JPH04307603A - Pitch error correcting method - Google Patents

Abstract

PURPOSE:To accurately correct the pitch error that is produced when the position of a driven object is controlled via a speed changing mechanism by eliminating the accumulation of rounding errors at the correcting point of the pitch error. CONSTITUTION:The quotient of the integer value obtained by dividing the pulse number corresponding to the reference shift value and a corrected distance D measured at the side of a rotary table 1 by a speed changing ratio N and the fraction remainder are defined as the reference positions of the table 1 respectively. Thus the correction data on a pitch error are set by a parameter at the side of a numerical controller 4. As a result, the pitch error can be corrected with high accuracy with a servo motor 3 when the position of the table 1 is controlled via a reduction gear 2.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a pitch error correction method for correcting pitch errors occurring in the mechanical position of a driven object.
In particular, the present invention relates to a pitch error correction method that can accurately correct the pitch error even when the gear ratio of the reduction gear takes an odd value with respect to the reference movement amount set on the driven object side.

0002

[Prior Art] Conventionally, when a numerical control unit (CNC) controls the motion of tools, work tables, etc. and causes a machine tool to perform machining of a programmed shape, the rotational force of a servo motor is transmitted through some kind of speed change mechanism. is transmitted to the driven object. By the way, pitch error correction has conventionally been performed when controlling machine tools that require highly accurate machining, such as hobbing machines.

[0003] When correcting pitch errors in a hobbing machine connected to a numerical control device, one
The number of pulses corresponding to the amount of movement per rotation and the number of correction points or correction intervals are set. Now, for example, correction value data is set on the rotating shaft of a hobbing machine with a detection accuracy of 360,000 pulses per rotation, and the pitch error correction is performed at 6 points per rotation on the servo motor side that drives this rotating shaft. shall be taken as a thing. If the reduction ratio between the servo motor and the rotating shaft is 20:1, the correction point may be set every 360000/20/6=3000 pulses on the servo motor side. Therefore, the operator sets the pitch error from the measured value of the command value corresponding to each machine position in advance in the numerical control device, and then automatically adjusts the pitch error when the program is executed based on the set value and the feedback pulse of the servo motor. Pitch error correction is performed.

0004

[Problem to be Solved by the Invention] However, since the above-mentioned reduction ratio is changed depending on the transmission mechanism that transmits the driving force of the servo motor to the rotating shaft, depending on the type of machine tool, the numerical control device side Depending on the set detection accuracy, an odd reduction ratio may be used. Here, an odd reduction ratio is a case where the number of pulses for designating the correction point to be set on the servo motor side is set to a value that is not an integer value, such as 35:1. In this case, even if the correction point is accurately determined by counting the number of unit pulses on the servo motor side, the actual position of the rotating shaft is not determined by an integer value, so the correct correction position cannot be determined. The error regarding this corrected position will not be eliminated unless it returns to the origin, and will accumulate as the servo motor rotates.

The present invention has been made in view of these points, and it is an object of the present invention to correct pitch errors that occur when controlling the position of a driven object through a transmission mechanism by eliminating the accumulation of rounding errors at correction points. It is an object of the present invention to provide a pitch error correction method that allows accurate correction.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a correction command pulse to the drive means based on preset error correction data, so that the target is numerically controlled via the transmission mechanism. In a pitch error correction method for correcting a pitch error occurring in the position of a driven object, the error is calculated based on the number of pulses corresponding to a reference position set on the driven object side and a correction interval set on the driving means side. In setting the correction data, the speed ratio N of the transmission mechanism and the value obtained by multiplying the correction interval by N are stored, and when giving a movement command to the drive means to numerically control the driven object, the movement command is divide the number of pulses corresponding to the gear ratio N, divide the reference position by the gear ratio N, and compare the integer and fractional parts of these quotients to determine the current state of the driven object relative to the reference position. Determine the relative distance to the driven object, divide the correction interval by the gear ratio N, and compare the integer and fractional parts of the quotient with the integer and fractional parts of the relative distance, respectively. A pitch error correction method is provided, characterized in that a correction point is determined and the error correction data set for each correction interval is output.

[0007]

[Operation] In the pitch error correction method of the present invention, the quotient of the integer value and the fractional remainder obtained by dividing the number of pulses corresponding to the reference movement amount L and the correction interval D on the driven object side by the gear ratio N are calculated on the driven object side. The pitch error correction data is set as a parameter using the reference position. The quotient of the integer part and the numerator of the fractional part can be processed as integer values inside the numerical control device, and the correction point M that outputs the pitch error correction pulse is similarly processed with the quotient Mi of the integer value and the numerator Mf, and the correction point M Coordinate values are determined.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a state in which a rotary table 1 and a servo motor 3 serving as its driving means are connected via a reduction gear 2. As shown in FIG. The servo motor 3 outputs a feedback pulse P corresponding to its rotation angle to the numerical control device 4, and the numerical control device 4 gives a position command to the rotary table 1. The rotary table 1 shall be numerically controlled by a servo motor 3 with an accuracy equivalent to 360,000 feedback pulses P per rotation, and the magnitude of the pitch error caused by the reduction gear 2 shall be measured in advance. . Here, the reduction gear 2 is adjusted according to the error correction data set as parameters in the numerical control device 4.
A method of correcting pitch errors for the rotary table 1 that is numerically controlled via the following will be described. Let us consider a case where the reduction ratio N of the reduction gear 2 is set to 35, and when the servo motor 3 rotates once, pitch error correction is performed at six equally spaced points (60°).

First, the numerical control device 4 is set to 3 as the reduction ratio N.
5. The number of pulses La corresponding to the amount of movement per one rotation of the rotary table 1 is 360,000, and the number of pulses Da corresponding to N times the pitch error correction interval is (La ÷ 3
5÷6)×35=60000 is set as a parameter. D
a is the correction interval set for the servo motor 3 with the reduction ratio N
Since it is multiplied, the magnitude is set based on the amount of one rotation on the rotary table 1 side, and no matter how odd the reduction ratio N is selected, it can always be set as an integer value.

In the numerical control device 4, these values La,
From Da, La/N and Da/N, which are converted into the number of pulses per revolution of the servo motor 3, are determined, but generally these pulse numbers do not become integer values. Therefore, inside the numerical control device 4, these values are set as parameters as two pairs of integer values (Li, Lf) and (Di, Df), respectively, according to the following equations.

[0011] L=La/N=Li+Lf/N

...(1) D=Da/N=Di+Df/N

...(2) Here, Li=10285, Lf=
25, Di=1714, and Df=10. Since the fractional part molecules Lf and Df correspond to the integer quotients Li and Di and the remainder part in this way, Lf and Df are determined to be integers in the range of 0 to N-1. When the servo motor 3 is actually rotated and the position data of the rotary table 1 is determined from the feedback pulse P, the numerical control device 4 similarly divides P by the reduction ratio N and calculates the pair of integer values (Pi ，
Pf). That is, the actual amount of rotation is Li=102
85, Lf=25, and the current position coordinates (Mi, Mf) of the rotary table 1 are updated. Position where pitch error correction amount should be given to servo motor 3 (Pi, Pf)
is similarly determined within the numerical control device 4 from the following equation.

P(j)=Pi(j)+Pf(j)/N
...(3)
Here, j is 1 to 6, and the current position coordinates (Mi, Mf
) matches any of these six sets [Pi(j), Pf(j)], a pulse based on the corresponding j-th error correction data is added to the command pulse and output to the servo motor 3. .

FIG. 2 is a flowchart showing the process performed by the numerical control device 4 when the return of the rotary table 1 to the origin is completed. FIG. 3 is a flowchart showing processing when setting parameters, and FIG. 4 is a flowchart showing processing after output pulse calculation. In the figure, the number following S is the step number. When the origin return command is detected, the completion of the origin return is monitored (step 11), and at the time of completion, the coordinate values for pitch error correction held in an internal register or the like are cleared (step 12). By returning to origin,
The current position coordinates (Mi, Mf) are cleared to (0, 0), and the correspondence between the internal state of the numerical control device 4 and the rotary table 1 is determined.

Thereafter, parameters are set for the position at which the pitch error correction pulse should be output (FIG. 3). That is, the data of the reduction ratio N of the reduction gear 2, the movement amount La per rotation for specifying the reference position of the rotary table 1, and the correction interval Da multiplied by N are read (step 21). Inside the numerical control device 4, the movement amount L and the correction interval D are divided into an integer part and a numerator part with N as the denominator, based on the above equations (1) and (2), and are divided into a pair of integer values (Li , Lf), (Di,
Df), and based on equation (3) above, n
Coordinates of the divided correction points [Pi (j), Pf (j)] (
j=1 to n) is determined (step 22). These internal data are used when setting the parameters of the error correction table (step 23).

Here, the subscripts i and f distinguish between the integer part and the fractional part of the quotient obtained by dividing the movement amount L and the correction interval D by the gear ratio N. Therefore, even if the reduction ratio N is an odd value,
The data always specifies the number of pulses as a pair of integer values, and the error in the position where the pitch error correction pulse is output can be suppressed to within one pulse per rotation angle of the servo motor 3. Therefore, it is possible to accurately specify the coordinate values at which the correction pulses for the machining program executed by the numerical control device 4 should be output.

On the other hand, in order to actually pass the pitch error correction data to the servo motor 3, it is necessary to convert the output pulse P into similar internally expressed data. Therefore, when giving a command to the servo motor 3 to numerically control the rotary table 1, the feedback pulse from the servo motor 3 is similarly divided by the gear ratio N, and a pair of integer values (Pi , Pf) (step 31). Next, this drive amount is rounded by the amount of movement corresponding to one rotation of the servo motor 3, that is, a pair of integer values (Li, Lf),
A relative distance M with respect to the reference position set in the error correction table is determined (step 32). The value of this relative distance M is similarly expressed internally by the integral and fractional parts of the quotient divided by the reduction ratio N, and is a value rounded by L/N for each revolution of the servo motor. Therefore, even when the reduction ratio N is an odd value, the rounding error is canceled out every rotation, so the error in the rotation angle to the current position expressed as the coordinate values (Mi, Mf) for pitch error correction is No matter how many times the servo motor rotates, it does not accumulate.

Next, in order to determine the timing to output the pitch error correction pulse, in step 33, the pitch error correction coordinate values (Mi, Mf) and the coordinates of the correction point divided into n [Pi(j), Pf(j)] (step 33). When it matches any correction point, the jth (
This is the timing for outputting the correction pulses of j=1 to n). That is, a pitch error correction pulse is output to the servo motor 3 based on the j-th pitch error correction data (
Step 34).

FIG. 5 is a block diagram of the hardware of a numerical control device used to implement the pitch error correction method of the present invention. The numerical control device is configured as a computer-type numerical control device, that is, CNC, and includes a CPU 11 configured by a microprocessor, a ROM 12 storing a system program, a RAM 13, and a machining program 1.
4a and a non-volatile memory 14 storing a pitch error correction correction table 14b for gear pitch error correction, and a CRT 15 that controls the display of a CRT 15 as a display device.
A control circuit 16 and a keyboard 1 into which user commands are input.
7 and an axis control circuit 18. Axis control circuit 18
is given a position command signal from the CPU 11, a signal regarding the rotational position of the servo motor 3 from the pulse coder 21 as a feedback signal, performs feedback calculation, and outputs a servo control command signal to the servo amplifier 19. . The servo amplifier 19 amplifies the servo control signal from the axis control circuit 18 and drives the servo motor 3 accordingly.

The servo motor 3 is coupled to the rotary table 1 at a reduction ratio N. That is, a small bevel gear 23 is attached to the output shaft 22 of the servo motor 3, and the small bevel gear 23 meshes with a large bevel gear 26 attached to the rotating shaft 25 of the rotary table 24. As a result, the rotation of the output shaft 22 of the servo motor 3 is controlled by the small bevel gear 23 and the large bevel gear 26.
The transmission is transmitted to the rotating shaft 25 by the engagement with the rotating shaft 25, and the rotary table 1 comes to rotate around the central axis of the rotating shaft 25. In numerical control equipment, non-volatile memory 1
Based on the pitch error correction value data stored in advance in 4.
A gear pitch error correction pulse is determined by software, and the small bevel gear 23 is sent from the CPU 11 to the shaft control circuit 18.
A position command signal is given to the servo motor 3 as a control signal after gear pitch error correction between the large bevel gear 26 and the large bevel gear 26. Note that these pitch error correction data are obtained in advance by precision measurement for each driven object of each machine.

In the above explanation, when pitch error correction is performed using a rotary table as a driven object, error correction data is set based on the number of pulses corresponding to the amount of movement per rotation of the rotary table. It can also be applied to pitch error correction of machine tools that include driven objects that move erratically.

[0021]

As explained above, in the present invention, the quotient of the integer value and the fractional remainder obtained by dividing the number of pulses corresponding to the reference movement amount L and correction interval D of the driven object side by the gear ratio N are calculated as follows: The configuration is such that pitch error correction data is set as a parameter using the reference position of the object. Therefore, the pitch error that occurs when controlling the position of the driven object via the transmission mechanism can be corrected with high accuracy by eliminating the accumulation of rounding errors at the correction point. That is, numerical control processing that requires highly accurate machining can be smoothly performed by transmitting the rotational force to the driven object via some kind of transmission mechanism.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a rotary table, a servo motor, etc. as its driving means for explaining an example of the method of the present invention.

FIG. 2 is a flowchart showing processing at the end of return to origin.

FIG. 3 is a flowchart showing processing when setting parameters.

FIG. 4 is a flowchart showing processing after calculation of output pulses.

FIG. 5 is a block diagram showing the hardware of the numerical control device.

[Explanation of symbols]

1 Rotary table 2 Reduction gear 3 Servo motor 4 Numerical control device

Claims (2)

[Claims] 1. A pitch error correction method that corrects a pitch error that occurs in the position of a driven object that is numerically controlled via a transmission mechanism by giving a correction command pulse to a driving means based on preset error correction data. In setting the error correction data based on the number of pulses corresponding to the reference position set on the driven object side and the correction interval set on the driving means side, the gear ratio N and the gear ratio N of the transmission mechanism are set. A value obtained by multiplying the correction interval by N is stored, and when giving a movement command to the driving means to numerically control the driven object, the number of pulses corresponding to the movement command is set as the speed ratio N.
divide the reference position by the gear ratio N, and compare the integer and fractional parts of these quotients to determine the relative distance from the reference position to the current position of the driven object, and Divide the correction interval by the speed ratio N, compare the integer part and fractional part of the quotient with the integer part and fractional part of the relative distance, respectively, to determine the correction point of the driven object, and calculate the correction point for each correction interval. A pitch error correction method characterized in that the error correction data set to . 2. The driven object is a rotary table connected to a servo motor via a speed reduction mechanism, and the driven object is configured to generate error correction data based on the number of pulses corresponding to the amount of movement per rotation of the rotary table. 2. The pitch error correction method according to claim 1, further comprising: setting a pitch error correction method.