US 7,126,109 B2 · Encoder scale error compensation employing comparison among multiple detectors

Abstract

An encoder calculates position error values and applies compensation values to encoder position measurements in-situ. The encoder includes a scale and a multi-section detector for detecting a spatially periodic pattern, such as an optical interference pattern, produced by the scale. The detector includes spatially separated first and second sections. A signal processor estimates respective phase values from detector sections and calculates a phase difference reflecting a spatial position error in the scale. A compensation value is calculated from the phase difference and included in the estimate of the scale position to compensate for this spatial position error. The compensation values may be calculated and used on the fly, or calculated and saved during an in-situ calibration operation and then utilized during normal operation to compensate uncorrected measurements.

Claims36

Dependent claims

An encoder, comprising:

a scale operative to produce a spatially periodic pattern;
and
a multi-section detector configured to detect multiple periods of the spatially periodic pattern, the detector comprising spatially separated first and second sections, the detector sections generating respective sets of detector output signals;
and
a signal processor operative in response to the detector output signals to:
(i) derive first and second measured phase values for the first and second detector sections respectively, the measured phase values being indicative of an uncorrected estimate of the position of the scale with respect to the detector;
(ii) calculate a position error value based on the difference between the first and second measured phase values;
(iii) calculate a compensation value from the position error value;
and
(iv) combine the compensation value with at least one of the first and second measured phase values to produce a corrected estimate of the position of the scale with respect to the detector.

7 more elements

A method of compensating for spatially varying position errors in a scale of an encoder, the scale being operative to produce a spatially periodic pattern, the method comprising:

(i) providing a multi-section detector configured to detect multiple periods of the spatially periodic pattern, the detector comprising first and second spatially separated sections, the first and second sections generating respective sets of output signals;
(ii) deriving first and second measured phase values for the first and second detector sections respectively, the measured phase values being indicative of an uncorrected estimate of the position of the scale with respect to the detector;
(iii) calculating a position error value based on the difference between the first and second measured phase values;
(iv) calculating a compensation value from the position error value;
and
(v) combining the compensation value with at least one of the first and second measured phase values to produce a corrected estimate of the position of the scale with respect to the detector.

3 more elements

Dependencies are inferred from the claim text.

Encoder scale error compensation employing comparison among multiple detectors

Life of this patent

Encoder scale error compensation employing comparison among multiple detectors

Life of this patent

Abstract

Claims36