Eccentric oscillation type reduction gear

Abstract

To improve the fatigue life of the internal pin. [Solution] The eccentric oscillating type reduction gear 1 comprises an external gear 21 and a plurality of internal pins 32 that are individually inserted into a plurality of internal pin holes 24 of the external gear 21 and transmit the rotation component of the external gear 21. The cross-sectional shape of the internal pins 32 in a plane perpendicular to the rotation center line O2 of the external gear 21 is a perfect circle or an ellipse with a larger radial width. The cross-sectional shape of the internal pin holes 24 in a plane perpendicular to the rotation center line O2 is such that the radial width a of the external gear 21 with respect to the rotation center P2 is smaller than the width b in the direction perpendicular to the radial direction.

Description

Technical Field

[0001] The present invention relates to an eccentric swing type reduction gear.

Background Art

[0002] Conventionally, an eccentric swing type reduction gear that obtains a reduced output using an externally toothed gear that swings eccentrically is known (see, for example, Patent Document 1). In an eccentric swing type reduction gear, a columnar inner pin provided on an output shaft (carrier) is inserted into a circular inner pin hole provided in an externally toothed gear. Thereby, the rotation component of the eccentrically swinging externally toothed gear is transmitted to the output shaft via the inner pin. During this torque transmission, a repeated load that varies in magnitude acts on the inner pin depending on the relative position between the inner pin and the externally toothed gear. This repeated load dominantly affects the fatigue life of the inner pin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to improve the fatigue life of the inner pin.

Means for Solving the Problems

[0005] The present invention includes an externally toothed gear, a plurality of inner pins individually inserted into a plurality of inner pin holes of the externally toothed gear and transmitting the rotation component of the externally toothed gear, and is an eccentric swing type reduction gear comprising: the cross-sectional shape of the inner pin in a plane perpendicular to the rotation center line of the externally toothed gear is a circular shape or an elliptical shape with a larger width in the radial direction, The cross-sectional shape of the internal pin hole in a plane perpendicular to the rotational center line is such that the radial width with respect to the rotational center of the external gear is smaller than the width in the direction perpendicular to the radial direction. [Effects of the Invention]

[0006] According to the present invention, the fatigue life of the internal pin can be improved. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view showing an eccentric oscillating type reduction gear according to an embodiment. [Figure 2] This diagram shows an external gear and its surrounding components as viewed from the axial direction according to an embodiment, illustrating the contact force acting on the internal pin and the internal pin hole. [Figure 3] This is a view of a conventional external gear and its surrounding components from the axial direction. [Figure 4] This graph shows the relationship between the contact force acting on the internal pin and the phase of the internal pin hole with respect to the eccentric direction. [Figure 5] This is a view from the axial direction of an external gear and its surrounding components according to a modified embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0009] [Overall configuration of an eccentric oscillating type speed reducer] Figure 1 is a cross-sectional view showing the eccentric oscillating type reduction gear 1 according to this embodiment. In the following, the direction along the central axis O1 in the diagram will be referred to as the "axial direction." Furthermore, within the axial direction, the side connected to the external driven member (left side in the diagram) will be referred to as the "load side," and the side opposite the load side (right side in the diagram) will be referred to as the "anti-load side."

[0010] As shown in Figure 1, the eccentric oscillating reduction gear 1 is a so-called center crank type eccentric oscillating reduction gear, and comprises an eccentric shaft 11, a plurality of external gears 21 (21A, 21B, 21C), an output shaft 31, a carrier 35, and a housing (casing) 41.

[0011] The eccentric shaft 11 is rotatably supported on the central axis O1 and has multiple (three in this embodiment) eccentric bodies 11a, 11b, and 11c. The output shaft of a motor (not shown) is connected to the eccentric shaft 11. The eccentric bodies 11a to 11c have a circular cross-sectional shape perpendicular to the central axis O1, and are eccentric in different directions relative to the central axis O1. Specifically, the eccentric phases of the eccentric bodies 11a to 11c are shifted by 120 degrees from each other.

[0012] Each external gear (curved plate) 21 is formed in a substantially circular disc shape perpendicular to the axial direction and has a through hole 22 in the center through which the eccentric shaft 11 is inserted. The three external gears 21A to 21C are arranged side by side in the axial direction and are rotatably supported relative to the eccentric bodies 11a to 11c by eccentric bearings 61a to 61c, which are respectively positioned between them and the eccentric bodies 11a to 11c. As a result, the external gears 21A to 21C oscillate in conjunction with the rotation of the eccentric bodies 11a to 11c. Each external gear 21 has a plurality of external teeth 23 on its outer circumferential surface. The plurality of external teeth 23 mesh with the internal gear 42, which is supported by the housing 41, on the eccentric side. Each external gear 21 has a plurality of internal pin holes 24 arranged equally on its circumference at positions offset from the central axis O1. An internal pin 32, erected on the output shaft 31, is inserted through each internal pin hole 24. The relationship between the shapes of the internal pin holes 24 and the internal pins 32 will be described later. Each external gear 21 is made of a metal material, such as steel or aluminum, although this is not particularly limited.

[0013] The output shaft 31 is disposed on the outer diameter side of the eccentric shaft 11 and on the load side of the external gear wheels 21A to 21C, and is connected to a driven member (not shown). The output shaft 31 has a plurality of cylindrical inner pins 32 erected on the anti-load side. Each inner pin 32 has a cylindrical inner roller 32a rotatably fitted on its outer periphery. Each inner pin 32 is inserted into the inner pin holes 24 of the corresponding external gear wheels 21A to 21C. Note that the inner pin 32 may be integral with or separate from the output shaft 31, or may be provided integrally with the carrier 35. Also, the inner roller 32a may not be provided. The carrier 35 is disposed on the anti-load side of the external gear wheels 21A to 21C and is fixed to the anti-load side ends of the respective inner pins 32. The carrier 35 and the output shaft 31 support the eccentric shaft 11 rotatably by means of eccentric shaft bearings 62a and 62b disposed between them and the eccentric shaft 11. The carrier 35 and the output shaft 31 are not particularly limited, but are made of, for example, a metal material such as a steel material.

[0014] The housing 41 is disposed on the outer diameter sides of the external gear wheels 21A to 21C, the output shaft 31, and the carrier 35. An internal gear 42 is provided on the inner peripheral portion of the housing 41. The internal gear 42 includes a plurality of internal gear pins 42a that form internal teeth and a plurality of internal gear grooves 42b that hold the internal gear pins 42a, and is internally meshed with the external gear wheels 21A to 21C (see FIG. 2). The internal gear pins 42a are cylindrical pins extending in the axial direction. The internal gear grooves 42b are grooves having a substantially semi-circular cross-section along the axial direction, are formed on the inner peripheral surface of the housing 41, and the internal gear pins 42a are rotatably disposed therein. The housing 41 supports the carrier 35 and the output shaft 31 rotatably by means of main bearings 63a and 63b disposed between it and the carrier 35 and the output shaft 31. The housing 41 and the internal gear pins 42a are made of, for example, a steel material such as high-carbon chromium bearing steel.

[0015] In the eccentric swing type reduction gear 1 having the above-described configuration, when the eccentric body shaft 11 rotates, the eccentric bodies 11a to 11c rotate eccentrically relative to the inside of the through holes 22 of the external gear wheels 21A to 21C. As a result, the external gear wheels 21A to 21C swing with different phases from each other (for example, phases shifted by 120 degrees), and the external teeth 23 farthest from the central axis O1 mesh with the internal gear wheel 42. This meshing position changes in the circumferential direction around the central axis O1 as the swing occurs, and makes one round in the circumferential direction every time the eccentric body shaft 11 makes one rotation. At this time, there is a difference in the number of teeth between the external gear wheel 21 (external teeth 23) and the internal gear wheel 42, and each external gear wheel 21 rotates by the difference in the number of teeth every time the eccentric body shaft 11 makes one rotation. That is, the rotational motion of the eccentric bodies 11a to 11c is decelerated at a ratio of "(the difference in the number of teeth between the internal gear wheel 42 and the external gear wheel 21) / (the total number of teeth of the external gear wheel 21)" and converted into the rotation of the external gear wheel 21. The rotational component of the external gear wheel 21 is transmitted to the output shaft 31 via the inner pin 32. That is, the rotational component of the external gear wheel 21 is synchronized with the output shaft 31 via the inner pin 32. Thereby, the rotational motion of the eccentric body shaft 11 is decelerated and transmitted to the driven member connected to the output shaft 31. Note that the output shaft 31 may be fixed and the output may be taken out from the housing 41. In this case, the rotational component of the external gear wheel 21 becomes fixed.

[0016] [Shape of inner pin hole] FIG. 2 is a view of the external gear wheel 21 and the surrounding components as seen from the axial direction, and shows the contact forces acting on the inner pin 32 and the inner pin hole 24. In FIG. 2, the inner pin hole 24 is shown by a thick line for emphasis. FIG. 3 is a view of a conventional external gear wheel and the surrounding components as seen from the axial direction. In FIGS. 2 and 3, the contact force F1 generated between the inner pin 32 and the inner pin hole 70 is vectorially indicated by a thick dashed line. Note that in the following description, the "inner pin 32" includes the inner roller 32a on its outer periphery unless otherwise specified. Also, in the following description, when simply referring to a "cross section", it refers to a plane (cross section) perpendicular to the central axis O1.

[0017] As shown in Figure 2, each internal pin hole 24 formed in the external gear 21 is formed in an elongated elliptical shape in the circumferential direction. More specifically, the cross-sectional shape of each internal pin hole 24 in a plane perpendicular to the central axis O1 is such that the radial width a with respect to the rotation center P2 of the external gear 21 is smaller than the width b in the direction perpendicular to the radial direction (circumferential direction). In other words, in this embodiment, each internal pin hole 24 is elliptical, but is not limited to this; the cross-sectional shape of each internal pin hole 24 in a plane perpendicular to the central axis O1 does not have to be elliptical as long as the radial width a with respect to the rotation center P2 of the external gear 21 is smaller than the width b in the direction perpendicular to the radial direction (circumferential direction). Here, "rotation center P2 of the external gear 21" is equal to the geometric center of the external gear 21 in a plane perpendicular to the central axis O1. Hereinafter, when referring to the shape of the internal pin hole 24 as "radial" or "circumferential," it means the radial direction (direction perpendicular to the axial direction) or the circumferential direction (direction of rotation around the rotation centerline O2 of the external gear 21) with respect to the rotation center P2 of the external gear 21. The "rotation centerline O2 of the external gear 21" is an axis that passes through the rotation center P2 and is parallel to the central axis O1. On the other hand, the cross-sectional shape of the inner pin 32, which is inserted through the inner pin hole 24, is circular (perfectly round), as described above.

[0018] Thus, while the cross-sectional shape of the inner pin 32 is a perfect circle, the cross-sectional shape of the inner pin hole 24 is an elongated ellipse in the circumferential direction. This allows the load acting on the inner pin 32 to be distributed, thereby reducing the maximum value of the load. In other words, as shown in Figure 3, when the inner pin 32 and inner pin hole 70 both have a circular cross-sectional shape, the contact force F1 acting between the inner pin 32 and the inner pin hole 70 is maximum in the inner pin hole 70 in a direction that is π / 2 phase different from the eccentric direction of the external gear (to the right in Figure 3) (hereinafter referred to as the "π / 2 direction"; upward in Figure 3). Since this maximum contact force F1 acts on the inner pin 32 as a repeated load, the larger the force F1, the more likely the inner pin 32 is to experience fatigue.

[0019] On the other hand, in this embodiment, as shown in Figure 2, while the cross-sectional shape of the inner pin 32 is circular, the cross-sectional shape of the inner pin hole 24 is such that the radial width a with respect to the rotation center P2 of the external gear 21 is smaller than the circumferential width b perpendicular to the radial direction. Therefore, compared to the case of the circular inner pin hole 70 described above, the amount of contact between the inner pin 32 and the inner pin hole 24 decreases in the π / 2 direction where the contact force F1 is maximum, while the amount of contact between the surrounding inner pins 32 and inner pin holes 24 (for example, on either side) increases. As a result, the meshing ratio of the inner pins 32 increases, and as shown in Figure 4, the load (contact force F1) acting on multiple inner pins 32 is more evenly distributed, thereby reducing the maximum contact force F1 acting in the π / 2 direction.

[0020] Furthermore, the cross-sectional shape of the inner pin 32 may not be a perfect circle, as shown in Figure 5, but rather an ellipse shape where the radial width is greater than the circumferential width with respect to the central axis O1. In this case as well, the maximum contact force F1 can be reduced in the same way as described above. However, a perfect circle cross-sectional shape of the inner pin 32 can reduce the maximum contact force F1 in the π / 2 direction more effectively than an ellipse cross-sectional shape. Furthermore, the difference between the radial width a and the circumferential width b in the cross-sectional shape of the inner pin hole 24 is on the order of microns, for example, less than 1 / 100 of the diameter of the inner pin 32. Note that in Figure 5, the elliptical shape of the inner pin hole 24 is exaggerated for clarity. In this case, all the inner pins 32 and the inner pin holes 24 contact at a single point near the position opposite to the eccentric direction (left side in the figure).

[0021] [Technical effects of this embodiment] As described above, according to this embodiment, the cross-sectional shape of the inner pin 32 in the plane perpendicular to the rotation centerline O2 of the external gear 21 is a perfect circle or an ellipse with a larger radial width, and the cross-sectional shape of the inner pin hole 24 in the plane perpendicular to the rotation centerline O2 is such that the radial width with respect to the rotation center P2 of the external gear 21 is smaller than the width in the direction perpendicular to the radial direction. This increases the engagement ratio of the inner pin 32, distributing the load (contact force F1) acting on the inner pin 32 and reducing the maximum contact force F1. Consequently, the fatigue life of the inner pin 32 can be improved. In turn, the inner pin 32 can be designed to be thinner, and the entire reduction gear can be made more compact.

[0022] Furthermore, according to this embodiment, the cross-sectional shape of the inner pin 32 in a plane perpendicular to the rotational centerline O2 is a perfect circle. This allows the inner pin 32 to be manufactured with simpler processing compared to the case where the inner pin 32 is formed in an elliptical shape, and also improves the fatigue strength of the inner pin 32. This is particularly suitable for metal inner pins 32, where the processing shape is more limited compared to resin inner pins. In addition, unlike the case where the inner pin 32 is elliptical, the inner roller 32a can be suitably fitted to the outer circumference of the inner pin 32.

[0023] [others] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. For example, in the above embodiment, the internal pin (output shaft) and external gear are made of metal, but these internal pin and external gear may be made of resin. Furthermore, although the above embodiment illustrates a center-crank type eccentric oscillating reduction gear in which the eccentric axis is located at the center, the present invention is also suitably applicable to eccentric oscillating reduction gears such as distribution type in which multiple eccentric axes are arranged at positions offset from the center. Furthermore, details shown in the above embodiments can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0024] 1. Eccentric oscillating type reduction gear 21, 21A, 21B, 21C External gears 24 internal pin holes 32 Inner pin 32a Inner roller a. Radial width of the inner pin hole b. Circumferential width of the inner pin hole F1 Contact force acting between the inner pin and the inner pin hole O2 Rotation centerline of external gear P2 Rotation center of the external gear

Claims

1. External gears and Multiple internal pins are individually inserted into multiple internal pin holes of the external gear and transmit the rotational component of the external gear, An eccentric oscillating type reduction gear is equipped with, The cross-sectional shape of the internal pin in a plane perpendicular to the rotational centerline of the external gear is either a perfect circle or an ellipse with a greater radial width. The cross-sectional shape of the internal pin hole in the plane perpendicular to the rotational center line is such that the radial width of the external gear with respect to the rotational center is smaller than the width in the direction perpendicular to the radial direction. Eccentric oscillating type speed reducer.

2. The cross-sectional shape of the inner pin in the plane perpendicular to the rotational centerline is a perfect circle. The eccentric oscillating type reduction gear according to claim 1.

3. The inner pin has an inner roller that is rotatably fitted to the outer circumference of the inner pin. The eccentric oscillating type reduction gear according to claim 2.

4. The cross-sectional shape of the internal pin hole is such that the difference between the radial width relative to the rotation center of the external gear and the width perpendicular to that radial direction is on the order of microns. The eccentric oscillating type reduction gear according to claim 1.

5. The external gear and the internal pin are made of metal. The eccentric oscillating type reduction gear according to claim 1.

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