Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1986-10-10
1988-05-10
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
'reset' systems
318609, G05B 1142
Patent
active
047438223
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a servo motor control method and apparatus which drives a machining device for a machining works on the basis of the commands sent from a numerical control apparatus and particularly to the technology for improving delay of response at the initial rotation and inversion of rotating direction of servo motor.
BACKGROUND ART
As shown in FIG. 23, for example, a servo motor control apparatus comprising a positional feedback loop is generally provided with a speed feedback loop for controlling a speed of revolution of motor 10 and a current feedback loop for controlling a current of motor 10, in addition to a positional feedback loop for controlling position of revolution of motor 10 or position of a mechanical movable part (not shown). In the current feedback loop, control is carried out so that deviation .DELTA.I between a motor current I.sub.d detected by a resistor 11 and a current command value I.sub.s sent from a proportional integral controller 12 becomes zero, while in the speed feedback loop, deviation (Ve) between a motor speed v.sub.d detected by speed detector such as a tachometer and a speed command value V.sub.s sent from D/A converter 14 becomes zero. Finally, the position of motor is controlled by a positional feedback loop so that difference between position of motor e.sub.d detected by position detector 15 such as a resolver or linearscale, etc. and a position command value e.sub.s given from a command pulse generating circuit 16 becomes zero. In FIG. 23, 17 is amplifier; 18a-18c are adders.
FIG. 24 is an electrical circuit which indicates a conventional structure including an adder 18b, a proportional integral controller 12 and an adder 18c shown in FIG. 23. An operational amplifier Q.sub.1, resistors R.sub.1 -R.sub.4 and a capacitor C.sub.1 form an adder 18b and a proportional integral controller 12, while an operational amplifier Q.sub.2 and resistors R.sub.5 -R.sub.8 form an adder 18c.
The relationship between motor current I.sub.d, a motor speed command V.sub.s and motor speed V.sub.d in a conventional servo motor control apparatus having the structure shown in FIG. 23, when the rotating direction of motor is reversed, can be indicated, for example, as the curves 30v.sub.r, 31v and 32i of FIG. 25, where motor current I.sub.d, motor speed command V.sub.s and motor speed V.sub.d are plotted on the vertical axis and the time t on the horizontal axis with the direction inversion command input time located at the origin. Here, I.sub.o is a value of friction torque of the machine converted in terms of a motor current. In this figure, a speed command is reduced with a constant deceleration from the positive to negative direction. As will be understood from this figure, when a speed command is input in the opposite direction when t=0, a motor current I.sub.d indicated by a curve 32i gradually reduces but a motor speed V.sub.d indicated by a curve 31v is zero until the motor current I.sub.d exceeds -I.sub.o and the motor starts to rotate when a motor current I.sub.d exceeds -I.sub.o. Namely, a time lag T.sub.1 is generated during the period from input of speed command in the opposite direction until start of motor in the reverse direction.
Such time lag naturally appears as a working error in numerical control. More specific, as shown in FIG. 26, the cutting should be done along a true circle shown by a curve 40 through distribution of command pulses of a true circle but actually such discrepancy occurs that the actual shape of work to be cut shows extruded portions as shown by the curve 41 at the quadrant exchange regions of circular cutting due to the delay of response generated when the rotating direction is inversed.
This phenomenon is further explained below. In FIG. 26, in the section I, only the X axis changes and Y axis does not change and the maximum speed is obtained. In the section II, the Y axis also changes but a true circle is not obtained. In the section III, both X and Y axes change and a true circle can be obtained. When the Y ax
REFERENCES:
patent: 3998409 (1976-12-01), Pistiner
Futami Shigeru
Kaku Yasuhiko
Yamamoto Yo-ichi
Bergmann Saul M.
Shoop Jr. William M.
Yaskawa Electric Mfg. Co. Ltd.
LandOfFree
Servo motor control method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Servo motor control method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Servo motor control method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1323059