Reference-point return method

Details Reference-point return method Reference-point return method

1990-03-23

1992-06-02

Shoop, Jr., William M.

Electricity: motive power systems

Positional servo systems

Program- or pattern-controlled systems

318626, 318571, 318572, 318594, 36447434, 250237G, 324165, G05B 1918

Patent

active

051190044

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to a reference-point return method and, more particularly, to a reference-point return method for returning a machine tool table or the like to a predetermined reference point by an output signal from a linear scale.
2. Background of the Invention
A reference-point return method is available for moving a machine tool in the direction of a predetermined reference point, reducing the reference-point return velocity in response to generation of a deceleration signal, and stopping a movable element in response to an initial one-revolution signal, which is indicative of one revolution of a motor, following the generation of a signal indicating the proximity of the reference point. FIG. 5 is a view for describing such a reference-point return method. Here a movable element (table) TB of a machine is provided with a limit switch LS, and a stationary portion MC of the machine is provided with a reference-point return dog DG in the vicinity of the machine reference point. If the reference-point return mode is established when the limit switch LW resides in a working area AIII on the left side of the dog DG, the movable element TB of the machine is moved toward the reference point at a rapid-traverse velocity V.sub.H. When the vicinity of the reference point is reached and the limit switch LS contacts the reference-point return dog DG at time t.sub.1, a limit signal LSS makes a transition from "1" (high level) to "0" (low level), as shown in FIG. 5. The reference point return velocity is reduced in response to the negative-going transition (deceleration signal) of the limit signal LSS. At time t.sub.2, the limit switch LS parts from the DG and the limit signal LSS reverts from "0" to "1". The traveling velocity at this time is V.sub.L. When the limit signal LSS reverts from "0" to "1" (rises), the movable element TB of the machine subsequently moves toward the reference point at the velocity V.sub.L and stops in response to generation of an initial one-revolution signal ORS, which is indicative of one-revolution of a motor, following the occurrence of the positive-going transition (reference-point proximity signal) of the limit signal LSS. OTA in FIG. 5 represents an over-travel area, and first, second and third areas AI, AII and AIII represent an area on the over-travel side, a reference-point proximity area, and a working area, respectively.
In order to stipulate a predetermined position such as a deceleration-start position in the prior art, a mechanical switch such as the limit switch LS switched at the predetermined position is required. By relying solely upon the signal from this switch, the accuracy of the reference-point return operation is greatly influenced by the mounting precision and operating precision of the switch. Accordingly, the prior art is such that reference-point return control is performed by making joint use of this signal and the motor one-revolution signal generated by a linear scale or rotary encoder originally mounted on an NC machine tool.
With the prior art, however, the fact that the limit switch is used raises cost and entails a complicated mounting operation.


SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a reference-point return method in which signals indicative of a deceleration starting position and a reference-point position are generated solely by a linear scale, and without using a mechanical switch, to return a movable machine element to the reference point.
The present invention relates to a reference-point return method for returning a movable element of a machine to a reference point using solely a linear scale, without relying upon a limit switch. In the present invention, the arrangement is such that a linear scale generates signals indicative of a deceleration starting position and a reference-point position. Reference-point return velocity is reduced using the signal indicating the deceleration starting position, and movement of the movable machine element is stopped in r

REFERENCES:
patent: 4225928 (1980-09-01), Ohkubo
patent: 4628314 (1986-12-01), Morinaga et al.
patent: 4782275 (1988-11-01), Sakamoto et al.
patent: 4847777 (1989-07-01), Konno
patent: 4956553 (1990-09-01), Matsui

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