Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2001-05-24
2003-02-04
Salata, Jonathan (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S568180, C318S568220, C318S615000, C318S618000, C318S632000
Reexamination Certificate
active
06515442
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a position controller provided with a compensation means for suppressing vibration produced in a mechanism driven by a motor when the motor controls a position by driving an object to be controlled and, in particular, it relates to a position controller capable of positioning with high accuracy in a short time when a low-frequency disturbance is large.
BACKGROUND OF THE ART
Generally, for position control, a position signal of an encoder and the like attached to a servomotor is differentiated to produce a speed feedback signal and speed control is performed, and based on a position feedback signal from a position detector such as a linear scale and the like attached to a movement section driven by the servomotor (or an encoder and the like attached to the servomotor), position control is performed. A block diagram of such a position control system is as shown in FIG.
9
.
In
FIG. 9
,
901
denotes a position control section and a position control gain is K
p
.
902
denotes a speed control section,
903
denotes a servomotor, and
904
denotes a movement section. Position deviation e
p
is determined by subtracting position feedback signal y
f
from position command y
r
outputted from a numerical value controller and speed command v
r
is determined by multiplying this position deviation by the position control gain K
p
. Speed deviation e
v
is determined by subtracting speed feedback signal v
f
from this speed command v
r
, torque command (current command) T
r
is determined based on said speed deviation e
v
in the speed control section
902
, and the servomotor
903
and the movement section
904
are driven based on said torque command T
r
.
A control method for a motor whereby position control is performed based on a signal from a position detector such as a linear scale attached to a movement section driven by a motor is known as a closed loop method. However, if a motor and a movement section are spring-connected and the rigidity of the connected portion is weak, the movement of the motor and movement section does not coincide and vibration occurs. In such a case, it is necessary to stabilize the loop by lowering a loop gain or to apply a method for stabilizing the loop, without lowering the loop gain, by correcting a torque command value based on a movement position, a movement speed and a motor position, or a motor speed. As a method for stabilizing the loop by correcting a torque command value, there is Japanese Unexamined Patent Publication No. Hei-3-110307, for example. Therein, the loop is stabilized by correcting the torque command value based on the difference between the movement section speed and motor speed. A method whereby the loop is stabilized by correcting the torque command value based on the difference between the movement section speed and motor speed has also been indicated in the literature and the like (for example in “The theory of AC servo system and practice of design” written and edited by Hidehiko SUGIMOTO, Sougo-denshi Shuppansha.)
FIG. 8
is a block diagram for explaining the prior-art method whereby the loop is stabilized by correcting the torque command value.
In
FIG. 8
,
12
denotes a position control section in which position command Pref and detected movement position Pfbl are inputted and from which speed command Vref is outputted, and which position-controls a motor so that the abovementioned two input signals coincide,
13
denotes a speed control section in which the speed command Vref and operated motor speed Vfbm are inputted and from which torque command Terf is outputted, and which speed-controls a motor so that the abovedescribed two input signals coincide,
18
denotes a speed processor which receives motor position signal Pfbm as an output signal from a motor position detector to differentiate the signal and outputs the abovedescribed motor speed Vfbm, and
32
denotes a movement section speed process or which receives movement position signal Pfbl as an output signal from a movement position detector to differentiate the signal and outputs movement speed Vfbl.
21
denotes a subtracter which subtracts the movement position Pfbl from the position command Pref and outputs a position deviation signal,
22
denotes a position controller which receives the position deviation signal and outputs speed command Vref,
23
denotes a subtracter which subtracts the motor speed signal Vfbm from the speed command Vref and outputs a speed deviation,
24
denotes a speed controller which receives the speed deviation and outputs torque command,
25
denotes a subtracter which operates the difference between the movement speed signal Vfbl and the motor speed signal Vfbm to output,
28
denotes a coefficient multiplier which multiplies the difference between the abovedescribed movement speed signal Vfbl and the motor speed signal Vfbm by a coefficient &agr; as a torque corrective gain and outputs the torque correction signal, and
31
denotes a subtracter which subtracts a torque correction signal from the torque command and outputs a new torque command Tref.
FIG. 10
is a system construction view to which the position control system is applied.
100
denotes a base,
101
denotes a ball screw,
102
denotes a table,
103
denotes a servomotor,
104
denotes a linear scale for detecting a position of the table, and
105
denotes a measuring head. The servomotor
103
drives the table
102
via the ball screw
101
. All of the drive mechanism and non-movement portions of to-be-driven bodies are fixed on the same base
100
and the base
100
is installed on the ground. The main body of the linear scale
104
is arranged on the base
100
and the measuring head
105
is attached on the table
102
. The control system position-controls the table
102
based on a position signal from the linear scale
104
.
In recent years, the demand for higher speed industrial machines has increased, therefore a command is issued with an acceleration (deceleration) time made as short as possible (that is, by increasing acceleration (deceleration) as far as possible). In a case where the base
100
with a mechanism having a low rigidity is arranged on the ground, when the table is driven at high acceleration (deceleration), the base
100
receives the reaction force of the acceleration (deceleration) and vibrates severely. For the control system, the vibration of the base
100
becomes a disturbance signal of a position signal. In addition, the lower the rigidity of the combination mechanism between the servomotor
103
and the table
102
is, the greater the influence on positioning by the vibration of the base
100
becomes.
However in the abovedescribed prior art of
FIG. 9
, there has been a great drawback in that positioning with high accuracy is impossible in a short time when a large low-frequency disturbance exists. In the abovedescribed prior art of
FIG. 8
, there have been problems in that when low-frequency disturbance exists and minute vibration occurs, the phase of the torque correction signal and the phase of the vibration do not match each other, so the disturbance cannot be suppressed, thereby affecting the response. Also, since a speed signal is operated based on a position signal, there have been problems in that when the vibration is minute, sufficient resolution as a torque correction signal cannot be obtained and the loop cannot be stabilized. For example, since the speed signal is determined by differentiating the position signal, when the position signal is vibrating at a rate of several pulses, the waveform of the speed signal becomes coarse and the accuracy declines. Since the torque correction signal takes the difference between the coarse speed signals, its waveform becomes coarser and sufficient resolution in not obtainable.
Therefore, the present invention aims to provide a position controller capable of solving these problems. Disclosure of the Invention.
In order to solve the abovedescribed problems, according to the present invention, a position controller co
Kaku Yasuhiko
Murata Ken-ichi
Okubo Tadashi
Zhang Wennong
Armstrong Westerman & Hattori, LLP
Duda Rina I.
Kabushiki Kaisha Yaskawa Denki
Salata Jonathan
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