Data processing: generic control systems or specific application – Generic control system – apparatus or process – Digital positioning
Reexamination Certificate
2000-06-07
2003-05-13
Follansbee, John (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Digital positioning
C700S055000, C700S057000, C700S058000, C318S116000, C318S370000, C318S375000, C318S379000, C360S077040, C360S077080
Reexamination Certificate
active
06564110
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a position controlling apparatus for performing the positioning of an object being moved with a high degree of precision.
A typical position controlling apparatus will now be explained with reference to FIG.
1
. The position controlling apparatus includes a position controller
1
, a velocity controller
2
, a motor drive
3
, a motor
4
for driving a load
5
that is an object to be controlled, a position detector
6
such as a pulse encoder that is provided to the motor
4
, a velocity computing unit
7
, and subtracters
8
and
9
. The subtracters
8
and
9
may be called a first subtracter and a second subtracter, respectively. The load
5
is, for example, an X—Y table for moving a piece to be worked on in the X and Y directions. In this case, as the motor
4
, a servo motor is suitable.
The function of the position controlling apparatus will hereafter be explained. From a setting unit not illustrated there is given a command value X
r
of position. The position detector
6
detects the displacement of the object to be controlled to thereby output a detected value X
m
of position. The velocity computing unit
7
differentiates the detected value X
m
of position to thereby compute a detected value of velocity. The subtracter
8
subtracts the detected value X
m
of position from the command value X
r
of position to thereby compute a position error. The position controller
1
amplifies the position error to thereby compute a command value of velocity and outputs this value. The subtracter
9
subtracts the detected value of velocity from the command value of velocity to thereby compute a velocity error. The velocity controller
2
amplifies the velocity error to thereby compute a command value i
c
of current. The command value i
c
of current that has been computed is applied to the motor drive
3
. The motor drive
3
drives the motor
4
in accordance with the command value i
c
of current.
FIG. 2
is a block diagram of FIG.
1
. The symbol G
p
(z) in
FIG. 2
represents a transfer function of the position controller
1
. G
v
(z) represents the transfer function of the velocity controller
2
. K
t
represents a torque constant of the motor
4
. (1/J
S
2
) represents the transfer function of the object to be controlled. (1 -z
-1
) represents the transfer function of the velocity computing unit
7
. Here, it is assumed that &tgr;
d
represents a disturbance torque. In this case, since the object to be controlled is driven by a sum of the motor torque &tgr;
m
and the disturbance torque &tgr;
d
an error occurs when the positioning operation is performed.
In order to decrease the occurrence of the error due to the disturbance torque &tgr;
d
, it has been considered appropriate to adjust the position controller
1
or velocity controller
2
. However, when increasing the gain of the position controller
1
or velocity controller
2
in order to obtain the effect of suppressing the disturbance, the control system is likely to become unstable. This is due to the mechanical vibrations of the object to be controlled or to a phase lag in the sampling period of the position controller
1
and the velocity controller
2
.
On the other hand, the detected value X
m
of position contains measurement noises X
n
. These measurement noises X
n
also cause the occurrence of errors at the time of the positioning operation. The measurement noises X
n
become a factor that makes the control system unstable when having increased the gain of the position controller
1
or velocity controller
2
. Especially, in a digital control system, the noises that are generated when performing the quantization of a sampling frequency band and when performing differentiation in the velocity computing unit
7
are high in level.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a position controlling apparatus which is capable of the effect of disturbance as small as possible by estimating a disturbance torque acting upon a drive mechanism and compensating for the torque correspondingly thereto in the position controlling apparatus.
Another object of the present invention is to eliminate the measurement noises when performing position detection to thereby prevent degradation of a disturbance suppression characteristic within a high-frequency band.
Still another object of the present invention is to reduce the effects of the measurement noises and differentiation noises within a sampling frequency band especially in a digital control system.
A position controlling apparatus according to the present invention comprises a position detector for detecting the position of a driven object to be driven by a motor, to thereby output a detected value of position. A Kalman filter estimates the position and velocity of the driven object from the detected value of position, thereafter outputting an estimated value of position and an estimated value of velocity. A disturbance estimating unit estimates the disturbance applied to the driven object from comparison with a command value of current and the estimated value of velocity, thereafter outputting this estimated current value of disturbance. A first subtracter computes a difference between a command value of position and the estimated value of position. A position controller computes a command value of velocity in accordance with the difference computed by the first subtracter. A second subtracter computes the difference between the estimated value of velocity and the command value of velocity. A velocity controller computes a target value of current in accordance with the difference computed by the second subtracter. A third subtracter computes a difference between the estimated current value of disturbance and the target value of current to thereby output this difference as the command value of current. The computed command value of current is applied to the disturbance estimating unit and a motor drive for driving a motor.
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Taeg-Joon Kweon, Dong-Seok Hyun; “High Performance Speed Control of Electric Machine Using Kalman Filter and Self-tuning Regulator”; 1998; Hanyang University, Korea; pp. 280-286.
Makino Kenichi
Mori Hidehiko
Tomita Yoshiyuki
Arent Fox Kintner Plotkin & Kahn
Follansbee John
Pham Thomas
Sumitomo Heavy Industrie's, Ltd.
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