Encoder measurement based on layer thickness

Optics: measuring and testing – Position or displacement – Position transverse to viewing axis

Reexamination Certificate

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C250S231130, C250S23700G

Reexamination Certificate

active

06970255

ABSTRACT:
An encoder includes a layer on the scale that has a thickness that varies as a function of position along the length of the scale. The position of the sensor head with respect to the scale may be determined by measuring the thickness of the layer or index of refraction, e.g., using a reflectometer, and converting the thickness to the lateral position. In one embodiment, the thickness of the layer is used to provide a rough position of the sensor head with respect to the scale and an alignment target that includes periodic patterns on both the sensor head and scale is used to provide a refined position.

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