A comprehensive compensation method for key errors in five-axis in-machine measurement

Abstract

This invention proposes a comprehensive compensation method for key errors in five-axis in-machine measurement. This method compensates for pre-travel errors along the normal vector in the machine tool coordinate system during five-axis in-machine measurement, avoiding the inaccuracy of compensation along the normal vector in the part coordinate system in existing technologies. Furthermore, a high-precision and stable laser interferometer is used to identify the positioning deviations of the two rotation axes, and the identified deviations are substituted into the machine tool kinematics chain to offset the rotational angle positioning deviations introduced in the five-axis in-machine measurement. The calculation method of this invention is simple and reliable, and can be extended to in-machine measurement on four-axis machine tools or other five-axis machine tools with different structures.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of precision measurement, and particularly relates to a comprehensive compensation method for key errors in five-axis in-machine measurement BACKGROUND

[0002] Adaptive machining technology is increasingly applied to the machining of complex structural parts of aircraft, such as impellers, blisks, casings and disc shafts. In-machine measurement technology, as an important part of adaptive machining technology, can identify the actual shape of a part through a probe installed on the spindle of a machine tool, and the measurement results can be used to correct deviations in the machining process of the part. At the same time, in-machine measurement technology can be used as a process detection means in the machining of key features, which can improve the current situation of manual measurement using gauges, and help to realize an efficient production mode of "one person operating multiple machines" in the machining workshop.

[0003] Five-axis in-machine measurement is suitable for the detection of complex structural parts of aircraft, but the measurement accuracy of such parts is currently low, which limits the popularization and application of in-machine measurement technology. In order to improve the in-machine measurement accuracy of complex structural parts, it is necessary to analyze and compensate for the error sources in the measurement system. The in-machine measurement system is composed of a machine tool, a probe and a part, and its detection accuracy is affected by many error sources. Studies have shown that the pre-travel error of a trigger-type probe and the positioning deviation of a rotary table are the main influencing factors. In terms of pre-travel error compensation, most current compensation methods compensate for the pre-travel error based on the normal vector at the measurement point in the part coordinate system, ignoring the fact that the position of the normal vector at the measurement point in space changes with the rotation of the rotary table. Therefore, this compensation direction is not suitable for pre-travel error compensation in five-axis in-machine measurement. In terms of rotary table positioning deviation, many scholars have focused on analyzing and establishing the influence model of rotary table positioning deviation on machining accuracy, but there is a lack of research on compensating for rotary table positioning deviation in five-axis in-machine measurement results. SUMMARY

[0004] In view of the defects in the prior art, in order to improve the in-machine measurement accuracy of complex structural parts, the application provides a comprehensive compensation method for key errors in five-axis in-machine measurement, which compensates for the pre-travel error and the positioning deviation of the rotary table in the measurement results to improve the accuracy of five-axis in-machine measurement.

[0005] The technical scheme of the application is as follows:

[0006] The comprehensive compensation method for key errors in five-axis in-machine measurement comprises the following steps:

[0007] Step 1: Construct the kinematic chain of the five-axis machine tool

[0008] Define the key coordinate systems in the five-axis in-machine measurement system, and give the nominal homogeneous transformation matrix from the machine tool coordinate system to the part coordinate system by means of the positional relationship between the coordinate systems Constructing the kinematic chain of the machine tool;

[0009] Step 2: Identify the positioning deviation of the machine tool rotary table:

[0010] First, identify the B-axis angle positioning deviation, wherein, when identifying the B-axis angle positioning deviation, within the set rotation angle range of the B-axis, sample according to the set angle interval; then, at each set sampling angle of the B-axis, identify the C-axis angle positioning deviation, wherein, when identifying the C-axis angle positioning deviation, within the set rotation angle range of the C-axis, sample according to the set angle interval;

[0011] Step 3: Calculate the pre-travel error compensation direction and compensation value in the machine tool coordinate system:

[0012] Step 3.1: Select the measurement feature and arrange the measurement points in the part coordinate system, and obtain the theoretical normal vector of each measurement point, denoted as n W Then, the normal vector n in the machine tool coordinate system is transformed as follows: M

[0013]

[0014] Step 3.2: First, based on the transformation relationship between the ball coordinate system and the part coordinate system and the measurement point coordinates in the part coordinate system, calculate the touch position on the ball that actually contacts the part during measurement; then, calibrate a series of evenly distributed calibration points on the standard ball, and then convert the calibration points to touch positions on the ball Construct a pre-travel error map composed of touch positions Finally, based on the pre-travel error map, interpolate to obtain the pre-travel error p corresponding to the actual touch position on the ball during measurement;

[0015] Step 4: Calculate the compensation amount and compensate the measurement result by fusing the pre-travel error and the rotary table positioning deviation:

[0016] Step 4.1: Plan the in-machine measurement process parameters of the feature to be measured;

[0017] Step 4.2: Calculate the rotation angles of the B-axis and the C-axis during measurement based on the kinematic chain of the machine tool, and then interpolate the positioning deviation corresponding to the two rotation angles in the identified rotary table positioning deviation result, to obtain the actual transformation matrix from the machine tool coordinate system to the part coordinate system

[0018] Step 4.3: The comprehensive compensation amount Δ of the pre-travel error and the rotary table positioning deviation is:

[0019]

[0020] Then, the compensation of the measurement result is as follows:​

[0021] m Last = m Meas + Δ

[0022] where m Meas is the measured point coordinate obtained in the numerical control system, and m Last is the final measured point coordinate after comprehensive compensation.

[0023] Further, in step 1, the key coordinate systems in the five-axis in-machine measurement include: the machine tool coordinate system O M -X M Y M Z M , the worktable coordinate system O G -X G Y G Z G , the B-axis coordinate system O B -X B Y B Z B , the C-axis coordinate system O C -X C Y C Z C , the part coordinate system O W -X W Y W Z W , and the ball coordinate system O P -X P Y P Z P ; the nominal homogeneous transformation matrix from the machine tool coordinate system O M -X M Y M Z M to the part coordinate system O W -X W Y W Z W is represented as:

[0024]

[0025] where T and R represent the translation and rotation transformation matrices, respectively; represents the translation transformation matrix from the C-axis coordinate system O C -X C Y C Z C to the part coordinate system O W -X W Y W Z W , represents the translation transformation matrix from the B-axis coordinate system O B -X B YB Z B to the C-axis coordinate system O C -X C Y C Z C the rotation transformation matrix of, denotes the translation transformation matrix from the machine tool coordinate system O G -X G Y G Z G to the B-axis coordinate system O B -X B Y B Z B the rotation transformation matrix of, denotes the translation transformation matrix from the machine tool coordinate system O M -X M Y M Z M to the worktable coordinate system O G -X G Y G Z G .

[0026] Further, in step 1, the key coordinate system definitions are as follows:

[0027] the origin of the machine tool coordinate system O M -X M Y M Z M is located at the center position of the spindle end when the machine tool is reset;

[0028] the origin of the worktable coordinate system O G -X G Y G Z G is established at the intersection of the rotation axes B-axis and C-axis when the machine tool is reset, and the origin position coordinates in the machine tool coordinate system are (ε x ,ε y ,ε z ), which do not change with the movement of the rotation axes, and in order to ensure the movement performance of the five-axis machine tool, the position needs to be calibrated periodically, and the three coordinate axes of the worktable coordinate system are parallel and in the same direction as the three axes of the machine tool coordinate system;

[0029] the B-axis coordinate system O B -X B Y B Z B is obtained by rotating the worktable coordinate system O G -X G Y G Z G around the Y G axis, and the C-axis coordinate system O C -XC Y C Z C From the B-axis coordinate system O B -X B Y B Z B Around Z B Obtained by rotating the axis;

[0030] Part coordinate system O W -X W Y W Z W The origin position is determined by the process engineer, and its coordinates in the machine tool coordinate system are (α). x ,α y ,α z The three axes of the part coordinate system are parallel to and in the same direction as the three axes of the machine tool coordinate system.

[0031] spherical coordinate system O P -X P Y P Z P The origin is established at the center of the measuring sphere, and its three axes are parallel and in the same direction to the three axes of the machine tool coordinate system.

[0032] Furthermore, in step 1,

[0033]

[0034]

[0035] Furthermore, in step 2, when identifying the B-axis positioning deviation, sampling is performed every 10° within the range of 0° to 90°, for a total of 10 angular positions; when identifying the C-axis positioning deviation, sampling is performed on the C-axis at 10 angular positions on the B-axis, and every 30° within the range of 0° to 360°, for a total of 12 angular positions.

[0036] Furthermore, in step 2, the positioning deviation of the machine tool turntable is identified using a laser interferometer system and a rotary axis calibration device.

[0037] Furthermore, in step 4.1, when planning the in-machine measurement process parameters for the feature to be measured, the following two principles need to be followed: the probe must not interfere with or collide with the blade or turntable during the measurement process; and the turntable should be kept from rotating violently.

[0038] Furthermore, in step 4.2, the rotation angles B' and C' of the B-axis and C-axis during measurement are calculated based on the machine tool kinematics chain. Then, the positioning deviation p corresponding to the two rotation angles B' and C' is obtained by interpolation from the identified turntable positioning deviation results. B p CThus, the actual transformation matrix from the machine tool coordinate system to the part coordinate system is obtained.

[0039]

[0040] in

[0041]

[0042]

[0043] Beneficial effects

[0044] This invention, based on the correction and optimization of existing pre-travel error compensation methods in in-machine measurement, proposes a comprehensive compensation method for pre-travel error and rotary table positioning deviation in five-axis in-machine measurement. This method compensates for pre-travel error along the normal vector in the machine tool coordinate system during five-axis in-machine measurement, avoiding the inaccuracy of compensation along the normal vector in the part coordinate system in existing technologies. Furthermore, it uses a high-precision and stable laser interferometer to identify the positioning deviations of the two rotation axes, and substitutes the identified deviation results into the machine tool kinematics chain to offset the rotational angle positioning deviation introduced in five-axis in-machine measurement. The calculation method of this invention is simple and reliable, and can be extended to in-machine measurement on four-axis machine tools or other five-axis machine tools with different structures.

[0045] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0047] Figure 1 A flowchart illustrating the implementation of this invention.

[0048] Figure 2 The key coordinate system defined in five-axis in-machine measurement.

[0049] Figure 3 Positioning deviation of the B-axis angle on the turntable.

[0050] Figure 4 Positioning deviation of the C-axis angle on the turntable.

[0051] Figure 5 The calibration points are uniformly distributed on the Northern Hemisphere of the standard sphere.

[0052] Figure 6 The contact position on the measuring ball in the measuring ball coordinate system.

[0053] Figure 7 A trefoil diagram of the pre-travel error established by the combination of angles on the measuring ball. Detailed Implementation

[0054] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0055] This embodiment takes a BC-axis cradle-type five-axis machine tool as an example, and the implementation process is as follows: Figure 1 As shown:

[0056] Step 1: Define the key coordinate system in the five-axis in-machine measurement system, such as... Figure 2 As shown, the nominal homogeneous transformation matrix from the machine tool coordinate system to the part coordinate system is given by means of the positional relationship between the coordinate systems, and the machine tool kinematic chain is constructed.

[0057] The key coordinate system is defined as follows:

[0058] 1) Machine tool coordinate system O M -X M Y M Z M The origin is located at the center of the spindle end when the machine tool is reset;

[0059] 2) Worktable coordinate system O G -X G Y G Z G The origin is established at the intersection of the B-axis and C-axis axes during machine tool reset, and the coordinates of the origin in the machine tool coordinate system are (ε... x ,ε y ,ε z This coordinate value does not change with the movement of the rotary axis. At the same time, in order to ensure the motion performance of the five-axis machine tool, this position needs to be calibrated in stages. The three coordinate axes of the worktable coordinate system are parallel to and in the same direction as the three axes of the machine tool coordinate system.

[0060] 3) B-axis coordinate system O B -X B Y B Z B From the worktable coordinate system O G -X G Y G Z G Around Y G The coordinate system O is obtained by rotating the axis. C -X C Y C Z C From the B-axis coordinate system O B -X B Y B Z BAround Z B Obtained by rotating the axis;

[0061] 4) Part coordinate system O W -X W Y W Z W The origin position is determined by the process engineer, and its coordinates in the machine tool coordinate system are (α). x ,α y ,α z The three axes of the part coordinate system are parallel to and in the same direction as the three axes of the machine tool coordinate system.

[0062] 5) Spherical coordinate system O P -X P Y P Z P The origin is established at the center of the measuring sphere, and its three axes are parallel and in the same direction to the three axes of the machine tool coordinate system.

[0063] Then from the machine tool coordinate system O M -X M Y M Z M To the part coordinate system O W -X W Y W Z W The nominal homogeneous transformation matrix is:

[0064]

[0065] In the formula, and Let be the translation transformation matrix, denoted as: and Let be the rotation transformation matrix, denoted as

[0066]

[0067] Step 2: Identify the positioning deviation of the machine tool rotary table using the prism in the laser interferometer system and the XR20-W wireless rotary axis calibration device. When identifying the B-axis positioning deviation, samples were taken at 10° intervals within the range of 0° to 90°, for a total of 10 angular positions. When identifying the C-axis positioning deviation, samples were taken at 30° intervals within the range of 0° to 360° at the 10 angular positions of the B-axis, for a total of 12 angular positions. During the calibration process, the machine tool feed rate was set to 2000° / min, the acquisition pause time was 4 seconds, and each experiment was performed bidirectionally linearly 5 times. The average value was taken as the final identification result of the rotary table positioning deviation. The fitted B-axis positioning deviation identification result is shown below. Figure 3 As shown, the C-axis positioning deviation identification results are as follows:Figure 4 As shown.

[0068] Step 3: Direction and value of pre-travel error compensation in computer tool coordinate system

[0069] Step 3.1: Select the measurement feature and arrange the measurement points in the part coordinate system, and obtain the theoretical normal vector of each measurement point, denoted as n. W Then the normal vector n of the measuring point in the machine tool coordinate system M It is expressed as follows:

[0070]

[0071] Step 3.2: In five-axis machine measurement, the orientation of the probe relative to the part coordinate system changes continuously with the rotation of the turntable. Therefore, to accurately obtain the pre-travel error generated when the probe is triggered during five-axis machine measurement, the process includes: First, based on the transformation relationship between the probe coordinate system and the part coordinate system, and the coordinates of the measurement point in the part coordinate system, calculate the actual contact position between the probe and the part during measurement; then, mark a series of uniformly distributed calibration points on the standard sphere, such as... Figure 5 As shown. The point to be calibrated is then transformed into the contact position on the measuring sphere in the measuring sphere coordinate system. like Figure 6 As shown, a structure is built based on the touch location. The pre-trip error trefoil diagram is as follows: Figure 7 As shown; finally, based on the trefoil diagram of the pre-travel error, the pre-travel error corresponding to the actual contact position on the measuring ball is calculated using the bilinear interpolation method, and is expressed as ρ.

[0072] Step 4: Calculate the compensation amount and compensation measurement results by integrating the pre-travel error and turntable positioning deviation.

[0073] First, plan the in-machine measurement process parameters for the feature to be measured. When planning the in-machine measurement process parameters for the feature to be measured, the following two principles should be followed: 1) The probe should not interfere with or collide with the blade or turntable during the measurement process; 2) Avoid violent rotation of the turntable.

[0074] Then, based on the machine tool kinematics chain, the rotation angles B' and C' of the B-axis and C-axis in the in-machine measurement are calculated. Furthermore, from the identified rotary table positioning deviation results, the positioning deviation p corresponding to the two rotation angles B' and C' is obtained using Lagrange interpolation. B p C Therefore, the comprehensive compensation amount Δ, which integrates the pre-travel error and the turntable positioning deviation, is:

[0075]

[0076] In the formula, The actual transformation matrix from the machine tool coordinate system to the part coordinate system:

[0077]

[0078] In the matrix middle, and remain unchanged.

[0079] The compensation for the measurement results is as follows:

[0080] m Last =m Meas +Δ (4)

[0081] In the formula, m Meas The coordinates of the measurement point obtained in the CNC system, m Last These are the final coordinates of the measurement points after comprehensive compensation.

[0082] The following is a five-axis in-machine measurement experiment of eight measurement points on a certain type of blade:

[0083] In this embodiment, the in-machine measurement system mainly includes: a JDGR200_A10H five-axis CNC machine tool, a RENISHAW OMP40-2 mechanical trigger probe, a probe with a diameter of 2mm and a length of 50mm, and a ceramic standard ball with a diameter of 19.9998mm.

[0084] Taking a certain type of blade as the subject of this study, eight measurement points were arranged on a single curve of the blade, and the normal vector corresponding to each measurement point was obtained. Simultaneously, a coordinate measuring machine was used to inspect the measurement points on the blade, and the inspection results were used as reference values ​​for the actual shape of the blade, as shown in Table 1.

[0085] Table 1. Coordinate measurement results of measurement points on the blade.

[0086]

[0087]

[0088] Based on the measurement process planning principles, a testing process for 8 measurement points was developed. Experiments were conducted and measurements were repeated 5 times, with the average value taken as the measurement result. The compensation process for the measurement results was as follows: First, based on the planned rotation angle during measurement, the positioning deviation corresponding to the rotation angle was interpolated in the turntable positioning deviation result diagram to obtain the positioning deviation. Next, the normal vector at the measurement point in the machine tool coordinate system was calculated using the machine tool kinematic chain, as shown in Table 2. Simultaneously, the pre-stroke error corresponding to the contact point of the measuring ball was interpolated in the established pre-stroke error clover diagram. Finally, the pre-stroke error and turntable positioning deviation introduced during blade measurement were compensated into the measurement results acquired by the CNC system. The final compensated measurement coordinates are shown in Table 3.

[0089] Table 2 Normal vectors of measurement points in the part coordinate system and machine tool coordinate system.

[0090]

[0091] Table 3 Coordinates of the measurement points after compensation

[0092]

[0093] The experimental results above show that the deviation between the final measurement result after compensation using the method of the present invention and the detection result of the coordinate measuring machine is about 0.0165 mm. Compared with the deviation value of 0.0306 mm before compensation, the in-machine measurement accuracy of the five-axis machine is improved by an average of about 46.07%, which demonstrates the effectiveness of the method of the present invention in improving the in-machine measurement accuracy of the five-axis machine.

[0094] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method of integrated compensation of key errors in five-axis in-machine measurement, characterized in that: The method comprises the following steps: Step 1: Constructing the kinematic chain of the five-axis machine tool: The key coordinate systems in five-axis machine measurement system are defined, and the nominal homogeneous transformation matrix from machine coordinate system to part coordinate system is given by means of the position relationship between coordinate systems , and the machine kinematic chain is constructed Step 2: Identifying the positioning deviation of the machine tool rotary table: First, identify the B-axis angle positioning deviation, wherein when identifying the B-axis angle positioning deviation, within the set rotation angle range of the B-axis, sampling is performed at a set angle interval; then at each set sampling angle of the B-axis, identify the C-axis angle positioning deviation, wherein when identifying the C-axis angle positioning deviation, within the set rotation angle range of the C-axis, sampling is performed at a set angle interval; Step 3: Calculating the pre-stroke error compensation direction and compensation value in the machine tool coordinate system: Step 3.1: Select the measurement feature and arrange the measurement points in the part coordinate system, and obtain the theoretical normal vector of each measurement point, denoted as The normal vector in the machine coordinate system is transformed as follows: ​ Step 3.2: Firstly, based on the transformation relationship between the probe coordinate system and the part coordinate system and the measurement point coordinates in the part coordinate system, the touch positions on the probe corresponding to the actual contact positions of the part are calculated; then, a series of evenly distributed points to be calibrated are calibrated on the standard sphere, and the points to be calibrated are converted into touch positions on the probe , a pre-travel error map composed of the touch positions is constructed; finally, based on the pre-travel error map, the pre-travel error corresponding to the actual touch position on the probe in the measurement is obtained by interpolation ; Step 4: Fusing the pre-stroke error and the rotary table positioning deviation to calculate the compensation amount and the compensation measurement result: Step 4.1: Planning the in-machine measurement process parameters of the to-be-measured feature; Step 4.2: Calculate the rotation angles of B-axis and C-axis in the measurement based on the kinematic chain of the machine tool, and then interpolate the positioning deviations corresponding to the two rotation angles in the identified positioning deviation results of the rotary table to obtain the actual transformation matrix from the machine tool coordinate system to the part coordinate system ; Step 4.3: Integrated compensation of fusion pre-travel error and turntable positioning bias is: Then, the compensation of the measurement result is as follows: In the formula, is the coordinate of the measurement point obtained in the numerical control system, is the final measurement point coordinate after comprehensive compensation.

2. The method of claim 1, wherein: In step 1, key coordinate systems in five-axis in-machine measurement, including: machine coordinate system , worktable coordinate system , B-axis coordinate system , C-axis coordinate system , part coordinate system and measuring ball coordinate system ; the nominal homogeneous transformation matrix from the machine coordinate system to the part coordinate system is represented as: where T and R represent translation and rotation transformation matrices, respectively; denotes a translation transformation matrix from the C-axis coordinate system to the part coordinate system denotes a rotation transformation matrix from the B-axis coordinate system to the C-axis coordinate system denotes a rotation transformation matrix from the table coordinate system to the B-axis coordinate system denotes a rotation transformation matrix from the machine coordinate system to the table coordinate system denotes a translation transformation matrix from the machine coordinate system to the table coordinate system denotes a translation transformation matrix from the machine coordinate system to the table coordinate system 3. The method of claim 2, wherein: In step 1, the key coordinate systems are defined as follows: Machine coordinate system origin is located at the center of the spindle tip when the machine is reset; Worktable coordinate system The origin of the worktable coordinate system is established at the intersection of the rotation axes B and C when the machine tool is reset, and the coordinates of the origin position are , not changed with the movement of the rotation axes, and in order to ensure the movement performance of the five-axis machine tool, the position needs to be calibrated periodically, and the three coordinate axes of the worktable coordinate system are parallel and in the same direction as the three axes of the machine tool coordinate system. B-axis coordinate system from the worktable coordinate system rotated about the C-axis coordinate system from the B-axis coordinate system rotated about the Z-axis Part coordinate system The origin position is determined by the process engineer, and its coordinates in the machine tool coordinate system are: The three axes of the part coordinate system are parallel to and in the same direction as the three axes of the machine tool coordinate system; spherical coordinate system The origin is established at the center of the measuring sphere, and its three axes are parallel and in the same direction to the three axes of the machine tool coordinate system.

4. The method of claim 3, wherein: In step 1, 、 ； 、 。 5. The method of claim 1, wherein: In step 2, when identifying the B-axis positioning deviation, sampling is performed at an interval of 10° within the range of 0°~90°, and a total of 10 angle positions are sampled; when identifying the C-axis positioning deviation, at the 10 angle positions of the B-axis, sampling is performed at an interval of 30° within the range of 0°~360°, and a total of 12 angle positions are sampled.

6. The method of claim 1, wherein: In step 2, the positioning deviation of the machine tool rotary table is identified by using a laser interferometer system and a rotary shaft calibration device.

7. The method of claim 1, wherein: In step 4.1, when planning the in-machine measurement process parameters of the to-be-measured feature, the following two principles need to be followed: the measuring needle cannot interfere with the blade and the rotary table during the measurement process; and the rotary table is prevented from rotating violently.

8. The method of claim 1, wherein: In step 4.2, the rotation angles of the B-axis and the C-axis in the measurement are calculated based on the kinematic chain of the machine tool 、 , and then the two rotation angles are obtained by interpolation in the identified positioning deviation results of the rotary table 、 corresponding to the positioning deviation 、 , so as to obtain the actual transformation matrix of the machine tool coordinate system to the part coordinate system : Wherein 、 ； 、 。

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