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

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial robots, in particular to a circular trajectory error measurement and offline compensation system and method based on an angle-mounted ball bar instrument. BACKGROUND

[0002] With the wide application of industrial robots in the fields of intelligent manufacturing, flexible processing and high-precision assembly, the precision guarantee problem of industrial robots in complex trajectory execution, especially in circular path processing tasks, is increasingly prominent. Industrial robots have high flexibility in structure, and can perform multi-axis linkage, complex posture and large-range trajectory operation. However, due to the low rigidity of the body structure and the multiple redundant degrees of freedom, the path precision is not as good as that of traditional CNC machine tools. Especially in the case of circular trajectory interpolation motion (such as drilling, rotary fitting, nested cavity, etc.), path distortion, roundness error and trajectory jitter are very common.

[0003] At present, the mainstream solutions for improving the trajectory precision of industrial robots include industrial robot body calibration (such as DH parameter identification, stiffness model reconstruction), end effector posture detection (through laser tracker, optical system, etc.), path compensation mechanism (based on measurement feedback to correct the trajectory control program), etc. Among them, path error compensation is the most direct and effective means, which is suitable for processing tasks with high precision tolerance requirements and repeated process trajectories. However, most of these compensation methods rely on high-cost measurement platforms and are not easy to implement at low cost.

[0004] At present, the mainstream trajectory error measurement systems include laser tracker and optical photographic measurement system. Laser tracker: with sub-millimeter level spatial precision, suitable for tracking the tool center point (TCP) of industrial robots, but the device is expensive and the installation and debugging are complex. Optical photographic measurement system: through double camera three-dimensional positioning path point, with certain precision, but is greatly affected by environmental light interference and precision depends on calibration quality.

[0005] Compared with the above, ball bar is a standardized high-resolution circular trajectory error detection tool, which is widely used in machine tool geometric precision detection. Its advantages are simple measurement principle, rapid deployment, high sampling frequency and stable results. However, the traditional ball bar only supports standard diameter circle measurement in the plane (such as XY plane 50 / 100 / 150 / 250mm circle radius), and cannot directly adapt to other sizes between the standard diameters, which seriously limits its application in robot processing path compensation. The small size diameter adapter provided by the ball bar manufacturer has a measurement angle of + / -20° when installed at an angle, which cannot meet the measurement range of larger angles. In addition, the current robot path error compensation process still mainly relies on high-cost measurement calibration instruments, lacks a general path error processing algorithm and interface scheme, the data processing flow is complex to interface with the robot control system, and the engineering application threshold is high.

[0006] It can be seen that the mainstream trajectory error measurement system has the following shortcomings: 1. The ball bar instrument is only suitable for fixed radius standard path, and cannot cover the error measurement requirements of the robot on the non-standard circular trajectory (such as the ball bar instrument device for a specific 50mm radius cannot measure other sizes within 35-50mm); 2. The small circle adapter provided by the ball bar instrument manufacturer has a small measurement angle range (+ / -20°) under angular installation, and cannot meet the larger measurement range; 3. There is a lack of standardized processing procedures for converting measurement error data into robot control programs; 4. Key influencing factors such as installation error, sampling interval, and path segment error are not considered, resulting in large fluctuations in compensation strategy effect.

[0007] Therefore, there is an urgent need for a circular trajectory error measurement and offline compensation system and method based on angularly installed ball bar, which can effectively improve the trajectory machining precision of workpiece circular machining tasks on existing industrial robot platforms, and has good portability and low-cost deployment characteristics. SUMMARY

[0008] The purpose of the present application is to provide a circular trajectory error measurement and offline compensation system and method based on angularly installed ball bar to solve the problems existing in the prior art.

[0009] To achieve the above purpose, the present application provides the following scheme: a circular trajectory error measurement and offline compensation system based on angularly installed ball bar,

[0010] It comprises a ball bar, an improved small circle adapter, a ball connecting rod, a main shaft, a fixed ball-connection thread integrated part, a magnetic force connecting seat and a multi-size length calibration plate; the ball connecting rod is installed on the main shaft through a tool holder, the main shaft is provided with an industrial robot away from the ball connecting rod, the ball connecting rod is magnetically connected with the scanning ball end of the ball bar away from the tool holder, the ball bar is connected and fixed with the improved small circle adapter through threads, one end of the improved small circle adapter is connected with the ball bar, the other end of the improved small circle adapter is connected with the fixed ball-connection thread integrated part through threads, the fixed ball of the fixed ball-connection thread integrated part is connected with the magnetic force connecting seat through magnetic force, the magnetic force connecting seat is magnetically connected with a workbench away from the fixed ball-connection thread integrated part, a cylindrical workpiece is detachably connected on the workbench, and the tool holder processes the cylindrical workpiece through a tool.

[0011] Preferably, the industrial robot adopts the industrial robot with six degrees of freedom of the series / parallel mechanism.

[0012] Preferably, one end of the improved small round adapter is provided with a positioning threaded hole, which is threadedly connected with the ball bar instrument; the other end of the improved small round adapter is provided with a screw fastening hole, which is threadedly connected with the fixed ball-connection threaded integrated part.

[0013] Preferably, the fixed ball of the fixed ball-connection threaded integrated part is rotatably connected with the magnetic force connecting seat through magnetic force.

[0014] Preferably, the improved small round adapter is provided with an opening groove, which is arranged between the positioning threaded hole and the screw fastening hole; one end of the ball connecting rod towards the main shaft is connected with the main shaft through the tool holder; the other end of the ball connecting rod away from the main shaft penetrates through the opening groove and is connected with the scanning ball of the ball bar instrument through magnetic force.

[0015] Preferably, the improved small round adapter is made of aluminum material and is completed through integral molding or milling processing.

[0016] Preferably, the main shaft is connected with the industrial robot through a transition flange and a screw.

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

[0018] A method for measuring and offline compensating a circular track error of a ball bar instrument based on an angle installation, comprising the following steps:

[0019] S1. Connect the ball bar instrument, the existing small round adapter and the fixed ball-connection threaded integrated part, and calibrate the standard size through a fixed size calibration plate; then use the multi-size length calibration plate to measure three sizes and record the measurement values; and then remove the existing small round adapter and the fixed ball-connection threaded integrated part.

[0020] S2. Connect and install the ball bar instrument, the improved small round adapter and the fixed ball-connection threaded integrated part, and calibrate the standard size through a fixed size calibration plate; then use the multi-size length calibration plate to measure three sizes and record the measurement values.

[0021] S3. Input the measurement values of the two ball bar instruments after calibration into an 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 ball bar, the non-standard radius Tr value required for measurement of the ball bar, and the measurement plane of the ball bar, calculate the required tilt installation angle; fix the ball connecting rod on the main shaft through the tool holder, install the magnetic connecting seat on the workbench, and adjust the positions of the ball bar and the main shaft according to the set angle; in combination with the used industrial robot platform, generate a corresponding measurement program.

[0023] S5. According to the set position of the ball bar under the angle installation, place the ball bar installed with the improved small round adapter in the industrial robot, and perform data measurement and equivalent trajectory error calculation under a predetermined non-standard measurement radius.

[0024] S6. According to the trajectory error value measured by the ball bar, perform path compensation value interpolation calculation in combination with the original machining program.

[0025] S7. According to the control command requirements of the industrial robot used, write a program with circular trajectory error compensation for automatic generation and interface docking.

[0026] S8. Disassemble the magnetic connecting seat and the ball bar, install the cylindrical workpiece on the workbench, the axis of the cylindrical workpiece is collinear with the axis of the magnetic connecting seat, install the tool on the main shaft through the tool holder, and make the center position of the installed tool coincide with the center position of the scanning ball of the ball bar connected by the magnetic force, and perform milling processing according to the selected machining parameters.

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

[0028] The present application breaks through the limitation of traditional ball bar which is only applicable to fixed posture and standard circular radius, so that it can adapt to the error measurement scene of non-standard circular trajectory of the robot. The present application provides a low-cost, high-precision and easy-to-integrate general solution for industrial robot path precision detection and compensation, and has wide engineering application prospect.

[0029] The angle-installed ball bar measurement device and data processing method provided by the present application not only facilitates the integration of the ball bar into different specifications of industrial robots, but also effectively expands the measurement radius and posture capability of the ball bar, and can cover the non-standard circular (for the specific measurement diameter of the ball bar) trajectory path of common workpieces. When the present application is used for circular workpiece processing, not only the roundness error is effectively improved, but also the distortion of the compensated circular trajectory is effectively reduced. At the same time, the present application also has good portability and low-cost deployment characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained based on these drawings without creative labor.

[0031] Figure 1 The overall structure of the present application is shown in the schematic diagram.

[0032] Figure 2 The structure of the ball rod instrument, the improved small round adapter and the ball connecting rod of the present application is shown in the schematic diagram.

[0033] Figure 3 The structure of the improved small round adapter of the present application is shown in the schematic diagram.

[0034] Figure 4 The structure of the present application when machining a workpiece is shown in the schematic diagram.

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

[0036] Figure 6 The maximum angle range that can be measured when the improved small round adapter of the present application is installed at an angle.

[0037] Figure 7 The size calibration process of the ball rod instrument and the size calibration plate based on the existing small round adapter is shown in the schematic diagram.

[0038] Figure 8 The calibration of the ball rod instrument and the size calibration plate based on the improved small round adapter of the present application is shown in the schematic diagram.

[0039] Figure 9 The installation error β of the ball rod instrument based on the improved small round adapter is shown in the schematic diagram.

[0040] Figure 10 The structure of the multi-size length calibration plate containing three specific calibration sizes is shown in the schematic diagram.

[0041] Figure 11 The polar coordinate distribution diagram of the workpiece size variation after cylindrical workpiece outer circle milling without using the compensation technology.

[0042] Figure 12 The polar coordinate distribution diagram of the workpiece size variation after cylindrical workpiece outer circle milling using the compensation technology.

[0043] Figure 13 The comparison diagram of the workpiece roundness value after cylindrical workpiece outer circle milling using and not using the compensation technology.

[0044] Wherein, 1, ball bar; 2, improved small circle adapter; 3, ball connecting rod; 4, main shaft; 5, industrial robot; 6, fixed ball-connection thread integrated part; 7, magnetic force connecting seat; 8, workbench; 9, tool; 10, tool holder; 11, transition flange; 12, cylindrical workpiece; 13, multi-size length calibration plate; 14, existing small circle adapter; 2-1, positioning thread hole; 2-2, screw fastening hole. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

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

[0047] Reference Figures 1-10 , the present application provides a kind of based on angle installation ball bar's circle track error measurement and offline compensation system,

[0048] Including ball bar 1, improved small circle adapter 2, ball connecting rod 3, main shaft 4, fixed ball-connection thread integrated part 6, magnetic force connecting seat 7 and multi-size length calibration plate 13;Ball connecting rod 3 is installed on main shaft 4 by tool holder 10, main shaft 4 is provided with industrial robot 5 away from ball connecting rod 3 one end, the end of ball connecting rod 3 away from tool holder 10 is connected with the scanning ball end of ball bar 1 magnetic force, ball bar 1 is fixed by thread and improved small circle adapter 2 is connected, one end of improved small circle adapter 2 is connected with ball bar 1, the other end of improved small circle adapter 2 is connected with fixed ball-connection thread integrated part 6 by thread, the fixed ball of fixed ball-connection thread integrated part 6 is connected with magnetic force connecting seat 7 by magnetic force, the end of magnetic force connecting seat 7 away from fixed ball-connection thread integrated part 6 is connected with workbench 8 by magnetic force, cylindrical workpiece 12 can be detachably connected on workbench 8, tool holder 10 processes cylindrical workpiece 12 by tool 9.

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

[0050] The included angle α between the axis composed of scanning ball of ball bar 1 and fixed ball-connection thread integrated part 6 and the direction of gravity is adjusted by industrial robot 5 (refer to Figure 6), to realize specific angle setting and make the rotation center of the club instrument 1 at a specific installation angle consistent with the actual measurement radius.

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

[0052] The main shaft 4 is used to drive the tool 9 to move and perform a circular trajectory machining action; the target cylindrical workpiece 12 is installed on the workbench 8 and surrounded between the rotation point at the end of the main shaft 4 and the reference fixed point through the 50 mm measurement path formed by the club instrument 1 and the improved small circle adapter 2, and the club instrument reading recorded in the machining process represents the geometric deviation between the actual motion trajectory and the theoretical motion trajectory of the tool center point of the tool 9 connected to the main shaft 4, which is used for subsequent path error compensation modeling.

[0053] The angle-installed club instrument measuring device and data processing method provided by the application not only facilitates the integration of the club instrument 1 into different specifications of industrial robots 5, but also effectively expands the measurement radius and posture capability of the club instrument 1, can cover the non-standard circular (for the specific measurement diameter of the club instrument 1) trajectory path of common workpieces, and when the cylindrical workpiece 12 is machined using the application, not only the roundness error is effectively improved, but also the distortion of the compensated circular trajectory is effectively reduced. At the same time, the application also has good portability and low-cost deployment characteristics.

[0054] Further optimization scheme, the industrial robot 5 adopts an industrial robot 5 with six degrees of freedom of a series / parallel mechanism. The club instrument 1 can be passively matched in the circular trajectory movement of the main shaft 4 through the industrial robot 5.

[0055] Further optimization scheme, the improved small circle adapter 2 is provided with a positioning threaded hole 2-1 at one end, the positioning threaded hole 2-1 is in threaded connection with the club instrument 1, and the improved small circle adapter 2 is provided with a screw fastening hole 2-2 at the other end, the screw fastening hole 2-2 is in threaded connection with the fixed ball-connection threaded integral piece 6.

[0056] By adjusting the inclination angle of the improved small circle adapter 2, the club instrument 1 can be adjusted within a certain angle range on the installation surface to adapt to different measurement posture requirements.

[0057] Further optimization scheme, the fixed ball of the fixed ball-connection threaded integral piece 6 is rotatably connected with the magnetic force connecting seat 7 through magnetic force. The angle freedom degree can be effectively provided and the consistency between the rotation center and the measurement radius can be ensured.

[0058] The distance between the fixed ball-connection threaded integral piece 6 and the scanning ball of the club instrument 1 is 50 mm, and the measurement range is ±1 mm.

[0059] Further optimization scheme, the improved small circle adapter 2 is provided with an opening groove, the opening groove is arranged between the positioning threaded hole 2-1 and the screw fastening hole 2-2, one end of the ball connecting rod 3 towards the main shaft 4 is connected with the main shaft 4 through the tool holder 10, and the other end of the ball connecting rod 3 away from the main shaft 4 penetrates through the opening groove and is connected with the scanning ball of the ball bar 1 through magnetic force.

[0060] Referring to Figure 2 , Figure 3 , Figure 5 and Figure 6 , the ball connecting rod 3 is connected with the scanning ball of the ball bar 1 through magnetic force at the end away from the main shaft 4, and is stably fixed and conveniently disassembled through the three-point support structure, and has high repeat positioning accuracy.

[0061] The ball connecting rod 3 penetrates through the opening groove and is connected with the scanning ball of the ball bar 1 through magnetic force, and the spherical surface contact between the fixed ball-connecting threaded integrated piece 6 and the magnetic force connecting seat 7 forms a motion condition that can complete the inclination angle α setting; in the conventional standard diameter ball bar measurement, the α angle value is 0 degree, representing that the connecting line composed of the ball bar 1 and the fixed ball of the fixed ball-connecting threaded integrated piece 6 coincides with the gravity direction, and the distance between the two is the common measurement radius of the ball bar (such as Nr=50mm); in the actual angle adjustment process, the required measurement radius (such as Tr=35mm) is usually smaller than the conventional measurement radius, and the horizontal movement (such as 35.7mm) of the axis of the scanning ball of the ball bar 1 driven by the main shaft 4 is required, so that the axis formed by the scanning ball of the ball bar 1 and the fixed ball of the fixed ball-connecting threaded integrated piece 6 and the gravity direction form a specific included angle α (such as α is 44.43°, according to the formula Thus, the ball bar 1 has the installation setting of being capable of measuring non-standard circle diameter.

[0062] Further optimization scheme, the improved small circle adapter 2 is made of aluminum material and is completed through integral molding or milling processing. It has high positioning accuracy and high rigidity, and ensures the measurement accuracy and assembly consistency.

[0063] Further optimization scheme, the main shaft 4 is connected with the industrial robot 5 through the transition flange 11 and the screw. The main shaft 4 is installed on the industrial robot 5 through the transition flange 11 and the screw, so that the industrial robot 5 can effectively drive the main shaft 4 to move in a circular track, and the ball bar 1 can be passively matched in the circular track movement of the main shaft 4.

[0064] Further optimization scheme, the multi-size length calibration plate 13 includes three specific size calibration devices. In actual use, size measurement can be carried out in combination with three coordinates according to the assembly result.

[0065] A method for measuring and offline compensating the circular track error of the ball bar based on the angle installation, comprising the following steps:

[0066] S1. Connect the ball bar 1, the existing small circle adapter 14, and the fixed ball-connection thread integrated piece 6, and perform standard size calibration through the fixed size calibration plate; then use the multi-size length calibration plate 13 to perform three size measurements and record the measurement values; then remove the existing small circle adapter 14 and the fixed ball-connection thread integrated piece 6.

[0067] S2. After connecting and installing the ball bar 1, the improved small circle adapter 2, and the fixed ball-connection thread integrated piece 6, perform standard size calibration through the fixed size calibration plate; then use the multi-size length calibration plate 13 to perform three size measurements and record the measurement values.

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

[0069] The readings of the ball bar 1 based on the existing small circle adapter 14 are corrected through the installation error β model; due to the actual machining error of the improved small circle adapter 2, there will be an included angle deviation β after installation with the ball bar 1, which will cause the actual measured error ε m to be the axial projection of the true error ε t . Anti-projection correction is required, and the correction model is:

[0070] ε m = ε t ·cos(β)

[0071]

[0072] The implementation of this process requires the use of a multi-size length calibration plate 13, which is obtained by comparing measurement values through experiments and fitting calculation results. Specifically, use the calibration plate provided by Renishaw to calibrate the ball bar 1 installed with the improved small circle adapter 2 and the original small circle adapter; use the multi-size length calibration plate 13 to measure and record the readings of the ball bar 1 installed with the two adapters respectively; substitute the measurement results into the above formula for calculation; calculate the average value of multiple size measurement results to obtain the installation angle β.

[0073] S4. Determine the installation position of the ball bar 1 and the non-standard radius Tr value required by the ball bar 1 for measurement and the measurement plane of the ball bar 1, calculate the required inclined installation angle; fix the ball connecting rod 3 on the main shaft 4 through the tool holder 10, install the magnetic connection seat 7 on the workbench 8, and adjust the positions of the ball bar 1 and the main shaft 4 according to the set angle; combine the used industrial robot 5 platform to generate the corresponding measurement program.

[0074] The installation position (knife point position [x1, y1, z1], which is equivalent to the ball center position of the scanning ball of the ball bar 1) of the ball bar 1 is determined, and the non-standard radius Tr value required for measurement of the ball bar 1 and the measurement plane of the ball bar 1 are determined. Assuming that the measurement plane is the YZ plane and the non-standard radius is Tr, according to the theoretical value Ln = 50 m that can be completed by the existing structure of the ball bar 1, it can be determined that the ball center position of the fixed ball of the fixed ball-connection thread integrated piece 6 connected and fixed by the magnetic force connection seat 7 is [x1, y1, z1-Ln], and the formula The required included angle a is calculated; according to the measurement plane (such as the YZ plane) of the ball bar 1 and the horizontal position of the main shaft 4, the axis formed by the scanning ball of the ball bar 1 and the fixed ball of the fixed ball-connection thread integrated piece 6 and the direction of gravity form a certain included angle a, and the position of the knife point after movement is [x1-Ln*cos(a), y1, z1]; in this way, the measurement requirement of the non-standard measurement radius Tr is formed, and then a measurement program is generated according to the measurement requirement Tr value.

[0075] S5. According to the set position of the ball bar 1 under the angle installation, the ball bar 1 installed 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 non-standard measurement radius.

[0076] Data equivalent reconstruction under the measurement radius is performed; in the case of angle installation, the actual motion trajectory of the ball bar 1 configured with the improved small circle adapter 2 is not on an ideal two-dimensional circle, but on a three-dimensional conical surface path. In order to effectively compensate for the motion trajectory of different radius circles, it is necessary to convert it into a circular trajectory in the equivalent two-dimensional measurement plane (YZ).

[0077] Assuming that the theoretical length of the ball bar is L N , the actual measurement value is the installation inclination angle L R , and the actual measurement value corresponding to the installation included angle a in the equivalent two-dimensional measurement plane can be expressed as:

[0078] RE a = Sin a * (L R -L N )

[0079] S6. According to the trajectory error value measured by the ball bar 1, the path compensation value interpolation calculation is performed in combination with the original machining program.

[0080] The collected high sampling rate ball bar measurement result RE a is divided into N1 segments according to the control point number preset by the industrial robot machining programming, and the average value e j(N1≥j≥1), and the trajectory error is decomposed into a directional vector e in the actual machining plane according to the directional angle of each control point in the circular trajectory jy and e jz (e.g., YZ plane):

[0081] X j ′=X j

[0082] Y j ′=Y j +e jy

[0083] Z j ′=Z j +e jz

[0084] wherein X j , Y j , and Z j represent the theoretical coordinate values of the industrial robot when performing circular arc motion in the YZ plane, X j ′, Y j ′, and Z j ′ represent the actual coordinate values of the circular arc motion trajectory error of the industrial robot in the YZ plane combined with the control points.

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

[0086] The compensated path control points are compiled through the Matlab program and converted into program codes suitable for the machining platform of the industrial robot, including control point numbers, speed settings, circular arc instruction structures, etc. Then, the program codes are input into the industrial robot controller for actual machining.

[0087] S8. The magnetic connecting seat 7 and the ball bar 1 are removed, and the cylindrical workpiece 12 is installed on the workbench 8, the axis of the cylindrical workpiece 12 is collinear with the axis of the magnetic connecting seat 7, the tool 9 is installed on the spindle 4 through the tool holder 10, and the center position of the installed tool 9 is coincided with the center position of the scanning ball of the ball bar 1, and milling is performed according to the selected machining parameters.

[0088] The present application has the following effects:

[0089] The angle measurement range based on the existing ball bar for angle installation is expanded, and the existing specific ball bar length (50mm / 100mm, etc.) can cover a larger non-standard ball bar measurement length (such as 35-50mm, for 50mm diameter).

[0090] The improved small circle adapter 2 installation angle error correction theory model is introduced to improve the measurement accuracy of the ball bar 1 based on the improved small circle adapter 2.

[0091] A general compensation path data processing framework is formed, which can be adapted to different brand industrial robot machining platforms.

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

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

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

[0095] System composition and structure configuration:

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

[0097] Adapter structure: self-made improved small circle adapter 2, aluminum material, 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 trajectory error compensation.

[0099] Cylindrical workpiece 12 material: 6061-T6 aluminum alloy cylinder, diameter 50mm, height 40mm.

[0100] Tool: diameter 12.6mm, hard alloy material, three cutting edges, right-handed, tool length 76.2mm.

[0101] Data processing environment: ball bar measurement data is used for error modeling and compensation calculation on this platform. The error compensation program of the circular trajectory path is automatically completed by the self-compiled script, and the TP format instruction is generated, and finally the path verification and visualization simulation are performed through the FANUC industrial robot simulation platform RoboGuide V10.

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

[0103] Take the cylindrical machining with a machining radius of 49.4 mm as an example, the data processing flow is analyzed according to the above data processing flow and the following results are obtained:

[0104] 1. On the standard size calibration plate and the multi-size length calibration plate 13, the measurement results of the ball bar 1 based on the existing small circle adapter and the ball bar 1 of the improved small circle adapter 2 are calibrated respectively, and the installation error angle β of the improved small circle adapter 2 caused by manufacturing error is calculated according to the data, which is 3°, and the angle value is used to process the subsequent circular trajectory error measurement value.

[0105] 2. According to the required machining radius of the cylindrical workpiece 49.4 mm, the non-standard measurement radius Tr of the ball bar 1 is determined as 49.4 mm, the device with the improved small circle adapter 2 is installed in the inclined state, and the installation angle is 8.4°; the working plane of the ball bar 1 is YZ plane, the non-standard radius to be measured is 49.4 mm, the feed speed of the ball bar 1 is 60 mm / min, counterclockwise rotation, and the circular trajectory path measurement is executed and the data is recorded.

[0106] 3. The collected circular trajectory error value is processed by equivalent conversion, the trajectory error value is segmented according to the preset control point number (360) in the path of the industrial robot 5, the average trajectory error value of each segment is calculated, and the error is decomposed into Y and Z direction components according to the theoretical direction angle of each control point in the circular trajectory, and the X axis coordinate is fixed and unchanged; finally, the trajectory error compensation value is interpolated to 360 theoretical control points and the TP program is output.

[0107] 4. In actual milling, the same machining parameters are used, and the workpieces are machined respectively with and without trajectory error compensation program; after the workpieces are machined, the roundness and actual radius value of the workpieces are measured by using a three-coordinate measuring instrument, the quality of the machined surface is evaluated by using a roughness meter, and the change of Ra is analyzed.

[0108] 5. The compensated workpiece contour roundness error is reduced from 44 μm to 14 μm, the roundness improvement degree is 68%, the surface quality is stable, and no significant change is found (see Figures 11-13 ).

[0109] The present application aims at the problem that the path error is difficult to be accurately measured by using the existing ball bar 1 device when the industrial robot 5 executes non-standard circular trajectory motion, the improved small circle adapter 2 component with structure adjustment ability is introduced, the installation angle correction model and the path trajectory error compensation algorithm based on control points are combined, good portability and low-cost deployment characteristics are achieved, the machining path program of the industrial robot 5 can be generated, and high-precision cylindrical workpiece circular arc trajectory machining is realized.

[0110] In the description of the present application, it needs to be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0111] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for measuring and compensating for circular trajectory errors based on an angle-mounted ball bar, characterized in that: The circular trajectory error measurement and offline compensation system comprises a ball bar (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 connecting seat (7) and a multi-size length calibration plate (13); the method of the circular trajectory error measurement and offline compensation system comprises the following steps: S1. Connect the ball bar (1), the existing small circle adapter (14) and the fixed ball-connecting thread integrated part (6), and perform standard size calibration through the fixed size calibration plate; then use the multi-size length calibration plate (13) to perform three size measurements and record the measurement values; then remove the existing small circle adapter (14) and the fixed ball-connecting thread integrated part (6); S2. After connecting and installing the ball bar (1), the improved small circle adapter (2) and the fixed ball-connecting thread integrated part (6), perform standard size calibration through the fixed size calibration plate; then use the multi-size length calibration plate (13) to perform three size measurements and record the measurement values; S3. Input the measurement values of the two calibrated ball bars (1) into the installation error β correction model, and correct the readings of the ball bar (1) based on the existing small circle adapter (14) through the installation error β model; Due to the actual machining error of the improved small circle adapter (2), there will be an included angle deviation β after the improved small circle adapter (2) and the ball bar (1) are installed, which will cause the actual measured error to be the axial projection of the true error, and the back projection correction needs to be performed through the installation error β correction model; Calculate the average value of multiple size measurement results to calculate the installation angle β and complete the installation error calculation and compensation; S4. Determine the installation position of the ball bar (1), the non-standard radius Tr value required to be measured by the ball bar (1) and the measurement plane of the ball bar (1), calculate the required inclined installation angle, fix the ball connecting rod (3) on the main shaft (4) through the tool holder (10), install the magnetic connecting seat (7) on the workbench (8), adjust the positions of the ball bar (1) and the main shaft (4) according to the set angle, and generate a corresponding measurement program in combination with the used industrial robot (5) platform; S5. According to the set position of the ball bar (1) under the angle installation, place the ball bar (1) with the improved small circle adapter (2) installed in the industrial robot (5) to perform data measurement and equivalent trajectory error calculation under a predetermined irregular measurement radius; S6. According to the trajectory error value measured by the ball bar (1), perform path compensation value interpolation calculation combined with the original machining program; S7. According to the requirements of the controller command of the industrial robot (5), write a program with circular trajectory error compensation for automatic generation and interface docking. S8. The magnetic connection seat (7), the ball bar (1) are disassembled, and the cylindrical workpiece (12) is installed on the workbench (8), the cylindrical workpiece (12) is collinear with the axis of the magnetic force connection seat (7), the cutter (9) is installed on the main shaft (4) through the tool holder (10), and the center position of the installed cutter (9) is coincided with the center position of the scanning ball of the ball bar (1) connected with the magnetic force, and the processing is carried out according to the selected processing parameters.

2. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 1, wherein: The ball connecting rod (3) is installed on the main shaft (4) through the tool holder (10), the main shaft (4) is provided with an industrial robot (5) away from the ball connecting rod (3), the end of the ball connecting rod (3) away from the tool holder (10) is magnetically connected with the scanning ball end of the ball bar (1), the ball bar (1) is connected and fixed with the improved small round adapter (2) through threads, one end of the improved small round adapter (2) is connected with the ball bar (1), the other end of the improved small round adapter (2) is connected with the fixed ball-connection threaded integrated piece (6) through threads, the fixed ball of the fixed ball-connection threaded integrated piece (6) is connected with the magnetic force connection seat (7) through magnetic force, the end of the magnetic force connection seat (7) away from the fixed ball-connection threaded integrated piece (6) is magnetically connected with the workbench (8), the cylindrical workpiece (12) is detachably connected on the workbench (8), the tool holder (10) processes the cylindrical workpiece (12) through the cutter (9).

3. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 2, characterized in that: The industrial robot (5) adopts the industrial robot (5) with six degrees of freedom of series / parallel mechanism.

4. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar 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), the positioning threaded hole (2-1) is threadedly connected with the ball bar (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 with the fixed ball-connection threaded integrated piece (6).

5. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 4, characterized in that: The fixed ball of the fixed ball-connection threaded integrated piece (6) is rotatably connected with the magnetic force connection seat (7) through magnetic force.

6. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 4, wherein: The improved small round adapter (2) is provided with an opening groove, the opening groove is arranged between the positioning threaded hole (2-1) and the screw fastening hole (2-2), one end of the ball connecting rod (3) facing the main shaft (4) is connected with the main shaft (4) through the tool holder (10), the other end of the ball connecting rod (3) away from the main shaft (4) penetrates through the opening groove and is connected with the scanning ball of the ball bar (1) through magnetic force.

7. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 1, wherein: The improved small round adapter (2) is made of aluminum material and is completed by integral molding or milling.

8. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 1, wherein: The main shaft (4) is connected with the industrial robot (5) through a transition flange (11) and a screw.

9. The method of a circular track error measurement and off-line compensation system based on angle mounted ball bar according to claim 1, wherein: The multi-size length calibration plate (13) comprises three calibration devices of specific sizes.

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