JP2012079358A - Error map creation method, device, and numerical control machine tool with an error map creation function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical control machine tool capable of accurately correcting errors in position and posture of a machine tool having a rotational feed spindle.SOLUTION: The numerical control machine tool with a linear feed spindle and a rotational feed spindle where a main spindle and a work table are provided relatively movably includes a measuring device for measuring a position of a reference sphere by a sensor at a desired measuring point, having the reference sphere on one side of the main spindle and the work table and the sensor on the other side, a computation part for computing a position error and a posture error of the measuring point based on measurement data measured by the measuring device and the coordinates values of the measuring point, and a storage part for storing the position error and the posture error computed by the computation part by associating them with a rotation angle of the rotational feed spindle at each lattice point positioned on a desired position in each axial direction of the linear feed spindle on the measuring point.

Description

  The present invention relates to measurement and correction of errors in a numerically controlled machine tool having a configuration in which a main shaft and a table are relatively movable, and having a linear feed shaft and a rotary feed shaft.

  Generally, in a machine tool having a linear feed axis and a rotary feed axis, an error occurs when the feed axis is moved in accordance with a movement command, so that it is difficult to position the tool at a desired position. For this reason, when performing a highly accurate process, it correct | amends according to the error of a machine. In order to perform the correction, it is necessary to accurately measure the machine error as a pre-stage of the correction. As a conventional technique for measuring and correcting an error, a technique disclosed below is known.

  In Patent Document 1, axial misalignment (position misalignment of the shaft center) of two rotary feed shafts of a machine tool having two rotary feed shafts (A, B) orthogonal to each other is measured in advance, and this misalignment is taken into account. Thus, it is disclosed that the coordinates of two rotary feed axes are obtained.

  In Patent Document 2, in a machine tool having three linear movement axes (X, Y, Z) orthogonal to each other and two rotary feed axes (A, C) orthogonal to each other, the machine to be actually moved A technique for correcting the position of the tool tip by determining the position based on the amount of deviation between the rotation axis center and the spindle turning center and moving the linear movement axis and the rotation feed axis to the determined machine position by the drive control means. It is disclosed.

  Patent Document 3 discloses a method of correcting an error of a tool unit of a machine tool of a parallel link mechanism based on an error map. The error map has error data calculated by calculation from the difference between the command value and the detected value of the position and orientation of the tool unit tip corresponding to the lattice point of the work space at the tool unit tip.

  Also, US Pat. No. 6,057,028 discloses a system and process that is automated and integrated with a numerical control system to measure, correct, and test the head and / or table of a numerically controlled machine tool. The system includes at least one support base having a plurality of distance sensors, at least one device of a gauge tool type comprising an elongated cylinder having a connecting means connected to a head at one end and a sphere at the other end, It has. The sphere is disposed adjacent to the distance sensor. The distance sensor can be moved to any position at any time to measure the distance away from the sphere. Thereby, the position in the Cartesian coordinate space is determined.

  The correction methods disclosed in Patent Document 1 and Patent Document 2 are for correcting the shaft misalignment of the rotating shaft, and there is a problem that errors that change depending on the waviness of the shaft itself or the position of the linear feed shaft cannot be corrected. . The error map disclosed in Patent Document 3 is obtained by using table tool data for errors at the tip of a tool unit driven by a parallel link mechanism, and there is a problem that it cannot be applied to a machine tool having a linear feed axis and a rotary feed axis. It was. In the measurement method disclosed in Patent Document 4, since only the deviation of the center position of the reference sphere is measured, it occurs due to an error in the relative posture between the spindle and the table when the tool length or the tool protrusion length changes. There was a problem that the displacement of the tool tip position could not be corrected.

Japanese Patent Publication No. 6-88192 JP 2004-272887 A JP-A-9-237112 International Publication No. 2004/034164 Pamphlet

  An object of the present invention is to solve the above-described problems of the prior art, and an object of the present invention is to create an error map for accurately correcting errors in a machine tool having a linear feed shaft and a rotary feed shaft. And a numerically controlled machine tool having an apparatus and an error map creation function.

  In order to achieve the above object, according to the present invention, in the error map creation method for a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft, the spindle and the table can be moved relative to each other. A step of defining a plurality of measurement points corresponding to the rotation angle of the rotary feed shaft at each lattice point at a desired position in each axial direction of the feed shaft, and a relative position of the main shaft and the table at each measurement point And measuring the relative posture, obtaining a position error and / or posture error of each measurement point, and calculating the position error and the posture error at a desired position in each axial direction of the linear feed axis. And a step of storing corresponding to the rotation angle of the rotary feed shaft in step (b).

  According to the present invention, in the step of determining the plurality of measurement points, a plurality of measurement regions are defined within a movable range of the linear feed axis, a lattice point is defined in each measurement region, and at least one of the measurement regions is determined. An error map creation method is provided in which two grid points determine the measurement points so that the grid points of the adjacent measurement area and the coordinate position of the linear feed axis are the same.

  According to the present invention, in the step of determining the plurality of measurement points, the interval between adjacent measurement points is constant, or the difference in position error or posture error between adjacent measurement points is constant. An error map creation method for determining measurement points is provided.

  According to the present invention, the step of measuring the relative position and the relative posture includes a reference sphere having a known outer dimension provided on one of the spindle and the table and a displacement sensor provided on the other. Using the measuring device, the rotary feed shaft is controlled while controlling the linear feed shaft so that the relative position between the center of the reference sphere and the displacement sensor does not change theoretically when the rotary feed shaft is operated. An error map that positions at a plurality of measurement points, measures the displacement of the position of the reference sphere at each measurement point by the displacement sensor, and obtains the relative position and the relative posture from the measured displacement and the coordinate value at the time of measurement. A creation method is provided.

  According to the present invention, in the step of measuring the relative position and the relative posture, the rotational feed shaft is positioned at a plurality of rotational angles, a test piece or a work attached to the table is processed, and the rotational feed is performed. The shaft is positioned at one of the plurality of rotation angles, and the displacement between the machining surface when machining at the one rotation angle and the machining surface when machining at another rotation angle is measured and measured. An error map creation method for obtaining the relative position and the relative attitude from the displacement and the coordinate value at the time of measurement is provided.

  Further, according to the present invention, the step of measuring the relative position and the relative attitude includes positioning the rotary feed shaft at a plurality of rotation angles, and measuring the test piece or workpiece 3 attached to the table at each rotation angle. When a surface is machined, the rotary feed shaft is positioned at one rotation angle of the plurality of rotation angles, and machining is performed at three rotation surfaces and another rotation angle when machining is performed at the one rotation angle. The difference in position and inclination between the three processed surfaces is measured with a touch probe attached to the spindle, and the relative position and the difference are determined from the measured position difference and inclination difference and the machine coordinate value at the time of measurement. An error map creation method for obtaining a relative attitude is provided.

  Further, according to the present invention, in the error map creation method for a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft so that the main shaft and the table can be moved relative to each other, the linear feed shaft and the rotary feed A step of determining a plurality of measurement points in a movable range of the shaft, and a test of a rectangular parallelepiped attached to the table at the determined rotation points by positioning the rotary feed shaft at a plurality of rotation angles. A step of machining three orthogonal surfaces of a piece or a workpiece, and a tilt of a machining surface when the rotary feed shaft is positioned at one rotation angle among the plurality of rotation angles and the other rotation angle is positioned. Measuring the posture error at each rotation angle, measuring the processed surface of the processed test piece or workpiece, and adding the processed workpiece at each rotation angle. Determining the position of the intersection of the three planes including the surface, and positioning and processing at the other rotation angle and the intersection of the three planes including the machining surface when the rotary feed shaft is positioned and processed at the one rotation angle. A position error at each measurement point from the difference in position with the intersection of the three planes including the processed surface and the determined attitude error, and the position error and the attitude error as the position of the linear feed axis and the position error And an error map creating method including the step of storing corresponding to the rotation angle of the rotary feed shaft.

  Further, according to the present invention, in the error map creation method for a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft so that the main shaft and the table can be moved relative to each other, the linear feed shaft and the rotary feed A step of determining a plurality of measurement points in a movable range of the shaft, and a test of a rectangular parallelepiped attached to the table at the determined rotation points by positioning the rotary feed shaft at a plurality of rotation angles. 3 including a step of machining three orthogonal surfaces of a piece or a workpiece, a machining surface of a machined test piece or workpiece, and the inclination of the machining surface machined at the rotation angle and the machining surface for each rotation angle A step of obtaining the position of the intersection of the planes, and the inclination of the machining surface and the other rotation angle when the rotary feed shaft is machined by positioning at one of the plurality of rotation angles. 3 including a step of obtaining an attitude error at each measurement point from the difference between the inclination of the processing surface when the processing is carried out by positioning, and a processing surface when processing is performed with the rotary feed shaft positioned at the one rotation angle. Obtaining a position error at each measurement point from the difference in position between the intersection of the plane and the intersection of the three planes including the machined surface when machining is performed at another rotation angle and the obtained attitude error; and And a step of storing the posture error corresponding to the position of the linear feed shaft and the rotation angle of the rotary feed shaft.

  Further, according to the present invention, in an error map creation apparatus for a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft and configured so that the spindle and the table can move relative to each other, one of the spindle and the table is provided. A measuring device that has a reference sphere provided and a sensor provided on the other, and that measures the position of the reference sphere with the sensor at a desired measurement point; measurement data measured by the measurement device; and A calculation unit that calculates a position error and a posture error of the spindle and the table based on the coordinate value, and a position error and a posture error calculated by the calculation unit are obtained in a desired direction in each axis direction of the linear feed shaft at the measurement point. There is provided an error map creation device comprising a storage unit that stores data corresponding to the rotation angle of the rotary feed shaft at each lattice point at a position.

  According to the present invention, in a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft so that the spindle and the table can be moved relative to each other, a reference ball provided on one of the spindle and the table A measuring device that measures the position of the reference sphere by the sensor at a desired measurement point, measurement data measured by the measurement device, and a coordinate value of the measurement point A calculation unit that calculates a position error and an attitude error of the spindle and the table, and each grid at a desired position in each axial direction of the linear feed axis at the measurement point, the position error and the attitude error calculated by the calculation unit. There is provided a numerically controlled machine tool having an error map creation function, and a storage unit that stores information corresponding to the rotation angle of the rotary feed shaft at a point.

  Further, according to the present invention, in a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft so that the main shaft and the table can be moved relative to each other, the test piece or work attached to the table, Based on the measuring device having a sensor provided on the spindle and measuring the processed surface of the test piece or workpiece by the sensor at a desired measuring point, the measurement data measured by the measuring device, and the coordinate value of the measuring point A calculation unit for calculating the position error and the posture error of the spindle and the table, and the position error and the posture error calculated by the calculation unit at each desired position in each axial direction of the linear feed shaft at the measurement point. There is provided a numerically controlled machine tool having an error map creation function, and a storage unit that stores data corresponding to the rotation angle of the rotary feed shaft at a lattice point.

  According to the invention, the numerical control machine tool corrects the command position or the position command of the linear feed shaft or the rotary feed shaft based on the position error and the posture error stored in the storage unit. There is provided a numerically controlled machine tool having an error map creation function further comprising a section.

  According to the error map creating method and apparatus of the present invention and the numerically controlled machine tool having the error map creating function, the position error and the posture error of the numerically controlled machine tool having the linear feed axis and the rotary feed axis are measured, An error map can be created. In the error map created in the present invention, the error data of the position error and the attitude error that change as the feed axis moves are stored separately, and the position command is corrected based on this error data. Therefore, according to the present invention, the tool tip or the machining point of the tool can be accurately positioned at the target position even if the tool length or the tool protrusion length changes. Further, when the measurement points having the same coordinate position of the linear feed axis are set in the adjacent measurement regions, the influence due to the mounting error of the measuring device can be eliminated. Further, when the interval between adjacent measurement points is set so that the difference in error is constant, the amount of error map data can be reduced while maintaining the desired correction accuracy. In addition, when an error map is created by measuring a processed test piece or workpiece, it can be corrected including errors caused by deflection of the spindle and tool due to rotation of the spindle and deflection of the machine and tool due to cutting load. .

  In the present invention, the command position is the position of the destination of the feed axis commanded by the machining program, and the position command is a command pulse sent from the interpolation unit to the servo unit based on the command position, command speed, etc. Of these, it is a command for controlling the position of the feed axis.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments with reference to the accompanying drawings.
1 is a side view of a numerically controlled machine tool according to the present invention. It is a block diagram showing one embodiment of a numerical control device of a numerical control machine tool according to the present invention. It is explanatory drawing which shows the lattice point of three-dimensional coordinate space. It is explanatory drawing which shows the two-dimensional data sheet (map data) related with each lattice point of FIG. It is explanatory drawing which shows the state which has measured the reference | standard sphere with which the front-end | tip of the tool was mounted | worn with the measuring apparatus with which the pallet was mounted | worn. It is the figure which looked at the measurement range of the reference sphere which has the support shaft from which length differs from the Y-axis direction. It is explanatory drawing which shows the determination method of a several measurement area | region. It is a flowchart explaining the 1st measuring method which measures a position error and a posture error. It is a detailed flowchart of M3 of the flowchart of FIG. It is explanatory drawing showing an attitude | position error by 2 variables. It is a figure which shows an example of the spindle rotation type machine by which the reference | standard sphere was mounted | worn with the pallet side and the measuring apparatus was mounted | worn with the spindle side. It is a figure which shows an example of the table rotation type machine by which the measuring apparatus was mounted | worn with the table, and the reference sphere was mounted | worn with the main axis | shaft. It is a flowchart explaining the 2nd measuring method which measures a position error and a posture error. It is explanatory drawing which shows the state which is processing each plane only by operation | movement of a linear feed axis. It is a development view of 5 surfaces of a rectangular parallelepiped showing a processing place for each indexing angle. It is explanatory drawing which shows the state which is processing the grid | lattice-like surface on a workpiece | work with the index angle of the rotational feed axes B and C. FIG. It is explanatory drawing which shows the state which is measuring each measurement surface calculated | required by the predetermined angle. It is explanatory drawing explaining the method of calculating | requiring the intersection of 3 planes. It is a flowchart which shows an example of the correction method using an error map.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. A numerically controlled machine tool according to the present invention includes a numerical control device that operates a machine according to a machining program. FIG. 1 shows the configuration of a 5-axis horizontal machining center having two rotary feed shafts on the main shaft side. Referring to FIG. 1, a machining center 1 includes a bed 2 installed on a floor, a column 3 erected on the bed 2 so as to be linearly movable in the Z-axis direction, and a Y-axis that is perpendicular to the column 3. And a headstock 5 that can move in the direction. A bracket 5a is supported on the head stock 5 so as to be rotatable in a C-axis direction around an axis parallel to the Z-axis. The spindle head 4 is supported on the bracket 5a so as to be rotatable in the A-axis direction around an axis parallel to the X-axis. A spindle for gripping the tool is rotatably supported on the spindle head 4.

  In addition, the machining center 1 includes a table 6 that stands on the bed 2 at a position facing the spindle head 4 and can move in the X-axis direction, which is a direction perpendicular to the paper surface. A work 7 is held on the table 6 via an scale 8.

  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 that calculates a command pulse based on a command position, a command speed, etc. for linearly or circularly interpolating the feed on each feed axis, and acquiring each command pulse A position command recognizing unit 24 for recognizing a position command to the axis, a calculation unit for calculating a position error and a posture error of the measurement point based on the measurement data measured by the measurement device 50 and the coordinates of the measurement point, and the calculation Are stored in the error data storage means 25 for storing the position error and the posture error calculated by the unit in correspondence with the position of the linear feed shaft and the rotation angle of the rotary feed shaft, and 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 error data, correction pulse calculation means 27 for obtaining a correction pulse for correcting the position command based on the correction data, a command pulse and a correction pulse, And adding means 28 for outputting a pulse to which the signal is added to the servo section 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.

  Next, an error map creation method will be described. In the error map, as shown in FIG. 3, each lattice point 31 at a desired position in each axial direction of the linear feed axes X, Y, and Z in the orthogonal coordinate system is set, and each lattice point 31 is set in FIG. The two-dimensional array data 33 corresponding to the rotation angle of the rotary feed shaft as shown in FIG. That is, the error map is composed of data of a five-dimensional array of X, Y, Z, A, and C.

  The error map is composed of a plurality of error data 34 measured by positioning each feed axis at a desired measurement point. The error data 34 includes a position error 34a and an attitude error 34b.

  Here, the position error 34a is an error of the relative position between the spindle and the table, and is represented by a three-dimensional coordinate value (x, y, z) generated when the feed shaft is positioned at a predetermined position or rotation angle. This is an error of the position to be performed. That is, the difference between the theoretical position commanded by the position command and the actual position is the position error.

  The attitude error 34b is an error in the relative attitude between the spindle and the table, and is an error expressed by an inclination angle that occurs when the feed axis is positioned at a predetermined position or rotation angle. That is, the difference between the theoretical tilt commanded by the position command and the actual tilt is the posture error.

  Here, the measurement interval of the error data 34 is set so that the difference between the position error 34a or the posture error 34b at adjacent measurement points becomes a predetermined value. In other words, the measurement interval is widened when the error difference between adjacent measurement points is small, and the measurement interval is narrowed when the error difference is large. By extending the measurement interval of the portion with a small error difference, the amount of data can be reduced and the burden on the memory can be reduced. By narrowing the measurement interval of the portion with a large error difference, the correction accuracy can be maintained. .

  Next, an example of a measurement method for measuring the position error 34a and the posture error 34b of a machine tool having the rotary feed axes A and C on the main shaft side will be described. As shown in FIGS. 5 and 6, the measuring device 50 is mounted on the spindle of a spindle rotating machine tool via a support shaft 40, and distances L1, L2 from the outer dimensions and control points to the spherical centers P1, P2. Is mounted on a pallet 54 fixed to a table, and includes a sensor bracket 53 having a non-contact sensor 55 in the X, Y, and Z directions. The non-contact sensor 55 can measure the distance to the reference sphere 52 in each direction without contact. The sensor of the present invention includes not only a non-contact type sensor but also a contact type sensor.

  Measurement is performed by dividing the measurement range of each rotary feed axis A and C at equal or unequal pitches, and simultaneously operating the linear feed axis so as to maintain the center position of the reference sphere 52 at each division point (measurement point). And measure. Here, the equal pitch is to determine measurement points for each predetermined angle, and the angular intervals between adjacent measurement points to be equal intervals. The unequal pitch is, for example, a point that exceeds a specified error value. The error data is included only in, and the angular intervals between adjacent measurement points are unequal.

  As shown in FIG. 9, first, the center position P1 of the reference sphere 52 is measured by the measuring device 50 having the non-contact sensor 55 in each of the directions X, Y, and Z orthogonal to each other. In order to obtain the actual relative posture and the actual control point, as shown in FIG. 6, a reference sphere having a different length of the support shaft 40 is mounted, and the center position P2 of the reference sphere 52 is measured again. By mounting the support shafts 41a and 41b having different lengths and measuring them, the relative posture between the spindle and the table can be obtained.

  The present invention includes a case where a support shaft whose length can be adjusted is used. In the present embodiment, the control point is set at the intersection of the rotation center of the first rotation feed shaft C and the rotation center of the second rotation feed shaft A. The relative posture is the relative inclination between the spindle and the table.

  The sensor bracket 53 of the measuring device 50 is mounted so as to be rotatable around an axis parallel to the Z axis. Therefore, if it is desired to measure all 360 degrees, the sensor bracket 53 is rotated 90 degrees around the axis parallel to the Z axis. The measurement may be performed four times.

  As shown in FIGS. 7 and 8, when the area to be measured is wide, the measurement area is divided into a plurality of areas. At that time, the operating range of the linear feed axes X, Y, and Z in the reference first measurement area 70a is measured using a laser measuring instrument, an indicator, etc., and adjusted so as to have sufficient accuracy with respect to the required accuracy. Keep it. The present invention includes a case where the error is calculated in consideration of the measurement result without adjusting the accuracy of the operation range of the linear feed axes X, Y, and Z in the first measurement region 70a. This is because the measurement results in the first measurement region 70a are limited to errors that occur when the rotary feed axes A and C are rotated.

  Further, the measurement points in the measurement areas 70a and 70b are determined so that one or more measurement points 71 having the same linear feed axis coordinate values as the measurement points in the adjacent measurement areas exist. This is performed in order to prevent an attachment error of the measurement device 50 from affecting the measurement result between the first measurement region 70a and the other measurement region 70b.

  By subtracting the error due to the difference in the rotation angle of the rotary feed shaft from the difference between the measurement results at the measurement points having the same linear feed axis coordinate value, the mounting error of the measuring device 50 can be obtained. By subtracting from the measurement result of the area, the same measurement result as when all the measurement areas are measured in one setup can be obtained.

  Next, a method for calculating the position error and the posture error will be described. First, the attitude error is obtained as follows. The relative inclination of the spindle and the table instructed from the command value of the rotation angle of the rotary feed axes A and C is obtained. Here, the angle formed between the rotation axis of the main shaft and a line perpendicular to the workpiece mounting surface of the scale is defined as the relative posture of the main shaft and the table. An angle formed by a line passing through the center positions P1 and P2 of the two reference spheres 52 from P1 and P2 and a line perpendicular to the workpiece mounting surface of the scale is obtained, and this is the relative inclination between the actual spindle and the table. And The difference between the relative inclination of the commanded spindle and table and the actual inclination of the spindle and table is obtained, and this is set as the posture error. The posture error is represented by an angle difference i with respect to the Z axis viewed from the X axis direction, an angle difference j with respect to the Z axis viewed from the Y axis direction, and an angle difference k with respect to the Y axis viewed from the Z axis direction. The present invention includes the case where the posture error is represented by two angles I and J as shown in FIG.

  Next, the position error is obtained as follows. In the present embodiment, the control point is set at the intersection of the rotation center of the first rotation feed shaft C and the rotation center of the second rotation feed shaft A, so that the rotation feed shaft can be at any rotation angle. The position of the theoretical control point does not change. Therefore, the position of the commanded control point is obtained from the command values of the linear feed axes X, Y and Z. Here, the position of the control point is a relative position between the reference point of the table and the control point of the spindle. On the line passing through P1 and P2 obtained in the step of obtaining the attitude error, the position of a point at a distance of L2 in the direction from P2 to P1 is obtained, and this is set as the actual position of the control point. A vector between the position of the commanded control point and the actual position of the control point is obtained, and this is set as a position error. The position error vector is divided into components in the X, Y, and Z axis directions and expressed in the form of (x, y, z). The present invention includes a case where the position error vector is expressed in other forms.

  FIG. 11 shows an embodiment in which a reference sphere 52 is mounted on the pallet 54 side and a displacement detection probe 58 is mounted on the spindle side in a spindle rotating machine. The displacement detection probe 58 is configured to be displaced in the normal direction of the measurement point of the object to be measured, and can detect the amount of the displacement.

  FIG. 12 shows an embodiment in which the present invention is applied to a table rotation type machine having rotation feed axes B and C on the table side. Also in the embodiment shown in FIGS. 11 and 12, the error of the feed shaft can be measured by the same principle as that of the embodiment shown in FIG.

  Next, an example of a measurement method for measuring the position error 34a and the posture error 34b of the machine tool having the rotary feed axes B and C on the table side will be described. FIG. 13 shows a flowchart of this measurement method. In this measurement method, a test piece or workpiece is machined on a machine without using a special measuring device, and the measured test piece or workpiece is measured with a touch probe attached to the spindle, thereby correcting the position error and posture error. It is a method to seek. In this embodiment, a cubic test piece is used.

  As shown in FIG. 13, first, the position error and posture error of the rotary feed axes B and C are determined to be sufficiently small with respect to the required accuracy (in this embodiment, the B axis is 0 degrees and the C axis is 0 degrees). As shown in FIG. 14, each plane (frame-shaped reference processing surface 61) of the test piece 60 whose normal direction is the X, Y, and Z axis directions is processed without operating the rotary feed shaft.

  The reason why the reference machining surface 61 is framed is to accurately obtain the posture error even when a large number of measurement points are provided, and it is more accurate to measure the tilt using the entire length of the test piece 60. Is required. Here, a ball end mill is used as the cutting tool 63. The reference machining surface 61 serves as a reference for measuring an attitude error at a predetermined rotation angle of the rotary feed shaft.

  Subsequently, as shown in FIG. 16, the rotary feed shaft is indexed to each measurement point, and the three mutually orthogonal surfaces of the test piece 60 are processed only by the operation of the linear feed shaft. As shown in FIG. 15, a predetermined place is assigned according to the index angle of the rotary feed shaft.

  Next, as shown in FIG. 17, the rotary feed axis is determined at each measurement point, P10 to P14 of the reference machining surface 61 are measured with the touch probe 64, and the actual inclination of the line passing through P10 and P11, P10 and P12. And the actual slope of the line passing through P13 and P14. The difference between the obtained three actual inclinations and the theoretical three inclinations calculated from the position command of the rotary feed shaft at the time of measurement is defined as an attitude error.

  Then, as shown in FIG. 18, the rotary feed shaft is indexed to the B axis 0 degree and the C axis 0 degree which are the reference rotation angles, the machining surfaces P15 to P20 processed at each rotation angle are measured, and the rotary feed axis is set. The difference between the positions of the processed surfaces P18 to P20 calculated by machining the B axis at 0 degrees and the C axis at 0 degrees and the positions of the processed surfaces P15 to P17 when processed at the other rotation angles is obtained.

  In the present invention, a difference in position and / or a difference in inclination between a machined surface machined at one rotation angle and a machined surface machined at another rotation angle is called a displacement of the machined surface.

  From the measurement data of the processed surfaces P18 to P20, an intersection P21 of three planes including the processed surfaces P18 to P20 when it is assumed that there is no attitude error is obtained. An intersection P22 of three planes including the processed surfaces P15 to P17 is obtained from the measurement data of the processed surfaces P15 to P17 and the obtained attitude error. The difference between the obtained intersection point P21 and intersection point P22 is defined as a position error. The present invention includes a case where a test piece or a workpiece is machined with a machine tool having a rotary feed shaft on the main shaft side, and a position error and a posture error are obtained from a measurement result of the machined surface.

  As shown in FIG. 4, the error obtained by the above method is associated with the positions of the linear feed axes X, Y, and Z and the rotation angles of the rotary feed axes B and C, and stored as an error map.

  Next, a method for correcting a position command using an error map including a position error and an attitude error will be described by taking a spindle rotation type machine (see FIGS. 1 and 2) having rotation feed axes A and C as an example.

  First, the command position of the machining program 21 is decoded by the reading / interpretation unit 22, and the interpolation unit 23 obtains command pulses for the feed axes X, Y, Z, A, and C every predetermined interpolation cycle.

  Subsequently, the position command recognizing means 24 recognizes the position commands of the feed axes X, Y, Z, A, and C every predetermined interpolation period from this command pulse.

  When the position of each feed axis in the position command is the same as the position of the measurement point stored in the error data storage means 25, error data 34 is acquired, and correction data is obtained based on the acquired error data 34. When the position of each feed axis in the position command is not the same as the position of the measurement point stored in the error data storage means 25, the error data is interpolated from the error data of the nearby measurement point by a known interpolation method such as interpolation. And correction data is obtained based on the error data after interpolation. The obtained correction data is added to the position command of the command pulse to obtain a new position command for each interpolation cycle. In this way, the position command is corrected, and each feed shaft can be positioned with high accuracy.

  Next, a correction method for correcting the position command by expressing the correction value calculated by the correction data calculation means 26 as a three-dimensional coordinate value will be described. For example, if there is a posture error in the B-axis direction that the machine does not originally have when the C-axis is 0 degree, the rotation feed shaft must be rotated greatly in order to correct the posture error in the B-axis direction. There is. In the present invention, this problem is called a singularity problem. The correction method described here is a correction method for avoiding this singularity problem. Note that the B axis is a rotary feed axis around an axis parallel to the Y axis.

FIG. 19 is a flowchart of this correction method. A calculation formula for obtaining a position correction vector based on the tool posture and posture error, the tool position and position error, and the tool protrusion length in this method is shown below.
L: Distance from command point to tool tip position [I, J, K]: Command tool posture [dl, dJ, dK]: Posture error [dX1, dY1, dZ1]: Position error [dX2, dY2, dZ2]: Tool tip position error caused by attitude error [dX3, dY3, dZ3]: Tool tip position error dX2 = L × (tan (J + dJ) / ((tan (I + dI)) ² + (tan (J + dJ)) ² +1) ^{1 / 2} −tan (J) / ((tan (I) ² + (tan (J)) ² +1) ^1/2 )
dY2 = L × (tan (I + dI) / ((tan (I + dI)) ² + (tan (J + dJ)) ² +1) ^1/2 −tan (I) / ((tan (I) ² + (tan (J) ) ² + 1) ^1/2)
dZ2 = L × (1 / ((tan (I + dI)) ² + (tan (J + dJ)) ² +1) ^1/2 −1 / ((tan (I)) ² + (tan (J)) ² +1) ^{1 / 2} )
dX3 = dX1 + dX2
dY3 = dY1 + dY2
dZ3 = dZ1 + dZ2

  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.

  Finally, 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, since the error of the tool tip position is corrected only by the movement of the linear feed axis, the rotary feed axis does not rotate when correcting the posture error 34b, and the singularity problem can be avoided.

  Thus, according to the present embodiment, it is possible to create an error map by measuring the position error and the posture error of a machine tool having a plurality of rotary feed axes. In addition, since the created error map stores the position error and the posture error as separate error data, the position command is corrected based on this error data, so that the tool tip position can be accurately set to the target position. It can be positioned and processed with high accuracy.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, the numerical controller 20 calculates a position error and a posture error of the measurement point based on the measurement data measured by the measurement device 50 and the coordinates of the measurement point, and the calculation unit Error data storage means 25 for storing the calculated position error and posture error in correspondence with the position of the linear feed shaft and the rotation angle of the rotary feed shaft, but a personal computer in place of the numerical controller 20 or other It is also possible for the apparatus to include an arithmetic unit and error data storage means 25.

Claims (10)

In an error map creation method for a numerically controlled machine tool having a linear feed axis and a rotary feed axis and configured so that the spindle and the table can move relative to each other,
A step of defining a plurality of measurement points corresponding to the rotation angle of the rotary feed shaft at each lattice point at a desired position in each axial direction of the linear feed shaft;
Measuring the relative position and relative orientation of the spindle and the table at each measurement point;
Obtaining a position error and / or posture error of each measurement point;
Storing the position error and the posture error corresponding to the rotation angle of the rotary feed shaft at each lattice point at a desired position in each axial direction of the linear feed shaft;
A method for creating an error map of a numerically controlled machine tool, characterized by comprising:   In the step of determining the plurality of measurement points, a plurality of measurement regions are defined within a movable range of the linear feed axis, the lattice points are defined in each measurement region, and at least one lattice point of each measurement region is adjacent to each other. The method for creating an error map for a numerically controlled machine tool according to claim 1, wherein the measurement points are determined so that the lattice points of the measurement area and the coordinate position of the linear feed axis are the same.   The step of determining the plurality of measurement points determines the measurement points so that an interval between adjacent measurement points is constant or a difference in position error or posture error between adjacent measurement points is constant. Or an error map creation method for the numerically controlled machine tool according to 2;   The step of measuring the relative position and the relative posture uses the measuring device having a base ball having a known outer dimension provided on one of the spindle and the table and a displacement sensor provided on the other, and rotating the rotation The rotary feed shaft is positioned at a plurality of measurement points while controlling the linear feed shaft so that the relative position between the center of the reference sphere and the displacement sensor does not change theoretically when the feed shaft is operated. 4. The displacement of the reference sphere at each measurement point is measured by the displacement sensor, and the relative position and the relative attitude are obtained from the measured displacement of the position and the coordinate value at the time of measurement. An error map creation method for a numerically controlled machine tool according to any one of the preceding claims.   The step of measuring the relative position and the relative posture includes positioning the rotary feed shaft at a plurality of rotation angles to process a test piece or a work attached to the table, and turning the rotary feed shaft at the plurality of rotation angles. Of these, positioning at one rotation angle, measuring the displacement of the position of the machining surface when machining at one rotation angle and the machining surface when machining at another rotation angle, and measuring the displacement and measurement of the measured position The method for creating an error map for a numerically controlled machine tool according to any one of claims 1 to 3, wherein the relative position and the relative attitude are obtained from coordinate values at the time.   The step of measuring the relative position and the relative posture includes positioning the rotary feed shaft at a plurality of rotation angles, machining three surfaces of a test piece or a workpiece attached to the table at each rotation angle, and rotating the rotary feed. The shaft is positioned at one of the plurality of rotation angles, and the positions of the three machining surfaces when machining at the one rotation angle and the three machining surfaces when machining at another rotation angle are determined. The difference between the difference and the inclination is measured with a touch probe attached to the spindle, and the relative position and the relative attitude are obtained from the measured difference in position and inclination and the machine coordinate value at the time of measurement. 4. An error map creation method for a numerically controlled machine tool according to any one of items 1 to 3. In an error map creation device for a numerically controlled machine tool that has a linear feed axis and a rotary feed axis and is configured such that the spindle and the table can move relative to each other.
A measuring device having a reference sphere provided on one of the spindle and the table and a sensor provided on the other, and measuring the position of the reference sphere with the sensor at a desired measurement point;
Based on the measurement data measured by the measurement device and the coordinate value of the measurement point, a calculation unit that calculates the position error and the posture error of the measurement point;
A storage unit for storing the position error and the posture error calculated by the calculation unit in correspondence with the rotation angle of the rotary feed shaft at each lattice point at a desired position in the axial direction of the linear feed shaft at the measurement point; ,
An error map creation device for a numerically controlled machine tool, comprising: In a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft and configured so that the spindle and the table can move relative to each other,
A measuring device having a reference sphere provided on one of the spindle and the table and a sensor provided on the other, and measuring the position of the reference sphere with the sensor at a desired measurement point;
Based on the measurement data measured by the measurement device and the coordinate value of the measurement point, a calculation unit that calculates the position error and the posture error of the measurement point;
A storage unit for storing the position error and the posture error calculated by the calculation unit in correspondence with the rotation angle of the rotary feed shaft at each lattice point at a desired position in the axial direction of the linear feed shaft at the measurement point; ,
A numerically controlled machine tool having an error map creation function. In a numerically controlled machine tool having a linear feed shaft and a rotary feed shaft and configured so that the spindle and the table can move relative to each other,
A test piece or workpiece attached to the table;
A measuring device having a sensor provided on the spindle, and measuring a processing surface of the test piece or a workpiece by the sensor at a desired measurement point;
Based on the measurement data measured by the measurement device and the coordinate value of the measurement point, a calculation unit that calculates the position error and the posture error of the measurement point;
A storage unit for storing the position error and the posture error calculated by the calculation unit in correspondence with the rotation angle of the rotary feed shaft at each lattice point at a desired position in the axial direction of the linear feed shaft at the measurement point; ,
A numerically controlled machine tool having an error map creating function.   The error map according to claim 8, further comprising a correction unit that corrects a command position or a position command of the linear feed shaft or the rotary feed shaft based on a position error and an attitude error stored in the storage unit. A numerically controlled machine tool with a creation function.

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