFs for SHM applications [37].
ASME District F - ECTC 2013 Proceedings - Vol. 12
Eyassu Woldesenbet
Mechanical Engineering Department
Louisiana State University
Baton Rouge, LA , USA
In order to fabricate sensors for macro-strain
measurements, the CNTs/CNFs were either stacked to form a
thin film (buckypaper) or dispersed in polymeric materials [712]. In buckypaper and CNT/CNF polymer nanocomposite
sensors, the CNTs/CNFs may have direct physical contact or
may be separated with small gaps so that the electrons tunnel
(hop) across the gaps [13]. Application of load or deformation
on the nanocomposites can increase/decrease the gap between
the conductive fillers. This gap variation affects the electrical
properties of the nanocomposite system. Accordingly,
buckypapers and CNT/CNF polymer nanocomposites have
been investigated for macro-strain measurement and damage
sensing applications [12, 14]. One of the benefits of CNT/CNF
based strain sensors over metallic alloy foil based sensors is
their use as embedded sensors for multidirectional sensing at
multiple locations [15].
Embedded sensors could help in identifying internal
defects and determining the extent and propagation rate of
cracks in the hosting composite. They could also provide
information for maintenance and replacement of the structural
members before catastrophic failure. However, sensing
elements that are embedded and used for SHM systems need to
have closely similar properties with the hosting composite. This
is because embedded sensors may create possible structural
strength degradation of the host material and can be considered
as defects if they have mechanical properties that are different
than the host composite [16].
Recently, the strain sensing properties of a nanocomposite
fabricated from a paper like structure consisting of glass
microballoons (GMBs) and CNFs (GMB-CNF structure) was
investigated [1]. The strain measurement was performed by
attaching the nanocomposite on the surface of tensile
specimens. In order to fabricate the nanocomposite (GMB-CNF
nanocomposite), epoxy was infiltrated into the GMB-CNF
structure. Due to the presence of the glass microballoons in the
GMB-CNF nanocomposite, the nanocomposite has been
reported to have similar properties with syntactic foams, which
are also fabricated by dispersing microballoons in polymeric
matrices [17]. Hence it is anticipated that embedding the GMBCNF nanocomposite in a syntactic foam structure would not
affect the mechanical properties of the hosting structure.
231
Therefore, in this paper, the potential use of the nanocomposite
as embedded sensor in syntactic foams was investigated.
order to maintain the wires on the sample surface and isolate
the electrical connections from the crosshead during the test.
EXPERIMENTAL
Fabrication of GMB-CNF nanocomposite sensors
Multilayered GMB-CNF nanocomposite sensors were
fabricated using a vacuum infiltration technique. Four GMBCNF structures were laid-up, one over the other, before the
infiltration process (Fig. 1a and b). A high purity bisphenol A
diglycidylether epoxy resin (D.E.R. 332) and an aliphatic
polyamine hardener (D.E.H. 24), both from DOW Chemical
Company, USA, were mixed at a volume ratio of 87:13.
Sufficient resin system was then poured around the region
represented by the green rectangle in Fig. 1a. After sealing the
vacuum bag, the resin system was infiltrated into the GMBCNF structures by applying a vacuum. The resin system was
sucked along the direction indicated in Fig. 1a. In order to
avoid warping of the nanocomposite, the structures were kept
between Teflon sheet covered plates. The bag was maintained
in vacuum for about 12 hours. The nanocomposites were then
removed from the bag and cured for 12 hours at room
temperature and post cured for 3 hours at 100 oC.
Fabrication of compression test samples
The multilayer sensor was embedded in samples prepared
for compression testing. The test samples fabricated were
syntactic foams containing 50 % by volume of S22 glass
microballoons. The matrix of the samples was composed of the
same epoxy resin system that was used to fabricate the GMBCNF nanocomposites. The dimension of the compression test
samples was 24.83 × 24.83 × 12.61 mm. In order to embed the
sensors, 5 mm wide strip of nanocomposite was first placed
across the length, in the middle of a mold prepared from Dow
corning 3120 RTV silicone rubber (Dow Corning Corporation,
USA) (Fig. 2a). A slurry prepared for compression test samples
was then poured into the molds and cured for 24 hours at room
temperature and post-cured for 3 hours at 100 οC. The
fabricated sensor-embedded syntactic foam samples are shown
in Fig. 2b. Compression test samples that did not contain
sensors were also fabricated using the same materials and
curing procedure.
Installation of electrical connections to the sensors
The procedures used for making electrical connections to
the embedded sensors are shown in Fig. 3. The exposed edges
of the sensor were first painted with PELCO conductive Silver
187 paste. Single stranded tinned-copper wires (MicroMeasurements, USA) were affixed at conductive silver painted
ends of the sensor. In order to avoid wire pulling during the
test, M-bond 200 (Micro-Measurements, USA) was used to
attach the wires at the locations indicated by the arrows as
shown in Fig. 3a. Conductive sliver paste was then applied on
top of the wire to minimize contact resistance as shown in Fig.
3b. Finally, a plastic tape was wrapped around the sample in
ASME District F - ECTC 2013 Proceedings - Vol. 12
(a)
Sucking
direction
(b)
Figure 1. Vaccum infiltration process; (a) figure showing
how the process was performed, (b) a magnified image of
the rectangular region in part (a).
Testing
Compression tests were conducted on the samples using
QTEST 150 universal testing equipment. The tests were
performed at the crosshead speed of 0.5 mm/min. Mechanical
strain (ε) developed along the thickness of the sample was
measured as the crosshead displacement normalized by the
gauge length (or platen separation) of the test specimen. The
samples that did not contain sensors were tested up to 60 % of
strain. Whereas, samples with the sensors were compressed up
to 15 % of strain while measuring the electrical resistance of
the sensors embedded in the samples. In order to record the
resistance, FLUKE 83 digital millimeter (Fluke Corporation,
USA) was used. Both the resistance and mechanical strain were
captured during the test and the change in resistance (∆R)
corresponding to the strain was obtained from the video. Fig. 4
shows the test setup and the orientation in which electrical
measurements were performed with respect to the applied strain
direction.
232
(a)
electron beam. These white regions are resin dominated thin
layers on the surface that hinder the transport of electrons to the
conductive fillers in the nanocomposite. When these regions
were carefully removed with 600 grit paper, the nanocomposite
was shown to have consistent electrical property. The
resistances of the nanocomposite sensors were measured using
FLUKE 83 digital multimeter. The average no load resistance
of the nanocomposite sensors (Ro) was 10.87 ± 2.29 KΩ.
(b)
Figure 2. (a) Strip of sensors placed in a silicone rubber
mold, (b) sensor-embedded syntactic foam sample.
(a)
(b)
Figure 3. Steps for making electrical connections; (a)
painting silver paste and bonding the wire, (b) applying
silver paste on the wire and wrapping with a plastic tape.
Applied strain
direction
Sensor
�� µm
Figure 5. SEM micrograph of an edge of a GMB-CNF
nanocomposite.
25
20
∆R/Ro (%)
15
Test
sample
10
5
0
Crosshead
Multimeter
-5
0
5
10
15
20
Strain (%)
Fixed support
Figure 4. Test setup showing strain direction and the
orientation of sensor in the compression test sample.
RESULTS AND DISCUSSION
Nanocomposite Characterization
A SEM micrograph of an edge of a fractured GMB-CNF
nanocomposite sensor is shown in Fig. 5. The average thickness
of the fabricate nanocomposite was 0.65 ± 0.16 mm. In Fig. 5,
white thin regions (see the arrows in the figure) are observed on
the opposite surfaces of the nanocomposite. Such an artifact on
an SEM image is attributed to a charging effect that appears
when a non-conductive material is scanned by high voltage
ASME District F - ECTC 2013 Proceedings - Vol. 12
Figure 6. Normalized change in resistance versus strain
plot.
Electromechanical Property and Sensitivity
Fig. 6 presents the average normalized change in resistance
(∆R/Ro) plot of the embedded sensors with respect to the
applied strain. As it can be observed in figure, the normalized
change in resistance versus strain curve has two distinct
regions. For the strains less than 6.5 %, the average normalized
change in resistance is observed to reduce with strain. This can
be explained by the decrease in the tunnel junction gap width
between the CNFs upon the compressive strain. A decrease in
the tunnel junction gap width between the CNFs reduces the
contact resistance between adjacent CNFs. Consequently, the
233
ASME District F - ECTC 2013 Proceedings - Vol. 12
could have a strong potential to be used as embedded sensor for
investigating cracks in a syntactic foam structure. Being
seamlessly integrated with the hosting structural member, it
could provide information for maintenance or replacement of
the structural members before failure. Consequently, the GMBCNF nanocomposite sensors developed in this study could have
significant importance for in-situ health monitoring
applications in syntactic foam structures.
(a)
Strain (%)
0
∆R/Ro (%)
0
2
4
6
8
∆R/Ro = -0.48ɛ - 0.66
R² = 0.909
-1
-2
-3
-4
30
Strain (%)
(b)
∆R/Ro = 2.6ɛ - 22.91
R² = 0.941
20
∆R/Ro (%)
volume resistance of the sensors reduces. After about 7.0 %
strain, the resistance of the embedded sensors is observed to
increase with strain. In Fig. 7, the average normalized change in
resistances for the two regions are plotted separately. The data
can be fitted with straight lines having coefficient of
determination (R2) values greater than 0.90. For the strains less
than 6.5 %, the sensors have a gauge factor of about -0.48. The
gauge factor is negative since the resistance decreases with
applied strain in this region. Negative gauge factor is not
unique to GMB-CNF nanocomposite sensors. Previous works
have also reported negative gauge factors for CNT based
sensors [18]. Commercial semiconductor strain sensors with ntype doping material have also a negative gauge factor [19].
The gauge factor of the sensors embedded in samples for
strains 7.0 – 15 % is 2.6.
The behavior seen at strain about 6.5 % is credited to the
evolution of damage in the sensor as a result of microballoons
crushing in the sensor. The effect of such damage caused loss of
contact and widening of the adjacent CNFs and significantly
increased the contact resistance after this strain. It is important
to note that both the nanocomposites and the syntactic foam
samples were fabricated using the same type of microballoons.
Hence, application of 6.5 % strain could also fracture
microballoons in the syntactic foam samples. However, from
Fig. 8, yielding of the syntactic foam samples when subjected
to a compressive stress appears at about 12 % of strain. This
yielding is also attributed to the crushing of microballoons in
the syntactic foam sample. It can be noted that strain at which
change in slope of the normalized resistance versus strain plots
of the sensor (6.5 %) is much less than the yield strain of the
hosting syntactic foam sample (12 %). This is because the
electrical resistance changes are more sensitive to
microballoons crushing than the yield stress. In the
nanocomposite sensors, increase in the electrical resistance can
be instigated by the fracture of only few microballoons and
keep increasing as more microballoons are crushed. On the
other hand, in the syntactic foam samples, although
microballoons start crushing at lower strain, yielding may not
be seen until a certain number of microballoons are fractured.
The fact that the electrical resistance of the sensor is sensitive
to the fracture of a few microballoons would be advantageous,
as the embedded sensor could be used to identify structural
defects or cracks prior to failure.
In order to identify cracks or defects prior to failure, series
studies at different external conditions could be done to
investigate the electrical resistance response of the embedded
sensor due to the applied strain. From the study, a relationship
between the applied strain and the generated electrical
resistance could be obtained for structural member with known
microstructural property. Once this is determined, any peculiar
electrical resistance generated in the sensor could be attributed
to cracks or defects in the structural member. The extent and
propagation rate of cracks in the structure could also be
determined based on the measured electrical resistance. Since
the electrical resistance of the GMB-CNF nanocomposite
sensor is sensitive for the fracture of few microballoons, it
10
0
6
9
12
15
18
-10
Figure 7. Normalized change in resistance versus strain
plots with best fitting curves, (a) for 0 – 6.5 % strain, (b)
for 7.0 – 15.0 % strain.
REFERENCES
[1] Zegeye, E., Ghamsari, A., Jin, Y., and Woldesenbet, E.,
2013, "The strain sensing property of carbon
nanofiber/glass microballoon epoxy nanocomposite,"
Smart Mater. Struct., 22 (2013), pp. 065010.
[2] Kessler, S. S.,2002, "Piezoelectric-based in-situ damage
detection of composite materials for structural health
monitoring systems," PhD thesis, Massachusetts Institute
of Technology, Cambridge, MA.
[3] Zhao, Q., Wood, J. R., and Wagner, H. D., 2001, "Stress
fields around defects and fibers in a polymer using carbon
nanotubes as sensors," Appl. Phys. Lett., 78 (12), pp.
1748-1750.
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120
Stress (Mpa)
100
80
60
40
20
0
0
10
20
30 40 50
Strain (%)
60
70
Figure 8. Typical stress-strain plot of syntactic foam
samples.
[4] Wood, J. R., Zhao, Q., Frogley, M. D., Meurs, E. R., Prins,
A. D., Peijs, T., Dunstan, D. J., and Wagner, H. D., 2000,
"Carbon nanotubes:From molecular to macroscopic
sensors," Phys. Rev. B, 62 (11), pp. 7571-7575.
[5] Zhang, W., Suhr, J., and Koratkar, N., 2006, "Carbon
Nanotube/Polycarbonate Composites as Multifunctional
Strain Sensors " J. Nanosci. Nanotech, 6 (4), pp. 960-964.
[6] Rein, M. D., Breuer, O., and Wagner, H. D., 2011,
"Sensors and sensitivity: Carbon nanotube buckypaper
films as strain sensing devices," Compos. Sci. Technol.,
71 (3), pp. 373-381.
[7] Su, C. C., Chang, N. K., Wang, B. R., and Chang, S. H.,
2012, "Two Dimensional Carbon Nanotube Based Strain
Sensor," Sensors Actuat. A-Phys., 176 (0), pp. 124–129.
[8] Li, X., Levy, C., and Elaadil, L., 2008, "Multiwalled
carbon nanotube film for strain sensing," Nanotech., 19
(4), pp. 045501.
[9] Kang, I., Schulz, M. J., Kim, J. H., Shanov, V., and Shi,
D., 2006, "A carbon nanotube strain sensor for structural
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[10] Loh, K. J., Kim, J., Lynch, J. P., Kam, N. W. S., and
Kotov, N. A., 2007, "Multifunctional layer-by-layer
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438.
[11] Hu, N., Karube, Y., Arai, M., Watanabe, T., Yan, C., Li, Y.,
Liu, Y., and Fukunaga, H., 2010, "Investigation on
sensitivity of a polymer/carbon nanotube composite strain
sensor," Carbon, 48 (3), pp. 680-687.
[12] Hu, N., Karube, Y., Yan, C., Masuda, Z., and Fukunaga,
H., 2008, "Tunneling effect in a polymer/carbon nanotube
nanocomposite strain sensor," Acta. Mater., 56 (13), pp.
2929–2936.
[13] Zhang, W., Dehghani-Sanij, A. A., and Blackburn, R. S.,
2007, "Carbon based conductive polymer composites " J.
Mater. Sci., 42 (10), pp. 3408–3418.
ASME District F - ECTC 2013 Proceedings - Vol. 12
[14] Park, J., Kim, D., Kim, S., Kim, P., Yoon, D., and
DeVries, K., 2007, "Inherent sensing and interfacial
evaluation of carbon nanofiber and nanotube/epoxy
composites using electrical resistance measurement and
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pp. 847–861.
[15] Pham, G. T., Park, Y. B., Liang, Z., Zhang, C., and Wang,
B., 2008, "Processing and modeling of conductive
thermoplastic/carbon nanotube films for strain sensing,"
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[16] Proper, A., Zhang, W., Bartolucci, S., Oberai, A. A., and
Koratkar, N., 2009, "In-Situ Detection of Impact Damage
in Composites Using Carbon Nanotube Sensor Networks,"
Nanosci. Nanotechnol. Lett., 1 (1), pp. 3-7.
[17] Zegeye, E., Pennington, K., Jin, Y., Abera, A., and
Woldesenbet, E., 2012, "Dynamic Mechanical Analysis of
Conductive Foam Films Fabricated From Free Standing
Glass Microballoon-CNF Structure," ECTC Proceedings
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LA, pp. 1-6.
[18] Grow, R. J., Wang, Q., Cao, J., Wang, D., and Dai, H.,
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Mechanical Sensors, Artech House, Inc., Norwood,
MA,Chap. 5.
235
ASME District F - Early Career Technical Conference Proceedings
ASME District F - Early Career Technical Conference, ASME District F – ECTC 2013
November 2 – 3, 2013 - Birmingham, Alabama USA
COGNITIVE EVIDENCE IN ENGINEERING DESIGN DOCUMENTATION
Sophoria Westmoreland
United States Naval Academy
Annapolis, Maryland, USA
ABSTRACT
In order to process knowledge during the engineering
design process certain cognitive tools are necessary. At a
surface level those tools are creativity, scientific, and process
knowledge. While some progress has been made recently in
exploring cognitive processes, reading between the lines, and
thinking about design thinking – much more work is yet to be
done in this expansive field.
The purpose of this paper is to present a method of
extracting cognitive evidence from engineering design
documentations-specifically capstone design journals from
undergraduate students-and the results from its application.
Attempting to reveal cognitive processes is a complex science,
as such methods and tools should be created to explore the
unknown realms of the engineer’s mind. Using different types
of engineering design documentation is one path to retrieving
cognitive information.
Capstone design journals are examined as part of a larger
study that partially fulfilled the requirements for the author’s
dissertation research. A Cognitive Coding Scheme was created
by the author to explore evidence of design thinking and
behavior. This paper seeks to identify patterns of behavior
found in a capstone design team using hand written design
journals.
INTRODUCTION
A wide array of engineering design studies on cognition
exist in literature that combine research from the engineering
and psychology domains [1-5]. This present work effort is a
part of a larger work which includes the authors’ dissertation
[6]. The goal of this work is to contribute to the understanding
of cognitive processes during engineering design.
The mixture of art and engineering is what design is all
about. Designers use what they know to create some “new”
artifact. Executing this skill requires the use of cognitive
activities that are the evidence of the process of a designers
thinking. Some examples of cognitive activities are analogical
thinking, questioning, and inquiry. The mind’s arrangement of
this information is used to energize the art of innovation.
ASME District F - ECTC 2013 Proceedings - Vol. 12
Linda Schmidt
University of Maryland – College Park
College Park, Maryland, USA
This study proposes a method for understanding those
cognitive methods and seeing how they are organized. The
results would support good design education and training
needed to produce quality engineers prepared to lead a global
society. According to one source promoting innovative thinking
can “drive future economic growth and continue to lead on the
global stage” [7].
Many things can be revealed by studying written
documentation. Thomas Jefferson’s letters, Albert Einstein’s
paper, and Leonardo da Vinci’s mirror writings are examples of
famous written documentation [8-10]. Visualizing the design
process can result in many forms of design documentation such
as design journals, final reports, presentations, notes, and
sketches. Using cognitive research techniques (i.e. a cognitive
coding scheme on students’ engineering design journals), this
study seeks to understand what happens in the mind during the
design process.
LITERATURE REVIEW: COGNITIVE PSYCHOLOGY
AND ENGINEERING DESIGN
According to Cross et al. design activities are among those
occurring at the highest possible human cognitive levels [11].
One definition of design from the engineer’s perspective is to
pull together something new or arrange existing things in a new
way to satisfy a recognized need of society [12]. A general
understanding of cognition and engineering design activities is
needed in the creation of a cognitive coding scheme.
Cognition
Research begins with starting with what we know. William
James says it clearly “the first fact is that thinking of some sort
goes on” [13]. Cognitive processes are a part of everyday life,
from the smallest tasks to the larger ones. Studying cognitive
processes reveals how people organize and use knowledge in
daily life and work situations. Many researchers have
successfully studied the mysteries of the mind, knowledge, and
thought processes [14-16]. These studies increase our
understanding of human thinking processes and maximize
usefulness of the tools created to promote learning methods and
learning metacognitive strategies. Common researcher
questions are, what is knowledge and where does it come from?
236
According to Alexander et al., knowledge is “an individual’s
personal stock of information, skills, experiences, beliefs, and
memories”[17].
It is important to note the interdisciplinary nature of the
fields of study that examine cognition. They include cognitive
science, cognitive psychology, and educational psychology.
These fields all have their foundation in psychology. Studies in
these fields can be complementary and are all focused on the
central theme of understanding the mind. Studying the mind
creates a path to understanding human behaviors.
Cognition in Design
The original way to learn about cognitive activities in
design was to study designer behavior. Studying designer
behavior can be done using a variety of methods such as verbal
protocol analysis [18], design prompts [19], direct observation
[20], coding design journal content [21, 22], and interviewing
designers [23]. Different methodologies were used in each
study based, at least partially, on the anticipated results. It is
useful to note that studying design does not solely belong to the
field of engineering. Of the studies mentioned above some are
from architecture, industrial design, and other engineering
disciplines that have design as a central tenant. Some of these
studies have focused on designer behavior and in the process
uncovered cognitive findings. The studies detailed below focus
on students’ design activities because they are the subjects used
in this current paper.
ABET requires students in engineering undergraduate
programs to take a course in capstone design towards the end of
their course studies[24]. Each engineering discipline is different
in how they present the course, but the goal is generally for
students (working in a team) to create an original design
product using the culmination of engineering subject
knowledge acquired during the previous years of study. This
course provides the perfect opportunity to study student design
behavior in a natural design setting. A deeper understanding of
team behavior is often also a result of these types of studies.
Grenier et al. analyzed design journal sketches and
notations of capstone design students to learn “how students are
learning and practicing design” [25]. Twelve student design
journals were used from a senior design course. The results
showed that positive links exist between sketching and
cognitive processes. Two cognitive operators were displayed in
the student sketches, generation and exploration; both are
critical for solving complex problems. Grenier’s study presents
promise for learning more about the cognitive processes of
engineering design students.
Another important study was done on team communication
by Stempfle [26]. The goal was to examine the thinking
processes of student design teams. Teams of mechanical
engineering design students were recorded (4-6 students per
team) designing a sun planetarium for six consecutive hours. A
coding system was created to analyze the team communication
in order to create a model of design team activity. Four basic
operations of design thinking were identified: generation,
exploration, comparison, and selection.
ASME District F - ECTC 2013 Proceedings - Vol. 12
A study by Shah fully integrated traditional engineering
based design with traditional psychology based labs [27-29].
The goal was to study the cognitive processes that happen
during the engineering design process through an ideation
experiment to create a cognitive model of the design process.
Models were pulled from cognitive psychology related to
information processing such as human problem solving, mental
imagery, and visual thinking. The resulting preliminary
cognitive model included six ideation components: provocative
stimuli, suspended judgment, flexible representation, frame of
reference shifting, incubation, and example exposure. The
design teams in the study were exposed to the six ideation
components, and the results were recorded. The study
concluded that introducing ideation components has a positive
effect on divergent thinking during idea generation. This
created a basis for linking cognitive psychology with
engineering design studies through a cross-disciplinary study
using terms from both fields.
Sobek implemented design journals for a senior capstone
design course at Montana State University in order to find the
correlation between thoughts and written documentation during
the design process[21, 22]. The students kept a design journal
and received a portion of their course grade for the contents.
Each member of the design team was required to keep a journal
documenting the process. A coding scheme was created and
applied to the design journals to find out what design process
variables affect the design outcome. It was concluded that
design process models do not suit novice designers as well as
they do expert designers. Sobek noted the importance of the
potential cognitive benefits students gain from using a design
journal.
This current study utilizes written documentation to create
a cognitive coding scheme for engineering design
documentation.
A COGNITIVE CODING SCHEME
A cognitive coding scheme is defined as a system
developed for the classification of design documentation
content for quantitative analysis. Many researchers have
created cognitive coding schemes for application to other types
of design documentation such as verbal protocol analysis and
design interviews [20, 30, 31]. A good cognitive coding scheme
is one suitable for extracting evidence to imply cognitive
activities from design documentation. Application of such a
coding scheme can benefit design researchers progress towards
developing design competency tools and help clarify the
differences between novice and professional design engineers.
The development of the coding scheme began with a
detailed literature search (both cognitive psychology and
engineering design) using an iterative process. A series of 4
design journal studies were conducted with students in senior
design courses at the University of Maryland- College Park to
apply and refine the coding scheme. The cognitive codes were
validated against similar coding schemes found in literature
[20, 32, 33]. We have confidence that our final version of the
coding scheme, as shown in Table 1, is useful for revealing the
237
cognitive activities that occur during the design process. The
individual cognitive codes are grouped into larger classes.
Table 1: Cognitive Coding Scheme Class and Related
Codes
Cognitive Codes
INFORMATION SEEKING AND NOTING
Search (1), References (2), Questioning (3), Price
Quotes (4), and Definitions (5)
PROBLEM UNDERSTANDING
Customer Requirements (6), Problem Statement
Clarification (7), Criteria Lists (8), and Engineering
Characteristics (9)
IDEA GENERATION
Project Ideas(10), Analogical Reasoning (11), and
Material Options (12)
ANALYSIS
Estimate (13), Assumptions (14), Calculations (15),
Testing Procedures (16), Variables (17), and
Explanations (18)
DECISIONS
Recommendations (19), Conclusions (20), and Design
Changes (21)
PROJECT MANAGEMENT
To Do Lists (22), Meeting Notes (23), Task Assignment
(24), Inventory (25), Task Completion (26), Project
Milestones (27), and Field Trip Notes (28)
REFLECTION
Personal Notes(29), Design Process Notes (30),
Revelations (31), Mistakes (32), and Cross References
(33)
OTHER
Illegible Entries (34), Designer Signature (35), and No
Evidence of Cognitive Activity (36)
METHODOLOGY: STUDENT DESIGN TEAMS STUDY
A design journal study was conducted in fall 2011 with a
team of students in Mechanical Engineering at the University of
Maryland. This study is one out of a larger group of similar
studies done for a larger work. The team presented in this paper
consisted of 5 members with only N=4 participating in the
study. The students were given a design journal at the
beginning of the course to capture the complete design process
experienced by each student (1 semester lasted 15 weeks). A
one page “Design Journal Guidelines” gave a brief overview of
the journaling process in the event that a team member was not
familiar with the process. A short presentation was given on the
first day of class introducing the study and giving details about
the journaling process and expectations. The students
participating in this study were volunteers but were
compensated for their time with gift cards to the local college
bookstore.
A journal is defined for this study as a bound notebook
with lined pages used as a permanent record of what happened
ASME District F - ECTC 2013 Proceedings - Vol. 12
during the design process. A sample design journal page is
shown in the Appendix as Figure 6.
The journals were reviewed weekly, and feedback was
given to the study participants. Dates of entries in the journal
are important for correlating them with course due dates and
team meeting times. Hence when the journals were checked
this was a priority and feedback was given to the students if
dates were missing from entries. The content of the journals
was left entirely up to the students in order to give them control
over how they utilize their journals to benefit them in the
design course. Students who participated in this study
completed an exit survey through e-mail.
Coding the Design Journals
Coding the design journals produces a design string
(Figure 1) which is an order of numbers that relate to
components in the coding process. The cognitive code
presented previously represents only one component in the
design string. For breadth and depth this study all captures
other important information from the students design journals.
Figure 1: Elements of the design string assigned to
each segment of a coded journal page
The design session includes all the written records found to
have occurred on a single date or during a single period of
concentration. The design segment is a section of work within
each session in the journal that is focused on the same design
thought, which can be described by a single cognitive code. The
design phases are conceptual design, embodiment design,
detailed design, and re-design in accordance with the course
text [12]. The cognitive codes are from Table 1. The concept
code indicated the concept (if any) to which the segment is
referring. The visual types classify a visual representation
found in the design segment such as sketches and free body
diagrams. A sample coded example is shown in Figure 2.
The main coder is the author of this paper and a trained
undergraduate assistant also coded a representative set of the
design journals in order to perform an inter-coder reliability
study. The Cohen’s Kappa was calculated at 64.7% at the
cognitive code level, which is a good strength of agreement.
RESULTS AND DISCUSSION
The students reported on in this study are all from the same
capstone design team. The team was made up of five students,
and four out of five of the students participated in the study.
Their project was to design a dynamic coring system, which is
a drill bit stand, over a 15 week period. Detailed information
about the students on this team is given below in Table 2.
238
members. A deeper understanding of the benefits of using a
design journal for a project like this would likely even out these
Conceptual Design
Detail Design
100%
Embodiment
Redesign
75%
50%
Figure 2: Coding Example
25%
Table 2: Detailed Team Information
0%
ID
Number of
Journal
Pages
Recorded
Design
Sessions
Design
Segments
Activity
Density
3
5
6
7
32
28
20
20
20
11
20
9
69
123
101
119
3.45
11.18
5.05
13.22
Variation between the number of design sessions and the
number of design segments is expected. Activity density is
defined as a measure of the amount of journaling activity
within a design session. A lower activity density indicates that
students were writing about a specific topic or had a narrower
focus during some of their design sessions. A higher activity
density indicates a wider range of cognitive activities each time
they sat for a design session.
The design phase coding results are shown in Figure 3. The
students in this study found the design journals to be most
useful during the conceptual design and embodiment design
phases of the design process. These stages involve activities
such as gathering information, conceptualization, concept
development, product architecture, and parametric design.
The cognitive coding results from the study are shown in
Table 3.
For spacing purposes cognitive codes that were not found
in this team’s design journals were omitted. These codes are
Definition, Estimates, Analogical Reasoning, Assumptions,
Variables, Meeting Notes, Task Assignments, Inventory, Field
Trip Notes, Task Completion, Design Changes, Mistakes, and
Designer Signature. These results present a good representation
of the cognitive codes across the students design journals.
Student 3 produced the lowest number of different types of
cognitive activities with only 9 (out of a possible 36). Student 7
produced the highest number of different types of cognitive
activities with 15 (out of a possible 36).
All 4 students in this study used their design journals for
Project Ideas more than anything else. It is clear that the journal
provided a convenient space to document their creativity and
share ideas for solutions to the problem amongst the group
ASME District F - ECTC 2013 Proceedings - Vol. 12
Student 3 Student 5 Student 6 Student 7
Figure 3: Design Phase Results
Table 3: Cognitive Code Results as a Percent
Students
Cognitive Code
3
5
6
7
Search
0%
0%
0%
0.84%
References
0%
13.82%
0%
0%
Questioning
4.35%
2.44% 3.88%
0%
Price Quotes
0%
0%
0%
0.84%
Customer
1.45%
3.25% 2.91% 3.36%
Requirements
PS Clarification
1.45%
1.63%
0%
2.52%
Criteria List
0%
0.81%
0%
7.56%
Engineering
0%
4.88%
0%
0%
Characteristics
Project Ideas
65.2%
29.2% 61.1% 53.78%
Material Options
7.25%
0%
1.94%
0%
Calculations
1.45%
2.44% 0.97% 0.84%
Testing
5.80%
9.76% 5.83% 1.68%
Procedures
Explanations
0%
5.69% 5.83%
0%
Recommendations
0%
0%
4.85%
0%
Conclusions
0%
6.50% 5.83% 5.04%
To Do Lists
10.14% 7.32% 0.97% 1.68%
Project
0%
0%
0%
0.84%
Milestones
Personal Notes
0%
0%
2.91% 1.68%
Design
Process
0%
0%
0.97%
0%
Notes
Revelations
0%
0%
0.97%
0%
Cross References
0%
0%
0%
2.52%
Illegible Entries
0%
1.63%
0%
2.52%
None
2.90%
8.94% 0.97% 14.29%
results. It would have been expected to see Engineering
Characteristics appear more in these design journals because of
the course requirement to make a House of Quality that
239
includes an engineering characteristics room. Only 1 student
had engineering characteristics entries in their design journal.
Figure 4: Cognitive Codes by Class
Figure 4 is suggestive of the behavior of the students, in
that they mostly used the journals the same. With the exception
of student 5, they all show a peak during idea generation. The
cognitive codes corresponding to each of the classes can be
found in Table 1. Understanding time constraints for the design
project, other course requirements, and the voluntary nature of
this study these are definitely promising results.
1
1
100%
100%
80%
8
8
2
60%
40%
40%
2
20%
20%
7
80%
60%
3
0%
6
7
4
3
0%
6
4
5
Student 5
1
100%
8
1
80%
80%
2
8
60%
40%
2
REFERENCES
40%
20%
7
60%
FUTURE WORK
An important next step is combining the cognitive coding
scheme results with a design performance measure to
understand the relationship between “good” design and
cognitive activities. It would be essential to involve
professional design experts in this process to identify student
projects that are of high quality. Creating a design performance
measure can effectively codify innovation early in the design
process. This path will lead to an increased understanding of
innovative design thinking.
ACKNOWLEDGEMENT
This material is based in part on work done for the author’s
dissertation. The authors are grateful for the student volunteers,
coding assistants, and the Mechanical Engineering department
at the University of Maryland for their support and assistance
with this work.
5
Student 3
code classes found in Table 1. The conceptual design phase is
mirrored for 3 of the 4 students participating in this study.
Students’ use of visual representations in the design
journals is important for this work because visuals are tools
used for understanding, explaining, modeling, and creating
during the design process. All the visuals found in the 4
students design journals were sketches, which is not surprising.
Sketching in engineering design is vital to innovation and the
outpouring of ideas from the mind. Many of these sketched
ideas become the final design or at least a subsystem.
The comprehensive cognitive coding scheme presented
here is shown to be a prescriptive method for extracting
cognitive evidence from engineering design journals. The use
of the design string coding method allows for quantitative
analysis and the collection of a rich data set. One of the
benefits to having students journal in a non-prescriptive manner
is to be able to see the differences in their behavior.
This research reveals the patterns of journaling behavior in
different phases of the design process. The larger study
generated a large amount of data that will provide research
results into the future. Working with educational psychologist
these results can be used to create tools for teaching innovative
strategies in engineering design courses.
20%
3
0%
7
6
4
5
3
0%
6
4
5
Student 6
Student 7
Figure 5: Cognitive Codes during Conceptual Design
Taking a closer look at the students’ design journal
behavior during the conceptual design phase is shown in Figure
5. The numbers in the figure correspond with the cognitive
ASME District F - ECTC 2013 Proceedings - Vol. 12
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241
APPENDIX
Figure 6: Design Journal Page Example
ASME District F - ECTC 2013 Proceedings - Vol. 12
242
ASME District F - Early Career Technical Conference Proceedings
ASME District F - Early Career Technical Conference, ASME District F – ECTC 2013
November 2 – 3, 2013 - Birmingham, Alabama USA
THE MODELING AND DESIGN OF A SUSTAINABLE PNEUMATIC ENERGY
DRIVING AUTOMOBILE SYSTEM
Shaobiao Cai
Yongli Zhao
Georgia Southern University
Statesboro, GA, USA
St. Cloud State University, MN, U.S.A.
St. Cloud, MN, USA
ABSTRACT
Sustainable, clean, efficient energy has become a central
concern with growing interest among industries and academic
researchers. This paper presents the modeling and prototyping
of an air-powered automobile simulator for field study, using
clean pneumatic energy, a potential candidate for a new
generation of hybrid-vehicle technologies. The simulator was
designed to explore the applications of sustainable, alternative,
clean, efficient energy and to gain an in-depth understanding of
the engineering processes and methods of modeling such a
complex system. A power chain was designed to convert the
stored pneumatic energy into torque and deliver the power to a
driving wheel. A chassis was designed to meet the loading
conditions; it is made of recycled steel and aluminum. The
stability and effectiveness of the power transmission are
addressed in the prototype. It presents a great potential of new
technology development in the relevant areas of application.
INTRODUCTION
The car became the primary transportation tool in the
United States soon after its introduction. While enjoying the
convenience of it, concerns were raised as well among public.
Air pollution due to emission and energy consumption were
among the major issues and became even more serious
concerns due to the ramping up of gas prices and global
warming. According to World Almanac 211 [1] and WRI171
[2], a traditional car’s engine uses about 65 percent of the
energy from the fuel just to move all its parts such as the
pistons and cams, plus what is wasted generating excess heat.
The transmission uses 6 percent of the energy from the fuel, the
accessory load 2 percent, and idling losses come to about 11
percent, leaving only about 16 percent of the energy to actually
make the wheels turn. Saving energy and increasing energy
efficiency thus became very important. In addition to energy
efficiency, pollution became another major concern with regard
to automobiles. Experimental data show that a gallon of gas
ASME District F - ECTC 2013 Proceedings - Vol. 12
burned produces about 20 pounds of CO2. Relevant work in
engine development and automotive performance has been
studied by researchers such as [3, 4]. Hybrid vehicles using
electrical batteries and hydrogen or various types of fuel cells
have been widely studied [5–8]. The studies of applications
using solar power [9] and biodiesel fuel [10] are discussed to
some extent in the literature. The using of pneumatic air, one of
the most promising options to address energy efficiency
emissions, is of a great interest among many researchers.
Fundamental theories for analysis and modeling, such as
thermodynamics, flow mechanics, heat transfer, energy, and
energy efficiency can be found in literature [11–13]. The
concepts of various pneumatic hybrid engine technologies are
proposed and studied based on those theories. For instance, the
vehicle may run on petrol but would use its reservoir of
compressed air to boost the engine's power through braking
energy generated compressed air [14]. Other researchers
modeled various types of Hybrid engines, such as the
simulation of a pneumatic hybrid motorcycle (which represent
the potential application of pneumatic energy to small scale
transportation system) [15], and the modeling and optimization
of two and four-stroke hybrid pneumatic engines [16]. A
significant fuel consumption reduction may be achieved
through the combination of engine downsizing, pneumatic
hybridization, as well as strategic operation [17]. These works
presented some very interesting and encouraging results on
hybrid pneumatic engine modeling.
It has been very encouraging that many global industrial
companies have adopted industrial ecology and sustainability
thinking as part of their practices [18–21]. The use of an air
propulsive engine in a purely pneumatic powered car like
AirPod has been developed. Energy efficiency at about 39.3%
from tank to wheel was reported by MDI [22]. However,
skepticism exists among engineers and researchers. Short
running distance is still among the major challenges. The tankto-wheel energy efficiency is yet to be proven or further
improved with more robust field data.
243
The development of field models using pneumatic air with
the capability to address sustainable clean energy issues, energy
efficiency, and noise and vibration issues is highly in need. This
work presents the modeling, design, and prototype of a
pneumatic, air-powered automobile simulator for the field, an
important stage in new technology development to explore the
applications of sustainable clean energy and efficiency in
automobiles. It was designed to study the efficiency and the
method to increase running distance with integrated energy
regeneration functions (not done yet in the current work) using
such as gravitational potential. Pneumatic air is chosen as the
driven power source for the simulator to address the
environmentally friendly applications. The mechanisms
utilizing sustainable clean pneumatic energy, with the capability
of driving a total of a 300-lb. load, are discussed in detail. A
power chain was designed to convert the stored energy to
torque and deliver the power to the driving wheel. A chassis
was designed to meet the loading conditions. The system
consists of recycled steel and aluminum and other metals. The
stability and effectiveness of the power transmission were
addressed in the prototype. Various supporting mechanisms
were engineered. Preliminary field tests were conducted and the
effectiveness of the simulator verified.
DESIGN CONSIDERATION
The simulator is considered to carry a driver, thus a total of
a 300-lb load due to the weights used. The wheels are 20 inches
in diameter. The system is preferable to run at a steady speed of
10 mph with a capability for further expansion and
configuration. The specific component design concepts and
selections were determined by using the initial preferable
loading capacity. The project began with a collection of old
unused bicycle frames. These recycled metal frames were
carefully examined, dissected, selected, cut, and shaped into the
desirable size and shape for the project. Figure 1 shows
examples of the lab planning and fabrication.
The design parameters listed above were used to calculate
the torque needed to run the system. The torque further
determines the capacity of the air motor, the key part for
converting pneumatic energy to mechanical energy. The
configurations and technical specifications of the air motor
were used to specify the energy storage device and pressure
tank, which were needed to provide a range of steady airflow
and power. The steady airflow with desirable pressure is
achieved by using an air regulator with a high-calibration
pinpoint control mechanism. The compressed pneumatic air is
regulated down to the air motor. The motor, in turn, delivers
power through a gear-chain system to the driving wheel. These
devices, including the pressure air tank, regulator, air filter, air
motor, and gear-chain system, make up the power chain
mechanism of the air automobile simulator. A chassis was
designed to carry a rider, power chain system, wheels, and other
necessary accessories. Supporting mechanisms for the air tank,
the air motor, the air filter, and the lubrication system were
designed and fabricated. The power chain was installed and
secured using the supporting mechanisms. The manufacturing
ASME District F - ECTC 2013 Proceedings - Vol. 12
techniques are not the focus of this paper, the details of which
are largely available in the literature [23, 24], and thus are not
presented here. The design and modeling are presented in the
following sections.
Figure 1. Planning and fabrication of the air-powered
automobile simulator
MODELING AND DESIGN
The mechanism design was based on the mentioned
loading conditions and desirable speed. Four wheels were used;
however, only two wheels support the total load in driving. The
rear one (of the two supporting wheels) serves as the driving
wheel. The major considerations were to ensure better
manipulation and reduction of energy loss due to friction. The
other two wheels (on the side) of the four are used as “training
wheels” to maintain stability for safety purposes. These two
wheels won’t touch the ground while the vehicle is moving. All
of the four wheels are the same size, 20 inches or 1.67 feet in
diameter. The two “training wheels” are mounted one inch
higher (from the ground) than the others. Thus, they do not
support the weight while driving. A gear-chain system is used
to reduce direct impact (a major factor known to cause damage
and instability to the motor) to the air motor so that a smooth
power transmission can be achieved.
Loading Condition
It is assumed that the weight of the driver (Wd) and the
simulator (Wa) will be 150 lbs., respectively. The total weight
(W) is distributed between the two wheels (because only the
central two wheels touch the ground while driving). The
reaction forces from the ground to the front wheel and the rear
wheel are Rf and Rr, respectively. The loading conditions are
shown in Figure 2.
244
Figure 2. Schematic of the loading conditions of the
system
The conditions of the force and moment balance of the
system at equilibrium give
ΣF = Rr + Rf - W = 0
(1)
ΣM = Rf (L1 +L2) - WL1 + FdLg = 0
(2)
where L1 and L2 are the distances from the line of action of the
weight W to the supporting points of the rear wheel and front
wheel, respectively. Here, L1 is 11 inches and L2 is 16 inches. Lg
is the vertical distance from the mass center of the system to the
ground. Because the air-drag force is relatively small at 10
mph, this element may be neglected in the preliminary
calculation. Based on the loading conditions, one can readily
calculate the reaction forces to the front wheel and the rear
wheel, which are Rf = 129 lb and Rr = 171 lb, respectively.
Motor Rotational Speed ωm (rpm) Determination
To determine the motor rotational speed, let’s first consider
the simulator traveling at a linear velocity of V. To achieve the
velocity V, the shaft of the driving wheel needs to run at a
rotational speed of ωd, where the subscription d indicates the
driving wheel. The linear travel velocity and the rotational
speed ωd have a relationship as follows:
ωd = V/R
(3)
where R is the radius of the driving wheel. Because the
simulator is meant to run at a speed of 10 mph and all of the
wheels are the same size, 20 inches, the rotational speed ωd is
168 rpm. For the gear-chain system, the gear attached to the
driving wheel has eighteen teeth, and the gear attached to the
motor has forty-four teeth, the gear ratio (GR) is 2.44. The
rotational speed of the motor ωm thus can be determined with
m 
d
GR
(4)
For the application here, the rotational speed ωd is 69 rpm.
ASME District F - ECTC 2013 Proceedings - Vol. 12
Motor Torque and Horsepower Determination
For the system to work as expected, the motor torque needs
to be able to overcome the maximum friction torque while
rolling. To acquire the rolling friction force, a simple
experiment was conducted. A 25-lb. bike with the same size
tires was put on straight and level concrete ground with a 160lb. person on the bike. It is known that any slip can lead to a
significant increase in the coefficient of friction. It was pulled
as slowly and carefully as possible. It was found that it took a
force of six pounds to overcome the rolling resistance. Thus, a
rolling coefficient of friction µk can be calculated. It was 0.03
based on the test. This result will be used as the preliminary
assumption when rolling. With µk, the friction force fk can be
found as follows:
f k  k N
(5)
where N is the total normal load, here, the same as the weight.
The frictional torque Tf can be determined as follows:
Tf  f k r
(6)
For this application, the friction force is about 10 lbs., and
the friction torque is 100 lb./in. This indicates that the motor
needs to provide 100 lb./in. for the system to run at a constant
speed. With this information, the power needed can be
estimated.
P  T f m
(7)
For the simulator to move at 10 mph, the motor needs to be
at least 0.11 hp with an output rotational speed of 69 rpm.
However, this is the situation of rolling. To start the simulator,
higher power is needed because the static friction is higher than
the rolling one. The static coefficient of friction varies from 0.2
to 0.6 [25, 26, 27]. Based on these considerations, an air motor
with 0.75 hp capacity having a 20:1 gear reducer was chosen to
provide enough torque for practical operations and to allow
room for future expansion. It also allows for providing slightly
larger ranges of velocity and acceleration for field tests.
● Energy Storage and Regulating Principles
The work-rate output is achieved using the airflow through
the motor as shown in Figure 3.
Consider the air flowing in from the inlet of the motor and
flowing out from the outlet. The work output rate through the
shaft is W . The governing equation for the control volume
(CV) (the area indicated by the dash line) is as follows [10]:

V2



e

d
(
h

 2  gz)V  ndA  Q  W
t CV
CS
(8)
245
where e is a specific heat term, ρ is the air density, h is the
enthalpy of the air, p is the pressure, V is the airflow velocity, g
is the gravitational acceleration, z is the elevation from a given
reference, n indicates the surface normal of the cross section

area A the air passing through, Q is the net energy passing the
CV boundary through heat transfer, and “•” indicates the time
rate of the relevant property.
pressure p2 at 1 atm. The simulator is meant to run steadily for
about fifteen minutes at 10 mph. To satisfy the design criteria
and the boundary conditions, equation (10) is used to estimate
the total energy needed. Two standard, carbon-fiber pressure
tanks with a total capacity of 46 standard cubic feet (SCF) and
a maximum pressure level of 2216 psi are used. A two-stage
regulating mechanism is used to provide a better steady flow.
The pressure is regulated down to 100 psi. This constant
pressure is then regulated down to a desirable pressure level
controlled by a pinpoint controller. Energy consumption and
analysis will be discussed in the later sections.
MECHANISMS
The mechanism design and engineering include component
design, fabrication, and assembly. These involve the power
chain, chassis, and core components and their supporting
mechanisms.
Figure 3. Schematic of the control volume (CV) for airflow
energy analysis
In this model, it is assumed the airflow is steady. For
simplicity, the heat transfer across the boundary may be
neglected at this point. Because there are rigid guides at the
inlet and outlet of the motor, the air flowing in and out can be
considered perpendicular to the cross sections of the inlet and
outlet. The vertical elevation between the inlet and outlet is
only 4 inches; thus, the effect of gravitational potential energy
is negligible. Based on these assumptions, equation (8) is
reduced to the following:
 (u 
p V2
 ) V  ndA  W
 2
(9)
where u is the internal energy of the air. Equation (9) provides
an estimation of the available work output from the motor shaft.
Equation (9) is a dynamic equation. The total energy initially
stored in the pressure tank can be estimated using a static form
of this equation. To estimate it, we may consider the pressure
vessel is control volume, and initially, no air passes through the
boundary (V = 0, W = 0). The equation for the energy stored in
the pressure vessel can be written as follows:
CS
● Power Chain
The power chain is made up of two pressure tanks, two
regulators, an air filter and a lubrication system, an air motor, a
gear-chain system, and relevant adaptors and connectors. shows
The power chain arrangement is shown in Figure 4 below. The
compressed air from the air tank is regulated to provide reliable
air flow. The air flow is guided to pass through an air
filter/lubricator before input into the air motor for protection
purposes. The energy carried by the airflow is converted to
mechanical torque through the air motor. The output torque
from the motor is then transmitted through the gear-chain
system to the driving wheel of the simulator.
p
E   (u  ) d  mh

(10)
where E is the total energy at the thermal dynamic state defined
by room temperature (T), pressure level (P), and volume (  );
m is the total mass of the air stored in the tank; and h is the
enthalpy of the air at room temperature and designated
pressure. For room temperature operations, T1 = T2, and inlet
location 1 has a pressure at p1. The outlet location 2 has a
CV
ASME District F - ECTC 2013 Proceedings - Vol. 12
Figure 4. Power chain architecture
● Chassis and Major Supporting Mechanisms
The chassis is made out of recycled aluminum and steel
bars. It consists of a center triangle frame with two additional
triangle frames (steel tubes with a wall thickness of 0.125 in.)
welded to each side to stabilize the system and provide the
necessary strength. The simulator has a total of four wheels and
the center rear wheel is the driving wheel. The major
considerations are to achieve better manipulation, stability and
safety, and a reduction of energy loss due to friction.
246
The mount made to hold the pressure tank is made up of a
square bar with a 45o chamfer on the bottom. Another smaller
square bar with a 45o chamfer is welded to the first bar to create
an “L” shape. The two thin pieces of steel metal are welded to
the larger square bar and bent around the tank to form two
adjustable metal bands. A short piece of angle steel is welded to
the end of each band. Lastly, a hole is drilled through each
piece of angle iron so that the bands can be adjusted and bolted
tightly around the pressure tank to ensure the stability and
reliability as shown in Figure 5.
The motor mount consists of a small piece of sheet metal
(76.2″ × 104.3″) welded to a piece of channel steel (C80 type).
The channel steel is welded to the chassis frame. Five holes are
drilled in the sheet metal. The center hole is for the motor’s
drive shaft, and the other four smaller holes around the
perimeter are for bolting the motor to the bracket. Their
function is to keep the motor in the proper position to satisfy
the alignment of the driving gear (attached to the motor) and
the gear attached to the driving wheel, as shown in Figure 6.
The completed air automobile simulator is presented in Figure
1 in the center.
PRELIMINARY RESULTS AND DISCUSSIONS
The simulator was designed to use compressed air without
any other power sources (i.e., batteries). Currently, the air tank
is filled by an air compressor powered by a solar station
established on campus previously. This makes the system
sustainable and environmentally friendly. In addition, the power
chain system is designed to maximize the energy efficiency. A
multistage regulating system is integrated for accurate and easy
airflow control to achieve smooth field driving. An in-line
lubrication system is integrated to ensure durability and
reliability.
Field-driving tests were conducted on a straight, level
concrete road. Firsthand preliminary data were obtained. The
performance indicators, average pick-up speed and
acceleration, for a 164 feet (or 50 m) distance tested by the
same driver are shown in Figure 7 (a) and (b). Figure 7 (a)
shows the average speed as a function of time. Average speed is
used since the measurements were done manually. It does not
sacrifice accuracy (since the system run at low speed), and it
gives clearer and more straightforward pictures of the system
performance. The average speed used here is defined as the
average speed achieved in a cumulative period from 0 to t. The
tests show that the simulator can pick up speed very quickly,
and all of the rides are smooth. It takes about ten seconds to
reach a target speed of 10 mph. Figure 7 (b) shows the
acceleration as a function of time for the field test. The
acceleration is larger at the beginning. It decreases with time
after reaching a certain speed level. The acceleration is reduced
to zero after about ten to eleven seconds. The simulator runs at
a constant speed of 10 mph when the acceleration is zero. The
transition from the start to the constant driving speed of 10 mph
is smooth, as one can observe from the figure. This is consistent
with the driver’s experiences during the field tests.
Figure 5. Pressure tank supporting mechanism
Figure 7a. Average picking-up speed vs. time
Figure 6. Motor supporting mechanism
ASME District F - ECTC 2013 Proceedings - Vol. 12
247
its current stage. An energy regeneration mechanism using
gravity when running down a slope or hill has been designed
but is not installed yet. The system’s on boarding data
acquisition system will also be designed and integrated into the
system as well in the near future. With both the regeneration
function and onboarding data colleting system, the firsthand
field data, such as vibration, noise, and environmental impact,
can be obtained. Those data will be expected to lead to further
insights of the relevant applications. Also, the prototype will
serve as an important stage in the process of exploring the
applications of sustainable, alternative, clean, and efficient
energy. These will also help to gain an in-depth understanding
of the engineering processes and methodologies of modeling
complex systems.
Figure 7b. Average picking-up speed vs. time
There are many factors that may affect the speed and
acceleration performance, such as the loading conditions,
operational pressure level, and the airflow rate regulated
(amount of air regulated in a certain time period). The
smoothness of all the rides is believed to be the result of the
well-designed mechanisms. For example, the speed is
controlled by regulating the airflow with a high caliper pinpoint
control mechanism. This pinpoint control mechanism leads to
an even airflow across the whole power chain. Because the
motor has a theoretical maximum rotational speed of 3000 rpm
with a gear reduction ratio of 20:1, the simulator has a
theoretical maximum linear speed of 22 mph. Due to safety
considerations, the limit was not tested.
CONCLUSIONS AND FUTURE WORK
The combination of pneumatic energy and other available
types of energy has a great potential to be a successful
candidate in new generation of hybrid technology applications.
This paper presents the design, modeling, and prototyping of an
automobile simulator powered purely by clean pneumatic air
with goals to investigate energy efficiency and running
distance. The mechanisms to utilize the sustainable clean
energy air to drive a 300 lb load to run at a steady speed of 10
mph for ten to fifteen minutes with a maximum up to 22 mph
were discussed. Engineering design theories and scientific
calculations were implemented in the modeling. These theories
were also used to guide the technological design and fabrication
work. A power chain was designed to convert the stored energy
into mechanical torque to deliver the power to the driving
wheel. The chassis was designed to meet the loading conditions
and was fabricated of recycled metals, such as steel and
aluminum. The stability and the effectiveness of power
transmission were addressed. Preliminary field tests were
conducted.
In addition, the prototype provides a significant field
model to further investigate pneumatic air-related clean energy
technologies, energy efficiency, and environmental impact. It is
worthy to mention that the system is not a “hybrid” system at
ASME District F - ECTC 2013 Proceedings - Vol. 12
ACKNOWLEDGEMENT
The project was funded by the PSU common campus
research fund. Greg Kurtz, an undergraduate student
contributed to the manufacturing of the work.
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[6] Sher, H. A. and Addoweesh, K. E., 2012, “Power Storage
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[12] Munson,B. R., Yong, D. F., Okiishi, T. H. and Huebsch,
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"Modelling and optimizing two- and four-stroke hybrid
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Mechanical Engineers, Part D (Journal of Automobile
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"Dynamic programming for hybrid pneumatic vehicles," 2009
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[18] Zhou, Z., Chen, Z. and Li, Y., 2012, “The Adoption
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Sustainable Energy. 4, 031802.
[19] Allenby, B.R., 1999, Industrial Ecology: Policy
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[20] Tester, J. W., Drake, E. M., Driscoll, M. J., Golay, M. W.,
Peters, W. A., 2005, Sustainable Energy Choosing Among
Options. The MIT press, Cambridge, MA.
[21] Socolow, R., Andrews, C., Berkhout, F. and Thomas, V.,
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46 Issue 11, p30-35.
[23] Groover, M. P., 2010, Fundamentals of Modern
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ASME District F - ECTC 2013 Proceedings - Vol. 12
249
ASME District F - Early Career Technical Conference Proceedings
ASME District F - Early Career Technical Conference, ASME District F – ECTC 2013
November 2 – 3, 2013 - Birmingham, Alabama USA
DESIGN AND CONTROL OF A LEG PRESS TRAINING MACHINE FOR WHOLE
BODY VIBRATION
Adetayo C. Faminu and Yong Zhu
Department of Mechanical Engineering
Georgia Southern University
Statesboro, GA 30458
ABSTRACT
Whole body vibration is the use of vibrating mediums to
heal, strengthen, and/or increase the flexibility in various parts
of the body. A passive leg press device was designed to key
these features to parts specifically found in the leg. This study
was conducted by controlling a pneumatic bellows cylinder, in
fluctuating in its height fast and far enough to be at the required
frequency to be considered a useful whole body vibration table.
An xPC target based control system was implemented so that
the control logic can be easily programmed, parameters can be
easily adjusted and good real-time performance can be
achieved. Both simulation and experimental results
demonstrated that the bellows cylinder position control was
feasible. However, the motion frequency was far below what a
vibration table would normally require since the thrust force
provided by the bellows cylinder far exceeds the intended load.
In the future, this might be partially mitigated if the subject
were able to bend and press down, which would create a
downward force of 2-3 times of body weight.
INTRODUCTION
Whole body vibration is the use of vibrating mediums to
heal, strengthen, and/or increase the flexibility in various parts
of the body. Whole body vibration has been widely used in
training [1][2][3][4][5][7] and rehabilitation [6] research. There
are required frequencies and changes in height of the vibrating
table for it to be an efficient and effective tool. Various studies
have proven that this form of exercise and training can be very
beneficial as opposed to traditional ways of exercise such as
resistive training for example. The only downside is that there
is no cardio involved with passive leg press training in the form
of whole body vibration, so a subroutine to include cardio
would be needed in the exercise routine of the individual.
Below is a look into the various studies that have been done
with whole body vibration and passive leg press training.
Previous research indicates that vibration exercise may
generally help improve flexibility, jump height, muscle power
and range of motion. A passive leg press training machine was
designed by Liu et al. [1] using an electrical motor, which
provided periodic motions between 0.5 and 2.5 Hz. The study
ASME District F - ECTC 2013 Proceedings - Vol. 12
tried to show that passive high contraction velocity can increase
muscle power and speed. Peer et al. [2] studied that
biomechanical muscle vibration using a commercial whole
body vibration device appeared to have significant acute
benefits for improving flexibility in healthy adults with ankle or
hamstring injuries. Trans et al. [3] used whole body vibration
exercise to improve muscle strength for women with
osteoarthritis in the knee. Melnyk et al. [4] showed that whole
body vibration appeared to have a positive effect on knee joint
stability. Annino et al. [5] further demonstrated that whole body
vibration training may be an effective and safe training strategy
to improve the muscle power in high-level ballet students.
Vargas [6] showed that whole body vibration can be used as a
rehabilitation tool for patients recovering from Anterior
Cruciate Ligament (ACL) injuries. Van den Tillaar’s research
[7] also indicated that whole body vibration may help improve
range of motion of hamstrings.
Commercial whole body vibration devices usually operate
up to very high frequencies, e.g. 30 Hz with 10 mm amplitude.
This study will be conducted by trying to control an actuator,
more specifically a bellows cylinder, in fluctuating in its height
fast and far enough to be at the required frequency to be
considered a useful vibration table. The bellows actuator we
will be using is a Festo single-bellows cylinder, which
traditionally is used in passive or active suspensions for highfrequency vibration isolation [8]. To the best of our knowledge,
there is almost no research that has been done in terms of using
a pneumatic bellows cylinder as an active actuator for whole
body vibration. This study would try to bridge this gap and
explore the possibility and advantages of using a pneumatic
bellows cylinder to drive a whole body vibration device for
training or rehabilitation purposes.
The paper is organized as follows. First, the mechanical
design of the whole body vibration table will be presented.
Then, the real time control system will be presented. After that,
simulation and experimental results will be given to
demonstrate the feasibility and limitation of controlling the
pneumatic bellows cylinder. Conclusions are drawn at the end.
250
MECHANICAL DESIGN
A prototype design showing the basic setup for the passive
leg press trainer was created using SolidWorks. It consists of a
bellows cylinder with a bottom and top plate attached to it.
Both the bottom and top plates consist of four holes each that
allow the attachment of a mechanical connector. The top plate
has an extra fifth whole to allow for the pneumatic connection
to the bellows cylinder. Each hole in the plates consists of a
diameter that is greater than the connection to allow for
clearance space. From the bottom plate extend two poles that
have a bar in between each other connecting them together. The
bar acts a support for test subjects to hold on to in order to
assist in generating the downward force needed from their legs
to make the passive leg press training machine useful. Figure 1
shows the front and isometric views of the basic leg press
layout. The first design was created under the thought that the
bellows cylinder would need springs to help support any
downward force put on it; this can be seen in the four open
cylinders connected to the top of the bottom plate and the four
open cylinders connected to the bottom of the top plate. To
quickly test this proof-of-concept design, the bars were not
implemented in this study.
drilled and cut through. The pre-final prototype design with
plexiglass bottom and top plates is shown in Figure 2.
Figure 2: Pre-final prototype design with plexiglass
bottom and top plates
CONTROL DESIGN
Control technologies are applied in almost every field of
industry around the world. These control designs are made up
of models, simulations, implementations, and evaluations.
Systems can be large and complicated, but the use of real-time
control allows for control experiments to become simple. In our
control system design, Simulink is used as the graphical user
interface while the xPC Target supports I/O hardware via its
block diagrams that can be integrated to the Simulink models.
Real-time environments do an excellent job of bridging the gap
between simulation modeling and hardware controlling while
maintaining a good performance level.
Figure 1: Front view and isometric view of the prototype
design
Figure 3: Overall system design schematic diagram
In order to have a functional prototype, a bottom and top
plate were needed. The bottom plate assists in preventing the
bellows cylinder from tilt, while the top plate would act as a
platform for the placement of feet so test subjects can stand on
it. The plates are made out of plexiglass, a material that is
durable enough for testing the passive leg press training
machine. Plexiglass is easy to manufacture, as it can be easily
Simulink model real-time testing environments were
created by connecting a host computer, target computer and any
hardware that is undergoing the experimental tests together. The
advantage of PC usage is in its computing power, flexibility,
and expandability. The host computer runs the Simulink
models, xPC Target, and a C compiler. The host computer is
then linked to the target computer via an Ethernet cable. The
target computer is then connected to the hardware via a NI
ASME District F - ECTC 2013 Proceedings - Vol. 12
251
SCB-68A I/O board. The host computer is the medium used to
design and model in Simulink, the target computer runs the
Simulink model in real-time with the xPC Target, and then the
hardware, i.e. actuators, sensors and valves, are controlled by
the system. By creating a real-time control system, the
hardware is controlled using the model created in Simulink.
The overall real time control system schematic is shown in
Figure 3.
xPC Target implements the Simulink model on a target
computer for hardware simulation, real-time testing solutions,
rapid control prototyping, and any other real-time testing
applications. It allows for the hardware in testing to be
monitored and for the data to be logged along with parameter
tuning.
SIMULATION
Soon after we started to look at the force-stroke curves
(Figure 4) of the Festo pneumatic bellows cylinder EB-385115, we realized that the force provided by the pneumatic
bellows cylinder far exceeds our intended load.
 Ψ ( Ps , P) for Av ≥ 0
Ψ ( Pu , Pd ) = 
Ψ ( P, Patm ) for Av < 0
(3)
A common mass flow rate model used for compressible gas
flowing through a valve [9] is the following:
C1C f Pu



T
Ψ ( Pu , Pd ) = 
C 2 C f Pu Pd (1 / k )
P

( )
1 − ( d ) ( k −1) / k

Pu
Pu
T
if
Pd
≤ C r (choked)
Pu
otherwise (unchoked)
(4)
where C f is the discharge coefficient of the valve, k is the ratio
of specific heats, Cr is the pressure ratio that divides the flow
regimes into choked and unchoked flow and C1 and C2 are
constants defined as:
C1 =
k 2 ( k +1) /( k −1)
and C 2 =
(
)
R k +1
2k
R(k − 1)
(5)
According to the force-stroke curves shown in Figure 4, the
stroke is a function of the pressure P (gage pressure between
0 and 8 bar) and thrust force F :
H = f1 ( P, F )
(6)
Referring to the volume-stroke curve shown also in Figure 4,
we can represent bellows volume V as a function of stroke H
:
Figure 4: Force-stroke curves of the bellows cylinder [10].
A simulation study was first carried out to verify this. If
the pressures and volume of the bellows is P and V , the mass
 , the rate of change of pressure within the
flow rate is m
bellows can be expressed as:
RT
PV
P =
m −
V
V
The nonlinear relationship between the valve orifice area
(1)
Av
m can be represented as a function of
the upstream pressure Pu and downstream pressure Pd ,
and the mass flow rate
m = Avψ ( Pu , Pd )
(2)
where Ψ is the area normalized mass flow rate, which can be
written as:
ASME District F - ECTC 2013 Proceedings - Vol. 12
V = f2 (H )
(7)
Simulating Equations 1-7 while assuming quasi-static
condition: F = Mg , where Mg is the gravitational force of
the test subject. Since Mg is so small when compared to the
thrust forces from 1 to 8 bar in Figure 4, that it became very
challenging to control the stroke with the desired frequency and
amplitude.
A simple proportional controller was used to make the
bellows actuator track sine wave inputs. Two cases are shown
in Figures 5 and 6 with period T = 20 and 10 seconds. Note that
5 Volt input for the valve corresponds to its neutral position,
meaning the mass flow rate ideally should be zero at 5V control
voltage. Since the valve mass flow rate is limited, to keep up
with the command, the amplitude was set to be only 1 mm. It
appears in Figure 5 that the stroke position tracking is generally
acceptable. When the sine wave period is reduced to T =10 sec,
the valve becomes saturated for most of the time and the actual
output cannot keep up with the input command as shown in
252
Figure 6. For both tests shown in Figures 5 and 6, the supply
pressure was kept at 40 psi.
Simulation of below sinusoidal position tracking (T = 20 sec)
Position (mm)
171
command
actual
170
169
168
167
10
20
30
40
50
60
70
20
30
40
50
60
70
20
30
40
Time (sec)
50
60
70
Pressure (kPa)
250
200
150
10
(Festo SPTW-P25R-G14-VD-M12) is attached to the air
chamber in order to measure the pressure in the bellows
cylinder. The bellows cylinder has a maximum tolerance of 8
bars pressure. An OTE HY3003-3 Triple output DC power
supply producing a voltage of 24 volts was used to power the
system. A linear potentiometer (Midori LP-100F) with 100 mm
maximum travel is used to measure the displacement of the
pneumatic bellows cylinder. A proportional valve (Festo
MPYE-5-M5-010-B) controls the fluid flow. An xPC Target
based real time control system shown in Figure 7 is used to
compile the Simulink model into C language. The target
application is then downloaded from the host computer via a
LAN connection (Ethernet), and the application is then
programmatically controlled by running through the target
computer. The data produced from the hardware is then
transferred back to the host computer to be evaluated as logged
signal data.
Voltage (V)
10
5
0
10
Figure 5: Simulation results of bellows actuator sinusoidal
position tracking (T=20 sec)
Simulation of bellow sinusoidal position tracking (T =10 sec)
Position (mm)
170
169.5
169
168.5
168
10
15
20
25
30
35
40
Pressure (kPa)
250
Figure 7: Testing set up with the controls and basic
components
200
150
10
15
20
25
30
35
40
15
20
25
Time (sec)
30
35
40
Voltage (V)
10
5
0
10
Figure 6: Simulation results of bellows actuator sinusoidal
position tracking (T=10 sec)
EXPERIMENTAL RESULTS
A Festo single-bellows cylinder (Festo EB-385-115) with a
piston diameter of 385 mm and stroke 115 mm was used as the
actuator for the whole body vibration device. A pressure sensor
ASME District F - ECTC 2013 Proceedings - Vol. 12
A closer look at the final prototype design with
displacement sensor attached is shown in Figure 8. An open
loop simple test was first carried out to analyze how fast the
valve was able to charge or discharge the bellows cylinder. The
valve was charged and discharged according to a pulse
generator input command that was set at an amplitude of 4.5V
(centered around 5V neutral position) with a pulse width of 50
percent of the pulse time (T = 20 seconds). This pulse setting
allowed for air to be discharged from the bellows cylinder for
10 seconds and then air to be charged back into the bellows
cylinder for another 10 seconds. The pulse width acts as a
percentage of the pulse time, and because the time was set to 20
seconds with a width of 50 percent the time for charge and
discharge was half of the time making them equal to 10
seconds. With this setting the top plate was able to rise
approximately two millimeters and decrease in height by 1.5
millimeters. This amplitude is close to being ideal for a
253
Bellow sinusoidal position tracking (T =10 sec)
52
Position (mm)
vibration table, but the frequency of the table was not high
enough. This verified our concern that the bellows cylinder
would not be able to move fast enough to serve as an effective
leg press machine and whole body vibration table.
command
actual
51
50
49
10
15
20
25
30
35
40
15
20
25
30
35
40
Pressure (kPa)
220
200
180
160
10
10
Voltage (V)
data1
5
0
10
Figure 8: Final prototype design with displacement sensor
attached.
A closed loop PID controller was created in the model to
track sine wave position command similar to the simulation
results shown in Figures 5 and 6. The experimental results
shown in Figures 9 and 10 are very similar to the simulation
results shown in Figures 5 and 6; this proves that our
understanding of the bellows cylinder was correct and verifies
that its thrust force is indeed too large for our intended load.
Bellow sinusoidal position tracking (T =20 sec)
Position (mm)
52
command
actual
51
50
49
48
10
20
30
40
50
60
70
Pressure (kPa)
220
200
180
160
10
20
30
40
50
60
70
20
30
40
Time (sec)
50
60
70
Voltage (V)
10
5
0
10
Figure 9: Experimental results of bellows actuator
sinusoidal position tracking (T=20 sec)
ASME District F - ECTC 2013 Proceedings - Vol. 12
15
20
25
Time (sec)
30
35
40
Figure 10: Experimental results of bellows actuator
sinusoidal position tracking (T=10 sec)
As a summary, the purpose of this experiment was to
design a control system that would allow a bellows cylinder to
act as vibration table. With the model used in Simulink, the
sinusoidal pattern of the bellows cylinder’s fluctuation was
created. It is possible to control the bellows cylinder to track
small amplitude and slow varying sine waves using the
proportional control valve, but not at a high enough frequency
to consider it a passive leg press training machine and whole
body vibration table. Based on these results, it was determined
that the load on the bellows cylinder was not large enough to
produce the proper amount of stroke change. The bellows
cylinder has a stiffness so large that when a person stands on it,
it is as if a miniscule load has been applied. In the future, this
might be partially mitigated if the subject were able to bend and
press down, which would normally create 2-3 times of body
weight. This feature was not implemented in the current design.
CONCLUSION
The greatest challenge of this study was trying to control
the bellows cylinder into fluctuating at a high enough frequency
to work as a useful leg press trainer. Though we were able to
get the actuator to change its height by charging and
discharging air into the system, we were unable to do so at a
fast enough frequency, one needed to be considered a useful
passive leg press trainer. The size of the valves may also need
to increase in order to allow enough air to flow in and out the
bellows cylinder causing a rapid increase and decrease in the
position of the top plate. Another future goal to mitigate this is
to implement the vertical bars so that the test subject could
bend and press hard downward to create a 2-3 times larger load
on the bellows cylinder.
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Overall, it appears that pneumatic bellows actuators,
especially the ones with large thrust force like we have been
using, may not be a good choice to be used as a relatively high
frequency actuator due to its intrinsic natural compliance and
requiring large load and large flow rate to achieve a fast stroke
change.
REFERENCES
[1] Liu, C., Chen C.-S., Ho W.-H., Füle R. J., Chung P.-H., and
Shiang T.-Y., 2013, “The effects of Passive Leg Press
Training on Jumping Performance, Speed, and Muscle
Power,” J Strength and Conditioning Research, 27(6), pp.
1479-1486.
[2] Peer, K. S., Barkley, J. E., and Knapp, D. M., 2009, “The
Acute Effects of Local Vibration Therapy on Ankle Sprain
and Hamstring Strain Injuries,” The Physician and Sports
Medicine, 37(4), pp. 31-38.
[3] Trans, T., Aaboe, J., Henriksen, M., Christensen, R.,
Bliddal, H., and Lund, H., 2009, “Effect of Whole Body
Vibration Exercise on Muscle Strength and Proprioception
in Females with Knee Osteoarthritis,” The Knee, 16(4), pp.
256-261.
[4] Melnyk, M., Kofler, B., Faist, M., Hodapp, M., Gollhofer,
A., 2008, “Effect of a Whole-Body Vibration Session on
ASME District F - ECTC 2013 Proceedings - Vol. 12
Knee Stability,” Int J Sports Medicine, 29(10), pp. 839844.
[5] Annino, G., et al., 2007, “Effect of Whole Body Vibration
Training on Lower Limb Performance in Selected High
Level Ballet Students,” J Strength and Conditioning
Research, 21(4), pp. 1072-1076.
[6] Vargas, S.R., 2011, “Whole Body Vibration in Anterior
Cruciate Ligament Rehabilitation,” Master’s thesis in
Health and Human Movement, Utah State University.
[7] Van den Tillaar, R., 2006, “Will Whole-Body Vibration
Training Help Increase the Range of Motion of the
Hamstrings?” J Strength and Conditioning Research, 20(1),
pp. 192-196.
[8] Porumamilla, H., 2007, “Modeling, Analysis and Nonlinear Control of a Novel Pneumatic Semi-active Vibration
Isolator: A Concept Validation Study,” Ph.D. dissertation in
Mechanical Engineering, Iowa State University.
[9] Richer, E., and Hurmuzlu, Y., 2000, “A High Performance
Pneumatic Force Actuator System: Part I-Nonlinear
Mathematical Model,” ASME J Dynamic Systems,
Measurement and Control, 122(3), pp. 416-425.
[10] Festo manual of bellows cylinders EB/EBS, available at
http://www.festo.com/cat/fi_fi/data/doc_engb/PDF/EN/EBEBS_EN.PDF
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