speed reducer

Abstract

To provide a gearbox that further reduces frictional resistance, reduces the temperature rise of the gearbox, and improves transmission efficiency. [Solution] The reduction gear of the embodiment comprises an internal gear having internal teeth and an external gear 15 having external teeth 15d that mesh with the internal teeth, and machining marks 30 are formed on each tooth surface of the internal gear and the external gear 15, and the machining marks 30 of the internal gear and the machining marks 30 of the external gear 15 are formed in directions that intersect each other in at least a portion of the way.

Description

[Technical Field]

[0001] The present invention relates to a speed reducer. [Background Art]

[0002] For example, speed reducers that reduce and output the rotation of a drive source such as an electric motor are used in industrial robots, machine tools, and the like. Among speed reducers of this type, there are, for example, eccentric oscillating type speed reducers. An eccentric oscillating speed reducer includes: a case (housing) integrally formed with an internal gear; a carrier provided radially inward of the case and rotatably provided relative to the case; a plurality of crankshafts rotatably supported by the carrier; and an external gear oscillated and rotated by an eccentric portion of the crankshaft. The external gear has external teeth that mesh with internal teeth of the internal gear.

[0003] The internal teeth are constituted by pin grooves formed on the inner circumferential surface of the case, and internal tooth pins (inner pins) fitted into the pin grooves. With the expansion of the usage environments for such speed reducers, there are cases where these speed reducers are used in environments involving high-speed rotation and high loads. In such cases, the speed reducer reaches a high temperature, friction loss increases at internal contact surfaces, and the transmission efficiency of the speed reducer decreases. For this reason, various techniques have been proposed to reduce friction in the speed reducer, suppress temperature increase, and improve transmission efficiency. For example, there is known a pin in which at least one of the internal tooth pin and the inner surface of the pin groove is processed such that the axial roughness is equal to or less than the circumferential roughness (see, for example, Patent Document 1). [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2013-185619 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] In recent years, there has been a growing demand for further improvements in transmission efficiency. However, the conventional technologies described above have limitations in reducing the frictional resistance of the gearbox, reducing the temperature rise of the gearbox, and improving transmission efficiency.

[0006] The present invention provides a gearbox that can further reduce frictional resistance, reduce the temperature rise of the gearbox, and improve transmission efficiency. [Means for solving the problem]

[0007] A gear reducer according to one aspect of the present invention comprises an internal gear having internal teeth and an external gear having external teeth that mesh with the internal teeth, wherein machining marks are formed on each tooth surface of the internal gear and the external gear, and at least a portion of the machining marks of the internal gear and the machining marks of the external gear are formed in directions that intersect each other.

[0008] This configuration reduces the contact area between the internal and external teeth. As a result, the peeling of the oil film on the surfaces of the internal and external teeth is suppressed, allowing the oil film to be maintained in good condition. Consequently, the gearbox reduces the frictional resistance of the internal and external teeth, reducing the temperature of the gearbox and improving transmission efficiency.

[0009] In the above configuration, the internal gear includes a cylindrical case with a plurality of pin grooves formed on its inner circumferential surface, the internal teeth include a plurality of internal tooth pins that fit into each of the pin grooves, machining marks are formed on the surfaces of the pin grooves and the internal tooth pins, at least a portion of the machining marks of the pin grooves and the machining marks of the internal tooth pins are formed in directions that intersect each other, and at least a portion of the machining marks of the internal tooth pins and the machining marks of the external gear are formed in directions that intersect each other.

[0010] In the above configuration, the machining marks on the internal tooth pin are formed along the circumferential direction of the internal tooth pin, and the machining marks on the pin groove and the external gear are formed along the axial direction of the internal tooth pin.

[0011] In the above configuration, the surface roughness of each tooth surface of the internal and external teeth is approximately Ra 0.6 to 0.2 μm. [Effects of the Invention]

[0012] The gear system described above can further reduce frictional resistance, reduce the temperature rise of the reduction gear, and improve transmission efficiency. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of a speed reducer in an embodiment of the present invention. [Figure 2] This is a cross-sectional view along the line II-II in Figure 1. [Figure 3] This is a perspective view showing the external teeth. [Figure 4] This is a perspective view showing the internal tooth pin. [Figure 5] This is a perspective view showing the pin groove of the internal tooth. [Figure 6] This graph shows the results of a test investigating the change in the average coefficient of friction for different surface roughness levels in gear test specimens. [Figure 7] This graph shows the expected gearbox life ratio based on the surface roughness of the gears. [Modes for carrying out the invention]

[0014] Next, embodiments of the present invention will be described with reference to the drawings.

[0015] <Deceleration device> Figure 1 is a cross-sectional view of the speed reducer 1. Figure 2 is a cross-sectional view along the line II-II in Figure 1. As shown in Figures 1 and 2, the speed reducer 1 reduces the rotation of an input shaft 101 connected to, for example, an electric motor (not shown), and outputs the reduced rotation speed. The speed reducer 1 is a so-called eccentric oscillating type speed reducer. The speed reducer 1 comprises a cylindrical case 2, a carrier 3 rotatably mounted radially inside the case 2, and a speed reduction mechanism 4 connected to the carrier 3. The central axis of the case 2 and the rotation axis of the carrier 3 coincide. In the following description, these center axis and rotation axis are collectively referred to as the first rotation axis A1. A direction parallel to the first rotation axis A1 is referred to as the axial direction. The rotation direction of the carrier 3 is referred to as the circumferential direction. The radial direction of the case 2, which is orthogonal to both the axial direction and the circumferential direction, is simply referred to as the radial direction.

[0016] <Case> An outer flange portion 2a projecting radially outward is integrally formed on the outer peripheral surface of the case 2. A plurality of bolt holes 2b are formed in the outer flange portion 2a. The bolt holes 2b are arranged at equal intervals in the circumferential direction. Unillustrated bolts are inserted into these bolt holes 2b, and the speed reducer 1 is fixed by tightening the bolts to, for example, an arm of an industrial robot.

[0017] A plurality of pin grooves 2c extending along the axial direction are formed on the inner peripheral surface of the case 2. The pin grooves 2c are arranged at equal intervals in the circumferential direction. An internal tooth pin 5 is fitted into each of the pin grooves 2c. The internal tooth pin 5 functions as an internal tooth that meshes with external gears 15 and 16 of the speed reduction mechanism 4, which will be described later. In the present embodiment, the internal tooth pins 5 fitted in the pin grooves 2c constitute the internal teeth 20 of the case 2. The case 2 functions as an internal gear 21 having the internal teeth 20. Main bearings 6 are respectively provided on both axial sides of the inner peripheral surface of the case 2. The carrier 3 is rotatably supported by the case 2 via the main bearings 6. The main bearing 6 is, for example, an angular contact ball bearing.

[0018] <Carrier> The carrier 3 includes a disk-shaped base plate portion 7 and an end plate portion 8 that are arranged opposite to each other in the axial direction, and three column portions 9 protruding from the base plate portion 7 toward the end plate portion 8. The column portions 9 are arranged at equal intervals in the circumferential direction. The end plate portion 8 is arranged on the tip end 9a of the column portion 9. The end plate portion 8 is fixed to the column portion 9 by bolts 10. In this state, a space having a constant width in the axial direction is formed between the base plate portion 7 and the end plate portion 8. A pin 11 is provided radially inward from the bolt 10 of the column portion 9. The pin 11 positions the end plate portion 8 relative to the base plate portion 7. The pin 11 is fitted into a pin hole 12 provided in the end plate portion 8.

[0019] The outer circumferential surfaces of the base plate portion 7 and the end plate portion 8 are rotatably supported by the case 2 via corresponding main bearings 6. Shaft insertion holes 7a and 8a are formed at the radial center of the base plate portion 7 and the radial center of the end plate portion 8, respectively. The two shaft insertion holes 7a and 8a are arranged coaxially. Three crank insertion holes 7b and 8b are formed in the base plate portion 7 and the end plate portion 8, respectively, between adjacent column portions 9 in the circumferential direction. Each crank insertion hole 7b and 8b is arranged coaxially. That is, the central axis A2 of axially opposing crank insertion holes 7b and 8b is parallel to the first rotation axis A1. Each crank insertion hole 7b and 8b is provided with a crank bearing 18. The crank bearing 18 is, for example, a tapered roller bearing.

[0020] <Deceleration mechanism> The reduction mechanism 4 rotates the carrier 3 at a rotational speed reduced by a constant ratio to the rotational speed of the input shaft 101. The reduction mechanism 4 comprises three crankshafts 13 inserted into each crank insertion hole 7b, 8b, a transmission spur gear 14 provided at the axial end of each crankshaft 13, and two external gears 15, 16 provided between the base plate portion 7 and the end plate portion 8, which oscillate and rotate in conjunction with the rotation of the crankshafts 13.

[0021] External transmission teeth 17 are formed on the outer circumference of the transmission spur gear 14. The transmission external teeth 17 mesh with external teeth 102 formed on the input shaft 101. When these transmission external teeth 17 and 102 mesh, the rotation of the input shaft 101 is transmitted to the transmission spur gear 14, causing the transmission spur gear 14 to rotate.

[0022] The crankshaft 13 is rotatably supported on the base plate portion 7 and end plate portion 8 of the carrier 3 via each crank bearing 18. The crankshaft 13 has a shaft body 13c that rotates about a central axis A2, and a first eccentric portion 13a and a second eccentric portion 13b formed in the axial center of the shaft body 13c. Both axial sides of the shaft body 13c are rotatably supported on the base plate portion 7 and end plate portion 8 of the carrier 3 via the crank bearings 18.

[0023] The shaft body 13c and the transmission spur gear 14 are arranged coaxially and integrated. That is, the crankshaft 13 and the transmission spur gear 14 rotate together as a single unit around the central axis A2. Hereinafter, the central axis A2 will be referred to as the second rotation axis A2 of the crankshaft 13.

[0024] The first eccentric portion 13a and the second eccentric portion 13b are eccentric from the second rotation axis A2. The first eccentric portion 13a and the second eccentric portion 13b are positioned adjacent to each other in the axial direction between the two crank bearings 18. In other words, the first eccentric portion 13a and the second eccentric portion 13b are positioned adjacent to each other in the axial direction between the base portion 7 and the end plate portion 8. The first eccentric portion 13a and the second eccentric portion 13b are positioned with a phase angle offset of 180°.

[0025] The inner circumferential surfaces of roller bearings 19 are fitted to each of the eccentric portions 13a and 13b. The roller bearings 19 are, for example, cylindrical roller bearings. The first external gear 15 and the second external gear 16 are rotatably supported on each crankshaft 13 via the roller bearings 19.

[0026] The first external gear 15 and the second external gear 16 are positioned in the space between the base plate portion 7 and the end plate portion 8. The first external gear 15 and the second external gear 16 have through holes 15a and 16a, respectively, into which the outer circumferential surfaces of the roller bearings 19 are fitted. As a result, when the first eccentric portion 13a and the second eccentric portion 13b oscillate due to the rotation of the crankshaft 13, the first external gear 15 and the second external gear 16 oscillate via the roller bearings 19.

[0027] The first external gear 15 and the second external gear 16 have openings 15b and 16b, respectively, to avoid interference with the column portion 9. Shaft insertion holes 15c and 16c are formed at the radial center of the first external gear 15 and the second external gear 16. External teeth 15d and 16d are formed on the outer circumference of the first external gear 15 and the outer circumference of the second external gear 16, respectively. The number of teeth on each external tooth 15d and 16d is a predetermined number less than the number of internal tooth pins 5 of case 2.

[0028] Under this configuration, as the first external gear 15 and the second external gear 16 oscillate, some of the external teeth 15d and 16d of each external gear 15 and 16 mesh with the internal tooth pin 5 of case 2. The number of teeth on each external tooth 15d and 16d is a predetermined number (for example, one) less than the number of internal tooth pins 5. Therefore, each external gear 15 and 16 rotates such that the meshing points of each external tooth 15d and 16d are sequentially shifted in the circumferential direction relative to the internal tooth pin 5 (case 2). This rotation is decelerated relative to the rotation of the crankshaft 13.

[0029] As each external gear 15 and 16 rotates, each crankshaft 13 also rotates on its own axis around the second rotation axis A2 while revolving around the first rotation axis A1. Each crankshaft 13 is rotatably supported on the carrier 3 (base plate portion 7, end plate portion 8). Therefore, the carrier 3 rotates in conjunction with the revolution of each crankshaft 13. As a result, the reducer 1 reduces the rotation of the input shaft 101 and outputs it from the carrier 3. If the carrier 3 is fixed to the arm of an industrial robot or the like, the reducer 1 can reduce the rotation of the input shaft 101 and output it from the case 2.

[0030] Figure 3 is a perspective view showing the external teeth 15d. The external teeth 15d and 16d of each external gear 15 and 16 have similar shapes. Therefore, the external teeth 15d will be described as representative in the following explanation. As shown in Figure 3, machining marks 30 are formed on the surface of the external teeth 15d. In this specification, "machining marks" refers to machining marks that occur when polishing is performed as a finishing process. Machining marks can be formed when cutting the tooth profile with a gear shaver or hobbing machine, or when grinding the surface with a grinding machine such as a honing machine. The machining marks 30 are formed along the tooth width direction of the external teeth 15d. In other words, the machining marks 30 are formed along the axial direction of the internal tooth pin 5. Ideally, the machining marks 30 should be formed over the entire width of the outer tooth 15d, but it is sufficient if they are formed over at least a portion of the width of the outer tooth 15d.

[0031] Figure 4 is a perspective view showing the internal tooth pin 5. As shown in Figure 4, machining marks 31 are formed on the surface of the internal tooth pin 5, similar to those on the external teeth 15d. These machining marks 31 can be formed during polishing as a finishing process, just as with the external teeth 15d. The machining marks 31 are formed along the circumferential direction of the internal tooth pin 5. Ideally, the machining marks 31 should be formed over the entire surface of the inner tooth pin 5, but it is sufficient if they are formed on at least a portion of the surface of the inner tooth pin 5.

[0032] Figure 5 is a perspective view showing the pin groove 2c of the internal tooth 20. As shown in Figure 5, machining marks 32 are formed on the surface of the pin groove 2c, similar to those of the external teeth 15d and internal tooth pins 5. These machining marks 32 can be formed during polishing as a finishing process, just as in the case of the external teeth 15d and internal tooth pins 5. The machining marks 32 are formed along the axial direction of the internal tooth pins 5. Ideally, the machining marks 32 should be formed over the entire surface of the pin groove 2c, but it is sufficient if they are formed on at least a portion of the surface of the pin groove 2c.

[0033] Therefore, the machining marks 31 of the internal tooth pin 5 and the machining marks 30 of the external tooth 15d are formed in directions perpendicular to each other. Similarly, the machining marks 32 of the pin groove 2c and the machining marks 31 of the internal tooth pin 5 are formed in directions perpendicular to each other. Furthermore, it is most desirable that the machining marks 31 of the internal tooth pin 5 and the machining marks 30 of the external tooth 15d are formed in directions perpendicular to each other. More specifically, it is desirable that the intersection angle be between 45° and 90°, but they do not necessarily have to be perpendicular as long as they intersect with each other. Similarly, the machining marks 32 of the pin groove 2c and the machining marks 31 of the internal tooth pin 5 do not necessarily have to be perpendicular as long as they intersect with each other.

[0034] A lubricating film is formed between the interlocking internal tooth pin 5 and the external tooth 15d. Additionally, a lubricating film is formed between the internal tooth pin 5, which is fitted into the pin groove 2c, and the pin groove 2c. As a result, the sliding resistance associated with rotation when the internal tooth 20 and the external tooth 15d are interlocked is reduced by the lubricating film.

[0035] The gearbox 1 may be operated in a variety of environments. For example, if the gearbox 1 is used in an environment with high rotation speed and high load, the oil film is more likely to peel off from the surfaces of the internal teeth 20 and external teeth 15d. In contrast, in this embodiment, the machining marks 31 of the internal tooth pin 5 and the machining marks 30 of the external teeth 15d are formed in directions perpendicular to each other. Similarly, the machining marks 32 of the pin groove 2c and the machining marks 31 of the internal tooth pin 5 are formed in directions perpendicular to each other.

[0036] Therefore, the contact area between the internal tooth 20 and the external tooth 15d when they slide against each other is reduced. More specifically, the contact area between the internal tooth pin 5 and the external tooth 15d is reduced, and the contact area between the pin groove 2c and the internal tooth pin 5 is reduced. As a result, the peeling of the oil film on the surfaces of the internal tooth 20 and the external tooth 15d is suppressed, and the oil film can be maintained in good condition.

[0037] Figure 6 is a graph showing the test results examining the change in the average coefficient of friction for each surface roughness of gear test pieces. In this test, a pressing member was applied to test specimens of each surface roughness, and the test specimens were rotated at a specified speed to investigate the coefficient of friction. The rotation speed of the test specimens was 40 rpm. As shown in Figure 6, when the surface roughness of the test specimen is Ra0.6μm and Ra0.2μm, it can be confirmed that the coefficient of friction is kept lower than 0.2 compared to when the surface roughness is Ra1.0μm and Ra0.03μm.

[0038] It is desirable that the coefficient of friction of the gearbox 1 is 0.2 or less. Below, the critical significance of a coefficient of friction of 0.2 or less will be explained using Figure 7. Figure 7 is a graph showing the expected gearbox life ratio based on the surface roughness of the gears. In Figure 7, the life ratio is set to 1 when the friction coefficient is 0.15. The friction coefficient of the pin gear section refers to the friction coefficient of the surfaces of the external teeth 15d, the internal tooth pins 5, and the pin grooves 2c. As shown in Figure 7, it can be confirmed that the life ratio decreases when the friction coefficient of the pin gear section exceeds 0.20.

[0039] As shown in Figures 6 and 7, a decrease in durability was observed in the gearbox 1 where the friction coefficient of the internal teeth 20 and external teeth 15d exceeded 0.20. Based on these results, the friction coefficient of the internal teeth 20 and external teeth 15d is set to 0.20 or less, and the surface roughness of the internal teeth 20 and external teeth 15d is set to Ra 0.6 to 0.2 μm. Therefore, the gearbox 1 can reduce the frictional resistance of the internal teeth 20 and external teeth 15d, thereby reducing the temperature rise of the gearbox 1 and improving the transmission efficiency.

[0040] As described above, in the gearbox 1 of this embodiment, the machining marks 31 and 32 of the internal teeth 20 and the machining marks 30 of the external teeth 15d are formed in directions that intersect each other in at least a portion of them. Therefore, the contact area between the internal teeth 20 and the external teeth 15d is reduced. As a result, the peeling of the oil film on the surfaces of the internal teeth 20 and the external teeth 15d is suppressed, and the oil film can be maintained in good condition. Consequently, the gearbox 1 can reduce the frictional resistance of the internal teeth 20 and the external teeth 15d, reduce the temperature rise of the gearbox 1, and improve the transmission efficiency.

[0041] Furthermore, in the gearbox 1 of this embodiment, the machining marks 32 of the pin groove 2c and the machining marks 31 of the internal tooth pin 5 are formed in directions that are at least partially perpendicular to each other. The machining marks 31 of the internal tooth pin 5 and the machining marks 30 of the external tooth 15d are formed in directions that are at least partially perpendicular to each other. As a result, the contact area between the pin groove 2c and the internal tooth pin 5 is reduced, and the contact area between the internal tooth pin 5 and the external tooth 15d is reduced. Therefore, the peeling of the oil film on the surfaces of the external tooth 15d, the internal tooth pin 5 and the pin groove 2c is suppressed, and the oil film can be maintained in good condition. Consequently, the gearbox 1 can reduce the frictional resistance of the external tooth 15d, the internal tooth pin 5 and the pin groove 2c, thereby reducing the temperature rise of the gearbox 1 and improving the transmission efficiency.

[0042] Furthermore, in the gearbox 1 of this embodiment, the machining marks 31 of the internal tooth pin 5 are formed along the circumferential direction of the internal tooth pin 5, and the machining marks 32 of the pin groove 2c and the machining marks 30 of the external teeth 15d are formed along the axial direction of the internal tooth pin 5. Therefore, the machining marks that occur when polishing is performed as a finishing process can be used as they are.

[0043] Furthermore, in the gearbox 1 of this embodiment, the surface roughness of each tooth surface of the internal teeth 20 and external teeth 15d is approximately Ra 0.6 to 0.2 μm. Therefore, the coefficient of friction of the surfaces of the internal teeth 20 and external teeth 15d can be kept within a suitable range. Consequently, the gearbox 1 can reduce the frictional resistance of the internal teeth 20 and external teeth 15d, thereby reducing the temperature rise of the gearbox 1 and improving the transmission efficiency.

[0044] In the above embodiment, machining marks 30, 31, and 32 are formed on the external teeth 15d, internal tooth pins 5, and pin grooves 2c, respectively, so as to extend in only one direction. However, the machining marks 30, 31, and 32 may extend in multiple different directions.

[0045] For example, machining marks 30 and 32 may be formed along the circumferential direction of the internal tooth pin 5. Also, machining mark 31 may be formed along the axial direction of the internal tooth pin 5. Furthermore, the machining marks 30, 31, and 32 do not necessarily have to be formed along the circumferential and axial directions of the internal tooth pin 5, and may be formed at an angle.

[0046] The present invention is not limited to the embodiments described above, and includes various modifications to the embodiments described above, without departing from the spirit of the invention.

[0047] Among the embodiments disclosed herein, those composed of multiple objects may be integrated, and conversely, those composed of a single object may be divided into multiple objects. Whether or not they are integrated, the invention can be constructed in a way that achieves its objective. [Explanation of Symbols]

[0048] 1...Reducer 2c...Pin groove 5…Inner tooth pin 15, 16… External gears 15d,16d…external teeth 20…Inner teeth 21... Internal gear 30,31,32...machining marks

Claims

1. An internal gear having internal teeth, An external gear having external teeth that mesh with the internal teeth, Equipped with, Machining marks are formed on the tooth surfaces of the internal gear and the external gear, respectively. The machining marks on the internal gear and the machining marks on the external gear are formed in directions that intersect each other, at least in part. reducer.

2. The internal gear includes a cylindrical case with a plurality of pin grooves formed on its inner circumferential surface. The internal teeth include a plurality of internal tooth pins that fit into each of the pin grooves, Machining marks are formed on the surface of the pin groove and the internal tooth pin. The machining marks of the pin groove and the machining marks of the internal tooth pin are formed in directions that intersect each other, at least in part. The machining marks on the internal tooth pin and the machining marks on the external tooth gear are formed in directions that intersect each other, at least in part. The gearbox according to claim 1.

3. The machining marks on the internal tooth pin are formed along the circumferential direction of the internal tooth pin. The pin groove and the machining marks on the external gear are formed along the axial direction of the internal pin. The gearbox according to claim 2.

4. The surface roughness of each tooth surface in the internal and external teeth is approximately Ra 0.6 to 0.2 μm. The gearbox according to claim 1.

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