Shape memory alloy microactuator having an electrostatic force and heating means

A microactuator for use as a valve in controlling the flow of a fluid, the microactuator comprising the combination of (a) a base formed with an orifice for directing the fluid therethrough;

• (b) a valve actuator which extends along a longitudinal axis and has a proximal end carried by the base and a distal end, said valve actuator comprising an elastic substrate, a shape change layer comprised of a shape memory alloy material having a phase change transition temperature, said material deforming the shape change layer by contraction from a low temperature shape toward a memory shape responsive to the material being heated through said phase change transition temperature, and means for mounting the shape change layer onto the substrate so that said contraction causes the valve actuator to bend along said longitudinal axis in a first direction for moving the distal end of the valve actuator relative to the base and orifice for controlling flow of the fluid through the orifice, said mounting of the substrate onto the shape change layer establishing a stress force in the substrate which is applied against the shape change layer in a second direction which opposes said first direction of bending of the valve actuator and with the stress force moving the distal end in the second direction when the shape memory alloy material is below its phase change transition temperature;
• (c) clamping means for applying an electrostatic force between the distal end and base for selectively clamping the distal end to the base;
• and (d) heating means for heating the shape memory alloy material through the phase change transition temperature.

A bistable microactuator for controlling an element between two actuation modes, the microactuator comprising the combination of (a) first and second bases mounted in spaced-apart relationship and separated by a gap;

• (b) an actuator member mounted within the gap between the bases, the actuator member extending along a longitudinal axis and having a proximal end and a distal end, said actuator member comprising first and second elastic substrates mounted in parallel relationship with the substrates having outer sides which face in directions outwardly of the actuator member, first and second shape change layers, each layer being comprised of a shape memory alloy material having a phase change transition temperature, said material deforming the shape change layer by change in volume from a low temperature shape toward a memory shape responsive to the material being heated through said phase change transition temperature, means for mounting the first and second shape change layers onto the outer sides of respective ones of the first and second substrates so that said change in volume of a selected one of the layers causes the actuator member to bend along said longitudinal axis in a direction toward the side of the selected layer whereby said distal end is moved toward respective first and second positions;
• said mounting of the shape change layers onto the substrates establishing stress forces in the substrates which are applied against the respective shape change layers in directions which oppose the bending of the actuator member and with the stress forces moving the distal end in directions away from said respective first and second positions when the shape memory alloy material is below its phase change transition temperature, and with said element being changed between said actuation modes responsive to movement of the distal end to either of its first or second positions;
• (c) clamping means for applying electrostatic forces between the distal end and bases for selectively clamping the distal end to the bases when the distal end is in either of said first or second positions;
• and (d) heating means for heating the shape memory alloy material through the phase change transition temperature of selected ones of the shape change layers.

A method of operating a microactuator for controlling an element between different actuation modes, the method comprising the steps of providing an actuator member having a shape change layer mounted on an elastic substrate in which the shape change layer is comprised of a shape memory alloy material having a phase change transition temperature, said material deforming the shape change layer by change in volume from a low temperature shape toward a memory shape responsive to the material being heated through said phase change transition temperature;

• providing a base which carries a proximal end of the actuator member, with the actuator member having a distal end;
• heating the shape change layer through the phase change transition temperature and enabling the actuator member to change in volume sufficient to bend the distal end in a first direction to one operating position relative to the base;
• establishing a stress force in the substrate and applying the stress force against the shape change layer in a second direction which yieldably opposes said bending of the distal end;
• cooling the shape change layer below the phase change transition temperature and applying the stress force against the actuator member to cause the actuator to change in volume to said low temperature shape while moving the distal end to an other operating position relative to the base;
• applying an electrostatic force between the distal end of the actuator member and the base sufficient to clamp the base to the actuator member in said one position;
• and controlling the element to first and second actuation modes responsive to bending of the distal end toward said respective one and other operating positions.