DESIGN OF EQUIPMENT FOR PULTRUSION MACHINE
IN THE SMART MATERIALS CENTRE AT
DALHOUSIE UNIVERSITY
By:
Benjamin Parks
Brent Langille
Matt Swinkels
Mark MacIsaac
Neil Gillis
December 2, 2002
Dr. Alex Kalamkarov, Supervisor
Dr. Anastasis Georgiades, Supervisor
Department of Mechanical Engineering
Dalhousie University, Sexton Campus
Halifax, Nova Scotia, Canada
MECH 4020
Design Project, Term 16
Table of Contents
List of Figures ...................................................................................................................... i
List of Tables ....................................................................................................................... i
Abstract ............................................................................................................................... 1
Introduction ......................................................................................................................... 2
The Pultrusion Process ........................................................................................................ 3
Design Requirements .......................................................................................................... 5
Resin Bath ....................................................................................................................... 5
Cut-Off Saw .................................................................................................................... 5
Sensor Saw ...................................................................................................................... 6
Resin Bath Design............................................................................................................... 6
Design Description.......................................................................................................... 7
Through-Cut Design ........................................................................................................... 9
Previous Method ........................................................................................................... 10
Translating Saw Design ................................................................................................ 10
Components .................................................................................................................. 11
Stand ........................................................................................................................ 11
Rollers and Runners ................................................................................................. 12
Platform.................................................................................................................... 12
Saw........................................................................................................................... 13
Clamp ....................................................................................................................... 13
Return Spring ........................................................................................................... 14
Stastical Analysis .............................................................................................................. 15
Conceptual Smart-Cut Design .......................................................................................... 17
Radial Arm vs. Table Saw ............................................................................................ 17
Creating the Loop ......................................................................................................... 18
Acting on the Signal...................................................................................................... 21
Components .................................................................................................................. 22
Twin-Bladed Saw..................................................................................................... 22
Restoring Spring and Elbow Shaped Member ......................................................... 23
Clamping / Rotating the Rod ................................................................................... 24
2
Linear Actuator ........................................................................................................ 25
Reasons Only Conceptual ............................................................................................. 27
Budget ............................................................................................................................... 27
The Actual Budget ........................................................................................................ 27
The Sensor Saw Budget ................................................................................................ 28
Conclusion ........................................................................................................................ 29
Acknowledgements ........................................................................................................... 30
Appendix ........................................................................................................................... 31
3
List of Figures
Figure 1: Schematic of the Pultrusion Process ................................................................... 4
Figure 2: The Resin Bath Design ........................................................................................ 7
Figure 3: Method of Assembly for the Bath and Tray ........................................................ 8
Figure 4: The Cut-Off Saw Design ................................................................................... 11
Figure 5: The Translating Platform................................................................................... 12
Figure 6: The Mounted Runners ....................................................................................... 13
Figure 7: The Clamp Positioning ...................................................................................... 14
Figure 8: The Return Spring ............................................................................................. 15
Figure 9: The Constructed Cut-Off Saw ........................................................................... 15
Figure 10: Through Cut Accuracy .................................................................................... 17
Figure 11: The Radial Arm Saw ....................................................................................... 18
Figure 12: The Twin Bladed Saw ..................................................................................... 23
Figure 13: Restoring Spring Assembly ............................................................................. 23
Figure 14: The Chuck Design ........................................................................................... 24
Figure 15: Chuck Positioning ........................................................................................... 25
Figure 16: The Linear Actuator ........................................................................................ 25
Figure 17: The Linear Actuator within the Design ........................................................... 26
List of Tables
Table 1: Through Cut Statistical Data .............................................................................. 16
Table 2: The Sensor Saw Budget ...................................................................................... 28
4
ABSTRACT
This report details an in depth analysis of the final designs that were selected for the
pultrusion machine located in the Smart Materials Center at Dalhousie University. As it
stood before this project went underway, the pultrusion machine and its process had three
separate limitations that had to be addressed.
During the shutdown process, it is necessary to remove the resin bath quickly away from
the fibers. This can be achieved since the bath is not an integral part of the machine.
However, the current method of holding the bath in place involved strapping it to the
machine by means of bungee cords, making removal extremely awkward. The first
problem was associated with improving this undesirable method. The second issue
addressed is the lack of capability to cut the composite rods while the pultrusion machine
is in operation. This inability places severe limitations on the length of rod that can be
formed at any give time. The final problem to be pondered is associated with the rods
that are pultruded with imbedded fiber optic sensors that are surrounded with a protective
plastic sheath. The current method used to cut these rods, by hand with a hacksaw, does
not provide the necessary precision to avoid penetrating the sheath.
The first two problems as stated above, have been analyzed and their appropriate
solutions have been constructed, as will be explained within this report. The final issue,
however, has not been constructed. It was left as a conceptual design, where its solution
is thoroughly described later on in this report. The reasons that it was left as a conceptual
design are also briefly outlined.
5
Equipment Design for the Pultrusion Machine in the Smart Material
Lab. At Dalhousie University
Introduction
In the Smart Materials Lab at Dalhousie University, Sexton campus, there is a composite
rod pultrusion machine. The pultrution machine forms composite rods of differing
materials that are then tested to determine their material properties. The researchers
associated with the Smart Materials Lab hope to use the existing machine to form
composite rods with imbedded fiber optic sensors in order to test the feasibility of
producing smart sensing reinforcement bars. The current setup requires alterations in
order to make construction of numerous imbedded sensor rods practical.
We have constructed two separate devices that address the restrictions placed on the
process by the nature of the previous machinery. Our project consisted of three separate
projects that were felt by the clients to be the areas in the process that require the most
improvement. Mechanical attachment of the resin bath to the pultrusion machine via a
permanently mounted cradle will greatly reduced the spillage of resin. The mechanical
apparatus of the through cut, inherently necessary in the manufacturing of the composite
rods, increased the efficiency and accuracy of the process by eliminating much of the
human induced error. As well our design allows for the composite rods to be cut while
the pultruding process is ongoing. Having a cutting system designed specifically for the
problem at hand results in increased speed and precision, while reducing the required
manual labour. The removal of excess rod from around the fiber-optic lead was the third
aspect to our project. The current method is tedious and not suitable for the level of
precision required. A conceptual design for how this problem could be solved was
developed and is discussed in detail.
The design of three separate pieces of equipment poses a complex challenge, and requires
expertise from numerous areas. Several elements of the courses from our previous years
of engineering education, as well as knowledge gained on work experience have
contributed to the formulation of the ideas presented in this report.
6
The Protrusion Process
The pultrusion process is one of the most cost-effective methods used for producing
composite materials of constant cross-section. It is a continuous process that produces
materials that exhibit excellent structural properties.
The first stage of the process
involves the pulling of continuous fibers through a bath of resin that is blended with a
catalyst. The fibers are then passed into a pre-forming section where they are shaped and
any excess resin is removed. The resin-coated fibers are then passed through a heated
die, where they are cured to the desired geometry of the finished product, before they are
cut to their desired length.
There are five main stations in the pultrusion process, which can be seen in the figure
below. These include:
(1) Material Feed - Fiber Creels.
The first section of the protrusion process consists of several spools of continuous
fiber strands. These creels are usually set on large rollers that are used to feed the
fibers into the resin bath.
(2) Resin Impregnation/Material Forming.
The resin impregnation process is one of the most important stages of the pultrusion
process. Fibers are passed over and under wet out bars, which are immersed in resin
that is held by a bath. This causes the fiber strands to spread out and become
thoroughly impregnated with resin. The fiber strands then proceed through a material
forming stage where they are aligned closer to what their final shape will be, before
they are heated.
(3) Die Heating.
During the die heating process, the resin/fiber strand combination is cured to its final
state by exposing it to heat. This involves one of the most critical process control
parameters as it determines the rate of reaction within the die. If the material is not
properly cured it will exhibit poor mechanical properties. If excess heat is applied,
7
the final product may suffer from thermal cracks that will in turn reduce its resistance
to corrosion and weaken its structural strength.
(4) Clamping/Pulling.
The pulling mechanism varies in design but can be narrowed down to three general
categories. These include; intermittent-pull reciprocating clamp, continuous pull
reciprocating clamp, and continuous belt or cleated chain. Either way, it is important
to leave sufficient time between the exit of the die and the puller's in order to allow
the hot pultruded product to properly cool so that it will not be deformed by the
substantial pulling force.
(5) Cut-off station.
Every continuous pultrusion line requires a means of cutting the final product. The
final stage of the protrusion process therefore consists of a cut-off station. Usually a
continuous grit carbide or diamond edged blade is used to cut the pultruded products.
It is standard that the rod be clamped during the cutting operation to ensure that the
cut is made straight and accurate.
Figure 1: Schematic of the Pultrusion Process
8
Pultruded rods are used for reinforcing structures such as dams and bridges, where they
are replacing other materials such as wood, aluminum and steel. Composite rods have
several advantages over conventional materials. They are strong, having a specific
strength exceeding that of steel. They are lightweight, having one quarter of the density
of steel and two-thirds that of aluminum. They are non-conductive providing excellent
electrical and thermal resistance. Finally, and perhaps most importantly, composite rods
are resistant to corrosive materials such as salts and acids over a wide range of
temperatures.
Design Requirements
The client specified design requirements at the beginning of the design process. Each of
the three projects had separate criterion that had to be met.
Resin Bath
The final design of the resin bath must meet the following criterion:

Bath must be lightweight

Bath must be durable

Must maintain simplicity of design

Must be able to be operated by one person

Must be easily removable from machine for cleaning

Conform to the existing geometry

Inexpensive material usage

Inexpensive fabrication cost

Safe design
Cut off Saw
The final design of the cut off saw must meet the following criterion:

Must be durable
9

Must maintain simplicity of design

Must be able to be operated by one person

Conform to the existing geometry

Constructed within budget

Safe design
Sensor Saw
The design requirements set out for the sensor saw are different in nature to the criterion
established for the other two projects. Due to the sensor saw being developed as a
conceptual design, it must meet the following criterion:

Must be durable

Must be able to be operated by one person

Safe design
Resin Bath Design
In order to select a final design for the bath, all aspects of the design had to meet the
desired requirements set forth by the client. Topping the list of these requirements was
the ability of the bath to be operated by a single person and with ease. To accomplish this
task, the design needed to be of a mechanical nature following a simplistic path. It also
had to be lightweight to ensure the operator experienced little strain or frustration.
Another important criterion was that the bath needed to match the existing geometry of
the pultrusion machine. Although minor alterations were performed to the frame of the
machine in order to accomplish this task, the overall shape and structure of the machine
was maintained. In addition to being durable and constructed from high quality,
inexpensive, material, the design needed to be simple with a minimal number of moving
joints to eliminate the effects of the resin's adhesive nature. A build up of resin due to
extensive use of the equipment is also a problem that has been experienced in the past.
Because of this issue, the client requested that the entire bath assembly have the ability of
being removed from the machine for cleaning purposes. This factor is also an asset in
10
case one of the components needs to be replaced sometime in the future. The final design
requirement apparent in every design is that it must be safe.
Design Description
The final design for the Resin Bath, as seen in the diagram below, consists of four steel
arms connected to a tray in which the bath is seated. The tray will follow an arc like
motion of 90o underneath the pultrusion machine proving to be the most efficient and
simplistic method to raise and lower the bath. In order for the tray to remain level
throughout the motion, all four arms needed to be of equal length. This posed problems
with positioning the arms so that they would not interfere with each other or with the
frame of the pultrusion machine at any time during the motion. A decision was made that
the arms on the sides of the tray would have to be offset from one another to prevent
them from overlapping. Due to existing limitations from the pultrusion machine, it was
decided that the arms could be a maximum of 14" in length. One arm will be connected
to the tray, 12" from the back and 1" from the top. The second arm will be located about
1" from the bottom of the tray and 1" in from the back. This offsetting of the arms causes
a problem when attaching them to the frame of the pultrusion machine. In order for the
tray to remain level during motion, the arms must remain parallel therefore they need to
be offset on the machine the same way they are offset on the tray. In order to do this
additional pieces must be made on the pultrusion machine to permit the offsetting of the
arms.
Figure 2: The Resin Bath Design
11
The material used for the tray consisted of 16 gage galvanized sheet metal which proved
to be overkill for this particular purpose. Although the sheet metal chosen is very durable,
the excess weight from a thicker material was undesirable, also trying to form the metal
was extremely labor intensive. The construction of the bath was more complex than that
of the tray due to the inclined slope on one end, because of this a thinner gage sheet metal
was found for the bath allowing it to be formed easier. A schematic showing the
construction of the bath and tray can be viewed below. In the figures, the sheet metal is
cut to the profiles illustrated and folded on the dotted lines. The remaining edges are
welded together creating the final outcome.
The Bath
The Tray
Figure 3: Method of Assembly for the Bath and Tray
The arms for the tray were made from 1/4" steel flat bar with two 3/8" diameter holes
drilled 14" apart. The top arms were bolted to the tray where as the bottom arms were
attached with pins. The reasoning behind this was due to space constraints between the
walls of the bath and tray. The head thickness of the bolt exceeded the limit of the
confined space, where as the head of the pin, approximately one third that of the bolts,
proved to be a perfect fit. The problem with using pins in this design was that they were
of variable length and none were an exact fit for our purpose, thus resulting in unstable
motion. To solve this problem, washers were inserted over the pins to fill in the space
12
between the pin supports and the arm themselves. Another minor problem that occurred
after construction was that the width of the bath proved to be more than originally
anticipated meaning that the arms could not attach to the machine. To solve this problem
3/4" steel spacers were inserted between the frame of the pultrusion machine and each
arm. In the case of the bottom arms, the additional pieces constructed to offset the arms
were made to a width of 3/4" to compensate for this problem. The length of these
additional pieces was dictated by the vertical distance that existed between the two arms,
which turned out to be 2.75".
Other minor issues were encountered in addition to the construction of all components of
the bath. The first of these issues was how to lock the bath in an upward position while
the pultrusion process was underway. To solve the problem, more holes were drilled into
the frame of the machine with corresponding holes drilled into the top arms of the bath
and tray where a pin was inserted, one on each side of the machine. Another additional
aspect was that the bath needed to be attached to the tray. The reason behind this is that
after the process is finished when the bath needs to be lowered, the resin may cause it to
stick to the frame of the machine. The solution to this problem was to use a pair of 1" Cclamps on the back wall of the bath and tray, which did not interfere with the frame of the
machine. After all the issues were solved the final product tested with respectful results
and with a minimal cost. The entire process can be performed by a single person in a
matter of seconds and maintains the structural stability required for repetitive processes.
Through-Cut Design
After the composite rods have been formed they need to be cut to their desired lengths. It
would be advantageous to be able to cut the composite rods as they are being pultruded,
since this will eliminate any need of stopping the pultrusion process. This in turn would
save valuable time by eliminating the need to pultrude an extremely long rod only to be
cut into desired lengths after the process has expired.
13
Previous Method
Before our design, the cutting process was performed manually with a hacksaw and
required two operators. A rod was continuously pultruded until its length ran out of the
Smart Materials Lab into an adjacent street with a total distance of up to 10 m. The
pultrusion process was then stopped when the rod could go no further and the rod was cut
into desired lengths with a hacksaw. This process was time consuming and labour
intensive. On top of this, the down time associated with stopping the pultrusion machine
resulted in less composite rod production. Perhaps the only advantage of such a method
is the simplicity, however, this benefit did not outweigh the disadvantages.
In order to design a system where the pultrusion process could be kept continuous, it was
decided that an additional cut off station was needed. Possible attempts to keep the
process continuous could result in briefly stopping the entire system while a cut was
being made. This unfortunately would damage a portion of the rod that remained sitting
in the thermal die that is maintained at constant temperature. Also, since a large amount
of product obstructed the adjacent street, a traffic officer (a.k.a. Gobinda) was required to
ensure no damage to any vehicles or the product was encountered. For all these reasons,
modification to the cutting process was desired.
Translating Saw Design
The design that was selected had to ensure a straight and clean cut. It was decided that
since stopping the pultrusion process was not an option, the translation of the saw along
with the rod was the only solution. The method chosen was to have the saw mounted on
a platform with the ability to move at the same velocity as the rod. This would be
achieved by mounting a clamp in front of the saw, which would clamp the rod, allowing
the platform and saw to translate. After the cut was made the clamp would then release
the rod and return to its original position via a spring. This was the basic idea behind the
translating saw, a full in-depth discussion on the individual design components will be
14
covered in the following paragraphs. The figure shown below shows a graphical view of
the entire Cut-Off Saw.
Figure 4: The Cut-Off Saw Design
Components
There were several components associated with the construction of the cut-off saw.
These components are all outlined and explained in the preceding discussion.
Stand
The entire translating saw assembly is mounted on a stand constructed from angle iron.
The stand is mounted on four locking wheels so that the cut-off station can be moved if
desired. C-clamps are used to attach the stand to the end of the pultrusion machine by the
pullers so that the force from the pultruded rod does not shift the saw out of position.
The stand, minus the wheels, can be seen in the diagram shown above.
15
Rollers and Runners
The method chosen for translating the saw was a set of runners that would be bolted
directly to the top of the stand as seen in the figure below. Also seen in the figure are the
rollers, which translate back and forth within the housing of the runners. Attached to
each of these rollers is an aluminum block onto which the platform is bolted. Aluminum
was chosen, due to the fact that these four blocks had to be exactly the same and
aluminum is easier to machine then steel.
Figure 00: The Translating Platform
Figure 5: The Translating Platform
Platform
As mentioned above, the platform is mounted to the rollers using the aluminum blocks.
The figure below shows the constructed platform mounted to the rollers and stand
assembly. The platform itself is made of a 3/8” thick steel plate and acts as the base
where the saw and clamp sit. The restoring spring is also attached to the bottom of the
platform, as well as to the stand, but will be discussed later on.
16
Figure 6: The Mounted Runners
Saw
The actual mounted saw is the most integral part of the cut-off saw design. The saw
blade should be strong and wear resistant and for this reason should be made of a
diamond carbide grid. The actual saw itself is a radial arm saw purchased at Canadian
Tire and is manually turned on and off by the operator.
Clamp
The clamping system is used to grab onto the rod and it provides enough strength to hold
it while the platform and the saw translate. The clamp can be seen mounted in front of
the saw in the diagram below. The figure below shows both the graphical and actual
pictures of the clamp. The actual clamp is made of steel and uses a heavy-duty door
hinge for it to open and close. A hole of slightly larger diameter than the rods is bored
into the metal as seen in the figure. A rubber lining is inserted into the hole to ensure the
rod will not slip while the clamp is engaged. The clamp is mounted to a separate piece of
steel bolted to the platform for the sole purpose of aligning the rod with the saw and
clamp. A handle was added to the top portion of the clamp to make it easier for the
operator to open and close it and it also assists in applying the required pressure to
17
translate the platform with the rod. This task can be accomplished with one hand,
allowing the operator to use the other hand to run the saw, making this a single person
operation.
Figure 7: The Clamp Positioning
Return Spring
Once the saw has cut the rod, the platform needs to return back to its original position to
be ready for the next cut. To accomplish this, the best design for a returning system
involved using a tension spring that when deformed would force the platform back to a
static position. The force that must be generated by the spring has to be large enough to
overcome the force of friction produced by the weight of the platform assembly. On the
other hand, this spring force must also be small enough that the platform can translate
with the rod. This was not a large issue though as the force produced by the exiting rods
from the pullers is approximately 2000 lbs. This now meant that the spring force needs
only to bring the platform back to its original position. Once the cut-off saw was built
and assembled, it was discovered that the rollers created very little friction. A tension
spring used for screen doors was selected and attached to the bottom of the platform as
well as to the front of the stand in order to pull the platform back into position. The
figure below shows a close up view of the spring as it is mounted underneath the platform
on the cut-off saw.
18
Figure 8: The Return Spring
The figure directly below shows the constructed final design of the cut-off saw. Note that
all of the design requirements were met including that it is now a one-person operation, it
is a durable and simple design, it fits the existing machine, and it was constructed within
the budget given.
Figure 9: The Constructed Cut-Off Saw
19
Statistical Analysis
The statistical analysis was performed on the cut off saw mainly for testing the reliability
of our constructed equipment. At the start of the year we were asked to design a cut off
saw capable of cutting the pultruded rods at different lengths as they were being produced
at variable speeds. The allotted tolerance in relation to the length of the final product was
relatively large, in fact, a total variance of +/- 6" was considered to be acceptable by the
client. The main reasoning behind this large tolerance was because the rods that are
currently being produced in the Smart Materials Center are for testing purposes only and
are not intended for sale or mass production. In order to perform our statistical analysis,
the pultrusion machine was run at high and low speeds cutting a sample size of 20 rods at
each speed. A length of 10 feet was desired for each cut and the actual lengths were
recorded with a tape measure. The procedure for cutting the rods was to record the
amount of time the rod was being pultruded, and based on the known speed of
production, a length could be calculated. After the desired amount of time had expired, a
blue mark was placed on the rod indicating where to cut, the cut was made and the
stopwatch was reset to begin recording the time for the next cut to commence. The excel
spread sheet of the recorded data can be viewed in the appendix. Shown below is a brief
summary of the statistical analysis.
High Speed
Average
Std Dev.
Precision Error
Low Speed
0.134
Average
0.071
Std Dev.
0.04557
Precision Error
0.114
0.066
0.041945
Bias Error
0.125
Bias Error
0.125
Total Error
0.133047
Total Error
0.13185
Min
119.867
Max
119.8682
Max
120.133
Min
120.1318
Interval
120+/-.133
Interval
120+/-.141
Table 1: Through Cut Statistical Data
20
Through Cut Accuracy
6
4
Error (inches)
2
9 inches per minute
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
6 inches per minuter
-2
-4
-6
Rod Number
Figure 10: Through Cut Accuracy
Conceptual Smart-Cut Design
Radial Arm vs. Table saw
Two possible design selections were considered in relation to the conceptual design
aspect of our project, a radial arm saw and a stationary table saw. Both of these designs
had their own individual benefits that are discussed in detail later on. The final decision
was to design the radial arm saw as it proved to be a more simplistic arrangement.
Before this is thoroughly explained a brief look into the idea of a table saw design will be
done. A twin-bladed table saw design was considered mainly due to the fact that the
blades could remain stationary allowing us to translate the rod into the blade. Due to the
delicate nature of the task trying to be accomplished, control is the main factor. The
translation of the rod toward the blades would offer a more controlled situation over
translating the saw because the mass of the rod is insignificant to that of the saw blades
making it easier to move. This brought about the question of how to move the rod
towards the blade. Multiple methods were considered including a conveyor belt with a
stationary clamp onto which the rod would be positioned, or a translating rack and pinion
design that followed the same principle. The system would also need to be bi-directional
so that when the interface between the sheath and the composite rod was detected, the rod
21
would begin to retreat from the blades. If this was the only requirement to complete the
process, this design would have been selected, unfortunately the rod also needed to be
rotated before an additional cut could be made. This issue drastically increased the
complications related to this design due to the fact our simple system of translating the
rod now needed to perform the task of rotating the rod as well. It was mostly due to this
issue that the table saw design was not selected.
Although the configuration of the radial arm saw was a little more involved than that of
the table saw, it allowed the idea of running two separate systems to perform the two
desired tasks of both cutting and rotating the rod.
In this situation, the cutting
requirement involves the downward rotation of the twin-bladed saw towards the rod from
a fixed pivot point. After the interface is detected the saw will then retract from the rod.
Once the saw has pulled away, another system will then rotate the rod exposing a new
surface for cutting and the process begins again. For the movement of the saw it was
decided that a linear actuator would push upward against an elbow shaped member
pinned to the saw platform as seen in the figure below. This motion allows the saw to
move downward towards the rod. The restoring force involved in this configuration is
provided by a torsion spring located at the pinned joint of the elbow shaped member.
This spring is loaded such that it wants to pull the saw away from the rod keeping the
elbow member in constant contact with the linear actuator. The method of rotating the
rod also required a means of clamping the rod in place so that contact of the saw blade
would be consistent. For this a chuck design was selected and is described in detail later
on.
Figure 11: The Radial Arm Saw
22
Creating the loop
In order to generate a current once the plastic sheath has been contacted, a complete
conducting path must exist from the voltage potential to the ground. To create this path,
three independent, but interconnected components are used. The first two consist of a
double bladed saw, where one of the blades holds a voltage charge and the other is
grounded. The third component will be a conductive sheath that will protect the fiber
optic lead. What happens is that when the saw is cutting through the composite rod, no
current flows, once the sheath is contacted, a signal (current) will be generated that can
then be acted upon with an attempt to prevent the saw from cutting the lead. An
explanation of the individual components of this and how they work is described below.
A positive potential with respect to ground is applied to one blade of the saw. This
charge is generated by allowing a wire brush to come in constant sliding contact with the
blade. This wire brush is to be constructed of metal where various forms are possible and
may be chosen based on its physical appearance. The most important issue involved with
generating a charge with a wire brush is that it maintains physical contact with the blade
surface at all times. Without constant contact the rest of our system will be isolated from
the power source and no current will be possible. It is therefore recommended that time
and consideration is given to ensure that this is the case.
To ground the opposite blade, a similar method will be utilized. A sliding contact will be
grounded and then put into place, touching the blade. The reason that this particular path
setup was chosen is because the alternative solution of grounding the rod itself proved to
be a difficult proposition. It would have had required a method, which would be able to
reliably make contact with the surface area of the sheath embedded in the composite rod.
This could only be accomplished destructively (i.e. penetrating the composite) and our
group felt that the reliably of the connection would be not be sufficient enough to
implement. In addition, we felt that the danger of damaging the fiber optic lead was too
great, and could be avoided by employing our double bladed saw method.
23
The sheath that protects the fiber optic lead was not originally put in place for our
purposes. It was found that lead at the exposed face of the composite rod was easily
sheared off at that location. To prevent these occurrences, a thin plastic sheath was
placed over the lead to provide for stress relief. The structural integrity of this sheath
must therefore be maintained but is capable of sustaining some minor damage without
effecting its intended role. That is why the blade is able to make repetitive contact with
the sheath, removing a small amount of material each time, without completely
destroying its purpose.
The sheath currently used is plastic and therefore is non-conducting. The sheath must be
conducting in order to complete our proposed circuit path. Investigation revealed that
electrically conductive plastic tubing, of the dimensions that we required, is
commercially available. The tubing is made conductive by embedding a electrically
conductive material, in a spiral fashion, around the circumference of the sheath.
However, due to the fact that our design requires that the sheath be conductive wherever
the blade may come into contact with it, and that may occur anywhere along the
circumference of the sheath in a plane directly underneath the path of the saw, these
products do not comply with our needs. Another option was to use a tubing material that
is made entirely of an electrically conductive material.
Unfortunately, no products
consisting of the dimensions required could be found during the design timeline. It is
believed by our group that if tubing exhibiting all the mechanical properties that our
current plastic tubing does, with the additional property of electrical conductivity, were
available then this material should be selected for use. Due to the fact that we did not
discover tubing such as this, we came up with the solution described below.
The method that we chose to use was to spatter coat our existing tubing. Spatter coating
is a process whereby a very thin film of metal, usually gold, is applied uniformly to the
outer surface of a specimen. This makes the surface of a non-conducting material
conductive. Using this technology we are able to achieve that the entire outer surface area
of the protective sheath be electrically conductive.
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To insure that the blade remains charged, it is necessary to isolate it from the rest of the
saw. This is why the doubled bladed saw actually consists of two separate saws side by
side, as will be better described below. Each blade spins on its own shaft that is powered
by its own motor. In addition, this set up suggests that non-conductive material should be
placed between the mounts of the blade to it’s own shaft (i.e. rubber gasket). This is
recommended so that the two blades will remain independent of each other, allowing the
current to be produced only under the conditions in which we designed for.
Acting on the Signal
Once the signal has been generated, via the path produced upon contact of the grounded
blade, charged blade, and conductive sheath, it must be acted on. Our proposal is to have
a current sensor located along the path to ground, between the grounded blade and the
actual physical connection to ground. In this situation, as long the current flows it will be
discovered.
The sensor itself must be wired to a control unit. This control unit will act on the
information received from the sensor and initiate the required actions to stop the advance
of the saw. This control can be provided in several different ways. Our design does not
attempt specify the optimal arrangement, rather it highlights the requirements with which
it must function.
The controller must be able to receive the electric signal from the sensor, stop the
advancement of the linear actuator, (which controls the forward arc motion of the saw),
and reverse its direction allowing it to retract to a certain pre-specified distance. It is
imperative that these steps be accomplished quickly enough so that the saw does not cut
through the sheath into the fiber optic lead. As well, we believe that the control of the
rod chuck could be implemented with the controller, allowing the rotation of the rod to
occur without operator input. As a final step, the linear actuator must be able to reengage
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in order for the process to repeat until the proper amount of pre-determined cuts have
been made.
The actual implementation of the control could be carried out using a PLC. These are
available from a wide variety of distributors. Another option would be to design a
custom-built hardware/software system. After discussions with engineers involved in
this area, our group believes that this is the most effective way to go. While the design of
this custom built system is beyond our skill set, it is not beyond that of an electrical
engineer. It is therefore our recommendation that this avenue be explored.
Sensor Saw Components
The previous discussion explained how a current was to be generated and once it was
how a signal would be detected. The preceding discussion will now break down each
component of the smart-cut design and fully explain their purposes and why each one
was chosen the way it was. The several components involved with this design are
therefore as follows:
Twin-Bladed Saw
The twin-bladed saw is the most important part of this conceptual design because not
only does it perform the cutting of the rod, but it is also the source of our signal
generation. Two identical saws rotating in opposite directions are needed to perform this
task. Due to the fact that the size of the pultruded rods are only 9.5 mm in diameter as
well as with the fact that the tolerances related to this process are rather high, a
conventional 12" diameter saw blade could not be used for this design. The maximum
blade diameter should be no more than 4" with the motor to rotate the blade
corresponding with this. The arm used to connect the two saws together also plays an
important aspect in the design, mainly because it can not be made of metal or any other
electrically conductive material. The two saws need to be electrically isolated from each
other so that the only path the current has to flow is when a conductive medium, such as
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the sheath, comes in contact with both blades. The connecting the two saws should
therefore be made of plastic or some other similar type of material that is non-conductive.
Figure 12: The Twin Bladed Saw
Restoring Spring and Elbow Shaped Member
The twin-bladed saw is pinned onto the two elbow-shaped members that are then pinned
to the platform as seen in the picture below. The two dimensions of interest with the
elbow are the lengths of the arms on both sides of the pin. These dimensions are at 12"
and 9" respectively. The shorter arm is where the saw is connected and was chosen such
that when the saw is attached, the additional distance to the shaft of the saw will equal the
length of the other arm. This gives the total distance of the each arm equal to 12" which
in turn gives an approximate 1:1 relationship when considering the velocity of the
actuator with that of the moving saw. The restoring spring is located between the two
elbow-shaped arms and is wrapped around the pin connecting the arms to the platform.
The spring acts like that of a mousetrap spring and pushes against the plate connecting
the two arms as well as the platform itself. The spring, as mentioned above, continuously
wants to pull the saw away from the rod keeping the arms in constant contact with the
actuator on the opposite side.
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Figure 13: Restoring Spring Assembly
Clamping/Rotating the Rod
Before the rod can be cut, it is firmly clamped in place by the use of a chuck, similar to
the kind that you would find on that of a lathe or an adjustable screwdriver. A hole is
bored into the back of the chuck to allow for the composite rod to extend through. Once
enough of the rod is exposed to allow for adequate cutting, three arms, as shown in the
diagram below extend out from the center of the chuck grasping around the diameter of
the rod, holding it firmly in place. Three arms were chosen since they allow enough
surface area too completely cover the circumference of the rod and at the same time they
do so without causing any interference between them.
Figure 14: The Chuck Design
The chuck is also used to rotate the rod. The entire chuck, except for the section that is
used to mount it, can rotate about its axis, as can a lathe found in a machine shop. The
diameter of the rod to be cut will dictate the number of increments required for each
revolution too fully expose the plastic sheath. For the nine-millimeter rods pultruded in
the Smarts Materials Lab, at least six cuts in each complete rotation of the chuck is
necessary (this means that after each cut to the sheath is made, the rod should be rotated
60 degrees before the next cut is completed). It may require as many as eight rotations
for each revolution, but further analysis on to the actual amount of rotations should be
conducted before the chuck is constructed. Each time the chuck is rotated, it is locked in
place until the cut has been made and further rotation is required. This process is
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repeated until the sheath is fully exposed. The diagram below outlines where the chuck
fits into the assembly of the system.
Figure 15: Chuck Positioning
Linear Actuator
The linear actuator was chosen based on two main criteria. Its movement had to be
extremely slow so that once the interface was detected, it would allow sufficient time for
the blade to be diverted away from the rod. Secondly, it had to be able to move in a bidirectional manner. This would allow the linear actuator to move back to its initial
position once the signal had been detected. The actuator that was chosen is shown in the
in the diagram below. This diagram shows both the solid edge drawing of the actuator as
well as a actual cross section of its internal features. The graphical drawing of this
display that the end of the actuator is cut at an angle. This is necessary so that it will
remain in constant contact with the elbow shaped member as previously described.
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Figure 16: The Linear Actuator
This particular actuator is known as the Smart Bug and can be purchased from a company
known as Ultramotion. It operates at extremely slow speeds, where it ranges in motion
from 0.001-20 inches per second. Its motion is bi-directional and it can extend through
two, four, and eight-inch strokes. This actuator was chosen with the intent of using the
slower speed of 0.001 inches per second and the lowest stroke of two. The diagram
below gives a better view as to how the linear actuator is incorporated within the design.
Figure 17: The Linear Actuator within the Design
As you can see from the diagrams above, the actuator is located under the L-shaped
member that is connected to the arm of the saw, instead of being connected directly under
the arm of the saw itself. This was done to ensure that the saw would never slip under its
own weight and cut through the lead. For example, if the actuator ever failed during the
cutting process, the saw would continue downward, cutting the lead. By placing the
actuator where it is, this will never be an issue. If the actuator did happen to fail, the
restoring spring would cause the saw to move into its initial upward position. On top of
this, by positioning the actuator where it is, if it takes a bit longer than expected for the
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actuator to switch directions once the signal has been detected, then the chance of the
sheath being severed is dramatically reduced.
Reasons Only Conceptual
It was decided from the beginning that the sensor saw design was not to be constructed
and would merely be a conceptual design pertaining to a proposed solution for exposing
the lead of rods with embedded sensors. The main reason why the design was not
constructed was due to the anticipated costs associated with the precision equipment
involved in the design. These costs, in combination with the estimated frequent use of the
device once it was constructed, were far too significant for the client to produce. In
addition to these costs, the two previous projects requested for construction were of more
importance to the client at this time therefore funding and time needed to complete these
two took priority over the sensor saw. Other aspects, which further complicated the
fabrication of this device, were the intense electrical circuiting needed to connect and
operate the system. Also determining the required voltages and currents needed to
generate a signal large enough for the sensor to detect the interface between the sheath
and composite rod was well beyond the capabilities of mechanical students, therefore the
remaining problems needed to be overcome are now an electrical engineers task.
Budget
The Actual Budget
A copy of the final budget can be viewed in the appendix. It is a modified version of the
budget that was originally handed in at the end of December and consisted of the
anticipated material needed to build the projects, the quantity of the material, an
estimated unit price as well as a total price for each individual item. The additions that
were made to this budget include columns that show exactly what was purchased and the
actual cost of the individual components that were purchased. It should be noted that
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there were a few anticipated items that were not purchased also there were a few minor
items that were purchased and were not included in the budget. Items that were not
purchased include the 17 gauge galvanized steel sheet, the diamond edge saw blade, the
rubber for inside the clamp and all 5/16" bolts. The sheet metal was not bought because it
proved to be difficult to form, therefore a thinner sheet was donated by the department
technicians to replace it. Also donated by the departments technicians was the rubber
used inside of the clamp, and the 5/16" bolts which were used to mount the clamp,
wheels and other smaller pieces to the saw platform. The diamond edge saw blade was
not purchased because it could not be found in any local hardware store. Although these
blades do exist, the proper size of the blade as well as the proper number of teeth for the
blade could not be found and would need to come from the manufactures as a special
order. Materials that were purchased and were not included in the budget were two 1" cclamps, two larger multi-clamps and a package of 3/8"washers with corresponding bolts,
and amounted to a total cost of about $25.
The Sensor Saw Budget
Component
Actuator
Restoring Spring
Steel Platform
Steel L-Shape Member
Saw and Motor
Steel Chuck
PLC Control
Sensors
Steel Brush
Ground Wire
Miscellaneous
Quantity
Individual Cost
Total Cost
1
1
1
2
2
1
1
1
2
1
$3,000
$10
$60
$20
$150
$100
$750
$200
$10
$15
$3,000
$10
$60
$40
$300
$100
$750
$200
$20
$15
$250
$250
Total
$4,745
Table 2: The Sensor Saw Budget
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This is an estimated budget including the major components for the Sensor Saw. The
most costly piece of equipment is the linear actuator, which was a suggested price from
the manufacturer. Ultamotion, a company that specializes in linear actuators, are the
manufacturers of the Smart Bug actuator that was used for our design calculations. There
are possibly other actuators available that may perform the same tasks at cheaper prices,
therefore a more in-depth search on other manufacturers should be considered. Another
major component needed to be considered is the type and function of the PLC which we
have an estimated price of $750. This price was an averaged from a known manufacturer
and did not take into consideration the exact functioning of the PLC. The next highly
priced item would have to be the two saws. These would have to be circular handsaws
and can be purchased a local hardware store for as low as $60, the reason why we
selected the more expensive saw is because the high quality precision cut desired. The
last major component that would need to be bought is the sensor used to detect the
current. This price was also averaged from a manufacturer's list mainly because the exact
sensor to perform the task is unknown. The remaining costs are related to the price of
metals required as well as other minor fittings and miscellaneous items undetermined at
this point in time. As seen above the project price of a project like this is roughly $5,000
but through rigorous bargain shopping and proper searching, the costs could be reduced
as much as $1500.
Conclusion
In looking back on the work that we have accomplished over the past 8 months and
comparing this to the problem descriptions that were given, it is clear to see that we have
finished what we originally set out to do. We have replaced the tedious, bungee cord
wrapped resin bath with a more simplistic, mechanical method which can be operated by
a single person. We have also designed a saw with the capability of translating with the
pultruded rod making the overall pultrusion process continuous.
Finally we have
designed a possible solution to exposing the essential fiber optic lead needed to relay
information from rods with embedded sensors. All of these projects were completed
under the allotted budget and within the required length of time while meeting the desired
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criterion. The gained knowledge and experience shall indeed help us as we venture
through life, along with the pure satisfaction of completing a seemingly endless task.
Acknowledgements
We would like to thank our Supervisors, Dr. Tasos Georgiades and Dr. Alex
Kalamkarov, for helping us through these past few months. We would also like to thank
Stewart Carr for his expert advise and for building all of our devices even when the
drawings didn't clearly indicate what was desired. The knowledge and assistance you all
have provided for us, along with your patients and understanding was greatly appreciated.
Thank you all for your support.
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