JP2011076640A - Method for controlling numerical value - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the same processing result as in the case of no error even at the time when there is an installation error between the position of a workpiece assumed by a processing program and the position of an actually installed workpiece to change the installation error every moment by rotating the workpiece during processing. <P>SOLUTION: Interpolation is performed with a coordinate value before performing error correction, and error correction is performed to a position after determined interpolation by interpolation point. Interpolation is performed such that a speed becomes the same as a relative speed when a relative speed between work and a tool has no error. When, as a result, an actual machine speed exceeds a clamp speed, the relative speed between the work and the tool is adjusted so as not to exceed the speed, preventing the relative speed from changing in the middle of a block. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a numerical control (hereinafter referred to as NC) apparatus, and relates to a numerical control method capable of obtaining a machining result similar to that when there is no error even when there is an error in setting a workpiece.

  When a workpiece is mounted and fixed on a machine tool, the workpiece may be mounted with a deviation from a position where it should be originally mounted, resulting in an installation error. That is, there is a difference between the installation position of the workpiece assumed in the machining program and the position of the workpiece actually attached. When a deviation occurs, at least one of translational movement errors Δx, Δy, Δz in the X, Y, and Z axis directions and rotational direction errors Δa, Δb, Δc about the X, Y, and Z axes occurs.

  In a three-axis machine tool that does not have a rotation axis, the rotation angle of the workpiece does not change during machining, and the installation error does not change due to rotation. Therefore, by using the workpiece offset setting and the three-dimensional coordinate conversion function, Installation error can be corrected.

  However, in simultaneous 5-axis machining in which the rotation angle of the workpiece changes during machining, the installation error cannot be corrected by the above method because the direction of the installation error changes due to the rotation of the workpiece. Patent Document 1 proposes a method for correcting an installation error in such simultaneous 5-axis machining.

JP 7-299697 A

  Patent Document 1 describes a method for correcting simultaneous 5-axis translation errors Δx, Δy, Δz, and rotation errors Δa, Δb, Δc. However, since Patent Document 1 only corrects the block end point of the machining program, correction of the path in the middle of machining, that is, each interpolation point in the block is not guaranteed. If the line segment length of one block is made as short as possible, the machining shape error will be reduced to some extent, but since it cannot be commanded below the minimum command unit that can be analyzed by the NC, machining with exactly the same machining as when there is no installation error is possible. This is not sufficient for the original purpose of error correction. Furthermore, the method of Patent Document 1 has a problem that the size of the machining program becomes very large.

  In addition, since the command speed of the machining program is originally the machine movement speed when there is no installation error, even if the movement after error correction is operated at the command speed as in Patent Document 1, the relative speed of the tool with respect to the workpiece. The speed is different from the speed assumed in the machining program, and as a result, there is a problem that the machining accuracy is deteriorated such as a roughened machining surface.

  The present invention has been made in view of the above, and in the case where there is a translational movement error and a rotational direction error between the position of the workpiece assumed in the machining program and the position of the workpiece actually attached, Even when the direction of the installation error changes every moment due to the rotation of the workpiece, the same workpiece can be obtained as when there is no error, and the relative speed of the tool with respect to the workpiece has no installation error. The purpose is to obtain a numerical control method capable of realizing the same speed.

  In order to solve the above-described problems and achieve the object, the NC device according to the present invention has three orthogonal movement axes and two rotation axes rotatable around the two movement axes in accordance with a machining program. In a numerical control method for machining a workpiece by driving a machine tool, it is orthogonal to the translational error in three orthogonal directions, which is the installation error between the workpiece position specified in the machining program and the actual workpiece mounting position. An installation error storing step for storing rotational direction errors around three axes, an interpolation processing step for interpolating a processing command for each block given by the processing program on the assumption that there is no translational movement error and rotational direction error, and the interpolation The coordinate position used in the interpolation processing is converted from the coordinate system used in the interpolation processing to an intermediate coordinate system in which the coordinate system used in the interpolation processing is rotated according to the rotation of the rotation axis. A first coordinate processing stage for executing processing for each interpolation point, and processing for correcting the error of the position of the interpolation point converted into the intermediate coordinate system using the stored translational error and rotational direction error for each interpolation point. And a second coordinate processing stage for executing processing for converting the position after error correction into a position in the machine coordinate system for each interpolation point, and output to the second coordinate processing stage. Based on this, the movement amounts of three orthogonal movement axes and rotation axes are obtained.

  According to the present invention, even when the direction of the installation error changes every moment due to the rotation of the workpiece (work) during machining, the error that has changed at each interpolation point is calculated and corrected. Thus, error correction is performed on the intermediate path, and even when there is a workpiece installation error, the same processing result as when there is no error can be obtained. Further, since the relative speed between the workpiece and the tool can be controlled at the same speed as when there is no installation error, the same processing accuracy as when there is no error can be maintained.

It is a conceptual diagram which shows an example of the 5-axis machine tool to which this invention is applied. It is a block diagram which shows the structure of a numerical control apparatus. It is a figure which shows the incorrect installation of a workpiece | work. 3 is a flowchart illustrating an entire operation procedure according to the first embodiment. 3 is a flowchart illustrating an error correction process in the operation procedure according to the first embodiment. It is a figure for demonstrating conversion from a machine coordinate system to a table coordinate system. It is a figure for demonstrating the installation error correction | amendment in a table coordinate system. 10 is a flowchart showing the entire operation procedure of the second embodiment.

  Embodiments of a numerical control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
Hereinafter, the first embodiment of the present invention is arranged on the side of the tool 22 that rotates around the Y axis in addition to the three movement axes (three orthogonal axes) of the X axis, the Y axis, and the Z axis as shown in FIG. Applicable to a mixed type 5-axis processing machine that has a B-axis that is a rotation axis and a C-axis that is a rotation axis on the side of the processing table 21 that rotates around the Z-axis and that processes a workpiece (workpiece) 23 on the table The case will be described. The present invention can also be applied to a 5-axis machine in which there are two rotation axes on the tool side and two rotation axes on the workpiece side.

  FIG. 2 is a block diagram showing the configuration of the NC device 1 according to the first embodiment of the present invention. The NC device 1 reads the machining program 2 and analyzes it, and the machining command described in the machining program. That is, the interpolation processing unit 12 that performs an interpolation process for decomposing a movement command from the block start point to the block end point into a movement command for each axis per interpolation cycle, and table coordinates in which the interpolated position is fixed to a table as an intermediate coordinate system Installation error amount measured by the first coordinate conversion unit 13 and the installation error measurement unit 4 (translation errors Δx, Δy, Δz in the X, Y, and Z axis directions, and around the X, Y, and Z axes) Of the rotation direction error Δa, Δb, Δc), and an error correction unit that corrects the installation error in the table coordinate system based on the installation error amount stored in the storage memory 18 5. Second coordinate conversion unit 16 that converts the corrected position of the table coordinate system into the machine coordinate system, and calculates the movement amount of each moving axis and rotating axis based on the converted position of the machine coordinate system, A movement amount output unit 17 that outputs a movement amount to a plurality of servo amplifiers 3 as drive units that drive the rotation shaft is provided. In the installation error measuring unit 4, when the workpiece is placed on the table, the installation error amount (translation movement errors Δx, Δy, Δz in the X, Y, Z axis directions and around the X, Y, Z axes). Rotation direction errors Δa, Δb, Δc) are measured, and the measured values are input to the memory 18. Although not shown, the positions of the respective movement axes (X axis, Y axis, Z axis) and the respective rotation axes (B axis, C axis) are detected and input to the NC apparatus 1.

  For example, as shown in FIG. 3, when the actual work 23 is attached with a deviation from the work attachment position A indicated by the broken line, the translational movement error Δx in the X-axis direction, the translational movement error Δy in the Y-axis direction, Further, an error of rotation direction error Δc around the Z axis occurs. Although FIG. 3 describes only errors on the XY plane for the sake of clarity, in reality, errors in the directions of the X, Y, and Z axes and around the respective axes occur. The translational movement errors Δx, Δy, Δz in the Y and Z axis directions and the rotation direction errors Δa, Δb, Δc around the X, Y, and Z axes are given.

  FIG. 4 is a flowchart showing the processing procedure of the first embodiment. First, the data of the first block of the machining program 2 is analyzed by the program analysis unit 11 (step S101), and the data of the analyzed block is interpolated by the interpolation processing unit 12 (step S102). In this interpolation processing, the movement command from the block start point to the block end point is decomposed into movement commands for each axis and at the same time, it is decomposed into movement commands to a plurality of interpolation points per interpolation cycle. Specifically, in this interpolation process, the position of the interpolation point next to the current position is obtained. In conventional error correction, first, installation error correction is performed at the start point and end point of the command block, and interpolation is performed between the start point and end point after installation error correction. In the first embodiment, correction of the installation error is performed before interpolation. And interpolation is performed assuming that there is no installation error. In this interpolation process, interpolation is performed at the command speed of the program with respect to the block start point and end point before error correction. That is, in this interpolation process, the interpolation process is performed at the moving speed specified by the machining program.

  Next, installation error correction processing is executed for the position after the interpolation (step S103). The installation error correction process will be described in detail later. Next, it is determined whether the interpolation processing in step S102 and the correction processing in step S103 have been executed up to the block end point of the block (step S104). If the determination is NO, the interpolation processing in step S102 and the processing in step S103 are performed. The correction process is repeated until the end point of the block. When the correction processing up to the block end point of the block is completed, it is determined whether or not there is data for the next block (step S105). If there is data for the next block, the procedure proceeds to step S101, and step The same procedure is repeated from S101. In this way, the processes in steps S101 to S103 are executed for all blocks.

  Next, the installation error correction process performed in step S103 will be described with reference to FIG. First, the first coordinate conversion unit 13 converts the position of the XYZ axes after interpolation (interpolation point next to the current position) from the machine coordinate system 42 to the table coordinate system 44 (step S110). As shown in FIG. 6, the machine coordinate system 42 is a fixed coordinate system that does not change due to the rotation of the table 21, and the machining program is created on the assumption that the workpiece rotates due to the rotation of the table 21. The table coordinate system 44 is a coordinate system as a result of the machine coordinate system 42 being fixed to the table 21 and the machine coordinate system 42 being rotated in conjunction with the rotation of the table 21. The coordinate system rotation matrix for rotating the machine coordinate system 42 around the C axis by θ degrees is Rc (θ), and the position of the C axis (table) rotation center viewed from the origin O of the machine coordinate system 42 is P0. The position of an arbitrary point 43 at P is P, and the position of the point 43 viewed from the table coordinate system 44 when the C axis is rotated by θ is * P.

The position * P of the point 43 as viewed from the table coordinate system 44 when the C-axis is rotated by θ is a vector Rc obtained by rotating the vector (P-P0) in the machine coordinate system 42 by −θ around the rotation center P0. This is equivalent to the position * P ′ when the point 43 ′ as a result of adding the vector P 0 to (−θ) · (P−P 0) is viewed from the machine coordinate system 42.
Therefore,
* P = Rc (−θ) · (P−P0) + P0 (1)
It can be expressed as.

Thus, the position of the XYZ axes in the machine coordinate system after interpolation is Pt (Xt, Yt, Zt), the position of the rotation axis B at that time is Bt, the position of the rotation axis C is Ct, and the position Pt is the table coordinate system. If the position converted into * Pt (Xb, Yb, Zb),
* Pt = Rc (-Ct). (P-P0) + P (2)
Can be calculated as

Next, a posture vector of the tool axis viewed from the table coordinate system is obtained from the angles of the rotation axes B and C. Since the tool axis orientation vector (tool orientation as viewed from the workpiece) when B = 0 and C = 0 is expressed as (0, 0, 1), the tool in the machine coordinate system at the position of the interpolation point Assuming that the axis orientation vector is rt (It, Jt, Kt), Jt as the Y component becomes zero from the position Bt of the rotation axis B rotating around the Y axis.
It = sin (Bt)
Jt = 0
Kt = cos (Bt)
It becomes.

Assuming that a vector obtained by converting this into a table coordinate system is * rt (Ib, Jb, Kb), a posture vector * rt (Ib, Jb, Kb) of the tool axis viewed from the table coordinate system is
Ib = cos (Ct) * It-sin (Ct) * Jt
= Cos (Ct) · sin (Bt) (3)
Jb = sin (Ct) · It + cos (Ct) · Jt
= Sin (Ct) · sin (Bt) (4)
Kb = Kt
= Cos (Bt) (5)
Can be calculated.

  Returning to FIG. 5, in step S111, error correction is performed on the table coordinate system. FIG. 7 shows an example in which there is an installation error between the original work position 51 (work position specified in the machining program) and the actual work position 52. A coordinate system corresponding to the original workpiece position 51 is called a machine installation coordinate system 53, and a coordinate system corresponding to the actual workpiece position 52 is called a workpiece installation coordinate system 54. When the position of the origin 55 of the workpiece installation coordinate system 54 viewed from the machine installation coordinate system 53 is PA, PA = (Δx, Δy, Δz). Δx, Δy, and Δz are translational movement errors in the X, Y, and Z axis directions stored in the memory 18 as described above.

  Here, the coordinate value of the position * Pt of the interpolation point 43 in the table coordinate system 44 in the table coordinate system 44 when the C-axis obtained in accordance with the above equation (2) is rotated by Ct degrees is set to the workpiece after the C-axis is rotated by Ct degrees. The position * Pt1 of the point 59 in the coordinate system 57 is considered, and the position * Pt1 is converted into a position * pt2 viewed from the table coordinate system 44. That is, it is assumed that the actual workpiece position 52 that has been misplaced is the original workpiece position 51, and in the workpiece placement coordinate system 54 that is set corresponding to the original workpiece position 51, the C axis is Ct degrees. The position * Pt1 of the point 59 having the same coordinate value as the coordinate value of the position * Pt of the interpolation point 43 in the table coordinate system 44 when rotated is converted into the position * pt2 as viewed from the table coordinate system 44. In other words, * Pt = * Pt1.

This conversion is: * Pt2 = RA · Pt1 + PA (6)
It can be expressed as. RA is a coordinate transformation matrix for rotating the table coordinate system 44 by Δa around the X axis, Δb around the Y axis, and Δc around the Z axis. Δa, Δb, and Δc are rotation errors about the X, Y, and Z axes between the machine coordinate system and the workpiece installation coordinate system, and are stored in the memory 18 as described above. The conversion process shown in Expression (6) is executed by the error correction unit 15.

  Further, the error correction unit 15 converts the tool axis attitude vector * rt (Ib, Jb, Kb) from the table coordinate system obtained by the above equations (3) to (5) into rotation errors Δa, Δb, It is rotated by Δc, and error correction in the rotation direction is performed. The process as described above is performed by the error correction unit 15 in step S111.

  Next, in step S112, the second coordinate conversion unit 16 converts the position of the table coordinate system after the error correction into the position in the machine coordinate system 42 before the rotation. That is, first, the rotation axis angle in the machine coordinate system is obtained from the tool posture vector in the table coordinate system in which the error correction in the rotation direction is performed. The rotation axis angle is calculated by performing the inverse transformation of the tool posture vector calculation described in the equations (3) to (5). The angle calculated in this way becomes the rotation axis angle after error correction. Further, the XYZ axis coordinate value of the machine coordinate system is obtained using this rotation axis angle. This conversion is also realized by performing the inverse conversion of the table coordinate value calculation described in Expression (2). The coordinate value obtained in this way becomes the interpolation point position in the machine coordinate system after error correction.

  Finally, in step S106, the movement amount output unit 17 obtains the difference between the interpolation point position after error correction and the current position, and outputs the obtained difference value to the servo amplifier 3 as the movement amount in the machine coordinate system.

  According to the first embodiment, the interpolation is performed without correcting the installation error, and the installation error is corrected every time the position after the interpolation is performed. Even when the direction of the position changes every moment, the midway path of each block is also corrected, and there is an effect that even if there is an installation error, a workpiece with exactly the same shape accuracy as when there is no error is obtained. . In addition, by performing interpolation at the program command speed for the block start point and end point before error correction, the relative speed of the tool with respect to the workpiece becomes the same speed as when there is no error, so the accuracy of the machining surface is set. The same as in the case of no error.

  In the case of a 5-axis machine tool having two rotation axes on the table side, coordinate conversion is performed in Formula (2), taking into consideration the rotation of another rotation axis. In other words, the machine coordinate system is rotated in accordance with the rotation of one or two rotation axes on the table side to obtain a table coordinate system as an intermediate coordinate system. Further, when there are two rotation axes on the tool side, the coordinate conversion of the equation (2) is performed with the angle of the rotation axis set to 0 degree.

Embodiment 2. FIG.
In the first embodiment, since the interpolation is performed so that the relative speed between the workpiece and the tool matches the command speed of the machining program, the actual machine speed may exceed the clamp speed. If the final moving speed of the machine is simply clamped, the relative speed of the tool with respect to the workpiece changes during the block, which is not preferable in terms of machining accuracy. Therefore, in the second embodiment, the relative speed between the workpiece and the tool is adjusted so as not to exceed the clamping speed. FIG. 8 is a flowchart showing an operation procedure according to the second embodiment. In FIG. 8, the processes in steps S201 to S210 are executed for each interpolation point, that is, every interpolation, as in the first embodiment.

  First, the machining program is analyzed in step S200, and interpolation is performed at the command speed F0 of the machining program in step S201. In step S202, coordinate conversion / error correction is performed on the obtained interpolation point, and in step S203, conversion to the machine coordinate system is performed again, and a movement amount in the machine coordinate system is obtained. The processes in steps S201 to S203 described above are the same as those described in the first embodiment, and the program analysis unit 11, the interpolation processing unit 12, the first coordinate conversion unit 13, the error correction unit 15, and the second coordinate. This is performed by the conversion unit 16 and the movement amount output unit 17.

  Next, in step S204, the movement amount output unit 17 calculates a movement speed F1 in the machine coordinate system from the movement amount in the machine coordinate system. In step S205, the moving speed F1 in the machine coordinate system is compared with the clamping speed Fmax. In the case of F1 ≦ Fmax, the clamp speed is not exceeded, so the movement amount obtained in step S203 is output as it is in step S210.

  When the movement speed F1 in the machine coordinate system exceeds the clamp speed Fmax, the movement amount output unit 17 does not exceed the clamp speed even if converted to the machine coordinate system according to F2 = F0 × (Fmax / F1). A moving speed F2 is obtained (step S206). Then, the movement amount output unit 17 outputs the obtained movement speed F2 to the interpolation processing unit 12.

  Next, in step S208 again, the interpolation processing unit 12 performs interpolation processing at the new moving speed F2, and in step S208, the first coordinate conversion unit 13 and the error correction unit 15 perform the same coordinate conversion and error correction as described above. In step S209, the second coordinate conversion unit 16 converts the machine coordinate system to obtain the movement amount of the machine coordinate system.

  Since the movement amount obtained in step S209 is guaranteed not to exceed the clamping speed Fmax, the movement amount output unit 17 does not perform the comparison with the clamping speed again, and the movement amount output unit 17 uses the movement amount obtained in step S209 as it is. Output to servo amplifier 3.

  As described above, in the second embodiment, as a result of performing the interpolation so that the relative speed between the workpiece and the tool matches the command speed of the machining program, the clamp speed exceeds the clamp speed even when the actual machine speed exceeds the clamp speed. By adjusting the relative speed between the workpiece and the tool so that the relative speed of the tool with respect to the workpiece becomes constant in the middle of the block, the machining accuracy can be maintained.

  As described above, the numerical control method according to the present invention is useful for a 5-axis machine tool having three orthogonal movement axes and two rotation axes rotatable around the two movement axes.

DESCRIPTION OF SYMBOLS 1 NC apparatus 2 Processing program 3 Servo amplifier 4 Installation error measurement part 11 Program analysis part 12 Interpolation processing part 13 1st coordinate conversion part 15 Error correction part 16 2nd coordinate conversion part 17 Movement amount output part 18 Memory 21 Processing table 22 Tool 23 Workpiece 42 Machine coordinate system 44 Table coordinate system 53 Machine installation coordinate system 54 Workpiece installation coordinate system

Claims (4)

In a numerical control method for machining a workpiece by driving a machine tool having three orthogonal movement axes and two rotation axes rotatable around the two movement axes in accordance with a machining program.
An installation error storage step for storing a translational movement error in the orthogonal three-axis direction, which is an installation error between the position of the workpiece specified by the processing program and the actual attachment position of the workpiece, and a rotational direction error around the three orthogonal axes;
An interpolation process step for interpolating the processing command for each block given by the processing program as having no translational movement error and rotational direction error;
A process of converting the interpolated position from the coordinate system used in the interpolation process to an intermediate coordinate system obtained by rotating the coordinate system used in the interpolation process according to the rotation of the rotation axis is executed for each interpolation point. A first coordinate processing stage;
An error correction stage for executing, for each interpolation point, processing for correcting the position of the interpolation point converted into the intermediate coordinate system using the stored translational movement error and rotation direction error;
A second coordinate processing stage for executing processing for converting the position after error correction into the position of the machine coordinate system for each interpolation point,
A numerical control method, comprising: obtaining movement amounts of three orthogonal movement axes and rotation axes based on an output of a second coordinate processing stage. In the first coordinate processing stage, a posture vector of the tool axis in the intermediate coordinate system is obtained based on the position of the rotation axis,
In the error correction stage, the tool axis posture vector in the intermediate coordinate system is rotated by the rotation direction error stored in the installation error storage stage, and the error in the rotation direction is corrected,
In the second coordinate processing stage, the angle of each rotation axis after error correction in the machine coordinate system is obtained from the attitude vector of the tool axis in the intermediate coordinate system in which the error correction in the rotation direction has been performed, The numerical control method according to claim 1, wherein the position of the machine coordinate system is obtained using an angle.   The numerical control method according to claim 1, wherein the interpolation process is performed at a moving speed specified by a machining program. When determining the movement amounts of the three orthogonal movement axes and the rotation axis based on the output of the second coordinate processing stage, the movement amount in the machine coordinate system is obtained according to the position of the machine coordinate system, and based on the movement amount Obtain the moving speed in the machine coordinate system, and if this moving speed exceeds the clamping speed, correct the moving speed so that it does not exceed the clamping speed.
Re-execute the interpolation process in the interpolation process step using the corrected moving speed,
Re-execute the conversion process to the intermediate coordinate system in the first coordinate processing stage using the re-executed interpolation process result,
Re-execute the error correction process in the error correction step using the re-executed conversion result to the intermediate coordinate system,
Re-execute the conversion process to the machine coordinate system in the second coordinate processing stage using the re-executed error correction process,
4. The numerical control method according to claim 3, wherein the movement amounts of the three orthogonal movement axes and rotation axes are obtained again using the re-executed conversion result to the machine coordinate system.

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