A method for calibrating the terminal position and posture of an industrial robot

Abstract

The present invention discloses a method for calibrating the terminal position and posture of an industrial robot, including: establishing an industrial robot terminal position and posture calibration system based on laser six-degree-of-freedom measurement; calibrating the transformation relationship between the industrial robot base coordinate system and the laser tracker coordinate system, and the transformation relationship between the industrial robot flange terminal coordinate system and the target coordinate system; comparing the nominal value of the industrial robot terminal position and posture with the measured value to obtain the terminal position and posture error of the industrial robot; establishing a linear equation group of the industrial robot terminal position and posture error and its kinematic parameter deviation; using the LM algorithm to solve the linear equation group to achieve preliminary identification of the kinematic parameters of the industrial robot; using the harmony search algorithm to further optimize the kinematic parameters to achieve secondary identification of the kinematic parameters of the industrial robot; and correcting the control parameters of the industrial robot. The present invention can greatly improve the position accuracy and attitude accuracy of the terminal of the industrial robot by applying the laser six-degree-of-freedom measurement technology.

Description

Technical Field

[0001] The invention belongs to the field of industrial robot calibration and laser application, and in particular relates to a method for calibrating the terminal position and posture of an industrial robot. Background Art

[0002] Industrial robots refer to multi-manipulators or multi-degree-of-freedom robots for the industrial field, which can replace humans in harsh environments to perform simple and repetitive tasks. According to the functional classification, industrial robots mainly include welding robots, palletizing robots, handling robots, packaging robots, spraying robots, cutting robots, etc. Compared with traditional multi-axis CNC equipment, industrial robots have the advantages of large operating space, high flexibility and high efficiency. With the continuous improvement of production and manufacturing process requirements, the precision requirements for industrial robots are also getting higher and higher. The accuracy of industrial robots is affected by errors such as processing, assembly, and connecting rod deformation, especially the absolute positioning accuracy, which is only 10% of the repeatability accuracy, or even lower. The low absolute positioning accuracy makes it difficult for industrial robots to complete tasks such as high-precision manufacturing, assembly and measurement, limiting the transformation and upgrading of industrial robots to high automation and high intelligence. In long-term use, the repeatability of industrial robots will change with the accuracy of the joint gear system and the resolution of the encoder, and the accuracy of industrial robots will change with geometric factors such as connecting rod parameters and definition deviation of the connecting rod working coordinate system, as well as non-geometric factors such as temperature and connecting rod deformation, which will cause the position of the end effector of the industrial robot to shift and affect the quality of related products. Therefore, there is an urgent need for a calibration method that can fully compensate for the end-point pose accuracy of industrial robots. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calibrating the position and posture of an industrial robot terminal, which can greatly improve the position accuracy and posture accuracy of the industrial robot terminal by applying laser six-degree-of-freedom measurement technology.

[0004] One aspect of the present invention provides an industrial robot end position calibration method, comprising:

[0005] Step S1: Install the six-degree-of-freedom target on the flange end of the industrial robot so that the flange end coordinate system O f -x f y f z f and the target coordinate system O t -x t y t z t In parallel, the laser tracker is mounted outside the industrial robot and faces the DOF target;

[0006] Step S2: calibrate the industrial robot base coordinate system O b -x b yb z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship And the industrial robot flange end coordinate system O f -x f y f z f With the target coordinate system O t -x t y t z t The transformation relationship

[0007] Step S3: Set the industrial robot end relative to the base coordinate system O b -x b y b z b The position and posture of the industrial robot are used as the nominal value to control the industrial robot to move to the above position and posture. The laser tracker and the six-degree-of-freedom target are used to obtain the position and posture of the industrial robot end relative to the laser tracker coordinate system O l -x l y l z l The pose measurement results are based on the industrial robot base coordinate system O b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship Transform the above pose measurement results to the industrial robot base coordinate system O b -x b y b z b Under the condition of the robot, the measured value is obtained, and the nominal value of the posture is compared with the measured value to obtain the end posture error of the industrial robot;

[0008] Step S4, using the DH model to establish the relationship between the terminal posture of the industrial robot and its kinematic parameters, further establishing a nonlinear relationship between the terminal posture error of the industrial robot and the deviation of its kinematic parameters, and linearizing the above nonlinear relationship into a linear equation system by ignoring high-order terms;

[0009] Step S5, according to the end position error of the industrial robot obtained in step S3, the LM algorithm is used to solve the linear equations in step S4 to achieve preliminary identification of the kinematic parameters of the industrial robot;

[0010] Step S6, taking the kinematic parameter identification result of the LM algorithm in step S5 as the initial value, taking the terminal posture error as the optimization target, and using the harmony search algorithm to further optimize the kinematic parameters to achieve secondary identification of the kinematic parameters of the industrial robot;

[0011] Step S7: correct the control parameters of the industrial robot according to the secondary identification result of the kinematic parameters in step S6 to improve the terminal position accuracy of the industrial robot.

[0012] Preferably, in step S2, the industrial robot base coordinate system O is calibrated as follows: b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship

[0013] The industrial robot is adjusted to a zero position state, the first joint is rotated independently, the three-dimensional position coordinates of multiple points are measured, and the above measurement points are fitted into a circle, and then the normal vector of the circle is used as the x-axis direction of the base coordinate system of the industrial robot;

[0014] Rotate the second joint alone and repeat the above measurement and fitting process to obtain the y-axis direction of the industrial robot base coordinate system;

[0015] Obtain the z-axis direction of the industrial robot base coordinate system through cross product;

[0016] Take the intersection of the z-axis and the horizontal plane as the origin of the industrial robot base coordinate system and obtain the industrial robot base coordinate system O b -x b y b z b In the laser tracking coordinate system O l -x l y l z l The position and posture of the following image are obtained, so as to obtain the transformation relationship between the two images.

[0017] Preferably, in step S2, the industrial robot flange end coordinate system O is calibrated as follows: f -x f y f z f With the target coordinate system O t -x t y t z t The transformation relationship

[0018] Control the six-degree-of-freedom target at the end of the industrial robot flange to move a point in its workspace, and use this point as a fixed apex point to record the posture of the end of the industrial robot flange at this time

[0019] Change the posture of the industrial robot, align the tip again, and record the posture of the flange end of the industrial robot at this time

[0020] By solving the equation Get the transformation relationship

[0021] Preferably, in step S3, the end position error of the industrial robot is obtained as follows:

[0022] In the motion space of the industrial robot, multiple sets of industrial robot ends are set relative to the base coordinate system O b -x b y b z b The pose P i , which is taken as the nominal value, where i = 1, 2, ..., N, where N is the number of groups at the end of the industrial robot;

[0023] Control the industrial robot to move to the above posture P i , the above pose P is obtained by using a laser tracker and a six-degree-of-freedom target i Relative to the laser tracker coordinate system O l -x l y l z l The pose measurement results are based on the transformation matrix Transform the above results to the industrial robot base coordinate system O b -x b y b z b Next, get the measured value;

[0024] The pose P i The average value of the difference between the nominal value and the measured value is taken as the end position error of the industrial robot.

[0025] Preferably, in step S4, the linear equation system is:

[0026] ΔP=JΔρ,

[0027] Among them, ΔP represents the end pose error of the industrial robot, Δρ represents the kinematic parameter deviation of the industrial robot, and J represents the Jacobian matrix.

[0028] Preferably, in step S5, the LM algorithm is used to iteratively solve the above linear equations, and the kinematic parameter deviation Δρ of the industrial robot in the kth iteration process isk for:

[0029] Δρ k = -[J(ρ k ) T J(ρ k )+μ k I] -1 J(ρ k ) T ΔP(ρ k )

[0030] Among them, J(ρ k ) is the Jacobian matrix of the k-th iteration process, μ k is the damping coefficient,

[0031] According to k+1 =ρ k +Δρ k Update the kinematic parameters of industrial robots.

[0032] According to the industrial robot terminal position and posture calibration method of the above aspects of the present invention, by applying the laser six-degree-of-freedom measurement technology, the position accuracy and posture accuracy of the industrial robot terminal can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0034] Figure 1 is a schematic diagram of an industrial robot terminal position and posture calibration system according to an embodiment of the present invention;

[0035] Figure 2 It is a flow chart of an industrial robot terminal position and posture calibration method according to an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of kinematic parameters of an industrial robot defined based on the DH model according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The embodiment of the present invention provides an industrial robot terminal posture calibration method. As an application environment of the industrial robot terminal posture calibration method of the embodiment of the present invention, Figure 1 The illustrated industrial robot terminal position calibration system includes a laser tracker 101, a six-degree-of-freedom target 102, an industrial robot 103, an industrial robot control cabinet 104, and a client 105. The above-mentioned parts are connected via an industrial bus to achieve data communication and synchronization.

[0039] The industrial robot 103 is a six-axis robot, and the six-degree-of-freedom target 102 is installed at the end of the industrial robot. The laser tracker 101 and the six-degree-of-freedom target 102 can cooperate to achieve the six-degree-of-freedom measurement of the end position of the industrial robot. Specifically, the six-degree-of-freedom target 102 has a built-in dual-axis inclinometer, a corner cube prism with a hole, a monocular camera and an embedded control board, and can achieve the measurement of the three-dimensional posture of the target with the incident laser; the laser tracker 101 emits laser to the corner cube prism of the six-degree-of-freedom target 102, and after reflection from the prism, the three-dimensional position of the target can be measured. The client 105 can display the end position measurement information of the industrial robot, and can identify the kinematic parameters of the industrial robot based on the end position error, and compensate the identification results to the industrial robot control cabinet 104.

[0040] The method for calibrating the end position of an industrial robot according to an embodiment of the present invention is as follows: Figure 2 The process shown includes steps S1 to S7.

[0041] Step S1: Establish Figure 1 The end position calibration system of the industrial robot shown in the figure, wherein the six-degree-of-freedom target 102 is installed on the flange end of the industrial robot, and the flange end coordinate system O f -x f y f z f and the target coordinate system O t -x t y t z t Parallel (ie, the two coordinate systems have only a translation relationship), the laser tracker 101 is installed a few meters away from the industrial robot and faces the six-degree-of-freedom target 102, and there are no obstacles between the laser tracker 101 and the six-degree-of-freedom target 102.

[0042] Preferably, during the installation of the laser tracker 101, the supporting tripod is continuously adjusted so that the laser tracker coordinate system O l -x l y l z l z l The axis is perpendicular to the horizontal plane, so the six-degree-of-freedom target 102 is relative to the laser tracker coordinate system Ol -x l y l z l The solution process of the attitude angle (azimuth angle α, pitch angle β, roll angle γ) is as follows:

[0043]

[0044] Wherein, γ′ is the angle between the x-axis of the built-in dual-axis inclinometer of the six-degree-of-freedom target 102 and the horizontal plane; β′ is the angle between the y-axis of the built-in dual-axis inclinometer of the six-degree-of-freedom target 102 and the horizontal plane; α0 is the incident laser in the target coordinate system O t -x t y t z t β0 is the azimuth of the incident laser in the target coordinate system O t -x t y t z t The pitch angle of the incident laser in the laser tracker coordinate system O l -x l y l z l The azimuth below.

[0045] Step S2: calibrate the industrial robot base coordinate system O b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship And the industrial robot flange end coordinate system O f -x f y f z f With the target coordinate system O t -x t y t z t The transformation relationship

[0046] Base coordinate system O b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship The calibration process is as follows: first, the industrial robot is adjusted to the zero position state, the first joint (the lowest joint of the six-axis robot) is rotated alone, the three-dimensional position coordinates of multiple points are measured, and the above-mentioned measurement points are fitted into a circle on the client 105, and then the normal vector of the circle is used as the x-axis direction of the industrial robot base coordinate system; secondly, the second joint (the second joint from the bottom of the six-axis robot) is rotated alone, similar to the above, the y-axis direction of the industrial robot base coordinate system can be obtained; then, the z-axis direction of the industrial robot base coordinate system can be obtained by cross multiplication; finally, the intersection of the z-axis and the horizontal plane is used as the origin of the industrial robot base coordinate system, thereby the industrial robot base coordinate system O can be obtained. b -x b y b z b In the laser tracking coordinate system O l -x l y l z l The position and posture below can be further used to obtain the transformation relationship between the two.

[0047] Flange end coordinate system O f -x f y f z f and the target coordinate system O t -x t y t z t The transformation relationship Only the translation relation t=[p x , p y , p z ] T , the multi-point alignment method is used for calibration. The process is as follows: first, the six-degree-of-freedom target 102 at the end of the industrial robot is controlled to move a point in its workspace, and this point is used as a fixed alignment point to record the posture of the end of the industrial robot flange in the industrial robot control cabinet 104 at this time. Secondly, change the posture of the industrial robot, align the tip again, and record the posture of the end of the industrial robot flange in the industrial robot control cabinet 104 at this time Finally, solving the equation The translation relationship t can be obtained, that is, the transformation relationship

[0048] Step S3: In the motion space of the industrial robot, randomly set multiple groups of industrial robot ends relative to the base coordinate system O. b -x b y b z b The pose P i =[p x , p y , p z, α, β, γ] T , as the nominal value. Control the industrial robot to move to the above posture P i , using the laser tracker 101 and the six-degree-of-freedom target 102 to obtain P i Relative to the laser tracker coordinate system O l -x l y l z l The pose measurement results are obtained by using the transformation matrix Transform the above results to the industrial robot base coordinate system O b -x b y b z b Next, we get the measured value P′ i Finally, P i The nominal value and the measured value are compared, and the average value of the deviation is used as the terminal posture error of the industrial robot. Wherein, i=1, 2, ..., N, N is the number of groups of the industrial robot terminal, N is 30 to 70, preferably 50.

[0049] Step S4: Use the DH (Denavit-Hartenberg) model to define the kinematic parameters of the industrial robot. Figure 3 As shown, including the connecting rod length α i , connecting rod offset d i , connecting rod angle α i and the joint angle θ i , the present invention is for a six-axis industrial robot, so i = 1, 2, ..., 6. Then, the end position of the industrial robot is established Furthermore, the industrial robot terminal position error [Δp x , Δp y , Δp z , Δα, Δβ, Δγ] T Deviation from the kinematic parameters of the industrial robot [Δa1, Δd1, Δα1, Δθ1, ..., Δa6, Δd6, Δα6, Δθ6] T The nonlinear relationship is negligible, and the higher-order terms are ignored, and the above nonlinear relationship is linearized into a system of linear equations.

[0050] The transformation relationship between adjacent joint coordinate systems is as follows:

[0051]

[0052] Industrial robot terminal posture Relationship with its kinematic parameters:

[0053]

[0054] Industrial robot terminal posture It can be expressed by translation and Euler angles, namely:

[0055]

[0056] The industrial robot end position error [Δp x , Δp y , Δp z , Δα, Δβ, Δγ] T Deviations from kinematic parameters [Δa1, Δd1, Δα1, Δθ1, ..., Δa6, Δd6, Δα6, Δθ6] T Linearization of the relationship:

[0057]

[0058] Step S5: According to the end position error of the industrial robot in step S3, the Levenberg Marquardt (LM) algorithm is used to solve the linear equations in step S4 to achieve preliminary identification of the kinematic parameters of the industrial robot.

[0059] Formula (5) can be written as a system of linear equations:

[0060] ΔP=J·Δρ (6)

[0061] Among them, ΔP represents the end pose error of the industrial robot, Δρ represents the kinematic parameter deviation of the industrial robot, and J represents the Jacobian matrix.

[0062] The Levenberg Marquardt algorithm is used to iteratively solve the above linear equations. The k-th iteration process is:

[0063] Calculate the Jacobian matrix J(ρ) according to the kinematic parameters of the industrial robot k ),

[0064] Calculation of kinematic parameter deviation Δρ of industrial robots k

[0065] Δρ k = -[J(ρ k ) T J(ρ k )+μ k I] -1 J(ρ k ) T ΔP(ρ k ) (7)

[0066] In the formula, μ k is the damping coefficient.

[0067] According to k+1 =ρk +Δρ k Update the kinematic parameters of industrial robots.

[0068] Step S6: Taking the kinematic parameter identification result of the LM algorithm in step S5 as the initial value and the terminal posture error as the optimization target, the Harmony Search Algorithm (HS) is used to solve the nonlinear relationship between the terminal posture error of the industrial robot and its kinematic parameter deviation, so as to further optimize the kinematic parameters and realize the secondary identification of the kinematic parameters of the industrial robot (with higher accuracy).

[0069] Step S7, compensating the kinematic parameter secondary identification result of step S6 to the industrial robot control cabinet 104 to improve the position and posture accuracy of the industrial robot end.

[0070] According to the method for calibrating the terminal posture of an industrial robot of the above-mentioned embodiment of the present invention, the terminal posture of the industrial robot is measured by a laser tracker 101 and a six-degree-of-freedom target 102, and the laser six-degree-of-freedom measurement technology is applied to the terminal posture calibration of the industrial robot, so that the position accuracy and the posture accuracy of the terminal of the industrial robot can be improved at the same time; by sequentially using the Levenberg Marquardt algorithm and the harmony search algorithm to perform secondary identification on the kinematic parameters of the industrial robot, the identification accuracy is higher than that of using any one of them alone, and the position accuracy and the posture accuracy of the terminal of the industrial robot can be greatly improved.

[0071] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for calibrating the end position of an industrial robot, characterized in that: include: Step S1: Install the six-degree-of-freedom target on the flange end of the industrial robot so that the flange end coordinate system O f -x f y f z f and the target coordinate system O t -x t y t z t In parallel, the laser tracker is installed outside the industrial robot and faces the 6-DOF target. The 6-DOF target measures the 3D posture of the target, and the laser tracker measures the 3D position of the target. Step S2: Calibrate the industrial robot base coordinate system O b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship And the industrial robot flange end coordinate system O f -x f y f z f With the target coordinate system O t -x t y t z t The transformation relationship Step S3: Set the industrial robot end relative to the base coordinate system O b -x b y b z b The position and posture of the industrial robot are used as the nominal value to control the industrial robot to move to the above position and posture. The laser tracker and the six-degree-of-freedom target are used to obtain the position and posture of the industrial robot end relative to the laser tracker coordinate system O l -x l y l z l The pose measurement results are based on the industrial robot base coordinate system O b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship Transform the above pose measurement results to the industrial robot base coordinate system O b -x b y b z b Under the condition of the robot, the measured value is obtained, and the nominal value of the posture is compared with the measured value to obtain the end posture error of the industrial robot; Step S4, using the DH model to establish the relationship between the terminal posture of the industrial robot and its kinematic parameters, further establishing a nonlinear relationship between the terminal posture error of the industrial robot and the deviation of its kinematic parameters, and linearizing the above nonlinear relationship into a linear equation system by ignoring high-order terms; Step S5, according to the end position error of the industrial robot obtained in step S3, the LM algorithm is used to solve the linear equations in step S4 to achieve preliminary identification of the kinematic parameters of the industrial robot; Step S6, taking the kinematic parameter identification result of the LM algorithm in step S5 as the initial value, taking the terminal posture error as the optimization target, and using the harmony search algorithm to further optimize the kinematic parameters to achieve secondary identification of the kinematic parameters of the industrial robot; Step S7: correct the control parameters of the industrial robot according to the secondary identification results of the kinematic parameters in step S6 to improve the terminal position accuracy of the industrial robot. In step S2, the industrial robot flange end coordinate system O is calibrated as follows: f -x f y f z f With the target coordinate system O t -x t y t z t The transformation relationship Control the six-degree-of-freedom target at the end of the industrial robot flange to move a point in its workspace, and use this point as a fixed apex point to record the posture of the end of the industrial robot flange at this time Change the posture of the industrial robot, align the tip again, and record the posture of the flange end of the industrial robot at this time By solving the equation Get the transformation relationship 2. The method according to claim 1, characterized in that In step S2, the industrial robot base coordinate system O is calibrated as follows: b -x b y b z b With the laser tracker coordinate system O l -x l y l z l The transformation relationship The industrial robot is adjusted to a zero position state, the first joint is rotated independently, the three-dimensional position coordinates of multiple points are measured, and the above measurement points are fitted into a circle, and then the normal vector of the circle is used as the x-axis direction of the base coordinate system of the industrial robot; Rotate the second joint alone and repeat the above measurement and fitting process to obtain the y-axis direction of the industrial robot base coordinate system; Obtain the z-axis direction of the industrial robot base coordinate system through cross product; Take the intersection of the z-axis and the horizontal plane as the origin of the industrial robot base coordinate system and obtain the industrial robot base coordinate system O b -x b y b z b In the laser tracking coordinate system O l -x l y l z l The position and posture of the following image are obtained, so as to obtain the transformation relationship between the two images.

3. The method according to claim 1 or 2, characterized in that: In step S3, the end position error of the industrial robot is obtained as follows: In the motion space of the industrial robot, multiple sets of industrial robot ends are set relative to the base coordinate system O b -x b y b z b The pose P i , which is taken as the nominal value, where i = 1, 2, ..., N, and N is the number of groups at the end of the industrial robot; Control the industrial robot to move to the above posture P i , the above pose P is obtained by using a laser tracker and a six-degree-of-freedom target i Relative to the laser tracker coordinate system O l -x l y l z l The pose measurement results are based on the transformation matrix Transform the above results to the industrial robot base coordinate system O b -x b y b z b Next, get the measured value; The pose P i The average value of the difference between the nominal value and the measured value is taken as the end position error of the industrial robot.

4. The method according to claim 1 or 2, characterized in that: In step S4, the linear equation system is: ΔP=JΔρ, Among them, ΔP represents the end pose error of the industrial robot, Δρ represents the kinematic parameter deviation of the industrial robot, and J represents the Jacobian matrix.

5. The method according to claim 4, characterized in that In step S5, the LM algorithm is used to iteratively solve the above linear equations. The kinematic parameter deviation Δρ of the industrial robot in the kth iteration process is k for: Dr. k =-[J(ρ k ) T J(r k )+μ k I] -1 J(r k ) T ΔP(ρ k ) Among them, J(ρ k ) is the Jacobian matrix of the k-th iteration process, μ k is the damping coefficient, According to ρ k+1 =ρ k +Δρ k Update the kinematic parameters of industrial robots.

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