Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
2002-11-13
2004-08-31
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C318S560000, C318S568200, C318S568240
Reexamination Certificate
active
06784632
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a positioning servo controller (position control apparatus) which performs positioning of a controlled object, and more particularly a positioning servo controller for positioning a motor.
BACKGROUND ART
FIG. 30
is a control block diagram showing the configuration of a conventional positioning servo controller. As shown in
FIG. 30
, the conventional positioning servo controller is configured by a position controller
1
, a speed controller
2
, a torque amplifier
3
, a motor
4
, and a differentiator
5
.
The positioning servo controller controls the position &thgr; [rad] of the motor
4
in which the inertia is J [N·m·s
2
].
The motor
4
is provided with an encoder (not shown), so that the position &thgr; of the motor
4
can be detected by the encoder. A position deviation (&thgr;r-&thgr;) between a position command &thgr;r which is supplied from a higher-level unit (not shown), and the position &thgr; of the motor
4
is input to the position controller
1
.
The position controller
1
is a proportional controller which outputs a value obtained by multiplying the deviation with a position loop gain Kp [1/s], as a speed command &ohgr;r [rad/s] for the motor
4
.
The differentiator
5
differentiates the position &thgr; [rad] of the motor
4
, and outputs the speed &ohgr; [rad/s] of the motor
4
.
The speed controller
2
is a proportional controller which receives a speed deviation between the speed command &ohgr;r [rad/s] and the speed &ohgr; [rad/s] of the motor
4
, and which outputs a value obtained by multiplying the deviation with a speed loop gain Kv [N·m·s], as a torque command Tref [N·m] for the motor
4
.
The torque amplifier
3
receives the torque command Tref, and generates a torque Tr to drive the motor
4
.
Namely, the positioning servo controller is used for causing the position &thgr; of the motor
4
to follow the position command &thgr;r. The position &thgr; of the motor
4
is a position response with respect to the position command &thgr;r.
In such a conventional positioning servo controller, the feedback control system in which a positioning control is conducted on the basis of the fed-back position response &thgr; of the motor
4
is used.
As described above, usually, the positioning servo controller has the speed loop process as a minor loop, in the position loop process.
In such a positioning servo controller of the feedback control system, however, the values of the position loop gain Kp and the speed loop gain Kv are finite values and have the upper limit.
Therefore, the position response &thgr; of the motor
4
fails to completely coincide with the position command &thgr;r, and so-called servo delay occurs.
FIGS.
31
(
a
) and
31
(
b
) are the graphes showing the operation of the conventional positioning servo controller.
In FIG.
31
(
a
), the position command &thgr;r and the position response &thgr; are shown, and, in FIG.
31
(
b
), differentials d&thgr;r/dt and d&thgr;/dt of the position command &thgr;r and the position response &thgr; are shown.
As shown in FIGS.
31
(
a
) and (
b
), d&thgr;r/dt is a command of accelerating the motor
4
at a constant acceleration, and, after the motor reaches a steady-state speed V [rad/s] and movement at the steady-state speed V is conducted for a predetermined time period, decelerating the motor at a constant acceleration.
In this case, the position deviation is V/Kp [rad] at the maximum, and the time period between a timing when the value of d&thgr;r/dt becomes 0 and that when the position response &thgr; actually reaches the value of the position command &thgr;r is prolonged in proportion to 1/Kp [s].
FIGS.
31
(
a
) and
31
(
b
) show manners of variations of the commands &thgr;r and d&thgr;r/dt and the responses &thgr; and d&thgr;/dt in the case where the acceleration/deceleration time=0.1 [s], the steady-state speed V=100 [rad/s], the predetermined time period=0.2 [s], the position loop gain Kp=25 [1/s], the speed loop gain Kv=200 [N·m·s], and the inertia J=1 [N·m·s
2
].
In FIGS.
31
(
a
) and
31
(
b
), the steady-state deviation is V/Kp=100/25=4 [rad], and the time period between a timing when d&thgr;r/dt becomes 0 and that when the value of the position response &thgr; actually reaches that of the position command &thgr;r is 0.1 [s].
In such a positioning servo controller, in order to eliminate the above-mentioned servo delay, the feedforward control system is sometimes used together with the feedback control system.
FIG. 32
is a control block diagram showing the configuration of a positioning servo controller in which the feedforward control system is used together with the feedback control system.
The positioning servo controller comprises feedforward controllers
6
and
7
in addition to the components of the positioning servo controller of FIG.
2
.
The feedforward controller
6
receives the position command &thgr;r, differentiates the position command &thgr;r, and outputs a value which is obtained by multiplying the differential value with a first feedforward gain Kff
1
[1/s].
The value is a first feedforward controlled variable which is to be added to the speed command &ohgr;r [1/s] that is output from the position controller
1
.
According to the configuration, in the positioning servo controller of
FIG. 32
, the speed loop process is conducted on the basis of the speed command which is directly produced from the position command &thgr;r, and which does not contain a servo delay element. Therefore, the servo delay can be further eliminated as compared with the case where only the feedback control is used.
The feedforward controller
7
receives a first feedforward compensation amount output from the feedforward controller
6
, differentiates the compensation amount, and outputs a value which is obtained by multiplying the differentiation with a second feedforward gain Kff
2
, as a second feedforward compensation amount.
The second feedforward compensation amount is added to the value output from the speed controller
2
, and the result of the addition is input as the torque command Tr to the torque amplifier
3
.
According to the configuration, the torque amplifier
3
can drive the motor
4
on the basis of the torque command Tr which does not contain a servo delay element.
As described above, in the positioning servo controller of
FIG. 32
, servo delay which may be generated by the feedback control can be compensated by conducting the speed feedforward control and the torque feedforward control.
FIG. 33
is a control block diagram showing the blocks of the positioning servo controller of
FIG. 32
in a simplified manner. As shown in
FIG. 33
, the control performance of the positioning servo controller depends on the values of the feedforward gains Kff
1
and Kff
2
.
In the positioning servo controller of
FIG. 32
, therefore, the motor
4
is controlled in a state where the feedforward gains Kff
1
and Kff
2
are set to optimum values so that servo delay is reduced to a degree as small as possible.
When the feedforward gain Kff
1
=1, the control block diagram of the positioning servo controller is as shown in FIG.
34
.
When the feedforward gain Kff
2
=J, the transfer function G from the position command &thgr;r to the position response &thgr; has a value of 1, and ideally no delay occurs between the position command &thgr;r and the position response &thgr;, so that servo delay of the positioning servo controller is 0.
In practice, however, it is often that physical quantities such as the inertia J of the motor
4
which is the controlled object are not completely grasped, and it is difficult to set the values of the feedforward gains Kff
1
and Kff
2
to optimum values.
In such a case, during a process of positioning the motor
4
, a
Kabushiki Kaisha Yaskawa Denki
Masih Karen
Sughrue & Mion, PLLC
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