An actuator using shape memory alloy (SMA) has large power/weight ratio and is able to generate relatively large displacement. However there are only few examples of practical application in precision engineering because its dynamic characteristics are very poor. An SMA actuator deforms by being heated up and cooled down with deforming force. It is usually easy to heat up fast. but difficult to cool down quickly since the cooling time depends on the amount of heat flow from inside to outside of SMA. So dynamic response of he actuator mainly depends on the time to cool down. In order to improve the dynamic characteristics of the SMA actuator, the present paper proposes to put the actuator in water bath for cooling down actuator quickly. The effect of setting the SMA in water bath is experimentally examined. Responses of linear actuators of SMA wires set in air and/or water are compared with each other. For miniaturzation, water jackets should be small. However if they are small. cooling ability becomes poor and temperature of water in the jacket rises up fast by repetitive drive. Therefore influences of size of the jackets, cycle time of repetitive drive and water temperature in the jacket are investigated.
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