Robotic system and control method

Abstract

A robot system (1) includes a robot (2) having a tool (S) attached to a front end wrist axis (10), a sensor (3) that detects a position and an orientation of a workpiece (W), and a control device (4) that controls the robot according to a program of movement including a plurality of teaching points that specify positions and orientations of the tool and movement commands that move in a direction in which a rotation amount to each joint between the teaching points is minimized. The control device corrects the position and the orientation of the tool at a first teaching point (P3) at which work is performed on the workpiece based on the position and the orientation of the workpiece detected by the sensor, determines whether an angle of the front end wrist axis at the first teaching point (P3) calculated based on the corrected position and the corrected orientation of the tool exceeds a movement limit, and changes the angle of the front end wrist axis at the first teaching point (P3) and one or more other teaching points (P2; approach positions) adjacent to the first teaching point to an angle within a movement range that is increased or decreased by 360°, respectively, in a case where it is determined that the movement limit is exceeded.

Description

Technical Field

[0001] This invention relates to robot systems and control methods. Background Technology

[0002] A robot system is known that repeatedly performs pick-up and phase alignment actions on multiple workpieces (e.g., see Patent Document 1). In this robot system, if the pick-up action is performed without rotating the wrist, the wrist rotation angle will approach the travel limit. Therefore, when the interval between workpieces increases, the wrist is rotated in a direction with a rotation angle close to 0°.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-58979 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] When the robot is moving linearly between three or more teach points, a motion is performed that continuously moves the robot in the direction that reduces the amount of rotation of each axis. In this case, for example, if the robot's posture at any teach point is to be corrected according to the posture of the workpiece to be manipulated, the angle of the fore-end wrist axis may exceed the motion limit, potentially causing an erroneous stop.

[0008] Since the range of motion of the wrist axis is usually set to more than 360°, if the range of motion is exceeded, it can be corrected to an angle that is 360° different to avoid stopping incorrectly. However, in this case, the wrist axis needs to be rotated significantly to an angle close to 360°.

[0009] When the robot performs large-angle rotational movements in the short distance between teaching points or when it approaches workpieces or other surrounding components, tools such as the hand mounted on the wrist may rotate rapidly or interfere with surrounding components.

[0010] Therefore, it is hoped that while avoiding erroneous stops caused by the angle of the modified front wrist axis exceeding the limit of motion, the sudden rotation of tools such as hands and interference with surrounding components can also be avoided.

[0011] Solution for solving the problem

[0012] One aspect of the present invention is a robot system comprising: a multi-jointed robot having a tool for working on a workpiece mounted on a front wrist axis having a range of motion of more than 360°; sensors for detecting the position and orientation of the workpiece; and a control device for controlling the robot according to an action program, the action program including: a plurality of teaching points defining the position and orientation of the tool; and action commands causing the teaching points to move in a direction that minimizes the rotation of each joint. The control device is configured to, based on the position and orientation of the workpiece detected by the sensors, correct the position and orientation of the tool at a first teaching point for working on the workpiece, determine whether the angle of the front wrist axis at the first teaching point, calculated based on the corrected position and orientation of the tool, exceeds the action limit, and if the action limit is exceeded, change the angle of the front wrist axis at the first teaching point and one or more other teaching points adjacent to the first teaching point to either increase or decrease the angle within the 360° range of motion. Attached Figure Description

[0013] Figure 1 This is a perspective view of a robot system according to one embodiment of the present invention.

[0014] Figure 2 It means Figure 1 A diagram illustrating an example of motion programs stored in the control unit of a robot system.

[0015] Figure 3 It means Figure 2 A three-dimensional diagram of an example of three teaching points set in the action procedure.

[0016] Figure 4 It is an explanation of being Figure 2 A diagram illustrating an example of the difference between the workpiece shown in the motion program of a robotic system and the position and orientation of the workpiece as obtained by a camera.

[0017] Figure 5 This is an explanation Figure 2 This is a diagram illustrating an example of how the change between the take-out position P3 and the approach position P2 is handled in the action procedure.

[0018] Figure 6 This is a flowchart illustrating a control method according to one embodiment of the present invention.

[0019] Figure 7 This is an explanation Figure 1 robotic systems and Figure 6 A three-dimensional diagram showing the effect of the control method. Detailed Implementation

[0020] Hereinafter, a robot system 1 and a control method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] like Figure 1 As shown, the robot system 1 of this embodiment includes: a robot 2; a camera (sensor) 3, which detects the position and orientation of the workpiece W manipulated by the robot 2; and a control device 4, which controls the robot 2.

[0022] Robot 2 is, for example, a vertical six-axis articulated robot, comprising: a base 5 disposed on the ground; a rotary body 6 capable of rotating relative to the base 5 about a first axis A extending in the vertical direction; and a first arm 7 capable of rotating relative to the rotary body 6 about a second horizontal axis B. Additionally, robot 2 comprises: a second arm 8 capable of rotating relative to the first arm 7 about a third axis C parallel to the second axis B; and a three-axis wrist unit 9 mounted at the front end of the second arm 8.

[0023] The wrist unit 9 has a wrist axis 10 at its front end with a range of motion of 360° or more, for example, -200° to +200°. A hand (tool) S for holding a workpiece W is mounted on the wrist axis 10, and the gripping point of the workpiece W held by the hand S is set as the tool tip point. Tool coordinates are set at the tool tip point, with the tool tip point as the origin and fixed to the hand S.

[0024] Camera 3 is positioned downwards above the workpiece W placed on the worktable 11, and can detect the position and orientation of the workpiece W by photographing it. The detected position and orientation information of the workpiece W is sent to the control device 4.

[0025] The control device 4 has at least one processor and a memory.

[0026] The control device 4 stores the pre-taught motion program and controls the robot 2 according to the motion program.

[0027] An example of an action program is as follows Figure 2 As shown.

[0028] In the figure, “position of each axis [1]” is the action command that moves robot 2 from its current position to position [1] by the movement of each axis. Here, position [1] is the delivery position P1 of workpiece W. In addition, “100%” indicates the movement speed of each axis.

[0029] Additionally, the positions [2] and [3] set as the destination of movement in the fourth to sixth rows surrounded by "Removal Start:" and "Removal End:" are selected as the positions for processing in this embodiment. Position [2] is the approach position of the hand S relative to the workpiece W (second teaching point) P2, and position [3] is the removal position of holding the workpiece W (first teaching point) P3.

[0030] The "straight line" in the diagram is a linear motion command that moves the tool tip point in a straight line. Linear motion commands cause each joint to move in the direction that minimizes rotation along the path from its current position to the target teach point. Figure 3 In the diagram, the movement towards position P2 and the removal position P3 constitutes a linear movement of the tool tip. "100mm / sec" refers to the speed along the direction of the linear movement.

[0031] like Figure 3 As shown, the approach position P2 is positioned relative to the take-out position P3, at a location that is moved vertically upward by a distance greater than the height of the workpiece W. The delivery position P1 is positioned, for example, sufficiently far away from the approach position P2 and the take-out position P3 in the horizontal direction.

[0032] Thus, the hand S can move from the delivery position P1 to the approach position P2, which allows the hand S to approach the workpiece W without interfering with the workpiece W, thus becoming a ready state for holding the workpiece W.

[0033] Furthermore, the hand S holding the workpiece W at the take-out position P3 is not immediately moved to the delivery position P1, but instead moves again to the approach position P2. This allows the hand S's grip on the workpiece W to be confirmed when the workpiece W is slightly lifted from the worktable 11.

[0034] In addition, when the camera 3 detects the position and orientation of the next workpiece W to be handled, the control device 4 corrects the position and orientation of the tool coordinates at the approach position P2 and the take-off position P3 based on the detected position and orientation.

[0035] Specifically, at position P3, based on the position and orientation of the workpiece W (represented by solid lines) detected by camera 3, corrections are made in... Figure 4 The dashed lines represent the position and orientation of the tool coordinates used to hold the workpiece W, as specified in the motion procedure. Additionally, at the approach position P2, the tool coordinates position and orientation are corrected to maintain the relative relationship with the removal position P3 as specified in the original motion procedure.

[0036] In this case, the result of correcting the tool coordinates at the extraction position P3 is that sometimes the rotation angles of each joint of robot 2 calculated based on the corrected tool coordinates position and orientation exceed the range of motion.

[0037] Specifically, such as Figure 5 As shown in the figure, the following example illustrates the situation: the angle of the front wrist axis 10 at the approach position P2 of the action program is +150°, and the angle of the front wrist axis 10 at the take-off position P3 is +190°.

[0038] Furthermore, assuming that the angle of the front wrist axis 10 at the extraction position P3 is +210° after correction based on the position and orientation of the workpiece W detected by camera 3, the angle of the front wrist axis 10 is corrected to +170° at the approach position P2, so that the relative relationship with the extraction position P3 is maintained even after correction.

[0039] In this case, in this embodiment, the control device 4 performs the following processing at the approach position P2 and the take-off position P3 selected in the operation program.

[0040] That is, it is determined whether the angle of the corrected front wrist axis 10, +210°, exceeds +200°, which is the limit of movement. If it does, the angle of the front wrist axis 10 is changed to -150°, which is within the movement range of -360° from +210°.

[0041] Furthermore, the angle of the corrected front wrist axis 10 at the near position P2 is +170°. Although it is within the range of motion, in order to maintain the relative relationship with the removal position P3 before the correction, it is changed to -190°, which is -360° different.

[0042] Next, the control method of the robot 2 of the robot system 1 configured as described in this embodiment will be explained.

[0043] like Figure 6 As shown, in the control method of this embodiment, firstly, the position and orientation of the workpiece W are detected by the camera 3 (step S1), and the tool coordinates are corrected at the extraction position P3 and the near position P2 based on the detected position and orientation (step S2).

[0044] Then, based on the corrected tool coordinates and posture, calculate the angles of each joint at the extraction position P3 and the near position P2 (step S3), and determine whether the angle of the front wrist axis 10 exceeds the movement limit (step S4).

[0045] Furthermore, in the control method of this embodiment, if it is determined that the action limit has been exceeded, the angle of the front wrist axis 10 at the take-out position P3 and the approach position P2 is changed to an angle that is 360° apart (step S5).

[0046] According to the robot system 1 and control method of this embodiment, corrections are made based on the detection results detected by the camera 3, thereby changing the angle of the front wrist axis 10 at the extraction position P3 to an angle 360° different from the maximum. Thus, the angle of the front wrist axis 10 is configured within the range of motion, preventing erroneous stops caused by exceeding the maximum range of motion.

[0047] In this case, in this embodiment, not only the forehand wrist axis 10 at the take-off position P3, which exceeds the limit of motion through correction, but also the forehand wrist axis 10 at the approach position P2, which does not exceed the limit of motion, is changed to an angle differing by 360°. Thus, as... Figure 7 As shown, the hand S is not rotated significantly between the approach position P2 and the removal position P3 when it approaches the workpiece W, thus preventing interference between the hand S and the workpiece W or surrounding objects. Conventionally, since the robot 2 only checks and controls the range of motion for the next target position, the following problems exist: for example, if the front wrist axis 10 is rotated 360° during the movement from the approach position P2 to the removal position P3, the hand S may interfere with surrounding objects or fail to hold the workpiece W. This problem can be avoided with the robot system 1 and control method of this embodiment.

[0048] On the other hand, for the delivery position P1 which is not selected in the motion procedure, since the front wrist axis 10 is not changed by 360°, the front wrist axis 10 rotates significantly during the movement from the delivery position P1 to the approach position P2. Since the delivery position P1 is positioned sufficiently far away from the approach position P2, even if the hand S rotates significantly along the path to the approach position P2, it will not interfere with the workpiece W and surrounding objects.

[0049] Furthermore, in this embodiment, for all teach points selected in the motion program by using “Retrieve Start:” and “Retrieve End:”, the following processing is performed: the angle of the front wrist axis 10 that exceeds the motion limit through correction is increased or decreased by 360°. Alternatively, a subroutine may be defined within the motion program, and the above processing may be performed only on all teach points within the subroutine, and may also be set as an additional instruction to each motion instruction (e.g., linear position [2] 100mm / sec retrieval). In addition, it is acceptable to apply the present invention to robot motion instructions as long as one knows how, and is not limited to the description method described in this embodiment.

[0050] Furthermore, in this embodiment, the above processing is performed on a single first teaching point, namely the take-out position P3, where the workpiece W is operated using the hand S, and a single adjacent second teaching point, namely the approach position P2. Alternatively, the above processing can be performed on multiple first teaching points and multiple second teaching points.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1: Robot System

[0053] 2: Robot

[0054] 3: Camera (sensor)

[0055] 4: Control device

[0056] 10: Front wrist axis

[0057] P2: Approaching Position (Second Teaching Point)

[0058] P3: Retrieve the location (first teaching point)

[0059] S: Hand (tool)

[0060] W: Workpiece

Claims

1. A robot system, characterized in that, have: A multi-jointed robot with a tool for working on a workpiece mounted on its forehand wrist axis, which has a range of motion of more than 360°. Sensors that detect the position and orientation of the workpiece; as well as A control device that controls the robot according to an action program. The action procedure includes: multiple teaching points, which specify the position and posture of the tool; And the action command, which causes the teach point to move in the direction that minimizes the rotation of each joint. The control device is used for, Based on the position and orientation of the workpiece detected by the sensor, the position and orientation of the tool at the first teaching point where it operates on the workpiece, and at one or more other teaching points adjacent to the first teaching point among the plurality of teaching points, are corrected. Determine whether the angle of the front wrist axis at the first teaching point, calculated based on the corrected position and posture of the tool, exceeds the movement limit. If the movement limit is exceeded, the angle at the first teaching point and the angle at the other teaching points that have been corrected are changed to angles within the range of motion that are increased or decreased by 360° beyond the center of the range of motion.

2. The robot system according to claim 1, characterized in that, In the action procedure, a first teaching point and one or more second teaching points adjacent to the first teaching point are selected. The control device increases or decreases the angle of the front wrist axis at the selected first teaching point and second teaching point by 360° respectively.

3. A control method for controlling a robot according to an action program in a robot system, the robot system comprising: a multi-jointed robot having a tool for working on a workpiece mounted on a fore-end wrist axis having a range of motion of more than 360°; and a sensor for detecting the position and orientation of the workpiece, characterized in that, The motion procedure includes: multiple teach points that define the position and orientation of the tool; and motion commands that cause the teach points to move in directions that minimize the amount of rotation between each joint. The control method includes: Based on the position and orientation of the workpiece detected by the sensor, the position and orientation of the tool at the first teaching point for operating on the workpiece and at one or more other teaching points adjacent to the first teaching point among the plurality of teaching points are corrected. Determine whether the angle of the front wrist axis at the first teaching point, calculated based on the corrected position and posture of the tool, exceeds the limit of motion; and If the movement limit is exceeded, the angle at the first teaching point and the angle at the other teaching points that have been corrected are changed to angles within the range of motion that are increased or decreased by 360° beyond the center of the range of motion.

4. The control method according to claim 3, characterized in that, Changing the angle of the front wrist axis at the first teaching point and one or more other teaching points adjacent to the first teaching point to increase or decrease the angle within the 360° range of motion includes: In the action procedure, a first teaching point and one or more second teaching points adjacent to the first teaching point are selected; and The angle of the front wrist axis at the selected first teaching point and second teaching point is increased or decreased by 360° respectively.

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