Patent ID: 6019113
Filing Date: 2000-02-01
Classification: F16K,Y10T

Abstract:
A control method for activating an actuator having a SMA element that assumes a deactivated state at ambient temperature and an activated state at an elevated temperature, the control method comprising the steps of:when activation of said actuator is desired:(a) applying a high voltage to the SMA element to initiate a transition from said deactivated state to said activated state, and monitoring a current through said element during the application of said high voltage;(b) when the monitored current reaches a first threshold corresponding to a resistivity of said SMA element that occurs when said SMA element has attained said activated state, lowering the voltage applied to said SMA element, and monitoring the current through the element during application of said lowered voltage; and(c) when the monitored current during the application of said lowered voltage reaches a second threshold corresponding to a resistivity of said SMA element that occurs prior to an onset of transition to said deactivated state, re-applying said high voltage and cyclically lowering said applied voltage in accordance with steps (b) and (c), so as to maintain the SMA element in a state of readiness to return to said deactivated state; andwhen deactivation of said actuator is desired, removing said applied voltage, and cooling said SMA element, so as to return said SMA element to said deactivated state.