Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2000-01-20
2001-10-30
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S568220, C318S569000, C318S572000, 36
Reexamination Certificate
active
06310457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller of a servomotor used as a driving source of various industrial machines including a machine tool, wire electric-discharge machine, and industrial robot.
2. Description of the Prior Art
A controller of a servomotor having been used so far will be described below by referring to a block diagram in FIG.
6
.
A movement command MCMD supplied every position/speed loop processing cycle is input to an error counter
30
from a controller (not illustrated) such as a numerical controller or the like. The error counter
30
obtains a positional deviation by subtracting a positional feedback value Pf sent from a position/speed detector
34
built in a servomotor
33
(or position/speed detector set to a machine to be driven by the servomotor
33
) every position/speed loop processing cycle from a movement command MCMD.
A speed command vc every position/speed loop processing cycle is obtained by multiplying the positional deviation by a positional loop gain Kp (block
31
). Then, a speed deviation (=vc−vf) is obtained by subtracting a speed feedback value vf fed back from the position/speed detector
34
from the speed command vc. Then, a torque command (current command) Tc is obtained by performing proportional-integral processing by a speed compensator
32
in accordance with the speed deviation and moreover, current loop processing is performed to drive the servomotor
33
and movable parts of a machine
35
.
The above described speed compensator
32
comprises an integral compensation term and a proportional compensation term. The integral compensation term has a speed-loop integral gain and the proportional compensation term has a speed-loop proportional gain. Moreover, in general, the above described servomotor is controlled by a software servo using a digital processor.
Herein, the above described speed-loop integral gain and proportional gain of the speed compensator
32
are set by parameters.
These set values are determined while checking the stability of a servo system.
To improve a control performance, it is necessary to raise a speed loop processing gain and moreover, a current loop processing gain. However, when the torque command Tc is saturated due to rapid traverse of a movable part, that is, when a machine is driven up to an acceleration/deceleration limit at a short acceleration/deceleration time constant, speed loop processing tends to be unstable. Therefore, set values of a speed loop gain and a current loop gain have been determined so far so that speed loop processing does not become unstable even if a machine is driven and controlled at a short acceleration/deceleration time constant (that is, at a large acceleration). As a result, the speed loop gain and current loop gain are kept relatively low and therefore, it is limited to improve the control performance.
As described above, a speed loop gain (and also, a current loop gain) is determined so as to prevent speed loop processing from becoming unstable due to saturation of a torque command or the like. Therefore, even when a speed loop gain is kept in an area having full scope in which a torque command is not saturated (that is, even when a determined gain can be further raised), control is continued with the gain determined low. Therefore, the control performance is prevented from being improved.
Particularly, in case of a machine tool for performing cutting by driving a servomotor, the cutting accuracy is controlled by a speed loop gain. Therefore, the fact that a speed loop gain cannot be sufficiently raised results in the fact that the cutting accuracy cannot be sufficiently raised.
Changing speed loop gains in accordance with an operation mode in a controller is disclosed in itself in Japanese Patent Application Laid-Open No. 3-121738. The controller controls the rotation of a spindle of a machine tool through a motor and the machine tool is operated in either of a turning operation mode for turning a rotating workpiece and a position control mode (C-axis operation mode) for controlling a rotational position of the spindle. When the turning operation mode is set by control mode change means, lower position loop gain and speed loop gain are used. On the other hand, when the turning operation mode is changed to the position control mode while turning is not performed, a higher loop gain and speed loop gain are used for acquiring the response characteristic suitable for cutting in the C-axis operation.
In case of the above controller, however, a motor for driving a machine tool is a spindle motor, not a servomotor, and the controller is not provided aiming at accomplishing a high accuracy by carrying out gain changing. Further, it is not suggested to change a current loop processing configuration to a proper configuration in accordance with the case of a turning operation mode or a positioning operation mode.
As described above, a conventional controller cannot simultaneously satisfy improvement of a control performance in servomotor control and stable control in an area in which a controlled variable is saturated.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a controller of a servomotor capable of improving the control performance and obtaining stable control even in an area in which a controlled variable is saturated.
To attain the above described object, a servomotor controller according to the present invention comprises operation mode judging means for judging whether the contents of a command indicate a cutting mode or a positioning mode, and speed loop gain storing means for storing a speed loop gain for cutting mode and a speed loop gain for positioning mode. And control is performed by selecting either of the speed loop gain for cutting mode or the loop gain for positioning mode stored in the speed loop gain storing means in accordance with a judgment result of the operation mode judging means.
Preferably, the servomotor controller according to the present invention further comprises current loop gain storing means for storing a current loop gain for cutting mode and a current loop gain for positioning mode. And control is performed by selecting either of the current loop gain for cutting mode or the current loop gain for positioning mode stored in the current loop gain storing means in accordance with a judgment result of the operation mode judging means.
Preferably, the servomotor controller according to the present invention further comprises a first current control configuration for performing proportional-plus-integral type current loop processing in accordance with a current command generated through speed loop processing and a feedback current fed back from a servo amplifier, and a second current control configuration for performing integral-plus-proportional type current loop processing in accordance with a current command generated through speed loop processing and a feedback current fed back from the servo amplifier. And switching from the first to second or the second to the first current control configuration is performed in accordance with a judgment result of the operation mode judging means.
More preferably, in the servomotor controller according to the present invention, when the operation mode judging means judges that contents of a command indicate a cutting mode, the speed loop gain changing means performs changeover of a speed loop gain to the speed loop gain for cutting mode, and also the current loop gain changing means performs changeover of a current loop gain to the current loop gain for cutting mode, and further the current loop configuration changing means performs changeover so that proportional-plus-integral type current loop processing is carried out. On the other hand, when said operation mode judging means judges that contents of a command indicate a positioning mode, the speed loop gain changing means performs changeover of a speed loop gain to the speed loop gain for positioning mode, and also the current loop gain
Iwashita Yasusuke
Okita Tadashi
Fanuc Ltd.
Ip Paul
Staas & Halsey , LLP
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