Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1994-04-26
1994-12-06
Ip, Paul
Electricity: motive power systems
Positional servo systems
'reset' systems
31856815, 318615, G05B 19407, G05D 312
Patent
active
053714520
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is related to U.S. patent application Ser. Nos. 07/855,002, 07/870,881 and 07/776,418.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an adjustable time constant control system for a servomotor, which controls operations of movable parts in a machine tool while determining accelerating and decelerating time constants, and in particular, to an adjustable time constant control system, which controls movable parts in a machine tool while determining the optimum adjustable time constant every block,
2. Description of the Related Art
In an adjusting operation of a numerical control unit in the field, an accelerating time constant and decelerating time constant for each servomotor are preset, each servomotors being operable to drive a corresponding one of respective drive shafts or axes, Hereinafter, a term "adjustable time constant" is used, which includes the accelerating and decelerating time constants. The adjustable time constant is greatly influenced by the conditions in which the numerical control unit is operated. This makes it difficult to uniformly determine the adjustable time constant. For this reason, the adjustable time constant is conventionally determined on the basis of judgment in experience, a tentative operation, or the like.
However, if the time constant is determined with a sufficient margin, a cycle time becomes long, conversely, if it is determined to a small value, positioning accuracy is lowered due to generation of vibration, or the like. Therefore, the time constant must be determined to an appropriate value, but it is difficult to find the objective standard of judgment in a short time. For this reason, in controlling movable parts in the machine tool by using an adjustable time constant with a sufficient margin, it is hard to improve an operation speed even if there is a sufficient margin of power in a torque generated by the servomotor.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances. Therefore, an object of the present invention is to provide an adjustable time constant control system for a servomotor, which determines an optimum adjustable time constant of the servomotor with respect to a moving amount, load, or the like.
In order to solve the above problems, according to the present invention, there is provided an adjustable time constant control system, which controls an operation of a machine tool while determining an optimum adjustable time constant of the servomotor every block, comprising the steps of: determining an output torque of the servomotor on the basis of a programmed velocity; determining an accelerating torque by subtracting a static load torque from said output torque; determining acceleration on the basis of said acceleration torque and load inertia of the servomotor; and determining an adjustable time constant on the basis of said acceleration.
The output torque of the servomotor is determined on the basis of the programmed velocity and a velocity vs. torque curve of the servomotor from which a viscous loss is previously subtracted, An accelerating torque for accelerating the load is obtained by subtracting the static load torque including a frictional torque, a gravity torque, or the like, from the output torque. Further, an adjustable time constant is determined on the basis of the accelerating torque, and thus, acceleration or deceleration of the machine tool is controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart showing an adjustable time constant control system for a servomotor according to the present invention;
FIG. 2 is a graph showing the relationship between a moving distance and achievable velocity of each shaft in a machine tool;
FIG. 3 is a graph showing the relationship between the velocity and torque of the servomotor; and
FIG. 4 is a schematic block diagram of a numerical control unit for carrying out the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An
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Fanuc Ltd.
Ip Paul
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