CN111546330B - Automatic calibration method for coordinate system of chemical part - Google Patents

Automatic calibration method for coordinate system of chemical part Download PDF

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CN111546330B
CN111546330B CN202010295372.7A CN202010295372A CN111546330B CN 111546330 B CN111546330 B CN 111546330B CN 202010295372 A CN202010295372 A CN 202010295372A CN 111546330 B CN111546330 B CN 111546330B
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coordinate system
displacement sensor
calibration
flange
workpiece
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CN111546330A (en
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庄睿
朱力军
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Zhejiang Wahaha Intelligent Robot Co ltd
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Zhejiang Wahaha Intelligent Robot Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1674—Programme controls characterised by safety, monitoring, diagnostic
    • B25J9/1676—Avoiding collision or forbidden zones
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00—Controls for manipulators
    • B25J13/08—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B25J13/088—Controls for manipulators by means of sensing devices, e.g. viewing or touching devices with position, velocity or acceleration sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/10—Programme-controlled manipulators characterised by positioning means for manipulator elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1679—Programme controls characterised by the tasks executed
    • B25J9/1692—Calibration of manipulator

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  • Robotics (AREA)
  • Mechanical Engineering (AREA)
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Abstract

The invention relates to the technical field of robots, in particular to an automatic workpiece coordinate system calibration method, which comprises the following steps: 1) manufacturing a calibration part on the tool, and fixing a displacement sensor in the base coordinate system; 2) enabling the calibration part to contact the displacement sensor for multiple times, and recording contact data of each contact point; 3) determining coordinate values of the contact points under a flange coordinate system according to the contact data; 4) obtaining a coordinate value of a point calibration part in the calibration part under a flange coordinate system and a normal vector of a direction calibration part under the flange coordinate system, and calculating to obtain a rotation matrix from a flange coordinate to a workpiece coordinate system; 5) and obtaining a translation matrix from the flange coordinate to the workpiece coordinate system, and completing the calibration of the workpiece coordinate system. The substantial effects of the invention are as follows: the sampling point is more convenient, the service life of the whole set of calibration device is prolonged, and the calibration efficiency is greatly improved; the calibration method can be conveniently reused on products with different structures.

Description

Automatic calibration method for coordinate system of chemical part
Technical Field
The invention relates to the technical field of robots, in particular to an automatic workpiece coordinate system calibration method.
Background
When the robot technology is applied to automatic processing, the problem of coordinate calibration of a workpiece clamped by the robot needs to be solved. For example, in a grinding and polishing robot system, the end of the robot holds a workpiece and the workpiece is operated to approach an abrasive belt machine to grind the workpiece. Due to errors such as clamping and the like, the conversion relation from the workpiece coordinate system to the robot flange coordinate system needs to be determined through calibration in an actual production environment. One of the existing coordinate calibration methods is a feature point method, firstly, a workpiece coordinate system is established in a simulation environment, a plurality of feature points are selected on a workpiece CAD model, and coordinate values of the feature points in the workpiece coordinate system are obtained; after the workpiece is clamped by the robot, sequentially finding out coordinates of corresponding points under a robot flange coordinate system; and finding out a coordinate system transformation relation between the two point sets, namely completing the calibration of the workpiece coordinate system. The other calibration scheme is a model point cloud matching method, wherein the surface of a workpiece is scanned by line laser to obtain point cloud data of the workpiece in a robot terminal coordinate system; dispersing the workpiece CAD model into point cloud; and matching the scanning point cloud and the model point cloud by an iterative neighboring point method (ICP) to obtain the relation of the coordinate systems of the scanning point cloud and the model point cloud, and completing calibration. However, the above two methods have the following disadvantages: the characteristic point method needs manual point alignment through a demonstrator, has large human error, needs repeated operation for clamping each time, and has low reusability. The feature point position is required to be selected, for example, points such as points which are easy to locate in an actual workpiece are required. And since the point is usually a point, the operation process is prone to damage to the workpiece and the auxiliary tool. In addition, the characteristic point method needs an explicit corresponding relationship, and an ICP neighbor search mode is adopted in patent CN 101097131a, which has requirements on the configuration and quality of the point location, otherwise, the problem of poor stability of the calculation result is likely to occur under the condition that the corresponding relationship of the acquired point location is unknown, which affects the reliability of the whole calibration result. The model point cloud matching method has high precision, but the line laser scanner has higher cost.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the prior method for calibrating the workpiece coordinate system has the technical problems of low precision or high cost. An automated workpiece coordinate system calibration method is provided that significantly improves workpiece calibration accuracy at a lower cost. The method gets rid of the dependence of the coordinate system calibration on the workpiece structure, and the calibration method can be conveniently reused for the condition that the workpiece needs to be frequently replaced.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: an automatic calibration method for a coordinate system of a workpiece is used for calibrating the coordinate system of the workpiece clamped by a robot hand, and comprises the following steps: 1) manufacturing a calibration part on the tool, and fixedly installing a displacement sensor in a base coordinate system of the manipulator, wherein the calibration part comprises a point calibration part and a direction calibration part; 2) the point marking part and the direction marking part on the mobile robot tool are contacted with the displacement sensor for multiple times respectively, and each contact point p is recordedi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000021
And displacement sensor readingsΔziWherein m is the sum of the contact times of the point marking part and the direction marking part with the displacement sensor,
Figure GDA0003130819600000022
is a contact point pi.i∈[1,m]The coordinate values of (a) are transformed from the base coordinate system to a 3 x 3 rotation matrix of the flange coordinate system,
Figure GDA0003130819600000023
is a contact point pi.i∈[1,m]The coordinate values of the flange are 3 multiplied by 1 translation matrixes from the base coordinate system to the flange coordinate system; 3) according to the homogeneous conversion relation
Figure GDA0003130819600000024
And displacement sensor reading Δ ziDetermining coordinate values of point calibration part in flange coordinate systemFP and normal vector of direction marking part in flange coordinate systemFV; 4) the dimensions of the tool and the workpiece and the clamping relation are known, so that the coordinate values of the point calibration part in the workpiece coordinate system are obtainedWP and the normal vector of the direction marking part in the workpiece coordinate systemWV, use ofFV andWv, calculating and obtaining a rotation matrix from the flange coordinate to the workpiece coordinate system by a Rodrigues formulaFRW(ii) a 5) ByFP、WP and rotation matrixFRWObtaining a translation matrix from flange coordinates to a workpiece coordinate systemFPW，FPW＝FP-FRW WP, thereby completing the calibration of the workpiece coordinate system. The robot arm enables the calibration part to move in the opposite direction of the motion vector of the displacement sensor after approaching the displacement sensor, and the sampling point is not directly on the workpiece, so that the consistency of the work fixture clamping the workpiece each time needs to be ensured. Each contact point pi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000025
Determined by the movement of the robot hand when contact is made, recorderThe contact point p can be obtained by the moving process of the manipulatori.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000026
The method is convenient and quick, can quickly calculate and obtain the calibration result of the workpiece coordinate system, and improves the working efficiency. The technical scheme that the calibration part moves in the opposite direction of the motion vector of the displacement sensor after being close to the displacement sensor by combining the displacement sensor and a robot hand is adopted, so that the accuracy of the position of the contact point can be improved, and the situation that the position of the contact point is strained due to impact or pressure during contact, the accuracy of the position of the contact point is reduced, and even elements are damaged is avoided.
Preferably, the point calibration unit is a standard ball fixed on the tool, the standard ball on the tool is contacted with the displacement sensor for multiple times by the mobile robot in step 2), and the calculation formula in step 3) is as follows:
Figure GDA0003130819600000027
substituting into a calculation formula:
(FPi-FPS)T(FPi-FPS)＝R2，i∈(1,n)
obtaining a calculation formula:
Figure GDA0003130819600000031
obtaining the coordinates of the tail end of the displacement sensor under a base coordinate system by adopting a nonlinear least square optimization algorithmBPΔMotion vector of displacement sensor end under base coordinate systemBV, and coordinates of the center of the standard sphere in the flange coordinate systemFPSFurther obtaining the coordinate value of the contact point i in the flange coordinate system each timeFPi,i∈[1,n]Wherein R is the radius of the standard ball, and n is the standard ball contact displacement sensingThe number of the devices is determined, in the step 4), the position of the standard ball center on the tool is known, namely the coordinate of the standard ball center under the workpiece coordinate system is known, and then the translation matrix from the flange coordinate system to the workpiece coordinate system is obtainedFPW. The standard ball contacts the displacement sensor for multiple times to obtain the center position of the standard ball, and the contact times are not less than the number of variables to be solved. And the precision that spherical surface processing technology can realize among the prior art is very high, for direct contact a point, adopts the mode that the sphere center is solved to the contact sphere, can improve the degree of accuracy of point location, and then promotes the degree of accuracy of work piece coordinate system demarcation.
Preferably, in step 2), the robot is moved to make the standard ball on the tool contact the displacement sensor for multiple times, and coordinates of the center of the standard ball in the flange coordinate system are calculated according to the contactFPSAnd calculating coordinates of the center of the standard ball under the flange coordinate system for multiple timesFPSTaking the mean value as the coordinate of the sphere center of the standard sphere in a flange coordinate systemFPS. The accuracy of the coordinate value of the sphere center position can be improved by solving and averaging for multiple times.
Preferably, the direction indicator is three standard balls fixed to the tool and formed by two other standard balls and the point indicator, the three standard balls on the tool are contacted with the displacement sensor by the mobile robot hand in step 2), and in step 3), the direction indicator is calculated by the following formula:
Figure GDA0003130819600000032
and calculating:
Figure GDA0003130819600000033
calculating to obtain a standard ball i, i epsilon [1,3 ] by adopting a nonlinear least square optimization algorithm]Coordinate value of each contact point in flange coordinate systemFPij,i∈[1,3],j∈[1,n]Center of standard ball i in flange coordinate systemCoordinates of lower
Figure GDA0003130819600000034
Coordinates of displacement sensor tail end under base coordinate systemBPΔAnd unit vector of motion vector of displacement sensor tail end under base coordinate systemBV, wherein n is the contact frequency of each standard ball, R is the radius of each standard ball, in the step 4), the positions of the centers of the three standard balls on the tool are known, namely the coordinates of the center of each standard ball under the workpiece coordinate system are known, and then the translation matrix from the flange coordinate system to the workpiece coordinate system is obtainedFPWAnd calculating the following formula:
Figure GDA0003130819600000041
obtaining the normal vector of the standard flat plate under the flange coordinate systemFAnd V. Three points can determine a plane and thus a normal vector. Preferably, the number of contacts is increased more and the final result is averaged. The calibration accuracy can be improved. Compared with a flat plate, the machining precision of the three standard balls is easier to guarantee, the precision of a calibration result is improved, but the contact times are increased, and the efficiency is slightly reduced. The contact times n of each standard ball are not less than the number of variables to be solved, so that the calculation of the calculation formula can be completed, the final value is calculated by multiple contacts and the average value is taken, and the accuracy of the result can be improved.
Preferably, the direction indicator is a standard flat plate fixed to the tool, the mobile robot brings the standard flat plate on the tool into contact with the displacement sensor three times in step 2), and the calculation formula in step 3) is:
Figure GDA0003130819600000042
obtaining the coordinate value of each contact point under the flange coordinate systemFPi,i∈[1,3]Wherein, in the step (A),BPΔis the coordinate of the tail end of the displacement sensor under a base coordinate system,Bv isThe unit vector of the motion vector of the tail end of the displacement sensor under the base coordinate system is calculated by the following formula:
FV＝(FP2-FP1)×(FP3-FP2)
obtaining the normal vector of the standard flat plate under the flange coordinate systemFAnd V. The normal vector of the plane can be determined by the standard flat plate contacting the displacement sensor for three times, so that the calculation of the rotation matrix is realized, and the calibration process is simple and quick.
Preferably, in step 2), the mobile robot makes the standard flat plate on the tool contact the displacement sensor for multiple times, and records each contact point pi.i∈[1,k]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000043
And displacement sensor reading Δ ziAnd k is the number of times that the standard flat plate contacts the displacement sensor, and in the step 3), the calculation formula is as follows:
Figure GDA0003130819600000044
obtaining the coordinate value of each contact point under the flange coordinate systemFPi,i∈[1,k]According to the constraint condition that a plurality of contact points are on the same plane under the flange coordinate system, the plane intercept equationFV·FPiThe calculated formula is obtained as 1:
Figure GDA0003130819600000045
obtaining a normal vector of the standard flat plate under a flange coordinate system by a nonlinear least square optimization algorithmFAnd V. And increasing more contact times, solving the average value of the final result, improving the calibration accuracy of the normal vector of the standard flat plate, but slightly reducing the calibration efficiency.
Preferably, in the teaching in step 2), the motion vector of the displacement sensor tip is made substantially along the normal direction of the surface of the calibration section at the contact point of the tool. The micro deformation of the displacement sensor caused by the calibration part can be reduced, the service life of the displacement sensor is prolonged, and the calibration precision is improved.
Preferably, in step 1), the hardness of the end of the displacement sensor used is lower than the hardness of the tool. The tail end of the displacement sensor is easier to replace, the machining and replacing cost of the tool is higher, the service life of the tool can be prolonged, and the cost is saved.
The substantial effects of the invention are as follows: 1) by adopting the telescopic displacement sensor and the special calibration part, the sampling point does not need to adopt an easily positioned sharp corner point on the workpiece like a characteristic point method, the damage to the workpiece and an auxiliary device in the operation process is avoided, and the service life of the whole set of calibration device is prolonged; 2) according to the invention, the sampling point is taught only once, all point positions are recorded through a program, the mechanical arm is controlled to automatically operate through the program subsequently, data are automatically collected, and a calibration result is automatically fed back after calculation is completed, so that the calibration efficiency is greatly improved; 3) the sampling point is not on the workpiece, the dependence of calibration on the workpiece structure is cancelled, and the calibration method can be conveniently reused on products with different structures for the condition that grinding and polishing products need to be frequently replaced.
Drawings
FIG. 1 is a block diagram illustrating a method for calibrating a coordinate system of an object according to an embodiment.
FIG. 2 is a schematic diagram of an exemplary calibration structure of the workpiece coordinate system.
Wherein: 100. the device comprises a flange, 200, a tool, 300, a workpiece, 401, a standard ball, 402, a standard flat plate, 501, a linear displacement mechanism, 502, a displacement sensor, 600 and an abrasive belt machine.
Detailed Description
The following provides a more detailed description of the present invention, with reference to the accompanying drawings.
The first embodiment is as follows:
an automatic calibration method for coordinate system of workpiece 300 held by robot hand, as shown in fig. 1, includes the following steps:
1) the calibration part is made on the tooling 200, and the displacement sensor 502 is fixedly installed in the base coordinate system of the robot hand, and the calibration part comprises a point calibration part and a direction calibration part. The flange 100 is installed on the robot, the tool 200 is clamped by the flange 100, the workpiece 300 is fixedly installed on the tool 200, and the abrasive belt machine 600 and the displacement sensor 502 are located in the working range of the robot. The point marking portion is a standard ball 401 fixed on the tool 200, and the direction marking portion is a standard flat plate 402 fixed on the tool 200, as shown in fig. 2. The end of the displacement sensor 502 used has a hardness lower than that of the tooling 200.
2) The mobile robot makes the standard ball 401 and the standard flat plate 402 on the tool 200 contact the displacement sensor 502 for multiple times respectively, the motion vector of the tail end of the displacement sensor 502 is basically along the normal direction of the surface of the calibration part at the contact point of the tool 200, and each contact point p is recordedi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000061
And displacement sensor 502 reading Δ ziWhere m is the sum of the number of times of contact of the point and direction designation portions with the displacement sensor 502,
Figure GDA0003130819600000062
is a contact point piThe coordinate values of (a) are transformed from the base coordinate system to a 3 x 3 rotation matrix of the flange coordinate system,
Figure GDA0003130819600000063
is a contact point piFrom the base coordinate system to the flange coordinate system by a 3 x 1 translation matrix.
3) Calculating the following formula:
Figure GDA0003130819600000064
substituting into a calculation formula:
(FPi-FPS)T(FPi-FPS)＝R2，i∈(1,n)
obtaining a calculation formula:
Figure GDA0003130819600000065
obtaining coordinates of the end of the displacement sensor 502 in a base coordinate systemBPΔMotion vector of the end of the displacement sensor 502 in the base coordinate systemBV, and coordinates of the center of the standard sphere 401 in the flange coordinate systemFPSFurther obtaining the coordinate value of the contact point i in the flange coordinate system each timeFPi,i∈[1,n]Where R is the radius of the standard sphere 401, and n is the number of times the standard sphere 401 contacts the displacement sensor 502;
calculating the following formula:
FV＝(FP2-FP1)×(FP3-FP2)
obtaining the normal vector of the standard flat plate 402 in the flange coordinate systemFV。
4) The dimensions and clamping relationship of the tool 200 and the workpiece 300 are known, so that coordinate values of the point calibration part in the workpiece coordinate system are obtainedWP and the normal vector of the direction marking part in the workpiece coordinate systemWV, use ofFV andWv, calculating and obtaining a rotation matrix from the flange coordinate to the workpiece coordinate system by a Rodrigues formulaFRW。
5) ByFP、WP and rotation matrixFRWObtaining a translation matrix from flange coordinates to a workpiece coordinate systemFPW，FPW＝FP-FRW WP, thereby completing the calibration of the workpiece coordinate system. The robot arm makes the calibration part move in the opposite direction of the motion vector of the displacement sensor 502 after approaching the displacement sensor 502, and because the sampling point is not directly on the workpiece 300, the consistency of the fixture 200 when clamping the workpiece 300 each time needs to be ensured. Each contact point pi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000071
The contact point p can be obtained by recording the moving process of the robot hand determined by the moving process of the robot hand when the contact is realizedi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000072
The method is convenient and quick, can quickly calculate and obtain the calibration result of the workpiece coordinate system, and improves the working efficiency. By adopting the technical scheme that the displacement sensor 502 is combined with a robot arm to enable the calibration part to move close to the displacement sensor 502 and then move along the reverse direction of the motion vector of the displacement sensor 502, the accuracy of the position of the contact point can be improved, and the situation that the position of the contact point is strained due to impact or pressure during contact, so that the accuracy of the position of the contact point is reduced, and even elements are damaged is avoided.
This example has the following modified embodiments: in step 2), the number of times that the mobile robot makes the standard ball 401 on the tool 200 contact the displacement sensor 502 exceeds four times, and the coordinates of the center of the standard ball 401 in the flange coordinate system are calculated by taking any four times of contactFPSAnd calculating coordinates of the center of the standard ball 401 in the flange coordinate system for multiple timesFPSTaking the mean value as the coordinate of the center of the standard ball 401 in the flange coordinate systemFPS. The accuracy of the coordinate value of the sphere center position can be improved by solving and averaging for multiple times.
In step 2), the mobile robot makes the standard flat plate 402 on the tool 200 contact the displacement sensor 502 for multiple times, and records each contact point pi.i∈[1,k]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure GDA0003130819600000073
And displacement sensor 502 reading Δ ziK is a standard flat plate402 number of contacts with the displacement sensor 502, step 3), from the calculation:
Figure GDA0003130819600000074
obtaining the coordinate value of each contact point under the flange coordinate systemFPi,i∈[1,k]According to the constraint condition that a plurality of contact points are on the same plane under the flange coordinate system, the plane intercept equationFV·FPiThe calculated formula is obtained as 1:
Figure GDA0003130819600000075
obtaining a normal vector of the standard flat plate 402 under a flange coordinate system by a nonlinear least square optimization algorithmFAnd V. The calibration accuracy of the normal vector of the standard flat plate 402 can be improved, but the calibration efficiency is slightly reduced.
The method for enabling the calibration part on the tool 200 to contact the displacement sensor 502 by the mobile robot hand comprises the following steps: 21) installing a displacement sensor 502 on a linear displacement mechanism 501, enabling the displacement sensor 502 to have a linear displacement stroke, enabling the displacement of the linear displacement mechanism 501 to be detected, enabling the linear displacement mechanism 501 to drive the displacement sensor 502 to move to a stroke starting point, and enabling the coordinate of the stroke starting point under a base coordinate system to be known; 22) moving the robot hand to enable the calibration part on the tool 200 to be located in the linear displacement travel range, wherein the position is determined through teaching; 23) the linear displacement mechanism 501 drives the displacement sensor 502 to move a preset distance from the starting point of the stroke, the preset distance enables the tail end of the displacement sensor 502 to touch the calibration part on the tool 200, and the reading delta z of the displacement sensor 502 is generatedi. The method can avoid the damage of the displacement sensor 502 caused by the fact that the robot causes the tool 200 to impact the displacement sensor 502. The linear displacement mechanism 501 may use an electric push rod, a hydraulic mechanism, a pneumatic cylinder, or a servo electric cylinder.
Example two:
in the embodiment, a direction calibration part different from the first embodiment is adopted, the direction calibration part in the embodiment is three standard balls 401 which are formed by two other standard balls 401 fixed on a tool 200 and a point calibration part, in step 2), a mobile robot enables the three standard balls 401 on the tool 200 to respectively contact a displacement sensor 502 for multiple times, and in step 3), the method comprises the following steps:
Figure GDA0003130819600000081
and calculating:
Figure GDA0003130819600000082
calculating to obtain a standard ball 401i, i belongs to [1,3 ] by adopting a nonlinear least square optimization algorithm]Coordinate value of each contact point in flange coordinate systemFPij,i∈[1,3],j∈[1,n]Coordinates of the center of the standard ball 401i in the flange coordinate system
Figure GDA0003130819600000083
Coordinates of the end of the displacement sensor 502 in the base coordinate systemBPΔAnd unit vector of motion vector of the end of the displacement sensor 502 in the base coordinate systemBV, where n is the number of contacts of each standard ball 401, R is the radius of the standard ball 401, and in step 4), the positions of the centers of the three standard balls 401 on the tool 200 are known, that is, the coordinates of the center of the standard ball 401 in the workpiece coordinate system are known, so as to obtain the translation matrix from the flange coordinate system to the workpiece coordinate systemFPWAnd calculating the following formula:
Figure GDA0003130819600000084
obtaining the normal vector of the standard flat plate 402 in the flange coordinate systemFAnd V. Three points can define a plane and thus a normal vector, the addition of three reference spheres 401The work precision is easier to guarantee. The rest steps are the same as the first embodiment. Compared with the first embodiment, the calibration result obtained by the present embodiment has higher accuracy, but the number of times of contact is increased, the calculation process is more complicated, and the calibration efficiency is slightly reduced.
The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.

Claims (8)

1. An automatic calibration method of a coordinate system of a workpiece is used for calibrating the coordinate system of the workpiece clamped by a robot hand and is characterized in that,
the method comprises the following steps:
1) manufacturing a calibration part on the tool, and fixedly installing a displacement sensor in a base coordinate system of the manipulator, wherein the calibration part comprises a point calibration part and a direction calibration part;
2) the mobile robot makes the point marking part and the direction marking part on the tool respectively contact with the displacement sensor for multiple times, and records each contact point pi.i∈[1,m]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure FDA0003273978490000011
And displacement sensor reading Δ ziWherein m is the sum of the contact times of the point marking part and the direction marking part with the displacement sensor,
Figure FDA0003273978490000012
is a contact point piThe coordinate values of (a) are transformed from the base coordinate system to a 3 x 3 rotation matrix of the flange coordinate system,
Figure FDA0003273978490000013
is a contact point piThe coordinate values of the flange are 3 multiplied by 1 translation matrixes from the base coordinate system to the flange coordinate system;
3) according to the homogeneous conversion relation
Figure FDA0003273978490000014
And displacement sensor reading Δ ziDetermining coordinate values of point calibration part in flange coordinate systemFP and normal vector of direction marking part in flange coordinate systemFV；
4) The dimensions of the tool and the workpiece and the clamping relation are known, so that the coordinate values of the point calibration part in the workpiece coordinate system are obtainedWP and the normal vector of the direction marking part in the workpiece coordinate systemWV, use ofFV andWv, calculating and obtaining a rotation matrix from the flange coordinate to the workpiece coordinate system by a Rodrigues formulaFRW；
5) ByFP、WP and rotation matrixFRWObtaining a translation matrix from flange coordinates to a workpiece coordinate systemFPW，FPW＝FP-FRW WP, thereby completing the calibration of the workpiece coordinate system.
2. The automated part coordinate system calibration method according to claim 1,
the point mark portion is for fixing the standard ball on the frock, and in step 2), the standard ball that mobile robot made on the frock contacts displacement sensor many times, and in step 3), by the formula of calculating:
Figure FDA0003273978490000015
substituting into a calculation formula:
(FPi-FPS)T(FPi-FPS)＝R2，i∈(1,n)
obtaining a calculation formula:
Figure FDA0003273978490000016
obtaining the coordinates of the tail end of the displacement sensor under a base coordinate system by adopting a nonlinear least square optimization algorithmBPΔMotion vector of displacement sensor end under base coordinate systemBV, and coordinates of the center of the standard sphere in the flange coordinate systemFPSFurther obtaining the coordinate value of the contact point i in the flange coordinate system each timeFPi,i∈[1,n]Wherein R is the radius of the standard ball, n is the number of times the standard ball contacts the displacement sensor, and in the step 4), the position of the center of the standard ball on the tool is known, namely the coordinate of the center of the standard ball under the workpiece coordinate system is known, so that the translation matrix from the flange coordinate system to the workpiece coordinate system is obtainedFPW。
3. The automated part coordinate system calibration method according to claim 2,
in step 2), the robot is moved to enable the standard ball on the tool to contact the displacement sensor for multiple times, and the coordinates of the center of the standard ball under the flange coordinate system are calculated according to the contactFPSAnd calculating coordinates of the center of the standard ball under the flange coordinate system for multiple timesFPSTaking the mean value as the coordinate of the sphere center of the standard sphere in a flange coordinate systemFPS。
4. The automated part coordinate system calibration method according to claim 2 or 3,
the direction mark portion is for fixing the standard flat board on the frock, and in step 2), the mobile robot hand makes the standard flat board on the frock contact displacement sensor for the cubic in step 3), by the formula of calculating:
Figure FDA0003273978490000021
obtaining the coordinate value of each contact point under the flange coordinate systemFPi,i∈[1,3]Wherein, in the step (A),BPΔfor the displacement sensor ending at the baseThe coordinates under the coordinate system are set as,Bv is a unit vector of a motion vector of the tail end of the displacement sensor under a base coordinate system, and is calculated by the following formula:
FV＝(FP2-FP1)×(FP3-FP2)
obtaining the normal vector of the standard flat plate under the flange coordinate systemFV。
5. The automated part coordinate system calibration method according to claim 4,
in the step 2), the mobile robot makes the standard flat plate on the tool contact the displacement sensor for multiple times, and records each contact point pi.i∈[1,k]The coordinate value of the robot is converted from the base coordinate system to the flange coordinate system of the robot in a homogeneous conversion relationship
Figure FDA0003273978490000022
And displacement sensor reading Δ ziAnd k is the number of times that the standard flat plate contacts the displacement sensor, and in the step 3), the calculation formula is as follows:
Figure FDA0003273978490000023
obtaining the coordinate value of each contact point under the flange coordinate systemFPi,i∈[1,k]According to the constraint condition that a plurality of contact points are on the same plane under the flange coordinate system, the plane intercept equationFV·FPiThe calculated formula is obtained as 1:
Figure FDA0003273978490000024
obtaining a normal vector of the standard flat plate under a flange coordinate system by a nonlinear least square optimization algorithmFV。
6. The automated part coordinate system calibration method according to claim 1 or 2,
in step 2), during teaching, the motion vector of the tail end of the displacement sensor is basically along the normal direction of the surface of the calibration part at the contact point of the tool.
7. The automated part coordinate system calibration method according to claim 1 or 2,
in the step 1), the hardness of the tail end of the used displacement sensor is lower than that of the tool.
8. The automated part coordinate system calibration method according to claim 1 or 2,
in step 2), the method for moving the robot hand to enable the calibration part on the tool to contact the displacement sensor comprises the following steps:
21) installing a displacement sensor on a linear displacement mechanism to enable the displacement sensor to have a linear displacement stroke, wherein the displacement of the linear displacement mechanism can be detected, the linear displacement mechanism drives the displacement sensor to move to a stroke starting point, and the coordinate of the stroke starting point under a base coordinate system is known;
22) moving the robot hand to enable the calibration part on the tool to be located in the range of the linear displacement stroke, and determining the calibration part on the tool through teaching;
23) the linear displacement mechanism drives the displacement sensor to move a preset distance from the stroke starting point, the preset distance enables the tail end of the displacement sensor to touch a calibration part on the tool, and the displacement sensor reading delta z is generatedi。
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