JPWO2011010397A1 - Error correction method and machine tool - Google Patents

Abstract

In a machine tool that has a plurality of linear feed axes and a plurality of rotary feed axes so that the spindle and the work table can be moved relative to each other, the error between the spindle and the work table, including the position error and the attitude error Based on the error data storage means 25 stored as a map and the posture error, tool information, and workpiece information, a correction amount for correcting the movement command for the linear feed axis is calculated so that the tool does not cut the workpiece too much. Correction data calculation means 26.

Description

  The present invention relates to an error correction method and a machine tool for correcting an error of a machine tool having a plurality of linear feed shafts and a plurality of rotary feed shafts so that a main shaft and a work table are relatively movable.

In general, in a multi-axis machine tool having a plurality of linear feed axes and a plurality of rotary feed axes, when a plurality of rotary feed axes are moved in accordance with a movement command, the machine generates position and orientation errors. Is difficult to position at a predetermined position. For this reason, when highly accurate machining is performed, the movement command is corrected according to the position and orientation errors by various methods. A conventional technique of a machine tool that corrects position and orientation errors is disclosed in Patent Document 1.
In Patent Document 1, an error map including a position error and an attitude error related to a rotation angle of a rotary feed shaft at an arbitrary lattice point of a three-dimensional orthogonal coordinate system is used. It is described that the position error and the posture error are corrected. In the third to seventh lines of paragraph number 0026, the position error and the attitude error are described as follows: “The position error 35a is a three-dimensional coordinate value generated when the rotary feed axes A and C are positioned at predetermined positions. The posture error 35b is a relative posture error between the spindle head 4 and the work table 6, and the rotation feed axes A and C orthogonal to each other are positioned at a predetermined rotation angle. It is an error expressed by the tilt angle that sometimes occurs. "
In this prior art, by correcting the movement command according to the position error and the posture error, the tip point of the tool having a predetermined protrusion length can be accurately positioned at the target position. Here, the tip end point of the tool is a point existing on the axis of the rotary tool, and can be set as the ball center position of the ball end mill or the tip end position of the square end mill or the radius end mill. As described above, the tip point of the tool differs depending on the type of the rotating tool. Further, the tip point of the tool does not coincide with the processing point as the contact point between the cutting edge of the tool and the processing surface of the workpiece. In other words, there is a deviation between the tool tip point and the machining point. If machining is performed with the tool tip point as the reference point, overcutting may occur, or conversely, machining may be performed with a shallow depth of cut. There are things to do.

JP 2008-269316 A

  An object of the present invention is to provide an error correction method and a machine tool that do not cause excessive workpiece cutting when the machine has a posture error and the axis of the tool is tilted.

To achieve the above object, according to the present invention, in an error correction method for correcting an error of a machine tool, the error of the machine tool is stored as an error map of a position error and an attitude error, and tool information of a tool to be used is used. And workpiece information of the workpiece to be machined, and based on the position error and the posture error and the input tool information and workpiece information, to calculate the feed axis correction amount so as not to overcut the workpiece, An error correction method is provided that corrects a movement command with the calculated correction amount.
Further, according to the present invention, there is provided an error correction method in which the tool information includes a tool type and a tool diameter, and the workpiece information includes a machining depth of the workpiece.
Further, according to the present invention, a rotary tool having a bottom blade is used at a corner portion where the end surface and the outer peripheral surface intersect, and the bottom blade causes the bottom surface of the workpiece to be tilted by the tilt error due to the posture error. An error correction method is provided for correcting a movement command for the linear feed axis of the machine tool so that the bottom blade moves away from the bottom surface of the workpiece so as not to cut too much.
According to the present invention, a rotating tool having an outer peripheral blade is used on the outer peripheral surface, and the outer peripheral blade is prevented from excessively shaving the wall surface of the workpiece when the rotary tool is inclined due to the posture error. An error correction method for correcting a movement command for the linear feed axis of the machine tool is provided so that the blade moves away from the wall surface of the workpiece.
Further, according to the present invention, in a machine tool having a plurality of linear feed axes and configured such that the spindle and the work table can be moved relative to each other, the error between the spindle and the work table is determined as the position error and the attitude error. An error data storage means for storing as an error map, and a correction amount of a movement command for the linear feed axis is calculated based on the posture error, tool information, and workpiece information so that the tool does not overcut the workpiece. There is provided a machine tool comprising: a calculation unit that performs correction; and a correction unit that corrects the movement command with a correction amount calculated by the calculation unit.

FIG. 1 is a side view of an embodiment of a machining center according to the present invention.
FIG. 2 is a block diagram of a numerical control apparatus having a function of correcting the position error and posture error of the machining center according to the present invention.
FIG. 3 is an explanatory diagram showing lattice points in a three-dimensional coordinate space.
FIG. 4 is an explanatory diagram showing a two-dimensional data sheet associated with each grid point in FIG.
FIG. 5 is a flowchart illustrating an example of a correction method using an error map.
FIG. 6 is an explanatory diagram showing a state where the wall surface of the workpiece is being excessively shaved by the rotary tool whose axis is inclined.
FIG. 7 is an explanatory view showing a state where the bottom surface of the workpiece is being excessively shaved by the rotary tool whose axis is inclined.

Embodiments of the present invention will be described below in detail with reference to the drawings. The machine tool of the present invention is not limited to the horizontal machining center having a horizontal spindle shown in the present specification, but includes all machine tools having a plurality of linear feed axes and a plurality of rotary feed axes, for example, a vertical spindle. The vertical machining center and other machine tools provided with a numerical control device are also included in the machine tool of the present invention. The machine tool according to the present embodiment includes a machine tool body having three linear feed axes that are orthogonal to each other, an X axis, a Y axis, and a Z axis, and a numerical control device that operates the machine tool body according to a machining program. Yes.
FIG. 1 shows a basic configuration of a 5-axis horizontal machining center 1. The horizontal machining center 1 has three orthogonal linear feed axes X, Y, Z and two rotary feed axes A, C.
In this specification, the X axis, the Y axis, and the Z axis that are three linear feed axes of the machine tool main body and the A axis and the C axis that are two rotary feed axes are defined as follows. A direction perpendicular to the axis of the main axis and perpendicular to the paper surface is taken as an X axis, a height direction perpendicular to the main axis is taken as a Y axis, and a direction coinciding with the main axis is taken as a Z axis. As for the two rotation feed axes A and C, the rotation around the axis parallel to the X axis is taken as the A axis, and the rotation around the axis parallel to the Z axis is taken as the C axis.
The machining center 1 includes a bed 2 installed on the floor, a column 3 standing on the bed 2 so as to be linearly movable in the Z-axis direction, and a column 3 capable of linearly moving in the Y-axis direction which is a vertical direction. A headstock 5 is provided. The spindle stock 5 is provided with a bracket 5a that can be rotationally fed by a servo motor 30 in the C-axis direction around an axis parallel to the Z-axis. In the bracket 5a, the spindle head 4 is provided so that it can be rotated and fed by a servo motor 30 in the A-axis direction around an axis parallel to the X-axis.
The machining center 1 is provided with a work table 6 which is erected on the bed 2 at a position facing the spindle head 4 and can move linearly in the X-axis direction which is a direction perpendicular to the paper surface. A work 7 is held on the work table 6 via the scale 8.
A rotating tool 9 having a predetermined protruding length and a predetermined diameter is rotatably held on the spindle head 4. Various end mills, drills, and the like can be applied to the rotary tool 9.
FIG. 2 is a block diagram showing the configuration of the numerical controller 20 that controls the position of the feed axis of the machine tool.
A numerical control device 20 shown in FIG. 2 has a function of correcting a position error and a posture error of a machine tool, reads and interprets a machining program 21, and calculates a command speed and a command position of each feed axis. A reading interpretation unit 22, an interpolation unit 23 for calculating a command pulse based on a command position, a command speed, etc. for linearly interpolating or circularly interpolating the feed at each feed axis, A position command recognizing means 24 for recognizing a position command to the feed axis, a calculation unit for calculating the position error of the measurement point based on the measurement data measured by the measuring device 50 and the coordinates of the measurement point, Error data storage means 25 for storing the calculated position error and posture error in correspondence with the position of the linear feed axis and the rotation angle of the rotary feed axis, and error data stored in the position command and error data storage means 25 Correction data calculation means 26 for calculating correction data for correcting the position command from the above, correction pulse calculation means 27 for obtaining a correction pulse for correcting the position command based on the correction data, and the command pulse and the correction pulse are added. And adding means 28 for outputting the pulse to the servo unit 29.
The motor 30 of each feed shaft is driven by the drive current amplified by the servo unit 29 and moves each feed shaft. The servo unit 29 controls each feed shaft to move to a desired position at a desired speed based on speed feedback from the motor 30 and position feedback from a position detection device (not shown).
The present invention also includes an apparatus configured to acquire and correct a command position from the reading interpretation unit 22 and input the corrected command position to the interpolation unit so that the motor moves to a desired position.
Further, the correction data calculation means 26 is provided with overcutting avoiding means for preventing the workpiece from being overcut when the machine has a posture error and the axis of the tool is inclined. Overcutting avoidance means is based on tool information such as attitude error, tool type and tool shape, workpiece information such as machining depth (groove depth), relative positional relationship between the machining surface and the tool, etc. A correction amount for correcting the movement command for the linear feed axis of the machine is calculated and added to the correction data so that the tool 9 does not cut the workpiece 7 too much.
Next, an error map will be described with reference to FIGS. In the error map, matrix-like two-dimensional array data 33 as shown in FIG. 4 is associated with each lattice point 31 of the three-dimensional orthogonal coordinate system as shown in FIG. That is, the error map is composed of a large number of two-dimensional array data 33 associated with each lattice point 31 of the three-dimensional orthogonal coordinate system.
Each two-dimensional array data 33 is composed of a large number of error data 34 measured at an arbitrary angle between the A axis and the C axis, with the horizontal axis being the A axis and the vertical axis being the C axis. The error data 34 is composed of a position error 35a and an attitude error 35b. The position error 35a is a position error represented by a three-dimensional coordinate value generated when the rotary feed axes A and C are positioned at a predetermined position. That is, an error in the position in the X, Y, and Z axis directions between the control point commanded by the program and the actual control point. The attitude error 35b is an error in the relative attitude between the spindle head 4 and the work table 6, and is represented by an inclination angle generated when the rotation feed axes A and C orthogonal to each other are positioned at a predetermined rotation angle. It is. The attitude error 35b is represented by [I, J, K], where I is an angle error viewed from the X direction, J is an angle error viewed from the Y direction, and K is an angle error viewed from the Z direction.
Thus, since the error data 34 includes both the position error 35a and the attitude error 35b, the machine can be positioned with high accuracy by correcting the movement command based on the error data 34. .
FIG. 5 shows a flowchart of a method for correcting the position error and the posture error. First, in step S0, the command position and command attitude commanded from the position command output from the interpolation unit 23 are recognized. In step S1, error data 34 corresponding to the command position is acquired from the error map. In step S2, a position correction vector for correcting the position error is calculated from the position error 34a of the error data 34.
On the other hand, from the attitude error 34b of the error data 34, an attitude correction value is calculated in step S5. In step S6, the posture correction value obtained in step S5 is added to the command posture read in step S3 to obtain a corrected posture. In step S7, a corrected command point is obtained from the corrected posture obtained in step S6 and the protruding length of the tool.
In step S4, a command point before correction is obtained from the commanded posture read in step S3 and the protruding length of the tool. In step S8, a correction vector for the position of the command point for correcting the posture error is calculated by subtracting the command point before correction obtained in step S4 from the command point after correction obtained in step S7. This is called an attitude correction vector.
When the tool held on the spindle is used as the control point, the posture correction vector moves the tip of the tool when the rotary feed shaft is rotated so that the posture error is corrected using the control point as a fulcrum. It is a vector that represents the magnitude and direction.
In step S9, the posture correction vector obtained in step S8 and the position correction vector obtained in step S2 are added.
In the present invention, the command point is the position of the tip of the tool (tool tip position). The tool tip position is the actual position of the tip of the tool, the position of the machining point at the tip of the tool, the tip of the ball end mill. This is the center of the hemisphere.
As described above, the tool tip position error is corrected only by the movement of the linear feed axis. Therefore, when the posture error 34b is corrected, the rotary feed axis does not rotate, and the correction causes the rotary feed axis to move greatly. Can be avoided.
The position error and posture error correction method described above is to rotate the rotary feed shaft for posture error correction by moving the tool tip point to the destination with a position command of a three-dimensional coordinate value, that is, a position correction vector. This is done without the attitude error itself being zero. For this reason, when the machine has a posture error, cutting is performed while the axis of the rotary tool is inclined by an amount corresponding to the error.
6 and 7 each show a state in which cutting is performed while the axis CL of the rotary tool 9 is inclined. As shown in FIG. 6, when the wall surface of the work 7 supported and fixed to the scale 8 is cut in a state where the axis CL of the rotary tool 9 having the outer peripheral blade on the outer peripheral surface is inclined at an angle θ, Overcutting may occur. A region Z1 illustrated in FIG. 6 indicates a region that is excessively cut due to the posture error. The size of the region Z1 is determined based on the angle θ as error information, the shape of the rotary tool 9 as tool information, the machining depth L as workpiece information, and the like. For this reason, in S10, the rotating tool 9 is moved so that the outer peripheral edge of the rotary tool 9 moves laterally away from the wall surface of the work 7 in the illustrated example so that the outer peripheral edge of the rotating tool 9 does not cut the wall surface of the work 7 too much. The position is corrected to a position translated by at least an excessive shaving correction amount β. The parallel movement of the rotary tool 9 can be performed by correcting the movement command for the linear feed axis.
Note that the rotary tool 9 cuts the wall surface of the workpiece 7 excessively due to the posture error when the rotary tool 9 is inclined toward the wall surface side of the workpiece 7. In the opposite case, the rotary tool 9 removes the wall surface of the workpiece 7. Don't cut too much. Therefore, the machining program describes the relative positional relationship between the wall surface and the rotary tool 9, and whether or not the rotary tool 9 cuts the wall surface of the workpiece 7 excessively based on error information, tool information, and workpiece information. If it is determined that the tool is overcut, the movement command for the linear feed axis is corrected.
Further, as shown in FIG. 7, the workpiece 7 supported and fixed to the scale 8 in a state where the axis CL of the rotary tool 9 having a bottom blade at the corner portion where the end surface and the outer peripheral surface intersect with each other is inclined at an angle θ. When the bottom surface is cut, the bottom surface of the workpiece 7 is overcut by the bottom blade. Examples of the rotary tool 9 having a bottom edge at the corner include a square end mill and a radius end mill. Since the ball end mill has an arc cutting edge, the cutting edge does not bite into the bottom surface of the workpiece 7 even when the axis CL of the tool 9 is inclined. A region Z2 shown in FIG. 7 indicates a region that is excessively cut due to the posture error. The size of the region Z2 is determined based on the angle θ as error information, the shape (diameter and the like) of the rotary tool 9 as tool information, the workpiece shape as workpiece information, and the like. For this reason, in the present embodiment, the rotary tool 9 is moved so that the bottom blade of the rotary tool 9 moves away from the bottom surface of the work 7 in the illustrated example so that the bottom blade of the rotary tool 9 does not cut the bottom surface of the work 7 excessively. 9 is corrected to a position translated at least by an excessive shaving correction amount δ. The parallel movement of the rotary tool 9 can be performed by correcting the movement command for the linear feed axis, as in the machining example shown in FIG.
As described above, according to the error correction method and the machine tool of the present embodiment, when the machine has a posture error and the tool axis is tilted, the posture error is corrected so that the workpiece is not excessively cut. Can be processed with high accuracy and high efficiency.

DESCRIPTION OF SYMBOLS 1 Machining center 7 Work piece 9 Rotating tool 25 Error data storage means 33 Error map 60 Overcutting avoidance means 70 Calculation part 80 Correction part

Claims (5)

In an error correction method for correcting an error of a machine tool,
Store the error of the machine tool as an error map of position error and attitude error,
Enter the tool information of the tool to be used and the workpiece information of the workpiece to be machined,
Based on the position error and the posture error and the input tool information and the workpiece information, a correction amount of the feed axis is calculated so as not to cut the workpiece too much,
An error correction method comprising correcting a movement command with the calculated correction amount.   The error correction method according to claim 1, wherein the tool information includes a tool type and a tool diameter, and the workpiece information includes a machining depth of the workpiece.   A rotary tool having a bottom blade is used at a corner portion where the end surface and the outer peripheral surface intersect, and the bottom blade does not overcut the bottom surface of the workpiece by tilting the rotary tool due to the posture error. The error correction method according to claim 1, wherein a movement command for the linear feed axis of the machine tool is corrected so that the blade moves away from the bottom surface of the workpiece.   A rotary tool having an outer peripheral blade on the outer peripheral surface is used, and the outer peripheral blade moves away from the wall surface of the workpiece so that the outer peripheral blade does not cut too much the wall surface of the workpiece by tilting the rotary tool due to the posture error. Thus, the error correction method according to claim 1, wherein a movement command for the linear feed axis of the machine tool is corrected. In a machine tool having a plurality of linear feed axes and configured so that the spindle and the work table can move relative to each other,
Error data storage means for storing an error between the spindle and the work table as an error map including a position error and an attitude error;
A calculation unit that calculates a correction amount of a movement command for the linear feed axis based on the posture error, tool information, and workpiece information so that the tool does not cut the workpiece too much;
A correction unit that corrects the movement command with a correction amount calculated by the calculation unit;
A machine tool characterized by comprising:

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