Electricity: motive power systems – Positional servo systems – Adaptive or optimizing systems including 'bang-bang' servos
Patent
1986-07-02
1987-09-22
Dobeck, Benjamin
Electricity: motive power systems
Positional servo systems
Adaptive or optimizing systems including 'bang-bang' servos
318615, G05B 1300
Patent
active
046957804
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a system for controlling the velocity of a servomotor used in a machine tool, an industrial robot and the like.
SUMMARY OF THE INVENTION
When subjecting the velocity of a servomotor to feedback control, it is necessary to sense the actual velocity of the motor. An example of conventional means for sensing actual velocity is a rotary encoder for sensing position. 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.
With a rotary encoder, however, the spacing between adjacent pulses becomes very wide and the pulses become discrete in nature, especially when the motor rotates at a low velocity. When these pulses are used as motor rotation information, irregular rotation is the result.
Thus, when it is attempted to employ a rotary encoder used for sensing position as means for sensing velocity, velocity resolution is poor in comparison with an analog sensor. For this reason, 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 system, in which when velocity is estimated by an estimating unit based on position information from a rotary encoder mounted on a servomotor, load torque, which is a cause of a steady-state estimating error, is estimated at the same time to enable smooth, highly precise velocity control.
According to the present invention, there is provided a servomotor velocity control system 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 system has an estimating unit for obtaining an estimated value of velocity of the servomotor based on position information from the rotary encoder, motor current of the servomotor and a load torque signal, and arithmetic means for calculating the torque command signal based on the estimated value of velocity outputted by the estimating unit and a velocity command signal.
In a case where the velocity of the servomotor is estimated by the estimating unit based on the position information from the rotary encoder, the servomotor velocity control system of the invention obtains the estimated value of velocity upon taking load torque, which is a cause of a steady-state estimating error, into account. This eliminates the shortcoming of the prior art, wherein the pulses from the rotary encoder become discrete when the servomotor is rotating at low velocity. This makes it possible to obtain a suitably interpolated value of estimated velocity and to control velocity in a highly accurate manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a velocity control system according to the invention.
FIG. 2(a) is a view illustrating a motor current loop processing level;
FIG. 2(b) is a view illustrating a velocity processing level;
FIG. 3 is a flowchart illustrating observer processing at a motor current loop level; and
FIG. 4 is a flowchart illustrating velocity loop processing.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described in detail based on an embodiment illustrated in the drawings.
FIG. 1 is a block diagram of a velocity control system according to the present invention. Numerals 1 through 3 denote arithmetic units, 4 an estimating unit, namely an observer, and 5 a servomotor. V.sub.c represents a velocity command, U a torque command, I motor current and I.sub.L current indicative of a load torque. V represents the velocity of the servomotor, .theta. position, k.sub.1 integration gain, k.sub.2 feedback gain, K.sub.m a motor constant, and T.sub.m a ratio between L.sub.a and R.sub.a, namely the value of L.sub.a /R.sub.a, where R.sub.a denotes motor winding resistance and L.sub.a represents inductance. Further, K.sub.t is a torque
REFERENCES:
patent: 4366422 (1982-12-01), Rhodes
patent: 4491776 (1985-01-01), Veale
patent: 4498037 (1985-02-01), Razavii
Kurakake Mitsuo
Sakamoto Keiji
Toyosawa Yukio
Dobeck Benjamin
Fanuc Ltd
LandOfFree
Servomotor velocity control system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Servomotor velocity control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Servomotor velocity control system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2060848