Absolute position encoder

Details Absolute position encoder Absolute position encoder

1989-01-19

1991-03-05

Shoop, Jr., William M.

Coded data generation or conversion

Digital pattern reading type converter

Optical

341 9, 341 15, 25023116, 324208, 32420725, H03M 122

Patent

active

049981056

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an absolute position encoder and, more particularly, to an absolute position encoder capable of detecting a rotational position or the like of a rotating shaft of a motor or the like for driving a machine tool or the like to an absolute position.


BACKGROUND ART

An absolute position encoder of this type is generally arranged as follows. A plurality of channels (slit array) formed on a rotary code plate fixed on a rotating shaft on the basis of a binary code notation or a Gray code notation are arranged in accordance with a desired resolving power. An amount of light emitted from a light-emitting element and passing through each channel formed on the rotary code plate and a fixed slit portion opposing each channel is detected by a light-receiving element (photoelectric conversion element) so that a rotational position of the rotary code plate is detected as an absolute position.
In this case, to improve the detecting precision (resolving power), the number of channels must be increased. For example, to detect angular data obtained by dividing one revolution into 4096, i.e., 2.sup.12, 12 channels are required (a 12-bit code is required), and a large code plate is required in correspondence with the number of channels.
To solve the above problems, the following method has been considered. Sine wave patterns for the plurality of channels are arranged on the rotary code plate so that a plurality of sine wave outputs having different numbers of cycles per revolution can be obtained (for example, a pattern for obtaining a sine wave output having one cycle per revolution serves as a first channel, a pattern for obtaining a sine wave output having 16 cycles per revolution serves as a second channel, and a pattern for obtaining a sine wave output having 256 cycles per revolution serves as a third channel). Angular data of one wavelength of each channel is interpolated into 16 pieces. Interpolated data of the channels thus obtained are sequentially synthesized, so that the rotational position of the code plate is detected as the absolute position.
In this case, the number of channels for obtaining identical resolving powers may be small compared with the number of channels formed according to the above-mentioned binary notation (for example, to detect the absolute position by dividing one revolution into 2.sup.12, only three channels as described above are required), thereby realizing a small-size rotary code plate.
FIG. 1 illustrates an absolute position encoder for detecting angular data using a rotary code plate in which sine wave patterns of a plurality of channels having different numbers of cycles are formed. In FIG. 1, first to third channels (represented by 1.lambda., 16.lambda., and 256.lambda.) are formed on the rotary code plate. In addition, a fourth channel (a pattern for obtaining a sine wave output having 4096 cycles per revolution is arranged and represented by 4096.lambda.) is arranged. Sine wave signals 1.lambda.sin, 16.lambda.sin, 256.lambda.sin, and 4096.lambda.sin, and cosine wave signals each having an electrical phase difference of 90.degree. with respect to the corresponding sine wave signal (e.g., the cosine wave signals can be obtained by detecting by a light-receiving element and photoelectrically converting light passing through a fixed slit portion shifted from a fixed slit portion for the sine wave signals by an electrical angle of 90.degree.) 1.lambda.cos, 16.lambda.cos, 256.lambda.cos, and 4096.lambda.cos are input from each of the channels.
Reference numerals 11 to 14 denote amplifiers for respectively amplifying the sine wave signals 1.lambda.sin to 4096.lambda.sin; 21 to 24, channel selection analog switches respectively connected to output sides of the amplifiers 11 to 14; 16 to 19, amplifiers for respectively amplifying the cosine wave signals 1.lambda.cos to 4096.lambda.cos; 26 to 29, channel selection analog switches respectively connected to output sides of the amplifiers 16 to 19. 21 and 26 are turned on, and therefore, sine

REFERENCES:
patent: 4346447 (1982-08-01), Takahama
patent: 4360730 (1982-11-01), Breslow
patent: 4445110 (1984-04-01), Breslow
patent: 4524347 (1985-06-01), Rogers
patent: 4587513 (1986-05-01), Burrowes et al.
patent: 4774464 (1988-09-01), Kubota et al.
patent: 4786891 (1988-11-01), Ueda et al.

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