Patent ID: 8706305

Claim:
A control feedback mechanism for regulating strain output of a shape memory alloy (SMA) actuator comprising: a stress sensor for outputting an indication of a force to a control processor, the stress sensor being a strain gauge for computing a load on an SMA element of the SMA actuator; a state sensor for outputting an indication of an amount of Austenitic phase of the SMA element relative to Martensitic phase, the state sensor comprising circuit elements for outputting a signal corresponding to an electrical resistance across the SMA element to the control processor; the control processor for computing an actuation signal for selectively heating the SMA element in dependence on physical characteristics of the SMA element, a desired strain output value of the SMA actuator, and the indications of force and amount of Austenitic phase; and a circuit for delivering the actuation signal as an electrical signal to selectively deliver power from a power source for direct electrical resistive heating of the SMA element; wherein the state sensor outputs the indication of amount of Austenitic phase to the control processor, regardless of whether the SMA actuator is actuated, by supplying a current to the SMA element that is less than a current required for SMA actuation, when the SMA element is not being heated.