A machine tool perpendicularity error calculation method based on R-test instrument

Abstract

This invention relates to the field of machine tool precision testing technology, and in particular to a method for calculating machine tool perpendicularity error based on an R-test instrument. The method includes: setting perpendicularity error elements; constructing a spatial error model of the tool tip point under the influence of machine tool perpendicularity error by combining the principle of homogeneous coordinate matrix transformation; setting a five-axis linkage detection trajectory based on RTCP according to the machine tool topology; measuring the error data during the movement of the detection trajectory using an R-test instrument; selecting combinations of rotation axis angles in the detection trajectory; establishing a set of perpendicularity error identification equations based on a specified position on the detection trajectory; and completing the decoupling of the machine tool perpendicularity error. This method enables accurate calculation of machine tool perpendicularity error.

Description

Technical Field

[0001] This invention relates to the field of machine tool accuracy testing technology, and in particular to a method for calculating machine tool perpendicularity error based on the R-test instrument. Background Technology

[0002] Perpendicularity error is a significant component of translational axis geometric error. As a geometric error describing the trend changes of each axis, it has a large order of magnitude and is relatively important. Traditional inspection mainly uses a marble ruler for local direct measurement, which is inefficient and has limited accuracy, making it difficult to meet the daily monitoring and maintenance needs of machine tools.

[0003] In the prior art, Chinese invention patent document with publication number CN112008492A and publication date December 1, 2020, and Ren Yongqiang et al. (Ren Yongqiang, Yang Jianguo, Shen Jinhua et al. Efficient measurement and analysis of machine tool perpendicularity error based on body diagonal [J]. China Mechanical Engineering, 2005, 16(6): 1435-1438) both proposed a method for identifying perpendicularity error based on diagonal. Both of the above methods require the use of a laser interferometer for measurement, but the installation and adjustment of the laser interferometer are time-consuming, dependent on the technical level of the operator, and also face the problem of low efficiency.

[0004] In the prior art, Chinese invention patent document CN110794766A, published on February 14, 2020, proposes a method for identifying the perpendicularity error of CNC machine tools based on a ballbar. This method involves synchronously moving three axes along an S-shaped trajectory on a curved surface to obtain a set of identification equations between the ballbar measurement error and the perpendicularity error. While this detection method is relatively novel, the ballbar itself can only detect axial errors, and the large number of detection points and long computation time limit its application efficiency. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for calculating machine tool perpendicularity error based on the R-test instrument, which can accurately calculate machine tool perpendicularity error.

[0006] This invention is achieved by adopting the following technical solution:

[0007] A method for calculating the perpendicularity error of a machine tool based on the R-test instrument includes the following steps:

[0008] Step S1. Set the perpendicularity error elements and, in conjunction with the principle of homogeneous coordinate matrix transformation, construct a spatial error model of the tool tip point under the influence of machine tool perpendicularity error;

[0009] Step S2. Based on the machine tool topology, set up a five-axis linkage detection trajectory based on RTCP, and use the R-test instrument to measure the error data during the operation of the detection trajectory;

[0010] Step S3. Select the rotation axis angle combination in the detection trajectory, establish a set of perpendicularity error identification equations based on the specified position of the detection trajectory, and complete the decoupling of the machine tool perpendicularity error.

[0011] The spatial error model of the tool tip point under the influence of machine tool perpendicularity error in step S1 is as follows:

[0012]

[0013] In the formula, y represents the Y-axis motion coordinate value, z represents the Z-axis motion coordinate value, L represents the sum of the rotation distance and the tool length, and S... XY S represents the angular error between the X and Y axes. XZ S represents the angular error between the X-axis and Z-axis. YZ This indicates the angular error between the Y-axis and the Z-axis.

[0014] Step S1 specifically includes the following steps:

[0015] Step S 11 According to the ISO standard definition, with the X-axis as the measurement reference axis, the error motion transformation matrix of the Y-axis... and the error motion transformation matrix along the Z-axis for:

[0016]

[0017] In the formula, S XY S represents the angular error between the X and Y axes. XZ S represents the angular error between the X-axis and Z-axis. YZ This indicates the angular error between the Y-axis and the Z-axis;

[0018] Step S 12 The tool tip, located at the end of the machine tool's motion chain, deviates from the theoretical command point, resulting in a spatial error:

[0019]

[0020] In the formula, T X T Y T Z These represent the theoretical translational motion matrices for the X, Y, and Z axes of the machine tool, respectively:

[0021]

[0022] In the formula, x, y, and z represent the X-axis, Y-axis, and Z-axis motion coordinates of the machine tool, respectively; P tool =[0 0 -L 1], representing the theoretical tool tip coordinates; L represents the sum of the rotation distance and the tool length;

[0023] Therefore, the spatial error model of the tool tip point under the influence of machine tool perpendicularity error is as follows:

[0024]

[0025] Step S2, which involves using the R-test instrument to measure error data during the trajectory's movement, specifically includes the following steps:

[0026] Step S 21 Set the sampling threshold value and the total number of samples t on the R-test instrument.

[0027] Step S 22 In RTCP mode, when the machine tool rotary axis moves to (A) i C i When paused, the ball center error data (e) is automatically determined. ix ,e iy ,e iz Real-time fluctuation data, i.e., if the following formula is satisfied simultaneously, then the ball center error data at the current position is recorded:

[0028] e ix <value∩e iy <value∩e iz <value;

[0029] Among them, (A) i C i The five-axis linkage detection trajectory is formed by rotating axes A and C, resulting in a series of motion angle combinations of A-axis angle and C-axis angle;

[0030] Step S 23 Repeat the above sampling process until the current number of samples reaches the set total number of samples t.

[0031] It also includes step S 24 Save the above error data into an error data file for each angle combination.

[0032] The step S 22 In the process, the five-axis linkage detection trajectory line exhibits a spiral-shaped curvature characteristic in space.

[0033] The step S 22 In the middle, when the machine tool's rotary axis moves to (A) i C i When paused, the pause time is 5 seconds.

[0034] Step S3 specifically includes the following steps:

[0035] Step S 31 In the five-axis linkage detection trajectory, select any combination of motion angles (A... i C i When the machine tool coordinate axes change, the coordinate changes of each axis are as follows:

[0036]

[0037] At this point, due to the influence of perpendicularity error, the spatial error caused by the change in the movement of the machine tool coordinate axes is:

[0038]

[0039] In the formula, P error,i This represents the spatial error vector for the i-th combination of motion angles under the detected trajectory;

[0040] Step S 32 By correlating the spatial error vectors of all motion angle combinations with all measured sphere center error data, we obtain the perpendicularity error identification equation set, which is then simplified into matrix form as follows:

[0041] H·V=B

[0042] in:

[0043]

[0044]

[0045]

[0046] Step S 33 According to the least squares solution of the overdetermined system of equations:

[0047] V=(H T H) -1 (H T B)

[0048] At this point, the values ​​of each element in V have been approximated by least squares, meaning that the machine tool perpendicularity error has been decoupled.

[0049] The step S 31 In the five-axis linkage detection trajectory, a combination of motion angles consisting of specific angles is selected (A). j :15°*j,C j :30°*j), j∈i,j≥2.

[0050] The step S 22In the middle, the combination of motion angles (A) i C i The specific method to obtain it is as follows:

[0051] Set the motion angles for the rotation axes A and C as follows:

[0052]

[0053] In the formula, PosA and PosC represent the maximum motion angles of the A-axis and C-axis, respectively; t = Δt*i, representing the total number of samples; Δt = π / num, num > 10, and Δt represents the set reasonable interval.

[0054] This results in a series of motion angle combinations (A and C axes) i C i ), where i represents the i-th motion angle combination.

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] 1. This invention proposes a five-axis linkage detection trajectory with variable curvature spiral characteristics. It innovatively integrates the three-axis linkage of the machine tool translation axis, which originally required spatial movement, into the rotary axis movement by utilizing the characteristics of RTCP. It also uses the R-test instrument to quickly complete the data acquisition of tool tip point error caused by perpendicularity error. Furthermore, the variable curvature feature can realize the movement of the three translation axes with different feed rates, further exposing the synchronous movement defects of the three axes that may be caused by perpendicularity error.

[0057] 2. This invention constructs a set of equations for identifying perpendicularity error by selecting specified position data of the five-axis linkage detection trajectory. It only requires data from a minimum of two different positions to decouple the perpendicularity error, making it more practical, more efficient in calculation, and significantly improving the detection efficiency of machine tool perpendicularity error.

[0058] 3. There is a pause time during error data collection, which allows for sufficient time buffering to collect error data. Attached Figure Description

[0059] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein:

[0060] Figure 1 This is a schematic diagram of the process of the present invention;

[0061] Figure 2 This is a schematic diagram of the bridge-type gantry CNC machine tool in this invention;

[0062] Figure 3 This is a schematic diagram of the perpendicularity error in this invention;

[0063] Figure 4 This is a schematic diagram of the five-axis linkage detection trajectory based on RTCP in this invention;

[0064] Figure 5 This is a schematic diagram of error detection based on the R-test instrument in this invention. Detailed Implementation

[0065] Example 1

[0066] As a basic embodiment of the present invention, the present invention includes a method for calculating the perpendicularity error of a machine tool based on the R-test instrument, comprising the following steps:

[0067] Step S1. Set the perpendicularity error elements and, in conjunction with the principle of homogeneous coordinate matrix transformation, construct a spatial error model of the tool tip point under the influence of machine tool perpendicularity error.

[0068] Step S2. Based on the machine tool topology, set up a five-axis linkage detection trajectory based on RTCP, and use the R-test instrument to measure the error data during the operation of the detection trajectory.

[0069] Step S3. Select the rotation axis angle combination in the detection trajectory, establish a set of perpendicularity error identification equations based on the specified position of the detection trajectory, and complete the decoupling of the machine tool perpendicularity error.

[0070] Example 2

[0071] In a preferred embodiment of the present invention, the present invention includes a method for calculating the perpendicularity error of a machine tool based on an R-test instrument, comprising the following steps:

[0072] Step S1. Set the perpendicularity error elements and, based on the principle of homogeneous coordinate matrix transformation, construct a spatial error model of the tool tip point under the influence of machine tool perpendicularity error:

[0073]

[0074] In the formula, y represents the Y-axis motion coordinate value, z represents the Z-axis motion coordinate value, L represents the sum of the rotation distance and the tool length, and S... XY S represents the angular error between the X and Y axes. XZ S represents the angular error between the X-axis and Z-axis. YZ This indicates the angular error between the Y-axis and the Z-axis.

[0075] Step S2. Based on the machine tool topology, set up a five-axis linkage detection trajectory based on RTCP, and use an R-test instrument to measure the error data (e) during the movement of the detection trajectory. ix ,e iy ,e iz ).

[0076] Step S3. Select the rotation axis angle combination in the detection trajectory, establish a set of perpendicularity error identification equations based on the specified position of the detection trajectory, and complete the decoupling of the machine tool perpendicularity error. This specifically includes the following steps:

[0077] Step S 31 In the five-axis linkage detection trajectory, select any combination of motion angles (A... i C i When the machine tool coordinate axes change, the coordinate changes of each axis are as follows:

[0078]

[0079] At this point, due to the influence of perpendicularity error, the spatial error caused by the change in the movement of the machine tool coordinate axes is:

[0080]

[0081] In the formula, P error,i This represents the spatial error vector for the i-th combination of motion angles under the detected trajectory;

[0082] Step S 32 By correlating the spatial error vectors of all motion angle combinations with all measured sphere center error data, we obtain the perpendicularity error identification equation set, which is then simplified into matrix form as follows:

[0083] H·V=B

[0084] in:

[0085]

[0086]

[0087]

[0088] Step S 33 According to the least squares solution of the overdetermined system of equations:

[0089] V=(H T H) -1 (H T B)

[0090] At this point, the values ​​of each element in V have been approximated by least squares, meaning that the machine tool perpendicularity error has been decoupled.

[0091] Example 3

[0092] As the preferred embodiment of the present invention, please refer to the appendix to the specification. Figure 1 This invention includes a method for calculating the perpendicularity error of a machine tool based on the R-test instrument, comprising the following steps:

[0093] Step S1. Set the perpendicularity error elements and, based on the principle of homogeneous coordinate matrix transformation, construct a spatial error model of the tool tip point under the influence of machine tool perpendicularity error. This specifically includes the following steps:

[0094] Step S 11 According to the ISO standard definition, with the X-axis as the measurement reference axis, the perpendicularity error formed by the Y-axis, Z-axis and X-axis of a CNC machine tool includes S... XY S XZ S YZ , representing the angular errors between the X and Y axes, the X and Z axes, and the Y and Z axes, respectively, with the following error motion transformation matrices:

[0095]

[0096] In the formula, These represent the error motion transformation matrices for the Y-axis and Z-axis, respectively. If all error values ​​are 0, then it is an identity matrix.

[0097] Step S 12 Because machine tool errors affect the theoretical motion of the machine tool, the tool tip, located at the end of the machine tool motion chain, deviates from the theoretical command point, thus creating a spatial error:

[0098]

[0099] In the formula, T X T Y T Z These represent the theoretical translational motion matrices for the X, Y, and Z axes of the machine tool, respectively:

[0100]

[0101] In the formula, x, y, and z represent the X-axis, Y-axis, and Z-axis motion coordinates of the machine tool, respectively; P tool =[0 0 -L 1], representing the theoretical tool tip coordinates; L represents the sum of the rotation distance and the tool length.

[0102] Therefore, the spatial error model of the tool tip point under the influence of machine tool perpendicularity error is as follows:

[0103]

[0104] Step S2. Based on the machine tool topology, set up a five-axis linkage detection trajectory based on RTCP, and use the R-test instrument to measure the error data during the operation of the detection trajectory.

[0105] In RTCP mode, the rotation axes A and C form a five-axis linkage detection trajectory, resulting in a series of motion angle combinations (A and C axis angles). i C i Let ), i≤num+1, representing the i-th motion angle combination. Specifically, since the R-test instrument measures the deviation of the ball's center in the ball head test, the theoretical center coordinates are (0,0,0). In this case, the RTCP function needs to be enabled. The CNC machine tool will keep the ball center stationary while the rotation axis moves. Taking a CA-type gantry machining center with a swivel head as an example, the mathematical expression involved in the RTCP principle is as follows:

[0106]

[0107] In the formula, x, y, and z represent the X-axis, Y-axis, and Z-axis motion coordinates of the machine tool.

[0108] It is clear from the above formula that the movement of the rotation axes A and C will cause the movement of the translation axes X, Y, and Z. If in the initial state (the movement angle of the A and C axes is 0), we have the following expression:

[0109]

[0110] In the formula, x0, y0, and z0 represent the initial positions of the X-axis, Y-axis, and Z-axis of the machine tool.

[0111] In RTCP mode, the five coordinate axes will move synchronously. Considering the motion limits of the machine tool's rotary axes A∈[-110°, 110°] and C∈[-360°, 360°], the motion angles of rotary axes A and C are set as follows:

[0112]

[0113] In the formula, PosA and PosC represent the maximum motion angles along the A-axis and C-axis, respectively. t = Δt*i represents the total number of samples, and a reasonable interval Δt = π / num, where num > 10, can be set according to actual needs, thus obtaining a series of motion angle combinations (A and C axis angles). i C i ), i≤num+1, represents the i-th motion angle combination.

[0114] Furthermore, the five-axis linkage detection trajectory formed by the rotating axes A and C exhibits a spiral-shaped curvature characteristic in space.

[0115] Although the five-axis machine tool is equipped with the RTCP function to keep the ball center point stationary, due to the machine tool's perpendicularity error, the ball head detector moving along the detection trajectory will experience a slight positional deviation in its center. This deviation value is the ball center error, which will be collected by the R-test instrument. Measuring the error data during the detection trajectory movement using the R-test instrument specifically includes the following steps:

[0116] Step S 21 Set the sampling threshold value and the total number of samples t on the R-test instrument.

[0117] Step S 22 In RTCP mode, when the machine tool rotary axis moves to (A) i C i When paused, the ball center error data (e) is automatically determined. ix ,e iy ,e iz Real-time fluctuation data, i.e., if the following formula is satisfied simultaneously, then the ball center error data at the current position is recorded:

[0118] e ix <value∩e iy <value∩e iz <value.

[0119] In particular, a 5-second pause instruction is set in the NC program for each combination of machine tool motion angles to provide sufficient time buffer for collecting error data.

[0120] Step S 23 Repeat the above sampling process until the current number of samples reaches the set total number of samples t.

[0121] Step S 24 Save the above error data into an error data file for each angle combination.

[0122] Step S3. Select the rotation axis angle combination in the detection trajectory, establish a set of perpendicularity error identification equations based on the specified position of the detection trajectory, and complete the decoupling of the machine tool perpendicularity error. Specifically, this includes the following steps:

[0123] Step S 31 In the five-axis linkage detection trajectory, select any combination of motion angles (A... i C i When the machine tool coordinate axes change, the coordinate changes of each axis are as follows:

[0124]

[0125] At this point, due to the influence of perpendicularity error, the spatial error caused by the change in the movement of the machine tool coordinate axes is:

[0126]

[0127] In the formula, P error,i This represents the spatial error vector for the i-th motion angle combination under the detected trajectory.

[0128] Furthermore, a combination of motion angles consisting of specific angles can be selected under a five-axis linkage detection trajectory (A). j :15°*j,C j :30°*j), j∈i,j≥2, can improve computational convenience.

[0129] Step S 32 By correlating the spatial error vectors of all motion angle combinations with all measured sphere center error data, we obtain the perpendicularity error identification equation set, which is then simplified into matrix form as follows:

[0130] H·V=B

[0131] in:

[0132]

[0133]

[0134]

[0135] Step S 33 According to the least squares solution of the overdetermined system of equations:

[0136] V=(H T H) -1 (H T B)

[0137] At this point, the values ​​of each element in V have been approximated by least squares, meaning that the machine tool perpendicularity error has been decoupled.

[0138] Example 4

[0139] As another preferred embodiment of the present invention, the present invention includes a method for calculating the perpendicularity error of a machine tool based on the R-test instrument, as detailed in the appendix to the specification. Figure 2 Included with instruction manual Figure 3 The perpendicularity error was tested and verified on the machine tool shown. First, compensation was made for the positioning accuracy of the machine tool's translational axes and the RTCP accuracy of its rotary axes to reduce the influence of other geometric errors on the measurement data. Second, an R-test measuring instrument was installed on the machine tool's worktable, and the measurement coordinate system and origin were set, as shown in the attached instruction manual. Figure 5 The center error of the standard sphere is measured as shown. Finally, with PosA = 90°, PosC = 360°, and Δt = π / 24, the resulting linkage detection trajectory is shown in the attached instruction manual. Figure 4 As shown in the table below, the NC program for the linkage detection trajectory was input into the machine tool end, and the ball center error data under multiple specific motion angle combinations were selected.

[0140]

[0141] At this point, the perpendicularity error identification matrix is ​​invoked, and the tool length L = 413.383. The perpendicularity error of the current experimental machine tool is shown in the table below.

[0142] 0.076 -0.046 0.0042

[0143] The obtained perpendicularity error compensation is updated in the CNC system, thereby improving the machining accuracy of the machine tool.

[0144] In summary, any other corresponding modifications made by those skilled in the art after reading this invention document, without requiring creative mental effort, based on the technical solutions and concepts of this invention, are all within the scope of protection of this invention.

Claims

1. A method for calculating the perpendicularity error of a machine tool based on the R-test instrument, characterized in that: Includes the following steps: Step S1. Set the perpendicularity error elements and, in conjunction with the principle of homogeneous coordinate matrix transformation, construct a spatial error model of the tool tip point under the influence of machine tool perpendicularity error; Step S2. Based on the machine tool topology, set up a five-axis linkage detection trajectory based on RTCP, and use the R-test instrument to measure the error data during the operation of the detection trajectory; Step S3. Select the rotation axis angle combination in the detection trajectory, establish a set of perpendicularity error identification equations based on the specified position of the detection trajectory, and complete the decoupling of the machine tool perpendicularity error; Step S2, which involves using the R-test instrument to measure error data during the trajectory's movement, specifically includes the following steps: Step S 21 Set the sampling threshold value and the total number of samples t on the R-test instrument. Step S 22 In RTCP mode, when the machine tool rotary axis moves to... When paused, automatically determine the ball center error data. Real-time fluctuations, i.e., if the following formula is satisfied simultaneously, then record the ball center error data at the current position: ； in, A five-axis linkage detection trajectory is formed for the rotation axes A and C, resulting in a series of motion angle combinations of A-axis angle and C-axis angle; Step S 23 Repeat the above sampling process until the current number of samples reaches the set total number of samples t.

2. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: The spatial error model of the tool tip point under the influence of machine tool perpendicularity error in step S1 is as follows: In the formula, y Represents the Y-axis motion coordinate value. z Represents the Z-axis motion coordinate value. L This represents the sum of the rotation distance and the tool length. This indicates the angular error between the X and Y axes. This indicates the angular error between the X-axis and the Z-axis. This indicates the angular error between the Y-axis and the Z-axis.

3. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 2, characterized in that: Step S1 specifically includes the following steps: Step S 11 According to the ISO standard definition, with the X-axis as the measurement reference axis, the error motion transformation matrix of the Y-axis... and the error motion transformation matrix along the Z-axis for: ， In the formula, This indicates the angular error between the X and Y axes. This indicates the angular error between the X-axis and the Z-axis. This indicates the angular error between the Y-axis and the Z-axis; Step S 12 The tool tip, located at the end of the machine tool's motion chain, deviates from the theoretical command point, resulting in a spatial error: In the formula, , , These represent the theoretical translational motion matrices for the X, Y, and Z axes of the machine tool, respectively: 、 、 In the formula, x , y , z respectively This represents the X-axis, Y-axis, and Z-axis motion coordinate values ​​of the machine tool. , representing the theoretical coordinates of the knife tip; L This represents the sum of the rotation distance and the tool length. Therefore, the spatial error model of the tool tip point under the influence of machine tool perpendicularity error is as follows: 。 4. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: It also includes step S 24 Save the above error data into an error data file for each angle combination.

5. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: The step S 22 In the process, the five-axis linkage detection trajectory line exhibits a spiral-shaped curvature characteristic in space.

6. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: The step S 22 In the middle, when the machine tool's rotating axis moves to When paused, the pause time is 5 seconds.

7. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: Step S3 specifically includes the following steps: Step S 31 In the five-axis linkage detection trajectory, select any combination of motion angles. At that time, the changes in the motion coordinates of each axis of the machine tool are as follows: At this point, due to the influence of perpendicularity error, the spatial error caused by the change in the movement of the machine tool coordinate axes is: In the formula, Indicates the first detection trajectory i Spatial error vector for a combination of motion angles; Step S 32 By correlating the spatial error vectors of all motion angle combinations with all measured sphere center error data, a set of perpendicularity error identification equations is obtained, which is then simplified into matrix form as follows: in: Step S 33 According to the least squares solution of the overdetermined system of equations: At this point, V The values ​​of each element in the solution were approximated by least squares, meaning that the machine tool perpendicularity error was decoupled.

8. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 7, characterized in that: The step S 31 In the five-axis linkage detection trajectory, a combination of motion angles consisting of specific angles is selected. , .

9. The method for calculating machine tool perpendicularity error based on the R-test instrument according to claim 1, characterized in that: The step S 22 In the middle, the combination of motion angles The specific method to obtain it is as follows: Set the motion angles for the rotation axes A and C as follows: In the formula, PosA , PosC These represent the maximum motion angles along the A-axis and the C-axis, respectively. t= Δ t*i , representing the total number of samples; Δ t =π / num , num >10, Δ t Indicates the set reasonable interval; This results in a series of motion angle combinations of A-axis angle and C-axis angle. , i Indicates the first i A combination of motion angles.

Images