Electricity: motive power systems – Positional servo systems – With stabilizing features
Reexamination Certificate
2003-08-05
2004-10-05
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Positional servo systems
With stabilizing features
C318S612000, C318S614000, C318S615000, C248S638000, C702S056000
Reexamination Certificate
active
06801010
ABSTRACT:
TECHNICAL FIELD
The invention relates to a positioning controller for performing positioning operation by driving load through use of a motor, and more particularly, to a technique for damping low-frequency vibration in a load or in a bed on which the load is to be disposed.
BACKGROUND ART
In pursuit of a demand for weight reduction and miniaturization of recent industrial machinery, the rigidity of a shaft used for connecting a motor with load and that of a bed on which a drive mechanism is to be disposed are becoming lower, and the natural frequency of a load system and that of the bed tend to decrease. In tandem with these tendencies, the performance of a servo control system and a response in the drive system also tend to be enhanced. In relation to the servo control system remaining under these circumstances, a problem of the load or the bed becoming susceptible to vibration is starting to become noticeable.
In order to dampen such vibration, a servo controller, such as that shown in
FIG. 3
, described in “Materials for Workshop in The Institute of Electrical Engineers of Japan” IIC-96-17, pp. 75 to 84, has already been put forth. In the drawing, reference numeral
31
designates an S-shaped position command generator;
32
designates a metastable pre-filter;
33
designates a semi-closed feedback position control system;
33
a
designates a transfer function from a position command of a feedback control system to the position of a motor; and
33
b
designates a transfer function from the position of the motor to the position of load. A natural vibration angular frequency of load in the feedback control system is &ohgr;
a
, which shows a case where a speed pattern &thgr;*
M
of an S-shaped position command assumes a trapezoidal shape as shown in
FIG. 5
, wherein an acceleration time and a deceleration time are equal to each other. Here, t
A
denotes an acceleration/deceleration time; and (t
D
−t
A
) denotes a constant speed time.
When the servo controller has such a control system, a vibration pole &ohgr;
a
of the feedback position control system
33
is canceled by a zero of a transfer function of the metastable pre-filter
32
, wherein the transfer function is defined as
F
1
(
S
)
=
S
2
+
ω
a
2
S
2
+
ω
a
n
2
·
ω
a
n
2
ω
a
2
.
(
1
)
Dampening control is accomplished by setting &ohgr;
an
so as to satisfy any term of Equation (2).
1−cos &ohgr;
an
t
A
=0, 1−cos &ohgr;
an
t
D
=0 (2)
The related art presents the following problems.
(1) When the acceleration/deceleration time and the constant speed time, both pertaining to the target position command &thgr;*
M
, are short, a position command &thgr;**
M
of the feedback system becomes steep (see
FIG. 6
, and detailed descriptions will be provided later).
(2) Equation (2) must be satisfied strictly. If Equation (2) is not satisfied, continuous vibrations develop. For instance, if the acceleration/deceleration time of the target position command &thgr;*
M
has been nominally changed by 5%, the position command &thgr;**
M
of the feedback system will continuously vibrate as shown in
FIG. 7
, which will be described later.
(3) If an attempt is made to implement the related-art metastable prefilter through use of computation means such as a CPU or the like, a critical stability pole of the metastable prefilter becomes unstable, for reasons of an error in a discrete approximations, which in turn makes the metastable prefilter unstable. For instance, even if a sampling time is nominally 100 &mgr;s, the position command &thgr;**
M
of the feedback system becomes unstable as shown in
FIG. 8
(i.e., the position command becomes divergent while vibrating).
When consideration is given to the problems of the related-art metastable prefilter, the true nature of all the problems resolves itself to a 0 attenuation term of the denominator of the filter. Simple application of a filter having an attenuation term to the metastable prefilter is usually conceivable as a solution. However, this solution ends in an increase in a delay time of the filter, thereby prolonging a positioning time. In the related-art, the attenuation term is considered to be set to zero for eliminating such a delay time. Therefore, following the conventional line of thought cannot produce the configuration of a prefilter “having high stability and involving a short positioning time.”
DISCLOSURE OF THE INVENTION
In order to solve such a basic problem, the invention aims at providing a vibration-damping positioning controller which can fix a position command of a feedback control system to a target position by setting an output from a prefilter to zero when the position command of the feedback control system coincides with a target command, thereby enabling stable positioning operation within a short period of time.
A vibration-damping positioning controller according to an invention of claim
1
produces a position command when given a differential value of a target position command that changes in a predetermined pattern, and causes load to follow the position command by inputting the position command to the feedback control system, wherein the controller comprises: an integrator for integrating a differential value of the target position command; a subtracter which subtracts the position command from an output of the intergrator, to thereby output a position command error; a stable prefilter which receives a differential value of the target position command and eliminates a frequency component identical with a vibration pole &ohgr;
0
of the feedback control system; command fixing means which receives an output from the stable prefilter and the position command error, judges that the command is started when a differential value of the target position command has changed from zero to a non-zero value, judges that the command is ended when the differential value of the target position command has changed from the non-zero value to zero, outputs zero from the time the position command error has assumed zero after the command is ended until the next command is started, and in other cases produces an output of the stable prefilter in an unmodified form; and a second integrator which integrates an output from the command fixing means, to thereby out put the position command.
A vibration-damping positioning controller according to an invention of claim
2
produces a position command when given a target position command that changes in a predetermined pattern, and causes load to follow the position command by inputting the position command to the feedback control system, wherein the controller comprises: a differentiator for differentiating the target position command; a subtracter which subtracts the position command from the target position command, to thereby output a position command error; a stable prefilter which receives a differential value of the target position command serving as an output from the differentiator and eliminates a frequency component identical with a vibration pole &ohgr;
0
of the feedback control system; command fixing means which receives an output from the stable prefilter and the position command error, judges that the command is started when a differential value of the target position command has changed from zero to a non-zero value, judges that the command is ended when the differential value of the target position command has changed from a non-zero value to zero, outputs zero from the time the position command error has assumed zero after the command is ended until the next command is started, and in other cases produces an output of the stable prefilter in an unmodified form; and a second integrator which integrates an output from the command fixing means, to there by output the position command.
By means of the foregoing configuration, even when low-frequency vibrations are present in load or a bed on which the load is to be placed, stable positioning can be performed within a short period of time.
As mentio
Kaku Yasuhiko
Okubo Tadashi
Zhang Wennong
Kabushiki Kaisha Yaskawa Denki
Leykin Rita
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