JP2009012083A - Motion error measuring method and device of machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide motion error measuring method and device of a machine tool, which highly accurately measures a turning motion error by turning shafts B and C without requiring a correction. <P>SOLUTION: In this measuring method, the motion error of the machine tool provided with: machining table 3 relatively moving in X, Y and Z-axis directions and relatively turning around the turning shaft B and the turning shaft C; and tool head 2 is measured by using a double ball bar 4. A holding part 6 of one ball of the double ball bar 4 is fixed to the machining table 3 so that a center of the ball 41 is located on an intersection of the turning shafts B and C, a holding part 5 of the other ball 40 is mounted and fixed to the tool head 2, and the double ball bar 4 is positioned to have a reference length fixed in advance. The tool head 2 is fed and moved along a circular feed passage P<SB>1</SB>having the reference length of the double ball bar 4 as a radius in a ZX plane. Based on a detection result of a change of the length of the double ball bar 4 for the time, an offset error of the turning shaft B is determined together with the motion error in the ZX plane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for measuring a movement error between a machining table and a tool head that move relative to each other in a machine tool such as a machining center, and an apparatus used for carrying out this method.

  The machining center is a machine tool that can perform various types of processing with high efficiency without changing the work piece, and has been widely used in the field of production of various industrial products in recent years. The machining by the machining center is executed by relatively moving a machining table to which a workpiece is fixed and a tool head to which a machining tool is attached according to a preset NC (Numerical Control) program. However, in this processing, the relative motion between the processing table (and the workpiece) and the tool head (and processing tool), the pitch error of the ball screw for feed driving, and the elasticity of the support part existing in each part of the feed driving system. There is a problem that errors due to mechanical factors such as lost motion of the feed drive system due to deformation inevitably occur, and the processing accuracy of the workpiece is lowered.

  As a method that makes it possible to easily measure the motion error generated in this way, a double ball bar formed by connecting two spheres (balls) processed with high precision by means of a telescopic connecting rod (bar). There is a method to be used (hereinafter referred to as DBB method) (see, for example, Patent Document 1).

  In this DBB method, a holding part is attached to each of a processing table and a tool head that maintain a predetermined positional relationship, and a ball at both ends of a double ball bar is attracted and held on a magnetic seat provided at the tip of these holding parts. In this state, the machining table and tool head are circularly fed in three orthogonal planes (XY plane, YZ plane, and ZX plane), and the amount of expansion and contraction of the bar on each feed path is detected. The

The ball held in the magnetic seat can be rotated 360 ° around the central axis of the magnetic seat, and can be rotated approximately 180 ° in the plane including the central axis. The movement error in the XY plane is obtained on the full circle locus by 360 ° rotation, and the error measurement in the YZ plane and ZX plane perpendicular to the machining table is on the semicircle locus by 180 ° rotation. Is obtained. In this way, the motion error in the XY, YZ, and ZX planes can be obtained including the distribution in the respective planes, and the cause of the motion error caused by analyzing the distribution pattern can be determined. You can also know.
JP 2001-92510 A

  The DBB method implemented as described above is an effective method in a three-axis control machining center having orthogonal three axes (X axis, Y axis, and Z axis), and is a measure for eliminating the cause of a motion error obtained by measurement. Since it can contribute to the improvement of machining accuracy at the machining center by appropriately executing the above, it has been adopted by ISO (International Standard Organization) and is widely spread in Japan and overseas.

  On the other hand, in recent years, in addition to the three orthogonal axes, the rotary axis C orthogonal to the XY plane and the rotary axis B orthogonal to the ZX plane or the YZ plane are provided. Alternatively, the use of a 5-axis control machining center capable of processing the workpiece on the processing table over the entire surface excluding the fixed surface by turning the tool head is expanding.

  The DBB method using a double ball bar can be applied as it is to the measurement of motion error with three orthogonal axes even in a 5-axis control machining center. Specifically, since the positional deviation error (offset error) of the pivot axes B and C with respect to the origin of the XYZ plane and the error (angular error) caused by the inclination of the pivot axes B and C are superimposed, high-precision measurement is performed. There is a problem that a result cannot be obtained, which is one of the factors that make it difficult to apply a 5-axis control machining center to machining a workpiece that requires high machining accuracy such as die machining.

  Thus, various attempts have been made to apply the conventional DBB method to the measurement of the error of the turning motion by the turning axes B and C. However, in these attempts, the center position of the sphere on the processing table side is moved for each measurement of different movements in order to avoid interference between the holding part that holds the spheres at both ends of the bar and the bar. Since the change in relative position (center-to-center distance and tilt angle) with the other sphere before and after the movement cannot be specified, the measurement result of the movement error obtained at each movement position is affected by the change in the relative position. As a result, satisfactory measurement accuracy cannot be obtained.

  In order to solve this problem, the reference sphere position is measured with a touch-type probe, and based on this result, the offset error of the turning axes B and C with respect to the X, Y, and Z axes is calculated, and the calculated offset error is calculated. There has also been proposed a method of correcting the measurement result of the swivel motion by the swivel axes B and C. This method requires a lot of labor for measurement and calculation of the offset error, and cannot detect the angle error of the swiveling axes B and C with respect to the X, Y, and Z axes, so it is effective in a small 5-axis control machining center. However, sufficient measurement accuracy cannot be obtained in a medium-size or larger 5-axis control machining center in which the influence of the angle error becomes significant.

  It is not impossible to obtain the angle error by mathematical processing of the respective calculation results, while performing the above-described measurement and offset error calculation by changing the reference sphere position in various ways. The accuracy of the results obtained is not sufficient.

  The present invention has been made in view of such circumstances, and it is possible to measure a motion error of a machine tool capable of measuring a rotational motion error by the rotational axes B and C with high accuracy without requiring any correction. It is an object of the present invention to provide a method and a motion error measuring apparatus used for carrying out the method.

  The method for measuring a motion error of a machine tool according to the present invention includes a relative movement in X, Y, and Z axis directions orthogonal to each other, a swing axis B substantially orthogonal to the YZ plane or the ZX plane, and a swing axis C substantially orthogonal to the XY plane. Motion error of a machine tool that measures the motion error of a machine tool equipped with a machining table and a tool head capable of relative swiveling around the center using a double ball bar formed by fixing spheres at both ends of an extendable connecting rod In the measurement method, a holding portion for holding one sphere of the double ball bar is fixed to the processing table, and the center of the sphere is positioned so as to maintain a predetermined positional relationship with respect to the intersection of the pivot axes B and C. And a step of attaching and fixing the holding portion for holding the other ball of the double ball bar to the tool head, and the working table or the tool head is relatively moved and held by the respective holding portions. Positioning the connecting rod so as to have a predetermined reference length, and along the circular feed path having the reference length as a radius in the YZ plane or the ZX plane with respect to the machining table or the tool head. A step of obtaining an offset error of the swivel axis B together with a linear motion error in the YZ plane or the ZX plane based on a detection result of a change in the length of the connecting rod during this period, and the machining table or tool A head is moved along a circular feed path having a radius of the reference length in the XY plane, and a linear motion error in the XY plane is detected based on a detection result of a change in the length of the connecting rod during this period. And a step of obtaining an offset error of the turning axis C.

  The method for measuring a motion error of a machine tool according to the present invention includes a relative movement in the X, Y, and Z axis directions orthogonal to each other, a swing axis B substantially orthogonal to the YZ plane or the ZX plane, and a swing axis approximately orthogonal to the XY plane. Movement of machine tool that measures a movement error of a machine tool having a machining table and a tool head capable of relative turning around C using a double ball bar in which balls are fixed to both ends of an extendable connecting rod. In the error measurement method, a step of fixing a holding portion for holding one sphere of the double ball bar to the processing table so that a center of the sphere is located away from the turning axis B or the turning axis C; A step of mounting and fixing the holding portion for holding the other ball of the ball bar to the tool head, and a relative movement of the processing table or the tool head and holding the ball held by each holding portion to the connecting rod A step of positioning so that the reference length is determined, and the processing table or tool head in a state where the connecting rod is substantially horizontal, the circular shape having the reference length as a radius in the YZ plane or ZX plane. The feed head is moved along the feed path, and the tool head or the machining table is swung around the swivel axis B in synchronism with the movement, and based on the detection result of the change in the length of the connecting rod in the meantime, The step of obtaining the angular error of the turning axis B, and the feed movement of the machining table or tool head along a circular feed path having the reference length as a radius in the XY plane with the connecting rod substantially vertical. In synchronism with this movement, the tool head or the machining table is swiveled around the swivel axis C, and the swivel is performed based on the detection result of the length change of the connecting rod during this time. Characterized in that it comprises a step of obtaining the C angular error.

  The motion error measuring device according to the present invention is a motion error measuring device used for carrying out the above motion error measuring method, wherein the holding parts for holding the spheres at both ends of the double ball bar are the machining table or the tool. The base fixed to the head and the base are connected with an inclination of approximately 45 °, and the sphere is supported at the tip of each base so as to be able to roll within a central angle exceeding 270 °. And a support rod.

  In the method for measuring a motion error of a machine tool according to the present invention, after positioning a holding part fixed to the machining table or the tool head with respect to the intersection of the turning axes B and C, a double ball held by these holding parts Simultaneously with measurement of linear motion errors in the XY, ZX, and YZ planes by moving the work table and tool head in the YZ plane, ZX plane, and XY plane while maintaining the bar reference length The offset error of the pivot axes B and C can be measured.

  In addition, after positioning the holding unit fixed to the processing table or the tool head with respect to the pivot axes B and C, the processing table and the tool head are maintained while maintaining the reference length of the double ball bar held by these holding units. The angle error of the swivel axes B and C can be measured by a procedure for feeding and moving the light in the YZ plane or the ZX plane and in the XY plane and performing a swivel movement around the swivel axes B and C. In this way, the error of the turning motion by the turning axes B and C can be measured with high accuracy without requiring any correction.

  Furthermore, in the motion error measuring device according to the present invention, the holding part for holding the spheres at both ends of the double ball bar includes a support bar extending in a direction of 45 ° obliquely from the base fixed to the processing table or the tool head. Since the sphere is held at the tip of the support bar, the circular interpolation feed in the XY, YZ and ZX planes necessary for the implementation of the motion error measuring method according to the present invention is performed over the entire circumference of each. Each measurement can be realized with high accuracy.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is an external perspective view showing an example of a machining center to which a motion error measurement method according to the present invention is applied.

  As shown in the figure, the machining center includes a base 10 installed on a floor surface, and a pair of side walls 11 and 11 and a rear wall 12 vertically installed on the upper surface of the base 10 so as to surround three sides except the front surface. And a support frame 1 having The upper surfaces of the side walls 11 and 11 and the rear wall 12 are configured as horizontal planes, and Y-direction guide rails 13 and 13 extending in the front-rear direction in parallel with each other are laid on the upper surfaces of the side walls 11 and 11. Both ends of the rails 13 and 13 are engaged and held, and a gate-shaped Y-direction moving body 14 is supported horizontally.

  The upper surface of the Y-direction moving body 14 is configured as a horizontal plane, and an X-direction guide rail 15 extending in the left-right direction (a direction orthogonal to the Y-direction guide rails 13 and 13) is laid on the upper surface. An X-direction moving body 16 is supported so as to be movable along the guide rail 15.

  The front portion of the X-direction moving body 16 projects forward from the front edge of the Y-direction moving body 14, and a rectangular support block 17 that is long in the vertical direction is fixed to the projecting portion. The support block 17 has a front surface configured as a vertical surface, and a Z-direction guide rail extending in the vertical direction (a direction perpendicular to the Y-direction guide rails 13 and 13 and the X-direction guide rail 15) on the front surface. A Z-direction moving body 19 is supported so as to be movable along the guide rail 15.

  A cylindrical head base 20 is fixed to the front surface of the Z-direction moving body 19 with the axis centered vertically, and a tool for detachably attaching the processing tool 2a to the lower end of the head base 20 The head 2 is supported so as to be rotatable on the same axis. The tool head 2 is rotationally driven together with the machining tool 2a attached to the lower end by transmission from a tool motor (not shown) built in the head base 20.

  With the above configuration, the tool head 2 and the processing tool 2a attached thereto are moved in the front-rear direction (Y direction) and the left-right direction (X direction) on the horizontal plane according to the movement of the Y-direction moving body 14 and the X-direction moving body 16. And can move in the vertical direction (Z direction) in the vertical plane according to the movement of the Z direction moving body 19. These movements are realized by converting the rotation of the feed motor provided for each of the X, Y, and Z directions into a linear motion by a motion conversion mechanism such as a ball screw mechanism. The feed motor and the motion conversion mechanism in each direction are not shown.

  On the other hand, on the rear wall 12 of the frame 1, a swivel base 30 that can swivel around a horizontal swivel axis B that extends in the front-rear direction is supported at a position spaced apart from the upper surface of the base 10 by an appropriate length. The swivel base 30 is provided with a table base 31 that extends downward in parallel with the swivel axis B at a position away from the swivel axis B and away from the upper surface of the base 10. A processing table 3 for fixing a workpiece (not shown) is provided on the upper surface of the table 31 so as to be capable of turning around a turning axis C orthogonal to the turning axis B.

  The workpiece fixed to the machining table 3 with the above-described configuration is obtained by combining the tool head 2 and the workpiece head 2 by the combination of the turning of the turntable 30 around the turning axis B and the turning of the processing table 3 around the turning axis C. The facing posture with respect to the processing tool 2a mounted thereon can be freely changed, and the tool head 2 and the processing tool 2a are rotated in a state where each facing posture is maintained, and these are moved in three directions of X, Y, and Z. By moving, the entire surface of the workpiece excluding the fixed surface to the processing table 3 can be processed.

  The motion error measurement method according to the present invention (hereinafter referred to as the present method) has five orthogonal axes (X axis, Y axis and Z axis) and swivel axes B and C, and is configured as described above. In the machining center, it is carried out to measure the movement error between the tool head 2 and the machining table 3. The 5-axis control machining center is not limited to the configuration shown in FIG. 1, but can be put into practical use by changing the configuration of the relative movement means in the X, Y, and Z axial directions and the turning means around the turning axes B and C. However, the method of the present invention described below is applicable regardless of the configuration of the moving means and the turning means.

  FIG. 2 is a side view of a motion error measuring device (hereinafter referred to as the present device) used for carrying out the method of the present invention. As shown in the figure, the device of the present invention includes a double ball bar 4 formed by connecting two balls 40 and 41 processed with high precision by a connecting rod 42 that can be expanded and contracted, and balls 4a and 4b at both ends of the double ball bar 4. Is provided with holding portions 5 and 6 that are rotatably held by magnetic seats provided at the respective tips.

  The double ball bar 4 is the same as that conventionally used, and in the middle of the connecting rod 42, detection for detecting expansion and contraction of the connecting rod 42 according to the relative position change of the balls 40 and 41 at both ends. A portion 43 is provided. This detection unit 43 utilizes the fact that the moire pattern generated when two parallel stripes with slightly different pitches are moved moves larger than the relative displacement of the parallel stripes, and thereby allows the connecting rod 42 to be slightly expanded and contracted. It can be constituted by a moire scale that can be enlarged and detected.

  The device of the present invention is characterized by the structure of the holding portions 5 and 6 that hold the balls 40 and 41 at both ends of the connecting rod 42. As shown in FIG. 2, one holding portion 5 includes a round bar-like base portion 50 which is coaxially fitted and fixed to the lower end of the tool head 2 instead of the machining tool 2 a, and an intermediate portion of the base portion 50 with respect to the axis. And a support ball 51 extending obliquely at an angle of 45 °. A ball 40 on one side of the double ball bar 4 is held by a magnetic seat provided at the tip of the support bar 51.

  FIG. 3 is an enlarged view of the magnetic seat provided at the tip of the support bar 51. The distal end portion of the support bar 51 has a tapered cylindrical shape with a reduced diameter in a tapered shape. Three support projections 52, 52, 52 are provided at the end edge of the tip portion so as to be equally distributed in the circumferential direction. Inside the support bar 51, the magnet 53 is positioned at a position that is separated from the tip edge by an appropriate length. Is fixed, and a magnetic seat is constituted by the support protrusions 52, 52, 52 and the magnet 53.

  As shown by a two-dot chain line in FIG. 3, the ball 40 on one side of the double ball bar 4 is seated on the support protrusions 52, 52, 52 provided at the tip of the support bar 51, The magnet 53 is attracted by the magnetic force and is attracted and held by the magnetic seat at the tip of the support bar 51. The tips of the support protrusions 52, 52, 52 are spherically processed into a concave shape having a center on the axis of the support bar 51 and having the same diameter as the sphere 40, and the support protrusions 52, 52, 52 The seated ball 40 is in surface contact with the tip of each of the support protrusions 52, 52, 52, and can freely roll while maintaining the concentricity with the support bar 51 while maintaining this seated state. In the device of the present invention, as shown in the figure, the diameter of the tip of the support bar 51 including the support protrusions 52, 52, 52 is sufficiently smaller than the diameter of the sphere 40 and is connected to the sphere 40. The connecting rod 42 is a round bar having a sufficiently small diameter compared to the diameter of the sphere 40. The ball 40 held on the magnetic seat by this dimension setting can roll within a central angle exceeding 270 ° under the condition that the support bar 5 and the connecting bar 42 do not interfere with each other.

  As shown in FIG. 2, the other holding portion 6 includes a first base 60 fixed to the upper surface of the processing table 3 (fixed surface of the workpiece) by appropriate means so as to rise perpendicularly to the upper surface. The second base 61 is provided on the upper portion of the first base 60. A cylindrical holding cylinder 62 having an axis inclined by 45 ° with respect to the height direction of the second base 61 is fixed to the upper part of the second base 61, and a support rod 63 is attached to the holding cylinder 62 in the axial direction. It is fitted and held so that it can be moved to.

  Similar to the support bar 51 in the holding part 5, the support bar 63 has a tapered tip that has a tapered diameter on the side protruding upward from the holding cylinder 62. There is provided a magnetic seat for attracting and holding the ball 41 on the other side of the double ball bar 4 so that it can roll within a central angle range exceeding 270 °.

  The first base portion 60 and the second base portion 61 of the holding portion 6 include a plurality of support balls 64 interposed between conical recesses provided at the center of each seating surface and arranged around the support balls 64. Are fixed via fixing means, so-called wobble plates, so that the seating surfaces are opposed to each other with a predetermined gap therebetween. The second base 61 fixed in this way can adjust the inclination angle with respect to the first base 60 within the range of the gap by adjusting the tightening degree of the fixing screws 65, 65.

  As a result of this adjustment, the sphere 41 attracted and held by the magnetic seat at the tip of the support rod 63 moves along a spherical surface centered on the support sphere 64 as indicated by the solid arrow in FIG. By utilizing this movement, the position of the sphere 41 can be finely adjusted without changing the fixing position of the holding portion 6 on the processing table 3.

  An adjustment knob 66 is provided on the lower side of the holding cylinder 62 from which the base portion of the support bar 63 protrudes so as to be rotatable on the same axis. The adjustment knob 66 is screwed into a screw portion (not shown) formed on the outer periphery of the base portion of the support rod 63 protruding on the same side. The support rod 63 rotates the adjustment knob 66 to rotate the holding cylinder 62. As a guide, the movement can be adjusted. This movement adjustment is executed to finely adjust the position of the sphere 41 held at the tip of the support rod 63 in the direction indicated by the broken arrow in FIG.

  As described above, the spheres 40 and 41 at both ends of the double ball bar 4 are rotated on the magnetic seats at the tips of the support rods 51 and 63 provided on the respective holding portions 5 and 6 within a central angle range exceeding 270 °. The movement is held as possible. The support bars 51 and 63 having magnetic seats have an inclination angle of about 45 ° with respect to the tool head 2 (the axis thereof) and the processing table 3 (the upper surface thereof) to which the holding portions 5 and 6 are fixed. Is inclined. Therefore, as shown in FIG. 2, the double ball bar 4 can realize a state in which the sphere 40 on the tool head 2 side is positioned vertically below the sphere 41 on the processing table 3 side.

  The procedure of the method of the present invention performed to measure the relative motion error between the tool head 2 and the machining table 3 using the device of the present invention configured as described above will be described below. 4 and 5 are explanatory diagrams showing the state of implementation of the method of the present invention. FIG. 4 shows the measurement state of the linear motion error in the ZX plane and the offset error of the swivel axis B. FIG. The measurement state of the linear motion error in the plane and the offset error of the turning axis C is shown.

  When performing these measurements, as shown in FIGS. 4 and 5, the holding unit 5 is fixed to the tool head 2, and the holding unit 6 is fixed to the upper surface of the processing table 3. As described above, the holding portion 5 is fixed to the tool head 2 by fitting and fixing the round bar-like base portion 50 to the lower end of the tool head 2 as described above. The holding unit 6 is fixed to the upper surface of the processing table 3 by fixing the first base 60. This fixing position is set to both X and Y from the center of the upper surface of the processing table 3 as shown in the figure. The position is a predetermined length away in the middle direction of the shaft.

  After fixing the holding portion 6 in this manner, the ball 41 on one side of the double ball bar 4 is adsorbed and held at the tip of the support bar 63 extending obliquely upward, and the centers of the balls 41 are the pivot axis B and the pivot axis C. Position to match the intersection of This positioning is performed by a procedure for detecting the absolute displacement of the sphere 41 by an appropriate means while performing the turning motion by the B-axis and the C-axis and searching for the position of the sphere 41 where the absolute displacement does not occur during the turning motion. At this time, the position adjustment of the sphere 41 is realized by changing the inclination angle of the second base 61 and changing the position of the support rod 63 in the axial direction as described above. The positioning procedure described above may be performed using an appropriate reference sphere processed to the same diameter as the sphere 41 of the double ball bar 4.

  After the positioning of the holding portion 6 on the processing table 3 is finished in this way, the tool head 2 is moved, and the holding portion 5 attached and fixed to the tool head 2 is roughly positioned with respect to the holding portion 6. In addition, the ball 40 on the other side of the double ball bar 4 is sucked and held at the tip of the support bar 51 extending obliquely downward. Next, in this state, the tool head 2 is slightly moved so that the double ball bar 4 becomes the reference length, more specifically, the tool head so that the separation length between the centers of the balls 40 and 41 on both sides becomes the reference length. The holding part 5 on the second side is positioned. This positioning is performed with reference to the detection result of the detector 43 in the middle of the connecting rod 42 that connects the balls 40 and 41.

  4 and 5, the state after the positioning as described above is indicated by a solid line. When measuring the linear motion error in the ZX plane and the offset error of the turning axis B, the holding unit 5 is positioned so that the double ball bar 4 has a reference length in the target ZX plane (in the vertical plane). The As described above, the balls 40 and 41 at both ends of the double ball bar 4 roll within a central angle range exceeding 270 ° by the magnetic seats at the tips of the support rods 51 and 63 of the separate holding parts 5 and 6. The support bars 51 and 63 are inclined by 45 ° with respect to the upper surface of the processing table 3 and the axis of the tool head 2. Therefore, as shown in FIG. 4, the ball 40 on the tool head 2 side can be positioned so as to be positioned vertically below the ball 41 on the processing table 3 side.

  When measuring the linear motion error in the XY plane and the offset error of the swivel axis C, the holding unit 5 is positioned so that the double ball bar 4 has a reference length in the XY plane (horizontal plane). Is done. In this case as well, positioning as shown in FIG. 5 is possible.

  The linear motion error in the ZX plane and the offset error of the swivel axis B are measured after the positioning shown in FIG. 4 is finished, and the tool head 2 is circularly interpolated in the ZX plane, and the double generated between these feeds. This is performed according to a procedure of detecting a change in the length of the ball bar 4 by a detection unit 43 provided in the middle of the connecting rod 42. Circular interpolation feed in the ZX plane can be realized with high accuracy by combining the movement of the X-direction moving body 16 and the Z-direction moving body 19.

In this ZX plane, the ball 40 on the tool head 2 side starts to move from the initial position shown by the solid line in FIG. 4 and returns to the initial position through the intermediate position shown by the two-dot chain line in FIG. The double ball bar 4 is moved along the entire circumference of a circular feed path P ₁ whose radius is the reference length of the double ball bar 4. During this time, the detection unit 43 and the ball 40 (center thereof) on the tool head 2 side are processed. An axial length direction component of the connecting rod 42 relative to the sphere 41 (center) on the table 3 side is detected. This detected displacement is caused by the influence of errors existing in each part of the feed drive system in the X direction and the Z direction, and the ZX plane is included in the detection result of the detector 43 obtained over the entire circumference of the feed path P _1. A linear motion error appears.

On the other hand, at this time, the sphere 41 on the processing table 3 side is positioned on the intersection of the turning axis B and the turning axis C as described above, and the turning axis B is in the ZX plane with respect to the center of the feed path P ₁ . When the position is shifted in the Y and Z directions, an error component (offset error) corresponding to the position shift amount of the turning axis B is superimposed on the detection result of the detection unit 43 and appears.

  The linear motion error in the XY plane and the offset error of the swivel axis C are measured after the positioning shown in FIG. 5 is finished and the tool head 2 is circularly interpolated in the XY plane, and a double generated between these feeds. This is performed by a procedure for detecting a change in the length of the ball bar 4. The circular interpolation feed in the XY plane is realized with high accuracy by a combination of the feed movement of the Y-direction feed table 14 and the X-direction moving body 16.

With this feed, the sphere 40 on the tool head 2 side starts moving from the initial position indicated by the solid line in FIG. 5 and returns to the initial position through the intermediate position indicated by the two-dot chain line in the XY plane. The double ball bar 4 is moved along the entire circumference of a circular feed path P ₂ whose radius is the reference length of the double ball bar 4. The detection result obtained in the detection unit 43 during this period corresponds to the motion error caused by the error existing in each part of the feed drive system in the X direction and the Y direction, and the positional deviation amount of the turning axis C in the XY plane. The offset error appears superimposed.

FIG. 6 is an explanatory diagram showing an example of a result obtained by carrying out the method of the present invention. This figure shows the results obtained in the measurement of the linear motion error in the XY plane and the offset error of the pivot axis C, and the measured value of the length of the double ball bar 4 at each position of the circular feed path P ₂ . It is shown replaced with a radius from the center O ₂ of the feed path P _2. The feed path P ₂ is represented as a circle centered on the center O ₂ and having a radius of the reference length of the double ball bar 4.

Detection result of the detector 43, as shown by a solid line in the figure is given as a distribution pattern on the circumference of the feed path P _2. Here, the misalignment due to the offset error appears in a state of being evenly distributed over the entire circumference of the feed path P _2. Therefore, if the virtual center O of the virtual circle obtained by averaging the detection results shown in FIG. a feed by comparison with the center O ₂ of path P _2, the offset error ΔY of the offset error ΔX and Y directions of the X direction can be accurately extracted. Note that the linear motion error in the XY plane can be obtained including the cause thereof, as is conventionally done, by analyzing the distribution pattern on the circumference of the virtual circle excluding the offset errors ΔX and ΔY. it can.

  The measurement of the linear motion error in the ZX plane and the offset error of the swing axis B performed as shown in FIG. 4 is the same as the measurement of the linear motion error in the XY plane and the offset error of the swing axis C. It can be realized by processing.

  Further, after the positioning state shown in FIG. 4 is obtained, the feed movements of the Y-direction moving body 14 and the Z-direction moving body 19 are combined, the tool head 2 is circularly fed in the YZ plane, and the double ball bar 4 generated in the meantime. The linear motion error in the YX plane can be measured by the procedure for detecting the change in length of. The detection results obtained in this way include the offset error in the Z direction of the turning axis B and the offset error in the Y direction of the turning axis C. These are obtained by the above-described procedure. Correction using the result makes it possible to measure the linear motion error in the YZ plane with high accuracy.

  7 and 8 are explanatory diagrams showing the implementation state of the method of the present invention. FIG. 7 shows the implementation state of the method for measuring the angular error of the pivot axis C. FIG. 8 shows the angular error of the pivot axis B. The implementation state of the measurement method is shown. In these measurements, the holding unit 5 on the tool head 2 side is similarly used with the same configuration. On the other hand, since the holding part 6 on the side of the processing table 3 does not need to be positioned, the base 67 that can be fixed to the upper surface of the processing table 3 and the base 67 extends in a direction of 45 ° obliquely. The support bar 68 is fixed to the processing table 3 as shown in the drawing.

  FIG. 9 is an explanatory diagram of the angle error of the turning axis C. FIG. The offset error (ΔX and ΔY) of the turning axis C obtained as shown in FIG. 6 by the procedure shown in FIG. 5 indicates the amount of displacement in the XY plane (reference plane) including the intersection with the turning axis B. Yes. When the turning axis C is inclined with respect to the Z axis, which is the vertical axis, this positional deviation amount has a different value at each position in the Z axis direction.

As shown in FIG. 9, the offset errors obtained from the above-described measurement results in the XY plane whose Z coordinate is Z ₀ are ΔX ₀ and ΔY ₀ , and the other XY plane whose Z coordinate is Z _1. When the offset error obtained from the result of the measurement is ΔX ₁ , ΔY ₁ , the angle errors C _x , C _Y (rad) of the turning axis C in the X and Y directions are given by the following equations.

C _x = (ΔX ₁ −ΔX ₀ ) / (Z ₁ −Z ₀ ) (1)
C _Y = (ΔY ₁ −ΔY ₀ ) / (Z ₁ −Z ₀ ) (2)

The angle errors C _x and C _Y are the X-axis direction component and the Y-axis direction component of the inclination of the turning axis C with respect to the Z axis. If these angle errors C _x and C _Y can be known, these are shown in FIG. By applying the offset errors ΔX ₀ , ΔY ₀ obtained in the reference plane by the procedure shown in (1) to (1) or (2), the offset errors ΔX ₁ , ΔY ₁ generated at any position in the Z-axis direction. Can be requested. In FIG. 9, the tilt of the turning axis C is shown in an enlarged manner, but the actual tilt angle is a minute angle.

The swivel axis C angle errors C _x and C _Y are measured by fixing the holding unit 5 to the tool head 2 and the holding unit 6 to the processing table 3 as described above, and then feeding the tool head 2. The holding unit 5 attached and fixed to the tool head 2 is roughly positioned above the holding unit 6 fixed to the processing table 3. In this state, the balls 40 and 41 at both ends of the double ball bar 4 are attracted and held on the magnetic seats provided at the tips of the support bar 51 of the holding unit 5 and the support bar 68 of the holding unit 6 to slightly move the tool head 2. Then, the double ball bar 4 is positioned so as to have a reference length.

  FIG. 7 shows a state after this positioning. The tool head 2 is positioned so that the double ball bar 4 is vertical between the holding portions 5 and 6 as shown in the figure. As for the angular error of the pivot axis C, after the above positioning is completed, the machining table 3 on the table base 31 is pivoted around the pivot axis C, and the tool head 2 is moved in the XY plane in synchronization with the pivot movement. Then, it can be obtained by a procedure for detecting the change in the length of the double ball bar 4 during circular interpolation feed.

In the circular interpolation feed of the tool head 2, the path P ₃ followed by the sphere 40 on the tool head 2 side by this feed, and the path P followed by the sphere 41 on the machining table 3 side by turning the machining table 3 around the turning axis C. It is carried out so that it becomes a circular path of the same diameter as ₄ . Such circular interpolation feeding can be realized in synchronism with the turning operation of the machining table 3 accurately by a combination of the feeding operations of the X-direction moving body 16 and the Z-direction moving body 19.

At this time, the path P ₃ of the sphere 40 on the side of the tool head 2 exists in the XY plane, whereas the path P ₄ of the sphere 41 on the side of the machining table 3 is orthogonal to the turning axis C of the machining table 3. When the turning axis C of the machining table 3 has an inclination with respect to the Z axis orthogonal to the XY plane, the length of the double ball bar 4 during execution of the above procedure is It changes in each part of the feed path.

FIG. 10 is an explanatory diagram showing an example of a result obtained by measuring the angle error of the turning axis C shown in FIG. This figure shows the detection value of the length change ΔZ of the double ball bar 4 obtained at each position on the paths P ₃ and P ₄ in an XY plane. The detected value of ΔZ indicated by the solid line in the figure is a circle centered on the origin O of the XY plane and offset in the X and Y directions with respect to the basic circle indicated by the broken line in the figure.

Therefore, if the X direction component of the offset amount existing between the virtual center O _Z of the circle and the center O of the basic circle is ΔZ _X and the Y direction component is ΔZ _Y , the angular error C _{x of the} turning axis C , C _Y can be obtained by the following equation using the reference length L of the double ball bar 4.

C _x = ΔZ _x / L (3)
C _Y = ΔZ _Y / L (4)

  In FIG. 10, the detection result of the length of the double ball bar 4 is shown as a simple circle. However, as shown in FIG. 6, the actual detection result is a distribution pattern that fluctuates at each position on the circumference. As given.

In order to obtain the angular errors C _x and C _Y of the swivel axis C with high accuracy, the double ball bar 4 needs to be set to the vertical correctly in the above-described positioning, but the difference in detection results caused by a slight difference in positioning angle. Is negligible, and it is not necessary to strictly manage the vertical of the double ball bar 4 during positioning. Further, since the length change of the double ball bar 4 due to the inclination of the turning axis C increases as the distance from the center of the turning axis C increases, the fixing position of the holding portion 6 on the processing table 3 side is as shown in FIG. However, if the holding position of the holding unit 6 is set so that the center of the sphere 41 does not coincide with the turning axis C, the angle error C _{x is} determined from the obtained detection result. , C _Y can be obtained.

  When measuring the angular error of the swivel axis B, as shown in FIG. 8, the tool head 2 is fed and moved to the outside of the processing table 3, and the support bar 51 of the holding part 5 and the support bar of the holding part 6 are measured. The balls 40 and 41 at both ends of the double ball bar 4 are attracted and held at the tip of the 68, and then the tool head 2 is moved minutely while maintaining this state, and the double ball bar 4 is positioned to the reference length. This positioning is performed so that the double ball bar 4 is horizontal between the holding portions 5 and 6 as shown in the figure.

The angular error of the swivel axis B is measured by moving the swivel base 30 around the swivel axis B after completing the above positioning and synchronizing the tool head 2 in the ZX plane in synchronization with this swivel movement. This is done by a procedure for detecting the change in length of the double ball bar 4 during this period. During the execution of this procedure, the sphere 40 on the side of the tool head 2 moves along an arc path existing in the ZX plane, whereas the sphere 41 on the side of the machining table 3 has a plane orthogonal to the turning axis B. It moves along the arc path that exists inside. Therefore, when the swivel axis B of the swivel base 30 has an inclination with respect to the Y axis perpendicular to the ZX plane, the detection result of the length change of the double ball bar 4 that occurs during the execution of the above procedure includes: The magnitude and direction of the inclination of the swivel axis B are included, and the angle errors B _x and B _z of the swivel axis B can be obtained based on the detection result of the length change of the double ball bar 4.

  In order to obtain a detection result that accurately corresponds to the angular error of the swivel axis B, the double ball bar 4 needs to be correctly leveled in the above-described positioning, but the difference in detection result caused by a slight difference in positioning angle is It is negligible, and it is not necessary to strictly manage the level of the double ball bar 4 during positioning. Further, since the change in the length of the double ball bar 4 due to the inclination of the swivel axis B increases as the distance from the swivel axis B increases, the fixing position of the holding portion 6 on the processing table 3 side is held as shown in FIG. It is desirable to set so that the sphere 41 attracted and held by the portion 6 is close to the upper surface of the processing table 3. The fixed position of the holding part 6 shown in FIG. 7 and FIG. 8 can be suitably used for measuring the angular error of the turning axes B and C.

  In the above embodiment, when measuring the linear motion error and the C-axis offset error in the ZX plane, the sphere 41 held by the holding unit 6 on the processing table 3 side is placed on the intersection of the turning axes B and C. In the case where the stroke required for turning the double ball bar 4 cannot be secured below the intersection, the ball 41 is positioned at a position offset above the intersection of the turning axes B and C. Then, the measurement may be performed. Even in this case, if the offset length from the intersection is known, the linear motion error and the offset error can be accurately obtained by the same procedure.

1 is an external perspective view showing an example of a machining center to which a motion error measurement method according to the present invention is applied. It is a side view of the movement error measuring device used for implementation of the method of the present invention. It is an enlarged view of the front-end | tip part of a support bar. It is explanatory drawing which shows the implementation state of the method of this invention. It is explanatory drawing which shows the implementation state of the method of this invention. It is explanatory drawing which shows an example of the result obtained by implementation of the method of this invention. It is explanatory drawing which shows the implementation state of the method of this invention. It is explanatory drawing which shows the implementation state of the method of this invention. It is explanatory drawing of the angle error of a turning axis. It is explanatory drawing which shows an example of the result obtained by the measurement of the angle error of the turning axis C shown in FIG.

Explanation of symbols

2 Tool head 3 Processing table 4 Double ball bar 5, 6 Holding part
14 Y-direction moving body
16 X direction moving body
19 Z-direction moving body
40, 41 balls
42 Connecting rod
43 Detector B, C Rotating axis

Claims (3)

Machining table and tool capable of relative movement in the X, Y, and Z axis directions orthogonal to each other and the rotation about the rotation axis B substantially orthogonal to the YZ plane or the ZX plane and the rotation axis C approximately orthogonal to the XY plane In a machine tool motion error measurement method for measuring a motion error of a machine tool including a head using a double ball bar in which balls are fixed to both ends of an extendable connecting rod,
Fixing a holding portion for holding one sphere of the double ball bar to the working table, and positioning the center of the sphere so as to maintain a predetermined positional relationship with respect to the intersection of the turning axes B and C;
Attaching and fixing a holding portion for holding the other ball of the double ball bar to the tool head;
A step of relatively moving the processing table or the tool head and positioning the spheres held in the respective holding portions so that the connecting rod has a predetermined reference length;
Based on the detection result of the change in the length of the connecting rod during this period, the working table or tool head is fed and moved along a circular feed path having the reference length as a radius in the YZ plane or ZX plane. Obtaining an offset error of the turning axis B together with a linear motion error in the YZ plane or the ZX plane;
The machining table or tool head is moved along a circular feed path having the reference length as a radius in the XY plane, and the XY plane is moved in the XY plane based on the detection result of the change in the length of the connecting rod. A method for measuring a motion error of a machine tool, comprising: calculating an offset error of the swivel axis C together with a linear motion error in Machining table and tool capable of relative movement in the X, Y, and Z axis directions orthogonal to each other and the rotation about the rotation axis B substantially orthogonal to the YZ plane or the ZX plane and the rotation axis C approximately orthogonal to the XY plane In a machine tool motion error measurement method for measuring a motion error of a machine tool including a head using a double ball bar in which balls are fixed to both ends of an extendable connecting rod,
Fixing the holding portion for holding one sphere of the double ball bar to the processing table so that the center of the sphere is located away from the turning axis B or the turning axis C;
Attaching and fixing a holding portion for holding the other ball of the double ball bar to the tool head;
A step of relatively moving the processing table or the tool head and positioning the spheres held in the respective holding portions so that the connecting rod has a predetermined reference length;
The work table or tool head is fed and moved along a circular feed path having a radius of the reference length in the YZ plane or ZX plane in a state where the connecting rod is substantially horizontal, and is synchronized with this movement. The tool head or the machining table is swiveled around the swivel axis B, and the angle error of the swivel axis B is determined based on the detection result of the change in the length of the connecting rod during this period;
The work table or tool head is fed and moved along a circular feed path having the radius of the reference length on the XY plane in a state where the connecting rod is substantially vertical, and the tool head is synchronized with this movement. Or a step of turning a machining table around the turning axis C and obtaining an angle error of the turning axis C based on a detection result of a change in the length of the connecting rod during the operation. Method for measuring machine motion error. A motion error measuring device used for carrying out the motion error measuring method for a machine tool according to claim 1 or 2,
The holding part that holds the spheres at both ends of the double ball bar,
A base fixed to the processing table or tool head;
And a support rod that supports the sphere at a tip of each base so as to be able to roll within a central angle exceeding 270 °. Movement error measuring device.

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