JPS6378206A - Following delay removal method using digital servo system in full close feedback nc system - Google Patents

Abstract

PURPOSE:To execute fine controls by comparing the rotary position of a shaft in a servomotor with the position of a table, copying with unstable factors and adjusting time when a correction command is added. CONSTITUTION:As for a position command 11 form an NC controller, a position gain Pg is calculated to become a speed command 12 to the servomotor. The speed command is translated into a torque command 13 to the servomotor to drive the servomotor 14. It dries the table in a machine tool, and according to its action, a position detector machine tool position detector 16 is operated. There is the play 15 of the tool between the motor 14 and the table. The output of the motor 14 is fed back as a motor speed feedback to the speed command. In such a full close feedback system, the output of the position detector 16 for the table is fed back as a nipple position feedback to the position command.

Description

[Detailed description of the invention] [Industrial application field] Is the present invention a numerical system using full-close feedback? This invention relates to a method for eliminating follow-up delay using a digital servo system in a 1l (NC) machine tool.

[Conventional technology]

There are two types of NC servo mechanisms for machine tools: full-closed feedback and semi-closed feedback. The former method provides position feedback by attaching a position detector to the table of the machine tool, and is generally more accurate than the latter, and compensates for errors caused by play in the mechanical system. Semi-closed feedback type machine tools detect the position from the motor's rotation axis, and although the position error is larger than that of the fully closed feedback type, the position error can be reduced by making appropriate corrections for play.

In a machine tool that uses full-closed feedback, there is theoretically no influence of play in the mechanical system, but if the table feed rate is large (the servo system's follow-up delay will cause the quadrant switching part of the arc to A shape error occurs when the direction of movement changes.This is because even if the motor reverses after passing the apex of the shape, there is a time when the table does not move, so even after the apex, a flat portion continues and the deviation from the command value This is because errors may occur.

[Problems to be Solved by the Invention] In view of the problems caused by the follow-up delay in a machine tool using a full-closed feedback NC system, an object of the present invention is to provide a correction command to be added to a position command from an NC controller when the direction of movement is reversed. Based on the idea that the end timing of the process is determined by comparing the position detection values of the servo motor and the machine tool table, the position error is small even if there are unstable factors such as friction in the mechanical system, and the shape of the workpiece is determined. The objective is to obtain an NC machine tool with fewer errors.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, the NC
Receive a position command from the controller, create a speed command to the servo motor, create a torque command to the servo motor from the speed command, drive the servo motor with the torque command, and perform machining with the output of the servo motor. A full-scale motor that drives a table of a machine, feeds back the output of a position detector provided on the table as table position feedback to the position command from the NC controller, and feeds back the output of the servo motor to the speed command. In a method for eliminating follow-up delay using a digital servo system in a close feedback NC system, a correction command with a correction amount of K△X and a correction time of 10 Pg+ is applied to a position command from an NC controller.
When the position error of the servo system that reverses as the table changes its moving direction becomes zero, it is added, the detected position value is obtained from the output of the servo motor, and the detected position value of the output of the servo motor and the detected table position value are added. Provided is a method comprising the steps described above, in which the values are compared and the addition of the correction commands is stopped when the values become equal. Here, ΔX is the amount of play in the table of the machine tool, pg is the position gain of the servo system, and K is the correction coefficient.

[Effect]

If you use the method described above, the appropriate correction command will be added at the optimal timing, and even if there is an unstable factor such as friction in the mechanical system, the rotational position on the servo motor axis and the table position can be compared. The addition time of the correction command can be adjusted in response to the instability factor. This enables more fine-grained control than when simply adding a correction command having a calculated constant correction amount and correction time.

〔Example〕

A block diagram showing each process of a control system for performing a method for eliminating follow-up delay using a digital servo system in a full-close feedback NC system as an embodiment of the present invention is shown in FIG. 1, and FIG. , a similar diagram is shown implementing the method using a prior art non-digital servo system.

In FIG. 1, position command 11 from the NC controller
is integrated with the position gain pg to become a speed command 12 to the servo motor, and this speed command becomes a torque command 13 to the servo motor to drive the servo motor 14.

The servo motor 14 drives the table of the machine tool and operates the position detector 16 in accordance with the movement of the table. There is mechanical play between the servo motor 14 and the table.
There are 15. The output of the servo motor 14 is fed back to the speed command as motor speed feedback. In the full-close feedback system, the output of the table position output device 16 is fed back to the position command as table position feedback.

In order to prevent tracking errors due to play in the mechanical system, this full-close feedback method adds a lost motion correction pulse as a correction command to the position command from the NC controller. This correction pulse is Xc as correction lXc.
=K·ΔX1 The correction time Tc takes a value of Tc=10Pg+, and the correction timing starts when the moving direction of the table changes and the position error of the reversing servo system becomes zero. Note that Δx, Pg, and K are as described above.

In this embodiment, the end of the correction timing is defined as follows. In the digital servo system, obtain a motor position feedback signal from the output of the servo motor 14 and compare it with the table position signal (17)
L, correction period side '4 so that the lost motion correction pulse 19 is not added to the position command 11 from the NC controller when the servo motor position becomes equal to the table position.
1118.

According to the embodiment described above, compared to the prior art example in FIG. 2, the steps shown by the broken lines in FIG.
Since it is provided in place of the correction pulse 200 shown in the figure, the stop timing of the correction pulse can be controlled, and even if there is an uncertain factor such as friction on the machine tool table, more fine-grained position control is possible.

〔Effect of the invention〕

According to the present invention, in an NC system using full-closed feedback, an appropriate correction command can be added and the correction end timing can be controlled by the difference in position between the servo motor and the table. It is possible to obtain an NC machine tool with a small positional error even if there are factors, and therefore with a small shape error of the workpiece.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing steps for performing a method according to an embodiment of the present invention, and FIG. 2 is a diagram similar to FIG. 1 in the prior art. (Explanation of symbols) 11...Position command from NC controller, 12...
・Speed command to servo motor, 13... Torque command to servo motor, 14... Servo motor, 15... Machine play, 16... Position detector of machine tool table, 17...
- Comparison, 18... Correction period control, 19... Lost motion correction pulse, 20... Correction pulse.

Claims (1)

[Claims] Receiving a position command from an NC controller, creating a speed command to a servo motor, creating a torque command to the servo motor from the speed command, and driving the servo motor by the torque command, The output of the servo motor drives the table of the machine tool, the output of a position detector provided on the table is fed back to the position command from the NC controller as table position feedback, and the output of the servo motor is fed back to the speed command. In a method for eliminating follow-up delay using a digital servo system in a full-close feedback NC system configured to provide speed feedback, a position detection value is obtained from the output of the servo motor, and play in the table of the machine tool is reduced by △X. , When the position gain of the servo system is Pg and the correction coefficient is K, a correction command with a correction amount of K・△X and a correction time of 1÷Pg÷K is applied to the position command from the NC controller, Addition is made when the position error of the servo system, which is reversed due to a change in the moving direction of the table, becomes zero, and the position detection value of the output of the servo motor is compared with the table position detection value, and the values are equal. A method for eliminating follow-up delay using a digital servo system in a full-closed feedback NC system, characterized in that the addition of the correction command is stopped when the correction command is reached.