Importance

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Abstract

An optical encoder assembly reduces the space required to mount multiple thumbwheels on a control panel by utilizing wheels with integral encoder patterns. An encoder pattern comprising two tracks of reflective dots is attached to the side of each wheel. Two optical transceivers are mounted on a printed circuit board next to each wheel so that the pattern elements in each of the tracks move past one of the transceivers as the wheels rotate. The transceivers send electrical pulses to a microprocessor each time a dot passes a transceiver. The dots in the two tracks are offset circumferentially to provide a 90 degree phase shift between the tracks as the wheels rotate on a common shaft. The use of dots reduces blurring of the pulse signals. A chassis is mounted to the panel and supports the shaft, the printed circuit board, and a rubber dust shield which rubs against the wheels to provide braking action. The chassis, printed circuit board and dust shield all include slots through which the wheels rotate. Protrusions in the printed circuit board slots guide the wheels as they rotate, and protrusions in the dust shield slots rub against the sides of the wheels to provide the braking action.

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First Claim