Differential capacitive position encoder

A capacitive transducer, comprising:

• a transmitter portion having a planar surface and incorporating a plurality of parallel conductive surfaces thereon arranged as a transmitter grating having length L and width W;
• a receiver portion having a planar surface and incorporating a plurality of parallel conductive surfaces of period P thereon arranged as a receiver grating having length L' comparable to length of said transmitter grating and width W' that is substantially less than width W of said transmitter grating;
• means mounting said transmitter and receiver portions for relative movement with said transmitter and receiver gratings a distance Y apart and in face-to-face complementary relationship in order to establish capacitive coupling between the respective conductive surfaces in said gratings, the relationship of said width dimensions W and W' of said gratings insuring that said transducer is insensitive to undesired movement of said transmitter and receiver portions in a transverse Z direction, the ratio W'/P being relatively small in order to minimize angular misalignment of the longitudinal axis of said receiver portion relative to said transmitter portion, and the ratio L'/P being relatively large in order to minimize the sensitivity of said transducer to non-uniform separation between said transmitter and receiver portions;
• moving means operable to relatively move said transmitter and receiver portions and their associated gratings with respect to one another;
• at least one alternating signal generator coupled to alternate conductive surfaces of said transmitter grating;
• an amplifier circuit having input and output connections and means interconnecting selected conducting surfaces of said receiver grating to the input connections of said amplifier circuit, said amplifier circuit thereby providing output signals indicative of both extent and direction of movement of said transmitter and receiver portions during relative movement.