Strain wave gear device

Abstract

A strain wave gear device (1) is provided with: a first flange (8) that supports an input shaft (6) via a first support bearing (7); and a second flange (10) that supports the input shaft (6) via a second support bearing (9). The external gear (3) is fastened and fixed to the first flange (8) by means of a first fastening bolt (11), and the internal gear (2) is fastened and fixed to the second flange (10) by means of a second fastening bolt (12). The fastening strength in the radial direction between the externally toothed gear (3) and the first flange (8) by the first fastening bolt (11) is set to a degree equal to or greater than the fastening strength between the internally toothed gear (2) and the second flange (10) by the second fastening bolt (12). As a result, eccentricity between the wave generator (4) and the first and second support bearings (7, 9) caused by radial deformation of the first and second flanges (8, 10) due to a radial load acting from the load side can be suppressed, and excessive radial force can be prevented from acting on the wave generator.

Description

TECHNICAL FIELD

[0001] The present application relates to a wave gear device in which an input shaft mounted to a wave generator is supported on both sides in the axial direction by support bearings, and the input shaft and the wave generator are coupled without a coupling such as a cross joint. BACKGROUND

[0002] As basic structural elements, the wave gear device has three components: a rigid internal gear; a flexible external gear; and a wave generator that causes the external gear to flex into an elliptical shape and partially mesh with the internal gear. By rotating the wave generator, the meshing position of the external gear with respect to the internal gear is moved in the circumferential direction, thereby generating relative rotation corresponding to the difference in the number of teeth of the two gears between the two gears. One gear is fixed and does not rotate, and the other gear outputs a decelerated rotation to the load side.

[0003] As a wave gear device, a structure is known in which an input shaft is mounted to a wave generator, and the input shaft is supported by support bearings at positions on both sides in the axial direction of the wave generator (Patent Documents 1 to 3). The support bearing that supports the axial side of the input shaft is fitted to a fixed side member such as a device housing, and the support bearing that supports the other side of the input shaft is fitted to an output side member (output shaft) that outputs a decelerated rotation. Of the internal gear and the external gear, the gear on the fixed side is mounted to the fixed side member, and the gear on the output side that outputs a decelerated rotation is mounted to the output side member. The load side member of the drive object is coupled to the output side member.

[0004] With regard to the wave gear device of this structure, the weight or the like load of the load side member of the drive object is applied to the output side member. The load applied to the output side member acts on the support bearing mounted to the output side member. As a result, eccentricity sometimes occurs between the support bearing and the wave generator coupled to the input shaft supported by the support bearing. With regard to the wave gear device described in Patent Document 1, the input shaft is coupled to the wave generator by a cross joint, and such eccentricity is absorbed by the cross joint.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-74450

[0008] Patent Document 2: Japanese Patent No. 5496426

[0009] Patent Document 3: Japanese Patent Application Publication No. 2002-21948 SUMMARY

[0010] When the cross joint or the like is not provided to the wave generator, in a case where a load acting from the load side is large or the like, a radial force is applied to the wave generator due to eccentricity generated thereby, and thus the reliability of the wave gear device can be impaired. The eccentricity is caused by radial deformation (deformation in a direction orthogonal to the axial direction) of the output side member and the fixed side member that support the bearing due to the load acting from the load side.

[0011] However, in the case of the conventional wave gear device, the fastening site that is fastened by the fastening bolt is designed based on the torsional moment (load torque), and since the fastening strength against the radial force of the fastening site is sufficient, the radial force has not been taken into consideration. That is, in the design of the fastening site, the radial deformation has not been taken into consideration at all.

[0012] In the case of designing based on the torsional moment (load torque), for example, the size and the number of the fastening bolts are set in such a manner that the fastening strength between the internal gear that is the gear on the output side and the output side member to which the internal gear is fastened and the fastening strength between the external gear that is the gear on the fixed side and the fixed side member to which the external gear is fastened are equal in the rotational direction. In the case of the top hat type wave gear device, the outer diameter of the boss of the external gear that is fastened to the fixed side member by the bolt is larger than the outer diameter of the internal gear that is fastened to the output side member by the bolt, and thus in the case of using the same size of the fastening bolt, the number of the fastening bolts on the external gear side required to ensure the fastening strength in the rotational direction can be smaller than the number of the fastening bolts on the internal gear side. As a result, the radial fastening strength between the external gear and the fixed side member is reduced as compared with the radial fastening strength between the internal gear and the output side member. If the radial fastening strength is low, the radial deformation that is the main cause of the eccentricity can be generated due to the radial force acting from the load side.

[0013] In view of the above-described problems, the object of the present application is to suppress the radial deformation at the fastening site due to the load acting from the load side so that the eccentricity does not occur between the wave generator and the bearing for a wave gear device in which the input shaft of the wave generator is supported by the bearing on both sides in the axial direction and the input shaft and the wave generator are coupled without the cross joint or the like.

[0014] The wave gear device of the present application is characterized by comprising:

[0015] an internal gear that is rigid;

[0016] an external gear that is flexible and is coaxially arranged inside the internal gear;

[0017] a wave generator that is coaxially arranged inside the external gear;

[0018] an input shaft coaxially mounted to the wave generator;

[0019] a first flange supporting a first shaft portion of the input shaft extending from the wave generator to one side in the axial direction rotatably by a first support bearing;

[0020] a second flange supporting a second shaft portion of the input shaft extending from the wave generator to the other side in the axial direction rotatably by a second support bearing;

[0021] a plurality of first fastening bolts fastening and fixing the outer gear to the first flange; and

[0022] a plurality of second fastening bolts fastening and fixing the inner gear to the second flange,

[0023] the wave generator is mounted to the input shaft without a coupling,

[0024] a radial distance from a rotation center to a fastening position of the first fastening bolt is greater than a radial distance from the rotation center to a fastening position of the second fastening bolt,

[0025] a radial fastening strength between the outer gear and the first flange based on the first fastening bolt is set to be the same as or greater than a radial fastening strength between the inner gear and the second flange based on the second fastening bolt.

[0026] Here, in order to position the outer gear and the first flange, a fitting portion of so-called recesses is sometimes formed therebetween. In this case, it is preferable to form the fitting portion of recesses in a transition fit state to suppress radial displacement. The same is true for a fitting portion formed between the inner gear and the second flange, and it is preferable to form it in a transition fit state. That is, with regard to the wave gear device of the present application, it is preferable that a first fitting portion be formed between the outer gear and the first flange such that one of them is fitted and fixed to the other in a transition fit state from the axial direction,

[0027] a second fitting portion be formed between the inner gear and the second flange such that one of them is fitted and fixed to the other in a transition fit state from the axial direction.

[0028] In this case, it is preferable to previously form press screw holes between the outer gear and the first flange in a manner that they can be easily disassembled. It is also preferable to similarly previously form press screw holes between the inner gear and the second flange.

[0029] On the other hand, in the case where no recess is provided between the external gear and the first flange, the press-in pin is pressed in and fixed in position at the above-mentioned portion, and radial deformation can be suppressed. Similarly, in the case where the press-in pin is pressed in at the above-mentioned portion between the internal gear and the second flange, radial deformation can also be suppressed.

[0030] Effects of the Invention

[0031] With the wave generator device of the present application, the radial fastening strength between the external gear and the first flange is set to the same degree as, or a strength greater than, the fastening strength between the internal gear and the second flange. Thus, eccentricity between the wave generator and the support bearing due to radial deformation caused by a radial load acting from the load side can be prevented or suppressed, and unnecessary radial force can be prevented from acting on the wave generator. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 (A) is a schematic longitudinal sectional view of a wave generator device to which the present application is applied, (B) is an end view as viewed from the side of the first flange which is a fixed side member thereof, and (C) is an end view as viewed from the side of the second flange which is an output side member thereof.

[0033] Figure 2 is a schematic longitudinal sectional view showing a wave generator device to which another embodiment of the present application is applied. DETAILED DESCRIPTION

[0034] Hereinafter, a wave generator device to which an embodiment of the present application is applied will be described with reference to the drawings. The embodiment described below shows one example of the present application, and the present application is not limited to the embodiment.

[0035] Reference Signs List Figure 1 The wave generator device 1 to which the embodiment of the present application is applied is provided with: a rigid internal gear 2 formed in a circular ring shape; a flexible external gear 3 coaxially arranged inside the internal gear 2 and capable of flexing in the radial direction; and a wave generator 4 coaxially arranged inside the external gear 3. The wave generator 4 flexes the external gear 3 into a non-circular shape, in this case into an elliptical shape, and partially engages with the internal gear 2, thereby moving the engagement position of the two gears 2, 3 in the circumferential direction.

[0036] The inner gear 2 and the outer gear 3 are supported in a state of being relatively rotatable by a main bearing 5 constituted of, for example, a cross roller bearing. In addition, an input shaft 6 for a rotational input from a motor or the like (not shown) is coaxially attached to the wave generator 4. The wave generator 4 of this example is provided with a cam plate 41 that is rigid, and a wave generator bearing 42 that is fitted to a non-circular outer circumferential surface of the cam plate 41, which is an elliptical outer circumferential surface in this example. The cam plate 41 can be formed so as to be integrated with the input shaft 6, or the cam plate 41 can be produced as a separate member and be coaxially fastened and fixed to the input shaft 6. The input shaft 6 is a hollow shaft, but can also be a solid shaft.

[0037] With respect to the input shaft 6, a portion extending toward one axial side from the cam plate 41 of the wave generator 4 is provided as a first shaft portion 61, and a portion extending toward the other axial side is provided as a second shaft portion 62. The first shaft portion 61 of the input shaft 6 is supported in a rotatable state by a first flange 8 (a fixed side member) by a first bearing 7 constituted of a ball bearing or the like. The second shaft portion 62 of the input shaft 6 is supported in a rotatable state by a second flange 10 (an output side member that outputs a decelerated rotation) by a second bearing 9 constituted of a ball bearing or the like. The inner gear 2, the outer gear 3, the wave generator 4, and the main bearing 5 are arranged between the first and second flanges 8, 10.

[0038] The outer gear 3 is a so-called top hat-shaped outer gear provided with a cylindrical main body portion 31 that can be flexed in a radial direction, a diaphragm 32 that extends toward the outside in the radial direction from one end of the cylindrical main body portion 31, a circular ring-shaped boss 33 that is integrally formed at an outer circumferential edge of the diaphragm 32, and outer teeth 34 that are formed at an outer circumferential surface portion of an open end side that is the other end of the cylindrical main body portion 31. The boss 33 of the outer gear 3 has an outer diameter that is larger than an outer diameter of the inner gear 2. The wave generator 4 is inserted into the inside of the cylindrical main body portion 31 in which the outer teeth 34 are formed. The outer teeth 34 of the outer gear 3 that are flexed into an elliptical shape by the wave generator 4 are engaged with the inner teeth 21 of the inner gear 2 at positions of both ends of a major axis of the elliptical shape.

[0039] The main bearing 5 is arranged in a state of coaxially surrounding a portion between the outer teeth 34 and the diaphragm 32 of the cylindrical main body portion 31 of the outer gear 3. An outer ring 51 of the main bearing 5 is coaxially fixed to the boss 33 of the outer gear 3. In this example, the three members of the outer circumferential side portion of the first flange 8, the boss 33 of the outer gear 3, and the outer ring 51 are fastened and fixed by a plurality of first fastening bolts 11. An inner ring 52 of the main bearing 5 is coaxially fixed to the inner gear 2. In this example, the three members of the outer circumferential side portion of the second flange 10, the inner gear 2, and the inner ring 52 are fastened and fixed by a plurality of second fastening bolts 12.

[0040] With respect to the wave gear device 1, if the wave generator 4 is rotated by the rotation input by the input shaft 6, the meshing position of the outer tooth gear 3 with respect to the inner tooth gear 2 moves in the circumferential direction. A relative rotation at a speed ratio prescribed by the difference in the number of teeth of the inner teeth 21 and the outer teeth 34 is generated between the inner tooth gear 2 and the outer tooth gear 3. In this example, the outer tooth gear 3 mounted on the first flange 8 side is provided as the fixed side, and the inner tooth gear 2 mounted on the second flange 10 side is provided as the rotating side. The decelerated rotation generated by the inner tooth gear 2 is output to a member on the load side, which is not shown, by the second flange 10.

[0041] In the wave generator 4 of the wave gear device 1 of this example, no joint such as a cross joint or the like is provided, and the cam plate 41 of the wave generator 4 is formed integrally with the input shaft 6. At times, a radial load (load torque) acting on the second flange 10 as the output side member from the load side (not shown) causes the first flange 8 and the second flange 10 to be deformed in the radial direction. Figure 1 (Eccentricity is generated between the first and second support bearings 7, 9 fitted to the first and second flanges 8, 10 and the wave generator 4, as indicated by an arrow A in (A).) The tightening strength of the fastening portions between the inner tooth gear 2 and the second flange 10 and between the outer tooth gear 3 and the first flange 8 is set in a manner that can reduce the radial deformation of the first and second flanges 8, 10 that is a cause of such eccentricity.

[0042] First, the first fastening bolts 11 for fastening and fixing the outer tooth gear 3 to the first flange 8 are mounted to the bosses 33, and the dimensions and the number thereof are set based on the torsional moment (load torque) applied to the fastening portions and also taking into account the radial force applied to the fastening portions. Similarly, the dimensions and the number of the second fastening bolts 12 for fastening and fixing the inner tooth gear 2 to the second flange 10 are set based on the torsional moment (load torque) applied to the fastening portions and also taking into account the radial force applied to the fastening portions. Thus, the radial deformation of the first and second flanges 8, 10 generated by the load acting from the load side is suppressed, and eccentricity between the first and second support bearings 7, 9 supported by the first and second flanges 8, 10 and the wave generator 4 can be prevented or suppressed. By setting the tightening strength taking into account the radial force, the radial tightening strength between the outer tooth gear 3 and the first flange 8 based on the first fastening bolts 11 is set to be the same as or higher than the radial tightening strength between the inner tooth gear 2 and the second flange 10 based on the second fastening bolts 12.

[0043] In the case of using the same size of fastening bolts, the radial fastening strength is proportional to the number of bolts. For example, the inner tooth gear 2 and the second flange 10 are fastened by 16 second fastening bolts 12 (e.g., M4 high-strength bolts) arranged at equal angular intervals. In this case, the boss 33 of the outer tooth gear 3 and the first flange 8 are fastened by 16 or more first fastening bolts 11 (e.g., M4 high-strength bolts) arranged at equal angular intervals. Thus, the radial fastening strength on the outer tooth gear 3 side can be made equal to or greater than that on the inner tooth gear 2 side.

[0044] Here, according to Figure 1 (B), (C), the outer diameter of the boss 33 of the outer tooth gear 3 formed in a top hat shape is greater than the outer diameter of the inner tooth gear 2. Therefore, the radial distance from the rotation center la to the mounting position of the first fastening bolt 11 of the boss 33 is greater than the distance from the rotation center la to the mounting position of the second fastening bolt 12 of the inner tooth gear 2. Therefore, in the case of using the same size and number of fastening bolts, the rotational direction fastening strength of the above fastening site is greater than the fastening strength on the outer tooth gear 3 side. Conventionally, the fastening site based on the fastening bolt is designed based on the rotational direction fastening strength. For example, in the case of using the same size of fastening bolts, the number of fastening bolts fastening between the outer tooth gear 3 and the first flange 8 is less than the number of fastening bolts fastening between the inner tooth gear 2 and the second flange 10. As a result, the radial fastening strength between the outer tooth gear 3 and the first flange 8 is lower than that between the inner tooth gear 2 and the second flange 10. If a greater radial force acts from the load side, a greater radial displacement occurs, and sometimes eccentricity occurs between the first and second support bearings 7, 9 and the wave generator 4. According to the wave gear device 1 of the present example, such drawbacks can be avoided.

[0045] Next, in the present example, in order to position and fix the outer tooth gear 3 and the first flange 8 from the axial direction, a fitting portion 13 in which a recess is formed therebetween is formed. As shown in Figure 1 (A), a circular inner peripheral surface 8a is formed in the outer peripheral portion of the first flange 8, and here, the circular outer peripheral surface 33a of the boss 33 of the outer tooth gear 3 is fitted from the axial direction. In this fitting portion 13, the circular outer peripheral surface 33a of the boss 33 is fitted to the circular inner peripheral surface 8a of the first flange 8 in a transition fit state. Thus, the radial displacement of the first flange 8 with respect to the boss 33 of the outer tooth gear 3 and the outer ring 51 of the main bearing 5 is suppressed.

[0046] Similarly, in order to position and fix the inner tooth gear 2 and the second flange 10 from the axial direction, a fitting portion 14 in which a recess is formed therebetween is formed. As shown in Figure 1(A) shown, a circular inner peripheral surface 10a is formed at the outer peripheral portion of the second flange 10, and the circular outer peripheral surface 2a of the inner tooth gear 2 is fitted from the axial direction at this portion. At the fitting portion 14, the circular outer peripheral surface 2a of the inner tooth gear 2 is fitted to the circular inner peripheral surface 10a of the second flange 10 in a transition fit state. Thus, the radial displacement of the second flange 10 with respect to the inner tooth gear 2 is suppressed.

[0047] Further, in the case where the outer tooth gear 3 and the first flange 8 are formed in a fitting state of a transition fit as described above, it is preferable to provide a press-fitted screw hole (not shown) in advance in the first flange 8 in consideration of the case where they are disassembled. It is also preferable to provide a press-fitted screw hole in the other second flange 10 as well.

[0048] As described above, in the wave gear device 1, the fastening strength between the outer tooth gear 3 and the first flange 8, particularly the radial fastening strength, is set to be the same degree or higher than the fastening strength between the inner tooth gear 2 and the second flange 10. Further, the fitting portion 13 of a transition fit is formed between the outer tooth gear 3 and the first flange 8, and the fitting portion 14 of a transition fit is also formed between the inner tooth gear 2 and the second flange 10. Thus, the radial deformation of the first and second flanges 8 and 10 due to the radial load acting from the load side can be suppressed. As a result, the eccentricity between the wave generator 4 and the first and second support bearings due to the radial deformation can be prevented or suppressed, and excessive radial force can be prevented from acting on the wave generator 4.

[0049] (Other Embodiments)

[0050] Figure 2 is a schematic longitudinal sectional view of a wave gear device according to another embodiment of the present application. The basic structure of the wave gear device 100 shown in this figure is the same as that of the wave gear device 1 of Figure 1 , and thus, the structure thereof will be simply described below.

[0051] The wave gear device 100 includes a rigid inner tooth gear 120, a flexible outer tooth gear 130 formed in a top hat shape and coaxially arranged inside the inner tooth gear 120, a wave generator 140 coaxially arranged inside the outer tooth gear 130, a main bearing 150 supporting the inner tooth gear 120 and the outer tooth gear 130 in a state where they are relatively rotatable, and an input shaft 160 coaxially attached to the wave generator 140. The wave generator 140 is attached to the input shaft 160 without the aid of a coupling or the like.

[0052] The input shaft 160 has a first shaft portion 161 extending to one axial side from the wobble generator 140, and a second shaft portion 162 extending to the other side. The first shaft portion 161 is supported by the first flange 180 in a rotatable state by a first bearing 170. The second shaft portion 162 of the input shaft 160 is supported by the second flange 200 in a rotatable state by a second bearing 190. The boss 133 of the outer gear 130 and the outer ring 151 of the main bearing 150 are fastened and fixed to the first flange 180 by a plurality of first fastening bolts 210. The inner gear 120 and the inner ring 152 of the main bearing 150 are fastened and fixed to the second flange 200 by a plurality of second fastening bolts 220. The fastening strength between the outer gear 130 and the first flange 180 based on the first fastening bolts 210 is set to be the same as or higher than the fastening strength between the inner gear 120 and the second flange 200 based on the second fastening bolts 220.

[0053] In addition, a fitting portion 240 is formed between the inner gear 120 and the second flange 200, which allows the circular outer peripheral surface 120a of the inner gear 120 to be fitted and fixed to the circular inner peripheral surface 200a of the second flange 200 in a transition fit state from the axial direction. The second flange 200 is provided with press-fitting holes 250 in a manner that allows the inner gear 120 to be easily separated. In contrast, a transition fit fitting portion is not formed between the outer gear 130 and the first flange 180. Instead, press-in pins 260 are punched into the first flange 180 side in the axial direction between the boss 133 of the outer gear 130 and the outer peripheral edge side of the first flange 180. The press-in pins 260 are arranged at a plurality of positions separated in the circumferential direction.

[0054] Thus, in the wobble gear device 100, the fastening strength, particularly the radial fastening strength, between the outer gear 130 and the first flange 180 is set to be the same as or higher than the fastening strength between the inner gear 120 and the second flange 200. In addition, the fitting portion 240 in a transition fit is formed between the inner gear 120 and the second flange 200, and the boss 133 of the outer gear 130 and the first flange 180 are positioned and fixed by the press-in pins 260. Thus, the radial deformation of the first and second flanges 180 and 200 due to the radial load acting from the load side can be suppressed. As a result, eccentricity between the wobble generator 140 and the first and second bearings 170 and 190 due to the radial deformation can be prevented or suppressed, and excessive radial force can be prevented from acting on the wobble generator 140.

Claims

1. A wave gear device characterized by comprising: a rigid internal gear; a flexible external gear coaxially disposed inside the internal gear; a wave generator coaxially disposed inside the external gear; an input shaft coaxially mounted to the wave generator; a first flange supporting a first shaft portion of the input shaft extending toward one side in an axial direction from the wave generator so as to be rotatable by means of a first support bearing; a second flange supporting a second shaft portion of the input shaft extending toward the other side in the axial direction from the wave generator so as to be rotatable by means of a second support bearing; a plurality of first fastening bolts fastening and fixing the external gear to the first flange; and a plurality of second fastening bolts fastening and fixing the internal gear to the second flange, the wave generator is mounted to the input shaft without a coupling, a radial distance from a rotation center to a fastening position of the first fastening bolt is greater than a radial distance from the rotation center to a fastening position of the second fastening bolt, a radial fastening strength between the external gear and the first flange based on the first fastening bolt is set to be the same as or greater than a radial fastening strength between the internal gear and the second flange based on the second fastening bolt.

2. The wave gear device according to claim 1, characterized by comprising: a first fitting portion is formed between the external gear and the first flange such that one of them is fitted and fixed to the other in a transition fit state from the axial direction, a second fitting portion is formed between the internal gear and the second flange such that one of them is fitted and fixed to the other in a transition fit state from the axial direction.

3. The wave gear device according to claim 2, characterized by comprising: a first press hole is formed between the external gear and the first flange, a second press hole is formed between the internal gear and the second flange.

4. The wave gear device according to claim 1, characterized by comprising: one or a plurality of first press-in pins pressed in from the axial direction with respect to the external gear and the first flange are used to position and fix the external gear and the first flange, one or a plurality of second press-in pins pressed in from the axial direction with respect to the internal gear and the second flange are used to position and fix the internal gear and the second flange. ​

Images