WO2023214625A1 - Dispositif et procédé d'étalonnage d'un robot articulé en utilisant des contraintes sur un effecteur terminal - Google Patents

Dispositif et procédé d'étalonnage d'un robot articulé en utilisant des contraintes sur un effecteur terminal Download PDF

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Publication number
WO2023214625A1
WO2023214625A1 PCT/KR2022/014680 KR2022014680W WO2023214625A1 WO 2023214625 A1 WO2023214625 A1 WO 2023214625A1 KR 2022014680 W KR2022014680 W KR 2022014680W WO 2023214625 A1 WO2023214625 A1 WO 2023214625A1
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WIPO (PCT)
Prior art keywords
socket
absolute
ball
articulated robot
relative
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PCT/KR2022/014680
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English (en)
Korean (ko)
Inventor
이승원
김영욱
황정훈
김동엽
김근환
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한국전자기술연구원
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Publication of WO2023214625A1 publication Critical patent/WO2023214625A1/fr

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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
    • B25J9/1679—Programme controls characterised by the tasks executed
    • B25J9/1692—Calibration of manipulator
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/06—Programme-controlled manipulators characterised by multi-articulated arms
    • 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
    • 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
    • B25J9/1628—Programme controls characterised by the control loop
    • B25J9/1633—Programme controls characterised by the control loop compliant, force, torque control, e.g. combined with position control
    • 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
    • B25J9/1628—Programme controls characterised by the control loop
    • B25J9/1653—Programme controls characterised by the control loop parameters identification, estimation, stiffness, accuracy, error analysis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1656—Programme controls characterised by programming, planning systems for manipulators
    • B25J9/1664—Programme controls characterised by programming, planning systems for manipulators characterised by motion, path, trajectory planning

Definitions

  • the present invention relates to a calibration device and method for a robot, and more specifically, to a device and method for calibrating an articulated robot using constraints of an end effector that performs calibration to improve the work precision of the articulated robot.
  • the model parameters of articulated robots installed at industrial sites may vary due to aging, replacement of parts, repetitive work, etc. Accordingly, periodic calibration must be performed to ensure the work accuracy of the articulated robot.
  • the measurement method for calibration is a method of measuring the position of the end effector using an external measurement sensor such as a laser tracker or camera, and a method of measuring the joint angle of an articulated robot using constraint conditions. There is a way.
  • the laser tracker tracks a reflector attached to the end effector and measures the position of the end effector with high resolution. Therefore, it is widely used in industry to ensure high work accuracy of articulated robots.
  • laser trackers are expensive equipment costing over hundreds of millions of won, and the measurement system is bulky and the installation and measurement process is complicated, making it difficult to use in the field.
  • the calibration method using a camera is simple to construct, but the measurement error is generally relatively large compared to the required work accuracy, making accurate estimation of model parameters difficult.
  • the calibration method using constraints is a method of creating a straight path or specific geometric constraints for the end effector using an arbitrary calibration jig and measuring the robot joint angles from the encoder.
  • differences in calibration accuracy occur depending on the shape of the jig, high manufacturing costs may be required to ensure the processing precision of the jig.
  • Absolute position information of the jig with respect to the reference coordinate system is required.
  • tasks such as a separate calibration process to find the jig's coordinate system or installing the jig in an absolute position relative to a previously known reference coordinate system are necessary. Therefore, because the existing constraint conditions are largely dependent on the field conditions where the articulated robot is installed, their application may be limited depending on the field conditions.
  • the purpose of the present invention is to provide a calibration device and method for an articulated robot using constraints of an end effector that can be applied flexibly and quickly without being significantly dependent on the field conditions where the articulated robot is installed.
  • Another object of the present invention is to provide a calibration device and method for an articulated robot using end effector constraints that can minimize installation costs.
  • Another object of the present invention is to provide a calibration device and method for an articulated robot using end-effector constraints with high calibration accuracy.
  • the present invention includes a ball installed on the end effector of an articulated robot; At least one absolute socket fixed at a known position with respect to the reference coordinate system of the articulated robot; And after contacting the ball with the absolute socket, creating various postures for the articulated robot while restraining the contact state between the absolute socket and the ball, calculating a set of joint angles from an encoder installed at the joint, and calculating a set of joint angles for each joint angle.
  • a control unit that calculates model parameters that minimize the position error between the position of the ball calculated by forward kinematics and the position of the absolute socket using a control unit that updates the existing model parameters with the calculated model parameters.
  • a calibration device for a joint robot is provided.
  • the present invention also includes a ball installed on the end effector of an articulated robot; At least one absolute socket fixed at a known position with respect to the reference coordinate system of the articulated robot; At least one relative socket fixed to an arbitrary position within the work area of the articulated robot; And after contacting the ball installed on the end effector of the articulated robot with the absolute and relative socket, an encoder installed on the joint creates various postures of the articulated robot while restraining the state in which the absolute and relative socket and the ball are in contact. Calculate a set of joint angles from this, calculate model parameters that simultaneously minimize the position error and relative position error calculated by forward kinematics using each joint angle, and replace the existing model parameters with the calculated model parameters.
  • a calibration device for an articulated robot including a control unit for updating is provided.
  • the joint angle set includes an absolute joint angle set calculated when the ball is in contact with the absolute socket, and a relative joint angle set calculated when the ball is in contact with the relative socket.
  • the position error is calculated as the difference between the absolute position of the ball and the absolute socket using regular kinematics using the absolute joint angle set.
  • the relative position error is calculated as the difference between the positions of the ball calculated by forward kinematics using the relative joint angle set.
  • the absolute socket and the relative socket each have a curved groove having a curvature corresponding to the ball formed on the upper surface so that the ball can rotate while being inserted and contacted.
  • the ball may be inserted into the curved groove and attached to the absolute socket and the relative socket by magnetic force.
  • the control unit may contact the ball to the absolute socket or relative socket through direct teaching or programming in torque control mode.
  • the known position of the reference coordinate system of the articulated robot is at least one of the robot body and the base jig on which the robot body is installed.
  • model parameters can be estimated using the nonlinear least squares method using Equation 1 below as the cost function.
  • model parameters can be estimated using the nonlinear least squares method using Equation 2 below as the cost function.
  • control unit can calculate optimal model parameters using Equation 3 below.
  • the present invention also includes the steps of fixing the absolute socket at a known position with respect to the reference coordinate system of the articulated robot; contacting the absolute socket with a ball installed on an end effector of the articulated robot; Calculating a set of joint angles from an encoder installed at a joint by creating various postures of the articulated robot while restraining the contact state between the absolute socket and the ball; Calculating model parameters that minimize the position error between the position of the ball calculated by forward kinematics and the absolute position of the absolute socket using each joint angle; and updating existing model parameters with the calculated model parameters.
  • a calibration method for an articulated robot including a step is provided.
  • the present invention includes the steps of fixing the absolute socket at a known position with respect to the reference coordinate system of the articulated robot, and fixing the relative socket at an arbitrary position within the work area of the articulated robot; contacting the absolute and relative sockets with a ball installed on an end effector of the articulated robot; Calculating a set of joint angles from an encoder installed at a joint by creating various postures of the articulated robot while restraining the contact state between the absolute and relative sockets and the ball; Calculating model parameters that simultaneously minimize the position error and relative position error calculated by forward kinematics using each joint angle; and performing calibration of the articulated robot using the calculated model parameters.
  • the relative position error is the first term part (in the absolute value) of Equation 2
  • the position error is the second term part (in the absolute value) of Equation 2.
  • the coordinate system of the jig is separately established to create constraint conditions for the existing end effector.
  • Tasks such as a separate calibration process for finding or installing a jig in an absolute position with respect to a previously known reference coordinate system can be omitted.
  • the robot calibration device according to the present invention is not significantly dependent on the field conditions where the articulated robot is installed and can be applied flexibly and quickly.
  • the robot calibration device makes contact with a ball joint mechanism between the ball installed in the end effector and the absolute socket, the joint angle can be obtained from the encoder by creating various postures while the ball is in contact with the absolute socket. Therefore, the absolute number of installed sockets can be minimized.
  • the robot calibration device restrains the state in which the ball and the absolute socket are in contact, creates several postures of the articulated robot, calculates a set of joint angles from the encoder, and uses each joint angle to calculate the forward kinematics ( It is possible to calculate model parameters that minimize the position error between the position of the ball calculated using forward kinematics and the absolute position of the absolute socket, and update the existing model parameters with the calculated model parameters.
  • the absolute socket position exists only in the area near the base jig of the articulated robot, so the arm length, tool length, and joint It may not be possible to obtain a wide configuration in the joint space due to angle limitations, interference, etc. This may reduce the observability of model parameters.
  • the robot calibration device additionally installs a relative socket at a random location within the work area of the articulated robot, and restrains the state in which the ball and the relative socket are in contact with a ball joint mechanism. , create several poses of the articulated robot, calculate a set of joint angles from the encoder, and use each joint angle to calculate the relative position error between the position of the ball calculated by forward kinematics and the relative position of the relative socket. And the robot calibration device according to the present invention can calculate model parameters that simultaneously minimize the position error and relative position error, and update existing model parameters with the calculated model parameters.
  • model parameters calculated based on position error and relative position error are used for calibration of an articulated robot, a wide configuration can be obtained, thereby improving the observability of model parameters. In other words, the accuracy of calibration can be improved.
  • the robot calibration device can calibrate an articulated robot through the installation of a ball, an absolute socket, and a relative socket. Furthermore, the relative socket can be placed anywhere within the robot work area, so it can be installed in a separate location. Since no decision work is required, there is an advantage in minimizing installation costs.
  • Figure 1 is a diagram showing a calibration device for an articulated robot using constraint conditions of an end effector according to a first embodiment of the present invention.
  • Figure 2 is a perspective view showing the ball tool of Figure 1.
  • FIG 3 is a perspective view showing the socket of Figure 1.
  • Figure 4 is a partial cross-sectional view showing a state in which the light of a ball tool is in contact with a socket.
  • Figure 5 is a diagram showing the state in which the robot is transformed into various postures while the ball is in contact with the absolute socket.
  • Figure 6 is a flowchart showing a calibration method of an articulated robot using the constraint conditions of the end effector according to the first embodiment of the present invention.
  • Figures 7 and 8 are diagrams showing a simulation process to confirm the accuracy of calibration according to the method of Figure 5,
  • Figure 7 is a graph showing the position error results before and after calibration for calibration data
  • Figure 8 is a graph showing the position error results before and after calibration for calibration verification data.
  • Figure 9 is a diagram showing a calibration device for an articulated robot using constraint conditions of an end effector according to a second embodiment of the present invention.
  • Figure 10 is a diagram showing a calibration device for an articulated robot using the constraint conditions of the end effector according to the third embodiment of the present invention.
  • Figure 11 is a flowchart showing a calibration method of an articulated robot using constraint conditions of an end effector according to a third embodiment of the present invention.
  • Figures 12 to 16 are diagrams showing simulation results to confirm the accuracy of calibration according to the method of Figure 11,
  • Figure 12 is a photograph showing the articulated robot and calibration device used in the experiment.
  • Figure 13 is a graph showing the position error before and after calibration for calibration measurement data
  • Figure 14 is a graph showing the relative position error before and after calibration for calibration measurement data
  • Figure 15 is a graph showing the position error before and after calibration for calibration verification data
  • Figure 16 is a graph showing the relative position error before and after calibration for calibration verification data.
  • FIGs 17 to 20 are diagrams showing the results of calibration algorithm experiments to confirm the accuracy of calibration according to the method of Figure 11,
  • Figure 18 is a graph showing the position error before and after calibration
  • Figure 18 is a graph showing the relative position error before and after calibration
  • Figure 19 is a graph showing the position error before and after calibration for calibration verification data
  • Figure 20 is a graph showing the relative position error before and after calibration for calibration verification data.
  • Figure 1 is a diagram showing a calibration device for an articulated robot using constraint conditions of an end effector according to a first embodiment of the present invention.
  • Figure 2 is a perspective view showing the ball tool of Figure 1.
  • Figure 3 is a perspective view showing the socket of Figure 1.
  • Figure 4 is a partial cross-sectional view showing a state in which the light of a ball tool is in contact with a socket.
  • Figure 5 is a diagram showing the state in which the robot is transformed into various postures while the ball is in contact with the absolute socket.
  • the calibration device 200 is a device that performs calibration of the articulated robot 100 using the constraint conditions of the end effector 30.
  • the calibration device 200 includes a ball 43, an absolute socket 50, and a control unit 90.
  • the ball 43 is installed in the end effector 30 of the articulated robot 100.
  • At least one of the absolute sockets 50 is fixed at a known position with respect to the reference coordinate system of the articulated robot 100.
  • the control unit 90 brings the ball 43 into contact with the absolute socket 50.
  • the control unit 90 creates various postures for the articulated robot 100 while restraining the contact state between the absolute socket 50 and the ball 43 and calculates a set of joint angles from the encoder installed at the joint.
  • the control unit 90 uses each joint angle to calculate model parameters that minimize the position error between the position of the ball 43 calculated through forward kinematics and the position of the absolute socket 50. Then, the control unit 90 updates the existing model parameters with the calculated model parameters.
  • the calibration device 200 may further include a storage unit 70.
  • the articulated robot 100 is installed on the base jig 80.
  • the articulated robot 100 includes a robot body 10 fixedly installed on the base jig 80, a robot arm 20 having multiple joints connected to the robot body 10, and an end of the robot arm 20. It includes an end effector (30) installed in.
  • encoders are installed at each of the plurality of joints included in the robot arm 20. The angle of the joint can be calculated from the encoder signal.
  • the ball 43 is installed in the end effector 30.
  • the ball 43 is installed in the end effector 30 in the form of a ball tool 40.
  • the ball tool 40 includes a tool body 41 and a ball 43. One side of the tool body 41 is installed on the end effector 30, and a ball 43 is installed on the other side.
  • the absolute socket 50 is installed at a known position with respect to the reference coordinate system of the articulated robot 100 and provides absolute position information of the reference coordinate system.
  • the known position with respect to the reference coordinate system of the articulated robot 100 includes the robot body 10.
  • the installation position of the absolute socket 50 is determined at the design or installation stage of the articulated robot 100.
  • the absolute socket 50 can be installed together when installing the articulated robot 100 on the base jig 80. For example, when the installation position of the absolute socket 50 is in the robot body 10, the installation position of the absolute socket 50 may be determined at the design stage of the articulated robot 100. When the installation position of the absolute socket 50 is in the base jig 80, the installation position of the absolute socket 50 may be determined in the installation step of the articulated robot 100.
  • the calibration device 200 according to the first embodiment is not significantly dependent on field conditions where the articulated robot 100 is installed and can be applied flexibly and quickly.
  • the absolute socket 50 is connected to the ball 43 so that the articulated robot 100 can create various postures while restraining the contact state.
  • a curved groove 51 having a curvature corresponding to the ball 43 is formed on the upper surface so that it can rotate while being inserted and contacted. That is, contact is made between the ball 43 installed on the end effector 30 and the absolute socket 50 using a ball joint mechanism.
  • the number of absolute position measurement points must be sufficiently large to provide more conditional expressions than the number of robot parameters.
  • the absolute socket 50 according to the first embodiment can create various postures while the articulated robot 100 is in contact with the ball 43 and calculate a set of joint angles from this, The number of absolute sockets (50) installed can be reduced compared to before.
  • the center of the ball 43 and the center of the curved groove 51 of the absolute socket 50 must exist within a precise position with respect to each reference coordinate system. There must be a precise position between the center of the ball 43 and the center of the sphere including the curved groove 51 of the absolute socket 50. And the ball 43 and the curved groove 51 must be processed to have precise sphericity. That is, the sphere formed by the ball 43 and the curved groove 51 is formed to have substantially the same size.
  • the curved groove 51 is formed smaller than the hemisphere.
  • a magnetic ball joint mechanism Magnetic Ball
  • the ball 43 is inserted and attached to the curved groove 51 by magnetic force in the absolute socket 50. Joint Mechanism).
  • the storage unit 70 stores a program necessary for controlling the operation of the calibration device 200 and information generated during execution of the program.
  • the storage unit 70 stores an executable program that performs calibration.
  • the execution program calculates the joint angle from the encoder signal and is a model that minimizes the position error between the position of the ball 43 calculated through forward kinematics using the calculated joint angle and the absolute position of the absolute socket 50. Parameters are calculated, and calibration of the articulated robot 100 is performed using the calculated model parameters.
  • control unit 90 is a microprocessor that performs overall control operations of the articulated robot 100.
  • control unit 90 performs overall control operations of the calibration device 200.
  • the control unit 90 can perform calibration of the articulated robot 100 using the ball 43 and the absolute socket 50 as follows. First, the control unit 90 drives the robot arm 20 to bring the ball 43 into contact with the curved groove 51 of the absolute socket 50. Next, the control unit 90 creates several postures for the articulated robot 100 while constraining the contact state between the absolute socket 50 and the ball 43 and calculates a set of joint angles from the encoder installed at the joint. Next, the control unit 90 calculates model parameters that minimize the position error between the position of the ball 43 calculated by forward kinematics and the position of the absolute socket 50 using each joint angle. Then, the control unit 90 updates the existing model parameters with the calculated model parameters.
  • control unit 90 can teach the articulated robot 100 to bring the ball 43 into contact with the absolute socket 50. Teaching can be performed through direct teaching or programming in torque control mode.
  • the control unit 90 may read encoder signals for various postures of the robot arm 20, calculate a set of joint angles for the read encoder signals, and store them in the storage unit 70.
  • the control unit 90 can calculate model parameters by solving an optimization problem such as Equation 1 below. There is. That is, the control unit 90 uses each joint angle to create a model that minimizes the position error between the position (f(qij, ⁇ )) of the ball 43 calculated by regular kinematics and the position (Pi) of the absolute socket 50. Calculate parameters.
  • Equation 1 is the cost function used to estimate model parameters.
  • model parameters can be estimated using the nonlinear least squares method using the value calculated by the cost function according to Equation 1.
  • control unit 90 can improve the work precision of the articulated robot 100 by performing calibration of the articulated robot 100 using the calculated model parameters.
  • FIG. 6 is a flowchart showing a calibration method of the articulated robot 100 using the constraint conditions of the end effector 30 according to the first embodiment of the present invention.
  • step S10 the absolute socket 50 is fixed at a known position with respect to the reference coordinate system of the articulated robot 100.
  • the absolute socket 50 may be installed in advance at the stage of installing the articulated robot 100 in the field.
  • step S20 the control unit 90 contacts the ball 43 installed on the end effector 30 of the articulated robot 100 with the absolute socket 50.
  • step S30 the articulated robot 100 is created in various postures while restraining the contact state between the absolute socket 50 and the ball 43, and the control unit 90 calculates a set of joint angles from the encoder installed at the joint. .
  • step S40 the control unit 90 calculates model parameters that minimize the position error between the position of the ball 43 calculated by forward kinematics and the absolute position of the absolute socket 50 using each joint angle. That is, the model parameters can be calculated using Equation 1.
  • step S50 the control unit 90 updates the existing model parameters with the calculated model parameters.
  • FIGS. 7 and 8 are diagrams showing a simulation process for confirming the accuracy of calibration according to the method of FIG. 5.
  • FIG. 7 is a graph showing the position error results before and after calibration for calibration data
  • FIG. 8 is a calibration verification diagram. This is a graph showing the position error results before and after calibration of the data.
  • the simulation progress is as follows.
  • Robostar RA004 as shown in Figure 9, was used as an articulated robot.
  • a virtual articulated robot 100 is created based on the model parameters.
  • a pose vector set is created with several orientations added for a given point.
  • approximately 80% are used for calibration and approximately 20% are used for verification.
  • the joint angles for the pose vector set are calculated using inverse kinematics. This corresponds to the joint angle read from the encoder in real life situations.
  • Model parameters were estimated by solving the nonlinear least squares method in the direction of minimizing the error (position error) between the given absolute position data and the TCP position of the nominal model corresponding to the joint angle.
  • Table 1 shows the errors before calibration
  • Table 2 shows the errors after calibration.
  • mean represents the average
  • min represents the minimum value
  • max represents the maximum value.
  • Table 3 shows the verification results before calibration
  • Table 4 shows the verification results after calibration
  • the calibration method according to the first embodiment significantly reduces the position error even when verifying an absolute socket. That is, it can be confirmed that the calibration method according to the first embodiment can achieve high work accuracy.
  • the robot calibration device 200 since the robot calibration device 200 according to the first embodiment contacts the ball 43 installed on the end effector 30 and the absolute socket 50 with a ball joint mechanism, the ball 43 ) Since the joint angle can be obtained from the encoder by creating various postures while in contact with the absolute socket 50, the number of installed absolute sockets 50 can be minimized.
  • the calibration device 200 restrains the state in which the ball 43 and the absolute socket 50 are in contact, creates several postures of the robot, calculates a set of joint angles from the encoder, and calculates a set of joint angles from the encoder. Using the angle, model parameters that minimize the position error between the position of the ball 43 calculated by forward kinematics and the absolute position of the absolute socket 50 are calculated, and the articulated robot 100 is calibrated using the calculated model parameters. It can be done.
  • the calibration device 200 according to the first embodiment can perform calibration without disassembling the articulated robot 100.
  • the calibration device 200 performs calibration using the constraint conditions of the ball 43 and the absolute socket 50, and the installation space is not large, so it can be applied even in a narrow work space and is a multi-joint device. It can be applied flexibly and quickly without being greatly dependent on the field conditions where the robot 100 is installed, and can be implemented at low cost compared to existing calibration devices.
  • the calibration device 200 according to the first embodiment can easily perform calibration regardless of the operator's skill level.
  • the calibration device 200 does not use a separate sensor, sensor error can be prevented.
  • the calibration device 200 according to the first embodiment is capable of automating periodic calibration.
  • the absolute socket 50 is installed on the base jig 80 , but it is not limited to this.
  • the absolute socket 50 may be installed on the robot body 10.
  • Figure 9 is a diagram showing the calibration device 300 of the articulated robot 100 using the constraint conditions of the end effector 30 according to the second embodiment of the present invention.
  • the calibration device 300 includes a ball 43, an absolute socket 50, and a control unit 90.
  • the ball 43 is installed in the end effector 30 of the articulated robot 100.
  • At least one of the absolute sockets 50 is fixed at a known position with respect to the reference coordinate system of the articulated robot 100.
  • the control unit 90 brings the ball 43 into contact with the absolute socket 50.
  • the control unit 90 creates various postures for the articulated robot 100 while restraining the contact state between the absolute socket 50 and the ball 43 and calculates a set of joint angles from the encoder installed at the joint.
  • the control unit 90 uses each joint angle to calculate model parameters that minimize the position error between the position of the ball 43 calculated by forward kinematics and the position of the absolute socket 50. Then, the control unit 90 updates the existing model parameters with the calculated model parameters.
  • the calibration device 300 according to the second embodiment may further include a storage unit 70.
  • the absolute socket 50 is installed at a known position with respect to the reference coordinate system of the articulated robot 100 and provides absolute position information of the reference coordinate system.
  • the known position of the reference coordinate system of the articulated robot 100 is the robot body 10.
  • An example in which a plurality of absolute sockets 50 are installed in the robot body 10 is disclosed.
  • the calibration device 300 according to the second embodiment has the same structure as the calibration device 200 according to the first embodiment, except that the absolute socket 50 is installed on the robot body 10.
  • the calibration device 300 according to the second embodiment has substantially the same structure as the calibration device 100 according to the first embodiment, the same effect as the calibration device 100 according to the first embodiment can be expected. there is.
  • the calibration devices 200 and 300 have disclosed an example of performing calibration using the ball 43 and the absolute socket 50, but are not limited to this.
  • at least one relative socket 60 is additionally fixed to an arbitrary position within the work area of the articulated robot 100, so that the ball 43, the absolute socket 50, and the relative socket ( Calibration of the articulated robot 100 can be performed using 60).
  • Figure 10 is a diagram showing the calibration device 400 of the articulated robot 100 using the constraint conditions of the end effector 30 according to the third embodiment of the present invention.
  • the calibration device 400 includes a ball 43, an absolute socket 50, a relative socket 60, and a control unit 90.
  • the ball 43 is installed in the end effector 30 of the articulated robot 100.
  • At least one of the absolute sockets 50 is fixed at a known position with respect to the reference coordinate system of the articulated robot 100.
  • At least one of the relative sockets 60 is fixed to an arbitrary position within the work area of the articulated robot 100.
  • the control unit 90 contacts the ball 43 installed on the end effector 30 of the articulated robot 100 with the absolute and relative sockets 60.
  • the control unit 90 creates several postures for the articulated robot 100 while constraining the contact state between the absolute and relative sockets 60 and the ball 43 and calculates a set of joint angles from encoders installed at the joints.
  • the control unit 90 calculates model parameters that simultaneously minimize the position error and relative position error calculated by forward kinematics using each joint angle. Then, the control unit 90 performs calibration of the articulated robot 100 using the calculated model parameters.
  • the joint angle set includes an absolute joint angle set calculated when the ball 43 is in contact with the absolute socket 50 and a relative joint angle set calculated when the ball 43 is in contact with the relative socket 60. Includes.
  • the position error is calculated as the difference between the position of the ball 43 and the absolute socket 50 using regular kinematics using a set of absolute joint angles.
  • the relative position error is calculated as the difference between each position calculated using the joint angle set. For example, it can be calculated as an error between the position of the ball 43 calculated using the first measured joint angle and the position of the ball 43 calculated using the remaining joint angles.
  • the calibration device 400 according to the third embodiment may further include a storage unit 70.
  • the relative socket 60 has a similar structure to the absolute socket 50, except that the installation location is different. That is, a curved groove 61 having a curvature corresponding to the ball 43 is formed on the upper surface of the mating socket 60 so that the ball 43 can be inserted and contacted.
  • the relative socket 60 improves the observability index for identifying model parameters when performing calibration and provides information to improve location accuracy in a designated work area. Since the relative socket 60 does not require absolute position information about the reference coordinate system, it can be placed at any position within the work area of the articulated robot 100.
  • the relative socket 60 can be directly fixed to any position within the work area of the articulated robot 100, but is fixed using a fixing jig 63 and an installation stand 65. That is, the fixing jig 63 is fixed to the work area of the articulated robot 100. An installation stand 65 having a certain height is installed on the fixing jig 63. And the counterpart socket 60 is installed at the top of the installation stand 65. Of course, the curved groove 61 of the counterpart socket 60 is installed so that it faces upward.
  • the relative socket 60 can be installed at various heights by adjusting the length of the installation stand 65. Since the relative socket 60 is fixed to an arbitrary position within the work area of the articulated robot 100, it is installed in a position farther from the robot body 10 than the absolute socket 50.
  • the ball 43 can be implemented as a magnetic ball joint mechanism in which the ball 43 is inserted and attached to the curved groove 61 by magnetic force to the mating socket 60. there is.
  • the control unit 90 can estimate model parameters using a nonlinear least squares method using Equation 2 below as a cost function.
  • control unit 90 calculates model parameters that simultaneously minimize the position error and the relative position error.
  • Equation 2 the right item corresponds to the position error, and the left item corresponds to the relative position error.
  • the position error is calculated as the difference between the position (f( ⁇ ;qij)) of the ball 43 and the absolute position (Pi) of the absolute socket 50 in forward kinematics using a set of absolute joint angles in Equation 2. .
  • the relative position error is calculated as the difference between each position calculated using the joint angle set.
  • the relative position error is the difference between the reference position (f( ⁇ ;qi)) of the position of the ball 43 calculated by regular kinematics using a set of joint angles corresponding to the relative socket and the position for each of the remaining joint angles. Calculated as the difference.
  • the reason why the calibration device 400 according to the third embodiment performs calibration using the absolute socket 50 and the relative socket 60 is as follows.
  • the position of the absolute socket 50 exists only in the area near the base jig 80 of the robot, It can be effectively used when the work area of the articulated robot 100 is not large.
  • the calibration device 400 additionally installs a relative socket 60 at an arbitrary position within the work area of the articulated robot 100, and the ball 43 and the relative socket 60 are ball joints. After restraining the contact state with a mechanism, several postures of the articulated robot 100 are created, a set of joint angles is calculated from the encoder, and the position of the ball 43 calculated by forward kinematics using each joint angle is calculated. The relative position error between the relative positions of the relative sockets 60 is calculated. And the calibration device 400 according to the third embodiment calculates model parameters that simultaneously minimize the position error and relative position error, and performs calibration of the robot with the calculated model parameters.
  • an absolute socket 50 is required for uniqueness of model parameters.
  • the absolute socket 50 provides absolute position information for uniqueness of model parameters, and the relative socket 60 obtains optimal model parameters in the entire work area or in the area of interest among them and improves the observability index.
  • control unit 90 can increase the accuracy of calibration by repeatedly performing the process of calculating model parameters. At this time, when the control unit 90 repeatedly estimates model parameters using the nonlinear least squares method, it can calculate optimal model parameters using Equation 3 below.
  • FIG. 11 is a flowchart showing a calibration method of the articulated robot 100 using the constraint conditions of the end effector 30 according to the third embodiment of the present invention.
  • step S110 the absolute socket 50 is fixed at a known position with respect to the reference coordinate system of the articulated robot 100, and the relative socket 60 is fixed at a random position within the work area of the articulated robot 100.
  • the absolute socket 50 may be installed in advance at the stage of installing the articulated robot 100 in the field.
  • the relative socket 60 can be fixed within the work area of the articulated robot 100 when performing calibration.
  • step S120 the control unit 90 contacts the ball 43 installed on the end effector 30 of the articulated robot 100 with the absolute and relative sockets 60.
  • step S130 the control unit 90 creates several postures for the articulated robot 100 while restraining the contact state between the absolute and relative sockets 60 and the ball 43 and calculates a set of joint angles from the encoder installed at the joint. do.
  • the joint angle set is calculated while the ball 43 is in contact with one of the absolute socket 50 and the relative socket 60.
  • the absolute joint angle set can be calculated first and then the relative joint angle set can be calculated.
  • the relative joint angle set can be calculated first and then the absolute joint angle set can be calculated.
  • step S140 the control unit 90 calculates model parameters that simultaneously minimize the position error and relative position error calculated by forward kinematics using each joint angle using Equation 2.
  • step S150 the control unit 90 updates the existing model parameters with the calculated model parameters.
  • control unit 90 may repeatedly perform steps S120 to S140 for calculating model parameters, and in this case, optimal model parameters may be calculated using Equation 3.
  • FIGS. 12 to 16 In order to confirm the accuracy of the calibration method according to the third embodiment, simulations were performed as shown in FIGS. 12 to 16.
  • Figure 12 is a photograph showing the articulated robot and calibration device used in the experiment.
  • Figure 13 is a graph showing the position error before and after calibration for calibration measurement data.
  • Figure 14 is a graph showing the relative position error before and after calibration for calibration measurement data.
  • Figure 15 is a graph showing the position error before and after calibration for calibration verification data.
  • Figure 16 is a graph showing the relative position error before and after calibration for the calibration verification data.
  • the simulation progress is as follows.
  • a virtual articulated robot 100 is created based on the model parameters.
  • a set of pose vectors is generated with some orientations added for the given absolute and relative socket points.
  • approximately 80% are used for calibration and approximately 20% are used for verification.
  • the joint angles for the pose vector set are calculated using inverse kinematics. This corresponds to the joint angle read from the encoder in real life situations.
  • the difference between the given absolute socket position data and the TCP position of the nominal model corresponding to the joint angle is defined as the absolute socket error (position error), and the relative socket corresponds to the position calculated based on the first measurement point and the remaining joint angle.
  • the error with the TCP location is defined as a relative socket error (relative position error).
  • Table 5 shows the errors before calibration
  • Table 6 shows the errors after calibration
  • Table 7 shows the verification results before calibration
  • Table 8 shows the verification results after calibration
  • Figures 17 to 20 are diagrams showing the results of a calibration algorithm experiment to confirm the accuracy of calibration according to the method of Figure 11.
  • Figure 18 is a graph showing the position error before and after calibration.
  • Figure 18 is a graph showing the relative position error before and after calibration.
  • Figure 19 is a graph showing the position error before and after calibration for calibration verification data.
  • Figure 20 is a graph showing the relative position error before and after calibration for the calibration verification data.
  • Table 5 shows the errors before calibration
  • Table 6 shows the errors after calibration
  • Table 11 shows the verification results before calibration
  • Table 12 shows the verification results after calibration.
  • the calibration method according to the third embodiment it can be confirmed that the error is significantly reduced in the verification of the absolute socket, relative socket, and both sockets. . In other words, it can be confirmed that the calibration method according to the third embodiment can achieve high work accuracy.
  • Fixing jig 65 Installation stand

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  • Engineering & Computer Science (AREA)
  • Robotics (AREA)
  • Mechanical Engineering (AREA)
  • Manipulator (AREA)
  • Numerical Control (AREA)

Abstract

La présente invention concerne un dispositif et un procédé d'étalonnage d'un robot articulé en utilisant des contraintes sur un effecteur terminal. Dans la présente invention, une douille absolue est fixée à une position connue par rapport au système de coordonnées de référence du robot articulé. Une bille installée sur l'effecteur terminal du robot articulé est amenée en contact avec la douille absolue. Un ensemble d'angles d'articulation est calculé à partir de codeurs installés sur des articulations en amenant le robot articulé à adopter diverses poses tout en contraignant la douille absolue et la bille à être en contact. Chaque angle d'articulation est utilisé pour calculer des paramètres de modèle qui minimisent l'erreur de position entre la position de la bille et la position de la douille absolue calculée par cinématique directe. Ensuite, les paramètres de modèle existants sont mis à jour avec les paramètres de modèle calculés.
PCT/KR2022/014680 2022-05-02 2022-09-29 Dispositif et procédé d'étalonnage d'un robot articulé en utilisant des contraintes sur un effecteur terminal WO2023214625A1 (fr)

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JP2000033586A (ja) * 1998-07-16 2000-02-02 Toshiba Corp ロボットの誤差補正方法及びその装置
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JP2000033586A (ja) * 1998-07-16 2000-02-02 Toshiba Corp ロボットの誤差補正方法及びその装置
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