A semiconductor thermocouple unit is provided for heating and cooling memory metal actuators. The semiconductor thermocouple unit is mounted adjacent to a memory metal actuator and has a heat sink attached to it. A flexible thermally conductive element extends between the semiconductor thermocouple and the actuator and serves as a heat transfer medium during heating and cooling operations

Wood, Charles

English

NASA Technical Reports Server

United States Patent [191 [11] Patent Number: 4,765,139 
Wood [45] Date of Patent: Amg. 23, 1988 
THERMOCOUPLE FOR HEATING AND 
COOLING OF MEMORY METAL 
ACIVATORS 
Inventor: Charles Wood, Flintridge, Calif. 
Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 76,956 
Filed: Jul. 23,1987 
Int, (3.4 ................................................ F03G 7/06 
U.S. Cl. ...................................................... 60/527 
Field of Search ................. 60/527, 528, 529, 530, 
60/531; 337/139, 140 
References Cited 
U.S. PATENT DOCUMENTS 
2,989,281 6/1961 Fritts ................................. 60/529 X 
3,194,010 7/1965 Lejon .................................... 60/531 
3,652,969 3/1972 Willson et al. . 
3,676,815 7/1972 Du Rocher . 
3,849,756 11/1974 Hickling . 
4,205,293 5/1980 Melton et al. . 
4,520,336 5/1985 Hastings et al. . 
4,544,988 10/1985 Hockstein . 
4,551,974 11/1985 Yaeger et al. . 
4,553,393 11/1985 Ruoff ................................ 60/527 X 
4,556,934 12/1985 Lemme et al. . 
FOREIGN PATENT DOCUMENTS 
219478 2/1985 Japan ..................................... 60/527 
Primary Examiner-Allen M. Ostrager 
Attorney, Agent, or Firm-Paul F. McCaul; John R. 
Manning; Thomas H. Jones 
[571 ABSTRACT 
A semiconductor thermocouple unit is provided for 
improving heating and cooling of memory metal actua- 
tors. The semiconductor thermocouple unit is mounted 
adjacent to a memory metal actuator and has a heat sink 
connected thereto. A flexible thermally conductive 
element extends between the semiconductor thermo- 
couple and the actuator and serves as a heat transfer 
medium during heating and cooling operations. 
15 Claims, 2 Drawing Sheets 
(-50 *J POWER SUPPLY 
https://ntrs.nasa.gov/search.jsp?R=19880019767 2020-03-23T19:57:25+00:00Z
U.S. 1988 
%\ 
Sheet 1 of 2 4,765,139 
44 1 ‘50 
20 
U.S. Patent Aug. 23,1988 Sheet 2 of 2 4,765,139 
7 3 4  
n 
4.765,139 
1 
THERMOCOUPLE FOR HEATING AND 
COOLING OF MEMORY METAL ACTUATORS 
BACKGROUND OF THE INVENTION 
1. Origin of the Invention 
The invention described herein was made in the per- 
formance of work under a NASA contract, and is sub- 
ject to the provisions of Public Law 96-517 (35 USC 
202) in which the Contractor has elected not to retain 
title. 
2. Field of the Invention 
The present invention relates to memory metal actua- 
tors, and more specifcally, to thermocouples for rap- 
idly heating and cooling memory metal actuators. 
3. Description of the Prior Art 
Memory metal actuators formed of alloys such as 
Nitinol have been known for many years. Memory 
metal actuators are manufactured by forming such al- 
loys into one shape while hot and another while cold. 
When a sufficient amount of heat is applied to the actua- 
tors to raise their temperature above the critical temper- 
ature of the alloy from which they are formed, the 
actuators snap from their cold shape to their hot shape. 
When the heat is removed, the actuators return to their 
cold shape. 
In the past, heating of memory metal actuators has 
been performed by many methods, including direct 
application of current and heat conduction from a heat 
source via metal wires or metal thermocouples. The 
heating times attained by the direct application of cur- 
rent have been adequate for most purposes, and have 
not generally been matched by other methods of heat- 
In contrast, the cooling times of memory metal actua- 
tors have not been quite as impressive. Common meth- 
ods of cooling memory metal actuators have included 
placement and operation of actuators in cool environ- 
ments such that convection is a continuouslv ongoing 
ing. 
tor thermoelectric generator. The thermally conductive 
element flexes to accomodate changes in shape of the 
actuator. 
5 BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 illustrates the semiconductor thermocouple 
unit of the present invention. 
FIGS. 2A and 2B illustrate the semiconductor ther- 
mocouple unit of FIG. 1 in its operable position adja- 
10 cent to a h e a r  memorv metal actuator. 
15 
20 
25 
30 
35 
- - -  
process, and by conduction of heat from the actuators 40 
to heat sinks via metal wires or metal thermocouples 
(see U.S Pat. No. 4,553,393 to Ruoff). 
In many instances, it is desirable to increase the heat- 
ing and/or cooling rate of memory metal actuators. It is 
especially desirable to increase the cooling rate of actu- 45 
ators in applications such as robotics in which actuators 
may be continuously cycled between their hot and cold 
shapes. In such applications, a disproportionate amount 
of each cycling period has conventionally been attribut- 
able to the cooling function. 
SUMMARY OF THE INVENTION 
The present invention is directed to an apparatus for 
improving the heating and cooling rates of memory 
metal actuators. The present invention includes a high 55 
efficiency semiconductor thermoelectric generator 
which may be mounted in proximity to the memory 
metal actuators. A flexible thermally conductive ele- 
ment extends between the semiconductor theremoelec- 
tric generator and the actuator and functions as a heat 60 
transmission medium. When a power supply is activated 
to supply DC current of a first polarity to the semicon- 
ductor thermoelectric generator, heat is generated 
which may be supplied to the actuators via the ther- 
mally conductive element. When cooling is desired, the 65 
polarity of the DC current may be reversed, biasing the 
thermally conductive element to draw heat from the 
actuator to a heat sink in contact with the semiconduc- 
50 
FIGS. 3A and 3B ilkstrate the semiconductor ther- 
mocouple unit of FIG. 1 in its operable position normal 
to the direction of deformation of memory metal actua- 
tors. 
FIG. 4 illustrates an alternate embodiment of the 
semiconductor thermocouple of the present invention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
The following description is of the best presently 
contemplated mode of carrying out the present inven- 
tion. This description is made for the purposes of illus- 
trating the general principles of the invention and is not 
to be taken in a limiting sense. The scope of the inven- 
tion is best determined by reference to the appended 
claims. 
The present invention is directed to increasing the 
rate of cycling, and especially the rate of cooling, of 
memory metal actuators. This is accomplished by plac- 
ing a high thermal efficiency semiconductor thermo- 
couple unit in contact with a memory metal actuator. 
By applying a DC current of a selected polarity to the 
semiconductor thermocouple unit, selective high effi- 
ciency heating or cooling of the actuator may be at- 
tained. 
FIG. 1 illustrates a semiconductor thermocouple unit 
20 of the present invention which includes a semicon- 
ductor thermoelectric generator 22. The semiconductor 
thermoelectric generator 22 includes a P-type conduc- 
tivity leg 24 and an N-type conductivity leg 26. The 
P-type leg 24 may be preferably formed of bismuth 
antimony telluride, and the N-type leg 26 may be pref- 
erably formed of bismuth tellurium selenide. Alter- 
nately, both the P-type and the N-type legs may be 
formed of the same material, such as lead telluride, 
germanium silicon alloys, bismuth telluride, or bismuth 
selenide, although other commonly known materials 
may be used. The top portions of both the P-type and 
N-type legs are electrically interconnected by a layer 28 
formed of a conductive material such as copper. The 
bottom portion of the P-type and the N-type legs are 
electrically isolated from one another and are con- 
nected to electrical contacts 30. 
When the opposing terminals of a power supply 40 
are connected to the respective contacts 30 of the P- 
type leg 24 and the N-type leg 26 of the semiconductor 
thermoelectric generator 22 via wires 42 and 44 and DC 
current is delivered to the contacts, the semiconductor 
thermoelectric generator 22 operates as a thermocouple 
having a thermal efficiency of 100 to 1,OOO or more 
times the thermal efficiency of conventional metal ther- 
mocouples. With appropriate adaptations, the semicon- 
ductor thermoelectric generator 22 may operate to very 
efficiently heat and/or cool memory metal actuators. 
In order for the semiconductor thermoelectric gener- 
ator 22 to operate well as a cooling apparatus for mem- 
ory metal actuators, a heat sink 50 is provided. The 
4,765, I39 
3 4 
finned metal heat sink 50 illustrated in FIG. 1 may be cient to accomodate the displacement of the actuator 60 
directly attached to an insulative layer 51 formed on the during shape changes. 
semiconductor thermoelectric generator 22. Alternate In cases where there is considerable motion of the 
types of heat sinks such a liquid cooled heat sinks may actuator 60, longer wires may be required for adequate 
be provided, and may also be placed h direct contact 5 flexibility. TKis, however, may considerably hamper 
with the insulation layer 51 located on the semiconduc- thermal conduction between the actuator and the semi- 
tor thermoelectric generator 22. As with heat sink 50, conductor thermoelectric generator 22. It may there- 
attachment of the alternate heat sinks to the insulative fore be desirable to mount the semiconductor thermo- 
layer is not necessary. couple unit 20 adjacent to a fixed end of the actuator 60 
The material from which the semiconductor thermo- 10 where the deflection of the actuator 60 is likely to be of 
electric generator 2% of FIG. 1 is made is typically is not a laser magmitude during shape transitions- Wires of a 
very flexible. Since memory metal actuators change smaller length may thew be utilized. The wires 54 may 
shape depending upon their temperature, some form of also be mounted normal to the plane of motion of the 
accomodation must be provided to allow the semicon- actuator, as illustrated in FIG. 3A for the actuator 60, 
ductor thermoelectric generator 22 to remain in con- 15 and as illustrated in FIG. 3B for a rotary actuator 70. In 
stant thermal contact with the actuators at temperatures FIGS. 3A and 318, the wires 54 contact the sides of the 
both above and below the transition temperature of the actuators as the actuators expand and contract in the 
actuators without flexing the semiconductor thermo- direction of the arrows 72 and 73 rather than directly 
electric generator 22. In the present invention, this is opposing the motion of the actuators. 
accomplished by providing a compressible or flexible 20 As illustrated in FIG. 4, it may also be possible to 
thermally conductive member 52, such as a wire brush, increase the heating and cooling rate of the semiconduc- 
which extends from the semiconductor thermoelectric tor thermocouple unit by providing additional semicon- 
generator 22. The thermally conductive member 52 ductor thermoelectric generators 22. If additional gen- 
should have a high thermal conductivity, allowing heat erators 22 are added, it may be desirable to modify the 
to travel to the actuator or to the semiconductor ther- 25 thermally conductive element so that the resulting in- 
moelectric generator 22, depending upon whether the creased rate of thermal conduction may be ac- 
semiconductor thermocouple unit is used to heat or comodated. For example, as illuserated h FIG. 4 ddi -  
cool an actuator. For example, if the themdy  conduc- tional metd wires may be provided for transmitting 
tive element 52 is formed of a wire brush, the brush heat bo and from an actuator. 
fibers 54 may be formed of tungsten, molybdenum, 30 The semiconductor thermocouple unit 20 described 
niobium, copper, nickel, silver, gold, aluminum or may be utilized in many manners. For example, the 
graphite fibers. The wire fibers 54 may emanate from a semiconductor thermocouple unit 20 described may be 
thermally conductive copper layer 56 located adjacent used as the sole means for heating and/or cooling a 
to a thermally conductive but electrically insulative metal memory actuator by varying the polarity of the 
layer 51 formed on the semiconductor thermoelectric 35 DC current applied over the .  The semkonductor ther- 
generator 22. The thermally conductive electrically mocouple unit 20 may also be used to supplement other 
insulative layer 58 may be formed, for example, of a methods of heating and/or cooling. For example, if the 
material such as beryllium oxide or aluminum oxide preferred method of heating a metal memory actuator is 
(alumina), as may be the insulative layer 51 which sepa- by the direct application of current, a semiconductor 
rates the semiconductor thermoelectric generator 22 40 thermocouple unit 20 may be utilized as a cooling 
. 
from the heat sink 50. 
FIG. 2A illustrates the semiconductor thermocouple 
unit 20 of FIG. 1 in its operable position adjacent to a 
memory metal actuator B(p. The memory metal actuator 
60 illustrated deforms at its transition temperature and is 
fured at its fist end 62. The semiconductor thermo- 
couple unit 20 is positioned with the flexible thermally 
conductive element 52 located adjacent to the opposite 
end 68 of the actuator 60, Thus, when the actuator 60 
expands linearly, as illustrated in FIG. 2B, the thermally 
conductive element 52 is flexed but remains in constant 
contact with the actuator 60. In this manner, thermal 
conduction k maintained between the actuator 60 and 
the semiconductor thermocouple unit 20 during shape 
transitions, preventing the flexing and possible destruc- 
tion of the semiconductor thermoelectric generator 22. 
If the thermally conductive element 52 is formed of a 
wire bmh, the semiconductor thermocouple unit 20 
should preferably be mounted such that the wires 54 are 
slightly flexed when the actuator 60 is in its furthest 
position from the semiconductor thermocouple unit 20. 
The wires 54 will therefore easily bend further when 
the distance between the semiconductor thermoelectric 
generator 23 and the actuator 60 decreaseso The length 
of the wires should preferably be minimized in order to 
maximize thermal transfer and hence the thermal efbi- 
ciency of the entire semiconductor thermocouple unit 
20. However, the length of the wires 54 should be suffi- 
means. ?%%en current i.5 being applied directly to the 
actuator during the heating stage, the semiconductor 
thermocouple unit 20 may also be activated to transmit 
heat to the actuator, supplementing the current imduced 
45 heat. Hw other applications, a f i t  semiconductor ther- 
mocouple unit may be used to heat a first portion of an 
actuator and a second semiconductor thermocouple 
unit may be used to coo% a second portion of the actua- 
tor. In such cases, one semiconductor thermocouple 
50 unit may be placed adjacent to each of the portions of 
the actuator, and current of opposite polarity may be 
applied to the thermocouple units, heating one portion 
of the actuator and cooling the other. 
We claim: 
1. An apparatus for cooling a memory metal actuator, 
a semiconductor thermocouple including a first por- 
tion having an N-type conductivity, a second por- 
tion havimg a P-type conductivity, and a third dec- 
trically conductive portion electrically connecting 
the first portion and the second portion; 
a flexible thermally conductive element extending 
between the semiconductor thermocouple and the 
memory metal actuator for transmitting heat there- 
a power supply for supplying DeS current through 
the first, second, and third portions to activate the 
semiconductor thermocouple. 
55 
comprising: 
60 
65 between; and 
5 
4,765,139 
6 
2. An apparatus according to claim 1, wherein the 
flexible thermally conductive element comprises a plu- 
rality of bendable metal wires attached to a common 
thermally conductive layer. 
the group consisting of beryllium oxide and aluminum 
oxide. 
12. An apparatus according to claim 3, further com- 
prising an insdative layer formed between the semicon- 
3. An apparatus according to claim 9, further com- 5 ductive thermocouple and the heat sink. 
prising a heat sink connected to the semiconductor 13. An apparatus according to claim 12, wherein said 
thermocoup~e, wherein the power supply supplies DC insdative member is composed of a member selected 
current to the semiconductor thermocoup~e, activating from the group consisting of beryllium oxide and alumi- 
the thermocouple to draw heat through the flexible num Oxide. 
thermally conductive element which is passed to the 10 14. A heat transmission apparatus for a memory metal 
actuator having a first shape at temperatures above a heat sink. 
4. An apparatus'according to claim 3, wherein the transition temperature and a second shape at tempera- 
heat sink comprises a finned metal stmcture cooled by tures below the transition temperature, the apparatus 
comprising: convection. '' An apparatus to 39 wherein the a flexible heat transmission element located between 
the semiconductor thermocouple and the memory heat sink is cooled by liquid flow. 
metal actuator for transmitting heat therebetween, 6. An apparatus according to claim 1, wherein the 
the compressible heat transmission element flexing first portion having N-type conductivity is formed of a 
conductor thermocouple and the memory metal tellurium selenide, lead telluride, bismuth telluride, bis- 
actuator at temperatures ofthe memory metal actu- muth selenide and an alloy of germanium silicon. 
7. An apparatus according to claim 1, wherein the ator both above and below the transition tempera- 
second portion having P-type conductivity is formed of ture. 
a member selected from the group consisting of bismuth 25 15. A heat transmission apparatus according to claim 
antimony telluride, lead telluride, bismuth telluride, 
bismuth selenide and an alloy of germanium silicon. a heat sink attached to the semiconductor thermo- 
8. An apparatus according to claim 1, wherein the couple; 
first Portion of N-tYPe conductivity has the Same corn- a power supply for passing a DC current of a first and 
position aS the second portion Of P-type conductivity. 30 second polarity though the semiconductor ther.. 
9. An apparatus according to claim 2, wherein the mocouple, wherein the semiconductor thermo- 
metal wire is composed of a member selected from the couple generates heat which is passed through the 
group consisting of tungsten, molybdenum, niobium, flexible heat transmission element to the actuator 
copper, nickel, silver, gold, aluminum and graphite. when the power supply passes a current of the first 
polarity to the semiconductor thermocouple, and 
prising a thermally conductive electrically insulative the semiconductor thermocouple draws heat from 
layer formed between the semiconductive thermo- the actuator which is passed to the heat sink when 
couple and the flexible thermally conductive element. the power supply passes a current of the second 
11. An apparatus according to claim 11, wherein said polarity to the semiconductor thermocouple. 
15 a semiconductor thermocouple; 
member form the goup consisting Of bismuth 20 to r e m h  in coneinuous contacg with both the semi- 
14, further comprising: 
10. An apparatus according to claim 1, further com- 35 
insulative layer is composed of a member selected from 40 * * * * *  
45 
50 
55 
60 
65 


Thermocouple for heating and cooling of memory metal actuators

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server