A new actuator of a joint mechanism is proposed, composed of two TiNi alloy wires. First, the static and dynamic properties of the TiNi alloy wire that were not known are analyzed. Then the mathemati cal model of the actuator is induced. Next, the control sys tems of the actuator are synthesized by pulse width modu lated (PWM) controllers, and the mathematical models of the control systems are then obtained. Finally, the experiments of the position and force control systems of the actuator are carried out. It is proved that the theoretical models obtained are valid and that the position and force controls of this actuator are possible. Moreover, the unknown characteristics of the other well- known type of actuator composed of a TiNi alloy wire and an ordinary spring are also analyzed by the above procedure. The mathematical models are presented.
The ordinary control method, pulse width modulation (PWM) control method, for the shape memory alloy (SMA) actuator has a basic defect: the response of an SMA actuator controlled by this method is very slow, because the maximum voltage supplied to the SMA must be kept low in order to prevent the SMA from burning because its temperature is unknown. In this paper, a new control method is proposed to improve the response speed of the SMA actuator by limiting the temperature of the SMA to below the limited value instead of by limiting the maximum voltage supplied to the SMA. Therefore this new control method allows us to use powerful drivers for supplying voltage to an SMA so as to increase the heating speed of the SMA. First, a temperature sensor system to detect the SMA's temperature was developed by solving several problems. Next, experiments of the position control by a new SMA actuator system with a temperature threshold for SMA were carried out. Results show that the response speeds are much faster than those using the ordinary control method. In addition, some conditions to further improve the response speed of the proposed control method for an SMA actuator were obtained.
To control a micromecha'tronic system, micro sensors and micro actuators are neccesary. So . , r a lot of sensors ma-; by using Si micro machining technology have been reported. On the other hand, a few micro actuators have been developed. In these micro actuators, micro SMA actuators have attracted strong attention because of their strong force, bigpower, faster response for their micro size and size reducibility by micro machining technology. In this plenary talk, the fabrication methods of micro SMA actuators and the motion control using the micro SMA actuator will be reviewed. 0-7803-6498-8/00/ $1 0.00 02000 IEEE.
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