Parallel linkage robot system and parallel linkage robot

Abstract

A parallel link robot system and a parallel link robot. Improve the reliability of picking and placing operations. A parallel link robot system (1) has a plurality of parallel link robots (7) for picking up workpieces in a first working area (Z1) and placing workpieces in a second working area (Z2), the parallel link robot having: a base (23); a movable part (25); and three arms (A1, A2, A3), each of which has an upper arm part (A1U, A2U, A3U) connected to the base part in a rotatable manner, and is configured so that one of the angular intervals of the upper arm parts in the circumferential direction around a central axis (AX) is less than 120°, and the other two angular intervals are equal to each other. The three arms connect the base part and the movable part, and the parallel link robot is configured so that two arms located at both ends of the angular interval less than 120° are closer to the first working area side than the central axis, and the other arm is closer to the second working area side than the central axis.

Description

Technical Field

[0001] The disclosed embodiments relate to a parallel link robot system and a parallel link robot. Background Art

[0002] Patent Document 1 describes a robot system in which a plurality of parallel link robots are arranged along a product conveyor and a container conveyor, and the parallel link robots transfer products conveyed by the product conveyor to containers conveyed by the container conveyor.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: European Patent Application Publication No. 3498430 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the above-mentioned prior art, it may not be possible to stably pick up products transported by a product conveyor, and a robot system capable of improving the reliability of the picking and placing operation is desired.

[0008] The present invention has been made in view of such a problem, and an object of the present invention is to provide a parallel link robot system and a parallel link robot capable of improving the reliability of a pick-and-place operation.

[0009] Means for solving problems

[0010] In order to solve the above-mentioned problems, according to one aspect of the present invention, a parallel linkage robot system is applied, wherein the parallel linkage robot system has at least one parallel linkage robot that picks up workpieces in a first working area and places workpieces in a second working area, the parallel linkage robot having: a base part; a movable part, on which an end effector is installed; and three arms, each of which has an arm part connected to the base part in a rotatable manner, and is configured so that one of the angular intervals of the arm parts in the circumferential direction around the central axis is less than 120°, and the other two angular intervals are equal to each other, the three arms connect the base part and the movable part, and the parallel linkage robot is configured so that the two arms located at the two ends of the angular interval less than the 120° are closer to the first working area side than the central axis, and the other arm is closer to the second working area side than the central axis.

[0011] In addition, according to another aspect of the present invention, a parallel linkage robot is used, which picks up a workpiece in a first working area and places the workpiece in a second working area, wherein the parallel linkage robot comprises: a base part; a movable part, on which an end effector is installed; and three arms, each of which has an arm part connected to the base part in a rotatable manner, and is configured so that one of the angular intervals of the arm parts in the circumferential direction around the central axis is less than 120°, and the other two angular intervals are equal to each other, and the three arms connect the base part and the movable part, and the parallel linkage robot is configured so that two of the arms located at both ends of the angular interval less than the 120° are closer to the first working area side than the central axis, and the other arm is closer to the second working area side than the central axis.

[0012] In addition, according to another aspect of the present invention, a parallel linkage robot is used, and the parallel linkage robot has: a base part; a movable part, on which an end effector is installed; three arms, which connect the base part and the movable part; three motors, which are arranged at the upper part of the base part and drive the three arms respectively; and three reducers, which are arranged at the lower part of the base part, reduce the power of the three motors and transmit it to the three arms respectively.

[0013] Effects of the Invention

[0014] According to the parallel link robot system and the like of the present invention, the reliability of the picking and placing operation can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram showing an example of the configuration of the parallel link robot system according to the first embodiment.

[0016] Figure 2 It is a perspective view showing an example of the structure of the parallel link robot according to the first embodiment.

[0017] Figure 3 It is a plan view showing an example of the structure of the parallel link robot according to the first embodiment.

[0018] Figure 4 yes Figure 3 Partial cross-sectional view of section IV-IV in FIG.

[0019] Figure 5 It is a schematic diagram showing an example of the configuration of a parallel link robot system according to the second embodiment.

[0020] Figure 6 It is a perspective view showing an example of the structure of a parallel link robot according to the second embodiment.

[0021] Figure 7 It is a plan view showing an example of the structure of a parallel link robot according to the second embodiment.

[0022] Figure 8 This is an explanatory diagram showing that the motions of the three arms are controlled so that the distal end of the upper arm portion does not come into contact with the top plate portion.

[0023] Fig. 9 This is a plan view showing an example of the structure of a parallel link robot according to a modification in which arms are arranged at equal intervals.

[0024] Fig.10 This is a plan view showing an example of the structure of a parallel link robot according to a modified example in which arms are arranged at equal intervals and a top plate is provided.

[0025] Fig.11 This is a plan view showing an example of the structure of a parallel link robot according to a modified example in which the rigidity of one arm is higher than the rigidity of the other two arms.

[0026] Fig.12 This is a block diagram showing a hardware configuration example of a robot controller.

[0027] Description of symbols

[0028] 1: parallel link robot system; 1A: parallel link robot system; 3: first transport conveyor (first transport device); 5: second transport conveyor (second transport device); 7: parallel link robot; 7A: parallel link robot; 7B: parallel link robot; 7C: parallel link robot; 7D: parallel link robot; 9: camera; 11: upper controller; 13: robot controller; 13A: robot controller; 19: FIG. Image processing unit; 21: first motion control unit; 23: base unit; 25: movable unit; 51: opening; 53: belt; 61: top plate unit; 63: base unit; 65: second motion control unit; A1, A2, A3: arms; A1U, A2U, A3U: upper arm unit (arm unit); AX: center axis line; M1, M2, M3: motors; R1, R2, R3: reducers; Z1: first working area; Z2: second working area; W: workpiece. DETAILED DESCRIPTION

[0029] <1. First Implementation Method>

[0030] Hereinafter, a first embodiment will be described with reference to the drawings.

[0031] (1-1. Structure of the parallel link robot system)

[0032] First, refer to Figure 1 An example of the configuration of the parallel robot system 1 according to the present embodiment will be described.

[0033] like Figure 1 As shown, the parallel link robot system 1 includes a first transfer conveyor 3 , a second transfer conveyor 5 , a plurality of (three in this example) parallel link robots 7 , a camera 9 , a host controller 11 , and a robot controller 13 .

[0034] The first transport conveyor 3 (an example of the first transport device) transports the workpiece W in a path including the first working area Z1 of each parallel link robot 7. The workpiece W is transported toward the first working area Z1 in the direction of the arrow 15 by the first transport conveyor 3. The first working area Z1 is a working area for each parallel link robot 7 to pick up (also referred to as grasping, adsorbing, holding, taking out, lifting, etc.) the workpiece W.

[0035] The second transport conveyor 5 (an example of the second transport device) transports the workpiece W in the path of the second working area Z2 including each parallel link robot 7. The workpiece W is transported from the second working area Z2 to the direction of the arrow 17 by the second transport conveyor 5. The second working area Z2 is an operating area for each parallel link robot 7 to place (also referred to as loading, handling, putting down, etc.) the workpiece W. The first transport conveyor 3 and the second transport conveyor 5 are configured so that their transport directions are substantially parallel to each other and are in the same direction (the direction of the arrows 15 and 17). In addition, the first transport conveyor 3 and the second transport conveyor 5 can also be configured so that their transport directions are in opposite directions.

[0036] The workpiece W is not particularly limited as long as it can be picked up and placed by the parallel link robot 7. For example, the workpiece W can be a mechanical component, an electrical component, a product, a commodity, a food, or the like.

[0037] The first transport conveyor 3 and the second transport conveyor 5 are not particularly limited as long as they can transport the workpiece W. For example, a belt conveyor, a roller conveyor, a chain conveyor, etc. can be used. In addition, other transport devices other than conveyors, such as an unmanned guided vehicle (AGV), a trolley, a cargo ship, a conveyor, etc., can also be used.

[0038] The parallel link robot 7 is supported by a platform (not shown) so as to be located above the first transport conveyor 3 and the second transport conveyor 5. The parallel link robot 7 picks up the workpiece W in the first operation area Z1 and places the workpiece W in the second operation area Z2. Figure 1In the figure, for example, a case where a large number of workpieces W transported by the first transport conveyor 3 at a random position are picked up and placed in a row on the second transport conveyor 5 is shown as an example. In addition, the method of picking up and placing is not limited to this. For example, it is also possible to adopt various other methods such as picking up the workpieces W contained in the container transported by the first transport conveyor 3 and storing the picked up workpieces W in a predetermined place of the container transported by the second transport conveyor 5 (so-called boxing).

[0039] The parallel link robot 7 has three arms A1, A2, and A3. The details will be described later, but the angular intervals of the arms A1, A2, and A3 in the circumferential direction around the central axis AX are 80° between the arms A1 and A3, and 140° between the arms A1 and A2 and between the arms A2 and A3 (see Figure 3 ). The parallel linkage robot 7 is configured so that the two arms A1 and A3 located at the two ends of an angular interval of 80° are located on the first working area Z1 side (i.e., the first conveyor 3 side) relative to the center axis AX, and the other arm A2 is located on the second working area Z2 side (i.e., the second conveyor 5 side) relative to the center axis AX. In detail, it is configured so that: the extension direction of the arm A2 is perpendicular to the conveying direction of the workpiece W conveyed by the conveyor 3, 5, and each arm is in the above-mentioned position. Moreover, the three parallel linkage robots 7 are arranged side by side in the same posture (same configuration orientation) as mentioned above, along the direction perpendicular to the extension direction of the arm A2 (i.e., the conveying direction of the workpiece W conveyed by the conveyor 3, 5).

[0040] In addition, regarding the number of parallel link robots 7, it can also be set to an appropriate number other than 3 (for example, 2 or 4 or more) according to the processing performance of each parallel link robot 7 and the number of workpieces W to be transported. In addition, if all workpieces W can be processed by one parallel link robot 7, it is not limited to a plurality of them, and it can also be set to one. In addition, regarding the parallel link robot 7, the arms A1 and A3 are located on the first working area Z1 side of the central axis AX, and the arm A2 is located on the second working area Z2 side of the central axis AX. The extension direction of the arm A2 does not necessarily have to be perpendicular to the transport direction of the workpiece W, and can also be appropriately inclined.

[0041] The camera 9 captures an image of the workpiece W transported by the first transport conveyor 3 upstream of the first work area Z1 , specifically upstream of the first work area Z1 of the parallel robot 7 located most upstream among the plurality of parallel robots 7 .

[0042] The host controller 11 is composed of, for example, a motion controller, a personal computer (PC), a programmable logic controller (PLC), etc. The host controller 11 has an image processing unit 19. The image processing unit 19 obtains an image of the workpiece W captured by the camera 9, and performs a predetermined image analysis process, thereby obtaining information related to at least one of the number, position, posture (orientation), shape, size, type, etc. of the workpiece W.

[0043] The robot controller 13 is composed of, for example, a motion controller, a personal computer (PC), a programmable logic controller (PLC), a servo amplifier, etc. The robot controller 13 has a first motion control unit 21. The first motion control unit 21 controls each parallel link robot 7 based on the image processing result of the image processing unit 19. Specifically, the first motion control unit 21 calculates the motor position command for each motor M1 to M3 for moving the fingertip position of the parallel link robot 7 to the position for picking up the workpiece W based on the information received from the image processing unit 19 of the host controller 11, controls the driving power supplied to each motor M1 to M3 based on the motor position command, and controls the picking action of the parallel link robot 7. In addition, the first motion control unit 21 calculates the motor position command for each motor M1 to M3 for moving the fingertip position of the parallel link robot 7 to the position for placing the workpiece W, controls the driving power supplied to each motor M1 to M3 based on the motor position command, and controls the placing action of the parallel link robot 7.

[0044] In addition, the robot controller 13 can be set as one control device or composed of multiple control devices. In the case of being set as one control device, one robot controller 13 can be used to uniformly control three parallel linkage robots 7. In the case of being set as multiple control devices, for example, three robot controllers 13 can control each parallel linkage robot 7 separately. In addition, the robot controller 13 and the upper controller 11 can also be formed as an integrated control device without being separated. In addition, the upper controller 11 can also be formed of multiple control devices.

[0045] In addition, in the present embodiment, the case where the workpiece W is picked up by the first transport conveyor 3 and placed on the second transport conveyor 5 is described as an example, but the workpiece W can also be picked up or placed in the working area other than the conveyor. For example, the workpiece W picked up by the conveyor can be placed on a workbench, a transport device other than the conveyor, a processing device that performs a prescribed process, etc. (an example of the second working area), and the workpiece W picked up by a workbench, a transport device other than the conveyor, a prescribed processing device, etc. (an example of the first working area) can also be placed on the conveyor. In addition, the workpiece W picked up by a workbench, a transport device other than the conveyor, a prescribed processing device, etc. can also be placed on a workbench, a transport device other than the conveyor, a prescribed processing device, etc.

[0046] In addition, the processing in the image processing unit 19, the first motion control unit 21, etc. is not limited to the example of sharing these processing, for example, it is also possible to use a smaller number of processing units (for example, one processing unit) for processing, and it is also possible to use a more detailed processing unit for processing. In addition, with regard to the robot controller 13, only the part (inverter, etc.) that supplies driving power to the motors M1 to M3 may be installed by an actual device, and the other functions may be controlled by the CPU 901 described later (see Fig.12 ) can be installed through a program executed by the computer, or part or all of it can be installed through an actual device such as an ASIC (application-specific integrated circuit), FPGA (field programmable gate array), or other circuits.

[0047] (1-2. Structure of parallel link robot)

[0048] Next, refer to Figure 2 and Figure 3 An example of the structure of the parallel link robot 7 according to the present embodiment will be described.

[0049] like Figure 2 As shown, the parallel link robot 7 has a base 23, a movable part 25, three arms A1, A2, A3 and three motors M1, M2, M3. In addition, each motor M1, M2, M3 is housed in a motor case MC1, MC2, MC3 (see Figure 4 ),exist Figure 1 and Figure 2 The motor cases MC1, MC2, and MC3 are shown in the figure.

[0050] The three arms A1, A2, and A3 are arranged at a predetermined angular interval in the circumferential direction around the central axis AX of the parallel link robot 7, and connect the base 23 and the movable part 25. The three motors M1, M2, and M3 are arranged on the upper part of the base 23 to drive the arms A1, A2, and A3 respectively. In this example, the base 23 is formed in a substantially circular plate shape, and substantially trapezoidal notches 27, 29, and 31 are formed at positions corresponding to the arms A1, A2, and A3, respectively. Through these notches 27, 29, and 31, the lifting height of the terminal end of the upper arm A1U, A2U, and A3U of each arm A1, A2, and A3 can be ensured to be within the range above the base 23, and the movable range of the movable part 25 can be expanded. In addition, the shape of the base 23 is not limited to a circle, and it can also be a polygonal shape such as a triangle, a quadrilateral, a pentagon, a hexagon, or a star. Furthermore, the shape may be left-right asymmetric with respect to the central axis AX. The shape of the notch portions 27, 29, 31 is not limited to a trapezoidal shape, and may be, for example, a triangle, a quadrilateral, an arc shape, or the like.

[0051] The three reducers R1, R2, and R3 that reduce the power of the three motors M1, M2, and M3 and transmit them to the three arms A1, A2, and A3 are arranged at the lower part of the base 23. In addition, each reducer R1, R2, and R3 is housed in a reducer case RC1, RC2, and RC3 (see Figure 4 ),exist Figure 2 The reducer housings RC1 and RC3 are shown in the figure. In this example, the movable part 25 is formed into a roughly hexagonal shape and has a mounting component 33 at the lower end. An end effector (not shown) such as a robot hand or a suction cup that can pick up and place the workpiece W is mounted on the mounting component 33. In addition, the shape of the movable part 25 is not limited to a hexagon, and may be, for example, a triangle, a quadrilateral, other polygons, or a circle.

[0052] The three arms A1, A2, and A3 have the same structure. The arms A1, A2, and A3 respectively have upper arm portions A1U, A2U, and A3U (an example of an arm portion) connected to the base portion 23 in a rotatable manner. In detail, the arm A1 has an upper arm portion A1U connected to the reducer R1, and two lower arm portions A1L connected to the upper arm portion A1U and the movable portion 25. The two lower arm portions A1L are respectively connected to the upper arm portion A1U through spherical bearings 35a, and are respectively connected to the movable portion 25 through spherical bearings 37a. The arm A2 has an upper arm portion A2U connected to the reducer R2, and two lower arm portions A2L connected to the upper arm portion A2U and the movable portion 25. The two lower arms A2L are connected to the upper arm A2U via spherical bearings 35b, and are connected to the movable part 25 via spherical bearings 37b. The arm A3 includes an upper arm A3U connected to the reducer R3, and two lower arms A3L connected to the upper arm A3U and the movable part 25. The two lower arms A3L are connected to the upper arm A3U via spherical bearings 35c, and are connected to the movable part 25 via spherical bearings 37c.

[0053] like Figure 3 As shown, the upper arm parts A1U, A2U, and A3U are linear parts, which are radially extended along the radial direction around the central axis AX. The arms A1, A2, and A3 are configured so that one of the angular intervals of the upper arm parts A1U, A2U, and A3U in the circumferential direction around the central axis AX is less than 120°, and the other two angular intervals are equal to each other. As a result, the arms A1, A2, and A3 are configured to be roughly Y-shaped when viewed from the direction of the central axis AX. In this embodiment, for example, the angle between arm A1 and arm A2 is 140°, the angle between arm A2 and arm A3 is 140° as described above, and the angle between arm A3 and arm A1 is 80°.

[0054] Along with the above-mentioned angular interval, the arrangement of the motors M1, M2, and M3 (motor housings MC1, MC2, and MC3) is also optimized. That is, the motors M2 and M3 (motor housings MC2 and MC3) are arranged on one side of the circumferential direction of the corresponding arms A2 and A3, and the motor M1 (motor housing MC1) is arranged on the other side of the circumferential direction of the corresponding arm A1. As a result, a structure is formed in which one motor M3 (motor housing MC3) is arranged between the arms A2 and A3, and two motors M1 and M2 (motor housings MC1 and MC2) are arranged between the arms A1 and A2, so that no motor is arranged between the arms A1 and A3 with a smaller angular interval. In addition, even if the motors M1, M2, and M3 can be arranged on the base 23 without the above-mentioned optimization, all the motors M1, M2, and M3 (motor housings MC1, MC2, and MC3) can be arranged on one side or the other side of the circumferential direction of the corresponding arms A1, A2, and A3 in a manner that is consistent in direction.

[0055] In addition, the angle interval less than 120° is not limited to 80°. That is, as long as the angle is set so that the extension dimension L of the arms A1 and A3 extending from the central axis AX in the width direction h2 perpendicular to the extension direction h1 of the arm A2 and the extension dimension of the base 23 extending from the central axis AX in the width direction h2 (in this example, the radius R of the base 23) are roughly the same, it can be (for example, 110°, 90°, 70°, etc.). In this way, the reduction in the balance of the load on each arm A1, A2, A3 and the increase in the size of the movable part 25 can be suppressed, and the width dimension of the parallel link robot 7 (the dimension in the width direction h2 mentioned above) can be reduced.

[0056] In addition, the spherical bearings 35a, 35b, 35c and the spherical bearings 37a, 37b, 37c are not limited to spherical joints, and may be, for example, rotary joints, universal joints, or linear joints, etc. In addition, each arm A1, A2, A3 is not limited to a link mechanism based on two arm parts, and may be composed of a link mechanism having three or more arm parts.

[0057] (1-3. Power transmission mechanism that transmits the power of the motor to the speed reducer)

[0058] Next, refer to Figure 4 An example of the structure of the power transmission mechanisms T1 , T2 , and T3 for transmitting the power of the motors M1 , M2 , and M3 to the speed reducers R1 , R2 , and R3 , respectively, will be described. Figure 4 yes Figure 3 The power transmission mechanisms T1, T2, and T3 are respectively of the same structure, and therefore, here, the power transmission mechanism T1 that transmits the power of the motor M1 to the speed reducer R1 will be described.

[0059] like Figure 4 As shown, the motor M1 that drives the upper arm portion A1U of the arm A1 is fixed to the upper portion of the base portion 23 through the support member 39. The motor M1 is a rotary motor, and a drive pulley 43 is provided on its shaft 41. The motor M1, the support member 39, the shaft 41, the drive pulley 43, etc. are housed in the motor case MC1 and covered. The motor case MC1 is formed, for example, in a substantially rectangular parallelepiped shape and has an opening 45 at the bottom. The motor case MC1 is fixed to the upper portion of the base portion 23, for example, by bolts (not shown) or the like in a manner such that the opening 45 is closed by the base portion 23.

[0060] The speed reducer R1 that reduces the power of the motor M1 and transmits it to the upper arm A1U of the arm A1 is arranged at the lower part of the base part 23. A driven pulley 49 is provided on the input shaft 47 of the speed reducer R1. An annular belt 53 is wound around the driving pulley 43 of the motor M1 and the driven pulley 49 of the speed reducer R1, and the belt 53 is inserted through the opening 51 formed in the base part 23, and the power of the motor M1 is transmitted to the speed reducer R1. The opening 51 is formed to a size required for inserting the belt 53, and the internal space of the motor case MC1 and the internal space of the speed reducer case RC1 are connected through the opening 51. The speed reducer R1 has an output shaft 55 on the side opposite to the input shaft 47, and the base end of the upper arm A1U is connected to the output shaft 55. The speed reducer R1, the input shaft 47, the driven pulley 49, etc. are housed in the speed reducer case RC1 and covered. The output shaft 55 passes through the opening 56 of the reducer housing RC1 and protrudes to the outside. The reducer housing RC1 has a support portion 57 for fixing the reducer R1. In addition, the reducer housing RC1 is formed in a substantially rectangular parallelepiped shape, for example, and has an opening 59 at the top. The reducer housing RC1 is fixed to the lower part of the base portion 23, for example, by bolts (not shown) or the like in a manner that the opening 59 is closed by the base portion 23.

[0061] According to the above structure, the power of the motor M1 is transmitted to the upper arm portion A1U of the arm A1 in a manner that the speed reducer R1 reduces the rotation speed and increases the torque. In addition, the power transmission mechanism T2 that transmits the power of the motor M2 to the speed reducer R2 and the power transmission mechanism T3 that transmits the power of the motor M3 to the speed reducer R3 are also the same structure as the above-mentioned power transmission mechanism T1.

[0062] In the above structure, the speed reducer case RC1 also serves as a support member for the speed reducer R1. However, a support member may be provided separately from the speed reducer case RC1 as in the case of the motor M1. Also, the motor M1 may be supported by the motor case MC1 as in the case of the speed reducer R1.

[0063] (1-4. Effects of the First Embodiment)

[0064] As described above, the parallel link robot system 1 of the present embodiment has at least one parallel link robot 7 for picking up a workpiece W in the first working area Z1 and placing it in the second working area Z2. The parallel link robot 7 has: a base portion 23; a movable portion 25, on which an end effector is mounted; and three arms A1, A2, and A3, which respectively have upper arm portions A1U, A2U, and A3U connected to the base portion 23 in a rotatable manner, and are configured as upper arm portions. One of the angular intervals of A1U, A2U, and A3U in the circumferential direction around the central axis AX is less than 120°, and the other two angular intervals are equal to each other. The three arms A1, A2, and A3 connect the base part 23 and the movable part 25. The parallel linkage robot 7 is configured so that the two arms A1 and A3 located at the two ends of the angular interval less than 120° are closer to the first working area Z1 side than the central axis AX, and the other arm A2 is closer to the second working area Z2 side than the central axis AX.

[0065] In this embodiment, one of the angular intervals of the three arms A1, A2, and A3 of the parallel robot 7 is smaller than 120°, so the width dimension (dimension in the width direction h2) of the parallel robot 7 can be reduced compared to the case where the three arms A1, A2, and A3 are arranged at equal angular intervals (120° intervals). Therefore, the overall miniaturization and space saving of the parallel robot system 1 can be achieved.

[0066] However, in the parallel link robot 7 configured as described above, the rigidity of the two arms A1 and A3 located at the two ends of the angular interval less than 120° increases, but there is a problem that the rigidity of the other arm A2 decreases. Therefore, when the movable part 25 is moved to the side of the one arm A2 with weaker rigidity, vibration or positional displacement due to vibration may occur.

[0067] On the other hand, in the pick-and-place operation, it is important to pick up the workpiece W without omission, and the accuracy of the pick-up operation is preferably higher than the accuracy of the placement operation. Therefore, in the parallel linkage robot system 1 of the present embodiment, the parallel linkage robot 7 is configured in such a manner that the two arms A1 and A3 with stronger rigidity are located on the side of the first working area Z1 where the pick-up operation is performed, and the one arm A2 with weaker rigidity is located on the side of the second working area Z2 where the placement operation is performed. As a result, in the pick-and-place operation, the pick-up operation that is more important and requires higher accuracy can be performed stably with high accuracy. As described above, a parallel linkage robot system 1 that saves space and can improve the reliability of the pick-and-place operation can be realized.

[0068] In addition, in the present embodiment, in particular, there is a plurality of (3) at least one parallel linkage robot 7, and the plurality of parallel linkage robots 7 are arranged side by side along a width direction h2 that is perpendicular to the extension direction h1 of the other arm A2, with two arms A1 and A3 being closer to the first working area Z1 side than the center axis AX, and the other arm A2 being closer to the second working area Z2 side than the center axis AX.

[0069] In this embodiment, the plurality of parallel robots 7 are arranged side by side along the width direction h2 perpendicular to the extension direction h1 of the arm A2, so the dimension in the width direction h2 can be greatly reduced according to the number of parallel robots 7. Therefore, the parallel robot system 1 can be made smaller and space-saving as a whole.

[0070] Furthermore, since a plurality of parallel link robots 7 are arranged side by side in the same posture, for example, compared with a case where the robots are arranged side by side in different postures (for example, a case where the arms A1 and A3 are arranged on the first operation area Z1 side relative to the central axis AX and the arm A2 is arranged on the second operation area Z2 side relative to the central axis AX, and a case where the arms A1 and A3 are arranged on the second operation area Z2 side relative to the central axis AX and the arm A2 is arranged on the first operation area Z1 side relative to the central axis AX, respectively), the two arms A1 and A3 having relatively strong rigidity can be always arranged on the first operation area Z1 side where the picking operation is performed. Thus, a parallel link robot system 1 can be realized that saves space and can improve the reliability of the picking and placing operation.

[0071] In addition, in the present embodiment, in particular, the parallel linkage robot system 1 also has a first transport conveyor 3, which transports the workpiece W in a path including the first working area Z1, and the parallel linkage robot 7 is configured so that the two arms A1 and A3 are closer to the first transport conveyor 3 than the center axis AX.

[0072] When picking up the workpiece W from the first transport conveyor 3 and placing it at another place, when picking up the workpiece W being transported, the end effector is made to follow the movement of the workpiece W to pick it up, so the picking operation requires high precision. In this embodiment, the parallel link robot 7 is arranged in such a way that the two arms A1 and A3 with strong rigidity are located on the side of the first transport conveyor 3. As a result, the picking operation of the workpiece W transported by the first transport conveyor 3 can be performed with high precision and stability.

[0073] In addition, in this embodiment, in particular, the parallel linkage robot system 1 also has a second transport conveyor 5, which transports the workpiece W in a path including the second working area Z2, and the parallel linkage robot 7 is configured so that the other arm A2 is closer to the second transport conveyor 5 side than the center axis AX.

[0074] When the workpiece W is picked up from the first transport conveyor 3 and placed on the second transport conveyor 5, as described above, the picking operation from the first transport conveyor 3 requires high precision, while the placing operation on the second transport conveyor 5 requires lower precision than the picking operation in many cases. In the present embodiment, the parallel link robot 7 is configured in such a manner that the two arms A1 and A3 with relatively strong rigidity are located on the first transport conveyor 3 side, and the one arm A with relatively weak rigidity is located on the second transport conveyor 5 side. Thus, the configuration direction of the parallel link robot 7 can be optimized according to the required precision of each picking and placing operation, and the reliability of the picking and placing operation can be improved.

[0075] In addition, in the present embodiment, in particular, the parallel linkage robot system 1 also has: a camera 9, which photographs the workpiece W transported by the first transport conveyor 3 on the upstream side of the first working area Z1; an image processing unit 19, which processes the image photographed by the camera 9; and a first motion control unit 21, which controls the parallel linkage robot 7 according to the image processing results.

[0076] According to the present embodiment, the picking operation can be performed after the position of the workpiece W transported by the first transport conveyor 3 is detected by image processing, so the reliability of the picking and placing operation can be further improved by the synergy with the two arms A1 and A3 having strong rigidity being located on the side of the first transport conveyor 3. In addition, compared with the case where the one arm A2 having weak rigidity is located on the side of the first transport conveyor 3, the processing accuracy required by the image processing can be suppressed to a lower level.

[0077] In addition, in this embodiment, in particular, the parallel linkage robot 7 has: three motors M1, M2, and M3, which are arranged at the upper part of the base 23, and drive the three arms A1, A2, and A3 respectively; and three reducers R1, R2, and R3, which are arranged at the lower part of the base 23, and reduce the power of the three motors M1, M2, and M3 and transmit it to the three arms A1, A2, and A3 respectively.

[0078] If both the directly connected motor and the speed reducer are arranged at the bottom of the base 23, a predetermined space is required behind the motor when performing maintenance such as motor replacement. Therefore, if the space between the parallel link robots 7 is small, it is difficult to perform maintenance work. On the other hand, if a space is ensured between the parallel link robots 7 for easy maintenance, the space becomes a dead space, resulting in an increase in the size of the parallel link robot system 1.

[0079] Furthermore, assuming that both the directly connected motor and the speed reducer are arranged on the upper part of the base 23, the rotation axis of the upper arm A1U, A2U, and A3U is located on the upper part of the base 23. Therefore, the rotation axis is close to the upper end of the robot, and the lifting height of the upper arm A1U, A2U, and A3U is limited, which limits the movable range of the movable part 25. In addition, in this case, in order to ensure the movable area of ​​the upper arm A1U, A2U, and A3U, a large notch is formed in the base 23 (for example, a notch from the outer periphery of the base 23 to the vicinity of the rotation axis of the upper arm). As a result, dirt or dust on the upper part of the base 23 may fall through the notch and adhere to or mix into the workpiece W. In particular, when the workpiece W is food or the like, it is not ideal in terms of hygiene.

[0080] In the present embodiment, the motors M1, M2, M3 and the reducers R1, R2, R3 are separated, and the motors M1, M2, M3 are arranged on the upper part of the base 23, and the reducers R1, R2, R3 are arranged on the lower part of the base 23. As a result, it is possible to ensure maintenance space for the motors M1, M2, M3 on the upper part of the base 23, so that maintenance work is easy to perform. In addition, there is no need to set a dead space between the parallel link robots 7, so the parallel link robot system 1 will not be enlarged. In addition, the rotation axis of the upper arm A1U, A2U, A3U (the output axis 55 of the reducer R1, R2, R3) is located at the lower part of the base 23, so the rotation axis is away from the upper end of the robot, which can increase the height at which the upper arm A1U, A2U, A3U can be lifted, and the movable range of the movable part 25 can be expanded. Furthermore, since a large notch is not required in the base 23 to ensure the movable area of ​​the upper arms A1U, A2U, A3U, it is possible to prevent dirt and dust from falling from the upper part of the base 23 and adhering to or mixing with the workpiece W. Therefore, the hygienic environment of the work area can be improved.

[0081] Furthermore, in the present embodiment, in particular, the parallel link robot 7 includes a belt 53 that is inserted through an opening 51 formed in the base portion 23 and transmits the power of the motors M1 , M2 , and M3 to the speed reducers R1 , R2 , and R3 .

[0082] Thus, the motors M1, M2, M3 and the reducers R1, R2, R3 can be separated and arranged by a simple structure such as belt transmission. In addition, the size of the opening 51 can be reduced within the range in which the belt 53 can be inserted, and the motor housings MC1, MC2, MC3 and the reducer housings RC1, RC2, RC3 can be sealed, so that the sanitary environment of the working area can be well maintained.

[0083] <2. Second Implementation Method>

[0084] Next, a second embodiment will be described with reference to the drawings.

[0085] (2-1. Structure of the parallel link robot system)

[0086] First, refer to Figure 5 An example of the configuration of the parallel robot system 1A according to the present embodiment will be described.

[0087] like Figure 5 As shown, the parallel robot system 1A has a top plate 61, which is arranged above the first working area Z1 and the second working area Z2, and three motors M1, M2, and M3 that drive the three arms A1, A2, and A3, respectively, are fixed to the upper part of the top plate 61 for each parallel robot 7A. The top plate 61 is divided for each parallel robot 7A and also serves as a base 63 of each parallel robot 7A. In other words, three bases 63 are arranged side by side in one direction, thereby constituting one top plate 61. The base 63 has a substantially rectangular shape with the extension direction h1 of the arm A2 as the long side and the width direction h2 (the conveying direction of the workpiece W) substantially perpendicular to the extension direction as the short side. The size of the long side of the base 63 is the length from the vicinity of the end of one side of the first conveying conveyor 3 to the vicinity of the end of the other side of the second conveying conveyor 5. The size of the base portion 63 is a size that includes the movable range of the movable portion 25 including the first working area Z1 and the second working area Z2 of each parallel link robot 7A.

[0088] A plurality of (three in this example) parallel link robots 7A are arranged by a not-shown frame so that the long sides of adjacent base parts 63 are in contact with each other without a gap. In addition, each parallel link robot 7A only needs to be arranged so that the long sides of adjacent base parts 63 are opposite to each other, and other components (such as beams of the frame, etc.) may be inserted between the long sides of the base parts 63.

[0089] The robot controller 13A has a second motion control unit 65 in addition to the first motion control unit 21. The second motion control unit 65 controls the motions of the three arms A1, A2, and A3 of each parallel link robot 7A so that the ends of the upper arms A1U, A2U, and A3U do not contact the top plate 61 (base 63).

[0090] As in the first embodiment, the parallel link robot 7A picks up the workpiece W transported by the first transport conveyor 3 in the first work area Z1 and places it in the second work area Z2 of the second transport conveyor 5. The first transport conveyor 3, the second transport conveyor 5, the upper controller 11, etc. are the same as those in the first embodiment, so the description thereof is omitted.

[0091] (2-2. Structure of the parallel link robot)

[0092] Next, refer to Figure 6 to Figure 8 An example of the structure of the parallel link robot 7A according to the present embodiment will be described.

[0093] like Figure 6 As shown, the parallel link robot 7A has a base 63, a movable part 25, three arms A1, A2, A3, and three motors M1, M2, M3. In addition, as in the first embodiment, each motor M1, M2, M3 is housed in a motor case MC1, MC2, MC3 (see Figure 4 ),exist Figure 5 and Figure 6 The motor cases MC1, MC2, and MC3 are shown in the figure.

[0094] Three motors M1, M2, and M3 (motor housings MC1, MC2, and MC3) are disposed on the upper portion of the base portion 63 to drive the arms A1, A2, and A3, respectively. Figure 7 As shown, in this example, the base portion 63 is formed in a substantially rectangular shape and has a planar dimension larger than that of the upper arm portions A1U, A2U, and A3U of the arms A1, A2, and A3 when the upper arm portions A1U, A2U, and A3U of the arms A1, A2, and A3 are horizontal. Figure 8 As shown, the motion of each arm A1, A2, A3 is controlled by the second motion control unit 65 in such a manner that when the upper arm A1U, A2U, A3U is lifted to the maximum extent, the tip is separated from the top plate 61 by a predetermined distance D (i.e., the tip does not contact the top plate 61). In addition, the shape of the base 63 is not limited to a rectangle, and may be, for example, a square, a hexagon, a trapezoid, or the like.

[0095] like Figure 7 As shown, similarly to the first embodiment, the arms A1, A2, and A3 are arranged such that one of the angular intervals of the upper arm portions A1U, A2U, and A3U in the circumferential direction around the central axis AX is less than 120°, and the other two angular intervals are equal to each other. For example, the angle between the arm A1 and the arm A2 is 140°, the angle between the arm A2 and the arm A3 is 140° as described above, and the angle between the arm A3 and the arm A1 is 80°.

[0096] In addition, the structures of the arms A1, A2, A3, the structures of the power transmission mechanisms T1, T2, T3 for transmitting the power of the motors M1, M2, M3 to the speed reducers R1, R2, R3, etc. are the same as those in the first embodiment, and thus the description thereof is omitted. Figure 4 ).

[0097] (2-3. Effects of the Second Embodiment)

[0098] As described above, the parallel linkage robot system 1A also has a top plate portion 61, which is arranged above the first working area Z1 and the second working area Z2. Three motors M1, M2, and M3 that drive the three arms A1, A2, and A3 respectively are fixed to the upper part of the top plate portion 61 according to each parallel linkage robot 7A, and the top plate portion 61 also serves as the base portion 63 of the parallel linkage robot 7A.

[0099] In this embodiment, the top plate 61 can be used to divide the lower space for the pick-up and place operations and the upper space for the motors M1, M2, and M3 (motor housings MC1, MC2, and MC3). This can prevent dirt or dust in the upper space of the top plate 61 from falling into the lower space and adhering to or mixing with the workpiece W, thereby improving the sanitary environment of the pick-up and place operation area. In addition, the top plate 61 also serves as the base 63 of the parallel link robot 7A, so the number of components can be suppressed from increasing.

[0100] In addition, in the present embodiment, the top plate portion 61 is divided for each parallel link robot 7A, and the divided base portion 63 has a substantially rectangular shape with the side in the extension direction h1 of the arm A2 as the long side and the side in the width direction h2 substantially perpendicular to the extension direction h1 as the short side. Thus, when a plurality of parallel link robots 7A are arranged side by side along the width direction h2 in which the width dimension is reduced, by combining the rectangular base portions 63 in such a manner that the long sides are adjacent, the orientation and positioning of the arrangement can be easily performed, and the workability can be improved.

[0101] In addition, in this embodiment, in particular, the parallel link robot system 1A further includes a second motion control unit 65, which controls the motion of the three arms A1, A2, and A3 in such a manner that the ends of the upper arms A1U, A2U, and A3U do not contact the top plate 61. As a result, the top plate 61 does not need a notch portion (notch portions 27, 29, 31, etc. in the first embodiment) for ensuring the movable area of ​​the upper arms A1U, A2U, and A3U, and thus the function of dividing the space above and below the top plate 61 can be improved. As a result, the sanitary environment of the pick-up and place operation area can be further improved.

[0102] <3. Modifications>

[0103] In addition, the disclosed embodiment is not limited to the above-mentioned one, and various modifications can be made within the scope of the gist and technical concept thereof.

[0104] For example, the above description describes the following situation: regarding the angular spacing of the arms A1, A2, A3 of the parallel link robot 7 (7A) in the circumferential direction around the central axis AX, the angle between the arms A1 and A3 is 80°, and the angle between the arms A1 and A2 and the angle between the arms A2 and A3 are both 140°. However, when the motors M1, M2, M3 and the reducers R1, R2, R3 are separately arranged above and below the base 23 (63) and both the maintainability is improved and the movable range is expanded, it is not necessary to set the angular spacing of the arms A1, A2, A3 to the above angles, and for example, they can be set to equal intervals (120°).

[0105] Fig. 9 An example of the structure of the parallel link robot 7B in this case is shown in FIG. Fig. 9 As shown, in the parallel linkage robot 7B, the arms A1, A2, A3 are arranged so that the angular intervals of the upper arms A1U, A2U, A3U in the circumferential direction around the central axis AX are 120°, respectively. In addition, notches 27, 29, 31 are respectively formed at positions in the base 23 corresponding to the arms A1, A2, A3 arranged at equal intervals. In addition, in this example, the motors M1, M2, M3 (motor housings MC1, MC2, MC3) are arranged on one side of the circumferential direction of the corresponding arms A1, A2, A3 in a consistent manner. In addition, the structure other than the above is the same as that of the first embodiment. In the parallel linkage robot system having the parallel linkage robot 7B of this modified example, it is also possible to simultaneously achieve both improved maintainability and expanded range of motion.

[0106] In addition, similarly, by providing a top plate portion 61 (base portion 63) that divides the lower space for picking and placing operations and the upper space for configuring the motors M1, M2, and M3 (motor housings MC1, MC2, and MC3), it is possible to prevent dirt or dust in the upper space of the top plate portion 61 from falling into the lower space and adhering to or mixing with the workpiece W. Furthermore, it is not necessary to set the angular intervals of the arms A1, A2, and A3 to the above-mentioned angles (80°, 140°, 140°), and for example, they can be set to equal intervals (120°).

[0107] Fig.10 An example of the structure of the parallel link robot 7C in this case is shown in FIG. Fig.10As shown, in the parallel linkage robot 7C, the arms A1, A2, and A3 are configured so that the angular intervals of the upper arms A1U, A2U, and A3U in the circumferential direction around the central axis AX are 120°, respectively. In addition, in this example, the motors M1, M2, and M3 (motor housings MC1, MC2, and MC3) are configured on one side of the circumferential direction of the corresponding arms A1, A2, and A3 in a consistent manner. In addition, the structure other than the above is the same as that of the second embodiment. In the parallel linkage robot system having the parallel linkage robot 7C of this modified example, it is also possible to prevent dirt or dust in the upper space of the top plate portion 61 (base portion 63) from falling into the lower space and adhering to or mixing with the workpiece W, and the sanitary environment of the picking and placing operation area can be improved.

[0108] In addition, as a modified example, for example, the rigidity of the arm A2 alone may be higher than the rigidity of each of the two arms A1 and A3 alone. Fig.11 An example of the structure of the parallel link robot 7D in this case is shown in FIG. Fig.11 As shown, the upper arm portion A2U of the arm A2 is, for example, thicker than the upper arm portions A1U and A3U of the arms A1 and A3, thereby increasing the rigidity. Similarly, although not shown in the figure, the lower arm portion A2L of the arm A2 is, for example, thicker than the lower arm portions A1L and A3L of the arms A1 and A3, thereby increasing the rigidity. In addition, the rigidity can be increased by changing the material instead of changing the thickness. Furthermore, the joint portion (spherical bearings 35b and 37b) of the arm A2 uses, for example, a bearing with higher rigidity, thereby increasing the rigidity compared to the joint portions (spherical bearings 35a and 37a and spherical bearings 35c and 37c) of the arms A1 and A3. In addition, as the motor M2 that drives the arm A2 with higher rigidity, a motor with a larger output (torque, rotation speed) than the other motors M1 and M3 can also be used. By forming such a structure, the imbalance of the rigidity of the three arms A1, A2, and A3 can be reduced, and the placement operation can be performed more stably.

[0109] <4. Example of controller hardware configuration>

[0110] Next, refer to Fig.12 The hardware configuration example of the robot controller 13, 13A that realizes the processing performed by the first motion control unit 21, the second motion control unit 65, etc. implemented by the program executed by the CPU 901 described above will be described. Fig.12 In the figure, the structure of the function of supplying driving power to the motors M1, M2, and M3 is omitted as appropriate. In addition, the host controller 11 may be set to the same hardware structure.

[0111] like Fig.12As shown, the robot controller 13, 13A includes, for example, a CPU 901, a ROM 903, a RAM 905, a dedicated integrated circuit 907 such as an ASIC or FPGA built for a specific purpose, an input device 913, an output device 915, a recording device 917, a driver 919, a connection port 921, and a communication device 923. These structures are connected via a bus 909 and an input / output interface 911 so as to be able to transmit signals to each other.

[0112] The program can be recorded in advance in, for example, the ROM 903, the RAM 905, or the recording device 917 constituted by, for example, a hard disk.

[0113] In addition, the program can be recorded temporarily or non-temporarily (permanently) on a removable recording medium 925 such as a floppy disk, various CDs, MO disks, DVDs, etc., or a semiconductor memory. Such a recording medium 925 can also be provided as so-called packaged software. In this case, the program recorded in these recording media 925 can be read by a driver 919 and recorded in the above-mentioned recording device 917 via the input / output interface 911 and the bus 909.

[0114] In addition, the program can also be recorded in advance in a download site, other computers, other recording devices, etc. (not shown). In this case, the program is transferred via a network NW such as a LAN or the Internet, and the communication device 923 receives the program. Then, the program received by the communication device 923 can also be recorded in the above-mentioned recording device 917 via the input / output interface 911 and the bus 909.

[0115] In addition, the program can also be recorded in advance in, for example, an appropriate external connection device 927. In this case, the program can be transferred via an appropriate connection port 921 and recorded in the recording device 917 via the input / output interface 911 and the bus 909.

[0116] Furthermore, the CPU 901 executes various processes according to the program recorded in the recording device 917, thereby realizing the processes performed by the first motion control unit 21 and the second motion control unit 65. At this time, the CPU 901 may, for example, directly read out the program from the recording device 917 and execute it, or may temporarily load it into the RAM 905 and execute it. Furthermore, when the CPU 901 receives the program via the communication device 923, the driver 919, or the connection port 921, for example, it may directly execute the received program without recording it in the recording device 917.

[0117] Furthermore, the CPU 901 may also perform various processes according to signals or information input from an input device 913 such as a mouse, a keyboard, or a microphone (not shown), as necessary.

[0118] Moreover, the CPU 901 can output the result after executing the above-mentioned processing from an output device 915 such as a display device or a sound output device. Furthermore, the CPU 901 can also send the processing result via the communication device 923 or the connection port 921 as needed, and can also record the processing result in the above-mentioned recording device 917 or the recording medium 925.

[0119] In addition, in the above description, when there are descriptions such as "perpendicular", "parallel", "plane", etc., these descriptions are not strictly defined. That is, these "perpendicular", "parallel", "plane" allow for tolerances and errors in design and manufacturing, and mean "substantially perpendicular", "substantially parallel", "substantially plane".

[0120] In addition, in the above description, when there are descriptions of "same", "identical", "equal", "different" and the like in terms of apparent dimensions, size, shape, position, etc., such descriptions are not strictly defined. That is, these "same", "identical", "equal", "different" allow for tolerances and errors in design and manufacturing, and mean "substantially the same", "substantially the same", "substantially equal", "substantially different".

[0121] In addition to the above, the above embodiments and modifications may be combined as appropriate. In addition, although not illustrated one by one, the above embodiments and modifications may be implemented with various modifications within the scope of the gist thereof.

Claims

1. A parallel linkage robot system, characterized in that: The parallel linkage robot system has: A first parallel link robot and a second parallel link robot, which pick up the workpiece in the first working area and place the workpiece in the second working area, The first parallel linkage robot and the second parallel linkage robot respectively have: a base portion, which is plate-shaped; a movable portion on which an end effector is mounted; and three arms, each of which has an arm portion connected to the base portion in a rotatable manner, and is configured so that one of the angular intervals of the arm portions in the circumferential direction around the central axis is less than 120°, and the other two angular intervals are equal to each other, and the three arms connect the base portion and the movable portion, The first parallel link robot and the second parallel link robot are arranged such that the two arms located at both ends of the angular interval less than 120° are closer to the first working area than the central axis, and the other arm is closer to the second working area than the central axis, and the first parallel link robot and the second parallel link robot are arranged adjacent to each other in a direction perpendicular to the extending direction of the other arm. The first parallel linkage robot and the second parallel linkage robot respectively have: three motors, which are arranged on the upper surface side of the base portion and drive the three arms respectively; three speed reducers disposed on the lower surface side of the base portion, which reduce the speed of the power of the three motors and transmit the power to the three arms respectively; and A belt is inserted into an opening penetrating the upper surface side and the lower surface side of the base portion to transmit the power of the motor to the speed reducer.

2. The parallel linkage robot system according to claim 1, characterized in that: The parallel link robot system further includes a first transport device, and the first transport device transports the workpiece in a path including the first working area. The first parallel link robot and the second parallel link robot are arranged so that the two arms are closer to the first transport device than the central axis.

3. The parallel linkage robot system according to claim 2, characterized in that: The parallel link robot system further includes a second transport device, and the second transport device transports the workpiece in a path including the second working area. The first parallel link robot and the second parallel link robot are arranged so that the other arm is closer to the second transport device than the central axis.

4. The parallel linkage robot system according to claim 2, characterized in that: The parallel linkage robot system also has: a camera that photographs the workpiece conveyed by the first conveying device at an upstream side of the first working area; an image processing unit for processing the image captured by the camera; as well as A first motion control unit controls the first parallel link robot and the second parallel link robot according to a result of processing the image.

5. The parallel linkage robot system according to any one of claims 1 to 4, characterized in that: The parallel linkage robot system further comprises a top plate portion, which is arranged above the first working area and the second working area, and three motors for driving the three arms are fixed to the upper part of the top plate portion according to the first parallel linkage robot and the second parallel linkage robot. The top plate portion also serves as the base portion of the first parallel link robot and the second parallel link robot.

6. The parallel linkage robot system according to claim 5, characterized in that: The top plate portion is divided into the first parallel link robot and the second parallel link robot, and has a substantially rectangular shape with the extending direction of the other arm as the long side and the direction substantially perpendicular to the extending direction as the short side.

7. The parallel linkage robot system according to claim 5, characterized in that: The parallel link robot system further includes a second motion control unit configured to control the motion of the three arms so that the distal ends of the arms do not come into contact with the top plate.

8. The parallel linkage robot system according to any one of claims 1 to 4, characterized in that: The other arm is configured to have higher rigidity than each of the two arms.

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