Optical rotary encoder with sub-code patterns

Details Optical rotary encoder with sub-code patterns Optical rotary encoder with sub-code patterns

1987-12-15

1989-08-22

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250211K, 250237G, G01D 534

Patent

active

048598453

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an optical rotary encoder, and more particularly to a rotary encoder having a code disk which is formed with an analog pattern, and having improved detection resolution.
2. Description of the Related Art
Generally, in an optical encoder, a light beam is projected from a photoemitter such as a LED onto a rotary disk formed with a digital code pattern, the disk being composed of glass, for instance. The light beam passes through or is reflected from the digital code pattern, and then passes through a photoreception window to be received by a photoreceptor such as a phototransistor. The received light is converted by the photoreceptor into an electrical signal to generate output pulses, for detection of the rotational speed and the rotational position of the disk.
A conventional optical rotary encoder, using the above-mentioned type of digital code pattern for detection, has a limited resolution because of the usage of the digital code pattern. That is, it is difficult to obtain a high resolution merely by narrowing the pattern width and the pattern interval of the minimum unit of division of the code pattern, i.e., by the use of a minute code pattern. Further, even if the minute pattern can be obtained, escape and diffraction of the light beam or the like occur, which adversely affect the resolution of the encoder.


SUMMARY OF THE INVENTION

The object of the present invention is to form an analog code pattern on a rotary encoder, to thereby provide a rotary encoder having high resolution which cannot be attained by the above-mentioned conventional digital code pattern.
To achieve the above-mentioned object, in a rotary encoder arranged to receive light from a photoemitter by a photoreceptor through a code pattern formed in a disk, to thereby detect a value of a parameter associated with rotation of the disk, according to the present invention, the code pattern consists of an analog code pattern, which is continuously formed in the disk in the direction circumferentially of the disk. The radial width of the analog code pattern is set to a value which is determined as a function of the rotational position of the disk. The photoreceptor is adapted to generate a signal proportional to an amount of light received through the analog code pattern.
As mentioned above, according to the present invention, the disk is formed with the analog code pattern the width of which continuously changes as a function of the rotational position of the disk. As a result, the output from the photoreceptor accurately follows the code pattern, and the rotary encoder obtains a high resolution.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a rotary encoder according to a first embodiment of the present invention;
FIG. 2 is a view showing, in relation to a photoreception window and in an expanded state, an analog code pattern formed in the disk of FIG. 1;
FIG. 3 is a view, similar to FIG. 2, showing a code pattern according to a second embodiment of the present invention;
FIG. 4 is a view showing, by way of example, a luminous intensity distribution of a LED;
FIG. 5 is a view showing an output from a photoreceptor in the case of using an increased maximum width of the code pattern in the first embodiment, together with an ideal output of the receptor;
FIG. 6 is a view, similar to FIG. 5, but relating to the second embodiment;
FIG. 7 is a view showing a code pattern according to a third embodiment of the present invention;
FIG. 8 is a view showing a code pattern of a fourth embodiment of the present invention;
FIG. 9 is a view explaining calculation of an amount of light with respect to a minute section;
FIG. 10 is a view explaining calculation of an output from the photoreceptor of the third embodiment; and
FIG. 11 is a view, similar to FIG. 10, but relating to the fourth embodiment.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a rotary encoder of a first embodiment of the present invention, whic

REFERENCES:
patent: 3128386 (1964-04-01), Hughes
patent: 3285123 (1966-11-01), Rantsch et al.
patent: 3859617 (1975-01-01), Oka et al.
patent: 3892961 (1975-07-01), Bachmann
patent: 4250380 (1981-02-01), Iyeta

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