Method and apparatus to detect absolute position using encoder h

Details Method and apparatus to detect absolute position using encoder h Method and apparatus to detect absolute position using encoder h

1995-02-13

1996-11-05

Le, Que T.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25023118, 377 17, G01D 534

Patent

active

055720188

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention generally relates to an absolute position detecting method using an encoder for detecting a position, such as a rotational position of a motor or a shift position of a table of a machine tool, and an arrangement of an encoder apparatus for executing the above method.
2. Description of the Related Art
An encoder, known as incremental encoder, has a code plate formed with numerous slits equally spaced along a circumferential periphery thereof. For one complete revolution of the code plate, attached to a rotor shaft or the like, the encoder generates a one-rotation signal and a pair of multiple-rectangular pulse signals having a predetermined phase difference therebetween. This kind of incremental encoder generally produces incremental signals on the basis of the above multiple-rectangular pulse signals independently in each of rotational directions. A counter accumulates these incremental signals to obtain a rotational shift amount (i.e. a rotational position) of the rotor in one revolution.
On the other hand, an absolute encoder has a code plate with a multi-channel pattern formed thereon as shown in FIG. 1. Using this code plate, the absolute encoder generates a code signal representing a rotational position. More specifically, as the code plate shown in FIG. 1 comprises eight channels, an eight digit binary code is outputted for expressing an absolute value of position.
In short, compared with an incremental encoder, an absolute encoder is generally complicated not only in the structure of its code plate but in the arrangement of the signal detecting and processing circuit.


SUMMARY OF INVENTION

The object of the present invention is to realize an absolute position detecting method and the arrangement of a related encoder apparatus by incorporating a simplified signal processing means into the signal processing system adopted in a conventional incremental encoder having a relatively simple structure, without providing the absolute encoder having the above-described disadvantage.
In order to accomplish this and other related objects, the present invention provides an absolute position detecting method using an encoder comprising steps in which rotation of a rotary plate fixed to a shaft of a detecting object is detected to produce a one-rotation signal and an incremental signal corresponding to division of one revolution into a plurality of equal sections and the incremental signal is counted by a counter to detect an absolute position. The method includes the steps of clearing a count value of the counter in response to a first one-rotation signal arriving first after the encoder starts a detecting operation; continuing to count up the incremental signal by the counter followed by rotation of the shaft of the detecting object after finishing the clearing step, without clearing the count value of the counter in response to second and succeeding one-rotation signals; and obtaining, based on the count value of the counter, an information on a distance from a position where the counter received the first one-rotation signal to a present position.
In the above absolute value detecting method, it is preferable that the incremental signal corresponding to division of one revolution into the plurality of equal sections is produced based on two different signals which are generated from the rotary plate with a 90.degree. phase difference therebetween, so that the counter can count up or down the count value in accordance with a rotational direction of the rotary plate. Moreover, the one-rotation signal produced from the encoder is transformed into a rectangular wave, and the counter is cleared in response to detection of a building up or a trailing edge of the rectangular wave in accordance with the rotational direction of the encoder.
It is further preferable that the incremental signal generates pulses equivalent to n-th power of 2 per revolution (n; positive integer), and the counter counts the incremental signal by binary count meth

REFERENCES:
patent: 4233592 (1980-11-01), Leichle
patent: 4473313 (1984-09-01), Nakano et al.
patent: 4833664 (1989-05-01), Shiragami et al.
patent: 5063576 (1991-11-01), Eguchi et al.

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