Reduction gear

Abstract

Provided is a reduction gear that is thinner than a conventional one without impairing performance and characteristics. The present invention is a reduction gear (1) comprising: an eccentric shaft (4) in which eccentric portions (41, 42) perform an eccentric motion by rotation of a shaft; planetary gears (51, 52) which perform an eccentric motion by the eccentric motion of the eccentric portions (41, 42); a case (9) which functions as internal teeth for the planetary gears (51, 52); and a carrier (7) which is connected to the planetary gears (51, 52) and which outputs rotation of the planetary gears (51, 52), wherein each component of the planetary gears (51, 52) and the carrier (7) is produced to have a thickness less than that of a conventional component by a proportion corresponding to the increase in torsional rigidity of each component due to shot peening when a material is processed, and thereafter shot peening is performed on a surface of the component so that the torsional rigidity is increased.

Description

Reducer

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

[0002] For joints of industrial robots, an electric motor as a driving source of a link and a reducer integrally connected to an output shaft of the electric motor are attached. The reducer is a device that converts the low-torque and high-speed rotation of the electric motor into high-torque and low-speed rotation and transmits it to the link. There are various problems with the reducers provided in the joints of industrial robots. Among them, (1) when two gears mesh, the teeth of both gears collide, and the gear mechanism is easily damaged, (2) the vibration is large, and (3) the control accuracy of the rotation position of the link is low, which are major problems.

[0003] Conventionally, as reducers for solving these problems, cycloid reducers (Cycloid Reducer) and RV reducers (Rotate Vector Reducer) are known and have been put into practical use. For example, Patent Document 1 describes a multi-joint robot provided with an RV reducer at a joint.

[0004] FIG. 18 is a skeleton diagram showing a gear mechanism of an RV reducer. The RV reducer 100 is a two-stage reduction type reducer including a first reduction part 110 and a second reduction part 120.

[0005] The first reduction part 110 is composed of a spur gear reduction mechanism combining one input gear 111 and three spur gears 113. Only the meshing part of the input gear 111 and one spur gear 113 is shown in FIG. 18. The diameter of the input gear 111 is smaller than the diameter of the spur gear 113, and the number of teeth of the input gear 111 is less than the number of teeth of the spur gear 113. An input shaft 112 is attached to the center of the input gear 111, and an output shaft 114 is attached to the center of the spur gear 113.

[0006] The rotation of the electric motor is input to the input shaft 112 of the input gear 111, and the rotation is output from the output shafts 114 of the three spur gears 113 at a reduced speed from the input rotation speed. The output rotation speed is the speed obtained by reducing the input rotation speed by the ratio of the number of teeth of the input gear 111 to the number of teeth of the spur gear 113.

[0007] Two eccentric portions 114A and 114B are provided axially on the output shaft 114 of the three spur gears 113. The eccentric portions 114A and 114B are eccentric cams that perform eccentric motion due to the rotation output from the first reduction unit 110. The eccentric portions 114A and 114B are components that transmit the eccentric motion to the two RV gears 122A and 122B of the second reduction unit 120, respectively. The centers of the eccentric portions 114A and 114B are eccentric by a predetermined amount from the center of the output shaft 114. The eccentric direction of the eccentric portion 114A and the eccentric direction of the eccentric portion 114B are opposite to each other.

[0008] The second reduction unit 120 is composed of an internal planetary gear mechanism comprising a fixed annular case 121, two disc-shaped RV gears 122A and 122B arranged eccentrically inside the case 121, and a holding member 123 that holds the two RV gears 122A and 122B in between and outputs the rotation of both RV gears 122A and 122B to the outside.

[0009] Numerous pin gears 121A are rotatably mounted at equal intervals inside the case 121 as internal circumferential teeth. The RV gears 122A and 122B are composed of trochoidal gears with a tooth profile formed on their outer circumference using a trochoidal curve. The number of teeth on the outer circumference of the RV gears 122A and 122B is one less than the number of teeth on the pin gears 121A. The retaining member 123 is rotatably supported on both sides of the eccentric portions 114A and 114B of the output shaft 114. The retaining member 123 is configured to transmit the rotation of the two RV gears 122A and 122B by a rotation transmission member (not shown).

[0010] RV gear 122A performs eccentric motion around the center of input gear 111 because its eccentric portion 114A moves eccentrically around the center of the rotation axis 114. RV gear 122B performs eccentric motion around the center of input gear 111 because its eccentric portion 114B moves eccentrically around the center of the rotation axis 114. Due to their eccentric motion, RV gears 122A and 122B rotate relative to case 121, with some of their outer teeth contacting the inner teeth (pin gear 121A) of case 121.

[0011] The RV gears 122A and 122B rotate at a speed such that the outer teeth of the RV gears 122A and 122B move by the width of one inner tooth of the case 121 for every one rotation of the spur gear 113. The holding member 123 also rotates in synchronization with the rotation of the RV gears 122A and 122B. The rotation of the holding member 123 is output from the output shaft 130 of the RV reducer 100 to the load (robot link).

[0012] Japanese Patent Publication No. 2012-056037 (Figures 1, 3 to 5)

[0013] The RV gearbox is a two-stage gearbox consisting of a first reduction section and a second reduction section, and has the advantage that the total reduction ratio over a wide range can be easily adjusted by adjusting the reduction ratio of the first reduction section. The RV gearbox uses an internal planetary gear mechanism consisting of pin gears and trochoid gears in the second reduction section, which is the main reduction section, and has the advantages of (1) being able to reduce backlash, (2) having high torsional rigidity, (3) being able to obtain a large reduction ratio, (4) being resistant to vibration, and (5) having high control accuracy.

[0014] RV speed reducers have many advantages that can solve the aforementioned problems of industrial robot speed reducers, and are therefore widely used as speed reducers for a wide variety of industrial robots. As the range of applications for industrial robots expands, there is a demand for further thinning, miniaturization, and weight reduction of RV speed reducers. However, since RV speed reducers have the first and second reduction sections arranged coaxially and combine numerous components constituting both reduction sections at high density and with high precision, it is difficult to achieve thinning, miniaturization, and weight reduction of RV speed reducers without compromising the performance of the RV speed reducer (transmission efficiency, backlash, lost motion, etc.) simply by thinning and miniaturizing each component.

[0015] This invention has been made in view of the above-mentioned problems, and aims to provide a precision control gearbox that can achieve further thinning, miniaturization, and weight reduction of current gearboxes without impairing performance or characteristics.

[0016] The reduction gear according to the present invention comprises an eccentric shaft having an eccentric portion on the shaft, the shaft rotating due to the rotation of a motor causing the eccentric portion to perform eccentric motion; planetary gears rotatably supported on the eccentric portion of the eccentric shaft and performing eccentric motion around the axis center of the eccentric shaft due to the eccentric motion of the eccentric portion; a case arranged around the planetary gears, with a plurality of outer peripheral pins rotatably attached to its inner surface, functioning as internal teeth for the external teeth of the planetary gears; and a carrier rotatably supported at both ends of the shaft beyond the eccentric portion, including two covers that clamp the planetary gears and outputting the rotation of the planetary gears based on the eccentric motion of the eccentric portion to the outside, wherein at least the planetary gears and carrier components are manufactured by reducing the thickness of each component by an amount equal to the increase in torsional rigidity of each component by applying shot peening under predetermined conditions when processing the material to manufacture each component, and the torsional rigidity of each component is increased by applying shot peening under predetermined conditions (Claim 1).

[0017] According to the preferred embodiment of the gearbox described above, the case may be subjected to a surface treatment of ultra-smooth polishing and oil reservoir processing in the grooves into which the outer peripheral pins are mounted after shot peening (Claim 2).

[0018] Furthermore, according to the preferred embodiment of the reduction gear described above, the material of the carrier and case is preferably ductile cast iron (Claim 3).

[0019] Furthermore, according to the preferred embodiment of the reduction gear described above, the material of the eccentric shaft, planetary gears, and multiple outer pins is preferably structural steel material that ensures hardenability (Claim 4).

[0020] Furthermore, according to the preferred embodiment of the reduction gear described above, each component of the eccentric shaft, planetary gear, and multiple outer pins is preferably subjected to heat treatment in the order of quenching, ultra-sub-zeroing, and tempering after the components have been manufactured by processing the material, and then surface treatment in the order of shot peening, ultra-smooth polishing, and oil reservoir processing (Claim 5).

[0021] Furthermore, according to the preferred embodiment of the reduction gear described above, the two covers are disc-shaped with a first through hole drilled in the center, and the two covers are rotatably mounted on the eccentric shaft with a first bearing interposed between the first through hole and the eccentric shaft, and are rotatably mounted on the case with a second bearing interposed between the outer circumference and the inner circumference of the case, and the first and second bearings are shot-peened on the entire raceway ring, and the surface treatments of ultra-smooth polishing and oil reservoir processing are preferably performed in this order on the parts of the raceway ring that come into contact with the rollers (Claim 6).

[0022] Furthermore, according to the preferred embodiment of the reduction gear described above, the planetary gear is disc-shaped with a second through hole drilled in its center, and the planetary gear is rotatably mounted on an eccentric shaft with a third bearing interposed between the second through hole and the eccentric portion, and the third bearing is shot-peened on the entire roller, and the surface treatment of the circumferential surface of the roller is preferably performed in this order: ultra-smooth polishing and oil reservoir processing (Claim 7).

[0023] According to a preferred embodiment of the gearbox described in claim 7, the first bearing is a tapered roller bearing, the second bearing is an angular contact bearing, and the third bearing is a caged needle roller bearing (claim 8).

[0024] Furthermore, according to a preferred embodiment of the reduction gear described above, a second spur gear is fixed to one end of an eccentric shaft, meshing with a first spur gear connected to the rotor of a motor, and reducing the rotational speed of the first spur gear and transmitting it to the eccentric shaft. The components of the first and second spur gears are manufactured by reducing the thickness of each component by an amount equal to the increase in torsional rigidity of each component by applying shot peening under predetermined conditions when processing the material to manufacture each component, and the torsional rigidity of each component is increased by applying shot peening under predetermined conditions (claims 9, 10, 11).

[0025] Furthermore, according to preferred embodiments of the speed reducer described in claims 9 to 11, the first spur gear and the second spur gear may undergo heat treatment in the order of quenching, ultra-sub-zeroing and tempering, followed by surface treatment in the order of shot peening, ultra-smooth polishing and oil reservoir processing (claims 12, 13).

[0026] The gearbox described in claim 1 has two disc-shaped covers and a planetary gear stacked so that the planetary gear is sandwiched between the two disc-shaped covers, and this stack is rotatably mounted on an eccentric shaft and housed in a case to form a disc shape. When manufacturing the planetary gear and the two covers by processing the materials, the thickness of the planetary gear and the two covers is made smaller than that of conventional parts by the amount by which the torsional rigidity of the planetary gear and the two covers is increased by shot peening. As a result, the thickness of the stack of the two covers and planetary gear can be made thinner than that of conventional gearboxes. In other words, it becomes possible to make the gearbox thinner and lighter.

[0027] Each component of the planetary gear and the two cover bodies, manufactured with a thinner profile than conventional parts, has its surface shot-peened to increase torsional rigidity. Therefore, it is possible to provide a gearbox that is thinner and lighter than conventional gearboxes without reducing torsional rigidity.

[0028] The gearbox described in claim 2 has multiple grooves on the inner circumference of the case, to which multiple outer pins are rotatably mounted, that have been ultra-smoothly polished. As a result, frictional resistance is reduced compared to conventional cases, and surface roughness and fatigue strength can be improved. Furthermore, since oil reservoir processing is performed after ultra-smooth polishing, the grooves of the case are finished to a plateau structure surface, which improves the lubricating oil retention function compared to conventional cases. This improves the operational efficiency of the case as internal gears. In addition, the temperature rise and noise generation of the gearbox are suppressed, and the lifespan of the gearbox can be extended.

[0029] The gearbox described in claim 3 uses tough cast iron, such as ductile cast iron, for the carrier and case materials, thereby enhancing torsional rigidity compared to conventional parts while retaining the properties of tough cast iron within the parts.

[0030] The gearbox described in claim 4 uses structural steel material with guaranteed hardenability for the eccentric shaft, planetary gears, and multiple outer pins. By strengthening the steel material through heat treatments such as quenching, ultra-subzero hardening, and tempering, and then performing shot peening, the torsional rigidity of these components can be sufficiently increased.

[0031] The gearbox described in claim 5 is manufactured by processing a material to produce an eccentric shaft, planetary gears, and a plurality of outer pins, and then performing heat treatments of quenching, ultra-sub-zero, and tempering in that order, thereby strengthening the material strength of these components. Furthermore, by performing surface treatments of shot peening, ultra-smooth polishing, and oil reservoir processing in that order, the torsional rigidity of these components is increased, and the frictional resistance and surface roughness of the rotating and meshing parts in the gear mechanism of these components are reduced, thereby improving the retention of lubricating oil.

[0032] The gearbox described in claim 6 is configured such that the entire raceway rings of the first bearing (e.g., a tapered roller bearing) and the second bearing (e.g., an angular contact bearing) are shot-peened, and the parts of the raceway rings that come into contact with the rollers are subjected to ultra-smooth polishing and oil reservoir processing in that order. This increases the strength of these bearings, reduces the frictional resistance and surface roughness of the raceway surface on which the rollers roll, and improves the retention of lubricating oil.

[0033] The gearbox described in claim 7 is configured such that the entire surface of the third bearing (for example, a caged needle roller) is shot peened, and the circumferential surface of the roller is subjected to ultra-smooth polishing and oil reservoir processing in that order, thereby increasing the torsional rigidity of the third bearing, reducing the frictional resistance and surface roughness of the parts of the roller that come into contact with the eccentric shaft and planetary gear, and improving the retention force of the lubricating oil.

[0034] In the speed reducer described in claims 9 to 11, the first spur gear and the second spur gear constituting the first reduction section are manufactured with a thickness that is smaller than that of conventional parts by the amount by which the torsional rigidity of the planetary gear and the two covers increases due to shot peening when processing the material to produce each part. As a result, the thickness of the first reduction section of the speed reducer can be made thinner than that of conventional speed reducers, making it possible to make the speed reducer thinner and lighter.

[0035] The speed reducer described in claims 12 and 13 is configured such that the first spur gear and the second spur gear constituting the first speed reduction section are subjected to heat treatments of quenching, ultra-sub-zero and tempering in that order, followed by surface treatments of shot peening, ultra-smooth polishing and oil reservoir processing in that order. This allows for a sufficient increase in the torsional rigidity of the first and second spur gears, as well as a reduction in the frictional resistance and surface roughness of the tooth surfaces of the first and second spur gears, thereby improving the retention of lubricating oil.

[0036] This is a side view (front view) of the speed reducer according to the present invention. This is a diagram showing the gear mechanism of the first reduction section of the speed reducer according to the present invention. This is a top view (plan view) of the speed reducer according to the present invention. This is a one-sided cross-sectional view taken along line A-A in Figure 1. This is a bottom view (bottom view) of the speed reducer according to the present invention. This is a longitudinal cross-sectional view of the speed reducer according to the present invention. This is a top view (plan view) of the front cover. This is a longitudinal cross-sectional view of the front cover. This is a bottom view (bottom view) of the back cover. This is a longitudinal cross-sectional view of the back cover. This is a top view (plan view) of the planetary gear. This is a longitudinal cross-sectional view of the planetary gear. This is a diagram showing the manufacturing process of each component of the front cover and back cover. This is a diagram showing the difference in thickness between the front cover of the speed reducer according to the present invention and a conventional front cover, where (a) is a front view of the front cover of the speed reducer according to the present invention and (b) is a front view of a conventional front cover. This is a diagram showing the manufacturing process of each component constituting the reduction gear mechanism, such as the first spur gear, second spur gear, and planetary gear. This is a diagram showing the relationship between the components of the speed reducer according to the present invention and the surface treatment applied to each component. This is a diagram showing the differences in performance and characteristics between the speed reducer according to the present invention and a conventional speed reducer. This is a skeleton diagram showing the gear mechanism of an RV speed reducer.

[0037] The gearbox according to the present invention will be described with reference to the drawings. The embodiments shown below are merely illustrative. The embodiments shown below can be modified in various ways without departing from the spirit of the present invention.

[0038] Figure 1 is a side view (front view) of the gearbox 1 according to the present invention. Figure 2 is a diagram showing the gear mechanism of the first reduction section 2 of the gearbox 1 (plan view of the first reduction section 2). Figure 3 is a top view of the gearbox 1 (plan view of the gearbox 1). The gearbox 1 is a two-stage reduction gearbox connecting the first reduction section 2 and the second reduction section 3, but the first spur gear 21 of the first reduction section 2 is attached to the motor M, and the second spur gear 22 of the first reduction section 2 is attached to the gearbox 1. The first spur gear 21 and the second spur gear 22 are meshed when the gearbox 1 and the motor M are assembled into the joint of the robot, so Figure 3 shows a plan view of the gearbox 1 with only the second spur gear 22 attached.

[0039] Figure 4 is a one-sided cross-sectional view taken along line A-A in Figure 1. Figure 5 is a view of the reducer 1 from below (bottom view of the reducer 1). Figure 6 is a longitudinal cross-sectional view of the reducer 1. Figures 4 to 6 also show the bottom view and cross-sectional view of the reducer 1 with only the second spur gear 22 attached.

[0040] The speed reducer 1 shown in Figures 1 to 6 is a two-stage speed reducer in which a first speed reducer 2, composed of a spur gear speed reducer, is provided in front of a second speed reducer 3 that uses an internal planetary gear mechanism.

[0041] The first reduction unit 2 is a spur gear reduction mechanism in which a disc-shaped first spur gear 21 and a disc-shaped second spur gear 22 mesh together (see Figures 1 and 2). The first spur gear 21 and the second spur gear 22 are involute gears. A connection part 211 is provided at the center of one plate surface of the first spur gear 21 (the upper plate surface in Figure 1). An electric motor M is connected to the connection part 211 as shown by the dashed line (see Figure 1). The second spur gear 22 is attached to the upper end of a hollow cylindrical eccentric shaft 4. The second spur gear 22 is fixed to the eccentric shaft 4 so as not to rotate by a concentric retaining ring 221 (see Figures 2 and 3). The eccentric shaft 4 corresponds to the input shaft of the second reduction unit 3, and when the second spur gear 22 rotates, the eccentric shaft 4 rotates.

[0042] As shown in Figure 6, the eccentric shaft 4 is positioned to extend below the second spur gear 22. In the following description, the orientation in which the eccentric shaft 4 extends below the second spur gear 22 will be described as the basic orientation of the reduction gear 1. Figure 1 is a side view (front view) of the reduction gear 1 in the basic orientation. In Figures 1 and 6, the direction along the axis center N of the eccentric shaft 4 is defined as the height direction, up-down direction, or vertical direction, and the direction perpendicular to the axis center N of the eccentric shaft 4 is defined as the width direction, left-right direction, or horizontal direction.

[0043] In the first reduction unit 2, when the first spur gear 21 rotates at a rotational speed ω1 [rpm] by the electric motor M, the second spur gear 22 rotates at a rotational speed ω2 (= n × ω1) [rpm] which is reduced by the gear ratio n (= Z1 / Z2) of the number of teeth Z1 of the first spur gear 21 and the number of teeth Z2 (> Z1) of the second spur gear 22. Since the eccentric shaft 4 is fixed to the second spur gear 22, the eccentric shaft 4 also rotates at the rotational speed ω2. The rotation at the rotational speed ω2 reduced by the first reduction unit 2 is input to the second reduction unit 3.

[0044] The second reduction unit 3 includes an eccentric shaft 4, a planetary gear 5 composed of two planetary gears 51 and 52, a plurality of pins 6, a carrier 7 composed of two cover bodies 71 and 72, a rotation transmission member 8, a case 9, tapered roller bearings 11A and 11B, needle rollers 12A and 12B with retainers, and angular bearings 13A and 13B (see FIG. 6). The planetary gear 51 and the planetary gear 52 are planetary gears having the same configuration. In the following description, when distinguishing between the planetary gear 51 and the planetary gear 52, the planetary gear 51 is referred to as the "first planetary gear 51", and the planetary gear 52 is referred to as the "second planetary gear 52". When collectively describing the two planetary gears 51 and 52, they are referred to as the "planetary gear 5".

[0045] The planetary gear 5 is a planetary gear of an internal type planetary gear mechanism. The planetary gear 5 is a disk-shaped gear using a trochoid curve as a tooth profile. FIG. 11 shows a top view (plan view) of the first planetary gear 51, and FIG. 12 shows a longitudinal sectional view of the first planetary gear 51. The two cover bodies 71 and 72 constituting the carrier 7 are components that function to output the rotation of the planetary gear 5 to the outside via the rotation transmission member 8 and also function to protect the upper and lower surfaces of the second reduction unit 3 by sandwiching the planetary gear 5. FIG. 7 shows a top view (plan view) of the front cover 71, and FIG. 8 shows a longitudinal sectional view of the front cover 71. FIG. 9 shows a bottom view of the back cover 72, and FIG. 10 shows a longitudinal sectional view of the back cover 72. In the following description, the cover body 71 that sandwiches the first planetary gear 51 from above is referred to as the "front cover 71", and the cover body 72 that sandwiches the second planetary gear 52 from below is referred to as the "back cover 72". The cover bodies 71 and 72 have a circular shape in plan view and have substantially the same size as the planetary gear 5 (see FIGS. 7, 9, and 11).

[0046] Case 9 functions as an internal gear in the internal planetary gear mechanism and also serves to protect the circumferential surface of the second reduction unit 3 by housing the planetary gear 5 (two planetary gears 51 and 52) sandwiched between the front cover 71 and the back cover 72. Case 9 has a hollow cylindrical shape, and its height H1 [mm] (see Figure 1) is slightly smaller than the height H1' [mm] (see Figure 1) of the portion where the planetary gear 5 is sandwiched between the front cover 71 and the back cover 72. A projection 901 is formed on the inner circumferential wall of case 9, projecting inward from the center in the height direction (see Figure 4). In Figure 6, the opening above the projection 901 of case 9 is the part where the front cover 71 is housed, and the opening below the projection 901 is the part where the back cover 72 is housed. The space inside case 9 surrounded by the projection 901 is the part where the planetary gear 5 is housed.

[0047] A flange 903 (see Figures 3 to 6) is provided on the outer circumference of the case 9, approximately in the center in the height direction. The flange 903 is for, for example, housing the reduction gear 1 in the joint of a robot. Multiple mounting holes 903A are provided in the circumferential direction of the flange 903. The diameters of both openings of the case 9 are set to be slightly larger than the diameters of the front cover 71 and the back cover 72. The diameter of the case 9 inside the protrusion 901 is slightly larger than the diameter of the planetary gear 5. The width of the protrusion 901 is approximately the same as or slightly larger than the thickness of the two planetary gears 51 and 52 stacked on top of each other (see Figure 6). Multiple grooves 902 (see Figure 4) (for example, 40) are drilled in the protrusion 901 at equal intervals in the circumferential direction. The cross-sectional shape of the grooves 902 is semicircular.

[0048] The plurality of pins 6 are components that function as internal teeth of the case 9 (internal gear). The length of the pin 6 is substantially the same as the length of the concave groove 902. The number of pins 6 is, for example, 40, and the pins 6 are rotatably attached to the concave grooves 902 of the protruding portions 901 (see FIG. 4). The number of teeth of the first planetary gear 51 and the second planetary gear 52 is set to a number (39) that is one less than the number of pins 6. Part of the outer teeth 511 (see FIG. 11) of the first planetary gear 51 and the outer teeth 521 of the second planetary gear 52 are in contact with a plurality of pins 6 respectively. In the longitudinal sectional view shown in FIG. 6, the outer teeth 511 on the right side of the first planetary gear 51 are in contact with the outer peripheral pins 6, and the outer teeth 521 on the left side of the second planetary gear 52 are in contact with the outer peripheral pins 6. Since the plurality of pins 6 are arranged around the outside of the outer teeth 511 and 521, they are referred to as "outer peripheral pins 6" in the following description.

[0049] The eccentric shaft 4 is a component that transmits the rotation output from the first reduction unit 2 to the first planetary gear 51 and the second planetary gear 52. Eccentric portions 41 and 42 project from substantially the center in the vertical direction of the eccentric shaft 4 with a small interval provided therebetween (see FIG. 6). The eccentric portions 41 and 42 are eccentric cams that are eccentric by a predetermined amount in the horizontal plane with respect to the axis center N of the eccentric shaft 4. The eccentric portions 41 and 42 are eccentric in opposite directions. The eccentric portion 41 is substantially the same as the thickness of the first planetary gear 51, and the eccentric portion 42 is substantially the same as the thickness of the second planetary gear 52 (see FIG. 6). In the following description, when distinguishing between the eccentric portion 41 and the eccentric portion 42, the eccentric portion 41 is referred to as the "first eccentric portion 41", and the eccentric portion 42 is referred to as the "second eccentric portion 42".

[0050] A retained needle roller 12A and a retained needle roller 12B are attached to the first eccentric portion 41 and the second eccentric portion 42 of the eccentric shaft 4, respectively (see Figure 6). The retained needle roller 12A and the retained needle roller 12B are identical parts. The retained needle rollers 12A and 12B are components for smoothly transmitting the eccentric motion of the first eccentric portion 41 and the second eccentric portion 4B, caused by the rotation of the eccentric shaft 4, to the first planetary gear 51 and the second planetary gear 52, respectively. The retained needle rollers 12A and 12B have a structure in which a plurality of needle rollers are rotatably mounted at equal intervals on the side surface of a retainer which is made of an annular frame. The height of the two retained needle rollers 12A and 12B is approximately the same as the thickness of the first eccentric portion 41 and the second eccentric portion 4B. In the following explanation, when referring to the two retained needle rollers 12A and 12B together, they will be referred to as "retained needle roller 12".

[0051] A first through-hole 51A is formed at the center of the first planetary gear 51 for fitting and mounting the first planetary gear 51 onto the eccentric shaft 4 (see Figure 11). A first through-hole 52A (not shown) is formed at the center of the second planetary gear 52 for fitting and mounting the second planetary gear 52 onto the eccentric shaft 4. The first planetary gear 51 is rotatably mounted on the eccentric shaft 4 by fitting the eccentric shaft 4, to which the retained needle rollers 12A are attached, into the first through-hole 51A, and then fitting the first through-hole 51A and the retained needle rollers 12A together. The second planetary gear 52 is rotatably mounted on the eccentric shaft 4 by fitting the eccentric shaft 4, to which the retained needle rollers 12B are attached, into the first through-hole 52A, and then fitting the first through-hole 52A and the retained needle rollers 12B together.

[0052] The first planetary gear 51, which is mounted on the first eccentric portion 41 of the eccentric shaft 4 with a retained needle roller 12A interposed therebetween, has a portion of its external teeth 511 in contact with a plurality of outer peripheral pins 6 provided on the inner circumference of the case 9 (see Figure 6). The second planetary gear 52, which is mounted on the second eccentric portion 42 of the eccentric shaft 4 with a retained needle roller 12B interposed therebetween, also has a portion of its external teeth 521 in contact with a plurality of outer peripheral pins 6 provided on the inner circumference of the case 9 (see Figure 6).

[0053] Case 9 is fixed. When the eccentric shaft 4 rotates, the rotation of the eccentric shaft 4 causes the two eccentric parts 41 and 42 to perform eccentric motion around the axis N of the eccentric shaft 4. The eccentric motion of the first eccentric part 41 is transmitted to the first planetary gear 51 via the retained needle roller 12A, and the first planetary gear 51 also performs eccentric motion around the axis N of the eccentric shaft 4. The eccentric motion of the second eccentric part 42 is transmitted to the second planetary gear 52 via the retained needle roller 12B, and the second planetary gear 52 also performs eccentric motion around the axis N of the eccentric shaft 4.

[0054] Due to the eccentric motion of the first planetary gear 51, the first planetary gear 51 revolves around the axis center N. Since a portion of the external teeth 511 of the first planetary gear 51 is in contact with the outer peripheral pin 6 of the case 9, the first planetary gear 51 revolves in a way that shifts the position of the external teeth 511 that roll and contact the outer peripheral pin 6 of the case 9. Due to the eccentric motion of the second planetary gear 52, the second planetary gear 52 also revolves around the axis center N. Since a portion of the external teeth 521 of the second planetary gear 52 is in contact with the outer peripheral pin 6 of the case 9, the second planetary gear 52 also revolves in a way that shifts the position of the external teeth 521 that roll and contact the outer peripheral pin 6 of the case 9. Since the eccentricity directions of the first eccentric portion 41 and the second eccentric portion 42 are opposite to each other, the position of the outer peripheral pin 6 on the inner circumferential surface of the case 9 where the outer teeth 511 of the first planetary gear 51 roll and the position of the outer peripheral pin 6 where the outer teeth 521 of the second planetary gear 52 roll and make contact move with a phase difference of 180 degrees.

[0055] During the orbital motion of the first planetary gear 51, the external teeth 511 that contact the outer peripheral pin 6 receive a reaction force from the outer peripheral pin 6, causing the first planetary gear 51 to rotate around the first eccentric portion 41 in the opposite direction to its orbital motion by the retained needle rollers 12A. This rotational motion is the rotational motion of the first planetary gear 51 around the first eccentric portion 41. The second planetary gear 52 also receives a reaction force from the outer peripheral pin 6 during its orbital motion, similar to the first planetary gear 51, and rotates (rotates) around the second eccentric portion 42 in the opposite direction to its orbital motion by the retained needle rollers 12B.

[0056] Therefore, the planetary gear 5 rotates on its own axis in accordance with the rotation of the eccentric shaft 4 while revolving around the axis center N of the eccentric shaft 4. The rotation of the planetary gear 5 is transmitted to the carrier 7 by the rotation transmission member 8, and output from the carrier 7 to the outside (for example, the link of a multi-joint robot). The configuration of the rotation transmission member 8 that transmits the rotation of the planetary gear 5 to the carrier 7 will be described later.

[0057] As shown in Figure 7, a through hole 71A is formed in the center of the front cover 71, and as shown in Figure 9, a through hole 72A is formed in the center of the back cover 72. The through hole 71A is a hole for fitting and attaching the front cover 71 at a position outside the eccentric portion 41 of the eccentric shaft 4 (upper position in Figures 1 and 6). The through hole 72A is a hole for fitting and attaching the back cover 72 at a position outside the eccentric portion 42 of the eccentric shaft 4 (lower position in Figures 1 and 6).

[0058] A tapered roller bearing 11A is installed between the mounting position of the front cover 71 of the eccentric shaft 4 and the through hole 71A of the front cover 71 (see Figure 6). A tapered roller bearing 11B is installed between the mounting position of the back cover 72 of the eccentric shaft 4 and the through hole 72A of the back cover 72 (see Figure 6). The tapered roller bearings 11A and 11B are the same part. By interposing the tapered roller bearing 11A between the eccentric shaft 4 and the through hole 71A of the front cover 71, and the tapered roller bearing 11B between the eccentric shaft 4 and the through hole 72A of the back cover 72, the eccentric shaft 4 rotatably supports the front cover 71 and the back cover 72.

[0059] The tapered roller bearings 11A and 11B, although not shown in the diagram, consist of two annular raceways (inner and outer rings), multiple rolling elements, and a cage. The rolling elements are frustoconical rollers. The cage is an annular frame with inclined sides, which holds multiple rollers rotatably at equal intervals in the circumferential direction. The inner and outer rings sandwich the cage, to which the multiple rollers are mounted, from the inside and outside, and the two rings provide inclined raceway surfaces for the multiple rollers. The inner ring, outer ring, and cage to which the multiple rollers are mounted are assembled such that the vertices of the cones of the inner and outer rings and the cone of the cage converge at a single point on the central axis.

[0060] The front cover 71, which is rotatably mounted on the eccentric shaft 4 by tapered roller bearings 11A, is housed in the upper opening of the case 9, and the back cover 72, which is rotatably mounted on the eccentric shaft 4 by tapered roller bearings 11B, is housed in the lower opening of the case 9. An angular contact bearing 13A is installed between the outer circumference of the front cover 71 and the inner circumference of the case 9, and an angular contact bearing 13B is installed between the outer circumference of the back cover 72 and the inner circumference of the case 9 (see Figure 6). The angular contact bearings 13A and 13B are components that allow the front cover 71 and back cover 72 to rotate smoothly within the case 9 when they rotate around the eccentric shaft 4.

[0061] Like the tapered roller bearings 11A and 11B, the angular contact bearings 13A and 13B are composed of two annular raceways (inner and outer rings), multiple rolling elements, and a cage. The rolling elements are needle rollers. The cage is an annular frame with inclined sides that holds multiple needle rollers rotatably at equal intervals in the circumferential direction. The inner and outer rings are components that sandwich the cage, to which the multiple needle rollers are mounted, from the inside and outside. The raceway surfaces of the inner and outer rings are inclined with respect to their sides (see Figure 6).

[0062] As described above, the rotation of the two planetary gears 51 is transmitted to the front cover 71 and the back cover 72 by the rotation transmission member 8. The front cover 71 is rotatably housed in the case 9 by tapered roller bearings 11A and angular contact bearings 13A, and the back cover 72 is rotatably housed in the case 9 by tapered roller bearings 11B and angular contact bearings 13B, so the carrier 7 (front cover 71 and back cover 72) rotates in sync with the rotation of the planetary gears 5 (the two planetary gears 51 and 52).

[0063] The front cover 71 and the back cover 72 sandwich the two planetary gears 51 and 52, which are mounted on the eccentric portions 41 and 42 of the eccentric shaft 4 via retained needle rollers 12A and 12B, respectively, and support both sides (upper and lower sides in Figure 6) of the two planetary gears 51 and 52 on the eccentric shaft 4. This double-support mechanism improves the torsional rigidity of the reduction gear 1 and increases its strength against overload.

[0064] The front cover 71 has a plurality of fastening holes 71B drilled at equal intervals on a circumference at a predetermined distance from the center of the through hole 71A, and a positioning hole 71C drilled on the same circumference between adjacent fastening holes 71B (see Figure 7). The fastening holes 71B are holes for inserting fastening members (e.g., bolts) that fasten the front cover 71 and the back cover 72 (see Figure 8). The positioning hole 71C is a hole for determining the position of the front cover 71 relative to the back cover 72 when fastening the front cover 71 and the back cover 72 (see Figure 8). A positioning pin 10 is inserted into the positioning hole 71C as shown in Figure 6.

[0065] Multiple mounting holes 72B are drilled at equal intervals on the circumference of the back cover 72, at a predetermined distance from the center of the through hole 72A (see Figure 9). The mounting holes 72B are for attaching the rotation transmission member 8. On one side of the back cover 72 (the upper side in Figure 6), fastening pins 72C are provided midway between adjacent fastening holes 72B (see Figure 9). Nuts are provided on the tip surface of the fastening pins 72C (see Figure 10). The fastening pins 72C are members that fasten the fastening member (bolt) inserted into the fastening hole 71B of the front cover 71 when fastening the front cover 71 and the back cover 72.

[0066] The first planetary gear 51 has multiple (for example, 16) second through holes 51B drilled at equal intervals on a circumference at a predetermined distance from the center of the first through hole 51A (see Figures 11 and 12). The second planetary gear 52 also has multiple (for example, 16) second through holes 52B drilled at equal intervals on a circumference at a predetermined distance from the center of the first through hole 52A, similar to the first planetary gear 51 (see Figures 11 and 12). The second through holes 51B and 52B are holes into which a fastening pin 72C formed on one surface of the back cover 72 (the upper surface in Figures 6 and 10) and a reaction force pin 81 attached to the other surface are inserted when the first planetary gear 51 and the second planetary gear 52 are sandwiched between the front cover 71 and the back cover 72.

[0067] The rotation transmission member 8 is a member that transmits the rotation of the first planetary gear 51 and the second planetary gear 52 to the carrier 7. The rotation transmission member 8 is composed of a reaction force pin 81 consisting of a plurality (for example, 8) solid pins 81A (hereinafter referred to as "support pins 81A") and a plurality (for example, 8) hollow pins 81B (hereinafter referred to as "hollow pins 81B") (see Figure 6). The support pins 81A are pins that are attached to the mounting holes 72B of the back cover 72. One end of the support pin 81A is provided with a step (base) for mounting into the mounting hole 72B of the back cover 72. A fastening nut is formed on the stepped end face of the support pin 81A, and a groove for fitting the positioning pin 10 is formed on the tip face of the support pin 81A (see Figures 6 and 10).

[0068] Multiple support pins 81A are each attached to multiple mounting holes 72B of the case back 72. Each support pin 81A is attached to each mounting hole 72B of the case back 72 by inserting its base into the mounting hole 72B of the case back 72 and fastening a fastening bolt inserted from the opposite side of the mounting hole 72B with a nut provided on the base. Reaction pins 81 are attached to each mounting hole 72B of the case back 72 by placing hollow pins 81B over the support pins 81A fixed to the mounting holes 72B of the case back 72.

[0069] The planetary gear 5 (two planetary gears 51 and 52) is fitted without gap between the eccentric shaft 4 and the angular bearings 13A and 13B. The planetary gear 5 is sandwiched between the front cover 71 and the back cover 72 to which the reaction pins 81 are attached, and the front cover 71 and the back cover 72 are integrated by fastening them with fastening members. Specifically, eight reaction pins 81 attached to the back cover 72 and eight fastening pins 72C protruding from the back cover 72 are inserted from the second planetary gear 52 side into the 16 second through holes 51B of the two planetary gears 51 and 52, respectively, and the positions of the eight positioning holes 71C of the front cover 71 and the reaction pins 81 attached to the back cover 72 are aligned. Then, positioning pins 10 are inserted into each of the eight positioning holes 71C, and fastening bolts (not shown) are inserted into the eight fastening holes 71B. Furthermore, by fastening each bolt to a nut formed on the tip surface of a support pin 81A facing each fastening hole 71B, the two planetary gears 51 and 52 are integrally sandwiched between the front cover 71 and the back cover 72.

[0070] When the two planetary gears 51 and 52, sandwiched between the front cover 71 and the back cover 72, rotate, the second through holes 51B and 52B come into contact with the reaction pin 81, and the rotation of the two planetary gears 51 and 52 is transmitted to the front cover 71 and the back cover 72. When the second through holes 51B and 52B come into contact with the reaction pin 81, a reaction force is generated from the reaction pin 81 to the second through holes 51B and 52B. Since the hollow pin 81B is rotatably attached to the support pin 81A, the reaction force on the second through holes 51B and 52B is absorbed by the smooth rotation of the hollow pin 81B, and the rotation of the two planetary gears 51 and 52 is effectively transmitted to the front cover 71 and the back cover 72.

[0071] The centers of the front cover 71 and the back cover 72 are rotatably supported on the eccentric shaft 4 by tapered roller bearings 11A and 11B, and the circumferential surfaces of the front cover 71 and the back cover 72 are rotatably supported on the case 9 by angular contact bearings 13A and 13B. As a result, the front cover 71 and the back cover 72 rotate smoothly in synchronization with the rotation of the two planetary gears 51 and 52. The rotation of the front cover 71 and the back cover 72 is the rotation output from the second reduction unit 3 (speed reducer 1).

[0072] Next, the characteristic configuration of the speed reducer 1 according to the present invention will be described.

[0073] As shown in Figures 1 and 3, the reducer 1 used in the joints of industrial robots has a disc shape. As shown in Figure 6, the reducer 1 achieves its disc shape by housing a carrier 7, in which two planetary gears 51 and 52 are sandwiched between a front cover 71 and a back cover 72, in a cylindrical case 9. To further reduce the thickness of this configuration, it is necessary to reduce the thickness of the front cover 71, the back cover 72, and the planetary gears 51 and 52, as well as to lower the height of the case 9 and shorten the length of the eccentric shaft 4. However, simply reducing the physical size of these parts can lead to problems such as a decrease in the characteristics of the reducer 1, such as torsional rigidity, and a decrease in performance such as backlash.

[0074] Since thinning the reducer 1 and improving its performance and characteristics are mutually exclusive, when reducing the thickness of components such as the front cover 71, back cover 72, first planetary gear 51, and second planetary gear 52, which are arranged inside the case 9, and shortening the length of the eccentric shaft 4, it is necessary to give full consideration to the decrease in the torsional rigidity of the reducer 1 and the decrease in the performance of the rotating and frictional parts inside the reducer 1. In particular, the gear mechanism of the reducer 1 is prone to a decrease in performance and characteristics, so it is necessary to take measures to suppress or improve the decrease in performance and characteristics of the gear mechanism of the reducer 1.

[0075] The speed reducer 1 according to this embodiment is thinner than conventional speed reducers by adjusting the size of the components related to the thinning of the speed reducer 1 in the height direction. Components related to the thinning of the speed reducer 1 include the eccentric shaft 4, the first spur gear 21, the second spur gear 22, the front cover 71, the back cover 72, the first planetary gear 51, the second planetary gear 52, and the case 9. For disc-shaped components such as the first spur gear 21, the second spur gear 22, the front cover 71, the back cover 72, the first planetary gear 51, and the second planetary gear 52, the size of the speed reducer 1 in the height direction is the "thickness" of the disc, while for the eccentric shaft 4 and the cylindrical case 9, the size of the speed reducer 1 in the height direction is the "height" or "length" of the cylinder.

[0076] The size of the components related to the thinning of the speed reducer 1 is adjusted so that the size of the conventional components is reduced by approximately (1-β) times, where β (<1) is the ratio of the increase in torsional rigidity when the conventional components (hereinafter referred to as "conventional components") are strengthened by applying a predetermined surface treatment (e.g., shot peening) to the original torsional rigidity. For example, if the torsional rigidity of the conventional component is Ka [Nm / rad], and the torsional rigidity when the conventional component is shot peened under predetermined conditions is Ka' (>Ka), then the ratio β of the increase in torsional rigidity is expressed as β = (Ka'-Ka) / Ka. If the thickness of the conventional component (original thickness) is t' [mm], and the thickness obtained by reducing that thickness by (β × t') (thickness after thinning adjustment) is t (<t') [mm], then the thickness t of the components related to the thinning of the speed reducer 1 is set to a relationship of t = t' × (1-β) with respect to the thickness t' of the conventional component.

[0077] Here, we will explain the technical significance of setting the thickness t of flat plate components such as planetary gears 5 and carriers 7 to the relationship t = t' × (1 - β) with respect to the thickness t' of conventional components.

[0078] If a flat plate component with thickness t' [mm] and torsional rigidity K' [Nm / rad] (hereinafter referred to as the "original flat plate component") is shot peened under predetermined conditions J, and the increase in torsional rigidity is ΔK', then the ratio β of the increase ΔK' to the original torsional rigidity K' is given by β = ΔK' / K' … (A1).

[0079] Let Δt [mm] be the amount by which the thickness of the original flat plate part is reduced. If this thickness reduction Δt corresponds to the ratio β of the increase in torsional stiffness with respect to the original thickness t' of the flat plate part, then the thickness reduction Δt can be expressed using equation (A1) as follows: Δt = β × t' = (ΔK' / K') × t' … (A2).

[0080] If the thickness of the original flat plate part is reduced by Δt, and the resulting thickness is t [mm], then the thickness t can be expressed using equation (A2) as t = t' - Δt = (1 - β) × t' ... (A3).

[0081] The stiffness (torsional stiffness) of a flat plate under shear (torsional deformation) load is said to be proportional to the product of the shear modulus G and the plate thickness. If the thickness of the original flat plate part is t' and its torsional stiffness is K', and the thickness of a thin flat plate part obtained by reducing the thickness of the original flat plate part is t and its torsional stiffness is K, then the torsional stiffness K of that part and the torsional stiffness K' of the original flat plate part are expressed as follows: K' = A × G × t' (A: proportionality constant) K = A × G × t (A: proportionality constant) Therefore, the relationship K = (t / t') × K' ... (A4) is obtained.

[0082] From equation (A3), we have t / t' = (1 - β), so substituting this into equation (A4), we obtain the relationship K = (1 - β) × K' ... (A5).

[0083] When a thin, flat plate component with torsional rigidity K is shot peened under condition J, an increase in torsional rigidity ΔK' is imparted. Therefore, the torsional rigidity Kb of the thin, flat plate component after shot peening is given by Kb = (1 - β) × K' + ΔK'. Substituting ΔK' from equation (A1) into this equation, we obtain the following relationship: Kb = (1 - β) × K' + β × K' = K' ... (A6).

[0084] Equation (A6) shows that if a thin flat plate part with a thickness of t is manufactured by reducing the thickness of the original flat plate part by a thickness Δt corresponding to the ratio β of the increase in torsional rigidity when the original flat plate part is shot peened under predetermined conditions J, then if the thin flat plate part is shot peened under predetermined conditions J, the torsional rigidity of the thin flat plate part, which has decreased to a torsional rigidity of K, can be increased to the torsional rigidity K' of the original flat plate part.

[0085] Therefore, in the gearbox 1 according to this embodiment, when manufacturing flat plate parts such as planetary gears 5 and carriers 7 by cutting metal material to produce flat plate parts with a predetermined shape and thickness, the thickness is made thinner than that of conventional parts by an amount equivalent to the percentage increase in torsional rigidity β (β × t') when conventional parts are shot peened under predetermined conditions J. Reducing the thickness compared to conventional parts reduces torsional rigidity, but in the gearbox 1 according to this embodiment, the reduced torsional rigidity of the thin flat plate parts is compensated for by performing shot peening under predetermined conditions J on the thin flat plate parts, thereby realizing thin flat plate parts without reducing torsional rigidity.

[0086] 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 projectiles (microspheres) onto the surface at high speed. When shot peening is applied to the surface of a metal part, the hardness of the part's surface is strengthened, and the torsional rigidity of the metal part can be increased. Shot peening has effects such as increasing the fatigue strength of the metal part, improving wear resistance, and improving the resistance to force corrosion cracking. Furthermore, because shot peening forms countless indentations (marks) on the surface of the metal part, it also has effects such as improving heat dissipation, reducing weight, and decreasing fluid resistance (oil retention effect). In addition, shot peening can remove impurities adhering to the surface of the part and fine burrs that have formed on the surface, eliminating abnormal layers in the surface structure.

[0087] The front cover 71 and back cover 72 function as protective members that sandwich the two planetary gears 51 and 52 and protect the front and back surfaces of the second reduction unit 3. The case 9 functions as a protective member that covers the circumferential surfaces of the front cover 71 and back cover 72 that sandwich the two planetary gears 51 and 52 and protects the outer circumferential surface of the second reduction unit 3. Furthermore, the carrier 7, consisting of the front cover 71 and back cover 72, functions as an output unit that outputs the rotation of the first planetary gear 51 and the second planetary gear 52 to a load connected to the reduction gear 1 (for example, a link of an industrial robot). For this reason, high torsional rigidity is required for the front cover 71 and back cover 72.

[0088] Since the carrier 7 and case 9 function as protective members for the reducer 1, they are made of cast iron, which has excellent mechanical strength, wear resistance, and heat resistance. The carrier 7 and case 9 are made of tough cast iron with enhanced tensile strength and ductility, such as ductile cast iron.

[0089] Figure 13 shows the manufacturing process for each component: the front cover 71, the back cover 72, and the case 9. Steps S5 and S6 are processes applied only to the case 9. Figure 14 shows the difference in thickness between the front cover 71 and the conventional front cover 71', where (a) is a front view of the front cover 71 and (b) is a front view of the conventional front cover 71'. The manufacturing methods for each component, the front cover 71, the back cover 72, and the case 9, will be explained below using the front cover 71 as an example.

[0090] Step S1 involves machining ductile cast iron to produce a part with the same shape as the conventional cover 71' but with a thinner thickness. The thickness t [mm] of the produced cover 71 is set to t = t' × (1 - β) relative to the thickness t' [mm] of the conventional cover 71' (see Figure 14). For example, if β = 0.25, the thickness t of the cover 71 is set to approximately 75 [%] of the thickness t' [mm] of the conventional cover 71' (0.75 × t' [mm]).

[0091] The surface of the fabricated cover 71 is subjected to shot peening treatment under conditions corresponding to the percentage increase in torsional rigidity β in the above formula (for example, conditions such as shot size, shot projection angle, impact velocity, and treatment time) (step S2). The relationship between the percentage increase in torsional rigidity β compared to the conventional cover 71' and the shot peening treatment conditions has been determined in advance.

[0092] Step S3 measures the torsional rigidity of the cover 71 after shot peening. Step S4 determines whether the measured torsional rigidity exceeds the torsional rigidity value (current value) of the conventional cover 71'. If the measured torsional rigidity does not exceed the torsional rigidity value of the conventional cover 71' (NO in Step S4), the process returns to Step S2 and shot peening is performed again, and this is repeated until the measured torsional rigidity exceeds the torsional rigidity value of the conventional cover 71' (loop of Steps S2 to S4). When the measured torsional rigidity exceeds the torsional rigidity value of the conventional cover 71' (YES in Step S4), the manufacturing process of the cover 71 is terminated.

[0093] Through the above manufacturing method, the front cover 71 retains the properties of ductile cast iron within the component while having torsional rigidity equivalent to or stronger than that of the conventional front cover 71'. For example, when β = 0.25, the thickness t of the front cover 71 is approximately 25% thinner than the thickness t' of the conventional front cover 71' without reducing the torsional rigidity or strength of the conventional front cover 71'. The back cover 72 and case 9 are also manufactured using the same method as the front cover 71, and their thickness t is approximately 25% thinner than that of the conventional back cover and case without reducing the torsional rigidity or strength of the conventional back cover and case. Furthermore, the front cover 71, back cover 72, and case 9 are also lighter due to their reduced thickness.

[0094] Multiple outer peripheral pins 6, rotatably mounted in multiple grooves 902 of case 9, function as internal gears for the first planetary gear 51 and the second planetary gear 52 (external gears). After the torsional rigidity of case 9 is strengthened by shot peening, the semicircular grooves 902 (see Figure 4) are subjected to ultra-smooth polishing (step S5) and further surface treatment with oil reservoir processing (step S6) to make the rolling contact between the external teeth of the first planetary gear 51 and the second planetary gear 52 and the internal teeth (outer peripheral pins 6) of case 9 as smooth as possible.

[0095] Ultrasmooth polishing is a polishing method that creates ultrasmooth optical surfaces for high-precision optical elements. Examples of known polishing methods include bloat polishing, EEM (elastic emission machining), and pole feed polishing. Oil reservoir machining is a process that uses a scraper tool to create depressions of a few micrometers in size on a flat surface to hold lubricating oil.

[0096] The surface of the groove 902 is subjected to an ultra-smooth polishing surface treatment, which removes abnormal layers in the surface structure and results in an ultra-smooth surface with an arithmetic mean roughness of Ra 0.0097. The surface of the groove 902 has reduced frictional resistance compared to the grooves of conventional cases, and its surface roughness and fatigue strength are improved. Furthermore, the surface of the groove 902 is finished with an oil reservoir process to create a plateau structure, improving the lubricating oil retention function (oil reservoir) by approximately 20% compared to the grooves of conventional cases. The groove 902 maintains good lubrication when the outer peripheral pin 6 rotates within the groove 902, thereby suppressing the rise in oil temperature and the generation of noise in the reducer 1. As a result, the operational efficiency of the internal teeth of the case 9 can be improved, and the lifespan of the case 9 can be extended.

[0097] As described above, while the case 9 contributes to the thinning of the reducer 1, the groove 902 of the case 9 greatly affects the performance of the reduction gear mechanism of the reducer 1. Therefore, not only is the torsional rigidity of the case 9 strengthened by shot peening the entire surface of the case 9, but the surface of the groove 902 is also treated with ultra-smooth polishing and oil reservoir processing to reduce the frictional resistance of the groove 902 and prevent the lubricating oil from running out. The outer peripheral pin 6, which is rotatably mounted in the groove 902, rotates smoothly, allowing the outer teeth 511, 521 (see Figure 11) of the first planetary gear 51 and the second planetary gear 52 to roll and contact the outer peripheral pin 6 (internal teeth) of the case 9 as smoothly as possible when they rotate, thereby suppressing the generation of noise during contact.

[0098] On the other hand, the first spur gear 21, the second spur gear 22, the first planetary gear 51, the second planetary gear 52, the eccentric shaft 4, etc., are components that make up the reduction gear mechanism, and are therefore manufactured using carbon-containing steel materials used for parts where strength and machinability are important. For example, the first spur gear 21, the first planetary gear 51, the second planetary gear 52, and the eccentric shaft 4 are manufactured using structural steel materials that guarantee hardenability, and the second spur gear 22 is manufactured using high-carbon chromium bearing steel materials. The first spur gear 21, second spur gear 22, first planetary gear 51, second planetary gear 52, and eccentric shaft 4, like the front cover 71, back cover 72, and case 9, share the common process of reducing their thickness by an amount that increases torsional rigidity by β × 100 [%] compared to conventional parts, followed by shot peening to enhance torsional rigidity. However, they differ in that they undergo additional heat treatments such as quenching, ultra-sub-zero treatment, and tempering, as well as surface treatments such as ultra-smooth polishing and oil reservoir processing. The reason for the additional heat treatment is that they are made of a different material than the carrier 7 and case 9.

[0099] Figure 15 shows the manufacturing process for each component that makes up the reduction gear mechanism, including the first spur gear 21, the second spur gear 22, the first planetary gear 51, and the second planetary gear 52. The manufacturing method for each component that makes up the reduction gear mechanism will be explained below, using the second spur gear 22 as an example.

[0100] For example, a part is manufactured by machining high-carbon chromium bearing steel to have the same shape as a conventional second spur gear but with a thinner thickness (step S11). For example, if β = 0.25, the thickness of the manufactured second spur gear 22 is set to approximately 75% of the thickness of the conventional second spur gear, similar to the manufacturing process of the cover 71. Subsequently, the manufactured second spur gear 22 is subjected to heat treatment in the following order: quenching (step S12), ultra-sub-zero treatment (step S13), and tempering (step S14). The reason for performing quenching, ultra-sub-zero treatment, and tempering before shot peening is to harden the structural steel material, improve its strength, and increase its fatigue resistance, since structural steel material with guaranteed hardenability is used.

[0101] Quenching is a process in which carbon-containing steel is heated to a temperature above its transformation point, and then rapidly cooled to transform the steel's structure into a martensitic structure. Since the martensitic structure is extremely hard, quenching can improve the hardness, strength, and fatigue resistance of high-carbon chromium bearing steel. Tempering is a process in which the steel is heated again after quenching to adjust the hardness and increase its toughness and ductility. Super sub-zero treatment is a process in which high-carbon chromium bearing steel is cooled to below -130 degrees Celsius before tempering to transform the austerite structure remaining after quenching into a martensitic structure. Super sub-zero treatment can further improve the hardness, strength, and fatigue resistance of high-carbon chromium bearing steel.

[0102] After tempering heat treatment, the surface of the second spur gear 22 is subjected to the shot peening described above (step S15). This shot peening is performed under shot peening conditions (for example, shot size, shot projection angle, impact velocity, processing time, etc.) corresponding to the percentage β of increase in torsional rigidity. This shot peening is continued until the measured value of the torsional rigidity exceeds the torsional rigidity value of the conventional second spur gear (loop of steps S15 to S17). Once the torsional rigidity of the second spur gear 22 is strengthened by shot peening, in order to make the meshing between the first spur gear 21 and the second spur gear 22 as smooth as possible, the outer surface of the external teeth 22A (see Figure 2) of the second spur gear 22 is subjected to ultra-smooth polishing (step S18), and further surface treatment with oil reservoir processing is performed (step S19).

[0103] The second spur gear 22 is subjected to a process in which its thickness is reduced compared to a conventional second spur gear, followed by quenching, ultra-subzero treatment, and tempering in that order. This process enhances the hardness of the second spur gear 22, ensures uniformity of dimensions and hardness, improves wear resistance, and prevents deterioration over time. The first spur gear 21, the first planetary gear 51, the second planetary gear 52, and the eccentric shaft 4 are subjected to the same heat treatment, thereby enhancing the hardness of these parts, ensuring uniformity of dimensions and hardness, improving wear resistance, and preventing deterioration over time.

[0104] Furthermore, since shot peening is performed on the surface of the second spur gear 22 after tempering, the second spur gear 22 is also endowed with the effects of the shot peening treatment described above (increased fatigue strength, improved wear resistance, improved force corrosion cracking characteristics, improved heat dissipation, weight reduction, and reduced fluid resistance (molten metal retention effect, etc.)). The first spur gear 21, the first planetary gear 51, the second planetary gear 52, and the eccentric shaft 4 are also subjected to the same shot peening treatment, thus endowed with the effects of the shot peening treatment described above. In addition, impurities adhering to the surface of the first spur gear 21, the second spur gear 22, the planetary gears 51, 52, and the eccentric shaft 4 are removed, and any abnormal layers in the surface structure are eliminated.

[0105] Each component of the first spur gear 21, second spur gear 22, first planetary gear 51, second planetary gear 52, and eccentric shaft 4 undergoes heat treatment including quenching, ultra-sub-zero treatment, and tempering after manufacturing, followed by shot peening. As a result, properties such as hardness, fatigue strength, and wear resistance are improved by at least 25% compared to conventional first spur gears, second spur gears, planetary gears, and eccentric shaft components.

[0106] Furthermore, the first spur gear 21 and the second spur gear 22 have ultra-smooth polishing and oil reservoir processing applied to the outer circumferential surfaces of the external teeth 21A and 22A (see Figure 2) that mesh with each other. As a result, compared to conventional first and second spur gears, the effect of the ultra-smooth polishing described above is improved by at least 30%, and the effect of the oil reservoir processing described above is improved by at least 20%. The first planetary gear 51 and the second planetary gear 52 have ultra-smooth polishing and oil reservoir processing applied to the outer circumferential surfaces of the external teeth 511 and 521 (see Figure 11) that make rolling contact with the outer circumferential pins 6 of the case 9, and to the inner circumferential surfaces of the through holes 51A and 52A (see Figure 11) into which the retained needle rollers 12A and 12B are mounted. As a result, compared to conventional planetary gears, the effect of the ultra-smooth polishing described above is improved by at least 30%, and the effect of the oil reservoir processing described above is improved by at least 20%.

[0107] The outer circumferential pin 6 functions as an internal tooth of the case 9 and is a component that the external teeth 511 and 521 of the first planetary gear 51 and the second planetary gear 52 roll into contact with. Therefore, like the second spur gear 22, it is manufactured using high-carbon chromium bearing steel. The reaction force pin 81 is a component that transmits the rotation of the planetary gear 5 to the carrier 7, and therefore, like the second spur gear 22, it is manufactured using high-carbon chromium bearing steel. The outer circumferential pin 6 and the reaction force pin 81 are also manufactured using the same manufacturing process as the second spur gear 22 described above (manufacturing process in Figure 15).

[0108] The outer perimeter pin 6 is manufactured by machining high-carbon chromium bearing steel to produce a part with the same shape as a conventional outer perimeter pin (step S11). Subsequently, the manufactured outer perimeter pin 6 is subjected to heat treatment in the following order: quenching (step S12), ultra-subzero treatment (step S13), and tempering (step S14). The support pin 81A is also manufactured by machining high-carbon chromium bearing steel to produce a part with the same shape as a conventional support pin, and the hollow pin 81B is also manufactured by machining high-carbon chromium bearing steel to produce a part with the same shape as a conventional hollow pin (step S11). The lengths of the support pin 81A and the hollow pin 81B are set shorter than the lengths of the conventional support pin and hollow pin, in accordance with the fact that the thickness of the first planetary gear 51 and the second planetary gear 52 is thinner than that of conventional planetary gears. Next, the fabricated support pin 81A and hollow pin 81B are subjected to the following heat treatments in this order: quenching (step S12), ultra-sub-zero treatment (step S13), and tempering (step S14).

[0109] After tempering heat treatment, the surface of the outer pin 6 is subjected to the shot peening described above (step S15). This shot peening is carried out until the measured torsional rigidity exceeds the conventional torsional rigidity value (current value) of the outer pin (loop of steps S15 to S17). After tempering heat treatment, the support pin 81A and the hollow pin 81B are also subjected to the shot peening described above on their surfaces until the measured torsional rigidity exceeds the conventional torsional rigidity values ​​(current values) of the support pin and hollow pin, respectively (YES in step S17) (step S15).

[0110] When the torsional rigidity of the outer peripheral pin 6 is enhanced by shot peening, the outer peripheral surface of the outer peripheral pin 6 is subjected to ultra-smooth polishing (step S18) and further oil reservoir surface treatment (step S19) in order to make the rolling contact with the external teeth 511 and 521 of the first planetary gear 51 and the second planetary gear 52 as smooth as possible. When the torsional rigidity of the support pin 81A is enhanced by shot peening, the outer peripheral surface of the support pin 81A is subjected to ultra-smooth polishing (step S18) and further oil reservoir surface treatment (step S19) in order to make the rotation of the hollow pin 81B as smooth as possible. When the torsional rigidity of the hollow pin 81B is enhanced by shot peening, the entire surface of the hollow pin 81B is subjected to ultra-smooth polishing (step S18) and further oil reservoir surface treatment (step S19) in order to make the rotation of the hollow pin 81B as smooth as possible.

[0111] The outer perimeter pin 6 undergoes heat treatment including quenching, ultra-sub-zero treatment, and tempering after the part is manufactured, and further shot peening is performed on the surface of the part. As a result, properties such as hardness, fatigue strength, and wear resistance are improved by at least 25% compared to conventional outer perimeter pins. In addition, the outer perimeter pin 6 undergoes ultra-smooth polishing and oil reservoir processing on its outer surface after shot peening. As a result, the effect of the ultra-smooth polishing is improved by at least 30% and the effect of the oil reservoir processing is improved by at least 20% compared to conventional outer perimeter pins.

[0112] The reaction force pin 81 undergoes heat treatment including quenching, ultra-sub-zero treatment, and tempering after the part is manufactured, and further shot peening is performed on the surface of the part. As a result, its properties such as hardness, fatigue strength, and wear resistance are improved by at least 25% compared to conventional reaction force pins. In addition, the support pin 81A undergoes ultra-smooth polishing and oil reservoir processing on its outer surface after shot peening, and the hollow pin 81B undergoes ultra-smooth polishing and oil reservoir processing on its inner surface after shot peening. As a result, compared to conventional support pins and conventional hollow pins, the effect of the ultra-smooth polishing described above is improved by at least 30%, and the effect of the oil reservoir processing described above is improved by at least 20%, respectively.

[0113] Each of the tapered roller bearings 11A, 11B, the caged needle roller bearings 12A, 12B, and the angular contact bearings 13A, 13B comprises two annular raceways (inner and outer rings) and a plurality of rollers or balls positioned between the two raceways. By rotating the plurality of rollers or balls in accordance with the rotation of the inner and outer rings, the bearings perform the function of smoothly rotating the inner ring side member and the outer ring side member, respectively.

[0114] In response to the strengthening of the overall strength of the eccentric shaft 4, planetary gear 5, and carrier 7 by shot peening, and the reduction of frictional resistance in the parts related to the gear mechanism and the prevention of oil depletion through ultra-smooth polishing and oil reservoir processing, the bearings 11A, 11B, 12A, 12B, 13A, and 13B are also strengthened by shot peening in the same procedure as steps S15 to S19 in Figure 15, and the reduction of frictional resistance in the parts related to the gear mechanism and the prevention of oil depletion through ultra-smooth polishing and oil reservoir processing.

[0115] In the tapered roller bearings 11A and 11B, shot peening is performed on the entire inner ring and the entire outer ring, which provide the raceway surface for the frustoconical rollers. Ultra-smooth polishing and oil reservoir processing are performed on the surfaces (raceway surfaces) on which the rollers of the inner and outer rings roll. Due to these surface treatments, the tapered roller bearings 11A and 11B have improved properties such as hardness, fatigue strength, and wear resistance by at least 25% compared to conventional tapered roller bearings. Furthermore, compared to conventional tapered roller bearings, the tapered roller bearings 11A and 11B show at least a 30% improvement in the effect of the ultra-smooth polishing and at least a 20% improvement in the effect of the oil reservoir processing.

[0116] In the caged needle rollers 12A and 12B, the entire needle roller component is shot peened. Furthermore, in the caged needle roller 12A, the circumferential surface of the needle roller that contacts the eccentric portion 41 of the eccentric shaft 4 and the through hole 51A of the first planetary gear 51 is subjected to ultra-smooth polishing and oil reservoir processing. In the caged needle roller 12B, the circumferential surface of the needle roller that contacts the eccentric portion 42 of the eccentric shaft 4 and the through hole 52A of the second planetary gear 52 is subjected to ultra-smooth polishing and oil reservoir processing. Due to these surface treatments, the caged needle rollers 12A and 12B exhibit at least a 25% improvement in properties such as hardness, fatigue strength, and wear resistance compared to conventional caged needle rollers. Furthermore, the circumferential surface of the retained needle rollers 12A and 12B shows at least a 30% improvement in the ultra-smooth polishing effect and at least a 20% improvement in the oil reservoir processing effect compared to conventional retained needle rollers.

[0117] In angular contact bearings 13A and 13B, shot peening is performed on the entire inner and outer rings that form the roller raceway surface, and ultra-smooth polishing and oil reservoir processing are performed on the surfaces (raceway surfaces) where the rollers of the inner and outer rings roll. Due to these surface treatments, the angular contact bearings 13A and 13B have improved properties such as hardness, fatigue strength, and wear resistance by at least 25% compared to conventional angular contact bearings. Furthermore, compared to conventional tapered roller bearings, the angular contact bearings 13A and 13B show at least a 30% improvement in the effect of the ultra-smooth polishing and at least a 20% improvement in the effect of the oil reservoir processing.

[0118] Figure 16 is a table showing the relationship between the components of the reduction gear 1 described above and the surface treatments applied to each component. In this table, "Material" indicates the type of steel used for each component, and specific examples are shown in parentheses. "Treatment 1" to "Treatment 6" indicate the order of treatments when multiple treatments are applied to each component.

[0119] As shown in the table, the reducer 1 uses spheroidal graphite cast iron for the carrier 7 and case 9, and carbon-containing steel for the other parts. In order to make the reducer 1 thinner and lighter, it is necessary to strengthen the torsional rigidity of the reducer 1, so basically all parts constituting the reducer 1 are shot-peened. Furthermore, parts made of carbon-containing steel are subjected to heat treatment of quenching, ultra-sub-zero treatment and tempering before shot-peening to further increase the strength of the steel. After increasing the strength of the parts by shot-peening, the parts of each part related to the reduction gear mechanism of the reducer 1 (contact parts and meshing parts between parts, bearing roller rolling parts, etc.) are subjected to ultra-smooth polishing and oil reservoir processing to further reduce frictional resistance, ensure sufficient lubrication and prevent oil depletion.

[0120] Figure 17 is a table comparing the product specifications of the gearbox 1 according to this embodiment with those of a conventional product.

[0121] As shown in Figure 17, when we prototyped the speed reducer 1 according to the present invention, we were able to reduce the thickness of the speed reducer 1 by at least 20% compared to conventional speed reducers (currently commercialized speed reducers), and reduce the weight of the speed reducer 1 by at least 17% compared to conventional speed reducers. In addition, the torsional rigidity of the speed reducer 1 was improved by 5 to 50 N·m compared to conventional speed reducers, and we were able to achieve a thinner and lighter speed reducer 1 without reducing the strength of the torsional rigidity.

[0122] Furthermore, by applying ultra-smooth polishing and oil reservoir processing to the parts related to the rotation, meshing, and contact of the reduction gear mechanism of the reducer 1, the frictional resistance and surface roughness of the friction and sliding surfaces are greatly reduced, and the oil reservoir of the lubricating oil is improved. As a result, the transmission efficiency, starting torque, no-load running torque, angular transmission error, backlash, lost motion, and noise of the reducer 1 have been significantly improved compared to conventional reducers.

[0123] In the above embodiment, a two-stage reduction gear 1 was described in which a first reduction gear 2 is provided before the second reduction gear 3. However, the present invention can also be applied to a reduction gear in which the first reduction gear 2 is omitted. In the above embodiment, a spur gear reduction mechanism combining two spur gears 21 and 22 is used as the first reduction gear 2, but a reduction device using a planetary gear mechanism may also be used for the first reduction gear 2.

[0124] As described above, the gearbox according to the present invention can be made thinner and lighter than conventional gearboxes without reducing strength such as torsional rigidity. Furthermore, by reducing the frictional resistance between friction parts compared to conventional parts and improving the lubrication oil retention function compared to conventional parts, the performance of the gearbox, such as transmission efficiency, starting torque, angle transmission error, backlash, and lost motion, can be significantly improved compared to conventional gearboxes.

[0125] Therefore, the reduction gear according to the present invention can be used to miniaturize and lighten industrial robots, and to enable smooth movement of the robot arm.

[0126] 1 Reducer 2 First reduction section 21 First spur gear 22 Second spur gear 3 Second reduction section 4 Eccentric shaft 41 First eccentric section 42 Second eccentric section 5 Planetary gear 51 First planetary gear 52 Second planetary gear 51A, 52A First through hole 51B, 52B Second through hole 6 Pin (outer pin) 7 Carrier 71 Cover (front cover) 71A Through hole (of front cover) 71B Fastening hole (of front cover) 71C Positioning hole (of front cover) 72 Cover (back cover) 72A Through hole (of back cover) 72B Mounting hole (of back cover) 72C Fastening pin (of back cover) 8 Rotation transmission member 81 Reaction pin 81A Support pin 81B Hollow pin 9 Case 901 Protrusion 902 Groove 903 Flange 10 Positioning pin 11A, 11B Tapered roller bearing 12A, 12B Needle roller bearing with cage 13A, 13B Angular contact bearing M Electric motor

Claims

1. A reduction gear comprising: an eccentric shaft having an eccentric portion, the shaft rotating due to the rotation of a motor causing the eccentric portion to perform eccentric motion; a planetary gear rotatably supported on the eccentric portion of the eccentric shaft, and performing eccentric motion around the axis center of the eccentric shaft due to the eccentric motion of the eccentric portion; a case arranged around the planetary gear, with a plurality of outer peripheral pins rotatably attached to its inner surface, functioning as internal teeth for the external teeth of the planetary gear; and a carrier rotatably supported on both ends of the shaft beyond the eccentric portion, including two covers that clamp the planetary gear, and outputting the rotation of the planetary gear based on the eccentric motion of the eccentric portion to the outside, A gearbox characterized in that, at least the planetary gear and the carrier components are manufactured by reducing the thickness of each component by an amount equal to the percentage by which the torsional rigidity of each component is increased by applying shot peening under predetermined conditions when processing the material to manufacture each component, and the torsional rigidity of each component is increased by applying shot peening under the predetermined conditions to each manufactured component.

2. The gearbox according to claim 1, characterized in that, after the shot peening, the case is subjected to a surface treatment of ultra-smooth polishing and oil reservoir processing in the groove into which the outer peripheral pin is mounted.

3. The gearbox according to claim 1 or 2, characterized in that the material of the carrier and the case is ductile cast iron.

4. The gearbox according to claim 1 or 2, characterized in that the material of the eccentric shaft, the planetary gear, and the plurality of outer pins is structural steel material with guaranteed hardenability.

5. The gearbox according to claim 1 or 2, characterized in that each component of the eccentric shaft, planetary gear, and plurality of outer pins is subjected to the following heat treatments in order: quenching, ultra-sub-zeroing, and tempering after the components are manufactured by processing the material, and then surface treatments in order: shot peening, ultra-smooth polishing, and oil reservoir processing.

6. The gearbox according to claim 5, characterized in that the two covers are disc-shaped with a first through-hole drilled in the center, the two covers are rotatably mounted on the eccentric shaft with a first bearing interposed between the first through-hole and the eccentric shaft, and the two covers are rotatably mounted on the case with a second bearing interposed between the outer circumference and the inner circumference of the case, the first bearing and the second bearing have shot peening applied to the entire raceway ring, and the surface treatment of the parts of the raceway ring that come into contact with the rollers is performed in this order: ultra-smooth polishing and oil reservoir processing.

7. The reduction gear according to claim 6, characterized in that the planetary gear is disc-shaped with a second through hole drilled in its center, the planetary gear is rotatably mounted on the eccentric shaft with a third bearing interposed between the second through hole and the eccentric portion, the third bearing has shot peening applied to the entire roller, and the circumferential surface treatment of the roller has been performed in this order: ultra-smooth polishing and oil reservoir processing.

8. The gearbox according to claim 7, characterized in that the first bearing is a tapered roller bearing, the second bearing is an angular contact bearing, and the third bearing is a caged needle roller bearing.

9. A gearbox according to claim 1 or 2, wherein a second spur gear is fixed to one end of the eccentric shaft, meshing with a first spur gear connected to the rotor of the motor, and reducing the rotational speed of the first spur gear and transmitting it to the eccentric shaft, and the components of the first spur gear and the second spur gear are manufactured by reducing the thickness of each component by an amount equal to the increase in torsional rigidity of each component by applying shot peening under predetermined conditions when manufacturing each component, and the torsional rigidity of each component is increased by applying shot peening under the predetermined conditions to each manufactured component.

10. A second spur gear is fixed to one end of the eccentric shaft, meshing with a first spur gear connected to the rotor of the motor, and reducing the rotational speed of the first spur gear and transmitting it to the eccentric shaft, wherein the components of the first spur gear and the second spur gear are manufactured by reducing the thickness of each component by an amount equal to the increase in torsional rigidity of each component by applying shot peening under predetermined conditions when manufacturing the components, and the torsional rigidity of each component is increased by applying shot peening under the predetermined conditions to the manufactured components, characterized in that the reduction gear according to claim 5.

11. A gearbox according to claim 7, wherein a second spur gear is fixed to one end of the eccentric shaft, meshing with a first spur gear connected to the rotor of the motor, and reducing the rotational speed of the first spur gear and transmitting it to the eccentric shaft, and the components of the first spur gear and the second spur gear are manufactured by reducing the thickness of each component by an amount equal to the increase in torsional rigidity of each component by applying shot peening under predetermined conditions when manufacturing each component, and the torsional rigidity of each component is increased by applying shot peening under the predetermined conditions to each manufactured component.

12. The gear reducer according to claim 9, characterized in that the first spur gear and the second spur gear are subjected to heat treatments of quenching, ultra-sub-zeroing and tempering in that order, followed by surface treatments of shot peening, ultra-smooth polishing and oil reservoir processing in that order.

13. The gear reducer according to claim 10, characterized in that the first spur gear and the second spur gear are subjected to heat treatments of quenching, ultra-sub-zeroing and tempering in that order, followed by surface treatments of shot peening, ultra-smooth polishing and oil reservoir processing in that order.

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