Method for detecting five-axis linkage precision of five-degree-of-freedom hybrid robot

Abstract

The invention discloses a five-degree-of-freedom hybrid robot five-axis linkage precision detection method, which comprises the following steps of: arranging a target ball at the tail end of an electric spindle of a robot, and correcting the coaxiality of the electric spindle and the target ball and the rotating center distance of the electric spindle; calculating position coordinates of different detection center points and a motorized spindle attitude reachable range, and determining the optimal detection position of the RTCP precision detection center point and the maximum change range of the motorized spindle attitude according to the size of the detection range; determining a detection track path and planning path parameters, and generating a corresponding detection instruction in combination with five-axis linkage characteristics; detecting the position of the center point of the target ball at the tail end of the robot in the space in real time through a laser tracker, and obtaining space position data when the robot moves along the detection track; and according to the spatial position data during the movement of the detection track, the tail end position error of the robot under different postures is calculated, and the five-axis linkage capability of the robot is evaluated. According to the invention, the detection precision is improved.

Description

Technical Field

[0001] The invention belongs to the field of robot technology precision detection, and in particular relates to a method for detecting the five-axis linkage precision of a five-degree-of-freedom hybrid robot. Background Art

[0002] Precision is one of the key performance indicators of a processing hybrid robot and is directly related to its application value. Precision can be understood as the accuracy of key components reaching the target position during the movement of the robot. The precision of a robot can generally be divided into three categories: static, dynamic, and working precision. Among them, working precision specifically refers to the actual performance of the robot when completing complex surface processing under different processing methods and interpolation paths. For a hybrid robot, working precision means the strength of the five-axis linkage processing capability. The five-axis linkage precision is crucial in robot precision detection. It can fully reflect the positioning and interpolation accuracy of each motion axis and is a key indicator for measuring the robot's processing precision and overall performance.

[0003] With the introduction of the Rotary Tool Tip Following (RTCP) function in five-axis machine tools, its accuracy detection method has gradually received attention. The traditional RTCP detection method installs a ball head probe on the machine tool spindle, and writes a special program to drive each joint to keep the ball head in a fixed position while the tool axis vector direction rotates. In this process, the ball head deviation is measured by a micrometer or a high-precision sensor to evaluate the RTCP accuracy performance. However, this cannot simultaneously measure the deviation of the tool tip point in three-dimensional space, and the errors caused by multiple installations of the measuring tool will reduce the measurement accuracy. In addition, factors such as the inability of the micrometer to export data online and installation accuracy limitations will also affect the accuracy of the detection results. Summary of the invention

[0004] The purpose of the present invention is to provide a five-axis linkage accuracy detection method for a five-degree-of-freedom hybrid robot based on the RTCP function. The problems of multiple installations and inability to export data in traditional methods are solved by optimizing the test method, planning the motion trajectory and using a laser tracker to measure, thereby ensuring the real-time and accuracy of the measurement, providing an efficient and accurate detection means, and being able to comprehensively evaluate the robot's five-axis linkage accuracy and working accuracy, providing a reliable basis for robot accuracy optimization.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A method for detecting the five-axis linkage accuracy of a five-degree-of-freedom hybrid robot, comprising:

[0007] Step 1: Set a target ball at the end of the robot's electric spindle to calibrate the coaxiality between the electric spindle and the target ball and the rotation center distance of the electric spindle;

[0008] Step 2: Calculate the position coordinates of different detection center points and the reachable range of the electric spindle posture, and determine the optimal detection position of the RTCP precision detection center point and the maximum variation range of the electric spindle posture according to the size of the detection range;

[0009] Step 3: Determine the RTCP inspection trajectory path and plan the path parameters, and generate the corresponding RTCP inspection instructions in combination with the characteristics of the five-axis linkage;

[0010] Step 4: Use a laser tracker to detect the position of the center point of the target ball at the end of the robot in space in real time, and obtain the spatial position data of the robot when it moves along the RTCP detection trajectory;

[0011] Step 5: According to the spatial position data of the RTCP detection trajectory during motion, calculate the robot end position error under different postures and evaluate the robot's five-axis linkage capability.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The present invention can reduce the errors caused by multiple installations of the measuring tool through optimized motion trajectory planning and real-time detection, thereby providing higher-precision five-axis linkage detection.

[0014] (2) The present invention combines the RTCP function with laser tracker measurement to achieve automated high-precision detection, prevent the micrometer from being unable to export data online and installation accuracy problems, and significantly improve detection efficiency and data reliability.

[0015] (3) The present invention can not only detect the RTCP accuracy of the robot end, but also evaluate the five-axis linkage capability and overall working accuracy of the robot under different working conditions, providing comprehensive data support for robot performance optimization and accuracy improvement, and is particularly suitable for high-precision processing of complex structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the five-axis linkage accuracy measurement principle of the five-degree-of-freedom hybrid robot RTCP;

[0017] Figure 2 This is a schematic diagram of a five-axis linkage measurement device for a five-degree-of-freedom hybrid robot;

[0018] Figure 3 It is a schematic diagram of the electric spindle attitude angle;

[0019] The numbers in the figure mean:

[0020] 1. Ground level iron, 2. Column, 3. Parallel module, 4. Series A\C swivel head, 5. Laser tracker; 6. Electric spindle, 7. Tool handle, 8. Target ball seat, 9. Target ball. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] This embodiment is a five-axis linkage accuracy detection method based on the RTCP function of a five-degree-of-freedom hybrid robot with a rotating bracket disclosed in Chinese patent publication number CN111941393A.

[0023] Combination Figure 1 and Figure 2 , briefly describe the structure of the five-degree-of-freedom hybrid robot disclosed in CN111941393A. The hybrid robot consists of a parallel module 3 and a series A\C rotary head 4 (where C represents a rotary pair perpendicular to the moving platform of the parallel module 3, and A represents a rotary pair perpendicular to the axis of the rotary pair C and the electric spindle 6), which is fixedly connected to the horizontal iron 1 through a column 2. The end effector of the series A\C rotary head 4 is the electric spindle 6, which can be connected to the tool handle 7 to achieve the function of clamping the tool and transmitting torque. In the process of detecting the five-axis linkage of the robot, the target ball seat 8 is clamped at the end of the tool handle 7, and the target ball 9 of the laser tracker is magnetically attracted to the target ball seat 8, and the spatial position of the target ball is measured with the help of the laser tracker to carry out precision detection.

[0024] The present invention provides a five-axis linkage accuracy detection method for a five-degree-of-freedom hybrid robot based on an RTCP function, which comprises the following steps:

[0025] Step 1: Set the target ball 9 on the electric spindle 6 to complete the correction of the coaxiality between the electric spindle 6 and the target ball 9 and the rotation center distance of the electric spindle 6.

[0026] 1.1 Fix the target ball 9 and calibrate the coaxiality between the target ball 9 and the electric spindle 6.

[0027] Before conducting the RTCP five-axis linkage accuracy verification, the target ball seat 8 is installed on the spindle tool handle 7, and the target ball 9 is magnetically attracted to the target ball seat 8. By rotating the tool handle 7, observe the position vector of the center point S of the target ball 9 in the measurement coordinate system of the laser tracker 5. By replacing the collet of the tool handle 7 or reinstalling the target ball seat 8, the coordinate change range of point S is kept within 15μm, ensuring that the center point S of the target ball 9 is always on the axis of the electric spindle 6 during the test.

[0028] 1.2 Correct the rotational moment between point Q on the electric spindle 6 and the center point S of the target ball 9.

[0029] The coordinates of the center point S of the target ball 9 are measured by a laser tracker. By rotating the A axis of the tandem A\C turn head 4 to fit a circle and determine the radius, the distance |PS| from the center point S of the target ball 9 to the intersection point P of the two rotation axes of the tandem A\C turn head 4 of the robot is obtained. The intersection point of the common perpendicular line between the axis of the electric spindle 6 and the A axis of the tandem A\C turn head 4 and the axis of the electric spindle is recorded as point Q (see attached). Figure 2 ), by rotating the tool handle 7 to fit the axis of the electric spindle 6, the distance |PQ| between point P and point Q is determined. Finally, the total length of the rotation moment of the electric spindle 6 is calculated.

[0030] Step 2: Determine the best detection point of the target ball center point S during RTCP accuracy detection The maximum range of coordinates and spindle posture change max(α max (S)).

[0031] 2.1 Determine the initial posture of the electric spindle and calculate the coordinates of the center point S of the target ball.

[0032] When the position of point P in the task space is determined, the length q of the three branches of the robot parallel module 3 can be obtained by inverse kinematics solution. f (f=1,2,3). According to the actual processing requirements, the posture of the robot electric spindle 6 when it is perpendicular to the upper surface of the horizontal iron 1 can be defined as the initial posture for inspection. When the position of point P is determined, the C-axis and A-axis driving angles of the tandem A\C turntable 4 that makes the electric spindle 6 in the initial posture for inspection are q 4 ,q 5 That is, when the electric spindle 6 is in the initial posture, once point P is determined, the driving amount q of the five active joints of the robot can be calculated. f (f = 1 to 5), the five active joints include three branches and the C axis and A axis of the A\C turntable 4 in series. The driving amount q through the five active joints of the robot f (f = 1 to 5) The correct solution obtains the position coordinates (x S y S z S ).

[0033] 2.2 Establish the detection point end coordinate system and calculate the maximum inclination angle α corresponding to the target ball center point S max (S).

[0034] At the center point S of the target ball 9, a terminal coordinate system S-xyz is established (the z-axis is perpendicular to the upper surface of the horizontal iron 1 and vertically upward, and the x-axis is perpendicular to the side of the horizontal iron 1, as shown in the attached figure). Figure 1 ), keep the spatial coordinates of the center point S of the target ball 9 unchanged, and constantly change the Figure 3The attitude angles α, β of the electric spindle 6 are shown (α, β represent the rotation angles around the y and z coordinate axes of the terminal coordinate system during the process of converting the z axis of the terminal coordinate system (i.e. the electric spindle in the initial attitude) to the center line SQ of the electric spindle. When the electric spindle 6 is in the initial attitude for inspection, α=β=0). The values ​​of the driving amounts of each active joint should be kept within the allowable driving range, i.e.

[0035] q f,min <q f <q f,max (f=1,2,3,4,5)

[0036] where q n,min and q n,max Indicates the minimum and maximum allowable driving amount of the robot. Under the premise of ensuring that the attitude angle β of the electric spindle 6 rotates from 0° to 360°, the maximum inclination angle α of the electric spindle attitude angle α corresponding to the center point S of the target ball 9 at different positions is obtained through forward and inverse calculations. max (S).

[0037] 2.3 Searching for the best detection point of the center point S of the target ball And the corresponding maximum range of the electric spindle posture max(α max (S)).

[0038] By changing the position of point P in the task space, we can search for different points P and their corresponding points S under α max (S), and remember that α max (S) reaches the maximum value max(α max (S)), the position coordinates of point S are And the inverse solution is used to obtain the driving amount of each active joint of the robot

[0039]

[0040] Among them, f(P) is the objective function, the coordinates of point P are x P ,y P , z P is the decision variable. The constraints are that point P should be in the task space Θ and that all active joint drive values ​​are within the reachable safety range.

[0041] Step 3: According to the characteristics of the robot workspace, determine the RTCP inspection trajectory and plan the path parameters, and combine the characteristics of the five-axis linkage to generate the corresponding RTCP detection instructions.

[0042] 3.1 Set up RTCP inspection track.

[0043] The RTCP test trajectory of point Q can be described by the equations for the changes in attitude angles A and B:

[0044]

[0045] The attitude angles A and B represent the rotation angles around the x and y axes of the terminal coordinate system during the process of converting the z axis of the terminal coordinate system (i.e. the electric spindle in the initial attitude) to the center line SQ of the electric spindle. The maximum value of the two rotation angles is A. max and B max , and neither can be greater than k A and k B is a parameter related to the shape of the detection trajectory, ω is a speed parameter, and t is time.

[0046] 3.2 Determine trajectory shape parameter k A and k B

[0047] The shape of the RTCP test trajectory is given by k A and k B OK. When k A =1, k B = 0, point Q of the electric spindle 6 only draws an arc in the S-yz plane, and the attitude angle B remains unchanged. A =0, k B = 1, the electric spindle point Q only draws an arc in the S-xz plane, and the attitude angle A remains unchanged. A =1, k B =2, point Q of the electric spindle 6 moves in the shape of an "8", and the attitude angles A and B change at the same time, covering a variety of speed states. The overall curvature of the optimized trajectory is larger, and it belongs to a variable curvature curve. It can evaluate the five-axis linkage capability of the robot at different speeds and comprehensively test the working accuracy performance of the five-degree-of-freedom hybrid robot within the full range of travel.

[0048] 3.3 Determine the trajectory speed parameter ω.

[0049] The ω parameter is a fixed value and does not affect the shape of the RTCP test trajectory. When point Q moves along the test trajectory, the instantaneous angular velocity and average angular velocity of the attitude angle A (B) are ω A (ω B )and

[0050] ω A =k A ωB max cos(k A ωt),ω B =k B ωB max cos(ωt)

[0051]

[0052] The relationship between the velocity of the motion trajectory of point Q in each coordinate axis direction of the terminal coordinate system and the angular velocity of the attitude angle is:

[0053]

[0054] v x , v y , v z They represent the velocity of point Q along the x, y, and z axes of the terminal coordinate system. The linear velocity v of point Q Q Size Satisfaction

[0055]

[0056] where ω maxB =k B ωB max Represents the maximum instantaneous angular velocity of the attitude angle B, which is set by the average angular velocity of the robot's attitude angle during the test and Or the linear velocity v of point Q Q The specific value of parameter ω can be inferred from the range of ω. Ensure that when the robot runs along the planned RTCP five-axis linkage precision trajectory, the movement speed and acceleration state of each axis are within the allowable range of the control motor to prevent the following error caused by insufficient system driving capacity.

[0057] 3.4 Determine the maximum step length l of trajectory linear interpolation max , generate trajectory motion instructions.

[0058] In the process of five-axis precision inspection, the RTCP inspection trajectory is fitted by straight line segment interpolation to determine the joint motion command. The acceleration of point Q of the electric spindle 6 on the inspection trajectory is

[0059]

[0060] Among them, a A and a B Respectively represent the acceleration of the change of attitude angle A and B in the test trajectory. x , a y , a z They represent the magnitude of the acceleration of point Q along the x, y, and z axes of the terminal coordinate system. The curvature radius ρ of the inspection trajectory is obtained according to the calculation method of the curvature radius of a complex spatial curve:

[0061]

[0062] Among them, v Q =(v x v y vz ) T and a Q =(a x a y a z ) T Represent the velocity and acceleration vector of point Q of the electric spindle 6 respectively. Taking the derivative of the curvature radius ρ with respect to time and setting it to 0, we can obtain the minimum curvature radius ρ when the mechanism moves along the trajectory. min The location where it appears.

[0063] Approximate the trajectory curve with a series of straight line segments of equal length. Set the maximum allowable approximation error value λ and solve the maximum step length l for linear interpolation of the trajectory max :

[0064]

[0065] Among them, ρ min is the minimum radius of curvature of the test trajectory. Ignore high-order small terms:

[0066]

[0067] Determine the motion path of the RTCP test trajectory and the maximum step length l of linear interpolation max After that, the main control computer generates the motion instructions required by the robot during the RTCP five-axis linkage accuracy inspection process. Based on the inspection trajectory, the coordinates of the current interpolation point Q and the linear interpolation step length l (l≤l max ), calculate the coordinates of the next interpolation point, and determine the feed amount and feed speed of the attitude angles A and B within the interpolation cycle. Then, perform inverse kinematics based on the updated attitude angles to find the drive amount of each motion axis required for the robot to reach the next interpolation point.

[0068] Step 4: Use the laser tracker 5 to detect the position of the center point S of the target ball 9 in space in real time, perform the RTCP five-axis linkage accuracy detection test, and obtain the detection data set.

[0069] Theoretically, the center point S of the target ball 9 remains stationary in the measurement coordinate system of the laser tracker 5. The five active joints of the hybrid robot are driven to move according to the preset instructions, so that the Q point of the electric spindle 6 moves periodically along the RTCP detection trajectory, and the actual space coordinates of the center point S of the target ball 9 in the measurement coordinate system of the laser tracker 5 are continuously collected to obtain a discretized detection data set Ω = {S ij |i=1~m;j=1~n}(m,n represent the number of repetitions of the periodic motion of the trajectory in one test and the number of sampling points in a complete trajectory cycle respectively), S ij =(x ij y ij z ij) represents the three-dimensional coordinates of the j-th sampling point S when running the i-th RTCP detection trajectory.

[0070] Step 5: After obtaining the RTCP detection dataset, data processing is performed to evaluate the five-axis linkage performance of the robot.

[0071] Compute the global extreme value deviation:

[0072]

[0073] Where |||| represents the Euclidean distance; calculate the maximum fluctuation range Δx of the position error of the measuring point S in the measuring coordinate system x, y, and z axes max ,Δy max ,Δz max :

[0074] Δx max =max(x ij )-min(x ij )

[0075] Δy max =max(y ij )-min(y ij )

[0076] Δz max =max(z ij )-min(z ij )

[0077] δ max and Δx max ,Δy max ,Δz max Construct a four-dimensional evaluation vector V = (δ max ,Δx max ,Δy max ,Δz max ), the five-axis linkage accuracy is qualified if and only if each component of the four-dimensional evaluation vector V is less than the preset threshold; the trajectory repeatability index is

[0078]

[0079] In the formula, is the mean of the i-th trajectory data points. If and only if max(σ i )-min(σ i When )(where i = 1 to m) is less than the preset value, the linkage trajectory repeatability is determined to be up to standard;

[0080] Although the present invention is described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention, and the above-mentioned specific embodiments are merely illustrative and not restrictive. Any equivalent transformation or improvement made on the basis of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for detecting the five-axis linkage accuracy of a five-degree-of-freedom hybrid robot, characterized in that: include: Step 1: Set a target ball at the end of the robot's electric spindle to calibrate the coaxiality between the electric spindle and the target ball and the rotation center distance of the electric spindle; Step 2: Calculate the position coordinates of different detection center points and the reachable range of the electric spindle posture, and determine the optimal detection position of the RTCP precision detection center point and the maximum variation range of the electric spindle posture according to the size of the detection range; Step 3: Determine the RTCP inspection trajectory path and plan the path parameters, and generate the corresponding RTCP inspection instructions in combination with the characteristics of the five-axis linkage; Step 4: Use a laser tracker to detect the position of the center point of the target point at the end of the robot in space in real time, and obtain the spatial position data of the robot when it moves along the RTCP detection trajectory; Step 5: According to the spatial position data of the RTCP detection trajectory during motion, calculate the robot end position error under different postures and evaluate the robot's five-axis linkage capability.

2. The detection method for the five-axis linkage accuracy of the five-degree-of-freedom hybrid robot according to claim 1 is characterized in that: Step 2 specifically includes: Point P is the intersection of the two rotation axes of the tandem A\C rotors. When the position of point P in the task space is determined, the initial posture of the robot's electric spindle is defined. Given the drive amounts of the robot's five active joints, the position coordinates of the center point S of the target ball are obtained by positive solution. Change the position of point P in the task space and search for the maximum tilt angle α under different points P and the corresponding center point S max (S), and keep in mind the maximum tilt angle α max (S) reaches the maximum value max(α max (S)), the position coordinates of the center point S are This point is then used as the optimal detection point for RTCP accuracy detection, and the driving amount of each active joint of the robot is obtained by inverse solution.

3. The five-axis linkage accuracy detection method of the five-degree-of-freedom hybrid robot according to claim 1 is characterized in that: The RTCP inspection trajectory path is: The attitude angles A and B represent the rotation angles around the x and y axes of the terminal coordinate system during the conversion of the z axis of the terminal coordinate system to the center line of the electric spindle. The origin of the terminal coordinate system S-xyz is point S. The z axis is perpendicular to the upper surface of the horizontal iron and vertically upward. The x axis is perpendicular to the side of the horizontal iron. The maximum value of the two rotation angles is A. max and B max , and neither can be greater than k A and k B is a parameter related to the shape of the detection trajectory, ω is a speed parameter, t is a time parameter, α max (S) is the maximum tilt angle of the electric spindle attitude angle α corresponding to the center point S of the target ball.

4. The five-axis linkage accuracy detection method of a five-degree-of-freedom hybrid robot according to claim 3 is characterized in that: The planning path parameters include the trajectory shape parameter k A and k B , trajectory velocity parameter ω and maximum step length l of trajectory linear interpolation max ; The trajectory shape parameter k A and k B Determined according to the shape of the detection trajectory; The intersection of the common perpendicular line between the electric spindle axis and the tandem head A axis and the electric spindle axis is point Q. The distance from this point to the center S of the target ball is the rotation moment |QS|. According to the planned RTCP detection trajectory velocity parameter ω, the instantaneous angular velocity and average angular velocity of the attitude angle A(B) are calculated as ω. A (ω B )and and the linear velocity v of point Q Q : oh A =k A ohB max cos(k A ωt),ω B =k B ohB max cos(ωt) where ω maxB =k B ωB max Represents the maximum instantaneous angular velocity of the attitude angle B, which is set by the average angular velocity of the robot's attitude angle during the test and Or the linear velocity v of point Q Q The specific value of parameter ω can be deduced from the range of Maximum step length ρ min To test the minimum curvature radius of the trajectory, λ is the maximum allowable approximation error value.

5. The five-axis linkage accuracy detection method of a five-degree-of-freedom hybrid robot according to claim 4 is characterized in that: The minimum curvature radius ρ is obtained by taking the derivative of the curvature radius ρ with respect to time and setting it to 0. min The location where v Q =(v x v y v z ) T and a Q =(a x a y a z ) T Represent the velocity and acceleration vectors of point Q of the electric spindle respectively; Among them, a A and a B They respectively represent the acceleration of the change of attitude angles A and B in the test trajectory.

6. The method for detecting the five-axis linkage accuracy of a five-degree-of-freedom hybrid robot according to claim 1, characterized in that: Determine the motion path and maximum step length l of the RTCP test trajectory max Finally, the main control computer is used to generate the motion instructions required by the robot during the RTCP five-axis linkage precision inspection process, and the five active joints of the hybrid robot are driven to move according to the preset instructions, so that the point Q of the electric spindle moves periodically along the RTCP detection trajectory, and the actual spatial coordinates of the center point S of the target ball in the laser tracker measurement coordinate system are continuously collected to obtain a discrete detection data set, that is, to obtain the spatial position data of the robot when it moves along the RTCP detection trajectory.

7. The method for detecting the five-axis linkage accuracy of a five-degree-of-freedom hybrid robot according to claim 1, characterized in that: Set the four-dimensional evaluation vector V and trajectory repeatability index to evaluate the robot's five-axis linkage capability: V=(δ max ,Δx max ,Δy max ,Δz max ) Δx max =max(x ij )-min(x ij ) Δy max =max(y ij )-min(y ij ) Δz max =max(from ij )-min(z ij ) Where ‖‖ represents the Euclidean distance, S ij =(x ij y ij z ij ) represents the three-dimensional coordinates of the jth sampling point S when running the i-th RTCP detection trajectory, Δx max ,Δy max ,Δz max Indicates the maximum fluctuation range of the position error of the measuring point S in each axis of the measuring coordinate system; Trajectory repeatability index: middle, is the mean of the i-th trajectory data points, and n is the number of sampling points when the i-th RTCP detects the trajectory.

8. The method for detecting the five-axis linkage accuracy of a five-degree-of-freedom hybrid robot according to claim 1, characterized in that: The correction of the rotational moment of the electric spindle is achieved by measuring the coordinates of the center point S of the target ball with the help of a laser tracker. By rotating the A-axis of the tandem A\C rotor to fit a circle and determine the radius, the distance |PS| from the center point S of the target ball to the intersection point P of the two rotation axes of the robot's tandem A\C rotor is obtained; the intersection point of the common perpendicular line between the axis of the electric spindle and the A-axis of the tandem A\C rotor and the axis of the electric spindle is denoted as point Q. The distance |PQ| between point P and point Q is determined by rotating the tool holder to fit the axis of the electric spindle.

Images