Patent ID: 7142500

Claim:
A movable system having capacitance-based position sensing, comprising: a pair of objects; an actuator configured to effect an operative range of relative motion between the objects along an axis; and a capacitance-based position sensor, including a first plate secured to one of the objects; and a pair of second plates secured to the other of the objects so that the second plates are adjacent and coplanar, and so that the second plates are spaced from, and parallel to, the first plate as the objects move relative to one another along the axis, and such that the second plates in use come into simultaneous overlap with the first plate, where the configuration of the first plate and second plates results simultaneously in two spaced-plate capacitors having capacitances that vary oppositely as the objects move relative to one another throughout the operative range along the axis, where the capacitance-based position sensor uses the capacitances to generate output usable to determine relative position of the objects along the axis throughout the operative range along the axis; where the capacitance-based position sensor is configured so that the output is substantially independent of perpendicular spacing variations occurring between the first plate and the second plates.