Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1989-05-08
1991-04-23
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318 39, 318573, 318569, 36447415, 3644743, G05B 1918
Patent
active
050102869
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a method of controlling an acceleration and deceleration of each of two motors for driving objects in each of two directions when machining is carried out while a rotational speed of a spindle of a machine tool and a relative translational speed between the spindle and a workpiece are synchronized. Accordingly, the present invention can be utilized as a method of synchronously controlling two motors to ensure that a screw pitch coincides with a rotation speed of a tool spindle and with a translation speed of the tool spindle relative to a workpiece during, for example, a tapping operation.
2. Background Art
In the prior art, a spindle motor driving a spindle and a feed servomotor feeding a spindle head are not always synchronized, even when a predetermined relationship should be established between a rotation of a tool spindle and a feed thereof in a straight line parallel to a central axis thereof, during a tapping operation. Instead, in this case, a spring is arranged at a mounting portion of the spindle to which a tool is attached, and an error of the translational feed speed, compared with the rotational speed against a screw pitch, is absorbed by the spring. However, a problem occurs in a ratchet mechanism etc. for converting a rotation of the feed servomotor to a linear motion to feed the spindle head along the central axis of the spindle, when the spindle motor is driven at a high rotational speed, and the accuracy of a machined screw is not always sufficient because the tapper tap is not fixed.
To solve this problem, a method of synchronously rotating the spindle motor driving the spindle and the feed servomotor feeding the spindle head is adopted. The acceleration of the feed servomotor feeding the spindle head is ten to twenty times higher than that of the spindle motor rotating the spindle, because the feed servomotor moves the spindle head linearly through the medium of a reduction gear, and generally, the spindle motor drives the spindle directly, not through a reduction gear. Consequently, the tapper tap is driven at the acceleration of the spindle motor having a lower acceleration, and under the condition of a constant torque, namely a constant acceleration or deceleration when two motors are rotated synchronously.
Nevertheless, the performance of the spindle motor is not always fully utilized in the synchronous operation under the above-mentioned condition of a constant torque, because a torque limit curve indicating a limit of an output torque versus a rotational speed of the spindle motor is not a constant level line. Therefore, there is still room for improvement from the view point of the efficiency of a machining process such as tapping.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the present invention is to obtain an optimum improvement of the efficiency of a machining process and to reduce a time needed for machining a workpiece, to thereby solve the above-mentioned problem.
Considering the above-mentioned object, the present invention provides a method of synchronous control of a spindle servomotor and a feed servomotor during machining by synchronizing a rotational speed of a spindle of machine tool to be rotated by the spindle servomotor with a translational speed, which is a relative translational speed between the spindle and a workpiece to be moved by the feed servomotor, characterized in that the spindle servomotor and the feed servomotor are driven synchronously along a torque limit curve of the spindle servomotor.
The machining is carried out most efficiently when the spindle servomotor is used along the torque limit curve indicating a limited performance of a rotational acceleration thereof, even though an acceleration of the spindle servomotor when the spindle is rotated is less than that of the feed servomotor when the spindle is moved linearly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanation diagram comparing an acceleration and deceleration synchronous pattern according to the pr
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Kimijima Masami
Kono Shinichi
Nakamura Kosei
Numai Kazuhisa
Fanuc Ltd.
Ip Paul
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