JPH07266190A - Numerical control system - Google Patents

Abstract

PURPOSE:To reduce a working error in the case where generating work is performed by installing a judging part, judging the hysteresis of a position command value, in a lost motion compensating part. CONSTITUTION:A position control value is fed to a feed direction storage part 12 and also fed to a hysteretic storage part 21 parallelly. In this hysteretic storage part 21, the position control value in time of sampling of up to specified frequency of the past is stored in memory. A lost motion compensating start judging part 22 performs a judgment inclusive of the hysteresis of a position command value stored in the hysteretic storage part 21 in addition to a feed direction change in this position command value and a code change in the speed command value. In brief, when the position command value is not changed the specified sampling frequency of the past, a command for compensating any lost motion is carried out even if there is no sign change in the speed command value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerical control device for a machine tool or the like, and more particularly to a lost motion correction device for a numerical control device for correcting lost motion existing in a feed drive system.

[0002]

2. Description of the Related Art FIG. 6 is a control block diagram for explaining a lost motion correction device of a numerical control device in the prior art. The main control unit 2 analyzes the NC program input from the paper tape 1 to calculate the movement amount per sampling and outputs the position command value X to the position control unit 3 of the servo system. The position control unit 3 calculates a speed command based on the difference between the position command value X and the position feedback signal Xb and outputs it to the speed control unit 5. The adder 4 adds the lost motion correction to the speed command to obtain the speed command value V. The position feedback signal Xb is a position detection signal obtained by indirectly detecting the mechanical position of the table 11 to be controlled by the position detection unit 8 connected to the motor 7. The speed controller 5 calculates the torque command T based on the difference between the speed command value V and the speed feedback signal Vb and outputs it to the power amplifier 6. The speed feedback signal Vb is a signal detected by the speed detector 9 mechanically connected to the motor 7. The power amplifier 6 outputs a current I for generating the torque command T to the motor 7. The torque generated in the motor 7 by the current I is transmitted to the ball screw 10. The ball screw 10 converts this transmitted torque into the propulsive force of the table 11.

In general, the feed shaft drive system is constructed so as to transmit the output torque of the motor 7 to a controlled object (for example, the table 11) via a mechanical portion such as a ball screw 10 as shown in FIG. Even when the backlash caused by play or the like is removed, there is a lost motion factor due to elastic deformation such as twisting and stretching of the ball screw 10 depending on the frictional force and rigidity of the drive unit. This lost motion amount is largely generated when the feed direction of the controlled object is reversed, and causes a processing error due to the follow-up delay of the controlled object.

A lost motion correction unit 18 is provided to correct this lost motion amount. The lost motion correction unit 18 stores data regarding deformation such as twist of the feed shaft to be controlled, and when the control for generating the lost motion is instructed, the lost motion is corrected based on the stored data. It is a thing. The lost motion correction section 18 is provided with a data setting section 17 for inputting data relating to the deformation characteristics of the feed axis to be controlled, and a lost motion data storage section 16 for storing this data. The lost motion correction unit 18 constantly monitors the position control value calculated by the main control unit 2, and the feed direction storage unit 12 stores the feed direction for each sampling cycle. In addition, the feed direction of the previous sampling cycle is the old position command feed direction storage unit 1
It is stored in 3. Then, in the lost motion correction activation determination unit 14, if there is a change by comparing the current feeding direction and the previous feeding direction stored in these storage units, and the sign of the speed command value is reversed, the lost motion correction is performed. Decide to make a correction. Then, based on this determination, the lost motion correction output unit 15 outputs the correction amount based on the data stored in the lost motion data storage unit 16 described above.

FIG. 7 is a flow chart showing the processing performed by the lost motion correction activation determination unit 14 of FIG. In step S1, it is determined whether the command value has changed. If the command value has changed, the process proceeds to step S2, and if it has not changed, the process ends. In step S2, it is determined whether the position command input from the feed direction storage unit 12 is positive or negative in the feed direction. In step S31, the old position command feed direction storage unit 13
It is determined whether the feed direction is positive or negative. If the result is negative, the process ends. If the result is positive, the feed direction is reversed to negative, so the process proceeds to step S51. In step S51, it is determined whether the sign of the speed command value V is reversed, and if not reversed, step S51
When repeated, the process goes to step S61. This loop waits for the timing when the positional deviation occurring at the time of reversal of the command value disappears due to the tracking delay. After step S61 and step S62, go to step S7,
In step S7, the feed direction stored in the old position command feed direction storage unit 13 is rewritten to a new command feed direction.

[0006]

By the way, the lost motion correction is performed after waiting for the timing when the feed direction instructing the servo system is reversed and the speed command value becomes 0 (the position deviation disappears). In the conventional device shown, there is a problem in that the output signal of the position detection unit has high-frequency vibration components and noise, so that the timing at which the lost motion correction is activated varies. As a specific example, a case of performing creation processing by the movement of the feed shaft in a machine tool will be described. FIG. 3 shows the relationship between the feed axis position and time, and the speed command value V and time when the feed axis is continuously reversed. In this case, the timing of the sign reversal of the speed command value V, which is the final trigger for the lost motion, does not deviate so much that a problem occurs in actual machining. FIG. 4 shows the relationship between the feed axis position and time, and the speed command value V and time when the feed axis is temporarily stopped and then reversed. FIG. 5 is an enlarged view of the relationship between the speed command value V and time in FIG. At the time when the position command value X does not change, the speed command value V becomes almost zero. However, when viewed microscopically, the output signal from the position detection unit contains high-frequency vibration components and noise with respect to the position command value X that is a constant value, and these deviations and the speed calculated from the deviations are included. A minute vibration component is generated in the command value V. Therefore, the time from the reversal of the position command value to the reversal of the sign of the speed command value V is not constant, so that there is a temporal variation in the timing at which the lost motion correction is activated. Therefore, even when the workpieces are continuously machined, the machining shape varies at the feed axis reversing portion. Further, it is difficult to remove high-frequency vibration components and noise of the output signal from the position detector without degrading the resolution and frequency response of the output signal.

The present invention has been made under the circumstances as described above, and an object of the present invention is to reduce a machining error in performing a generating process by activating a lost motion correction at an appropriate time. It is an object of the present invention to provide a lost motion correction device in a numerical control device that is made possible.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a lost motion amount which is a control deviation amount due to a deformation of a drive mechanism of a numerical controller for controlling the drive shaft of a machine tool. In the lost motion correction unit that corrects, the first determination unit that determines that the feed direction of the position command value has been changed, and the second determination unit that determines the history of the position command value
A determination unit, a third determination unit that determines that the sign of the speed command value is changed, and a case where the determination is performed by the first determination unit and the determination unit is performed by the second determination unit. ,
Alternatively, the first determination unit makes the determination and the third determination is made.
The determination unit has an activation determination unit that gives an instruction to correct the lost motion amount when the above determination is made. Alternatively, the lost motion correction unit includes a first determination unit that determines that the feed direction of the position command value has been changed, a second determination unit that determines the history of the position command value, a position command value and the actual feed axis. A third determination means for determining that the sign of the deviation from the position is changed, and the first determination unit makes the determination and the second determination unit makes the determination unit, or And a start determination unit that gives a correction instruction of the lost motion amount when the first determination unit makes the determination and the third determination unit makes the determination.

[0009]

According to the present invention, after the position command value is reversed, the history of the position command value before the reversal is judged, and when the feed axis is immediately reversed without stopping, the speed command value or the position deviation is maintained as usual. Lost motion compensation is output after waiting for the sign reversal, and when the feed axis is temporarily stopped or when reversing from a state where the feed speed is very slow, the lost motion is not waited for the sign reversal of the speed command value or position deviation. Output the correction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a control block diagram showing an embodiment of a numerical controller according to the present invention, and the components other than the lost motion correction section 20 are the same as those of the conventional device shown in FIG. Also, with respect to each component in the lost motion correction unit 20, the same components as those in the conventional device are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, the position control value is the feed direction storage unit 1.
2 is sent to the history storage unit 21 at the same time. The history storage unit 21 stores the position control value at the time of sampling up to a predetermined number of times in the past. The number of control values stored, that is, the number of sampling cycles stored as a history can be changed by the data setting unit 23. In addition to the conventional determination criteria, that is, the change in the feed direction of the position command value and the change in the sign of the speed command value, the lost motion correction activation determination unit 22 newly includes the history storage unit 2.
The determination is made including the history of the position command value stored in 1.
That is, if the position command value has not changed over a predetermined number of samplings in the past, a command for correcting the lost motion is issued even if there is no sign inversion of the speed command value.

FIG. 2 shows a lost motion correction activation determination unit 2
The process performed in 2 is shown in a flowchart. In step S1, it is determined whether the command value has changed. If the command value has changed, the process proceeds to step S2, and if it has not changed, the process ends. In step S2, it is determined whether the position command input from the feed direction storage unit 12 is positive or negative in the feed direction. In step S31, it is determined whether the feed direction stored in the old position command feed direction storage unit 13 is positive or negative. When the result is negative, the process is terminated, and when the result is positive, the feed direction is inverted to negative.
Go to 41. In step S41, the position command values before feed direction reversal stored in the data setting section 17 are compared by the number of times the history judgment is performed. If they are the same, the process proceeds to step S61, and if they change, the process proceeds to step S51. In step S51, it is determined whether the sign of the speed command value V is reversed. If not reversed, step S51 is repeated, and if reversed, the process proceeds to step S61. This loop waits for the timing when the positional deviation occurring at the time of reversal of the command value disappears due to the tracking delay. Step S61 and step S62
After that, the process proceeds to step S7, and in step S7, the feed direction stored in the old position command feed direction storage unit 13 is rewritten to the feed direction to be newly instructed.

Next, the operation of this embodiment will be described.
By adding step S41, in the feed motion in which there is a temporary stop before reversal, the lost motion correction is activated without waiting for the sign reversal of the speed command value, so that there is a temporal variation in the timing at which the lost motion correction is activated. Can be prevented. In the prior art, the lost motion correction was started after the sign of the speed command value was inverted, because the point at which the tracking delay with respect to the command becomes small after the position command value is reversed is selected. If the position command value has not changed the number of times, the tracking delay becomes negligibly small, so there is no need to wait for the sign reversal of the speed command value. On the other hand, in the case where there is no stopping motion and immediate reversal motion is performed,
Lost motion correction starts after waiting for the sign reversal of the speed command value as in the past. That is, it is possible to appropriately determine the situation before the feed direction is reversed and determine the start timing of the lost motion correction. The present invention is not limited to the above embodiment, and for example, it may be determined in step S41 that the case where the change amount of the position command value is smaller than the set amount continues for the set number of times. .

[0013]

As described above, according to the lost motion correction device of the numerical controller of the present invention, the lost motion correction is performed at a more appropriate time without variation regardless of the state before the reversal of the feed axis, and the creation processing is performed. It is possible to reduce the processing error when performing.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an example of a lost motion correction device of a numerical control device according to the present invention.

FIG. 2 is a flowchart showing an example of a lost motion correction device of the numerical control device of the present invention.

FIG. 3 is a diagram for explaining a start timing of lost motion correction when the feed axis is continuously reversed in the prior art.

FIG. 4 is a diagram illustrating a start timing of lost motion correction when the feed shaft is temporarily stopped and then reversed after the conventional technique.

FIG. 5 is an enlarged view of FIG.

FIG. 6 is a control block diagram showing an example of a lost motion correction device in the related art.

FIG. 7 is a flowchart showing an example of a lost motion correction device in the related art.

[Explanation of symbols]

 1 Paper Tape 2 Main Control Section 3 Position Control Section 4 Adder 5 Speed Control Section 6 Power Amplifier 7 Motor 8 Position Detection Section 9 Speed Detection Section 10 Ball Screw 11 Table 12 Feed Direction Storage Section 13 Old Position Command Feed Direction Storage Section 14 Lost Motion Correction start determination unit 15 Lost motion correction output unit 16 Lost motion data storage unit 17 Data setting unit 18 Lost motion correction unit 20 Lost motion correction unit 21 History storage unit 22 Lost motion correction start determination unit 23 Data setting unit

Claims (2)

[Claims] 1. A numerical control device for controlling the drive of a feed shaft of a machine tool, comprising: a lost motion correction unit for correcting a lost motion amount which is a control deviation amount caused by deformation of a drive mechanism. The correction unit determines a first determination unit that determines that the feed direction of the position command value has changed, a second determination unit that determines the history of the position command value, and determines that the sign of the speed command value has changed. And a third determination means that performs the determination by the first determination unit and the determination unit by the second determination unit, or the first determination unit and the determination by the first determination unit. Three
A numerical control device comprising: a start determination unit that gives a correction instruction of a lost motion amount when the determination unit makes the above determination. 2. A numerical controller for controlling the drive of a feed shaft of a machine tool, comprising a lost motion correction unit for correcting a lost motion amount which is a control deviation amount caused by deformation of a drive mechanism, wherein the lost motion is included. The correction unit includes a first determination unit that determines that the feed direction of the position command value has changed, a second determination unit that determines the history of the position command value, and a position command value and the actual position of the feed axis. Third determination means for determining that the sign of the deviation has been changed, and the first determination portion makes the determination and the second determination portion makes the determination portion, or the first determination Department made the above determination and the third
A numerical control device comprising: a start-up determination unit that gives an instruction to correct the lost motion amount when the determination unit makes the above determination.