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Incremental encoder has go-cheaper stripes

01 September, 2000

Incremental encoder has go-cheaper stripes

Encoder specialist Hohner Automation has come up with a new precision reading system for incremental encoders which rivals the accuracy of systems based on diffraction gratings but at a much lower cost.

Incremental encoders, whether linear or angular, are based on an encoding disc or linear scale with transparent and opaque, or reflecting and non-reflecting, patterns. The other vital ingredients are a light source and photodetectors.

The patterns transmit or reflect the light in pulses which are picked up by the detectors. An optical mask between the encoding element and the light source or detector enhances the encoder performance and makes it possible to read extremely fine lines.

Hohner`s invention does away with the need for the encoding mask. It does so by using "stripes" of light that can be adjusted to match the pattern of the encoding element. The stripes are produced by creating interference patterns between coherent, monochromatic beams of light.

An encoding disk is placed in the area of interference so that its pattern is parallel to that of the interference pattern. Moving the encoding element causes its lines to close the interference pattern periodically, changing the amount of light passing through, or reflected by, the element. These changes are sensed by the photodetectors and can be used to provide precise linear or angular measurements, according to Hohner.

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