Optical rotary encoder with adjustably positioned light source

Details Optical rotary encoder with adjustably positioned light source Optical rotary encoder with adjustably positioned light source

1986-06-18

1988-04-12

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250237G, G01D 534

Patent

active

047376350

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to an optical rotary encoder, and more particularly, to an optical rotary encoder for converting a rotational angle of a shaft rotatably supported in a base member or flange into an output of an electrical digital quantity.
2. Background Art
Generally, in low resolution type optical rotary encoders with an output of about several hundred pulses (for example, 200) per one revolution, wide use is made of a structure in which a light source such as a light-emitting diode (LED), a laser-beam projector or the like is attached to and positioned mechanically at a predetermined location with respect to a light-receiving system including a light-detecting element, i.e., a photo-electric conversion element such as a photodiode, a photoconductor or the like. In the case of such an attaching structure, since an attaching position for the light source is univocally fixed, the work for attachment thereof is easy and can be automated. However, since the position of the light source cannot be adjusted, the reliability of the encoders decreases upon variations in the orientation of the light source, the dimensional precision of component parts, etc. Therefore, such an attaching structure is not suitable for high resolution rotary encoders.
In a high resolution optical rotary encoder with an output of several thousand pulses (for example, 2000) or more, wide use is made of a method of adjusting the three-dimensional position of the light source by hand, to obtain the optimal output waveform of an photoelectric conversion system, then fixing the light source to a fixed support by an adhesive. However, in the case of using such a method, the direction of the adjustment of the position of the light source is not defined, so adjustment is not made by set amounts, which factor results in the disadvantage that a certain time must be taken for the adjustment. Further, since such a non-set manual adjustment is required, it is difficult to automatically assemble the encoders.


DISCLOSURE OF THE INVENTION

According to the present invention, there is provided an optical rotary encoder for converting a rotational angle of a shaft rotatably supported in a base member into an output of an electrical digital quantity, comprising: a light-receiving system fixed to a certain place of the base member; a stationary encoding plate fixed to the base member so as to face the light-receiving surface of the light-receiving system; a rotary encoding plate fixed to the shaft so as to be in opposition to the stationary encoding plate; a light-source support member arranged rotatably about the axis of the shaft with respect to the base member; a light source attached to the light-source support member so as to be in opposition to the rotary encoding plate; and a fixing means for fixing the light-source support member to the base member.
In the above-mentioned encoder, the location of the light source in relation to the light-receiving system can be easily performed by adjusting the position of the light-source support member in the rotating direction thereof. That is, in the first place, the rotary encoding plate is matched in position with the stationary encoding plate, and then the light-source support member is matched in place with the base member in the rotating direction thereof. The light-source support member is then fixed to the base member by means of the fixing means at the position where the waveform of the output from the light-receiving system is optimal. In this way, since the light-source support member supporting the light source can only rotate about the axis of the shaft, the adjustment of the position of the light source can be performed easily by set amounts, thus enabling automation of the assembly of the encoder and adjustment work for the light source. Consequently, it is possible to easily manufacture high resolution type optical rotary encoders.
In a preferred embodiment of the present invention, the light-receiving system includes at least a pair of light-detect

REFERENCES:
patent: 3902063 (1975-08-01), Oelsch et al.
patent: 4031441 (1977-06-01), Garrett
patent: 4512184 (1985-04-01), Ernst et al.

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