Control device for a robot with an arm

Abstract

To provide a control device of a robot having an arm that simply stops an arm as compared with a conventional one, by generating a load of a suitable magnitude to an operator at the time of lead-through.SOLUTION: A control device of a robot having an arm, includes a motor that generates torque in each shaft of the robot, a torque generation control portion that controls the motor so as to generate cancellation torque cancelling the friction of each shaft of the robot when the robot is controlled by external force following, and a torque changing portion that changes the cancellation torque to be a reference value or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a control device for a robot having an arm.

Background Art

[0002] When directly teaching a robot having an arm (hereinafter sometimes referred to as an "arm robot"), or when manually operating the robot in a collaborative work between the robot and an operator, a technique for causing a lead-through operation is generally used.

[0003] Here, "lead-through" specifically refers to a teaching method in which an operator grips an arm or a hand provided on the robot and moves the robot to perform teaching.

[0004] As one of the existing technologies for realizing lead-through, there is a control method in which a torque for amplifying the force applied by the operator to the arm and a torque for canceling the friction generated at each axis of the robot (canceling torque) are applied to the components constituting the robot.

[0005] In this regard, in a control device used for flexible control of a robot having at least one joint, a technique for calculating a friction compensation torque according to speed from a friction model is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the lead-through techniques using the existing technologies described above, the torque element includes torque that completely cancels out friction, so the robotic arm behaves as if there were no friction.

[0008] Therefore, in the field of robotic arms, there is a problem in that during lead-through, the arm moves due to motor torque resulting from estimation errors in the force applied by the operator, making it difficult to stop. In addition, there is a problem in that an appropriate load is not generated for the operator during lead-through at a constant speed.

[0009] Therefore, during the lead-through of the robotic arm, it is desirable to be able to stop the arm more easily than before by generating a load of an appropriate size on the operator. [Means for solving the problem]

[0010] One aspect of the present disclosure is a control device for a robot having an arm, comprising: a motor that generates torque on each axis of the robot; a torque generation control unit that controls the motor to generate a counteracting torque to counteract friction on each axis of the robot when controlling the robot by following an external force; and a torque changing unit that changes the counteracting torque to a reference value or less. [Effects of the Invention]

[0011] According to one embodiment, a moderate load is generated on the operator during lead-through, making it possible to stop the arm more easily than in conventional methods. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the lead-through method in the first embodiment. [Figure 2] This is a functional block diagram of the control device in the first embodiment. [Figure 3] This figure shows the operational range of the robotic arm in the first embodiment. [Figure 4] This is a functional block diagram of the control device in the second embodiment. [Modes for carrying out the invention]

[0013] [1. First Embodiment] The control device 1, which is the first embodiment of the present invention, will be described below with reference to Figures 1 to 3.

[0014] [1.1 Structure of the Invention] Figure 1 is a diagram showing the lead-through teaching method assumed in this embodiment. In the example shown in Figure 1, the arm robot 2 comprises an arm 21 and a robot body 22. Furthermore, the arm 21 comprises links 23A to 23C, joints 24A to 24C, and a hand 25. More specifically, joint 24A rotatably connects link 23A and link 23B, joint 24B rotatably connects link 23B and link 23C, and joint 24C rotatably connects link 23C to the robot body 22. Furthermore, joint 24 of link 23A A A hand 25 is installed at the opposite end. This hand 25 becomes the tip of the arm 21.

[0015] Furthermore, each of the joints 24A to 24C is equipped with a servo motor 27 for generating rotational driving force (torque).

[0016] Operator 3 performs teaching on the robotic arm 2 by moving the arm 21 while gripping either the arm 21 or the hand 25.

[0017] Figure 2 is a functional block diagram of the control device 1 according to this embodiment. The control device 1 includes a torque generation control unit 11 and a torque modification unit 12.

[0018] As shown in FIG. 1, when controlling the arm robot 2 by lead-through (external force following), the torque generation control unit 11 controls the servo motor 27 to cancel the friction of the joints 24A to 24C of the arm robot 2 and generates a cancellation torque.

[0019] The torque change unit 12 changes the cancellation torque to be below the reference value. As a result, the torque generated by the servo motor 27 is changed to be below the reference value.

[0020] Particularly in this embodiment, a speed detection unit 28 for detecting the speed of the servo motor 27 is provided in the arm robot 2, and the speed value of the servo motor 27 detected by the speed detection unit 28 is fed back to the torque change unit 12. The torque change unit 12 changes the cancellation torque to be below the reference value based on this speed feedback value.

[0021] Note that the speed detection unit 28 can be realized, for example, using a rotary encoder.

[0022] Further, when the speed feedback value is below the first threshold, the torque change unit 12 may change the cancellation torque to be 0 or more and below the second threshold, and when the speed feedback value is above the third threshold which is larger than the first threshold, the torque change unit 12 may change the cancellation torque to be 0 or more and below the fourth threshold which is larger than the second threshold.

[0023] For example, when the speed feedback value is relatively small and below the first threshold, the torque change unit 12 sets the gain multiplying the cancellation torque to a value close to 0 within the range of 0 to 1, and when the speed feedback value is relatively large and above the third threshold, the torque change unit 12 may adjust the gain multiplying the cancellation torque within the range of 0 to 1.

[0024] Figure 3 shows the movable range of the arm 21 of the robotic arm 2 shown in Figure 1. The robotic arm 2 has a movable range as shown in Figure 1. When the hand 25 reaches the boundary of the movable range during lead-through teaching, the robotic arm 2 stops. Since operator 3 is not clearly aware of the boundary of the movable range, if the robotic arm 2 suddenly stops, operator 3 may not be able to react to the sudden movement of the robotic arm 2 and may be injured. In addition, a large load is placed on the robotic arm 2, increasing the risk of malfunction.

[0025] Therefore, as shown in Figure 3, the torque changing unit 12 may change the torque such that the distance x and the gain used to change the cancellation torque have a positive correlation when the distance x between the boundary of the arm's movable region and the center point (TCP: Tool Center Point) of the arm's tip is less than or equal to a fifth threshold α, and may set this gain to 0 when the distance x is 0.

[0026] [1.2 Effects of the First Embodiment] The control device 1 according to this embodiment includes a torque generation control unit 11 that controls the servo motor 27 to generate a counteracting torque to counteract the friction of each axis of the arm robot 2 when controlling the arm robot 2 by external force tracking, and a torque modification unit 12 that changes this counteracting torque to a reference value or less.

[0027] Therefore, during lead-through, a moderate load is generated on the operator, making it easier to stop the arm than before.

[0028] Furthermore, in the control device 1 according to this embodiment, the torque changing unit 12 changes the cancellation torque based on the speed feedback value from the servo motor 27.

[0029] Therefore, depending on the lead-through operation, the ease of stopping and the load on operator 3 can be appropriately adjusted.

[0030] Furthermore, in the control device 1 according to this embodiment, the torque changing unit 12 changes the cancellation torque to 0 or more and 2 or less when the speed feedback value is 1 or less than or equal to a first threshold, and changes the cancellation torque to 0 or more and 4 or less when the speed feedback value is 1 or more than a third threshold which is greater than the first threshold, and 2 or less when the speed feedback value is 1 or more than a third threshold which is greater than the first threshold.

[0031] Therefore, when lead-through is not performed, it becomes possible to achieve both the ease of stopping the arm robot 2, which is due to the stability resulting from the reduction in counteracting torque, and the ease of movement, which is due to the optimal load achieved by the increase in counteracting torque when lead-through is performed.

[0032] Furthermore, in the control device 1 according to this embodiment, the torque changing unit 12 changes the torque such that the distance between the boundary of the movable area of ​​the arm 21 and the center point (TCP) of the tip of the arm 21 has a positive correlation with the gain used to change the cancellation torque when the distance between the boundary and the center point (TCP) of the tip of the arm 21 is less than or equal to a fifth threshold, and sets the gain to 0 when the distance is 0.

[0033] Therefore, when the arm 21 of the robotic arm 2 reaches the boundary of its operating range, it is prevented from coming to a sudden stop and can be brought to a smooth stop.

[0034] [2. Second Embodiment] Hereinafter, with reference to Figure 4, a control device 1A, which is a second embodiment of the present invention, will be described. For the sake of clarity, in the following, only the differences between control device 1A and control device 1 will be described, and other points will be omitted from the explanation.

[0035] [2.1 Structure of the Invention] Figure 4 is a functional block diagram of the control device 1A according to this embodiment. Unlike the control device 1, the control device 1A includes a torque changing unit 12A instead of the torque changing unit 12.

[0036] The torque modification unit 12A obtains an estimated value of the force applied by the operator 3 to the arm 21 from the force estimation unit 29 located in the arm 21 or hand 25 of the robotic arm 2, and changes the counteracting torque to a value below a reference value based on this estimated value. The force estimation unit 29 is implemented, for example, by a force sensor.

[0037] [2.2 Effects of the Second Embodiment] In the control device 1A according to this embodiment, the torque changing unit 12A changes the torque based on an estimated value of the force applied by the operator to the arm 21.

[0038] Therefore, depending on the lead-through operation, the ease of stopping and the load on operator 3 can be appropriately adjusted. [Explanation of Symbols]

[0039] 1,1A control device 2 Arm Robot 3 Operators 11 Torque generation control unit 12,12A Torque change section 21 Arms 25 hands 27 Servo motor 28 Speed ​​detection unit 29 Force estimation section

Claims

1. A control device for a robot having an arm, When controlling the robot by tracking an external force, a torque generation control unit controls the motor to generate a counteracting torque that cancels out the friction of the robot's axis, A torque adjustment unit adjusts the cancellation torque to a reference value or less such that a predetermined load is generated in response to the external force applied to the arm, based on either the speed feedback value from the motor or the estimated value of the external force applied to the arm. A control device equipped with the following features.

2. A control device for a robot having an arm, When controlling the robot by tracking an external force, a torque generation control unit controls the motor to generate a counteracting torque that cancels out the friction of the robot's axis, A torque changing unit adjusts the cancellation torque to a reference value or less such that a predetermined load is generated in response to an external force applied to the arm, by multiplying the cancellation torque by a gain of 0 or more and less than 1 based on the distance between the boundary of the movable region of the arm and the center point of the tip of the arm. A control device equipped with the following features.

3. The control device according to claim 1, wherein the torque changing unit adjusts the cancellation torque to a value below the reference value by adjusting it to a value below the second threshold or a value below the fourth threshold, and when the speed feedback value from the motor or the estimated value of the external force applied by the user to the arm is below the first threshold, the cancellation torque is adjusted to be 0 or more and below the second threshold, and when the speed feedback value or the estimated value is greater than or equal to a third threshold greater than the first threshold, the cancellation torque is adjusted to be 0 or more and below the fourth threshold greater than the second threshold.

4. The control device according to claim 2, wherein the torque changing unit adjusts the cancellation torque such that the distance and the gain used to change the cancellation torque have a positive correlation when the distance between the boundary of the movable region of the arm and the center point of the tip of the arm is less than or equal to a fifth threshold, and sets the gain to 0 when the distance is 0.

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