Robot and its control method

Abstract

To realize a robot which can directly teach more precise action with a smaller force.SOLUTION: A robot (1) includes a robot hand (11), a robot arm (12), a force sensor (13), and a control device (15). The control device (15) determines a position of the robot hand (11) according to a force detected by the force sensor (13) through admittance control and commands the robot arm (12) to move the robot hand (11) to the determined position. Further, the control device (15) records the command to the robot arm (12) as teaching data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a robot equipped with a robot arm and a robot hand, and also to a method for controlling such a robot. [Background technology]

[0002] Direct teaching has been used as a conventional teaching method for teaching a robot to perform an action. Direct teaching is a method in which an instructor teaches a robot an action by directly moving the robot hand or robot arm. Patent Document 1, for example, is an example of a document disclosing direct teaching. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2019-018340 Summary of the Invention [Problem to be solved by the invention]

[0004] In the working robot described in Patent Document 1, the robot arm is subjected to impedance control (motion input / force output type control) during direct teaching. As a result, a relatively large force is required when the instructor directly moves the robot arm or robot hand. Furthermore, due to the influence of inertia of each link, it is difficult for the instructor to move the robot arm as desired. As a result, it is difficult to directly teach precise movements to the robot.

[0005] One aspect of the present invention has been made in view of the above problems, and its object is to realize a robot that can be directly taught more precise movements with less force. [Means for solving the problem]

[0006] A robot according to one aspect of the present invention includes a robot arm, a robot hand attached to the robot arm, a force sensor that detects a force acting on the robot hand, and a control device. The control device determines the position of the robot hand by admittance control (force input / motion output type control) in accordance with the force detected by the force sensor, commands the robot arm to move the robot hand to the determined position, and records the command to the robot arm as teaching data.

[0007] A method for controlling a robot according to the present invention is a method for controlling a robot including a robot arm, a robot hand attached to the robot arm, and a force sensor for detecting a force acting on the robot hand, and includes a control step of determining the position of the robot hand by admittance control (force input / motion output type control) in accordance with the force detected by the force sensor, commanding the robot arm to move the robot hand to the determined position, and recording the command to the robot arm as teaching data. [Effects of the Invention]

[0008] According to one aspect of the present invention, a robot can be realized that can be directly taught more precise movements with less force. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating a configuration of a robot according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the functions of a control device provided in the robot shown in FIG. [Figure 3] 10 is a graph showing the change over time in the amount of operation input to the operation device, the position of the robot hand, and the force sensitivity detected by the force sensor, obtained when the admittance control unit does not have a force sensitivity attenuation function. [Figure 4]10 is a graph showing the change over time in the amount of operation input to the operation device, the position of the robot hand, and the force sensitivity detected by the force sensor, obtained when the admittance control unit has a force sensitivity attenuation function. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Robot configuration) A robot 1 according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the configuration of the robot 1 according to this embodiment.

[0011] The robot 1 is a robot that can be directly taught any operation. In this embodiment, the operation that can be directly taught to the robot 1 is assumed to be a press-fitting operation in which a second member W2 (e.g., a metal pin) is press-fitted into an opening or recess of a first member W1 (e.g., a metal collar). However, the operation that can be directly taught to the robot 1 is arbitrary and is not limited to this.

[0012] As shown in FIG. 1, the robot 1 includes a robot hand 11, a robot arm 12, a force sensor 13, an operating device 14, and a control device 15.

[0013] The robot hand 11 is a mechanism for gripping a workpiece (a second member W2 in this embodiment). In this embodiment, a chuck is used as the robot hand 11. The robot arm 12 is a mechanism for moving the robot hand 11. In this embodiment, a vertical multi-joint arm is used as the robot arm 12.

[0014] The robot hand 11 is attached to the tip of the robot arm 12 via a force sensor 13. The force sensor 13 is a sensor for detecting forces in three directions (x-, y-, and z-axis directions) acting on the robot hand 11, particularly forces in three directions when a user attempts to move the robot hand 11 in direct teaching. In this embodiment, a six-axis force sensor is used as the force sensor 13. However, any sensor that can detect forces in three directions can be used as the force sensor 13.

[0015] An operating device 14 is attached near the tip of the robot arm 12. The operating device 14 is a device for accepting an operation to specify the speed of the robot hand 11 in one direction (z-axis direction), or the speed in one direction at which the user intends to move the robot hand 11 in direct teaching. In this embodiment, a joystick is used as the operating device 14. However, any device can be used as the operating device 14 as long as it is capable of accepting an operation to specify the speed in one direction.

[0016] The control device 15 determines the position of the robot hand 11 according to the force detected by the force sensor 13 and the amount of operation input to the operating device 14 (the tilt of the joystick in this embodiment), and commands the robot arm 12 to move the robot hand 11 to the determined position. The control device 15 then records the command to the robot arm as teaching data. This realizes teaching. In this embodiment, a PC (Personal Computer) is used as the control device 15. However, any device can be used as the control device 15 as long as it can realize the functions of the control device 15 described below.

[0017] The control device 15 operates in either a first operation mode or a second operation mode. Here, the first operation mode is a mode in which the force F x ,F y ,F zThe second operation mode is an operation mode in which the positions x, y, and z of the robot hand 11 in three directions are determined by admittance control (force input / motion output type control) according to the force F in two directions detected by the force sensor 13. x ,F y In this mode, the positions x and y of the robot hand 11 in two directions are controlled by admittance in accordance with the operation amount θ input to the operation device 14, and the position z of the robot hand 11 in one direction is determined by speed control in accordance with the operation amount θ input to the operation device 14. The functions of the control device 15 will be described in detail below.

[0018] (Controller function) The functions of the control device 15 provided in the robot 1 will be described with reference to Fig. 2. Fig. 2 is a functional block diagram showing the functions of the control device 15.

[0019] The control device 15 includes an admittance control unit 151, a multiplication unit 152, an integration unit 153, and a mode switch 154. The control device 15 receives the force F x ,F y ,F z and the operation amount θ (for example, the tilt of the joystick) input to the operation device 14. x ,F y ,F z may be the force detected by the force sensor 13 itself, or may be the force detected by the force sensor 13 shaped by a dead zone.

[0020] In the first operation mode, the admittance control unit 151 calculates the force F in three directions detected by the force sensor 13. x ,F y ,F z In response to this, the positions x, y, and z of the robot hand 11 in three directions are determined by admittance control. Specifically, the positions x, y, and z of the robot hand 11 in three directions are determined by solving (integrating) the following equation of motion (1).

[0021]

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[0022] Here, x' represents the first derivative of the position x, dx / dt (velocity), and x" represents the second derivative of the position x, d 2 x / dt 2 (acceleration). Also, y' represents the first derivative of the position y, dy / dt (velocity), and y" represents the second derivative of the position y, d 2 y / dt 2 (acceleration). Also, z' represents the first derivative of position z, dz / dt (velocity), and z" represents the second derivative of position z, d 2 z / dt 2 (acceleration). Also, m x ,m y , m z is a constant representing the virtual mass (e.g., 10 kg). x ,c y , c z is a constant representing the virtual viscosity coefficient (for example, 100 kg / s). x ,α y ,α z is a constant (for example, 1) that indicates the force sensitivity. Note that the position x can be expressed by other equations of motion, for example, x' = α x F x The same applies to the positions y and z.

[0023] In the second operation mode, the admittance control unit 151 also calculates the force F in two directions detected by the force sensor 13. x ,F y In response to this, the positions x and y of the robot hand 11 in two directions are determined by admittance control. Specifically, the positions x and y of the robot hand 11 in two directions are determined by solving (integrating) the following equation of motion (2a).

[0024]

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[0025] Here, x' represents the first derivative of the position x, dx / dt (velocity), and x" represents the second derivative of the position x, d 2 x / dt 2 (acceleration). Also, y' represents the first derivative of the position y, dy / dt (velocity), and y" represents the second derivative of the position y, d 2 y / dt 2 (Acceleration) .Ma t, m x ,m y is a constant representing the virtual mass (e.g., 10 kg). x ,c y is a constant representing the virtual viscosity coefficient (for example, 200 kg / s). x ,α y is a constant (for example, 1) that indicates the force sensitivity. Note that the position x can be expressed by other equations of motion, for example, x' = α x F x The same applies to the position y.

[0026] In the second operation mode, the multiplication unit 152 and the integration unit 153 determine the position z of the robot hand 11 in the remaining one direction by speed control in accordance with the operation amount θ input to the operation device 14. Specifically, the multiplication unit 152 and the integration unit 153 determine the position z of the robot hand 11 in the remaining one direction by solving (integrating) the following equation of motion (2b).

[0027]

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[0028] Here, K is a conversion coefficient (for example, 0.0005) that converts the manipulated variable θ into the velocity z'. Note that the position z can be calculated using other equations of motion, for example, z" = -( c z / m z )z'+(α z / m z )θ.

[0029] The mode switch 154 is a switch for switching the operation mode according to the operation amount θ input to the operation device 14. Specifically, when θ=0, that is, when z'=0, the operation mode is switched to the first operation mode, and when θ≠0, that is, when z'≠0, the operation mode is switched to the second operation mode.

[0030] According to the above configuration, in the first operation mode, the three-directional forces F detected by the force sensor 13 are x ,F y ,F z The three positions x, y, and z of the robot hand 11 can be determined by admittance control according to the position of the robot hand 11. That is, in the first operation mode, the force of the user trying to move the robot hand 11 can be assisted by the control of the robot arm 12 by the control device 15. This allows the user to perform more precise direct teaching with less force.

[0031] However, in addition to the user's force to move the robot hand 11, a reaction force in the z-axis direction may act from the workpiece on the robot hand 11. For example, in a press-fitting operation, in addition to the user's force to move the robot hand 11, a reaction force in the z-axis direction may act on the robot hand 11 from the second member W2. In such a case, in the first operation mode in which three-way admittance control is performed, it becomes difficult to move the robot hand 11 to a position desired by the user.

[0032] In contrast, according to the above configuration, in the second operation mode, the two-directional forces F detected by the force sensor 13 are x ,F yThe positions x and y of the robot hand 11 in two directions can be determined by admittance control in accordance with the operation amount θ input to the operation device 14, and the position z of the robot hand 11 in one direction can be determined by speed control in accordance with the operation amount θ input to the operation device 14. Therefore, even if a reaction force in the z-axis direction acts on the robot hand 11 from the workpiece, it becomes easy to move the robot hand 11 to a position desired by the user by switching the operation mode from the first operation mode to the second operation mode.

[0033] The switch from the first operation mode to the second operation mode is triggered by the operation amount θ of the operation device 14 no longer being 0. For example, if the operation device 14 is a joystick, the switch from the first operation mode to the second operation mode occurs when the user touches the joystick and the joystick begins to tilt. Therefore, the user can transition to control using the operation device 14 with a natural operation without being particularly conscious of the switch in operation mode.

[0034] Furthermore, the control device 15 includes a safety switch 155. The safety switch 155 detects the force F detected by the force sensor 13 in the second operation mode. x ,F y ,F z , and a switch for setting the velocity z' of the robot hand 11 to 0 (stopping the movement in the z-axis direction) according to the position z of the robot hand 11. Specifically, where z0 is a predetermined constant, z>z0 and F x ≠0, F y ≠0 or F z If z′ is not 0, the velocity z′ of the robot hand is set to 0. Here, z0 is, for example, the position of the robot hand 11 when the height of the lower surface of the second member W2 and the height of the upper surface of the first member W1 are the same.

[0035] According to the above configuration, when z>z0, if a force acts on the robot hand 11, the velocity z' of the robot hand 11 in the z-axis direction becomes 0 regardless of the operation amount θ of the operating device 14. This reduces the possibility of injuring the user, for example, if the user's hand gets caught between the first member W1 and the second member W2. Note that if z≦z0, even if a force acts on the robot hand 11, the velocity z' of the robot hand 11 in the z-axis direction becomes Kθ. Therefore, even if a reaction force in the z-axis direction acts on the robot hand 11 from the second member W2, the press-fitting operation of the second member W2 can be completed.

[0036] (Additional information on the function of the admittance control section) In the second operation mode, the admittance control unit 151 calculates the force F acting on the robot hand 11. x ,F y The number of times the sign of x ,n y Depending on the force sensitivity α x ,α y Specifically, the force sensitivity α is determined according to the following formula (3): x ,α y In the following formula (3), r is a constant greater than 1 that represents the attenuation rate.

[0037]

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[0038] When the first member W1 and the second member W2 are fitted together, chattering may occur during the press-fitting operation. Here, chattering refers to, for example, the following actions being repeated: (1) the side surface of the second member W2 collides with the inner wall of the opening on the x-axis positive side of the first member W1, resulting in a force Fx in the x-axis negative direction, (2) the second member W2 moves in the x-axis negative direction, (3) the side surface of the second member W2 collides with the inner wall of the opening on the x-axis negative side of the first member W1, resulting in a force Fx in the x-axis positive direction, and (4) the second member W2 moves in the x-axis positive direction. In contrast, with the above configuration, the force F xEach time the sign of changes, the force sensitivity α x Since the vibration can be attenuated, the occurrence of chattering can be suppressed.

[0039] FIG. 3 shows the force F detected by the force sensor 13 when the admittance control unit 151 does not have this function. x ,F y ,F z , the operation amount θ input to the operation device 14, the position x, y, z of the robot hand 11, and the force sensitivity α x ,α y 10 is a graph showing the change over time in force sensitivity α x ,α y Since is constant, the force F x ,F y ,F z It can be seen that chattering occurs, with the position y fluctuating slightly.

[0040] FIG. 4 shows the force F detected by the force sensor 13, which is obtained when the admittance control unit 151 has this function. x ,F y ,F z , the operation amount θ input to the operation device 14, the position x, y, z of the robot hand 11, and the force sensitivity α x ,α y 10 is a graph showing the change over time in force sensitivity α x ,α y It can be seen that the chattering that occurs when the control device 15 does not have this function is suppressed because the signal attenuates rapidly.

[0041] (Additional notes) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means included in the above-described embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0042] 1. Robot 11. Robot Hand 12. Robot arm 13 Force sensor 14...Operating device 15. Control device

Claims

1. A robotic arm, a robot hand attached to the robot arm; a force sensor that detects a force acting on the robot hand; a control device that determines the position of the robot hand by admittance control in accordance with the force detected by the force sensor, commands the robot arm to move the robot hand to the determined position, and records the command to the robot arm as teaching data; an operating device, The control device In a first operation mode, the positions of the robot hand in three directions are determined by admittance control in accordance with the forces in three directions detected by the force sensor; a robot in which, in a second operation mode, the positions of the robot hand in two directions are determined by admittance control in accordance with the forces in two directions detected by the force sensor, and the position of the robot hand in the remaining direction is determined by speed control in accordance with the operation amount input to the operation device.

2. In the first operation mode, the control device detects a force F ｘ , F ｙ , F ｚ and force sensitivity α ｘ , α ｙ , α ｚ and determining the x, y, and z positions of the robot hand by solving a motion equation including:

2. The robot according to claim 1 .

3. The equation of motion is the following equation (1):

3. The robot according to claim 2. [Equation 1] Here, m ｘ , m ｙ , m ｚ is a constant representing the virtual mass, and c ｘ , c ｙ , c ｚ is a constant representing the virtual viscosity coefficient.

4. In the second operation mode, the control device detects the force F ｘ , F ｙ and force sensitivity α ｘ , α y to determine the positions x, y of the robot hand, and by solving a second equation of motion including an operation amount θ input to the operation device, determine the position z of the robot hand. The robot according to any one of claims 1 to 3.

5. The first equation of motion is the following equation (2a), and the second equation of motion is the following equation (2b):

5. The robot according to claim 4. [Equation 2] [Equation 3] Here, m ｘ , my is a constant indicating the virtual mass, and c ｘ , c y are constants representing virtual viscosity coefficients, and K is a conversion coefficient for converting the manipulated variable θ into a velocity z′.

6. In the second operation mode, the control device adjusts the force sensitivity α ｘ , α ｙ Attenuate the 6. The robot according to claim 4 or 5.

7. and in the second operation mode, the control device determines the position of the robot hand in one direction according to the force detected by the force sensor and the position of the robot hand so that the velocity of the robot hand in the one direction becomes 0. The robot according to any one of claims 1 to 6.

8. the operation device is a joystick attached to the robot arm, and the operation amount is a tilt of the joystick. The robot according to any one of claims 1 to 7.

9. 9. The robot according to claim 1, wherein the motion to be taught is a motion of press-fitting a second member into an opening or a recess of a first member.

10. A method for controlling a robot including a robot arm, a robot hand attached to the robot arm, and a force sensor that detects a force acting on the robot hand, comprising: a control step of determining a position of the robot hand by admittance control in accordance with the force detected by the force sensor, commanding the robot arm to move the robot hand to the determined position, and recording the command to the robot arm as teaching data; In a first operation mode, the positions of the robot hand in three directions are determined by admittance control in accordance with the forces in three directions detected by the force sensor; In a second operation mode, the positions of the robot hand in two directions are determined by admittance control in accordance with the forces in two directions detected by the force sensor, and the position of the robot hand in the remaining one direction is determined by speed control in accordance with the operation amount input to the operation device. A robot control method comprising:

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