Power transmission device

Abstract

A power transmission device capable of transmitting power with high precision. [Solution] One rotating body 2 comprises a rotating body base 4 that is rotatably supported and meshing portions 8 arranged radially at equal intervals in the circumferential direction of the rotating body base 4, the meshing portions 8 having a circular circumferential surface 8d in an axial view, and the other rotating body 3 comprises a plurality of teeth 10 arranged at equal intervals on its outer peripheral edge that mesh with the meshing portions.

Description

Technical Field

[0001] The present invention relates to a power transmission device used, for example, in a joint mechanism of a robot arm or the like.

Background Art

[0002] In recent years, autonomous operation type robot devices have been actively used in various scenes such as cleaning and construction. In such autonomous operation type robot devices, a multi-joint robot arm that enables complex operations is required to replace human work. As a basic structure of the joint mechanism of a robot arm, it includes a driving bevel gear connected to a rotating shaft that is driven to rotate, and a driven bevel gear that meshes with the teeth of the driving bevel gear, and power is transmitted between two intersecting axes.

[0003] For example, in Patent Document 1, the intersecting gears have teeth that mesh with each other. Here, the tooth thickness (circumferential thickness) of the teeth on the pitch circle connecting the pitch points where the meshing teeth contact each other is smaller than the width of the tooth groove of the teeth (the separation width between adjacent teeth in the circumferential direction), and backlash (clearance) is formed between adjacent teeth in the meshing state.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The backlash formed between adjacent teeth, when appropriately sized, prevents wear between meshing teeth and maintains smooth operation between gears. However, when gears are operated with rotation in only one direction, the contact between adjacent teeth is maintained. Nevertheless, when the rotation direction of the driving gear is frequently switched, a problem arises where lost motion occurs, which is an error caused when the teeth of the driving gear are positioned in the forward and reverse directions. As a result, a dead zone occurs where the movement of the driving means is not transmitted to the driven gear, which may reduce the operational accuracy of precision equipment that performs delicate movements, such as robot arms.

[0006] This invention was made in view of these problems, and aims to provide a power transmission device that can transmit power with high precision. [Means for solving the problem]

[0007] To solve the above problems, the power transmission device of the present invention is In a power transmission device comprising a pair of rotating bodies whose axes intersect each other, One of the rotating bodies comprises a rotating body base that is rotatably supported, and meshing portions arranged radially at equal intervals in the circumferential direction of the rotating body base, The aforementioned meshing portion has a circumferential surface that is circular in an axial view, The other rotating body is characterized by having multiple teeth arranged at equal intervals on its outer edge that mesh with the meshing portion. This feature allows the meshing portion on one of the rotating bodies to roll along the tooth surface of the teeth on the other rotating body it meshes with. This prevents wear on the meshing portions and teeth of both bodies and maintains smooth operation between them. In addition, because the meshing portion rolls against the tooth surface, the contact state with the tooth surface is always maintained regardless of the rotation direction of the driving body. This prevents lost motion and allows for accurate power transmission, even when the rotation direction of the driving body is frequently switched.

[0008] The tooth root portion, which is formed by the root portion of the tooth surface of an adjacent pair of teeth, is characterized by having a curved surface that follows the circumferential surface of the occlusal portion. This feature ensures that the circumferential surface of the occlusal portion conforms to the root portion of the tooth surface, thereby reliably preventing lost motion at the root portion and enabling precise power transmission.

[0009] The aforementioned meshing portion is characterized by its conical shape. According to this feature, by applying pressure to the other rotating body in one axial direction, the tooth surfaces are reliably and gaplessly pressed against the circumferential surface of the conical meshing portion, enabling accurate power transmission.

[0010] The meshing portion is characterized by connecting the rotating body base and a ring member located radially inward of the rotating body base. This feature allows the other rotating body to restrict axial movement by having its outer edge sandwiched between the base of the first rotating body and the ring member, resulting in a high degree of design flexibility.

[0011] The other rotating body has a mortar-like shape with its outer periphery rising at an angle, The ring member of one of the rotating bodies is characterized by having a tapered surface that runs along the outer peripheral edge of the other rotating body. According to this feature, the driven rotating body is rotatably supported by the ring member of the driven rotating body with its diagonally rising outer edge parallel to it. Therefore, the driven rotating body can be guided and held in an appropriate relative position to the driven rotating body with a simple structure.

[0012] The rotating body having the meshing portion is arranged in a pair opposite to the other rotating body, and each of the rotating bodies is driven to rotate, while the other rotating body is driven to rotate. According to this feature, it is possible to exhibit the functions and performances of high efficiency, high output, and space saving resulting from driving and rotating two rotating bodies. In addition, since substantially no slip occurs between the meshing portion and the teeth due to the rotation of the meshing portion, it is possible to prevent the occurrence of a difference in slip ratio in the meshing state of each of the pair of driven and rotated rotating bodies, and power can be transmitted accurately.

Brief Description of the Drawings

[0013] [Figure 1] It is a perspective view showing a joint mechanism of a robot arm to which the power transmission device in an embodiment of the present invention is applied. [Figure 2] It is a perspective view showing the power transmission device in an embodiment of the present invention. [Figure 3] It is an exploded perspective view of the driving bevel gear viewed from the rotating body base side. [Figure 4] It is an exploded perspective view of the driving bevel gear viewed from the ring member side. [Figure 5] It is an exploded perspective view of a connecting member constituting the meshing portion. [Figure 6] It is a plan view of the connecting member. [Figure 7] (a) is a side view of the driven bevel gear, and (b) is a plan view of the driven bevel gear viewed from the driving bevel gear side. [Figure 8] (a) to (d) are image diagrams for explaining the process in which the teeth of the driven bevel gear mesh with the connecting member of the driving bevel gear. [Figure 9] (a) to (d) are image diagrams for explaining the process in which the meshing between the teeth of the driven bevel gear and the connecting member of the driving bevel gear is disengaged. [Figure 10] It is a side view showing the power transmission device.

Mode for Carrying Out the Invention

[0014] A mode for carrying out the power transmission device according to the present invention will be described below based on an embodiment.

Embodiment

[0015] The power transmission device according to the embodiment will be described with reference to Figures 1 to 10.

[0016] The power transmission device in this embodiment is used in the joint mechanism of a multi-joint robot arm. As shown in Figure 1, the joint mechanism J of the multi-joint robot arm connects a first link J1 and a second link J2, and in this embodiment, the second link J2 has free control of pitch and roll (or yaw) relative to the first link J1.

[0017] The joint mechanism J incorporates a power transmission device 1, as shown in Figure 2. The power transmission device 1 comprises a pair of drive bevel gears (rotating bodies) 2, 2 and driven bevel gears (rotating bodies) 3 that mesh with these drive bevel gears 2, 2 respectively. The drive bevel gears 2 are incorporated into the first link J1 side of the joint mechanism J, and the driven bevel gears 3 are incorporated into the second link J2 side of the joint mechanism J.

[0018] The pair of drive bevel gears 2,2 are each individually driven by separate actuators or other driving means. In the power transmission device 1, when these pair of drive bevel gears 2,2 rotate synchronously in different directions, the driven bevel gear 3 does not rotate along its own axis, and the driven bevel gear 3 moves in the circumferential direction of the drive bevel gears, that is, the second link J2 tilts on the pitch axis relative to the first link J1. Conversely, when these pair of drive bevel gears 2,2 rotate synchronously in the same direction, the driven bevel gear 3 rotates along its own axis due to the drive bevel gears 2,2, and the second link J2 rotates on the roll axis relative to the first link J1.

[0019] Thus, the joint mechanism J in this embodiment constructs a so-called 2-input, 2-joint output type differential joint structure. As a result, when the manipulator wrist or the like is located before the first link J1, the envelope characteristics of the manipulator wrist or the like are improved due to the space saved after the roll axis. In addition, the effects of increased efficiency, increased output, and space saving are obtained because the driving force of the power transmission device 1 can be distributed to two driving means.

[0020] Figure 3 is an exploded perspective view showing the drive bevel gear 2, where only one of the pair of drive bevel gears 2,2 is shown. In this embodiment, the pair of drive bevel gears 2,2 are identical in shape, so a detailed description of the other drive bevel gear 2 is omitted.

[0021] As shown in Figures 2 and 3, the drive bevel gear 2 mainly consists of an annular rotating body base 4, an annular ring member 5 that is slightly smaller than the rotating body base 4 and positioned inside the rotating body base 4, and connecting members 6 that connect the rotating body base 4 and the ring member 5. Multiple connecting members 6 are equally spaced radially between the rotating body base 4 and the ring member 5, which are spaced apart in the radial direction.

[0022] As shown in Figures 3 and 4, the rotating body base 4 is composed of two annular members 7A and 7B, which are stacked in the direction of the rotation axis and have an opening in the center. One annular member 7A has recesses 17a that are equally spaced in the circumferential direction into which one longitudinal end of the connecting member 6 fits so that it is approximately half embedded. The other annular member 7B has recesses 17b formed in the circumferential direction at positions corresponding to the recesses 17a into which one longitudinal end of the connecting member 6 fits so that it is approximately half embedded.

[0023] The rotating body base 4 is assembled by overlapping the annular members 7A and 7B in the direction of the rotation axis and fastening them together with screws (not shown). In the assembled rotating body base 4, the recesses 17a and 17b combine to form a circular hole, into which one end of the connecting member 6 in the longitudinal direction is fitted and supported.

[0024] Furthermore, the annular members 7A and 7B each have mortar-shaped tapered surfaces 4a, 4a on the inner side of the surface facing the ring member 5 in the direction of rotation, and recesses 17a (the aforementioned hole) and recesses 17b (the aforementioned hole) are formed in these tapered surfaces 4a.

[0025] The ring member 5, which faces the rotating body base 4 in the axial direction, has a tapered surface 5a that is substantially parallel to and opposite the tapered surface 4a of the rotating body base 4, and a hole 15 is formed in this tapered surface 5a into which the other end of the connecting member 6 in the longitudinal direction is fitted.

[0026] As shown in Figures 2 to 4, the connecting member 6 is positioned between the tapered surface 4a of the rotating body base 4 and the tapered surface 5a of the ring member 5, which are spaced apart in the direction of rotation, and connects the rotating body base 4 and the ring member 5. The drive bevel gear 2, which is constructed by connecting the rotating body base 4 and the ring member 5 with the connecting member 6, has an opening 2a that penetrates axially in the central part of the inner diameter side.

[0027] As shown in Figure 5, the connecting member 6 is mainly composed of a rod 8 in the center of its longitudinal direction and bearings 9A and 9B attached to both ends of the rod 8 in the longitudinal direction, which constitute one end and the other end of the connecting member 6, respectively.

[0028] As shown in Figures 5 and 6, the rod 8 has a substantially conical shape, with its longitudinal ends 8a and 8b supported by holes 9c and 9c of bearings 9A and 9B, respectively, and its central portion 8c tapering toward the other longitudinal end 8b on the ring member 5 side. The rod 8 of the connecting member 6 of the drive bevel gear 2 constitutes the meshing portion with the teeth 10 of the driven bevel gear 3.

[0029] Next, the structure of the driven bevel gear 3 will be explained using Figures 7(a) and (b). The driven bevel gear 3 has an opening 3a in the center of its inner diameter side and a mounting portion 3b that is attached to the rotating shaft. On the axial side opposite the mounting portion 3b, there is a roughly mortar-shaped main body portion 3c that expands radially. Multiple teeth 10 are equally spaced on the outer diameter edge of the main body portion 3c.

[0030] As shown in Figure 7(b), all teeth 10 arranged in the circumferential direction are identical in shape, and the tooth surfaces (side surfaces of the teeth) 10f arranged in the circumferential direction have a curved shape that forms a roughly S-shape, formed by a series of arcs with different radii of curvature. More specifically, the tip of the tooth surface 10f, together with the tips of adjacent tooth surfaces 10f, forms a sharp tooth apex 10e, and the central part of the tooth surface 10f in the depth direction, from the upper end to the vicinity of the tooth root 10g formed by the root portions of the tooth surfaces 10f of adjacent teeth 10, has a curved shape that gently bulges outward. Note that the term "arc shape" here refers to a curve that forms a smooth arch shape, such as an arc with the same radius of curvature or an arc formed by a series of arcs with different radii of curvature.

[0031] Furthermore, the tooth root portion 10g, which is formed by the root portions of the tooth surfaces 10f of adjacent teeth 10, forms a roughly semicircular contact surface with a central angle of 180 degrees or less, along the circumferential surface 8d (see Figure 6) of the rod 8 of the connecting member 6 of the drive bevel gear 2. More specifically, the radius of curvature of the curved shape of the tooth root portion 10g is equal to the radius of curvature of the circumferential surface 8d at the point of contact with the tooth root portion 10g in the axial direction of the rod 8. In the power transmission device 1, the relative positions of the drive bevel gear 2 and the driven bevel gear 3 are set such that, when the rod 8 of the drive bevel gear 2 is in its deepest meshing state between adjacent teeth 10, 10, the rotation center of this rod 8 is at the same position as the center of the circle of curvature that constitutes the curved surface of the meshed tooth root portion 10g.

[0032] Next, the process of meshing between the drive bevel gear 2 and the driven bevel gear 3 will be explained in detail, mainly using Figures 8 and 9. For the sake of clarity, Figures 8 and 9 will describe the opposing tooth surfaces 10f1 and 10f2 of two adjacent teeth 10A and 10B in the driven bevel gear 3, and the single rod 8 of the drive bevel gear that meshes between these tooth surfaces 10f1 and 10f2. Therefore, in Figure 8, only the single connecting member 6 of the drive bevel gear 2 is shown, and the other components are omitted. Furthermore, the explanation will use the case where the drive bevel gear 2 is rotated in the forward rotation direction as an example.

[0033] When the drive bevel gear 2 rotates in the forward direction, at the meshing point between the drive bevel gear 2 and the driven bevel gear 3, the rod 8 of the drive bevel gear 2 first rolls from the tooth apex (upper end of tooth surface 10f1) 10e of tooth 10A towards the tooth root 10g between teeth 10A and 10B along tooth surface 10f1.

[0034] The rod 8 is rolled by the rotational drive of the drive bevel gear 2, with its circumferential surface 8d constantly pressed against the tooth surface 10f1. This rotational drive of the drive bevel gear 2 pushes against the tooth surface 10f1, causing the driven bevel gear 3 to rotate. In other words, the rotational drive of the drive bevel gear 2 directly presses the circumferential surface 8d of the rod 8 against the region from the tooth apex 10e (the upper end) to the tooth root 10g (the lower end) of the tooth surface 10f1.

[0035] When the rod 8 reaches the tooth root 10g, the rotational center of the rod 8 becomes the same as the center of the circle of curvature that constitutes the curved surface of the tooth root 10g, and the circumferential surface 8d of the rod 8 is fitted to conform to the curved shape of the tooth root 10g. In this state where the rod 8 has completed fitting to the tooth root 10g, the rod 8 is in a neutral state, not being pressed against the tooth surfaces 10f1 and 10f2 that constitute the tooth root 10g.

[0036] As the drive bevel gear 2 continues to rotate in the forward direction, adjacent rods 8, 8 sequentially mesh with the tooth root 10g. As shown in Figure 9, when the drive bevel gear continues to rotate in the forward direction after the leading rod 8 has moved to the tooth root 10g between teeth 10A and 10B, the subsequent rod 8 (not shown) moves toward the tooth root 10g between teeth 10B and 10C.

[0037] The subsequent bar 8, like the preceding bar 8, presses against the tooth surface 10f3 due to the rotational drive of the drive bevel gear 2, thereby driving the driven bevel gear 3 to rotate. The preceding bar 8 also separates from the tooth surface 10f1 and rolls while being pressed against the tooth surface 10f2 by the driven rotation of the driven bevel gear 3, and at the upper end of the tooth surface 10f2 it separates from all the tooth surfaces of the driven bevel gear 3 (the meshing state is released). In this way, the circumferential surface 8d of the bar 8 is indirectly pressed by the driven bevel gear 3, which is driven to rotate by the rotational drive of the drive bevel gear 2, in the region from the tooth root 10g, which is the lower end of the tooth surface 10f2, to the tooth apex 10e.

[0038] The drive bevel gear 2 in the power transmission device 1 is equipped with multiple rod members 8, which are meshing parts that can rotate axially. These rod members 8 mesh with the teeth 10 of the driven bevel gear 3. As the rod members 8 roll along the tooth surface 10f of the teeth 10 of the driven bevel gear 3 with which they mesh, the contact points gradually move in the circumferential direction, thus preventing wear on the meshing rod members 8 and teeth 10, and maintaining smooth operation between the drive bevel gear 2 and the driven bevel gear 3.

[0039] In addition, the contact between the rod 8 and the teeth 10 is maintained at all times regardless of the rotation direction of the drive bevel gear 2. In other words, there is virtually no backlash, so even when the rotation direction of the drive bevel gear 2 is frequently switched, lost motion can be prevented and power can be transmitted with high precision.

[0040] Furthermore, since both ends of the rod 8 in the longitudinal direction are connected to bearings 9A and 9B, which are so-called bearings, the rod 8 rotates smoothly when the circumferential surface 8d of the rod 8 comes into contact with the tooth surface 10f of the tooth 10, thereby ensuring a reduction in friction and preventing localized wear.

[0041] Furthermore, the tooth root portion 10g, which is formed by the root portions of the tooth surfaces 10f, 10f of adjacent teeth 10, 10, has a curved surface that follows the circumferential surface 8d of the rod material 8. By having the circumferential surface 8d of the rod material 8 follow the tooth root portion 10g, lost motion can be reliably prevented at this tooth root portion 10g, and power can be transmitted with high precision.

[0042] Furthermore, because the meshing portion, the rod 8, is conical in shape, the drive bevel gear 2 and the driven bevel gear 3 are pressurized in a direction that brings them relatively closer together. This guides the tooth surfaces 10f to the circumferential surface 8d of the conical rod 8, resulting in a state where the tooth surfaces 10f and the circumferential surface 8d of the rod 8 are pressed together without any gaps, enabling reliable and accurate power transmission.

[0043] The rod 8 connects the rotating body base 4 and the ring member 5 that constitute the drive bevel gear 2, and the outer peripheral edge of the driven bevel gear 3 having teeth 10 is sandwiched between the rotating body base 4 and the ring member 5 connected by the rod 8, thereby restricting its axial movement. Therefore, the bearing that rotatably supports the driven bevel gear 3 only needs to be provided on one side in the axial direction, which increases the design freedom of the power transmission device 1. In this embodiment, the central openings 2a and 3a of the drive bevel gear 2 and the driven bevel gear 3 can be connected at their intersection, and harnesses can be routed across these intersecting and communicating central openings 2a and 3a.

[0044] The power transmission device 1 in this embodiment constructs a so-called 2-input, 2-joint output type differential joint structure. This improves the envelope characteristics of the manipulator wrist and other parts due to space saving on the tip side of the second link J2 beyond the roll axis, and also achieves higher efficiency, higher output, and space saving due to the distribution of the driving force of the joint mechanism J to two actuators. In addition, since the rod 8 rolls against the tooth surface 10f, substantially no slip occurs between the rod 8 and the teeth 10, preventing the occurrence of differences in the slip rate in the meshing state between the rod 8 of each of the pair of drive bevel gears 2 and the teeth 10 of the driven bevel gear 3, and enabling accurate power transmission. In other words, the configuration of the meshing part between the drive bevel gear 2 and the driven bevel gear 3 in this embodiment is optimal for exhibiting the characteristics of a 2-input, 2-joint output type differential joint structure.

[0045] Furthermore, as shown in Figure 7(a), the driven bevel gear 3 has a mortar-shaped outer edge that rises diagonally, and the ring member 5 that constitutes the drive bevel gear 2 is conical. The driven bevel gear 3 is positioned so that the diagonally rising outer edge of the main body 3c of the driven bevel gear 3 is parallel to the tapered surfaces 5a, 5a of the ring members 5, 5 of the pair of drive bevel gears 2, 2. As a result, the outer edge of the main body 3c of the driven bevel gear 3 is parallel to the tapered surfaces 5a, 5a of the ring members 5, 5 of the drive bevel gears 2, 2, allowing the second link J2 to tilt stably around the pitch axis relative to the first link J1.

[0046] Furthermore, the tapered surfaces 5a, 5a of the ring members 5, 5 and the tapered surfaces 4a, 4a of the rotating body bases 4, 4 are aligned parallel to the front and back surfaces of the inclined outer peripheral edge of the main body portion 3c of the driven bevel gear 3. This allows the driven bevel gear 3 to be guided and held in an appropriate relative position relative to the driving bevel gears 2, 2 with a simple structure. Specifically, when the rod 8 is in its most deeply meshed state with the teeth 10, the rotation center of the rod 8 is at the same position as the center of the circle of curvature that constitutes the curved surface of the meshed tooth root portion 10g. This allows the relative position of the driven bevel gear 3 in the radial direction of the driving bevel gear 2 to be easily and reliably positioned.

[0047] Furthermore, since the tooth surface 10f of the tooth 10 has an arc shape in which the central part in the depth direction bulges outward, a sufficiently long area can be secured for the rod material 8 to roll, and the meshing operation can be performed smoothly.

[0048] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.

[0049] For example, the structure of the driving bevel gear and the structure of the driven bevel gear in the above embodiment may be swapped.

[0050] Furthermore, the connecting member 6 of the drive bevel gear 2 is not limited to a configuration in which both longitudinal ends of the rod 8 rotate relative to the bearings 9A and 9B, but may also be configured such that both longitudinal ends of the rod are fixed to the rotating body base 4 and the ring member 5 in a manner that prevents rotation.

[0051] Furthermore, the connecting member 6 of the drive bevel gear 2 may be, for example, a shaft member whose longitudinal ends are fixed to the rotating body base 4 and the ring member 5 so as not to rotate, and a roller that is rotatably supported on this shaft member.

[0052] Furthermore, the rod material 8 of the drive bevel gear 2 does not necessarily have to have a taper on its circumferential surface 8d.

[0053] Furthermore, although it affects smooth meshing, the tooth surface 10f of the teeth 10 of the driven bevel gear 3 is not limited to a curved shape; it may also be a straight shape.

[0054] Furthermore, the opening 2a of the driving bevel gear 2 and the opening 3a of the driven bevel gear 3 may be omitted.

[0055] Furthermore, although the power transmission device in the above embodiment was described as being used in the joint mechanism of a multi-joint robot arm, it is not limited to this and may be used for the purpose of transmitting power in, for example, a moving vehicle. [Explanation of Symbols]

[0056] 1. Power transmission device 2. Drive bevel gear (rotating body) 2a aperture 3. Driven bevel gear (rotating body) 3a aperture 3b Mounting part 3c Main body 4. Rotating base 4a Tapered surface 5 Ring Member 5a Tapered surface 6. Connecting Members 7A, 7B Annular members 8. Rod material (interlocking part) 8c central part 8d circumferential surface 9A, 9B bearings 10 teeth 10e Tooth apex 10f tooth surface 10g (tooth base) 15 Hole 17a, 17b recess J-joint mechanism J1 1st Link J2 2nd Link

Claims

1. In a power transmission device comprising a pair of rotating bodies whose axes intersect each other, One of the rotating bodies comprises a rotating body base that is rotatably supported, and meshing portions arranged radially at equal intervals in the circumferential direction of the rotating body base, The aforementioned meshing portion has a circumferential surface that is circular in an axial view, The other rotating body is characterized by having multiple teeth arranged at equal intervals on its outer peripheral edge that mesh with the meshing portion.

2. The power transmission device according to claim 1, characterized in that the tooth root portion, which is formed by the root portion of the tooth surface of an adjacent pair of teeth, has a curved surface that follows the circumferential surface of the occlusal portion.

3. The power transmission device according to claim 2, characterized in that the meshing portion is conical in shape.

4. The power transmission device according to claim 1, characterized in that the meshing portion connects the rotating body base and a ring member located radially inward of the rotating body base.

5. The other rotating body has a mortar-like shape with its outer periphery rising at an angle, The power transmission device according to claim 4, characterized in that the ring member of one of the rotating bodies has a tapered surface along the outer peripheral edge of the other rotating body.

6. The power transmission device according to any one of claims 1 to 5, characterized in that one of the rotating bodies having the meshing portion is arranged opposite to the other rotating body, each of the rotating bodies is driven to rotate, and the other rotating body is driven to rotate.

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