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Browse Prior Art Database

Capacitive Rotary Motion Digitizer

IP.com Disclosure Number: IPCOM000049200D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Quinn, PA: AUTHOR [+2]

Abstract

A rotary motion digitizer detects capacitance changes resulting from relative movement of circular patterns of regularly spaced conducting pads arranged on two closely spaced wheels. Two offset patterns serve to provide direction information, and by using pairs of pads on one wheel opposing single pads on the other, differential signal techniques may be used to reduce noise through cancellation.

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Capacitive Rotary Motion Digitizer

A rotary motion digitizer detects capacitance changes resulting from relative movement of circular patterns of regularly spaced conducting pads arranged on two closely spaced wheels. Two offset patterns serve to provide direction information, and by using pairs of pads on one wheel opposing single pads on the other, differential signal techniques may be used to reduce noise through cancellation.

Referring to Fig. 1, a first wheel 10 of digitizer assembly 8 is fixed and a second wheel 12 is mounted in closely spaced relationship thereto to rotate with a shaft 14. Wheel 10 includes patterns 18 and 20 of pads 16 with each pattern having pairs of inner and outer pads at each radial pad position. Wheel 12 has individual pads 22 that extend over an area corresponding to the overall area for a pad pair on wheel 10. The pads 22 are arranged in regular patterns 24 and 26 which are arranged to align with the patterns 18 and 20 of wheel 10. A quadrature offset is introduced between the patterns 24 and 26 to permit detection of direction of rotation.

Referring to Fig. 2, a pulsating voltage is supplied from a source 50 to the pads 16 of patterns 18 and 20 through resistors 52-55. The inner and outer sets of pads 16 are connected to opposite terminals of the source 50. The voltages at the respective sets of pads 16 are applied to opposite terminals of a differential amplifier (denoted 56 and 58 for patterns 18 and 20, respectively) through r...