Robot with torque sensors and torque estimation unit, as well as a robot system with movement restriction beyond an axis line

Abstract

Robots (100, 101), comprehensive: a wrist unit (60) comprising a plurality of wrist joints (5, 6, 7); a multitude of base joints (1, 2, 3, 4) which are arranged to determine the position of the wrist unit (60) in a three-dimensional space, several motors (MT1 to MT6), wherein the motors (MT4 to MT6) are configured to each drive a wrist joint (5, 6, 7); a current detection unit (11) configured to detect current supplied to each motor (MT1 to MT6); and a torque estimation unit (13) which is configured to estimate a torque of each of the wrist joints (5, 6, 7) about the axis line (J4, J5, J6) based on the detected current, wherein only the base joints (1, 2, 3, 4) are equipped with torque sensors (S1, S2, S3) which are configured to detect a torque of the base joints (1, 2, 3, 4) about axis lines (J1, J2, J3, J4).

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a robot and a robot system. GENERAL STATE OF THE ART

[0002] A conventionally known robot includes a high-power servomotor for driving each of the first and third shafts, and a low-power servomotor for driving each of the fourth and sixth shafts (see, for example, JP H11-77571 A). A known human-cooperative robot system performs direct teaching, in which the movement of an arm is permitted when an operator directly touches and moves the arm (see, for example, JP 2018-111174 A).

[0003] Furthermore, GB 2 541 986 A shows a robot having a robot arm with a compound joint between a first link of the arm and a second link of the arm, the second link of the arm being distal from the first link.

[0004] Furthermore, JP H11-42574 A discloses a robot control method and a control apparatus for controlling a force by driving a robot manipulator with a motor. CITATION LISTPATENT LITERATURE JP H11-77571 A JP 2018-111174 A GB 2 541 986 A JP H11-42574 A SUMMARY OF THE INVENTION TECHNICAL TASK

[0005] The collaborative robot disclosed in JP 2018-111174 A, which performs a collaborative task together with the operator, includes a highly sensitive torque sensor on each shaft to detect contact with the operator to ensure operator safety. If the torque sensor is provided on each shaft, the robot becomes expensive because the highly sensitive torque sensor is expensive.

[0006] The present invention is intended to provide a robot and a robot system capable of achieving cost reduction while ensuring the safety of an operator. SOLUTION TO THE TASK

[0007] In order to achieve the above-described object, the present invention provides the solution described below.

[0008] One aspect of the present invention provides a robot comprising: a wrist unit comprising a plurality of wrist joints; and a plurality of base joints configured to determine the position of the wrist unit in a three-dimensional space; a plurality of motors, the motors configured to each drive a wrist joint; a current detection unit configured to detect current supplied to each motor; and a torque estimation unit configured to estimate the torque of each wrist joint about the axis line based on the detected current. Only the base joints are provided with torque sensors configured to detect a torque of the base joints about axis lines.

[0009] According to the present aspect, the position of the wrist unit in three-dimensional space is determined by operating the plurality of base joints, and the attitude of a tool attached to a tip of the wrist unit is determined by operating the plurality of wrist joints included in the wrist unit. When an operator comes into contact with an optional position of the robot, the torque of each base joint about the axis line is detected by any one of the torque sensors respectively provided at the plurality of base joints. Accordingly, when no torque of the wrist joints about the axis lines is detected, the contact between the operator and the robot can be detected with high sensitivity. In addition, cost reduction can be achieved by not providing torque sensors at the wrist joints.

[0010] With this configuration, when no torque sensor is installed at each wrist joint, the torque of the wrist joint about the axis line is estimated by the torque estimation unit based on the current to the motor configured to drive the wrist joint. Accordingly, cost reduction can be achieved by eliminating the need to install expensive torque sensors at the wrist joints, and operator safety can be ensured by detecting the operator's contact with a tool attached to the wrist unit.

[0011] The above-described aspect may further include a control unit configured to operate each base joint in a direction identical to the direction of the detected torque when a torque generated around the axis line of each base joint by an external force is detected by each torque sensor.

[0012] With this design, when an external force is applied to the wrist unit or the tool, each base joint is driven by the control unit in a direction identical to the direction of the external force, allowing the wrist to be easily moved in a desired direction in three-dimensional space. At the same time, the wrist unit is not controlled to operate in the direction of the external force, allowing the posture of the tool to be maintained after the external force is absorbed.

[0013] The aspect described above may include the three base joints, and each base joint may be provided with the torque sensor.

[0014] With this design, the three-dimensional position of the wrist unit can optionally be determined by actuating the three base joints. Furthermore, the three-dimensional torque can be detected by the torque sensor provided at each base joint.

[0015] The aspect described above may include the four base joints, and each base joint may be provided with the torque sensor.

[0016] With this configuration, one of the four base joints can function as a redundant axis, and a base shaft comprising the plurality of base joints can be changed into a variety of states while the wrist unit is fixed at an optional position in the three-dimensional space. When the operator comes into contact with an optional position of the robot, the torque of each base joint about the axis line is detected by any of the torque sensors provided at each of the four base joints. Accordingly, when no torque of the wrist joints about the axis lines is detected, the contact between the operator and the robot can be detected with high sensitivity. In addition, cost reduction can be achieved by not providing torque sensors at the wrist joints.

[0017] The above-described aspect may include the four base joints, and three of the base joints, excluding one of the base joints as a redundant axis, may each be provided with the torque sensor.

[0018] With this configuration, one of the four base joints can function as a redundant axis, and a base shaft comprising the plurality of base joints can be changed into a variety of states while the wrist unit is fixed at an optional position in the three-dimensional space. When the operator comes into contact with an optional position of the robot, the torque of each base joint about the axis line is detected by any of the torque sensors provided at each of the three base joints, excluding the redundant axis. Accordingly, when no torque of the wrist joints about the axis lines is detected, the contact between the operator and the robot can be detected with high sensitivity. In addition, cost reduction can be achieved by not providing torque sensors at the wrist joints and by providing one base joint as the redundant axis.

[0019] According to the aspect described above, the torque sensors provided at the base joints may be identical to each other.

[0020] With this design, costs can be reduced by reducing the number of component types.

[0021] According to the above-described aspect, the wrist unit may have a pinch protection structure.

[0022] This configuration can prevent the operator from being squeezed by the wrist unit on which no torque sensor is arranged, thereby improving the operator's safety.

[0023] Another aspect of the present invention provides a robot system comprising a robot comprising: a wrist unit comprising a plurality of wrist joints, a plurality of base joints configured to determine the position of the wrist unit in a three-dimensional space, wherein only the base joints are provided with torque sensors configured to detect a torque of the base joints about axis lines, and a controller configured to control the robot. Outline shape information of the robot is stored in the controller. The controller restricts a range of motion of at least one of the base joints and the wrist joints to prevent the outline of the robot from overlapping the axis line of at least one of the base joints.

[0024] Another aspect of the present invention provides a robot system comprising a robot comprising: a wrist unit comprising a plurality of wrist joints, a plurality of base joints configured to determine the position of the wrist unit in a three-dimensional space, wherein only the base joints are provided with torque sensors configured to detect a torque of the base joints about axis lines, and a controller configured to control the robot. A mechanism restricts a range of motion of at least one of the base joints and the wrist joints to prevent the outline of the robot from overlapping the axis line of at least one of the base joints.

[0025] According to the above-described aspect, a tool may be attached to a tip of the wrist unit, the control unit may store outline shape information of the tool, and the control unit may restrict a range of motion of at least one of the base joints and the wrist joints to prevent the outline of the tool from overlapping the axis line of at least one of the base joints.

[0026] The present invention offers an effect of achieving cost reduction while ensuring the safety of an operator. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic plan view of a robot according to an embodiment of the present invention. Fig. 2 is a schematic side view of a part in which a base and a rotary cylinder are connected to each other in the robot of Fig. 1 are connected. Fig. 3 is a block diagram of the torque control of a motor from a controller of the robot of Fig. 1. Fig. 4 is a schematic plan view of the robot of Fig. 1 according to a modification. Fig. Figure 5 is a schematic overall view of a robot system comprising the robot of Fig. 1. DESCRIPTION OF EMBODIMENTS

[0027] Hereinafter, a robot 100 according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0028] The robot 100 according to the present embodiment is a vertical articulated robot comprising six joints that are rotated about respective axis lines.

[0029] As in Fig. 1, the robot 100 comprises a base (base joint) 1 fixed to an installation surface, a rotary cylinder (base joint) 2 supported on the base 1 so as to be rotatable about a shaft (axis line) J1 extending in the vertical direction, a first arm (base joint) 3 supported on the rotary cylinder 2 so as to be rotatable about a horizontal shaft (axis line) J2 orthogonal to the shaft J1, a second arm (base joint) 4 supported on the first arm 3 so as to be rotatable about a shaft (axis line) J3 parallel to the shaft J2, a first wrist element (wrist joint) 5 supported on the second arm 4 so as to be rotatable about a shaft (axis line) J4 twisted with respect to the shaft J3, a second wrist element (wrist joint) 6 supported on the first wrist element 5 so as to be rotatable about a shaft (axis line) J5 orthogonal to the shaft J4 and a third wrist element (wrist joint) 7,which is rotatably supported on the second wrist element 6 about a shaft (axis line) J6 orthogonal to the shaft J5. Hereinafter, the base 1 to the second arm 4 is also referred to as a base shaft 50, and the first wrist element 5 to the third wrist element 7 is also referred to as a wrist unit 60.

[0030] The robot 100 also includes a first torque sensor (torque sensor) S1 arranged between the base 1 and the rotary cylinder 2 and configured to detect a torque about the shaft J1, a second torque sensor (torque sensor) S2 arranged between the rotary cylinder 2 and the first arm 3 and configured to detect a torque about the shaft J2, and a third torque sensor (torque sensor) S3 arranged between the first arm 3 and the second arm 4 and configured to detect a torque about the shaft J3. The torque sensors S1, S2, and S3 are identical to each other. The robot 100 does not include a torque sensor configured to detect a torque of the wrist unit 60 about the shafts J4, J5, and J6.

[0031] The robot 100 also includes motors MT1 to MT6, which are configured to drive the respective components around the shafts J1 to J6, and a controller 10, which is configured to control the motors MT1 to MT6. Fig. 1, reference numerals EN1 to EN6 denote encoders configured to detect the rotation angles of the motors MT1 to MT6 around the shafts J1 to J6. The motor MT1, which drives the rotary cylinder 2 around the shaft J1 with respect to the base 1, and the encoder EN1 are shown in Fig. 2, but not in Fig. 1, illustrated.

[0032] The controller 10 includes a CPU, a ROM, and a RAM (not illustrated). The controller 10 executes the function of a computer program stored in the ROM when the CPU loads the computer program into the RAM.

[0033] As in Fig. 3, the controller 10 drives the motors MT1 to MT6 by outputting drive current to the motors MT1 to MT6 included in the robot 100. In Fig. 3, for ease of illustration, the motors MT1 to MT6 are collectively arranged at a position separated from the robot 100.

[0034] The controller 10 includes a current detection unit 11 configured to detect the drive current to the motors MT1 to MT6, a torque estimation unit 13 configured to estimate the estimated torque Tr around the shafts J4 to J6 based on the detected drive current, and a control unit 12 configured to perform position feedback based on the rotation angles detected by the encoders EN1 to EN6 and current feedback based on the drive current detected by the current detection unit 11, and to control the motors MT1 to MT6 based on the estimated torque Tr estimated by the torque estimation unit 13 and the detection torque T detected by each torque sensor.

[0035] The torque estimation unit 13 estimates the torque Tr around the shafts J4 to J6 based on the drive current to the motors MT4 to MT6 of the wrist unit 60 detected by the current detection unit 11.

[0036] In a teaching mode, when the detection torque T is detected by the torque sensors S1 to S3, the control unit 12 outputs a torque to the motors MT1 to MT3 to rotate the base shaft 50 around the shafts J1 to J3 in a direction that is the same as the direction of the torque acting around the shafts J1 to J3. In other words, the control unit 12 controls the motors MT1 to MT3 to generate a torque that assists the rotation around the shafts J1 to J3 caused by an external force. The assisting torque can be changed according to the magnitude of the detection torque T obtained from the torque sensors S1 to S3, or it can be constant.

[0037] When external force acts on the wrist unit 60 or a tool mounted on the wrist unit 60, the control unit 12 detects the contact of an operator on the tool based on the estimated torque Tr estimated by the torque estimation unit 13 after a change in the drive current to the motors MT4 to MT6, and controls the motors MT1 to MT6 to stop or retract the robot 100.

[0038] Next, effects of the robot 100 according to the present embodiment thus configured will be described.

[0039] The position of the wrist unit 60 in the three-dimensional space is determined by rotating the three base joints of the base shaft 50, and the attitude of a tool attached to a tip of the wrist unit 60 is determined by operating the three wrist joints of the wrist unit 60.

[0040] For example, when the operator comes into contact with an optional position of the robot 100, any one of the torque sensors S1 to S3 determines that external force is being applied to the robot 100 as a torque about the shafts J1 to J3. When the operator comes into contact with the wrist unit 60 or the tool, the estimated torque Tr is estimated by the torque estimation unit 13, and the operator's contact is detected.

[0041] Accordingly, when no torque is detected around the shafts J4 to J6, the contact between the operator and the robot 100 can be detected with high sensitivity. Furthermore, torque sensors do not need to be provided for the shafts J4 to J6, thus reducing the cost of the robot 100.

[0042] Since the torque estimation unit 13 estimates the torque around the shafts J4 to J6 based on the current to the motors MT4 to MT6 detected by the current detection unit 11, no torque sensors need to be arranged on the shafts J4 to J6. Accordingly, the cost of the robot 100 can be reduced by not installing expensive torque sensors on the shafts J4 to J6, and operator safety can be ensured by detecting the operator's contact with tools attached to the shafts J4 to J6.

[0043] In teaching mode, when external force is applied to the wrist unit 60 or the tool, the control unit 12 drives the shafts J1 to J3 in a direction identical to the direction of the external force. Accordingly, the position of the wrist unit 60 in three-dimensional space can be easily changed by applying external force to the robot 100. At the same time, the control unit 12 does not control the wrist unit 60 according to the external force, and thus the posture of the tool can be maintained after receiving the external force.

[0044] The robot 100 according to the above-described embodiment includes the base shaft 50 comprising the three base joints around the shafts J1 to J3 and the wrist unit 60 comprising the three wrist joints around the shafts J4 to J6. Instead, a robot 101 comprising a redundant joint around a shaft Ja (redundant axis) in addition to the six joints around the shafts J1 to J6 may be used, as shown in Fig. 4. The robot 101 includes a redundant arm 8 configured to rotate, relative to the first arm 3, about the shaft Ja orthogonally to the shaft J2, and a motor MTa configured to drive the redundant arm 8. The robot 101 includes a torque sensor configured to detect a torque about the shaft Ja.

[0045] According to this seven-shaft articulated robot 101, the base shaft 50 can be changed into a variety of states, while the redundant joint fixes the wrist unit 60 in one position in three-dimensional space. The redundant joint may not include a torque sensor.

[0046] The wrist unit 60 according to the above-described embodiment may include a protective structure to prevent the operator from being crushed. For example, in the protective structure, a seam at a portion where the second wrist member 6 and the third wrist member 7 are connected to each other is reduced, and the size of the gap between the second wrist member and the third wrist member is sufficiently large where the members are closest to each other. This configuration can, for example, prevent an operator's arm from being crushed in the seam or gap, thereby improving operator safety.

[0047] A robot system 300 comprising the robot 100 described above and a controller 200 described below may be used.

[0048] Specifically, the controller 200 can store the outline shape of the robot 100 and restrict the operation of at least one of the shafts J1 to J6 to prevent the outline shape of the robot 100 from overlapping the axis line of at least one of the shafts J1, J2, and J3. Accordingly, the external force acting on any of the outer surfaces of the robot 100 can be reliably detected by the torque sensors S1 to S3 provided on the shafts J1 to J3.

[0049] For example, the external force acting on any one of the outer surfaces of the robot 100 can be detected by the first torque sensor S1 provided on the shaft J1 by executing the operation restriction to prevent outline shapes of the shafts J2 to J6 from overlapping the axis line of the shaft J1, as shown in Fig. 5 illustrates.

[0050] When a tool 110 is attached to the tip of the wrist unit 60, the controller 200 can also memorize the outline shape of the tool 110 and restrict the operation of at least one of the shafts J1 to J6 to prevent the outline shape of the tool 110 from overlapping the axis line of at least one of the shafts J1, J2, and J3. Accordingly, the external force acting on any of the outer surfaces of the tool 110 can be reliably detected by any of the torque sensors S1 to S3 provided on the shafts J1 to J3. The above-described operation restriction can be implemented by software or a mechanism. LIST OF REFERENCE SYMBOLS 1 base (basal joint) 2 rotation cylinders (base joint) 3 first arm (basal joint) 4 second arm (basal joint) 5 first wrist element (wrist joint) 6 second wrist element (wrist joint) 7 third wrist element (wrist joint) 11 Current detection unit 12 Control unit 13 Torque estimation unit 60 wrist unit 100, 101 robots 110 tools 200 Control 300 robot system J1, J2, J3, J4, J5, J6 axis line Yes redundant axis MT1 to MT6 engine S1 first torque sensor (torque sensor) S2 second torque sensor (torque sensor) S3 third torque sensor (torque sensor)

Claims

[1] Robot (100, 101), comprising: a wrist unit (60) comprising a plurality of wrist joints (5, 6, 7); a plurality of base joints (1, 2, 3, 4) arranged to determine the position of the wrist unit (60) in a three-dimensional space, several motors (MT1 to MT6), wherein the motors (MT4 to MT6) are each arranged to drive a wrist joint (5, 6, 7); a current detection unit (11) configured to detect current supplied to each motor (MT1 to MT6); and a torque estimation unit (13) configured to estimate a torque of each of the wrist joints (5, 6, 7) about the axis line (J4, J5, J6) based on the detected current, wherein only the base joints (1, 2, 3, 4) are provided with torque sensors (S1, S2, S3) which are arranged to detect a torque of the base joints (1, 2, 3, 4) about axis lines (J1, J2, J3, J4). [2] The robot (100, 101) according to claim 1, further comprising a control unit (12) configured to operate each base joint (1, 2, 3, 4) in a direction identical to the direction of the detected torque when a torque generated about the axis line (J1, J2, J3, J4) of each base joint (1, 2, 3, 4) by an external force is detected by each torque sensor (S1, S2, S3). [3] Robot (100, 101) according to claim 1 or 2, comprising the three base joints (1, 2, 3, 4), wherein each base joint (1, 2, 3, 4) is provided with the torque sensor (S1, S2, S3). [4] Robot (100, 101) according to claim 1 or 2, comprising the four base joints (1, 2, 3, 4), wherein each base joint (1, 2, 3, 4) is provided with the torque sensor (S1, S2, S3). [5] Robot (100, 101) according to claim 1 or 2, comprising the four basic joints (1, 2, 3, 4), wherein three of the basic joints (1, 2, 3, 4), excluding one of the basic joints (1, 2, 3, 4) as a redundant axis (Ja), are each provided with the torque sensor (S1, S2, S3). [6] Robot (100, 101) according to any one of claims 1 to 5, wherein the torque sensors (S1, S2, S3) provided on the base joints (1, 2, 3, 4) are identical to each other. [7] The robot (100, 101) according to any one of claims 1 to 6, wherein the wrist unit (60) has an anti-pinch structure. [8] Robot system (300), comprising: a robot (100, 101) comprising: a wrist unit (60) comprising a plurality of wrist joints (5, 6, 7); a plurality of base joints (1, 2, 3, 4) arranged to determine the position of the wrist unit (60) in a three-dimensional space, wherein only the base joints (1, 2, 3, 4) are provided with torque sensors (S1, S2, S3) which are arranged to detect a torque of the base joints (1, 2, 3, 4) about axis lines (J1, J2, J3, J4) and a controller (200) configured to control the robot (100, 101), wherein Outline shape information of the robot (100, 101) is stored in the controller (200), and the controller (200) limits a range of motion of at least one of the base joints (1, 2, 3, 4) and the wrist joints (5, 6, 7) to prevent the outline of the robot (100, 101) from overlapping the axis line (J1, J2, J3, J4) of at least one of the base joints (1, 2, 3, 4). [9] Robot system (300), comprising: a robot comprising: a wrist unit (60) comprising a plurality of wrist joints (5, 6, 7); a plurality of base joints (1, 2, 3, 4) arranged to determine the position of the wrist unit (60) in a three-dimensional space, wherein only the base joints (1, 2, 3, 4) are provided with torque sensors (S1, S2, S3) which are arranged to detect a torque of the base joints (1, 2, 3, 4) about axis lines (J1, J2, J3, J4) and a controller (200) configured to control the robot (100, 101), wherein a mechanism restricts a range of motion of at least one of the base joints (1, 2, 3, 4) and the wrist joints (5, 6, 7) to prevent the outline of the robot (100, 101) from overlapping the axis line (J1, J2, J3, J4) of at least one of the base joints (1, 2, 3, 4). [10] Robot system (300) according to claim 8 or 9, wherein a tool (110) is attached to a tip of the wrist unit (60), Outline shape information of the tool (110) is stored in the control unit (12), and the control unit (12) limits a range of motion of at least one of the base joints (1, 2, 3, 4) and the wrist joints (5, 6, 7) to prevent the outline of the tool (110) from overlapping the axis line (J1, J2, J3, J4) of at least one of the base joints (1, 2, 3, 4).

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