Eap actuator and drive method

Abstract

An electroactive polymer actuator comprises an electroactive polymer structure and a driver for providing an actuation drive signal. In one aspect a first drive signal with an overdrive voltage is used to change the charge of the electroactive polymer structure needed for switching the structure from one to another actuation state. When or after the electroactive polymer structure actuation is near or at the another actuation state, a drive voltage is used to bring to and hold the electroactive polymer structure at the actuated state. This temporary overdrive scheme improves the speed response without damaging the electroactive polymer structure.

1 . A method of driving an actuator, wherein the actuator comprises an electroactive polymer structure, wherein the electroactive polymer structure is arranged to adopt at least a first actuation state and a second actuation state, wherein the second actuation state is different from the first actuation state, wherein the first actuation state has a first voltage associated with it and the second actuation state has a second voltage associated with it the method comprising:
 applying an overdrive period of a drive signal,   wherein the drive signal has a drive signal voltage,   wherein the drive signal voltage is applied to the electroactive polymer structure for switching the electroactive polymer structure from the first actuation state to the second actuation state,   wherein the overdrive period comprises a change the drive signal voltage from the first voltage to an overdrive voltage by an amount that exceeds the difference between the second voltage and the first voltage; and   applying a holding period of the drive signal, wherein the drive signal voltage is at the second voltage at least at the beginning the holding period.   
     
     
         2 . The method as claimed in  claim 1 , wherein the second voltage is applied only when or after the electroactive polymer structure reaches the second actuation state for the first time during the application of the electrical drive signal. 
     
     
         3 . The method as claimed in  claim 1 , wherein the second voltage is maintained at least as long as the overdrive voltage. 
     
     
         4 . The method as claimed in  claim 1 ,
 wherein the electroactive polymer structure comprises electrodes,   wherein the electrodes are arranged to receive the electrical drive signal,   wherein the electrodes define a capacitor having a capacitance,   wherein the overdrive voltage is applied until the voltage across the capacitance differs from the second voltage by a predetermined amount,   wherein voltage across the capacitance changes to the second voltage after the voltage across the capacitance differs from the second voltage by a predetermined amount.   
     
     
         5 . The method as claimed in  claim 4 , wherein the predetermined amount is less than 50%. 
     
     
         6 . The method as claimed in  claim 4 , wherein the overdrive voltage is applied until the voltage across the capacitance is equal to or less than the second voltage. 
     
     
         7 . The method as claimed in  claim 4  wherein the overdrive voltage is applied until the voltage across the capacitance exceeds the second voltage by the predetermined amount, such that the voltage across the capacitance changes back to the second voltage after the voltage across the capacitance exceeds the second voltage by the predetermined amount. 
     
     
         8 . The method as claimed in  claim 1 , wherein during the overdrive period the overdrive voltage is substantially constant. 
     
     
         9 . The method as claimed in  claim 1 ,
 wherein the combination of the overdrive period and the holding period is a cycle,   wherein the period of the cycle is larger than a period corresponding to a resonant frequency of the electroactive polymer structure.   
     
     
         10 . A computer program product comprising computer readable code stored on a nonvolatile storage medium, wherein the computer readable code, when run on a computer, causes a driver circuit to perform the method of  claim 1 . 
     
     
         11 . An actuator device comprising:
 an actuator, the actuator comprising:
 an electroactive polymer structure, 
 wherein the electroactive polymer structure is arranged to adopt at least a first actuation state and a second actuation state, 
 wherein the second actuation state is different from the first actuation state, 
 wherein the first actuation state is associated with a first voltage associated, 
 wherein the second actuation state is associated with a second voltage; and 
   a driver circuit arranged to apply a drive signal to the electroactive polymer structure,   wherein the drive signal has a drive signal voltage,   wherein the drive signal is arranged to switch the electroactive polymer structure from the first actuation state to the second actuation state,   wherein the drive signal comprises an overdrive period and a holding period,   wherein the drive signal voltage is changed from the first voltage to an overdrive voltage by an amount that exceeds the difference between the second voltage and the first voltage during the overdrive period,   wherein the drive signal voltage is set at the second voltage at least during the beginning of the holding period,   wherein the holding period occurs after the overdrive period.   
     
     
         12 . The actuator device as claimed in  claim 11 ,
 wherein the actuator comprises electrodes connected to the driver circuit,   wherein the driver circuit is arranged to apply the drive signal to the electroactive polymer structure.   
     
     
         13 . The actuator device as claimed in  claim 11 ,
 wherein the actuator device comprises a memory storing a lookup table,   wherein the lookup table lists a plurality of switching action data entries,   wherein each data entry relates to a particular switching from a first actuation state to a second actuation state and providing for at least one switching response time value achievable for that particular switching of an overdrive voltage and an overdrive period.   
     
     
         14 . The actuator device as claimed in  claim 11 , further comprising a feedback system,
 wherein the feedback system determines an actuation state of the actuator,   wherein the feedback system sets and/or changes one or more of the level, duration or waveform shape of the overdrive voltage based on the determined actuation state.   
     
     
         15 . (canceled) 
     
     
         16 . The method as claimed in  claim 1 , wherein the second voltage is maintained at least twice as long as the overdrive voltage. 
     
     
         17 . The method as claimed in  claim 1 , wherein during the overdrive period the overdrive voltage changes from an initial value to the second voltage 
     
     
         18 . The actuator device as claimed in  claim 11 ,
 wherein the electroactive polymer structure comprises electrodes connected to the driver circuit, and   wherein the driver circuit is arranged to apply the drive signal to the electroactive polymer structure.   
     
     
         19 . The actuator device as claimed in  claim 11 ,
 wherein the electroactive polymer structure comprises electrodes,   wherein the electrodes are arranged to receive the electrical drive signal,   wherein the electrodes define a capacitor having a capacitance,   wherein the overdrive voltage is applied until the voltage across the capacitance differs from the second voltage by a predetermined amount,   wherein voltage across the capacitance changes to the second voltage after the voltage across the capacitance differs from the second voltage by a predetermined amount.   
     
     
         20 . The actuator device as claimed in  claim 19 , wherein the overdrive voltage is applied until the voltage across the capacitance is equal to or less than the second voltage. 
     
     
         21 . The actuator device as claimed in  claim 19 , wherein the overdrive voltage is applied until the voltage across the capacitance exceeds the second voltage by the predetermined amount, such that the voltage across the capacitance changes back to the second voltage after the voltage across the capacitance exceeds the second voltage by the predetermined amount.