Apparatus and method for low cost control of shape memory alloy actuators

Abstract

A method of controlling a shape memory alloy actuator includes applying power to a shape memory alloy actuator. A measured actuation parameter is obtained from the shape memory alloy actuator. An operational characteristic parameter is derived based upon the power and the measured actuation parameter. An actuation state parameter is identified from the operational characteristic parameter. The actuation state parameter is used to modify the control of the shape memory alloy actuator.

1 . A method of controlling a shape memory alloy actuator, comprising: 
 applying power to a shape memory alloy actuator;    obtaining a measured actuation parameter from said shape memory alloy actuator;    deriving an operational characteristic parameter based upon said power and said measured actuation parameter; and    identifying an actuation state parameter from said operational characteristic parameter, said actuation state parameter for use in modifying the control of said shape memory alloy actuator.    
     
     
         2 . The method of  claim 1  wherein applying power to said shape memory alloy actuator includes applying current to said shape memory alloy actuator.  
     
     
         3 . The method of  claim 1  wherein obtaining a measured actuation parameter includes obtaining a measured actuation parameter selected from voltage, time, and location limit.  
     
     
         4 . The method of  claim 1  wherein deriving an operational characteristic parameter includes deriving an operational characteristic parameter selected from resistance and position.  
     
     
         5 . The method of  claim 1  wherein identifying an actuation state parameter includes identifying an actuation state parameter selected from position and cycle duration.  
     
     
         6 . The method of  claim 1  wherein applying power to said shape memory alloy actuator includes applying current to said shape memory alloy actuator and obtaining a measured actuation parameter includes obtaining a transistor voltage, said method further comprising mapping said current and said transistor voltage to a selected resistor value of a plurality of disparate resistor values.  
     
     
         7 . The method of  claim 6  further comprising identifying, based upon said selected resistor value, an actuation state parameter in the form of a shape memory alloy actuator position value.  
     
     
         8 . The method of  claim 1  wherein applying power to said shape memory alloy actuator includes applying current to said shape memory alloy actuator and obtaining a measured actuation parameter includes obtaining a time value, said method further comprising mapping said current and said time value to a selected resistor value of a plurality of disparate resistor values.  
     
     
         9 . The method of  claim 1  wherein obtaining a measured actuation parameter includes obtaining a first location limit value and a second location limit value, said method further comprising identifying, based upon said first location limit value and said second location limit value, an actuation state parameter in the form of actuation cycle duration.  
     
     
         10 . The method of  claim 9  wherein identifying includes processing said first location limit value, said second location limit value, and a take-off time value.  
     
     
         11 . The method of  claim 10  wherein processing includes processing a take-off time value derived from a transistor resistor characteristic.  
     
     
         12 . A mechanical actuator, comprising: 
 a shape memory alloy;    a controller connected to said shape memory alloy, said controller being adapted to apply power to said shape memory alloy; 
 derive an operational characteristic parameter based upon a measured actuation parameter;  
 identify an actuation state parameter from said operational characteristic parameter; and  
 alter the application of power to said shape memory alloy based upon said actuation state parameter.  
   
     
     
         13 . The mechanical actuator of  claim 12  wherein said controller applies current to a transistor connected to said shape memory alloy.  
     
     
         14 . The mechanical actuator of  claim 13  wherein said controller maps a power value in the form of a current value and a measured actuation parameter in the form of a transistor voltage to a selected resistor value of a plurality of disparate resistor values.  
     
     
         15 . The mechanical actuator of  claim 14  wherein said controller identifies, based upon said resistor value, an actuation state parameter in the form of a shape memory alloy position.  
     
     
         16 . The mechanical actuator of  claim 12  wherein said controller maps a power value in the form of a current value and a measured actuation parameter in the form of a measured time value to a selected resistor value of a plurality of disparate resistor values.  
     
     
         17 . The mechanical actuator of  claim 16  wherein said controller identifies, based upon said resistor value, an actuation state parameter in the form of a shape memory alloy position.  
     
     
         18 . The mechanical actuator of  claim 12  wherein said controller identifies, based upon a first location limit value and a second location limit value, an actuation state parameter in the form of actuator cycle duration.  
     
     
         19 . The mechanical actuator of  claim 18  wherein said controller identifies said actuation state parameter using a take-off time value.  
     
     
         20 . The mechanical actuator of  claim 19  wherein said controller derives said take-off time value from a transistor resistor characteristic.  
     
     
         21 . The mechanical actuator of  claim 12 , wherein said controller includes a fixed current supply to provide stable control, without feedback, during load fluctuations.