Accurate and rapid control of shape memory alloy actuators

In this thesis, relay control is applied to a pair of antagonistic Shape Memory Alloy (SMA) actuators for rapid and accurate regulation and tracking of position and force. Similar control is applied for the attenuation of impulse disturbances in the case of vibration isolation. When SMA actuators are used in an antagonistic configuration, relay control has the advantage that the SMA hysteresis is not a concern. This provides a major simplification for the modelling and control of SMA devices. Force and position models for the SMA actuators relevant to control are proposed. Both models are based on a theoretically derived current-stress model for a single SMA fiber. The models are sufficiently true to the original system that control design can be done in simulation and the resultant controllers applied to the actual system without tuning.Three applications are explored in this work: force control, position control, and impulse disturbance attenuation for vibration isolation. Both the step response and tracking are examined for the constrained force control using a two stage multi-relay controller that switches on the sign of the error. The same two stage controller is used to control position and examine the effects of varying the load on the system. As the applied load increases, the limit cycle magnitude increases, greatly diminishing the accuracy of the response. A position/velocity relay controller is proposed to reduce the limit cycle magnitude to a low level, subject to sensing and sampling rate limitations, even with a difficult undamped inertial load. For vibration isolation, an acceleration/jerk pulse relay controller is presented that rapidly attenuates an impulse disturbance. The presented experimental results set a new standard for accurate and rapid control of SMA devices