Stable electro-mechanical comb drive actuators

1. An apparatus, comprising:

an electro-mechanical actuator comprising:

a comb drive having a first capacitor plate and a second capacitor plate, the capacitor plates having teeth capable of inter-digitating, the comb drive having a mechanical stability threshold; and

a deformable connector configured to apply a mechanical restoring force to the first capacitor plate; and

wherein the deformable connector is configured to restore the first capacitor plate to be at an equilibrium rest position in response to no control voltage being applied across the comb drive, the comb drive being more engaged when the first capacitor plate is at the equilibrium rest position than when the first capacitor plate is at the mechanical stability threshold of the comb drive, the first and second capacitor plates being disengaged such that the teeth thereof are separated by a gap along a movement direction of the first capacitor plate when the first capacitor plate is at the equilibrium rest position, the first capacitor plate being at the mechanical stability threshold when positioned at the one of the intercepts of the tangent lines to the positive slope part of the capacitance slope function for which the comb drive is most engaged.

2. The apparatus of claim 1 , wherein the first capacitor plate has a unique equilibrium position for each control voltage applied across the comb drive.

3. The apparatus of claim 1 , wherein the electro-mechanical actuator further comprises:

a second comb drive having a third capacitor plate and a fourth capacitor plate, the third and fourth capacitor plates having teeth capable of inter-digitating, the second comb drive having a mechanical stability threshold, a movable one of the capacitor plates of the second comb drive being at the mechanical stability threshold thereof when positioned at the one of the intercepts of the tangent lines to the positive slope part of the capacitance slope function of the second comb drive for which the second comb drive is most engaged;

a second deformable connector configured to apply a restoring force to the third capacitor plate; and

a voltage source connected to apply voltages across the comb drives such that both comb drives can become disengaged and such that each comb drive is more engaged when a movable one of its plates is at its equilibrium rest position than when the movable one of its plates is at its mechanical stability threshold.

4. The apparatus of claim 3 , wherein the voltage source is configured to apply one nonzero voltage across the second comb drive to cause the first capacitor plate to move to an equilibrium position and be disengaged from the second capacitor plate.

5. The apparatus of claim 4 , wherein the voltage source is configured to apply voltages to the comb drives such that the movable one of the plates of each comb drive is more engaged at its effective equilibrium rest position than at its mechanical stability threshold.

6. The apparatus of claim 3 , wherein the voltage source is configured to apply control voltages that cause the first capacitor plate to be engaged in the comb drive containing the first capacitor plate when the third capacitor plate is disengaged in the comb drive containing the third capacitor plate.