Strain wave gearing

Abstract

This cup-shaped strain wave gearing (1) comprises a rigid internally toothed gear (2), a cup-shaped flexible externally toothed gear (3), a wave generator (4), an output member (5) to which output rotation is transmitted from the externally toothed gear (3), a cross roller bearing (6) that supports the externally toothed gear (3) so as to be capable of rotating relative to the internally toothed gear (2), and a device hollow portion (7) that extends through a device center portion in the direction of the device axis (1a). An annular boss (33) defining a cup bottom surface portion of the externally toothed gear (3) is coaxially connected to the output member (5) via an intermediate member (8). It is possible to realize a strain wave gearing with which the hollow diameter of the device hollow portion (7) can be increased and connection torque between the externally toothed gear (3) and the output member (5) can be ensured without deforming the output member (5).

Description

Strain wave gearing

[0001] The present invention relates to a hollow wave gear device having a hollow portion that penetrates the center portion of the device in the direction of the device axis, and more specifically to a hollow wave gear device that can increase the hollow diameter while ensuring fastening torque between a cup-shaped flexible external gear and an output member.

[0002] A known strain wave gearing device is a cup-type strain wave gearing device equipped with a cup-shaped flexible external gear. The cup-shaped external gear includes a cylindrical body portion that is flexible in the radial direction, a disk-shaped diaphragm extending radially inward from one end of the cylindrical body portion, a rigid boss formed in the center of the diaphragm, and external teeth formed on the outer circumferential surface portion on the other end side of the cylindrical body portion. A wave generator is fitted inside the cylindrical body portion on which the external teeth are formed. The wave generator includes a rigid cam plate and a wave bearing mounted between the elliptical outer circumferential surface of the cam plate and the inner circumferential surface of the cylindrical body portion of the external gear.

[0003] In a hollow wave gear device equipped with a cup-shaped external gear, a central through hole is formed in each of the rigid boss of the external gear and the rigid cam plate of the wave generator to form a hollow device section that penetrates the center of the device in the direction of the device axis. The hollow diameter of the hollow device section is usually determined by the inner diameter of the central through hole formed in the rigid boss of the external gear. In order to increase the hollow diameter, it is necessary to increase the inner diameter of the central through hole of the rigid boss of the external gear. The rigid boss is a location for attaching an output member to which the rotation of the external gear is transmitted, and because it is necessary to ensure fastening torque between the external gear and the output member, it is sometimes not possible to increase the inner diameter of the central through hole of the rigid boss.

[0004] In a cup-type strain wave gearing device, the following measures can be considered to increase the hollow diameter and ensure sufficient fastening torque between the external gear and the output member: (1) A wine-glass-shaped external gear with a large-diameter annular flange that is fastened and fixed to the output member is used as the cup-shaped external gear. (Patent Document 1 describes a strain wave gearing device with a wine-glass-shaped external gear.) (2) A screw-fastening method is used in which the hollow through-hole of one of the rigid boss of the external gear and the output member is a threaded hole, and a male thread formed on the other is screwed into the threaded hole to secure them. (Patent Documents 2 and 3 describe strain wave gearing devices using the screw-fastening method.) (3) A welding method is used in which the rigid boss of the external gear and the output member are fixed by welding. (Patent Document 4 describes a strain wave gearing device using the welding method.)

[0005] Japanese Utility Model Publication No. 4-38122 Japanese Patent Application Laid-Open No. 2000-9191 Japanese Patent Application Laid-Open No. 2001-336588 Japanese Patent Application Laid-Open No. 2014-206265

[0006] However, these methods still have problems to be solved. When a wine-glass-shaped external gear is used, the axial length of the external gear becomes longer than that of a normal cup-shaped external gear, which results in a correspondingly longer axial length of the entire device. In addition, a wine-glass-shaped external gear is more difficult to process than a normal cup-shaped one.

[0007] On the other hand, the screw fixing method and the welding method have the problem that the output member is easily deformed. In particular, if the output member is a component that is sensitive to deformation, such as a cross roller bearing or a component of a torque sensor, adopting the screw fixing method or the welding method may have an adverse effect on the performance of the component. Furthermore, once the external gear is fixed to the external gear, it is difficult to disassemble the external gear and the output member, which reduces the design freedom of the output member.

[0008] In view of the above, the main object of the present invention is to provide a cup-type strain wave gear device that can have a large hollow diameter without deforming the output member and that can ensure the fastening torque between the external gear and the output member.

[0009] The present invention is characterized in that, in a wave gear device comprising a rigid internal gear, a cup-shaped flexible external gear, a wave generator, and a hollow device portion extending through the device central portion in the direction of the device axis, an annular boss defining the cup bottom portion of the external gear is coaxially connected to an output member via an intermediate member.

[0010] That is, the present invention is a strain wave gear device comprising: a rigid internal gear; a cup-shaped flexible external gear arranged coaxially inside the internal gear; a wave generator arranged coaxially inside the external gear and bending the external gear non-circularly to partially mesh with the internal gear, thereby moving the meshing position of both gears in the circumferential direction; an output member arranged coaxially with the external gear and to which the rotation of the external gear is transmitted; and a device hollow section extending through the device central section in the direction of the device axis, characterized in that the strain wave gear device comprises: an annular intermediate member located between the output member and an annular boss that defines the cup bottom portion of the external gear; a first fixing part that fixes the intermediate member to the boss of the external gear; and a second fixing part that fixes the intermediate member to the output member.

[0011] Each of the first fixing portion and the second fixing portion can be one of the following: a bolt-fastening type fixing mechanism in which two members are fastened together with a fastening bolt; a screw-fastening type fixing mechanism in which a male threaded portion formed on one of the two members is screwed into a screw hole formed on the other member; or a weld-joint type fixing mechanism in which two members are welded together.

[0012] By appropriately selecting the fixing mechanism, it is possible to reduce deformation of the output member caused by fixing to the external gear, unlike when the boss of the external gear and the output member are directly fixed to each other.

[0013] The first fixing portion and the second fixing portion may be different fixing mechanisms. For example, a welded joint may be used as the fixing mechanism between the boss of the external gear and the intermediate member, and a screwed fixing portion may be used as the fixing mechanism between the intermediate member and the output member. This configuration can reduce deformation of the output member caused by fixing to the external gear, and is therefore particularly effective when the output member is a component that is sensitive to deformation, such as a cross roller bearing or a torque sensor.

[0014] According to the present invention, a cup-type strain wave gear device can be obtained that can have a large hollow diameter without deforming the output member and can ensure the fastening torque between the external gear and the output member.

[0015] (A) is a schematic end view showing a cup-type strain wave gearing device according to a first embodiment to which the present invention is applied, and (B) is a schematic longitudinal sectional view. (A) is a schematic half-longitudinal sectional view showing a modified example of the strain wave gearing device of Fig. 1. (A) is a schematic end view showing a strain wave gearing device according to a second embodiment to which the present invention is applied, and (B) is a schematic longitudinal sectional view, and (C) is an enlarged half-longitudinal sectional view. (B) is a schematic half-longitudinal sectional view showing an example of a strain wave gearing device having a configuration in which separate parts such as an oil seal and bearings are assembled to an intermediate member.

[0016] A wave gear device according to an embodiment of the present invention will be described below with reference to the drawings, although the present invention is not limited to the following embodiment.

[0017] (Embodiment 1) Fig. 1(A) is a schematic end view of a cup-type strain wave gear device according to Embodiment 1 of the present invention, and Fig. 1(B) is a schematic longitudinal cross-sectional view thereof. The strain wave gear device 1 comprises a rigid internal gear 2, a cup-shaped flexible external gear 3, a strain wave generator 4, an output member 5, and a cross roller bearing 6, which serves as a main bearing that supports the external gear 3 in a state where it can rotate relatively to the internal gear 2. A device hollow section 7 is formed in the center of the device, extending through in the direction of the device axis 1a. The strain wave gear device 1 also comprises an intermediate member 8, via which the external gear 3 and the output member 5 are coaxially connected.

[0018] In this example, the outer peripheral portion of the internal gear 2 functions as the inner ring 61 of the cross roller bearing 6. An inner ring raceway groove (V-groove) of the inner ring 61 is formed on the circular outer peripheral surface of the internal gear 2, and internal teeth 21 are formed on the circular inner peripheral surface. An external gear 3 is arranged coaxially inside the internal gear 2. The external gear 3 includes a radially flexible cylindrical body 31, a disk-shaped diaphragm 32 extending radially inward from one end of the cylindrical body 31, a rigid boss 33 integrally formed at the center of the diaphragm, and external teeth 34 formed on the outer peripheral surface at the other end of the cylindrical body 31. The rigid boss 33, which defines the cup bottom portion of the external gear, has an annular shape with a central through-hole 35. The external teeth 34 can mesh with the internal teeth 21, and the external gear 3 is arranged so that the external teeth 34 face the internal teeth 21.

[0019] The wave generator 4 is arranged coaxially inside the portion of the cylindrical body portion 31 of the external gear 3 where the external teeth 34 are formed. The wave generator 4 includes a rigid cam plate 41 with a non-circular contour, in this example an elliptical contour, and a wave bearing 42 attached to the elliptical outer circumferential surface of the cam plate 41. The cam plate 41 is an annular part formed with a central through hole 43 whose inner diameter is slightly larger than the central through hole 35 of the boss 33. The device hollow portion 7 extends through the central portion of the device in the direction of the device axis 1a, passing through the central through holes 35, 43.

[0020] An annular intermediate member 8 is disposed coaxially around the outer periphery of the boss 33 of the external gear 3, and an annular output member 5 is disposed coaxially around the outer periphery of the intermediate member 8. In this way, the intermediate member 8 is disposed coaxially between the boss 33 and the output member 5 in the radial direction. In this example, the boss 33 and the intermediate member 8 are fixed by a threaded fixing portion 10 (first fixing portion). The intermediate member 8 and the output member 5 are fixed by a bolt fastening portion 20 (second fixing portion).

[0021] That is, the boss 33 of the external gear 3 has an externally threaded portion 33a on its circular outer peripheral surface, and the intermediate member 8 has a threaded hole 81 on its circular inner peripheral surface. The externally threaded portion 33a of the boss 33 is screwed into the threaded hole 81 of the intermediate member 8 from the direction of the device axis 1a, thereby fixing the two members coaxially.

[0022] On the other hand, bolt holes 82 that extend through in the direction of the device axis 1 a are formed in an outer peripheral portion of the intermediate member 8. The output member 5 is formed with a disk-shaped mounting flange 51 that extends inward from its circular inner peripheral surface, and the mounting flange 51 is formed with bolt insertion holes 52 that extend through in the direction of the device axis 1 a at positions that correspond to the bolt holes 82. The mounting flange 51 of the output member 5 is overlapped on the intermediate member 8 from the direction of the device axis 1 a so that the bolt insertion holes 52 are positioned in the bolt holes 82, and both members are fastened and fixed coaxially from the direction of the device axis 1 a by a plurality of fastening bolts 9.

[0023] The portion of the external gear 3 where the external teeth 34 are formed is bent into an elliptical shape by the wave generator 4, and the external teeth 34 mesh with the internal teeth 21 at the major axis of the ellipse. Rotation is input to the cam plate 41 of the wave generator 4 from a rotation input member (not shown). When the cam plate 41 rotates, the meshing position of the external gear 3 with respect to the internal gear 2 moves circumferentially. In a wave gear device in which the external gear 3 is bent into an elliptical shape and meshes with the internal gear 2 at two circumferential locations, the number of teeth of the external gear 3 is generally 2n fewer than the number of teeth of the internal gear 2 (n is a positive integer). Depending on this difference in the number of teeth, the external gear 3 generates a reduced rotation that is significantly slower than the input rotation. The rotation of the external gear 3 is transmitted to the output member 5, which is coaxially connected to the external gear 3, via the intermediate member 8, and then transmitted from the output member 5 to a load-side device (not shown).

[0024] As explained above, in the wave gear device 1, the intermediate member 8 is interposed between the external gear 3 and the output member 5, and the external gear 3 and the intermediate member 8 are coaxially fixed by a threaded fixing portion 10 (first fixing portion) consisting of the male thread portion 33a and the threaded hole 81, and the intermediate member 8 and the output member 5 are coaxially fixed by a bolt fastening portion 20 (second fixing portion) consisting of the fastening bolt 9, bolt insertion hole 52 and bolt hole 82. By using the intermediate member 8, it is possible to ensure the fastening torque between the external gear 3 and the output member 5 while ensuring a large hollow diameter.

[0025] Furthermore, unlike when the external gear 3 and the output member 5 are directly fixed to each other, it is possible to reduce deformation of the output member 5 caused by fixing it to the external gear 3. Therefore, the present invention is particularly effective when the output member 5 is a component that is sensitive to deformation, such as a component such as the inner ring of a cross roller bearing or a component of a torque sensor. In addition, unlike when the output member 5 is directly screwed and fixed to the boss 33 of the external gear 3, the output member 5 that is fixed to the intermediate member 8 by bolting can be easily separated from the intermediate member 8, and there are also advantages such as an increased degree of freedom in designing the output member 5.

[0026] Modification of First Embodiment Figure 2 is a schematic half-longitudinal cross-sectional view showing a modification of the above-described harm gearing device 1. The basic configuration of the harm gearing device 1A shown in this figure is the same as that of the above-described harm gearing device 1, so corresponding parts are denoted by the same reference numerals and their description is omitted. In the harm gearing device 1A as well, an intermediate member 8A is interposed between the external gear 3 and the output member 5, and the external gear 3 and the output member 5 are coaxially fixed via the intermediate member 8A. The harm gearing device 1A of this example differs from the above-described harm gearing device 1 in that the first fixing portion connecting and fixing the boss 33A of the external gear 3 to the intermediate member 8A is a welded fixing portion 10A rather than a threaded fixing portion. The second fixing portion 20 connecting and fixing the intermediate member 8A to the output member 5 is bolted, as in the case of the above-described harm gearing device 1.

[0027] The boss 33A of the external gear 3A has an annular shape, and the intermediate member 8A is formed with a central hole 84 with a circular inner peripheral surface that can be inserted into the boss 33A. The boss 33A is inserted into the central hole 84 of the intermediate member 8A from the direction of the device axis 1a until its annular end face 36 coincides with the annular end face 86 on the inner peripheral edge side of the intermediate member 8A. In this state, the outer peripheral edge of the annular end face 36 of the boss 33A and the inner peripheral edge of the central hole of the intermediate member 8A are joined, for example, by full-circumference welding.

[0028] In the strain wave gearing 1A, an intermediate member 8A is interposed between the external gear 3A and the output member 5, the first fixing portion between the external gear 3A and the intermediate member 8A is a welded fixing portion 10A formed by full-circumference welding, and the second fixing portion between the intermediate member 8A and the output member 5 is a bolted fixing portion 20 formed by fastening bolts 9, bolt insertion holes 52, and bolt holes 82. By using the intermediate member 8A, it is possible to ensure fastening torque toward the output member 5 while ensuring a large hollow diameter for the device hollow portion 7. Furthermore, unlike when the external gear 3A and the output member 5 are directly welded and fixed, deformation of the output member 5 caused by fixing to the external gear 3A can be reduced. This is particularly effective when the output member 5 is a component that is sensitive to deformation, such as a component of a torque sensor.

[0029] (Embodiment 2) Fig. 3(A) is an end view of a strain wave gear device according to embodiment 2 of the present invention, Fig. 3(B) is a longitudinal cross-sectional view thereof, and Fig. 3(C) is an enlarged semi-longitudinal cross-sectional view thereof. The strain wave gear device 100 includes a rigid internal gear 120, a cup-shaped flexible external gear 130, a wave generator 140, an output member 150, and a cross roller bearing 160, which serves as a main bearing and supports the internal gear 120 and the external gear 130 in a relatively rotatable state. A device hollow portion 170 is formed in the center of the device, extending through the device in the direction of the device axis 100a. The strain wave gear device 100 also includes an intermediate member 180, through which the external gear 130 and the output member 150 are coaxially connected. In this example, the output member 150 and an inner ring 161 of the cross roller bearing 160 are manufactured as a single component. The outer peripheral portion of the output member 150 is a portion that functions as an inner ring 161 having an inner ring raceway groove (V groove) formed on its circular outer peripheral surface.

[0030] A cup-shaped external gear 130 is arranged coaxially inside the internal gear 120. As shown in Figure 3(C) , the external gear 130 includes a cylindrical body 131 that is flexible in the radial direction, a disk-shaped diaphragm 132 that extends radially inward from one end of the cylindrical body 131, a rigid boss 133 that is integrally formed in the center of the diaphragm 132, and external teeth 134 that are formed on the outer circumferential surface of the other end of the cylindrical body 131. The boss 133 has an annular shape with a central through-hole 135 formed therein, and the external teeth 134 are positioned opposite the internal teeth 121 and can mesh with the internal teeth 121.

[0031] The wave generator 140 is coaxially disposed inside the portion of the cylindrical body 131 of the external gear 130 where the external teeth 134 are formed. As shown in Figure 3(C), the wave generator 140 includes a rigid cam plate 141 with a non-circular contour, in this example an elliptical contour, and a wave bearing 142 attached to the elliptical outer circumferential surface of the cam plate 141. The cam plate 141 is an annular part formed with a central through-hole 143 with an inner diameter larger than the central through-hole 135 of the boss 133. The device hollow portion 170 extends through the center of the device in the direction of the device axis, passing through the central through-holes 135, 143.

[0032] An annular intermediate member 180 is disposed coaxially around the outer periphery of the boss 133 of the external gear 130, and the output member 150, which functions as an inner ring 161, is disposed coaxially around the outer periphery of the intermediate member 180. The intermediate member 180 is disposed coaxially between the boss 133 and the output member 150 in the radial direction. In this example, the boss 133 and the intermediate member 180 are fixed together by a welded joint 10B (first fixing portion). The intermediate member 180 and the output member 150 (inner ring 161) are fixed together by a bolt fastening portion (second fixing portion) 20B.

[0033] That is, the boss 133 of the external gear 130 is coaxially mounted on the annular intermediate member 180, and the annular end face 136 of the boss 133 and the annular end face 181 of the intermediate member 180 are located at the same position in the direction of the device axis 100a. The outer peripheral edge of the annular end face 136 of the boss 133 and the inner peripheral edge of the annular end face 181 of the intermediate member 180 are welded, for example, along the entire circumference. Meanwhile, the output member 150 (inner ring 161) is formed with a narrow annular mounting flange 151 extending inward from its circular inner peripheral surface. Bolt insertion holes 152 are formed in the mounting flange 151 at a constant pitch along the circumferential direction. Bolt holes 182 are also formed in the outer peripheral portion of the intermediate member 180 at the same pitch along the circumferential direction. The mounting flange 151 and the intermediate member 180 are overlapped from the direction of the device axis 100a so that the bolt holes 182 are aligned with the bolt insertion holes 152, and in this state, these two members are fastened together coaxially by a plurality of fastening bolts 190 that are screwed from the bolt insertion holes 152 into the bolt holes 182.

[0034] The external gear 130, which has been bent into an elliptical shape by the wave generator 140, meshes with the internal gear 120 at the position of the major axis of the ellipse. When the cam plate 141 of the wave generator 140 rotates, the meshing position of the external gear 130 with the internal gear 120 moves circumferentially, and reduced rotation, which has been reduced in accordance with the difference in the number of teeth between the two gears, is output from the external gear 130 to the output member 150.

[0035] In the strain wave gearing 100, an intermediate member 180 is interposed between the external gear 130 and the output member 150 which functions as the inner ring 161, and the external gear 130 and the intermediate member 180 are coaxially fixed by a welded joint 10B (first fixing portion) formed by a full periphery weld, and the intermediate member 180 and the output member 150 are coaxially fixed by a bolt fastening portion 20B (second fixing portion) formed by a fastening bolt, a bolt insertion hole, and a bolt hole. By using the intermediate member 180, it is possible to ensure fastening torque while ensuring a large hollow diameter.

[0036] Furthermore, in this example, the output member 150 is a component that functions as the inner ring 161 of the cross roller bearing 160, which is sensitive to deformation. By connecting the external gear 130 and the output member 150 via the intermediate member 180, deformation of the inner ring 161 can be suppressed compared to when they are directly connected. In addition, unlike when the output member 150 is directly welded or screwed to the boss 133 of the external gear 130, the output member 150 that is fixed to the intermediate member 180 by bolting has the advantage of being easily detachable from the intermediate member 180, and also has the advantage of increasing the degree of freedom in designing the output member 150.

[0037] While in the above examples the first and second fixing portions are bolted portions or welded joints, the fixation between the boss of the external gear and the intermediate member, and the fixation between the intermediate member and the output member are not limited to these, and various fixing forms can be adopted, such as press-fitting, pin-driving, or the combined use of different fixing mechanisms.

[0038] In each of the above examples, it is also possible to assemble separate parts such as oil seals, bearings, etc. to the intermediate member that connects the external gear and the output member. For example, in the wave gear device 1B shown in Fig. 4, a separate part 11 such as an oil seal or bearing is attached coaxially to the inner circumferential surface of the intermediate member 8A in the wave gear device 1A that is a modified example of the first embodiment shown in Fig. 2.

Claims

1. A strain wave gear device comprising: a rigid internal gear; a cup-shaped flexible external gear coaxially arranged inside the internal gear; a wave generator coaxially arranged inside the external gear and bending the external gear non-circularly to partially mesh with the internal gear, thereby moving the meshing position of both gears circumferentially; an output member coaxially arranged with the external gear to which rotation of the external gear is transmitted; and a device hollow section extending through the device center in the direction of the device axis, characterized in that the strain wave gear device also comprises: an annular intermediate member located between the output member and an annular boss defining the cup bottom portion of the external gear; a first fixing part that fixes the intermediate member to the boss of the external gear; and a second fixing part that fixes the intermediate member to the output member.

2. A wave gear device according to claim 1, wherein each of the first and second fixed parts is a bolt-fastening type fixing mechanism in which two members are fastened together with a fastening bolt, a screw-fastening type fixing mechanism in which a male thread formed on one member is coaxially screwed into a threaded hole formed on the other member, or a weld-joint type fixing mechanism in which two members are welded together.

3. A wave gear device according to claim 2, wherein the first fixed portion and the second fixed portion are fixed mechanisms that are different from each other.

4. A wave gear device according to claim 2, wherein the first fixing part is the welding-joint type fixing mechanism or the screw-fixing type fixing mechanism, and the second fixing part is the bolt-tightening type fixing mechanism.

5. A strain wave gear device according to claim 1, wherein the output member is a component of a torque sensor.

6. A wave gearing device according to claim 1, further comprising a bearing that supports the external gear so that it can rotate relative to the internal gear, and the output member is the inner ring of the bearing.

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