Absolute position miniature grating encoder readhead using fiber optic receiver channels

Abstract

An absolute position fiber optic encoder readhead having multiple readhead portions for sensing the displacement of respective scale grating tracks of a scale is disclosed. The detector channels of the readhead portions are fiber optic detector channels having respective phase grating masks. The fiber optic encoder readhead portions are configured to detect the displacement of a self-image of a respective scale grating track of the scale. In various exemplary embodiments, the fiber optic readhead portions are constructed according to various design relationships that provide a relatively high signal-to-noise ratio. Accordingly, high levels of displacement signal interpolation may be achieved, allowing submicrometer displacement measurements. The fiber optic encoder readhead portions may be assembled in a particularly accurate and economical manner and may be provided in a package with dimensions on the order of 1-2 millimeters, resulting in a very small overall absolute readhead dimension that is dependent on the number of readhead portions that are incorporated. Optical fiber receiver channels carrying binary optical signals derived from a scale code track may be provided in the readhead, to provide an extended absolute measurement range.

Description

technical field

[0001] In general, the present invention relates to displacement detection optical encoders, and in particular to absolute position optical encoders, which use optical fibers as receiver elements for providing extremely compact high precision absolute position system ). Background technique

[0002] A variety of motion or position encoders are currently available for detecting linear, rotary, or angular motion. These encoders are generally based on optical systems, magnetic scales, inductive or capacitive sensors. Some of these encoders are designed to make relative rather than absolute measurements. In such relative position encoders, where measurement is generally performed by detecting the relative position change of the scale relative to a reference position, it is necessary to continuously detect changes in the scale pattern so that repetitions of said pattern can be counted. The relative measurements require establishing a new reference or zero posit...

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