Electricity: motive power systems – Positional servo systems – Adaptive or optimizing systems including 'bang-bang' servos
Patent
1986-09-08
1987-07-14
Dobeck, Benjamin
Electricity: motive power systems
Positional servo systems
Adaptive or optimizing systems including 'bang-bang' servos
318615, 318433, G05B 1300
Patent
active
046805184
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of controlling the velocity of a servomotor for driving a load such as a machine tool or industrial robot.
BACKGROUND ART
When subjecting the velocity of a servomotor to feedback control, it is necessary to sense the actual velocity of the motor. To this end, conventional practice is to use a rotary encoder, by way of example. The rotary encoder is adapted to generate from several thousand to 20,000 pulses per revolution of the motor, the frequency of these output pulses being proportional to the rotational velocity of the motor.
Accordingly, the spacing between adjacent output pulses becomes very wide and the pulses become discrete in nature, especially when the servomotor rotates at a low velocity. When these pulses are used as motor rotation information in digital control, irregular rotation is the result.
Thus, when a rotary encoder for sensing the position of a mechanical load is used for sensing the velocity of a servomotor, velocity resolution is poor in comparison with an analog sensor and highly precise, smooth velocity control cannot be carried out.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a servomotor velocity control method, in which when velocity is estimated based on position information from a rotary encoder, load torque such as Coloumb friction, which is a cause of a steady-state estimating error, is estimated at the same time to obtain an estimated value of velocity, and in which an observer (estimating unit) is used for obtaining the estimated value of velocity, use or non-use of the observer is selected in dependence upon the motor velocity, thereby lightening the burden on a central processing unit (CPU).
According to the present invention, there is provided a servomotor velocity control method in which position information from a rotary encoder mounted on a servomotor driving a mechanical load is fed back and a torque command signal is produced for application to the servomotor. The method comprises steps of comparing a reference velocity set for the servomotor and the motor velocity, calculating an estimated value of load torque when the motor velocity is less than the reference velocity, calculating an estimated value of velocity of the servomotor based on position information from the rotary encoder, motor current of the servomotor and the estimated value of load torque, and calculating the torque command signal based on the estimated value of velocity and a velocity command signal.
The servomotor velocity control method of the invention is such that when velocity is sensed by using the observer for obtaining the estimated value of velocity while the motor load torque is estimated, use or non-use of the observer is selected in dependence upon the motor velocity. This lightens the burden on the central processing unit (CPU) and enables velocity to be sensed accurately in a low-velocity region.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart illustrating observer processing at a motor current loop level according to the present invention,
FIG. 2 is a block diagram of a control circuit to which the ve1ocity control method of the present invention can be applied,
FIG. 3(a) is a view for describing a motor current loop processing level,
FIG. 3(b) is a view for describing a velocity processing level,
FIG. 4 is a flowchart illustrating observer processing at a motor current loop level, and
FIG. 5 is a flowchart illustrating velocity loop processing.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will now be described in detail with reference to the drawings.
FIG. 2 is a block diagram of a velocity control method according to the present invention. Numerals 1 through 3 denote arithmetic units, 4 an estimating unit (observer) and 5 a motor. V.sub.c represents a velocity command, U a torque command signal, I motor current and I.sub.L current indicative of a load torque. V represents the velocity of the motor, .theta. a position signal, k.sub.1 integratio
REFERENCES:
patent: 4366422 (1982-12-01), Rhodes
patent: 4491776 (1985-01-01), Veale
patent: 4498037 (1985-02-01), Razaui
Kurakake Mitsuo
Sakamoto Keiji
Toyosawa Yukio
Dobeck Benjamin
Fanuc Ltd.
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