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Development of shape-memoryalloy actuators. Performanceassessment and introduction of anew composing approachShigeo Hirose a , Koji Ikuta b & Yoji Umetani ca Tokyo Institute of Technology, 2-12-1 Ookayama,Meguro-ku, Tokyo 152, Japanb Tokyo Institute of Technology, 2-12-1 Ookayama,Meguro-ku, Tokyo 152, Japanc Tokyo Institute of Technology, 2-12-1 Ookayama,Meguro-ku, Tokyo 152, JapanPublished online: 02 Apr 2012.

To cite this article: Shigeo Hirose , Koji Ikuta & Yoji Umetani (1988) Development ofshape-memory alloy actuators. Performance assessment and introduction of a newcomposing approach, Advanced Robotics, 3:1, 3-16, DOI: 10.1163/156855389X00145

To link to this article: http://dx.doi.org/10.1163/156855389X00145

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Development of shape-memory alloy actuators. Performance

assessment and introduction of a new composing approach

SHIGEO HIROSE, KOJI IKUTA and YOJI UMETANI

Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152, Japan

Received for JRSJ 17 June 1985; English version received 6 June 1988

Abstract-A servo actuator using shape-memory alloy (SMA actuator), which performs special functions not found in conventional actuators, is expected to be a new driving source for future robots. This paper evaluates its performance and discusses the fundamental issues in designing such actuators. Being driven by the thermal martensitic transformation of the SMA itself, an SMA actuator is a driving system which can in principle, perform without any frictional parts, can be designed at a high output/weight ratio especially when a light-weight actuator is to be constructed But has low energy efficiency due to its mechanical characteristics of operating at a small temperature difference, and has a relatively low response. Our study shows some ways of overcoming these disadvantages by a special design approach. The method is called ξ- array and is characterized by SMA wires being connected in parallel structurally and in series electrically. This approach enables the response to be enhanced due to the increased surface area. The diameter of the power-supplying lead can be reduced due to the increased electrical resistance of the SMA. The power source and power control system can be simplified, and the SMA sensor function can be used positively. The above observations are reviewed by the experimental production and operation of an antagonistic SMA servo actuator system using control based on the ξ-array. Consequently, the resistance-feedback is able to produce a servo less susceptible to variations in ambient temperature.

1. INTRODUCTION

Actuators are one of the bottlenecks in the progress of robot technology. Technical innovations have been accomplished with regard to controls, as a result of the tremendous advancements in microelectronics. However, actuators, which are the

driving elements of a robot, depend on electric motors or hydraulic devices which have

basically remained unchanged for a century. Although these devices are technically matured, robots will benefit more if they are equipped with actuators of better

performance. In this connection, it is no exaggeration to say that the key to designing robot hardware successfully is to overcome the poor mechanical performance of actuators. As future robots will have more degrees of freedom, the introduction of innovative technology in the field of actuators will have a significant bearing on

promoting the progress of robotics. Based on such a standpoint, we have focused our attention on applying SMA

(shape-memory alloy) to servo actuators of robots for solving one of the serious technical problems.

Japan was one of the leading forces in the world in the research and development of

applying SMA to robot actuators. Pioneering work was conducted by Honma et al.

[1], followed by experimental construction of robot hands [2] and other important

investigations. This work revealed the usefulness of SMA for new robot actuators.

Nevertheless, SMA is not used in practical models. On the contrary, the difficulty in

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handling the new material, revealed in those investigations, rather dampened efforts to

step up experimental designs to commercial applications. We intend to evaluate SMA from an overall viewpoint, not restricting attention only

to its phenomenal novelty and direct application feasibility, but also including its

potential merits and demerits so that a new design principle can be introduced to pave the way for commercial applications. In this respect, the present study will first

establish the basic form of SMA actuators, secondly consider items to be discussed

before adapting SMA to actuators, and lastly investigate their characteristics in

comparison with actuators of other principles. Then a new design approach called the

?-array will be introduced as a way of constructing an actuator that enhances the

performance to overcome some weak point of SMA. Finally, a test model will be

constructed adopting the control method and design techniques proposed in this

paper in order to check the practicability of the principle.

2. BASIC FORM OF AN SMA ACTUATOR

Figure 1 shows our idea of the form of an SMA actuator. Temperature is controlled by

heating with the Joule effect by applying an electric current to the SMA and cooling by air or water flow. One pair of SMA wire-springs is arranged antagonistically.

Heating and cooling produce a stroke motion. For temperature control, warm/cool- water circulation [3], a heat-sink [4], the use of the Peltier effect [5] and some others

[6] have so far been proposed. We believe the system of Fig. 1 is the simplest and most

efficient, and we have developed the study in line with this idea. An antagonistic form is

used because SMA usually exhibits a one way characteristic. In the past, many

experiments were conducted based on a bias spring technique in which either of the

antagonistic pairs of Fig. 1 was used. For removing the power generated by the SMA

as efficiently as possible, we used the antagonistic arrangement of SMAs shown in

Fig. 1 as the most appropriate form.

3. COMPARISON WITH OTHER ACTUATORS

The following basic characteristics of an SMA actuator are compared with those of

conventional actuators: (1) output/weight ratio; (2) energy efficiency; (3) response

speed; (4) independence index; and (5) others.

Figure 1. Basic SMA actuator configuration.

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3.1. Output/weight ratio

The ratio of output against weight is the yardstick used to evaluate the basic

performance of an actuator. Although there is no generally accepted absolute definition. In this regard we would like to propose a new method for assessing robot actuators. It is considered reasonable that the basic output is the power comprising both concepts of force and velocity. This concept depends largely on the mass of the actuator. Accordingly, the evaluation method currently proposed is represented by Fig. 2, in which P/W (W/kg) (power P against unit mass M) is compared with the mass of the actuator.

A similar approach was used by Akagi [7] in terms of kg/HP, giving the

performance in horsepower. However, it was used to represent the performance of

large internal combustion engines and gas turbines. It is unrealistic to apply the

concept, as it is, to show the output of a compact robot actuator. It is also not in SI units. In the P/M-M characteristic diagram of Fig. 2, the data are plotted after

converting the units of catalogue data, to compare a broader range of actuators and avoid the problems mentioned above.

The data in Fig. 2 will be explained as follows: Both DC and AC motors are assessed

including the mass of the reduction gear. A reduction gear is essential conventional

motors, which produce their highest efficiency at high revolution speeds from 2000 to 5000 rpm, to a robot actuator. When a motor has a specified reduction gear, the weight of the gear is added. When not, the AC motor weight is summed with the mass of a harmonic driven reducer matching the motor output. On average, the reducer weight is roughly equal to the motor weight.

The data of hydraulic devices and pneumatic systems, respectively, are based on those summarized in refs 8 and 9. The motor characteristics of automobiles, railroad

engines, aircraft and ships were taken from ref. 7. These data do not include the

weights of reducers. They are just included in the diagram for rough comparison purposes as they are obviously unsuitable for any robot actuators.

Figure 2 indicates that the output/weight ratio increases when the mass of the actuator increases. As regards the trend of individual actuators, an electric motor is more appropriate in the mass range from 10-' to 102 kg, exhibiting a characteristic of 10 to 50 W/kg. Hydraulic devices are suitable in the 10-10? kg range, giving a high output/weight ratio of 103 (W/kg). Gas turbines are good in the 102-5 x102 kg range

0 DC motor + reduction gear o AC motor + harmonic drive @ motor (railroad car) 2 2 cycle gasoline engine (motor car) M 4 cycle gasoline engine (motor car) @ rotary engine (motor car) + pistone engine (aircraft) [!] Diesel engine (railroad car) IKI 4 cycle high speed Diesel engine (motor car) 4 4 cycle high speed Diesel engine (ship)

gas turbine (aircraft)

g gas turbine (ship) A hydraulic motor A pneumatic motor f!J SMA actuator

ixwj J

Figure 2. Power weight ratio vs. weight diagram of actuator.

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at a ratio of 104 W/kg. It is interesting to note that different types of actuators have specific output/weight ratios and different mass ranges for the most efficient

performance. In such a distribution of force, where are SMA actuators positioned? This has not

yet been evaluated precisely. As a rule of thumb, the performance of an SMA actuator was estimated based on some specific assumptions. The result was P/M = - 230 W/kg and M = - 0.05 kg. This suggests that an SMA actuator has a potential performance equivalent to that of electric motors in terms of the output/weight ratio, as the data are in the mass range applicable to electric motors in Fig. 2. In addition, SMA actuators can theoretically be designed in very small sizes. Therefore, an output/weight ratio which could not be realized by conventional actuators weighing 10- 2 kg or less can be achieved by a compact actuator. This possibility is confirmed quantitatively by the

P/M-M characteristic in Fig. 2.

3.2. Energy efficiency .

An SMA actuator works through phase change of metals. It is substantially a thermal device which converts heat energy in to mechanical action. In the past, some discussions erroneously assessed the efficiency of SMA actuators based only on the ratio of the obtainable mechanical work to the input electric power on heating, neglecting the cooling process. An actuator is not useful unless it can 'continuously' perform thermal-mechanical energy conversion, instead of only one time conversion. On this account, the efficiency should be evaluated through all phases of cyclic actions including the cooling process. Accordingly, when SMA is used in an actuator, the upper limit of the efficiency is regulated by the Carnot efficiency as a thermal device [10-12].

As a typical case of Ti-Ni, let the high thermal source temperature Th be 350 K at Af and the low thermal source temperature T, be 310 K at A,, I}c = 11 %. The energy efficiency of SMA actuators is surprisingly low in comparison with the approximately 80% electric- mechanical energy conversion rate of an electric motor. This problem should be taken into consideration in the future development of SMA actuators to avoid inappropriate applications. Such a low level of energy efficiency is inherent in a thermal device of small temperature differences.

The SMA actuator of Fig. 1 converts electric energy into heat and subsequently changes it in to mechanical energy. Both electric and mechanical actions are regarded to be good quality energy, while heat is a low quality energy. As a result, the conversion

process wastes some energy. To compensate for this, Honma et al. [3] proposed to

improve the overall energy efficiency by making use of water warmed by waste heat. In considering the energy efficiency of SMA, we tentatively define a 'Carno

coefficient rl*' to show the extent to which the Carno efficiency is attained by means of system construction. q is the ratio of q against the actual efficiency of the actuator; in other words, rl* = I}/I} C' Increasing rl* is therefore the problem to be solved for SMA actuators with regard to energy efficiency.

3.3. Response speed

The shape-memory effect of SMA takes place almost instantaneously depending on the temperature, caused by martensitic transformation, instead of diffusion of metal atoms. Therefore, the response speed of an SMA actuator is a factor of the

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temperature-changing speed of SMA itself. On the other hand, in the case of the system shown in Fig. 1, the heating speed is governed by the heat-source volume and the

cooling speed by the heat transmission property with the external fluid. The most influential factor in governing the speed is the heat transmission property. In this

respect, it is theoretically unrealistic to expect SMA actuators to have a response speed as fast as those of electric or hydraulic systems. The response characteristic of an SMA

actuator, however, can be enhanced by improving the heat transmission property within given limits. Figure 3 shows the theoretical discussion of the dependence of the

response speed of an SMA on the cooling system. The calculation suggests that several methods will be available for improving the

response speed of SMA actuators. For instance, the cooling fluid should be water instead of air. SMA wires should be as fine (small diameter) as possible and should be bundled together in the required quantity. This has also been confirmed by experiment [13]. Also, the use of fine SMA wire has the effect of reducing the resistance to

deformation, so that it is said to contribute to improving the response characteristic. In

summary, unless an SMA actuator requires a specially high response characteristic,

requirements at the usual level can be satisfied by appropriate design.

3.4. Independence

For evaluating the performance of SMA actuators, the conventional yardstick mentioned above is not enough. Another important element which should be taken into account is an assessment standard newly named the 'independence index'. It is an evaluated amount indicating the degree of restrictiveness of an umbilical cord between an actuator and remote assisting equipment when the actuator cannot function without external assistance.

Figure 3. Time constant of SMA actuator in various cooling conditions.

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The umbilical cord was seldom taken into consideration in earlier of assessments. The concept is still ambiguous even at present and is difficult to handle in a

quantitative manner. Nevertheless, introducing some assessment factor concerning the umbilical cord is considered to be important for future actuator systems of multiple degrees of freedom (DOFs). Therefore, at this stage, we attempt to introduce an assessment index for the independence. The index is a non-dimensional parameter:

where the main body of the actuator is L3 in terms of cubic volume equivalent, L is the

representative dimension and d is the diameter of the umbilical cord. Figure 4 shows a

comparison of two actuators relating the weights with the independence index. For assessing the independence, not only the space factor mentioned above but also

such an element as the stiffness of the umbilical cord should be included. Nevertheless, the independence may be evaluated from a macroscopic viewpoint based on the table of Fig. 4 and equation (1).

Figure 4 indicates a high independence of electric motors, because they have only two cables, and a relatively low independence of pneumatic/hydraulic devices, as they have high pressure pipes for linkage.

What is labelled as the 'conduit wire' in Fig. 4 is a system consisting of a pipe and a

pulling wire threaded inside it. The structure enables the pulling force to be transmitted to the tip. A very simple model of this idea is exemplified by the braking mechanism of a bicycle. This system is an excellent actuator in terms of P/M (output/weight ratio), as it can produce a relatively large output with a lightweight body. Nevertheless, its independence is low as seen in Fig. 4, mainly because the umbilical cord is relatively thick. So, a pipe-wire system is found to be unsuitable for a micro-actuator.

How about the independence index of an SMA actuator? The data of the SMA actuator shown in Fig. 4 are of the experimental device produced for the present study and are considered to be good. We will propose a new construction of an SMA

Figure 4. Proposed chart of independence index vs. actuator weight.

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actuator in Section 4, as the conventional design shown in Fig. 1 cannot be improved for independence. In Ti-Ni alloy, the specific resistivity is (50 x 100) x S2m, which is only 50-fold of 2 x 10-8 Om of copper. (Copper-based SMA has a smaller ratio than this, as a matter of course.) So, when power is supplied to SMA for heating, in order to keep the lead at a temperature tower than that of SMA itself, it is necessary to use thick copper lead, the diameter of which is more than 1/7 (= 1/ 50) of that of Ti-Ni SMA. This is the same for the parallel array design shown in fig. 5. Especially when an actuator body is to be down-sized with increased DOFs, a relatively bulky bundle of fine leads can pose problems for the manoeuvrability by the low 'indepen- dence'. Consequently, the new approach proposed in Section 4 is important.

3.5. Others

The other important characteristics of an SMA actuator are as follows: It has no frictional parts as seen in electric and hydraulic devices. The so-called 'solid state' actuator does not generate noise in operation and is dust-free so that it is suitable for

operation in a clean room. Its mechanical simplicity results in excellent maintainability and reliability, but the durability needs to be improved from the metallurgical viewpoint [15].

4. PROPOSAL FOR NEW CONSTRUCTION (4-ARRAY)

In the preceding section, the problem of insufficient independence was discussed. In order to overcome this issue effectively, the new method proposed in this section has

improved electric connections, as shown in Fig. 6, but is mechanically the same as the conventional one shown in Fig. 5.

In other words, the new system connects SMA wires in parallel from the mechanical

viewpoint and in series from the electrical viewpoint. It is called the '(-array' because of the affinity of its shape to the Greek letter xi.

Figure 5. Conventional parallel array of SMA actuator.

Figure 6. Proposed ç-array of SMA actuator.

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The SMA actuator of Fig. 1 is the basic design. The one in Fig. 5 is an improved version which uses much finer wires with enhanced heat transmission but has a low electrical resistance. The newly proposed ?-array design of Fig. 6 can increase the resistance significantly. For instance, when n pieces of SMA are rearranged from

parallel to series connection, the electric resistance becomes n'-fold of the original system. Consequently, the (-array can produce the following effects:

(1) The lead can be designed finer to enhance independence. Consequently, the increased resistance of the SMA actuator allows a higher voltage drive to supply the same amount of power. Thus, the energy loss at the copper lead, which is the heat generation in other words, can be restricted to a negligible extent, so that the diameter of the lead can be sufficiently reduced. Thus, the independence index, which posed some problems in the preceding section, can be increased sharply. By the

way, the independence index of the SMA actuator in Fig. 4 is based on this (-array test model (see section 5).

For fluid cooling, the existence of a fluid duct is considered not to reduce the

independence of the actuator significantly because a single duct can supply sufficient

low-pressure fluid to a group of multiple DOF actuators, apart from the case of a

hydraulic system.

(2) Construction is easy for the power source and motor-control circuit. These effects are brought about because the SMA actuator can be driven at high voltage. For instance, to supply 100 W of power, it is easy to construct a power source of 100 V-1 A, but it is hard to design a 1 V-100 A combination. The experimental model at a relatively small output reported so far used a relatively large current of 30?0 A [2]. For increasing the output in the future, it is essential to introduce a high- voltage drive, and (-array construction will be all the more valuable. By the way, altering some series connections of the ?-array to parallel connections can change the resistance as required, so that designing is possible to match the current-voltage.

(3) The response characteristic can be enhanced. This effect is not peculiar for the (-array. It is the same as the effect of the parallel array of Fig. 5 as mentioned before. As the ?-array assumes the use of fine SMA wires, an enhanced heat transmission characteristic of the SMA will result in amelioration of the

response characteristic.

(4) SMA can serve as a sensor. Another significant advantage of the ?-array in addition to the merits stated above is the function which can very easily monitor the variation of electrical resistance

following the SMA phase change. When SMA changes its phase, the resistance also changes by 10-20%. Besides, the

extent of the phase change is also dependent on stress, by the effect of SIM (stress- inducing martensite). Making use of these characteristics, it is possible to provide SMA with a sensor function for displacement and force. This characteristic of SMA was

pointed out previously by Honma et al. [1]. Variation of the resistance was not easily utilized by conventional SMA actuator construction, because the varying degree of the resistance was too fine to allow steady detection. The resistance itself is enlarged by the

?-array so that amplified variation can be measured accurately by a simple system;

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thus the result can be used for a servo signal and monitoring signal to preventing

overheating of the SMA. These functions will contribute to the simplification of the

structure of SMA actuators.

Thus, the introduction of a ?-array not only enhances the independence index of an

SMA actuator but also improves a couple of other properties.

5. CONSTRUCTION AND EXPERIMENT OF RESISTANCE-CONTROL ANTAGONISTIC SMA

ACTUATORS

A basic SMA actuator model was made and tested for specifically investigating

possible improvements in SMA actuators. The design specification, control system and test results are presented below.

5.1. Specifications of the test actuator

The diameter of the strand was 0.2 mm. The diameter of the coil was 1.0 mm. the

number of winding turns was 28. The SMA coil memorizes the shape at contact

winding and has a natural length of 11 mm. Six pieces of the SMA coil-springs were

connected in a ?-array manner. Each set of the coil-springs was combined in an

antagonistic manner in which each set balances in the state at 1 % of surface shearing strain. As a result, the overall length of the actuator was 42 mm; the driving stroke was

6 mm (0.6-1.4% in terms of the shearing strain). The total electrical resistance of one

side of the coil-spring in the antagonistic arrangement was approximately 25 S2, as a

result of introducing a The resistance variation resulting from the phase

change was approximately 4 n. The SMA resistance-driving circuit was designed

according to a simple bridging pattern as shown in Fig. 7(a). The detecting circuit

enables resistance to be measured to sufficient precision. Figure 7(b) shows the SMA

servo system using such resistance feedback to individual SMAS. in Fig. 7(b) is a

parameter in which SMA resistance is normalized. It is an entirely new approach to servo-control an SMA actuator of antagonistic

type based on the ratio of the resistance of both SMAs monitoring the resistances. To

control the normalized resistances 1 and A2 of antagonizing SMAs 1 and 2, a method

is introduced to change A, to 0-1 while constantly satisfying the equation + A2 = 1

as shown in Fig. 7(b). The system is designed to be cooled by air, which flows squarely to the coil springs at

a velocity of 2 m/s. The SMA used is Ti-Ni alloy weighing about 0.1 g at operation. To

have them memorize the shape, they were kept at 450°C for 1 h and subsequently were

allowed to cool gradually. The phase-change temperatures measured by DSC were

324 K for AS' 339 K for Af, 327 K for Ms and 313 K for Mf.

5.2. Results and observations

The experimental actuator system shown in Fig. 8 was assembled and the drive-

control was tested. The results were as follows:

(1) It was possible to drive the system at 14 V-0.6 A powered by a normal source

under the usual operation state. Oxygen-free copper was used for the lead (0.5 mm

diameter). No problems, e.g. heat generation, occurred at room temperature. Conse-

quently, a sufficiently high independence was assumed to have been attained.

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A :ratio of resistance variation

rl,r2:value of resistance desired resistance for antagonistic SMA

Figure 7. (a) PWM controller with SMA resistance detector. (b) SMA servo system based on resistance feedback control.

Figure 8. Experimental antagonistic type ?-array SMA actuator and its experimental system.

(2) Figure 9 shows one of the driving test results. As the system had resistance feedback only, the data included the variation caused by load under the SIM effect. Under the same load, however, a reasonably good position-control characteristic with small hysteresis was obtained.

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Figure 9. The experimental results of SMA servo system based on resistance feed back control in two load (P) conditions.

Figure 10. The response of SMA actuator when the cooling condition changed.

Attaching an external detector such as a potentiometer to the SMA actuators would

significantly improve the position-control. But in order to realize a super-compact actuator, the servo construction technique presented here will need to be perfected in

the future.

(3) Figure 10 shows measurements of the position variation of the actuator when the

cooling air flow was suddenly shut off in the way shown in Fig. 10(a). This drastic

change of the cooling condition hardly affected the actuator displacement, as shown in

Fig. 10(b), because the resistance servo system restricted the heating current

[Fig. 10(c)].

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The system always monitors the SMA phase-change rate for feedback by measuring the SMA electric resistance, and this technique seems to bring about a

steady response as shown in Fig. 9. Such a characteristic could not have been achieved

theoretically by the conventional control method [16] based on the duty ratio of the

heating current only. Even in comparison with similar control by a potentiometer only, the present system is considered to give a better response because the resistance servo system directly monitors the state of the SMA itself. On this account, even when an SMA actuator is connected to a potentiometer, it is considered effective to connect the resistance feedback system in a minor-loop manner.

(4) Other characteristics of the test model were as follows: The response character- istic was about 0.2 Hz of the break frequency, 18 W/kg of output/weight ratio was assessed based on the weight of SMA only, as this model did not need to curtail the

weight of the housing. The independence index was approximately 12 (obtained from the ratio of the representative length of the overall volume occupied by the SMA coil-

springs to the wire diameter). The efficiency was about 0.02%. The efficiency was deduced from the ratio of the input electric energy to the output

work, for a one-cycle motion from pulling up the load through to returning to the

original position. These values might appear to be much poorer than those estimated in the past. We

would like to point out that these levels are rather realistic as long as an SMA actuator is designed following the generally accepted technique. However, significant improve- ment in the characteristics will be possible in the future by detailed studies.

6. CONCLUSION

SMA actuators will not completely replace conventional actuators. Nevertheless, they have high potential as a new type of actuator for future robots with the introduction of such special design approaches as the (-array or the peculiar controls discussed in Section 5. This study has demonstrated this by using an experimental model.

The application fields where SMA actuators will be most effectively utilized will be

investigated hereafter, building on these discussions and on an objective comparison with conventional systems as mentioned in Section 3. We believe that SMA actuators are suitable for the driving system [17] of multi-DOF manipulators to be used for the maintenance of the internal systems of atomic reactors, for clean room manipulators, and for the assembly of positive junctions of medical endoscopes [18].

Acknowledgements

We are grateful to Mr. Masahiro Tsukamoto of our University for his cooperation in

producing and testing the actuator; and to Dr. Yuichi Suzuki and Mr. Yuichi Tamura of the Central Research Institute of Furukawa Denko Co. Ltd. for valuable advice and

support of our project.

REFERENCES

1. D. Honma, K. Miwa and N. Iguchi, "Digital actuator using shape-memory effect," J. Jpn Soc. Machinery, 1983.

2. Y. Hosoda, M. Fujie and Y. Kojima, "Three-fingered hand using SMA," Proc. Jpn Soc. Robotics, 1983.

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ABOUT THE AUTHORS

Shigeo Hirose (M'83) was born in Tokyo, Japan in 1947. He received his B.E. degree in Mechanical Engineering from Yokohama National University in 1971, and M.E. and Dr.E. degrees in Control Engineering from Tokyo Institute of Technology in 1973 and 1976, respectively. From 1976 to 1979 he was a Research Associate and he is at present the Associate Professor of the Department of Mechanical Engineering Science at the Tokyo Institute of Technology. His research interests are in the design of mechanisms, actuators, sensors and control systems of Robots.

Koji Ikuta (M'83) was born in Osaka, Japan in 1953. He received B.Eng. in Material Science & Engineering and in Biophysical engineering at Osaka University in 1977 and 1979 respectively, the M.Eng. in Biophysical Engineering at Osaka university, and Dr.Eng. in Control Engineering at Tokyo Institute of Technology in 1987. Since 1987 he has worked at the center for robotic systems in microelectronics, University of California, U.S.A. His research interests are in robotics in general and the application of shape memory alloy for engineering and medical fields.

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Yoji Umetani (M'83) was born in Osaka, Japan in 1932. He received his B.E. degree in Mechanical Engineering from Kyoto University in 1956, and Dr.E. degree from Tokyo Institute of Technology in 1968. From 1959 he was the Lecturer of the University of Tokyo. From 1970 he was the Associate Professor of the Tokyo Institute of Technology. From 1975 till now he is the Professor of Department of Mechanical Engineering Science at the Tokyo Institute of Technology. His research interests are in the study of process control, biomechanics and robotics.

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