JP3994378B2 - Numerical control device and pitch error correction method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a device for correcting a pitch error in a numerical control device having a control shaft driven by two motor drives, and a pitch error correcting method thereof.
[0002]
[Prior art]
FIG. 3 is a diagram illustrating a configuration example of a tandem control shaft in which a control shaft is driven by two motors in a conventional numerical control device for NC machine tools (hereinafter referred to as an NC device). Conventionally, as shown in FIG. 3, there are a servo drive and a motor for a master axis and a slave axis for one machine control axis that drives a driven object , respectively, and for each command position commanded from the NC unit, Independent position control is performed using servo drives, motors and encoders. The motors of the master shaft and the slave shaft are coupled to a ball screw, and the rotational motion of the motor is converted into a translational motion by the ball screw, and the drive target is driven. Further, the driving object moves while being supported by a guide rail called a linear guide.
[0003]
FIG. 4 is a block diagram showing an example of processing for pitch error correction of a conventional tandem control axis. Here, the pitch error is a machine position error due to the lead error of the ball screw used for the feed shaft, and the pitch error correction is a correction amount to the position command output from the NC device. This is a method of correcting by adding. Reference numeral 1 in FIG. 4 is an input device of an NC apparatus capable of setting a pitch error correction amount, and is used in common for the master axis and the slave axis. In the figure, 2 is an internal memory for storing the set pitch error correction amount, 3 in the figure is a calculation unit for calculating the pitch error correction amount at the current position from the set pitch error correction amount, and 4 in the figure is A superimposing unit that superimposes the pitch error correction amount output from the pitch error correction amount calculating unit 3 on the command position. Reference numeral 5 in the figure denotes a position control unit that controls the position of the motor based on the command position. These 2 to 5 exist in each of the master axis and the slave axis as shown in FIG.
[0004]
When the pitch error correction amount is set by the input device 1 of the NC device, the operator positions the machine at a plurality of measurement points (for example, measurement points 0 to 6) as shown in FIG. Measure the distance between the reflector and the mirror mounted on the instrument, and determine the difference (generally a length of several μm) between the command position of the NC unit and the measurement position of the laser measuring instrument. The correction amount. These values are set to the same values for the master axis and the slave axis by key input or the like in the pitch error correction amount input device 1 . Then, the set correction amount for each measurement point is stored in the pitch error correction amount setting memory 2 . The pitch error correction amount calculation unit 3 calculates the pitch error correction amount at each command position for each interpolation period from the pitch error correction amount at the measurement point near the current position stored in the pitch error correction amount setting memory 2 . As a calculation method thereof, there is a method of obtaining a pitch error correction value that is linearly approximated based on a pitch error correction amount at a pitch error measurement point before and after the command position of the NC device at that time. For example, the pitch error correction amount _{P x} at position _{p x} of a point between the measuring points 1 and measurement point 2, the position and pitch error correction amount set value at the measurement point 1 and measurement point 2, respectively p _{1, p 2} , P ₁ and P ₂ , they are represented by the following formulas.
[0005]
_{P x = P 1 + (P} 2 -P 1) * (p x -p 1) / (p 2 -p 1)
Further, the pitch error correction amount superimposing unit 4 adds the pitch error correction amount at each command position for each interpolation cycle calculated by the pitch error correction amount calculation unit 3 to the command position for each interpolation cycle output from the command creation unit. Then, the command position after the pitch error correction is created and output to the position controller 5 . The position control unit 5 operates the servo motor while controlling the position of the servo motor at the command position for each given interpolation cycle.
[0006]
In the case of a tandem control shaft, pitch error correction may be performed for the following purposes in addition to the above-described pitch error correction for correcting the lead error of the ball screw.
[0007]
For example, as shown in FIG. 6, when there is distortion in the mounting of the linear guide and there is an error in the parallelism of the linear guide, the driving body is in a non-energized state at a position where the interval between the linear guides is narrow. Compared with the state of the position of an appropriate space | interval, it will be in the distorted state. In FIG. 6, the left side of the linear guide of the slave axis is attached to the master axis linear guide so as to be inclined in the master axis direction, so that the distance between the master axis and the slave axis is narrow on the left side of FIG. 6. In this case, since the distance between the master axis and the slave axis becomes narrower as the drive target moves to the left side of FIG. 6, the drive target is slightly inclined with respect to the master axis at the position on the left side of FIG. It will be in the state where extra force is not applied to the guide. The difference between the stop position of the master axis and the slave axis due to the tilt of the drive target at this time is determined by assuming that the difference between the position of the master axis and the slave axis at the right end position in FIG. Increases as it moves to the left in FIG. That is, at the position on the left side of FIG. 6, the output data positions of the motor encoders of the master axis and the slave axis are shifted by −Δd and + Δd, respectively, with respect to the center between the linear guides with respect to the command position of the NC device. the value of the state and Do Ri Δd is driving the dynamic object is large enough to move to the left in FIG. 6. Such a shift in the position of Δd is detected by an encoder attached to a motor for detecting the positions of the master axis and the slave axis. In the non-energized state of the motor, as described above, the master axis position and the slave axis position are stopped with a deviation of −Δd and + Δd, respectively. However, in the energized state of the motor, the servo drive uses a motor that uses the encoder described above. Since position control works and Δd is not added to the command position from the NC unit, the servo drive controls each motor position so that Δd becomes 0 . Torque (hereinafter corrected torque ) is generated. This correction torque increases as the distortion Δd increases, and in some cases, the torque during acceleration / deceleration is insufficient.
[0008]
In order to eliminate such correction torque, the value of Δd (n) at each pitch error correction amount measurement position n (n = 0, 1,. -Δd (n) is added to the previously measured pitch error correction amount, and for the slave axis, + Δd (n) having the opposite sign to the master axis is added to the pitch error amount in the same manner. A position command that matches the amount of distortion at the measurement position n can be output from the NC device. Further, at a position deviated from the measurement position, the pitch error correction amount at the position is obtained and corrected by interpolation processing from the pitch error correction amount at the measurement position in the vicinity thereof. When such pitch error correction is performed, the command position from the NC device has a difference of 2Δd (n) , which is the difference in pitch error correction amount, between the master axis and the slave axis as shown in FIG. It becomes. Here, when 2Δd (n) is obtained, the first pitch error correction value of the master axis and the slave axis is set to the respective axes by the method introduced with reference to FIG. 5 and moved to the respective correction positions. Both are deenergized, and a value of 2Δd (n) can be obtained from the difference between the detected position of the encoder of the master axis and the detected position of the encoder of the slave axis.
[0009]
Thus, by adjusting and setting the pitch error correction amount according to the distortion amount at each measurement position, it is possible to prevent the correction torque described above from working.
[0010]
Thus, in the prior art, by setting different values for the pitch error correction amount in the NC device for each of the master axis and slave axis of the tandem control axis, the ball screw lead error and the like are corrected, and further machine distortion is caused. The resulting torque was also corrected.
[0011]
[Problems to be solved by the invention]
However, when the above-described pitch error correction is performed, if the axis moving perpendicular to the tandem control axis is configured on the tandem control axis, an error may occur in the position accuracy of the tandem control axis depending on the position of the orthogonal axis. May occur.
[0012]
FIG. 8 is a front view of a general machining center as an example, where the Y axis is a tandem control axis, the Y1 axis is the master axis, and the Y2 axis is the slave axis. In addition, an X axis is configured on the Y axis drive body, and a Z axis is mounted on the X axis, on which a main shaft to which a machining tool is attached is mounted.
[0013]
FIG. 9 is a plan view showing the configuration of the machine of FIG. 8 from above.
[0014]
In the machine shown in FIG. 8 and FIG. 9, when the pitch error is measured at the X-axis center position and the above-described pitch error correction is performed, when the main axis moves to a position away from the center on the X-axis, As shown in FIG. 9, the position in the Y-axis direction is shifted by Δe with respect to the center position due to the pitch error correction amount components set with different values for both axes of the tandem control axis.
[0015]
As described above, in the related art, when the axis that moves perpendicularly to the tandem control axis is configured on the tandem control axis, there is a problem that an error occurs in the position of the tandem control axis.
[0016]
The present invention is intended to solve such a conventional problem, and even when another axis different from the tandem control axis is configured, the pitch error of the tandem control axis caused by distortion of the tandem control axis. The pitch error amount of the tandem control axis is corrected by the position of another axis different from the tandem control axis, improving the position accuracy of the tandem control axis and using the appropriate torque for the tandem control axis. The purpose is to control.
[0017]
[Means for Solving the Problems]
In the present invention, in order to solve the above-mentioned problem, the current position of another axis different from the tandem axis is considered with respect to the first pitch error correction amount of the tandem control axis set by the conventional method, A second pitch error correction amount is calculated from the position of the axis at that time and the first pitch error correction amount, and is superimposed on the first pitch error correction amount to correct the pitch error.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a processing example of pitch error correction of a tandem control axis in the NC device of the present invention. Here, reference numeral 1 in the figure denotes an input device of the NC device that can set the first pitch error correction amount, and is used in common for the master axis and the slave axis.
In the figure, 2 is an internal memory for storing the first set pitch error correction amount, and 3 in the figure is the first pitch error at each command position for each interpolation period from the set first pitch error correction amount. A calculation unit for calculating the pitch error correction amount, 7 in the figure is a superimposition unit that superimposes the pitch error correction amount on the command position, and 5 in the figure is a position control unit. Here, the first pitch error correction amount represents a conventional pitch error correction amount, and therefore the first pitch error correction amount input device 1 and the first pitch error correction amount setting memory in the figure. 2. The first pitch error correction amount calculation unit 3 and the position control unit 5 are equivalent to the prior art, and function independently on both axes (master axis and slave axis) of the tandem control axis. Reference numeral 7 in the figure is the same function as the conventional pitch error correction amount superimposing unit 4 , but differs from the conventional one in that a second pitch error correction amount described later is also superimposed.
[0019]
In this processing example of the present invention, from the current command position of the axis orthogonal to the tandem control axis and the first pitch error correction amount of each of the master axis and slave axis of the tandem control axis, based second joined by calculating unit 6 for obtaining a pitch error correction amount, the second pitch error correction amount determined by the calculation unit 6, to both axes of the tandem control axis, the pitch error correction amount in the figure 7 The superimposition unit adds the first pitch error correction amount to the command position for each interpolation cycle to the command position for each interpolation cycle output from the command position creation unit, and outputs the command position after pitch error correction. The
[0020]
Here, a calculation formula for obtaining the second pitch error correction amount of the tandem control shaft of the present invention is given by the following formula.
[0021]
P2 = ((P1M-P1S) / 2) * X / L (Formula 1)
here,
P2: Second pitch error correction amount P1M: First pitch error correction amount of the master axis (ball screw lead error -Δd)
P1S: First pitch error correction amount of the slave axis (ball screw lead error + Δd)
L: Distance between master axis and slave axis X: Position of the main axis on the X axis when the center of the master axis and slave axis is 0
[Delta] d: half the difference between the stop position of the master axis and the slave axis when the motor is not energized The second pitch error correction amount is obtained according to this calculation formula.
[0022]
The second pitch error correction amount obtained in this way is the same as the first pitch error correction amount in accordance with the first pitch error correction amount for each interpolation period and the position of the axis orthogonal to the tandem control axis. It is superimposed on the command position for each interpolation cycle. In this case, the second pitch error correction amount is set to the same value for both the master axis and the slave axis of the tandem control axis. In this way, as shown in FIG. 2, the position of the tandem control axis is set to + Δe by the second pitch error correction amount even when there is an error of −Δe as shown in FIG. Since it is corrected, it can be moved to the correct position.
[0023]
【The invention's effect】
As described above, according to the present invention, even when the machine has a tandem control axis and another axis different from the tandem control axis is configured, the tandem control axis is caused by distortion of the tandem control axis. The pitch error amount of the tandem control axis can be corrected by the position of another axis different from the tandem control axis and the position accuracy of the tandem control axis can be improved. The tandem control axis can be controlled by torque.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of pitch error correction processing for a tandem control axis according to the present invention. FIG. 2 is an example of correction for a position error of a tandem control axis according to the present invention. 4 is a block diagram of pitch error correction of a conventional tandem control axis. FIG. 5 is a block diagram of pitch error measuring means. FIG. 6 is an example of distortion and position error of a linear guide of a tandem control axis. Example of correcting linear guide distortion of shaft [Fig. 8] Front view of machining center having tandem control axis as an example [Fig. 9] Example of error due to position of axis orthogonal to tandem control axis [Explanation of symbols]
1 (first) pitch error correction amount input device
2 (First) pitch error correction amount setting memory
3 (First) pitch error correction calculator
4 Conventional pitch error correction amount superposition unit
5 position controller
6 Second pitch error correction amount calculation unit of the present invention
7 Pitch error correction amount superimposing unit of the present invention

Claims (2)

First pitch error correction for correcting a pitch error of different values for command positions to two motors in a numerical control device having a tandem control shaft that drives one control axis of a machine with two motors And an X-axis orthogonal to the tandem control axis, and when the first pitch error correction of the tandem control axis causes an error due to the influence of the X-axis position, the X-axis position at that time is considered. And a second pitch error correction means for superimposing a second pitch error correction amount on the command positions for the two motors of the tandem control shaft, and the second pitch error correction amount is calculated by the following formula: Numeric controller to give.
P2 = ((P1M-P1S) / 2) * X / L
here,
P2: Second pitch error correction amount P1M: Master shaft first pitch error correction amount (ball screw lead error -Δd)
P1S: Slave axis first pitch error correction amount (ball screw lead error + Δd)
L: Distance between master axis and slave axis X: Position of X axis when the center of master axis and slave axis is 0
Δd: half the difference between the stop position of the master axis and slave axis when the motor is de-energized In a pitch error correction method for a numerical control apparatus having a tandem control shaft that drives one control axis of a machine with two motors, first pitch error corrections having different values with respect to command positions to the two motors was carried out, the has an X-axis orthogonal to the tandem control shaft, when producing the first error in the pitch error correction of the tandem control axis under the influence of the position of the X-axis, taking into account the position of the X-axis at that time A pitch error correction method for a numerical controller that gives a second pitch error correction amount to the command positions for the two motors of the tandem control shaft by the following calculation formula.
P2 = ((P1M-P1S) / 2) * X / L
here,
P2: Second pitch error correction amount P1M: Master shaft first pitch error correction amount (ball screw lead error -Δd)
P1S: Slave axis first pitch error correction amount (ball screw lead error + Δd)
L: Distance between master axis and slave axis X: Position of X axis when the center of master axis and slave axis is 0
Δd: half the difference between the stop position of the master axis and slave axis when the motor is de-energized

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