Adaptive control apparatus and shaking table

Details Adaptive control apparatus and shaking table Adaptive control apparatus and shaking table

2001-08-15

2004-02-24

Patel, Ramesh (Department: 2121)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Optimization or adaptive control

C700S280000, C700S032000, C074S664000

Reexamination Certificate

active

06697682

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an adaptive control device and a shaking table and in particular to an adaptive control device for controlling the shaking table system so that a response from a process to be controlled is matched with a target and to a shaking table using the device.
The adaptive control is a control method for adaptively changing a control parameters in real time so as to achieve a desired input-output characteristics even when dynamic characteristics of the process to be controlled are changed by operating conditions and an environment. As such a control method, there is a method which identifies the process to be controlled in real time and the identification result is used to determine control coefficients of an adaptive filter so as to modify an input signal to the process to be controlled in real time or a method which creates a filter in real time to agree a response signal from the process to be controlled with a desired response signal, so that an adaptive filter having the same characteristics as this filter is used for real-time modification of an input signal to the process to be controlled. These control methods have been used mostly for control process having a large time constant such as a liquid or a flow rate control in chemical plants.
There are also attempts to use these methods for compensating the transfer characteristic fluctuation of a shaking table on which an object to be tested is loaded (for example, Ide et al “Control of Electro-hydraulic Shaking Tables” The Japan Society of Mechanical Engineers, Dynamics and Design Conference 1999, Proceeding Vol. B (1999), pp. 15-18, and Maekawa et al “Advanced Control of Three-dimensional Shaking Table, 1
st
Symposium on the Improvement of seismic disasters based on the structure crash process analysis, Proceeding (2000-3), pp. 51-54). Here, the shaking table is one of the seismic test devices.
FIG. 2
shows a configuration example thereof. In
FIG. 2
, a table
6
is supported on a basement
121
via a bearing
120
. The bearing is not necessarily required depending on the configuration of the shaking table. The table
6
is connected to an actuator
5
mounted on the basement
121
. Moreover, shaking table state measurement means
122
is set on the table
6
. The actuator
5
is controlled by a feedback controller
4
using as feedback signals shaking table state variables measured by the shaking table state measurement means
122
. A specimen
3
loaded on the table
6
is excited, for example, by seismic acceleration, so that its behavior is observed and structual reliability is evaluated. In case of a shaking table control, the upper limit of the control frequency range is, for example, 50 Hz or above. That is, the time constant is small as compared with chemical plants.
FIG. 3
is a block diagram of an example of the shaking table control system using an adaptive control. A controlled object
1
includes a shaking table
2
and a specimen
3
. The shaking table
2
includes a feedback controller
4
, an actuator
5
, and a table
6
. Identification means
15
includes a digital filter
10
, a subtractor
16
, and adaptive means
14
. A command signal
101
generated by a signal generator
7
is modified into a modified command signal
102
by an adaptive filter
8
and fed to the feedback controller
4
. The feedback controller performs PID compensation and feedback compensation and generates a drive signal
103
. The drive signal
103
is fed to the actuator
5
so as to excite the table
6
and the specimen
3
loaded on this table. Here, a reaction force from the specimen
3
is added to the table and as a result, the shaking table transfer characteristics fluctuate. To solve this problem, the subtractor
16
is used to determine an estimated error
108
of a signal
107
obtained by supplying an actual shaking table response signal
106
to the digital filter
10
against a desired shaking table response signal
105
obtained by supplying the modified command signal
102
to a reference signal generator
9
. In order to minimize this error, the adaptive means
14
determines by control coefficient
109
of the digital filter
10
using, for example, the least mean square (LMS) method in real time, and the fluctuation of the shaking table transfer characteristic due to the specimen is compensated by matching the characteristics of the adaptive filter
8
to the characteristics of the digital filter
10
.
In the aforementioned example of the shaking table control, it is known that when the order of the digital filter
10
is not sufficiently higher than the order of the adaptive filter
8
required for compensation, identification cannot be performed because of the effect of noise contained in the shaking table response signal
106
and the effect of the higher-order vibration mode of the specimen and the shaking table itself other than for the compensation. Therefore, it is necessary to determine a control coefficient for a higher-order digital filter
10
, which requires a very long time such as 5 minutes for calculation. This causes a problem that the identification cannot be performed for an earthquake wave which lasts only for several seconds for several tens of seconds.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an adaptive control apparatus capable of compensating only a desired frequency band and significantly reducing the time required for identifying a process to be controlled, and a shaking table capable of real-time compensation of the shaking table transfer characteristic fluctuation by a specimen or the like.
The present invention provides a shaking table including:
a table to load a specimen;
actuators to excite the table;
a feedback controller for generating a drive signal for the actuator so that an inputted second command signal is agreed with a response signal indicating a vibration state of the table having the same dimension as this second command signal;
an adaptive filter having variable filter coefficient which is supplied with an external first command signal indicating a target value of the response signal and generates the second command signal so as to compensate the transfer characteristics from the feedback controller to the table loading the specimen;
a mask signal generator for generating a mask signal having no frequency component in the frequency band compensated by the adaptive filter;
a first adder for adding the mark signal to the second command signal; and
a second adder for adding the mask signal to the response signal;
an identification unit which is supplied with the outputs of the first and the second adders for calculating the filter coefficients of the adaptive filter for compensating the transfer characteristic and supplying the calculated coefficient to the adaptive filter.
Moreover, the present invention provides a shaking table includes:
a table for loading a specimen;
a actuator for actuating the table;
a feedback controller for generating a drive signal for the actuator so that an inputted second command signal is agreed with a response signal indicating a vibration state of the table having the same dimension as this second command signal;
an adaptive filter having variable filter coefficients which is supplied with an external first command signal indicating a target value of the response signal and generates the second command signal so as to compensate the transfer characteristics from the feedback controller to the table loading the specimen;
a mask signal generator for generating a mask signal having no frequency component in the frequency band to be compensated by the adaptive filter;
a reference signal generator which is supplied with the second command signal and calculates the target value of the response signal using a desired transfer characteristics or a transfer characteristics of a predetermined non-load state;
a first adder for adding the mask signal to an output signal from the reference signal generator; and
a second adder for adding the mask sig

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