JPH07186008A - Pitch error correction method - Google Patents

Abstract

PURPOSE:To provide a pitch error correction method for a ball screw in which speed of a work during movement can be set to be almost constant, and in which movement of the work in the case of movement around a changing point in a stage can be performed smoothly. CONSTITUTION:An integrated value Ii of correction quantity data to each stage, and increase ratio Ti=D1/P1 at the stage are determined based on correction quantity data Di as pitch error at the stage separated at a specified correction interval Pa. Using this integrated value Ii and the increase ratio Ti, a pitch error correction value DELTA at a current work position (PB) is determined at every specified time, and rotation speed of a servo motor to drive a ball screw is controlled based on the correction value DELTA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw pitch error correction method in a machine tool or a general industrial machine which has a power transmission mechanism composed of gears and ball screws and whose position is controlled by a servomotor.

[0002]

2. Description of the Related Art In a machine tool or the like which has a power transmission mechanism composed of gears and a ball screw and uses a servo motor to control the position of a workpiece, the rotation of the servo motor is controlled in consideration of the pitch error of the ball screw. There is. In a machine tool or the like that performs control in consideration of a pitch error, a user sets a parameter for correcting the pitch error in a control device of the machine tool or the like before operating the machine tool or the like.

As such parameters, a correction start point for starting the pitch error correction control, a correction interval for dividing the correction control range into a plurality of sections, and each section or stage divided by the correction intervals are specified. There is a stage number for this. After setting the parameters as described above, the user sets one correction amount data for each of the stages with the stage numbers. This correction amount data is set as an increase or decrease pulse number with respect to the normal pulse number supplied to the servo motor when the work moves on each stage.

In such a machine tool or the like, normally,
The work moves within a correction control range including a plurality of stages that start from the previously set correction start point and are separated at each correction interval.

Next, a conventional pitch error correction method will be described with reference to the drawings.

As shown in FIG. 5, the correction control range in which the work moves is divided into predetermined correction intervals as described above, and the stage numbers i-2 and i- are assigned to each stage.
1, ..., i + 2 and correction amount data D _i-2 , D _i-1 ,
..., D _{i + 2} is set. Now, a case where the work is at the position P _C and the user moves the work to the position P _G will be described as an example. When the user operates the machine tool or the like to move the work whose current position is displayed as the position P _C to the position P _G , the control unit of the machine tool or the like first causes the position P to be changed.
_The number of pulses to be supplied to the servo motor to move the work from _C to position P _G is calculated. This number of pulses is
This is the theoretical number of pulses assuming that the ball screw has no pitch error. Next, the control unit controls the switching point P of the stage included in the range from the position P _C to the position P _G.
i-2 , P _i-1 and P _i are specified, and the correction amount data D _i-2 , D _i-1 and D _i of the respective stages are added to the theoretical pulse number calculated above. The number is supplied to the servo motor and the servo motor is driven at a constant speed to move the work to the position P _G. Here, in the conventional pitch error correction method, the pitch error is not corrected in the range from P _i to position P _G in FIG.

Further, while the work is moving from the position P _C to the position P _G , the control unit performs the current position management calculation for displaying the position of the work to the user at predetermined time intervals. This current position management calculation is a calculation for displaying at which position of the setting position axis in FIG. 5 the work is located. Specifically, the current position management calculation is based on the number of pulses supplied to the servo motor up to that point and the correction amount. It is performed based on the number of pulses excluding the minutes.

As described above, in the conventional pitch error correction method, the current position management calculation is performed every predetermined time in order to display the current position of the work.

[0009]

In such a conventional method, all of the correction amount is added to the movement amount at the switching point of the stage. Therefore, for example, as shown in FIG. 6, when the user instructs to move the work 2 to the right across the switching point P _i of the stage number i of the correction amount data D _i = −10, the user is There is a problem in that a mechanism such as a servo motor of a machine tool is unexpectedly impacted and smooth operation of the machine is hindered depending on conditions such as a moving speed set by. Moreover, in this case, the work is 2 + (− 10) =
-8, that is, despite the movement to the left by eight, the display of the current position also indicates that the movement to the right is two.

In the conventional method, the number of pulses to which the correction amount to be supplied to the servo motor is added is calculated before moving the work, and the calculated pulse is supplied to the servo motor at a constant frequency. The rotation speed of the servo motor becomes constant. Therefore, when the ball screw has a pitch error, the moving speed of the work does not become a constant speed as shown in FIG. Therefore, the conventional method is unsuitable for a machine tool such as an automatic lathe that is required to move a work at a constant speed.

An object of the present invention is to correct the pitch error at every predetermined time so that the speed of the moving work can be made substantially constant, and the work can be performed by interposing the stage switching point. It is an object of the present invention to provide a pitch error correction method capable of maintaining a smooth operation of a machine tool or the like even when a small amount is moved.

[0012]

In order to achieve the above object, the present invention has a power transmission mechanism having a ball screw, and the ball screw is rotated by supplying a drive pulse to a servomotor to rotate the ball screw. In the ball screw pitch error correction method of a machine for moving an engaged work, a correction control range of the ball screw is divided into a plurality of sections at predetermined correction intervals from the correction start point, and the ball screw pitch error in the section is divided. Correction amount data converted into the drive pulse is set for each of the plurality of sections, the position of the work is measured every predetermined time, and the pitch error correction amount according to the measured position of the work is set. Is calculated using the correction amount data, and the driving force is supplied to the servo motor according to the calculated pitch error correction amount. It is characterized in changing a pulse.

[0013]

According to the present invention, the correction range of the ball screw is divided into a plurality of sections at predetermined correction intervals from the correction start point in advance, and the pitch error of the ball screw for each section is corrected by the servo for rotating the ball screw. The correction amount data converted into the number of drive pulses of the motor is set. In the above state, the position of the work is measured at predetermined time intervals from the number of drive pulses supplied to the servo motor, and the pitch error correction amount corresponding to the position of the work is calculated from the correction amount data described above. Then, the pitch error of the ball screw is corrected by changing the drive pulse supplied to the servo motor according to the calculated pitch error correction amount.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First, the positioning control system of the servo motor used in this embodiment will be described.

FIG. 1 is a block diagram showing the configuration of a positioning control system of a deviation counter type servo motor used in this embodiment. In FIG. 1, reference numeral 1 denotes a controller composed of a microcomputer or the like. When a target value (moving target position of the work) from a user is input, a command pulse is output according to the target value and at a predetermined time interval. The pitch error correction value (pulse) is output according to the procedure described later.

The sum of the command pulse and the pitch error correction value is input to the deviation counter 2, multiplied by the feed forward gain G _F, and then output to the motor amplifier 3. In the motor amplifier 3, an added value of a value obtained by multiplying the sum of the command pulse and the pitch error correction value by the feedforward gain G _F and a value obtained by multiplying the output value of the deviation counter 2 by the position loop gain G _L is given. input. The motor amplifier 3 drives the servomotor 4 according to this input value. The work engaged with the ball screw moves as the servo motor 4 rotates, and a pulse generator (PG)
A feedback pulse P _B is output from 8. This feedback pulse is output to the deviation counter 2 and also to the controller 1 to be used for calculating the pitch error correction value.

When the integrated value P _{out of the} pulse output from the controller 1 to the deviation counter 2 is the command current position and the integrated value P _B of the feedback pulse is the actual current position, the deviation counter 2 outputs the command current position. The value obtained by subtracting the actual current position from the position will be output. Therefore, when the command current position and the actual current position match, that is, when the workpiece reaches the target position, the output of the deviation counter 2 becomes zero and the rotation of the motor 4 stops.

Next, the pitch error correction value in this embodiment will be described. Also in this embodiment, the user sets parameters for correcting the pitch error in the control device of the machine tool or the like prior to the operation of the machine tool or the like, as in the conventional example. That is, the user determines the start point P of the correction control range.
_S , the correction interval P _I , the stage number i and the correction amount data D _i are set prior to the operation of the machine.

When the above parameters are set,
The controller 1 shown in FIG. 1 creates the data table shown in Table 1 below by initial calculation.

[0021]

[Table 1]

In Table 1, the integrated value I _i is the correction start point P
It is the integrated value of the correction amount data from _S to stage i,
The increase rate T _i represents the increase rate of the correction amount data in stage i obtained by dividing the correction amount data D _i in stage i by the correction interval. The mutual relationship of these data is shown in FIG.

Based on the data table shown in Table 1, the controller 1 shown in FIG. 1 calculates and outputs a pitch error correction value by the procedure described below every time the current position management calculation of the work is performed.

FIG. 3 shows the movement of the work (when the motor is rotating).
3 is a flowchart showing a procedure in which the controller 1 calculates a pitch error correction value.

In step S1, the position (command current position) corresponding to the number of pulses P _out that the controller 1 has already output.
Is within the correction control range. Then, if the determination is negative, the process ends, and if the determination is positive, the process proceeds to step S2.

In step S2, the work moving distance L ₁ is calculated from the previous output pulse number and the current output pulse number.

In step S3, the moving distance L ₁ is compared with the correction interval P _I, and if L ₁ > P _I , the stage where the work was at the time of the previous calculation and the work at the time of this calculation Since it is different from a certain stage, the process proceeds to step S4 and the stage number at the time of this calculation is obtained from the command current position. If L ₁ ≤P _I in step S3, there is a possibility that the previous and current stages are the same, so the process proceeds to step S5 without updating the stage number.

In step S5, the stage number i of the stage where the workpiece is actually found is obtained using the integrated value P _B of the feedback pulses from the pulse generator (PG). In step S6, it is determined whether or not the stage number i obtained in step S5 matches the stage number of the previous step. If they match, the process proceeds to step S8, and if they do not match, the process proceeds to step S7. After updating the stage number to i obtained in step S5, the process proceeds to step S8.

In step S8, the pitch error correction value Δ is calculated by the following equation using the data table shown in Table 1 based on the stage number i at which the workpiece is currently located.

[0030]

## EQU1 ## Δ = (P _B −P _i−1 ) × T _i + I _i−1 This pitch error correction value Δ is corrected at the position (P _B ) where the workpiece is currently located, as shown in FIG. Is a value,
It is a correction value obtained by the linear interpolation method.

As described above, in this embodiment, the pitch error correction value is calculated every time the current position management calculation is performed, and the value is added to the command pulse and output to the deviation counter. Therefore, the current position management calculation based on the integrated value of the command pulse number can be performed more easily than before.

FIG. 4 is a diagram showing a movement state of the work in this embodiment. As shown in FIG. 4, according to this embodiment, a correction value is output every time the current position management calculation is performed,
Since the rotation speed of the servo motor is controlled according to the pitch error, the work can be moved at a substantially constant speed. Further, since the correction is also performed at the intermediate position of the stage by using the linear interpolation method, the movement can be smoothly performed even when the work is moved minutely across the switching point of the stage.

[0033]

As described above, according to the present invention, the speed of a moving work can be made substantially constant, and the work can be carried out even when the work is moved a little while sandwiching the switching point of the stage. The smooth operation of the machine etc. can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control system according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining a mutual relationship of data according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure to be processed by the controller.

FIG. 4 is an explanatory diagram showing a movement state of a work in the machine according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining a conventional pitch error correction method.

FIG. 6 is an explanatory diagram for explaining a conventional pitch error correction method.

FIG. 7 is an explanatory diagram showing a movement state of a work in a machine according to a conventional pitch error correction method.

[Explanation of symbols]

 1 Controller 2 Deviation Counter 3 Motor Amplifier 4 Servo Motor 5 Pulse Generator

Claims (3)

[Claims] 1. A method of correcting a pitch error of a ball screw of a machine having a power transmission mechanism having a ball screw, wherein the ball screw is rotated by supplying a drive pulse to a servo motor to move a work engaged with the ball screw. In the above, the correction control range of the ball screw is divided into a plurality of sections from the correction start point at a predetermined correction interval, and the correction amount data obtained by converting the pitch error of the ball screw in the section into the drive pulse is divided into a plurality of sections. Set for each, measure the position of the work every predetermined time, calculate the pitch error correction amount according to the measured position of the work using the correction amount data, the calculated pitch Pitch error correction, characterized in that the drive pulse supplied to the servo motor is changed according to an error correction amount. Method. 2. The pitch error correction amount is a first pitch error obtained by adding all of the correction amount data corresponding to the section included between the correction start point and the measured workpiece position. The sum of the correction amount and the second pitch error correction amount calculated from the correction amount data of the section according to the distance from the start point of the section to which the measured work position belongs to the measured position of the work. The pitch error correction method according to claim 1, wherein: 3. The pitch error correction method according to claim 2, wherein the second pitch error correction amount is obtained by using a linear interpolation method.