Development of a Thermal Device for a Haptic Display
by
Michelle Judith Berris
B.S. Mechanical Engineering
Massachusetts Institute of Technology, 1999
Submitted to the Department of Mechanical Engineering in Partial Fulfillment
of the Requirements for the Degree of
MASTER OF SCIENCE IN MECHANICAL ENGINEERING
AT THE
MASSACHUSETTS INSTITTUE OF TECHNOLOGY
SEPTEMBER 2002
MASSACHUSETTS INSTITUTE
OF TECHNOLOGY
OCT 2 5 2002
LIBRARIES
C 2002 Massachusetts Institute of Technology. All rights reserved.
Signature of Author .......................................
Depa rtment of Mechanical Engineering
August 9, 2002
C ertified by....................................................
ILynette A. Jones
Principal Research Scientist in Mechanical Engineering
Thesis Supervisor
Accepted by................................................
Ain A. Sonin
Chairman, Department Committee on Graduate Students
Development of a Thermal Device for a Haptic Display
by
Michelle Judith Berris
Submitted to the Department of Mechanical Engineering
on 09 August 2002 in partial fulfillment of the
requirements for the Degree of Master of Science in
Mechanical Engineering
Abstract
This research involves the development of a thermal display for a haptic device. A
comprehensive review of human temperature perception is presented along with a
description of existing thermal display technologies. The results from preliminary testing
of prototypes for the thermal display are described together with the layout of the future
design. Results from physiological experiments indicated that finger thermal responses
were not consistent between subjects and showed little to no relation to the material in
contact with the hand. Results from psychophysical experiments confirmed that
successful material discrimination is limited to material pairs where differences in
thermal conductivities are large and in the range of 200-300 W/m0 C. A fast responding
thermal display has been designed and tested using a single RTD as both a heater and
sensor. The cold temperature source is provided by a thin-walled tube with water
flowing through it.
Thesis Supervisor: Lynette A. Jones
Title: Principal Research Scientist
2
Acknowledgements
My most sincere thanks are extended to Dr. Lynette Jones for her thoroughness as a
scientist and thesis advisor, and for introducing me to the haptics community. She
exemplifies the ideal balance between a successful academic and devoted parent. Thank
you to Professor Ian Hunter for keeping me on my toes and reminding me that there is
always more to learn.
The greatest asset of the Bioinstrumentation Laboratory is the commitment of its
students. The current research would not have been completed without the assistance of
the following people: Aimee Angel for training in the machine shop, Bryan Crane for
guidance in Visual Basic programming, Robert David for reviewing heat transfer, Laura
Proctor for suggestions in electronic circuit design and Peter Madden who has mastered
all of these and many more fields during his tenure in the lab.
Completion of a postgraduate degree demands perseverance and intellect, but more
importantly, a sense of humor. The days in which I could not laugh at myself, James
Tangorra provided comic relief. Rachel Peters endured my ever-changing moods, and
encouraged discussions equally important but often unrelated to mechanical engineering.
I am grateful for her friendship, perspective, and genuine willingness to help in whatever
way possible.
Finally, I thank all the members of the Newman Lab and specifically those who
participated in these experiments. This research was supported through the Advanced
Decision Architectures Collaborative Technology Alliance sponsored by the U.S. Army
Research Laboratory under Cooperative Agreement DAAD 19-01-2-0009.
3
Table of contents
Abstract ...............................................................................................................................
Acknow ledgem ents........................................................................................................
Table of contents .................................................................................................................
1. Introduction.....................................................................................................................
2. Physiology.......................................................................................................................
2.1. General description...............................................................................................
2.2. Blood flow ..........................................................................................................
2.3. Theoretical tissue - heat m odel ............................................................................
2.4. Biomaterial properties.........................................................................................
2.5. Therm oreceptors .................................................................................................
2.5. 1. Firing rates ......................................................................................................
2.5.2. Speed of inform ation transm ission ...............................................................
3. Therm al sensing ............................................................................................................
3.1. Perceptual studies ...............................................................................................
3.1.1. Thresholds....................................................................................................
3.1.2. Spatial sum mation.........................................................................................
3.2. Heat transfer modalities......................................................................................
4. Effects of contact force ...............................................................................................
4.1. Influence on blood flow ......................................................................................
4.2. Pressure profile with fingerpad compression.......................................................
5. M aterial discrim ination.............................................................................................
6. Tem perature transducers...........................................................................................
6.1. Therm ocouples....................................................................................................
6.2. RTD s......................................................................................................................24
6.2.1. Platinum RTDs................................................................................................25
6.2.2. Heat flow and self-heating ...........................................................................
6.3. Peltier device......................................................................................................
7. Existing technology ....................................................................................................
8. Prelim inary testing ....................................................................................................
8.1. Sensor selection .................................................................................................
8.2. JP Technologies thin film RTD .............................................................................
8.3. Hot and cold transients ......................................................................................
8.3.1. Therm al transients via water ........................................................................
8.3.2. M aterial induced transients...........................................................................
8.3.3. Force sensors integrated with therm al testing.............................................
8.4. Peltier prototype..................................................................................................
8.5. Psychophysical testing.........................................................................................
9. RTD therm al display.....................................................................................................
9.1. Circuit design......................................................................................................
9.2. RTD testing............................................................................................................
9.3. Future work............................................................................................................
10. Conclusion ..................................................................................................................
References.........................................................................................................................
4
2
3
4
6
7
7
8
9
11
12
13
14
15
15
15
16
17
19
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21
23
23
26
27
29
33
33
34
36
36
38
42
43
46
49
50
51
53
54
55
Appendix A: Visual Basic code to control data acquisition ..........................................
A. 1. Code for force and temperature sensors and recirculating chiller .....................
A.2. Code to separate incoming streaming data ........................................................
Appendix B: MathCad 2001i script .............................................................................
B. 1. Converting voltage measured with RTD to temperature ...................................
B.2. Mathematical reversion for polynomials ..........................................................
Appendix C: C++ code to interface between National Instruments Data Acquisition
Board and MathCad 2001i.............................................................................................
C .1. A/D Function ......................................................................................................
C .2. D /A Function .........................................................................................................
C .3. Tim er Function ..................................................................................................
5
60
60
66
68
68
70
71
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72
73
1. Introduction
Touch is one of the more complex senses; it pervades our daily exploration of the
environment and facilitates interactions with tools. Haptic interfaces, a relatively new
field of research, involve the kinesthetic and tactile senses in a real or computer generated
environment. Two types of feedback can be presented in a haptic interface, force
feedback which conveys information about the mechanical properties of objects, and
tactile feedback which conveys information about an objects material and geometrical
properties.
Haptic interfaces were introduced in the early 1940s to assist in the handling of hazardous
materials. The operator of a grasper or manipulator could remotely perform tasks that
would otherwise compromise human safety. Force and tactile cues in human-machine
interfaces provide the feedback about the task being performed. Early haptic interfaces
also provided communication media for the deaf and blind.
This research describes the development of a thermal display for a haptic device. A
comprehensive review on human temperature perception is presented along with a
description of existing thermal display technologies. This is followed by a description of
preliminary testing of prototypes for the thermal display and a layout of the future design.
6
2. Physiology
2.1. General description
Skin, the largest organ of the human body, contains an outer epidermal shell of cellular,
stratified epithelium, and a deeper dermal layer consisting of connective tissue (see
Figure 1). In addition to protecting against invasion from microbes or injury, skin
provides the primary elements for heat regulation through sensors, sweat, and blood
vessels (Moore & Agur, 1995).
An integrated control system maintains a constant temperature of 37*C for the vital
organs in the trunk and head, and minimizes environmentally-induced surface
temperature fluctuations. Thermoreceptors in the skin signal temperature changes to the
hypothalamus, which in turn sends out efferent commands for control of blood flow.
Blood acts as a conduit, transporting heat from the heart, and conveying it to the
peripheral circulatory system. This network cools the blood from the body core, elevates
the skin surface temperature, and enhances the removal of metabolically generated heat
in muscle tissue (Fulton, 1956).
7
/t"Iu
Ayr/.'
0,110
Aspill",1
pdinoal
ItyI))dl
-I'.
II ryl 'y "
Figure 1. Anatomical structure of skin and subcutaneous tissue (Visual Encyclopedia, 1999).
2.2. Blood flow
Blood flow, the main source of nutrition and heat for the human body, is ultimately
responsible for surface temperature regulation. Analysis of biological heat exchange
ascribes the blood-tissue interaction to the surface areas of capillaries, arterioles and
venules (Weinbaum & Jiji, 1985), and more recently to larger (100-500 Am 2 ) deeper
countercurrent vessels (Weinbaum & Jiji, 1985). Countercurrent vessels transfer heat
between a pair of vessels with opposing directions of flow. They continuously branch,
shrinking in size, spacing and flow velocity with depth.
Systemic cooling and heating prompt vasomotor activity in the extremities. During
vasodilation, the blood vessels expand to deliver more blood for cooling in the peripheral
system. Conversely, vasoconstriction inhibits blood flow to the peripheral system, so as
to preserve core body temperature.
8
In the arm, blood flows through the radial and ulnar arteries and branches into the palmar
arches to supply the fingertips and phalanges. The arteriovenous anastomoses (AVAs)
regulate flow between the superficial arteries and veins. AVAs close once the body
cools, reducing blood flow through the hand and redirecting blood back to the core
through deep veins. Heat input to the hand declines with reduced flow and countercurrent heat exchange. Blood in the hand travels at 0.5-50 mL/min per 100 ml of tissue,
and increases in the fingers, due to the presence of more AVAs (Spray, 1986).
2.3. Theoretical tissue - heat model
Shitzer et al. (1996) assess bioheat transfer in the hand with a lumped-parameter tissue
temperature model. In this model, a single artery and vein transport heat to a gloved
semispheric finger. Heat balance at the finger is based on heat storage, environmental
heat exchange, and heat clearance through blood perfusion as given by:
pc
at
= hA(T -T)+ pbWbcb(T - T),
where A is fingertip surface area, h is the heat transfer rate, Wb is the blood perfusion
rate, cb is the blood heat capacity, Pb is blood density, Tb is blood temperature and T is
tissue temperature.
The initial conductive heat transfer between a finger and solid object can be modeled as a
step change in surface temperature for two semi-infinite solids (Myers, 1971). This
representation remains valid for a short time period in a small contact region. Assuming
no surface resistance, both the finger and object instantaneously achieve a common
temperature, Tc, upon contact. Substituting the solution to the semi-infinite solid
problem, with an initial temperature ti,
t(x,0) =ti +(t, - ti)
e-0 d
ef
,
2
2
into Fourier's law of heat conduction
q = -K
aT
-
&x
yields the relation
9
3
...
.
....
........
k x(te -ti)
4
;r
where q is the equivalent heat flow into the finger or out of the wall and k is the thermal
conductivity of the object. Bergamasco et al. (1997) utilize partial and ordinary
differential equations (PDE, ODE) to illustrate finger-object interactions. Their first
model portrays the transition from core temperature to surface temperature for a one
dimensional finger in equilibrium with the surrounding air (20*C). The deterministic
model is described by a Taylor expansion. Thermal material properties for human tissues
are derived from the relative composition of water (75%), fat and protein in the tissue.
An equivalent density calculation for a composite material is as follows:
1
Peq =
MI+
A
2 +
P2
5
3
P3
where m is percent of total mass for each material. The solution to the model is
expressed as a linear combination of exponential functions as shown in Figure 2.
36
35.5
35 0-
34.5
I~34
33.5
k
33
32.5
32 0
2
4
6
8
10
Depth from surface of skin (mm)
Figure 2. Model of finger temperature as it transitions from
core to skin surface (Bergamasco et al., 1997).
The ODE evaluation assumes that the finger is a homogenous, thermally passive, semiinfinite solid. The model partitions the cutaneous tissue into ten layers each with
different material properties, bisects the object into two identical sections and neglects
lateral blood flow, thermal radiation, and metabolic affects. The contact temperature is
10
constant with time and the solution from the earlier non-contact model defines initial
value conditions. The inner layer xi' is given as:
2k [T -x (t)]+
2k
1
Di +D
D.
Dipc
[x(t)-x t)]
6
where Di and D, are dimensions of the inner and superficial layer. Bergamasco et al. use
this model to simulate a 1 s step input for a finger in contact with aluminum, marble or
wood. The resulting graphs show the initial skin temperature at 30'C, followed by a
spike in temperature within the first 100 ms which settles to a steady state value after 1 s.
The spike associated with aluminum is more pronounced than spikes associated with
marble and wood. The final model depicts an experiment in which an object is contacted
for 10 s then released.
2.4. Biomaterial properties
Specification of biological material properties largely depends on testing conditions. For
example, thermal conductivity of skin is greater in-vivo than in-vitro, and decreases
proportionally with temperature. Table 1 lists properties relevant to the preceding
models.
11
Table 1. Biomaterial properties (Chato, 1985; GE, 1977).
Thermal conductivity
Human skin at body temp (in vivo)
Human skin at body temp (in vitro)
Water
Blood
Fat at body temp (in vitro)
W/mOC
0.28-0.48
0.21-0.41
0.59
0.51
0.094-0.37
Thermal diffusivity
m 2/S
0.82x10 7 - 1.2x10 7
0.4x10 7 - 1.6x10 7
Skin at body temp (in vitro)
Skin at body temp (in vivo)
Specific heat
Tissue
Blood
kJ/kg0 C
3.899
3.136
Density
Tissue
Blood
kg/m 3
1,057
1,050
Heat transfer coefficient
Finger
W/m 0 C
8.09
Emmitance
Skin
Ratio
0.993
2.5. Thermoreceptors
Thermoreceptors are categorized into cold and warm sensors and are differentiated by
their responses to changes in temperature. The cold and warm sensors are free nerve
endings and the associated axons are small myelinated AS and unmyelinated "c" fibers.
Warm receptors are 1-2 yim in diameter and 150 jim below the skin surface, in contrast to
cold receptors which are 3 ptm in diameter and 300 pm deep (cf Fulton, 1956). The
receptive field of warm and cold receptors is less than 1 mm in diameter (Yarnitsky &
Ochoa, 1991). Although thermoreceptor concentration varies with body site, cold
receptors are always more numerous than warm receptors as illustrated in Table 2 and are
most abundant in the tongue, face and scrotum (Darian-Smith, 1984). Cold and likely
warm fibers innervating the glabrous skin of the fingers and palm populate the hand with
a density of 0.5-0.7 fibers/mm 2 (Darian-Smith et al. 1973).
12
Table 2. Thermoreceptor concentration density measured in points
responding to stimulation per 100 mm 2 (Fulton, 1956).
Cold
Warm
Forearm
14
1-2
Hand
2.5
1
Face
10
2
Increases in skin temperature augment warm receptor firing, and reductions in
temperature amplify cold receptor firing. Warm receptors fire constantly at skin
temperatures above 30'C with peak intensities between 41-47'C (Spray, 1986). Cold
receptors, which overlap warm receptors at 37'C, respond over a wider temperature range
of approximately 5-43*C with peak intensities of 4-6 impulses/s. Heat pain commences
abruptly at 45'C and cold pain has a slower onset at temperatures below 15-18'C
(Darian-Smith, 1984). This presumably explains the inclination to withdraw quickly a
finger in contact with a hot object, and the less abrupt response to a cool object in these
temperature zones. Cold and heat pain are not mediated by thermoreceptors, but by
specialized thermal nociceptors.
Cold fibers reportedly fire in bursts at temperatures below 30 0 C and fire paradoxically
above 45*C which is associated with cutaneous vasodilation and secondary effects (Chen,
1997; Darian-Smith, 1973, 1984; Dodt & Zotterman, 1952b; Spray, 1986). Continued
exposure of thermoreceptors to extreme temperatures leads to fiber destruction.
2.5.1. Firing rates
Thermoreceptors discharge with frequencies of 1-6 impulses/s for skin temperatures
between 30-35'C as depicted in Figure 3 (Darian-Smith et al., 1973; Spray, 1986). Dodt
and Zotterman (1952a) reported 1.5-3.7 impulses/s over the range of 37.5-40'C for warm
fibers dissected from the median nerve of a rhesus monkey which is 70% higher than the
equivalent value for cold sensors at temperatures below 22 0 C (Dodt & Zotterman, 1952b;
Hensel & Zotterman, 1951).
13
6
5
43 -3
S2-
0
20
40
30
50
60
Adaptation temperatue (*C)
Figure 3. Discharge frequencies of cold (blue) and warm (red) receptors (Schmidt, 1983).
The firing rate depends on the steady state temperature and the rate of change of
temperature (Darian-Smith, 1984; Darian-Smith et al., 1973). Time constants for the
response to dynamic cold stimuli are 2.2 s in the cat tongue, and 15-30 s in the monkey
hand (Darian-Smith et al., 1973). Warm receptor responses decay within 5-12 s (DarianSmith, 1984), independent of the adapting temperature. The warm receptors are also
characterized by a linear correlation between firing rate and magnitude of a temperature
step for steps in the range of 1-8*C above the adaptation temperature. Most receptors
adapt to static stimuli within 30 minutes, but do not entirely cease firing.
2.5.2. Speed of information transmission
Conduction velocities of both warm and cold fibers are in the range of 0.4-20 m/s
(Schmidt, 1983). Darian-Smith et al. (1973) dissected apart individual median nerve
fibers in the upper arm of monkeys. Stimulation of thermoreceptors below the wrist
elicited conduction velocities of 1.2 m/s and 14.5 m/s for warm and cold fibers
respectively (Darian-Smith, 1984). The faster conduction velocity of cold receptors
results from the large diameter myelinated axons whereas warm receptors have small
diameter unmyelinated axons. Increases in epidermal thickness lengthen the pathway to
the receptor and also influence response time (Chen, 1997).
14
3. Thermal sensing
3.1. Perceptual studies
Human skin temperature is typically 32-351C, although it fluctuates in the range of 2040'C depending on the time of day, ambient temperature, and physical activity. Over the
temperature range of 30-36'C, humans do not sense fluctuations in temperature, although
receptors are spontaneously firing (Schmidt, 1983). Beyond this range, the ability to
detect changes in temperature depends on a number of variables including the area of
stimulation, the rate of change in temperature, and the amplitude of the change. Thermal
adaptation occurs some time after stimulation and results in neutral sensation. For small
temperature steps, a thermal stimulus is adapted before the skin temperature has
stabilized, but a large temperature step allows the skin temperature to stabilize before
adaptation (Schmidt, 1983).
3.1.1. Thresholds
Human thermal sensory thresholds are influenced by body site, age, area, duration of
exposure, and rate of temperature change. An absolute thermal threshold is defined as
the smallest temperature change above or below skin temperature that is detected. The
minimal heat energy required to elicit warm sensation is 6.28x10- 3 kgJ/m 2s (cf Fulton,
1956).
A thorough investigation of thresholds in 13 regions of the body of subjects aged from
18-88 years determined that there was a 100-fold variation in sensitivity (Stevens &
Choo, 1998). The area encircling the mouth is the most sensitive region and the lower
extremities are the least sensitive (Stevens & Choo, 1998). All body zones are more
sensitive to cold stimulation than to warm stimulation. For example, the warm threshold
for the toe in people aged 65 and older is 10 C, whereas the equivalent cold threshold is 2.7'C. Darian-Smith (1984) identified the thenar eminence and volar forearm as the most
sensitive portions of the hand and forearm. Within the hand, low thresholds are reported
on the dorsal hairy skin of the fingers, and volar surface of the forearm, whereas higher
thresholds are recorded on the finger and palmar pads (Johnson et al., 1973). Thermal
15
sensitivity declines with age, most profoundly at the extremities, and less significantly at
the more central regions such as the mouth and belly. Gender has no apparent effect on
thermal thresholds (Dyck et al., 1974; Stevens & Choo, 1998).
In a neutral environment and an initial skin temperature of 34'C, human subjects can
discriminate a temperature change of 0.01 C for warming and 0.048'C for cooling
(Johnson et al., 1973). The range of thresholds measured using other experimental
methods is as small as 0.00P1C for warm and 0.004'C for cold (Fulton, 1956) and as high
as 5.27*C and 3.23'C for warm and cold respectively (Yarnitsky & Ochoa, 1991). An
increase in initial skin temperature from 31 C to 36C doubles the cooling and halves the
warming threshold (Darian-Smith, 1984). Thresholds are influenced by the duration of
thermal stimulation. A linear tradeoff is apparent between the threshold and the duration
of a stimulus for periods less than 1 s. The thermal threshold increases dramatically for
slower changes (Schmidt, 1983).
3.1.2. Spatial summation
Spatial summation of stimuli is a common feature of information processing in the
thermal modality. An increase in the area of a thermal stimulus is perceived as indicating
a more intense stimulus. This is different from vision for example, where a bigger visual
cue specifies magnification in size, not in brightness. In thermal perception, intensity and
area are inversely proportional until high intensities near the pain threshold are reached.
At temperatures of 45'C, the area of stimulation has no influence on perceived intensity,
although the stimulus is more accurately located (Stevens et al., 1974). The lower spatial
summation threshold is 100 mW/mm 2 while the upper boundary is 100 W/mm 2 (cf
Stevens et al., 1974).
The perceived magnitude of a thermal stimulus is independent of the rate of temperature
change for rates faster than 0.5 0 C/s (Molinari et al., 1977). Experimentation conducted
with temperature changes greater than 1 0 C/s showed that perceived cold increases
linearly as a function of area (maximum 2380 mm 2 ) with constant slope. In contrast,
16
warmth estimation, increases logarithmically as a function of area, and converges with
different intensity curves at higher intensities (Stevens & Marks, 1979).
3.2. Heat transfer modalities
The three modes of heat transfer are convection, conduction and radiation. Convection
refers to energy exchange by means of one medium flowing over another, prompted by a
difference in density or forcefully with a pump, compressor or fan. The heat flux or
energy flow per unit of time is defined by:
QCONV
= h, (I - T2).A,
7
where A is surface area and the heat transfer coefficient, he, is a function of media
temperature and nature of the flow field, which follows Newton's law of cooling. In the
context of human thermal studies, heat transfer via convection occurs when the body is
exposed to natural or forced air provided by a fan, and when it is immersed in a bath of
hot or cold water (Chen, 1997; Mills, 1999).
The Fourier conduction law relates the heat transfer rate to the temperature gradient
between two objects in physical contact according to
QCOND
=-A(T -T
L
2
)Y
8
where k is thermal conductivity and L is length of contact. An example of conductive
stimulation is a Peltier device or material sample in contact with the skin. This is the
most frequently used of the three modes of heat transfer in human thermal studies.
Electromagnetic radiation transfers energy within one object, released upon photon
collision, to another object. The wavelength and frequency determine the type of
radiation. The net radiant energy interchange between two surfaces is given by:
RAD
=Ar
=~ ,
T
-Tj9
2 '
where hr is the radiation heat transfer coefficient. Radiative sources for artifical thermal
stimulation include quartz or infrared (0.1 - 100 ptm) heat lamps. This was used in earlier
studies of thermal stimulation (Stevens et al., 1974), but is less frequently used now. In
17
addition, evaporative heat loss from the body accounts for energy exchange, but is
negligible for the hand.
18
77
4. Effects of contact force
The force imposed by a finger on an object may affect thermal responses in two ways.
First, compressing the cutaneous tissue of the index finger may enhance thermal sensing
by increasing the area of contact with the object. Compressing the finger may also affect
finger temperature by collapsing blood vessels in the region which prevents continuous
tissue-heat exchange.
4.1. Influence on blood flow
Of the blood flow to the finger tip, 90% is bound for temperature regulation (cf Mascaro,
2002). Although the digital arteries, which are protected by the underlying bone, are
unaffected by contact pressure exerted by the finger pad, the larger, more compliant
digital veins which run lateral to the bone (Figure 4) have a lower internal blood pressure
and collapse. This results in accumulation of blood pools in capillaries under the nail bed
and impedes the continuous warming process.
Figure 4. Vascular anatomy of the fingertip, digital arteries and veins
are red and blue respectively (cf Mascaro, 2002).
4.2. Pressure profile with fingerpad compression
When the finger makes contact with an object, the contact area on the finger pad begins
as a single point, expanding exponentially in size with surface compression. Contact
distribution is symmetric in the medial-lateral direction but not in the proximal-distal
direction (Pawluk & Howe, 1999). A force of 1 N applied normal to the finger pad
compresses two thirds of the corresponding contact area compressed by a force of 10 N
19
(Westling & Johansson, 1987). If there is a circular pressure profile, there will be a 0-6
mm radius change from 0-1 N (Westling & Johansson, 1987).
Pawluk & Howe (1999) introduced a theoretical model for a distributed pressure response
of the index finger pad to a flat surface with dynamic 0-2 mm displacements for 0-2 N of
force. This is given by:
t(e)(U)=
m
emu(t) -1]
10
where u(t) is the deformation at the point of maximum indentation on the fingerpad. The
model is derived from an interaction between an incompressible, linear isotropic,
homogenous, elastic sphere and a rigid plane. Constants b and m were generated
empirically by accelerating 64 indentor tactors spaced 2 mm apart into the index finger of
five subjects at 200 Hz.
20
5. Material discrimination
Thermal and tactile cues are both used to recognize and discriminate between materials.
The hand is extremely good at discriminating texture. For example, a matrix of 6 Am
high, 50 Am diameter dots etched onto a glass plate, is detected by stroking the finger
across the surface with 0.2 N of force (Srinivasan et al., 1990).
In contrast, subjects can differentiate materials with only large differences in thermal
conductivity and heat capacity (Jones & Berris, 2002). It takes a subject 3-5 s on
average, to discriminate between an ice cube, heated soldering iron, aluminum block, and
insulation foam (Caldwell & Gosney, 1993). A plot of finger skin temperature versus
time as the finger contacts various material samples shows a horizontal line at 32'C
representing initial finger temperature, a nearly vertical drop upon material contact
(2.5*C in less than 0.5 s for aluminum) followed by another horizontal line at a lower
steady state temperature (Ino et al., 1993).
Clinical neurological testing includes evaluation of thermal sensations in patients with
diseases characterized by small fiber damage. A testing apparatus named the "Minnesota
thermal disks" (Dyck et al., 1974) is composed of 18 mm diameter disks made of copper,
stainless steel, PVC and glass. Copper is always presented to the subject along with one
of the other materials for 2 s. The subject must determine which material of the pair is
warmer, at seventeen different points on the body. Of the three different material
combinations, discrimination between copper and PVC is best, and between copper and
stainless steel the worst. This corresponds to the largest and smallest difference in
thermal conductivity respectively. Correct discrimination occurs most frequently on the
forehead and is least accurate on the back and thigh.
Ino et al. (1993) and Caldwell & Gosney (1993) have both developed thermal displays
that simulate contact with various materials, using a Peltier device. On the basis of the
change in finger temperature upon contact with the material, Ino et al. simulate contact
with aluminum, glass, rubber, polyacrylate, and wood. During testing, a subject
21
identifies both materials presented in the display by name. Presentation of two aluminum
samples is correctly identified 100% whereas presentation of polyacrylate and glass are
successfully identified only 6% of the time.
Using a robot and data glove system, Caldwell & Gosney (1993) presented an ice cube,
heated soldering iron, aluminum block, and insulation foam. A signal from a
thermocouple on the robot indicated the type and magnitude of thermal transient, which
was presented to the subject who wore a glove fitted with a Peltier device. Subjects
successfully identified each material 80% of the time.
22
6. Temperature transducers
Most materials respond in some way to a change in temperature. This has resulted in the
development of a myriad of temperature sensors ranging from embedded semiconductors
to simple bimetallic strips (Capgo, 1998). The most reliable sensors which are targeted at
small, high speed, precision applications, are thermocouples and resistive temperature
detectors (RTDs).
6.1. Thermocouples
Thermocouples are the most common and versatile of temperature sensors. A
thermocouple circuit contains two metals joined together at a measurement junction as
shown in Figure 5. A voltage generated by the temperature gradient from the union of
dissimilar materials, known as the Seebeck effect, provides the output signal for the
sensor. The Seebeck voltage comprises a Peltier voltage, proportional to the junction
temperature, and a Thomson voltage, VT, derived from the gradient along the wires. The
latter of the two accounts for the majority of the mV signal range and is described by,
T2
VT =
(QA
11
- QB)dT
where QA and QB are the temperature independent thermal transport constants for the
respective materials.
metal 1
Junction
metal 2
small voltage
Figure 5: Thermocouple (Capgo, 1998).
Thermocouples do not require power for excitation and thus do not self heat. Response
time varies with design; thermocouples sealed by a sheath may not respond for 75 s,
whereas an exposed thermocouple registers within 2 s. Sensitivity ranges from 10-70
AV/*C. Thermocouples are internationally standardized with 12 types, each with a
different material combination and respective Seebeck voltage curve. Use of a
thermocouple requires voltage compensation and linearization.
23
=AM
6.2. RTDs
The resistance of a resistor is determined by delivering an excitation current and
measuring the voltage across its leads according to the relation
V=I-R.
12
An RTD is essentially a variable resistor; the resistance of a heated metal increases due to
the reduction of the mean free path of free valence band electrons. The temperature
coefficient of resistance (TCR) for metals varies between 0.003 and 0.007 DI 0P/C and is
influenced by very slight differences in material composition. The average coefficient
for a given metal between 0*C and 100 C can be calculated by:
R 100 - RO
100R0
13
where RO is the ice point, or resistance at 00 C. RTDs are manufactured in two package
types, either by encasing a coil of wire in a ceramic tube or plating a thin film as shown
in Figure 6.
ceramic wubstrate
wire coil
ceramic holder
Figure 6: Wire wound and thin film RTDs (Capgo, 1998).
The quantity of conductive material embedded in an RTD is calculated at ice point and
fine tuned with laser trimming according to:
PL
A'=
A
where p is conductor density, L is conductor length and A is cross sectional area.
24
14
6.2.1. Platinum RTDs
Platinum is favored over other RTD metals for its precision, linear relation between
temperature and resistance, and stability in air over a large temperature range (see Figure
7).
5-
I
I
0
-100
0
'4
32
3004 00 500 6 30
572 7192 932 11 12
Temperature
100
200
212
392
700
1292
Figure 7: Relative resistance vs. temperature of typical RTDs (Honeywell, 1998).
The Callendar Van Dusen polynomial (Honeywell, 1998) specifies RT, the resistance at a
temperature T for platinum RTDs with constants A, B, C, a, fl, and 6:
RT =
RO(I+ AT + BT2 -100CT' +CT ),
i
ag
100
B =
CTo =
-aS
,
1002
a
, and
100 4
RO(l+a -260)- R2
4.16.-R *a
For T > 0, f= 0 and C= 0 which simplifies the equation to an easily solved quadratic
where T is a function of R:
- RA+
A2R2 -4R2B(RO - RT
2ROB
25
1
As was noted for thermocouples, platinum RTDs also conform to an International
Standard (IEC75 1). Standards for both sensor types have updated calibrations to reflect
ITS-90, the International Temperature Scale change of 1990.
6.2.2. Heat flow and self-heating
The excitation current of an RTD induces an effect referred to as "self heating."
Manufacturers recommend limiting operating current to 5 mA in order to avoid the
additional heat factor. The magnitude of this term depends on thermal diffusivity
Y=-
21
p-c sec
as defined by density p, thermal conductivity K,and specific heat c, in addition to RTD
geometry, and the thermal power dissipated which is given by:
V
2
22
P=-=I-V,
R
where V is voltage output, I is input current, and R is the calculated resistance.
RTD
_i X=0
L
TI
Mounting Surface
Figure 8: RTD model (Honeywell, 1998).
The general solution to the heat conduction equation, approximated as a one-dimensional
problem for a thin film RTD drawn in Figure 8, is composed of a time independent
temperature distribution and a series sum of exponentially damped orthogonal functions:
____W si23
w
u(x,t)=(T2 -7).- +7j+be
L
n=1
,
23
where t is time, x = 0 at TI, x =L at T2 and
b =
x
2
-
-
26
sin
24
where f(x) equals temperature distribution at t = 0. Applying Equation 3 as a boundary
condition to Equation 24, reduces the self heating factor to
PL
7 = -- +T2,
25
A2Y
where A2 is the RTD surface area (Honeywell, 1998).
6.3. Peltier device
A thermoelectric cooler or Peltier device, pumps and produces heat without any moving
parts according to the Peltier effect previously described. N and P-doped semiconductors
connected in parallel thermally, and in series electrically, are sandwiched between two
ceramic substrates. A unidirectional heat flows between the substrate, in proportion to an
input current traveling through each N and P pair generates a hot and cold side (see
Figure 9).
Heat Absorptian Side
Ceramic
Substrate
3
TE Element
E'lctncal Interconnect
C arriers Moving Heat
tffitwstptronSide
DC Power source
Figure 9: Schematic diagram of a thermoelectric cooler (Capgo, 1998).
A heat sink must be integrated with the Peltier module in order to dissipate heat from the
cold side. Liquid cooled and forced convection heat sinks work best, removing 0.0050.5*C/Watt, while maintaining a temperature of 10-20*C above ambient.
The heat pumping capacity of a Peltier device, Qc, depends on the temperature
differential dT, power input, and module thermal conductivity Km:
QC=SMTCI-
2
27
KM dT,
26
where SM, the Seebeck coefficient is a combination of polynomial expressions for both
hot and cold sides with module specific coefficients.
SM
SMT(h,c) =sT
27
(SMTh -SMTC)
dT
s2 T 2
+ 2
2
+
s3 T 3
3
3
+
s4 T4
4
4
28
Km and RM in Equation 26 mimic Equations 27 and 28, replacing the variable S, with K
and R respectively. The power input has a thermal and an electrical term due to the input
voltage,
V,, = SdT
+ IRm.
29
The time t, to reach a desired temperature can be estimated from
t=
Qt0 +Qt
(dT).
Qto is the initial heat pumping capacity when dT=O, and Qtt is the heat pumping capacity
once the desired temperature is attained (Ferrotec, 2002).
28
30
7. Existing technology
Haptic displays are used for training, entertainment, and industrial applications. They
transmit force feedback and/or tactile information using physical models of object
properties and behavior. Haptic displays range from gross force feedback found in
computer or video games to vibrotactile displays used to convey surface features in
simulated environments developed for surgical training.
Innovation in thermal display technology has been propelled by novel applications in
medical diagnostics (Jamal et al., 1984; Pepler et al., 1985), physiological research
(Kenshalo & Bergren, 1975; Monkman & Taylor, 1993) and virtual environments (VE)
(Caldwell et al., 1996; Dionisio, 1997; MacLean & Roderick, 1999; Ottensmeyer &
Salisbury, 1997). Contemporary displays consist of a Peltier thermoelectric device,
temperature sensor and a heat sink, controlled by a computer or microprocessor. These
structurally rigid assemblies are often retrofitted to pre-existing haptic interfaces (Yee,
2000; Caldwell & Gosney, 1993; Mukai et al., 2000) and are limited by their size and
temporal response to temperature changes. At best, they output 20'C/s with a 15x1 5 mm
surface area.
A patent search of haptic thermal display technology identified two corporate ventures,
one sponsored by Fanuc America, and the other by Mitsubishi, as well as an individual
application. Fanuc submitted patent requests in 1997 for a remote controlled masterslave robot system composed of an exoskeleton, video console and user glove. The
thermal display, which consists of a Peltier device, heater and temperature sensor, is
adapted to Virtual Technology's Dataglove as shown in Figure 10. At least one
prototype was developed, but the project was abandoned by the company in 2000.
29
Data
Glove-
4
-
-
Thermal
Display
Figure 10. Dataglove and retrofitted thermal display, Fanuc America. Thermal display includes
sensor closest to skin, followed by heater, thermoelectric cooler and vibrator (Yee, 2000).
The Mitsubishi application discusses general concepts of a medical simulator providing
various types of sensor feedback and refers to a thermal display associated with another
haptic device. The independent application submitted by Lander & Haberman (1999)
introduces an internet based multi-user haptic interface. Hand position is tracked in order
to simulate interactions between two individuals located in different places. Neither of
these two concepts produced a thermal display. Finally, an unpatented Displaced
Temperature Sensing System was developed by CS Research, and consisted of an eight
thermode display with a thin film RTD sensor and thermoelectric heat pump. This device
was unsuccessful in the original equipment manufacturer market (OEM).
The Phantom (SensAble Technologies), a 6 degree of freedom force-reflecting interface
with position tracking (shown in Figure 11), is one of a number of commercially
successful haptic devices embraced by the haptic and VE communities (Salisbury &
Srinivasan, 1997). In 1997, Ottensmeyer appended the Thermostylus (Ottensmeyer &
Salisbury, 1997) to the Phantom platform. The thermal interface is a Peltier device
covered by an aluminum plate. The index finger makes contact with the temperature
display by holding the Thermostylus in a three jaw chuck configuration where the thumb
0
is in opposition to the index and middle fingers. Heating and cooling rates of 11 C/s and
4.50 C/s respectively are achieved with a water based heat sink, proportional integrated
(PI) control, and 0.1 Hz system bandwidth. Ottensmeyer combines force feedback with
the thermal display to simulate palpation of a feverish patient, dragging a probe through a
viscous fluid, feeling the heat at the interior of the sun and experiencing gravitational
forces.
30
Figure 11. Phantom (SensAble Technologies, MA).
Another invention, "the haptic doorknob" from Interval Research, illustrated in Figure
12, features torque, haptic, auditory and thermal displays (MacLean & Roderick, 1999).
The designers aspired to convey clues about the space beyond the door such as the mood
or number and type of people inside. A Peltier device is embedded in the mechanical
portion of the doorknob while the stationary aluminum back doubles as a heat sink. The
display outputs approximately 10*C above and below ambient temperature in 30 s peak
to peak. The real time system architecture updates torque at 1 kHz, auditory output at 88
Hz, and proportional integrated derivative (PID) control of the thermal display at 20 Hz.
Figure 12. Haptic doorknob (Interval Research, CA).
There are several research groups working on thermal displays: Caldwell in England
(1993, 1996), Bergamasco in Italy (1994, 1997), Ino in Japan (1993) and Dionisio in
Germany (1997). Dionisio (1997) emphasizes global integration of all heat transfer
modalities. He introduced the ThermoPad, a thermal kit for graphics-based virtual reality
31
applications, that can be used in conjunction with force-feedback devices. As the user
walks through a computer based virtual reality scenario, the hardware delivers
corresponding conductive (Peltier), convective (fan) and radiative (IR lamp) heat
(Dionisio et al., 1997). The ThermoPad can be integrated with other hardware (Phantom)
to simulate collision detection and grasping for arthroscopy training.
Bergamasco et al. (1994) investigated dextrous manipulation and exploration for both
virtual environment and teleoperation applications using a 7-degree-of-freedom
exoskeleton. His prototype integrates thermal feedback and indentation stimulation using
Peltier devices and air pressure. He presents several theoretical finger-object thermal
models including a full description of finger-Peltier interaction, and describes PID control
for the Peltier device.
Caldwell et al. (1993, 1996) built a teleoperated robot hand as part of a master-slave
system from PVC bones, Kevlar tendons and pneumatic muscle actuators with three
fingers and a thumb. The robot's sensors evaluate dynamic slip, texture, pressure, shape,
hardness, and temperature. Tactile feedback is channeled back to the user through a
glove outfitted with various transducers and Hall-effect position sensors. The thermal
display, positioned on the dorsal side of the first proximal phalanx of the index finger,
includes an aluminum plate heat sink and a thermocouple in contact with the skin and
Peltier device. A 16 channel A/D converter with 12 bit resolution scans both components
at 5 kHz (Caldwell & Gosney, 1993).
Ino et al. (1993) have also studied thermal transients targeted for master-slave robotic
systems and virtual reality applications. They conducted psychophysical testing to
understand how to present the quality of different materials using thermal feedback.
Finger contact with aluminum, rubber and wood samples at room temperature showed
decreases in skin temperature of 6.9*C, 2.6'C and 1.7*C respectively. These data were
used to simulate the three materials with the Peltier device. Presentation of two
simulated aluminum samples was correctly identified 100%, whereas presentation of
polyacrylate and glass were successfully identified only 6% of the time.
32
8. Preliminary testing
The objective of the current research was to create a structurally flexible, servocontrolled, thermally conductive display that could be used for psychophysical testing.
An integrated heater and temperature sensor attached to thin-walled plastic tubing
replaces the traditional Peltier designs. System response speed comes from 16 bit A/D
and D/A conversion, along with electronic components. Initially, various temperature
sensors were evaluated in terms of performance. A Peltier-based system was then
designed and built to determine the appropriate size and distribution of thermal elements
in a display that was to be used with the hand. Finally, a series of experiments were
conducted to determine the physiological and psychophysical responses to thermal
stimuli and materials with varying thermal conductivity.
8.1. Sensor selection
Criteria for selecting a temperature sensor included geometry, robustness and
performance. A custom manufactured thin film RTD (JP Technologies, NC) a J-type
thermocouple (iron-constantan, accuracy ± 1.2-2.2'C), and a standard Omega thin film
RTD (F3105) represent small, inexpensive temperature sensors that function over a range
of 0-100 0 C. These three sensors were fixed to a Melcor Peltier device (DT 6-6) which
was in turn mounted with thermal grease (Omegatherm 201) to a fluid cooled (30%
ethylene glycol, 70% water) heat sink (VWR Recirculating Chiller). The temperature of
the Peltier device was manually controlled with a DC Power Supply (Hewlett Packard,
E3632A). A Visual Basic program commanded the data acquisition unit (Agilent
34970A), and sampled the sensors at 4 Hz.
Thermocouple leads were connected directly to the high/low terminals of the data
acquisition module, whereas the RTDs were connected in a four-wire configuration
(Figure 13). A large supply current which passed through the RTDs induced superfluous
current from lead resistance. By sampling the voltage with leads separate from the
current carrying wires, measurement accuracy was improved.
33
L7
1,
L3
Figure 13. Honeywell Microswitch 4-wire setup (Honeywell, 1998).
The three sensors were initially at room temperature (30*C) and responded similarly to
the changes in temperature generated by the Peltier device. A series of 10 trials were
repeated with different input voltage steps in the range of 0-7 V to heat and cool the
Peltier device. Figure 14 shows an example of one of these trials in which the Peltier
device charged to 5 V after 100 s, and returned to null voltage after 350 s. The JP
Technologies RTD responded most sensitively to temperature fluctuations as shown by
the peaks and troughs in Figure 14. This was presumably due to its lower thermal inertia.
This response profile made it the sensor of choice.
60
50
40-
20
100
0
100
300
200
400
500
600
Time (sec)
Figure 14. Sensor comparison; Red is JP Technologies RTD,
blue is thermocouple and green is Omega RTD.
8.2. JP Technologies thin film RTD
The JP Technologies custom-made platinum serpentine resistor is 4.2 mm x 5.6 mm x 5
tim thick, emulating a typical strain gauge design (Figure 15). The polyimide exterior
with the following thermal properties: 0.121 W/m0 C in conductivity, 1090 J/kg0 C in heat
capacity and 400'C melting point, encapsulates the pure platinum characterized by 69.1
34
W/m*C in conductivity, 1340 J/ kg*C in heat capacity and 1769 0 C melting point. A
summation of the 25 jim wide trace, scanned with magnifying lenses and a video camera
(Sony 1394), reveals a conductor surface area of 2.6 mM (Figure 16). The fragile
2
platinum ribbon leads have recently been replaced with more durable 36 gage wire.
0.107to.010
r0210
0.220*0.010
*D
0.001 X 0.015 NOMINAL
Figure 15. JP Technologies Thin Film Resistor (JP Technologies, 2001).
Figure 16. Serpentine resistor of RTD.
The platinum current density is approximately 107 A/m 2 , and like all conductors, it selfheats in response to a supply current. The 100 1 ice point RTD is specified for
maximum operation at 5 V, which translates into 0.050 A.
In order to understand better RTD self heating, a series of experiments analyzed the RTD
response to a current input. Current was delivered to the RTD and the corresponding
voltage from the power supply was recorded using the same leads. Current was
35
controlled manually, increasing in steps of 5 mA. During the first trial, the RTD was
suspended in free air, exposed only to natural convective cooling. For the remaining five
trials, the RTD was glued to a heat sink with temperatures ranging from 10-80'C. The
heat sink was made of plastic tubing with water flowing through it. The effect of the
water's large heat capacity in comparison to the cooling effects of free flowing air is
evident in the data shown in Figure 17. The varying heat sink temperatures had a greater
impact at higher input currents. At 50 mA, there was a 1.7 V difference in RTD output
between a 10*C and an 80'C heat sink. At 0.040 A, the polyamide began to burn into a
white ash which radiated outward with increasing current.
14 -
-
12 -
-
10
-
8
--
-
Free air (23C)
- 20*C
-60
4000 C
C
80C
-6
4
2
0 4
0
0.01
0.03
0.02
0.04
0.05
0.06
Current (A)
Figure 17. RTD response to water circulating through a thin-walled vessel.
8.3. Hot and cold transients
The next series of experiments was concerned with quantifying the response of the pad of
the index finger to hot and cold temperature transients. The first set of experiments
measured the finger temperature as it contacted a thin-walled tube streaming with water.
In the second set of experiments, finger temperature was measured as the finger made
contact with forty different materials with varying thermal conductivity.
8.3.1. Thermal transients via water
Fixture one was built to examine a finger's response to hot and cold constant
temperatures. It was an open-ended hollow cavity, which minimized convective effects,
and was equipped with a 4 mm diameter tube through which water was constantly
36
flowing (Figure 18). The RTD was bonded to the external contour of the tube. The
finger was not in contact with the tube for the first 10 s of the trial. The subject then
placed her finger on top of the sensor and the hand remained immobile for the completion
of the trial which lasted 500 s.
Figure 18. Fixture one.
A Visual Basic program (Appendix A) controlled the data acquisition and chiller as
previously described, and temperature was sampled at approximately 1 Hz. Ambient
temperature was measured with an RTD suspended in air (24*C) and initial skin
temperature was taken with an RTD held between two fingers (31.6'C). A hot (43*C)
temperature was delivered by the recirculating chiller using a PID controller. The actual
temperature at the fingertip was measured with the RTD attached to the tube.
Figure 19 illustrates the change in RTD temperature as the finger approaches the tube
(the vertical portion), makes contact with the tube (the spike), and then remains stationary
on the surface. Finger temperature converges to fluid temperature in approximately 500
s. These data are similar to Bergamasco et al.'s (1997) model generated using Equation
6.
37
46 -
C
0 1
42
38
34
-
30
600
400
200
0
Time (sec)
Figure 19. Time response of index finger to heat.
A second experiment involving Fixture one analyzed finger thermal responses to 12
intermittent temperature input steps to a temperature of 45*C. The subject made contact
with the tube for 20 s, removed her hand, suspended it in air, and then replaced it on the
tube 20 s later. The trend line as seen in Figure 20, stabilized after 250 s of contact. This
setup did not control for the contact location nor for the surface area between the finger
and sensor with repeated trials.
504642-
38E-
3430 0
100
200
300
400
500
Time (sec)
Figure 20. Time response of index finger to 20 s interval heat input steps.
8.3.2. Material induced transients
Fixture two was designed to control finger repositioning and contact pressure, and tested
the finger's thermal response to a range of 40 materials at ambient temperature. The
fixture layout included a vacuum formed plastic mold of a finger that was screwed into a
delrin base (Figure 21). The mold, pulled over an epoxy coated plaster cast, was
38
originally made by immersing the hand in Earthium (MSW Creative, NV), a biofriendly
silicone-like medium. The base contained a 12.5 mm diameter slot into which 12.4 mm
diameter material samples could be inserted and exchanged during testing. The samples
were turned from 12.7 mm (% inch) rod stock, milled and sanded to provide a flat,
smooth contact surface with minimal textural cues. The sensor used for measuring finger
pad temperature was offset laterally to enable direct material contact and was affixed
with a biocompatible cyanoacrylate (Dermabond, Closure Medical). A second sensor
was fastened to the material sample with 25 lim double-sided tape (Medical grade 1512,
3M) and monitored its temperature.
Figure 21. Test fixture two (left) and example of material samples (right).
Three female subjects between the ages of 24 and 27 participated in this experiment.
Each signed a consent form. An RTD was glued to the side of the index finger. Initial
skin (finger) temperatures ranged from 20-30*C and ambient temperature was 24*C ± 2
as measured with an RTD in free air. The subjects were instructed to insert their fingers
into the plastic finger mold for 2-3 s. The finger then stayed in contact with the material
for the remainder of the 12 s trial. The data were sampled at approximately 30 Hz. This
arrangement was repeated once for all 40 material samples, with 30 s breaks between
trials. The experiment lasted approximately 60 minutes.
Figure 22 illustrates the initial finger temperature and response to contact with naval
brass, PVC and stainless steel for the three subjects. The initial skin temperature of each
subject varied during the testing period, and only a minimal change in temperature was
39
detected upon contact. There was no consistent change in temperature associated with a
specific material. Average skin temperature for Subject 1 was 21.5*C which increased
0.7 0 C upon contact. At 2 seconds after contact, the temperature of Subject 2 increased on
average 0.4-0.6*C above its initial range of 25-31 C. Initial skin temperature of Subject
3 averaged 28*C, varied 5.54C during testing and changed 0.1 C upon contact.
32
28
26
*L
E0
Subject 2
Subject 1
-
30
28
24
26
22
2
24-
20
22
18
0
2
4
6
8
0
10
4
2
23.5
Subject 3 1
30
23.4
28
23.3
u 26
a.
2
2
0.
0.
E
10
8
Time (sec)
Time (sec)
32
6
24
23.2
23.1
23
22
0
2
4
6
8
0
10
2
4
6
8
8
10
Time (sec)
Time (sec)
Figure 22. Finger temperature results for three different subjects contacting naval brass (blue),
stainless steel (red) and PVC (green) in top left and right, and bottom left;
0.5 0C scaled response for subject 2 to HDPE in bottom right.
The thermal response of the finger to contact with the 3 materials was fairly consistent
for the same subject but varied between subjects. This may be due to differences in the
initial skin temperatures and the varying ways in which the subject made contact with the
material.
In the lower right graph of Figure 22, the temperature scale is reduced from 10*C to
0.5'C. This shows the 0.3 0 C increase in the finger temperature of Subject 2 upon contact
40
__________________________________________________________________________
JJ
Ii"'*
''~J~IinIUWL[
with the material at an initial skin temperature of 23.1 4C. The skin temperature initially
overshoots and settles to a temperature of 23.3*C approximately 3 s after contact. The
initial peak of skin temperature may be explained by the increased pressure inside the
mold as the finger approaches the material, similar to a piston compressing air in a closed
cavity.
A steady decrease in skin temperature occurred in all three subjects throughout the one
hour testing period, independent of material contact. This was attributed to a lack of
finger motion after attachment of the sensor. An additional experiment was therefore
conducted in which the hand was rewarmed to 30'C prior to each trial by placing it on
the recirculating chiller for several minutes. This experiment followed the procedure
described above, although only seven material samples were presented to a single subject.
The results from this experiment are shown in Figure 23. All seven temperature curves
follow the same profile, peaking at full finger contact, followed by a decrease in skin
temperature to below 30'C. The final steady state temperature is a function of ambient
and normal skin temperature. Finger contact with metals resulted in a larger temperature
increase than for insulators, but no specific correlation was observed for final steady state
temperatures.
31
30.8
-
30.6
-
Aluminum
A luminum Bronze
Stainless Steel
--
-
-
-
-
-
Naval Brass
Nickel
Polyester
-PBT
Linen
30.4
30.2
30 29.8
29.6 29.4
29.2 29
0
2
6
4
8
10
Time (sec)
Figure 23. Finger temperature results for hand rewarmed to
30*C prior to contact with each of seven materials.
41
12
8.3.3. Force sensors integrated with thermal testing
A force sensor was added to the test fixture to identify the point of finger contact with the
material and to help explain unexpected changes in finger temperature. Miniature force
sensitive resistors such as the FSR (Interlink electronics, CA) and FlexiForce (Tekscan,
MA) have been easily used in haptic displays (Caldwell et al., 1996; Monkman & Taylor,
1993). They operate in low force ranges (0-2 N) in which resistance decreases with
force. These pressure sensitive transducers achieve equilibrium after 30 s and so are
recommended for use in threshold or switch applications.
Load cells, albeit cumbersome and more costly, are a better option for accurate real time
force measurement. An Omega load cell with an operating range of 0-9.8 N was
positioned under Fixture two so that the forces transmitted by the finger through the
material sample could be measured by the load cell below. The load cell was connected
to the Agilent Data Acquisition Unit and controlled using a Visual Basic program similar
to the one used to measure temperature (Appendix A).
In an effort to minimize noise, a signal conditioning amplifier (Measurement Group, NC)
was added to the setup. Comparison of the constant force response with and without the
signal conditioning amplifier (SCA) confirmed that it was useful for voltage gains up to
one order of magnitude (Figure 24).
0.002
--
0.001
0
-0.001
-0.002
0
20
10
30
40
Time (sec)
Figure 24. Force measurements with a unity gain signal conditioning amplifier (blue) and reading
directly into the acquisition system (red).
42
Larger gains, however, amplified the noise to that produced without the SCA. Figure 25
displays the force-voltage relation measured using calibrated weights from 0-1 kg. The
sensor can be used in the linear zone by preloading to 25% of its full range.
0.008
--
250
0.0007x - 6E-05
> 200
---------
0.006
0.006
y
=
-
-
-150
0.004
100
>
0.002
- 50 -
0
0
0
2
4
6
8
10
0
500
1000
Mass (g)
Force (N)
Figure 25. Calibration for force sensor (left) and accuracy of the value with varying mass (right).
Several material contact experiments as described above were repeated with the force
sensor now recording the forces generated by subjects as they made contact with the
material. The force data facilitated identification of contact time and the average force
measurements matched previously reported values of 0-2 N (Caldwell et al., 1996; Ino et
al., 1993; Pawluk & Howe, 1999; Westling & Johansson, 1987).
8.4. Peltier prototype
This prototype was designed as a portable interactive display to determine the number
and size of individual thermal units required for a display. The user interface comprised
a concave mold of the human hand with eight Peltier devices inserted at five digit and
three palmar locations (Figure 26).
Figure 26. Distribution of peltier devices on hand mold.
43
........
..
The plastic thermoform was pulled over a detailed mold of the hand as described in
section 8.3.2. The miniature Peltier device (MIl01T, Marlow) contained 2 negative and
positive doped semiconductor pairs as shown in Figure 27. The performance of these
devices is illustrated in Figure 28.
Figure 27. Peltier device (Marlow, TX).
Hot Side Temperature: 500C
Hot Side Temperature: 27*C
60.0
.U
40.0
20.0
0.0 0
w
CD
I-J
0
60.0
40.0
20.0
0.0
0.8
0.6
0.4
HEAT
LOAD
(WATTS)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
80.0
HEAT
LOAD
(WATTS)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
80.0
0.8
-
-
0.2
0.0
0.0 0.2
w 0.6
CD
I0.4
-J
0
0.2
T=0
0.4 0.6 0.8 1.0
CURRENT (AMPS)
0.0
0 .0 0.2 0.4 0.6 0.8 1.0
CURRENT (AMPS)
1.: 2
Q=0
A T=0
1.2
Figure 28. Performance characteristics of specific peltier device (Marlow, TX).
44
The form was mounted on an electrical project box with power switches labeled on the
exterior (Figure 29). Each Peltier device had independent on/off control via a dual in-line
parallel (DIP) switch. This feature facilitated future testing for thermal stimulus
locations.
Figure 29. Peltier prototype.
The Peltier devices operated best with a current source (Bergamasco et al., 1997) and
together the eight devices drew 1 A. A current source circuit selected from Horowitz &
Hill (1989) converted voltage from two 1.5 V batteries in series to satisfy the portable
prototype specification. A follower was chosen to isolate the voltage divider in Equation
31, from the load,
V
R2
2
i
31
where R1 is a 10 kO resistor and R2 a 10 kQ potentiometer. A unity gain stable Burr
Brown operation amplifier (OPA337PA) offered very high impedance such that the
calculated resistance was determined by the voltage divider resistance. The op amp could
not source sufficient current and was replaced by two NPN transistors in series. An
emitter follower, characterized by input impedance much greater than output impedance,
had a large current gain without voltage gain. The emitter of a transistor by definition
was 0.7 V less positive than the base. If the base did not exceed this value, the emitter sat
at ground. A total 1.4 V drop was therefore included in the circuit calculations between
voltage divider output and load input.
Closure of the first normally-open Peltier dipswitch (P1) triggered a large voltage jump.
A 10 kO resistor was added in parallel with the Peltier devices to minimize the transition
45
from no-load condition. The negative feedback of an op amp would also have
compensated in this situation. The complete circuit diagram is shown in Figure 30.
Future improvements to the circuit include adding a resistor in parallel with the
potentiometer to maintain current flow when the potentiometer is at its rail, and changing
the battery to one with less decay over time.
G2
PI P2 P3 P4 P5 P6
3V
-R3
P7
P
.
I1OK<
Batery
10K
I OKZ
Fow~er
T Supply
Figure 30. Peltier prototype ciruitry.
The operation of the prototype was confirmed using both power and battery supplies
(Figure 31) by fastening an RTD to each Peltier surface with double sided tape to
measure the temperature response. The power supply charged each Peltier device with
0.194 V while the battery delivered 0.119 V to each Peltier.
35
-
33
33
31
31
-----
35
-
-
-
29
-
27
------Digit 2
25
--
--- Digit 3
Digit 4
-
Digit 5
23
Thumb
2
Thumb
Digit 2
Digit 3
29 -
1
S 2
25
'
0
---
--------
23T
4
6
Time (sec)
8
0
10
2
4
6
8
10
Time (sec)
Figure 31. Prototype performance with power supply (left) and battery (right).
8.5. Psychophysical testing
The last set of experiments set out to identify what differences in material thermal
conductivity could be discriminated by subjects. A material discrimination task was
designed that required subjects to discriminate between two materials presented to the
fingers. Five female and five male subjects between the ages of 22 and 45 participated in
this experiment. There were five different materials selected: copper, brass, stainless
46
......
--- _-. .................................
steel, nickel and nylon. The thermal conductivities of these materials ranged from 0.48 to
388 W/m0 C.
Before testing, the subjects signed a consent form, and washed their hands with soap.
Subjects inserted their left and right index fingers into separate delrin compartments as
shown in Figure 32. Two 50 mm x 12mm samples were inserted into the compartments
prior to each trial. Subjects were discouraged from lateral scanning of the test surface,
but lifting and replacing the finger was recommended for improved discrimination.
Figure 32. Material discrimination fixture.
Every possible combination of materials including presenting the same material to both
hands was tested. This resulted in 15 combinations which were repeated five times. The
procedure was a two alternative forced-choice method in which the subject had to choose
the warmer of the two samples. They were also asked to provide a confidence rating on a
scale of 1-5 with one being the most confident. Each set of 15 pairs took approximately
five minutes to present and there was a one minute break between each set of 15 trials.
Table 3 shows the group data for discriminating between different materials. Nylon was
the most easily discriminated material which was possibly due to textural cues. The
difference in thermal conductivity between nylon and the other materials is at least three
orders of magnitude. Nickel and stainless steel were the only other material combination
that was correctly discriminated above the specified threshold level of 75%. The
difference in their thermal conductivities is 35 W/m0 C.
47
Table 3. Percent of correctly identified material in pair presented to subject.
Nylon
Stainless Steel
Nickel
Brass
Copper
Nylon
x
x
x
x
x
Stainless steel
90
x
x
x
x
Nickel
92
76
x
x
x
Brass
96
56
56
x
x
Copper
88
60
58
58
x
When the same materials were presented together, the subjects performed at chance as
shown in Figure 33, and did not show any response bias in terms of the left and right
hand.
80
60 O 40 20 0Brass
Copper
Stainless
steel
Nylon
Nickel
Figure 33. Percentage of trials in which subjects indicated that the left (red) or right (blue) hand was
presented with the warmer material, when the same material was presented to both hands.
48
9. RTD thermal display
The initial research goal was to create a unique thermal display that was adaptable in
terms of the size and location of the elements as well as the temperature output control.
The final part of this research project was to design an electronic circuit to enable
combined temperature sensing and output with the use of a single RTD. This would
provide the basis of a future thermal display.
Sampling rate limitations experienced with the Visual Basic program and Agilent
hardware led to modifications in hardware and software. A National Instruments board
with 8 A/D and 2 D/A channels (PCI- MIO- 1 6XE- 10) replaced the Agilent Data
Acquisition modules, and MathCad 2001i (Appendix B) was used to control data
acquisition and analysis. A C++ program (Appendix C) interfaced between the two.
The initial electronics layout of a dual function RTD sensed temperature with a low
frequency signal and heated with a higher frequency AC signal. To induce a high
frequency ripple from a steady DC voltage source required at a minimum, oscillator and
wave rectifying circuits. However, initial experimentation began with a single supply
that produced heat and sampled temperature at the same frequency.
49
9.1. Circuit design
Current output to the RTD was controlled by the MathCad program and was delivered via
a D/A channel, and temperature was sampled through an A/D channel. A power
amplifier (PA26, Apex) converted the computer output voltage to a higher current with a
gain of 10 mA/V with resistor values RI, R2 and R3 as shown in Figure 34 (Fox, 1978).
Vs+
H.68uF
.47uF
R2 10K
Vs+
out
In
IL 4 R3
13 100
)H&.47uF
Vs-
-) & .68uF
Figure 34. Final prototype circuit.
System equations were derived with Kirchoff's voltage and current laws, along with the
amplifier rule demanding equivalent inverting and non-inverting inputs.
IL
2
V = IR3
Ri
IL
32
3 9
, and
K(+R
V
R3 )R I
33
34
An Amp02 instrumentation amplifier (Analog Devices, MA) measured the voltage across
the RTD load without drawing current. A dual tracking power supply (HP E3631A)
output +12 V to both amplifiers satisfying the requirements to swing the power amplifier
inputs to zero, while minimizing self-heating effects. To prevent power supply
oscillations, a high frequency bypass ceramic capacitor (0.47 liF) and low frequency
bypass (10 ,LF/A of peak output current) tantalum capacitor were inserted between
50
ground and both sides of the voltage supply. The maximum power dissipation (PD) for a
pure resistive load occurred when the amplifier output voltage was
2 supply
voltage (6
V) and estimated at 0.36 W according to:
PD =
35
.
4RL
9.2. RTD testing
A 100 0 resistor was used in place of the RTD during circuit construction to prevent
accidental burning of the platinum device. Figure 35 shows the output behavior
difference between the resistor and RTD loads, with manual voltage inputs from the
power supply and measured from the Amp02. The deviation from linearity seen in the
RTD load was an artifact of voltage data fluctuating on the Data Acquisition Unit.
10
----
------------
7
---------y
68
5
=
2
3
128822x - 1485.7x + 1 18.06x - 0.0055
2
R I
6
4
3
4
2
0I
00
0
2
4
0
6
Voltage In (V)
0.01
0.02
0.03
0.04
Current In (Amps)
Figure 35. Comparison of RTD load (red) and 1000 resistor load (blue) on the left and
RTD output acquired with universal source on the right.
Testing of the circuit with the more precise Hewlett Packard 3458A Multimeter and
3245A Universal Source produced the curve on the right with a perfect polynomial trend
line. The time response of the RTD for relevant step inputs appears in Figure 36.
51
9
.050A
.015A
.025A
8
-.
O1OA
-.
-
020A
.030A
7
6
E8
-4
3
2
1
I
0
0
a
F
- --
-
I
I I
2
--
4
6
Time (sec)
8
10
12
Figure 36. Time response of RTD with current step inputs.
Voltage from the Amp02 output was converted to a resistance value based on system
equations and then redefined by a corresponding temperature using Equation 20. In order
to servo control the heat output, the system must determine temperature as a function of
current input and current as a function of temperature. The exponential nature of the
voltage-temperature relationship limited the techniques available for bi-directional
conversion to mathematical reversion (Spiegel, 1968; see Appendix B), and inverting the
x and y axes. The reversion curve in Figure 37 corresponded to axis inversion for the
first three data points and drifted thereafter.
52
0.04
---
y
=6E-05x
3
-
0.00 11x 2
+
0.0099x
-
3E-05
R2=0.9999
0.03 -
0.02
1.o
0.01 -
.
0
0
2
4
6
8
10
Voltage (V)
Figure 37. Comparison of inversion of current and voltage axes (red)
and mathematical reversion (blue).
9.3. Future work
The next steps in this project include complete servo control of the temperature display
and integration of an additional 8 channel A/D board to enable up to ten active RTD
elements to be controlled. A mechanical interface similar to the Peltier prototype should
be designed that integrates the RTD with a water-based cooling system.
A 5*C mixture of ethylene glycol and water in contact with the faster responding RTD
will generate precise temperature transients. To date, two meter length plastic tubing
with 0.5 mm wall thickness, enclosed in cylindrical insulation decreases 10 0 C between
the fluid bath and user interface. A 15'C heat output to the user for example, would not
require additional heating from the RTD, while a 23*C output would be compensated
with heat produced by the RTD. Tubing with 20-150 Jim wall thickness minimizes
temperature transients through the tube wall and should be tested with the circulating
fluid.
53
10. Conclusion
A review of thermoreceptor physiology, thermal sensing and thermal display technology
has been presented. Results from initial experiments indicated that skin temperature
upon contact with various materials, was a function of initial skin temperature, ambient
temperature, and material properties. Finger thermal responses were not consistent
between subjects and showed little to no relation to material type. A maximum of 0.7*C
change in skin temperature was measured upon contact with a material at room
temperature. The finger temperature reached a new steady state value 0.5 s after contact.
The time required for the finger temperature to reach steady state in response to a
constant conductive heat source (45'C ) was 500 s, three orders of magnitude longer than
the time required to reach steady state for contact with a material at room temperature.
Intermittent exposure to the same constant heat source reduced the steady state time
constant to 250 s. Results from psychophysical experiments confirmed that successful
material discrimination is limited to material pairs where differences in thermal
conductivities are large and in the range of 200-300 W/m 0 C.
Challenges were encountered in designing experimental systems for human testing
including variation in the applied forces, finger position and initial finger temperature.
Heating the finger prior to each experiment minimized variations in initial skin
temperature. A future method to control applied force and finger position would be to
constrain the hand in a fixed position and have a repeatable apparatus perform the tests.
A fast responding thermal display has been designed and tested using a single RTD as
both a heater and sensor. The integration of a temperature sensor is necessary to monitor
skin temperature due to unpredictable responses to thermal stimulation. The fluid heat
sink used to provide cold transients is most effective at temperatures in the range of 510 0 C. Continued efforts should lead to a fully functional bench-top prototype with ten
individually controlled thermal units.
54
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59
Appendix A: Visual Basic code to control data acquisition
Controls
Initialize Agilent
Initialize Chiller
Specific Heat
Volume Flow Rate (L/rin)
.....
................................
f.....
Save Data
1...........................
T emperature Setpoint (C)
Run Full Test
Trial 1
Set File Path
Force Gages (N)
.6
2
51.5
Volume (L)
2
Max number of Sweeps
25
Status
5-
5-
4-
4-
3-
3-
Sensor 1 (C)
2-
2
Sensor 2 (C)
Fluid Temperature (C)
1-
Sensor 3 (C)
0Left Force Sensor
Left
Right
Hand
Hand
Right Force Sensor
Sweep No.
Figure A.1. Visual Basic graphical user interface.
A.1. Code for force and temperature sensors and recirculating chiller
Option Explicit
'DeI
ne-11
Global Vm-riI)les
Ih
'Start with CIr
oIlT
'Start wvith Agilent on
Dim TempSet As Double
Dim FluidSet As Double
Dim SpecificHeat As Double
Dim Volume As Double
Dim VolumeFlowRate As Double
Dim valueCh() As String
Dim dataCh As String
Dim TVAg() As String
60
Dim SensorData() As String
Dim dataAg As String
Dim dataA As String
Dim slp As New sleep
Dim cnt As Double
Dim SensTempl() As Double
Dim SensTemp2() As Double
Dim SensTemp3() As Double
Dim SensForcel() As Double
Dim SensForce2() As Double
Dim timelogo As Double
Dim SamplingTime As Long
Dim i As Long
Dim NumSamples As Long
Dim imax As Long
object hor delay class
t imer I counter
Private Sub cmdTempSetChange()
End Sub
Private Sub cmdVolFlowRateChange()
End Sub
'Pri vale St iu C\VSlidc POinterValuehanged(Bval Pointer As Lon,
\Variant)
(W\"SIie IN.
ForceGag2Ve.Vailte
1(d Su
Valtie As
Private Sub FormLoadO
'I Porthill Port( )pcn
False TheI
If PortAgilent.PortOpen
=
'Iitialiie C hiller
'Ititaii/le A(i lent 3497()A
False Then
PortAgilent.PortOpen = True
End If
End Sub
Private Sub FormUnLoad(Cancel As Integer)
"o'
Portgilet.Potpn
'Ne d to tilt-t ott chiii icr
I' uls coilrollcr o il
ls
PortAgilent.PortOpen = False
'PortChill.PortOpen = False
61
End Sub
Private Sub InitAgilentClick()
PortAgilent.Output = "SYST:INT RS232" + vbCrLf
Call slp.SleepMS(100)
'Set to R S-232 mode
PortAgilent.Output = "*RST" + vbCrLf
LIect ory Reset
Call slp.SleepMS(100)
PortAgilent.Output = "SYST:REM" + vbCrLf
Call slp.SleepMS(100)
'Set to relot e mode
PortAgilent.Output = "CONF:TEMP FRTD,85,100, (@103)" + vbCrLf
Call slp.SleepMS(100)
PortAgilent.Output = "UNIT:TEMP C,(@103)" + vbCrLf
Call slp.SleepMS(100)
PortAgilent.Output = "CONF:VOLT:DC .1, 0.001, (@105)" + vbCrLf
Call slp.SleepMS(100)
PortAgilent.Output = "FORM:READ:ALAR OFF" + vbCrLf
' dont otpt alarm"11 staflus
Call slp.SleepMS(100)
PortAgilent.Output = "FORM:READ:CHAN OFF" + vbCrLf
' output channel number oHf
Call slp.SleepMS(100)
PortAgilent.Output = "FORM:READ:TIME OFF" + vbCrLf
' out put limec olff
Call slp.SleepMS(100)
PortAgilent.Output = "FORM:READ:UNIT OFF" + vbCrLf
'Do not record uits in (lata
measurement
Call slp.SleepMS(100)
PortAgilent.Output = "ROUT:SCAN (@103,105)" + vbCrLf
'set scan list olf hannels
Call slp.SleepMS(100)
txtSensl.Text = 0
txtSens2.Text = 0
txtSens3.Text = 0
txtForcel.Text = 0
txtForce2.Text = 0
'Fore~iaGeI .ale =
'Force(Gwue2.alue (
Timerl.Enabled = False
End Sub
Private Sub InitChillClick()
'(OM
1I A NIMS
r RS-23ii? not case seisit Ie
62
-
4in
1113
__
- -
-
-
-
I
-
I
'0 = OK
1 Out of range, not accepted
'2 = Ott o a14c, and accepted
'3 =in reognt ized comniand
'4 =tunreconited Irameter
'A I conttrmiis link
'S?= dIspIyk\ setpoint of controller
'S 3 =. = sets cont roller to eip o1 30. 1
'F? isplay currenclt 111uid temp11
'U =display rcadout iI (iegrtees C. F or I
U JOr I = Chantiuc controller to C.
'C or
,
F or
&&&&&& &
'& L Hilnl= sets hiIgIh limit
'&L f in sets low limit
high limit
'&I?. =displkly crreti
& I ? = diplay curtrenit lo\w 1imiII
o 1 decimal~ p1laces
'&P? =- disphiy
3 ciames oF le(cimal places
'& P ( or I or 2 or
& R in sets attto retriu selpomt
setponit
'& R? - displiy aito retri
1 =- cang es t ) internal or I externa l ---- might
'& X ( or
'& X? displays 1nt ext probe
'&1n iumi er bet ween 1-30 1I[Ir Iax di IF
be reversed
'~ssss 5sSSSS55SSSSSSSSSSSsYSSSSSSSSSSSSSSSSSSSSSSSSS
ing Flow rate iII IPM
displays I'll) T
'SIF sets low rate
displays PID I lunine Volutme in it1ers
S\.'
in I itrs
'S\ PI) Tining Voluiic
displays PID lttning Specie Heat
'SS?
's- sets Specific [teat
I)Isplavs degrees (1) t ser I nits Constant
SK I IK2.K3.?
Constanits decrees (I I
Sets
SK 1 K2IK3
'SZ resets all paramtiters to tactorV (iclaut Its
'5P sets PItIImP speed
SF
cont iuous data logeinc
mginiode
disables l
t
'0I IF urn1s controll er oFT
tunis on tilt aid RS232
)N
cil
-
coIII
cmue in \S(CII mod
inIcat
(Hi
ves help
PortChill.Output = "ON" + vbCrLf
'Tnuis unit oil and RS232 commniicatioii
63
-
Call slp.SleepMS(100)
PortChill.Output = "$Z" + vbCrLf
Call slp.SleepMS(10000)
'I need these loll
uilt, takes about 10 sec
'reset to kctorv (I
pauses. ot herwise. the ehi ill1er loesn'i
read anvhing
TempSet = CDbl(txtTempSet.Text)
VolumeFlowRate = CDbl(txtVolFlowRate.Text)
Volume = CDbl(txtVol.Text)
SpecificHeat = CDbl(txtSpecHeat.Text)
PortChill.Output = "S" + CStr(TempSet) + vbCrLf
Call slp.SleepMS(10000)
PortChill.Output = "$F" + CStr(VolumeFlowRate) + vbCrLf
'Set \otllle flow rate
Call slp.SleepMS(10000)
'Set volume
PortChill.Output = "$V" + CStr(Volume) + vbCrLf
Call slp.SleepMS(10000)
'Set Specific Heal
PortChill.Output = "$S" + CStr(SpecificHeat) + vbCrLf
Call slp.SleepMS(10000)
han ge controller to C
msec is 1o short
'Sets 1111m11 speecd
PortChill.Output = "UC" + vbCrLf
Call slp.SleepMS(5000)
PortChill.Output = "$P 1" + vbCrLf
Call slp.SleepMS(5000)
PortChill.Output = "&LH70" + vbCrLf
Call slp.SleepMS(5000)
PortChill.Output = "&LL-50" + vbCrLf
Call slp.SleepMS(5000)
PortChill.Output = "&P3" + vbCrLf
Call slp.SleepMS(5000)
PortChill.Output = "&R50" + vbCrLf
'Sets ligh limit
'Sets low limit
'Scs i
'Seis autoteip set poilit
End Sub
Private Sub cmdRunTestClicko
imax = CDbl(txtlmax.Text)
cmdRunTest.Enabled = False
ReDim
ReDim
ReDim
ReDim
ReDim
ReDim
ReDim
(I Cc places
SensTemp 1(1 To imax) As Double
SensTemp2(1 To imax) As Double
SensTemp3(1 To imax) As Double
SensForcel(l To imax) As Double
SensForce2(1 To imax) As Double
valueCh(1 To imax) As String
timelog(1 To imax) As Double
64
For i = 1 To imax
txtCounter.Text
=i
dataAg = PortAgilent.Input
PortAgilent.Output = "INIT" + vbCrLf
Call slp.SleepMS(100)
PortAgilent.Output = "fetch?" + vbCrLf
Call slp.SleepMS(150)
dataAg = PortAgilent.Input
'keeps user aware ot sweCep nnmher
clear hi. 11'er
'ini11t
ids scaln
col leci ing saiplIes
retrieves dat a
tra nsmits (tata,
'R Ids (tat aIromIi bl (Ter
'Asks for current flui(d temperature
'vh1r
'Portiill.uutput = "= "
'CatI sIp.S eepMS (300)
data(11 = PtO
hill.input
')ala 1rom output lufer (f chiller, string
) t (tat aCh
'aiueC(i
'I may\ havec to do sonmc operatio(n on I hc dat a conm1ing in, uc. remove alI hut #s
TVAg = Split(dataAg, ",")
'E-xtracts data Ir111 string to array. "0" hased into substrin1g.s
rcdtetines TVA,, data in its substrings
SensTempl(i)= TVAg(0)
'SensTemp2(i)= TVAg(1)
'SensTemp3(i)= TVAg(1)
SensForcel (i)= TVAg(1)
'SensForce2(i)= TVAg(1)
'I xtFnidTeipi.Text = ata(
txtSens1.Text= SensTempl(i)
1t\tSens).Tcxt
ScnsTcmp( i)
SensIeip3()
txtForcel.Text
SensForcel(i)
txt Force2.Text
Senstorcc2(i)
't\tSenKIsc.xt
di splyaCurirenlt tliui1d temp
disphly cii rruet sensor I temp
'display cuurreit sensor torce
'Forice~iage I.'\a Inc Senstorce I()
2. Vuinc Scnsorcc.(i)
'orce(a
'I need to deal with thc record sinele data points...
'Split onlv Funuict0io1s oi a 1x somicthine array
cnt
=
'Set tinmer to )
0
Timeri.Enabled = True 'Two different timers, this one is for loop counting
timelog(i) = Timer
'TFhis onc is fIor Ictuial ttime1.
Idj ust sinc
have t io
but I \\ III
it couits seconds tromi
mlidnigt
Next i
cmdRunTest.Enabled = True
'con-t iII uCs loop
End Sub
65
Private Sub cmdSaveClick()
Open "d:\work\experimentdata\" & txtFileName.Text & ".txt" For Output As #1
Print #1, "Time (s)" +"
For i = 1 To imax
"+
Print #1, CStr(timelog(i))+"
"Sensor 1 (C)" +"
"+
"
+ "Force Sensor 1 (N)"
CStr(SensTempl(i)) +"
" + CStr(SensForcel(i))
Next i
Close #1
End Sub
A.2. Code to separate incoming streaming data
Private Sub cmdSaveClick()
imax = NumSamples
Dim
Dim
Dim
Dim
Dim
Dim
firstcomma As Long
secondcomma As Long
xcomma As Long
Datal As String
Data2 As String
DataArray(500, 2) As Double
'Ii 1 edaif
chanil] 10",
Open "d:\work\experimentdata\" & txtFileName.Text & ".txt" For Output As #1
Print #1, "Time (s)"+
"
"
+ "Sensor 3 (C)"
secondcomma = 0
'unit
i/zes secon(dcommnn1m to Ihe sltir1 ol hi'ICr
For i = 1 To imax
xcomma = secondcomma
firstcomma= InStr(secondcomma + 1, dataAg, ",")
'relurns posilon (of 1he firsl occurrence in sin1g
secondcomma = InStr(firstcomma + 1, dataAg, ",")
whereCslo sT-. ?1(d is slrine.
I im(2 comCs iIn secold and dl l in Ii rsl
If i = I Then
Datal = Mid(dataAg, firstcomma + 1, secondcomma - firstcomma - 1)
lime dLn u
DataArray(i, 1)= CDbl(Datal)
Data2 = Left(dataAg, firstcomma - 1)
66
hehore
'ch annel 10"
'use left since it is the first niinmher comin2 in w oti comma
DataArray(i, 2)
Else
=
CDbl(Data2)
If secondcomma = 0 Then
'string. start, length
Datal = Right(dataAg, 7)
't iie at a
DataArray(i, 1) = CDbl(Datal)
Data2 = Mid(dataAg, xcomma + 1, firstcomma - xcomma - 1)
DataArray(i, 2)
Else
=
'channel 103
CDbl(Data2)
Datal = Mid(dataAg, firstcomma + 1, secondcomma - firstcomma - 1)
string, start, length
't i me datal
DataArray(i, 1)= CDbl(Datal)
Data2 = Mid(dataAg, xcomma + 1, firstcomma - xcomma - 1)
'channel I 03
DataArray(i, 2) = CDbl(Data2)
End If
End If
'This is all to d(eal with Get that In first datapoint. there is no comma to start with.....
\x\x x
axixxinit ially I was nust repeat ing first
'Data comes in like "x\x xxxxxxxx1.
2 points over id over
Print #1, CStr(DataArray(i, 1))+"
"+
CStr(DataArray(i, 2))
Next i
Close #1
End Sub
67
Appendix B: MathCad 2001i script
B.1. Converting voltage measured with RTD to temperature
SYSTEM EOUATIONS FOR CIRCUIT
R, := 9992
ohms
R2 := 9973
ohms
R3:= 100.43
ohms
RL:= 100
ohms
Vin:= 3
Volts
I3:= V.
13 =
inR3- R
IL:= 1
+
R2
Vin
R3
R,
U
R2
Gain:= (
R3)
RI
I2:= ~IL + 13
11 := -12
10
mAmps
Volt
12
=
I
=
V2:= 12*R2
V2
V3 :=
:3-R3
V3
VAN DUSEN EQUATION VARIABLES DEFINED
C
A := 3.908 10-3
B:= -5.77510
R := 100
7
Resistance at OC
68
I
=
SETTINGS FOR SAMPLING LOOP
N:= 1000
At:=
Hz
500
OutputRate
At
OutputRate
texp =i
texp:= N-At
sec
sec
i:= 0.. N
Output
time +- timei(At)
for i e
0..
N
timei(0)
Vset +- da(0,V i )
n
Vinst +- ad(0)
(-Vinst)
R. +I
Gain-Vin
Temp, I(- -Ro.A +
R02 .A 2
-
4R 0 .B.(Ro - R,)]
2R 0 -B
Vset
+-
da(0,0.0)
Temp
U
Output i
i. At
Time (s)
69
B.2. Mathematical reversion for polynomials (Spiegel, 1968)
If
5
6
2
3
4
y :=cl*x+ c2 'x + c 3'x + c4 -x + c5 'x + c6 'x.
Then
4
x:= b,-y + b2 'y2 + b3*y3 + b 4.y + b5.y
5
6
+ b6*y .....
i -bl =I CI
3
c1 3 b2 = ' -c 2
2
5
c15 b3 = u 2c2 - c-c3
2
3
7
ci -b4 =, 5c-c 2 -c3 - 5c2 ~ cl -c
4
2
2
9
2
3
cl -b5 = 6c1 -c2 c4 + 3c1 -c3 - c1 -c + 14c 2
5
Cl
11
-b6 =
4
-
2
21c 1 -c2 .C3
3
3
2
2
4
2 2
3
7c, .c2 -c5 + 84c 1-c2 .c3 + 7c, c3 -c4 - 28cl -C2-c3 - c 1 .c6 - 28c -C2
Polynomial equation generated from RTD output in circuit
y := 12882Lx3) - (1485.7x) 2 + 1 18.06x - .0055
c3:= 128822
c2:= -1485.7
c, := 118.06
b y = 8.47 x 10- 3
ci
-C2
b2
b 2 = 9.029x 10
3
ClI
(2c2 2 - cl-c3
5
cI
4
b3 = -4.706x 10~
x:= (8.4710- 3y) + 9.02910~ 4y 2 - 4.70610
70
4 3
y + .0055
- 42C2
Appendix C: C++ code to interface between National
Instruments Data Acquisition Board and MathCad 2001i
C.1. A/D Function
*(C) Ser1e laI ont aine I997-2012*
#include <nidaqex.h>
#include <mcadincl.h>
extern FUNCTIONINFO ad;
LRESULT adFunction( LPCOMPLEXSCALAR
LPCCOMPLEXSCALAR CH);
FUNCTIONINFO ad =
V,
{
"ad",
hich nmliiiathcd(I wilI re(c
Namie hy\
ni/e the tilctiOn
he cailled as ad(channel)
l \\
description o' ad(ch antIel)
pointer to the execiit ile code
the ret urn tvpc is also a complex scalar
"channel",
"return a/d sample from channel",
(LPCFUNCTION)adFunction,
COMPLEXSCALAR,
1,
the hinction takes on I artiment
the armiIent is a complex scalar
{COMPLEXSCALAR}
};
LRESULT adFunction( LPCOMPLEXSCALAR
LPCCOMPLEXSCALAR CH)
V,
{
static
static
static
static
static
static
static
i 16
i 16
i 16
i 16
i16
f64
i 16
iStatus = 0;
iRetVal = 0;
iDevice = 1;
iChan = 1;
iGain = 1;
dVoltage = 0.0;
ilgnoreWarning = 0;
static int load=0;
if(load==0) {
iRetVal = NIDAQErrorHandler(iStatus, "AlVRead",
ilgnoreWarnin g);
load=l;
}
first check to make sure
a has I Imalinary component
retuIrnI
MlAKLSII1(Th
1.
otherwise. all is well so add a and h
iChan = (int)(CH->real);
iStatus = AIVRead(iDevice, iChan, iGain, &dVoltage);
71
4
!6- - -
-R
=4
--
-
-
-- - -
-
--
= i
z-
"
- --
V->real = dVoltage;
return (iStatus=0?0:2); // return 0 to indicate there was no error
}
C.2. D/A Function
* (() Secgc La ont ainc 1997-2992*
#include "nidaqex.h"
#include "mcadincl.h"
extern FUNCTIONINFO da;
LRESULT daFunction( LPCOMPLEXSCALAR RC,
LPCCOMPLEXSCALAR
CH,
V);
LPCCOMPLEXSCALAR
FUNCTIONINFO da =
{
"da",
"Ch,V",
"d/a convertion of V"
(LPCFUNCTION)daFunction
COMPLEXSCALAR,
2,
Name by which mathicad wviI recogniz theilifctiol
transpose wvil he aCcd as da(C(.V)
dese ri p1 ion
poilter to the exeitilhic Code
the oupu is a complex scalar
the func ion takcs on 2arciuments
COMPLEXSCALAR, COMPLEXSCALAR}
the input types are a Complex scalirs
LRESULT daFunction( LPCOMPLEXSCALAR
LPCCOMPLEXSCALAR CH
LPCCOMPLEXSCALAR V )
{
RC,
static i16 iStatus = 0;
i16 iRetVal = 0;
il6 iDevice = 1;
il6 iChan = 0;
f64 dVoltage = 0.0;
i16 iIgnoreWarning = 0;
static int load=O;
if(load=0) {
iRetVal = NIDAQErrorHandler(iStatus, "AOVWrite",
iIgnoreWarning);
load=1;
}
iChan = (int)(CH->real);
static
static
static
static
static
dVoltage = V->real;
iStatus = AOVWrite(iDevice, iChan, dVoltage);
RC->real=iStatus;
return (iStatus==0?0:2);
return ) to indeate there was no crror
}
72
II =
C.3. Timer Function
*( C)Scire Ialj
1
taine
7-
2
#include <Wtypes.h>
#include <Winbase.h>
#include "nidaqex.h"
#include "mcadincl.h"
extern FUNCTIONINFO timer;
LRESULT timerFunction( LPCOMPLEXSCALAR RC,
DT);
LPCCOMPLEXSCALAR
FUNCTIONINFO timer =
{
\ame hy \which mat hcad wv ill recogn ie lie funt0on
"timer",
"dt",
timier will Ibe cal led as I mer( dt)
"sleep to next dt"
(LPCFUNCTION)timerFunction,
COMPLEXSCALAR,
1,O
{ COMPLEX_SCALAR }
descript ion of Iimer(kdi)
poInIIer to 1he executihle code
11le output is a complex scalar
the function takes on I argument
the input type is a complex array
LRESULT timerFunction( LPCOMPLEXSCALAR
LPCCOMPLEXSCALAR DT )
{
RC,
typedef struct _TIME {
unsigned long low;
unsigned long high;
} TIME;
static TIME Time, Freq;
static double second, s, freq, period;
static double Dt;
static double MS = (2.*(double)((unsigned)1<<31));
if( DT->real>O.) {
Dt = DT->real;
QueryPerformanceFrequency((LARGEINTEGER *)(&Freq));
freq=(double)Freq.low;
period=(1./freq);
QueryPerformanceCounter((LARGEINTEGER *)(&Time));
second = (MS*Time.high+(double)Time.low)/freq;
RC->real=second;
return(0);
}
s = second + Dt;
do {
QueryPerformanceCounter((LARGEINTEGER *)(&Time));
second = (MS*Time.high+(double)Time.low)*period;
73
}while(second<s);
RC->real=second;
return (0);
retlurn ) to ind(icatc there
}
74
\\
as no error