Actuator

Abstract

To provide an actuator which can reduce weight of a shaft body constituted of a motor shaft and an input shaft.SOLUTION: An actuator comprises: a motor having a motor shaft 12; and a speed reducer having an input shaft 16 in which rotation of the motor shaft 12 is input, wherein the input shaft 16 is a separate body from the motor shaft 12, coupled to the motor shaft 12 to be integrally rotated by a coupling member 46, and specific gravity of the motor shaft 12 is smaller than specific gravity of the input shaft 16. The input shaft 16 may be constituted of a ferrous material, and the motor shaft 12 may be constituted of a light metallic material.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to actuators. [Background technology]

[0002] Patent Document 1 discloses an actuator including a motor having a motor shaft and a reducer having an input shaft to which the rotation of the motor shaft is input. The motor shaft and input shaft of this actuator form a shaft body that can rotate integrally. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-142033 Summary of the Invention [Problem to be solved by the invention]

[0004] The shaft body of Patent Document 1 has a monocoque structure in which the motor shaft and the input shaft are integrally molded. The inventors of the present application recognized that there is room for improvement in reducing the weight of such a shaft body.

[0005] One object of the present disclosure is to provide an actuator that can reduce the weight of a shaft body formed by a motor shaft and an input shaft. [Means for solving the problem]

[0006] The actuator of the present disclosure is an actuator comprising a motor having a motor shaft and a reducer having an input shaft to which the rotation of the motor shaft is input, wherein the input shaft is separate from the motor shaft and is connected to the motor shaft by a connecting member so as to be rotatable integrally with the motor shaft, and the motor shaft is an actuator having a specific gravity smaller than that of the input shaft. [Effects of the Invention]

[0007] According to the present disclosure, an actuator can be provided that can reduce the weight of the shaft body formed by the motor shaft and the input shaft. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a side cross-sectional view showing the actuator of the first embodiment. [Figure 2] FIG. 2 is a side cross-sectional view showing a part of the shaft body of the first embodiment. [Figure 3] FIG. 10 is an enlarged side cross-sectional view of a portion of a shaft body of a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment for implementing the actuator of the present disclosure will be described. The same or equivalent elements will be given the same reference numerals, and duplicate explanations will be omitted. In each drawing, for the sake of convenience, components will be omitted, enlarged, or reduced as appropriate. The drawings should be viewed in accordance with the orientation of the reference numerals.

[0010] (First embodiment) The actuator 10 is capable of driving a driven device (not shown) by outputting rotation. The driven device is, for example, at least a part of various machines such as (1) industrial machines such as machine tools and construction machines, (2) robots such as industrial robots and service robots, (3) transportation equipment such as conveyors, and (4) vehicles. The actuator 10 is an integrated actuator in which a motor casing 22 and a reducer casing 32, which will be described later, are integrated.

[0011] The actuator 10 includes a motor 14 having a motor shaft 12, and a reducer 18 having an input shaft 16 to which the rotation of the motor shaft 12 is input. Hereinafter, the direction along the rotation center line C48 of a shaft body 48 formed by the motor shaft 12 and the input shaft 16 will be simply referred to as the axial direction, and the radial and circumferential directions of a circle centered on the rotation center line C48 will be simply referred to as the radial and circumferential directions. In addition, the side in the axial direction from the motor 14 toward the reducer 18 (the left side of the paper in FIG. 1) will be referred to as the load side, and the opposite side in the axial direction (the right side of the paper in FIG. 1) will be referred to as the anti-load side.

[0012] The motor 14 includes a motor body 20 that generates a rotating magnetic field, the motor shaft 12 that rotates due to the rotating magnetic field generated by the motor body 20 , and a motor casing 22 that houses the motor body 20 .

[0013] The motor main body 20 includes a motor rotor 24 and a stator 26 that cooperates with the motor rotor 24 to generate a rotating magnetic field. The motor rotor 24 is disposed on the outer periphery of the motor shaft 12 and is rotatable integrally with the motor shaft 12 by, for example, an interference fit, adhesive bonding, etc. The type of the motor rotor 24 is not particularly limited, and may be, for example, a permanent magnet rotor, a squirrel-cage rotor, a wound rotor, a coreless rotor, etc. The stator 26 is disposed on the inner periphery of the motor casing 22 and is fixed to the motor casing 22 by, for example, an interference fit, adhesive bonding, etc. The type of the stator 26 is not particularly limited, and may be, for example, a permanent magnet stator, a wound stator, a coreless stator, etc.

[0014] The motor shaft 12 includes a rotor mounting portion 12a where the motor rotor 24 is mounted, and a rotor restricting portion 12b that restricts axial movement of the motor rotor 24. In this embodiment, the rotor restricting portion 12b is provided on the axial load side of the motor rotor 24 and restricts axial movement of the motor rotor 24 by contacting the motor rotor 24. The motor casing 22 accommodates the motor shaft 12 in addition to the motor main body 20.

[0015] The speed reducer 18 includes an input shaft 16 to which rotation output from the motor main body 20 is input via the motor shaft 12, a speed reduction mechanism 30 that reduces the rotation of the input shaft 16, a speed reducer casing 32 that houses at least a portion of the speed reduction mechanism 30, a load-side cover 34 disposed on the axial load side of the speed reduction mechanism 30, and a non-load-side cover 36 disposed on the axial non-load side of the speed reduction mechanism 30. The speed reduction mechanism 30 of this embodiment includes an external gear 40 and an internal gear 42 that mesh with each other. The speed reduction mechanism 30 of this embodiment is an eccentric oscillating speed reduction mechanism that rotates one of the external gear 40 and the internal gear 42 by oscillating the external gear 40 using eccentric bodies 52A and 52B, and extracts the rotation component using an output member 44. The output member 44 extracts the rotation reduced by the speed reduction mechanism 30 and outputs it to a driven device. The output member 44 of this embodiment is formed by the load-side cover 34.

[0016] The input shaft 16 is separate from the motor shaft 12. The input shaft 16 is connected to the motor shaft 12 by a connecting member 46 so as to be rotatable together with the motor shaft 12. Details of the connecting member 46 will be described later. The motor shaft 12 and the input shaft 16 form a shaft body 48 which is rotatable together with the motor shaft 12. The shaft body 48 in this embodiment has a hollow portion 48a which passes through the shaft body 48 in the axial direction.

[0017] The input shaft 16 includes an operating unit 50 that operates the reduction mechanism 30 when the input shaft 16 rotates. The operating unit 50 of the input shaft 16 is positioned so as to radially overlap the reduction mechanism 30. The operating unit 50 of the input shaft 16 used in an eccentric oscillating reduction mechanism is composed of eccentric bodies 52A and 52B. The eccentric bodies 52A and 52B have a circular shape eccentric with respect to the rotational center line C48 of the shaft body 48. The input shaft 16 of this embodiment includes two eccentric bodies 52A and 52B, but the number is not particularly limited and may be one or three or more. The eccentric bodies 52A and 52B of this embodiment include a load-side eccentric body 52A on the load side and a counter-load-side eccentric body 52B on the counter-load side. Although not described here, if the reduction mechanism 30 is a flexible mesh reduction mechanism, the operating unit 50 of the input shaft 16 is composed of a vibrator that flexes and deforms a flexible gear.

[0018] The external gear 40 of this embodiment is provided corresponding to the eccentric bodies 52A, 52B and is supported by the corresponding eccentric bodies 52A, 52B via eccentric bearings 54A, 54B. The internal gear 42 of this embodiment is provided on the inner periphery of the reducer casing 32. A pin 56 that penetrates the external gear 40 protrudes from the load side cover 34 of this embodiment. The pin 56 directly or indirectly abuts against the external gear 40, enabling the rotation component of the external gear 40 and the load side cover 34 to be synchronized.

[0019] The eccentric bearings 54A, 54B of this embodiment include a load-side eccentric bearing 54A corresponding to the load-side eccentric body 52A and a counter-load-side eccentric bearing 54B corresponding to the counter-load-side eccentric body 52B. The eccentric bearings 54A, 54B include a plurality of rolling elements 54a. The eccentric bearings 54A, 54B may include a cage that holds the plurality of rolling elements 54a. The eccentric bearings 54A, 54B of this embodiment do not include dedicated outer and inner rings, and the plurality of rolling elements roll on the inner periphery of the external gear 40 and the outer periphery of the eccentric bodies 52A, 52B. Alternatively, the eccentric bearings 54A, 54B may include dedicated outer and inner rings. The input shaft 16 of this embodiment includes a bearing restricting portion 16a that restricts axial movement of the eccentric bearings 54A, 54B. The bearing restricting portion 16a is provided between axially adjacent eccentric bearings 54A, 54B. The bearing restricting portion 16a restricts the axial movement of the load side eccentric bearing 54A by contacting it from the anti-load side, and restricts the axial movement of the anti-load side eccentric bearing 54B by contacting it from the load side.

[0020] The reducer casing 32 is disposed on the load side relative to the motor casing 22. The reducer casing 32 is connected to the motor casing 22 by screws or the like (not shown). The reducer casing 32 accommodates at least a part of the reduction mechanism 30 (here, the external gear 40), as well as the input shaft 16, the load-side cover 34, a main bearing 58 (described later), and the like. The reducer casing 32 in this embodiment includes a first casing member 32a and a second casing member 32b provided on the load side of the first reducer casing 32. The casing members 32a, 32b are connected by screws or the like (not shown).

[0021] The load side cover 34 in this embodiment includes a first load side cover member 34a and a second load side cover member 34b that is provided on the load side of the first load side cover member 34a. The cover members 34a, 34b are connected by screws or the like (not shown). A main bearing 58 that supports the output member 44 is disposed between the reducer casing 32 and the load side cover 34. A load side support bearing 60 that supports the input shaft 16 is disposed between the load side cover 34 and the input shaft 16.

[0022] The counter-load side cover 36 is connected to the reducer casing 32 by a screw member or the like (not shown). A counter-load side support bearing 62 that supports the input shaft 16 is disposed between the counter-load side cover 36 and the input shaft 16.

[0023] The actuator 10 optionally includes an encoder 64 disposed on the anti-load side of the motor body 20. The encoder 64 includes an encoder disk 64a fixed to the shaft body 48 via a circuit board 66 or the like, and an encoder sensor 64b fixed to the motor casing 22 via a circuit board 68 or the like. The encoder sensor 64b detects the rotation of the shaft body 48 by detecting a change in a predetermined physical quantity (magnetic field, light amount, etc.) when the encoder disk 64a rotates together with the shaft body 48.

[0024] Here, the motor shaft 12 has a smaller specific gravity than the input shaft 16. The specific gravity here refers to the ratio of the density of the object to the density of a reference substance (water at 4°C). Also, the input shaft 16 has a smaller Young's modulus (N / mm 2 ) and tensile strength (N / mm 2 ) becomes higher. The conditions regarding specific gravity, Young's modulus, and tensile strength here refer to the materials of the two elements being mentioned. For example, the condition regarding specific gravity means that the material that makes up the motor shaft 12 has a lower specific gravity than the material that makes up the input shaft 16. The conditions regarding the specific gravity, etc. of the motor shaft 12 and the input shaft 16 listed here are referred to as the first material conditions.

[0025] Specific examples of materials for the input shaft 16 and the motor shaft 12 that satisfy the first material condition are not particularly limited. To satisfy the first material condition, for example, the input shaft 16 may be made of an iron-based material, and the motor shaft 12 may be made of a light metal-based material with a lower specific gravity. Here, "iron-based material" refers to a material primarily made of the specified material. When the specified material is a metal such as an iron-based material, an alloy of that metal may also be primarily made of the specified material. Iron-based materials are primarily made of iron, such as steel and cast iron. Light metal-based materials are primarily made of light metals such as aluminum and titanium. Both iron-based and light metal-based materials may be made solely of the primary material, or may be made of a composite material containing the primary material and another material. Here, composite materials refer to, for example, fiber-reinforced metals.

[0026] Typically, iron-based materials have a higher Young's modulus and tensile strength than light metal-based materials, and light metal-based materials have a lower specific gravity than iron-based materials. Therefore, by using an iron-based material for the input shaft 16 and a light metal-based material for the motor shaft 12, the first material condition can be easily met. Alternatively, to meet the first material condition described above, the input shaft 16 may be made of a metal-based material and the motor shaft 12 may be made of a resin-based material. Here, metal-based materials include iron-based materials and light metal-based materials.

[0027] The motor shaft 12 has a lower specific gravity than the output member 44, and the output member 44 has a higher Young's modulus and tensile strength than the motor shaft 12. These conditions regarding the specific gravity, etc. of the output member 44 and the motor shaft 12 are referred to as second material conditions. Specific examples of the materials of the motor shaft 12 and the output member 44 that satisfy the second material conditions are not particularly limited. For example, the output member 44 may be made of an iron-based material, and the motor shaft 12 may be made of a light metal-based material, so as to satisfy the second material conditions. Alternatively, the output member 44 may be made of a metal-based material, and the motor shaft 12 may be made of a resin-based material, so as to satisfy the second material conditions.

[0028] Refer to FIG. 2. One of the motor shaft 12 and the input shaft 16 has an outer fitting portion 70, and the other fitting portion has an inner fitting portion 72 that is spigot-fitted with the outer fitting portion 70. The spigot-fitting here refers to a structure in which the inner fitting portion 72 is fitted into the outer fitting portion 70. In this embodiment, the motor shaft 12 has the outer fitting portion 70, and the input shaft 16 has the inner fitting portion 72. The outer fitting portion 70 is cylindrical, and the inner fitting portion 72 is provided in a position that radially overlaps with the outer fitting portion 70. Hereinafter, the motor shaft 12 or the input shaft 16 that has the outer fitting portion 70 will be referred to as the outer shaft 74, and the shaft that has the inner fitting portion 72 will be referred to as the inner shaft 76. In this embodiment, the motor shaft 12 is the outer shaft 74, and the input shaft 16 is the inner shaft 76, but the reverse is also possible.

[0029] A fitting hole 75 is formed on the inside of the outer fitting portion 70. The inner fitting portion 72 is axially inserted into the fitting hole 75 in the outer fitting portion 70, thereby fitting with the outer fitting portion 70 via a spigot. The inner fitting portion 72 may be fitted with the outer fitting portion 70 via a clearance fit or a transition fit. This improves the ease of inserting the inner fitting portion 72 into the outer fitting portion 70 compared to when the outer fitting portion 70 and the inner fitting portion 72 are fitted with a spigot by an interference fit. Alternatively, the inner fitting portion 72 may be fitted with the outer fitting portion 70 via an interference fit. The cross-sectional shape of the inner periphery of the outer fitting portion 70 perpendicular to the axial direction may be, for example, a circle or a polygon. The cross-sectional shape of the outer periphery of the inner fitting portion 72 perpendicular to the axial direction may be a circle, a polygon, or the like, which can be fitted into the outer fitting portion 70.

[0030] In this embodiment, the outer fitting portion 70 and the inner fitting portion 72 are spigot-fitted without using a spline connection. Therefore, it is not necessary to form a female spline on the inner periphery of the outer fitting portion 70 or a male spline on the outer periphery of the inner fitting portion 72 for the spline connection, which simplifies the structures of the outer fitting portion 70 and the inner fitting portion 72. Consider the axial length La over which the outer fitting portion 70 and the inner fitting portion 72 overlap when viewed from the radial direction. This axial length La may be shorter than the axial length L24 of the motor rotor 24, for example.

[0031] The connecting member 46 is composed of a fastening member 78 that radially fastens the input shaft 16 and the motor shaft 12. The fastening member 78 radially fastens the mating portions 72, 74 of the motor shaft 12 and the input shaft 16, respectively. The fastening member 78 has a shaft portion 78a extending radially. Here, "radially fastening" means that the fastening member 78 having such a radially extending shaft portion 78a is used to connect the input shaft 16 and the motor shaft 12 at positions that are aligned in the radial direction. In this embodiment, a male thread portion is formed on the shaft portion 78a. In this embodiment, the fastening member 78 is described as being an example formed by a set screw (set screw), but this is not limited thereto, and head screws, bolts, etc. may also be used. When these are used as the fastening member 78, the input shaft 16 and the motor shaft 12 are fastened by threaded fastening. Alternatively, the fastening member 78 may be a rivet such as a blind rivet.

[0032] The fastening member 78 serving as a set screw does not have a head on either axial side of the shaft portion 78a. A tool hole 78b is provided at the radially outer end of the shaft portion 78a, allowing insertion of a tool for rotating the fastening member 78. A pressing portion 78c, such as a recessed tip, is provided at the radially inner end of the shaft portion 78a of the fastening member 78 serving as a set screw. An outer fastening hole 70a is formed in the outer fitting portion 70, through which the shaft portion 78a of the fastening member 78 is inserted. In this embodiment, the outer fastening hole 70a is provided with a female thread portion 79 into which the shaft portion 78a of the fastening member 78 is threaded. When the fastening member 78 serving as a set screw is tightened against the female thread portion 79, the pressing portion 78c is pressed against the outer periphery of the inner fitting portion 72, thereby fastening the motor shaft 12 and the input shaft 16 together. Although only a single fastening member 78 is illustrated here, multiple fastening members 78 may be provided at intervals in the circumferential direction. When a setscrew is used, the cross-sectional shape of the inner fitting portion 72 perpendicular to the axial direction may be, for example, a simple circular cylindrical shape.

[0033] The effects of the actuator 10 described above will now be described.

[0034] The motor shaft 12 has a smaller specific gravity than the input shaft 16. This allows the shaft body 48 to be lighter than if the motor shaft 12 and the input shaft 16 had the same specific gravity.

[0035] Let us consider a case where the motor shaft 12 and the input shaft 16 are integrally molded into a monocoque shaft body 48. In this case, we consider assembling multiple annular parts such as the motor rotor 24 and support bearings 60, 62 into the shaft body 48. In this case, the method of assembling the annular parts into the shaft body 48 is limited to the following two ways. (A1) The annular part is disposed on the anti-load side of the shaft body 48, and is assembled by moving the annular part relative to the shaft body 48 toward the load side. (A2) The annular part is disposed on the load side of the shaft body 48, and is assembled by moving the annular part relative to the shaft body 48 on the anti-load side.

[0036] For this reason, the overall outer shape of the shaft body 48 is limited to satisfying either a first outer shape condition, in which the outer diameter gradually increases from a small outer diameter portion at one axial end to a maximum outer diameter portion at the other end, or a second outer shape condition, in which the outer diameter gradually increases from the small outer diameter portions at both axial ends to a maximum outer diameter portion at the center. This makes it easy for the outer diameter of the maximum outer diameter portion of the shaft body 48 to become large, making it easy for wasted material to occur in the shaft body 48. Furthermore, if a hollow portion 48a is formed in the shaft body 48, dead space is likely to occur within the hollow portion 48a.

[0037] In contrast, in the actuator 10 of this embodiment, the motor shaft 12 and the input shaft 16 are separate bodies and are connected by a connecting member 46 so that they can rotate together. Therefore, in addition to the following (B1) and (B2), the annular part can also be assembled to the motor shaft 12 or the input shaft 16 using (B3) and (B4). Note that all of the following (B1) to (B4) are assumed to be performed with the motor shaft 12 and the input shaft 16 separated. (B1) The annular part is disposed on the anti-load side of the motor shaft 12, and is assembled by moving the annular part relative to the motor shaft 12 toward the load side. (B2) The annular part is disposed on the load side of the input shaft 16, and is assembled by moving the annular part relative to the input shaft 16 on the anti-load side. (B3) The annular part is disposed on the load side of the motor shaft 12, and is assembled by moving the annular part relative to the motor shaft 12 on the anti-load side. (B4) The annular part is disposed on the anti-load side of the input shaft 16, and is assembled by moving the annular part relative to the input shaft 16 toward the load side.

[0038] Therefore, when the motor shaft 12 and the input shaft 16 are separate bodies, the overall outer shape of the shaft body 48 is not limited to satisfying either the first or second outer shape condition, allowing for greater freedom in its outer shape. For example, to allow multiple annular components to be attached to the motor shaft 12 and the input shaft 16, each of the motor shaft 12 and the input shaft 16 may have an outer shape that satisfies either the first or second outer shape condition. Therefore, compared to a monocoque structure, it is easier to reduce the outer diameter of the maximum outer diameter portion of the shaft body 48. Accordingly, compared to the shaft body 48 with the monocoque structure described above, excess material is less likely to be generated in the shaft body 48, which is advantageous for reducing the weight and cost of the shaft body 48. Furthermore, when a hollow portion 48a is formed in the shaft body 48, it is advantageous in that dead space is less likely to be generated within the hollow portion 48a.

[0039] In this way, since excess material is less likely to be generated on the shaft 48, there is greater freedom in the outer diameter of the various components arranged around the shaft 48. Here, components refer to, for example, the various components of the motor 14 (motor rotor 24, stator 26, etc.), the various components of the reducer 18 (speed reduction mechanism 30, support bearings 60, 62, etc.), the encoder 64, the brake, etc. This also has the advantage of making it easier to select components with an appropriate outer diameter according to the performance that the actuator 10 is to exhibit. In particular, when components are selected from ready-made products, there are limitations on the outer diameter of the components that can be selected, which can easily result in excessive performance and weight. In this regard, since it is easier to select components with an appropriate outer diameter, this is advantageous for reducing cost and weight.

[0040] The input shaft 16 is connected to the motor shaft 12 by a connecting member 46 so as to be rotatable together with the motor shaft 12. Therefore, before the input shaft 16 and the motor shaft 12 are connected by the connecting member 46, the input shaft 16 and the motor shaft 12 can be handled as independent, separate components. This makes it easier to inspect and evaluate the performance of only the input shaft 16 or only the motor shaft 12.

[0041] The input shaft 16 is required to have appropriate rigidity and tensile strength because it functions to transmit torque through sliding contact or rolling contact with other mechanical elements (such as eccentric bearings 54A and 54B) in the operating section 50 that operates the reduction mechanism 30. For example, in the case of an eccentric oscillating reducer, the other mechanical elements here are the eccentric bearings 54A and 54B. Also, in the case of a flexible meshing reducer, the other mechanical elements here are, for example, exciter bearings disposed between the exciter and the flexible gear.

[0042] In contrast, the rigidity and tensile strength required for the motor shaft 12 to hold an object (such as the motor rotor 24) are relatively low compared to the rigidity and tensile strength required for the input shaft 16. Generally, when the specific gravity is reduced, the Young's modulus and tensile strength often also decrease. In this embodiment, the input shaft 16, which requires high rigidity and tensile strength, has a higher Young's modulus and tensile strength than the motor shaft 12, while the motor shaft 12, which requires low rigidity and tensile strength, has a lower specific gravity than the input shaft 16. Therefore, even if the specific gravity of the motor shaft 12 is made lower than that of the input shaft 16, the rigidity and tensile strength required for the motor shaft 12 can be easily ensured. This is advantageous for reducing the weight of the shaft body 48 while ensuring the rigidity and tensile strength required for the input shaft 16 and the motor shaft 12, respectively.

[0043] The input shaft 16 is made of an iron-based material, and the motor shaft 12 is made of a light metal-based material. This allows the material of the motor shaft 12 to have a lower specific gravity than the material of the input shaft 16, while also allowing the material of the input shaft 16 to have a higher Young's modulus and tensile strength than the material of the motor shaft 12. As a result, as described above, this is advantageous for reducing the weight of the shaft body 48 while ensuring the rigidity and tensile strength required of the input shaft 16 and the motor shaft 12. For example, if the motor shaft 12, which makes up half of the shaft body 48, is made of aluminum and the remaining input shaft 16 is made of steel, the weight of the shaft body 48 can be reduced by approximately 15% compared to when both shafts are made of steel. Furthermore, if the input shaft 16 is made of an iron-based material and the motor shaft 12 is made of a light metal-based material, it is easier to make the surface hardness of the operating portion 50 of the input shaft 16 higher than the surface hardness of the outer circumferential surface of the motor shaft 12. This is also advantageous for ensuring the required surface hardness of the operating portion 50 of the input shaft 16.

[0044] The transmission torque required for the shaft body 48, which rotates at high speed, is much smaller than the transmission torque required for the output member 44, which rotates at low speed. Accordingly, the rigidity and tensile strength required for the motor shaft 12, which is part of the shaft body 48, are lower than the rigidity and tensile strength required for the output member 44. In this embodiment, the output member 44, which requires higher rigidity and tensile strength, has a higher Young's modulus and tensile strength than the motor shaft 12, while the motor shaft 12, which requires lower rigidity and tensile strength, has a lower specific gravity than the output member 44. Therefore, even if the motor shaft 12 has a lower specific gravity than the output member 44, the rigidity and tensile strength required for the motor shaft 12 can be easily ensured. This is advantageous for reducing the weight of the shaft body 48 while ensuring the rigidity and tensile strength required for the motor shaft 12 and the output member 44, respectively.

[0045] For example, the case where the motor shaft 12 and the input shaft 16 are fastened in the axial direction by a fastening member 78 is referred to as axial fastening. Here, "axial fastening" means that a fastening member 78 having a shaft portion 78a extending in the axial direction is used to connect multiple fastened elements at positions aligned in the axial direction. When axial fastening is used, it is necessary to secure a position on the motor shaft 12 and the input shaft 16 through which the shaft portion 78a of the fastening member 78 passes in the axial direction. Furthermore, when axial fastening is used, the axial length of the fastening member 78 tends to be long. As a result, excess material that increases the outer diameter of the motor shaft 12 and the input shaft 16 is likely to occur over a wide axial range including the fastening member 78.

[0046] In this regard, in this embodiment, the motor shaft 12 and the input shaft 16 are fastened together in the radial direction by the fastening member 78. When fastening in the radial direction in this manner, it is not necessary to provide a location in the motor shaft 12 and the input shaft 16 through which the shaft portion 78a of the fastening member 78 passes, as is the case with axial fastening. Furthermore, when fastening in the radial direction is used, it is easier to shorten the axial dimension of the fastening member 78 compared to when axial fastening is used. Therefore, compared to when axial fastening is used, it is less likely that excess material will be generated in the motor shaft 12 and the input shaft 16, which would increase the outer diameter, over a wide axial range including the fastening member 78. As a result, this is advantageous for reducing the weight of the motor shaft 12 and the input shaft 16.

[0047] The input shaft 16 and the motor shaft 12 each have fitting portions 70, 72 that are spigot-fitted to each other. Therefore, simply by fitting the inner fitting portion 72 into the outer fitting portion 70, the input shaft 16 and the motor shaft 12 can be easily aligned with each other.

[0048] The fastening member 78 is configured as a set screw, and is screwed into the female thread portion 79 of the outer fitting portion 70. Therefore, it is not necessary to provide the female thread portion 79 in the inner fitting portion 72, which is advantageous for reducing the radial thickness of the inner fitting portion 72. Furthermore, the fastening member 78, which serves as a set screw, does not have a head, which is advantageous for reducing the radial dimension of the fastening member 78.

[0049] Next, other features of the actuator 10 will be described. The motor shaft 12 has a first maximum outer diameter portion 80, which is the largest outer diameter on the motor shaft 12. The input shaft 16 has a second maximum outer diameter portion 82, which is the largest outer diameter on the input shaft 16. FIG. 2 shows the outer diameter R80 of the first maximum outer diameter portion 80 and the outer diameter R82 of the second maximum outer diameter portion 82. In this embodiment, the first maximum outer diameter portion 80 is formed by the rotor restricting portion 12b of the motor shaft 12, but a specific example thereof is not particularly limited. In this embodiment, the second maximum outer diameter portion 82 is formed by the bearing restricting portion 16a, but a specific example thereof is not particularly limited. In this specification, the outer diameter of a portion of the shaft body 48 refers to the radius of a circle circumscribing a point whose center is the rotational center line C48 of the shaft body 48.

[0050] At least one of the motor shaft 12 and the input shaft 16 is provided between the first maximum outer diameter portion 80 and the second maximum outer diameter portion 82 and includes arrangement portions 86A and 86B in which the annular components 84A and 84B are arranged. In this embodiment, the input shaft 16 includes a first arrangement portion 86A in which the first annular component 84A is arranged, and a second arrangement portion 86B in which the second annular component 84B is arranged.

[0051] The first annular component 84A is the counter-load side eccentric bearing 54B, and the second annular component 84B is the counter-load side support bearing 62. The annular components 84A and 84B are annular as a whole. Specific examples of the second annular component 84B are not particularly limited, and may be a brake rotor, a motor rotor, an encoder disk, an oil seal, or the like. In this embodiment, the counter-load side eccentric bearing 54B (rolling element) constituting the first annular component 84A is rotatably mounted in the first arrangement portion 86A. In this embodiment, the counter-load side support bearing 62 constituting the second annular component 84B is attached to the second arrangement portion 86B by an interference fit. The second annular component 84B may be rotatably mounted in the arrangement portion 86B, or may be attached by adhesive or the like.

[0052] In this embodiment, the arrangement portions 86A, 86B are provided at least on the input shaft 16. The arrangement portions 86A, 86B may be provided on the motor shaft 12 in addition to the input shaft 16, or may be provided only on the motor shaft 12. The number of arrangement portions 86A, 86B is not particularly limited and may be either one or multiple. When there are multiple arrangement portions 86A, 86B, the types of annular components 84A, 84B arranged in the respective arrangement portions 86A, 86B may be different or the same.

[0053] The outer diameters R86A, R86B of the arrangement portions 86A, 86B are smaller than the outer diameter R80 of the first maximum outer diameter portion 80 of the motor shaft 12 and the outer diameter R82 of the second maximum outer diameter portion 82 of the input shaft 16. In this embodiment, the outer diameter R86A of the first arrangement portion 86A and the outer diameter R86B of the second arrangement portion 86B each satisfy this condition. Note that in this embodiment, the outer diameter R80 of the first maximum outer diameter portion 80 is larger than the outer diameter R82 of the second maximum outer diameter portion 82.

[0054] Consider a hypothetical case where the monocoque shaft 48 has arrangement portions 86A and 86B in which the annular components 84A and 84B are arranged between the first maximum outer diameter portion 80 of the motor shaft 12 and the second maximum outer diameter portion 82 of the input shaft 16. In this case, as described above, the outer shape of the entire shaft 48 is limited by the first outer shape condition and the second outer shape condition. Therefore, the outer diameters must be increased or decreased in the order of the first maximum outer diameter portion 80, arrangement portions 86A and 86B, and then the second maximum outer diameter portion 82. For this reason, the outer diameters of the arrangement portions 86A and 86B must be larger than the outer diameter of either the first or second maximum outer diameter portion 80, 82. This results in an increase in the outer diameters of the annular components 84A and 84B arranged in the arrangement portions 86A and 86B.

[0055] In this regard, according to the present embodiment, as described above, the degree of freedom in the outer shape of the shaft body 48 can be increased. Therefore, the outer diameters R86A and R86B of the arrangement portions 86A and 86B located between the first maximum outer diameter portion 80 and the second maximum outer diameter portion 82 can be made smaller than the outer diameters R80 and R82 of the first maximum outer diameter portion 80 and the second maximum outer diameter portion 82, respectively. Therefore, compared to the shaft body 48 having a monocoque structure, this is advantageous for reducing the outer diameters of the annular components 84A and 84B located between the first maximum outer diameter portion 80 and the second maximum outer diameter portion 82. Therefore, it becomes easier to select annular components 84A and 84B with appropriate outer diameters according to the performance to be exhibited by the actuator 10.

[0056] (Second embodiment) See Figure 3. The actuator 10 of this embodiment differs from the first embodiment in the structure surrounding the fastening member 78. In the following embodiments, the same content as in the first embodiment may be applied to the components described in the first embodiment but not described below.

[0057] The fastening member 78 in this embodiment is configured as a head screw having a head 78d at the outer end of a shank 78a. As in the first embodiment, the head 78d of the fastening member 78 may be provided with a tool hole 78b such as a hexagonal socket. The outer fastening hole 70a of the outer fitting portion 70 is an unthreaded hole without an internal thread. The inner fitting portion 72 is formed with an inner fastening hole 72a through which the shank 78a of the fastening member 78 is inserted. The inner fastening hole 72a is formed with an internal thread portion 79 into which the shank 78a of the fastening member 78 is screwed. In this way, the internal thread portion 79 may be formed on either the outer fitting portion 70 or the inner fitting portion 72. In this embodiment, the effects described above can be obtained except for the effects related to the set screw.

[0058] When the female thread portion 79 is formed in the inner fitting portion 72 as in this embodiment, a counterbore portion 70b on which the head 78d of the fastening member 78 seats may be formed at the outer peripheral end of the outer fastening hole 70a in the outer fitting portion 70. In this case, it is sufficient that at least a part of the head 78d of the fastening member 78 is disposed within the counterbore portion 70b. Alternatively, the cross-sectional shape of the outer fitting portion 70 may be a polygonal cylinder, and one surface portion of the outer peripheral surface itself may be used as a seating surface for the head 78d of the fastening member 78.

[0059] When forming the female thread portion 79 on the inner fitting portion 72 in this way, it is preferable that the inner shaft 76 having the inner fitting portion 72 has a higher Young's modulus and tensile strength than the outer shaft 74. This allows the fastening member 78 to be tightly fastened to the female thread portion 79 of the inner fitting portion 72, which is advantageous in ensuring the connection strength of the fastening member 78. To satisfy this condition, for example, the input shaft 16, which serves as the inner shaft 76, may be made of an iron-based material, and the motor shaft 12, which serves as the outer shaft 74, may be made of a light metal-based material.

[0060] Next, variations of the components described above will be described.

[0061] The specific example of the reduction mechanism 30 of the reducer 18 is not particularly limited. The reduction mechanism 30 may be an eccentric oscillating reduction mechanism, a simple planetary gear reduction mechanism, a flexible mesh reduction mechanism (including cylindrical, top hat, and cup types), a right-angle gear reduction mechanism, a parallel-axis gear reduction mechanism, or other gear mechanism. The reduction mechanism 30 may be a friction transmission mechanism or other mechanism in addition to a gear mechanism. The eccentric oscillating reduction mechanism has been described as a center crank type in which the input shaft 16 is disposed on the rotational centerline of the output member 44, but may also be a split type in which the input shaft 16 is disposed at a position radially offset from the rotational centerline. The output member 44 may be configured by the reducer casing 32 instead of the load-side cover 34.

[0062] When forming the female thread portion 79 on the outer fitting portion 70 as in the first embodiment, it is preferable that the outer shaft 74 having the outer fitting portion 70 has a higher Young's modulus and tensile strength than the inner shaft 76. This allows the fastening member 78 to be tightly fastened to the female thread portion 79 of the outer fitting portion 70, which is advantageous in ensuring the connection strength of the fastening member 78.

[0063] The motor shaft 12 and the input shaft 16 only need to satisfy the aforementioned conditions regarding specific gravity, and do not necessarily need to satisfy the conditions regarding Young's modulus and tensile strength. For example, the input shaft 16 may be greater than the motor shaft 12 in terms of specific gravity, while the input shaft 16 may be less than the motor shaft 12 in terms of Young's modulus and tensile strength. The motor shaft 12 and the output member 44 may also have the same specific gravity, or the same Young's modulus and tensile strength. Although the motor shaft 12 and the input shaft 16 have been described as being composed of a single member, they may also be composed of multiple members.

[0064] There are no particular limitations on the specific example of the connecting member 46. The connecting member 46 may be a coupling or the like instead of the fastening member 78. The input shaft 16 and the motor shaft 12 may be connected without using the fitting portions 70, 72. For example, the input shaft 16 and the motor shaft 12 may each have a flange portion, and the flange portions may be butted against each other and then connected by the connecting member 46. In this case, the connecting member 46 may be a fastening member 78 that fastens the motor shaft 12 and the input shaft 16 together in the axial direction.

[0065] The outer diameter of the arrangement portions 86A, 86B provided between the first maximum outer diameter portion 80 of the motor shaft 12 and the second maximum outer diameter portion 82 of the input shaft 16 may be larger than the outer diameter of either the first maximum outer diameter portion 80 or the second maximum outer diameter portion 82. The relationship in size between the outer diameter of the first maximum outer diameter portion 80 and the outer diameter of the second maximum outer diameter portion 82 is not particularly limited. For example, the outer diameter of the second maximum outer diameter portion 82 may be larger than the outer diameter of the first maximum outer diameter portion 80.

[0066] The content of each component described in the above embodiments is merely illustrative. The abstract technical concepts should not be construed as being limited to the content of this specification. The content of each component described in the embodiments is subject to many design changes, such as modifications, additions, and deletions. Contents subject to such design changes are emphasized by the notation "this embodiment" or "embodiment." However, design changes are also permitted even in content without such notation. Hatching on cross sections in the drawings does not limit the material of the hatched object. Any combination of the above components is also valid. In the description of this specification, a component composed of a single member may be composed of multiple members. Similarly, a component composed of multiple members may be composed of a single member. [Explanation of symbols]

[0067] 10...actuator, 12...motor shaft, 14...motor, 16...input shaft, 18...reduction gear, 30...reduction mechanism, 44...output member, 46...connecting member, 70...outer fitting portion, 72...inner fitting portion, 78...fastening member, 79...female thread portion, 80...first maximum outer diameter portion, 82...second maximum outer diameter portion, 84A, 84B...annular parts, 86A, 86B...arrangement portion.

Claims

1. a motor having a motor shaft; a reducer having an input shaft to which rotation of the motor shaft is input, the input shaft is separate from the motor shaft and is connected to the motor shaft by a connecting member so as to be rotatable integrally with the motor shaft; The motor shaft of the actuator has a specific gravity smaller than that of the input shaft.

2. The input shaft has a Young's modulus (N / mm ２ ) and tensile strength (N / mm ２ 2. The actuator according to claim 1, wherein the resistance is high.

3. The input shaft is made of an iron-based material, The actuator according to claim 1 , wherein the motor shaft is made of a light metal material.

4. the reducer includes an output member that outputs rotation reduced by a reduction mechanism, 2. The actuator according to claim 1, wherein the motor shaft has a specific gravity smaller than that of the output member, and the output member has a Young's modulus and a tensile strength greater than those of the motor shaft.

5. The actuator according to claim 1 , wherein the connecting member is formed of a fastening member that fastens the motor shaft and the input shaft together in a radial direction.

6. one of the input shaft and the motor shaft includes an outer fitting portion; The actuator according to claim 1 , wherein the other of the input shaft and the motor shaft has an inner fitting portion that is spigot-fitted with the outer fitting portion.

7. the connecting member is configured by a fastening member that fastens the motor shaft and the input shaft in a radial direction, 7. The actuator according to claim 6, wherein the fastening member is a set screw that is screwed into a female thread formed in the outer fitting portion.

8. the connecting member is configured by a fastening member that fastens the motor shaft and the input shaft in a radial direction, The actuator according to claim 6 , wherein the fastening member is screwed into a female thread formed in the inner fitting portion.

9. the motor shaft includes a first maximum outer diameter portion where the outer diameter of the motor shaft is largest, the input shaft includes a second maximum outer diameter portion where the outer diameter of the input shaft is maximum, At least one of the motor shaft and the input shaft includes a mounting portion provided between the first maximum outer diameter portion and the second maximum outer diameter portion, and an annular component is mounted on the mounting portion; The actuator according to claim 1 , wherein the outer diameter of the arrangement portion is smaller than the outer diameters of the first maximum outer diameter portion and the second maximum outer diameter portion.

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