Electricity: motive power systems – Positional servo systems – With particular motor control system responsive to the...
Patent
1984-12-13
1986-05-13
Dobeck, B.
Electricity: motive power systems
Positional servo systems
With particular motor control system responsive to the...
318561, 318594, 318611, 318678, G05F 100
Patent
active
045889376
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a position control apparatus for stopping or positioning the spindle of a machine tool or the like at a predetermined rotational angle. More particularly, the invention relates to a position control apparatus capable of enhancing servo rigidity when a spindle is stopped.
To stop a spindle at a predetermined rotational angle in an NC machine tool, by way of example, an error quantity, which is the difference between a commanded position and the present position of the spindle, is subjected to a digital-to-analog conversion by a DA converter to obtain a velocity control command signal, and the velocity of a motor for rotating the spindle is controlled by the control command signal.
In performing such position control, the gain of a velocity loop is made higher at the time of orientation (when the spindle is brought to a stop at a reference position) than at the time of ordinary rotation, thereby enhancing servo stability at the stopping time to increase the holding force.
In the prior art, gain changeover timing is taken at the instant at which a certain angular range is reached, such as a half revolution short of a target stopping position for orientation, and control is exercised in such a manner that the gain of a velocity amplifier is raised when the point one-half revolution short of the target stopping position is reached. In this way about twice the servo rigidity can be obtained in comparison with a case where orientation is performed at the gain which prevails during ordinary rotation.
However, the gain of the velocity amplifier is affected by the size of the applied velocity command signal. When the gain is raised while the velocity is high, as at the point one-half revolution short, the operating characteristic of the velocity amplifier becomes unstable. Consequently, the gain cannot be raised very much. In other words, a required, satisfactory servo rigidity cannot be obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention seeks to solve the aforementioned problem encountered in the prior art.
In particular, it is an object of the present invention to provide a position control apparatus capable of sufficiently raising the gain of a servo control system for controlling an NC machine tool spindle or the like, thereby allowing high servo rigidity to be obtained.
In order to attain the objects of the invention set forth above, the present invention provides a position control apparatus comprising a servo control circuit for rotating a motor by following an offset between a commanded velocity and an actual velocity, and an orientation control circuit for stopping the motor at a predetermined position upon receiving an orientation signal as the commanded velocity. The position control apparatus is characterized in that the servo control circuit is internally provided with a velocity amplifier having changeover means capable of making servo loop gain higher than that which prevails during servo control (which is when the motor is controlled by following the offset between the commanded velocity and the actual velocity), and in that there is provided a low velocity sensing circuit for sensing a predetermined low velocity just before the motor is stopped, wherein when the rotational velocity of the motor drops to the predetermined low velocity just before stoppage during orientation control, servo loop gain is raised by changing over the velocity amplifier in response to a signal from the low velocity sensing circuit. Further, according to the present invention, a position control apparatus is also provided in which the foregoing arrangement is additionally equipped with a switch control circuit, motor velocity sensing means, low-velocity sensing means, and a gate circuit.
In this way a high gain can be set in a range where the velocity amplifier input signal is small, so that the object of obtaining a sufficiently high servo rigidity can be attained. If this object is realized, the operating characteristic of the velocity ampl
REFERENCES:
patent: 4342950 (1982-08-01), Kohzai et al.
patent: 4347470 (1982-08-01), Kohzai et al.
patent: 4355273 (1982-10-01), Du Vall
patent: 4379987 (1983-04-01), Kohzai et al.
Fujioka Yoshiki
Hirota Mitsuhiko
Ota Naoto
Dobeck B.
Fanuc Ltd.
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