Self-weight compensation mechanism, hoisting device, and robot

Abstract

This self-weight compensation mechanism includes at least one first device, a first member, a second member, and a hoisting part fixed to the first member and the second member. The at least one first device includes: a first shaft; and a first rotating body, a second rotating body, and a biasing member provided on the first shaft. The first rotating body and the second rotating body are rotatable relatively and have different outer diameters. The biasing member connects the first rotating body and the second rotating body. The first member is stretched over the first rotating body, and the second member is stretched over the second rotating body. The hoisting part is fixed to the first member and the second member, and moves together with the first member and the second member in a second direction intersecting a first direction parallel to a central axis of the first shaft.

Description

Weight compensation mechanism, lifting device and robot

[0001] The present disclosure relates to a weight compensation mechanism, a lifting device, and a robot.

[0002] There are known weight compensation mechanisms that compensate for the weight of a driven body that has been driven to a desired position. For example, Japanese Patent Application Laid-Open No. 2003-84087 describes a device that includes a stage that is movable in the direction of gravity, a counterweight, a connecting member that connects the counterweight and the stage, a pulley that wraps around and supports the connecting member to compensate for the weight of the entire stage, and a counterweight guide that allows the counterweight to move only in the direction of gravity.

[0003] In the device described in JP 2003-84087 A, the counterweight is configured to balance the weight of the entire stage, including the stage and any loads on the stage, but depending on the counterweight, there is a risk that the weight of the entire device will increase.

[0004] The present disclosure has been made to solve the above-mentioned problems, and can be realized, for example, in the following aspects.

[0005] According to a first aspect of the present disclosure, there is provided a gravity compensation mechanism. The gravity compensation mechanism includes at least one first device, a first member, a second member, and an elevating unit. The at least one first device includes a first shaft, a first rotating body, a second rotating body, and an urging member. The first rotating body and the second rotating body are mounted on the first shaft. The first rotating body and the second rotating body are rotatable. The first rotating body and the second rotating body are configured to rotate relative to each other. The outer diameter of the first rotating body is different from the outer diameter of the second rotating body. The urging member connects the first rotating body and the second rotating body. The first member is suspended across the first rotating body. The second member is suspended across the second rotating body. The elevating unit is fixed to the first member and the second member. The elevating unit is configured to move together with the first member and the second member in a second direction intersecting a first direction parallel to the central axis of the first shaft.

[0006] According to a second aspect of the present disclosure, there is provided a lifting device including the weight compensation mechanism.

[0007] According to a third aspect of the present disclosure, there is provided a robot, the robot including the lifting device and a robot arm attached to the lifting section.

[0008] FIG. 1 is a diagram illustrating a robot system including a robot. FIG. 2 is an explanatory diagram of a weight compensation mechanism according to the first embodiment. FIG. 3 is an explanatory diagram of a weight compensation mechanism according to the first embodiment. FIG. 4 is a diagram illustrating a weight compensation force generated when the lifting unit is moved in the −Z-axis direction from the position indicated by the dashed line E1. FIG. 5 is a diagram illustrating a weight compensation force generated when the lifting unit is moved in the −Z-axis direction from the position indicated by the dashed line E1. FIG. 6 is a diagram illustrating setting of the weight compensation force. FIG. 7 is an explanatory diagram illustrating a portion of the weight compensation mechanism according to the second embodiment. FIG. 8 is an explanatory diagram of a weight compensation mechanism according to the third embodiment. FIG. 9 is an explanatory diagram of a weight compensation mechanism according to the third embodiment. FIG. 10 is an explanatory diagram of a portion of the weight compensation mechanism according to the fourth embodiment. FIG. 11 is an explanatory diagram of a portion of the weight compensation mechanism according to the fifth embodiment. FIG. 12 is an explanatory diagram of a portion of the weight compensation mechanism according to the sixth embodiment. FIG. 13 is an explanatory diagram of a weight compensation mechanism according to the seventh embodiment. FIG. 14 is an explanatory diagram of a weight compensation mechanism according to the eighth embodiment. Fig. 15 is an explanatory diagram of a weight compensation mechanism in a ninth embodiment. Fig. 16 is an explanatory diagram of a weight compensation mechanism in a tenth embodiment. Fig. 17 is an explanatory diagram of a weight compensation mechanism in an eleventh embodiment. Fig. 18 is an explanatory diagram of a weight compensation mechanism in a twelfth embodiment.

[0009] <First embodiment> Fig. 1 is a schematic diagram showing a robot system 100 including a robot 1 according to an embodiment of the present disclosure. The robot system 100 includes the robot 1 and a control device 9 that controls the robot 1. The robot 1 performs, for example, a pick-and-place operation in which a workpiece W placed at a transfer source is transported to a transfer destination. In Fig. 1, the robot 1 picks up a workpiece W from a first container C1 placed on a shelf S and transfers the workpiece W to a second container C2.

[0010] The shelf S has a plurality of shelf boards s1 arranged at intervals in the vertical direction. The first container C1 is placed on the shelf boards s1. On the shelf S, a work space H is present between the first container C1 and the shelf board s1 located above the first container C1, allowing the robot arm 4 to enter.

[0011] The robot 1 comprises a cart 11, a lifting device 2 placed on the cart 11, a robot arm 4 attached to the lifting device 2, a robot wrist 7 attached to the tip of the robot arm 4, and a hand 8 attached to the tip of the robot wrist 7.

[0012] The robot 1 moves by traveling on a carriage 11. The carriage 11 is, for example, an AVG (Automated Guided Vehicle). The carriage 11 includes a box-shaped main body 110. The main body 110 has an upper surface 111 and a recess 112 recessed downward from the upper surface 111. The upper surface 111 also functions as a mounting surface for a container or the like. In the example shown in FIG. 1 , a second container C2 is loaded on the upper surface 111.

[0013] The lifting device 2 lifts and rotates the robot arm 4. The lifting device 2 includes a housing 200 extending in the vertical direction, a rotation mechanism 30, and a weight compensation mechanism 20. The central axis of the housing 200 is also referred to as the lifting axis U. The housing 200 is attached to the carriage 11 so as to be rotatable around the lifting axis U. In the example shown in FIG. 1 , the housing 200 is attached to a recess 112 of the carriage 11. The rotation mechanism 30 includes various actuators configured to rotate the robot arm 4 around the lifting axis U. The weight compensation mechanism 20 is configured to compensate for the weight of the robot arm 4 and move the robot arm 4 along the lifting axis U. The weight compensation mechanism 20 will be described in detail below.

[0014] The robot arm 4 is a linear-acting telescopic arm that extends and retracts in the direction of a forward / backward axis V that intersects with the elevation axis U. The robot arm 4 moves the robot wrist 7 and hand 8 by extending and retracting.

[0015] The control device 9 includes a processor such as a CPU that performs various arithmetic operations, and a storage device. The storage device includes, for example, a nonvolatile memory and a volatile memory. The CPU controls the robot 1 by expanding and executing various programs stored in the memory. The control device 9 outputs commands to the robot control device 10 included in the robot system 100, for example, to move a lifting section 201 (described below) of the lifting device 2 in a direction parallel to the lifting axis U or to rotate the lifting device 2. The robot control device 10 includes a processor such as a CPU that performs various arithmetic operations, and a storage device. The storage device includes, for example, a nonvolatile memory and a volatile memory. The CPU of the robot control device 10 expands and executes various programs stored in the memory, thereby controlling various actuators of the robot 1 in accordance with commands from the control device 9.

[0016] In Figure 1, the Z-axis direction is shown as a direction parallel to the lifting axis U. Within the Z-axis direction, the direction away from the carriage 11 is also referred to as the +Z-axis direction, and the opposite direction is also referred to as the -Z-axis direction. In this embodiment, the Z-axis direction is the vertical direction. The +Z-axis direction is the vertically upward direction, and the -Z-axis direction is the vertically downward direction.

[0017] 2 and 3 are schematic diagrams of the weight compensation mechanism 20. The weight compensation mechanism 20 cancels or reduces the effect of the weight of a heavy object in a mechanism for holding and moving the object. The weight compensation mechanism 20 includes at least one first device 21, a first member 27, a second member 28, and an elevator 201 fixed to the first member 27 and the second member 28. The weight compensation mechanism 20 compensates for the weight of the elevator 201 and an object attached to the elevator 201. The object is, for example, a robot arm 4. As shown in FIG. 2 , in this embodiment, the weight compensation mechanism 20 is supported by frames 202 and 203 extending in the Z-axis direction. The frames 202 and 203 are spaced apart in the X-axis direction, which is perpendicular to the Z-axis direction. The frames 202 and 203 are fixed to a housing 200. The weight compensation mechanism 20 may be directly supported by the housing 200. Hereinafter, within the X-axis direction, the direction from frame 202 to frame 203 will also be referred to as the +X-axis direction, and the opposite direction will also be referred to as the −X-axis direction. Figure 3 also shows the Y-axis direction, which is perpendicular to the X-axis direction and the Z-axis direction.

[0018] The weight compensation mechanism 20 of this embodiment includes one first device 21. The first device 21 includes a first shaft 210, a first rotating body 211 and a second rotating body 214 provided on the first shaft 210, and a biasing member 22 provided on the first shaft 210. In this embodiment, the first shaft 210 is supported by a frame upper end 206, which is the end of the frames 202 and 203 in the +Z-axis direction. The weight compensation mechanism 20 further includes a second shaft 250, and a third rotating body 253 and a fourth rotating body 254 provided on the second shaft 250. The second shaft 250 is supported by a frame lower end 207, which is the end of the frames 202 and 203 in the −Z-axis direction. In Figure 2, in order to explain the arrangement of the frames 202, 203, the shafts 210, 250 in the gravity compensation mechanism 20, and the rotating bodies 211, 214, 253, and 254, the first member 27 and the second member 28 are shown with dashed lines, and the rotating bodies 211, 214, 253, and 254 and the shafts 210, 250 are shown in cross section parallel to the Z-axis direction.

[0019] The first device 21 will now be described in detail. The first shaft 210 included in the first device 21 extends in a direction intersecting the Z-axis direction. In this embodiment, the central axis (axis line) AX1 of the first shaft 210 is parallel to the X-axis direction. In this embodiment, the first shaft 210 is fixed to the frames 202 and 203.

[0020] The first rotating body 211 and the second rotating body 214 are each rotatable freely and can rotate relatively to each other. The first rotating body 211 and the second rotating body 214 can rotate relatively to each other, meaning that the first rotating body 211 can rotate independently of the second rotating body 214, and the second rotating body 214 can rotate independently of the first rotating body 211. In this embodiment, the first rotating body 211 and the second rotating body 214 are rotatably mounted on the first shaft 210 via bearings 212 and 215, thereby allowing them to rotate relatively to each other.

[0021] 3, the outer diameter D1 of the first rotating body 211 is different from the outer diameter D2 of the second rotating body 214. The outer diameter is also referred to as the diameter. In this embodiment, the outer diameter D1 of the first rotating body 211 is smaller than the outer diameter D2 of the second rotating body 214. The first rotating body 211 and the second rotating body 214 are spaced apart in the X-axis direction.

[0022] The biasing member 22 is an elastic body having a spring constant against torsion. The biasing member 22 directly or indirectly connects the first rotating body 211 and the second rotating body 214. In this embodiment, the biasing member 22 is disposed between the first rotating body 211 and the second rotating body 214. The biasing member 22 includes a main body 220 through which the first shaft 210 is inserted, a first end 221 connected to the first rotating body 211, and a second end 224 connected to the second rotating body 214. In this embodiment, the biasing member 22 is a torsion spring. The first end 221 and the second end 224 are also referred to as arms or legs of the torsion spring. As will be described in detail later, the first member 27 and the second member 28 are fixed to the lifting unit 201, and therefore the first member 27 and the second member 28 are displaced (rotated, moved) by the same amount of displacement. At this time, a difference (radius difference) between the outer diameter D1 of the first rotating body 211 and the outer diameter D2 of the second rotating body 214 causes a difference in the amount of rotation between the first rotating body 211 and the second rotating body 214. When the first member 27 and the second member 28 are displaced by the same amount in the −Z axis direction, the first rotating body 211 and the second rotating body 214 rotate in the second rotation direction R2 about the central axis AX1, causing the urging member 22 to wind. Furthermore, when the first member 27 and the second member 28 are displaced by the same amount in the +Z axis direction together with the elevating unit 201, the first rotating body 211 and the second rotating body 214 rotate in the first rotation direction R1, which is opposite to the second rotation direction R2, causing the urging member 22 to unwind.

[0023] The second shaft 250, the third rotating body 253, and the fourth rotating body 254 provided at the frame lower end portion 207 will be described. In this embodiment, the second shaft 250 is rotatably supported by the frames 202 and 203 via bearings 251 and 252. The central axis AX2 of the second shaft 250 is parallel to the central axis AX1 of the first shaft 210. The position of the central axis AX2 of the second shaft 250 in the Y-axis direction is the same as the position of the central axis AX1 in the Y-axis direction.

[0024] The third rotating body 253 is provided on the second shaft 250 and rotates integrally with the second shaft 250. The fourth rotating body 254 is rotatably provided on the second shaft 250 via a bearing 255. Therefore, the third rotating body 253 and the fourth rotating body 254 rotate relative to each other. The positions of the third rotating body 253 and the fourth rotating body 254 in the X-axis direction are the same as the positions of the first rotating body 211 and the second rotating body 214 in the X-axis direction, respectively. In this embodiment, the outer diameter of the third rotating body 253 and the outer diameter of the fourth rotating body 254 are different. The outer diameter of the third rotating body 253 is equal to the outer diameter D1 of the first rotating body 211. The outer diameter of the fourth rotating body 254 is equal to the outer diameter D2 of the second rotating body 214.

[0025] The first member 27 is stretched between the first rotating body 211 and the third rotating body 253. The second member 28 is stretched between the second rotating body 214 and the fourth rotating body 254. In this embodiment, the first member 27 and the second member 28 are formed in an endless shape (loop shape). The third rotating body 253 and the fourth rotating body 254 cooperate with the first rotating body 211 and the second rotating body 214 to function as supports that rotate and support the first member 27 and the second member 28, respectively. In this embodiment, the first rotating body 211, the second rotating body 214, the third rotating body 253, and the fourth rotating body 254 are sprockets. The first member 27 and the second member 28 are roller chains.

[0026] The lifting / lowering unit 201 is fixed by a fixing member 204 to the +Y-axis direction side of the extending portions of the first member 27 and the second member 28 along the Z-axis direction. The lifting / lowering unit 201 is configured to allow an object such as the robot arm 4 to be attached and detached. In this embodiment, the frames 202 and 203 are formed in the shape of a rail extending in the Z-axis direction, and the frames 202 and 203 are provided with slide members 205 that slide in the Z-axis direction. The end of the lifting / lowering unit 201 in the +X-axis direction and the end in the −X-axis direction are slidably supported on the frames 202 and 203 by the slide members 205.

[0027] As shown in FIG. 2 , the weight compensation mechanism 20 further includes an electric motor 29. The motor 29 is operably coupled to the second shaft 250. When the motor 29 is driven, the third rotating body 253 rotates integrally with the second shaft 250. This drives (rotates) the first member 27. The motor 29, the second shaft 250, and the third rotating body 253 also function as a driving unit in the weight compensation mechanism 20. Note that the fourth rotating body 254 is provided on the second shaft 250 via a bearing 255, and therefore does not rotate directly when the second shaft 250 rotates.

[0028] The operation of each part of the weight compensation mechanism 20 and the weight compensation force generated by the weight compensation mechanism 20 will be described below. As described above, in this embodiment, the first member 27 rotates when the second shaft 250 and the third rotating body 253 are rotated by the power of the motor 29. Furthermore, as the first member 27 rotates, the first rotating body 211 rotates around the axis AX1 of the first shaft 210. At this time, the lifting unit 201 moves (displaces) in the Z-axis direction in association with the rotation of the first member 27. Because the second member 28 is fixed to the lifting unit 201 by the fixing member 204, the second member 28 rotates in association with the movement of the lifting unit 201 in the Z-axis direction. As a result, the second rotating body 214 rotates around the axis AX1. The fourth rotating body 254 rotates around the axis AX2 in response to the rotation of the second member 28.

[0029] In the first device 21, when the first rotating body 211 and the second rotating body 214 rotate in the first rotation direction R1, the first member 27 and the second member 28 move the lifting / lowering unit 201 in the +Z axis direction. When the first rotating body 211 and the second rotating body 214 rotate in the second rotation direction R2, the first member 27 and the second member 28 move the lifting / lowering unit 201 in the -Z axis direction. In other words, the first rotation direction R1 is the rotation direction of the first rotating body 211 and the second rotating body 214 when the first member 27 and the second member 28 move the lifting / lowering unit 201 in the +Z axis direction. The second rotation direction R2 is the rotation direction of the first rotating body 211 and the second rotating body 214 when the first member 27 and the second member 28 move the lifting / lowering unit 201 in the -Z axis direction.

[0030] 4 and 5 show the state in which the lifting unit 201 of the gravity compensation mechanism 20 has been moved in the −Z-axis direction from the position indicated by the dashed line E1. As described above, as the first member 27 and the second member 28 move in the −Z-axis direction, the first rotating body 211 and the second rotating body 214 rotate in the second rotation direction R2. Because the outer diameter D1 of the first rotating body 211 and the outer diameter D2 of the second rotating body 214 are different, when the first member 27 and the second member 28 are displaced by the same amount in the −Z-axis direction, a difference occurs between the amount of rotation of the first rotating body 211 and the amount of rotation of the second rotating body 214. The amount of rotation is the degree of rotation. The amount of rotation can also be referred to as the number of rotations or the angle of rotation. Here, the amount of rotation θ1 of the first rotating body 211 is expressed by the following equation (1) using the diameter D1 of the first rotating body 211 and the amount of movement Δz of the lifting unit 201 in the Z-axis direction. The rotation amount θ2 of the second rotating body 214 is expressed by the following formula (2) using the diameter D2 of the second rotating body 214 and the movement amount Δz in the Z-axis direction of the lifting unit 201. Furthermore, the difference in the rotation amounts Δθ is expressed by the following formula (3) using formulas (1) and (2).

[0031]

[0032]

[0033]

[0034] The force acting on the biasing member 22 when the lifting unit 201 is moved in the −Z-axis direction from the position indicated by the dashed line E1 will be described. The first end 221 of the biasing member 22 rotates (turns, displaces, moves) as the first rotating body 211 rotates in the second rotation direction R2 due to the displacement (Δz) of the first member 27. Similarly, the second end 224 of the biasing member 22 rotates (turns, displaces, moves) as the second rotating body 214 rotates in the second rotation direction R2 due to the displacement (Δz) of the second member 28. At this time, due to the difference in rotation amount Δθ between the first rotating body 211 and the second rotating body 214, a difference in rotation amount Δθ also occurs between the first end 221 and the second end 224. This difference Δθ twists the biasing member 22. As a result, spring torques are generated in opposing directions between the first end 221 and the second end 224. For example, a spring torque is generated at the first end 221 in the direction indicated by arrow T1 in FIG. 4 , and a spring torque is generated at the second end 224 in the direction indicated by arrow T2. The spring torque in the direction indicated by arrow T1 and the spring torque in the direction indicated by arrow T2 are balanced. This spring torque can be expressed by the spring constant Kθ of the biasing member 22 and the difference in rotation amount Δθ. Therefore, the spring torque generated at the first rotating body 211 can be expressed by the following equation (4) using the spring constant Kθ, the difference in rotation amount Δθ, the tension F1 generated at the first member 27, and the radius (D1 / 2) of the first rotating body 211. The spring torque generated at the second rotating body 214 can be expressed by the following equation (5) using the spring constant Kθ, the difference in rotation amount Δθ, the tension F2 generated at the second member 28, and the radius (D1 / 2) of the second rotating body 214.

[0035]

[0036]

[0037] The difference ΔF between the tension F1 calculated from equation (4) and the tension F2 calculated from equation (5) is the force in the Z-axis direction acting on the lifting unit 201 via the first member 27 and the second member 28, i.e., the weight compensation force. As shown in the following equation (6), the weight compensation force ΔF can be expressed as the value obtained by multiplying the movement amount Δz by the spring constant Kz of the spring that has a biasing force in the Z-axis direction, which in this embodiment is the vertical direction. The spring constant Kz can be expressed by the following equation (7) using the relationships from equations (1) to (6).

[0038]

[0039]

[0040] In this way, although the weight compensation mechanism 20 of this embodiment does not directly use a spring having a vertical spring constant, it can apply a spring force in the +Z axis direction to the lifting section 201 by using a spring having an apparent vertical spring constant Kz.

[0041] Next, setting of the weight compensation force in the weight compensation mechanism 20 will be described with reference to Figure 6. Figure 6 shows an image diagram illustrating the relationship between the number of times n that the lifting unit 201, more specifically the position of the upper end of the lifting unit 201, has been moved from position E1 to position E2, and the magnitude Fn of the weight compensation force generated in the lifting unit 201. In setting the weight compensation force, after the lifting unit 201 has been moved from position E1 to position E2, the fixation of the lifting unit 201 to the first member 27 and the second member 28 by the fixing member 204 is released, and the lifting unit 201 is returned to position E1 again without displacing the first member 27 and the second member 28, and then the next movement is performed.

[0042] With respect to the hatched region Fn1, the width w of region Fn1 at a predetermined position in the Z-axis direction indicates the magnitude of the weight compensation force at that predetermined position. This is also true for the other regions Fn2, Fn3, and FnN. During the first movement (n = 1) of the lifting unit 201, the weight compensation force at position E1 is 0 (zero), but the weight compensation force increases according to the amount of movement Δz in the Z-axis direction. The weight compensation force at positions E1 and E2 increases according to the number of movements from position E1 to position E2. Therefore, the desired weight compensation force can be obtained by moving the lifting unit 201 in the Z-axis direction a desired number of times. Furthermore, as can be seen by comparing the regions Fn1, Fn2, Fn3, and FnN, as the number of movements n increases, the ratio between the weight compensation force at position E1 and the weight compensation force at position E2 decreases. Therefore, by increasing the number of movements, the amount of change in the magnitude of the weight compensation force relative to the amount of movement Δz can be reduced. In this way, a desired weight compensation force can be set in advance in the weight compensation mechanism 20 .

[0043] As described above, the weight compensation mechanism 20 of this embodiment can generate a biasing force in the Z-axis direction (vertical direction) by utilizing the fact that the biasing member 22 is twisted around the first shaft 210 due to the diameter difference between the first rotating body 211 and the second rotating body 214. Therefore, the weight of the lifting unit 201 can be compensated for by this vertical biasing force.

[0044] Furthermore, according to this embodiment, compared to a configuration in which a counterweight is used to compensate for the weight, the overall weight of the weight compensation mechanism 20 can be reduced and the size of the weight compensation mechanism 20 can be prevented from increasing. Furthermore, for example, when the weight compensation mechanism 20 is applied to the robot 1 shown in FIG. 1 , the power required to raise and lower the robot arm 4 can be reduced. In other words, the weight compensation mechanism 20 of this embodiment contributes to power saving.

[0045] Furthermore, the first end 221 and the second end 224 of the biasing member 22 rotate in the same rotational direction due to the rotation of the first rotating body 211 and the second rotating body 214, and are rotated by different rotational amounts due to the difference in diameter between the first rotating body 211 and the second rotating body 214. Therefore, compared to a configuration in which a constant force spring is used to compensate for the weight, even if the rotational amount of the biasing member 22 is relatively small, a biasing force can be applied to the biasing member 22 and the durability of the biasing member 22 can be improved. As a result, the durability of the weight compensation mechanism 20 can be improved.

[0046] The weight compensation mechanism 20 of this embodiment further includes a slide member 205 fixed to the lifting / lowering unit 201. The slide member 205 is slidably mounted on frames 202 and 203 formed in the shape of rails extending in the Z-axis direction. This allows the lifting / lowering unit 201 to move smoothly in the Z-axis direction.

[0047] As described above, spring torques are generated in the first rotating body 211 and the second rotating body 214 in opposing directions, and the tension F1 of the first member 27 and the tension F2 of the second member 28 act in different directions. In this embodiment, the tension F1 of the first member 27 acts in the +Z-axis direction, and the tension F2 of the second member 28 acts in the -Z-axis direction. Therefore, as shown in FIG. 4 , a rotational moment M is generated in the lifting / lowering unit 201, causing the lifting / lowering unit 201 to rotate around an imaginary axis parallel to the Y-axis direction. However, in this embodiment, the lifting / lowering unit 201 is supported by the slide member 205 on rail-like frames 202 and 203 extending in the Z-axis direction. Therefore, rotation of the lifting / lowering unit 201 due to the rotational moment M is suppressed.

[0048] In the first embodiment, the first member 27 and the second member 28 are driven by the power of the motor 29 to rotate the second shaft 250 and the third rotor 253 that rotates integrally with the second shaft 250. The manner in which the first member 27 and the second member 28 are driven is not limited to that of the first embodiment and can be modified as appropriate. In the following second and third embodiments, weight compensation mechanisms in which the manner in which the first member 27 and the second member 28 are driven will be described.

[0049] Second Embodiment FIG. 7 shows a portion of a weight compensation mechanism 20a according to a second embodiment. In the following embodiments, the same reference numerals are used for components similar to those in the above-described embodiments, and descriptions thereof will be omitted where appropriate. In this embodiment, a first shaft 210a of a first device 21a is rotatably supported by frames 202 and 203 via bearings 216 and 217. A first rotating body 211a is fixed to the first shaft 210a, and a second rotating body 214 is mounted on the first shaft 210a via a bearing 215. Therefore, the first rotating body 211a and the second rotating body 214 are rotatable relative to each other. In this embodiment, a motor 29 is operably coupled to the first shaft 210a. Although the outer diameters D1 and D2 are not shown in the drawings, the outer diameter D1 of the first rotating body 211a is smaller than the outer diameter D2 of the second rotating body 214. This also applies to the following third to ninth embodiments.

[0050] In the present embodiment, when the motor 29 is driven, the first shaft 210a and the first rotor 211a rotate around the axis AX1. This causes the first member 27 to rotate. In the second embodiment, the motor 29, the first shaft 210a, and the first rotor 211a function as a drive unit. The remaining configuration of the weight compensation mechanism 20a is the same as that of the weight compensation mechanism 20 of the first embodiment. Therefore, the present embodiment also achieves the same effects as those of the first embodiment.

[0051] <Third Embodiment> Figures 8 and 9 show a weight compensation mechanism 20b according to a third embodiment. The first device 21 in the weight compensation mechanism 20b has the same configuration as in the first embodiment. In this embodiment, the motor 29 is operably coupled to a second shaft 250b provided at the frame lower end 207. This embodiment differs from the above-described embodiments in that the outer diameters of the third and fourth rotors 253b and 254b are equal and the third and fourth rotors 253b and 254b are fixed to the second shaft 250b. Although not shown in Figure 8, as shown in Figure 9, the weight compensation mechanism 20b further includes a third shaft 260b, and a fifth and sixth rotors 261 and 262 rotatably provided on the third shaft 260b. The fifth rotating body 261 and the sixth rotating body 262 are arranged so that the first member 271 and the second member 28 extend parallel to the rail-equipped frames 202 and 203 in the +Y-axis direction. The central axis AX3 of the third shaft 260b is parallel to the X-axis direction. The first member 27 is suspended between the first rotating body 211, the third rotating body 253b, and the fifth rotating body 261. The second member 28 is suspended between the second rotating body 214, the fourth rotating body 254b, and the sixth rotating body 262. The fifth rotating body 261 and the sixth rotating body 262 are driven by the rotation of the first member 27 and the second member 28, respectively.

[0052] When the motor 29 is driven, the third rotor 253b and the fourth rotor 254b rotate integrally with the second shaft 250b around the axis AX2. This causes the first member 27 and the second member 28 to rotate. In this embodiment, the motor 29, the second shaft 250b, the third rotor 253b, and the fourth rotor 254b function as a drive unit that applies power to the first member 27 and the second member 28. The remaining configuration of the weight compensation mechanism 20b is the same as that of the weight compensation mechanism 20 of the first embodiment. Therefore, this embodiment also achieves the same effects as the first embodiment.

[0053] <Fourth Embodiment> Figure 10 shows a portion of a weight compensation mechanism 20c according to a fourth embodiment. In this embodiment, a first shaft 210c of a first device 21c is rotatably supported by the frames 202 and 203 via bearings 216 and 217. A first rotating body 211c is fixed to the first shaft 210c and rotates integrally therewith. A second rotating body 214c is attached to the first shaft 210c via a bearing 215. Therefore, the first rotating body 211c and the second rotating body 214c are rotatable relative to each other. In this embodiment, the first rotating body 211c, the second rotating body 214c, and the biasing member 22c are arranged on the first shaft 210c in this order in the +X-axis direction. The second rotating body 214c can also be said to be disposed between the first rotating body 211c and the biasing member 22c. Because the first rotating body 211c and the second rotating body 214c are adjacent to each other on the first shaft 210c, the distance between the first rotating body 211c and the second rotating body 214c in the X-axis direction is shorter than in the above-described embodiment, and therefore the distance between the first member 27 and the second member 28 in the X-axis direction is shorter than in the above-described embodiment.

[0054] In this embodiment, the biasing member 22c is a spiral spring. A first end 221c of the biasing member 22c is fixed to the first shaft 210c. Because the first rotating body 211c is fixed to the first shaft 210c, it can be said that the first end 221c is connected to the first rotating body 211c via the first shaft 210c. A second end 224c of the biasing member 22c is connected to the second rotating body 214c via a case 223c. The case 223c is coupled to the second rotating body 214c and configured to rotate integrally with the second rotating body 214c. The spiral spring serving as the biasing member 22c is wound around the central axis AX1 when the first rotating body 211c and the second rotating body 214c rotate in the second rotation direction R2. The remaining configuration of the weight compensation mechanism 20c in this embodiment is similar to that of the weight compensation mechanism 20 in the first embodiment. Therefore, this embodiment also achieves the same effects as the above-described embodiment. In addition, because the first rotating body 211c and the second rotating body 214c are adjacent to each other in the X-axis direction, the distance in the X-axis direction between the first member 27 and the second member 28 can be shortened. Therefore, the moment M acting on the lifting / lowering unit 201 can be reduced. As a result, it is possible to simplify the configuration for suppressing rotation of the lifting / lowering unit 201, for example, by reducing the size of the slide member 205.

[0055] Fifth Embodiment FIG. 11 shows a weight compensation mechanism 20d according to a fifth embodiment. In this embodiment, a first shaft 210d of a first device 21d is rotatably supported by the frames 202 and 203 via bearings 216 and 217. As in the fourth embodiment, a first rotating body 211d is fixed to the first shaft 210d and rotates integrally therewith. A second rotating body 214d is provided on the first shaft 210d via a bearing 215. Therefore, the first rotating body 211c and the second rotating body 214c are rotatable relative to each other. In this embodiment, a seventh rotating body 219d is further provided on the first shaft 210d. The seventh rotating body 219d is fixed to the first shaft 210d and rotates integrally therewith. The outer diameter of the seventh rotating body 219d is equal to the outer diameter D1 of the first rotating body 211c.

[0056] The weight compensation mechanism 20d further includes a third member 26. The third member 26 is suspended between a rotor (not shown) provided at the frame lower end 207 and a seventh rotor 219d. The lifting unit 201 is fixed to the first member 27, the second member 28, and the third member 26 by a fixing member 204.

[0057] In this embodiment, the distance between the second rotating body 214d and the first rotating body 211d in the X-axis direction is approximately equal to the distance between the second rotating body 214d and the seventh rotating body 219d. The seventh rotating body 219d is disposed symmetrically with the first rotating body 211d with respect to an imaginary plane P that passes through the center of the second rotating body 214d in the X-axis direction and is parallel to the YZ plane. Furthermore, the third member 26 is disposed symmetrically with the first member 27 with respect to the imaginary plane P.

[0058] With the above configuration, as the first rotor 211d rotates, the seventh rotor 219d rotates integrally with the first shaft 210d. Therefore, the third member 26 is displaced in the Z-axis direction in synchronization with the first member 27. Because the first end 221c is fixed to the first shaft 210d, the spring torque of the biasing member 22c acts on the first rotor 211d and the seventh rotor 219d. Therefore, the tension F1 described in the first embodiment is distributed to the first member 27 and the third member 26. Therefore, the rotational moment M acting on the lifting unit 201 can be reduced.

[0059] Furthermore, in this embodiment, the third member 26 is disposed symmetrically to the first member 27 with respect to the imaginary plane P, and therefore the tension F1 described in the first embodiment is equally distributed to the first member 27 and the third member 26. As a result, the rotational moment M acting on the lifting unit 201 is canceled.

[0060] Sixth Embodiment FIG. 12 shows a weight compensation mechanism 20e according to a sixth embodiment. As in the fifth embodiment, a first rotating body 211e, a second rotating body 214e, and a seventh rotating body 219e are provided on a first shaft 210e in this order in the +X-axis direction. The first shaft 210e is rotatably supported by the frames 202 and 203 via bearings 216 and 217. The first rotating body 211e is fixed to the first shaft 210e and rotates integrally therewith. The second rotating body 214e is provided on the first shaft 210e via a bearing 215. Therefore, the first rotating body 211e and the second rotating body 214e are rotatable relative to each other. Furthermore, the second rotating body 214e and the seventh rotating body 219e are rotatable relative to each other.

[0061] The first device 21e includes two biasing members 22e and 23e. In this embodiment, the biasing members 22e and 23e are torsion springs. The biasing member 22e is disposed between the first rotating body 211c and the second rotating body 214e. A first end 221e of the biasing member 22e is connected to the first rotating body 211e, and a second end 224e of the biasing member 22e is connected to the second rotating body 214e. Therefore, similar to the above-described embodiment, the biasing member 22e is twisted around the axis AX1 of the first shaft 210e due to the diameter difference between the first rotating body 211e and the second rotating body 214e. The biasing member 23e is disposed between the second rotating body 214e and the seventh rotating body 219e. A first end 231e of the biasing member 23e is connected to the seventh rotating body 219e, and a second end 234e of the biasing member 23e is connected to the second rotating body 214e. Therefore, the biasing member 23e is twisted around the first shaft 210e due to the difference in diameter between the second rotating body 214e and the seventh rotating body 219e. The remaining configuration of the weight compensation mechanism 20e is the same as that of the fifth embodiment.

[0062] Similar to the weight compensation mechanism 20d of the fifth embodiment, the weight compensation mechanism 20e of the present embodiment can cancel the rotational moment M acting on the lifting unit 201 by using the seventh rotating body 219e and the third member 26. Furthermore, the weight compensation mechanism 20e includes a biasing member 22e connected to the first rotating body 211c and the second rotating body 214c, and a biasing member 23e connected to the second rotating body 214c and the seventh rotating body 219d. Therefore, compared to the above-described embodiments, the tension acting in the +Z axis direction can be increased, and as a result, the weight compensation force can be increased.

[0063] Seventh Embodiment Fig. 13 shows a weight compensation mechanism 20f according to a seventh embodiment. The weight compensation mechanism 20f according to this embodiment includes a plurality of first devices 21 arranged in the Z-axis direction. The plurality of first devices 21 are arranged at positions corresponding to the range of movement of the lifting unit 201 in the Z-axis direction. The configuration of the first devices 21 according to this embodiment is the same as that according to the first embodiment. As shown in Fig. 13, the orientation of the biasing member 22 in each first device 21 is opposite to that of the adjacent first device 21 in the Z-axis direction. The orientation of the biasing member 22 in each first device 21 corresponds to the orientation in which a biasing force is applied to the biasing member 22 by the rotation of the first rotating body 211 and the second rotating body 214.

[0064] The frame lower end 207 is provided with a second shaft 250f, and a third rotating body 253f and a fourth rotating body 254f fixed to the second shaft 250f. As in the third embodiment, the second shaft 250f is rotatable relative to the frames 202, 203 and is operably connected to a motor 29 (not shown). The outer diameters of the third rotating body 253f and the fourth rotating body 254f are equal. The frame upper end 206 is provided with a third shaft 260f. The third shaft 260f is provided with a fifth rotating body 261f and a sixth rotating body 262f. The fifth rotating body 261f and the sixth rotating body 262f are rotatable relative to the third shaft 260f. The first member 27 is suspended between each of the first rotating bodies 211, the third rotating body 253f, and the fifth rotating body 261f in the plurality of first devices 21. The second member 28 is suspended between each second rotating body 214, a fourth rotating body 254f, and a sixth rotating body 262f in the plurality of first devices 21. The manner in which the first member 27 and the second member 28 are driven is the same as in the third embodiment. The fifth rotating body 261f and the sixth rotating body 262f are driven by the rotation of the first member 27 and the second member 28, respectively.

[0065] According to this embodiment, the weight compensation mechanism 20f includes multiple first devices 21, thereby increasing the biasing force of the weight compensation mechanism 20f. Furthermore, by arranging multiple first devices 21 at positions corresponding to the range of movement of the lifting unit 201 in the Z-axis direction, the biasing force can be increased without increasing the size of the weight compensation mechanism 20f. Furthermore, since multiple first devices 21 are included, even if the biasing force of one biasing member 22 unintentionally decreases, the other biasing members 22 can prevent the lifting unit 201 from falling. This improves the safety of the weight compensation mechanism 20f. In other words, the weight compensation mechanism 20f of this embodiment can achieve a fail-safe.

[0066] Eighth Embodiment FIG. 14 shows a weight compensation mechanism 20g according to an eighth embodiment. The weight compensation mechanism 20g of this embodiment includes a plurality of first devices 21c arranged in the Z-axis direction. The configuration of the first devices 21c is the same as that of the fourth embodiment. The remaining configuration of the weight compensation mechanism 20g is the same as that of the weight compensation mechanism 20f of the seventh embodiment. As in the seventh embodiment, the orientation of the biasing member 22c in each first device 21c is opposite to that of the adjacent first device 21c in the Z-axis direction. The orientation of the biasing member 22c in each first device 21c is such that a biasing force is applied to the biasing member 22c by rotation of the first rotating body 211c and the second rotating body 214c.

[0067] According to this embodiment, the weight compensation mechanism 20g includes multiple first devices 21c. As in the seventh embodiment, the biasing force of the weight compensation mechanism 20g can be increased without increasing the size of the weight compensation mechanism 20g. Furthermore, the weight compensation mechanism 20g can achieve a fail-safe. Furthermore, as in the fourth embodiment, in each first device 21c, the first rotating body 211c and the second rotating body 214c are adjacent to each other in the X-axis direction. Therefore, the distance between the first member 27 and the second member 28 in the X-axis direction can be shortened. Therefore, the moment M acting on the lifting unit 201 can be reduced.

[0068] Ninth Embodiment FIG. 15 shows a weight compensation mechanism 20h according to the ninth embodiment. The weight compensation mechanism 20h differs from the first embodiment in that a first member 27h and a second member 28h cooperate with the lifting / lowering unit 201 to form an endless loop. The first member 27h includes an end 271h and an end 272h. The end 271h is fixed to the end of the lifting / lowering unit 201 in the negative Z-axis direction, and the end 272h is fixed to the end of the lifting / lowering unit 201 in the positive Z-axis direction. Similarly, the second member 28h includes an end 281h and an end 282h. The end 281h is fixed to the end of the lifting / lowering unit 201 in the negative Z-axis direction, and the end 282h is fixed to the end of the lifting / lowering unit 201 in the positive Z-axis direction. The endless loop is realized by the second member 28h and the lifting / lowering unit 201. Other configurations of the weight compensation mechanism 20h are the same as those in the first embodiment, so that the present embodiment also provides the same effects as those in the first embodiment.

[0069] 10th Embodiment Fig. 16 shows a portion of a weight compensation mechanism 20i according to a tenth embodiment. In this embodiment, a first shaft 210i of a first device 21i is rotatably supported by frames 202 and 203 via bearings 216 and 217. A first rotating body 211i is fixed to the first shaft 210i and rotates integrally with the first shaft 210i. A second rotating body 214i is provided on the first shaft 210i via a bearing 215. Therefore, the first rotating body 211i and the second rotating body 214i are rotatable relative to each other.

[0070] The biasing member 22i is a torsion spring. A first end 221i of the biasing member 22i is fixed to the first shaft 210i. Because the first rotating body 211c is fixed to the first shaft 210i, it can be said that the first end 221i is connected to the first rotating body 211i via the first shaft 210i. A second end 224i of the biasing member 22i is connected to the second rotating body 214i. The remaining configuration of the weight compensation mechanism 20i in this embodiment is the same as that of the weight compensation mechanism 20 in the first embodiment. Therefore, this embodiment also achieves the same effects as the above-mentioned embodiment.

[0071] 11th Embodiment Fig. 17 shows a portion of a weight compensation mechanism 20j according to the 11th embodiment. In this embodiment, the first device 21j includes a leaf spring as a biasing member 22j. The biasing member 22j is not provided on the first shaft 210. A first end 221j of the biasing member 22j is connected to the first rotating body 211, and a second end 224j of the biasing member 22j is connected to the second rotating body 214. The remaining configuration of the weight compensation mechanism 20j is similar to that of the weight compensation mechanism 20 according to the first embodiment. Therefore, this embodiment also achieves the same effects as the above-described embodiments.

[0072] 12th Embodiment FIG. 18 shows a portion of a weight compensation mechanism 20k according to the twelfth embodiment. In this embodiment, the first device 21k includes a rubber-like elastic body as a biasing member 22k. The biasing member 22k is formed in a hollow cylindrical shape with a hollow portion 222k, and a top surface 221k and a bottom surface 224k are connected to the first rotating body 211 and the second rotating body 214, respectively. The top surface 221k and the bottom surface 224k can be considered as a first end and a second end of the biasing member 22k. The remaining configuration of the weight compensation mechanism 20k is similar to that of the weight compensation mechanism 20 according to the first embodiment. Therefore, this embodiment also achieves the same effects as the above-described embodiments.

[0073] <Correspondence> The correspondence between each component (feature) of the above embodiment and each component (feature) of the present disclosure or invention is shown below. However, each component of the embodiment is merely an example and does not limit each component of the present disclosure or invention.

[0074] The weight compensation mechanisms 20, 20a, 20b, 20c, 20d, 20e, 20f, 20g, 20h, 20i, 20j, and 20k are examples of "weight compensation mechanisms." The first devices 21, 21a, 21c, 21d, 21e, 21i, 21j, and 21k are examples of "first devices." The first shafts 210, 210a, 210c, 210d, 210e, and 210i are examples of "first shafts." The first rotating bodies 211, 211a, 211c, 211d, 211e, and 211i, and the seventh rotating body 219e are examples of "first rotating bodies." The second rotating bodies 214, 214c, 214d, 214e, and 214i are examples of "second rotating bodies." The biasing members 22, 22e, 23e, 22i, 22j, and 22k are examples of "biasing members." The first ends 221, 221c, 221e, 231e, 221i, and 221j, and the top surface 221k are examples of "first ends." The second ends 224, 224c, 224e, 234e, 224i, and 224j, and the bottom surface 224k are examples of "second ends." The first members 27 and 27h are examples of "first members." The second members 28 and 28h are examples of "second members." The lifting unit 201 is an example of an "lifting unit." The X-axis direction is an example of a "first direction." The Y-axis direction is an example of a "second direction." The +Y-axis direction and the -Y-axis direction are examples of an "upward direction" and an "downward direction," respectively. The rotation directions R1 and R2 are examples of a "first rotation direction" and a "second rotation direction," respectively. The frames 202 and 203 and the rail shapes provided on the frames 202 and 203 are examples of a "guide rail." The slide member 205 is an example of a "slide member." The third member 26 is an example of a "third member." The seventh rotating bodies 219d and 219e are examples of "rotating bodies." The motor 29, the second shaft 250, and the third rotating body 253 are examples of a "drive unit that drives the first member or the second member." The motor 29, the second shaft 250b, the third rotating body 253b, and the fourth rotating body 254b are examples of a "drive unit that drives the first member and the second member." The motor 29, the second shaft 250f, the third rotating body 253f, and the fourth rotating body 254f are examples of a "drive unit that drives the first member and the second member." The first shaft 210a is an example of a "drive shaft."The second shafts 250, 250b, and 250f are examples of "second shafts." The third rotating bodies 253, 253b, and 253f are examples of "third rotating bodies." The fourth rotating bodies 254, 254b, and 254f are examples of "fourth rotating bodies." The housing 200 is an example of a "housing." The lifting device 2, the robot arm 4, and the robot 1 are examples of an "lifting device," a "robot arm," and a "robot," respectively.

[0075] The weight compensation mechanism according to the present disclosure is not limited to the above-described embodiment. For example, the following non-limiting examples are possible. Furthermore, at least one of these modifications may be adopted in combination with the weight compensation mechanisms 20 to 20k of the embodiments and at least one of the features described in the claims.

[0076] A single guide rail may be provided between the frame 202 and the frame 203, and the slide member 205 may be supported by the guide rail. The slide member and the guide rail may be omitted as appropriate, for example, when the rotation moment M of the lifting unit is canceled.

[0077] In the first to third, sixth, seventh, and ninth embodiments described above, a torsion spring was used as the biasing member, but a spiral spring may also be used. Similarly, in the fourth, fifth, and ninth embodiments, a spiral spring was used as the biasing member, but a torsion spring may also be used. Alternatively, a leaf spring or a rubber-like elastic body may also be used as the biasing member. The biasing members 22, 22c, 22e, 23e, 22i, 22j, and 22k in the above embodiments may be elastic bodies having a torsional spring constant.

[0078] In the various embodiments described above, the Z-axis direction is the vertical direction, but the Z-axis direction may be a substantially vertical direction. The substantially vertical direction may be a direction whose angle with the vertical direction is within a range of −10° to +10°.

[0079] The outer diameter D1 of the first rotating bodies 211, 211a, 211c, 211d, 211e, and 211i and the outer diameter D2 of the second rotating bodies 214, 214c, 214d, 214e, and 214i may be different. As in the above embodiment, the outer diameter D1 may be smaller than the outer diameter D2. Alternatively, the outer diameter D1 may be larger than the outer diameter D2.

[0080] In the above embodiment, the second members 28 and 28h may function as the "first member" of the present disclosure, and the first members 27 and 27h may function as the "second member" of the present disclosure. In this case, the second rotating bodies 214, 214c, and 214i function as the "first rotating body" of the present disclosure, and the first rotating bodies 211, 211c, and 211i function as the "second rotating body" of the present disclosure.

[0081] In the weight compensation mechanism according to the above embodiment, the configuration for rotating (driving) the first and second rotating bodies can be modified as appropriate as long as the first and second rotating bodies are rotatable and configured to rotate relative to each other. In the weight compensation mechanism, if the outer diameters of the third and fourth rotating bodies are different, one of the third and fourth rotating bodies may be fixed to the second shaft, and the other may be rotatably mounted on the second shaft. In other words, if the outer diameters of the third and fourth rotating bodies are different, the drive unit may be configured so that the third and fourth rotating bodies rotate relative to each other. Furthermore, if the outer diameters of the third and fourth rotating bodies are equal, the drive unit may be configured so that the third and fourth rotating bodies rotate relative to each other, or so that the third and fourth rotating bodies rotate synchronously (integrally).

[0082] In the third embodiment described above, the third rotating body 253b and the fourth rotating body 254b may be configured as a single rotating body. In this case, the portion of the single rotating body around which the first member is suspended is an example of the "third rotating body" of the present disclosure, and the portion around which the second member is suspended is an example of the "fourth rotating body" of the present disclosure.

[0083] In the above embodiment, each of the rotating bodies may be a sprocket or a pulley. The first members 27, 27h, the second members 28, 28h, and the third member 26 may be a chain or a belt.

[0084] The weight compensation mechanism can be applied to various mechanisms that require weight compensation. The weight compensation mechanisms 20 to 20g are highly durable and therefore more suitable for mechanisms that move up and down frequently. For example, the weight compensation mechanism is not limited to elevators that raise and lower robot arms, but may also be applied to forklifts, balancers, etc.

[0085] The weight compensation force of the weight compensation mechanism may be obtained by moving the lifting unit 201 in the −Z axis direction by manual operation by an operator, etc. The motor 29 is not an essential component.

[0086] The present disclosure is not limited to the above-described embodiments and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following aspects. The technical features in the above embodiments corresponding to the technical features in each aspect described below can be appropriately replaced or combined to solve some or all of the problems of the present disclosure or to achieve some or all of the effects of the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0087] (1) According to a first aspect of the present disclosure, there is provided a weight compensation mechanism. The weight compensation mechanism includes at least one first device, a first member, a second member, and an elevating unit. The at least one first device includes a first shaft, a first rotating body, a second rotating body, and an urging member. The first rotating body and the second rotating body are provided on the first shaft. The first rotating body and the second rotating body are rotatable. The first rotating body and the second rotating body are configured to be rotatable relative to each other. The outer diameter of the first rotating body and the outer diameter of the second rotating body are different. The urging member connects the first rotating body and the second rotating body. The first member is suspended across the first rotating body. The second member is suspended across the second rotating body. The elevating unit is fixed to the first member and the second member. The lifting unit is configured to move together with the first and second members in a second direction intersecting a first direction parallel to the axis of the first shaft. According to this configuration, the first and second members are fixed to the lifting unit, so the first and second members are displaced (rotated and moved) by the same amount (amount of rotation and movement). Because the outer diameters of the first and second rotating bodies are different, a difference in the amount of rotation occurs between the first and second rotating bodies. Therefore, a biasing force (elastic energy) is applied to the biasing member connecting the first and second rotating bodies. This biasing force can compensate for the weight of the lifting unit. Furthermore, because the weight of the lifting unit can be compensated for using the first and second rotating bodies on the first shaft and the biasing member connecting the first and second rotating bodies, the overall weight of the weight compensation mechanism can be reduced and the size of the weight compensation mechanism can be suppressed compared to a configuration in which the weight is compensated for using a counterweight. In this embodiment, the connection of the biasing member to the first rotating body and the second rotating body includes a case where the biasing member is directly connected (fixed, coupled) to the first rotating body and a case where the biasing member is indirectly connected to the first rotating body, and also a case where the biasing member is directly connected (fixed, coupled) to the second rotating body and a case where the biasing member is indirectly connected to the second rotating body.

[0088] (2) In the weight compensation mechanism described in the above aspect (1), the second direction may be a substantially vertical direction. The first rotating body and the second rotating body may be rotatable in a first rotational direction about the central axis and a second rotational direction about the central axis, the second rotational direction being opposite to the first rotational direction. The first rotational direction may correspond to a rotational direction of the first member and the second member when the lifting unit moves upward in the second direction. The second rotational direction may correspond to a rotational direction of the first member and the second member when the lifting unit moves downward in the second direction, opposite to the upward direction. The at least one first device may be configured to bias the lifting unit in the upward direction by rotating the biasing member in the second rotational direction about the central axis due to rotation of the first rotating body and the second rotating body in the second rotational direction. According to this aspect, by rotating the first rotating body and the second rotating body in the second rotation direction, a biasing force can be applied to the biasing member, and the lifting section can be biased upward.

[0089] (3) In the weight compensation mechanism described in the above aspect (2), the biasing member may have a first end connected to the first rotating body and a second end connected to the second rotating body. The at least one first device may be configured to bias the lifting unit in the upward direction by rotating the first end and the second end around the central axis in the second rotational direction due to rotation of the first rotating body and the second rotating body in the second rotational direction. According to this aspect, when the first rotating body and the second rotating body rotate in the second rotational direction, a difference in rotation amount occurs between the first end connected to the first rotating body and the second end connected to the second rotating body, and a biasing force is applied to the biasing member. This biasing force can bias the lifting unit in the upward direction. Note that in this aspect, connecting the first end to the first rotating body includes being directly connected (fixed, coupled) to the first rotating body and being indirectly connected to the first rotating body. Similarly, the connection of the second end to the second rotating body includes the second end being directly connected (fixed, coupled) to the second rotating body and the second end being indirectly connected to the second rotating body.

[0090] (4) In the weight compensation mechanism according to any one of the above aspects (1) to (3), the biasing member may be an elastic body having a spring constant against torsion. According to this aspect, the biasing member provided on the first shaft is twisted around the central axis due to the diameter difference between the first rotor and the second rotor, thereby applying a biasing force to the biasing member. The elastic body having a spring constant against torsion may be, for example, a torsion spring, a spiral spring, or a member made of a synthetic resin such as rubber.

[0091] (5) The weight compensation mechanism according to any one of the above aspects (1) to (4) may further include a guide rail extending in the second direction and a slide member. The slide member may be provided on the guide rail so as to be slidable in the second direction. The lifting / lowering unit may be fixed to the slide member. According to this aspect, the lifting / lowering unit can be moved smoothly in the second direction. Because the lifting / lowering unit is supported on the guide rail by the slide member, it is possible to prevent the lifting / lowering unit from rotating around a virtual axis perpendicular to the first direction and the second direction due to a difference in tension between the first member and the second member.

[0092] (6) In the weight compensation mechanism according to any one of the above aspects (1) to (5), one of the first rotating body and the second rotating body may be disposed between the other of the first rotating body and the second rotating body and the biasing member in the first direction. According to this aspect, the distance between the first rotating body and the second rotating body in the first direction can be shortened, thereby reducing the rotational moment acting on the lifting unit due to the difference in tension between the first member and the second member. Disposing one of the first rotating body and the second rotating body between the other of the first rotating body and the second rotating body and the biasing member in the first direction may mean that the first rotating body and the second rotating body are adjacent to each other in the first direction.

[0093] (7) In the weight compensation mechanism according to any one of the above aspects (1) to (6), the at least one first device may be a plurality of first devices aligned in the second direction. According to this aspect, the biasing force in the weight compensation mechanism is increased. Furthermore, a fail-safe can be achieved in the weight compensation mechanism. Note that in this aspect, the plurality of first devices may be arranged in the second direction so as to correspond to the extending portions of the first member and the second member in the second direction. According to this aspect, the biasing force, i.e., the weight compensation force, can be increased without increasing the size of the weight compensation mechanism.

[0094] (8) In the weight compensation mechanism described in any one of the above aspects (1) to (7), the first shaft may be rotatable. The first rotating body or the second rotating body may be provided on the first shaft so as to rotate integrally with the first shaft. In this aspect, one of the first rotating body and the second rotating body may rotate integrally with the first shaft, and the other of the first rotating body and the second rotating body may be rotatable relative to the first shaft. When this aspect (8) is applied to the weight compensation mechanism described in the above aspect (7), for example, the first rotating body may rotate integrally with the first shaft, and the second rotating body may be rotatably provided on the second shaft. Furthermore, the first end may be fixed to the first shaft and connected to the first rotating body via the first shaft, and the second end may be connected to the second rotating body. According to this aspect, the distance in the first direction between the first rotating body and the second rotating body can be shortened by rational arrangement, and as a result, the rotational moment acting on the lifting unit can be reduced.

[0095] (9) The gravity compensation mechanism according to any one of the above aspects (1) to (8) may further include a third member fixed to the lifting unit. The at least one first device may further include a third rotating body provided on the first shaft and having the third member suspended therebetween. According to this aspect, the third member can reduce the rotational moment acting on the lifting unit. In this aspect, the third rotating body may be provided on the opposite side of the first rotating body with respect to the second rotating body in the second direction. Furthermore, the gravity compensation mechanism may be configured so that the third rotating body and the first rotating body rotate synchronously. The third member may be configured so that the third rotating body moves in the second direction synchronously with the first member. The outer diameter of the first rotating body may be equal to the outer diameter of the third rotating body. Furthermore, the distance between the third rotating body and the second rotating body in the second direction may be equal to the distance between the first rotating body and the second rotating body. According to this aspect, the rotational moment acting on the lifting unit can be canceled by the third member.

[0096] (10) The weight compensation mechanism according to any one of the above aspects (1) to (9) may further include a drive unit that drives the first member or the second member. The first rotating body and the second rotating body may be configured to be rotatable relative to the first shaft. According to this aspect, the drive unit can rotate the first member or the second member to rotate the first rotating body. Furthermore, the first member can rotate the second member by moving the lifting unit in the second direction, and the second rotating body can rotate in response to the rotation of the second member. Alternatively, the second member can rotate the first member by moving the lifting unit in the second direction, and the first rotating body can rotate in response to the rotation of the first member. In this aspect, when the drive unit rotates the first member, (i) the first rotating body rotates, (ii) the first end rotates in conjunction with the rotation of the first rotating body, (iii) the lift unit moves in the second direction, (iv) the second member and the second rotating body rotate in conjunction with the movement of the lift unit in the second direction, and (v) the second end rotates in conjunction with the rotation of the second rotating body. Alternatively, in this aspect, when the drive unit rotates the second member, (i) the second rotating body rotates, (ii) the second end rotates in conjunction with the rotation of the second rotating body, (iii) the lift unit moves in the second direction, (iv) the first member and the first rotating body rotate in conjunction with the movement of the lift unit in the second direction, and (v) the first end rotates in conjunction with the rotation of the first rotating body. In this embodiment, the drive unit may include a motor, a second shaft operably connected to the motor, and a third rotating body that rotates integrally with the second shaft and has the first member suspended therearound.

[0097] (11) The weight compensation mechanism according to any one of the above aspects (1) to (9) may further include a drive unit that drives the first member and the second member. The first rotating body and the second rotating body may be rotatable relative to the first shaft. According to this aspect, the drive unit can rotate the first rotating body and the second rotating body by driving the first member and the second member. This allows the first end and the second end to rotate around the central axis. In this aspect, when the drive unit rotates the first member and the second member, (i) the lifting unit moves in the second direction, (ii) the first rotating body rotates, and the first end rotates in conjunction with the rotation of the first rotating body, and (iii) the second rotating body rotates, and the second end rotates in conjunction with the rotation of the second rotating body. In this aspect, the drive unit may include a motor, a second shaft operably connected to the motor, and third and fourth rotating bodies fixed to the second shaft. The third rotating body and the fourth rotating body may have the same outer diameter. The first member may span the first rotating body and the third rotating body, and the second member may span the second rotating body and the fourth rotating body.

[0098] (12) In the weight compensation mechanism according to any one of the above aspects (1) to (9), the first shaft may be a drive shaft. The first rotating body may rotate integrally with the first shaft, and the second rotating body may be rotatable relative to the first shaft. According to this aspect, by driving the first shaft, the first rotating body and the second rotating body can be rotated relatively around the central axis. In this aspect, the weight compensation mechanism may include a motor operably connected to the first shaft. The motor, the first shaft, and the first rotating body may function as a drive unit.

[0099] (13) The weight compensation mechanism according to any one of the above aspects (1) to (12) may further include a second shaft extending parallel to the first direction, and a third rotating body and a fourth rotating body provided on the second shaft, each of which is rotatable. The first member and the second member may be endless. The first member may be suspended between the first rotating body and the third rotating body. The second member may be suspended between the second rotating body and the fourth rotating body. According to this aspect, in a weight compensation mechanism including a first member suspended between the first rotating body and the third rotating body and a second member suspended between the second rotating body and the fourth rotating body, the weight of a lifting unit fixed to the first member and the second member can be compensated for.

[0100] (14) According to a second aspect of the present disclosure, there is provided a lifting device including the weight compensation mechanism according to any one of the above aspects (1) to (13). The lifting device may include the weight compensation mechanism and a housing that accommodates the weight compensation mechanism. In this aspect, the lifting device may further include a motor that raises and lowers the lifting unit.

[0101] (15) According to a third aspect of the present disclosure, there is provided a robot including the lifting device according to the above-described aspect (14) and a robot arm attached to the lifting section. According to this aspect, the robot arm can be moved in the second direction while the weight of the robot arm is compensated for by the weight compensation mechanism.

[0102] 1: Robot, 4: Robot arm, 7: Robot wrist, 8: Hand, 9: Control device, 10: Robot control device, 11: Cart, 110: Main body, 111: Top surface, 112: Recess, C1: First container, C2: Second container, H: Work space, S: Shelf, s1: Shelf, U: Lifting axis, V: Advance / retract axis, W: Work, 100: Robot system, 2: Lifting device, 30: Rotation mechanism, 200: Housing, 20, 20a, 20b, 20c, 20d, 20e, 20f, 20g, 20h, 20i, 20j, 20k: Weight compensation mechanism, 2 1, 21a, 21c, 21d, 21e, 21i, 21j, 21k: first device, 22, 22c, 22e, 23e, 22i, 22j, 22k: biasing member, 220: main body, 221, 221c, 221e, 231e, 221i, 221j, 221k: first end, 224, 224c, 224e, 234e, 224i, 224j, 224k: second end, 222k: hollow portion, 223c: case, 27, 27h: first member, 28, 28h: second member, 26: third member, 271h, 272h: end, 281h, 282h: end, 2 9: motor, 201: lifting unit, 202, 203: frame, 206: upper end of frame, 207: lower end of frame, 204: fixed member, 205: slide member, 210, 210a, 210c, 210d, 210e, 211i: first shaft, 211, 211a, 211c, 211d, 211e, 211i: first rotating body, 212, 215, 216, 217: bearing, 214, 214c, 214d, 214e, 214i: second rotating body, 219d, 219e: seventh rotating body, 250, 250b, 250f: second shaft , 251, 252, 255: bearings, 253, 253b, 253f: third rotating body, 254, 254b, 254f: fourth rotating body, 260b, 260f: third shaft, 261, 261f: fifth rotating body, 262, 262f: sixth rotating body, AX1, AX2, AX3: central axis, D1, D2: diameter, E1, E2: position, F1, F2: tension, Fn1, Fn2, Fn3, FnN: area, M: rotation moment, P: virtual plane, R1: first rotation direction, R2: second rotation direction, ΔF: gravity compensation force, Δz: movement amount, θ1, θ2: rotation amount

Claims

1. A gravity compensation mechanism comprising: at least one first device comprising: a first shaft; a first rotating body and a second rotating body provided on the first shaft, each of which is freely rotatable and relatively rotatable, the first rotating body and the second rotating body having different outer diameters; and a biasing member connecting the first rotating body and the second rotating body; a first member hung across the first rotating body; a second member hung across the second rotating body; and an elevating unit fixed to the first member and the second member, which moves together with the first member and the second member in a second direction intersecting a first direction parallel to the central axis of the first shaft.

2. A gravity compensation mechanism as described in claim 1, wherein the second direction is a substantially vertical direction, the first rotating body and the second rotating body are rotatable in a first rotation direction about the central axis and a second rotation direction opposite to the first rotation direction, the first rotation direction corresponds to the rotation direction of the first member and the second member when the lifting unit moves upward in the second direction, and the second rotation direction corresponds to the rotation direction of the first member and the second member when the lifting unit moves downward in the second direction opposite to the upward direction, and the at least one first device urges the lifting unit upward by rotating the urging member in the second rotation direction about the central axis due to the rotation of the first rotating body and the second rotating body in the second rotation direction.

3. A gravity compensation mechanism as described in claim 2, wherein the biasing member has a first end connected to the first rotating body and a second end connected to the second rotating body, and the at least one first device biases the lifting section in the upward direction by rotating the first end and the second end around the central axis in the second rotation direction due to rotation of the first rotating body and the second rotating body in the second rotation direction.

4. A gravity compensation mechanism according to claim 1, wherein the biasing member is an elastic body having a spring constant against torsion.

5. A gravity compensation mechanism as claimed in claim 1, further comprising: a guide rail extending in the second direction; and a slide member provided on the guide rail so as to be slidable in the second direction, wherein the lifting section is fixed to the slide member.

6. A gravity compensation mechanism according to claim 1, wherein the at least one first device is a plurality of first devices arranged in the second direction.

7. A gravity compensation mechanism as described in claim 1, wherein one of the first rotating body and the second rotating body is disposed between the other of the first rotating body and the second rotating body and the biasing member in the first direction.

8. A gravity compensation mechanism as claimed in claim 1, wherein the first shaft is rotatable, and the first rotating body or the second rotating body is provided on the first shaft so as to rotate integrally with the first shaft.

9. A gravity compensation mechanism as claimed in claim 1, comprising a third member fixed to the lifting section, and the at least one first device further comprising a rotating body provided on the first shaft and around which the third member is suspended.

10. A gravity compensation mechanism as claimed in claim 1, further comprising a drive unit that drives the first member or the second member, and wherein the first rotating body and the second rotating body are rotatable relative to the first shaft.

11. A gravity compensation mechanism as claimed in claim 1, further comprising a drive unit for driving the first member and the second member, wherein the first rotating body and the second rotating body are rotatable relative to the first shaft.

12. A gravity compensation mechanism according to claim 1, wherein the first shaft is a drive shaft, the first rotating body rotates integrally with the first shaft, and the second rotating body is rotatable relative to the first shaft.

13. A gravity compensation mechanism as described in claim 1, comprising: a second shaft extending parallel to the first direction; and a third rotating body and a fourth rotating body provided on the second shaft, wherein the first member and the second member are endless, the first member is suspended between the first rotating body and the third rotating body, and the second member is suspended between the second rotating body and the fourth rotating body.

14. An elevator comprising: the gravity compensation mechanism according to claim 1; and a housing for accommodating the gravity compensation mechanism.

15. A robot comprising the lifting device according to claim 14 and a robot arm attached to the lifting section.

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