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Capacitive Encoder With Improved Signal-To-Noise Ratio

IP.com Disclosure Number: IPCOM000047723D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Kilen, RS: AUTHOR

Abstract

High frequency capacitive encoders are typically used in motor speed control systems as rate feedback devices. An example of a portion of a rotary capacitive encoder showing the circuit patterns on the rotor and stator is shown in Fig. 1. It has been found that if the spokes in the pattern on the rotor are shortened, as shown in Fig. 2, the signal-to-noise ratio is improved because stray capacitance between patterns D and E can be reduced faster than the signal capacitance between pattern D on the rotor and pattern B on the stator or pattern E on the rotor and pattern B on the stator. In practice, the stator and rotor are positioned face-to-face on a common axis, with a small gap (typically 0.25 mm) between them.

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Capacitive Encoder With Improved Signal-To-Noise Ratio

High frequency capacitive encoders are typically used in motor speed control systems as rate feedback devices. An example of a portion of a rotary capacitive encoder showing the circuit patterns on the rotor and stator is shown in Fig. 1. It has been found that if the spokes in the pattern on the rotor are shortened, as shown in Fig. 2, the signal-to-noise ratio is improved because stray capacitance between patterns D and E can be reduced faster than the signal capacitance between pattern D on the rotor and pattern B on the stator or pattern E on the rotor and pattern B on the stator. In practice, the stator and rotor are positioned face-to-face on a common axis, with a small gap (typically 0.25 mm) between them. The rotor is attached to the shaft whose angular velocity is to be monitored, and the stator is mounted in a fixed position. No electrical connections are made to the rotor. The encoder shown in Fig. 1 consists of one channel, whose output is taken from circuit pattern B. Ring patterns A and C are driven by high frequency clock signals (typically 100 KHz to 1 MHz) which are 180OE out of phase with each other. The signals on patterns A and C are capacitively coupled to patterns D and E on the rotor and from there to pattern B on the stator as the rotor brings the spokes of pattern D and E across the spokes of pattern B. In the rotor of Fig. 2, the spokes of patterns D and E have been trimmed. By trimm...