Five-axis control machine tool, error identification method thereof, and storage medium

Abstract

The present application provides a 5-axis control machine tool and its error identification method, storage medium, which can identify the inter-axis geometric error with high precision without the influence of the geometric error of the single axis of the straight-axis. The following steps are performed: a contact probe is installed on the main shaft, and a ball array is fixed on the worktable; the initial position of the ball array is measured by the contact probe; the reference angle of each rotary shaft for positioning the ball array at the reference position is calculated according to the measured value in the initial position measurement step; each rotary shaft is indexed to a plurality of index angles with respect to the reference angle, and the center positions of the balls of the ball array fixed on the worktable at each index angle are measured by the contact probe; and the positioning error, straightness error and perpendicularity error of the straight-axis, and the position error and inclination error of each rotary shaft are identified based on the measured value in the corrector measurement step.

Description

Technical Field

[0001] The present invention relates to a method for identifying geometric errors in a 5-axis machine tool such as a 5-axis control machining center, a storage medium storing an error identification program for executing the method, and a 5-axis machine tool capable of executing the method. Background Technology

[0002] Figure 1 This is a schematic diagram of a 5-axis machining center with 3 linear axes and 2 rotary axes. The spindle head 2 can perform 2 degrees of freedom translational motion relative to the bed 1 via the X and Z axes, where the X and Z axes are linear axes and are perpendicular to each other. The worktable 3 can perform 1 degree of freedom rotational motion relative to the cradle 4 via the C-axis, which is a rotary axis. The cradle 4 can perform 1 degree of freedom rotational motion relative to the trunnion 5 via the A-axis, which is a rotary axis. The A-axis is perpendicular to the C-axis. Furthermore, the trunnion 5 can perform 1 degree of freedom translational motion relative to the bed 1 via the Y-axis, where the Y-axis is a linear axis and is perpendicular to the X and Z axes. Therefore, the spindle head 2 can perform 3 degrees of freedom translational motion and 2 degrees of freedom rotational motion relative to the worktable 3. Each feed axis is driven by a servo motor controlled by a CNC device (not shown). The workpiece is fixed on the worktable 3, the tool is mounted on the spindle head 2 and rotated, and the relative position and relative posture of the workpiece and the tool can be controlled for machining.

[0003] The main factors affecting the motion accuracy of 5-axis machining centers include errors in the center position of rotary axes (offset relative to the intended position), tilt errors of rotary axes (perpendicularity and parallelism between axes), and geometric errors between axes. For example, in Figure 1 In a 5-axis controlled machining center, there are three inter-axis geometric errors related to the linear axis: XY axis perpendicularity, YZ axis perpendicularity, and ZX axis perpendicularity. There are two inter-axis geometric errors related to the spindle: tool-Y axis perpendicularity and tool-X axis perpendicularity. There are eight inter-axis geometric errors related to the rotary axis: C-axis center position X-direction error, CA-axis deviation error, A-axis angle deviation error, CA-axis perpendicularity, A-axis center position Y-direction error, A-axis center position Z-direction error, AZ-axis perpendicularity, and AY-axis perpendicularity.

[0004] In addition, within the straight shaft unit, there are also geometric errors of each shaft unit, such as positioning errors and straightness. These errors are the main reasons affecting the motion accuracy of the machine.

[0005] If these geometric errors exist, the motion accuracy of the machine tool and the machining accuracy of the workpiece will deteriorate. Countermeasures typically involve manufacturing or adjusting to reduce geometric errors, or correcting and controlling the positional errors of the tool relative to the workpiece caused by these geometric errors. To perform such corrective control, it is necessary to measure or identify the inherent geometric errors of the machine tool.

[0006] As a method for identifying inter-axis geometric errors, the inventors of this application have proposed a method similar to that in Patent Document 1. In this method, the worktable is indexed into multiple angles by rotation / tilt using a rotating axis. A contact probe mounted on the spindle is used to measure the center position of a ball fixed to the worktable, and the inter-axis geometric errors can be identified based on the measured values. Alternatively, by simply setting the ball on the worktable, a series of measurements can be automatically performed to automatically identify geometric errors. This method has the advantage that even if the machine operator lacks the knowledge or skills for measurement, geometric errors can still be identified.

[0007] On the other hand, as a method for identifying the geometric error of a single shaft, Patent Document 2 shows the following method: In a three-dimensional measuring machine, the orientation of a stepped gauge with multiple gauge blocks is changed to multiple directions, the distance between the gauge blocks is measured, and the overall stretching component (first-order component) of the positioning error of the three straight axes and the perpendicularity between the three straight axes are identified.

[0008] In addition, Patent Document 3 shows a method in which the orientation of a ball array having multiple balls is changed to multiple directions in a machine tool, and the distance between multiple balls in the ball array is measured separately using a contact probe mounted on the spindle, and the first-order component of the positioning error of the three linear axes and the perpendicularity between the three linear axes are identified.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2011-38902

[0012] Patent Document 2: Japanese Patent Application Publication No. 2007-101279

[0013] Patent Document 3: Japanese Patent Application Publication No. 2020-46301 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] The contact probes mainly used in patent documents 1-3 are devices that output signals when in contact with an object. When in contact with the object, a control device detects the signal and obtains the detection position of the linear axis detected by the position detector at the moment the signal is received, or at the moment considering the delay. This allows for the measurement of the object's position. Therefore, the measurement results of the ball by the contact probe are affected by the geometric errors (positioning errors, straightness) of each linear axis unit.

[0016] Therefore, in the method of Patent Document 1, when the geometric error of each straight shaft is large, there is a problem that the geometric error between shafts cannot be identified with high precision.

[0017] On the other hand, in the methods of Patent Documents 2 and 3, the first-order component (overall extension component) of the positioning error of each straight axis and the perpendicularity between each axis can be identified, but in the identification of perpendicularity, there is a problem that it is affected by the true straightness of the straight axis.

[0018] Furthermore, changing the orientation of stepped gauges and ball arrays requires altering the angle of the clamps used for their installation, which is cumbersome for operators. If the orientation is changed incorrectly, a collision could occur. Additionally, installing a drive mechanism on the rotating unit of the clamp increases its cost.

[0019] Therefore, the purpose of this invention is to provide an error identification method for a 5-axis controlled machine tool, a storage medium storing an error identification program, and a 5-axis controlled machine tool that can identify inter-axis geometric errors with high precision without being affected by the individual geometric errors of the linear axis, and can automatically identify the individual geometric errors of the linear axis and the inter-axis geometric errors even without the knowledge or measurement skills of a machine tool operator.

[0020] Methods for solving problems

[0021] To achieve the above objectives, the first structure of the present invention is an error identification method for a 5-axis machine tool, which identifies errors in the 5-axis machine tool, which includes: a spindle capable of mounting tools and rotating; a worktable capable of fixing workpieces and / or fixtures; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable.

[0022] The error identification method for the 5-axis machine tool is characterized by performing the following steps:

[0023] Preparation steps: Install the position measuring sensor tool on the spindle, and fix the calibrator with more than 3 balls on the worktable;

[0024] The initial position measurement step involves using the position measurement sensor tool to measure the initial position of the calibrator.

[0025] The reference angle calculation step calculates the reference angles of each of the rotating axes used to position the corrector at a specified reference position, based on the measured values ​​in the initial position measurement step.

[0026] The calibration measurement step involves dividing each of the rotating axes relative to the reference angle into multiple graduation angles, and using the position measurement sensor tool to measure the center position of the ball of the calibration device fixed to the worktable at each graduation angle; and

[0027] The error identification step identifies the positioning error and straightness error of the straight axis, the perpendicularity error between each straight axis, and the position error and tilt error of each rotating axis based on the measurement values ​​in the calibrator measurement step.

[0028] The characteristic of another aspect of the first structure of the present invention is that, in the above structure, during the error identification step,

[0029] Using the measurement values ​​in the calibration measurement step, the positioning error and straightness error of the two straight axes, the three perpendicularity errors of the straight axes, the expansion component of the positioning error of the other straight axis besides the two straight axes, and the position error and tilt error of each of the rotating axes are identified.

[0030] The characteristic of another aspect of the first structure of the present invention is that, in the above structure, the following circular arc measurement step is performed in the calibrator measurement step:

[0031] By drawing an arc track with the spheres of the calibrator, while one of the rotation axes is indexed to any of the indexing angles, another rotation axis is sequentially indexed to a plurality of the indexing angles, thereby measuring the center position of at least one sphere in the calibrator.

[0032] The characteristic of another aspect of the first structure of the present invention is that, in the above structure, the following steps are performed in the calibrator measurement step:

[0033] In the parallel measurement step, each of the rotation axes is indexed with the orientation of the calibrator parallel to the axes of the two linear axes, and the center of three or more spheres in the calibrator is measured using the position measurement sensor tool; and

[0034] The planar diagonal measurement step involves indexing each of the rotation axes in such a way that the orientation of the calibrator is diagonally opposite to the plane formed by the axes of the two straight axes, and measuring the center positions of three or more spheres in the calibrator using the position measurement sensor tool.

[0035] The characteristic of another aspect of the first structure of the present invention is that, in the above structure, the following steps are performed in the calibrator measurement step:

[0036] In the parallel measurement step, each of the rotation axes is indexed with the orientation of the calibrator parallel to the axes of the two linear axes, thereby using the position measurement sensor tool to measure the center positions of three or more spheres in the calibrator; and

[0037] In the spatial diagonal measurement step, each of the rotation axes is indexed so that the orientation of the corrector is diagonally opposite to the axis of the space formed by the three straight axes, and the center positions of the three or more spheres in the corrector are measured using the position measurement sensor tool.

[0038] To achieve the above objectives, the second structure of the present invention is a storage medium storing an error identification program for a 5-axis machine tool. The error identification program is characterized in that it enables the CNC device of the 5-axis machine tool to execute the error identification method of the present invention. The 5-axis machine tool comprises: a spindle capable of mounting tools and rotating; a worktable capable of fixing workpieces and / or fixtures; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable.

[0039] To achieve the above objectives, the third structure of the present invention is a 5-axis controlled machine tool, comprising: a spindle capable of mounting tools and rotating; a worktable capable of fixing workpieces and / or fixtures; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable.

[0040] The 5-axis controlled machine tool is characterized by having:

[0041] An initial position measuring unit uses a position measuring sensor tool mounted on the spindle to measure the initial position of the calibrator, which has three or more balls and is fixed to the worktable.

[0042] The reference angle calculation unit calculates the reference angle of each of the rotating axes for positioning the corrector at a specified reference position, based on the measurement value measured by the initial position measurement unit.

[0043] The calibrator measurement unit divides each of the rotating axes relative to the reference angle into multiple graduation angles, and uses the position measurement sensor tool to measure the center position of the calibrator ball fixed to the worktable at each graduation angle; and

[0044] The error identification unit identifies the positioning error and straightness error of the straight axis, the perpendicularity error between the straight axes, and the position error and tilt error of the rotating axis based on the measurement values ​​measured by the corrector measurement unit.

[0045] The effects of the invention

[0046] According to the present invention, it is possible to simultaneously identify the individual geometric errors (positioning error, straightness) of the linear axes and the inter-axis geometric errors (perpendicularity between linear axes, center error of rotary axes, tilt error of rotary axes) of a 5-axis controlled machine tool. Therefore, it is possible to identify inter-axis geometric errors with high precision, regardless of the individual geometric errors of the linear axes.

[0047] Furthermore, by utilizing the 5-axis control of the machine tool's rotary axes, a series of measurements can be automatically performed. Even without the knowledge or measurement skills of a machine tool operator, the geometric errors of individual axes and the geometric errors between axes of the linear axis can be automatically identified. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of a 5-axis controlled machining center.

[0049] Figure 2 This is a flowchart of the error identification method.

[0050] Figure 3 This is a schematic diagram of a contact probe and a ball array.

[0051] Figure 4 This is a schematic diagram of the initial setup position of the sphere array.

[0052] Figure 5 This is a schematic diagram of the position of the sphere array in the X-axis parallel direction measurement.

[0053] Figure 6 This is a schematic diagram of the position of the sphere array in the Y-axis parallel direction measurement.

[0054] Figure 7 This is a schematic diagram of the position of the sphere array in the diagonal measurement along the XY axis.

[0055] Figure 8 This is a schematic diagram of the position of the sphere array in the diagonal measurement along the YZ axis.

[0056] Figure 9 This is a schematic diagram of the position of the sphere array in the diagonal measurement along the ZX axis.

[0057] Figure 10 This is a schematic diagram of the position of the sphere array in a diagonal spatial measurement.

[0058] Figure 11 This is a schematic diagram showing the positions of the spheres in a sphere array measured by a circular arc centered on the C-axis.

[0059] Figure 12 This is a schematic diagram showing the positions of the spheres in a sphere array measured by a circular arc centered on axis A.

[0060] Figure 13 This is a detailed flowchart of S8.

[0061] Figure 14 This is a detailed flowchart of S9.

[0062] Explanation of reference numerals in the attached figures

[0063] 1: Bed, 2: Spindle head, 3: Worktable, 4: Cradle, 5: Trunnion, 10: Contact probe, 11: Ball array, Q1~Q5: Balls. Detailed Implementation

[0064] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0065] In this embodiment, an example of a 5-axis controlled machine tool implementing the error identification method of the present invention is also as previously described. Figure 1 A 5-axis controlled machining center. Therefore, repeated descriptions are omitted. This 5-axis controlled machining center includes the initial position measurement unit, the reference angle calculation unit, the corrector measurement unit, and the error identification unit of the present invention, and executes the error identification method of the present invention according to the error identification program stored in the CNC device. Hereinafter, based on Figure 2 The flowchart illustrates the process of the error identification method.

[0066] First, in step 1 (abbreviated as "S", the same applies below), preparations for the measurement are made. Specifically, as follows... Figure 3 As shown, the contact probe 10 is mounted on the spindle head 2. Additionally, a calibrator, i.e., a ball array 11 with balls Q1 to Q5 fixed to it, is mounted on the worktable 3. Then, the feed axis is actuated to position the front end of the contact probe 10 approximately directly above the balls Q1 (preparation step).

[0067] Next, in S2, the initial position of the ball array 11 is measured (initial position measurement step). The center positions of balls Q1 and Q2 are measured using the contact probe 10.

[0068] Here, the contact probe 10 is a detector that outputs a trigger signal when the ball at its front end contacts the object. The CNC device that receives the trigger signal can measure the position of the object by obtaining the current positions of the X, Y, and Z axes at the moment the trigger signal is received. By contacting the ball at 4 or more points (3 or more points if the diameter of the ball is known), the center position of the ball can be measured.

[0069] Next, in S3, based on the measured values ​​of the initial position, the reference angle of the rotation axis of the ball array 11 when it is in the reference position is calculated (reference angle calculation step). Here, as... Figure 5 As shown, the reference position of the ball array 11 is set so that the ball array 11 is parallel to the X-axis. Therefore, the reference angle A along the A-axis is... O The angle is 0° (C-axis is parallel to Z-axis). The reference angle of the C-axis is the C-axis angle when the ball array 11 is parallel to the X-axis.

[0070] With the A-axis at 0°, such as Figure 4 As shown, when the ball array 11 is set on the worktable 3, if the measured center coordinates of ball Q1 are set as PI1 = (XI1, YI1, ZI1), the center coordinates of ball Q2 are set as PI2 = (XI2, YI2, ZI2), and the unit vector parallel to the X-axis is set as VX = (1, 0, 0), then the setting angle θ0 of the ball array 11 is calculated by the following mathematical formula 1. Furthermore, if the C-axis angle measured at the initial position is set as C... C Then the reference angle C along the C-axis O It can be obtained from the following mathematical expression 2.

[0071] [Mathematical Expression 1]

[0072] θ0=tan -1 {(VP×VX) / (VP·VX)}

[0073] Here, VP = (PI2 - PI1) / |PI2 - PI1|

[0074] [Mathematical Expression 2]

[0075] C O =C C +θ0

[0076] Next, in S4, based on the correction value of the center position of each ball in the ball array 11, the ball array setting angle θ0, the reference angle of each rotation axis, and the rotation axis angle used to set the preset measurement position, a list of command values ​​for each axis is generated (command value list generation step).

[0077] Next, in steps S5 to S7, each rotary axis is indexed according to the generated command value list, and the center position of the ball on the ball array 11 is measured at each position (calibrator measurement step). Additionally, it can be checked whether each command position in the command value list is within the operating range of each axis; if outside the range, the command position is deleted / omitted, or an alarm is output.

[0078] In S5, the rotation axis is indexed so that the orientation of the ball array 11 is parallel to the X-axis and Y-axis respectively, and the center positions of the balls Q1 to Q5 of the ball array 11 are measured (parallel measurement step).

[0079] When the X-axis is parallel, such as Figure 5 As shown, the A-axis angle is indexed to A... O Scale the C-axis angle to C O To perform the measurement.

[0080] When the Y-axis is parallel, such as Figure 6 As shown, the A-axis angle is indexed to A... O Scale the C-axis angle to C O The measurement was performed at -90°.

[0081] In S6, the rotation axis is indexed so that the orientation of the ball array 11 is parallel to the diagonal direction of the two linear axes, and the center positions of the balls Q1 to Q5 of the ball array 11 are measured (planar diagonal measurement step).

[0082] In the case of diagonal directions along the X and Y axes, such as Figure 7 As shown, the A-axis angle is indexed to A... O Scale the C-axis angle to C O -θxy. Set θxy to ±45° to perform measurements in two directions. Measurements can also be performed in any single direction.

[0083] In the case of diagonal directions of the Y and Z axes, such as Figure 8 As shown, the A-axis angle is indexed to A... O -θyz, scales the C-axis angle to C O-90°. θyz is set to ±45° for measurements in two directions. Measurements can also be performed in any direction. However, if it's impossible to measure all the balls in the ball array 11 due to the relationship between the Z-axis's movable range and the A-axis's center position, the absolute value of θyz is set to a smaller value. In this case, the closer to 0°, the greater the identification error in S8; therefore, it's preferable to set it to the largest possible value. If more than two balls can be measured, the identification calculation in S8 can be performed, but the smaller the maximum measured distance between the balls, the greater the identification error.

[0084] In the case of diagonal directions of the Z and X axes, such as Figure 9 As shown, the A-axis angle is indexed to A... O -90°, scale the C-axis angle to C O -θzx. θzx is set to ±45° for measurements in two directions. However, in Figure 3 In such a contact probe 10, the contact probe 10 or the spindle head 2 interferes with the ball array 11, allowing only a portion of the balls to be measured. Therefore, the identification error in S8 increases. Furthermore, since some balls cannot be measured due to the relationship between the movable range of the Z-axis and the center position of the A-axis, the absolute value of θzx is set to a smaller value in this case. If more than two balls can be measured, the identification calculation in S8 can be performed, but the smaller the maximum measured distance between the balls, the greater the identification error.

[0085] It can also replace measurements in the diagonal directions of the Z and X axes, and be used for... Figure 10 The measurement of the spatial diagonal directions of the X, Y, and Z axes (spatial diagonal measurement procedure). In this case, the A-axis angle is scaled to A... O -φsd, adjusts the C-axis angle to C... O -θsd. Set φsd to -45° and θsd to ±45°, and perform measurements in two directions. Here, in cases where some balls cannot be measured due to the relationship between the Z-axis's range of motion and the A-axis's center position, set the absolute value of at least one of φsd and θsd to a smaller value. In this case, the closer to 0°, the greater the identification error in S8; therefore, it is preferable to set it to the largest possible value. If more than two balls can be measured, the identification calculation in S8 can be performed, but the smaller the maximum measured distance between the balls, the greater the identification error.

[0086] In addition, measurements can be set to two directions for each diagonal direction, but measurements can also be performed in only one direction.

[0087] On the other hand, measurements can be performed in four spatial diagonal directions, without measuring the diagonal directions along the X and Y axes, Y and Z axes, or Z and X axes. In this case, if the angle of axis A is set as A...O -φsd, sets the C-axis angle to C O If -θsd, then the measurement is performed with φsd ±45° and θsd ±45°.

[0088] In S7, by drawing an arc track with the balls on the ball array 11, while one of the two rotation axes is indexed to an arbitrary angle, the other rotation axis is sequentially indexed to multiple angles, thereby measuring the center position of the ball Q5 on the ball array 11 (arc measurement step).

[0089] In circular arc measurement centered on the C-axis, such as Figure 11 As shown, the A-axis angle is indexed to A... O , change the C-axis angle from C O The scale is divided into multiple angles to measure the center position of ball Q5 at each angle.

[0090] In the circular arc measurement centered on axis A, such as Figure 12 As shown, the C-axis angle is indexed to C... O -90°, change the A-axis angle from A O -φra is graduated with a spacing of Δφra to measure the center position of sphere Q5 at various angles. Figure 12 The αf shown is the deviation angle of the center position of sphere Q5 in the YZ plane.

[0091] Alternatively, the ball being measured can be any of the balls from Q1 to Q4 instead of Q5. Furthermore, multiple balls can be measured.

[0092] In S8, the geometric error of the straight axis is identified and calculated using the measured values ​​from S5 and S6 (error identification step). Details will be explained later.

[0093] In S9, the measured values ​​from S7 and the geometric error identification values ​​of the straight axis identified in S8 are used to perform the geometric error identification calculation of the rotating axis (error identification step). Details will be explained later.

[0094] based on Figure 13 The flowchart below provides a detailed explanation of S8.

[0095] In S8-1, identify the X-axis error (positioning error, straightness).

[0096] The center positions of each ball in the ball array 11 are calibrated using a 3D measuring machine or similar device. The vector of the calibration value of the center position of ball Qi (i = 1 to 5) (the 3D coordinate values ​​of the center of each ball in the coordinate system of ball array 11 with the center of ball Q1 as the origin) is set as MOi = (XMi, YMi, ZMi). Here, the calibration value can be corrected in conjunction with the temperature of the ball array 11.

[0097] If the center position measurement vector of ball Qi in the X-axis parallel measurement in S5 is set as PPXi = (XPXi, YPXi, ZPXi), then the X-axis parallel measurement error vector of each ball is DPXi = (dXPXi, dYPXi, dZPXi) as shown in the following formula.

[0098] [Mathematical Expression 3]

[0099] DPXi = PPXi - PPX1 - MOi

[0100] If the nth approximation curve of dXPXi is set as FXX(x), then the positioning error EXX(x) of the X-axis is obtained by the following formula.

[0101] [Mathematical Expression 4]

[0102] EXX(x)=FXX(x)

[0103] If we set the least square straight line of dYPXi as SYX(x) and the nth approximation curve (n≥2) as FYX(x), then the true straightness Y component of the X-axis, EYX(x), can be obtained by the following formula.

[0104] [Mathematical Expression 5]

[0105] EYX(x)=FYX(x)-SYX(x)

[0106] If we set the least square straight line of dZPXi as SZX(x) and the nth approximation curve (n≥2) as FZX(x), then the true straightness Z component of the X-axis, EZX(x), can be obtained by the following formula.

[0107] [Mathematical Expression 6]

[0108] EZX(x)=FZX(x)-SZX(x)

[0109] Next, in S8-2, identify the Y-axis error (positioning error, straightness).

[0110] Rotate the correction vector MOi of the center position of each ball 90° around the Z-axis with the center of ball Q1 as the center, and set the rotated correction vector as MYi.

[0111] If the center position measurement vector of the ball Qi in S5, measured in parallel along the Y-axis, is set as PPYi = (XPYi, YPYi, ZPYi), then the Y-axis parallel measurement error vector of each ball is DPYi = (dXPYi, dYPYi, dZPYi) as shown in the following formula.

[0112] [Mathematical Expression 7]

[0113] DPYi = PPYi - PPY1 - MYi

[0114] If the nth approximation curve of dYPYi is set as FYY(y), then the positioning error EYY(y) of the Y-axis is calculated by the following formula.

[0115] [Mathematical Expression 8]

[0116] EYY(y)=FYY(y)

[0117] If we set the least square straight line of dZPYi as SZY(y) and the nth approximation curve (n≥2) as FZY(y), then the true straightness Z component of the Y-axis, EZY(y), can be obtained by the following formula.

[0118] [Mathematical Expression 9]

[0119] EZY(y)=FZY(y)-SZY(y)

[0120] If we set the least square line of dXPYi as SXY(y) and the nth approximation curve (n≥2) as FXY(y), then the straightness X component of the Y-axis, EXY(y), can be obtained by the following formula.

[0121] [Mathematical Expression 10]

[0122] EXY(y) = FXY(y) - SXY(y)

[0123] Next, in S8-3, the influence of the errors in the X and Y axes identified in S8-1 and S8-2 is removed from the measured values ​​measured in the diagonal direction.

[0124] When the center position measurement vector of ball Qi (i = 1 to 5) in the j-th diagonal direction of S6 is set as PDji = (XDji, YDji, ZDji), the center position measurement vector of each ball after correction of the positioning error and straightness of the X and Y axes is obtained by the following formula: CDji = (XCji, YCji, ZCji).

[0125] [Mathematical Expression 11]

[0126] XCji=XDji-{EXX(XDji)+EXY(YDji)}

[0127] YCji=YDji-{EYX(XDji)+EYY(YDji)}

[0128] ZCji=ZDji-{EZX(XDji)+EZY(YDji)}

[0129] Next, in S8-4, the perpendicularity between each axis and the Z-axis error (positioning error scaling (gradient) component) are calculated.

[0130] If the correction vector of the center position of ball Qi (i = 1 to 5) in the j-th diagonal direction measurement in S6 is rotated around the center of ball Q1 around the C and A axes, and the correction vector after rotation is set as MDji = (XMDji, YMDji, ZMDji), then the error vector of the diagonal direction measurement DDji = (dXDji, dYDji, dZDji) is as shown in the following formula.

[0131] [Mathematical Expression 12]

[0132] DDji = CDji - CDj1 - MDji

[0133] Let the angle of axis A measured in the j-th diagonal direction be A. O +αj, set the C-axis angle to C O +γj. In this case, the unit vector along the length of the sphere array 11 is VDj=(cosγj,-cosαj·sinγj,sinαj·sinγj), and the gradient component dLji of the error in the distance between the center of sphere Q1 and the center of each sphere is obtained by the following formula. Here, i=2~5.

[0134] [Mathematical Expression 13]

[0135] dLji=(DDji-DDj1)·VDj / (XMi-XM1)

[0136] The relationship between the YZ perpendicularity EAYZ, ZX perpendicularity EBZX, XY perpendicularity ECXY, and the Z-axis positioning error scaling component KZ and dLji is shown in the following formula.

[0137] [Mathematical Expression 14]

[0138] dLji=Sj1*KZ+Sj2*EAYZ+Sj3*EBZX+Sj4*ECXY

[0139] Sj1=-sin 2 αj*sin 2 γj

[0140] Sj2=-sin2αj*sin 2 γj / 2

[0141] Sj3=-sinαj*sin2γj / 2

[0142] Sj4=-cosαj*sin2γj / 2

[0143] By solving mathematical equation 14 as a simultaneous equation, EAYZ, EBZX, ECXY, and KZ can be obtained. For example, if the vector with KZ, EAYZ, EBZX, and ECXY as components is XX, the vector with dLji as components is BB, and the matrix with Sj1 to Sj4 as components is AA, then EAYZ, EBZX, ECXY, and KZ can be obtained according to the following formula.

[0144] [Mathematical Expression 15]

[0145] XX = (AA) T *AA) -1 *AA T *BB

[0146] Errors can also be calculated separately. In this case, the influence of other errors and errors outside the object being identified can be eliminated.

[0147] The perpendicularity of the X and Y axes is identified solely based on measurements taken along the diagonal directions. With θxy = ±45° (i.e., α1 = 0°, γ1 = -45° and α2 = 0°, γ2 = -45°), the perpendicularity of the X and Y axes is calculated using the following formula. Here, mean() is a function for calculating the average value. This calculation is unaffected by errors in the Z-axis or the Z-direction errors of the X and Y axes.

[0148] [Mathematical Expression 16]

[0149] ECXY = mean(-dL1i + dL2i)

[0150] Next, based on the measurement results of the YZ diagonal direction, the YZ perpendicularity EAYZ and the Z-axis positioning error scaling component KZ are identified. When θyz = ±45°, i.e., α3 = -45°, γ3 = -90° and α4 = 45°, γ4 = -90°, the YZ perpendicularity EAYZ and the Z-axis positioning error scaling component KZ are calculated using the following formula. In this case, it is not affected by the X-axis error or the X-direction error of the Y and Z axes.

[0151] [Mathematical Expression 17]

[0152] KZ = mean(-dL3i-dL4i)

[0153] EAYZ = mean(dL3i - dL4i)

[0154] Next, the perpendicularity of ZX, EBZX, is identified based on the results of the spatial diagonal measurement. When φsd = 45°, θsd = ±45°, i.e., α5 = -45°, γ5 = -45°, and α6 = -45°, γ6 = 45°, the perpendicularity of ZX, EBZX, is calculated using the following formula.

[0155] [Mathematical Expression 18]

[0156] EBZX=(2^0.5)*mean(-dL5i+dL6i)

[0157] Next, based on Figure 14 The flowchart provides a detailed explanation of S9.

[0158] In S9-1, the effects of positioning errors, straightness, and perpendicularity between axes (geometric errors of the straight axis) of the X, Y, and Z axes identified in S8 are removed from the ball center measurement position measured in S7.

[0159] If the center position measurement vector of ball Q5 at the k-th division angle in the j-th circular arc measurement (j=1 is the circular arc measurement centered on the C-axis, j=2 is the circular arc measurement centered on the A-axis) is set as PRjk=(XRjk, YRjk, ZRjk), then the center position correction measurement vector of each ball after removing the positioning error of the X, Y, and Z axes, the straightness error of the X and Y axes, and the perpendicularity error between each axis is obtained by the following formula.

[0160] [Mathematical Expression 19]

[0161] XLjk=XRjk-{EXX(XRjk)+EXY(YRjk)-ECXY*YRjk+EBZX*ZRjk}

[0162] YLjk=YRjk-{EYX(XRjk)+EYY(YRjk)-EAYZ*ZRjk}

[0163] ZLjk=ZRjk-{EZX(XRjk)+EZY(YRjk)+KZ*ZRjk}

[0164] In S9-2, calculate the arc error of the group of measured values ​​for the center position of each ball, obtained in S7 by indexing the rotation axis in the manner of depicting an arc track. The arc error refers to the radius error, the lateral and longitudinal deviation of the center, which can be represented by the 0th order coefficient, the 1st order cosine coefficient, and the 1st order sine coefficient of Fourier coefficients, respectively.

[0165] In the circular arc measurement centered on the C-axis in S7, the angle of the A-axis is fixed at A. O Scale the C-axis angle to C O The measurement is performed using +γck (k = 1 to nc). Here, γck = Δθra*(k-1).

[0166] If the commanded position of the center of ball Q5 under the k-th graduation angle of the j-th measurement condition is set as PO1k = (XO1k, YO1k, ZO1k), the axial vector of the C-axis is set as VA1k, the radial vector is set as VR1k, and the tangential vector is set as VT1k, then the axial error EA1k, radial error ER1k, and tangential error ET1k in the C-axis circular arc measurement can be calculated according to the following formula.

[0167] [Mathematical Expression 20]

[0168] EA1k=(CL1k-PO1k)·VA1k

[0169] ER1k=(CL1k-PO1k)·VR1k

[0170] ET1k=(CL1k-PO1k)·VT1k

[0171] If the Fourier coefficients of the axial component are set as A0A1, A1A1, and B1A1, the Fourier coefficients of the radial component are set as A0R1, A1R1, and B1R1, and the Fourier coefficients of the tangential component are set as A0T1, A1T1, and B1T1, then the relationship between EA1k, ER1k, ET1k and each Fourier coefficient can be expressed by the following formula. By solving the simultaneous equations of nc formulas for each direction, the arc error in each direction of the C-axis arc measurement can be obtained.

[0172] [Mathematical Expression 21]

[0173] EA1k=A0A1+A1A1*cosγck+B1A1*sinγck

[0174] ER1k=A0R1+A1R1*cosγck+B1R1*sinγck

[0175] ET1k=A0T1+A1T1*cosγck+B1T1*sinγck

[0176] In the circular arc measurement centered on axis A in S7, the angle of axis C is fixed at C. O -90° and scale the A-axis angle to A. O The measurement is performed using +αck (k = 1 ~ na). Here, we assume αck = -φra - Δφra(k-1) - αf (αf is the deviation angle of the center position of sphere Q5 in the YZ plane).

[0177] If the commanded position of the center of ball Q5 under the k-th graduation angle of the j-th measurement condition is set as PO2k=(XO2k,YO2k,ZO2k), the axial vector of the A-axis is set as VA2k, the radial vector is set as VR2k, and the tangential direction vector is set as VT2k, then the axial error EA2k, radial error ER2k, and tangential direction error ET2k in the A-axis circular arc measurement can be calculated according to the following formula.

[0178] [Mathematical Expression 22]

[0179] EA2k=(CL2k-PO2k)·VA2k

[0180] ER2k=(CL2k-PO2k)·VR2k

[0181] ET2k=(CL2k-PO2k)·VT2k

[0182] If the Fourier coefficients of the axial component are set as A0A2, A1A2, and B1A2, the Fourier coefficients of the radial component are set as A0R2, A1R2, and B1R2, and the Fourier coefficients of the tangential component are set as A0T2, A1T2, and B1T2, then, similarly to the C-axis circular arc measurement, the error of each directional component can be expressed by the following formula using each Fourier coefficient. By solving the simultaneous equations of na formulas for each direction, the circular arc error in each direction in the A-axis circular arc measurement can be obtained.

[0183] [Mathematical Expression 23]

[0184] EA2k=A0A2+A1A2*cosαck+B1A2*sinαck

[0185] ER2k=A0R2+A1R2*cosαck+B1R2*sinαck

[0186] ET2k=A0T2+A1T2*cosαck+B1T2*sinαck

[0187] In S9-3, the rotation axis error (center error (position error) and tilt error of the rotation axis) is calculated based on the arc error in each direction obtained in S9-2.

[0188] The relationships between the arc errors in each direction obtained in S9-2 and the following equations are given: X-direction error of C-axis center position dXca, CA-axis deviation error dYca, Y-direction error of A-axis center position dYax, Z-direction error of A-axis center position dZax, A-axis angular deviation error dAca, CA-axis perpendicularity dBca, AZ-axis perpendicularity dBax, and AY-axis perpendicularity dCax. Here, Zc is the Z-axis position of the center of sphere Q5 in the C-axis arc measurement relative to the center of the A-axis, Rc is the radius of rotation of sphere Q5 in the C-axis arc measurement, and Ra is the radius of rotation of sphere Q5 in the A-axis arc measurement.

[0189] [Mathematical Expression 24]

[0190] A1R1=-dXca-Zc*dBax

[0191] B1R1=-dYca-dYax+Zc*dAca

[0192] A1R2=-dYax

[0193] B1R2=-dZax

[0194] A1A1=Rc*(dBca+dBax)

[0195] B1A1=-Rc*dAca

[0196] A1A2=-Ra*dCax

[0197] B1A2=-Rc*dBax

[0198] By solving mathematical formula 24, the geometric error of the rotation axis can be determined. Since the identified geometric error of the rotation axis is determined by eliminating the influence of the geometric error of the linear axis unit, it can be identified with higher accuracy than before.

[0199] Thus, the error identification method described above, the storage medium storing the error identification program, and the 5-axis control machining center perform the following steps: Preparation step S1: Install the contact probe 10 (position measurement sensor tool) on the spindle head 2 (spindle), and fix the ball array 11 (calibrator) with 5 balls Q1 to Q5 on the worktable 3; Initial position measurement step S2: Use the contact probe 10 to measure the initial position of the ball array 11; Reference angle calculation step S3: Calculate the reference angle based on the measured value in the initial position measurement step to make the ball array 11 position... The reference angles of the A-axis and C-axis (rotation axes) at the reference position; the calibration measurement steps S5 to S7, in which the A-axis and C-axis are divided into multiple graduation angles relative to the reference angles, and the center positions of the balls Q1 to Q5 of the ball array 11 fixed on the worktable 3 are measured at each graduation angle using the contact probe 10; and the error identification steps S8 and S9, in which the positioning error, straightness error and perpendicularity error between the X, Y and Z axes, as well as the position error and tilt error of the A-axis and C-axis are identified based on the measurement values ​​in the calibration measurement steps.

[0200] Based on this structure, it is possible to simultaneously identify the individual geometric errors (positioning error, straightness) of the X, Y, and Z axes, as well as the inter-axis geometric errors (perpendicularity between the X, Y, and Z axes, center error of the C and A axes, and tilt error of the C and A axes). Therefore, it is possible to identify inter-axis geometric errors with high precision, unaffected by the individual geometric errors of the straight axes.

[0201] Furthermore, by utilizing the C-axis and A-axis of the 5-axis control machining center, a series of measurements can be performed automatically. Even without the knowledge and measurement skills of a machine tool operator, the geometric errors of individual axes and the geometric errors between axes of the linear axis can be automatically identified.

[0202] Alternatively, tools other than contact probes can be used as position measuring sensors, and the calibrator can also adopt a structure other than the ball array described above. For example, the number of balls only needs to be three or more.

[0203] 5-axis machine tools are not limited to machining centers as described above.

Claims

1. A method for error identification in a five-axis machine tool, wherein errors are identified in the five-axis machine tool, the machine tool comprising: a spindle capable of mounting and rotating a tool; a worktable capable of fixing a workpiece and / or a fixture; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable. The error identification method for the five-axis controlled machine tool is characterized by performing the following steps: Preparation steps: Install the position measuring sensor tool on the spindle, and fix the calibrator with more than 3 balls on the worktable; The initial position measurement step involves using the position measurement sensor tool to measure the initial position of the calibrator. The reference angle calculation step calculates the reference angle of each of the rotating axes for positioning the corrector at a specified reference position, based on the measured values ​​in the initial position measurement step. The calibration measurement step involves dividing each of the rotating axes relative to the reference angle into multiple division angles, and using the position measurement sensor tool to measure the center position of the ball of the calibration device fixed to the worktable at each of the division angles. as well as The error identification step, based on the measured values ​​in the corrector measurement step, identifies the positioning error and straightness error of the straight axis, the perpendicularity error between the straight axes, and the position error and tilt error of each rotating axis. In the calibrator measurement step, the following steps are performed: In the parallel measurement step, each of the rotation axes is indexed with the orientation of the calibrator parallel to the axes of the two linear axes, and the center of three or more spheres in the calibrator is measured using the position measurement sensor tool. as well as In the diagonal measurement step, the rotation axis is indexed such that the orientation of the calibrator is diagonally opposite to the plane formed by the axes of the two linear axes or diagonally opposite to the space formed by the axes of the three linear axes, and the center position of the three or more balls in the calibrator is measured using the position measurement sensor tool.

2. The error identification method for a five-axis controlled machine tool according to claim 1, characterized in that, In the error identification step, Using the measurement values ​​in the calibration measurement step, the positioning error and straightness error of two of the three straight axes, the three perpendicularity errors of the straight axes, the expansion component of the positioning error of the other straight axis, and the position error and tilt error of each of the rotating axes are identified.

3. The error identification method for a five-axis controlled machine tool according to claim 1 or 2, characterized in that, In the calibrator measurement step, the following circular arc measurement step is performed: By drawing an arc track with the spheres of the calibrator, while one of the rotation axes is indexed to any of the indexing angles, another rotation axis is sequentially indexed to a plurality of the indexing angles, thereby measuring the center position of at least one sphere in the calibrator.

4. A storage medium storing an error identification program for a five-axis machine tool, the error identification program being used to cause the CNC device of the five-axis machine tool to execute the error identification method for a five-axis machine tool according to any one of claims 1 to 3, wherein... The five-axis machine tool has: a spindle capable of mounting tools and rotating; a worktable capable of fixing workpieces and / or fixtures; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable.

5. A five-axis machine tool comprising: a spindle capable of mounting a tool and rotating; a worktable capable of fixing a workpiece and / or a fixture; three linear axes perpendicular to each other and capable of relative movement of the spindle relative to the worktable; and two rotary axes capable of rotating and / or tilting the worktable. The five-axis controlled machine tool is characterized by having: An initial position measuring unit uses a position measuring sensor tool mounted on the spindle to measure the initial position of the calibrator, which has three or more balls and is fixed to the worktable. The reference angle calculation unit calculates the reference angle of each of the rotating axes for positioning the corrector at a specified reference position, based on the measurement value measured by the initial position measurement unit. The calibrator measurement unit divides each of the rotating axes relative to the reference angle into multiple graduation angles, and uses the position measurement sensor tool to measure the center position of the calibrator ball fixed to the worktable at each graduation angle. as well as The error identification unit, based on the measurement values ​​measured by the corrector measurement unit, identifies the positioning error and straightness error of two of the three straight axes, the three perpendicularity errors of the straight axes, the scaling component of the positioning error of the other straight axis, and the position error and tilt error of each of the rotating axes. The calibrator measurement unit includes: The circular arc measuring unit measures the center position of at least one ball in the calibrator by drawing a circular arc track with the ball of the calibrator, and by sequentially dividing another rotation axis to multiple division angles while dividing one rotation axis to any division angle. The parallel measurement unit indexes each of the rotation axes in such a way that the orientation of the calibrator is parallel to the axes of the two linear axes, and uses the position measurement sensor tool to measure the center of three or more spheres in the calibrator. as well as The diagonal measuring unit indexes each of the rotation axes in such a way that the orientation of the corrector is diagonal to the plane formed by the axes of the two linear axes or diagonal to the space formed by the axes of the three linear axes, and uses the position measuring sensor tool to measure the center position of three or more balls in the corrector.

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