Balancer unit for balancing a rotating element of a machine, and machine

Abstract

Conventionally, there has been a need for technology which makes it possible to realize a reduction in the size and weight of a balancer unit while reducing the concentration of stress occurring in a casing for the balancer unit.　A balancer unit 50 comprises: a biasing mechanism 54 that generates a moment by biasing a rotary element 16; and a casing 52 that is rotatably supported by the machine with support shafts 56, 58 therebetween, and that accepts the biasing mechanism 54. The casing 52 has a peripheral wall 66 that surrounds the biasing mechanism 54 and hollow shaft-accepting parts 68, 70 that are provided to the peripheral wall 66 so as to protrude inwardly from the inner peripheral surface of the peripheral wall 66, and that accept the support shafts 56, 58 in a manner enabling relative rotation.

Description

Technical Field

[0001] The present disclosure relates to a balancer unit for balancing a rotating element of a machine and a machine.

Background Art

[0002] A balancer unit for balancing a rotating element of a machine is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, there has been a demand for a technology capable of reducing stress concentration generated in the casing of a balancer unit while achieving miniaturization and weight reduction of the balancer unit.

Means for Solving the Problems

[0005] In one aspect of the present disclosure, a balancer unit that applies a moment to a rotating element of a machine to balance the rotating element includes a biasing mechanism that generates a moment by biasing the rotating element, and a casing that is rotatably supported by the machine via a support shaft and receives the biasing mechanism. The casing has a peripheral wall that surrounds the biasing mechanism, and a hollow shaft receiving portion that is provided on the peripheral wall so as to project inward from the inner peripheral surface of the peripheral wall and rotatably receives the support shaft.

Effects of the Invention

[0006] According to the present disclosure, by supporting the rotational movement of the balancer unit by means of a shaft receiving portion provided so as to project inward of the peripheral wall, stress concentration in the casing is suppressed, and thereby, deformation and breakage of the casing can be prevented. As a result, the casing of the balancer unit can be made thinner, and thus, miniaturization and weight reduction of the balancer unit can be achieved.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

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Figure 5

Figure 6

Figure 7

Figure 8

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Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the various embodiments described below, the same reference numerals are given to the same elements, and redundant descriptions are omitted. First, with reference to FIG. 1, a machine 10 according to an embodiment will be described. In the present embodiment, the machine 10 is a vertical articulated robot, and includes a robot base 12, a swivel body 14, a lower arm 16, an upper arm 18, and a wrist 20.

[0009] The robot base 12 is fixed on the floor of the work cell or on an automated guided vehicle (AGV). The swivel body 14 is provided on the robot base 12 so as to be rotatable around an axis A1. The axis A1 is, for example, parallel to the vertical direction. More specifically, the swivel body 14 has a base portion 14a and a pair of support walls 14b and 14c (FIG. 2) that rise from the base portion 14a so as to face each other.

[0010] The lower arm 16 is provided on the swivel body 14 so as to be rotatable around an axis A2. The axis A2 is orthogonal to the axis A1 (for example, parallel to the horizontal direction). More specifically, the lower arm 16 has a base end portion 16a that is rotatably supported between the pair of support walls 14b and 14c, and a tip end portion 16b on the side opposite to the base end portion 16a.

[0011] The upper arm 18 has a base end arm portion 18a provided at the tip end portion 16b of the lower arm 16 so as to be rotatable around an axis A3, and a tip end arm portion 18b provided at the tip end portion of the base end arm portion 18a so as to be rotatable around an axis A4. The axis A3 is parallel to the axis A2, and the axis A4 is orthogonal to the axis A3.

[0012] The wrist 20 has a wrist base 20a provided at the tip end portion of the tip end arm portion 18b so as to be rotatable around an axis A5, and a wrist flange 20b provided on the wrist base 20a so as to be rotatable around an axis A6. The axis A5 is orthogonal to the axis A4, and the axis A6 is orthogonal to the axis A5.

[0013] The machine 10 rotates the slewing body 14, the lower arm portion 16, the base end arm portion 18a, the tip end arm portion 18b, the wrist base 20a, and the wrist flange 20b around the axes A1, A2, A3, A4, A5, and A6, respectively, to place an end effector (not shown) attached to the wrist flange 20b at an arbitrary position. Therefore, each of the slewing body 14, the lower arm portion 16, the base end arm portion 18a, the tip end arm portion 18b, the wrist base 20a, and the wrist flange 20b constitutes a rotating element of the machine 10.

[0014] The machine 10 further includes a balancer unit 50 that applies a moment Mc to the rotating element to balance the rotating element of the machine 10. In the present embodiment, the balancer unit 50 is provided on the slewing body 14 to balance the lower arm portion 16. Hereinafter, the balancer unit 50 will be described with reference to FIG. 2.

[0015] The balancer unit 50 includes a casing 52 and a biasing mechanism 54. The casing 52 is a hollow member having a central axis A7 and receives the biasing mechanism 54. The casing 52 is rotatably supported by the slewing body 14 via a pair of support shafts 56 and 58.

[0016] In the following description, the direction along the axis A7 is referred to as the axial direction, the radial direction of the circle centered on the axis A7 is referred to as the radial direction, and the direction around the axis A7 is referred to as the circumferential direction. Also, for convenience, the direction indicated by the arrow B in the figure is referred to as the rear in the axial direction. The casing 52 has a casing body 60 and a lid body 62 fixed to the casing body 60.

[0017] Hereinafter, the casing body 60 will be described with reference to FIGS. 3 to 5. The casing body 60 has a bottom wall 64, a peripheral wall 66, and a pair of shaft receiving portions 68 and 70. The bottom wall 64 is a flat plate member that defines the rear end in the axial direction of the casing body 60. The peripheral wall 66 is cylindrical and extends forward in the axial direction from the bottom wall 64.

[0018] More specifically, the peripheral wall 66 has a central wall 72 and a pair of bulging walls 74 and 76. In the present embodiment, the central wall 72 is a cylindrical member having the axis A7 as the central axis, and has an inner peripheral surface 72a and an outer peripheral surface 72b. The central wall 72 is divided into two arc-shaped portions by the bulging walls 74 and 76, and a substantially cylindrical inner space S1 is defined by the inner peripheral surface 72a of the central wall 72.

[0019] Each of the bulging walls 74 and 76 is integrally formed with the central wall 72 so as to bulge radially outward from the outer peripheral surface 72b of the central wall 72. Each of the bulging walls 74 and 76 has a rectangular outer shape when viewed in the axial direction and extends from the front end in the axial direction to the rear end in the axial direction of the central wall 72.

[0020] More specifically, the bulging wall 74 has a pair of side wall portions 74a and 74b that extend radially outward from the outer peripheral surface 72b facing each other, and an end wall portion 74c that extends between the side wall portions 74a and 74b. The side wall portions 74a and 74b and the end wall portion 74c are substantially orthogonal. A substantially quadrangular prism-shaped inner space S2 is defined by the inner surface 74d of the side wall portion 74a, the inner surface 74e of the side wall portion 74b, and the inner surface 74f of the end wall portion 74c. This inner space S2 communicates with the inner space S1 and is defined so as to bulge radially outward from the inner space S1.

[0021] On the other hand, the bulging wall 76 has a rotationally symmetric shape obtained by rotating the bulging wall 74 by 180° about the axis A7. Specifically, the bulging wall 76 has a pair of side wall portions 76a and 76b that extend from the outer peripheral surface 72b in a direction opposite to that of the bulging wall 74, and an end wall portion 76c that extends between the side wall portions 76a and 76b. A substantially quadrangular prism-shaped inner space S3 is defined by the inner surface 76d of the side wall portion 76a, the inner surface 76e of the side wall portion 76b, and the inner surface 76f of the end wall portion 76c. This inner space S3 communicates with the inner space S1 and is defined so as to bulge radially outward from the inner space S1.

[0022] Further, the inner peripheral surface 66a of the peripheral wall 66 is defined by the inner peripheral surface 72a of the central wall 72 and the inner surfaces of the bulging walls 74 and 76 (specifically, the inner surfaces 74d, 74e, 74f, 76d, 76e, and 76f). On the other hand, the outer peripheral surface 66b of the peripheral wall 66 is defined by the outer peripheral surface 72b of the central wall 72 and the outer surfaces of the bulging walls 74 and 76. In the present embodiment, the bulging walls 74 and 76 extend in a constant width W (FIG. 5) from the front end in the axial direction to the rear end in the axial direction of the central wall 72 as viewed in the radial direction of the central wall 72.

[0023] The shaft receiving portions 68 and 70 are hollow and are provided on the peripheral wall 66 so as to protrude inward from the inner peripheral surface 66a of the peripheral wall 66 and protrude outward from the outer peripheral surface 66b of the peripheral wall 66. Specifically, the shaft receiving portion 68 is integrally provided on the end wall portion 74c so as to protrude radially inward from the inner surface 74f of the end wall portion 74c and protrude radially outward from the outer surface 74g of the end wall portion 74c.

[0024] The shaft receiving portion 68 is a cylindrical member having a central axis A8 and relatively rotatably receives the above-described support shaft 56 (FIG. 2). The axis A8 is orthogonal to the axis A7. The radially inner end surface 68a of the shaft receiving portion 68 is an arcuate surface centered on the axis A7. The end surface 68a may have the same radius of curvature as the inner peripheral surface 72a of the central wall 72, or may have a larger (or smaller) radius of curvature than the inner peripheral surface 72a.

[0025] On the other hand, the shaft receiving portion 70 has a rotationally symmetric shape obtained by rotating the shaft receiving portion 68 by 180° about the axis A7. Specifically, the shaft receiving portion 70 is a cylindrical member having a central axis A9 and relatively rotatably receives the above-described support shaft 58 (FIG. 2). The shaft receiving portion 70 is integrally provided on the end wall portion 76c so as to protrude radially inward from the inner surface 76f of the end wall portion 76c and protrude radially outward from the outer surface 76g of the end wall portion 76c.

[0026] Further, the end face 70a on the radially inner side of the shaft receiving portion 70 is an arcuate surface centered on the axis A7. The end face 70a may have the same radius of curvature as the inner peripheral surface 72a of the central wall 72, or may have a larger (or smaller) radius of curvature than the inner peripheral surface 72a. In the present embodiment, the axes A8 and A9 coincide with each other (that is, they are aligned on the same straight line), and the shaft receiving portions 68 and 70 are arranged concentrically with reference to the axes A8 and A9.

[0027] Referring again to FIG. 2, the lid body 62 has a main body portion 62a and a guide portion 62b. The main body portion 62a is a flat plate-like member that is fixed to the axial front end of the peripheral wall 66 by a fastening tool (not shown) such as a bolt, and closes an opening defined on the axial front side of the casing main body 60. A through hole 62c is formed in the central portion of the main body portion 62a.

[0028] The guide portion 62b is cylindrical and is integrally formed with the main body portion 62a so as to extend axially rearward from the main body portion 62a. Note that the guide portion 62b may be provided so as to further extend axially forward from the main body portion 62a. The inner peripheral surface 62d of the guide portion 62b communicates axially with the through hole 62c of the main body portion 62a. In the state where the lid body 62 is fixed to the casing main body 60 as shown in FIG. 2, the central axis of the guide portion 62b substantially coincides with the axis A7. In the present embodiment, the inner peripheral surface 62d is constituted by a sliding bearing.

[0029] The casing 52 is disposed between the support walls 14b and 14c of the swivel body 14 so as to be rotatable around the support shaft 56 provided on the support wall 14b and the support shaft 58 provided on the support wall 14c. In the state where the casing 52 is supported by the support shafts 56 and 58 as shown in FIG. 2, the central axis of the support shaft 56 coincides with the axis A8, and the central axis of the support shaft 58 coincides with the axis A9.

[0030] That is, the shaft receiving portions 68 and 70 and the support shafts 56 and 58 are arranged concentrically with reference to the axes A8 and A9 and extend in a direction orthogonal to the axial direction (i.e., the radial direction). Further, the axes A8 and A9 are substantially parallel to the axis A2 (in other words, the axial direction of the casing 52 is substantially orthogonal to the axis A2).

[0031] The biasing mechanism 54 generates a moment Mc in the lower arm portion 16 by biasing the lower arm portion 16. The biasing mechanism 54 includes a rod 80 and a biasing element 82. The rod 80 is arranged substantially concentrically with the casing 52 with reference to the axis A7 and is receivable in the guide portion 62b of the lid body 62 so as to be able to advance and retreat.

[0032] Specifically, the rod 80 has a columnar shaft portion 80a extending straight in the axial direction, a disk-shaped flange portion 80b protruding outward from the axial rear end of the shaft portion 80a, and a cylindrical portion 80c fixed to the axial front end of the shaft portion 80a. The shaft portion 80a is inserted through the guide portion 62b and the through hole 62c so as to be able to advance and retreat in the axial direction.

[0033] The flange portion 80b is accommodated in the internal space S1, while the cylindrical portion 80c is exposed outside the casing 52. The shaft portion 80a and the flange portion 80b are surrounded by the peripheral wall 66 of the casing main body 60 and are arranged concentrically with the central wall 72 of the peripheral wall 66 with reference to the axis A7.

[0034] In this embodiment, the outer peripheral surface 80d of the flange portion 80b is arranged slightly spaced radially inward from the inner peripheral surface 72a of the central wall 72. The outer peripheral surface 80d of the flange portion 80b is substantially parallel to the inner peripheral surface 72a of the central wall 72, and the end faces 68a and 70a of the shaft receiving portions 68 and 70.

[0035] Alternatively, the outer peripheral surface 80d of the flange portion 80b and the inner peripheral surface 72a of the central wall 72 may be in contact with each other. In this case, the inner peripheral surface 72a may be constituted by a sliding bearing, or lubricating oil may be applied to the inner peripheral surface 72a. The cylindrical portion 80c has a central axis A10, and a connecting shaft 84 is received therein so as to be relatively rotatable. The axis A10 is orthogonal to the axis A7 (or parallel to the axis A2).

[0036] The biasing element 82 is accommodated in the internal space S1 and biases the rod 80. In the present embodiment, the biasing element 82 is an elastic member (more specifically, a compression coil spring), and is interposed between the flange portion 80b of the rod 80 and the main body portion 62a of the lid body 62. The biasing element 82 biases the rod 80 axially rearward by applying an elastic force to the flange portion 80b so as to separate the flange portion 80b from the main body portion 62a.

[0037] The cylindrical portion 80c of the rod 80 is rotatably connected to the lower arm portion 16 via the connecting shaft 84. More specifically, a cylindrical portion 16c is fixedly provided at the base end portion 16a of the lower arm portion 16 so as to project outward from the base end portion 16a. The cylindrical portion 16c is arranged concentrically with the cylindrical portion 80c of the rod 80 with respect to the axis A10 and receives the connecting shaft 84. Thus, the rod 80 is rotatably connected to the cylindrical portion 16c of the lower arm portion 16 via the connecting shaft 84 with its cylindrical portion 80c.

[0038] When the lower arm portion 16 rotates around the axis A2 from an upright posture substantially parallel to the vertical direction and tilts toward a horizontal posture substantially parallel to the horizontal direction, a gravitational moment Mg (FIG. 1) acts on the lower arm portion 16 due to gravity. In order to cancel such a gravitational moment Mg, the biasing mechanism 54 biases the lower arm portion 16 to apply a moment Mc to the lower arm portion 16 in a direction opposite to the gravitational moment Mg.

[0039] More specifically, when the lower arm portion 16 tilts toward the horizontal posture, the rod 80 is pulled forward in the axial direction by the cylindrical portion 16c that rotates around the axis A2 via the connecting shaft 84. As a result, it is pulled out from the casing 52 and advances forward in the axial direction. Then, the biasing element 82 is compressed in the axial direction, and as a reaction force, an elastic force in the axial rear direction is applied to the rod 80 (specifically, the flange portion 80b), thereby biasing the rod 80 in the axial rear direction.

[0040] As a result, the rod 80 biases the lower arm portion 16 in a direction opposite to the gravitational moment Mg by applying a force to the cylindrical portion 16c via the connecting shaft 84, thereby generating a moment Mc in the lower arm portion 16. In this way, the balancer unit 50 balances the lower arm portion 16 with respect to gravity.

[0041] On the other hand, as the lower arm portion 16 rises toward the vertical posture, the rod 80 retreats in the axial rear direction and is pushed into the inside of the casing 52. Such an axial advance and retreat operation of the rod 80 is guided by the guide portion 62b of the lid body 62. Then, the balancer unit 50 rotates around the support shafts 56 and 58 (that is, the axes A8 and A9) according to the advance and retreat operation of the rod 80. The shaft receiving portions 68 and 70 of the casing main body 60 support such an axial advance and retreat operation of the rod 80 and a rotational operation of the balancer unit 50 around the axes A8 and A9.

[0042] As described above, in the present embodiment, the casing 52 has a peripheral wall 66 that surrounds the biasing mechanism 54 (specifically, the shaft portion 80a and the flange portion 80b), and shaft receiving portions 68 and 70 provided on the peripheral wall 66 so as to protrude inward from the inner peripheral surface 66a of the peripheral wall 66.

[0043] Here, the inventor of the present invention performed a simulation analysis of the stress generated in the casing 52 during the operation of the balancer unit 50, and as a result, found that by forming the shaft receiving portions 68 and 70 so as to protrude inward from the peripheral wall 66, stress concentration generated in the casing 52 can be reduced.

[0044] According to the present embodiment, by supporting the forward and backward movement of the rod 80 and the rotational movement of the balancer unit 50 by the shaft receiving portions 68 and 70 provided so as to project inward of the peripheral wall 66, stress concentration in the casing 52 (specifically, the casing body 60) is suppressed, and thereby, deformation and breakage of the casing 52 can be prevented.

[0045] As a result, since stress concentration can be suppressed without increasing the thickness of the casing body 60, generation of air bubbles (so-called casting defects) in the material during molding of the casing body 60 can be prevented, and the casing body 60 can be made thinner. Therefore, an increase in the size and weight of the casing body 60 can be avoided. Thus, miniaturization and weight reduction of the balancer unit 50 can be achieved. Further, by suppressing stress concentration, uneven load on the casing body 60 is avoided, and long life of the balancer unit 50 can be realized.

[0046] Further, in the present embodiment, the shaft receiving portions 68 and 70 further project outward from the outer peripheral surface 66b of the peripheral wall 66. According to this configuration, while reducing the protruding length of the shaft receiving portions 68 and 70 protruding radially outward from the outer peripheral surface 66b, the lengths of the shaft receiving portions 68 and 70 in the directions of the axes A8 and A9 can be set large. Thereby, stress concentration in the casing body 60 can be effectively suppressed, and the strength of the shaft receiving portions 68 and 70 can be increased.

[0047] Further, in the present embodiment, the peripheral wall 66 has a central wall 72 arranged concentrically with the biasing mechanism 54 (specifically, the shaft portion 80a and the flange portion 80b), and bulging walls 74 and 76 bulging outward from the outer peripheral surface 72b of the central wall 72. The shaft receiving portions 68 and 70 are provided on the bulging walls 74 and 76 so as to project inward from the inner peripheral surfaces (specifically, the inner surfaces 74f and 76f) of the bulging walls 74 and 76.

[0048] According to this configuration, while minimizing the dimensions (i.e., radius) of the central wall 72, the strength of the bulging walls 74 and 76 where the shaft receiving portions 68 and 70 are provided can be increased by bulging the bulging walls 74 and 76 laterally. Thereby, an increase in the total weight of the casing body 60 can be suppressed.

[0049] Further, in the present embodiment, the bulging walls 74 and 76 extend from the axial front end to the axial rear end of the central wall 72 and extend with a constant width W when viewed in the radial direction of the central wall 72. According to this configuration, the strength of the bulging walls 74 and 76 can be effectively increased. Further, in the present embodiment, the bulging walls 74 and 76 have a rectangular outer shape when viewed from the axial direction of the central wall 72. According to this configuration, the strength of the bulging walls 74 and 76 can be more effectively increased.

[0050] Further, in the present embodiment, the biasing mechanism 54 includes a rod 80 that is connected to a rotating element (specifically, the lower arm portion) 16 and is received in the casing 52 so as to be able to advance and retreat, and a biasing element 82 that is housed inside the casing 52 and biases the rod 80. The support shafts 56 and 58 extend in a direction (i.e., the radial direction) orthogonal to the advancing and retreating direction (i.e., the axial direction) of the rod 80.

[0051] According to this configuration, the biasing force generated by the biasing element 82 can be efficiently applied to the rotating element 16 through the rod 80, and since the casing 52 can rotate around the support shafts 56 and 58 (specifically, the axes A7 and A8) according to the advancing and retreating operation of the rod 80, the advancing and retreating operation of the rod 80 can be effectively supported. Thereby, a moment Mc can be effectively generated in the rotating element 16.

[0052] In addition, in the present embodiment, the biasing element 82 includes an elastic member (compression coil spring) that is inserted between the rod 80 (specifically, the flange portion 80b) and the casing 52 (specifically, the main body portion 62a of the lid body 62), and biases the rod 80 by applying an elastic force to the rod 80. According to this configuration, an elastic force can be effectively applied to the rod 80 by an elastic member having a relatively simple structure such as a compression coil spring.

[0053] In the present embodiment, the connection portion between the central wall 72 and the side wall portion 74a or 74b, the central wall 72 and the side wall portion 76a or 76b, the side wall portion 74a or 74b and the end wall portion 74c, the side wall portion 76a or 76b and the end wall portion 76c, the shaft receiving portion 68 and the end wall portion 74c, or the shaft receiving portion 70 and the end wall portion 76c may be formed as rounded corners (so-called rounded R portions). Thereby, stress concentration generated in the casing main body 60 can be more effectively avoided.

[0054] Further, the protruding length L1 (FIG. 5) in which the shaft receiving portion 68 protrudes radially inward from the inner surface 74f of the end wall portion 74c and the protruding length L2 in which the shaft receiving portion 68 protrudes radially outward from the outer surface 74g of the end wall portion 74c may be L1 = L2, L1 > L2, or L1 < L2. Similarly, the protruding length L1 in which the shaft receiving portion 70 protrudes radially inward from the inner surface 76f of the end wall portion 76c and the protruding length L2 in which the shaft receiving portion 70 protrudes radially outward from the outer surface 76g of the end wall portion 76c may be L1 = L2, L1 > L2, or L1 < L2.

[0055] Further, the biasing element 82 described above may be composed of a tension coil spring inserted between the flange portion 80b and the main body portion 62a. In this case, the biasing element 82 biases the rod 80 forward in the axial direction by applying an elastic force to the flange portion 80b so as to bring the flange portion 80b closer to the lid body 62.

[0056] Incidentally, various modifications are conceivable for the casing body 60. Hereinafter, with reference to FIGS. 6 to 11, a modification of the casing body 60 will be described. The casing body 90 shown in FIG. 6 is different from the above-described casing body 60 in the peripheral wall 92. The peripheral wall 92 includes the above-described central wall 72 and a pair of bulging walls 94 and 96 that are integrally formed with the central wall 72 so as to bulge radially outward from the outer peripheral surface 72b of the central wall 72.

[0057] Each of the bulging walls 94 and 96 extends such that the width W decreases from the axial front end to the axial rear end of the central wall 72. More specifically, the bulging wall 94 has a pair of side wall portions 94a and 94b that extend radially outward from the outer peripheral surface 72b while facing each other, and an end wall portion 94c that is orthogonal to the side wall portions 94a and 94b.

[0058] An internal space S2 that bulges radially outward from the internal space S1 is defined by the inner surface 94d of the side wall portion 94a, the inner surface 94e of the side wall portion 94b, and the inner surface 94f of the end wall portion 94c. The side wall portions 94a and 94b extend so as to approach each other from the axial front end to the axial rear end of the central wall 72, and are connected to each other at their axial rear ends. As a result, the width W of the bulging wall 94 decreases toward the axial rear.

[0059] On the other hand, the bulging wall 96 has a rotationally symmetric shape obtained by rotating the bulging wall 94 by 180° about the axis A7. Specifically, the bulging wall 96 has side wall portions 96a, 96b, and an end wall portion 96c that respectively correspond to the side wall portion 94a, the side wall portion 94b, and the end wall portion 94c. An internal space S3 that bulges radially outward from the internal space S1 is defined by the inner surface 96d of the side wall portion 96a, the inner surface 96e of the side wall portion 96b, and the inner surface 96f of the end wall portion 96c.

[0060] Also, the inner peripheral surface 92a of the peripheral wall 92 is defined by the inner peripheral surface 72a of the central wall 72 and the inner surfaces (inner surfaces 94d, 94e, 94f, 96d, 96e, and 96f) of the bulging walls 94 and 96. On the other hand, the outer peripheral surface 92b of the peripheral wall 92 is defined by the outer peripheral surface 72b of the central wall 72 and the outer surfaces of the bulging walls 94 and 96.

[0061] The shaft receiving portion 68 is integrally provided on the end wall portion 94c so as to protrude radially inward from the inner surface 94f of the end wall portion 94c and radially outward from the outer surface 94g of the end wall portion 94c. On the other hand, the shaft receiving portion 70 is integrally provided on the end wall portion 96c so as to protrude radially inward from the inner surface 96f of the end wall portion 96c and radially outward from the outer surface 96g of the end wall portion 96c.

[0062] In addition, the bulging walls 94 and 96 may be formed so as to have a substantially elliptical outer shape when viewed from the directions of the axes A8 and A9 (that is, the radially outer side). According to this configuration, the aesthetic property of the casing main body 90 can be improved. Further, the bulging walls 94 and 96 may extend from the axial front end of the central wall 72 to the axial rear, and terminate at a position axially forward of the bottom wall 64. In this case, the axial rear end of the central wall 72 becomes annular, the bottom wall 64 has the same outer shape as the central wall 72, and is integrally provided at the axial rear end of the central wall 72.

[0063] In addition, the connection portions between the central wall 72 and the side wall portions 94a or 94b, between the central wall 72 and the side wall portions 96a or 96b, between the side wall portions 94a or 94b and the end wall portion 94c, between the side wall portions 96a or 96b and the end wall portion 96c, between the shaft receiving portion 68 and the end wall portion 94c, or between the shaft receiving portion 70 and the end wall portion 96c may be formed as rounded corners.

[0064] The casing main body 100 shown in FIGS. 7 and 8 is different from the above-described casing main body 60 in the peripheral wall 102. The peripheral wall 102 has the above-described central wall 72 and a pair of bulging walls 104 and 106 integrally formed on the central wall 72 so as to bulge radially outward from the outer peripheral surface 72b of the central wall 72.

[0065] Each of the bulging walls 104 and 106 has a circular outer shape when viewed axially. More specifically, the bulging wall 104 extends in an arc shape so as to bulge radially outward from one circumferential edge 104a to the other circumferential edge 104b, and extends from the axial front end to the axial rear end of the central wall 72 with a constant width W (FIG. 8). The arc-shaped inner circumferential surface 104c of the bulging wall 104 defines an inner space S2 that bulges radially outward from the inner space S1.

[0066] Similarly, the bulging wall 106 extends in an arc shape so as to bulge radially outward from one circumferential edge 106a to the other circumferential edge 106b, and extends from the axial front end to the axial rear end of the central wall 72 with a constant width W. The arc-shaped inner circumferential surface 106c of the bulging wall 106 defines an inner space S3 that bulges radially outward from the inner space S1. Each of the bulging walls 104 and 106 has a smaller radius of curvature than the central wall 72, the end faces 68a and 70a.

[0067] The inner circumferential surface 102a of the peripheral wall 102 is defined by the inner circumferential surface 72a of the central wall 72 and the inner circumferential surfaces 104c and 106c of the bulging walls 104 and 106. On the other hand, the outer circumferential surface 102b of the peripheral wall 102 is defined by the outer circumferential surface 72b of the central wall 72, the outer circumferential surface 104d of the bulging wall 104, and the outer circumferential surface 106d of the bulging wall 106.

[0068] The shaft receiving portion 68 is integrally provided on the bulging wall 104 so as to protrude radially inward from the inner circumferential surface 104c of the bulging wall 104 and radially outward from the outer circumferential surface 104d of the bulging wall 104. Further, the shaft receiving portion 70 is integrally provided on the bulging wall 106 so as to protrude radially inward from the inner circumferential surface 106c of the bulging wall 106 and radially outward from the outer circumferential surface 106d of the bulging wall 106.

[0069] In the present embodiment, since the bulging walls 104 and 106 have a circular outer shape when viewed in the axial direction, it is possible to effectively suppress the occurrence of stress concentration in the bulging walls 104 and 106. Therefore, the strength of the bulging walls 104 and 106 can be improved. Note that the connection portion between the central wall 72 and the bulging wall 104 or 106, the connection portion between the shaft receiving portion 68 and the end wall portion 94c, or the connection portion between the shaft receiving portion 70 and the end wall portion 96c may be formed at a rounded corner portion.

[0070] The casing body 110 shown in FIGS. 9 and 10 is different from the above-described casing body 60 in the peripheral wall 112. The peripheral wall 112 has an elliptical outer shape having a major axis parallel to the extending directions of the support shafts 56 and 58. More specifically, the peripheral wall 112 has an elliptical outer shape having a major axis that coincides with the axes A8 and A9 and a minor axis that is orthogonal to the axes A7, A8, and A9.

[0071] Each of the shaft receiving portions 68 and 70 is integrally formed with the peripheral wall 112 so as to protrude radially inward from the inner peripheral surface 112a of the peripheral wall 112 and also protrude radially outward from the outer peripheral surface 112b of the peripheral wall 112. In the present embodiment, since the peripheral wall 112 has an elliptical outer shape, it is possible to effectively suppress the occurrence of stress concentration in the peripheral wall 112. Therefore, the strength of the peripheral wall 112 can be increased.

[0072] Note that the connection portion between the peripheral wall 112 and the shaft receiving portion 68 or 70 may be formed at a rounded corner portion. Further, the peripheral wall 112 is not limited to an ellipse and may have an outer shape of any shape (for example, a polygon such as a rectangle, a rhombus, or a hexagon) having a longitudinal direction in the directions of the axes A8 and A9 when viewed in the axial direction.

[0073] The casing body 120 shown in FIG. 11 is different from the above-described casing body 60 in the shaft receiving portions 68' and 70'. In the present embodiment, the shaft receiving portion 68' protrudes radially inward from the inner surface 74f of the end wall portion 74c, while not protruding outward from the outer surface 74g of the end wall portion 74c.

[0074] Similarly, the shaft receiving portion 70' protrudes radially inward from the inner surface 76f of the end wall portion 76c, while not protruding outward from the outer surface 76g of the end wall portion 76c. Note that the connection portion between the end wall portion 74c and the shaft receiving portion 68', or between the end wall portion 76c and the shaft receiving portion 70', may be formed as a rounded corner portion. Also in this embodiment, stress concentration in the casing body 120 is suppressed, whereby the casing body 120 can be made thinner, thus realizing miniaturization and weight reduction of the balancer unit 50.

[0075] Note that the shaft receiving portions 68' and 70' may be applied to the above-described casing bodies 90, 100, or 110. In this case, the shaft receiving portions 68' and 70' protrude inward from the inner peripheral surface of the peripheral walls 92, 102, or 112, while not protruding outward from the outer peripheral surface of the peripheral walls 92, 102, or 112.

[0076] Note that in the above-described embodiment, the case where the biasing mechanism 54 has the biasing element 82 which is an elastic member has been described. However, the biasing element may be composed of a fluid. Such a form is shown in FIG. 12. The balancer unit 50' shown in FIG. 12 has a casing 52 and a biasing mechanism 54'. The biasing mechanism 54' has a rod 80' and a biasing element 82'. The rod 80' has the above-described shaft portion 80a and cylindrical portion 80c, and a flange portion 80b' protruding outward from the axial rear end of the shaft portion 80a. The flange portion 80b' has the same outer shape as the peripheral wall 66 and is slidably in close contact with the inner peripheral surface 66a of the peripheral wall 66.

[0077] In this embodiment, the biasing element 82' is a fluid enclosed in the spaces S1, S2, and S3 between the rod 80' and the casing 52. More specifically, the biasing element 82' is, for example, a gas or oil, and is enclosed in the space between the flange portion 80b' of the rod 80' and the bottom wall 64 of the casing body 60 among the internal spaces S1, S2, and S3 of the casing 52.

[0078] For example, when a negative pressure is applied to the biasing element 82', the biasing element 82' acts in the same manner as the biasing element 82 composed of a compression coil spring, and applies pressure to the flange portion 80b' to separate the flange portion 80b' from the lid body 62, thereby biasing the rod 80' axially rearward.

[0079] On the other hand, when a positive pressure is applied to the biasing element 82', the biasing element 82' acts in the same manner as the biasing element 82 composed of a tension coil spring, and applies pressure to the flange portion 80b' to bring the flange portion 80b' closer to the lid body 62, thereby biasing the rod 80' axially forward.

[0080] A fluid inlet 64a is formed in the bottom wall 64 of the casing body 60, and the biasing element 82' may be introduced into the internal spaces S1, S2, and S3 of the casing 52 through the fluid inlet 64a. After the introduction of the biasing element 82', the fluid inlet 64a may be tightly closed by a plug 114.

[0081] Note that at least one of the above-described axes A8 and A9 may be inclined with respect to the axis A7 (or the axis A2). Further, the shaft receiving portions 68 or 70 are not limited to a cylindrical shape, and may have, for example, a polygonal outer shape, or may have any hollow shape. Further, the above-described central wall 72 is not limited to a cylindrical shape, and may be, for example, an elliptical shape having a major axis that coincides with the axes A8 and A9, or may have any other outer shape. Further, the bulging walls 74, 76, 94, 96, 104, or 106 are not limited to a rectangular or circular shape when viewed axially, and may have any outer shape.

[0082] Also, in the above-described embodiments, the case where the pair of shaft receiving portions 68 and 70 are provided in the casing main bodies 60, 90, 100, and 110 has been described. However, the present invention is not limited to this, and one of the shaft receiving portions 68 and 70 may be omitted. For example, in the casing main bodies 60, 90, 100, or 110, instead of the shaft receiving portion 70, a support shaft 58' protruding radially outward from the peripheral walls 66, 92, 102, or 112 may be integrally formed with the peripheral wall 66, and the casing main body 60 may be rotatably supported by the turning body 14 via the support shaft 58' and the support shaft 56. Similarly, for the casing main body 120, one of the pair of shaft receiving portions 68' and 70' may be omitted.

[0083] In addition, in the above-described embodiments, the case where the balancer units 50 and 50' are provided in the turning body 14 to balance the lower arm portion 16 has been described. However, the present invention is not limited to this, and the balancer unit 50 or 50' may be provided, for example, at the tip portion 16b of the lower arm portion 16 to balance the upper arm portion 18, or may be provided to balance any of the rotating elements 14, 16, 18a, 18b, 20a, 20b of the machine 10.

[0084] Further, the machine 10 is not limited to a vertically articulated robot, and may be any type of machine having a rotating element, such as a horizontally articulated robot, a parallel link robot, or a rotary positioner that rotates a workpiece. Although the present disclosure has been described through the embodiments above, the above-described embodiments do not limit the invention according to the claims.

Description of Reference Numerals

[0085] 10 Machine 14, 16, 18a, 18b, 20a, 20b Rotating Elements 50 Balancer Unit 52 Casing 54, 54' Biasing Mechanism 56, 58 Support Shafts 60, 90, 100, 110, 120 Casing Main Bodies 62 Cover 66, 92, 102, 112 Peripheral Wall 68, 68’, 70, 70’ Shaft Receiving Portion 72 Central Wall 74, 76, 94, 96, 104, 106 Bulging Wall 80, 80’ Rod 82, 82’ Biasing Mechanism

Claims

1. A balancer unit that applies a moment to a rotating element of a machine to balance the rotating element, a biasing mechanism that generates the moment by biasing the rotating element, and a casing that is rotatably supported by the machine via a support shaft and houses the biasing mechanism. The casing has a peripheral wall that surrounds the biasing mechanism, and a hollow shaft receiving portion that is provided on the peripheral wall so as to project inward from the inner peripheral surface of the peripheral wall and rotatably receives the support shaft.

2. The shaft receiving portion further projects outward from the outer peripheral surface of the peripheral wall. The balancer unit according to claim 1.

3. The peripheral wall has a central wall arranged concentrically with the biasing mechanism, and a bulging wall that bulges outward from the outer peripheral surface of the central wall. The shaft receiving portion is provided on the bulging wall so as to project inward from the inner peripheral surface of the bulging wall. The balancer unit according to claim 1 or 2.

4. The bulging wall extends from one axial end to the other end of the central wall. The balancer unit according to claim 3.

5. The bulging wall extends with a constant width from the one end to the other end when viewed in the radial direction of the central wall, or extends such that the width decreases from the one end to the other end. The balancer unit according to claim 4.

6. The bulging wall has a rectangular or circular outer shape when viewed in the axial direction of the central wall. The balancer unit according to any one of claims 3 to 5.

7. The peripheral wall has an elliptical outer shape having a major axis parallel to the extending direction of the support shaft. The balancer unit according to claim 1 or 2.

8. The biasing mechanism has a rod connected to the rotating element and received in the casing so as to be able to advance and retreat, and a biasing element housed inside the casing that biases the rod. The support shaft extends in a direction orthogonal to the advancing and retreating direction of the rod. The balancer unit according to any one of claims 1 to 7.

9. The biasing element is an elastic member that is inserted between the rod and the casing and biases the rod by applying an elastic force to the rod, or is a fluid that is enclosed in the space between the rod and the casing and biases the rod by applying pressure to the rod. The balancer unit according to claim 8.

10. A machine comprising the balancer unit according to any one of claims 1 to 9.

11. The machine is an articulated robot having an arm as the rotating element, wherein the balancer unit gives the moment in a direction opposite to the gravitational moment acting on the arm due to gravity by the biasing mechanism biasing the arm, and balances the arm with respect to the gravity, the machine according to claim 10.

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