Circular trajectory error measurement and off-line compensation system and method based on angle installation ball bar

Abstract

The invention relates to the technical field of industrial robots, in particular to a circular trajectory error measurement and off-line compensation system and method based on angle installation of a ball bar, a ball connecting rod is installed on a main shaft through a tool holder, and an industrial robot is arranged at the end, away from the ball connecting rod, of the main shaft; the end, away from the tool holder, of the ball connecting rod is in magnetic connection with the scanning ball end of the ball bar, the ball bar is fixedly connected with the improved small circle adapter through threads, one end of the improved small circle adapter is connected with the ball bar, and the other end of the improved small circle adapter is connected with the fixing ball-connecting thread integrated piece through threads. A fixed ball of the fixed ball-connecting thread integrated piece is connected with the magnetic connecting base through magnetic force, and the end, away from the fixed ball-connecting thread integrated piece, of the magnetic connecting base is magnetically connected with a workbench. The invention provides a universal solution which is low in cost, high in precision and easy to integrate for industrial robot path precision detection and compensation, and has a wide engineering application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial robots, and in particular to a circular trajectory error measurement and off-line compensation system and method based on an angle-mounted ballbar. Background Art

[0002] With the widespread application of industrial robots in intelligent manufacturing, flexible machining, and high-precision assembly, the challenge of ensuring precision in complex trajectory execution, particularly circular path machining tasks, has become increasingly prominent. While industrial robots are structurally highly flexible and capable of multi-axis linkage, complex postures, and wide-range trajectory operations, their low structural rigidity and numerous redundant degrees of freedom result in path accuracy inferior to that of traditional CNC machine tools. This is particularly true in applications involving circular interpolation motion (such as drilling, rotational fit, and nested cavities), where path distortion, roundness error, and trajectory jitter are common.

[0003] Currently, mainstream solutions for improving the trajectory accuracy of industrial robots include calibration of the robot body (such as DH parameter identification and stiffness model reconstruction), end-effector posture detection (using laser trackers, optical systems, etc.), and path compensation mechanisms (correcting the trajectory control program based on measurement feedback). Path error compensation is the most direct and effective method, suitable for machining tasks with repetitive process paths and high precision tolerances. However, most of these compensation methods rely on high-cost measurement platforms, making them difficult to implement cost-effectively.

[0004] Currently, mainstream trajectory error measurement systems include: laser trackers and optical photogrammetry systems; laser trackers: have sub-millimeter spatial accuracy and are suitable for tracking the tool center position (TCP) of industrial robots, but the equipment is expensive and the installation and debugging are complicated; optical photogrammetry systems: use dual cameras to locate path points in three dimensions and have a certain degree of accuracy, but are greatly affected by ambient light interference and the accuracy depends on the calibration quality.

[0005] In contrast, the ballbar is a standardized, high-resolution circular trajectory error detection tool widely used for machine tool geometric accuracy testing. Its advantages lie in its simple measurement principle, rapid deployment, high sampling frequency, and stable results. However, traditional ballbars only support the measurement of standard diameter circles within a plane (such as 50 / 100 / 150 / 250mm circle radius in the XY plane), and cannot directly adapt to other sizes between the standard diameters, severely limiting their application in robot machining path compensation. The small-size diameter adapters provided by ballbar manufacturers only have a measurement angle of + / -20° when installed at an angle, which cannot meet the requirements of a larger measurement range. In addition, the current robot path error compensation process is still dominated by high-cost measurement and calibration instruments, lacking a universal path error processing algorithm and interface solutions. The data processing process is complex to interface with the robot control system, and the threshold for engineering application is high.

[0006] It can be seen that mainstream trajectory error measurement systems have the following shortcomings: 1. The ballbar is only suitable for standard paths with a fixed radius and cannot cover the error measurement needs of the robot on non-standard circular paths (for example, a ballbar device with a specific 50mm radius cannot measure other dimensions within 35-50mm). 2. The small circle adapter provided by the ballbar manufacturer has a small measurement angle range (+ / -20°) when installed at an angle and cannot meet the requirements of a larger measurement range. 3. There is a lack of standardized processing procedures for converting measured error data into robot control programs. 4. Insufficient consideration of key influencing factors such as installation error, sampling spacing, and path segment error leads to large fluctuations in the effectiveness of the compensation strategy.

[0007] Therefore, there is an urgent need for a circular trajectory error measurement and offline compensation system and method based on an angle-mounted ballbar, which can effectively improve the trajectory processing accuracy of circular machining tasks of workpieces on existing industrial robot platforms by having good portability and low-cost deployment characteristics. Summary of the Invention

[0008] The object of the present invention is to provide a circular trajectory error measurement and offline compensation system and method based on an angle-mounted ballbar, so as to solve the problems existing in the above-mentioned prior art.

[0009] To achieve the above object, the present invention provides the following solution: a circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar,

[0010] The invention comprises a ballbar, an improved small circle adapter, a ball connecting rod, a main shaft, a fixed ball-connecting threaded integrated part, a magnetic connection seat and a multi-size length calibration plate; the ball connecting rod is mounted on the main shaft via a tool holder, an industrial robot is provided at one end of the main shaft away from the ball connecting rod, the end of the ball connecting rod away from the tool holder is magnetically connected to the scanning ball end of the ballbar, the ballbar is connected and fixed to the improved small circle adapter via a thread, one end of the improved small circle adapter is connected to the ballbar, the other end of the improved small circle adapter is connected to the fixed ball-connecting threaded integrated part via a thread, the fixed ball of the fixed ball-connecting threaded integrated part is connected to the magnetic connection seat via magnetic force, the end of the magnetic connection seat away from the fixed ball-connecting threaded integrated part is magnetically connected to a workbench, a cylindrical workpiece is detachably connected to the workbench, and the tool holder processes the cylindrical workpiece via a tool.

[0011] Preferably, the industrial robot is a serial / parallel mechanism with six degrees of freedom.

[0012] Preferably, a positioning threaded hole is provided at one end of the improved small circle adapter, and the positioning threaded hole is threadedly connected to the ballbar; a screw fastening hole is provided at the other end of the improved small circle adapter, and the screw fastening hole is threadedly connected to the fixed ball-connecting threaded integrated part.

[0013] Preferably, the fixing ball of the fixing ball-connecting thread integrated part is rotatably connected to the magnetic connection seat through magnetic force.

[0014] Preferably, an opening slot is provided on the improved small circle adapter, and the opening slot is provided between the positioning threaded hole and the screw fastening hole. The end of the ball connecting rod facing the main shaft is connected to the main shaft through the tool clamp, and the end of the ball connecting rod away from the main shaft passes through the opening slot and is magnetically connected to the scanning ball of the ballbar.

[0015] Preferably, the improved small round adapter is made of aluminum and is completed by one-piece molding or milling.

[0016] Preferably, the main shaft is connected to the industrial robot via a transition flange and screws.

[0017] Preferably, the multi-size length calibration plate includes three calibration devices of specific sizes.

[0018] A method for circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar comprises the following steps:

[0019] S1. Connect the ballbar, the existing small circle adapter, and the fixed ball-connecting threaded integrated part, and perform standard size calibration using a fixed size calibration plate; then use the multi-size length calibration plate to measure three sizes and record the measured values; then remove the existing small circle adapter and the fixed ball-connecting threaded integrated part.

[0020] S2. After the ballbar, the improved small circle adapter, and the fixed ball-connecting threaded integrated part are connected and installed, standard size calibration is performed using a fixed size calibration plate; then, the multi-size length calibration plate is used to measure three sizes and record the measured values.

[0021] S3. Input the measurement values ​​of the two calibrated ballbars into the installation error β correction model, calculate the installation angle β, and complete the installation error calculation and compensation.

[0022] S4. Determine the installation position of the ballbar, the non-standard radius Tr value to be measured by the ballbar, and the measurement plane of the ballbar, and calculate the required tilt installation angle; secure the ball connecting rod to the spindle via the tool holder, mount the magnetic connection base on the workbench, and adjust the positions of the ballbar and the spindle according to the set angle; and generate a corresponding measurement program in combination with the industrial robot platform used.

[0023] S5. Based on the set position of the ballbar under angle installation, the ballbar equipped with the improved small circle adapter is placed in the industrial robot to perform data measurement and equivalent trajectory error calculation under a predetermined unconventional measurement radius.

[0024] S6. Perform path compensation value interpolation calculation based on the trajectory error value measured by the ballbar and the original machining program.

[0025] S7. According to the controller command requirements of the industrial robot, a program with circular trajectory error compensation is written to automatically generate and interface with the program.

[0026] S8. Remove the magnetic connection base and the ballbar, and install the cylindrical workpiece on the workbench, with the axis of the cylindrical workpiece and the axis of the magnetic connection base being collinear. Install the tool on the spindle through the tool holder, and make the center position of the installed tool coincide with the center position of the scanning ball of the ballbar magnetically connected to the ball connection rod, and perform milling according to the selected processing parameters.

[0027] The present invention discloses the following technical effects:

[0028] This invention overcomes the limitations of traditional ballbars, which are limited to fixed postures and standard circular diameters, and is now adaptable to robot error measurement scenarios involving non-standard circular trajectories. It provides a low-cost, high-precision, and easily integrated universal solution for industrial robot path accuracy detection and compensation, promising broad engineering applications.

[0029] The angle-mounted ballbar measurement device and data processing method proposed in the present invention not only facilitate the integration of the ballbar into industrial robots of different specifications, but also effectively expand the ballbar's measurement radius and attitude capabilities, covering the non-standard circular trajectory paths (with respect to the specific measurement diameter of the ballbar) of common workpieces. When the present invention is used to process circular workpieces, it not only effectively improves the roundness error but also effectively reduces the distortion of the circular trajectory after compensation. At the same time, the present invention also has good portability and low-cost deployment characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0032] Figure 2 Schematic diagram of the ballbar, improved small circle adapter and ball connecting rod structure of the present invention;

[0033] Figure 3 This is a schematic structural diagram of the improved small round adapter of the present invention;

[0034] Figure 4 This is a schematic structural diagram of the present invention when processing a workpiece;

[0035] Figure 5 The maximum angle range that can be installed when the existing small circle adapter is installed at an angle;

[0036] Figure 6 The maximum angular range that can be measured when the improved small circle adapter of the present invention is installed at an angle;

[0037] Figure 7 Schematic diagram of the dimension calibration process of a ballbar and dimension calibration plate based on an existing small circle adapter;

[0038] Figure 8 A schematic diagram of calibration of a ballbar and a size calibration plate based on an improved small circle adapter according to the present invention;

[0039] Figure 9 Schematic diagram of the installation error β of the ballbar based on the improved small circle adapter;

[0040] Figure 10 A schematic diagram of a multi-size length calibration plate structure including three specific calibration sizes;

[0041] Figure 11 Polar coordinate distribution diagram of workpiece size change after cylindrical workpiece external milling without using compensation technology;

[0042] Figure 12 Polar coordinate distribution diagram of workpiece size change after external milling of cylindrical workpiece using compensation technology;

[0043] Figure 13 This is a comparison chart of the roundness values ​​of a cylindrical workpiece after outer circle milling with and without the use of the compensation technology;

[0044] Among them, 1. Ballbar; 2. Improved small circle adapter; 3. Ball connecting rod; 4. Spindle; 5. Industrial robot; 6. Fixed ball-connecting threaded integrated part; 7. Magnetic connection seat; 8. Workbench; 9. Cutting tool; 10. Tool holder; 11. Transition flange; 12. Cylindrical workpiece; 13. Multi-size length calibration plate; 14. Existing small circle adapter; 2-1. Positioning threaded hole; 2-2. Screw fastening hole. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Reference Figures 1-10 The present invention provides a circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar.

[0048] The invention comprises a ballbar 1, an improved small circle adapter 2, a ball connecting rod 3, a spindle 4, a fixed ball-connecting threaded integrated part 6, a magnetic connecting seat 7 and a multi-size length calibration plate 13; the ball connecting rod 3 is mounted on the spindle 4 via a tool holder 10, an industrial robot 5 is provided at the end of the spindle 4 away from the ball connecting rod 3, the end of the ball connecting rod 3 away from the tool holder 10 is magnetically connected to the scanning ball end of the ballbar 1, the ballbar 1 is connected and fixed to the improved small circle adapter 2 via a thread, one end of the improved small circle adapter 2 is connected to the ballbar 1, the other end of the improved small circle adapter 2 is connected to the fixed ball-connecting threaded integrated part 6 via a thread, the fixed ball of the fixed ball-connecting threaded integrated part 6 is connected to the magnetic connecting seat 7 via magnetic force, the end of the magnetic connecting seat 7 away from the fixed ball-connecting threaded integrated part 6 is magnetically connected to a workbench 8, a cylindrical workpiece 12 is detachably connected to the workbench 8, and the tool holder 10 processes the cylindrical workpiece 12 via a tool 9.

[0049] The distance between the axis of the magnetic connection seat 7 and the axis of the ball connection rod 3 is controlled by programming of the controller of the industrial robot 5, and the distance is equal to the radius of the measured circle.

[0050] The industrial robot 5 adjusts the angle α between the axis formed by the scanning ball of the ballbar 1 and the fixed ball-connecting threaded integral part 6 and the direction of gravity (refer to Figure 6) to achieve a specific angle setting and keep the rotation center of the ballbar 1 at a specific installation angle consistent with the actual measurement radius.

[0051] The ballbar 1 is a common ballbar 1 product with an existing measurement radius of 100 mm.

[0052] The spindle 4 is used to drive the tool 9 and perform circular machining. The target cylindrical workpiece 12 is mounted on the worktable 8. The 50mm measurement path formed by the ballbar 1 and the improved small circle adapter 2 surrounds the rotation point at the end of the spindle 4 and the reference fixed point. The ballbar readings recorded during the machining process represent the geometric deviation between the actual motion trajectory of the tool center point of the tool 9 connected to the spindle 4 and the theoretical motion trajectory, which is used for subsequent path error compensation modeling.

[0053] The angle-mounted ballbar measuring device and data processing method proposed in the present invention not only facilitate the integration of the ballbar 1 into industrial robots 5 of different specifications, but also effectively expand the radius and attitude measurement capabilities of the ballbar 1, and can cover the trajectory paths of non-standard circles (for the specific measurement diameter of the ballbar 1) of common workpieces. When the present invention is used to process cylindrical workpieces 12, not only the roundness error is effectively improved, but also the distortion of the circular trajectory after compensation is effectively reduced. At the same time, the present invention also has good portability and low-cost deployment characteristics.

[0054] As a further optimization solution, the industrial robot 5 is a serial / parallel mechanism with six degrees of freedom. The industrial robot 5 enables the ballbar 1 to passively cooperate with the circular trajectory movement of the spindle 4.

[0055] To further optimize the solution, a positioning threaded hole 2-1 is provided at one end of the improved small circle adapter 2, and the positioning threaded hole 2-1 is threadedly connected to the ballbar 1, and a screw fastening hole 2-2 is provided at the other end of the improved small circle adapter 2, and the screw fastening hole 2-2 is threadedly connected to the fixed ball-connecting threaded integrated part 6.

[0056] By adjusting the tilt angle of the improved small circle adapter 2, the ballbar 1 can be adjusted within a certain angle range formed on the mounting surface to meet different measurement posture requirements.

[0057] In a further optimized solution, the fixed ball of the fixed ball-connecting threaded integrated part 6 is rotatably connected to the magnetic connection seat 7 by magnetic force. This can effectively provide angular freedom and ensure that the rotation center and the measurement radius remain consistent.

[0058] The distance between the fixed ball-connecting threaded integral part 6 and the scanning ball of the ballbar 1 is 50 mm, and its measuring range is ±1 mm.

[0059] To further optimize the solution, an opening slot is provided on the improved small round adapter 2, and the opening slot is provided between the positioning threaded hole 2-1 and the screw fastening hole 2-2. The end of the ball connecting rod 3 facing the main shaft 4 is connected to the main shaft 4 through the tool holder 10, and the end of the ball connecting rod 3 away from the main shaft 4 passes through the opening slot and is magnetically connected to the scanning ball of the ballbar 1.

[0060] Reference Figure 2 、 Figure 3 、 Figure 5 and Figure 6 The ball connecting rod 3 and the end away from the main shaft 4 are magnetically connected to the precision scanning ball on the ballbar 1, and a three-point support structure is adopted to achieve stable fixation and convenient disassembly, with high repeatability accuracy.

[0061] The ball connecting rod 3 extends through the opening slot to form a magnetic connection with the scanning ball of the ballbar 1. At the same time, the spherical contact between the fixed ball-connecting threaded integrated component 6 and the magnetic connection base 7 creates a motion condition that allows the inclination angle α to be set. During conventional standard diameter ballbar measurement, the angle α is 0 degrees, indicating that the line connecting the ballbar 1 and the fixed ball of the fixed ball-connecting threaded integrated component 6 coincides with the direction of gravity, and the distance between the two is the common measurement radius of the ballbar (e.g., Nr = 50 mm). During actual angle adjustment, the required measurement radius (e.g., Tr = 35 mm) is usually smaller than the common measurement radius. Therefore, the spindle 4 is required to drive the horizontal movement of the axis of the scanning ball of the ballbar 1 (e.g., 35.7 mm) so that the axis formed by the scanning ball of the ballbar 1 and the fixed ball of the fixed ball-connecting threaded integrated component 6 forms a specific angle α with the direction of gravity (e.g., α is 44.43°, according to the formula The ballbar 1 is now equipped with an installation configuration capable of measuring non-standard circle diameters.

[0062] To further optimize the solution, the improved small circle adapter 2 is made of aluminum and is completed through one-piece molding or milling. It has high positioning accuracy and high rigidity, ensuring measurement accuracy and assembly consistency.

[0063] In a further optimization, the spindle 4 is connected to the industrial robot 5 via a transition flange 11 and screws. By attaching the spindle 4 to the industrial robot 5 via the transition flange 11 and screws, the industrial robot 5 can effectively drive the spindle 4 in circular motion, allowing the ballbar 1 to passively cooperate with the circular motion of the spindle 4.

[0064] Further optimizing the solution, the multi-size length calibration plate 13 includes three calibration devices of specific sizes. In actual use, the size measurement can be performed based on the assembly results combined with the three coordinates.

[0065] A method for circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar comprises the following steps:

[0066] S1. Connect the ballbar 1, the existing small circle adapter 14, and the fixed ball-connecting threaded integrated part 6, and perform standard size calibration using a fixed size calibration plate; then use the multi-size length calibration plate 13 to measure three dimensions and record the measured values; then remove the existing small circle adapter 14 and the fixed ball-connecting threaded integrated part 6.

[0067] S2. After the ballbar 1, the improved small circle adapter 2, and the fixed ball-connecting threaded integral part 6 are connected and installed, standard size calibration is performed using a fixed size calibration plate; then three sizes are measured using a multi-size length calibration plate 13 and the measured values ​​are recorded.

[0068] S3. Input the measurement values ​​of the two calibrated ballbars 1 into the installation error β correction model to calculate the installation angle β (refer to Figure 9 ) to complete the installation error calculation and compensation.

[0069] The reading of the ballbar 1 based on the existing small circle adapter 14 is corrected by the installation error β model; due to the actual processing error of the improved small circle adapter 2, there will be an angle deviation β between it and the ballbar 1 after installation, resulting in the actual measured error ε m is the true error ε t Axial projection. Back-projection correction is required, and the corrected model is:

[0070] ε m =ε t cos(β)

[0071]

[0072] This process requires the use of a multi-size length calibration plate 13, obtained through experimental comparison of measured values ​​and fitting of calculated results. Specifically, the Renishaw calibration plate is used to calibrate the ballbar 1 with both the improved small circle adapter 2 and the original small circle adapter. The multi-size length calibration plate 13 is then used to measure the calibration distances of the ballbar 1 with both adapters and record the readings. The measurement results are then substituted into the above formula for calculation. The average of these multiple dimensional measurements is then taken to calculate the installation angle β.

[0073] S4. Determine the installation position of the ballbar 1, the non-standard radius Tr value to be measured by the ballbar 1, and the measurement plane of the ballbar 1, and calculate the required tilt installation angle. Secure the ball connecting rod 3 to the spindle 4 via the tool holder 10, mount the magnetic connector 7 on the workbench 8, and adjust the position of the ballbar 1 and spindle 4 according to the set angle. Generate a corresponding measurement program based on the industrial robot 5 platform used.

[0074] Determine the installation position of the ballbar 1 (the tool position [x1, y1, z1], which is equivalent to the center of the ballbar's scanning ball), and determine the non-standard radius Tr and the measurement plane of the ballbar. If the measurement plane is the YZ plane, the non-standard radius is Tr, and the theoretical value Ln = 50m allowed by the existing structure of the ballbar 1, the center of the fixed ball of the magnetic connection base 7 connecting the fixed ball to the threaded connection unit 6 can be determined as [x1, y1, z1-Ln]. Combined with the formula Calculate the required angle α. Based on the measurement plane (e.g., the YZ plane) where the ballbar 1 is located, move the horizontal position of the spindle 4 so that the axis formed by the scanning ball of the ballbar 1 and the fixed ball of the fixed ball-connecting threaded integral part 6 forms a specific angle α with the direction of gravity. The position of the tool position after movement is [x1-Ln·cos(α), y1, z1]. This creates a measurement requirement for a non-standard measurement radius Tr, and a measurement program is then generated based on the measurement requirement Tr value.

[0075] S5. Based on the set position of the ballbar 1 under angle installation, the ballbar 1 equipped with the improved small circle adapter 2 is placed in the industrial robot 5 to perform data measurement and equivalent trajectory error calculation under a predetermined unconventional measurement radius.

[0076] Equivalent data reconstruction is performed at the measurement radius. When mounted at an angle, the actual motion trajectory of the ballbar 1 equipped with the improved small circle adapter 2 does not lie on a perfect two-dimensional circle, but rather on a three-dimensional conical path. To effectively compensate for circular motions of varying radii, these need to be converted to circular trajectories within the equivalent two-dimensional measurement plane (YZ).

[0077] Assume the theoretical length of the ballbar is L N The actual measured value is the installation angle L R , when the installation angle is α, the actual measurement value corresponding to the equivalent two-dimensional measurement plane can be expressed as:

[0078] RE a =Sinα*(L R -L N )

[0079] S6. Perform path compensation value interpolation calculation based on the trajectory error value measured by the ballbar 1 and the original machining program.

[0080] The acquired high sampling rate ballbar measurement results RE a The control points are divided into N1 segments according to the preset number of control points in the industrial robot processing programming, and the average value of the trajectory error of each segment is calculated as e j(N1≥j≥1), and decompose the trajectory error into the direction vector e in the actual processing plane according to the direction angle of each control point in the circular trajectory jy and e jz (Take the YZ plane as an example):

[0081] X j ′=X j

[0082] Y j ′=Y j +e jy

[0083] Z j ′=Z j +e jz

[0084] Among them, X j ,Y j and Z j They represent the theoretical coordinate values ​​of the industrial robot when performing circular motion in the YZ plane, X j ′,Y j ′ and Z j ′ represents the actual coordinate value of the arc motion trajectory error of the industrial robot combined with the control point in the YZ plane.

[0085] S7. According to the controller command requirements of the industrial robot 5, a program with circular trajectory error compensation is automatically generated and connected to the interface.

[0086] The compensated path control points are compiled by Matlab program and converted into program codes suitable for the industrial robot processing platform, including control point numbers, speed settings, arc instruction structures, etc.; they are then input into the industrial robot controller for actual processing.

[0087] S8. Remove the magnetic connection base 7 and the ballbar 1, and install the cylindrical workpiece 12 on the workbench 8, with the axis of the cylindrical workpiece 12 and the axis of the magnetic connection base 7 being collinear. Install the tool 9 on the spindle 4 through the tool holder 10, and make the center position of the installed tool 9 coincide with the center position of the scanning ball of the ballbar 1 magnetically connected to the ball connection rod 3, and perform milling according to the selected processing parameters.

[0088] The present invention has the following effects:

[0089] Extends the angular measurement range of existing ballbar-based angle mounts, and covers larger, non-standard ballbar lengths (e.g. 35-50mm for a 50mm diameter) alongside existing specific ballbar lengths (50mm / 100mm etc).

[0090] A theoretical model for correcting the installation angle error of the improved small circle adapter 2 is introduced to improve the measurement accuracy of the ballbar 1 based on the improved small circle adapter 2.

[0091] A universal compensation path data processing framework is formed, which can be adapted to industrial robot processing platforms based on different brands.

[0092] The compensation accuracy is significant, which can effectively improve the roundness error improvement rate (experimental results show that the improvement rate can reach 60%) and reduce circular trajectory distortion.

[0093] The surface processing quality remains stable, and after applying the compensation method, there is no significant change in the surface roughness Ra value, which verifies the safety and applicability of the strategy.

[0094] Specific application cases, taking the FANUC F200iB industrial robot machining platform as an example:

[0095] System composition and structural configuration:

[0096] Ballbar: Model: Renishaw QC-20W, sampling rate 1000 Hz, resolution ±0.1 μm, measurement range + / - 1 mm, equipped with a standard size calibration plate and small circle adapter.

[0097] Adapter structure: Homemade improved small round adapter 2, made of aluminum, adjustable range -30° to +45°.

[0098] Industrial robot-based machining platform: FANUC F200iB industrial robot system, FANUC R-30iB MatePlus robot controller, capable of performing circular path error compensation.

[0099] The cylindrical workpiece 12 is made of 6061-T6 aluminum alloy, with a diameter of 50 mm and a height of 40 mm.

[0100] Tool: 12.6mm diameter, carbide material, three cutting edges, right-hand rotation, tool length 76.2mm.

[0101] Data processing environment: Ballbar measurement data is used on this platform for error modeling and compensation calculations. The circular path error compensation process is automated using a custom script, generating TP-formatted instructions. Path verification and visual simulation are then performed using the FANUC industrial robot simulation platform, RoboGuide V10.

[0102] Processing parameters: spindle speed is 10000RPM, axial cutting depth is 8mm, radial cutting depth is 0.1mm, and feed rate is 60mm / min.

[0103] Taking the machining of a cylinder with a radius of 49.4 mm as an example, the above data processing flow is used for analysis and processing, and the following results are obtained:

[0104] 1. Calibrate the ballbar 1 using the existing small circle adapter and the improved small circle adapter 2 on a standard-size calibration plate and a multi-size length calibration plate 13. Based on this data, calculate the installation error angle β = 3° of the improved small circle adapter 2 due to manufacturing error. This angle is used to process subsequent circular trajectory error measurements.

[0105] 2. Based on the required cylindrical workpiece radius of 49.4mm, the non-standard measurement radius Tr of the ballbar 1 is determined to be 49.4mm. The ballbar 1, equipped with the improved small circle adapter 2, is tilted and mounted at an angle of 8.4°. The working plane of the ballbar 1 is the YZ plane, and the non-standard measurement radius to be measured is 49.4mm. The ballbar 1 is rotated counterclockwise at a feed rate of 60mm / min to perform circular path measurements and record the data.

[0106] 3. Perform equivalent conversion processing on the collected circular trajectory error values, segment the trajectory error values ​​according to the preset number of control points (360) in the path of the industrial robot 5, calculate the average trajectory error value of each segment, and decompose the error into directional components in the Y and Z directions according to the theoretical direction angle of each control point in the circular trajectory, while the X-axis coordinate remains fixed; finally, interpolate the trajectory error compensation value to 360 theoretical control points and output the TP program.

[0107] 4. In actual milling, the same machining parameters are used, and the workpiece is machined with and without the trajectory error compensation program respectively. After the workpiece is machined, the roundness and actual radius of the workpiece are measured using a three-coordinate measuring machine, and the quality of the machined surface is evaluated using a roughness tester to analyze the changes in Ra.

[0108] 5. After compensation, the roundness error of the workpiece contour is reduced from 44μm to 14μm, and the roundness is improved by 68%. The surface quality is stable and no significant changes are found (refer to Figure 11-13 ).

[0109] The present invention addresses the problem that when an industrial robot 5 performs non-standard circular trajectory motion, path errors are difficult to accurately measure using the existing ballbar 1 device. The present invention introduces a component of an improved small circle adapter 2 with structural adjustment capabilities, combines an installation angle correction model with a control point-based path trajectory error compensation algorithm, and has good portability and low-cost deployment characteristics. It can be used to generate a machining path program for the industrial robot 5, and achieve high-precision circular arc trajectory machining of cylindrical workpieces.

[0110] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0111] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar, characterized by: It comprises a ballbar (1), an improved small circle adapter (2), a ball connecting rod (3), a main shaft (4), a fixed ball-connecting thread integrated part (6), a magnetic connection seat (7) and a multi-size length calibration plate (13); The ball connecting rod (3) is mounted on the spindle (4) via a tool holder (10); an industrial robot (5) is provided at one end of the spindle (4) away from the ball connecting rod (3); one end of the ball connecting rod (3) away from the tool holder (10) is magnetically connected to the scanning ball end of the ball bar (1); the ball bar (1) is connected and fixed to the improved small circle adapter (2) via a thread; one end of the improved small circle adapter (2) is connected to the ball bar (1); and the improved small circle adapter (2) is connected to the ball bar (1). The other end of the distributor (2) is connected to the fixed ball-connecting threaded integral part (6) through a thread, and the fixed ball of the fixed ball-connecting threaded integral part (6) is connected to the magnetic connection seat (7) through magnetism. The end of the magnetic connection seat (7) away from the fixed ball-connecting threaded integral part (6) is magnetically connected to a workbench (8), and a cylindrical workpiece (12) is detachably connected to the workbench (8). The tool holder (10) processes the cylindrical workpiece (12) through a tool (9).

2. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 1, characterized in that: The industrial robot (5) adopts a serial / parallel mechanism with six degrees of freedom.

3. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 1, characterized in that: One end of the improved small round adapter (2) is provided with a positioning threaded hole (2-1), and the positioning threaded hole (2-1) is threadedly connected to the ballbar (1); the other end of the improved small round adapter (2) is provided with a screw fastening hole (2-2), and the screw fastening hole (2-2) is threadedly connected to the fixed ball-connecting threaded integrated part (6).

4. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 3, characterized in that: The fixing ball of the fixing ball-connecting threaded integral part (6) is rotationally connected to the magnetic connection seat (7) through magnetic force.

5. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 3, characterized in that: The improved small circle adapter (2) is provided with an opening slot, wherein the opening slot is provided between the positioning threaded hole (2-1) and the screw fastening hole (2-2); the end of the ball connecting rod (3) facing the main shaft (4) is connected to the main shaft (4) through the tool holder (10); the end of the ball connecting rod (3) away from the main shaft (4) passes through the opening slot and is connected to the scanning ball of the ballbar (1) through magnetic force.

6. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 1, characterized in that: The improved small round adapter (2) is made of aluminum and is completed by integral molding or milling.

7. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 1, characterized in that: The main shaft (4) is connected to the industrial robot (5) via a transition flange (11) and screws.

8. The circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to claim 1, characterized in that: The multi-size length calibration plate (13) includes three calibration devices of specific sizes.

9. A method for a circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar, the method being based on the circular trajectory error measurement and offline compensation system based on an angle-mounted ballbar according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Connect the ballbar (1), the existing small circle adapter (14), and the fixed ball-connecting threaded integrated part (6), and perform standard size calibration using a fixed size calibration plate; then use the multi-size length calibration plate (13) to perform three-dimensional measurements and record the measured values; then remove the existing small circle adapter (14) and the fixed ball-connecting threaded integrated part (6); S2. After the ballbar (1), the improved small circle adapter (2), and the fixed ball-connecting threaded integral part (6) are connected and installed, standard size calibration is performed using a fixed size calibration plate; then, three size measurements are performed using the multi-size length calibration plate (13) and the measured values ​​are recorded; S3. The measurement values ​​of the two ballbars (1) that have been calibrated are input into the installation error β correction model to calculate the installation angle β, and the installation error calculation and compensation are completed; S4. Determine the installation position of the ballbar (1), the non-standard radius Tr value required to be measured by the ballbar (1), and the measuring plane of the ballbar (1), and calculate the required tilt installation angle; fix the ball connecting rod (3) on the spindle (4) through the tool holder (10), install the magnetic connection seat (7) on the workbench (8), and adjust the position of the ballbar (1) and the spindle (4) according to the set angle; generate a corresponding measurement program in combination with the industrial robot (5) platform used; S5. According to the set position of the ballbar (1) under the angle installation, the ballbar (1) equipped with the improved small circle adapter (2) is placed in the industrial robot (5), and data measurement and equivalent trajectory error calculation are performed under the predetermined unconventional measurement radius; S6. performing interpolation calculation of the path compensation value based on the trajectory error value measured by the ballbar (1) in combination with the original machining program; S7. According to the controller command requirements of the industrial robot (5), a program with circular trajectory error compensation is automatically generated and interfaced; S8. Remove the magnetic connection seat (7) and the ball bar (1), and install the cylindrical workpiece (12) on the workbench (8), with the axis of the cylindrical workpiece (12) and the axis of the magnetic connection seat (7) being collinear, and install the tool (9) on the spindle (4) through the tool holder (10), and make the center position of the installed tool (9) coincide with the center position of the scanning ball of the ball bar (1) magnetically connected to the ball connection rod (3), and perform processing according to the selected processing parameters.

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