Optical interrupter system with vibration compensation

DETAILED DESCRIPTION The present invention provides an improved optical encoder system for monitoring the rotational position of an encoder disc having optical flags arranged in a row on the disc, which is significantly more effective in compensating for vibration of the system.
The system purposely blurs edge transistions of optical flags and includes signal processing circuitry designed to sense the passing of intermediate portions of waveforms detected in the optical encoding of rotational positions, maximizing insensitivity of the system to vibrational errors.
Briefly and in general terms, an optical encoder apparatus according to the invention includes a moving member having a sequence of optical flags, interposed between a source of illumination and a detector, such that as the optical flags of the moving member are illuminated and detected, the detector generates a signal having a waveform with a first portion less than a first threshold, a second portion greater than the first threshold and less than a second threshold, and a third portion greater than the second threshold.
Signal processing circuitry operates to generate a count signal indicating a transition between the first and third waveform portions.
In a preferred embodiment, the moving member of the optical encoder apparatus is a rotational disc, and the optical encoder determines rotational phase position of the disc.
The shape of each optical flag is preferably designed to cause the detector to generate a signal having waveform with a leading edge, a leading intermediate portion, a central portion, a trailing intermediate portion, and a trailing edge portion.
The optical flags are most preferably formed in the shape of a rectilinear cross.
Other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings, which illustrate by way of example the features of the invention.