Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-09-30
1992-10-27
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318573, 318630, 36447431, G05B 1918
Patent
active
051592517
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a position correcting system for a machine tool having a plurality of workpiece machining positions, and more particularly to a position correcting system which corrects the positions of machining heads in each of a plurality of workpiece machining positions.
BACKGROUND ART
There is known an automatic lathe having a cylindrical workpiece holder to which a plurality of workpieces are fixed in respective positions and also having a plurality of machining heads corresponding to the positions where the workpieces are securely held on the cylindrical workpiece holder. In operation, the cylindrical workpiece holder rotates about its own axis to advance the workpieces respectively to next machining positions in which the machining heads machine the respective workpieces. The machining process for each workpiece is completed after it has been machined successively by the machining heads in the machining positions.
For example, an end surface of each workpiece is cut in a first machining position by a first machining head. After the end surface of the workpiece has been cut, the workpiece holder rotates to bring the workpiece to a second machining position. In the second machining position, a second machining head machines the workpiece roughly to a desired outside diameter. After the workpiece has been machined in the second machining position, the workpiece holder rotates to move the workpiece into a third machining position in which a third machining head machines the workpiece roughly to a desired inside diameter. In this manner, the workpiece holder rotates to bring the workpiece to a next machining position where the workpiece is machined in a next machining cycle. The above process is repeated until the workpiece is machined in a final machining position, whereupon the machining process for the workpiece is completed.
When a workpiece moves from one machining position to another, however, the relative position between the workpiece and each machining head varies, resulting in a reduction in the accuracy with which the workpiece is machined. The positioning accuracy of the workpiece with respect to each machining head may be increased by a mechanical means, but it would be highly difficult to position many workpieces relatively to each of the machining heads with a desired level of accuracy.
DISCLOSURE OF THE INVENTION
In view of the aforesaid drawbacks of the conventional workpiece positioning system, it is an object of the present invention to provide a position correcting system for a machine tool having a plurality of workpiece machining positions.
To achieve the above object, there is provided in accordance with the present invention a position correcting system in a machine tool having a plurality of workpiece machining positions, comprising a position correcting register for storing position correctives corresponding to said workpiece machining positions, pre-processing means for calculating distributed data from a machining program, an adder for adding said position correctives to said distributed data to output position commands for machining heads corresponding to said workpiece machining positions, respectively, interpolating means responsive to said position commands, for effecting pulse interpolation to produce output pulses, and axis control modules for controlling servomotors in response to said output pulses.
Previously in the respective machining positions, correctives corresponding to relative errors between the workpieces and the machining heads are stored in the position correcting register. When the workpieces reach the respective workpiece machining positions, the correctives are added to the distributed data, and the pulse interpolation is carried out. Errors between the workpieces and the machining heads are corrected in all the machining positions, so that the workpieces can be machined with accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a position correcting system according to the present invention;
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Fujibayashi Kentaro
Sasaki Takao
Sato Morimasa
Fanuc Ltd
Ip Paul
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