Turning – Process of turning
Patent
1989-09-25
1991-07-02
Schmidt, Frederick R.
Turning
Process of turning
82129, 82118, B23B 300
Patent
active
050276808
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a machine tool having two spindles and, more particularly, to a method of controlling simultaneous operation of the spindles of a machine tool such as a lathe adapted to control two spindles in order to machine a workpiece efficiently.
2. Description of the Related Art
The machine tool of a multiple-spindle head unit is widely employed to realize a shorter piece time when machining workpieces. As is seen in an NC lathe, by way of example, two or more spindles are provided for each tool rest, and the spindles are controlled by independent spindle motors to shorten the time needed for mounting and unmounting workpieces. Alternatively, the flexibility with which workpieces are machined is enhanced by spindle motors having different functions.
When workpieces are regripped at a plurality of spindles, the same velocity command is applied to each spindle motor and, when the velocities coincide, a transition is made to the next machining operation without stopping the workpiece, which is in the rotating state.
With the conventional machine tool in which two spindles are disposed to oppose each other on the same axis and a tool rest is capable of machining the workpiece at either spindle, it is required that the velocities of both spindles coincide reliably at workpiece regripping. If this is not achieved, the workpiece may be damaged by a chuck or is in danger of being deformed. When the spindle motors differ, however, it is difficult to bring their rotational velocities into perfect coincidence. In addition, owing to the load, the rotational velocities fluctuate even though the velocity commands are the same.
Furthermore, with conventional control for synchronous spindle operation, the rotational angular positions of both spindles do not readily coincide even if the velocities can be made to coincide, and it is difficult to correct for a deviation in chuck meshing position.
SUMMARY OF THE INVENTION
The present invention has been devised in order to solve the foregoing problems and its object is to provide a machine tool having two spindles, in which synchronous operation is performed reliably upon achieving coincidence between the rotational angles of the spindles.
In accordance with the invention, there is provided a machine tool having two spindles in which rotational velocity of a first spindle is made to coincide with rotational velocity of a second spindle and a workpiece is transferred between the spindles, comprising command means for supplying respective velocity controllers of the first and second spindles with identical velocity commands, mode setting means for cutting off the velocity command to the velocity controller of the second spindle and setting an operation control mode for synchronizing the second spindle with the first spindle, arithmetic means for computing a position error related to rotational angles of the first and second spindles in the synchronous operation control mode, and correcting means for correcting the velocity command to the velocity controller of the second spindle in such a manner that a detected position error becomes zero.
Further, in accordance with the invention, there is provided a spindle synchronous operation control method for applying synchronous operation control to first and second spindles having mutually independent velocity control circuits, characterized by having a first step of bringing velocity commands to the first and second spindles into coincidence, a second step of detecting actual velocity and rotational angular position of each spindle and computing an error between these velocities and an error between these positions, a third step of correcting one of the velocity commands by the computed velocity error, and a fourth step of correcting one of the velocity commands by the computed position error.
Thus, a machine tool having two spindles in accordance with the invention is such that the velocity error signal of the first and second spindles and the position error signal of
REFERENCES:
patent: 4457193 (1984-07-01), Matthey
patent: 4683787 (1987-08-01), Link
patent: 4719676 (1988-01-01), Sansone
patent: 4827814 (1989-05-01), Wilkins
patent: 4934882 (1990-06-01), Phillips
Kohari Katsuo
Kono Shinichi
Takahashi Hironobu
Cruz Lawrence
Fanuc Ltd.
Schmidt Frederick R.
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