A guy measuring device, a method for determining a position of a guy exit point, and a robot distance error calibration method

Abstract

The application discloses a pull line measuring device, a pull line outlet point position determination method and a robot distance error calibration method, and belongs to the technical field of robot calibration. The pull line measuring device can change the pull line from a horizontal state to a vertical downward state, and make the pull line bypass a pulley installed on a base through a rotatable guide line ladder shaft connected with the base, so that accurate measurement of any point position in a three-dimensional space is realized, and the flexibility and accuracy of measurement are significantly improved. Further, through the pull line outlet point position determination method and the robot distance error calibration method, the outlet point position can be accurately measured, the difference between an actual pull line path and an ideal path is compensated through accurate measurement of the outlet point position, and the measurement accuracy of the pull line measuring device is further improved.

Description

TECHNICAL FIELD

[0001] The application relates to a pull wire measuring device, a pull wire outlet point position determination method and a robot distance error calibration method, and belongs to the technical field of robot calibration. BACKGROUND

[0002] With the continuous progress of automation technology, especially the rapid expansion of the field of robots, manufacturing is gradually changing from relying on manual assistance to full automation. The acceleration of this technological change has promoted the widespread application of new robot technology in industry and scientific research. In this process, robot calibration technology, as a key step to ensure the accuracy of robot operation, has been highly valued by scientific research institutions.

[0003] In order to solve the problem of high cost and complex operation of the existing calibration technology, the pull wire sensor is widely used as an effective optimization scheme. However, the current pull wire sensor technology has limitations, mainly manifested in that it can only measure along a single fixed axis, which limits its ability to accurately measure in three-dimensional space. At the same time, the existing pull wire measuring device usually takes the horizontal tangent point of the guide pulley as the measurement reference, ignoring the position offset of the outlet point when the robot measurement position changes. This offset causes the actual measurement path to be not a straight line, but a combination of circular arcs and straight lines, thereby introducing measurement errors. SUMMARY

[0004] The application provides a pull wire measuring device, which can convert the pull wire from a horizontal state to a vertical downward state, and make the pull wire pass through the pulley installed on the base through the rotatable guide wire stepped shaft connected with the base, so as to realize accurate measurement of any point in three-dimensional space, and significantly improve the flexibility and accuracy of measurement. Further, a pull wire outlet point position determination method and a robot distance error calibration method are provided, which compensate for the difference between the actual pull wire path and the ideal path by accurately measuring the outlet point position, and further improve the measurement accuracy of the pull wire measuring device.

[0005] The technical scheme of the application is as follows:

[0006] According to a first aspect of the application, a pull wire measuring device is provided, comprising a pull wire sensor 1, a pull wire guide mechanism 3, and a multi-axis force sensor 4; the pull wire guide mechanism 3 is connected with the pull wire sensor 1, and the multi-axis force sensor 4 is connected with the pull wire guide mechanism 3.

[0007] Further, the pull wire guiding mechanism 3 comprises an upper wire guiding mechanism, a wire guiding mechanism, and a lower wire guiding mechanism; the upper wire guiding mechanism is connected with the wire guiding mechanism and the lower wire guiding mechanism through the wire guiding mechanism; the upper wire guiding mechanism is used to guide the pull wire on the pull wire sensor 1 out of the wire guiding mechanism; the wire guiding mechanism is used to guide the pull wire guided out of the upper wire guiding mechanism to the lower wire guiding mechanism; and the lower wire guiding mechanism is used to guide the pull wire guided by the wire guiding mechanism out of the wire guiding mechanism.

[0008] Further, the upper wire guiding mechanism comprises a first upper base 11, a second upper base 12, a first pulley 8-1, and a first shaft 10-1; the second upper base 12 and the first upper base 11 are respectively fixed inside the pull wire sensor 1; the two ends of the first shaft 10-1 are respectively in interference fit with the mounting holes on the second upper base 12 and the first upper base 11; the first pulley 8-1 is mounted on the first shaft 10-1; the pull wire on the pull wire sensor 1 is guided to the first entry point of the first pulley 8-1 through the guide column, and then guided out of the wire guiding mechanism through the first exit point of the first pulley 8-1.

[0009] Further, the wire guiding mechanism comprises a wire ladder shaft 13, a self-aligning ball bearing 15, and a thrust ring 14; the wire ladder shaft 13 is in interference fit with the inner ring of the self-aligning ball bearing 15; the thrust ring 14 is arranged above the self-aligning ball bearing 15 and clamps the self-aligning ball bearing 15 through the shaft shoulder of the wire ladder shaft 13; the outer ring of the self-aligning ball bearing 15 is in interference fit with the lower shell 6; the pull wire guided out of the first exit point of the first pulley 8-1 in the upper wire guiding mechanism is guided to the second entry point of the second pulley 8-2 in the lower wire guiding mechanism through the wire guiding mechanism.

[0010] Further, the lower wire guiding mechanism comprises a first lower base 16, a second lower base 17, a second pulley 8-2, and a second shaft 10-2; the first lower base 16 and the second lower base 17 are connected and clamp the wire ladder shaft 13 in the wire guiding mechanism; one end of the second shaft 10-2 is in interference fit with the mounting hole on the first lower base 16; the other end of the second shaft 10-2 is in clearance fit with the mounting hole on the second lower base 17 and protrudes out of the hole to be in fit with the multi-shaft force sensor 4; the second shaft 10-2 is fixedly mounted on the first lower base 16 and the second lower base 17; and the second pulley 8-2 is mounted on the second shaft 10-2; the pull wire guided to the second entry point of the second pulley 8-2 in the wire guiding mechanism is guided out of the reference point / second exit point of the second pulley 8-2 through the lower wire guiding mechanism.

[0011] According to the second aspect of the present application, a method for determining the position of the pull wire exit point in a pull wire measuring device is provided, comprising the following steps:

[0012] Step 1: Place the wire measurement device and the target object to be calibrated on the same workbench plane, pull the wire out of the wire measurement device reference point in a direction parallel to the workbench plane by a predetermined length L1; then subtract the length L2 measured by the wire sensor 1 from the length L1, and the value obtained after subtraction is the distance from the wire measurement device reference point to the initial position of the wire sensor 1, referred to as the reference distance; establish a measurement coordinate system at the wire measurement device reference point, record the force direction of the multi-axis force sensor 4 corresponding to the length L1 of the wire pulled out in the wire measurement device, and determine the contact point of the wire pulled out from the first pulley 8-1 with the second pulley 8-2 according to the wire measurement device reference point and the force direction of the multi-axis force sensor 4, which is referred to as the second entry point;

[0013] Step 2: Connect the end of the wire of the wire measurement device to the end of the target object to be calibrated;

[0014] Step 3: Control the target object to be calibrated to move to a plurality of teaching points in turn, obtain the position and joint parameter information of the plurality of teaching points of the target object to be calibrated, and obtain the rope length between the wire measurement device reference point and the plurality of teaching points and the corresponding force direction of the multi-axis force sensor 4;

[0015] Step 4: According to the plurality of force directions obtained in step S3 and the second entry point position determined in step 1, determine a plurality of second exit point positions.

[0016] According to a third aspect of the present application, a robot distance error calibration method is provided, and the specific steps of the method are as follows:

[0017] Step 1: When the object to be calibrated is a robot, determine the plurality of second exit point positions corresponding to the movement of the robot to be calibrated to a plurality of teaching points in turn according to the method for determining the position of the wire exit point in the wire measurement device;

[0018] Step 2: According to the plurality of teaching point positions, the plurality of rope lengths, and the plurality of second exit point positions of the robot to be calibrated, determine the distances from the plurality of teaching point positions of the robot to the reference point, referred to as actual distances;

[0019] Step 3: According to the joint parameter information displayed by the robot teach pendant, establish a homogeneous transformation matrix equation of the robot end coordinate system to the robot base coordinate system, and calculate the nominal position of the robot end coordinate system to the robot base coordinate system, referred to as the nominal position;

[0020] Step 4: According to the nominal position and the actual distance, calculate the nominal position of the reference point in the robot base coordinate system, referred to as the nominal reference point position;

[0021] Step5: According to the nominal reference point position and the nominal position, the nominal distance from the robot end to the nominal reference point position is calculated, which is referred to as the nominal distance;

[0022] Step6: The nominal distance and the actual distance are subtracted to obtain the distance error of the robot end relative to the reference point, which is referred to as the distance error;

[0023] Step7: According to the nominal distance, the nominal position and the to-be-calibrated robot joint parameter information, a relationship between the distance error and the robot parameter error is established, which is referred to as the distance error model; the distance error is brought into the distance error model, and the error of the robot joint parameter can be obtained through the least square method.

[0024] The beneficial effects of the present application are:

[0025] (1) For the problem of accurately measuring any point position in three-dimensional space, the existing pull wire sensor technology has obvious limitations, mainly manifested as that they can only measure along a single fixed axis, which limits their ability to accurately measure any position in three-dimensional space. The present application adopts a solution, which effectively overcomes this difficulty by introducing a pull wire guiding mechanism. The mechanism first changes the pull wire from a horizontal posture to a vertical downward position, and then makes the pull wire pass through a pulley installed on the lower base through a wire ladder shaft connected to the lower base and rotatable. This design enables the present application to accurately measure any point position in three-dimensional space, greatly improving the flexibility and accuracy of measurement.

[0026] (2) The wire guiding mechanism is installed inside the pull wire measuring device, improving the compactness of the entire measuring mechanism. When carrying or using, the wire guiding mechanism is inside the pull wire measuring device, which can well avoid damage to the device caused by accidental touch. The entire calibration tool has the advantages of simple structure, portability, practicality, simple operation, low cost, strong universality, and is suitable for robot calibration in different occasions, and has high market application value.

[0027] (3) The rotation of the pull wire measuring device changes the sliding motion into rolling motion through the bearing, improving the accuracy of the pull wire measuring device in measuring any point position in space.

[0028] (4) For the problem of pulley out-line point measurement, the existing pull line measurement device usually takes the horizontal tangent point of the guide pulley as the reference, ignores the position offset of the out-line point caused by the change of the robot measurement position, and the actual path is not a complete straight line, but a combination of circular arc and straight line, so there is a problem of insufficient precision, especially in long distance measurement. The present application provides a robot calibration method, which accurately measures the distance between the robot end and the reference point by introducing a pull line sensor and a multi-axis force sensor, thereby improving the calibration accuracy. Compared with the prior art, the calibration method of the present application reduces the measurement error, improves the operation accuracy of the robot, and the operation process is more simple. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the pull line measurement device of the present application;

[0030] Figure 2 It is an exploded schematic diagram of the pull line measurement device of the present application;

[0031] Figure 3 It is a hidden schematic diagram of the upper shell of the pull line measurement device of the present application;

[0032] Figure 4 It is a hidden schematic diagram of the lower shell of the pull line measurement device of the present application;

[0033] Figure 5 It is a pull line guide schematic diagram of the pull line measurement device of the present application;

[0034] Figure 6 It is a schematic diagram of the part number of the guide mechanism of the pull line measurement device of the present application;

[0035] Figure 7 It is a flowchart of the calibration method of the present application;

[0036] Figure 8 It is a schematic diagram of the geometric relationship of the reference point and the in-line point;

[0037] Figure 9 It is a schematic diagram of the geometric relationship of the out-line point;

[0038] The numbers in the figure are: pull line sensor 1, pull line shell 2, pull line guide mechanism 3, multi-axis force sensor 4, upper shell 5, lower shell 6, first deep groove ball bearing 7-1, first pulley 8-1, first shaft sleeve 9-1, first shaft 10-1, second deep groove ball bearing 7-2, second pulley 8-2, second shaft sleeve 9-2, second shaft 10-2, first upper base 11, second upper base 12, lead wire stepped shaft 13, thrust ring 14, self-aligning ball bearing 15, first lower base 16, second lower base 17. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0040] Example 1: As Figures 1-6 As shown, according to a first aspect of the present invention, a pull wire measuring device is provided, including a pull wire sensor 1, a pull wire guiding mechanism 3, and a multi-axis force sensor 4; the pull wire guiding mechanism 3 is connected to the pull wire sensor 1, and the multi-axis force sensor 4 is connected to the pull wire guiding mechanism 3.

[0041] Furthermore, such as Figure 1 , 2 As shown, the pull wire measuring device also includes a pull wire housing 2, which includes an upper housing 5 and a lower housing 6. The upper housing 5 is used to open / close the lower housing 6, and the two are connected by bolts or other detachable means.

[0042] Furthermore, the pull wire guiding mechanism 3 includes an online guiding mechanism, a line guiding mechanism, and a offline guiding mechanism. The online guiding mechanism is connected to the offline guiding mechanism through the line guiding mechanism. The online guiding mechanism is used to lead the pull wire on the pull wire sensor 1 to the line guiding mechanism. The line guiding mechanism is used to guide the pull wire led out by the online guiding mechanism to the offline guiding mechanism. The offline guiding mechanism is used to lead out the pull wire guided by the line guiding mechanism.

[0043] Furthermore, such as Figure 6 As shown, the online guiding mechanism includes a first upper base 11, a second upper base 12, a first pulley 8-1, a first deep groove ball bearing 7-1, a first shaft 10-1, and a first bushing 9-1. The second upper base 12 and the first upper base 11 are respectively connected to the inside of the pull-wire sensor 1 by two screws. The two ends of the first shaft 10-1 are respectively interference-fitted with the mounting holes on the second upper base 12 and the first upper base 11. The inner ring of the first deep groove ball bearing 7-1 is interference-fitted with the first shaft 10-1, and the outer ring of the first deep groove ball bearing 7-1 is interference-fitted with the first pulley 8-1. The first bushing 9-1 with clearance fit is installed on the first shaft 10-1 to axially limit the first deep groove ball bearing 7-1 installed between the two first bushings. The pull wire on the pull-wire sensor 1 is guided to the first entry point of the first pulley 8-1 via the guide post, and then led out to the line guiding mechanism via the first exit point of the first pulley 8-1.

[0044] Furthermore, such as Figure 6As shown in the figure, the wire guide mechanism includes a wire guide stepped shaft 13, a self-aligning ball bearing 15, and a thrust ring 14. The wire guide stepped shaft 13 is in interference fit with the inner ring of the self-aligning ball bearing 15. The thrust ring 14 is arranged above the self-aligning ball bearing 15 and clamps the self-aligning ball bearing 15 through the shoulder of the wire guide stepped shaft 13. The outer ring of the self-aligning ball bearing 15 is in interference fit with the lower housing 6. The pull wire led out of the first wire exit point of the first pulley 8-1 is guided to the second wire entry point of the second pulley 8-2 in the wire guide mechanism.

[0045] Further, as shown in the figure, Figure 6 The wire guide mechanism includes a first lower base 16, a second lower base 17, a second pulley 8-2, a second deep groove ball bearing 7-2, a second shaft 10-2, and a second shaft sleeve 9-2. The first lower base 16 and the second lower base 17 are connected by three bolts and clamp the wire guide stepped shaft 13 in the wire guide mechanism by eight clamping screws. One end of the second shaft 10-2 is in interference fit with the mounting hole on the first lower base 16. The other end of the second shaft 10-2 is in clearance fit with the mounting hole on the second lower base 17 and protrudes from the hole to cooperate with the multi-axis force sensor 4 (i.e., the multi-axis force sensor can be mounted on one side of the second lower base 17 by four screws). The second shaft 10-2 is fixedly installed on the first lower base 16 and the second lower base 17. The inner ring of the second deep groove ball bearing 7-2 is in interference fit with the second shaft 10-2. The outer ring of the second deep groove ball bearing 7-2 is in interference fit with the second pulley 8-2. The second shaft sleeve 9-2 in clearance fit is installed on the second shaft 10-2 to axially limit the second deep groove ball bearing 7-2 installed between the two second shaft sleeves. The pull wire guided by the wire guide mechanism to the second wire entry point of the second pulley 8-2 is led out of the reference point / second wire exit point of the second pulley 8-2.

[0046] As shown in the figure, Figures 1-9 According to the second aspect of the embodiment of the present application, a method for determining the position of the pull wire exit point in the pull wire measuring device is provided, which includes the following steps:

[0047] Step 1: Place the wire measurement device and the target object to be calibrated on the same workbench plane, pull the wire in the wire measurement device out of the wire measurement device reference point in a direction parallel to the workbench plane by a predetermined length L1, for example, 500 mm; then subtract the length L2 measured by the wire sensor 1 from the length L1, and take the value obtained after subtraction as the distance from the wire measurement device reference point to the initial position of the wire sensor 1, called the reference distance; establish a measurement coordinate system on the wire measurement device reference point, record the force direction of the multi-axis force sensor 4 corresponding to the length L1 of the wire pulled out in the wire measurement device, and determine the contact point of the wire pulled out from the first pulley 8-1 with the second pulley 8-2 according to the wire measurement device reference point and the force direction of the multi-axis force sensor 4, which is referred to as the second entry point;

[0048] The equation for determining the second entry point in step 1 is specifically:

[0049]

[0050] Where P is the second entry point, D is the intersection of the force direction of the wire pulled out by a predetermined length on the wire measurement device in a direction parallel to the plane with the center of the second pulley, and G is the reference point.

[0051] The geometric relationship is shown in Figure 8 It can be seen from Figure 8 that the reference point is G, F is the force direction of the multi-axis force sensor 4, the intersection of the force direction and the wire is D, and the distance between DG and PD is equal, thereby determining the position of P, which is the second entry point. It should be noted that the reference point is the point where the end of the wire in the wire measurement device contacts the second pulley 8-2 in the initial state;

[0052] Step 2: Connect the end of the wire of the wire measurement device to the end of the target object to be calibrated;

[0053] Step 3: Control the target object to be calibrated to move to a plurality of teaching points in turn, obtain the position and joint parameter information of a plurality of teaching points of the target object to be calibrated, and obtain the rope length between the wire measurement device reference point and a plurality of teaching points and the corresponding force direction of the multi-axis force sensor 4;

[0054] Step 4: According to the plurality of force directions obtained in step S3 and the position of the second entry point determined in step 1, determine a plurality of second exit point positions.

[0055] The equation for determining the second exit point position in step 4 is specifically:

[0056]

[0057] Wherein, P is the second entry point, D' is the intersection of the force direction of the second pulley 8-2 and the center of the second pulley when the pull measuring device moves to the teaching point, and G' is the second exit point.

[0058] The geometric relationship is as shown in the figure. Figure 9 As shown in the figure, taking the teaching point at N as an example, the second entry point is P, F is the force direction of the multi-axis force sensor 4, i.e. the force direction of the second pulley 8-2, the intersection of the force direction and the pull is D', the distance between PD' and D'G' is equal, and thus the second exit point position corresponding to the teaching point N is determined as G'. Figure 9

[0059] As shown in the figure, according to the third aspect of the embodiment of the application, a robot distance error calibration method is provided, which is used for a robot as the object to be calibrated, and the specific steps of the method are as follows: Figures 1-9

[0060] Step 1: when the object to be calibrated is a robot, the positions of the second exit points corresponding to the multiple teaching points of the robot are determined according to the method for determining the position of the pull exit point of the pull measuring device;

[0061] Step 2: the distances from the multiple teaching point positions of the robot to the reference point, i.e. the actual distances, are determined according to the multiple teaching point positions of the robot to be calibrated, the multiple rope lengths and the multiple second exit point positions.

[0062] The equation for determining the actual distance in the Step 2 is specifically as follows:

[0063]

[0064] Wherein, S is the rope length from the reference point to the teaching point, and is the arc length from the reference point to the second exit point, R is the radius of the second pulley 8-2, and β is the radian of the arc segment , and l m is the actual distance.

[0065] The radian α is obtained from and the radius R of the second pulley 8-2, the radian α' is obtained from and the radius R of the second pulley 8-2, and therefore the radian β of is: β = α' - α.

[0066] The rope length from the reference point to the teaching point is specifically obtained by subtracting the reference distance from the reading of the pull sensor 1 when the pull measuring device pulls the pull to the teaching point.

[0067] ​​​​Step3: According to the joint parameter information displayed by the teach pendant of the robot to be calibrated, a homogeneous transformation matrix equation of the robot end coordinate system to the robot base coordinate system is established, and the nominal position of the robot end coordinate system to the robot base coordinate system, referred to as the nominal position, is calculated.

[0068] Taking a six-degree-of-freedom robot as an example, the homogeneous transformation matrix in step 6 is specifically:

[0069]

[0070] Wherein, represents the coordinate transformation matrix from the i-1 joint to the i joint; Specifically,

[0071]

[0072] Wherein, Sθ i =sinθ i , Cθ i =cosθ i , Sα i-1 =sinα i-1 , Cα i-1 =cosα i-1 , (i=1, 2, …, N) is the joint number, a i-1 is the length of the i-1 joint connecting rod, α i-1 is the torsion angle of the i-1 joint connecting rod, d i is the offset of the i-1 joint connecting rod, θ i is the rotation angle of the i-1 joint.

[0073] Step4: According to the nominal position and the actual distance, the nominal position of the reference point in the robot base coordinate system, referred to as the nominal reference point position, is calculated. It should be noted that according to the nominal position and the actual distance, the nominal position of the reference point in the robot base coordinate system, referred to as the nominal reference point position, is calculated. Specifically: A matrix is obtained according to the nominal position, and b matrix is obtained according to the nominal position and the actual distance; according to A matrix and b matrix, the nominal position of the reference point in the robot base coordinate system is obtained by least square method;

[0074] Step5: According to the nominal reference point position and the nominal position, the distance between the nominal position of the robot end and the nominal reference point position, referred to as the nominal distance, is calculated. Specifically: according to the nominal reference point position and the nominal position, the nominal distance is calculated according to the Euclidean distance;

[0075] Step6: The nominal distance and the actual distance are subtracted to obtain the distance error of the robot end relative to the reference point, referred to as the distance error.

[0076] Step 7: according to the nominal distance, the nominal position and the to-be-calibrated robot joint parameter information, a relationship between the distance error and the robot parameter error is established, which is referred to as a distance error model; the distance error is brought into the distance error model, and through the least square method, the error of the robot joint parameter can be obtained.

[0077] The distance error model in Step 7 is specifically:

[0078]

[0079] Wherein, Δl is the distance error, P t is the nominal position, P base is the nominal reference point position, l t is the nominal distance, ΔX is the robot joint parameter error, and j represents the jth teaching point; J is the Jacobian matrix, and the specific expression form is:

[0080]

[0081] Wherein, a i-1 is the length of the i-1 joint connecting rod, a i-1 is the torsion angle of the i-1 joint connecting rod, d i is the offset of the i-1 joint connecting rod, θ i is the i-1 joint rotation angle, and (i = 1, 2, …, N) is the joint number.

[0082] Embodiment 2: Taking the EFORT industrial robot as an example, the optional specific embodiment of the application is described as follows in combination with specific simulation:

[0083] Step 1: the pull wire measuring device designed in the application is placed on the same workbench plane as the to-be-calibrated robot, the pull wire in the pull wire measuring device is pulled out 500 mm in length along the direction parallel to the workbench plane from the pull wire measuring device reference point; when the pull wire in the pull wire measuring device is pulled out 500 mm, the length L2 measured by the pull wire sensor 1 is subtracted from 500 mm, and the value obtained after subtraction is taken as the distance from the pull wire measuring device reference point to the initial position of the pull wire sensor 1, which is referred to as the reference distance; the measurement coordinate system is established on the pull wire measuring device reference point, and the force direction of the multi-axis force sensor 4 corresponding to the pull wire pulled out 500 mm in length in the pull wire measuring device is recorded, and the contact point of the pull wire pulled out from the first pulley 8-1 and the second pulley 8-2 is determined according to the pull wire measuring device reference point and the force direction of the multi-axis force sensor 4, which is referred to as the second entry point; the geometric relationship is as shown in Figure 4 ;

[0084] Step 2: the end of the pull wire of the pull wire measuring device is connected to the end of the to-be-calibrated robot;

[0085] Step 3: Control the robot to be calibrated to move to 50 teaching points in turn through the teach pendant, obtain 50 end teaching point positions and joint parameter information of the robot to be calibrated, and obtain the rope lengths between the reference point of the pull wire measuring device and the 50 teaching points and the force direction corresponding to the multi-axis force sensor 4;

[0086] Step 4: Determine 50 second out-line point positions according to the plurality of force directions obtained in step S3 and the second in-line point position determined in step 1; the geometric relationship is as shown in Figure 9

[0087] Step 5: Determine the distances from the 50 end positions of the robot to the reference point, referred to as actual distances, according to the 50 end teaching point positions of the robot to be calibrated, the 50 rope lengths, and the 50 second out-line point positions;

[0088] Step 6: According to the joint parameter information displayed by the teach pendant of the robot to be calibrated, establish a homogeneous transformation matrix equation of the robot end coordinate system to the robot base coordinate system, and calculate the nominal position of the robot end coordinate system to the robot base coordinate system, referred to as the nominal position; a total of 50 nominal positions are obtained;

[0089] The kinematic parameters of the industrial robot are shown in Table 1.

[0090] Table 1 Kinematic parameters of industrial robot

[0091]

[0092] In Table 1, lx, ly, and lz represent the length information of the pull wire adapter in three coordinate directions.

[0093] Step 7: Calculate the nominal position of the reference point in the robot base coordinate system according to the nominal position and the actual distance, referred to as the nominal reference point position;

[0094] Step 8: Calculate the distance from the nominal position of the robot end to the nominal reference point position, referred to as the nominal distance, according to the nominal reference point position and the nominal position;

[0095] Step 9: Subtract the nominal distance from the actual distance to obtain the distance error of the robot end relative to the reference point, referred to as the distance error;

[0096] ​Step 10: according to the nominal distance, the nominal position and the information of the joint parameters of the robot to be calibrated, a relationship between the distance error and the error of the joint parameters of the robot is established, which is referred to as a distance error model; the distance error is brought into the distance error model, and the error of the joint parameters of the robot is obtained through the least square method. The error of the joint parameters of the robot is compensated into the joint parameters of the robot, and then the robot to be calibrated is controlled to move to the plurality of teaching points in sequence according to the compensated joint parameters of the robot, and finally the distance error is obtained for verification, and the verification result is shown in Table 2.

[0097] Table 2: comparison results of distance errors after calibration by the traditional calibration method and the method of the present application

[0098] Maximum (mm) Mean (mm) Standard deviation (mm) Conventional calibration method 0.76461 0.13188 0.17486 Method of the invention 0.35468 0.08245 0.10283

[0099] It can be known from the above technical solution that the method of the present application can reduce the measurement error by determining the second exit point and participating in compensation. The simulation results of robot calibration by the method of the present application and the traditional calibration method are shown in Table 2, and it can be known from Table 2 that the maximum value accuracy of the method of the present application is improved by 53.61% compared with the result of the traditional calibration method using the pull line measuring device (i.e. without considering the second exit point), the average value accuracy is improved by 37.48%, and the standard deviation accuracy is improved by 41.19%.

[0100] The specific embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.

Claims

1. A wire measuring device, characterized in that, It includes a pull wire sensor (1), a pull wire guide mechanism (3), and a multi-axis force sensor (4); the pull wire guide mechanism (3) is connected to the pull wire sensor (1), and the multi-axis force sensor (4) is connected to the pull wire guide mechanism (3); The pull wire guiding mechanism (3) includes an online guiding mechanism, a line guiding mechanism, and a offline guiding mechanism; the online guiding mechanism is connected to the offline guiding mechanism through the line guiding mechanism; the online guiding mechanism is used to lead the pull wire on the pull wire sensor (1) to the line guiding mechanism, the line guiding mechanism is used to guide the pull wire led out by the online guiding mechanism to the offline guiding mechanism, and the offline guiding mechanism is used to lead out the pull wire guided by the line guiding mechanism. The online guiding mechanism includes a first upper base (11), a second upper base (12), a first pulley (8-1), and a first shaft (10-1); the second upper base (12) and the first upper base (11) are respectively fixed inside the pull wire sensor (1), and the two ends of the first shaft (10-1) are respectively interference-fitted with the mounting holes on the second upper base (12) and the first upper base (11). The first pulley (8-1) is installed on the first shaft (10-1), and the pull wire on the pull wire sensor (1) is guided to the first entry point of the first pulley (8-1) through the guide post, and then led out to the line guiding mechanism through the first exit point of the first pulley (8-1); The wire guiding mechanism includes a stepped conductor shaft (13), a self-aligning ball bearing (15), and a thrust ring (14). The stepped conductor shaft (13) is interference-fitted with the inner ring of the self-aligning ball bearing (15). The thrust ring (14) is located above the self-aligning ball bearing (15). The self-aligning ball bearing (15) is clamped by the thrust ring (14) and the shoulder of the stepped conductor shaft (13). The outer ring of the self-aligning ball bearing (15) is interference-fitted with the lower housing (6). The wire guiding mechanism guides the pull wire led out from the first exit point of the first pulley (8-1) in the upper guide mechanism to the second entry point of the second pulley (8-2) in the lower guide mechanism. The line guide mechanism includes a first lower base (16), a second lower base (17), a second pulley (8-2), and a second shaft (10-2). The first lower base (16) is connected to the second lower base (17) and clamps the wire step shaft (13) in the line guide mechanism. One end of the second shaft (10-2) is interference-fitted with the mounting hole on the first lower base (16), and the other end of the second shaft (10-2) is clearance-fitted with the mounting hole on the second lower base (17) and extends out of the hole to cooperate with the multi-axis force sensor (4). The second shaft (10-2) is fixedly installed on the first lower base (16) and the second lower base (17), and the second pulley (8-2) is installed on the second shaft (10-2). The pull wire that guides the line guide mechanism to the second entry point of the second pulley (8-2) through the line guide mechanism is led out from the reference point / second exit point of the second pulley (8-2).

2. A method for determining the position of the pull wire exit point in a pull wire measuring device, characterized in that, Includes the following steps: Step 1: Place the wire measuring device described in claim 1 and the target object to be calibrated on the same workbench plane. Pull the wire in the wire measuring device from the reference point of the wire measuring device out a predetermined length L1 in a direction parallel to the workbench plane. Then, subtract the length L1 from the length L2 measured by the wire sensor (1). Use the value obtained after subtraction as the distance from the reference point of the wire measuring device to the initial position of the wire sensor (1), which is called the reference distance. Establish the measurement coordinate system on the reference point of the wire measuring device. Record the force direction of the multi-axis force sensor (4) corresponding to the time when the wire in the wire measuring device is pulled out to a length L1. Determine the contact point between the wire pulled out from the first pulley (8-1) and the second pulley (8-2) based on the reference point of the wire measuring device and the force direction of the multi-axis force sensor (4). The contact point is simply referred to as the second entry point. Step 2: Connect the end of the pull wire of the pull wire measuring device to the end of the target object to be calibrated; Step 3: Control the target object to be calibrated to move sequentially to multiple teaching points, obtain the position and joint parameter information of the multiple teaching points of the target object to be calibrated, obtain the rope length between the reference point of the string measuring device and the multiple teaching points, and the force direction corresponding to the multi-axis force sensor (4); Step 4: Based on the multiple force directions obtained in step S3 and the position of the second entry point determined in step 1, determine the positions of multiple second exit points.

3. A method for calibrating robot distance error, characterized in that, When the object to be calibrated is a robot, the specific steps of the method are as follows: Step 1: When the object to be calibrated is a robot, determine the positions of multiple second wire exit points corresponding to the robot moving to multiple teaching points in sequence according to the method for determining the position of the wire exit point in the wire measuring device described in claim 2; Step 2: Based on the multiple teaching point positions, multiple rope lengths, and multiple second exit point positions of the robot to be calibrated, determine the distance from the multiple teaching point positions of the robot to the reference point, referred to as the actual distance; Step 3: Based on the joint parameter information displayed by the robot teach pendant to be calibrated, establish the homogeneous transformation matrix equation from the robot end-effector coordinate system to the robot base coordinate system, and calculate the nominal position from the robot end-effector coordinate system to the robot base coordinate system, referred to as the nominal position; Step 4: Calculate the nominal position of the reference point in the robot base coordinate system based on the nominal position and the actual distance, referred to as the nominal reference point position; Step 5: Based on the nominal reference point position and the nominal position, calculate the distance from the nominal position of the robot end effector to the nominal reference point position, referred to as the nominal distance; Step 6: Subtract the nominal distance from the actual distance to obtain the distance error of the robot end relative to the reference point, referred to as the distance error; Step 7: Based on the nominal distance, nominal position, and the joint parameter information of the robot to be calibrated, establish the relationship between the distance error and the robot parameter error, referred to as the distance error model; substitute the distance error into the distance error model, and obtain the error of the robot joint parameters through the least squares method.

Images