Control of a shape memory alloy actuation apparatus

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. While 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. While 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. While applying open-loop control, the control signal is generated taking into account the electrical characteristics of the SMA actuator measured during a calibration stage.

主权项

1. A method of determining the ambient temperature of an SMA actuation arrangement comprising an SMA actuator arranged on contraction caused by heating to drive movement of a movable element relative to a support structure, the method comprising:
supplying drive current through the SMA actuator, wherein, when the SMA actuator is in an unheated state, the drive current is applied initially to cause a resistance of the SMA actuator to rise to a local maximum resistance; 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; and deriving a measure of an electrical characteristic of the SMA actuator that is representative of the ambient temperature, said electrical characteristic of the SMA actuator being the difference between the resistance of the SMA actuator in the unheated state when the drive current is initially applied and the maximum resistance of the SMA actuator.