speed reducer

Abstract

This invention provides a gearbox that can adjust the concentricity between planetary gears and carriers with high precision. [Solution] The reducer 1 comprises a case 3 with a plurality of outer peripheral pins 31 formed on its circular inner surface, an eccentric shaft 2 positioned at the center of the case 3 and converting input rotation into eccentric rotation, and a planetary gear 4 whose external teeth partially mesh with the outer peripheral pins 31 and which is rotatably supported by the eccentric shaft 2, and which revolves around the case 3 while rotating on its own axis due to the eccentric rotation transmitted from the eccentric shaft 2. The planetary gear 4 has a plurality of fitting holes 4B formed at equal intervals in the circumferential direction of the plate surface, and the step shape in the thickness direction of the plate is formed identically on the front and back surfaces, so that it can be used without distinguishing between the front and back.

Description

Technical Field

[0001] The present invention relates to a speed reducer used for joints of industrial robots and the like.

Background Art

[0002] A joint portion of an industrial robot is equipped with an electric motor as a driving source of a link and a speed reducer integrally connected to an output shaft of the electric motor. The speed reducer is a device that reduces the low torque and high-speed rotation of the electric motor to high torque and low-speed rotation. Conventionally, as such a speed reducer, a cycloid speed reducer that combines an internal planetary gear mechanism and an isokinetic internal gear mechanism is known.

[0003] The cycloid speed reducer includes, as necessary components: (i) an eccentric shaft provided with an eccentric portion on a part of the shaft, which converts the input rotation into eccentric rotation by the eccentric portion; (ii) one or more planetary gears rotatably attached to the eccentric portion of the eccentric shaft and performing eccentric rotation (revolution around the eccentric shaft) by the rotation of the eccentric shaft; (iii) a cylindrical case that houses the planetary gears and also functions as an internal gear that meshes with a part of the external teeth of the planetary gears; (iv) a carrier rotatably supported by the eccentric shaft and the case on both the front and back sides of the planetary gears, and outputting the rotation of the planetary gears based on the eccentric rotation (low-speed rotation obtained by reducing the high-speed rotation of the eccentric shaft); and (v) a parallel crank mechanism composed of a plurality of holes provided on the plate surface of the planetary gears and a plurality of pins fixed to the carrier and having tip ends engaged with the holes of the planetary gears, which transmits the rotation of the planetary gears to the carrier and rotates the carrier at a low speed.

[0004] A cycloidal gearbox achieves miniaturization, thinning, and compactness by arranging one or more disc-shaped planetary gears and disc-shaped carriers in a stacked configuration on the front and back sides of the planetary gears, and housing these components in a space enclosed by an eccentric shaft and a case. In particular, thinning is achieved by minimizing the height gap between the stacked planetary gears and the two carriers, and miniaturization is achieved by minimizing the diameter of the disc shapes of the planetary gears and carriers.

[0005] For example, Patent Document 1 describes an eccentric oscillating type speed reducer (corresponding to a cycloidal speed reducer) comprising an input shaft with two eccentric parts (corresponding to configuration (i)), two external gears (corresponding to configuration (ii)), a casing with a plurality of internal tooth pins on its inner surface (corresponding to configuration (iii)), two carriers (corresponding to configuration (iv)) positioned on both sides of the two external gears, and a parallel crank mechanism (corresponding to configuration (v)) composed of a plurality of internal pin holes provided in the planetary gears and a plurality of carrier pin holes provided in the carriers, and a plurality of internal pins and carrier pins fixed to the carriers and engaged with the internal pin holes and carrier pin holes. In this speed reducer, the two planetary gears and two carriers are arranged in a stacked manner within the space sandwiched between the input shaft and the casing, making the speed reducer thinner and more compact. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-169628 [Overview of the project] [Problems that the invention aims to solve]

[0007] A cycloidal speed reducer has a configuration in which one or more planetary gears, with some of their external teeth engaged, and two carriers positioned on both the front and back sides of the planetary gears are stacked inside a case. Multiple pins fixed to the carriers engage with multiple holes provided in the planetary gears, thereby outputting the rotation of the planetary gears to the carriers. For this reason, the centers of the pitch circles of the multiple holes in the planetary gears (hereinafter referred to as "engagement holes") (corresponding to the rotation center of the planetary gears) and the centers of the pitch circles of the multiple pins provided in the carriers (corresponding to the rotation center of the carriers) must coincide with a high degree of precision. In addition, the centers of each of the multiple engagement holes in the planetary gears and the centers of each of the multiple fixing holes that fix the pins in the carriers must also coincide with a high degree of precision.

[0008] The planetary gears and carriers used in cycloidal speed reducers are manufactured with predetermined precision in the diameters of the multiple engagement holes and fixing holes, as well as the diameter of the pitch circle between the multiple engagement holes and fixing holes. However, in the process of assembling multiple planetary gears and two carriers in a stacked configuration, there are multiple combinations of rotational alignment of the multiple engagement holes in the planetary gears and the multiple fixing holes in the carriers, and the concentricity of the planetary gears and carriers differs for each combination. Therefore, it is necessary to perform rotational alignment work on the planetary gears and carriers for each combination and adjust them to the rotational position with the least concentricity.

[0009] If the front and back of a planetary gear are determined by the shape of its plate surface, the number of rotational alignments required between the planetary gear and the carrier is equal to the number of engagement holes drilled in the planetary gear. If there is no distinction between the front and back of the planetary gear's plate surface, the planetary gear can be flipped over to align it with the carrier in the rotational direction. This increases the number of alignments, allowing for more precise adjustment of the concentricity between the planetary gear and the carrier. However, conventionally, no technology for designing planetary gears from the perspective of the rotational alignment process described above has been disclosed, nor has there been any description suggesting such a method.

[0010] This invention has been made in view of the above problems, and aims to provide a speed reducer that can adjust the concentricity between planetary gears and carriers with high precision. [Means for solving the problem]

[0011] The reduction gear according to the present invention comprises a case with an internal gear formed on its circular inner surface, an eccentric shaft positioned at the center of the case which converts input rotation into eccentric rotation, and a planetary gear whose external teeth partially mesh with the internal gear of the case and which is rotatably supported by the eccentric shaft and which revolves around the inside of the case while rotating on its own axis due to the eccentric rotation transmitted from the eccentric shaft, wherein the planetary gear has multiple holes formed at equal intervals in the circumferential direction of its plate surface and the same stepped shape in the thickness direction of the plate on the front and back surfaces, and can be used without distinguishing between the front and back sides (Claim 1).

[0012] According to a preferred embodiment of the reduction gear described above, the planetary gear includes a first planetary gear and a second planetary gear that revolve eccentrically in opposite directions to each other, and further comprises a carrier rotatably supported on an eccentric shaft, with a plurality of pins attached to its plate surface corresponding to a plurality of holes in the first and second planetary gears, wherein the planetary gear and the carrier are connected by aligning the rotational positions of the plurality of holes in the first planetary gear and the plurality of holes in the second planetary gear, and the plurality of pins attached to the carrier are rotatably fitted into the plurality of holes in the first and second planetary gears, and the rotation of the planetary gear is output to the carrier by the plurality of holes and the plurality of pins (Claim 2). [Effects of the Invention]

[0013] For example, in the case of a gearbox comprising two planetary gears, a carrier that generates the rotation of these planetary gears, and a parallel crank mechanism consisting of multiple holes formed in the plate surfaces of the two planetary gears and multiple pins fixed to the plate surface of the carrier, with their tips engaging with the holes in the planetary gears, the concentricity between the two planetary gears and the carrier needs to be adjusted to the smallest possible value.

[0014] The concentricity of the two planetary gears and the carrier is adjusted by aligning the rotational alignment of multiple holes in the two planetary gears and multiple holes in the carrier for fixing pins, and then determining the combination of holes in the planetary gears and the carrier that minimizes the concentricity between the planetary gears and the carrier. When mounting the planetary gears to an eccentric shaft, if the planetary gears have a front and back side, the number of combinations of rotational alignment of the holes in the planetary gears and the carrier will be equal to the number of holes in the planetary gears and the carrier.

[0015] According to the reduction gear of the present invention, a planetary gear having multiple holes formed at equal intervals in the circumferential direction of its plate surface has the same stepped shape in the thickness direction on both the front and back surfaces, allowing it to be used without distinguishing between the front and back. Therefore, in the rotational alignment work of the holes in the planetary gear and the holes in the carrier, the front and back of the planetary gear can be reversed to align it with the holes in the carrier. As a result, the number of combinations of rotational alignment of the holes in the planetary gear and the holes in the carrier increases compared to when the planetary gear has a front and back, allowing for more precise adjustment of the concentricity between the planetary gear and the carrier (Claim 1, 2). [Brief explanation of the drawing]

[0016] [Figure 1] This is a side view (front view) of the speed reducer according to the present invention. [Figure 2] This is a top view (plan view) of the gearbox according to the present invention. [Figure 3] This is a view (bottom view) of the gearbox according to the present invention, seen from below. [Figure 4] Figure 2 is a longitudinal cross-section along the CC cutting line. [Figure 5] This is a cross-sectional view along line AA in Figure 1. [Figure 6] This is a cross-sectional view along line BB in Figure 1. [Figure 7] This is a longitudinal cross-section of an eccentric shaft. [Figure 8] This is a view of the upper shaft from below (bottom view). [Figure 9]It is a view of the lower shaft seen from above (plan view). [Figure 10] It is a view for explaining the coupling structure of the upper shaft and the lower shaft. [Figure 11] It is a longitudinal sectional view of a modified example of the eccentric shaft. [Figure 12] It is a view of a modified example of the upper shaft seen from below (bottom view). [Figure 13] It is a view of a modified example of the lower shaft seen from above (plan view). [Figure 14] It is a view for explaining the connection structure when the motor is directly connected to the speed reducer.

Embodiments for Carrying out the Invention

[0017] Referring to the drawings, the speed reducer according to the present invention will be described. The following embodiments are merely illustrative. The following embodiments can be variously modified without departing from the gist of the present invention.

[0018] FIG. 1 is a view of the speed reducer 1 according to the present invention seen from the side (front view of the speed reduction unit 1). FIG. 2 is a view of the speed reducer 1 seen from above (plan view of the speed reduction unit 1). FIG. 3 is a view of the speed reducer 1 seen from below (bottom view of the speed reducer 1). FIG. 4 is a longitudinal sectional view taken along the C-C cutting line of FIG. 2. FIG. 5 is a cross-sectional view taken along the A-A line of FIG. 1, and FIG. 6 is a cross-sectional view taken along the B-B line of FIG. 1. In the following description, the posture of the speed reducer 1 shown in FIGS. 1 and 4 will be taken as the basic posture, and the vertical direction in that basic posture will be referred to as the "vertical direction" or "longitudinal direction", and the horizontal direction will be referred to as the "lateral direction" or "transverse direction" for explanation.

[0019] The gear reducer 1 shown in Figures 1 to 4 is a cycloidal reducer. A cycloidal reducer is a gear reducer that combines an internal planetary gear mechanism and a constant-velocity internal gear mechanism. The internal planetary gear mechanism is a planetary gear mechanism composed of an internal gear and planetary gears that are supported so as to be eccentrically rotatable along the inner circumference of the internal gear, with a portion of the external teeth of the internal gear in contact with or meshing with the internal teeth on the inside of the internal gear. The constant-velocity internal gear mechanism is an internal gear mechanism in which the tooth profile of the internal gear is an arc tooth profile (for example, a pin gear), and the tooth profile of the planetary gears is a tooth profile using an epitrochoidal parallel curve, with a portion of the planetary gears in contact with or meshing with the internal gear.

[0020] A cycloidal gearbox is, (A) A case in which internal teeth are formed by pin gears on the inner circumference of a circle. (B) One or more planetary gears in which external teeth are formed using an epitrochoidal parallel curve, and a portion of these external teeth contact or mesh with a pin gear of the case. (C) A shaft into which high-speed rotation output from an electric motor is input. (D) Eccentric cams attached to or integrally formed with the shaft, which convert the rotation of the shaft into eccentric rotation and transmit it to the planetary gears, causing the planetary gears to rotate along the inner circumference of the case (causing the planetary gears to revolve within the case). (E) The rotation (slow rotation) of the planetary gears inside the case, which is generated by the revolution of the planetary gears, is extracted into a carrier. (F) Rotation transmission mechanism that transmits the rotation of planetary gears to the carrier It is composed of these as its basic components.

[0021] In a cycloidal gearbox, the rotation input to the shaft is converted into eccentric rotation by an eccentric cam and transmitted to the planetary gears, which then revolve within the case, moving their contact position (or meshing position) with the internal teeth of the case. During this revolution, the external teeth of the planetary gears make rolling contact with the pin gears of the case, receiving a reaction force from the pin gears, causing the planetary gears to revolve while simultaneously rotating on their own axis.

[0022] If the orbital speed of the planetary gear is ω1 [rad / s], the rotational speed of the planetary gear is ω2 [rad / s], the number of pin gears in the case is Z1, and the number of external teeth of the planetary gear is Z2, then according to planetary gear theory, the relationship ω2 / ω1 = -(Z1-Z2) / Z2 holds. This relationship shows that the rotational speed ω2 of the planetary gear is the speed obtained by reducing the orbital speed ω1 to (Z1-Z2) / Z2. The rotation of the planetary gear is transmitted to the carrier by the rotation transmission mechanism, and for example, if Z1-Z2=1, then a low-speed rotation is obtained by reducing the high-speed rotation to 1 / Z2 on the carrier.

[0023] The gearbox 1 shown in Figures 1 to 4 includes an eccentric shaft 2, a case 3, planetary gears 4, a carrier 5, a plurality (e.g., 8) of internal pins 6, a cover 7, a ball bearing 8, a needle roller bearing 10, and shim members 11, 12. In this embodiment, the planetary gears 4 consist of two planetary gears 41, 42 arranged vertically, and the carrier 5 also consists of two carriers 51, 52. The planetary gears 4 may consist of one or three or more. The internal pins 6 consist of a rod-shaped pin 61 and one or more collars 62 attached to the pin 61. The cover 7 includes a first cover 71 located on the upper side of the gearbox 1 and a second cover 72 located on the lower side, and the rotation of the planetary gears 4 is taken out by the second cover.

[0024] The ball bearing 8 includes a first ball bearing 81 mounted between the eccentric shaft 2 and the first carrier 51 located below the planetary gear 4, a second ball bearing 82 mounted between the eccentric shaft 2 and the second carrier 52 located above the planetary gear 4, and a third ball bearing 83 mounted between the second carrier 52 and the second cover 72. The first ball bearing 81 and the second ball bearing 82 are bearings of the same size and structure. The third ball bearing 83 is different in size from the first and second ball bearings 81 and 82, but has the same basic structure.

[0025] In the following explanation, to allow for intuitive distinction between the first carrier 51 and the second carrier 52, the first carrier 51 will be referred to as the "lower carrier 51" and the second carrier 52 as the "upper carrier 52". When the lower carrier 51 and the upper carrier 52 are not distinguished, they will be referred to as "carrier 5". To allow for intuitive distinction between the first ball bearing 81 and the second ball bearing 82, the first ball bearing 81 will be referred to as the "lower ball bearing 81" and the second ball bearing 82 as the "upper ball bearing 82". When the basic structure of the lower ball bearing 81, the upper ball bearing 82, and the ball bearing 83 are not distinguished, they will be referred to as "ball bearing 8".

[0026] The needle roller bearing 10 includes a first needle roller bearing 10A mounted between the eccentric shaft 2 and the first planetary gear 41 located on the upper side, and a second needle roller bearing 10B mounted between the eccentric shaft 2 and the second planetary gear 42 located on the lower side. Needle roller bearings 10A and 10B are identical needle roller bearings.

[0027] In the following explanation, to allow for intuitive distinction between the first planetary gear 41 and the second planetary gear 42, the first planetary gear 41 will be referred to as the "upper planetary gear 41" and the second planetary gear 42 as the "lower planetary gear 42". When the upper planetary gear 41 and the lower planetary gear 42 are not distinguished, they will be referred to as "planetary gear 4". To allow for intuitive distinction between the first needle roller bearing 10A and the second needle roller bearing 10B, the first needle roller bearing 10A will be referred to as the "upper needle roller bearing 10A" and the second needle roller bearing 10B as the "lower needle roller bearing 10B". When the upper needle roller bearing 10A and the lower needle roller bearing 10B are not distinguished, they will be referred to as "needle roller bearing 10".

[0028] The first shim member 11 includes three ring-shaped shim members 11A, 11B, and 11C. Shim members 11A, 11B, and 11C are the same shim member. The second shim member 12 includes two ring-shaped shim members 12A and 12B, which have a larger diameter than the first shim member 11. Shim members 12A and 12B are the same shim member.

[0029] In the following explanation, to allow for intuitive distinction between the first shim member 11 and the second shim member 12, the first shim member 11 will be referred to as the "shim ring 11" and the second shim member 12 as the "shim plate 12". When the three shim rings 11A, 11B, and 11C are not distinguished, they will be referred to as the "shim ring 11", and when the two shim plates 12A and 12B are not distinguished, they will be referred to as the "shim plate 12".

[0030] The eccentric shaft 2 is a component corresponding to the shaft (C) and eccentric cam (D) of the constituent elements. The eccentric shaft 2 functions to convert the high-speed rotation input from the electric motor (not shown) into two eccentric high-speed rotations with a phase difference of 180 degrees, transmitting one eccentric rotation to the upper planetary gear 41 and the other eccentric rotation to the lower planetary gear 42. Figure 7 is a longitudinal cross-sectional view of the eccentric shaft. As shown in Figure 7, the eccentric shaft 2 is composed of two hollow shafts 21 and 22 with different axial lengths. The axial length L1 [mm] of the first shaft 21 is slightly longer than the axial length L2 [mm] of the second shaft 22.

[0031] In the basic configuration of the reduction gear 1, the first shaft 21 is positioned on the upper half of the eccentric shaft 2, and the second shaft 22 is positioned on the lower half of the eccentric shaft 2. The first shaft 21 and the second shaft 22 are joined by fitting. In the following description, in order to intuitively distinguish between the first shaft 21 and the second shaft 22, the first shaft 21 will be referred to as the "upper shaft 21" and the second shaft 22 as the "lower shaft 22".

[0032] Figure 8 is a view of the upper shaft 21 from below (bottom view), and Figure 9 is a view of the lower shaft 22 from above (top view). Figure 10 is a diagram illustrating the fitting structure of the upper shaft 21 and the lower shaft 22. As shown in Figures 8 and 9, the upper shaft 21 and the lower shaft 22 are hollow cylindrical shapes. A first eccentric portion 21A is provided at the lower end of the upper shaft 21, and a second eccentric portion 22A is provided at the upper end of the lower shaft 22.

[0033] The first eccentric portion 21A and the second eccentric portion 22A are the parts that convert the rotation of the eccentric shaft 2 into eccentric rotation, and correspond to the eccentric cam (D). The two eccentric portions 21A and 22A are provided in correspondence with the two planetary gears 41 and 42 to which the eccentric rotation is transmitted. In the following description, in order to intuitively distinguish between the first eccentric portion 21A and the second eccentric portion 22A, the first eccentric portion 21A will be referred to as the "upper eccentric portion 21A" and the second eccentric portion 22A as the "lower eccentric portion 22A".

[0034] The upper eccentric portion 21A is formed by projecting (or bulging) an annular member having a predetermined thickness onto the outer surface of the upper shaft 21. The thickness of the upper eccentric portion 21A is approximately the same as the thickness of the upper needle roller bearing 10A. If the difference between the radius r1 of the upper eccentric portion 21A and the radius r0 of the upper shaft 21 is Δr (=r1-r0) [mm], then the center Oa of the upper eccentric portion 21A is eccentric by Δr with respect to the hollow center O of the upper shaft 21 (the rotation center O of the eccentric shaft 2) (see Figure 7).

[0035] The lower eccentric portion 22A, like the upper eccentric portion 21A, is formed by projecting (or bulging) an annular member having a predetermined thickness onto the outer surface of the lower shaft 22. The center Ob of the lower eccentric portion 22A is eccentric by Δr with respect to the center O of the lower shaft 22 (the rotation center O of the eccentric shaft 2) (see Figure 7). When the eccentric shaft 2 rotates, the upper eccentric portion 21A and the lower eccentric portion 22A rotate around the rotation center O, so both eccentric portions 21A and 22A function as eccentric cams.

[0036] A fitting portion 211 is formed at the lower end of the upper shaft 21 (see Figure 8), and a fitting portion 221 is formed at the upper end of the lower shaft 22 (see Figure 9). The fitting portions 211 and 221 are a mechanism for fitting the upper shaft 21 and the lower shaft 22 together. The fitting portion 211 of the upper shaft 21 consists of a plurality of (for example, 8) positioning holes 211A drilled at equal intervals in the thickened part of the lower end surface of the upper shaft 21, and a circular recess 211B drilled in the lower end surface of the upper shaft 21, having a diameter intermediate between the hollow inner diameter and the hollow outer diameter (see Figures 8 and 10). The plurality of positioning holes 211A are arranged at equal intervals along the edge of the recess 211B.

[0037] The fitting portion 221 of the lower shaft 22 consists of a plurality (for example, 8) of positioning holes 221A drilled at equal intervals in the thickened portion of the upper end surface of the lower shaft 22, and a protrusion 221B projecting from the upper end surface of the lower shaft 22, having the same diameter as the inner diameter of the recess 211A (see Figures 9 and 10). The plurality of positioning holes 221A are arranged at equal intervals along the edge of the protrusion 221B.

[0038] Positioning holes 211A and 221A serve to determine the rotational position of the upper shaft 21 and the lower shaft 22 when they are fitted together. Positioning holes 211A and 221A also function as press-fit holes for press-fit pins 23 to fix the fitted state. When assembling the eccentric shaft 2, the fitting portions 211 and 221 are fitted together so that the upper shaft 21 and the lower shaft 22 are eccentric in opposite directions.

[0039] In Figure 8, if the eight positioning holes 211A of the upper shaft 21 are numbered 1, 2, 3, ... 8 counterclockwise starting from the positioning hole 211A located eccentrically from the center Oa (the rightmost positioning hole 211A in Figure 8), then positioning hole 211A labeled "No. 1" is the reference positioning hole. In Figure 9, if the eight positioning holes 221A of the lower shaft 22 are numbered 1, 2, 3, ... 8 counterclockwise starting from the positioning hole 221A located eccentrically from the center Ob, then positioning hole 221A labeled "No. 5" (the rightmost positioning hole 221A in Figure 9) is the reference positioning hole.

[0040] The eccentric shaft 2 is assembled according to the following procedure. (Step 1) Press-fit pins 23 are pressed into each of the eight positioning holes 221A of the lower shaft 22. (Step 2) The upper shaft 21 is positioned above the lower shaft 22 into which the press-fit pin 23 has been press-fitted, aligning the positioning hole 211A of the upper shaft 21 with the positioning hole 221A of the lower shaft 22. In this alignment, the reference hole of the upper shaft 21 and the reference hole of the lower shaft 22 are aligned. (Step 3) The upper shaft 21 is lowered and the recess 211B of the upper shaft 21 is fitted into the protrusion 221B of the lower shaft 22 to manufacture the eccentric shaft 2. At this time, the upper ends of the eight press-fit pins 23 that are press-fitted into the lower shaft 22 are press-fitted into the eight positioning holes 211A of the upper shaft 21.

[0041] The procedure described above involves fitting the upper shaft 21 onto the lower shaft 22, but it may also be a procedure where the lower shaft 22 is fitted onto the upper shaft 21. In the assembly of the eccentric shaft 2 described above, by simply aligning the reference hole of the positioning hole 221A of the lower shaft 22 with the reference hole of the positioning hole 211A of the upper shaft 21, the hollow center O of the upper shaft 21 and the hollow center O of the lower shaft 22 can be aligned, and the upper eccentric portion 21A and the lower eccentric portion 22A can be separated by Δr [mm] in opposite directions with respect to the rotation center O of the eccentric shaft 2.

[0042] In this embodiment, the number of positioning holes 211A and 221A is set to eight, but it is not limited to eight. If the number of positioning holes 211A and 221A is increased, the spacing between the holes becomes narrower, which reduces the strength of the fitting portions 211 and 221 of the eccentric shaft 2. If the number is decreased, the spacing between the holes becomes wider, which reduces the fitting strength of the fitting portions of the eccentric shaft 2. In this embodiment, the appropriate number of positioning holes 211A and 221A is set to eight, taking both problems into consideration.

[0043] When rotational force is input from an electric motor to the eccentric shaft 2, either directly or indirectly via an intermediate reduction gear, the eccentric shaft 2 rotates around the rotation center O, but the upper eccentric portion 21A and the lower eccentric portion 22A rotate eccentrically around the rotation center O. Since the center Oa of the upper eccentric portion 21A and the center Ob of the lower eccentric portion 22A are separated in opposite directions, the upper eccentric portion 21A and the lower eccentric portion 22A rotate eccentrically around the rotation center O with a phase difference of 180 degrees. Therefore, the upper eccentric portion 21A and the lower eccentric portion 22A function as eccentric cams that convert the high-speed rotation input from an electric motor (not shown) into two eccentric rotations with a phase difference of 180 degrees.

[0044] The eccentric shaft 2 shown in Figures 7 to 10 has a fitting portion 211 of the upper shaft 21 and a fitting portion 221 of the lower shaft 22 composed of a circular recess 211B and a cylindrical protrusion 221B. However, the connection between the upper shaft 21 and the lower shaft 22 may also be made by a fitting using an involute spline (hereinafter referred to as "spline fitting").

[0045] Figures 11 to 13 illustrate a modified example in which the upper shaft 21 and the lower shaft 22 are joined by a spline fit. Figure 11 is a longitudinal cross-sectional view of the modified eccentric shaft 2. Figure 12 is a view from below (bottom view) of the modified upper shaft 21, and Figure 13 is a view from above (top view) of the modified lower shaft 22.

[0046] The modified versions of the eccentric shaft 2 shown in Figures 11 to 13 differ only from the eccentric shaft 2 shown in Figures 8 to 10 in the coupling structure between the upper shaft 21 and the lower shaft 22. Therefore, the following explanation will only cover the coupling structure.

[0047] A fitting portion 212 is formed at the lower end of the upper shaft 21 (see Figures 11 and 12), and a fitting portion 222 is formed at the upper end of the lower shaft 22 (see Figures 11 and 13). The fitting portion 212 of the upper shaft 21 is a male spline 212A with external teeth formed by an involute curve (see Figure 12). The fitting portion 222 of the lower shaft 22 is a female spline 222A with internal teeth formed by an involute curve (see Figure 13). The shape of the internal teeth of the female spline 222A is substantially the same as the shape of the external teeth of the male spline 212A, and the fitting portion 212 of the upper shaft 21 and the fitting portion 222 of the lower shaft 22 are connected by fitting the male spline 212A into the female spline 222A (see Figure 11).

[0048] The fitting method shown in Figures 7 to 10 consists of a recess 211B, a protrusion 221B, and multiple press-fit pins 23, but the spline fitting method shown in Figures 11 to 13 has the advantage of a simpler fitting structure because it consists only of a male spline and a female spline. Furthermore, the formation of the male spline and the female spline using involute curves is easy to process, which has the advantage of making it easier to manufacture the upper shaft 21 and the lower shaft 22.

[0049] In Figure 11, a male spline 212B using an involute curve is also formed at the upper end of the upper shaft 21. This male spline 212B is a mechanism for connecting, for example, a coupling to directly connect the rotor of an electric motor (see coupling 15 in Figure 14). The coupling will be described later.

[0050] The eccentric shaft 2 is manufactured using carbon steel (for example, chromium-molybdenum steel). The eccentric shaft 2 is manufactured using the following procedure. (Step 11) The upper shaft 21 and lower shaft 22 are manufactured by machining carbon steel into a predetermined cylindrical shape. In this machining process, the fitting portion 211 of the upper shaft 21 and the fitting portion 221 of the lower shaft 22 are also formed integrally. (Step 12) The upper shaft 21 and lower shaft 22 manufactured in (Step 11) are subjected to the following heat treatments in this order: carburizing, nitriding, sub-zero treatment, and tempering. (Step 13) The fitting portion 211 of the upper shaft 21 and the fitting portion 221 of the lower shaft 22 are subjected to cylindrical grinding. (Step 14) The positioning hole 211A of the upper shaft 21 and the positioning hole 221A of the lower shaft 22 are polished. (Step 15) The fitting portion 211 of the upper shaft 21 and the fitting portion 221 of the lower shaft 22 are fitted together and integrated using the procedure described in (Step 1) to (Step 3) above (assembly of the eccentric shaft 2). (Step 16) The surface of the eccentric shaft 2 assembled in (Step 15) (the outer surface other than the eccentric parts 21A and 22A and the entire surface of the eccentric parts 21A and 22A) is polished to a finish. (Step 17) After the eccentric shaft 2 has been finished with polishing, shot peening is performed, followed by smoothing and oil reservoir treatment in that order.

[0051] Step 12, carburizing and nitriding, is a heat treatment in which carbon (C) and nitrogen (N) are simultaneously impregnated into the surface of carbon steel to increase the carbon concentration, followed by quenching and tempering. Carburizing and nitriding improves the toughness and wear resistance of the upper shaft 21 and lower shaft 22, thereby improving their strength. Sub-zero treatment is a process in which the steel material is rapidly cooled to below -80°C after quenching, transforming the austemite structure remaining after quenching into a martensitic structure. Sub-zero treatment further hardens the upper shaft 21 and lower shaft 22, improving their strength and fatigue resistance.

[0052] Tempering is a process that involves reheating after quenching to adjust hardness and increase toughness and ductility. The tempering process stabilizes the structure of the upper shaft 21 and lower shaft 22 and improves their toughness. (Step 12) This process produces high-strength upper shaft 21 and lower shaft 22 with excellent toughness and wear resistance.

[0053] The cylindrical grinding in (Step 13) is a process to smooth the fitting operation of the fitting portion 211 of the upper shaft 21 and the fitting portion 221 of the lower shaft 22, and to ensure the alignment accuracy of the center O of the upper shaft 21 and the center O of the lower shaft 22. The grinding of the positioning holes 211A and 221A in (Step 14) is a grinding process to ensure the press-fitting accuracy when the positioning hole 211A of the upper shaft 21 and the positioning hole 221A of the lower shaft 22 are aligned and the press-fit pin 23 is press-fitted into both positioning holes 211A and 221A.

[0054] In step 15, the eccentric shaft 2 is assembled by aligning the positioning hole 211A of the upper shaft 21 with the positioning hole 221A of the lower shaft 22, and then pressing in the press-fit pins 23 into the positioning holes 211A and 221A, thereby connecting the upper shaft 21 and the lower shaft 22 in the longitudinal direction (axial direction of the eccentric shaft 2). When the fitting portion 211 of the upper shaft 21 and the fitting portion 221 of the lower shaft 22 are fitted together, the axis center Oa of the eccentric portion 21A of the upper shaft 21 and the axis center Ob of the eccentric portion 22A of the lower shaft 22 are separated by a small distance 2Δr [mm] on the diameter of the hollow shaft, as described above (see Figure 7). In other words, the eccentric portion 21A of the eccentric shaft 2 is eccentric by +Δr [mm] from the rotation center O of the eccentric shaft 2, and the fitting portion 22A of the eccentric shaft 2 is eccentric by -Δr [mm] from the rotation center O of the eccentric shaft 2.

[0055] (Step 17) Shot peening is a surface treatment that increases the strength of a metal surface by projecting a large number of ferrous or non-ferrous metal abrasives (microspheres) onto the metal surface at high speed. By performing shot peening on the eccentric shaft 2 that has been finished polished in (Step 16), the hardness of the surface of the eccentric shaft 2 is strengthened and the torsional rigidity of the eccentric shaft 2 is increased. In addition, impurities adhering to the surface of the eccentric shaft 2 and fine burrs that have formed on the surface of the eccentric shaft 2 are removed, and abnormal layers in the surface structure of the eccentric shaft 2 are eliminated. Since countless depressions (marks) are formed on the surface of the eccentric shaft 2, the eccentric shaft 2 is also given effects such as improved heat dissipation, weight reduction, and reduced fluid resistance (oil retention effect).

[0056] Step 17, smoothing polishing, is a surface treatment to make the surface of the eccentric shaft 2 smooth (to a mirror finish). The surface of the eccentric shaft 2 is finished to a mirror finish using polishing methods such as buffing or electrolytic polishing. By performing smoothing polishing on the surface of the eccentric shaft 2, impurities are prevented from adhering to the eccentric shaft 2, rust prevention and cleaning are performed. Step 17, oil reservoir processing, is a process in which a few micrometers in size depressions are made on a flat surface using a scraper tool. These depressions are for accumulating lubricating oil, and by creating these depressions, ringing during the rotational movement of the eccentric shaft 2 is prevented, and lubricating oil is accumulated on the surface, enabling the eccentric shaft 2 to rotate smoothly.

[0057] The above-described procedure for manufacturing the eccentric shaft 2 is for the embodiment shown in Figures 7 to 10, but the same procedure is used to manufacture the eccentric shaft 2 for the modified examples shown in Figures 11 to 13.

[0058] Case 3 is a component corresponding to case (A) of the components. Case 3 functions as an internal gear of the internal planetary gear mechanism and also serves to protect the side of the reducer 1 by housing the upper planetary gear 41 and the lower planetary gear 42. Case 3 has a hollow cylindrical shape, and its height is slightly larger than the height of the upper planetary gear 41 and the lower planetary gear 42 attached to the eccentric shaft 2 (see Figures 4 and 5). Since the upper planetary gear 41 and the lower planetary gear 42 are housed in the hollow portion of Case 3, the inner diameter of the hollow portion of Case 3 is approximately the same as the diameter of the circular orbit traced by the outermost point when the side planetary gear 41 and the lower planetary gear 42 rotate eccentrically inside Case 3.

[0059] Multiple grooves 3A (50 in the example of Figures 5 and 6) are formed on the inner surface of case 3. The grooves 3A have a semicircular cross-sectional shape and extend in the height direction of case 3 (see Figure 4). A rod-shaped pin 31, which functions as a pin gear, is rotatably fitted into each groove 3A. The length of the pin 31 is approximately the same as the length of the groove 3A. In the example of Figures 5 and 6, case 3 is provided with 50 internal teeth. The pins 31 are pins (internal teeth) that engage with the arc-shaped external teeth formed on the planetary gears 41 and 42, and are located on the outer circumference of the upper planetary gear 41 and the lower planetary gear 42, so in the following description they will be referred to as "outer circumference pins 31".

[0060] A flange 3B is provided protruding from the center of the height direction of the outer surface of case 3. The flange 3B is a flange used to sandwich and fix case 3 between the upper cover 71 and the lower cover 72. The surface that forms a step between the outer surface of case 3 and the flange 3B (hereinafter referred to as the "step surface") is a press-fit surface into which the upper cover 71 and the lower cover 72 are press-fitted when the upper cover 71 and the lower cover 72 are sandwiched and fixed to case 3 (see Figure 4). The step surface of case 3 is polished so that its concentricity with the pitch circle diameter (hereinafter referred to as "PCD") of the multiple grooves 3A of case 3 is within a predetermined range.

[0061] The upper and lower stepped surfaces of case 3 are at the same height, and the vertical cross-sectional shape of case 3 is symmetrical in the height direction (see Figure 4). The flange 3B is provided with multiple (e.g., 10) positioning holes 32 (see Figure 5). The multiple positioning holes 32 serve to align the rotational position of these parts when case 3 is sandwiched and fixed between the upper cover 71 and the lower cover 72, and also function as holes for inserting fixing pins. As will be described later, the upper cover 71 is also provided with multiple (e.g., 10) positioning holes 71B, and the lower cover 72 is also provided with multiple (e.g., 10) positioning holes 72B. The positioning holes 71B and 72B also serve the same function as the positioning holes 32 of case 3.

[0062] Here, we will explain the alignment of the upper cover 71, the lower cover 72, and the case 3 in the rotational direction.

[0063] The reduction gear 1 consists of a gear mechanism that eccentrically rotates two planetary gears 41 and 42, which are arranged concentrically with the eccentric shaft 2 inside an annular case 3, and outputs the rotation generated in the two planetary gears 41 and 42 by this eccentric rotation (a low-speed rotation obtained by reducing the high-speed rotation input to the eccentric shaft 2) to two carriers 51 and 52, which are arranged concentrically with the eccentric shaft 2.

[0064] In this configuration, two planetary gears 41 and 42, two carriers 51 and 52, and case 3 are arranged in a stacked and concentric manner with respect to the center of the eccentric shaft 2. Therefore, the concentricity of these components greatly affects the characteristics of the reducer 1, such as rotational efficiency. When disc-shaped components such as planetary gears 4 and carriers 5 are attached to the eccentric shaft 2 in a stacked manner, the concentricity of these components changes depending on their relative positions in the direction of rotation. Therefore, during the assembly of the reducer 1, it is necessary to adjust them to the relative positions in the direction of rotation that minimize the concentricity.

[0065] The same applies to the carrier 5, which is rotatably mounted on the eccentric shaft 2, and the case 3, which rotatably supports the outer surface of the carrier 5. The concentricity of these parts changes when the relative position of the carrier 5 with respect to the case 3 in the direction of rotation is changed. Therefore, during the assembly of the reduction gear 1, it is necessary to adjust the relative position of the carrier 5 with respect to the case 3 in the direction of rotation to a position where the concentricity of the two parts is minimized.

[0066] One method for changing the relative rotational position of the planetary gears 4 and carrier 5, which are arranged in a stacked configuration, is to provide multiple positioning holes (through holes) on the plate surfaces of the planetary gears 4 and carrier 5 at equal intervals in the circumferential direction using the same PCD. After overlapping the positioning holes of the planetary gears 4 and carrier 5, the carrier 5 is rotated in the rotational direction relative to the planetary gears 4 by the pitch of the positioning holes, changing the position to various combinations in which the positioning holes of both parts overlap.

[0067] As described later, the upper planetary gear 41 and the lower planetary gear 42 are each provided with multiple mounting holes 41B and multiple mounting holes 42B, and the mounting holes 41B and 42B also function as positioning holes as described above. Also, as described later, the lower carrier 51 and the upper carrier 52 are each provided with multiple mounting holes 51A and multiple mounting holes 52A, and the mounting holes 51A and 52A also function as positioning holes as described above.

[0068] In the case of case 3 and carrier 5, since case 3 rotatably supports the outer surface of carrier 5 via bearings, it is not possible to provide positioning holes in case 3 and carrier 5 to change the relative position of the two components in the rotational direction. Therefore, in the reducer 1 according to this embodiment, a lower cover 72 is provided on the lower side of case 3, and this lower cover 72 and lower carrier 51 are connected by a bearing section 9 having the same structure as the bearing structure of a cross roller bearing. The relative position of case 3 and lower cover 72 in the rotational direction is then changed in the manner described above. The multiple positioning holes 32 provided in the flange 3B of case 3 and the multiple positioning holes 72B provided in the lower cover 72 are holes used during the assembly of the reducer 1 to change the relative position of case 3 and lower cover 72 in the rotational direction, adjust them to a position where the concentricity of the two components is minimized, and then fix them in that position. The configuration of connecting the lower cover 72 and lower carrier 51 with the bearing section 9 will be described later.

[0069] As will be described later, the upper cover 71 has a disc shape (see Figure 2), and the lower cover 72 has an annular shape (see Figure 3). When the cylindrical case 3 is sandwiched and fixed between the disc-shaped upper cover 71 and the annular-shaped lower cover 72, it is necessary to make the centers of the three parts coincide as much as possible (to make the concentricity of the three parts as small as possible). In the reduction gear 1 according to this embodiment, during the assembly of the upper cover 71, lower cover 72 and case 3, the position where the positioning hole 32 of case 3, the positioning hole 71B of the upper cover 71, and the positioning hole 72B of the lower cover 72 overlap is changed relatively in the rotational direction so that the concentricity of the three parts falls within a predetermined range. The assembly method of the upper cover 71, lower cover 72, and case 3 will be described later.

[0070] Ten positioning holes 32 are provided at equal intervals in the circumferential direction of the flange 3B. By having 10 positioning holes 32, the shape of the case 3 in plan view is symmetrical in both the vertical and horizontal directions (see Figure 5). In this embodiment, the number of positioning holes 32 is 10, but any number other than 10 is acceptable as long as the shape of the case 3 in plan view is symmetrical in the vertical and horizontal directions. Since the vertical cross-sectional shape of the case 3 is symmetrical in the height direction, and the shape in plan view is symmetrical in both the vertical and horizontal directions, the case 3 can be used without distinguishing between the front and back when assembling the reducer 1.

[0071] Case 3 also functions as a protective component for the reducer 1, and is therefore manufactured using cast iron, which has excellent mechanical strength, wear resistance, heat resistance, and vibration damping properties. For example, Case 3 is manufactured using tough cast iron (e.g., ductile cast iron) with enhanced tensile strength and ductility.

[0072] Case 3 was manufactured using the following procedure. (Step 21) A cylindrical case 3 is manufactured by machining ductile cast iron, in which multiple semicircular grooves 3A are formed on the inner surface at equal intervals in the circumferential direction, and a flange 3B is formed in the center of the outer surface in the height direction. (Step 22) Shot peen the entire surface of Case 3. (Step 23) After performing a smoothing surface treatment on the semicircular groove surface (see Figure 5) of each groove 3A in case 3, an oil reservoir surface treatment is performed.

[0073] The shot peening method in (Step 22) is the same as the shot peening method in (Step 16) in the manufacturing process of the eccentric shaft 2 described above. In (Step 22), the surface strength of case 3 is improved and residual stress is removed by shot peening. The smoothing and oil reservoir processing method in (Step 23) is the same as the smoothing and oil reservoir processing method in (Step 16). In (Step 23), the surface treatment of smoothing and oil reservoir processing improves the lubricating oil retention capacity of the groove 3A and reduces frictional resistance. By manufacturing case 3 in (Steps 21) to (Step 23), a case 3 with high strength and vibration damping properties is obtained while retaining the characteristics of ductile cast iron inside the part.

[0074] The outer periphery pin 31 is manufactured, for example, by machining high-carbon chromium bearing steel. Since the outer periphery pin 31 is rotatably fitted into a groove 3A formed on the inner surface of the case 3, the diameter of the outer periphery pin 31 is slightly smaller than the diameter of the groove 3A, and the length of the outer periphery pin 31 is approximately the same as the length of the groove 3A.

[0075] The outer pin 31 is manufactured using the following procedure. (Step 31) A rod-shaped outer pin 31 having a predetermined shaft diameter and length is manufactured by machining a carbon-chromium bearing steel material. (Step 32) The outer pin 31 manufactured in (Step 31) is subjected to heat treatment in the order of hardening, sub-zero treatment, and tempering to strengthen the outer pin 31. (Step 33) Shot peening is performed on the entire surface of the outer pin 31 to strengthen the surface strength and torsional rigidity of the outer pin 31. (Step 34) Surface treatments of the outer surface of the outer pin 31 are performed in this order: smoothing and oil reservoir processing, to improve the lubricating oil retention capacity of the outer pin 31 and reduce frictional resistance.

[0076] The heat treatment method in (Step 32) is the same as the quenching, sub-zero treatment, and tempering treatment method in (Step 12) in the manufacturing process of the eccentric shaft 2 described above. The shot peening method in (Step 33) is the same as the shot peening method in (Step 16) in the manufacturing process of the eccentric shaft 2. The surface treatment method in (Step 34) is the same as the smoothing polishing and oil reservoir processing method in (Step 16).

[0077] The outer circumferential pin 31 manufactured in steps 31 to 34 has been adjusted to the desired level in terms of strength and rolling friction resistance in rolling contact with the two planetary gears 41 and 42. Furthermore, by adjusting the shaft diameter of the outer circumferential pin 31 with high precision, the meshing accuracy with the two planetary gears 41 and 42 (for example, the accuracy of the backlash characteristics) is adjusted to the desired level.

[0078] The upper planetary gear 41 and the lower planetary gear 42 are components corresponding to the planetary gear (B) of the constituent element. The reason why planetary gear (B) is composed of two planetary gears is that if planetary gear (B) is rotated eccentrically by the high-speed rotation of the constituent element shaft (C), bending stress will be generated in shaft (C). By composing planetary gear (B) with two planetary gears that rotate eccentrically with a phase difference of 180 degrees, the bending stress generated in shaft is suppressed, and only torque is generated in the two planetary gears 41 and 42. In this embodiment, the number of planetary gears 4 is set to two, but it may be three or more. If the number of planetary gears 4 is three or more, eccentric portions corresponding to the number of planetary gears 4 are provided on the eccentric shaft 2, and the phase difference of the eccentric rotation of each eccentric portion is set to 360 / m (m is the number of gears).

[0079] The upper planetary gear 41 and the lower planetary gear 42 have the same size and shape. As shown in Figures 5 and 6, the planetary gear 4 is a disc-shaped gear with external teeth 4C formed on its outer circumference using an epitrochoidal parallel curve tooth profile. A mounting hole 4A (mounting hole 41A for the upper planetary gear 41, and mounting hole 42A for the lower planetary gear 42) is formed in the center of the planetary gear 4 for rotatably mounting the planetary gear 4 on the eccentric shaft 2 via a needle roller bearing 10. Multiple (for example, 8) insertion holes 4B for inserting an internal pin 6 are formed at equal intervals on the plate surface of the planetary gear 4 in the circumferential direction.

[0080] As shown in Figure 4, the upper planetary gear 41 is mounted on the eccentric shaft 2 via an upper needle roller bearing 10A at a position slightly below the axial center (around the fitting portion 211 of the upper shaft 21; hereinafter referred to as the "upper planetary gear mounting position"). The lower planetary gear 42 is mounted on the eccentric shaft 2 via a lower needle roller bearing 10B at a position lower than the upper planetary gear mounting position (hereinafter referred to as the "lower planetary gear mounting position"). The upper needle roller bearing 10A is a component for rotatably mounting the upper planetary gear 41 on the eccentric shaft 2, and the lower needle roller bearing 10B is a component for rotatably mounting the lower planetary gear 42 on the eccentric shaft 2. The upper needle roller bearing 10A and the lower needle roller bearing 10B have the same size and shape.

[0081] The needle roller bearing 10 is a bearing that uses elongated cylindrical rollers (needle rollers) as rolling elements. The needle roller bearing 10 consists of a plurality of needle rollers and a cage that holds the plurality of needle rollers in a ring-shaped arrangement at equal intervals, allowing each needle roller to rotate freely. The inner diameter of the ring-shaped arrangement of the needle rollers in the needle roller bearing 10 is approximately the same as the outer diameter of the eccentric shaft 2, and the outer diameter of the same roller arrangement is approximately the same as the inner diameter of the mounting hole 4A of the planetary gear 4. The thickness of the needle roller bearing 10 is slightly larger than the thickness of the planetary gear 4.

[0082] Since the needle roller bearing 10 is a caged needle roller bearing without an inner ring and an outer ring, the upper needle roller bearing 10A is mounted on the eccentric shaft 2 by press-fitting the roller row into the upper planetary gear mounting position, and the lower needle roller bearing 10B is mounted on the eccentric shaft 2 by press-fitting the roller row into the lower planetary gear mounting position. The upper planetary gear 41 is mounted on the upper needle roller bearing 10A by press-fitting the mounting hole 41A into the roller row of the upper needle roller bearing 10A mounted on the eccentric shaft 2. The lower planetary gear 42 is mounted on the lower needle roller bearing 10B by press-fitting the mounting hole 42B into the roller row of the lower needle roller bearing 10B mounted on the eccentric shaft 2.

[0083] In the mounting structure of the planetary gear 4 to the eccentric shaft 2, the roller row of the needle roller bearing 10 is in direct contact with the outer surface of the eccentric shaft 2 and the mounting hole 4A of the planetary gear 4. Therefore, the eccentric rotation of the eccentric shaft 2 is directly transmitted to the planetary gear 4, allowing the planetary gear 4 to rotate eccentrically with high efficiency.

[0084] A groove is provided between the mounting position of the upper planetary gear and the mounting position of the lower planetary gear on the eccentric shaft 2, and a shim ring 11B is fitted into this groove. As will be described later, the lower ball bearing 81 and the upper ball bearing 82 are mounted below the lower planetary gear mounting position and above the upper planetary gear mounting position on the eccentric shaft 2, but a groove is provided between the upper needle roller bearing 10A and the upper ball bearing 82 on the upper shaft 21, and a shim ring 11A is fitted into this groove. In addition, a groove is provided between the lower needle roller bearing 10B and the lower ball bearing 81 on the lower shaft 22, and a shim ring 11C is fitted into this groove.

[0085] The three shim rings 11A, 11B, and 11C are identical in shape and size. The shim rings 11A, 11B, and 11C prevent the needle roller bearing 10, which is press-fitted onto the eccentric shaft 2, from spinning freely. Shim ring 11B prevents contact between the upper needle roller bearing 10A and the lower needle roller bearing 10B during rotation. Shim ring 11A stabilizes the rotation of the rollers in both bearings by applying preload to the upper needle roller bearing 10A and the upper ball bearing 82, thereby suppressing vibrations and noise generated in both bearings 10A and 82. Shim ring 11C stabilizes the rotation of the rollers in both bearings by applying preload to the lower needle roller bearing 10B and the lower ball bearing 81, thereby suppressing vibrations and noise generated in both bearings 10B and 81.

[0086] The shim ring 11 is manufactured using a vibration-damping alloy with excellent vibration damping properties. While flake graphite cast iron or ductile cast iron can be used as the vibration-damping alloy, flake graphite cast iron is preferred. For example, the shim ring 11 is manufactured by machining flake graphite cast iron to create a shim ring of a predetermined ring shape. Then, heat treatment (e.g., normalizing, gas nitriding, gas nitriding) is performed to improve the material's strength and remove residual stress, and polishing is used to adjust it to a predetermined thickness (wall thickness). The thickness of the shim ring 11A is such that an appropriate preload is applied to the upper needle roller bearing 10A and the upper ball bearing 82, and the thickness of the shim ring 11C is such that an appropriate preload is applied to the lower needle roller bearing 10B and the lower ball bearing 81. By appropriately adjusting the thickness of the shim rings 11A and 11C, an appropriate axial preload can be applied to the upper and lower needle roller bearings 10A and 10B and the upper and lower ball bearings 81 and 82. The surface strength of the shim ring 11 is further improved by shot peening, and the vibration damping properties of the vibration damping alloy (e.g., flake graphite cast iron) are maintained.

[0087] The planetary gear 4, mounted on the eccentric shaft 2 via a needle roller bearing 10, has some of its external teeth 4C in contact with or meshing with the outer peripheral pin 31 of the case 3. The position where the upper planetary gear 41 and the outer peripheral pin 31 make contact or mesh (hereinafter referred to as "meshing position K1") is where a straight line extending from the rotation center O of the eccentric shaft 2 towards the center Oa of the upper eccentric portion 21A intersects the inner surface of the case 3. The position where the lower planetary gear 42 and the outer peripheral pin 31 make contact or mesh (hereinafter referred to as "meshing position K2") is where a straight line extending from the rotation center O of the eccentric shaft 2 towards the center Ob of the lower eccentric portion 22A intersects the inner surface of the case 3. Since the center Oa of the upper eccentric portion 21A and the center Ob of the lower eccentric portion 22A are eccentric in opposite directions with respect to the rotation center O, the meshing positions K1 and K2 are located 180 degrees apart on the inner surface of case 3.

[0088] The carrier 5, composed of an upper carrier 52 and a lower carrier 51, is a component corresponding to the carrier (E) of the constituent elements. The multiple (e.g., 8) mounting holes 4B and multiple (e.g., 8) internal pins 6 of the planetary gear 4 are components corresponding to the rotation transmission mechanism (F) of the constituent elements. The multiple mounting holes 4B and multiple internal pins 6 constitute a parallel crank mechanism and transmit the rotational motion of the planetary gear 4 to the lower carrier 51. The lower carrier 51 is located below the lower planetary gear 42 and is a component from which the rotation of the planetary gear 4 is extracted by the mounting holes 42B and internal pins 6 of the lower planetary gear 42. The upper carrier 52 is located above the upper planetary gear 41 and is a component that supports the linkage mechanism between the internal pins 6 and the carrier 51.

[0089] The lower carrier 51 has a disc shape, with a circular recess 511 formed on its upper surface into which the lower ball bearing 81 is fitted, and a circular recess 512 formed on its lower surface into which the connection part on the load side (for example, the joint of an industrial robot) is fitted (see Figure 4). The diameter of the recess 512 is larger than the diameter of the recess 511. In Figure 4, since the lower ball bearing 81 is fitted into the recess 511, the inner surface of the recess 511 is in contact with the outer surface of the lower ball bearing 81. The lower carrier 51 is connected to the lower cover 72 by a bearing section 9 which has the same structure as the bearing structure of a cross roller bearing, so as will be described later, the outer surface of the lower carrier 51 constitutes the inner ring of the bearing section 9. The diameter of the outer surface of the lower carrier 51 is approximately the same as the inner diameter of the case 3.

[0090] Multiple mounting holes 51A are drilled at equal intervals in the circumferential direction on the upper surface of the lower carrier 51, outside the recess 511 (see Figure 3). The mounting holes 51A are for attaching the inner pin 6. The mounting holes 51A have the same function as the positioning holes used to adjust the concentricity of the two disc-shaped parts described above, and are also used to adjust the rotational relative position of the lower carrier 51 and the planetary gear 4 in order to adjust the concentricity between the lower carrier 51 and the planetary gear 4. The PCD of the mounting holes 51A of the lower carrier 51 is the same as the PCD of the insertion holes 4B of the planetary gear 4.

[0091] A fixing hole (screw hole) is formed on the lower end surface of the pin 61 of the inner pin 6 for fixing with a fixing pin 63 (bolt). The pin 61, which is press-fitted into the mounting hole 51A, is fixed to the lower carrier 51 by the fixing pin 63, which is inserted into the fixing hole of the inner pin 6 from the lower surface side of the lower carrier 51 (see Figure 4). A collar 62 is rotatably attached to the pin 61 fixed to the mounting hole 51A of the lower carrier 51. The collar 62 has an inner surface that contacts the pin 61 and an outer surface that contacts the mounting hole 4B, so as to fill the gap between the pin 61 and the mounting hole 4B of the planetary gear 4.

[0092] The multiple mounting holes 4B of the planetary gear 4 rotate around the center of the planetary gear 4 in accordance with the rotation of the planetary gear 4. This rotational motion of the mounting holes 4B is transmitted to the pin 61 via the collar 62, and further transmitted to the lower carrier 51 via the pin 61. The collar 62 serves to smoothly transmit the rotational motion of the mounting holes 4B to the pin 61 and also reduces wear on both parts due to friction between the mounting holes 4B and the pin 61. Since the lifespan of the inner pins 6 is an important factor affecting the lifespan of the reducer 1, the collar 62 is replaceable. Because the degree of deterioration of the multiple inner pins 6 varies, multiple collars 62 with different dimensions and precisions are provided according to the precision of the mounting holes 4B of the planetary gear 4, and a collar 62 with appropriate performance is applied to each mounting hole 4B.

[0093] In the example shown in Figure 4, one collar 62 is attached to each pin 61, but multiple collars 62 may be attached depending on the number of planetary gears 4. In this embodiment, since two planetary gears 4, an upper planetary gear 41 and a lower planetary gear 42, a collar 62 for the lower planetary gear 42 and a collar 62 for the upper planetary gear 41 may be attached to a single pin 61.

[0094] In the example shown in Figure 4, one collar 62 is fitted to the portion of the pin 61 that extends from the mounting hole 41B of the upper planetary gear 41 to the mounting hole 42B of the lower planetary gear 42. However, one collar 62 may be divided into two longitudinal sections, with one section placed opposite the mounting hole 41B of the upper planetary gear 41 of the pin 61 and the other section opposite the mounting hole 42B of the lower planetary gear 42. If the number of planetary gears 4 is three or more, the same approach can be used to divide one collar 62 into m longitudinal sections (where m is the number of planetary gears 4), and each divided collar 62 should be placed opposite the mounting hole 4B of each planetary gear 4.

[0095] The outer surface of the lower carrier 51 is connected to the inner surface of the lower cover 72 by a bearing section 9, which has the same structure as the cross roller bearing (see Figures 3 and 4). The cross roller bearing is a bearing composed of a ring-shaped inner ring with a 90-degree V-groove formed on its outer surface, a ring-shaped outer ring with a 90-degree V-groove formed on its inner surface, and a plurality of rollers (cylindrical rollers) arranged circumferentially with their roller axes alternately perpendicular to each other in a ring-shaped space (the space constituting the raceway) with a rectangular cross-sectional shape sandwiched between the V-grooves of the inner and outer rings. Therefore, a V-groove (a 90-degree V-groove) corresponding to the inner ring of the bearing section 9 is formed on the outer surface of the lower carrier 51.

[0096] The lower cover 72 functions as a fixing member that secures the reducer 1 to the load-side housing (for example, the housing of an industrial robot), and also functions as a protective member that protects the reducer 1. Since the lower cover 72 is fixed to an external device of the reducer 1, when the reducer 1 is operating, the lower cover 72, case 3, and upper cover 71 are fixed, and the eccentric shaft 2, upper carrier 52, and planetary gear 4 rotate within the space enclosed by the lower cover 72 and lower carrier 51, which are connected by the bearing section 9, the upper cover 71, and case 3.

[0097] The lower cover 72 has an annular shape, and a projection 721 is formed on its inner surface, projecting inward approximately at the center in the height direction (see Figure 4). A portion corresponding to the outer ring of the bearing 9 is formed on the inner surface of the projection 721. The upper and lower inner surfaces of the lower cover 72, excluding the projection 721 (surfaces representing steps; hereinafter referred to as "step surfaces"), function as press-fit surfaces when the upper cover 71 and lower cover 72 are press-fitted into the case 3. The height of the step surface of the lower cover 72 is the same as the height of the step surface of the case 3. As shown in Figure 4, the cross-sectional shape of the step portion of the lower cover 72 is the same as the cross-sectional shape of the step portion of the case 3, and the step surface of the lower cover 72 and the step surface of the case 3 constitute the fitting portion of the two parts.

[0098] A V-groove (a V-groove at a 90-degree angle) corresponding to the outer ring of the bearing portion 9 is formed on the inner surface of the protruding portion 721 of the lower cover 72. Multiple rollers are housed in a rectangular cross-sectional space (the space constituting the raceway) sandwiched between the V-groove of the lower carrier 51 of the bearing portion 9 and the V-groove of the lower cover 72. The multiple rollers have the same diameter as the length of the slope of the V-groove of the lower carrier 51 and the lower cover 72, and their length is slightly shorter than their diameter. The multiple rollers are housed in the space constituting the raceway with the orientation of each roller alternating so that the axial directions of the rollers are alternately perpendicular to each other. One of the perpendicular rollers' axial directions is inclined at +45 degrees with respect to the axial direction of the eccentric shaft 2, and the other is inclined at -45 degrees with respect to the axial direction of the eccentric shaft 2.

[0099] The space between the V-groove of the lower carrier 51 of the bearing section 9 and the V-groove of the lower cover 72 (hereinafter referred to as the "roller storage space") is filled with liquid crystal lubricant as a lubricant. Liquid crystal lubricant is a lubricant composed solely of liquid crystal compounds. Liquid crystal lubricant has excellent adhesion to metal surfaces, evaporation properties, and durability, and is a lubricant that has higher lubrication performance than conventional gear oils. In the reducer 1 according to this embodiment, the space sealed by the lower carrier 51, case 3, and upper carrier 52 in which the planetary gear 4 is housed (hereinafter referred to as the "internal space of the reducer 1") is sealed with replaceable high-viscosity gear oil with excellent extreme pressure properties and low volatility for the purpose of lubricating the planetary gear 4, the needle roller bearing 10, and the outer peripheral pin 31 of the case 3.

[0100] As shown in Figures 5 and 6, three inlet ports 3C are provided on the outer surface of the flange 3B of the case 3 for injecting gear oil into the internal space of the reducer 1. The internal space of the reducer 1 is filled with high-viscosity gear oil, for example, in the range of "ISO VG320" to "ISO VG460", through the inlet ports 3C, and the inlet ports 3C are sealed with cap bolts.

[0101] Since a different type of lubricant is used in the bearing portion 9 of the lower carrier 51 and lower cover 72 than the lubricant in the internal space of the idler reducer 1, the roller housing space of the bearing portion 9 is sealed at the upper and lower gaps by oil seals 13A and 13B, respectively, in order to separate the two lubricants (see Figure 4). In this embodiment, a high-viscosity gear oil is used as the lubricant in the internal space of the idler reducer 1, but a liquid crystal lubricant may also be used as the lubricant in that internal space.

[0102] Since the bearing section 9 of the lower carrier 51 and the lower cover 72 has the same bearing structure as a cross roller bearing, the bending force (bending moment load) in the axial direction of the eccentric shaft 2, the radial force (radial load) in the coaxial direction, and the thrust force (load in the longitudinal direction of the shaft) in the coaxial direction are all suppressed by the cross roller bearing structure of the lower carrier 51 and the lower cover 72, and the rigidity of the reducer 1 is strengthened compared to conventional reducers.

[0103] Instead of interposing a cross roller bearing between the lower carrier 51 and the lower cover 72, the inner ring of the cross roller bearing is formed on the outer surface of the lower carrier 51, and the outer ring of the cross roller bearing is formed on the inner surface of the lower cover 72. By directly connecting the lower carrier 51 and the lower cover 72 with a cross roller bearing bearing structure, the radial size of the reduction gear 1 can be reduced.

[0104] In the above explanation, the component connecting the lower carrier 51 and the lower cover 72 was described as having a configuration in which the lower carrier 51 and the lower cover 72 are connected with the same bearing structure as a cross roller bearing. However, from a different perspective, it may also be understood as a component in which the lower carrier 51 is formed on the inner ring portion of a cross roller bearing, and the lower cover 72 is formed on the outer ring portion.

[0105] In conventional speed reducers, in order to rotatably support the lower carrier between the eccentric shaft and the lower cover, a configuration is adopted in which, for example, a ball bearing is interposed between the eccentric shaft and the lower carrier, and a roller bearing is interposed between the lower carrier and the lower cover. In this configuration, if a cross roller bearing is used for the bearing between the lower carrier and the lower cover, the cross roller bearing is larger in the radial direction than a ball bearing or a roller bearing, which hinders the miniaturization of the speed reducer 1. Therefore, in this embodiment, instead of interposing a separate cross roller bearing between the lower carrier and the lower cover, the lower carrier configuration is formed on the inner ring of the cross roller bearing, and the lower cover configuration is formed on the outer ring of the cross roller bearing, thereby realizing a small and compact component that connects the lower carrier and the lower cover.

[0106] A ball bearing 81 is mounted below the mounting position of the lower planetary gear on the eccentric shaft 2. The inner diameter of the inner ring of the ball bearing 81 is approximately the same as the shaft diameter of the eccentric shaft 2. The ball bearing 81 is attached to the eccentric shaft 2 (lower shaft 22) by press-fitting the eccentric shaft 2 into the inner ring. Although not shown in the figure, the ball bearing 81 is a bearing that uses metal balls as rolling elements. The ball bearing 81 consists of a ring-shaped inner ring, a ring-shaped outer ring, a plurality of balls, and a cage that rotatably holds the plurality of balls at equal intervals. The cage that holds the plurality of balls is housed in the space (the space that constitutes the raceway) sandwiched between the inner ring and the outer ring, and this space is filled with liquid crystal lubricant, similar to the bearing structure of a cross roller bearing. The space filled with liquid crystal lubricant is sealed using a DDU type seal system.

[0107] Multiple (for example, 10) positioning holes 72A are formed on the periphery of the lower cover 72 (the part outside the protruding portion 721) (see Figures 3 and 4). The positioning holes 72A serve to determine the rotational position of the upper cover 71 and the case 3. In Figure 3, fixing holes 72B are provided between adjacent positioning holes 72A; these fixing holes 72B are screw holes for fixing the upper cover 71 and the lower cover 72. The PCD of the multiple positioning holes 72A in the lower cover 72 is the same as the PCD of the multiple positioning holes 32 in the case 3.

[0108] The lower carrier 51 and lower cover 72, connected by a cross-roller bearing structure, are rotatably mounted on the eccentric shaft 2 by press-fitting the recess 511 of the lower carrier 51 into a ball bearing 81 attached to the eccentric shaft 2. Each of the multiple mounting holes 51A of the lower carrier 51 is fixed with an internal pin 6 by a press-fit bolt. The case 3 is mounted on the upper side of the lower cover 72, but since the cross-sectional shape of the stepped portion of the lower cover 72 and the cross-sectional shape of the stepped portion of the case 3 are the same, the case 3 is fitted into the lower cover 72 by press-fitting. When fitting the case 3 into the lower cover 72, the rotational position is aligned so that the multiple positioning holes 72A of the lower cover 72 and the multiple positioning holes 32 of the case 3 overlap.

[0109] A shim plate 12B is installed in the gap between the main body of case 3 (the part not with flange 3B) and the lower cover 72. A shim plate 12A is also installed in the gap between the main body of case 3 and the upper cover 71, which will be described later. Shim plates 12A and 12B have a ring shape that is approximately the same as the width of the upper and lower surfaces of the main body of case 3 (including the outer peripheral pin 31). Like the shim ring 11, the shim plate 12 is made of a vibration-damping alloy with excellent vibration damping properties. As the vibration-damping alloy, flake graphite cast iron or ductile cast iron can be used, but flake graphite cast iron is preferably used. The shim plate 12 is manufactured in the same way as the manufacturing method of the shim ring 11 described above, and is adjusted to a predetermined thickness by polishing.

[0110] The upper carrier 52 is supported between the eccentric shaft 2 and the case 3 by fitting a ball bearing 82 between its inner surface and the eccentric shaft 2, and a ball bearing 83 between its outer surface and the upper cover 71. The shim plate 12A applies an adjustable preload to the gap between the case 3 and the bearing 83 so that the preload on the upper carrier 52 due to the fitting of the ball bearing 82 is the same as the preload on the upper carrier 52 due to the fitting of the ball bearing 83. The lower carrier 51 is supported between the eccentric shaft 2 and the lower cover 72 by fitting a ball bearing 81 between its inner surface and the eccentric shaft 2, and its outer surface is connected to the lower cover 72 by a bearing portion 9. The shim plate 12B applies an adjustable preload to the gap between the case 3 and the lower cover 72 so that the preload on the lower carrier 51 due to the fitting of the ball bearing 81 is the same as the preload on the lower carrier 51 due to the bearing portion 9.

[0111] The shim plates 12A and 12B are manufactured, for example, by processing flake graphite cast iron to create shim plates of a predetermined shape, then adjusting them to a predetermined thickness by grinding, and applying an appropriate preload. By applying preload to the shim plates 12A and 12B, the clamping rigidity values ​​of the components inside the case 3 and the clamping rigidity values ​​of the external components of the reducer 1 can be adjusted. In addition, minute axial vibrations and noise generated when the reducer 1 is in operation can be reduced.

[0112] The lower planetary gear 42 and the upper planetary gear 41 are housed inside the case 3 attached to the lower cover 72. As described above, the lower planetary gear 42 is rotatably mounted on the eccentric shaft 2 by press-fitting its mounting holes 42A into the lower needle roller bearing 10B, which is attached to the eccentric shaft 2. Multiple internal pins 6, fixed to multiple mounting holes 51A of the lower carrier 51, are fitted into each of the multiple mounting holes 42B of the lower planetary gear 42. The upper planetary gear 41 is rotatably mounted on the eccentric shaft 2 by press-fitting its mounting holes 41A into the upper needle roller bearing 10A, which is attached to the eccentric shaft 2. Multiple internal pins 6, fixed to multiple mounting holes 72B of the lower cover 72, are also fitted into each of the multiple mounting holes 42B of the lower planetary gear 42. Since the outer diameters of the upper planetary gear 41 and the lower planetary gear 42 are approximately the same as the inner diameter of the case 3, some of the external teeth of the upper planetary gear 41 and the lower planetary gear 42 mesh with the outer peripheral pin 31 of the case 3.

[0113] The upper carrier 52, like the lower carrier 51, has an annular shape, and a circular recess 521 is formed on its lower surface into which the upper ball bearing 82 is fitted (see Figure 4). The diameter of the recess 521 is approximately the same as the outer diameter of the upper ball bearing 82. The outer diameter of the upper carrier 52 is smaller than the outer diameter of the lower carrier 51 and is approximately the same as the inner diameter of the ball bearing 83, which will be described later. Multiple (for example, 8) mounting holes 52A are drilled at equal intervals in the circumferential direction on the lower surface of the upper carrier 52, outside the recess 521. The mounting holes 52A are holes for fixing the upper end of the inner pin 6. The mounting holes 52A have the same function as the positioning holes used to adjust the concentricity of the two disc-shaped parts described above, and are also used to adjust the relative rotational position of the upper carrier 52 and the planetary gear 4 when adjusting the concentricity between the upper carrier 52 and the planetary gear 4. The PCD of the mounting hole 52A of the upper carrier 52 is the same as the PCD of the insertion hole 4B of the planetary gear 4.

[0114] An upper ball bearing 82 is mounted above the mounting position of the upper planetary gear on the eccentric shaft 2. The raceway ring of the upper ball bearing 82 is also sealed with the same liquid crystal lubricant as the lower ball bearing 81. The inner diameter of the inner ring of the upper ball bearing 82 is approximately the same as the shaft diameter of the eccentric shaft 2. The upper ball bearing 82 is attached to the eccentric shaft 2 by press-fitting the eccentric shaft 2 into the inner ring. The recess 521 of the upper carrier 52 is press-fitted into the upper ball bearing 82, thereby allowing the upper carrier 52 to rotatably attach to the eccentric shaft 2 via the upper ball bearing 82.

[0115] A ball bearing 83 is press-fitted onto the outer circumference of the upper carrier 52, which is attached to the upper ball bearing 82. The ball bearing 83 is a component that allows the upper carrier 52 to rotatably support the upper carrier 52 with the upper cover 71. Like the ball bearings 81 and 82, the ball bearing 83 is a bearing that uses metal balls as rolling elements. The ball bearing 83 has the same structure as the ball bearings 81 and 82 described above, and liquid crystal lubricant is sealed in the raceway ring. The inner diameter of the inner ring of the ball bearing 83 is approximately the same as the outer diameter of the upper carrier 52. The outer diameter of the outer ring of the ball bearing 83 is approximately the same as the inner diameter of the recess 711 of the upper cover 71 that houses the upper carrier 52 and the ball bearing 83. The ball bearing 83 is attached to the upper carrier 52 by press-fitting the upper carrier 52 into the inner ring.

[0116] The upper cover 71 functions as a protective member that protects the upper surface of the reduction gear 1, and also functions as a connection part for connecting a device that rotates at high speed (for example, an electric motor or a gear reduction mechanism) to the eccentric shaft 2. Furthermore, the upper cover 71, together with the lower cover 72, functions as a fixing member that sandwiches the case 3 and secures the case 3.

[0117] The upper cover 71 is disc-shaped, and its outer diameter is approximately the same as the outer diameter of the case 3 (see Figure 2). A mounting hole 71A for attaching the rotor of the electric motor or the output shaft of the gear reduction mechanism is formed in the center of the upper cover 71. The diameter of the mounting hole 71A is set to a size that creates a gap of a predetermined length relative to the diameter of the eccentric shaft 2. The gap between the eccentric shaft 2 and the mounting hole 71A functions as a hole for attaching a coupling (shaft coupling) to connect the rotor of the electric motor or the output shaft of the gear reduction mechanism to the eccentric shaft 2.

[0118] A circular recess 711 is formed on the lower surface of the upper cover 71 into which a ball bearing 83 is fitted. The diameter of the recess 711 is approximately the same as the outer diameter of the ball bearing 83. Multiple (for example, 10) positioning holes 71B are provided at equal intervals in the circumferential direction on the peripheral edge of the upper surface of the upper cover 71 (see Figure 2). The positioning holes 71B serve to determine the rotational position in the same way as the positioning holes 72B of the lower cover 72 described above when the case 3 is sandwiched and fixed between the upper cover 71 and the lower cover 72. The PCD of the multiple positioning holes 71B is the same as the PCD of the multiple positioning holes 32 of the case 3.

[0119] The upper cover 71 is rotatably attached to the upper carrier 52 by press-fitting a recess 711 into a ball bearing 83 attached to the upper carrier 52. The upper cover 71 attached to the upper carrier 52 is fixed to the lower cover 72 using multiple pins inserted into multiple fixing holes (not shown).

[0120] In this embodiment, the case 3 is sandwiched and fixed between the upper cover 71 and the lower cover 72. As shown in Figure 4, protrusions (parts where the inside of the case 3 protrudes vertically relative to the flange 3B) are formed on the upper and lower surfaces of the case 3, and recesses are formed on the upper cover 71 and the lower cover 72. The protrusions on the upper surface of the case 3 are fitted into the recesses of the upper cover 71, and the protrusions on the lower surface of the case 3 are fitted into the recesses of the lower cover 72. However, the formation of the protrusions and recesses may be reversed. That is, recesses may be formed on the upper and lower surfaces of the case 3, and protrusions may be formed on the upper cover 71 and the lower cover 72. The recesses on the upper surface of the case 3 are fitted into the protrusions of the upper cover 71, and the recesses on the lower surface of the case 3 are fitted into the protrusions of the lower cover 72.

[0121] Figure 14 is a diagram illustrating the connection configuration when an electric motor is directly connected to a reduction gear 1. In this diagram, a coupling 15 is attached to the eccentric shaft 2 of the reduction gear 1, and the rotor 141 of the electric motor 14 is fixed to the coupling 15. The reduction gear 1 and coupling 15 are shown in cross-sectional views, while the electric motor 14 is shown in a front view.

[0122] As shown in Figure 14, the rotor 141 of the electric motor 14 and the eccentric shaft 2 of the reduction gear 1 are connected by a coupling 15. The coupling 15 has a cylindrical shape with an axial step, connecting two cylinders with different inner diameters. The wall thickness of the small cylindrical part 151 with a smaller inner diameter and the large cylindrical part 152 with a larger inner diameter of the coupling 15 is approximately the same as the size of the gap between the mounting hole 71A of the upper cover 71 (see Figure 2) and the eccentric shaft 2. The small cylindrical part 151 has an inner diameter approximately the same as the outer diameter of the rotor 141 of the electric motor 14, and the large cylindrical part 152 has an inner diameter approximately the same as the outer diameter of the eccentric shaft 2.

[0123] Multiple (for example, 8) holes 152A are provided on the periphery of the surface to which the small cylindrical portion 151 of the large cylindrical portion 152 is connected. The coupling 15 is fixed to the eccentric shaft 2 by placing the large cylindrical portion 152 over the upper end of the eccentric shaft 2 (fitting the tip of the large cylindrical portion 152 into the gap between the mounting hole 71A of the upper cover 71 and the eccentric shaft 2), inserting bolts into the multiple holes 152A, and screwing them into the screw holes provided at the upper end of the eccentric shaft 2. The electric motor 14 is fixed to the coupling 15 by press-fitting the rotor 141 into the small cylindrical portion 151 of the coupling 15.

[0124] Figure 14 shows a configuration in which the rotor 141 of the electric motor 14 is directly connected to the reduction gear 1. However, by fixing the output shaft of the gear reduction mechanism to the small cylindrical part 151 of the coupling 15 fixed to the eccentric shaft 2, a configuration in which the gear reduction mechanism is interposed between the reduction gear 1 and the electric motor 14 (a two-stage reduction configuration) can be achieved.

[0125] In the eccentric shaft 2 using the spline fitting method shown in Figures 11 to 13, as shown in Figure 11, a male spline 212B using an involute curve is formed at the upper end of the upper shaft 21. Therefore, the coupling 15 used for this coupling has a female spline formed on the inner surface of the large cylindrical portion 152 that fits with the male spline 212B. This coupling has the advantage of simplifying the connection work between the electric motor 14 or gear reduction mechanism and the reducer 1, as connection can be made simply by fitting the male spline and the female spline together.

[0126] Next, the reduction operation of the reducer 1 will be briefly explained using the geared motor shown in Figure 14 as an example. However, the number of outer peripheral pins 31 on the case 3 of the reducer 1, Z1, will be 50, and the number of external teeth Z2 on the planetary gear 4 will be 49.

[0127] When the rotor 141 of the electric motor 14 rotates at an angular velocity ω1 [rad / s], the eccentric shaft 2 directly connected to the rotor 141 rotates at an angular velocity ω1. The high-speed rotation of the eccentric shaft 2 is transmitted to the planetary gear 4 via the needle roller bearing 10, causing the planetary gear 4 to rotate eccentrically inside the case 3 at an angular velocity ω1. This eccentric rotation causes the planetary gear 4 to revolve around the rotation center O of the eccentric shaft 2, while moving the meshing positions K1 and K2 with the outer peripheral pins 31 of the case 3.

[0128] During the orbital motion of the upper planetary gear 41, the external teeth 41C that roll and contact the outer peripheral pin 31 receive a reaction force from the outer peripheral pin 31. Therefore, the upper planetary gear 41 rotates around the center Oa of the upper eccentric portion 21A at an angular velocity ω2 [rad / s] in the opposite direction to the orbital direction, supported by the upper needle roller bearing 10A. The lower planetary gear 42 also receives a reaction force from the outer peripheral pin 31 during its orbital motion, similar to the upper planetary gear 41, and rotates around the center Ob of the lower eccentric portion 22A at an angular velocity ω2 in the opposite direction to the orbital direction, supported by the upper needle roller bearing 10B.

[0129] As described above, the relationship between angular velocities ω1 and ω2 is expressed as ω2 / ω1 = -(Z1-Z2) / Z2, so ω2 / ω1 = -1 / 49. The upper planetary gear 41 and the lower planetary gear 42 rotate in the opposite direction to the orbital direction, with the rotational speed ω2 obtained by reducing the rotational speed ω1 of the eccentric shaft 2 to 1 / 49. When the planetary gear 4 rotates, its rotation is transmitted to the carrier 5 by a parallel crank mechanism consisting of the 8 insertion holes 4B and 8 internal pins 6 of the planetary gear 4, causing the carrier 5 to rotate at a rotational speed ω2 (=ω1 / 49). Of the carriers 5, the lower carrier 51 is connected to the load, so the low-speed rotation ω2 extracted to the lower carrier 51 is transmitted to the load.

[0130] Next, the characteristic configuration and effects of the gearbox 1 according to this embodiment will be described.

[0131] (1) Eccentric shaft 2 composed of an upper shaft 21 and a lower shaft 22 In a cycloidal speed reducer, a needle roller bearing is attached to the eccentric cam portion of the eccentric shaft, and a planetary gear is attached to this needle roller bearing. In an eccentric shaft in which a disc-shaped cam is eccentrically attached to the axial center of a cylindrical shaft, if the eccentricity Δr (the amount of displacement between the hollow center of the shaft and the center of the cam) exceeds the difference Δr (=r1-r0) between the radius r1 of the cam and the radius r0 of the shaft, a part of the outer surface of the cam will be located inside the outer surface of the shaft, which creates a problem in that the cam cannot be attached to the shaft.

[0132] As mentioned above, the reduction ratio R of a cycloidal gearbox is expressed as R = |(Z1-Z2) / Z2| (Z1: number of internal teeth of the case (number of outer pins), Z2: number of external teeth of the planetary gear), and the maximum reduction ratio R is determined by R = 1 / (Z1-1) once the number of internal teeth of the case Z1 is determined. To miniaturize the cycloidal gearbox by reducing the diameter of the cylindrical case while maintaining the number of outer pins Z1, it is necessary to make the outer pins thinner. However, making the outer pins thinner reduces their rigidity, leading to a shorter lifespan for the gearbox 1, so there is a limit to how thin the outer pins can be.

[0133] In the design of a miniaturized cycloidal gearbox, once the case size is determined, the number of internal teeth Z1 is determined according to that case size, and the number of external teeth Z2 and the eccentricity Δr of the planetary gear are designed based on the number of internal teeth Z1 and the desired reduction ratio R. With conventional eccentric shafts, the eccentricity Δr must be designed so that the above problems do not occur, and this limitation on the design of the eccentricity Δr reduces the design freedom of the cycloidal gearbox.

[0134] In this embodiment, the eccentric shaft 2 separates the rod-shaped upper shaft 21 to which the upper needle roller bearing 10A is attached and the rod-shaped lower shaft 22 to which the lower needle roller bearing 10B is attached. Since an eccentric portion 21A is provided at the lower end of the upper shaft 21 and an eccentric portion 22A is provided at the upper end of the lower shaft 22, the problem of the needle roller bearing 10 not being able to be attached to the eccentric shaft 2 due to the eccentricity Δr does not occur. In this embodiment, there are no restrictions on the design of the eccentricity Δr of the eccentric shaft 2, so the degree of freedom in the miniaturization design of the cycloidal reducer can be improved and the types of parts that can be used for the needle roller bearing 10 can also be increased.

[0135] In conventional eccentric shafts, to avoid the above problems, increasing the diameter of the eccentric cam according to the design value of the eccentricity Δr necessitates increasing the outer diameter of the needle roller bearing accordingly. When the outer diameter of the needle roller bearing increases, the inner diameter of the mounting holes for the planetary gears, which are press-fitted into the needle roller bearing, increases. This reduces the radial size of the plate surface where the multiple mounting holes for the planetary gears are drilled, and consequently, the strength of the planetary gears decreases. In conventional eccentric shafts, changing the design value of the eccentricity Δr changes the radial size of the plate surface where the multiple mounting holes for the planetary gears are drilled, requiring a redesign of the planetary gear's strength, making it difficult to miniaturize cycloidal reducers.

[0136] In the eccentric shaft 2 according to this embodiment, the radial size of the plate surface where multiple mounting holes for the planetary gears are drilled can be fixed regardless of the design value of the eccentricity Δr. This reduces the work required to redesign the strength of the plate surface of the planetary gear 4 in response to changes in the design value of the eccentricity Δr, and facilitates the miniaturization design of the cycloidal reducer 2.

[0137] (2) Lower carrier 51 and lower cover 72 connected by a cross roller bearing bearing structure The carrier, composed of an upper carrier and a lower carrier, has ball bearings interposed between the eccentric shaft and each carrier, and between each carrier and each cover, to allow each carrier to rotate freely between each cover and the eccentric shaft. If cross roller bearings, which can withstand larger loads than ball bearings and are resistant to bending moment, radial load, and thrust load, were to be used instead, cross roller bearings would be larger than ball bearings. Therefore, simply changing the parts would be disadvantageous in terms of cost and size for designing a smaller and more compact gearbox.

[0138] In the gearbox 1 according to this embodiment, the joint between the lower carrier 51 and the lower cover 72 (hereinafter referred to as the "lower exterior part") is made into a bearing section 9 identical to the bearing structure of a cross roller bearing, thereby matching the size of the lower exterior part attached to the eccentric shaft 2 via a ball bearing 81 to the size of the case 3. As a result, a gearbox 1 that is smaller and has a higher load capacity than conventional gearboxes can be realized.

[0139] Furthermore, since the lower cover 72 of the lower exterior component is a separate part from the case 3, the rotational alignment of these components can be performed with high precision during the assembly of the upper carrier 52, case 3, and lower carrier 51, making it possible to realize a reduction gear 1 in which the concentricity of these components is minimized.

[0140] (3) Planetary gear 4 that can be used without distinguishing between the front and back surfaces In the reduction gear 1 according to this embodiment, planetary gears with the same cross-sectional shape and symmetrical height direction, where the step shape on the front and back surfaces is the same, are used for the upper planetary gear 41 and the lower planetary gear 42. That is, the same planetary gear is used for the upper planetary gear 41 and the lower planetary gear 42 without distinguishing between the front and back surfaces. Even when the number of planetary gears 4 is three or more, the same planetary gear is used for each planetary gear without distinguishing between the front and back surfaces.

[0141] In the design of the speed reducer 1, it is necessary to keep the concentricity of the planetary gear 4 and the carrier 5 within a predetermined tolerance range. In the speed reducer 1 according to this embodiment, the same planetary gear can be used for the upper planetary gear 41 and the lower planetary gear 42 without distinguishing between the front and back surfaces. This simplifies the assembly of the upper planetary gear 41 and the lower planetary gear 42, and also has the effect of minimizing the concentricity of both planetary gears 41 and 42 as much as possible during the assembly process.

[0142] When adjusting the concentricity of multiple parts to the minimum value, reversing the front and back of each part and aligning them in the rotational direction can sometimes improve the adjustment accuracy. Applying planetary gears that can be used even when reversed to the upper planetary gear 41 and lower planetary gear 42 increases the number of combinations of relative positions in the rotational direction of the two circular parts compared to when they cannot be reversed. This improves the accuracy of adjusting to the position where the concentricity is minimized, which is an extremely superior effect not found in conventional speed reducers.

[0143] (4) Case 3 with a cross-sectional shape that is symmetrical vertically In the design of the speed reducer 1, the concentricity of the upper cover 71, case 3, and lower cover 72 must also be within a predetermined tolerance range. In the speed reducer 1 according to this embodiment, the case 3 is sandwiched and fixed between the upper cover 71 and the lower cover 72. Since it is not necessary to distinguish between the upper and lower parts of the case 3 during assembly, the assembly process becomes easier. Furthermore, the relative positions of the upper cover 71, case 3, and lower cover 72 in the rotational direction can be changed to adjust to the position where the concentricity is minimized, thus ensuring that the concentricity of these parts is within a predetermined tolerance range.

[0144] In the process of adjusting the concentricity of the upper cover 71, case 3, and lower cover 72, the number of alignments performed by changing the relative position of case 3 in the rotational direction with respect to the upper cover 71 and lower cover 72 is greater when case 3 is inverted vertically than when it cannot be inverted vertically. Therefore, the minimum value of concentricity can be adjusted to a smaller position.

[0145] (5) A configuration that uses two different types of lubricants. In the gearbox 1 according to this embodiment, liquid crystal lubricant is used as a lubricant for the bearing section 9 connecting the lower carrier 51 and the lower cover 72, and for the first to third ball bearings 81, 82, and 83, while high-viscosity gear oil is used as a lubricant for the internal space of the gearbox 1, thus using two different types of lubricants. Different types of lubricants are used for parts related to high-speed rotation of the gearbox 1 and parts related to low-speed rotation, and the two types of lubricants are used separately to prevent mixing.

[0146] By using a liquid crystal lubricant with excellent adhesion to metal surfaces, evaporation properties, and durability, and higher lubrication performance than gear oil, in the bearing portion (low-speed rotation portion) that rotatably holds the upper carrier 52 and lower carrier 51, the low-speed rotation output performance to the carrier 5 can be improved. In conventional speed reducers, grease (oil) is generally used as a lubricant in the internal space, but in speed reducer 1, high-viscosity gear oil is used as a lubricant in the internal space (high-speed rotation portion), which prevents oil deterioration and oil film breakdown due to reduced volatilization (gas generation), and prevents temperature rise and noise in speed reducer 1.

[0147] By selecting lubricants with appropriate types and characteristics for high-speed and low-speed rotating components, it is possible to improve performance compared to conventional gearboxes, including increased rotational efficiency, enhanced durability, and reduced vibration and noise. Furthermore, the increased flexibility in lubricant specifications makes it easier to design smaller, thinner, and more compact gearboxes.

[0148] (6) Vibration suppression by shim ring 11 and shim plate 12 In the reduction gear 1 according to this embodiment, shim rings 11 are attached to the portion that rotatably supports the planetary gear 4. Specifically, three shim rings 11A, 11B, and 11C are attached to the upper end of the upper planetary gear mounting position on the eccentric shaft 2, the lower end of the lower planetary gear mounting position, and midway between the two planetary gear mounting positions. In addition, two shim plates 12A and 12B are attached to the gap between the case 3 and the upper cover 71 and the gap between the case 3 and the lower cover 72.

[0149] Since preload is applied to the lower ball bearing 81 and upper ball bearing 82, which are press-fitted onto the eccentric shaft 2, by shim rings 11A and 11C, the axial tightening of the eccentric shaft 2 to both bearings 81 and 82 can be appropriately performed, and vibrations and noise generated in both bearings 81 and 82 can be suitably suppressed. In addition, the shim plate 12 allows adjustment of the tightening rigidity value of the parts inside the case 3 and the tightening rigidity value of the external parts of the reducer 1. Furthermore, it is possible to reduce minute axial vibrations and noises caused by the meshing of the eccentric shaft 4 and the outer pin 31 when the reducer 1 is in operation. [Industrial applicability]

[0150] The present invention, through the characteristic configuration described above, can provide a gearbox that has superior performance compared to conventional gearboxes, including (i) being smaller, thinner, and more compact, (ii) having high vibration damping, (iii) having high rotational efficiency, (iv) having a long lifespan, (v) having high durability against loads applied to the gearbox, and (vi) having a small temperature rise. [Explanation of symbols]

[0151] 1 Reducer 2 Eccentric Shaft 21 Upper shaft (first shaft) 21A Upper eccentric portion (first eccentric portion) 211,212 Fitting part 211A Positioning hole 211B Recess 212A Male spline 22 Lower shaft (second shaft) 22A Lower eccentric section (second eccentric section) 221,222 Fitting part 221A Positioning hole 221B protrusion ,222A Female spline 23 Press-fit pins 3 cases 3A groove 3B flange 3C inlet 31 Outer edge pins 32 positioning holes 33 mounting holes 4 Planetary gears 41 Upper planetary gear (first planetary gear) 42 Lower planetary gear (second planetary gear) 41A, 42A mounting holes 41B,42B insertion hole 5 Carriers 51 Lower carrier (first carrier) 52 Upper carrier (second carrier) 51A, 52A Mounting holes 511,521 recess 6. Inner pin 61 pins 62 Colors 7 Cover 71 Upper cover (first cover) 72 Lower cover (second cover) 71A, 72A mounting holes 71B, 72B Positioning holes 71C, 72C mounting holes 711 recess 721 Protrusion 8 ball bearings 81 Lower ball bearing (first ball bearing) 82 Upper ball bearing (second ball bearing) 83. Ball bearing (third ball bearing) 9 Bearing section 10 Needle roller bearings 10A Upper needle roller bearing (first needle roller bearing) 10B Lower needle roller bearing (second needle roller bearing) 11, 11A, 11B, 11C Shim ring (first shim member) 12, 12A, 12B Shim plate (second shim member) 14 Electric motor 141 Rotor 15 Couplings

Claims

1. An annular case having internal teeth on its inner surface, An eccentric shaft is positioned at the center of the aforementioned case and has an eccentric portion that is eccentric from the axis center of the shaft, A planetary gear is provided, in which a portion of the external teeth of the case mesh with the internal teeth of the case, and is rotatably supported on the eccentric portion of the eccentric shaft, and rotates and revolves inside the case while rotating on its own axis due to the eccentric rotation transmitted from the eccentric shaft. The system comprises a disc-shaped carrier rotatably supported on the eccentric shaft, from which the rotation of the planetary gear is output, Multiple first positioning holes are formed on the plate surface of the planetary gear at equal intervals in the circumferential direction. The plate surface of the carrier is provided with a plurality of second positioning holes at equal intervals in the circumferential direction, with the same pitch circle diameter as the first positioning holes. The planetary gear and the carrier are configured to be concentric by adjusting the combination of overlapping the first positioning hole and the second positioning hole. The aforementioned planetary gear has identical stepped shapes in the thickness direction on both its front and back surfaces, and can be used without distinguishing between the front and back surfaces by adjusting the concentricity. A gearbox characterized by the following features.

2. A plurality of internal pins are provided, one end of which is fixed to the plurality of second positioning holes of the carrier, and the other end of which is rotatably fitted into the plurality of first positioning holes of the planetary gear, and the rotation of the planetary gear is output to the carrier by a parallel crank mechanism consisting of the plurality of first positioning holes and the plurality of internal pins. The gearbox according to feature 1.

3. The inner pin comprises a rod-shaped pin, one end of which is fixed to a second positioning hole of the carrier and the other end of which is fitted into a first positioning hole of the planetary gear, and a collar that is rotatably mounted in the gap between the other end of the pin and the first positioning hole. The gearbox according to feature 2.

4. The planetary gear includes a plurality of planetary gears arranged in the axial direction of the eccentric shaft, Multiple pins, which are fitted into multiple first positioning holes that are superimposed on the multiple planetary gears, have multiple collars attached to them in the axial direction of each pin, corresponding to the first positioning hole of each planetary gear. The gearbox according to feature 3.

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