Robot power transmission mechanism for transmitting rotational force and robot drive device

Abstract

A robot power transmission mechanism according to the present invention is provided with a strain wave gearing reducer including: a wave generating member including an elliptical cam; an elastic cylindrical member having first teeth; and an annular member having second teeth that mesh with the first teeth. A shaft that transmits the rotational force of an electric motor has a spline shaft part having protrusions formed on the outer circumferential surface thereof. The wave generating member includes insertion holes having a recessed shape corresponding to the shape of the protrusions of the spline shaft part. Between the spline shaft part and the insertion holes, there is a gap having a size sufficient to allow the wave generating member to align through movement made possible by the elasticity of the elastic cylindrical member.

Description

[Technical Field]

[0001] The present invention relates to a power transmission mechanism for a robot that transmits rotational force, and a driving device for the robot. [Background technology]

[0002] A robot can change the position and posture of a work tool by driving components such as an arm. A robot is provided with a drive unit including an electric motor for moving the components. For example, if the robot has a joint, a drive unit is provided for moving the components at the joint. The drive unit includes a power transmission mechanism for transmitting rotational force from one member to another.

[0003] It is known that a reducer is disposed in a power transmission mechanism to amplify the rotational force of an electric motor. As a reducer, in addition to a gear reducer having a structure in which many gears mesh with each other, a strain wave gear reducer having an elliptical member into which rotational force is input is known (for example, JP 2021-175916 A). A strain wave gear reducer is characterized by having a small number of parts and being small in size. It is known that strain wave gear reducers are used in the drive devices of robots (for example, JP 3-202292 A). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-175916 [Patent Document 2] Japanese Patent Application Publication No. 3-202292 Summary of the Invention [Problem to be solved by the invention]

[0005] The drive unit transmits the rotational force of the shaft output from the electric motor to the input member of the reducer. If the reducer is a wave gear reducer, it transmits the rotational force of the shaft output from the electric motor to a wave generator (wave generating member) serving as the input member. For example, key grooves are formed on the outer surface of the output shaft of the electric motor and on the inner surface of the insertion hole of the input member of the reducer. A key shaped to fit into the key groove is inserted. Furthermore, a key connection can be achieved by fixing the key with a hexagon socket set screw or the like. A key connection can prevent the connected members from slipping circumferentially.

[0006] However, with keyed connections, the key may deteriorate over time. This may result in the inability to reliably transmit torque. In other words, there is a problem with low reliability in maintaining the function of transmitting torque. Furthermore, with keyed connections, hexagon socket set screws and the like are inserted in one radial direction. As a result, misalignment may occur between the rotation axis of the input member of the reducer and the rotation axis of the output shaft of the electric motor. This may cause vibration when the drive unit is operated. To prevent this vibration, it is necessary to align the input member or output shaft of the reducer so that the rotation axis of the input member of the reducer coincides with the rotation axis of the output shaft of the electric motor.

[0007] Alternatively, to eliminate the need to adjust the position of the rotating shaft, it is possible to arrange an Oldham coupling between the output shaft of the electric motor and the input member of the reducer. By arranging an Oldham coupling, it is possible to transmit rotational force while reliably aligning the rotating shaft even if there is misalignment, and to suppress the generation of vibration. However, adopting an Oldham coupling increases the number of parts, making the drive unit expensive. Another problem is that the drive unit becomes longer in the axial direction because space is required to accommodate the Oldham coupling. [Means for solving the problem]

[0008] A power transmission mechanism for a robot according to an embodiment of the present disclosure includes a shaft that transmits the rotational force of an electric motor, and a strain wave gear reducer that amplifies the rotational force of the electric motor. The strain wave gear reducer includes a wave generating member including a cam that is oval in shape when viewed from the direction of the rotation axis, an elastic tubular member that has a plurality of first teeth on its outer circumferential surface and is capable of elastic deformation, and an annular member that has a plurality of second teeth on its inner circumferential surface. Some of the first teeth on the elastic tubular member and some of the second teeth on the annular member are engaged with each other. The shaft has a splined shaft portion that has a plurality of convex portions formed in the circumferential direction on its outer circumferential surface. The wave generating member includes an insertion hole into which the splined shaft portion is inserted and that has a concave shape that corresponds to the shape of the convex portions on the splined shaft portion. The splined shaft portion and the insertion hole are formed by the splined shaft portion. and The elastic cylindrical member has a shape in which there is a radial gap between it and the insertion hole, and the gap is large enough to allow the central axis of rotation of the wave generating member to constantly move in a direction that offsets the eccentricity of the central axis of the elastic cylindrical member due to the elasticity of the elastic cylindrical member, thereby allowing for alignment. The cross-sectional shape of the convex portion and the concave portion is formed by an involute curve.

[0009] A driving device for a robot according to an aspect of the present disclosure includes the above-described power transmission mechanism and an electric motor that rotates a shaft. [Effects of the Invention]

[0010] According to aspects of the present disclosure, it is possible to provide a robot power transmission mechanism and a robot drive device that suppress vibrations. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of a robot according to an embodiment. [Figure 2] 1 is a schematic cross-sectional view of a drive device including a power transmission mechanism according to an embodiment. [Figure 3] FIG. 2 is an enlarged schematic cross-sectional view of a power transmission mechanism. [Figure 4] 1 is a schematic partial cross-sectional view of a reducer according to an embodiment. [Figure 5] 10 is an enlarged schematic cross-sectional view of a portion where a shaft and a wave generating member are engaged in an embodiment. FIG. [Figure 6] FIG. 10 is an enlarged schematic cross-sectional view of a power transmission mechanism according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1 to 6, a robot power transmission mechanism and a robot drive device including the power transmission mechanism according to an embodiment will be described. The power transmission mechanism of this embodiment transmits the rotational force of an electric motor from one member to another. The drive device of this embodiment rotates one component of the robot relative to the other component.

[0013] FIG. 1 is a perspective view of a robot according to this embodiment. The robot 1 according to this embodiment is an articulated robot including a plurality of joints. The robot 1 includes a plurality of rotatable components. Each component is configured to rotate around drive axes J1 to J6. The driving devices according to this embodiment are disposed in the joints of the robot to drive the components of the robot.

[0014] The robot 1 includes a base unit 14 fixed to an installation surface and a swivel base 13 supported by the base unit 14. The swivel base 13 rotates relative to the base unit 14 around a drive axis J1. The robot 1 includes a forearm arm 11 and an upper arm arm 12. The upper arm arm 12 rotates relative to the swivel base 13 around a drive axis J2. The forearm arm 11 rotates relative to the upper arm arm 12 around a drive axis J3. The forearm arm 11 also rotates around a drive axis J4. The robot 1 includes a wrist 15 supported by the forearm arm 11. The wrist 15 rotates around a drive axis J5. The wrist 15 also includes a flange 16 that rotates around a drive axis J6. A work tool is fixed to the flange 16 depending on the work to be performed by a robotic device equipped with the robot 1.

[0015] The robot 1 of this embodiment includes, as its components, a base 14, a swivel base 13, an upper arm 12, a forearm 11, and a wrist 15. The robot of this embodiment has six drive shafts, but is not limited to this. A robot whose position and posture can be changed by any mechanism can also be used.

[0016] Figure 2 shows a cross-sectional view of a drive unit in this embodiment. With reference to Figures 1 and 2, this embodiment will be described taking as an example a drive unit 2 for rotating the forearm 11 around drive axis J4. The drive unit 2 is disposed at the end of the forearm 11 opposite the end where the wrist 15 is disposed. The drive unit 2 is disposed, for example, so that the direction indicated by arrow 96 is the direction in which the wrist 15 is disposed.

[0017] The drive unit 2 includes an electric motor 45 including a rotor 45a and a stator 45b. The rotor 45a is fixed to a shaft 21. The shaft 21 functions as the output shaft of the electric motor 45. The shaft 21 is formed to be elongated. The shaft 21 of this embodiment has a hollow hole. That is, the shaft 21 of this embodiment is a hollow shaft having a cylindrical shape. The shaft 21 rotates around the drive shaft J4 as the rotation axis.

[0018] The rotational force of shaft 21 is transmitted to flange 25 via reducer 31. Flanges 25 and 26 are fixed to each other with bolts 56. Flanges 26 and 27 are fixed to each other with bolts 57. Flanges 25, 26, and 27 rotate integrally. Flange 27 is fixed to, for example, a housing that rotates around drive shaft J4 of forearm 11.

[0019] The drive unit 2 includes a housing 22 in which an electric motor 45 is disposed. A shaft 21 that transmits the rotational force of the electric motor 45 is supported for rotation by bearings 51 and 52. The bearing 51 is fixed to the housing 22. The drive unit 2 includes a housing 23 in which an electromagnetic brake 46 is disposed, and a housing 24 in which an encoder 47 that serves as a rotational position detector is disposed. The electromagnetic brake 46 brakes the shaft 21. The encoder 47 detects the rotational position of the electric motor 45.

[0020] In this embodiment, housing 22 is fixed to a housing of forearm 11 that does not rotate around drive axis J4. Housings 22, 23, and 24 are fixed to one another with fastening members such as bolts. A bearing fixing member 28 for fixing bearing 52 is disposed between housings 22 and 23. Bearing fixing member 28 is fixed to housing 23 with fastening members such as bolts. By removing the fastening members, housings 24, 23, 22 and bearing fixing member 28 can be removed from the direction opposite to the direction indicated by arrow 96.

[0021] A protective tube 66 made of resin is disposed inside the shaft 21. The protective tube 66 is cylindrically formed along the inner surface of the shaft 21. A wire such as an electric wire, an air pipe, or an optical communication cable is inserted inside the protective tube 66. The protective tube 66 is fixed by clamping a clamping portion 66a between the flanges 26 and 27. By disposing the protective tube 66, the wire can be disposed inside the joint of the robot 1.

[0022] In this embodiment, shaft 21 has steps 21a and 21b for restricting movement of shaft 21 in the direction in which the rotation axis thereof extends. Bearings 51 and 52 are engaged with steps 21a and 21b. Bearing 51 is fixed by housing 22, and bearing 52 is fixed by bearing fixing member 28.

[0023] Oil seals 61 and 62 are arranged on the outer circumferential surface of shaft 21 to prevent the internal lubricating oil from leaking out and to prevent foreign matter from entering from the outside. In addition, oil seal 63 is arranged to prevent the internal lubricating oil from leaking out of main bearing 41 and to prevent foreign matter from entering from the outside.

[0024] 3 shows an enlarged schematic cross-sectional view of the power transmission mechanism of the drive device in this embodiment. With reference to FIGS. 2 and 3, drive device 2 includes power transmission mechanism 5 that transmits the rotational force output by electric motor 45 to flanges 25, 26, and 27. Power transmission mechanism 5 includes shaft 21 and reducer 31 that amplifies the rotational force of shaft 21.

[0025] FIG. 4 shows a schematic partial cross-sectional view of the reducer of this embodiment. FIG. 4 is a partial cross-sectional view of the reducer 31 when viewed in the direction opposite to the arrow 96 along the rotation axis. Referring to FIGS. 2 to 4, the reducer 31 of this embodiment is a strain wave gear reducer. The reducer 31 has a wave generating member 32 as an input section to which rotational force is input. The wave generating member 32 is called a wave generator. The wave generating member 32 includes a hub 36 that has an elliptical shape (planar shape) when viewed along the rotation axis, and a ball bearing 37 arranged on the outer peripheral surface of the hub 36. The hub 36 functions as a cam with an elliptical planar shape. In particular, the hub 36 of the wave generating member 32 functions as the input section of the reducer 31. The inner ring of the ball bearing 37 is fixed to the elliptical hub 36. The outer ring of the ball bearing 37 is formed to be elastically deformable in response to the rotation of the hub 36 via balls.

[0026] The reducer 31 has an elastic tubular member 33 that is capable of elastic deformation. The elastic tubular member 33 is an external gear and is called a flexspline. The elastic tubular member 33 is arranged on the outside of the wave generating member 32. The elastic tubular member 33 has a plurality of first teeth 33a formed on its outer circumferential surface. The elastic tubular member 33 is formed so as to deform in accordance with the rotation of the hub 36. In this embodiment, the elastic tubular member 33 is fixed to the housing 22 by bolts 55. While the wave generating member 32 rotates, the elastic tubular member 33 is fixed so as not to rotate.

[0027] The reducer 31 has an annular member 34. The annular member 34 is an internal gear called a circular spline. The annular member 34 has rigidity that makes it difficult for it to elastically deform. The annular member 34 is disposed on the outside of the elastic tubular member 33. A plurality of second teeth 34a are formed on the inner circumferential surface of the annular member 34. Because the hub 36 has an elliptical shape, the first teeth 33a and the second teeth 34a engage with each other in the direction of the major axis of the ellipse. In other words, some of the first teeth 33a of the elastic tubular member 33 engage with some of the second teeth 34a of the annular member 34.

[0028] Here, the number of teeth of the first toothed portion 33a of the elastic tubular member 33 is smaller than the number of teeth of the second toothed portion 34a of the annular member 34. For example, the number of teeth differs by two. When the wave generating member 32 rotates once, the annular member 34 rotates slightly depending on the difference in the number of teeth of the toothed portions 33a, 34a. In this embodiment, the annular member 34 functions as the output part of the reducer 31. The reducer 31 can reduce the speed at a reduction ratio depending on the number of teeth of the elastic tubular member 33 and the number of teeth of the annular member 34.

[0029] The reduced rotational force is output from the annular member 34. A main bearing 41 is disposed to the side of the annular member 34. In this embodiment, the main bearing 41 is a cross roller bearing. The main bearing 41 has an inner ring 41a and an outer ring 41b. The outer ring 41b is fixed to the housing 22 together with the elastic tubular member 33 by bolts 55. The outer ring 41b is a member that does not rotate relative to the housing 22. In contrast, the inner ring 41a is fixed to the flange 25 and the annular member 34 by bolts 39. As a result, the inner ring 41a, the annular member 34, the flanges 25, 26, and 27, and the protective tube 66 rotate integrally. The rotational force of the annular member 34 is transmitted via the flanges 25, 26, and 27 to the housing, which rotates around the drive axis J4 of the forearm 11.

[0030] Fig. 5 shows an enlarged cross-sectional view of the engagement portion between the shaft and the hub of the wave generating member. With reference to Figs. 3 to 5, the power transmission mechanism 5 transmits the rotational force of the shaft 21 to the hub 36 of the wave generating member 32, which serves as the input part of the reducer 31. In this embodiment, the rotational force of the shaft 21 is transmitted to the hub 36 by a spline connection.

[0031] The shaft 21 has a splined shaft portion 21e on which a plurality of protrusions 21d are formed at predetermined intervals in the circumferential direction of its outer circumferential surface. The splined shaft portion 21e is a portion that extends along the axial direction. The splined shaft portion 21e is formed in the area indicated by the arrow 97. The splined shaft portion 21e is formed in the area facing the hub 36. The protrusions 21d are formed so as to protrude outward. The protrusions 21d extend along the axial direction. In the circumferential direction, protrusions 21d and recesses that correspond to the teeth of a gear are formed.

[0032] The hub 36 of the wave generating member 32 has an insertion hole 36b into which the splined shaft portion 21e is inserted. In this embodiment, the insertion hole 36b penetrates from one end face to the other end face in the axial direction of the hub 36. The insertion hole 36b has a shape corresponding to the shape of the splined shaft portion 21e. A recess 36a is formed on the inner circumferential surface of the insertion hole 36b. The recess 36a extends along the axial direction.

[0033] The convex portion 21d on the outer peripheral surface of the spline shaft portion 21e and the concave portion 36a on the inner peripheral surface of the insertion hole 36b are formed along a perfect circle in cross section. In this way, a plurality of teeth are formed on the outer peripheral surface of the shaft 21, and a plurality of teeth that engage with the teeth of the shaft 21 are formed on the inner peripheral surface of the hub 36. A spline coupling engagement portion is formed in the area where the plurality of teeth face each other. By employing a spline coupling, rotational force can be transmitted reliably.

[0034] The power transmission mechanism 5 of this embodiment includes a movement restriction portion that restricts movement of the wave generating member 32 in the axial direction (direction of the rotation axis). Because a thrust load acts on the wave generating member 32 due to the elasticity of the elastic cylindrical member 33, it is necessary to restrict movement. The movement restriction portion of this embodiment restricts movement of the wave generating member 32 in two axial directions. The movement restriction portion of this embodiment includes a C-ring 35 as a retaining ring that is arranged so as to contact the axial end face of the hub 36. The C-ring 35 has a shape that restricts movement of the wave generating member 32 in the axial direction. The C-ring 35 restricts movement of the hub 36 in the direction indicated by arrow 96.

[0035] A recess 21f corresponding to the shape of the C-ring 35 is formed in the spline shaft portion 21e of the shaft 21. The C-ring 35 is fitted into the recess 21f extending in the circumferential direction. By using a C-ring as the movement restricting portion, the axial movement of the wave generating member 32 can be restricted with a simple structure. Furthermore, the C-ring 35 can be easily removed. This makes it easy to disassemble the power transmission mechanism and remove the reducer 31. The retaining ring is not limited to a C-ring, and a member having any ring shape can be used. For example, an E-ring can be used as the retaining ring. A structure other than a ring can be used as long as it can restrict movement.

[0036] Furthermore, the movement restricting portion of this embodiment includes a step portion 21c formed on the shaft 21, where the outer diameter of the shaft 21 changes. The step portion 21c can be formed in the region of the spline shaft portion 21e where the convex portion 21d is formed. That is, the step portion 21c can be formed so that the height of the convex portion 21d is increased. The step portion 21c is formed so as to contact the axial end face of the wave generating member 32. The step portion 21c has a shape that restricts the axial movement of the wave generating member 32. The step portion 21c restricts movement of the wave generating member 32 in the direction opposite to the direction indicated by the arrow 96. By configuring the movement restricting portion as a step portion, it is possible to restrict the axial movement of the wave generating member without using a separate member that restricts movement.

[0037] The step portion is not limited to this configuration and may be formed at the terminal end of the spline shaft portion 21e. In other words, the step portion may be formed at the boundary between an area where a convex portion is formed and an area where a convex portion is not formed. Furthermore, any member that restricts the axial movement of the wave generating member can be used as the movement restricting portion. For example, the wave generating member may be fixed to the shaft with a bolt or adhesive. Alternatively, this step portion may be replaced with a C-ring.

[0038] 5, the spline shaft portion 21e and the insertion hole 36b have a shape in which a gap 91, which is a narrow space, exists between the spline shaft portion 21e and the insertion hole 36b. In particular, the gap 91 is formed in the radial direction in a cross section taken along a plane perpendicular to the axial direction. That is, the insertion hole 36b has a shape of the recessed portion 36a that corresponds to the shape of the protruding portion 21d of the spline shaft portion 21e, and is formed so as to be slightly larger than the width of the teeth of the spline shaft portion 21e in the circumferential direction.

[0039] The shaft 21 is supported by bearings 51 and 52 fixed to the housing 22. The rotation axis of the shaft 21 is determined by the positions of the bearings 51 and 52. In contrast, the outer ring of the ball bearing 37 is in contact with the inner circumferential surface of the elastic tubular member 33. In the direction of the major axis of the elliptical shape of the hub 36, the teeth 33a of the elastic tubular member 33 are in contact with the teeth 34a of the annular member 34. Here, the wave generating member 32 is assembled so as to be inserted into the elastic tubular member 33, and the elastic tubular member 33 is elastically deformed so as to be pushed outward. The force of the elastic tubular member 33 trying to return to its original shape creates a function that automatically aligns the central axis of rotation of the wave generating member 32 with the central axis of the elastic tubular member 33.

[0040] The elastic cylindrical member 33 has an elliptical shape when viewed from the direction of the rotation axis. A force acts on the elastic cylindrical member 33 to return the shape viewed from the direction of the rotation axis to a perfect circle. The hub 36 is supported in the radial direction only by the elastic cylindrical member 33 and is suspended in mid-air relative to the shaft 21. Torque is distributed and transmitted by the multiple teeth of the spline while the rotation axis of the wave generating member 32 is always aligned. In other words, the rotation axis is aligned at all rotation positions of the wave generating member 32. At this time, a thrust force acts in the axial direction of the wave generating member 32, but the function of the movement restriction unit described above prevents the wave generating member 32 from moving in the axial direction.

[0041] Here, the position of the rotation axis of the hub 36 of the wave generating member 32 and the position of the rotation axis of the shaft 21 may differ slightly due to factors such as processing errors. In this embodiment, a gap 91 is formed between the inner circumferential surface of the insertion hole 36b of the hub 36 and the outer circumferential surface of the spline shaft portion 21e of the shaft 21. Therefore, the gap 91 can absorb the above-mentioned error in the position of the rotation axis.

[0042] The gap 91 has a size that allows the central axis of rotation of the wave generating member 32 to constantly move in a direction that offsets the eccentricity of the elastic cylindrical member 33 relative to the center of the elastic cylindrical member 33, thereby achieving alignment, due to the elasticity of the elastic cylindrical member 33. More specifically, the gap 91 is preferably formed large so as not to impede the function of aligning the wave generating member 32. If the gap 91 is too small, the elastic force of the elastic cylindrical member 33 may not allow the wave generating member 32 to move sufficiently, resulting in insufficient alignment and possibly causing vibration.

[0043] On the other hand, when the rotational component of the gap 91 between the spline shaft portion 21e and the insertion hole 36b of the hub 36 is large, the angular transmission error reflected in the output portion of the reducer 31 increases. This angular transmission error corresponds to the value obtained by dividing the magnitude of the rotational component of the gap 91 by the reduction ratio of the reducer 31. In this way, it is preferable to keep the gap 91 small to a level that does not substantially adversely affect the function of the reducer, i.e., the operation of the robot.

[0044] Fig. 6 shows an enlarged schematic cross-sectional view of a power transmission mechanism in a comparative example. The power transmission mechanism in the comparative example includes a shaft 84 to which the rotational force of an electric motor is transmitted. In the power transmission mechanism in the comparative example, the rotational force of the shaft 84 is transmitted to a hub 83 of a wave generating member 82 by a key connection. A key groove 84a is formed in the shaft 84. In addition, a key groove 83a is formed in the hub 83. A rectangular parallelepiped key 85 is inserted into the area of ​​the mutually opposing key grooves 83a, 84a.

[0045] A set screw (hexagon socket set screw) 86 is inserted into the hub 36. The key 85 is fixed by the set screw 86. The set screw 86 is inserted radially inward, as shown by arrow 98. As a result, the shaft 84 is pressed in the direction shown by arrow 98. Meanwhile, a force opposite to the direction shown by arrow 98 acts on the wave generating member 82 due to a reaction force of the axial force of the set screw 86. Due to the influence of the fit gap between the shaft 84 and the hub 83, the wave generating member 82 may be positioned so that it rotates on an axis of rotation that is offset from the inherent axis of rotation of the reducer 31. In this case, vibration may occur when the reducer is driven.

[0046] Alternatively, to suppress vibrations caused by misalignment of the rotation axes, an Oldham coupling can be arranged between the shaft 84 and the wave generating member 82. The Oldham coupling has a configuration in which a radially movable insert is arranged between one member and the other member. For example, one member of the Oldham coupling can be fixed to the shaft 84, and the other member can be fixed to the wave generating member 82. The reducer can be driven smoothly while maintaining a misalignment between the rotation axis of the shaft 84 and the rotation axis of the wave generating member 82.

[0047] However, the use of an Oldham coupling increases the axial length of the power transmission mechanism, making it larger. Furthermore, the power transmission mechanism of the comparative example uses a key coupling as a coupling method to reliably transmit torque. Key couplings are unreliable because, over long periods of use, the keys can wear unevenly due to increased surface pressure caused by uneven contact.

[0048] 3 to 5, in contrast, in the power transmission mechanism of this embodiment, the elastic force of the elastic tubular member 33 allows the wave generating member 32 to be aligned. The wave generating member 32 can rotate around the rotation axis at an optimal position. Furthermore, if the position of the rotation axis of the wave generating member 32 and the position of the rotation axis of the shaft 21 are slightly different, the difference in the position of the rotation axis can be absorbed by the gap 91 between the inner circumferential surface of the wave generating member 32 and the outer circumferential surface of the shaft 21. As a result, the reducer 31 can be driven smoothly while suppressing vibration. The power transmission mechanism of this embodiment does not use other parts such as an Oldham coupling, so the number of parts can be reduced.

[0049] Furthermore, since the power transmission mechanism of this embodiment does not use key grooves or keys, damage to the keys will not occur even if the mechanism is used for a long period of time, and the reliability of the reducer can be maintained for a long period of time.

[0050] In this embodiment, the shaft 21 is a cylindrical member having a hollow hole. Because hollow shafts have a thin wall, it is difficult to ensure a keyway depth (torque transmission area) sufficient to transmit torque. In this embodiment, by forming the convex portion of the spline shaft small and providing a large number of teeth, a structure can be formed that reliably transmits torque even with a hollow shaft. In this way, even if the shaft that outputs the torque of an electric motor is a hollow shaft, it is possible to provide a power transmission mechanism that reliably transmits torque while ensuring long-term reliability.

[0051] Referring to FIG. 5, the cross-sectional shapes of the convex portion 21d of the shaft 21 and the concave portion 36a of the hub 36 are preferably configured as involute curves. In other words, it is preferable to transmit rotational force via an involute spline. This configuration increases the strength of the teeth on the spline shaft and the insertion hole, making them more resistant to axial sliding and radial oscillation. Furthermore, torque can be evenly distributed to each convex portion. Furthermore, involute splines feature automatic alignment when torque is transmitted. However, to prevent wear due to insufficient lubrication, it is desirable to apply a sufficient amount of the same lubricant as that applied to the meshing portions of the reducer teeth during assembly to the meshing portions of the spline teeth. Note that the spline is not limited to an involute spline; splines with convex portions of any shape can be used. For example, a rectangular spline with a convex portion having a substantially square cross-sectional shape can be used.

[0052] 2 and 3, drive unit 2 of the present embodiment can be disassembled to remove and replace reducer 31. When disassembling drive unit 2, flange 27 can be removed from flange 26 by removing bolt 57. Furthermore, protective tube 66 is released from its fixed position, allowing protective tube 66 to be removed in the direction indicated by arrow 96. Next, bolt 56 can be removed from flange 25. Next, bolt 39 can be removed to remove flange 25.

[0053] Next, by removing the C-ring 35 and the bolt 55, the reducer 31 and the main bearing 41 can be removed. In this way, the drive unit 2 can be disassembled to replace the reducer 31. Furthermore, it is also possible to replace the bearings 51, 52 and the oil seals 61, 62, 63. When assembling the drive unit 2, the disassembly procedure can be reversed. The drive unit 2 in this embodiment can be easily disassembled by removing the fastening members, allowing parts to be replaced.

[0054] In the above embodiment, the power transmission mechanism that drives the components around the drive axis J4 of the robot 1 and the drive device of the robot are described, but the present invention is not limited to this. The power transmission mechanism and drive device of the present embodiment can be used as a power transmission mechanism that transmits the rotational force of any component of the robot and as a drive device that drives any component of the robot.

[0055] The above-described embodiments can be combined as appropriate. In each of the above-described drawings, the same or equivalent parts are designated by the same reference numerals. Note that the above-described embodiments are merely examples and do not limit the invention. Furthermore, the embodiments include modifications of the embodiments as set forth in the claims. [Explanation of symbols]

[0056] 1. Robot 2. Drive unit 5 Power transmission mechanism 21 Shaft 21c Step 21d Convex part 21e Spline shaft 31 Reducer 32 Wave generating member 36 Hub 36a Recess 36b insertion hole 37 Ball bearings 33 Elastic cylindrical member 33a Teeth 34 Annular member 34a Teeth 35 C-ring 45 Electric motor 91 Gap

Claims

1. a shaft that transmits the rotational force of the electric motor; a strain wave gear reducer that amplifies the rotational force of the electric motor, The strain wave gear reducer includes a wave generating member including a cam having an elliptical shape when viewed from the direction of the rotation axis, an elastic cylindrical member having a plurality of first teeth on its outer peripheral surface and capable of elastic deformation, and an annular member having a plurality of second teeth on its inner peripheral surface, a first tooth portion of a part of the elastic tubular member and a second tooth portion of a part of the annular member are engaged with each other; the shaft has a spline shaft portion on which a plurality of convex portions are formed in the circumferential direction of an outer circumferential surface, the wave generating member includes an insertion hole into which the spline shaft portion is inserted and which has a recessed portion shaped to correspond to the protruding portion of the spline shaft portion, the spline shaft portion and the insertion hole have a shape in which a radial gap exists between the spline shaft portion and the insertion hole, the gap has a size that allows the rotational axis of the wave generating member to be constantly moved and aligned in a direction that offsets the eccentricity of the elastic cylindrical member relative to the central axis of the elastic cylindrical member due to the elasticity of the elastic cylindrical member, A power transmission mechanism for a robot, wherein the cross-sectional shapes of the convex portion and the concave portion are configured as involute curves.

2. The robot power transmission mechanism according to claim 1 , further comprising a movement restriction part that restricts movement of the wave generating member in two axial directions.

3. the shaft includes a step portion that contacts an end surface of the wave generating member in the axial direction and whose outer diameter changes, The robot power transmission mechanism according to claim 1 , wherein the step portion has a shape that limits axial movement of the wave generating member.

4. The power transmission mechanism for a robot according to claim 1 , wherein the shaft is a hollow shaft having a cylindrical shape.

5. The robot power transmission mechanism according to claim 1; and an electric motor that rotates the shaft.

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