Inch-Worm Stepper Motor

Microactuators with virtually unlimited travel distances can be realized using inch-worm steppper motors. A stepper motor, such as the conceptual model shown below has two principal components, a glider and a fixed confining rail structure that limits the movement of the glider to one dimension. Electrical contact to the glider is via sliding contacts as indicated in the figure and the glider moves in a series of steps. A single step cycle commences when the rear end (relative to the displacement direction) of the glider is immobilized against the substrate by means of the rear electrostatic clamp while the front end of the glider is unclamped. The piezoelectric extender/contractor is then extended which moves the front end of the glider forward. The front end is then clamped to the substrate by front end electrostatic clamp. The rear end electrostatic clamp is then deactivated and the piezoelectric bar is allowed to contract, thus moving the rear end of the glider forward. Deactivation of the front clamp and activation of the rear clamp positions the glider for another stepping sequence. An alternative geometry is also feasible in which the piezoelectric expander/contractor bar has one end attached to the substrate and it pushes a glider. This latter arrangement avoids the problems with sliding electrical contacts. Macroscale versions of the actuator have been fabricated and tested. Design and fabrication of a microscale version will commence in the fall of 1995.

Figure 1. Conceptual linear stepper micromotor using the inch-worm mode of operation.

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