Opto-electronic scale reading apparatus
AssigneeRenishaw PLC
InventorsWilliam F. N. Stephens, Stephen E. Lummes
Life of this patent
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Abstract
An opto-electronic scale reading apparatus comprises a light source (20) which projects light via an index grating (22) onto a reflective scale (10). Light is reflected from the scale (10), passes through an auxiliary grating (36) and is incident upon an analyser grating (28), at which a plurality of periodic light patterns are formed. Light from the light source (20) travels initially parallel to the scale plane, and is subsequently deflected through 90.degree. by a beam splitter cube (26); the light is thus incident upon and reflected and off the scale (10) at 90.degree. to the scale plane. This arrangement enables large movements of the readhead in a direction perpendicular to the scale.
Claims7
Opto-electronic scale reading apparatus comprising a reflective scale defined by a series of spaced-apart lines, and a readhead movable relative to the scale in the direction of spacing of the lines, the readhead comprising:
- an index grating;
- an analyser, the index grating and analyser occupying spatially distinct positions;
- a light source for illuminating the scale via the index grating, thereby to generate a periodic light pattern in the plane of the analyser, and a modulation of light intensity upon relative movement of the scale and readhead;
- means for generating from said intensity modulation a plurality of phase-shifted electrical signals, each signal having a frequency corresponding to the frequency of said modulation;
- wherein:
- means are provided for directing the light
- a) along a first path from the index grating to an intersection point;
- b) from the intersection point, to the scale and back to the intersection point along a common path in a direction substantially perpendicular to the scale;
- and
- c) from the intersection point to the analyser, along a second path.
Dependencies are inferred from the claim text.