JP2013010149A - Method of detecting inter-axis offset of six-axis robot - Google Patents

Abstract

In a six-axis robot, a deviation amount of an offset between axes is measured and corrected.
A light emitting diode is provided on a flange at the tip of a robot arm, and a hand is moved to a plurality of movement target positions on an X (Xb) axis of robot coordinates. At this time, the position of the light emitting diode is measured by a three-dimensional measuring device, and the inter-axis offset amount F is detected based on the position of the light emitting diode when the hand is correctly moved to the movement target position and the actual movement position. The DH parameter is corrected by the offset amount F between the axes.
[Selection] Figure 16

Description

  The present invention relates to a method for detecting an offset between axes of a six-axis robot that detects and corrects an offset between a first rotary joint having rotational axes in directions orthogonal to each other and second, third, and fifth rotary joints.

  When the 6-axis robot is given position data represented by fixed three-dimensional Cartesian coordinates, the 6-axis robot converts the position data into rotational joint angle data and moves the hand to the position indicated by the position data. It is configured. In this case, the link (arm) length, the angle between the rotation joint and the rotation axis of the next rotation joint (hereinafter referred to as the torsion angle), the link origin position and the motor origin due to machining errors or assembly errors of the robot components. If there is an error in the relationship with the position (hereinafter referred to as the motor origin position), or if the drive system bends (hereinafter simply referred to as bend) due to the load torque acting on the drive system of each rotary joint, the position of the hand And the posture is displaced, and the absolute position accuracy is lowered.

  In order to improve the absolute position accuracy, various methods for correcting the rotation angle of the rotary joint in consideration of the above-described error and deflection have been considered so far. For example, Non-Patent Document 1 discloses a method of detecting an error regarding a link length and a twist angle and correcting the error. Patent Documents 1 to 4 disclose error detection and correction methods for the motor origin position. Regarding the deflection of the drive system, the load torque acting on the motor of each rotary joint is calculated from the mass of each link and the posture of each link, and further, the torsional deformation of the drive system is calculated from this load torque and the spring constant of the drive system. There is known a method of correcting the deflection of the drive system by obtaining an angle, obtaining a deflection angle of each link from the twist deformation angle, and obtaining a motor rotation angle that reduces the deflection angle of each link.

Japanese Patent Laid-Open No. 2003-220587 JP 2009-274186 A JP 2009-274187 A JP 2009-274188 A

Issued by the Japan Robot Industry Association Commissioned by the Ministry of International Trade and Industry, Institute of Industrial Science and Technology, 1997 Survey and research on standardization of intelligent robots for plants Result report Page 52 4.3.2.3 Paired-even identification method

  The inventor obtained the link length error, the torsion angle error, the motor origin position error, the deflection of the drive system using the above method for the 6-axis robot, and after correcting the rotation angle of each rotary joint from the results, An experiment was conducted to determine whether the hand moves to the position indicated in the position data. However, the result of this experiment did not satisfy the absolute position accuracy originally planned by the inventor.

  The present invention has been made in view of the above circumstances, and the object of the present invention is still satisfactory even when the above-described link length error, torsion angle error, motor origin position error, and drive system deflection are corrected in a 6-axis robot. It is an object to further improve the absolute position accuracy of the robot by estimating a factor that could not obtain the absolute position accuracy and providing a method for measuring an error amount due to the estimated factor.

  The present inventor has factors that cause position errors other than link length error, torsion angle error, motor origin position error, and drive system deflection as the reason for the lack of absolute position accuracy, and this is the offset between axes. I guessed it.

Here, when the positions of the second, third, and fifth rotary joints after assembly are shifted from the normal positions in the direction of the rotation center line, this shift is referred to as an inter-axis offset.
That is, if the second, third, and fifth rotary joints deviate from their normal positions due to processing errors and assembly errors of the robot component parts, the coordinates of the second, third, and fifth links are designed. And the rotation axis of each of the second, third, and fifth rotary joints will shift, and as a result, the robot hand moves from the target position specified by the position on the robot coordinates. It will shift by the offset.
Therefore, if the offset between axes is measured and corrected, the absolute position accuracy can be further increased. However, conventionally, no proposal has been made to measure the offset between the axes considering the relationship between the offset between the axes and the absolute position accuracy.

The method of offset between axes according to the present invention is as follows.
(Claim 1)
In the invention of claim 1, first, a measurement point that operates integrally with the sixth link is provided at a position away from the rotation center line of the sixth link, and an appropriate rotation position of the first link is set to the initial position of the first link. The rotational position of the sixth link at the initial rotational position of the first link is defined as the initial rotational position of the sixth link. The rotation center line of the rotation axis of the fifth rotation joint is parallel to the rotation center lines of the rotation axes of the second and third rotation joints, and the rotation center line of the rotation axis of the sixth rotation joint is the first rotation joint. The first link is rotated to three or more arbitrary rotation positions different from each other while maintaining a state parallel to the rotation center line of the rotation axis.

  At each rotational position of the first link, the sixth link is the first when the first link is rotated from the initial rotational position of the sixth link to the current rotational position. The position of the measurement point is measured by a three-dimensional measuring means in a state of being rotated by a rotation angle from the initial rotation position of the first link to the current rotation position in the rotation direction opposite to the rotation direction of the link. The center position of a circle that passes through these three or more positions and the normal of the plane that includes these three or more positions are obtained from the three or more positions of the point, the center of the obtained circle is the origin, the origin A straight line parallel to the normal passing through Z axis, Z axis passing through the origin and perpendicular to the Z axis, X axis passing through the origin, and a straight line perpendicular to both the Z and X axes as Y axis Define the reference coordinates.

  Next, an arbitrary plurality of positions on an arbitrary plane including the rotation center line of the rotation axis of the first rotation joint extending from the rotation center line of the rotation axis of the first rotation joint are determined as the movement target positions. When the hand is moved to each of the movement target positions on the plane, the first to sixth rotation drive systems including the rotation axes of the first to sixth rotation joints are used. Origin position error of the motor driving each of the six links, deflection of the first to sixth rotation drive systems, length error of each of the first to sixth links, and the rotation axis of the rotation joint and the next rotation joint Correction processing is performed so that a hand position error does not occur due to an angle error.

  Then, by rotating the rotation shafts of at least two of the second, third, and fifth rotation joints, the rotation center line of the rotation shaft of the fifth rotation joint becomes the second rotation joint and the third rotation joint. In the state where the rotation center line of the rotation axis of the sixth rotation joint is parallel to the rotation center line of the rotation axis of the first rotation joint and the target position reaching posture is maintained. When the first link is rotated from the initial rotation position of the first link to the measurement position at each movement target position, the sixth link is moved from the initial rotation position of the sixth link to the measurement position. In a state opposite to the rotation direction of the first link by a rotation angle from the initial rotation position of the first link to the measurement position, the position of the measurement point is measured by the three-dimensional measurement means, and this is measured. Measurement point position for offset calculation And, coordinate transformation of the measurement point position for calculating the offset position on the reference coordinates.

Thereafter, the XY coordinate value on the reference coordinate of each offset calculation measurement point position is obtained, and the XY coordinate value of the obtained offset calculation measurement point position is plotted on the XY plane of the reference coordinate to connect the plotted points. A line segment is defined as a measurement-dependent line segment, and the length of a perpendicular drawn from the origin of the reference coordinates is calculated as a shift amount on a straight line obtained by extending the measurement-dependent line segment. The total offset amount between axes.
The absolute position accuracy can be further improved by correcting, for example, the DH parameter based on the offset amount between the axes obtained as described above.

(Claim 2)
According to a second aspect of the present invention, in the first aspect, an arbitrary plurality of positions on an arbitrary plane extending from the rotation center line of the rotation axis of the first rotary joint are determined as movement target positions, and the movement targets on the one plane are determined. The movement of the hand to each position is performed on two planes extending in opposite directions from the rotation center line of the rotation axis of the first rotary joint, and the movement of the hand from one plane to the other plane is performed. The shift is performed by inverting the robot arm by rotating the rotation shafts of at least two of the second, third, and fifth rotary joints with the first link fixed.

The measurement dependence line segment that connects the positions of the measurement points when moving the hand to one of the multiple planes on one plane and the robot arm is inverted to move the hand to any multiple positions on the other plane The measurement-dependent line segment formed by connecting the positions of the measurement points when the is moved is a saddle located on a straight line. When not positioned on a straight line, a method for setting reference coordinates, a motor origin position error, deflection of each of the first to sixth rotary drive systems, or a length error of each of the first to sixth links Therefore, it is considered that there was an error in the technique for preventing the position error of the hand from occurring.
For this reason, according to the invention of claim 2, it is possible to confirm whether or not the offset amount between the axes is correctly obtained.

(Claim 3)
In the invention of claim 3, when the hand is moved to any of a plurality of movement target positions in place of the operation until the amount of offset between the axes is obtained after the reference coordinates are determined in claim 1 or 2. , Origin position errors of the motors driving the first to sixth links via the first to sixth rotary drive systems including the rotation axes of the first to sixth rotary joints, first to sixth, Correction processing is performed so that the position error of the hand due to the bending of each rotation drive system, the length error of each of the first to sixth links, and the angle error between the rotation joint and the rotation axis of the next rotation joint does not occur. The rotation center line of the rotation shaft of the fifth rotation joint is kept parallel to the rotation center lines of the rotation shafts of the second and third rotation joints, and the first rotation joint and the second rotation joint By rotating the rotation shafts of at least two of the three or five rotary joints, The rotation center line of the rotation axis of the sixth rotation joint is moved parallel to the rotation center line of the rotation axis of the first rotation joint, and is moved to a plurality of arbitrarily determined movement target positions. At the position, the sixth link is reverse to the rotation direction of the first link when the first link is rotated from the initial rotation position of the first link to the current rotation position from the initial rotation position of the sixth link. In the rotation direction, the position of the measurement point is measured by the three-dimensional measuring means in the state of being rotated by the rotation angle from the initial rotation position of the first link to the current rotation position, and the position of the fixed point measured at each movement target position XY coordinate values on the reference coordinates of a plurality of offset calculation measurement point positions by converting the offset calculation measurement point positions at the respective movement target positions to positions on the reference coordinates. Further, the XY coordinate value of each movement target position is converted into the XY coordinate value of the reference coordinate to obtain a movement target position on the reference coordinate. For each movement target position, the movement target position of the measurement point on the XY plane of the reference coordinate XY coordinate values and XY coordinate values of offset calculation measurement point positions are plotted, the length of the line segment from the origin of the reference coordinates to the movement target position on the XY plane is set as the target position radius, and the XY plane The length of a perpendicular line drawn from the above-mentioned offset calculation measurement point position to the straight line passing through the origin of the reference coordinates and the movement target position on the XY plane is used as an offset error component, and for each movement target position, the target position radius and the offset The relationship with the error component is plotted on a graph in which the moving target position radius is taken on one of the two orthogonal axes and the offset error component is taken on the other axis, and the plotted points are directly connected. When the line is an error straight line, the length of the perpendicular line drawn from the origin of the graph to the error straight line is obtained as a deviation amount, and the obtained deviation amount is calculated as the total inter-axis offset amount of the second, third, and fifth rotary joints. To do.
Even if it does in this way, the effect similar to Claim 1 can be acquired.

(Claim 4)
A fourth aspect of the present invention provides the robot arm according to the third aspect, wherein the movement of the hand to any of a plurality of movement target positions of the reference coordinates includes a forward bending posture of the robot arm and a backward bending posture in which the robot arm is reversed from the forward bending posture. It is characterized by performing both.

  By doing so, when plotting the relationship between the target position radius and the offset error component for each moving target position on the graph, the plotted points are positioned in a straight line between the forward bending position and the backward bending position. Whether or not the inter-axis offset is correctly obtained can be confirmed in the same manner as in the second aspect.

The perspective view of the robot apparatus which shows the 1st Embodiment of this invention Sectional view showing the outline of the rotary joint Side view of the robot with the rotation axis of each rotary joint set to the origin position Perspective view showing coordinates set for each link Table showing DH parameters Table showing specific values of DH parameters Block diagram showing the controller Perspective view of flange part Process diagram showing the procedure of the present invention It is a figure for demonstrating the setting of a reference coordinate, (a) is a perspective view, (b) is a top view. Explanatory drawing of deflection of rotary drive system Perspective view showing the movement target position Side view showing the forward bending state of the robot Side view showing back-bending state of robot The figure which shows the simultaneous conversion matrix for converting a camera coordinate into a reference coordinate Explanatory drawing for obtaining the offset amount between axes The figure which shows the 2nd Embodiment of this invention Explanatory drawing for obtaining the offset amount between axes

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a 6-axis vertical multi-rotation joint type robot apparatus 1. The robot apparatus 1 includes a 6-axis vertical articulated robot (hereinafter simply referred to as a robot) 2, a control apparatus (robot control means) 3 that controls the operation of the robot 2, and a robot 2 connected to the control apparatus 3. Is provided with a teaching pendant (manual operation means) 4.

  The robot 2 has a shoulder (first link) 7, a lower arm (second link) 8, and a base (base link) 5 fixed to an installation surface, for example, a horizontal floor surface of a factory. The first upper arm (third link) 9, the second upper arm (fourth link) 10, the wrist arm (fifth link) 11, and the flange (sixth link) 12 are rotated in the first to sixth rotations. The joints J1 to J6 (not shown in FIG. 1) are sequentially connected.

  That is, the shoulder 7 is connected to the base 5 by the first rotary joint J1 so as to be pivotable in the horizontal direction around the first axis Lc-1, and the lower arm 8 is connected to the tip of the shoulder 7 by the second rotary joint J2. The first upper arm 9 is supported so as to be pivotable in the vertical (vertical) direction around the two axes Lc-2, and the first upper arm 9 is vertically moved around the third axis Lc-3 by the third rotary joint J3 at the tip of the lower arm 8. The second upper arm 10 is supported so as to be rotatable about the fourth axis Lc-4 by the fourth rotary joint J4 at the distal end portion of the first upper arm 9, and the wrist arm 11 is supported. Is supported at the tip of the second upper arm 10 by a fifth rotary joint J5 so as to be pivotable in the vertical direction about the fifth axis Lc-5, and the flange 12 is supported on the wrist arm 11 by a sixth rotary joint J6. Supports rotation by twisting around the axis Lc-6 It is.

  The outline of the first to sixth rotary joints J1 to J6 is shown in FIG. As shown in FIG. 2, the rotary joints J <b> 1 to J <b> 6 of each of the links 7 to 12 include a rotary shaft 14 that is rotatably supported by a previous-stage link via a bearing 13, and the next-stage link is connected to the rotary shaft 14. They are connected directly or via a joint material. The rotary shaft 14 is rotationally driven by a servo motor 15 as a drive source fixed to the previous-stage link via a speed reducer, for example, a gear speed reducer 16, and the rotation of the rotary shaft 14 causes the next-stage link to turn or twist. It is designed to rotate.

  Here, the first axis Lc-1 to the sixth axis Lc-6 correspond to the rotation center line Lc of the rotary shaft 14 of each of the first to sixth rotary joints J1 to J6. The directivity directions of the first axis Lc-1 to the sixth axis Lc-6 are as follows. That is, the first axis Lc-1 that is the rotation center of the shoulder 7 is orthogonal to the installation surface, and the second axis Lc-2 that is the rotation center of the lower arm 8 is parallel to the direction orthogonal to the first axis Lc-1. That is, assuming that the base 5 is installed on the floor of a factory, for example, the first axis Lc-1 is set to be perpendicular (vertical) to the installation floor and the second axis Lc-2 is set to be horizontal. The third axis Lc-3 that is the rotation center of the first upper arm 9 is parallel or horizontal to the second axis Lc-2, and the fourth axis Lc-4 that is the rotation center of the second upper arm 10. Is parallel to the direction orthogonal to the third axis Lc-3, the fifth axis Lc-5, which is the rotation center of the wrist arm 11, is orthogonal to the fourth axis Lc-4, and the sixth axis Lc, which is the rotation center of the flange 12. -6 is defined in a direction orthogonal to the fifth axis Lc-5.

  When the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, and the servo motor 15 that drives each rotary shaft 14 of the flange 12 are at the origin position, the shoulder 7, lower The arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 are at the origin position. Here, when the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 are all at the origin position, the robot arm 6 is vertical as shown in FIG. The posture is upward (the lower arm 8, the first upper arm 9, the second upper arm 10, and the wrist arm 11 are vertical). Then, each servo motor 15 rotates in the positive (plus) direction and the reverse (minus) direction from the origin position, so that the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, and the wrist arm. 11 and the flange 12 also rotate in the positive (plus) direction and the reverse (minus) direction from the origin position.

  As shown in FIG. 4, three-dimensional coordinates R1 to R6 are defined for the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12, respectively. . The origins O1 to O6 of these coordinates R1 to R6 are the first axis Lc that is the rotation center line of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12. -1 to the sixth axis Lc-6 are determined at predetermined positions, and the Z1 to Z6 axes, which are the Z axes of the coordinates R1 to R6, respectively coincide with the first axis Lc-1 to the sixth axis Lc-6. Yes.

  In addition, among the coordinates R1 to R6, the X1 axis that is the X axis of the coordinate R1 of the shoulder 7 is horizontal, and is a common vertical line (indicated by h line in FIG. 1) of the first axis Lc-1 and the second axis Lc-2. .) And the Y1 axis, which is the Y axis, is horizontal, and is determined in the direction obtained by the cross product of the vectors of the Z1 axis and the Y1 axis (a direction orthogonal to both the Z1 axis and the Y1 axis). It has been. The X2 to X6 axes, which are the X axes of the other coordinates R2 to R6, are obtained by rotating the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 to the origin position. The coordinate R1 is defined in a direction parallel to the X1 axis, and the Y2 to Y6 axes, which are Y axes, are determined in the direction determined by the outer product of the vectors of the Z2 to Z6 axes and the Y2 to Y6 axes. In addition, the plus directions of the X1 to X6 axes, the Y1 to Y6 axes, and the Z1 to Z6 axes are directions indicated by arrows in FIG.

  Coordinates R0 and Rf are also defined on, for example, the tip surface of the flange 12 which is the tip of the base 5 and the robot arm 6. While the coordinates R1 to R6 change in position and orientation with the rotation of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12, the base A coordinate R0 of 5 is immobile and is a robot coordinate. The origin O0 of the robot coordinate R0 is located on the first axis Lc-1 that is the rotation center line of the shoulder 7, and in this embodiment is determined at a position that coincides with the origin O1 of the coordinate R1. Further, the Z0 axis that is the Z axis of the robot coordinate R0 coincides with the first axis Lc-1, and the X0 axis that is the X axis and the Y0 axis that is the Y axis are the shoulder 7 when the shoulder 7 is at the origin position. This coincides with the X1 axis and the Y1 axis of the coordinate R1.

  The coordinate Rf of the front end surface of the flange 12 is a hand coordinate, and the origin Of is a predetermined position on the sixth axis Lc-6, in this embodiment, the intersection of the sixth axis Lc-6 and the front end surface of the flange 12, That is, as shown in FIG. 8, the flange 12 is determined so as to coincide with the center P of the circular tip surface, the Zf axis that is the Z axis coincides with the sixth axis Lc-6, and the Xf axis that is the X axis. The Yf axis which is the Y axis is defined in parallel with the X6 axis and the Y6 axis of the coordinate R6 of the flange 12 (see FIG. 4). The center P of the front end surface of the flange 12 is determined at the hand which is the tip of the robot arm 6, and the origin Of of the hand coordinates Rf coincides with the position of the hand.

  Among the coordinates R0 to R6 and Rf described above, the origins O1 to O6 and Of of the coordinates R1 to R6 and Rf excluding the robot coordinate R0 are one plane including the X1 axis and the Z1 axis of the coordinate R1 in this embodiment. When (vertical Z1X1 plane) is assumed, it is located on this one plane. During the operation of the robot arm 6, the origins O2 to O6 and Of of the coordinates R2 to R6 and Rf move on the Z1X1 plane of the coordinate R1.

  The mutual positional relationship between the coordinates R0 to R6 and Rf defined as described above is indicated by a well-known DH parameter. FIG. 5 summarizes the DH parameters in a table. For example, for the J1 line, the coordinate R1 is translated by a1 in the X1 axis direction, not moved in the Y1 axis direction, and d1 translated in the Z1 axis direction. Then, by rotating the torsion angle −π / 2 around the X1 axis, the coordinate R2 is obtained. For example, for the J6 line, the coordinate R6 is moved in the X6 axis direction and the Y6 axis direction. This shows that the hand coordinates Rf can be obtained by performing d6 translation in the Z6 axis direction. The relationship between the robot coordinate R0 and the coordinate R1 of the shoulder 7 is not shown in FIG. 5 because the coordinate R1 coincides with the robot coordinate R0 when the shoulder 7 is at the origin position. FIG. 6 shows specific numerical examples of a, b, and d.

  As shown in FIG. 7, the control device 3 includes a CPU (control means) 17, a drive circuit (drive means) 18, and a position detection circuit (position detection means) 19. The CPU 17 includes a ROM (storage means) 20 for storing various data such as a robot language and DH parameters for creating a system program and an operation program for the entire robot 2, and a RAM (storage means) for storing the operation program for the robot 2. ) 21 is connected, and the teaching pendant 4 used when performing teaching work or the like is also connected. As shown in FIG. 1, the teaching pendant 4 includes various operation units 4a and a display 4b made of liquid crystal.

  The position detection circuit 19 is connected to a rotary encoder 22 as a rotation sensor coupled to a rotation shaft (not shown) of each servo motor 15. The position detection circuit 19 detects the rotation angles of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, and the flange 12 based on the rotation angle detection information of each rotary encoder 22. Then, the rotation angle detection information is given to the CPU 17.

  Here, the CPU 17 determines the position of the hand on the robot coordinate R0 (the position of the origin Of of the hand coordinate Rf) and the posture (the orientation of the Xf axis, the Yf axis, and the Zf axis of the hand coordinate Rf on the robot coordinate R0). Given the rotation angle of the shoulder 7, lower arm 8, first upper arm 9, second upper arm 10, wrist arm 11, and flange 12 so that the hand takes its position and posture, the Jacobian matrix is used. It is obtained by a well-known calculation method of inverse kinematics.

  Conversely, when the rotation angles of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 are given, the order in which coordinate conversion is used from these rotation angles. The position and posture of the hand on the robot coordinate R0 can be obtained by a well-known calculation method of kinematics. As is well known, the DH parameter indicating the mutual relationship between the coordinates R0 to R6 and Rf is used for the calculation by the inverse kinematics and forward kinematics calculation methods.

  When the CPU 17 obtains the target position on the robot coordinate R0 of the hand from the operation program, the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist from the target position of the hand. A target operation angle of the arm 11 and the flange 12 is calculated, and an operation command based on the target operation angle is given to the drive circuit 18. The drive circuit 18 drives each servo motor 15 based on the given operation command. At this time, the CPU 17 uses the rotation angle detection information of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 given from the position detection circuit 19 as feedback information. The servo motor 15 is feedback controlled.

  By the way, as described above, the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12, the coordinates R1 to R6, and the origins O1 to O6 of the hand coordinates Rf. , Of are present on a vertical plane including the X1 axis and the Z1 axis of the coordinate R1 of the shoulder 7. Therefore, if the robot 2 is assembled with high accuracy, the center P of the tip surface of the flange 12 that is the hand coincides with the origin Of of the designed hand coordinates Rf, and the shoulder 7, the lower arm 8, and the first upper arm By rotating the arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 by the target operation angle, the hand is correctly moved to the target position.

  However, the position of each rotary shaft 14 of the rotary joints J2, J3, and J5 of the lower arm 8, the first upper arm 9, and the wrist arm 11 due to manufacturing errors and assembly errors of the components of the robot 2 is the second axis Lc. -2, the third axis Lc-3, and the fifth axis Lc-5 are displaced in the directing direction and an error (interaxial offset) occurs between the normal position and the actual hand (the center of the tip surface of the flange 12). The position P) is shifted in the horizontal direction from the origin of the designed hand coordinates Rf.

  Then, even if the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12 are rotated by the target operating angle, the actual movement position of the hand is determined as the rotational joint J2. , J3 by the sum of the offsets between the axes 14 (when the fifth axis Lc-5 is vertical), or by the sum of the offsets between the axes 14 of the rotary joints J2, J3, J5 ( When the fifth axis Lc-5 is horizontal), the fifth axis Lc-5 is shifted in the horizontal direction from the target position. Since the rotational axis 14 of the rotary joint J5 is short, the offset between the axes of the rotary joint J5 alone is considered to be small, and the sum of the offsets between the rotary axes 14 of the rotary joints J2 and J3 and the rotary joints J2, J3 and J3. It is considered that there is almost no difference from the sum of the offsets between the axes of the rotary shafts J5.

The method of the present invention estimates the sum of the offsets between the rotary shafts 14 of the rotary joints J2, J3, and J5, corrects the DH parameter by the estimated offset between axes, and sets the actual movement position of the hand to the target position. Try to get as close as possible.
In the method of the present invention, when the teaching pendant 4 is operated to move the hand to a plurality of target positions, the actual movement position of the hand is measured by the three-dimensional measuring instrument (three-dimensional measuring means) 23 shown in FIG. A deviation amount from the target position is obtained, and an offset between the axes is estimated from the deviation amount. In this case, the deviation between the actual movement position of the hand and the target position is caused by factors other than the offset between the axes, that is, the deflection of the rotary drive system of each rotary joint J1 to J6, the origin position error of each servo motor 15, and each link 7 This is also caused by a length error of -12 and a torsional angle error between the rotary shafts 14 of the rotary joints J1 to J6, so that it is necessary to perform correction processing in advance so as not to cause a position error due to these factors.

  The three-dimensional measuring instrument 23 includes, for example, a three-dimensional measuring instrument (for example, Toyo Technica Co., Ltd .; robot calibration ROCAL system) provided with three CCD cameras. Note that the three-dimensional measuring instrument 23 may be a laser tracker or the like. With respect to the three-dimensional measuring instrument 23, a support base 24 is attached to the front end surface of the flange 12 at an arbitrary position away from the center P, as shown in FIG. A light emitting diode 25 is attached. Then, the three-dimensional measuring instrument 23 measures the position of the light emitting diode 25.

  The measurement position of the light emitting diode 25 by the three-dimensional measuring instrument 23 is on a three-dimensional coordinate (hereinafter referred to as camera coordinates) Rc preset in the three-dimensional measuring instrument 23 by a measurement control device (measurement control means) 26 formed of a personal computer. Indicated by the position of. The distance represented by one scale of the camera coordinates Rc is determined to be equal to the distance when the hand moves by a distance corresponding to one scale of the robot coordinates R0. Accordingly, the length of one scale (unit length) of the robot coordinate R0 and the length of one scale (unit length) of the camera coordinates Rc represent the same distance.

  Now, the method of the present invention is performed according to the procedure shown in FIG. First, the position of the robot coordinate R0 on the camera coordinate Rc and the directions of the X0 axis, the Y0 axis, and the Z0 axis of the robot coordinate R0 are unknown. Therefore, in this embodiment, the reference coordinate Rb is set on the camera coordinate Rc as a coordinate to replace the robot coordinate R0 (step S1 in FIG. 9). The operation of the robot arm 6 for setting the reference coordinate Rb is performed using the teaching pendant 4.

  Here, the function of the teaching pendant 4 will be described. The teaching pendant 4 includes a shoulder 7, a lower arm 8, a first upper arm 9, a second upper arm 10, a wrist arm 11, and a servo motor 15 for the flange 12. The shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, and the flange 12 are rotated in desired forward and reverse directions from their respective origin positions by individually rotating by a desired angle. It is configured to be able to rotate by an angle.

In addition, the teaching pendant 4 can designate the rotational position of the shoulder 7, the position and posture of the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, the flange 12, and the hand using robot coordinates R0. When the position and orientation on the robot coordinate R0 are designated by the teaching pendant 4, the CPU 17 of the robot apparatus 1 executes the shoulder 7, the lower arm 8, the first upper arm 9, and the second upper arm. 10. The rotation angle of the wrist arm 11 and the flange 12 is calculated, and each servo motor 15 is driven so as to be the rotation angle. Thereby, the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, the flange 12, and the hand operate so as to take the designated position and posture.
Here, the positions and postures of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11, the flange 12, and the hand are synonymous with the positions and postures of the coordinates R1 to R6 and Rf. It is.

  Furthermore, when it is desired to know the position and posture of the current shoulder 7, lower arm 8, first upper arm 9, second upper arm 10, wrist arm 11, flange 12 and hand, The CPU 17 acquires the rotation angles of the shoulder 7, the lower arm 8, the first upper arm 9, the second upper arm 10, the wrist arm 11 and the flange 12, and from the rotation angles, the shoulder 7, the lower arm 8, and the first The position and posture of the upper arm 9, the second upper arm 10, the wrist arm 11, the flange 12, and the hand can be calculated and displayed on the display 4a of the teaching pendant 4 with the position and posture on the robot coordinate R0. It is also.

  In order to set the reference coordinate Rb on the camera coordinate Rc, first, the initial positions of the shoulder 7 and the flange 12 are set. That is, the operation unit 4a of the teaching pendant 4 is operated, and the lower arm 8 and the first upper arm 9 are rotated from the vertically upward state in FIG. 3 so that the robot arm 6 moves to the front side of the shoulder 7 as shown in FIG. Make a forward-bend posture that falls to the positive side of the X1 axis. Note that the robot arm 6 may be in the backward bending posture of FIG. Then, the shoulder 7 is rotated to an appropriate (arbitrary) position.

  The fifth axis Lc-5, which is the rotation center line of the rotation shaft 14 of the fifth rotation joint J5, is changed to the second axis Lc-2, which is the rotation center line of the rotation shaft 14 of the second and third rotation joints J2, J3. The sixth axis Lc-6, which is parallel to the third axis Lc-3, that is, in a horizontal state, and the rotation center line of the rotation axis 14 of the sixth rotation joint J6 is the rotation center of the first rotation joint J1. It is parallel to the first axis Lc-1, which is a line, that is, a vertical state, for example, downward. Then, the flange 12 is rotated to an appropriate rotation position. The sixth axis Lc-6 may be in a vertically upward state parallel to the first axis Lc-1.

  As described above, when the shoulder 7 is rotated to an appropriate rotational position by operating the teaching pendant 4 and the flange 12 is rotated to an appropriate rotational position, these rotational positions are set to the initial rotational position of the shoulder 7 and the initial position of the flange 12. Determined as rotational position. At this time, the initial rotational position of the flange 12 is a position where the light emitting diode 25 is easily photographed by the three-dimensional measuring instrument 23 regardless of the position of the hand, that is, the position closer to the three-dimensional measuring instrument 23 than the sixth axis Lc-6. It is preferable to set the rotation position as described above.

  After the initial rotational positions of the shoulder 7 and the flange 12 are determined as described above, the fifth axis Lc-5 is parallel to the second axis LC-2 and the third axis Lc-3, and the sixth axis Lc-6. While rotating in parallel with the first axis Lc-1, the shoulder 7 is rotated around the first axis Lc-1 to a plurality of different rotational positions C1, C2,. )reference). At each rotational position, the flange 12 is moved in a direction opposite to the rotational direction of the shoulder 7 when the shoulder 7 is rotated from the initial rotational position to the current rotational position from the initial rotational position of the flange 12. Is rotated by the rotation angle from the initial rotation position to the current rotation position.

  For example, when the robot arm 6 is viewed from the positive side of the Z0 axis of the robot coordinate R0, that is, from the upper side, if the shoulder 7 is rotated to a position rotated 30 ° clockwise from the initial rotation position, the flange 12 is initially rotated. The position is rotated by 30 ° counterclockwise from the position. In this way, by rotating the flange 12 by the same angle in the opposite direction to the rotation direction of the shoulder 7 at each rotation position of the shoulder 7, the light emitting diode 25 changes the robot coordinate R0 as shown in FIG. When translated from the sixth axis Lc-6 and viewed from the plus side of the Z0 axis, it always exists at the same position as the initial position.

  Then, at each rotational position of the shoulder 7, the position of the light emitting diode 25 as the reference coordinate setting measurement point is measured with the three-dimensional measuring instrument 23 in a state where the flange 12 is rotated by the same angle in the direction opposite to the rotational direction of the shoulder 7. Measure by The measurement positions d1, d2,... Dn at three or more different points of the light emitting diode 25 are circular rotations about a vertical axis parallel to the first axis Lc-1 (Z0 axis) as shown in FIG. It exists on the locus E. The measurement control device 26 obtains the rotational center position Ob of the light emitting diode 25 from the plurality of positions d1, d2,... Dn on the rotational locus E of the light emitting diode 25 measured by the three-dimensional measuring instrument 23 by the least square method. A normal Lv of one plane including the plurality of positions d1, d2,. Then, the position Ob of the rotation center is the origin of the reference coordinate Rb, the straight line that passes through the origin Ob and is parallel (in the same direction) to the normal Lv, that is, the vertical axis parallel to the first axis Lc-1 is the reference coordinate Rb. Zb axis (Z axis).

  Further, an arbitrary straight line passing through the origin Ob and orthogonal to the Zb axis, for example, a straight line connecting the position P0 of the light emitting diode 25 and the origin Ob when the shoulder 7 is rotated to the origin position is the Xb axis of the reference coordinate Rb. (X axis), a straight line orthogonal to both axes is obtained from the outer product of the Zb axis and Xb axis vectors, and the straight line is defined as the Yb axis (Y axis) of the reference coordinate Rb. Note that the length of one scale on the reference coordinate Rb is determined to be the same as the length of one scale on the camera coordinates Rc, and thus the robot coordinate R0.

  As described above, the reference coordinate Rb is set on the camera coordinate Rc. In the reference coordinate Rb set in this way, the Zb axis is parallel to the first axis Lc-1 and therefore the Z0 axis of the robot coordinate R0, and the XbYb plane is parallel to the X0Y0 plane. If the position of the light emitting diode 25 is on the X0Y0 plane when setting the reference coordinate Rb, the XbYb plane coincides with the X0Y0 plane.

  The Zb axis is at a predetermined distance from the Z0 axis in a predetermined direction. That is, the positional relationship between the Z0 axis and the Zb axis is the same as the positional relationship between the sixth axis LC-6 and the light emitting diode 25 when the flange 12 is initially in the rotational position, and the direction from the Z0 axis toward the Zb axis is The distance from the sixth axis Lc-6 to the light emitting diode 25 when the flange 12 is initially in the rotational position is the same as the distance from the Z0 axis to the Zb axis and the distance from the sixth axis Lc-6 to the light emitting diode 25. The same.

  If there is no inter-axis offset, the Xb axis and Yb axis are parallel to the X0 axis and Y0 axis of the robot coordinate R0. However, when there is an inter-axis offset, when the reference coordinate Rb is set, the position P0 of the light emitting diode 25 when the shoulder 7 is rotated to the origin position (0 °) is shifted in the X0Y0 direction by the inter-axis offset. The Xb axis and the Yb axis are not parallel to the X0 axis and the Y0 axis, but tilt according to the offset between the axes as shown in FIG.

  After setting the reference coordinates Rb, as shown in FIG. 12, an arbitrary plane A1 including the first axis Lc-1 extending from the first axis Lc-1 is assumed. In this case, an arbitrary plane A1 is designated by an angle β formed with the X0 axis. In order to position the hand on, for example, a plane with an angle formed with the X0 axis plus 30 °, the shoulder 7 is moved from the origin. Rotate by plus 30 ° (when there is no offset between axes).

  In the present embodiment, as shown in FIG. 12, a plane A1 including the Z0 axis extending in one direction from the Z0 axis of the robot coordinate R0 that is coaxial with the first axis Lc-1 and toward the opposite direction. An extended one plane A2 is assumed. The one plane A1 and the other plane A2 are one plane A that is flush with each other. In this embodiment, it is assumed that a plurality of such planes A are set (only one is shown in FIG. 12), and one of the planes includes the X0 axis (β = 0 °).

  Arbitrary plural positions are selected as movement target positions on one plane A1 extending in one assumed direction and one plane A2 extending in the opposite direction. The selected movement target position is indicated by a white circle in FIG. At this time, the movement target position is designated by the coordinate value of the robot coordinate R0. In order to obtain the offset between the axes at these movement target positions, the hand of the robot arm 6 is moved as described later.

  Here, the plurality of movement target positions selected on the planes A1 and A2 are designated by the coordinate value of the robot coordinate R0. Then, the attitude (flange) in which the fifth axis Lc-5 is parallel to the second axis LC-2 and the third axis Lc-3 and the sixth axis Lc-6 is parallel to the first axis Lc-1. When the hand moves to the movement target position at 12 target position reaching posture), the shoulder 12 rotates from the initial rotation position of the flange 12 to the current movement target position at each movement target position. In this case, the shoulder 7 is rotated by the rotation angle from the initial rotation position of the shoulder 7 to the current movement target rotation position in the direction opposite to the rotation direction of the shoulder 7 (initial position holding operation).

  Then, the positional relationship between the light emitting diode 25 and the hand (center P of the front end surface of the flange 12) at that time is the same as the positional relationship between the reference coordinate Rb and the robot coordinate R0 in the X0 (Xb) and Y0 (Yb) directions. It becomes. That is, when viewed from the positive side of the Z0 axis, if the position of the hand is moved in the direction from the origin O0 of the robot coordinate R0 to the origin Ob of the reference coordinate Rb by a distance from the origin O0 to the origin Ob, the light emitting diode There is a relationship of 25 positions.

  Therefore, the X0 and Y0 coordinate values at the robot coordinate R0 indicating the movement target position of the hand and the light emitting diode in the state where the flange 12 is in the target position reaching posture and initially held when the hand moves to the movement target position. The Xb and Yb coordinate values of the reference coordinate Rb indicating the position of 25 are the same value (in the case of no inter-axis offset). The position on the XbYb coordinate on the reference coordinate Rb of the light emitting diode 25 at this time is set as the movement target position of the light emitting diode 25. When the hand moves to the movement target position, if there is an offset between the axes, the actual movement position of the hand is shifted from the movement target position in the X0Y0 direction by the amount of offset between the axes. As a result, the position of the light emitting diode 25 also moves. Since it shifts in the XbYb direction according to the target position, the offset amount between the axes can be obtained from the shift amount of the light emitting diode 25.

  Prior to moving the hand of the robot arm 6 to the movement target position selected on each of the planes A1 and A2, errors other than the offset between the axes (deflection of the rotational drive system, origin position error of the servo motor 15, twist angle) A process of eliminating the movement position error of the hand due to the error and the link length error) is performed.

  First, the bending of the rotational drive system refers to bending in the twisting direction due to the transmission torque from the rotating shaft of the servo motor 15 to the rotating shaft 14 of the rotary joints J1 to J6 through the gear reduction device 16. It is assumed that the rotating shaft 14 does not bend in an arc shape in the axial direction. The deflection of the rotational drive system can be obtained from the torque acting on the rotational drive system and the spring constant of the rotational drive system. Among them, the spring constant is known in the robot 2, and its value is stored in advance in the ROM 20 of the control device 3. The torque acting on the rotational drive system is considered for the second axis Lc-2, the third axis Lc-3, and the fifth axis Lc-5 (the first axis Lc-2, the fourth axis Lc-3, the sixth axis Lc). -5 does not receive a large torque and does not cause bending that causes an absolute position error.)

  As shown in FIG. 11, the torque acting on the rotary drive system can be obtained by the product of the mass W of the link L supported by the rotary shaft 14 and the distance D from the rotary shaft 14 to the center of the link L. When the hand of the robot arm 6 is moved to a plurality of selected positions on the plane A, the shoulder 7 is rotated to an angular position that the plane A makes with the X0 axis, and the fifth axis Lc-5 is set to the second position. The three arms Lc-2 and Lc-3 are held in parallel, and at least two of the lower arm 8, the first upper arm 9 and the wrist arm 11, all in this embodiment are rotated to move the hand. The flange 12 is moved to the movement target position, and at each movement target position, the flange 12 is operated to hold the initial position and reach the target position. At this time, the robot arm 6 takes a forward bending posture or a backward bending posture depending on the movement target position.

  Then, the rotation angles of the second upper arm 10, the lower arm 8, the first upper arm 9, the wrist arm 11, and the flange 12 when moving to each movement target position are read from the teaching pendant 4. The torques acting on the second axis Lc-2, the third axis Lc-3, and the fifth axis Lc-5 are calculated from the rotation angles, and the deflection (angle) α of these rotary drive systems is obtained (see above, FIG. Step S2 of 9), the rotation angle of the servo motor 15 is adjusted by the calculated deflection α of the rotational drive system so that it is equivalent to the case where no deflection occurs. In other words, in FIG. 11, assuming that the position of the link indicated by the solid line is the movement target position when the rotation drive system is not considered to be the deflection, and the position indicated by the broken line is the actual movement position when the rotation drive system is deflected, the servo The rotation angle of the motor 15 is decreased by the deflection α. As a result, the link reaches the movement target position indicated by the solid line in a state where the rotational drive system is bent.

The motor origin position error is detected by, for example, the methods disclosed in Patent Documents 1 to 4. Further, the twist angle error and the link length error are detected by the direction disclosed in Non-Patent Document 1, for example. The method of Non-Patent Document 1 measures the rotation trajectory of the hand when the robot arm 6 is rotated about each of the first axis Lc-1 to the sixth axis Lc-6 with a three-dimensional measuring instrument, The position of the center of rotation and the normal of one plane including the rotation locus are calculated. Since the length of each link is obtained from the position of the rotation center and the direction of each axis is obtained from the direction of the normal line, the link length error and the torsion angle error can be obtained from the length of the link and the axial direction. (Step S3 in FIG. 9).
Then, the DH parameter is corrected based on the obtained motor origin position error, link length error and torsion angle error so that these errors do not appear as absolute position errors (step S4 in FIG. 9).

  After performing the above processing, the teaching pendant is operated to move the hand to the movement target position on each plane A. In order to move the hand to each plane A, first, the shoulder 7 is rotated from the origin position by an angle β formed by the plane A1 and the X0 axis, and the X1 axis of the coordinate R1 is positioned on the plane A. Thereby, with the shoulder 7 fixed, by rotating the rotary shafts 14 of the second rotary joint J1, the third rotary joint J3, and the fifth rotary joint J5, the flange 12 takes the target position reaching posture. The hand can be moved to the movement target position on the planes A1 and A2.

  Next, the flange 12 is operated to hold the initial position, and the lower arm 8, the first upper arm 9, and the wrist arm 11 are rotated while the flange 12 is kept in the target position reaching posture, so that it can be arbitrarily set on the planes A1 and A2. The hand is moved to a plurality of selected movement target positions. At this time, the robot arm 6 assumes the same posture as when the torque acting on the rotation drive system is obtained, and the rotation angle of the servo motor 15 is set according to the deflection of the rotation drive system previously obtained for each movement target position. It is something to adjust.

  When the hand is moved to a plurality of arbitrarily selected movement target positions on the planes A1 and A2, the robot arm 6 moves the second, third and fifth rotary joints J2, J3 and J5 as shown in FIG. By rotating the rotating shaft 14 in one direction, the hand 7 can be moved to the movement target position on one plane A1 in a posture (forward bending posture) that falls forward from the shoulder 7 and is bent forward.

  When moving the hand to the movement target position on the other plane A2, the robot arm 6 rotates the rotation shaft 14 of the second, third, and fifth rotary joints J2, J3, and J5 in the other direction, As shown in FIG. 14, the movement target on the other plane A <b> 2 in the posture that is reversed and falls back from the shoulder 7 to the other side (the robot arm 6 falls back to the rear side of the shoulder 7). Move to position. Then, at each movement target position, the position of the light emitting diode (offset measurement measurement point) 25 is measured by the three-dimensional measuring instrument 23 (step S5 in FIG. 9).

Note that the initial position holding operation of the flange 12 is not limited to before the hand is moved to the movement target position after the X1 axis is positioned on the plane A1, but when the hand is moved to each movement target position. However, since the movement to each movement target position is performed while the shoulder 7 is fixed, if the initial position holding operation is performed when moving to the first movement target position, the movement target moved after that is moved. In the position, it is not necessary to perform the initial position holding operation.
Since the position measured by the three-dimensional measuring instrument 23 is the position of the camera coordinate Rc, it is converted to the position of the reference coordinate Rb. This conversion is performed by the simultaneous conversion matrix shown in FIG. 15 (step S6 in FIG. 9).

  FIG. 16 shows the movement target position of the hand (indicated by the coordinate value of the robot coordinate R0) viewed from the plus side of the Z0 axis, the movement target position of the light emitting diode 25 (indicated by the coordinate value of the reference coordinate Rb), and the hand. The actual hand position when the hand moves to the movement target position, and the position of the light emitting diode 25 when the hand moves to the movement target position (converted from the coordinate value of the camera coordinate Rc to the coordinate value of the reference coordinate Rb). Indicates. In FIG. 16, for simplification of description, it is assumed that the planes A1 and A2 are on the X0 axis, and the position of the hand movement target position on the X0 axis is selected. In FIG. 16, the double circle is the target movement position of the hand, the white circle is the actual movement position of the hand, the black circle is the movement target position of the light emitting diode 25, and the x mark is the actual movement of the light emitting diode 25. Indicates the position.

  When the hand is moved to the movement target position, pre-processing is performed so that no error occurs in the movement position due to bending of the rotational drive system, motor origin error, link length error, and torsion angle error. The error between the target position and the actual movement position (the same as the error between the movement target position of the hand and the actual movement position) is considered to be caused by the inter-axis offset. The error caused by the inter-axis offset is that the actual movement position is aligned on a straight line parallel to the X0 axis that is shifted from the movement target position by the inter-axis offset because the movement target position is on the X0 axis. It will be distributed along a straight line if not lined up correctly).

  The inter-axis offset amount is a distance between the movement target position of the hand and the actual movement position in the X0Y0 direction. This is the movement target of the light emitting diode 25 when there is no inter-axis offset (Xb axis is parallel to the X0 axis). This is the same as the distance between the position and the actual movement position in the XbYb direction. For this reason, a line segment connecting a plurality of actual movement positions of the light emitting diode 25 is created on the XbYb plane, the line segment is defined as a measurement dependent line segment B, and a straight line Bb obtained by extending the measurement dependent line segment B When the shortest distance (the length of the perpendicular line from Ob to Bb) of the reference coordinate Rb with the origin Ob is obtained, this shortest distance becomes the inter-axis offset amount F (step S7 in FIG. 9).

In this case, the measurement dependence line segment B connecting the actual movement position when the robot arm 6 is bent forward and moved to the movement target position on the extension line A1, and the robot arm 6 is bent backward on the extension line A2. If the measurement dependence line segment B connecting the actual movement positions when moving to the movement target position of the line is not a single straight line (including the fact that it is not aligned in the vicinity of a single straight line) Since it is considered that there was an inconvenience somewhere in the process, in this case, the process starts again from the first step S1. In this way, by setting the movement target position on the two extension lines A1 and A2, it becomes possible to detect a problem in implementation.
The offset between the axes appears in the XbYb direction and is independent of the position in the Zb direction. Therefore, when the movement target position of the hand is not on the X0 axis, only the Xb coordinate value and the Yb coordinate value are used for the light emitting diode 25. The movement position may be plotted on the XbTb plane.

  Now, the inter-axis offset amount F is obtained in the same manner as described above for the movement target positions determined on other similar planes other than the planes A1 and A2 including the Xb axis. Also in this case, since the actual movement positions of the light emitting diodes 23 should be aligned on a straight line, the same applies to the measurement-dependent straight line B formed by connecting the actual movement positions (Xb coordinate values and Yb coordinate values) of the light emitting diodes 25. Measure the shortest distance from the origin Ob. The shortest distance between each measurement-dependent straight line B and the origin Ob should be the same for any measurement-dependent straight line B, but in practice, it is often not always the same due to a measurement error or the like. In such a case, the average of the shortest distance between the measurement dependent straight line B and the origin Ob is obtained to obtain the offset between the axes. As a result, the offset between axes can be obtained more accurately.

  The inter-axis offset obtained as described above is the sum of the inter-axis offsets generated in the second axis Lc-2, the third axis Lc-3, and the fifth axis Lc-5, and it is analyzed which axis is the offset. Can not. For this reason, among the HD parameters shown in FIG. 5, the value of the offset between axes is added to any of the d columns of J2 and J3 or added separately to the d columns of J2 and J3. Since the fifth axis Lc-5 can take any angle from horizontal to vertical by the rotation of the fourth axis Lc-4, if the inter-axis offset is distributed to the column d of J5, the absolute position accuracy is reduced. I will let you. For this reason, the offset between axes is not distributed to the column d of J5.

  In order to check whether the absolute position accuracy has been improved by adding the value of the offset between axes in either the d column of J2 or J3 or in the d column of J2 or J3, the offset between axes is set. Using the added DH parameter, a plurality of target positions were determined on the Xb axis, and the hand was moved to the target position in the same manner as described above, and an experiment was performed to measure the actual movement position.

  As a result, the position error on the XbYb plane decreased from 0.67 mm to 0.17 mm. The position error in the Zb axis direction also decreased from 0.9 mm to 0.06 mm. From this, it can be said that the position error is reduced from 1.12 mm to 0.18 mm in the three-dimensional direction of XbYbZb.

  As described above, according to the present embodiment, the offset between the axes can be quantitatively grasped, and the DH parameter is corrected by the offset between the axes so that there is no error due to the offset between the axes, or the error does not occur as much as possible. The absolute position accuracy can be increased.

(Second Embodiment)
17 and 18 show a second embodiment of the present invention. In this embodiment, the reference coordinate Rb is obtained in the same manner as in the first embodiment, but the method of obtaining the offset amount between axes is different.
In the present embodiment, when a plurality of arbitrary positions are set as the movement target positions of the hand within the movable range of the hand and the hand is moved to the plurality of movement target positions, the movement target position of the light emitting diode 25 and the actual movement position are determined. The offset between the axes is obtained based on the difference from the movement position.

That is, first, an arbitrary plurality of positions on the robot coordinate R0 are selected as movement target positions. In FIG. 17, a plurality of positions selected as the movement target positions are indicated by double circles. FIG. 17 shows only the position in the horizontal direction (X0Y0 direction, XbYb direction). Among these, the movement of the hand to the movement target position where the X0 coordinate value is on the plus side (right side of the Y0 axis) is performed in the forward bending posture of the robot arm 6 and to the movement target position on the minus side (left side of the Y0 axis). The movement of the hand is assumed to be performed in a backward bending posture of the robot arm 6.
Similarly to the first embodiment, prior to moving the hand to a plurality of selected movement target positions, each error other than the offset between axes (deflection of the rotational drive system, origin position error of the servo motor 15, twist angle) A process of eliminating the movement position error of the hand due to the error and the link length error) is performed.

Thereafter, the hand is moved to the plurality of selected movement target positions in the target position reaching posture. The movement at this time is the first rotary joint J1 and at least two rotary joints among the second, third, and fifth rotary joints J2, J3, and J5, and the second, third, and fifth rotary joints J2 in this embodiment. , J3, and J5 by rotating the rotating shafts 14 of the three rotating joints. In order to hold the fifth axis Lc-5 horizontally, the rotary shaft 14 of the fourth rotary joint J4 is not rotated. Then, at each movement target position, the position of the light emitting diode 25 is measured by the three-dimensional measuring instrument 23 in a state in which the flange 12 is initially held.
Since the position measured by the three-dimensional measuring instrument 23 is the position of the camera coordinate Rc, it is converted to the position of the reference coordinate Rb. The measurement positions of the light emitting diodes 25 at the respective movement target positions are indicated by x in FIG.

  In order to obtain the offset between axes from the movement target position of the light emitting diode 25 and the actual movement position, it is necessary to obtain the Xb coordinate value and the Yb coordinate value on the reference coordinate Rb of the movement target position of the light emitting diode 25. As described in the first embodiment, when there is no inter-axis offset, since the Xb axis and Yb axis of the reference coordinate Rb are parallel to the X0 axis and the Y0 axis, the X0 coordinate value indicating the movement target position of the hand And the Y0 coordinate value are the same as the Xb coordinate value and the Yb coordinate value when the movement target position of the light emitting diode 25 is indicated by the robot coordinate Rb.

  The position indicated by the Xb coordinate value and the Yb coordinate value on the reference coordinate Rb of the obtained movement target position of the light emitting diode 25 is plotted as shown by a black circle in FIG. 17, and a line segment from the origin Ob to the movement target position is plotted. The length is set as the target position radius D0, and the length of the perpendicular drawn from the measurement position of the light emitting diode 25 to the straight line passing through the origin Ob and the movement target position is set as the offset error component M0.

  Then, as shown in FIG. 18, a graph is created with the target position radius D0 on the horizontal axis and the offset error component M0 on the vertical axis, and the target position radius D0 and offset error for each moving target position are created on this graph. A relationship with the component M0 is plotted, and a straight line passing through these plotted points is defined as an error straight line G. When a perpendicular is drawn from the origin of the graph to the error straight line G, the length of this perpendicular becomes the total inter-axis offset amount F of the second, third, and fifth rotary joints.

(Other embodiments)
The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The mounting surface of the base 5 is not necessarily horizontal.
The measurement point is not limited to the light emitting diode 25. It may be a simple mark, preferably a dotted mark.
The Xb axis of the reference coordinate Rb is not necessarily parallel to the X0 axis. What is necessary is just to set to the arbitrary straight lines which pass through the origin Ob. In this case, since the angle formed by an arbitrary straight line (Xb axis) and the X0 axis is obtained from the angle formed by the X1 axis and the X0 axis when the Xb axis is determined and the initial position of the light emitting diode 25, the Xb axis The position on the reference coordinate Rb and the position on the robot coordinate R0 can be converted to each other by obtaining the relationship between the reference coordinate Rb and the robot coordinate R0 based on the angle formed with the X0 axis and performing coordinate conversion. Just do it.

In the first embodiment, when moving the hand from the plane A1 (plane extending in one direction from the Zb axis) to the movement target position of the plane A2 (plane extending in the opposite direction from the Zb axis), depending on the selected position of the movement target position If the rotary shafts 14 of the two rotary joints J2, J3, and J5 of the second, third, and fifth rotary joints are rotated, the robot arm 6 can be reversed to move the hand to the movement target position. it can.
In the second embodiment, when the hand is moved to a plurality of arbitrarily selected movement target positions, all of the second, third and fifth rotary joints J2, J3 and J5, or the rotation axes of any two rotary joints 14 may be rotated, but depending on the selection position of the movement target position, in addition to the first rotary joint J1, the rotation axes of two rotary joints of the second, third, and fifth rotary joints J2, J3, and J5 If the hand 14 is rotated, the hand can be moved to the movement target position. That is, the rotation shafts of at least two rotary joints may be rotated.

  In the drawings, 3 is a control device, 5 is a base (base link), 6 is a robot arm, 7 is a shoulder (first link), 8 is a lower arm (second link), and 9 is a first upper arm (third). Link), 10 is a second upper arm (fourth link), 11 is a wrist arm (fifth link), 12 is a flange (sixth link), 23 is a three-dimensional measuring instrument (three-dimensional measuring means), 25 is A light emitting diode (measurement point) is shown.

Claims (4)

A 6-axis robot in which first to sixth links constituting a robot arm are sequentially connected to a base link fixed to a mounting surface by first to sixth rotary joints, The rotation center line of the rotation axis of the second rotation joint connecting the second link to one link is orthogonal to the rotation center line of the rotation axis of the first rotation joint connecting the first link to the base link. The rotation center line of the rotation axis of the third rotation joint connecting the third link to the second link is parallel to the rotation center line of the rotation axis of the second rotation joint, The rotation center line of the rotation axis of the fourth rotation joint connecting the fourth link to the link is parallel to the direction perpendicular to the rotation center line of the rotation axis of the third rotation joint, and the fourth link The fifth rotary joint connecting the fifth link The rotation center of the rotation shaft of the sixth rotation joint that connects the sixth link to the fifth link so that the rotation center line of the rotation shaft is parallel to the direction orthogonal to the rotation center line of the rotation shaft of the fourth rotation joint. A line is set in parallel to a direction perpendicular to the rotation center line of the rotation axis of the fifth rotation joint, and
The robot coordinates are set on the rotation center line of the rotation axis of the first rotation joint, and the coordinates of the first to sixth links are respectively set on the rotation center lines of the rotation axes of the first to sixth rotation joints. In the 6-axis robot that is set and the coordinates of the hand are set at the same position with the predetermined position existing on the rotation center line of the rotation axis of the sixth rotation joint in the sixth link,
A measurement point that operates integrally with the sixth link is provided at a position away from the rotation center line of the sixth link, and a three-dimensional measurement means that can measure the three-dimensional position of the measurement point is provided,
The appropriate rotational position of the first link is defined as the initial rotational position of the first link, and the appropriate rotational position of the sixth link at the initial rotational position of the first link is defined as the initial rotational position of the sixth link. Set
The rotation center line of the rotation axis of the fifth rotation joint is parallel to the rotation center lines of the rotation axes of the second and third rotation joints, and the rotation center line of the rotation axis of the sixth rotation joint is the first rotation axis. While maintaining a state parallel to the rotation center line of the rotation axis of the rotary joint, the first link is rotated to three or more arbitrary rotation positions different from each other, and the sixth link is rotated at each rotation position of the first link. From the initial rotation position of the sixth link to the rotation direction opposite to the rotation direction of the first link when the first link is rotated from the initial rotation position of the first link to the current rotation position. The position of the measurement point is measured by the three-dimensional measuring means in a state of being rotated by a rotation angle from the initial rotation position of the first link to the current rotation position,
A plane including a center position of a circle passing through these three or more positions and three or more positions of these measurement points from three or more positions of the measurement points measured at the respective rotational positions of the first link. The normal of the circle is obtained as the origin, the straight line passing through the origin is parallel to the Z axis, the straight line passing through the origin and perpendicular to the Z axis is the X axis, and the origin A reference coordinate with the straight line perpendicular to both the Z and X axes passing through the Y axis as the Y axis,
A plurality of positions on any one plane including the rotation center line of the rotation axis of the first rotation joint extending from the rotation center line of the rotation axis of the first rotation joint are set as movement target positions;
At least two of the second, third, and fifth rotary joints in a state where the rotation center line of the rotation shaft of the fifth rotation joint is parallel to the rotation center lines of the rotation axes of the second and third rotation joints. By rotating the rotation shafts of the two rotation joints, the rotation center line of the rotation shaft of the sixth rotation joint maintains a target position arrival posture parallel to the rotation center line of the rotation shaft of the first rotation joint, When the hand is moved to each of the movement target positions,
Origin position errors of the motors driving the first to sixth links via the first to sixth rotary drive systems including the rotation axes of the first to sixth rotary joints; The position error of the hand does not occur due to the deflection of each sixth rotational drive system, the length error of each of the first to sixth links, and the angle error between the rotation joint and the rotation axis of the next rotation joint. After performing correction processing on
At least two of the second, third, and fifth rotary joints in a state where the rotation center line of the rotation shaft of the fifth rotation joint is parallel to the rotation center lines of the rotation axes of the second and third rotation joints. By rotating the rotation shafts of the two rotary joints, the hand is moved to the plurality of movement target positions in a state where the target position reaching posture is maintained,
The first link when the sixth link is rotated from the initial rotation position of the sixth link to the current rotation position at each movement target position from the initial rotation position of the first link. The position of the measurement point is measured by the three-dimensional measuring means in a state in which the first link is rotated by a rotation angle from the initial rotation position to the current rotation position in a rotation direction opposite to the rotation direction of the first link. This is the offset calculation measurement point position,
The XY coordinate value on the reference coordinate of each offset calculation measurement point position is obtained by coordinate-converting each offset calculation measurement point position to the position on the reference coordinate,
The obtained XY coordinate value of the offset calculation measurement point position is plotted on the XY plane of the reference coordinate, and a line segment connecting these plotted points is defined as a measurement dependent line segment, and the measurement dependent line segment is extended to a straight line. Obtain the length of the perpendicular drawn from the origin of the reference coordinates as a deviation amount,
A method for detecting an inter-axis offset of a robot, wherein the obtained deviation amount is set as a total inter-axis offset amount of the second, third, and fifth rotary joints. The method for detecting an offset between axes of a robot according to claim 1,
The operation of determining an arbitrary plurality of positions on one plane extending from the rotation center line of the rotation axis of the first rotary joint as a movement target position, and moving the hand to each of the movement target positions on the one plane, Two planes extending in opposite directions from the rotation center line of the rotation axis of the first rotary joint are performed, and the transition from one plane to the other plane is performed while the first link is fixed. A method for detecting an offset between axes of a robot, wherein the robot arm is inverted by rotating the rotation axes of at least two of the second, third, and fifth rotation joints. In place of the operation until the inter-axis offset amount is obtained after determining the reference coordinates in claim 1 or claim 2,
The plurality of arbitrary positions are determined as the movement target position of the hand,
At least two of the second, third, and fifth rotary joints in a state where the rotation center line of the rotation shaft of the fifth rotation joint is parallel to the rotation center lines of the rotation axes of the second and third rotation joints. By rotating the rotation shafts of the two rotation joints, the rotation center line of the rotation shaft of the sixth rotation joint maintains a target position arrival posture parallel to the rotation center line of the rotation shaft of the first rotation joint, When the hand is moved to each of the movement target positions,
Origin position errors of the motors driving the first to sixth links via the first to sixth rotary drive systems including the rotation axes of the first to sixth rotary joints; The position error of the hand due to the deflection of each sixth rotational drive system, the length error of each of the first to sixth links, and the angle error between the rotation joint and the rotation axis of the next rotation joint does not occur. After performing the correction process,
With the rotation center line of the rotation axis of the fifth rotation joint parallel to the rotation center lines of the rotation axes of the second and third rotation joints, the first rotation joint and the second, third, and fifth rotation joint lines By rotating the rotation shafts of at least two of the rotary joints, the hand is moved to the plurality of movement target positions while maintaining the target position arrival posture, and at each movement target position, The rotation direction of the first link when the sixth link is rotated from the initial rotation position of the sixth link to the current rotation position of the first link. In a reverse rotation direction, the position of the measurement point is measured by a three-dimensional measuring means while being rotated by a rotation angle from the initial rotation position to the current rotation position of the first link,
The position of the measurement point measured at each movement target position is set as a measurement point position for offset calculation, and the obtained measurement point position for offset calculation at each movement target position is converted to a position on the reference coordinate, XY coordinate values on the reference coordinates of a plurality of offset calculation measurement point positions are obtained, and the XY coordinate values of the respective movement target positions are converted into XY coordinate values on the reference coordinates to move on the reference coordinates The target position,
For each movement target position, the XY coordinate value of the movement target position and the XY coordinate value of the offset calculation measurement point position are plotted on the XY plane of the reference coordinates, and the origin of the reference coordinates is plotted on the XY plane. The length of the line segment to the movement target position is set as a target position radius, and the offset calculation measurement point position on the XY plane passes through the origin of the reference coordinates and the movement target position on the XY plane. The length of the perpendicular line drawn as a straight line is used as the offset error component,
For each moving target position, the relationship between the target position radius and the offset error component is a graph in which the moving target position radius is taken on one of the two orthogonal axes and the offset error component is taken on the other axis. When the straight line connecting the plotted points is plotted as the error line, the length of the perpendicular line drawn from the origin of the graph to the error line is obtained as the deviation amount,
A method for detecting an inter-axis offset of a robot, wherein the obtained deviation amount is set as a total inter-axis offset amount of the second, third, and fifth rotary joints. The method for detecting an offset between axes of a robot according to claim 3,
Arbitrary plural positions within the movable range of the robot arm are set as movement target positions, and the operation of moving the hand to the plural movement target positions is as follows:
By rotating at least the second and third rotary joints of the second, third and fifth rotary joints in one direction and the other direction among the second, third and fifth rotary joints with the rotary axis of the first rotary joint fixed. A method for detecting an offset between axes of a robot, wherein the arm is performed in both a forward bending posture in which the arm is tilted to one side from the first link and a backward bending posture in which the arm is tilted to the other side.

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