JP2022190915A - power transmission device - Google Patents

Abstract

To reduce backlash in a power transmission device at low cost.SOLUTION: A speed reducer 1 comprises: an input member 10 having first rolling element engaging grooves 13 in side surfaces on both sides in an axial direction; a pair of fixing members 5 having second rolling element engaging grooves 16; a plurality of balls 4 engaged with the first rolling element engaging grooves 13 and the second rolling element engaging grooves 16; and a pair of output members 31, 32 having a plurality of pockets 17 for holding the plurality of balls 4 in a circumferential direction. The first rolling element engaging groove 13 is formed along a circle having a center of curvature eccentric from a rotation center X. The second rolling element engaging groove 16 is formed along a wavy curve that alternately intersects with a pitch circle having a center of curvature on the rotation center X. An elastic member 35 for imparting elastic force in the circumferential direction to both the output members 31, 32 is interposed between the pair of output members 31, 32.SELECTED DRAWING: Figure 1

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission device that transmits rotation input to an input rotary portion to a coaxially arranged output rotary portion at a predetermined gear ratio.

As an example of a power transmission device, Patent Document 1 describes a speed reduction device that transmits rotational torque in an axial direction at a predetermined gear ratio via rolling elements.

As shown in FIG. 12, this type of power transmission device 201 includes an input member 210 having first rolling element engaging grooves 213 on both sides in the axial direction; A pair of fixed members 205 having two rolling element engagement grooves 216 and an input member 210 and a pair of fixed members 205 are provided axially between the first rolling element engagement grooves 213 and the second rolling element engagement grooves. A plurality of balls 204 engaged with the moving body engaging grooves 216 and a plurality of pockets 217 are provided between the input member 210 and the pair of fixed members 205 in the axial direction to hold the plurality of balls 204 in the circumferential direction. and a pair of output members 231 and 232 that are connected to each other. A pair of output members 231 and 232 are connected by a connecting member 233 . Input member 210 is rotatably supported with respect to input shaft 207 via bearing 209 . The output members 231 and 232 are rotatably supported on the input shaft 207 via bearings 211 .

The first rolling element engagement groove 213 is formed along a circle having a center of curvature O1 that is eccentric from the rotation center X by an eccentricity amount a. The second rolling element engaging grooves 216 are formed along wavy curves that alternately cross a pitch circle having a center of curvature on the rotation center X. As shown in FIG.

When the input shaft 207 is rotated around the rotation center X, the input member 210 whirles around the rotation center X and makes a revolution motion with a radius a. When the input member 210 revolves, each ball 204 engaged with the circular first rolling element engaging groove 213 moves along the wavy second rolling element engaging groove 216 formed in the fixed member 205 . to move. The balls 204 engage with the pockets 217 of the output members 231 and 232 in the circumferential direction, and the contact force generated thereby acts as a force to rotate the output members 231 and 232 in the same direction as the input shaft 207 . This contact force causes the output members 231 and 232 to rotate about the rotation center X while being reduced in speed at a constant speed reduction ratio.

JP 2020-051572 A

The speed reducer 201 is required to have good responsiveness, and in order to achieve good responsiveness, it is necessary to reduce backlash inside the speed reducer as much as possible. A portion of the reduction gear that causes backlash is the gap between the ball and the pocket that retains the ball in the circumferential direction. In order to reduce the backlash, it is necessary to reduce the gap between the ball and the pocket, but in order to reduce the gap, it is necessary to improve the machining accuracy of the ball and the pocket, which increases the machining cost. Moreover, it is generally difficult to always maintain high machining accuracy of parts during mass production. On the other hand, if the gap between the ball and the pocket is made too small, there is a possibility that the gap between the ball and the pocket will become negative due to variations in machining accuracy. If the ball and the pocket come into contact with each other in the negative gap, the movement of the ball is restricted, which causes problems such as reduction in transmission efficiency, generation of vibration and noise, and shortening of the life of the reduction gear.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to reduce the backlash inside a power transmission device at a low cost in a power transmission device that transmits rotational torque in the axial direction via rolling elements.

In order to solve the above-described problems, a power transmission device according to the present invention is a power transmission device that transmits rotation input to an input rotation portion to an output rotation portion arranged coaxially at a predetermined gear ratio, A first member having first rolling element engagement grooves on both side surfaces in the axial direction, and a pair of second members provided on both sides in the axial direction of the first member and having second rolling element engagement grooves, respectively. , which are provided between the first member and the pair of second members in the axial direction, and are engaged with the first rolling element engaging groove and the second rolling element engaging groove that are axially opposed to each other. A plurality of balls, and a pair of third members having a plurality of pockets that are provided between the first member and the pair of second members in the axial direction and hold the plurality of balls in the circumferential direction. In this speed reducer, one of the first rolling element engaging groove and the second rolling element engaging groove is a circle having a center of curvature eccentric from the rotation centers of the input rotating portion and the output rotating portion. and the other of the first rolling element engaging groove and the second rolling element engaging groove alternately intersects a pitch circle having a center of curvature on the center of rotation. any one of the first member, the pair of second members, and the pair of third members is provided to the input rotary part, and the first member and the pair of second members are formed along a curve; A member and the other one of the pair of third members are provided on the output rotary portion.

In this power transmission device, according to the present invention, an elastic member is interposed between the pair of third members for applying elastic force in the circumferential direction to both the third members.

As a result, the pair of third members that receive the elastic force of the elastic members rotate in opposite directions. As a result, the ball accommodated in the pocket of one third member is pressed against one of the inner surfaces on both sides in the circumferential direction of the pocket, and the ball accommodated in the pocket of the other third member is pressed against the other inner surface of the pocket. pressed against. Therefore, it is possible to reduce the backlash when rotating the input rotating part in the forward and reverse directions after that, and it is possible to rotate the third member in the same direction immediately after the start of rotation without a time lag. Therefore, the responsiveness of the power transmission device can be enhanced.

In the present invention, in this power transmission device, the elastic force of the elastic member of the torque transmission portion is set to a size that does not change the circumferential position of one of the pair of third members with respect to the other when the maximum torque is transmitted. can be set to

As a result, the ball and the inner surface of the pocket are kept in contact with each other at all times, so that the responsiveness of the reduction gear transmission can be improved.

The elastic member can be made of a metal material or a resin material.

When the power transmission device has a bearing that rotatably supports the first member, the bearing that rotatably supports the first member only needs to support a radial load. It can be made smaller. Further, by limiting the direction of the load applied to the bearing, the torque loss inside the bearing can be reduced.

In the power transmission device described above, for example, the first member may be provided at the input rotary portion, the pair of third members may be provided at the output rotary portion, and the pair of second members may be fixed members. In this way, by using the second member as the fixed member, the contact force generated between the ball and the second rolling element engagement groove can be supported by the fixed member. This eliminates the need for large bearings for Further, by providing the third member in the output rotary portion, only the contact force in the circumferential direction (rotational direction) is generated between the ball and the pocket of the output rotary portion (third member), so that the third member is supported. The load applied to the bearing is reduced, the size of the bearing can be reduced, and the torque loss inside the bearing can be reduced.

In the power transmission device described above, since each pair of the second member and the third member is provided, there is concern about an increase in cost due to an increase in the number of parts. Therefore, if the pair of second members and the pair of third members are made to have the same shape, the manufacturing cost of each member can be reduced by sharing the parts, so that the cost increase due to the increase in the number of parts can be suppressed.

As described above, according to the present invention, the balls housed in each pocket of the third member are pressed against the inner surface of the pocket. Therefore, it is possible to reduce the backlash when rotating the input rotating part in the forward and reverse directions after that, and it is possible to rotate the third member in the same direction immediately after the start of rotation without a time lag. Therefore, the responsiveness of the power transmission device can be enhanced.

1 is a cross-sectional view of a reduction gear transmission according to an embodiment of the present invention; FIG. It is a front view of an input member (first member). It is a front view of a fixing member (second member). It is a front view of an output member (third member). FIG. 5 is an enlarged view of a V portion of FIG. 4; FIG. 4 is an exploded perspective view schematically showing an input member, an output member, a fixing member, and balls; FIG. 4 is a front view showing contact forces applied to a ball; FIG. 2 is an enlarged view of the reduction gear of FIG. 1; FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1; (a) is a cross-sectional view taken along line BB in FIG. 1, and (b) is a cross-sectional view showing an enlarged region S in FIG. (a) is a cross-sectional view taken along line CC in FIG. 1, and (b) is a cross-sectional view showing an enlarged region T in FIG. 1(a). and FIG. 11 is a cross-sectional view of a conventional speed reducer.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a speed reducer 1 as a power transmission device according to an embodiment of the present invention includes an input rotary portion 2, an output rotary portion 3, balls 4 as rolling elements, a fixed member 5, It mainly includes a housing 6 that accommodates them. In the illustrated example, the housing 6 includes a first housing member 6a provided on one axial side (left side in FIG. 1) which is the input side, and a first housing member 6a provided on the other axial side (right side in FIG. 1) which is the output side. and a second housing member 6b. Both housing members 6a and 6b are fixed by appropriate means such as bolts 23 or the like. The input rotary part 2 and the output rotary part 3 are arranged coaxially and have a common center of rotation X. As shown in FIG. The fixed member 5 is fixed to the housing 6 .

The input rotary portion 2 has an input shaft 7 , an eccentric cam portion 8 , a rolling bearing 9 and an input member 10 . The input shaft 7 is rotatable around the rotation center X with respect to the housing 6 . In this embodiment, the input shaft 7 is rotatably supported with respect to the housing 6 by a plurality of rolling bearings 11 mounted between the output rotating portion 3 and the inner peripheral surface thereof. In the illustrated example, two bearings 11 are provided on each side of the eccentric cam portion 8 in the axial direction. A sealing member 21 is provided between the outer peripheral surface of the input shaft 7 and the inner peripheral surface of the first housing member 6a to prevent the grease or oil filled in the housing 6 from leaking out. The eccentric cam portion 8 is provided on the outer periphery of the input shaft 7, and is provided integrally with the input shaft 7 in the illustrated example. The center line O1 (see FIG. 9) of the cylindrical outer peripheral surface 8a of the eccentric cam portion 8 is radially eccentric with respect to the rotation center X by the amount of eccentricity a. The input member 10 has a substantially disk shape, and the center line of the input member 10 coincides with the center line O1 of the cylindrical outer peripheral surface 8a of the eccentric cam portion 8. As shown in FIG. A rolling bearing 9 is mounted between the cylindrical outer peripheral surface 8 a of the eccentric cam portion 8 and the inner peripheral surface of the input member 10 . This allows the input member 10 to rotate relative to the eccentric cam portion 8 .

The fixed members 5 are provided on both axial sides of the input member 10 . The fixing member 5 has an annular shape, and in the illustrated example, both fixing members 5 are made of the same material and have the same shape. Each fixing member 5 is fixed to the housing 6 by appropriate means. In the illustrated example, a restricting member 24 is provided to restrict circumferential movement of the fixing member 5 with respect to the housing 6 . The regulating member 24 is mounted in key grooves provided on the inner peripheral surface of each housing member 6a, 6b and the outer peripheral surface of each fixing member 5, and engages with these in the circumferential direction, thereby locking the housing 6 of the fixing member 5. restricts circumferential movement relative to

The input member 10 and each fixed member 5 are arranged side by side in the axial direction at predetermined intervals. First rolling element engaging grooves 13 are formed on both side surfaces of the input member 10 in the axial direction. Each fixed member 5 is formed with a second rolling element engaging groove 16 that axially faces the first rolling element engaging groove 13 . That is, in the present embodiment, the first member having the first rolling element engaging groove 13 is provided as the input member 10 in the input rotating part 2, and the second member having the second rolling element engaging groove 16 is fixed. A member 5 is used.

As shown in FIG. 2, the raceway center line L1 of the first rolling element engaging groove 13 formed in the input member 10 is formed in a circular shape with a radius of r. The center of curvature of the raceway center line L1 of the first rolling element engagement groove 13 coincides with the cylindrical outer peripheral surface 8a of the eccentric cam portion 8 and the center line O1 of the input member 10 . That is, the center of curvature of the track center line L1 (that is, the center line O1) is eccentric with respect to the rotation center X of the input rotary unit 2 by the eccentricity amount a. By engaging with the first rolling element engagement groove 13, each ball 4 is held at a predetermined radial position while being movable in the circumferential direction (direction along the track center line L1). The track center line L1 of the first rolling element engagement groove 13 means the locus of the center of the ball 4 when the ball 4 is moved along the first rolling element engagement groove 13 .

As shown in FIG. 3, the raceway center line L2 of the second rolling element engagement groove 16 formed in the fixed member 5 rotates at a constant pitch with respect to the reference pitch circle C having the center of curvature on the rotation center X. It is formed by alternately intersecting wavy curves. That is, the second rolling element engaging groove 16 is formed by a wavy curve in which the distance R from the rotation center X fluctuates with respect to the reference pitch circle radius PCR. In this embodiment, the wavy curve of the track center line L2 has 10 crests whose distance R from the rotation center X is greater than the reference pitch circle radius PCR, and whose distance R from the rotation center X is smaller than the reference pitch circle radius PCR. Ten valleys are provided. The second rolling element engaging grooves 16 formed in both fixing members 5 have the same shape and are arranged in the same phase. The track center line of the second rolling element engaging groove 16 means the locus of the center of the ball 4 when the ball 4 is moved along the second rolling element engaging groove 16 .

As shown in FIG. 1 , the output rotary portion 3 includes a first output member 31 provided on one axial side (left side in the drawing) of the input member 10 and a first output member 31 provided on the other axial side (right side in the drawing) of the input member 10 . and an elastic member 35 arranged between the first output member 31 and the second output member 32 . The first output member 31 has a cylindrical shaft portion 31a and a disc portion 31b extending radially outward from the shaft portion 31a. The second output member 32 has a shaft portion 32a functioning as an output shaft and a disk portion 32b extending radially outward from the shaft portion 32a. The shaft portion 32a of the second output member 32 has a cylindrical portion 32a1 and a lid portion 32a2 that closes the opening of the cylindrical portion 32a1. The lid portion 32a2 is provided with a connecting portion for connecting another member to which the reduced rotation is to be transmitted. In the illustrated example, the shaft portion 31a and the disc portion 31b of the first output member 31 are integrally formed, and the shaft portion 32a and the disc portion 32b of the second output member 32 are integrally formed.

The output rotating part 3 is rotatable around the rotation center X with respect to the housing 6 . In this embodiment, both output members 31 and 32 are integrally rotatable via an elastic member 35 which will be described later. Specifically, the rolling bearing 14 mounted between the outer peripheral surface of the shaft portion 31a of the first output member 31 and the inner peripheral surface of the fixed member 5 on one side in the axial direction, and the shaft portion of the second output member 32 The output rotating part 3 is integrally rotatably supported with respect to the housing 6 by the rolling bearing 15 mounted between the outer peripheral surface of 32a and the inner peripheral surface of the fixed member 5 on the other side in the axial direction. A sealing member 22 is provided between the outer peripheral surface of the shaft portion 32a of the second output member 32 and the inner peripheral surface of the second housing member 6b to prevent the grease or oil filled in the housing 6 from leaking out. be provided.

The disk portion 31b of the first output member 31 and the disk portion 32b of the second output member 32 are formed with a plurality of pockets 17 for holding the balls 4, respectively. That is, in the present embodiment, a pair of third members having the pocket 17 are provided as the output members 31 and 32 in the output rotary section 3 . As shown in FIG. 4, the pocket 17 is formed as an elongated hole extending radially in the radial direction around the center of rotation X of both the output members 31 and 32 . The pockets 17 are formed at equal intervals in the circumferential direction on the same circumference. In this embodiment, the pockets 17 provided in both output members 31 and 32 are provided at the same position within a plane perpendicular to the axial direction, and one ball 4 is arranged in each pocket 17 . The number of pockets 17 formed in each of the output members 31, 32 (that is, the number of balls 4 arranged between each of the output members 31, 32 and the input member 10) is It is 11 pieces, which is one more than the number of portions or valleys (10 pieces).

As shown in FIG. 5, the ball 4 can move within each pocket 17 in the radial direction about the reference pitch circle C within a range of a predetermined amount m. In this embodiment, the peripheral wall of each pocket 17 is provided with a pair of parallel flat surfaces 17a facing each other in the circumferential direction. diameter). Thereby, each ball 4 is held at a predetermined circumferential position by each pocket 17 in a radially movable state.

As shown in FIG. 6, the input member 10 and both the output members 31 and 32 have a common center of rotation X, and on this center of rotation X the axes of both the fixed members 5 are arranged. The central axis O1 of the input member 10 (that is, the center of curvature of the raceway center line L1 of the first rolling element engaging groove 13) is eccentric with respect to the rotation center X by the amount of eccentricity a. The balls 4 arranged in the pockets 17 of the output members 31 and 32 protrude from the pockets 17 in the axial direction. 5 is engaged with the second rolling element engaging groove 16 (see FIG. 1). 6, unlike FIG. 4 showing the conceptual configuration, the pocket 17 is an elongated hole that does not open on the outer peripheral surfaces of the output members 31 and 32. As shown in FIG.

In the speed reducer 1 of the present embodiment, the second rolling element engaging groove 16 has 10 peaks (or 10 valleys) along the raceway center line L2, and 11 balls 4. Therefore, the speed reduction ratio i obtained by the following equation is 1/11.
Reduction ratio i = (number of balls - number of ridges) / number of balls The number of ridges is defined as the number of balls ± 1, and when the reduction ratio i is a negative value, the rotation of the input rotating part 2 It means that the rotation direction of the output rotation part 3 is opposite to the direction.

The shape of the raceway center line L2 of the second rolling element engagement groove 16 is set so that the decelerated rotary motion is transmitted from the input rotary part 2 to the output rotary part 3 by synchronous rotation. Specifically, when the speed reduction ratio of the speed reducer 1 is i, the output rotary portion 3 is engaged with the first rolling element engagement groove 13 at the rotation angle θ of the input shaft 7 at the rotation angle iθ. The shape of the second rolling element engaging groove 16 is set so that the ball 4 engages with the second rolling element engaging groove 16 to transmit torque. Specifically, the distance R between the rotation center X of the input rotary portion 2 and the output rotary portion 3 and the raceway center line L2 of the second rolling element engagement groove 16 satisfies the following formula (1). The shape of the rolling element engagement groove 16 is set.
R=a·cos(ψ/i)+√{r ² −(a·sin(ψ/i)) ² } (1)
however,
R: Distance between the rotation center X and the raceway center line L2 of the second rolling element engagement groove 16 a: Eccentricity i of the center O1 of the raceway center line L1 of the first rolling element engagement groove 13 with respect to the rotation center X : Reduction ratio ψ: Rotational angle r of the output rotating part 3: Radius of the raceway center line L1 of the first rolling element engaging groove 13

Of the input member 10, both output members 31 and 32, and both fixing members 5, at least the sidewall of the first rolling element engaging groove 13 that contacts the ball 4, the sidewall of the second rolling element engaging groove 16, and It is preferable that the peripheral wall of the pocket 17 be provided with a surface hardness similar to that of the ball 4 in order to reduce wear caused by a difference in surface hardness from that of the ball 4 . For example, it is preferable to set the surface hardness of the side wall of the first rolling element engaging groove 13, the side wall of the second rolling element engaging groove 16, and the peripheral wall of the pocket 17 within the range of HRC50-60. Specifically, the input member 10, the output members 31 and 32, and the fixed member 5 are formed using carbon steel for machine structural use such as S45C or S50C, or alloy steel for machine structural use such as SCM415 or SCM420. The above-mentioned surface hardness can be obtained by performing an overall heat treatment or a carburizing heat treatment. Alternatively, the above surface hardness can be obtained by forming each of the above members using bearing steel such as SUJ2 and subjecting them to overall heat treatment or high-frequency heat treatment.

Next, the operation of the reduction gear transmission 1 of this embodiment will be summarized. When the input shaft 7 of the input rotating portion 2 shown in FIG. 1 is rotated, the input member 10 performs orbital motion around the rotation center X with a whirling radius a. At this time, since the input member 10 is rotatable with respect to the eccentric cam portion 8 provided on the input shaft 7, it hardly rotates. As a result, the relative amount of friction between the first rolling element engagement groove 13 and the ball 4 is reduced, and the rotational torque transmission efficiency is enhanced.

When the input member 10 revolves, each ball 4 engaged with the circular first rolling element engaging groove 13 moves along the second rolling element engaging groove 16 formed in the fixed member 5. do. Specifically, when the center line O1 of the input member 10 revolves in the direction of the arrow from the position shown in FIG. Upon engagement, a substantially upward contact force F1 acts on each ball 4 . When the ball 4 engages with the second rolling element engaging groove 16, a contact force F2' with the ball 4 acts on the second rolling element engaging groove 16. A contact force F2 acts due to contact with the rolling element engagement groove 16 of . The ball 4 moves in the circumferential direction along the second rolling element engaging groove 16 due to the circumferential direction component F2a of the contact force F2. The ball 4 engages with the pocket 17 of the output rotary portion 3 in the circumferential direction, and the contact force F3' generated thereby acts as a force to rotate the output rotary portion 3 in the same direction as the input shaft 7 (FIG. 4). reference).

The force that rotates the output rotating part 3 (that is, the contact force F3′ acting from the ball 4 on the pocket 17 of each output member 31, 32 ≈ contact force F2 that the ball 4 receives from the second rolling element engagement groove 16 The directional component F2a) varies depending on the contact state between the ball 4 and the wavy second rolling element engaging groove 16, so the magnitude differs depending on the position of each ball 4 (see FIG. 4). Since the balls 4 are arranged around the rotation center X of the input rotation part 2 and the output rotation part 3, the force for rotating the output rotation part 3 is distributed around the rotation center X. Specifically, in the wavy second rolling element engaging groove 16, the contact is made near the center between the peaks of the peaks and the peaks of the valleys (the portion having a large inclination angle with respect to the pitch circle centered on the rotation center X). The balls 4 at the upper and lower ends in the figure have a large force to rotate the output rotating part 3, and are located near the peaks of the ridges or the troughs of the second rolling element engaging groove 16 of the wave shape (about the center of rotation X). The ball 4 at both the left and right ends in the drawing, which contacts the portion having a small inclination angle with respect to the pitch circle, has a small force to rotate the output rotating portion 3 .

In the reduction gear transmission 1 described above, the pair of fixed members 5, the pair of output members 31 and 32, and the plurality of balls 4 are arranged axially symmetrically with the input member 10 as the center. As a result, as shown in FIG. 8, the input member 10 receives a contact force F1' from the balls 4 provided on both sides in the axial direction, and the axial component F1a' of this contact force F1' is canceled. As a result, the load in the axial direction is not transmitted to the bearing 9 that supports the input member 10 and the bearing 11 (see FIG. 1) that supports the input shaft 7, so the bearings 9 and 11 can be made smaller, and the reduction gear 1 can be made smaller. can be Further, by limiting the directions of the loads applied to the bearings 9 and 11, the torque loss inside the bearings is reduced, and the torque transmission efficiency of the reduction gear transmission 1 is enhanced.

Further, in the speed reducer 1 described above, the contact force F2' between the ball 4 and the second rolling element engaging groove 16 is supported by the fixed member 5 fixed to the housing 6, so that the contact force F2' is No need for large bearings to support. Further, since the ball 4 engages with the pocket 17 in the rotational direction while reciprocating in the radial direction, only the contact force F3' in the rotational direction is applied from the ball 4 to the output rotating portion 3. Since the direction of the contact force F3′ is limited to the rotational direction in this way, the bearings 14 and 15 that support the output rotating portion 3 can be miniaturized, and the reduction gear 1 can be miniaturized. A loss is reduced, and the torque transmission efficiency of the speed reducer 1 is enhanced.

As described above, during torque transmission, a contact force F3′ in the circumferential direction due to contact with the balls 4 is applied to the pillars provided between the pockets 17 of the disk portions 31b and 32b of the respective output members 31 and 32. . Therefore, there is concern that the pillars provided between the pockets 17 of the discs 31b and 32b may be damaged by the contact force F3' received from the ball 4. FIG. In particular, if the number of pockets 17 (that is, the number of balls 4) is increased in order to increase the speed reduction ratio, the circumferential width of the pillars between the pockets 17 becomes narrower. There is a growing concern that the

Regarding this point, in this embodiment, as shown in FIG. and contributes to torque transmission. Therefore, compared to the case where torque is transmitted only by the balls 4 above the rotation center X, the contact force F3′ applied from the balls 4 to the disk portions 31b and 32b is dispersed, so that the disk portions 31b and 32b are dispersed. The load applied to each column is reduced. In particular, in the present embodiment, by providing the output members 31 and 32 on both sides of the input member 10, the contact points between the ball 4 and the output members 31 and 32 are increased, so the load at each contact point can be further reduced. Furthermore, in the present embodiment, as described above, the surface hardness of the peripheral wall of the pocket 17 is increased to HRC50 or more by selecting the material for the disk portions 31b and 32b and by heat treatment. As described above, the durability of the pillars between the pockets 17 of the output members 31 and 32 can be enhanced, or the load capacity can be increased while maintaining the durability of the pillars.

Thus, the rotation input to the input shaft 7 of the input rotating portion 2 is transmitted to the output rotating portion 3 via the balls 4 . At that time, the second rotation is performed so that the distance R between the rotation center X of the input rotation portion 2 and the output rotation portion 3 and the raceway center line L2 of the second rolling element engagement groove 16 satisfies the above formula (1). Since the raceway center line L2 of the rolling element engaging groove 16 is designed, the output rotating part 3 always rotates in synchronization with the input shaft 7 at a reduced rotational speed.

Next, a characteristic configuration of the speed reduction transmission 1 described above will be described.

In this reduction gear transmission 1, as shown in FIG. 6, the output member 31 on one side in the axial direction is provided with a protruding portion 31c that protrudes in the axial direction toward the output member 32 on the other side in the axial direction. The output member 12 on the other side in the axial direction is provided with a protruding portion 32c that protrudes in the axial direction toward the output member 31 on the one side in the axial direction. The projecting portions 31c and 32c are formed on the outer peripheral edge portions of the disk portions 31b and 32b, and the inner and outer peripheral surfaces thereof are formed in a cylindrical shape. The protrusions 31c and 32c are formed in a range slightly narrower than 180 degrees in the circumferential direction. As shown in FIG. 9, the output members 31 and 32 are arranged in a phase such that the protruding portions 31c and 32c do not overlap in the circumferential direction. Circumferential direction end faces 31c1 of the projecting portion 31c of the output member 31 on one side in the axial direction face circumferentially end faces 32c1 of the projecting portion 32c of the output member 32 on the other side in the axial direction, Circumferential gaps P and Q are formed between the end faces 31c1 and 32c1. The gaps P and Q are formed at positions separated by 180° in the circumferential direction.

The elastic member 35 in a compressed state is arranged in one of the two gaps P and Q between the end faces 31c1 and 32c1 facing each other in the circumferential direction. Torque transmission between the pair of output members 31 and 32 is performed via the elastic member 35 . The material and form of the elastic member 35 can be arbitrarily selected as long as the elastic member 35 can obtain a necessary elastic force and has a strength sufficient to enable the torque transmission. The elastic member 35 can be made of a metal material or a resin material. For example, a metal spring or a solid resin composition can be used as the elastic member 35 .

As already described, the output members 31 and 32 are rotatably supported by the bearing 11 with respect to the input rotating portion 2 and are rotatably supported with the fixed member 5 by bearings 14 and 15 . Therefore, in the example of FIG. 9, the output members 31 and 32 that have received the elastic force of the elastic member 35 rotate in the direction in which the gap P on the upper side in the figure expands and the gap Q on the lower side narrows. Accordingly, as shown in FIGS. 10A and 11A, the output member 31 on one side in the axial direction rotates in the counterclockwise direction Z1 in the drawing, and the output member 32 on the other side in the axial direction rotates. rotates in the clockwise direction Z2 in the drawing.

As a result, as shown in FIG. 10(b), the ball 4 accommodated in the pocket 17 of the output member 31 on one side in the axial direction moves clockwise on the flat surfaces 17a on both sides of the pocket 17 in the circumferential direction. It is pressed against the located flat surface 17a1. Further, as shown in FIG. 11(b), the ball 4 accommodated in the pocket 17 of the output member 32 on the other side in the axial direction moves toward the counterclockwise direction of the flat surfaces 17a on both sides of the pocket 17 in the circumferential direction. It is pressed against the located flat surface 17a2.

Thereby, even if the pocket 17 is formed with a width larger than the diameter of the ball 4, play between the output members 31, 32 and the ball 4 can be eliminated in both forward and reverse rotation directions. Therefore, it is possible to reduce the backlash when rotating the input rotating part 2 in the forward and reverse directions after that, and the output members 31 and 32 can be rotated in the same direction immediately after the start of rotation without a time lag. Therefore, the responsiveness of the speed reducer 1 can be enhanced, and good response characteristics can be obtained even when the speed reducer 1 of the present embodiment is used in, for example, the joints of a robot arm. Further, even if the pocket 17 is formed with a width larger than the diameter of the ball 4, there is no problem in responsiveness. Therefore, it is possible to reduce the manufacturing cost of the output member. By forming the pocket 17 with a width larger than the diameter of the ball 4, it is possible to prevent a negative gap between the pocket and the ball due to variations in machining accuracy.

The elastic force of the elastic member 35 is greater than the rotational force acting between the two output members 31, 32 during maximum torque transmission so that the ball 4 is always pressed against the flat surfaces 17a1, 17a2 of the pocket 17. preferably set. In other words, it is preferable to set the elastic force of the elastic member 35 to a magnitude that does not change the circumferential position of one of the pair of third members 31 and 32 with respect to the other when the maximum torque is transmitted.

In the above description, the case where the elastic member 35 is arranged in the gap P in a compressed state has been exemplified. Obtainable.

Embodiments of the present invention are not limited to the above. Other embodiments of the present invention will be described below, but descriptions of the same points as those of the above-described embodiments will be omitted.

In the above embodiment, the case where the circular first rolling element engagement groove 13 is continuous over the entire circumference was shown, but the present invention is not limited to this, and the first rolling element engagement groove 13 may be, for example, a circular A plurality of (for example, the same number as the rolling elements) arcuate grooves formed along the raceway center line L1 may be used.

Further, in the above embodiment, the input member 10 is rotatable with respect to the input shaft 7, but the input member 10 and the input shaft 7 may be configured to rotate integrally. In the above embodiment, the input shaft 7 and the eccentric cam portion 8 are integrally formed. An eccentric cam portion 8 may be fixed to the outer peripheral surface of 7 .

Further, in the above embodiment, the shaft portion 31a, the disc portion 31b, and the projecting portion 31c of the first output member 31 and the shaft portion 32a, the disc portion 32b, and the projecting portion 32c of the second output member 32 are integrally formed. However, these members may be formed separately. Also, if the first output member 31 and the second output member 32 are formed from the same material and in the same shape, the manufacturing cost thereof can be reduced.

Further, in the above-described embodiment, the case where the present invention is applied to the speed reducer 1 having a speed reduction ratio i of 1/11 was exemplified. can be suitably applied to a speed reducer having a speed reduction ratio of any size within the range of In this case, the number of ridges/troughs of the wavy curve of the raceway center line of the rolling element engagement groove, and the number of pockets and balls of the fixing member may be appropriately set according to the reduction ratio i.

In the above embodiment, the first member having the first rolling element engaging groove 13 is the input member 10, the second member having the second rolling element engaging groove 16 is the fixing member 5, and the pocket 17 is provided. Although the output members 31 and 32 are used as the third member, the present invention is not limited to this. , the fixed member, and the output rotating portion, the power transmission mode can be arbitrarily changed.

1 reduction gear (power transmission device)
2 Input rotating part 3 Output rotating part 4 Ball 5 Fixed member (second member)
6 housing 7 input shaft 8 eccentric cam portion 10 input member (first member)
13 First rolling element engagement groove 16 Second rolling element engagement groove 17 Pockets 31, 32 Output member (third member)
35 Elastic member F1, F1' Contact force between ball and first rolling element engaging groove F2, F2' Contact force between ball and second rolling element engaging groove F3, F3' Contact force between ball and pocket L1 Raceway center line of first rolling element engagement groove L2 Raceway center line of second rolling element engagement groove O1 Curvature center of raceway center line of first rolling element engagement groove (center line of input member)
X Rotation center of input rotary part and output rotary part

Claims (8)

A power transmission device that transmits rotation input to an input rotating part to a coaxially arranged output rotating part at a predetermined gear ratio,
A first member having first rolling element engagement grooves on both side surfaces in the axial direction, and a pair of second members provided on both sides in the axial direction of the first member and having second rolling element engagement grooves, respectively. , which are provided between the first member and the pair of second members in the axial direction, and are engaged with the first rolling element engaging groove and the second rolling element engaging groove that are axially opposed to each other. a plurality of balls, and a pair of third members each provided between the first member and the pair of second members in the axial direction and having a plurality of pockets for holding the plurality of balls in the circumferential direction,
One of the first rolling element engagement groove and the second rolling element engagement groove is formed along a circle having a center of curvature eccentric from the rotation centers of the input rotary portion and the output rotary portion. , the other of the first rolling element engaging groove and the second rolling element engaging groove is formed along a wavy curve that alternately intersects a pitch circle having a center of curvature on the center of rotation. is,
Any one of the first member, the pair of second members, and the pair of third members is provided in the input rotating portion, and the first member, the pair of second members, and the pair of third members are provided. Any other of the three members is provided on the output rotary unit,
A power transmission device according to claim 1, wherein an elastic member is interposed between the pair of third members to apply elastic force in a circumferential direction to both the third members. 2. The power according to claim 1, wherein the elastic force of said elastic member of said torque transmission portion is set to a magnitude that does not change the circumferential position of one of said pair of third members with respect to the other when said maximum torque is transmitted. transmission device. 3. A power transmission device according to claim 1, wherein said elastic member is made of a metal material. 3. A power transmission device according to claim 1, wherein said elastic member is made of a resin material. The power transmission device according to any one of claims 1 to 4, further comprising a bearing that rotatably supports the first member. 6. The apparatus according to any one of claims 1 to 5, wherein the first member is provided on the input rotary section, the pair of third members are provided on the output rotary section, and the pair of second members are fixed members. power transmission. The power transmission device according to any one of claims 1 to 6, wherein the pair of second members have the same shape. The power transmission device according to any one of claims 1 to 7, wherein the pair of third members have the same shape.

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