Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2002-08-02
2004-05-18
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
C702S145000
Reexamination Certificate
active
06736018
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mechanical constant estimating device for estimating a mechanical constant such as an inertial moment in a drive machine such as a machine tool or a robot employing an actuator such as a motor.
BACKGROUND ART
To control a drive machine such as a machine tool or a robot employing an actuator such as a motor at high precision and stably, it is required to estimate the mechanical constant such as an inertial moment for the drive machine correctly.
FIG. 6
is a block diagram of a velocity control system containing a conventional mechanical constant estimating device, which has the configuration equivalent to that of a control device for an electric motor servo system having an auto-tuning function capable of setting the convergence of control gain as described in JP-A-11-313495.
In
FIG. 6
, reference numeral
30
denotes a torque command generating portion for generating a torque command &tgr;r based on a velocity command (not shown),
31
denotes an actuator such as a motor for generating a drive torque &tgr;m in accordance with the torque command &tgr;r,
32
denotes a drive machine that is driven by the actuator
31
,
33
denotes a velocity detector for detecting a machine velocity vm of the drive machine
32
, and
34
denotes a mechanical constant estimating device for estimating an inertial moment estimated value Je by inputting the machine velocity vm and the torque command &tgr;r. Reference symbol &tgr;d denotes a disturbance torque applied to the drive machine
32
.
Also, the torque command generating portion
30
alters the internal constant such as a gain (auto-tuning), based on the inertial moment estimated value Je output from the mechanical constant estimating portion
34
, and generates the torque command &tgr;r in accordance with the inertial moment estimated value Je.
FIG. 7
is a block diagram showing the configuration of a conventional mechanical constant estimating device, which is equivalent to the configuration of a mechanical constant estimating device based on an inertial moment estimating operation expression using a sequential least squares method as described in the Institute of Electrical Engineers of Japan, treatise journal, Vol.114-D, No.4, p.424-p.431.
In
FIG. 7
, reference numeral
41
denotes an acceleration variation signal generating portion for generating an acceleration variation signal da through the signal processing by inputting a machine velocity vm,
42
denotes a torque variation signal generating portion for generating a torque variation signal d&tgr; through the signal processing by inputting a torque command &tgr;r,
43
denotes a multiplication circuit for calculating the product of the acceleration variation signal da and a previous inertial moment estimated value Je(k−1) held in an inertial moment estimated value holding portion
47
,
44
denotes a subtracter for subtracting the product of the acceleration variation signal da and the previous inertial moment estimated value Je (k−1) calculated in the multiplication circuit
43
from the torque variation signal d&tgr;, and
45
denotes an estimation gain portion for inputting a signal in which the product of the acceleration variation signal da and the previous inertial moment estimated value Je(k−1) is subtracted from the torque variation signal d&tgr; and outputting an error from the previous inertial moment estimated value Je(k−1). Also, reference numeral
46
denotes an operating portion for adding the previous inertial moment estimated value Je(k−1) to the error output from the estimation gain portion
45
and outputting the inertial moment estimated value Je(k), and
47
denotes an inertial moment estimated value hold portion for holding the inertial moment estimated value Je.
Referring to
FIGS. 6 and 7
, the operation of the conventional mechanical constant estimating device will be described below. It is assumed here that the driving torque &tgr;m actually produced in the actuator
31
coincides with the torque command &tgr;r.
Supposing that the machine velocity of the drive machine
32
detected by the velocity detector
33
is vm, the machine acceleration am of the drive machine
32
is represented by the following expression (1).
am=s·vm
(1)
In the above expression, s is the Laplace operator.
Also, supposing that the disturbance torque applied to the drive machine
32
is &tgr;d, and the inertial moment (true value) for the drive machine
32
is J, the torque commander &tgr;r is represented by the following expression (2).
&tgr;
r=&tgr;d+J·am
(2)
For simpler explanation, if the torque command &tgr;r is denoted in a continuous time system, and the torque variation signal generating portion
42
obtains a difference between the input torque command &tgr;r at present and the previous torque command &tgr;r, and generates a torque variation signal d&tgr; from this differential value, the torque variation signal d&tgr; is represented by the following expression (3).
d&tgr;=s·&tgr;r
(3)
Since the machine velocity vm detected by the velocity detector generally contains the noise component of high frequency, the use of pure differentiation will increase the noise component, causing an estimation error for the mechanical constant. Therefore, the acceleration variation signal generating portion
41
obtains an acceleration variation signal da for the input machine velocity vm by pseudo differential operation having the low pass filter characteristic, instead of pure differentiation. Assuming that the low pass filter characteristic function is F(s), the pseudo acceleration signal af is represented by the following expressions (4) and (5), and the acceleration variation signal da is calculated by the following expression (6).
af=s·F
(
s
)·
vm
(4)
af=F
(
s
)·
am
(5)
da=s·af
(6)
If the expressions (2), (3), (5) and (6) are put together, and the low pass filter characteristic function F(s) is ignored as the ideal filter, the torque variation signal d&tgr; can be represented by the following expression (7).
d&tgr;=s·&tgr;d+J·da
(7)
In the expression (
7
), because the right side first term becomes zero in a steady state where there is no disturbance torque &tgr;d, the inertial moment J can be represented by the following expression (8), whereby the inertial moment J for the drive machine
32
can be estimated as a ratio of the torque variation signal d&tgr; to the acceleration variation signal da.
J=d&tgr;/da
(8)
The mechanical constant estimating device as shown in
FIG. 7
employs a sequential least square method in the expression (8) to improve the estimation precision.
Supposing that the inertial moment estimated value at the k-th point of time is Je (k) and the inertial moment estimated value at the previous ((k−1)-th) point of time is Je(k−1), the operation expression for estimating the inertial moment based on the sequential least square method is shown in the following expressions (9) to (11).
Je
(
k
)=
Je
(
k
−1)+
P
(
k
)·
da
(
k
)·(
d
&tgr;(
k
)−
da
(
k
)·
Je
(
k
−1)) (9)
P
(
k
)=
P
(
k
−1)/(&lgr;+
P
(
k
−1)·
da
(
k
)2) (10)
G
(
k
)=
P
(
k
)·
da
(
k
) (11)
In the above expressions, &lgr; is a constant called a forgetfulness factor, and is chosen to be slightly smaller than one to cope with a change in the inertial moment of the drive machine. Also, P(k) is an estimation gain parameter of one kind provided in the mechanical constant estimating operation, and updated while changing as the acceleration variation signal da is varied in magnitude.
The estimation gain G(K) in the estimation gain portion
45
is represented by the expression (11) including the operation expression (10) for the estimation gain parameter P(k).
If the inertial moment estimated value Je(k−1) at the previous ((k−1)-th) point of ti
Lefkowitz Edward
Miller Takisha S
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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