CN113910239B - Industrial robot absolute positioning error compensation device and method - Google Patents
Industrial robot absolute positioning error compensation device and method Download PDFInfo
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- CN113910239B CN113910239B CN202111318288.3A CN202111318288A CN113910239B CN 113910239 B CN113910239 B CN 113910239B CN 202111318288 A CN202111318288 A CN 202111318288A CN 113910239 B CN113910239 B CN 113910239B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1656—Programme controls characterised by programming, planning systems for manipulators
- B25J9/1664—Programme controls characterised by programming, planning systems for manipulators characterised by motion, path, trajectory planning
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1694—Programme controls characterised by use of sensors other than normal servo-feedback from position, speed or acceleration sensors, perception control, multi-sensor controlled systems, sensor fusion
Abstract
The invention discloses an absolute positioning error compensation device of an industrial robot, which comprises a plurality of photoelectric scanning angle measurement base stations and targets; the 6D target is installed at the tail end of the robot, at least 6 photoelectric receivers which are different in orientation and are not in the same plane are installed on the outer surface of the target, the orientation of each receiver is in the normal vector direction of the plane where the receiver is located, and the mutual position relation among the spherical centers of the receivers is fixed and calibrated in advance; also disclosed is an absolute positioning error compensation method, comprising: the method comprises the steps of calibrating the relative position relation among a target coordinate system, a robot base coordinate system and a wMPS coordinate system, providing a space grid two-step method division strategy, establishing and updating a space error library in real time, solving the absolute positioning error value of a key node on the motion track of the robot by an interpolation algorithm, correcting the coordinate value in a control program, and completing the online compensation of the absolute positioning error of the robot on the premise of not influencing the running rhythm.
Description
Technical Field
The invention relates to absolute positioning error compensation of an industrial robot, in particular to an efficient absolute positioning error compensation device and method of the industrial robot based on a working space measurement positioning system.
Background
The wide application of the industrial robot accelerates the modern industrial automation process, greatly improves the production efficiency, frees people from complicated work, and simultaneously puts forward higher requirements on the machining precision of the robot. The precision evaluation of the robot mainly comprises two aspects: absolute positioning accuracy and repeated positioning accuracy. The absolute positioning accuracy refers to the deviation between an actual value and a nominal value when the robot reaches a certain position on the premise of off-line programming, and the repeated positioning accuracy refers to the deviation degree when the robot reaches the same position for multiple times. Generally speaking, the repetitive positioning accuracy of an industrial robot is in the sub-millimeter level and the absolute positioning accuracy is in the millimeter level. In the case of a robot on an industrial mass production line, the work can be completed only by sufficiently high repetitive positioning accuracy, but the absolute positioning accuracy is more important for a robot applied to the field of precision machining. The absolute positioning error of the robot is dynamically changed in the production operation process, and in order to improve the absolute positioning accuracy of the robot on the premise of not influencing the running rhythm, the error on-line compensation is required to be completed in the interval of two operation cycles.
The existing robot absolute positioning error compensation method generally comprises error compensation based on a kinematic parameter model and error compensation of a non-kinematic parameter model, wherein the error compensation based on the kinematic parameter model establishes a pose error model according to kinematic parameters of a robot, then a high-precision measuring device is used for measuring a terminal pose error, the measured error is substituted into the error model to identify an actual kinematic parameter value, and finally the error is compensated. And estimating and compensating the absolute positioning error of the robot by a curve fitting method, a neural network method or a spatial interpolation method based on the error compensation of the non-kinematic parameter model.
Patent CN112873199A discloses a robot absolute positioning accuracy calibration method based on kinematics and spatial interpolation, which achieves the purpose of improving the robot absolute positioning accuracy by combining geometric parameter identification and spatial interpolation algorithm. Patent CN102374847A discloses a dynamic measuring device and method for working space pose with six degrees of freedom, in the method, a six-degree-of-freedom sensor is mentioned, inside of the sensor is provided with a wMPS receiver for receiving optical signals sent by a transmitting station, the six-degree-of-freedom sensor calculates angle information of the rotating table of a transmitter according to the output of the receiver after receiving the optical signals, the sensor is a cuboid, each side surface and edge are divided into an upper row and a lower row, 8 wMPS receivers are installed in a staggered manner, the wMPS receivers on the six-degree-of-freedom sensor are distributed on two planes, in practical application, base station signals in the working space are easily blocked by other objects, and it cannot be ensured that signals of all base stations can be completely collected by the receivers. Patent CN112276999A discloses a method and a device for calibrating the rod length of an industrial robot based on a laser tracker, which respectively measures and fits the circumferential radius and the circle center position of each axis during single-axis rotation to calculate the actual kinematic geometric parameters and complete the geometric parameter error correction of the robot. Patent CN110385720A discloses a robot positioning error compensation method based on a deep neural network, which obtains a correction value of a coordinate of a target point by means of pose data acquisition, neural network training and positioning error prediction. Patent CN107421441A discloses an external measurement device assisted robot positioning error online compensation method, which directly measures the three-dimensional position information of an end effector by a laser tracker, and then compensates the positioning information. Patent CN106247932A discloses a robot online error compensation device and method based on a camera system, which jointly complete the measurement of the three-dimensional attitude of the tail end of a robot by combining a multi-camera combined camera measurement system and a two-dimensional inclinometer with an encoder of the industrial robot, and obtain a compensation value through data fusion and comparison to control the industrial robot to compensate errors. However, in the above methods, the off-line error compensation method based on the parametric model can only compensate the absolute positioning error caused by the kinematic factors, and has no compensation capability for the absolute positioning error introduced by the non-kinematic factors in the working process of the robot, the error on-line compensation method based on the non-parametric model is limited by the measurement equipment, and the pose information cannot be obtained easily due to shielding in a complicated industrial field, and if the interpolation compensation positioning error in a mode of establishing a spatial error base is selected in an operation cycle gap, a large amount of pose information needs to be acquired, the existing measurement equipment cannot be completed in a short time, and the operation process is complicated, the requirement on operators is high, the process is complicated, the automation degree is poor, and the compensation timeliness is insufficient.
Therefore, a device and a method for realizing online compensation aiming at the real-time compensation requirement of the absolute positioning error of the industrial robot are needed.
Disclosure of Invention
The invention aims to provide a method and a device for efficiently compensating an absolute positioning error of an industrial robot, which are simple and convenient to operate and high in universality and real-time performance.
The purpose of the invention is realized by the following technical scheme:
the online compensating device of absolute positioning error of industrial robot, including multiple photoelectric scanning angle measurement base stations and 6 degrees of freedom posture targets, abbreviated as 6D targets;
wherein, each base station is distributed around the robot, and the combined measuring space comprises the whole moving space of the robot;
the target is a 6D target arranged on a flange at the tail end of the robot, the outer contour of the target is a polyhedron and comprises at least six faces, at least 6 photoelectric receivers which face different directions and are not in the same plane are arranged on the outer surface of the target, the directions of the receivers are in the direction of a normal vector of the plane, and the mutual position relation among the spherical centers of the receivers is fixed and calibrated in advance;
and the common scanning area of the light planes of the two adjacent base stations is not less than 1/2 of the surface area of the target, and the light signals of each two adjacent base stations can be received by at least one receiver during the movement of the robot.
Preferably, the cross section of the target is a regular hexagon.
The industrial robot absolute positioning error online compensation method using the absolute positioning error compensation device comprises the following steps:
the method comprises the following steps: arranging a plurality of base stations at the periphery of the robot, wherein the combined measurement space of the base stations covers the whole motion space of the robot, mounting a 6D target on a flange at the tail end of the robot, selecting one base station as a master base station, and using the other base stations as slave base stations to finish the calibration of the pose relationship between the master base station and each slave base station;
step two: controlling the robot to do single-axis rotary motion around axes 1, 3 and 6 respectively in the working space of the robot, selecting a plurality of points in the motion process as measuring points, and calibrating the relative position relation among a target coordinate system, a robot base coordinate system and a wMPS coordinate system; wherein the measuring points are uniformly distributed in the working space, and the number of points of each axis is at least 8;
step three: uniformly and randomly selecting space points in a working space to measure absolute positioning error values of the space points, selecting a grid division strategy according to the Pearson coefficient value of the difference value between any two space points and the corresponding absolute positioning error vector to divide the working space into cubic grids with different side lengths, controlling the robot to move by using the coordinate values of grid nodes in a robot base coordinate system, and in the moving process of the robot, measuring the actual coordinate values of the nodes by using wMPS and converting the actual coordinate values into the robot base coordinate system to obtain the absolute positioning error values of the nodes so as to establish a space error library;
step four: and (3) selecting an important node in the motion track of the robot, predicting the absolute positioning error value of the important node by using an interpolation method, correcting the coordinate of the important node in a Cartesian coordinate space according to the space positioning error library obtained in the third step, and replacing a nominal coordinate value under a robot base coordinate system with the corrected coordinate value in a robot motion control program to drive the robot to move so as to realize the compensation of the absolute positioning error.
Further, the second step specifically comprises the following steps:
step 2-1: controlling the robot to do single-axis motion around the axes 1, 3 and 6 in a working space, recording the current position coordinates at intervals of 5-10 degrees in the motion process, wherein each axis has at least 8 measuring points;
step 2-2: fitting the motion tracks of the shafts 1, 3 and 6 according to the coordinates of the measuring points and the circumference fitting model to obtain the normal vector of the circular surface, the circumference radius and the coordinates of the circle center;
step 2-3: unitizing the normal vector of the circular surface to obtain a rotation matrix from a robot base coordinate system to a wMPS measurement coordinate system;
step 2-4: obtaining the position offset of the target relative to the central point of the end flange according to the obtained normal vector of the circular surface and the circumference radius;
step 2-5: and obtaining a translation vector in the conversion relation between the robot base coordinate system and the wMPS measurement coordinate system according to the coordinate value of the time-base coordinate system and the coordinate value of the wMPS coordinate system of the robot at the mechanical zero point.
Further, the third step specifically includes the following steps:
step 3-1: uniformly and randomly sampling in a working space to obtain absolute positioning error values at a plurality of positions, calculating a Pearson coefficient of the difference between the distance between any two points in the sampling points and the corresponding absolute positioning error value, and roughly dividing the working space into a plurality of cubic grid areas by taking a space distance value L with the Pearson coefficient equal to 0.7 as a length value of a diagonal line of a cubic grid;
step 3-2: taking the central point of the cubic grid region divided in the step 3-1 as a measurement starting point, respectively making linear motion along XYZ directions of a robot base coordinate system to a region boundary, and recording a current coordinate value every moving distance to obtain an absolute positioning error value, so as to obtain a series of nested cubic grids with gradually increased side lengths, wherein the central point is taken as the starting point; the moving distance is obtained by calculation according to the space distance value and the actual running beat of the robot;
step 3-3: 3-2, knowing the absolute positioning error value of 6 surface center points of each grid in the nested cubic grid, sequentially calculating the deviation between the interpolation result of the positioning error of the center points of each grid and the real measurement result of the positioning error of the center points according to the sequence of the side length from large to small until the deviation meets the set threshold condition, namely selecting the length value of the corresponding grid edge as the length value of the diagonal line of the fine grid division in the roughly divided cubic area obtained in the step 3-1, and dividing the working space according to the obtained length value of the grid edge to finish the grid secondary division of the working space;
step 3-4: controlling the robot to move by taking the coordinate value of the grid node under the base coordinate system as a nominal coordinate value, enabling the robot to traverse all the grid nodes, and stopping for a stopping time at each node to record the coordinate value of the node under a wMPS coordinate system, wherein the stopping time is calculated according to the wMPS single measurement time consumption and a proportionality coefficient;
step 3-5: according to formula PB＝R-1·(PT-T) converting the coordinate values of the nodes in the wMPS coordinate system to the robot-based coordinate systemObtaining the actual value of the coordinates;
wherein, PBIs the coordinate value of the robot base coordinate system, R is the rotation matrix from the robot base coordinate system to the wMPS measurement coordinate system, PTIs the coordinate measurement value of the wMPS coordinate system, and T is the translation vector of the relative relation between the robot base coordinate system and the wMPS measurement coordinate system;
step 3-6: and obtaining absolute positioning error values at all nodes by subtracting the obtained nominal value and the actual value.
Further, the fourth step specifically includes the following steps:
step 4-1: selecting important nodes influencing the processing precision in a motion control program of the robot, selecting absolute positioning error values at 8 grid nodes adjacent to the important nodes from an established spatial error library, and predicting the absolute positioning error values at the important nodes by using an inverse distance weighting method;
step 4-2: and adding the predicted absolute positioning error value at the important node on the basis of the obtained nominal value to obtain a modified coordinate value, and replacing the nominal coordinate value under the robot base coordinate system in a robot motion control program by using the modified coordinate value to drive the robot to move so as to realize the absolute positioning error compensation of the robot.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the absolute positioning error compensation method of the robot can quickly acquire absolute positioning error information of the robot at each point of a working space, and realizes coordinate measurement of the full position and the full position in the working space by arranging a plurality of photoelectric scanning angle measurement base stations at the periphery of the robot and installing a 6D target at the tail end, thereby quickly realizing the establishment and real-time update of a space error library and realizing the online compensation of the absolute positioning error on the premise of not influencing the running rhythm; the absolute positioning error compensation of the robot is realized by means of a working space measurement positioning system (wMPS), the error prediction of any point in a space is realized by gridding measurement of a compensation space in advance, different machining procedures can be calibrated and compensated, the reusability of the robot system is enhanced, the timeliness is good, the operation is simple, the machining precision of the robot can be obviously improved, and the popularization and the application of the robot in the field of precision machining are facilitated.
Drawings
FIG. 1 is a flow chart of an industrial robot absolute positioning error online compensation method according to the invention;
FIG. 2 is a schematic layout of a robot and the absolute positioning error compensation device according to an embodiment;
FIG. 3 is a flow chart of the calculation of step two of the method for compensating the absolute positioning error of the industrial robot in the invention;
FIG. 4 is a flow chart of the calculation of step three of the method for compensating the absolute positioning error of the industrial robot in the invention;
fig. 5 is a schematic diagram of the robot compensation space meshing in the three steps of the online compensation method for the absolute positioning error of the industrial robot according to the present invention.
Wherein the content of the first and second substances,
1: the robot 2: target 3: the base station 21: photoelectric receiver
Detailed Description
In order to make the objects, technical solutions, beneficial effects and significant progress of the embodiments of the present invention clearer, in the following, the absolute positioning error online compensation of the ABB-IRB6700 robot is taken as an example, and the technical solutions in the embodiments of the present invention are clearly and completely described with reference to the drawings provided in the examples of the present invention, and it is obvious that all the described embodiments are only some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
The invention realizes the on-line compensation of the absolute positioning error of the robot by means of a working space measurement positioning system (wMPS), establishes a space error library to predict the error of any point in the space by gridding measurement of a compensation space in advance, can calibrate and compensate different processing procedures, enhances the reusability of the robot system, has good timeliness and simple operation, can obviously improve the processing precision of the robot, and is beneficial to the popularization and application of the robot in the field of precision processing. The method has the advantages that the online compensation can be realized, because the method is very fast to realize, the updating of the spatial error library can be completed in 1-2 minutes, the real-time maintenance of the precision is guaranteed, and the running rhythm of the robot is not influenced.
As shown in fig. 2, the absolute positioning error compensation device of the industrial robot comprises a plurality of photoelectric scanning angle measuring base stations 3 and a 6D target 2; wherein a plurality of base stations 3 are distributed around the robot 1, and the combined measuring space thereof contains the whole motion space of the robot. Wherein, the motion robot comprises six-axis rotation, which is well known to those skilled in the art and is not described in detail herein.
The target 2 is a 6D target and is fixedly connected with a flange at the tail end of a shaft 6 of the robot 1, the cross section of the target is a regular hexagon, photoelectric receivers 21 are arranged on the corresponding side surfaces of each side of the regular hexagon, each receiver faces to the direction of a plane normal vector, the mutual position relation among the spherical centers of the receivers is fixed and is calibrated in advance, four photoelectric scanning angle measuring base stations 3 are arranged on the periphery of the robot, the common scanning area of the optical planes of two adjacent base stations is not less than 1/2 of the surface area of the target, the optical signals of every two adjacent base stations can be received by at least one receiver in the moving process of the robot, at least four receivers can receive the optical signals in the example, and the three-dimensional coordinate measurement can be realized only by not less than three receivers which can receive the optical signals of the base stations according to the measurement principle of the 6D target.
As shown in fig. 1, the method for compensating the absolute positioning error of the industrial robot on line by using the absolute positioning error compensating device comprises the following steps:
the method comprises the following steps: arranging four wMPS base stations 3 around the robot (base station measuring typical range 3-25m), mounting a target 2 on the robot end flange, mounting at least 6 photoelectric receivers facing different directions and not in the same plane on the target; establishing a space angle measurement model, selecting one base station as a master base station, and finishing the calibration of the pose relationship between the master base station and slave base stations by using the other base stations as slave base stations;
step two: fig. 3 is a flowchart of computing a coordinate transformation rotation matrix and a translation vector of a wMPS coordinate system and a robot base coordinate system, and a translation vector of a target coordinate system and a robot base coordinate system in step two of the online compensation method for absolute positioning errors of an industrial robot according to the present invention, and includes the following specific steps:
step 2-1: in the working space of the robot, a demonstrator is used for controlling the robot to respectively do single-axis motion around 1 axis, 3 axis and 6 axis, the robot pauses once every 5-10 degrees of motion to record the position coordinate measured by the current wMPS system as the coordinate of a measuring point, if the rotating angle in a certain direction is less, the included angle between two measurements can be properly adjusted to meet the requirement that the coordinate values of at least 8 measuring points are recorded in the rotating process of each rotating shaft;
step 2-2: fitting the motion tracks of three circumferences of the shafts 1, 3 and 6 according to the coordinates of the measuring points and the circumference fitting model, and calculating the normal vector of the plane where the circumference is located, the radius value of the circumference and the circle center coordinate n1,n3,n6,r1,r3,r6,o1,o3,o6；
Step 2-3: unitizing the normal vectors of the three circular surfaces according to [ n ]6 n3 n1]The rotation matrix R from the robot base coordinate system to the wMPS measurement coordinate system is obtained by the sequential arrangement of the following steps:
step 2-4: and obtaining the position offset of the target 2 relative to the central point of the end flange plate by the obtained normal vector of the circular surface and the circumference radius:
ΔY＝|r6·n3| (2)
ΔZ＝|r6·n1| (3)
Δ＝[ΔXΔYΔZ] (5)
wherein X0The coordinate system center point of the end flange at the mechanical zero point position is the X coordinate value in the robot base coordinate system. Since the target is made of a material with a small temperature coefficient, the position of each photoelectric receiver 21 of the target 2 is relatively fixed.
Step 2-5: and establishing a robot Tool coordinate system Tool1 according to the obtained position offset, wherein the attitude angle of the Tool1 is consistent with that of the tail end Tool coordinate system, and the subsequent compensation process is carried out on the basis of the Tool1 coordinate system. Coordinate value of time-base coordinate system of robot at mechanical zero point
And coordinate values of wMPS coordinate system
Substitution formula
And obtaining a translation vector T in the conversion relation between the robot base coordinate system and the wMPS measurement coordinate system.
Step three: the purpose of the first three steps in the third step is to divide the working space of the robot into cubic grids with different side lengths, as shown in fig. 4-5, the specific steps are as follows:
step 3-1: at Lx×Ly×LzThe method comprises the steps of uniformly sampling in a working space to obtain positioning error values at a plurality of positions, calculating a Pearson coefficient value between the distance between any two points in sampling points and the difference value of the positioning errors of the two points, and regarding the Pearson coefficient value to be more than or equal to 0.7 according to mathematical definition as obvious linear correlation between two variables, so that a space distance value L with the Pearson coefficient being equal to 0.7 is taken as a length value of a diagonal line of a cubic grid, and calculating the number of equally divided parts n along each direction of a robot base coordinate system XYZx，ny，nzDividing the working space into nx×ny×nzA cubic grid space, and it is considered that the positioning error value can be calculated by interpolation in the space:
wherein L is a spatial distance value with a Pearson coefficient equal to 0.7;
step 3-2: in order to further refine the mesh to improve the interpolation accuracy, as shown in fig. 5, the central point of the cubic mesh divided in step 3-1 is used as a measurement starting point, and linear motions are respectively performed to the region boundary along the XYZ direction of the robot base coordinate system, and each motion moving distance h records the current coordinate value to obtain a positioning error value, so as to obtain a series of nested cubic meshes with increasing side length, which use the central point as the starting point:
h＝k×a (8)
wherein, k is in a value range of [ 5%, 10% ] according to the actual running beat of the robot.
Step 3-3: according to the absolute positioning error value of the known 6 surface central points of each grid, sequentially calculating the interpolation predicted value E of the absolute positioning error of each grid to the central points according to the sequence of the side lengths from large to smallinAbsolute positioning error measurement true value E with central pointmnDeviation e ofi(i ═ 1,2, 3.., n, n +1) until the deviation meets a set threshold c1，c2Namely, selecting the corresponding grid edge length value as the finely divided grid diagonal length L in the cubic grid region obtained in the step 3-1, and further obtaining the region (L)ix×Liy×Liz) Number n of equal shares along each direction of robot base coordinate system XYZix，niy，niz(see formulas (6-7)) dividing the region into nix×niy×nizThe cubic grid space is divided, so that a grid is finely divided, and a cubic grid set with different side lengths as shown in fig. 5 is obtained;
en＝|Ein-Emn|≤c1 (9)
|en-en+1|≤c2 (10)
wherein E isinA central point absolute positioning error vector predicted value obtained by interpolation of an inverse distance weighting method, EmnThe true value of the central point absolute positioning error vector measured for wMPS;
step 3-4: calculating the nominal coordinate value P of each grid nodenUsing a nominal value writing program to enable the robot to traverse the grid nodes and stop at each node for a stopping time length t;
t＝c×T (11)
wherein T is the time consumed by single measurement of wMPS, c is a proportionality coefficient, and the proportionality coefficient is selected according to the actual test result;
step 3-5: according to formula PB＝R-1·(PT-T) converting the coordinate value of the node in the wMPS coordinate system into the coordinate actual value P obtained in the robot base coordinate systemr；
Wherein, PBIs the coordinate value of the robot base coordinate system, R is the rotation matrix from the robot base coordinate system to the wMPS measurement coordinate system, PTIs the coordinate measurement value of the wMPS coordinate system, and T is the translation vector of the relative relation between the robot base coordinate system and the wMPS measurement coordinate system;
step 3-6: the obtained nominal value and the actual value are differed to obtain an absolute positioning error value e which is P at the noden-PrAnd a spatial error library is established for storing the obtained absolute positioning error values.
Step four: the method comprises the following specific steps:
step 4-1: selecting important nodes influencing the processing precision as points to be compensated in a motion control program of the robot, selecting absolute positioning error values at 8 grid nodes adjacent to the important nodes from a space error library established in the third step, and predicting the absolute positioning error values at the important nodes by using an inverse distance weighting method:
wherein q isiFor mesh vertex PiWeight of influence on point P to be compensated, diFor mesh vertex PiDistance from P, E is the absolute positioning error vector interpolation of P, EiIs PiAbsolute positioning error vector measurements of;
step 4-2: and adding the predicted absolute positioning error value at the important node on the basis of the obtained nominal value to obtain a modified coordinate value, and replacing the nominal coordinate value under the robot base coordinate system in a robot motion control program by using the modified coordinate value to drive the robot to move so as to realize the absolute positioning error compensation of the robot.
The calibration method of the relative position relationship between the transmitting stations related in the technical scheme of the invention can refer to the following documents: "Yanglinhui, can continue to be precious, Zhang Guangjun, Yeshenhua" adopts the working space measuring and positioning system orientation method of standard ruler [ J ]. proceedings of Tianjin university, 2012,45(09): 814-;
the calibration method of the robot base coordinate system and the measuring coordinate system can refer to the following documents: "Zhang Bo, Wei Zheng Zhong, Zhang Guangdong Jun. method for quickly converting robot coordinate system and laser tracker coordinate system [ J ] Instrument and meters bulletin, 2010,31(09): 1986) 1990";
the calibration space cube grid division method can refer to the following documents: "Zhou, Kongo and Tianwei. Industrial robot precision compensation method theory and test based on spatial interpolation [ J ] Mechanical engineering report, 2013,49(03): 42-48.";
the track node interpolation calculation mathematical model can refer to the following documents: "Sun Jian Ping Nu, Jeff Xi, Tomby. robot precision compensation method of approximation weighted average interpolation study [ J ] Instrument and Meter report, 2019,40(11): 128-.
Although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made on the technical solutions described in the foregoing embodiments, or some or all of the technical features of the embodiments can be replaced with equivalents, and the corresponding technical solutions do not depart from the technical solutions of the embodiments.
Claims (4)
1. An industrial robot absolute positioning error online compensation method using an absolute positioning error compensation device, the absolute positioning error compensation device: the system comprises a plurality of photoelectric scanning angle measuring base stations and 6-degree-of-freedom attitude targets, namely 6D targets for short;
wherein, each base station is distributed around the robot, and the combined measuring space comprises the whole moving space of the robot;
the target is a 6D target arranged on a flange at the tail end of the robot, the outer contour of the target is a polyhedron and comprises at least six faces, at least 6 photoelectric receivers which are different in orientation and are not in the same plane are arranged on the outer surface of the target, the orientation of each receiver is in the direction of a normal vector of the plane, and the mutual position relation among the spherical centers of the receivers is fixed and calibrated in advance;
moreover, the common scanning area of the light planes of the two adjacent base stations is not less than 1/2 of the surface area of the target, and the light signals of each two adjacent base stations can be received by at least one receiver in the moving process of the robot;
the method comprises the following steps:
the method comprises the following steps: arranging a plurality of base stations at the periphery of the robot, wherein the combined measurement space of the base stations covers the whole motion space of the robot, mounting a 6D target on a flange at the tail end of the robot, selecting one base station as a master base station, and using the other base stations as slave base stations to finish the calibration of the pose relationship between the master base station and each slave base station;
step two: controlling the robot to do single-axis rotary motion around axes 1, 3 and 6 respectively in the working space of the robot, selecting a plurality of points in the motion process as measuring points, and calibrating the relative position relation among a target coordinate system, a robot base coordinate system and a wMPS coordinate system; wherein the measuring points are uniformly distributed in the working space, and the number of points of each axis is at least 8;
step three: uniformly and randomly selecting space points in a working space to measure absolute positioning error values of the space points, selecting a grid division strategy according to the Pearson coefficient value of the difference value between any two space points and the corresponding absolute positioning error vector to divide the working space into cubic grids with different side lengths, controlling the robot to move by using the coordinate values of grid nodes in a robot base coordinate system, and in the moving process of the robot, measuring the actual coordinate values of the nodes by using wMPS and converting the actual coordinate values into the robot base coordinate system to obtain the absolute positioning error values of the nodes so as to establish a space error library;
step four: and (3) selecting an important node in the motion track of the robot, predicting the absolute positioning error value of the important node by using an interpolation method, correcting the coordinate of the important node in a Cartesian coordinate space according to the space positioning error library obtained in the third step, and replacing a nominal coordinate value under a robot base coordinate system with the corrected coordinate value in a robot motion control program to drive the robot to move so as to realize the compensation of the absolute positioning error.
2. The industrial robot absolute positioning error online compensation method according to claim 1, wherein the second step specifically comprises the steps of:
step 2-1: controlling the robot to do single-axis motion around the axes 1, 3 and 6 in a working space, recording the current position coordinates at intervals of 5-10 degrees in the motion process, wherein each axis has at least 8 measuring points;
step 2-2: fitting the motion tracks of the shafts 1, 3 and 6 according to the coordinates of the measuring points and the circumference fitting model to obtain the normal vector of the circular surface, the circumference radius and the coordinates of the circle center;
step 2-3: unitizing the normal vector of the circular surface to obtain a rotation matrix from a robot base coordinate system to a wMPS measurement coordinate system;
step 2-4: obtaining the position offset of the target relative to the central point of the end flange according to the obtained normal vector of the circular surface and the circumference radius;
step 2-5: and obtaining a translation vector in the conversion relation between the robot base coordinate system and the wMPS measurement coordinate system according to the coordinate value of the time-base coordinate system and the coordinate value of the wMPS coordinate system of the robot at the mechanical zero point.
3. The industrial robot absolute positioning error online compensation method according to claim 1, wherein the third step specifically comprises the steps of:
step 3-1: uniformly and randomly sampling in a working space to obtain absolute positioning error values at a plurality of positions, calculating a Pearson coefficient of the difference between the distance between any two points in the sampling points and the corresponding absolute positioning error value, and roughly dividing the working space into a plurality of cubic grid areas by taking a space distance value L with the Pearson coefficient equal to 0.7 as a length value of a diagonal line of a cubic grid;
step 3-2: taking the central point of the cubic grid region divided in the step 3-1 as a measurement starting point, respectively making linear motion along XYZ directions of a robot base coordinate system to a region boundary, and recording a current coordinate value every moving distance to obtain an absolute positioning error value, so as to obtain a series of nested cubic grids with gradually increased side lengths, wherein the central point is taken as the starting point; the moving distance is obtained by calculation according to the space distance value and the actual running beat of the robot;
step 3-3: 3-2, sequentially calculating the deviation of each grid from the interpolation result of the positioning error of the central point and the real measurement result of the positioning error of the central point according to the sequence of the side length from large to small by knowing the absolute positioning error value of the central point of 6 surfaces of each grid in the nested cubic grid obtained in the step 3-2 until the deviation meets the set threshold condition, namely selecting the length value of the corresponding grid side as the length value of the diagonal line of the grid fine division in the roughly divided cubic area obtained in the step 3-1, and dividing a working space according to the obtained length value of the grid side fine division so as to finish the grid secondary division of the working space;
step 3-4: controlling the robot to move by taking the coordinate value of the grid node under the base coordinate system as a nominal coordinate value, enabling the robot to traverse all the grid nodes, and stopping for a stopping time at each node to record the coordinate value of the node under a wMPS coordinate system, wherein the stopping time is calculated according to the wMPS single measurement time consumption and a proportionality coefficient;
step 3-5: according to formula PB＝R-1·(PT-T) converting the coordinate value of the node under the wMPS coordinate system into a robot base coordinate system to obtain a coordinate actual value;
wherein, PBIs the coordinate value of the robot base coordinate system, R is the rotation matrix from the robot base coordinate system to the wMPS measurement coordinate system, PTIs the coordinate measurement value of the wMPS coordinate system, and T is the translation vector of the relative relation between the robot base coordinate system and the wMPS measurement coordinate system;
step 3-6: and obtaining absolute positioning error values at all nodes by subtracting the obtained nominal value and the actual value.
4. The industrial robot absolute positioning error online compensation method according to claim 1, wherein the fourth step specifically comprises the steps of:
step 4-1: selecting important nodes influencing the processing precision in a motion control program of the robot, selecting absolute positioning error values at 8 grid nodes adjacent to the important nodes from an established spatial error library, and predicting the absolute positioning error values at the important nodes by using an inverse distance weighting method;
step 4-2: and adding the predicted absolute positioning error value at the important node on the basis of the obtained nominal value to obtain a modified coordinate value, and replacing the nominal coordinate value under the robot base coordinate system in a robot motion control program by using the modified coordinate value to drive the robot to move so as to realize the absolute positioning error compensation of the robot.
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