Abstract: An SMA actuation assembly comprising SMA actuator wires connected in tension between a support structure and a movable element is controlled to drive movement of the movable element with respect to the support structure by supplying drive signals to the SMA actuator wire. Target signals representing desired positions of the movable element are set, varying within a predetermined spatial envelope. Measures of resistance of the SMA actuator wires are derived and the power of the drive signals is controlled under closed loop control on the basis of the target signals and feedback signals obtained from the measures of resistance. Electrical characteristics of the SMA actuator wires are monitored and used to detect when a motion limit of the movement is reached. In response thereto, the spatial envelope is adjusted to restrict the movement to be within the detected motion limit.

Abstract: An SMA actuation assembly comprising SMA actuator wires connected in tension between a support structure and a movable element is controlled to drive movement of the movable element with respect to the support structure by supplying drive signals to the SMA actuator wire. Target signals representing desired positions of the movable element are set, varying within a predetermined spatial envelope. Measures of resistance of the SMA actuator wires are derived and the power of the drive signals is controlled under closed loop control on the basis of the target signals and feedback signals obtained from the measures of resistance. Electrical characteristics of the SMA actuator wires are monitored and used to detect when a motion limit of the movement is reached. In response thereto, the spatial envelope is adjusted to restrict the movement to be within the detected motion limit.