| 摘要 |
A system is provided for monitoring signals from a linear or rotary encoder or scale to provide a warning of a malfunction of the encoder or to be able to predict a future malfunction. The system includes a feedback circuit for comparing the output of the detector in the encoder with a voltage reference and for either raising or lowering the voltage to the light source for maintaining constant maximum detected light amplitude regardless of dirt build-up on the scale with the amount of voltage correction to the light source being an indicator of the level of functioning of the encoder. The system also assures constant amplitude output signals from reflectance-type encoders in which the light source and detector are on the same side of the scale and in which the subject servo system maintains a constant amplitude reflected beam. In one embodiment, an absolute voltage reference check is provided such that when the error signal used to control the light source voltage exceeds a predetermined threshold, an outright failure alarm indicator is actuated. The system, as a by-product, also provides a constant amplitude output signal for the encoder to simplify downstream processing, a feature uniquely applicable to reflecting scales such as ruled steel, which suffer not only from contamination, but also due to the variation in distance between the surface of the scale and both the light source and detector.
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