CONTROL OF A SHAPE MEMORY ALLOY ACTUATION ARRANGEMENT

摘要

An SMA actuation arrangement comprises: an SMA actuator arranged on contraction caused by heating to drive movement of a movable element relative to a support structure; a current source operative to supply drive current through the SMA actuator to heat the SMA actuator; and a detector circuit operative to detect a measure of the resistance of the SMA actuator. Whilst detecting a measure of the resistance of the SMA actuator and controlling the drive current on the basis of the measure of the resistance of the SMA actuator; there is derived a measure of an electrical characteristic of the SMA actuator that is representative of the ambient temperature. Whilst applying closed-loop control an offset is added to the control signal which reduces the steady-state value of an error between the measure of the resistance of the SMA actuator and a target value. Whilst applying open-loop control, the control signal is generated taking into account the electrical characteristics of the SMA actuator measured during a calibration stage.