A method for measuring five-degree-of-freedom geometric motion error of a guide rail of a numerical control machine tool

Abstract

A method for measuring the five-degree-of-freedom geometric motion error of a CNC machine tool guideway is disclosed. Before measurement, three arbitrary non-collinear fixed points are identified on the guideway. A reference coordinate system is set for the guideway cross-section, and the three fixed points are connected sequentially to form triangle ABC. During measurement, after the CNC machine tool guideway moves a certain distance, the three fixed points move to A1, B1, and C1. Using the reference coordinate system as a reference, the three points are connected sequentially to form a new triangle A1B1C1. The roll angle, yaw angle, and pitch angle errors are calculated. This method is repeated at all sampling positions to obtain the distribution of the three angle errors at all positions of the guideway. The offsets in the X and Y directions represent the horizontal and vertical straightness errors of the guideway. This invention can effectively and quickly obtain the three angle errors and two straightness errors.

Description

Technical Field

[0001] This invention relates to the field of CNC machine tool error detection technology, and in particular to a method for measuring the five-degree-of-freedom geometric motion error of CNC machine tool guideways. Background Technology

[0002] A spatial object has six degrees of freedom: linear motion in the X, Y, and Z directions and rotational motion around the X, Y, and Z axes. Therefore, the guide rail of a CNC machine tool includes six motion errors: three linear errors and three angular errors. The three linear errors include positioning error, horizontal straightness, and vertical straightness, while the three angular errors include yaw angle, pitch angle, and roll angle.

[0003] Currently, there are two methods for measuring the geometric motion error of CNC machine tool guideways: single-item geometric error measurement (CN202111026242.4, a machine tool geometric error separation method based on a double ballbar) and comprehensive geometric error measurement (CN201721045299.8, a comprehensive error measurement system for CNC machine tools based on in-machine inspection). Single-item geometric error measurement measures one of the six geometric errors individually. Each geometric error requires a different measuring instrument, such as measuring positioning errors based on a laser interferometer, straightness measurements based on a straightedge and autocollimator, and angular errors based on an autocollimator and level. This method is simple but time-consuming, and only one of the six errors can be obtained at a time, resulting in low measurement efficiency. Comprehensive geometric error measurement measures all six dimensions of the machine tool guideway's errors as a whole, and then processes and analyzes the overall measurement data to obtain the total six-dimensional error. This method can improve measurement efficiency, but the solution algorithm is often complex.

[0004] To address the aforementioned technical issues, a new method for measuring the geometric motion error of CNC machine tool guideways needs to be designed, which meets the design requirements of simultaneously measuring multiple errors of the guideways and having a simple structure and algorithm. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for measuring the five-degree-of-freedom geometric motion error of CNC machine tool guideways, which can effectively and quickly obtain three angular errors and two linear errors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for measuring the five-degree-of-freedom geometric motion error of a CNC machine tool guideway includes the following steps:

[0008] 1) Before measurement, find three non-collinear fixed points A, B, and C on the CNC machine tool guide rail. Set a reference coordinate system for the cross section of the guide rail and determine the two-dimensional coordinates of the three fixed points. Connect the three fixed points in sequence to form triangle ABC. With AB as the base, determine the height of triangle ABC, which is defined as L. With BC as the base, determine the height of triangle ABC, which is defined as h.

[0009] 2) During measurement, after the CNC machine tool guide rail moves a certain distance, the three fixed points move to A1, B1, and C1. Using the reference coordinate system in step 1) above as a benchmark, determine the two-dimensional coordinates of the three points after the movement. Connect the three points in sequence to form a new triangle A1B1C1. With A1B1 as the base, determine the height of triangle A1B1C1, which is defined as L1; with B1C1 as the base, determine the height of triangle A1B1C1, which is defined as h1.

[0010] 3) Solve for the three angular errors: roll angle, yaw angle, and pitch angle;

[0011] 4) Repeat steps 2) to 3) for all sampling positions to obtain the distribution of the three angular errors at all positions of the entire CNC machine tool guideway;

[0012] 5) Based on the coordinates of the three points of triangle ABC before measurement and the coordinates of the three points of triangle A1B1C1 after the CNC machine tool guide rail has moved and deformed, the offsets in the X and Y directions in the two-dimensional plane are the horizontal straightness error and vertical straightness error of the CNC machine tool guide rail.

[0013] Step 3) of solving for the three angular errors of roll angle, yaw angle, and pitch angle is specifically as follows:

[0014] 3.1) The angle between the height h of triangle ABC and the height h1 of triangle A1B1C1 is the roll angle α;

[0015] 3.2) The altitude L of triangle ABC is rotated around the Y-axis to the altitude L1 of triangle A1B1C1, coinciding with L1. The rotation angle is the deflection angle β.

[0016] 3.3) The height h of triangle ABC is rotated around the X-axis to the height h1 of triangle A1B1C1, which coincides with h1. The rotation angle is the pitch angle γ.

[0017] In step 1), the points A, B, and C before the CNC machine tool guideway moves and the points A1, B1, and C1 after the CNC machine tool guideway moves are obtained in the following way:

[0018] Three quadrant detectors are arranged at points A, B, and C. A light source projects light onto points A, B, and C, and light spots appear on the corresponding quadrant detectors. After the CNC machine tool guide rail moves, the light spots will shift by ΔX and ΔY on the photosensitive surface of the quadrant detectors. Based on the photoelectric conversion principle of the quadrant detectors, the offset of points A1, B1, and C1 relative to the center of the quadrant detectors can be obtained.

[0019] Before the CNC machine tool guide rail moves, points A, B, and C are pre-calibrated to establish the reference coordinate system in step 1) above. The reference coordinate system is defined by the user and the two-dimensional coordinates of points A, B, and C are obtained. After the CNC machine tool guide rail moves, the offsets of the three positions are obtained by combining the four-quadrant detector and unified in the reference coordinate system described in step 1) to obtain the two-dimensional coordinates of points A1, B1, and C1.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] Because this invention employs laser projection combined with the photoelectric conversion principle of a photoelectric sensor, it can simultaneously measure the horizontal and vertical straightness errors, roll angle errors, yaw angle errors, and pitch angle errors of the guide rail, achieving simultaneous measurement of multiple guide rail errors. This invention measures the two-dimensional coordinates of three fixed points on the CNC machine tool guide rail to form a triangle. Using the height defined by the reference triangle and the height of the triangle after movement, the three angular errors of the CNC machine tool guide rail are solved. The entire solution process requires only simple analytical geometry knowledge, making the method simple and reliable. Compared to methods using instruments to measure single geometric errors, this method has the advantage of high measurement efficiency. Compared to existing methods that simultaneously measure multiple errors, this method has the advantages of simple optical path structure and simple solution algorithm. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the six-dimensional error of the CNC machine tool guideway according to the present invention.

[0023] Figure 2 This is a schematic diagram illustrating the principle of measuring the roll angle error of CNC machine tool guideways according to the present invention.

[0024] Figure 3 This is a schematic diagram illustrating the principle of measuring the sway angle error of the CNC machine tool guideway according to the present invention.

[0025] Figure 4 This is a schematic diagram illustrating the principle of measuring the pitch angle error of the CNC machine tool guideway according to the present invention.

[0026] Figure 5 This is a schematic diagram of the measurement principle of the four-quadrant detector of the present invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0028] A method for measuring the five-degree-of-freedom geometric motion error of a CNC machine tool guideway includes the following steps:

[0029] 1) Before measurement, find three non-collinear fixed points A, B, and C on the CNC machine tool guide rail. Set a reference coordinate system for the cross section of the CNC machine tool guide rail to determine the two-dimensional coordinates of the three fixed points. Connect the three fixed points in sequence to form a right triangle ABC. With AB as the base, determine the height of triangle ABC, which is defined as L. With BC as the base, determine the height of triangle ABC, which is defined as h.

[0030] 2) During measurement, after the CNC machine tool guide rail moves a certain distance, the three fixed points move to A1, B1, and C1. Using the reference coordinate system from step 1) above as a benchmark, determine the two-dimensional coordinates of the three points after the movement. Connect the three points in sequence to form a new right triangle A1B1C1. With A1B1 as the base, determine the height of triangle A1B1C1, which is defined as L1; with B1C1 as the base, determine the height of triangle A1B1C1, which is defined as h1.

[0031] 3) Solve for the three angular errors: roll angle, yaw angle, and pitch angle. Specifically:

[0032] 3.1) Reference Figure 1 and Figure 2 Before measurement, the height of right triangle ABC is h. After the CNC machine tool guide rail moves a certain distance, due to the roll angle error of the CNC machine tool guide rail, the CNC machine tool guide rail deflects in the Z direction. During measurement, right triangle ABC is deformed and transformed into right triangle A1B1C1. The height of right triangle A1B1C1 is h1. The angle between h and h1 is the roll angle α.

[0033] We can obtain the following formula:

[0034]

[0035] 3.2) Reference Figure 1 and Figure 3 Before measuring the height L of right triangle ABC, after the CNC machine tool guide rail moves a certain distance, due to the yaw angle error of the CNC machine tool guide rail, the CNC machine tool guide rail deflects in the Y direction. During the measurement, right triangle ABC is deformed and transformed into right triangle A1B1C1. The height of right triangle A1B1C1 is L1. Then, the height L of right triangle ABC rotates around the Y axis until it coincides with the height L1 of A1B1C1. The rotation angle is the yaw angle β.

[0036] We can obtain the following formula:

[0037]

[0038] 3.3) Reference Figure 1and Figure 4 Before measuring the height h of right triangle ABC, after the CNC machine tool guide rail moves a certain distance, due to the pitch angle error of the CNC machine tool guide rail, the CNC machine tool guide rail deflects in the X direction. During the measurement, right triangle ABC is deformed and transformed into right triangle A1B1C1. The height of right triangle A1B1C1 is h1. Then, the height h of right triangle ABC rotates around the X axis until it coincides with the height h1 of A1B1C1. The rotation angle is the pitch angle γ.

[0039] We can obtain the following formula:

[0040]

[0041] 4) Repeat steps 2) to 3) for all sampling positions to obtain the distribution of the three angular errors at all positions of the entire CNC machine tool guideway;

[0042] 5)Reference Figure 1 Based on the characteristic that the change in the spatial vector direction formed by the machine tool during its movement is only related to the angular displacement error of the machine tool axis and not to the linear displacement error, and using the coordinates of the three points of the right triangle ABC before measurement, and the coordinates of the three points of the right triangle A1B1C1 after the CNC machine tool guide rail has moved a certain distance, the offset in the X and Y directions in the two-dimensional plane is the horizontal straightness error and the vertical straightness error of the guide rail. Thus, we can obtain the five errors in the geometric motion error of the CNC machine tool guide rail: roll angle, yaw angle, pitch angle, horizontal straightness error, and vertical straightness error.

[0043] In step 1), the points A, B, C before the CNC machine tool guideway moves and the points A1, B1, C1 after the move are obtained in the following way:

[0044] Reference Figure 5 Three quadrant detectors are arranged at points A, B, and C. A semiconductor laser is selected as the light source to project light onto the three points A, B, and C. A light spot will appear on the quadrant detector at the corresponding position. During the movement of the CNC machine tool guide rail, due to the existence of geometric motion error, the light spot will be offset by ΔX and ΔY on the photosensitive surface of the quadrant detector. By combining the photoelectric conversion principle of the quadrant detector, the offset of points A1, B1, and C1 relative to the center of the quadrant detector can be obtained.

[0045] Before the CNC machine tool guide rail moves, points A, B, and C are pre-calibrated to establish the reference coordinate system in step 1) above. This system can be defined by the user, and the two-dimensional coordinates of points A, B, and C can then be obtained.

[0046] After the CNC machine tool guide rail moves, the offset of the three positions is obtained by combining the four-quadrant detector and unified in the reference coordinate system described in step 1). Then, the two-dimensional coordinates of points A1, B1, and C1 can be obtained. Thus, the two-dimensional coordinates of points A, B, C, A1, B1, and C1 before and after the CNC machine tool guide rail moves can be obtained.

[0047] The beneficial effects of this embodiment are as follows: by using laser projection combined with the photoelectric conversion principle of photoelectric sensors, the measurement of five geometric motion errors of CNC machine tool guideways is realized. The light spots formed on the three photoelectric sensors are connected end to end to form a planar triangle. Using simple analytical geometric relationships, three angular errors and two linear errors can be obtained effectively and quickly. Compared to positioning error measurement based on laser interferometers, straightness measurement based on straightedges and autocollimators, and angular error measurement based on autocollimators and levels, which use measuring instruments to measure single errors, this invention offers higher measurement efficiency by simultaneously measuring multiple errors. In contrast, methods for measuring comprehensive geometric errors, such as measuring four errors of a guide rail based on a single collimated laser beam, or measuring six degrees of freedom using four laser beams, four sets of displacement measuring instruments, and four-quadrant photodetectors with optical mirror groups, are costly and have complex optical path structures. Therefore, most of these methods are still in the research and testing stage and have not yet been put into practical application. This invention uses three laser beams combined with three four-quadrant detectors to achieve simultaneous measurement of five errors. Compared to the above measurement methods, it is lower in cost, has a simpler optical path structure, and offers higher measurement efficiency.

Claims

1. A method for measuring five degrees of freedom geometric motion errors of a guideway of a numerically controlled machine tool, characterized in that, The method comprises the following steps: 1) Before measurement, find three fixed points A, B and C which are not collinear on the guide rail of the numerical control machine tool, set the reference coordinate system of the cross section of the guide rail, determine the two-dimensional coordinates of the three fixed points, connect the three fixed points in turn to form a triangle ABC, in the reference coordinate system, the point A is above the side BC of the triangle, and the three fixed points A, B and C are distributed counterclockwise; determine the height of the triangle ABC with AB as the base, and define it as L, and determine the height of the triangle ABC with BC as the base, and define it as h; 2) During measurement, after the guide rail of the numerical control machine tool moves a distance, the three fixed points move to A1, B1 and C1, determine the two-dimensional coordinates of the three points after movement based on the reference coordinate system in step 1) above, connect the three points in turn to form a new triangle A1B1C1, determine the height of the triangle A1B1C1 with A1B1 as the base, and define it as L1, and determine the height of the triangle A1B1C1 with B1C1 as the base, and define it as h1; 3) Solve the roll angle, yaw angle and pitch angle errors, specifically: 3.1) the included angle between the height h of the triangle ABC and the height h1 of the triangle A1B1C1 is the roll angle α; 3.2) the rotation angle of the height L of the triangle ABC around the Y axis to the height L1 of the triangle A1B1C1 to coincide with L1 is the yaw angle β; 3.3) the rotation angle of the height h of the triangle ABC around the X axis to the height h1 of the triangle A1B1C1 to coincide with h1 is the pitch angle γ; 4) repeat steps 2) to 3) for all sampling positions to obtain the distribution of the three angle errors of the numerical control machine tool guide rail at all positions; 5) according to the three-point coordinates of the triangle ABC before measurement and the three-point coordinates of the triangle A1B1C1 after the deformation of the numerical control machine tool guide rail, the offset in the X direction and the Y direction is the horizontal straightness error and the vertical straightness error of the numerical control machine tool guide rail.

2. The method of claim 1, wherein, The points A, B, C before and after movement of the numerical control machine tool guide rail in step 1) are obtained in the following manner: At the positions of points A, B and C, three four-quadrant detectors are arranged correspondingly, the positions of points A, B and C are projected by a light source, and light spots will appear on the four-quadrant detectors corresponding to the positions; after the movement of the numerical control machine tool guide rail, the position of the light spot on the photosensitive surface of the four-quadrant detector is offset by ΔX and ΔY; combined with the photoelectric conversion principle of the four-quadrant detector, the offset of points A1, B1 and C1 relative to the center of the four-quadrant detector is obtained; Before the movement of the numerical control machine tool guide rail, points A, B and C are calibrated in advance to establish the reference coordinate system in step 1) above, which is self-defined to obtain the two-dimensional coordinates of points A, B and C; after the movement of the numerical control machine tool guide rail, the offset of the three positions is obtained by the four-quadrant detector, and it is unified in the reference coordinate system in step 1) to obtain the two-dimensional coordinates of points A1, B1 and C1.

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