US 4,335,306 A · Surveying instrument

Abstract

A tacheometer includes two angle encoders each utilizing a method of eccentricity correction wherein three detectors responsive to encoded angular displacement are arranged linearly along a line passing through the desired axis of angular displacement. Two of the detectors are disposed diametrically opposite each other, at equal distances from and on opposite sides of the desired axis. In the absence of eccentricity the actual axis of angular displacement is the desired axis, and the outputs of the diametrically opposed detectors are complementary. The presence of eccentricity causes the two axes to separate, and produces a corresponding change in the outputs of the diametrically opposed detectors, rendering them non-complementary. The degree of change is measured and used to correct an angular displacement detected by the third detector, located at a different distance from the desired axis.

Claims10

Dependent claims

A shaft angle encoder comprising:

an encoder disc for periodically modulating first and second signals, the signals being modulated as a function of angular displacement;
first, second and third detectors linearly aligned, said first and second detectors having inputs coupled to receive the first signal, said third detector coupled to receive the second signal, each detector having an output, each detector generating a signal upon its respective output responsive to the signal input thereto;
processor means coupled to the outputs of said first, second and third detectors for determining the eccentricity error from signals responsive to the outputs of said first and second detectors, modifying the measurement of the angular displacement determined from said third detector in response to the determined error, and combining angular displacements derived from said detectors to obtain a single angular displacement.

In a shaft angle encoding apparatus in which an angularly encoded element rotates relative to a detector element having a plurality of detectors, the method of correcting for the eccentricity error associated with displacement between the rotational axis of the angularly encoded element and the rotational axis of the detector element comprising the steps of:

detecting angular encoding at linearly aligned first, second and third locations, the first and second locations diametrically opposed and substantially equally distant from the rotational axis of the detector element, the third location at a substantially different distance distant from the rotational axis of the detector element;
algebraically combining the angular detections of said first and second locations to produce a correction factor;
and
algebraically combining the correction factor with the detection at said third location to produce a signal representative of the shaft angle corrected for the eccentricity error.

1 more element

In a shaft angle encoder having an encoder disc for providing periodically modulated first and second signals as a function of angular displacement relative to a means for detecting the signals, an improvement for compensating the encoded shaft angle for the eccentricity error associated with displacement between the rotational axis of the encoder disc and the rotational axis of the means for detecting the signals wherein:

the means for detecting the signals comprises first, second and third detectors linearly aligned, said first and second detectors diametrically opposed at substantially equal distances from the rotational axis of the means for detecting and coupled to receive the first signal, said third detector at a substantially different distance from the rotational axis of the means for detecting and coupled to receive the second signal, each detector having an output, each detector generating a signal on its respective output responsive to the signal received thereby;
first means coupled to the outputs of said first and second detectors for providing an eccentricity error signal in response to the signals generated by the first and second detectors;
and
second means for providing a first signal representative of the shaft angle compensated for the eccentricity error in response to the signal generated by the third detector and the eccentricity error signal.

1 more element

Dependencies are inferred from the claim text.

Surveying instrument

Life of this patent

Surveying instrument

Life of this patent

Abstract

Claims10