Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1988-07-08
1989-11-21
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
3185681, 318574, 36416701, G05B 1929
Patent
active
048825280
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a digital servo system, more particularly, to a digital servo system able to control the position of a object having a small friction resistance to motion.
2. Background of the Invention
FIG. 1 is a block diagram showing the main flows of control signals in a digital servo system using transfer functions. When the system receives a position command, using the feedback position (rotation angle of a motor) a deviation of the position from the position commanded is detected. The deviation of the position is amplified by a position angle K.sub.p and is output as a velocity command V.sub.cmd. By comparing the velocity command with a feedback value of a velocity (an angular velocity of rotation in motor .omega.), a deviation E is detected. The deviation E of the velocity is amplified and is output as a torque command T.sub.cmd. If the torque command is greater than a load such as a friction resistance to motion, the motor can be driven.
The output of the torque command T.sub.cmd has a wave shape which corresponds approximately to a transfer function K.sub.1 /s (K.sub.1 is a integration constant for proportional integration) as shown in FIG. 2. The torque command has a integration wave shape having an inclination proportional to the deviation E, and increasing linearly, when the deviation obtained by subtracting the velocity feedback value from the velocity command V.sub.cmd is not zero, and even after the deviation E is made zero, the torque command maintains the value after the time the deviation E became zero. The torque command as mentioned above is effective in a system where an object having a great friction resistance to motion is driven because the torque increases until the torque overcomes the friction resistance.
But, if an object having a small friction resistance is driven by the torque command as mentioned above, once a velocity command is output the torque command increases linearly, and even after the difference between the velocity command and the velocity feedback value became zero, the torque command does not decrease and a high value torque command is maintained, therefore, the object continues to move as before to go beyond the target position. Next, the velocity of the position beyond the target position is detected, this results in a torque command in the opposite direction to the preceding torque command. Due to the torque command in the opposite direction, the object moves to the opposite direction, then passes over the target position again. Subsequently, similar operations are repeated, i.e., the object vibrates around the target position at which the object should stop.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a digital servo system which can stop a moving object, having a small friction resistance to motion, at a position where the object should stop, immediately and without vibration.
A digital servo system according to the present invention comprises a position detecting device which detects an actual position of a object; a position deviation detecting device which detects and outputs a deviation of the actual position of the object from a predetermined position by a command; a velocity command generating device which outputs a velocity command to move the object according to the output of the position deviation detecting means; a velocity detecting means which detects an actual velocity of the object; a velocity deviation detecting means which detects and outputs a deviation of the actual velocity of the object from the velocity command; a torque command generating means which outputs a torque command to drive a motor according to the output of the velocity deviation detecting means; and a motor driving means which moves the object according to the torque command: in which the torque command increases according to the output of the velocity deviation detecting means up to a predetermined saturation value, and decreases swiftly to zero at the time that the output of the veloc
REFERENCES:
patent: 4701839 (1987-10-01), McNally et al.
patent: 4712052 (1987-12-01), Omae et al.
patent: 4772831 (1988-09-01), Casler et al.
Matsubara Shunsuke
Okuda Kanemasa
Sakamoto Keiji
Sogabe Masatoyo
Bergmann Saul M.
Fanuc Ltd.
Shoop Jr. William M.
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