Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1989-09-07
1992-03-03
Ip, Paul
Electricity: motive power systems
Positional servo systems
'reset' systems
318561, 318609, 318615, 364164, 364148, G05B 1300
Patent
active
050936093
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This application is cross-referenced to U.S. Ser. No. 07/368,291, filed on May 24, 1989, to Sakamoto et al.
BACKGROUND OF THE INVENTION
The present invention relates to a method of controlling a servomotor. More particularly, the present invention is directed to a servomotor control method for continuously switching a control loop from a PI control mode to an I-p control mode for increased response and stability.
PI and I-p control modes are widely employed for the control of current and speed loops of servomotors. The control process of each of the PI and I-p control modes is carried out in a fixed manner.
The PI control mode is highly responsive, but has low stability and accuracy. Conversely, the I-p control mode is highly stable and accurate, but responds poorly.
SUMMARY OF THE INVENTION
In view of the aforesaid drawback of the known control modes, it is an object of the present invention to provide servomotor control method for continuously switching a control loop from a PI control mode to an I-p control mode for increased response and stability.
To accomplish the above object, there is provided a method of stably controlling a servomotor stably at a high speed, the method comprising the step of continuously switching a control loop from a PI control mode to an I-p control mode.
By thus continuously switching the control loop from the PI control mode to the I-p control mode, the response of the PI control mode and the stability and accuracy of the I-p control mode are combined to allow optimum control.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an arrangement for carrying out a servomotor control method according to an embodiment of the present invention;
FIG. 2 is is an equivalent block diagram of the arrangement shown in FIG. 1, when a variable .alpha.-1;
FIG. 3 is a diagram showing the relationship between an error e and the variable .alpha.;
FIG. 4 is a graph of the response of a conventional PI control mode;
FIG. 5 is a graph of the response of a conventional I-p control mode by way of example; and
FIG. 6 is a diagram showing the response of the servomotor control method according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
An embodiment of the present invention will hereinafter be described with reference to the drawings.
FIG. 1 is a block diagram of an arrangement for carrying out a servomotor control method according to an embodiment of the present invention. A control loop employed here is a current control loop. Denoted at R(s) is a current command value, Y(s) a current output, 1 a proportional arithmetic unit for the current command value, k2 a proportional gain, and .alpha. a variable for multiplying the proportional gain, the variable .alpha. being variable in the range of 0 .ltoreq..alpha..ltoreq.1. The manner in which the variable u varies will be described in detail later on.
Denoted at 2 is an arithmetic unit for producing as an output the difference between the current command value R(s) and the current output Y(s), 3 an integrator, k1 an integral gain, 4 an arithmetic unit for adding the output from the proportional arithmetic unit 1 and the output from the integrator 3, subtracting the product of the current output Y(s) and the proportional gain k2 from the sum, and producing the difference as an output, 5 a servomotor winding, and L the inductance of the servomotor winding.
When .alpha.=0, since the path of .alpha.k2 is eliminated, the control mode of the arrangement of FIG. 1 becomes an I-p control mode. When .alpha.=1, the arrangement of FIG. 1 becomes equivalent to a control loop shown in FIG. 2, which is a PI control mode. Those parts shown in FIG. 2 which are identical to those of FIG. 1 are designated by identical reference characters, and will not be described in detail.
The manner in which the variable .alpha. is controlled will be described below. By way of example, the variable .alpha. is controlled as a function of an error e. FIG. 3 illustrates the relationship between the
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Iwashita Yasusuke
Sakamoto Keiji
Seki Shinji
Fanuc Ltd.
Ip Paul
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