Robot arm, robot system, and suppression method

Abstract

A robot arm, a robot system, and a suppression method for suppressing the generation of resonance between a belt and a motor. This robot arm is provided with: a first joint; the first arm unit has a first driving part which includes a motor and a belt for transmitting an output of the motor, the first driving part driving the first joint, and a pressing device which presses the belt at a predetermined position of the belt; a second arm unit connected to the first arm unit via the first joint; and an inertial sensor provided on the second arm unit, the natural vibration frequency of the belt pressed by the pressing device being outside the range of the operating frequency of the motor.

Description

Technical Field

[0001] The present disclosure relates to a robotic arm, a robotic system, and a suppression method. Background Art

[0002] Patent Document 1 describes a technique related to a robot that performs feedback control using output from an inertial sensor.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2012-139807

[0004] In the case of a belt that transmits the power of the motor to the arm, resonance may occur due to the coincidence of the operating frequency of the motor and the natural vibration frequency of the belt. Sometimes, due to the generation of resonance, the operation of feedback control based on the output of the inertial sensor becomes unstable, and the feedback system oscillates. Therefore, a technology that can suppress the generation of resonance is desired. Summary of the invention

[0005] The present disclosure can be implemented as the following aspects.

[0006] (1) According to one embodiment of the present disclosure, a robot arm is provided. The robot arm comprises: a first joint; a first arm unit having a first drive unit and a pressing device, the first drive unit including a motor and a belt for transmitting the output of the motor, the first drive unit driving the first joint, and the pressing device pressing the belt at a predetermined position of the belt; a second arm unit connected to the first arm unit via the first joint; and an inertial sensor provided on the second arm unit, wherein the natural vibration frequency of the belt pressed by the pressing device is outside the range of the operating frequency of the motor.

[0007] (2) According to other aspects of the present disclosure, a method for suppressing vibration of a robot arm is provided. The method for suppressing vibration of a robot arm is provided in a robot system having a robot arm, an inertial sensor, and a control unit. The robot arm has a motor, a belt for transmitting the output of the motor, and a pressing device for pressing the belt. The inertial sensor is provided on the robot arm. In the method for suppressing vibration, the robot arm is prepared, and the pressing of the belt by the pressing device is adjusted at a predetermined position of the belt so that the natural vibration frequency of the belt becomes outside the range of the operating frequency of the motor. In a state where the belt is pressed by the pressing device, the control unit causes the robot arm to operate. The control unit suppresses vibration of the robot arm based on a signal output by the inertial sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram showing the overall structure of the robot system.

[0009] Figure 2is a block diagram showing the main parts of the robot system.

[0010] Figure 3 This is an exploded perspective view of the arm unit.

[0011] Figure 4 This is a diagram for explaining the tensioner.

[0012] Figure 5 This is a diagram explaining gain margin.

[0013] Description of Reference Numerals

[0014] 1: robot system; 100: robot; 105: base; 120: arm; 120a, 120b, 120c, 120d, 120e, 120f: arm unit; 121: main body; 123: connecting component; 130: drive unit; 130a, 130b, 130c, 130d, 130e, 130f: drive unit; 131: motor; 132: reducer; 133: angle sensor; 140: force sensor; 150: end effector; 161: first inertial sensor; 162: second inertial sensor ; 170: power transmission mechanism; 171: first pulley; 172: second pulley; 173: belt; 180: tensioner; 180a: pressing part; 180b: pressing part; 500: robot controller; 510, 510a~510f: driving substrate; 520: control substrate; 521: upper control part; 522, 522a~522f: lower control part; 530: power substrate; J1, J2, J3, J4, J5, J6: joints; L1, L2: distance; RC: robot coordinate system; P1, P2: position. DETAILED DESCRIPTION

[0015] A. Implementation method:

[0016] Figure 1 1 is a schematic diagram showing the overall configuration of a robot system 1 according to the present embodiment. The robot system 1 includes a robot 100 and a robot controller 500 .

[0017] The robot 100 is a vertical multi-joint robot. The robot 100 is controlled by a robot controller 500, and performs, for example, assembly work as part of a manufacturing process on a production line. The robot 100 is also referred to as a robot arm. The robot 100 includes a base 105, an arm 120, six drive units 130, a force sensor 140, an end effector 150, a first inertial sensor 161, and a second inertial sensor 162. Figure 1 The driving unit 130 , the first inertial sensor 161 , and the second inertial sensor 162 are not shown in the figure.

[0018] The base 105 supports the components constituting the robot 100. In the embodiment, with the position of the base 105 as a reference, the coordinate system defining the space in which the robot 100 is set is set as the robot coordinate system RC. The robot coordinate system RC is a three-dimensional orthogonal coordinate system defined by an X-axis and a Y-axis that are orthogonal to each other on a horizontal plane, and a Z-axis along a vertical direction. The positive direction of the Z-axis is vertically upward. The angular position of rotation around the X-axis is set to RX, the angular position of rotation around the Y-axis is set to RY, and the angular position of rotation around the Z-axis is set to RZ. Any position in the robot coordinate system RC can be represented by a position in the X-axis direction, a position in the Y-axis direction, and a position in the Z-axis direction. In addition, any posture in the robot coordinate system RC can be represented by an angular position Rx, an angular position RY, and an angular position RZ.

[0019] The arm 120 includes arm units 120a, 120b, 120c, 120d, 120e, and 120f. The arm 120 includes six joints J1 to J6 that connect the arm units. The joints J1 to J6 are rotation joints.

[0020] The arm unit 120a is connected to the upper end of the base 105 via the joint J1. The arm unit 120a rotates relatively to the base 105 around the rotation axis of the joint J1. The arm unit 120b is connected to the front end of the arm unit 120a via the joint J2. The arm unit 120b rotates relatively to the arm unit 120a around the rotation axis of the joint J2. The arm unit 120c is connected to the front end of the arm unit 120b via the joint J3. The arm unit 120c rotates relatively to the arm unit 120b around the rotation axis of the joint J3.

[0021] The arm unit 120d is connected to the front end of the arm unit 120c via the joint J4. The arm unit 120d rotates relative to the arm unit 120c around the rotation axis of the joint J4. The arm unit 120e is connected to the front end of the arm unit 120d via the joint J5. The arm unit 120e rotates relative to the arm unit 120d around the rotation axis of the joint J5. The arm unit 120f is connected to the front end of the arm unit 120e via the joint J6. The arm unit 120f rotates relative to the arm unit 120e around the rotation axis of the joint J6.

[0022] Figure 2 1 is a block diagram showing the main parts of the robot system 1. The six driving units 130 are driving units 130a to 130f. Figure 2 , only a part of the six drive units 130 is shown. Hereinafter, the drive units 130a to 130f may be simply referred to as the drive unit 130.

[0023] The driving units 130a to 130f drive the corresponding joints respectively according to the control of the robot controller 500. The driving unit 130a drives the joint J1. The driving unit 130b drives the joint J2. The driving unit 130c drives the joint J3. The driving unit 130d drives the joint J4. The driving unit 130e drives the joint J5. The driving unit 130f drives the joint J6. As a result, the end effector 150 is configured in a designated posture at a designated position in the robot coordinate system RC.

[0024] Each drive unit 130 includes a motor 131, a speed reducer 132, an angle sensor 133, and a power transmission mechanism 170. The drive units 130a to 130b further include a tensioner 180. Figure 1 , 2 , the power transmission mechanism 170 and the tensioner 180 are not shown. The driving unit 130a is provided inside the base 105. The driving unit 130b is provided inside the arm unit 120a. The driving unit 130c is provided inside the arm unit 120b. The driving unit 130d is provided inside the arm unit 120c. The driving unit 130e is provided inside the arm unit 120d. The driving unit 130f is provided inside the arm unit 120d and the arm unit 120e separately.

[0025] The motor 131 is supplied with electric current from the robot controller 500, and generates an output, i.e., torque, for driving the corresponding joint. The motor 131 is, for example, a servo motor. The reducer 132 converts the input from the motor 131 into an output with a low rotation speed, i.e., reduces speed. The angle sensor 133 detects the rotation angle (position of the shaft) of the output shaft of the motor 131 as the rotation angle of its joint. The angle sensor 133 detects the rotation angle at a certain time interval, and outputs the detected rotation angle together with the detection time to the robot controller 500. The certain time interval is, for example, 100 milliseconds. The angle sensor 133 is, for example, an encoder, a potentiometer, or a rotary transformer. The power transmission mechanism 170 and the tensioner 180 are described in detail later.

[0026] like Figure 1 As shown, the force sensor 140 is mounted on the arm unit 120e. The force sensor 140 detects the magnitude of the force acting on the end effector 150 in parallel with the X-axis, Y-axis and Z-axis detection axes and the magnitude of the torque around each detection axis in a sensor coordinate system different from the robot coordinate system RC. The sensor coordinate system is a three-dimensional orthogonal coordinate system with a point on the force sensor 140 as the origin. The force sensor 140 outputs the detection value to the robot controller 500.

[0027] The end effector 150 is attached to the arm unit 120e via the force sensor 140. The end effector 150 is a device for holding a workpiece (not shown). The end effector 150 is controlled by the robot controller 500. Figure 1 In order to make the technology easier to understand, the end effector 150 is shown as a cylindrical component.

[0028] Figure 2 The first inertial sensor 161 shown is an angular velocity sensor provided inside the arm unit 120a. The first inertial sensor 161 detects the angular velocity of the arm unit 120a about the rotation axis of the joint J1. The first inertial sensor 161 outputs a detection signal indicating the detected angular velocity to the robot controller 500.

[0029] The second inertial sensor 162 is an angular velocity sensor provided inside the arm unit 120b. The second inertial sensor 162 detects the angular velocity around the rotation axis of the joint J2. The second inertial sensor 162 outputs a detection signal indicating the detected angular velocity to the robot controller 500. The first inertial sensor 161 and the second inertial sensor 162 are also referred to as inertial sensors.

[0030] The robot controller 500 is connected to the arm 120 and the end effector 150 of the robot 100 via a signal line and a power line. The robot controller 500 controls the position of the control point of the robot 100 in the robot coordinate system RC. The control point of the robot 100 is set, for example, to the center of the point where the end effector 150 contacts the object. The control point is sometimes referred to as TCP (Tool Center Point). The robot controller 500 changes the position and posture of the robot 100 by driving the robot 100. Therefore, the robot controller 500 can configure the end effector 150 installed at the front end of the arm 120 of the robot 100 at a specified position with a specified posture. The robot controller 500 can communicate with a control device not shown in the figure, and control the arm 120 and the end effector 150 of the robot 100 according to the action instructions received from the control device. The control device is, for example, a programmable logic controller.

[0031] The robot controller 500 includes six drive substrates 510 , a control substrate 520 , and a power supply substrate 530 .

[0032] The six drive substrates 510 are drive substrates 510a to 520f. Figure 2 , only a part of the six drive substrates 510 is shown. Hereinafter, the drive substrates 510a to 520f may be simply referred to as the drive substrate 510.

[0033] The drive substrates 510a to 520f receive control signals from the control substrate 520 and drive the corresponding drive units 130 respectively. The drive substrate 510a drives the drive unit 130a. The drive substrate 510b drives the drive unit 130b. The drive substrate 510c drives the drive unit 130c. The drive substrate 510d drives the drive unit 130d. The drive substrate 510e drives the drive unit 130e. The drive substrate 510f drives the drive unit 130f.

[0034] Each drive substrate 510 has a motor driver for driving the motor 131 of the corresponding drive unit 130. The drive substrates 510a to 510e are respectively provided inside the base 105 and the arm units 120a to 120d as the drive units 130a to 130e. The drive substrate 510f is provided inside the arm unit 120d or the arm unit 120e.

[0035] The control substrate 520 includes an upper control unit 521 and six lower control units 522. The upper control unit 521 includes a memory and a processor, and outputs instructions related to the operation of the robot 100 to the lower control units 522 by executing a control program stored in the memory.

[0036] Specifically, the upper control unit 521 calculates the target position of the control point based on the content of the processing performed by the robot 100, and generates a trajectory for moving the control point to the target position. Then, the upper control unit 521 generates a position command Pc for each of the drive units 130a to 130f based on the rotation angle detected by the angle sensor 133 of each drive unit 130a to 130f, so that the control point moves along the generated trajectory.

[0037] The six lower control units 522 are lower control units 522a to 522f. Figure 2 , only a part of the six lower control units 522 is shown. Hereinafter, the lower control units 522a to 522f may be simply referred to as the lower control unit 522.

[0038] The lower control units 522a to 522f each include a processor, and perform feedback control on the driving of the corresponding drive substrate 510. The lower control units 522a to 522f each include one integrated circuit.

[0039] Since the arm units 120 a and 120 b are provided with inertial sensors, feedback control based on detection signals of the inertial sensors is performed on the arm units 120 a and 120 b.

[0040] The lower control unit 522a performs feedback control to control the drive current of the drive unit 130a using the position command Pc related to the drive unit 130a, the detection signal of the angle sensor 133 of the drive unit 130a, and the detection signal of the first inertial sensor 161. The lower control unit 522a performs proportional control (PI control) as feedback control.

[0041] In the lower control unit 522a, feedback control is performed as follows.

[0042] The lower control unit 522a receives the position command Pc regarding the drive unit 130a from the upper control unit 521. Furthermore, the lower control unit 522a receives the detection signal of the angle sensor 133 of the drive unit 130a and the detection signal of the first inertial sensor 161.

[0043] The lower control unit 522a calculates the target value ωc of the angular velocity by a predetermined operation using the rotation angle of the drive unit 130 calculated based on the detection signal of the angle sensor 133 of the drive unit 130a and the position command Pc. The lower control unit 522a calculates the angular velocity ωm1 of the drive unit 130a based on the detection signal of the angle sensor 133 of the drive unit 130a.

[0044] In addition, the lower control unit 522a limits the frequency range of the detection signal of the first inertial sensor 161 to a range smaller than a predetermined frequency band upper limit value (first frequency band upper limit value) through low-pass filtering. The first frequency band upper limit value is determined based on the operating frequency of the motor 131 and the natural vibration frequency of the belt 173. The detection signal of the first inertial sensor 161 within the frequency range above the first frequency band upper limit value is not used for feedback control. This is to suppress the oscillation of the feedback system when the operating vibration frequency of the motor 131 and the natural vibration frequency of the belt 173 coincide and produce resonance. The lower control unit 522a multiplies the angular velocity ωA1 detected by the first inertial sensor 161 by a predetermined coefficient (feedback gain) to calculate the correction value ωA1s.

[0045] The lower control unit 522a adds the correction value ωA1s to the angular velocity ωm1 to calculate the angular velocity feedback value ωfb. The lower control unit 522a subtracts the angular velocity feedback value ωfb from the target angular velocity value ωc, performs arithmetic processing using predetermined coefficients, namely, proportional gain and integral gain, and generates a drive signal to be supplied to the drive unit 130a.

[0046] Thus, the lower control unit 522a performs feedback control so that the rotation angle of the drive unit 130a calculated based on the detection signal of the angle sensor 133 of the drive unit 130a is equal to the position command Pc, and the target value ωc of the angular velocity of the drive unit 130a described later is equal to the angular velocity feedback value ωfb. That is, the lower control unit 522a suppresses the vibration of the arm unit 120a based on the signal output by the first inertial sensor 161.

[0047] The lower control unit 522b performs feedback control using the position command Pc related to the drive unit 130b, the detection signal of the angle sensor 133 of the drive unit 130b, and the detection signal of the second inertial sensor 162, similarly to the lower control unit 522a, to control the drive current of the drive unit 130c. That is, the lower control unit 522b suppresses the vibration of the arm unit 120b based on the signal output by the second inertial sensor 162. Thus, by suppressing the vibration of at least one arm unit in the robot arm having the plurality of arm units 120a to 120f, the vibration of the entire robot arm is suppressed.

[0048] Since the arm units 120c to 120f are not provided with inertial sensors, the feedback control of the lower control units 522c to 522f is performed as follows. Hereinafter, the lower control unit 522c will be described as an example.

[0049] The lower control unit 522c performs feedback control using the position command Pc about the drive unit 130c and the detection signal of the angle sensor 133 of the drive unit 130c to control the drive current of the drive unit 130c. The lower control unit 522c performs proportional control (P control) as feedback control.

[0050] In the lower control unit 522c, feedback control is performed as follows.

[0051] The lower control unit 522c receives the position command Pc regarding the drive unit 130c from the upper control unit 521. In addition, the lower control unit 522c receives the detection signal of the angle sensor 133 of the drive unit 130c.

[0052] The lower control unit 522c calculates the target value ωc of the angular velocity by a predetermined operation using the rotation angle of the drive unit 130 calculated based on the detection signal of the angle sensor 133 of the drive unit 130c and the position command Pc. The lower control unit 522c calculates the angular velocity ωm1 of the drive unit 130a based on the detection signal of the angle sensor 133 of the drive unit 130a.

[0053] In addition, the lower control unit 522c multiplies the angular velocity ωm1 by a predetermined coefficient (feedback gain) to calculate the angular velocity feedback value ωfb. Furthermore, the lower control unit 522c subtracts the angular velocity feedback value ωfb from the target angular velocity value ωc, performs arithmetic processing using predetermined coefficients, namely, proportional gain and integral gain, and generates a drive signal supplied to the drive unit 130a.

[0054] Thus, the lower control unit 522c performs feedback control so that the rotation angle of the drive unit 130a calculated based on the detection signal of the angle sensor 133 of the drive unit 130c is equal to the position command Pc, and the angular velocity feedback value ωfb is equal to the angular velocity target value ωc representing the target value of the angular velocity of the drive unit 130c.

[0055] Similar to the lower control unit 522 c , the lower control units 522 d to 522 f perform feedback control using the position command Pc related to the corresponding drive unit 130 and the detection signal of the corresponding angle sensor 133 , thereby controlling the drive current of the corresponding drive unit 130 .

[0056] The power board 530 has a power circuit that generates power to be supplied to the drive boards 510a to 510f and the control board 520. The power circuit converts the frequency and voltage of the power supplied from an external AC power source such as a commercial power source, and supplies the converted power to the six drive boards 510 and the control board 520. The power board 530 is arranged inside the housing of the robot controller 500. Figure 2 In order to facilitate the understanding of the drawings, the illustration of the power supply lines from the power substrate 530 to the drive substrates 510a to 510f is omitted.

[0057] Next, the power transmission mechanism 170 will be described.

[0058] Figure 3 is an exploded perspective view of the arm unit 120d. Figure 3 Part of the structure of the arm unit 120d is omitted from illustration. Figure 3 In , an orthogonal coordinate system different from the robot coordinate system RC is set for convenience. Figure 3 The orthogonal coordinate system set in is a coordinate system fixed with respect to the arm unit 120d.

[0059] The arm unit 120d includes a body 121, a connecting member 123, and a driving unit 130. The body 121 is a hollow housing formed of aluminum or an aluminum alloy. The connecting member 123 includes a cylindrical member 123a and a cylindrical member 123b, and connects the arm unit 120d and the arm unit 120e.

[0060] A motor 131, a speed reducer 132, an angle sensor 133, and a power transmission mechanism 170 are arranged inside the main body 121. Figure 3 In the figure, the reduction gear 132 and the angle sensor 133 are omitted.

[0061] The power transmission mechanism 170 transmits the output of the motor 131 to the rotation axis of the joint. The power transmission mechanism 170 includes a first pulley 171, a second pulley 172, and a belt 173. The first pulley 171 is connected to the rotation axis of the motor 131. The first pulley 171 rotates around the rotation axis of the motor 131. The second pulley 172 is arranged separately from the first pulley 171. The second pulley 172 is supported by the shaft of the speed reducer 132 (not shown). The second pulley 172 rotates around an axis parallel to the rotation axis of the motor 131. Figure 3 In the embodiment, the rotation axes of the first pulley 171 and the second pulley 172 are parallel to the X axis. The belt 173 is mounted on the first pulley 171 and the second pulley 172. The belt 173 transmits the rotation of the first pulley 171 to the second pulley 172. Therefore, the joint J5 can be driven by the rotation force of the motor 131.

[0062] The arm units other than the arm unit 120d also have the same power transmission mechanism 170. It should be noted that the shape of the main body 121 of the arm units other than the arm unit 120d is configured according to the joints of each arm unit. In addition, the number of parts and the shape of each of the connecting parts 123 of the arm units other than the arm unit 120d are configured according to the joints of the arm units. Figure 3 , an example in which the rotation axis of the pulley is parallel to the X-axis is shown, but the rotation axis of the pulley may be parallel to the Y-axis or the Z-axis.

[0063] As described above, the first inertial sensor 161 is provided inside the arm unit 120a. The vibration of the belt 173 is transmitted to the first inertial sensor 161 via the main body 121 supporting the power transmission mechanism 170. Therefore, the first inertial sensor 161 detects not only the vibration of the arm unit 120a but also the vibration of the belt 173. The detection signal of the angular velocity detected by the first inertial sensor 161 used in the feedback control is caused by the vibration of the arm unit 120a and the vibration of the belt 173. Therefore, in the past, the frequency band of the detection signal used for feedback control was limited to a frequency band condition value or less determined according to the natural vibration frequency of the belt 173.

[0064] In addition, sometimes a state occurs in which the vibration of the belt 173 resonates with the vibration of the arm unit 120a. As a result, the magnitude of the vibration detected by the first inertial sensor 161 is larger than the original vibration of the arm unit 120a. In this case, feedback control is performed to offset the vibration of the arm unit 120a and the belt 173, and the movement of the arm unit 120a becomes unstable. In addition, even in the case where the motor 131 operates at an operating vibration frequency different from the natural vibration frequency of the belt 173, there is a situation in which the operating frequency of the motor 131 changes due to the vibration of the arm unit 120a, etc., through feedback control, and the operating frequency of the motor 131 coincides with the natural vibration frequency of the belt 173 and resonates. The same problem also exists with respect to the arm unit 120b provided with the second inertial sensor 162. Therefore, it is desirable to have a technology that can suppress the vibration of the belt.

[0065] Figure 4 1 is an explanatory diagram of the tensioner 180. As described above, the drive units 130a and 130b are provided with the tensioner 180. In the feedback control regarding the driving of the drive units 130a and 130b, the detection signal of the inertial sensor is used. The tensioner 180 is provided in order to suppress the vibration of the belt 173. The joint J1 is also referred to as the first joint. The arm unit 120a connected to the base 105 via the joint J1 as the first joint is also referred to as the second arm unit. The drive unit 130a is also referred to as the first drive unit. The motor 131 of the drive unit 130a is also referred to as the motor. The rotation axis of the first pulley 171 of the drive unit 130a is also referred to as the first axis. The rotation axis of the second pulley 172 of the drive unit 130a is also referred to as the second axis. In addition, the joint J2 is also referred to as the first joint. The arm unit 120a is also referred to as the first arm unit. The arm unit 120b connected to the arm unit 120a via the joint J2 as the first joint is also referred to as the second arm unit. The drive unit 130b is also referred to as the first drive unit. The motor 131 of the driving unit 130b is also referred to as a motor. The rotation axis of the first pulley 171 of the driving unit 130b is referred to as a first axis, and the rotation axis of the second pulley 172 of the driving unit 130b is referred to as a second axis. The driving units 130c to 130f do not include the tensioner 180. The arm units 120c to 120f are arm units that perform feedback control without using detection signals of inertial sensors. The arm units 120c to 120f are also referred to as third arm units.

[0066] exist Figure 4 In the example, an orthogonal coordinate system different from the robot coordinate system RC is set for convenience. Figure 4 The power transmission mechanism 170 is shown as viewed along the rotation axis direction of the motor 131. The tensioner 180 is also referred to as a pressing device. The rotation axis of the motor 131 rotates counterclockwise, that is, in the rotation direction R1.

[0067] The tensioner 180 is a device for pressing the belt 173. The tensioner 180 includes pressing parts 180a and 180b. The pressing parts 180a and 180b are, for example, block-shaped parts formed of an aluminum alloy. The pressing parts 180a and 180b are bolted to an unillustrated device adjacent to the first pulley 171 and the second pulley 172 inside the arm unit using bolts. The unillustrated device adjacent to the first pulley 171 and the second pulley 172 is a device for the movement of the arm unit. If the original movement of the unillustrated device is not hindered by fixing the tensioner 180, the object to which the tensioner 180 is fixed is arbitrary. Alternatively, the pressing parts 180a and 180b may be fixed to the unillustrated device inside the arm unit by means of an unillustrated mounting component.

[0068] Before the robot 100 moves, the tensioner 180 is fixed in advance. In addition, the degree of pressing of the belt 173 is adjusted as needed. Therefore, when the robot 100 starts to move, as described later, the natural vibration frequency of the belt 173 changes from the natural vibration frequency in the state where it is not pressed.

[0069] The pressing portion 180a presses the belt 173 from the +Z side to the -Z side at a predetermined position P1 of the path (moving path) of the belt 173 from the first pulley 171 to the second pulley 172. The position P1 is the midpoint of the path of the belt 173 from the first pulley 171 to the second pulley 172. The pressing portion 180b presses the belt 173 from the -Z side to the +Z side at a position P2 of the path of the belt 173 from the second pulley 172 to the first pulley 171. The position P2 is the midpoint of the path of the belt 173 from the second pulley 172 to the first pulley 171. Thus, the pressing portions 180a and 180b press the belt 173 at predetermined positions P1 and P2 of the belt 173. The position P1 is also referred to as the first position. The position P2 is also referred to as the second position. In addition, the position P1 and the position P2 are also referred to as contact points with the pressing parts 180a and 180b.

[0070] The belt 173 is pressed by the pressing parts 180a and 180b, and the span length of the belt 173 is divided. The span length is the distance between the points of contact of the common tangent of the two pulleys, that is, the distance between the point of contact of the belt 173 and the first pulley 171 and the point of contact of the belt 173 and the second pulley 172. In addition, dividing the span length of the belt 173 means dividing the span length of the belt 173 into the distance from the point of contact with the first pulley 171 to the point of contact with the pressing parts 180a and 180b and the distance from the point of contact with the pressing parts 180a and 180b to the point of contact with the second pulley 172. The natural vibration frequency of the belt 173 is calculated using the inverse of the distance between the points of contact of the belt. The natural vibration frequency of the belt 173 whose span length is divided is higher than the natural vibration frequency of the belt 173 when the span length is not divided. Therefore, by reducing the distance between the points of contact, the natural vibration frequency of the belt 173 can be increased.

[0071] Therefore, the natural vibration frequency of the belt 173 whose span length is divided is higher than the natural vibration frequency of the belt 173 when the span length of the belt 173 is not divided. The tensioner 180 applies force to the belt 173 to such an extent that the natural vibration frequency of the belt 173 whose span length is divided becomes a value outside the range of the operating frequency of the motor 131, that is, exceeds the upper limit value of the operating frequency of the motor 131. Since the natural vibration frequency of the belt 173 is outside the range of the operating frequency of the motor 131, the occurrence of resonance can be suppressed.

[0072] The natural vibration frequency of the belt 173 in the pressed state can be made higher than the natural vibration frequency of the belt 173 in the unpressed state. Therefore, the first frequency band upper limit value can be set higher than the previous frequency band upper limit value (second frequency band upper limit value) corresponding to the natural vibration frequency of the belt 173 in the unpressed state. In the past, the lower control unit 522a cut off the detection signal of the first inertial sensor 161 above the frequency band upper limit value (second frequency band upper limit value) corresponding to the natural vibration frequency of the belt 173 in the unpressed state. Therefore, the detection signal above the second frequency band upper limit value cannot be used for feedback control. However, according to the present embodiment, the detection value reaching the first frequency band upper limit value higher than the second frequency band upper limit value can be used for feedback control. In addition, depending on the natural vibration frequency of the belt 173 in the pressed state, there is also the possibility that the low-pass filtering process can be omitted.

[0073] In the embodiment, the span length is divided into two equal parts because the tensioner 180 presses the belt 173 at the positions P1 and P2, which are the middle positions of the common tangent lines with the first pulley 171 and the second pulley 172. By dividing the span length into two equal parts, the distances L1 and L2 between the points after the span length is divided can be minimized.

[0074] Figure 51 is an explanatory diagram of the gain margin when the natural frequency of the belt 173 increases. Figure 5 In the gain diagram and phase diagram of the Bode diagram shown, the horizontal axis represents frequency. The vertical axis of the gain diagram represents gain. The vertical axis of the phase diagram represents phase. In the gain diagram and the phase diagram, the gain characteristic and phase characteristic of the feedback control system when the belt 173 in the unpressed state is used are shown by a single-point dashed line, and the gain characteristic and phase characteristic of the feedback control system when the belt 173 in the pressed state is used are shown by a solid line. The natural vibration frequency of the belt 173 in the unpressed state is 200 Hz, and the natural vibration frequency of the belt 173 in the pressed state is 400 Hz. The gain margin of the belt 173 in the unpressed state represented by the reference numeral M1 is 25 dB. The gain margin of the belt 173 in the pressed state represented by the reference numeral M2 is 40 dB. As a result, since the natural vibration frequency of the belt 173 in the unpressed state can be higher than that of the belt 173, the gain margin can be increased. By increasing the gain margin, it is possible to adjust the proportional gain in the feedback control, and the degree of freedom of the gain adjustment is increased.

[0075] B. Other implementation methods:

[0076] B1 Other implementation methods 1:

[0077] In the embodiment, an example in which the position P1 and the position P2 are pressed by the tensioner 180 is described. Alternatively, the belt 173 may be pressed at the position P1 and the position P3, which divide the path of the belt 173 from the first pulley 171 to the second pulley 172 into three equal parts. The distance from the contact point of one side of the first pulley 171 and the second pulley 172 to the position P1, the distance from the position P1 to the position P3, and the distance from the position P3 to the contact point of the other side of the first pulley 171 and the second pulley 172 are equal, and are the distances obtained by dividing the path of the belt 173 from the first pulley 171 to the second pulley 172 into three equal parts. Moreover, the belt 173 may be pressed similarly at the position P2 and the position P4, which divide the path of the belt 173 from the second pulley 172 to the first pulley 171 into three equal parts.

[0078] B2 Other implementation methods 2:

[0079] The first pulley 171 and the second pulley 172 are two-stage pulleys, and two belts may be laid between the first pulley 171 and the second pulley 172. In this case, for example, by pressing the middle position between the respective contact points of the two belts, the same effect as in the embodiment can be obtained.

[0080] B3 Other implementation methods 3:

[0081] In the embodiment, an example of the tensioner 180 including the block-shaped pressing parts 180a and 180b has been described. Alternatively, as the tensioner 180, an idler pulley including a rotatably arranged cylindrical rotating member may be used.

[0082] B4 Other implementation methods 4:

[0083] In the embodiment, the example in which the first inertial sensor 161 and the second inertial sensor 162 are angular velocity sensors is described. Alternatively, the first inertial sensor 161 and the second inertial sensor 162 may also be acceleration sensors that detect acceleration around the rotation axis of the joint. In addition, alternatively, the first inertial sensor 161 and the second inertial sensor 162 may also be angular acceleration sensors that detect angular acceleration around the rotation axis of the joint.

[0084] B5 Other implementation methods 5:

[0085] In the embodiment, an example in which the first inertial sensor 161 and the second inertial sensor 162 are provided in the robot 100 is described. However, it is also possible that there is only one inertial sensor, and feedback control based on its detection value is performed. Alternatively, three or more inertial sensors may be provided in the robot 100, and feedback control based on the respective detection values ​​may be performed. The inertial sensor is preferably provided in an arm unit close to the base 105.

[0086] B6 Other implementation methods 6:

[0087] In the embodiment, an example is described in which the upper control unit 521 outputs the position command Pc to the lower control units 522a to 522f, and the lower control units 52a to 522f perform feedback control using the position command Pc related to the corresponding drive unit. However, the present invention is not limited to this.

[0088] The upper control unit 521 calculates the target position of the control point based on the content of the processing performed by the robot 100, and generates a trajectory for moving the control point to the target position. Then, the upper control unit 521 generates an angular velocity command Ac for each of the drive units 130a to 130f using an angular velocity calculated based on the rotation angle detected by the angle sensor 133 of each drive unit 130a to 130f, so that the control point moves along the generated trajectory.

[0089] The lower control unit 522a performs feedback control to control the drive current of the drive unit 130a using the angular velocity command Ac related to the drive unit 130a, the detection signal of the angle sensor 133 of the drive unit 130a, and the detection signal of the first inertial sensor 161. The lower control unit 522b is similar.

[0090] The lower control units 522 c to 522 f perform feedback control using the angular velocity command Ac related to the drive unit 130 a and the detection signal of the angle sensor 133 of the drive unit 130 a , and control the drive current of the corresponding drive unit 130 .

[0091] B7 Other implementation methods 7:

[0092] In the embodiment, an example is described in which six drive substrates 510a to 520f, a control substrate 520, and a power substrate 530 are provided. However, two or more of the six drive substrates 510a to 520f, the control substrate 520, and the power substrate 530 may be integrated. In addition, although an example is described in which six lower control units 522a to 522f perform feedback control on the drive of the corresponding drive substrates 510a to 520f, six lower control units 52a to 522f may not be provided, but one lower control unit 522 may perform feedback control on the drive of the six drive substrates 510a to 520f in a time-divided manner. In this case, one lower control unit 522 may also be composed of one integrated circuit. In addition, although an example is described in which the six lower control units 522a to 522f are each composed of one integrated circuit, it may also be configured so that two or more of the six lower control units 522a to 522f are included in one integrated circuit. Alternatively, the upper control unit 521 and the lower control unit 522 may be formed of one integrated circuit.

[0093] B8 Other implementation methods 8:

[0094] In the embodiment, an example of a six-axis vertical articulated robot is described, but the robot 100 may also be a horizontal articulated robot.

[0095] The present disclosure is not limited to the above-mentioned embodiments, and can be implemented by various structures within the scope of its main purpose. For example, in order to solve part or all of the above-mentioned technical problems, or to achieve part or all of the above-mentioned effects, the technical features in the embodiments corresponding to the technical features in each method recorded in the content of the invention can be appropriately replaced or combined. In addition, if its technical features are not described as necessary features in this specification, they can be appropriately deleted.

[0096] COther methods:

[0097] (1) According to a first aspect of the present disclosure, a robot arm is provided. The robot arm comprises: a first joint; a first arm unit having a first drive unit and a pressing device, the first drive unit including a motor and a belt for transmitting the output of the motor, the first drive unit driving the first joint, and the pressing device pressing the belt at a predetermined position of the belt; a second arm unit connected to the first arm unit via the first joint; and an inertial sensor provided on the second arm unit, wherein the natural vibration frequency of the belt pressed by the pressing device is outside the range of the operating frequency of the motor.

[0098] According to the above aspect, the pressing device presses the belt to make the natural frequency of the belt outside the range of the operating frequency of the motor, that is, to exceed the upper limit of the operating frequency of the motor, thereby suppressing the occurrence of resonance.

[0099] (2) In the robot arm of the above aspect, the natural vibration frequency of the belt when the span length of the belt is divided by the pressing device may be higher than the natural vibration frequency of the belt when the span length is not divided.

[0100] According to the above aspect, by pressing the belt, the natural frequency of the belt is increased, and thus the occurrence of resonance can be suppressed.

[0101] (3) In the robot arm of the above-mentioned method, it may also be that the first driving part has: a first pulley connected to the output shaft of the motor and rotating around a first axis; and a second pulley configured to be separated from the first pulley and rotating around a second axis parallel to the first axis, the belt is mounted on the first pulley and the second pulley, and the rotation of the first pulley is transmitted to the second pulley, and the belt is pressed at a first position and a second position by the pressing device, the first position is the midpoint of the moving path of the belt from the first pulley to the second pulley, and the second position is the midpoint of the moving path of the belt from the second pulley to the first pulley.

[0102] The natural frequency of the belt is calculated using the inverse of the distance between the contact points of the belt. Since the distance between the contact points is reduced by dividing the span length of the belt, the natural frequency of the belt can be increased.

[0103] (4) According to a second aspect of the present disclosure, there is provided a robot system having a robot arm and a control unit of the above aspect. In the robot system, the control unit performs the following actions: performs a low-pass filter processing that specifies a predetermined first frequency band upper limit value on the signal output by the inertial sensor; and performs feedback control on the second arm unit based on the signal that has been subjected to the low-pass filter processing, wherein the first frequency band upper limit value is higher than a second frequency band upper limit value specified for the low-pass filter processing when the pressing device is not pressing the belt.

[0104] In the past, the detection values ​​above the second frequency band upper limit value corresponding to the natural vibration frequency of the belt in the unpressed state were cut off, and the detection values ​​above the second frequency band upper limit value could not be used for feedback control. According to the above method, the detection values ​​reaching the first frequency band upper limit value higher than the second frequency band upper limit value can be used for feedback control. That is, the control of vibration suppression in the frequency band ranging from the second frequency band upper limit value to the high first frequency band upper limit value can be performed.

[0105] (5) In the robot system of the above-mentioned method, it is also possible that the robot system further includes a third arm unit, the third arm unit has the same structure as the first arm unit, the third arm unit is not provided with an inertial sensor, and the third arm unit does not have a pressing device, and the control unit performs the following actions: for the first arm unit, the feedback control based on the signal of the inertial sensor is executed, and for the third arm unit, the feedback control without using the signal of the inertial sensor is executed.

[0106] According to the above aspect, the arm unit provided with the inertial sensor and performing feedback control using the detection value of the inertial sensor and the arm unit not provided with the inertial sensor are controlled independently.

[0107] (6) In the robot system of the above aspect, the gain margin in a state where the belt is pressed by the pressing device may be larger than the gain margin in a state where the belt is not pressed by the pressing device.

[0108] If the gain margin increases, the degree of freedom in adjusting the proportional gain in feedback control increases. In addition, by increasing the proportional gain, the responsiveness of the robot control can be improved.

[0109] (7) According to the third embodiment of the present disclosure, a method for suppressing vibration of a robot arm is provided. The method for suppressing vibration of the robot arm is provided in a robot system having a robot arm, an inertial sensor, and a control unit. The robot arm has a motor, a belt for transmitting the output of the motor, and a pressing device for pressing the belt. The inertial sensor is provided in the robot arm. In the method for suppressing vibration, the robot arm is prepared, and the pressing of the belt by the pressing device is adjusted at a predetermined position of the belt so that the natural vibration frequency of the belt becomes outside the range of the operating frequency of the motor. In a state where the belt is pressed by the pressing device, the control unit moves the robot arm, and the control unit suppresses vibration of the robot arm based on a signal output by the inertial sensor.

[0110] According to the above aspect, the belt is pressed by the pressing device, the tension of the belt is increased, and the distance between the contact points is shortened. As a result, the natural vibration frequency of the belt is set outside the range of the operating frequency of the motor, thereby suppressing the occurrence of resonance.

Claims

1. A robotic arm, characterized in that: have: First joint; a first arm unit having a first driving part and a pressing device, wherein the first driving part includes a motor and a belt for transmitting the output of the motor, the first driving part drives the first joint, and the pressing device presses the belt at a predetermined position of the belt; a second arm unit connected to the first arm unit via the first joint; as well as an inertial sensor, provided on the second arm unit, The natural vibration frequency of the belt pressed by the pressing device is outside the range of the operating frequency of the motor.

2. The robotic arm according to claim 1, characterized in that: The natural vibration frequency of the belt when the span length of the belt is divided by the pressing device is higher than the natural vibration frequency of the belt when the span length is not divided.

3. The robotic arm according to claim 2, characterized in that: The first driving unit includes: a first pulley connected to the output shaft of the motor and rotating around a first axis; and a second pulley separated from the first pulley and rotating around a second axis parallel to the first axis. The belt is mounted on the first pulley and the second pulley, and transmits the rotation of the first pulley to the second pulley. Pressing the belt at a first position and a second position by the pressing device, The first position is a midpoint of a path of movement of the belt from the first pulley toward the second pulley, and the second position is a midpoint of a path of movement of the belt from the second pulley toward the first pulley.

4. A robot system, characterized in that: The robot system comprises the robot arm and a control unit according to claim 3, The control unit performs the following actions: performing a low-pass filter process that specifies a predetermined upper limit value of a first frequency band on a signal output by the inertial sensor; and performing feedback control on the second arm unit based on the signal subjected to the low-pass filtering process, The first frequency band upper limit value is higher than a second frequency band upper limit value specified for low-pass filter processing in a state where the belt is not pressed by the pressing device.

5. The robot system according to claim 4, characterized in that: The robot system further comprises a third arm unit, The third arm unit has the same structure as the first arm unit, No inertial sensor is provided in the third arm unit, The third arm unit does not have a pressing device, The control unit performs the following actions: executing the feedback control based on the signal of the inertial sensor for the first arm unit, For the third arm unit, the feedback control without using the signal of the inertial sensor is performed.

6. The robot system according to claim 5, characterized in that: The gain margin in a state where the belt is pressed by the pressing device is larger than the gain margin in a state where the belt is not pressed by the pressing device.

7. A method of suppression, characterized in that: The suppression method suppresses vibration of the robot arm in a robot system including a robot arm, an inertial sensor, and a control unit, wherein the robot arm has a motor, a belt for transmitting output of the motor, and a pressing device for pressing the belt, and the inertial sensor is provided on the robot arm. In the suppression method, preparing the robotic arm, At a predetermined position of the belt, the pressing device adjusts the pressing of the belt so that the natural vibration frequency of the belt is outside the range of the operating frequency of the motor. The control unit operates the robot arm while the belt is pressed by the pressing device. The control unit suppresses vibration of the robot arm based on the signal output by the inertial sensor.

Images