Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1982-12-10
1985-10-15
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340347P, G08C 906, H03K 1302
Patent
active
045476675
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to devices for measuring displacement, and particularly to devices for measuring displacement of the type which employs a coding member which is provided to an object to be measured and has a coding section capable of causing sensing elements to generate signals which can be discriminated as "0"and "1", and sensing means adapted to sense the coding section of the coding member for generating detection signals in response to displacement of the coding member. More particularly, the invention relates to the above-mentioned type of displacement measuring device which can be effectively used in an angular displacement measuring equipment wherein measurement error due to play and/or eccentricity in the rotating shaft of an object to be measured can be compensated whereby rotational angle or rotating speed of the rotating body can be measured with high accuracy.
BACKGROUND
Conventionally, a device for measuring the rotational angle of a rotating body with influence due to play and/or eccentricity in the rotating shaft being has been known and described in Japanese Patent Application Pre-examination Public Disclosure No. Sho 55-67608 published on May 21, 1980. The rotational angle measuring device which is described as prior art in this public disclosure is a photoelectric rotational angle measuring device as shown in the block diagram of FIG. 1, wherein a rotating coding disk 2, which has radial slit gratings 2A arranged annularly at equal angular pitches P as shown in FIG. 2, is fixed to a rotating shaft 1, which is an object to be measured, for rotation together with the rotating shaft 1, with the slit gratings in a substantially concentric relationship with the rotating shaft 1. Opposed to and concentrically with the rotating disk 2, an unrotatable index disk 3 is provided. This index disk 3 is provided with two groups of index slit gratings 3A, 3B arranged in a diametrically opposing relationship with an angular difference of ##EQU1## (wherein n is an integer) therebetween as shown in FIG. 3. Light sources 4A, 4B and photoelectric conversion element 5A, 5B are located to put therebetween the index gratings 3A, 3B and the rotating code disk 2. Upon rotation of the rotating shaft 1, sinusoidal signals as indicated at 4A and 4B in FIG. 4 are generated respectively from the photoelectric conversion elements 5A, 5B. The output signals from the photoelectric conversion elements 5A, 5B are directly supplied to a differential amplifier 6 for cancelling direct current components in the respective signals, and then supplied to a Schmitt circuit 7 where the signal is converted into rectangular waves, which are in turn converted by a pulse generating circuit 8 into pulses which correspond to the leading or trailing edges of the rectangular waves. The pulses generated from the pulse generating circuit 8 are counted by a counter 9, and the counted value is converted into a rotational angle of the rotating shaft 1 and is displayed by a display unit 10.
The pulse generating circuit 8 of the above-described conventional rotational angle measuring device has been composed from a differentiating circuit employing a capacitor and a resistor for deriving pulses which correspond to the leading or trailing edge or both edges of a detection signal.
The capacitor and resistor employed in the differentiating circuit, however, are highly dependent on temperature, and thus the threshold level may be varied by the influence of variation of temperature to cause an error, resulting in decreased reliability. Further, differentiating circuits of the number corresponding to the necessary number of edge detections are required, resulting in an increased number of components. Because of this and because capacitors and resistors cannot be easily realized in an integrated circuit, the construction of an electronic circuit is inevitably complicated and is prevented from being small-sized.
On the other hand, the above-described conventional device, even if output signals of the photoelectric conversion el
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patent: 4194184 (1980-03-01), Hartmann et al.
patent: 4240069 (1980-12-01), Hullein et al.
patent: 4300039 (1981-11-01), Avins
Takashi Imai, "Easily Understandable Method of Electronic Measurement", Denshi Kagaku Series, Sep. 30, 1977.
Shinzaburo Inomata, "Velocity and Revolution," Keiryo Kanri Gijutsu Sosho, Nov. 30, 1961.
Masaji Sawabe, "What You Want to Know About Automization of Measurement," Japan Machinist, Oct. 1, 1971.
Kondo Fumitomo
Ohtomo Fumio
Sasaki Tsuneo
Yokokura Takashi
Tokyo Kogaku Kikai Kabushiki Kaisha
Westin Edward P.
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