Deflection-insensitive optical rotary encoder

Details Deflection-insensitive optical rotary encoder Deflection-insensitive optical rotary encoder

1989-04-13

1990-05-22

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250237G, 25023114, 356152, G01D 534

Patent

active

049280090

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to a deflection-insensitive optical rotary encoder, wherein a particular optical rotary encoder is used to detect deflection of a rotary shaft from the center of a bearing in order to correct detected values of a rotation angle of the rotary shaft in accordance with the deflection.
2. Background Art
Recently, as accuracy of positioning, etc., in processing with a machine tool has been improved, a rotation angle detection apparatus of high-resolution and high-accuracy has been required. Conventionally, an optical rotary encoder is generally known as an apparatus for detecting a rotation angle with high-resolution and high-accuracy. This type of optical rotary encoder detects a rotation angle around a rotary shaft by providing an angle detection pattern on a rotary disk which is coupled to the rotary shaft and by detecting a ray of light having penetrated the angle detection pattern at a rotation angle detector.
In above described optical rotary encoder, however, there is a defect in that it cannot detect an accurate rotation angle because the rotary disk deflects when the rotary shaft deflects from the center of the bearing due to the influence of an external force.
To improve on this defect, an optical rotary encoder having a function of correcting the deflection was proposed in unexamined Patent Publication (Kokai) No. 61-029021. The optical rotary encoder in this publication comprises another rotation angle detector (called the second rotation detector), which is the same as the rotation angle detector (called the first rotation detector) provided in a conventional optical rotary encoder, in a symmetrical position with respect to the rotation axis, and calculates an arithmetical mean of the rotation angles which are detected in the first rotation detector and the second rotation detector, respectively. In this way, as errors of the rotation angles due to the deflection of the rotary shaft included in the respective detected rotation angles are arithmetically averaged to be canceled out, a corrected rotation angle around the center of the bearing of the rotary shaft (referring this center to an imaginary center) is obtained.
In the optical rotary encoder described in the above publication, however, the corrected rotation angle is not a rotation angle with respect to the center of the rotary shaft but to an imaginary center of the bearing, and as direction and magnitude of deflection are not detected for the reason that contribution of the deflection of the rotary shaft is canceled out, a problem arises in that it cannot deal with ultra-accurate processing in a machine tool.


DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a deflection-insensitive optical rotary encoder which can detect deflection of a rotary shaft from a center of a bearing to be able to detect a rotation angle around the axis of the rotary shaft despite the deflection.
According to the invention, there is provided a deflection-insensitive optical rotary encoder comprising a rotary disk which is coupled to a rotary shaft, a light reception part for detecting an angle which receives only a ray of the light having penetrated an angle detection pattern which is formed on said rotary disk among the light emitted from a light source, and an angle detection part which detects a rotation angle of said rotary shaft according to an output signal from said light reception part for detecting an angle, characterized in that the encoder further comprises a deflection detection pattern which is formed on said rotary disk and which varies in intensity of light penetration depending on deflection of said rotary shaft, a light reception part for detecting deflection whose output signal is varied depending on variation of said intensity of penetration light, a deflection detection part which detects the deflection of said rotary shaft according to the variation of the output signal of said light reception part for detecting deflection, and a calculation part which correct

REFERENCES:
patent: 4108539 (1978-08-01), Gort et al.
patent: 4266125 (1981-05-01), Epstein et al.
patent: 4593193 (1986-06-01), Michaelis

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