Calibration method for robot arm

Abstract

To provide a calibration method for a robot arm that collaborates with a chuck device, which has high precision and does not require teaching to be performed.SOLUTION: The calibration method for a robot arm comprises: a step of making a robot hand 101 hold a reference work-piece W; a step of moving the robot hand in X, Y and Z-directions to make the reference work-piece contact a plurality of claws 12; a step of calculating an original point on the basis of an X, Y, Z coordinate of contact positions between the reference work-piece and the claws, with a point of intersection of a surface of a chuck body 11 with a spindle center line as the original point; a step of specifying a user coordinate in which a coordinate of the original point is set to (X,Y,Z,W,P,R)=(0,0,0,0,0,0); and a step of setting the coordinate of the original point in the user coordinate, at a position of (0,0,0,0,0,0) in a tool coordinate. This can treat all of posture-coordinate W, P, R around axes of X, Y,Z in the tool coordinate as zero, so that a user can intuitively understand a position and a posture of the robot hand.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for calibrating a robot arm that cooperates with a chuck device, and more particularly to a method for calibrating a robot arm that is highly accurate and does not require teaching. [Background technology]

[0002] When a robot hand at the tip of a robot arm grasps an object to be grasped, such as a workpiece fixed to a chuck device, or when an object to be grasped that is held by the robot hand is fixed to a chuck device, it is necessary to determine the relationship between coordinates such as world coordinates and tool coordinates that serve as the basis for robot control (hereinafter referred to as "robot coordinates") and coordinates indicating the position of the chuck (hereinafter referred to as "user coordinates") through calibration. For example, Patent Document 1 discloses a technique in which a first teaching member is fixed to a chuck, and with a second teaching member held by a robot hand, the second teaching member is brought into contact with the first teaching member from multiple directions, thereby calculating the position of the robot hand, calculating the deviation between the central axis of the chuck and the central axis of the robot hand, and correcting the deviation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6647308 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology in Patent Document 1 has the problem that it requires the use of two members, a first teaching member and a second teaching member, which is cumbersome, and that it is necessary to teach the robot hand every time the type of object to be grasped (workpiece) changes, which is also cumbersome. Furthermore, since a robot arm can move the tool (robot hand, etc.) at its tip along the axes of a three-dimensional Cartesian coordinate system (X-axis, Y-axis, Z-axis), as well as rotate it around each of the X, Y, and Z axes, the coordinates express the tool's position and orientation information in the XYZWPR format. Expressing the tool's position and orientation using six variables (X, Y, Z, W, P, R) presents the problem of time-consuming teaching, as the user cannot intuitively understand the tool's position and orientation.

[0005] In consideration of the above-mentioned problems, the present invention relates to a method for calibrating a robot arm that cooperates with a chuck device, and an object of the present invention is to provide a method for calibrating a robot arm that is highly accurate and does not require teaching. [Means for solving the problem]

[0006] A method for calibrating a robot arm according to the present invention is a method for calibrating a robot arm when a robot hand at the tip of the robot arm transfers a grasped object to a chuck device attached to a spindle, the method comprising the steps of: having the robot hand grasp a reference workpiece; moving the robot hand in X, Y, and Z directions to bring the reference workpiece into contact with a plurality of jaws; defining the intersection of the surface of the chuck body and the center line of the spindle as the origin and calculating the X, Y, and Z coordinates of the origin based on the X, Y, and Z coordinates of the contact points between the reference workpiece and the jaws; defining user coordinates in which the coordinates of the origin are (X,Y,Z,W,P,R)=(0,0,0,0,0,0); and setting the coordinates of the origin in the user coordinates (X,Y,Z,W,P,R)=(0,0,0,0,0,0) to the position (0,0,0,0,0,0,0) in the tool coordinates. The position at which the torque value of the drive motor of the robot arm increases when the reference workpiece is brought into contact with the claws is calculated as the X, Y, and Z coordinates of the contact point. [Effects of the Invention]

[0007] In this invention, the intersection of the surface of the chuck body and the spindle centerline is defined as the origin, and user coordinates are defined with the coordinates of the origin (X, Y, Z, W, P, R) = (0, 0, 0, 0, 0, 0). Furthermore, the coordinates of the origin (X, Y, Z, W, P, R) = (0, 0, 0, 0, 0, 0) are set to the position (0, 0, 0, 0, 0, 0) in the tool coordinate system. This allows the robot hand to operate based on tool coordinates that take the deviation into account, even if the spindle centerline deviates from its reference value. In other words, the orientation coordinates W, P, and R around the X, Y, and Z axes in the tool coordinate system can all be treated as zero, allowing the user to intuitively understand the position and orientation of the tool (robot hand) by looking at the coordinates.

[0008] When using a robot hand to grasp an object fixed to a chuck device, the user only needs to input the length of the object (the length after processing) into the operation panel; there is no need to input the X, Y, Z, W, P, and R coordinates. In this way, teaching the robot hand, which was previously required for the transfer of the object to be grasped between the chuck device and the robot hand, is no longer necessary, and a so-called teaching-less robot arm system can be constructed. When calculating the X, Y, and Z coordinates of the contact point between the reference workpiece and the claw, it is possible to use a method in which the robot hand comes into contact with the claw and find the position where the torque value of the drive motor increases.This makes it possible to keep costs down by utilizing the existing mechanisms of the robot hand system. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the appearance of a chuck device, a robot arm, and a robot hand; [Figure 2] Robot arm system block diagram [Figure 3] FIG. 2A is a side view showing the structure of the chuck device, FIG. 2B is a front view of the chuck device, and FIG. 2C is a side view showing a state in which an object to be gripped is fixed to the chuck device. [Figure 4] A side view showing the misalignment between the spindle center line and the robot hand center line [Figure 5] Diagrams (a) and (b) for explaining the calibration method [Figure 6] Diagrams (a) to (c) to explain the calibration method [Figure 7] Diagrams (a) and (b) for explaining the calibration method [Figure 8] Diagram showing the operation panel [Figure 9] Calibration Method Flowchart DETAILED DESCRIPTION OF THE INVENTION

[0010] A method for calibrating a robot arm according to the present invention (hereinafter, sometimes simply referred to as "calibration method") will be described. The calibration method of the present invention is carried out to accurately transfer a gripped object 20 (FIG. 3(c)) to a chuck device 10 attached to a spindle 1 using a robot hand 101 at the tip of a robot arm 100, as shown in Fig. 1. The spindle 1 is supported by a headstock 2 so that it can rotate freely around its axis.

[0011] As shown in FIG. 2, the robot arm 100 and the robot hand 101 are controlled by a computer C. A robot arm, also known as a vertical articulated robot, is an industrial robot that can replicate the movements of a human arm by combining multiple links and joints. A typical robot arm is one that can move along six axes, combining two links and three joints, but this is not the only option.

[0012] The computer C includes a drive control unit 200, a storage unit 201, etc. The drive control unit 200 controls the computer C by reading out various programs and various information stored in the storage unit 201 and executing them as appropriate. The robot arm 100 and the robot hand 101 are equipped with drive motors 202, 203 (servomotors), and a drive control unit 200 controls the drive of the drive motors 202, 203 based on a program to operate the robot arm 100 and the robot hand 101. The drive control unit 200 may be configured as a single control unit or may be configured as multiple control units. For example, the drive control unit 200 may be a programmable logic controller (PLC).

[0013] 3(a) and (b), the chuck device 10 is composed of a chuck body 11 and a plurality of (three in this embodiment) jaws 12, and each jaw 12 can move toward or away from the spindle center line L1 in the direction indicated by the arrow. As shown in FIG. 3(c), the chuck device 10 grips the object 20 by pressing the outer periphery of the object 20 with the corners of the jaws 12. 4, if the spindle center line L1 and the robot hand 101 center line L2 are misaligned, the object to be grasped 20 cannot be accurately transferred between the chuck device 10 and the robot hand 101. To accurately transfer the object to be grasped 20, it is necessary to obtain, by calibration, the relationship between the user coordinates that indicate the position of the chuck device 10 and the tool coordinates that serve as the reference for controlling the drive of the robot hand 101, and in the present invention, this is done by the following procedure.

[0014] When a three-dimensional Cartesian coordinate system (X, Y, Z) is defined with the horizontal plane as the XY plane as shown in FIGS. 5 and 9, the robot hand 101 is first made to grasp a reference workpiece W (step S101). The dimensions of the reference workpiece W are not particularly limited as long as they are within a range that can be grasped by the robot hand 101, but in this embodiment, the reference workpiece W has a cylindrical shape with a diameter of 50 mm and a height of 50 mm. Next, the drive control unit 200 drives the robot arm 100 based on the command coordinates stored in the memory unit 201, and moves the robot hand 101 closer to the claws 12 from the X direction. The drive control unit 200 automatically drives the robot arm 100 based on a program. It is preferable to keep the positions of the claws 12 at the maximum distance (maximum open state).

[0015] As described above, the robot arm 100 is connected to the drive motor 202, and when the reference workpiece W held by the robot hand 101 comes into contact with the surface of the claw 12 (step S102) as shown in FIG. 6(a), the torque value of the drive motor 202 increases due to resistance, and the current value of the servo amplifier (not shown) also increases. By detecting this increase in the current value (torque value), the drive control unit 200 determines the rotation angle of the drive motor 202 based on a signal from an encoder (not shown) obtained at that timing, and calculates the X coordinate (current coordinate) of the surface of the claw 12 that the reference workpiece W has come into contact with. Here, the X coordinate is assumed to be 1.8.

[0016] Similarly, the robot arm 100 is driven to move the robot hand 101 closer to the claw 12 from the Y direction. Then, as shown in Figure 6(b), the reference workpiece W is brought into contact with the claw 12 from the Y direction, thereby calculating the Y coordinate (current coordinate) of the inner surface of the claw 12. Here, the Y coordinate is assumed to be 2.3. Furthermore, the reference workpiece W is brought closer to the jaw 12 in the Z direction, and as shown in Figure 6(c), the reference workpiece W is brought into contact with the jaw 12 in the Z direction to calculate the Z coordinate (current coordinate) of the inner surface of the jaw 12. Here, the Z coordinate is assumed to be 3.1.

[0017] Next, as shown in FIGS. 7(a) and 7(b), the intersection of the surface of the chuck body 11 and the spindle center line L1 is set as the origin O, and the X, Y, and Z coordinates of the origin O are calculated based on the X, Y, and Z coordinates of the contact point between the reference workpiece W and the jaws 12 (step S103). Various information such as the shape of the robot hand 101, the shape of the jaws 12, and the attachment position of the jaws 12 relative to the chuck body 11 is stored in advance as CAD data in the storage unit 201. Therefore, if the coordinates (current coordinates) of the point where the reference workpiece W moved in the X, Y, and Z directions comes into contact with the jaws 12 are known, the X, Y, and Z coordinates (current coordinates) of the origin O can be calculated by considering the difference between the current coordinates and the command coordinates at the contact point. Here, it is assumed that the current coordinates of the origin O are (X, Y, Z) = (1.8, 2.3, 3.1).

[0018] Next, the drive control unit 200 defines the user coordinates with the coordinates of the origin O being (X, Y, Z, W, P, R) = (0, 0, 0, 0, 0) (step S104). In other words, the coordinates of the origin O, expressed as (X,Y,Z)=(5.1,-2.0,3.4) in the current coordinate system, are expressed as (X,Y,Z,W,P,R)=(0,0,0,0,0,0) in the work coordinate system. Then, the drive control unit 200 sets the coordinates (X, Y, Z, W, P, R) of the origin O in the user coordinate system to (0, 0, 0, 0, 0, 0) in the tool coordinate system (step S105).

[0019] According to the calibration method represented by steps S101 to S105, even if the spindle center line L1 deviates from a reference value, the robot hand 101 can be operated based on tool coordinates that take the deviation into consideration. In other words, it becomes possible to treat the posture coordinates W, P, and R around the X, Y, and Z axes in the tool coordinates as all zero, allowing the user to intuitively understand the position and posture of the tool (robot hand 101) by looking at the coordinates. For example, when fixing the object 20 held by the robot hand 101 to the chucking device 10, the user only needs to input "90 mm" as the length of the object 20 (length before processing) into "Mounting L" on the operation panel, as shown in Figure 8, and does not need to input the coordinates of X, Y, Z, W, P, and R.

[0020] Furthermore, when the robot hand 101 grips the object 20 fixed to the chuck device 10, the user only needs to input "85 mm" as the length of the object 20 (length after processing) into "Remove L" on the operation panel, as shown in Figure 8. There is no need to input the coordinates of X, Y, Z, W, P, and R. Note that E indicates the height of the jaws 12. In this way, there is no need to teach the robot hand 101 about the transfer of the object to be grasped 20 between the chucking device 10 and the robot hand 101. For example, if it becomes necessary to rotate the robot hand 101 by 90 degrees, the tool coordinates would be set to (0,0,0,0,90,0), but this setting work can be automated by a program. Therefore, the operator does not need to input the W, P, and R coordinates to rotate the robot hand 101.

[0021] Furthermore, once the above calibration has been performed, there is no need to perform it again when replacing the jaws 12. This is because the position of the origin O, i.e., the position of the intersection between the surface of the chuck body 11 and the spindle center line L1, does not change even when replacing the jaws 12. However, if the chuck device 10 is moved to a different location, the inclination of the spindle center line L1 may have changed, so calibration must be performed again. [Industrial Applicability]

[0022] The present invention relates to a method for calibrating a robot arm that cooperates with a chuck device, and in particular to a method for calibrating a robot arm that is highly accurate and does not require teaching, and has industrial applicability. [Explanation of symbols]

[0023] C Computer L1 Spindle center line L2 Center line of robot hand O Origin W Standard workpiece 1 spindle 2 Headstock 10. Chuck device 11 Chuck body 12 nails 20 Object to be grasped 100 Robot Arm 101 Robot Hand 200 Drive control unit 201 Storage section 202,203 Drive motor

Claims

1. A method for calibrating a robot arm when a robot hand at the tip of the robot arm transfers a gripped object to a chuck device attached to a spindle, comprising: a step of causing the robot hand to grasp a reference workpiece; moving the robot hand in X, Y, and Z directions to bring the reference workpiece into contact with the plurality of claws; A step of setting the intersection point between the surface of the chuck body and the center line of the spindle as the origin and calculating the X, Y, and Z coordinates of the origin based on the X, Y, and Z coordinates of the contact point between the reference workpiece and the jaws; defining user coordinates with the coordinates of the origin being (X, Y, Z, W, P, R) = (0, 0, 0, 0, 0); A method for calibrating a robot arm, comprising a step of setting the coordinates (X, Y, Z, W, P, R) of the origin in the user coordinate system (0, 0, 0, 0, 0, 0) to the position (0, 0, 0, 0, 0, 0) in the tool coordinate system.

2. The method for calibrating a robot arm according to claim 1, characterized in that the position at which the torque value of the drive motor of the robot arm increases when the reference workpiece is brought into contact with the claw is calculated as the X, Y, and Z coordinates of the contact point.

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