SLACK SMA WIRE IN SMA ACTUATOR ASSEMBLIES

摘要

A measure of the degree of slack of a length of SMA wire is derived from an electrical characteristic measured while supplying a drive signal sufficient to cause contraction. The measure may be the difference between the maximum resistance as contraction starts and the minimum resistance as contraction ceases. This provides an accurate measure which may be used during manufacture of an SMA actuator assembly. Similarly, when using a closed-loop control loop to control drive signals supplied to opposed lengths of SMA wire in an SMA actuator assembly that are slack in the absence of drive signals, signals in the control loop are adjusted by an offset that is derived from measured electrical characteristics of the lengths of SMA wire and compensates for the degrees of slack of the lengths of shape memory alloy wire.