Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1987-06-15
1989-07-25
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
With stabilizing features
318615, G05B 501
Patent
active
048517542
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a velocity control system and, more particularly, to a velocity control system in which velocity is controlled by using an observer to estimate velocity on the basis of position information.
By virtue of the rapid progress which has been made in technology, digital feedback control of a variety of motors by microcomputer has become commonplace. When subjecting a motor to feedback control by using a microcomputer, 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.
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 directly as motor velocity information, irregular rotation is the result.
Thus, when an attempt is made to use a position sensing rotary encoder for sensing velocity as well, highly precise, smooth velocity cannot be carried out due to the fact that velocity resolution is poor in comparison with an analog-type sensor.
Accordingly, a velocity control system has been proposed in which, when an observer is used to estimate velocity based on position information from a rotary encoder, load torque, which is a cause of a steady-state estimating error, is estimated at the same time to enable highly precise, smooth velocity control.
FIG. 2 is a block diagram of such a velocity control system. Numerals 1 through 3 denote arithmetic units, 4 an observer, 5 a motor and 6 an I-P controller formed by an integration element K.sub.1 /S and a proportion element K.sub.2. 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 velocity, .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 Ra denotes motor winding resistance and L.sub.a represents inductance. Further, K.sub.t is a torque constant, J stands for inertia which is the total of the load and motor inertia, and K.sub.p is a conversion coefficient decided by the rotary encoder. S represents d/dt. Further, the observer per se is one commonly in use. An arrangement in which a velocity sensor is combined with the observer has been proposed in Japanese patent application No. 59-55114.
The operation of this velocity control system will now be described.
First, the arithmetic unit 1 produces an output indicative of the difference between the velocity command and an estimated value V of velocity, described below. The output signal is integrated and then applied to the arithmetic unit 2. The result of multiplying the estimated value V of velocity by the feedback gain k.sub.2 is applied to the arithmetic unit 2, which outputs the difference between its two input signals as the torque command U, thereby controlling the motor 5. The velocity of the motor is output as V, and the position .theta. is sensed by a rotary encoder. The information indicative of the position .theta. includes the results of adding the current I.sub.L, which is indicative of the load torque (Coulomb friction), at the arithmetic unit 3.
In this velocity control system, the estimated value of velocity is obtained by using the observer 4. At this time the load torque, which is a cause of a steady-state estimation error, is estimated simultaneously. Specifically, the position information .theta., which takes into account the motor current I and the current I.sub.L indicative of load torque, is applied to the observer 4, which proceeds to output the estimated value V of velocity.
Let us describe this point in detail. If an identity observer is constructed for the motor current I, velocity V, position .thet
REFERENCES:
patent: 4109190 (1978-08-01), McNaughton
patent: 4418305 (1983-11-01), Otsuki et al.
patent: 4691152 (1987-09-01), Ell et al.
patent: 4695780 (1987-09-01), Kurakake
Patent Abstracts of Japan, vol. 9, No. 56, Mar. 12, 1985-JP-A-59 194 689.
Patent Abstracts of Japan, vol. 8, No. 239, Nov. 2, 1984 & JP-A-59 117 478.
Sakamoto Keiji
Toyosawa Yukio
Fanuc Ltd
Ro Bentsu
LandOfFree
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 Velocity control system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Velocity control system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2360705