Wave generator arrangement and stress wave gear

Abstract

Wave generator arrangement for a stress wave transmission (1), with a wave generator (2) which comprises a bearing seat (3) with an elliptical cross-section for a radially flexible rolling bearing (4) and an extended section (11) with an elliptical cross-section, wherein the extended section (11) extends in the axial direction from the bearing seat (3), wherein the wave generator arrangement comprises a retaining ring (12) for axially securing the radially flexible rolling bearing (4), and wherein a retaining ring groove (13) arranged on the extended section (11) is provided for receiving the retaining ring (12), characterized in that the retaining ring (12) is a closed ring, and in that the retaining ring groove (13) is designed in the form of two groove sections (13a, 13b) which are arranged opposite one another on the circumference of the extended section (11).

Description

[0001] The present invention relates to a wave generator arrangement according to the preamble of claim 1 and a stress wave transmission according to claim 8.

[0002] Stress wave gears are well-known and are used in various applications, for example, in steering gears or industrial robots. Such stress wave gears comprise three essential components. The first component is an elliptical drive component, known as a wave generator. The second component is an elastically deformable, externally toothed transmission component, also called a flexspline. The third component is a rigid gear component, also called a circular spline, which has a circular internal toothing. The flexspline and the circular spline are rotatable relative to each other.

[0003] The wave generator deforms the flexspline, particularly into an elliptical shape, so that its external teeth partially mesh with the internal teeth of the rigid transmission component. The wave generator comprises an input shaft and is used to generate a wave motion in the flexspline. The rotationally driven input shaft and the elliptically shaped part of the wave generator transmit the elliptical shape circumferentially to the elastically deformable flexspline. By rotating the wave generator, the engagement between the external and internal teeth shifts in the circumferential direction. The internal teeth of the rigid transmission component have fewer teeth than the external teeth of the flexspline. The internal teeth, for example, have two fewer teeth than the external teeth.Due to the different number of teeth between the external gearing and the internal gearing, the drive by the shaft generator results in a relative movement with a high transmission ratio between the shaft generator and the flexspline.

[0004] Advantages of stress wave gears include relatively compact dimensions with very high gear ratios and high positioning accuracy between input and output. Such stress wave gears are used, for example, in industrial robots. The wave generator of the stress wave gear is usually driven by an electric motor.

[0005] The wave generator has a bearing seat on its outer circumference for a rolling bearing, which is arranged between the wave generator and the flexspline. An outer ring of the rolling bearing also deforms circumferentially during operation in accordance with the rotation of the wave generator. The rolling bearing allows for rotation between the wave generator and the flexspline and simultaneously transmits the wave motion of the elliptically shaped wave generator to the elastically deformable flexspline and its external gearing. For this purpose, at least parts of the rolling bearing are elastically deformable in the radial direction. In other words, the rolling bearing is radially flexible.

[0006] In practice, the fit of the radially flexible rolling bearing or its inner bearing ring on the bearing seat of the wave generator has proven to be insufficiently secure, which can lead to damage to the stress wave gear and its components. This is due to the following reasons: The inner and outer bearing rings of the radially flexible rolling bearing are generally designed with a very thin and therefore flexible cross-section in order to achieve the required flexibility and elasticity. The radially flexible rolling bearing is mounted on the elliptical bearing seat, whereby the bearing also assumes an elliptical shape. The radially flexible bearing is therefore held in position both axially and circumferentially by forces that must be generated by bending the bearing rings, especially the inner bearing ring.Therefore, the achievable contact pressures in terms of a bearing fit are limited, and axial movements, known as creep, of the radially flexible rolling bearing on the bearing seat cannot be completely prevented during operation. Therefore, state-of-the-art mechanical axial locking devices are used to limit the axial creep of the bearing on the elliptical bearing seat to a tolerable level.

[0007] For example, EP 3 214 344 A1 discloses a wave generator for a stress wave transmission, in which a retaining ring is proposed for securing the rolling bearing to the bearing seat. This retaining ring prevents axial movement of the radially flexible rolling bearing opposite to the sliding direction of the rolling bearing during operation of the wave generator in a stress wave transmission.

[0008] The object of the present invention is to improve such a wave generator for a stress wave transmission, in particular with regard to a reliable and safe operation of the stress wave transmission.

[0009] This object is achieved by a wave generator arrangement having the features of claim 1 and by a stress wave transmission according to claim 8. Advantageous embodiments are specified in the respective dependent claims.

[0010] A wave generator arrangement for a stress wave transmission is proposed, comprising a wave generator having a bearing seat with an elliptical cross-section for a radially flexible rolling bearing. The wave generator has an extension section with an elliptical cross-section that extends axially from the bearing seat. A retaining ring is provided for axially securing the radially flexible rolling bearing on the bearing seat. The axial securing provided by the retaining ring ensures that movements of the radially flexible rolling bearing in the axial direction are positively limited, so that the radially flexible rolling bearing is held on the bearing seat even at high speeds and high torque loads. To accommodate the retaining ring, the wave generator has a retaining ring groove on the extension section.A retaining ring held in a retaining ring groove is required to achieve a positive and thus secure fixation of the radially flexible rolling bearing on the shaft generator. According to the invention, the shaft generator assembly comprises a retaining ring designed as a closed ring for axially securing the radially flexible rolling bearing on the bearing seat.

[0011] Conventional retaining rings intended for axial locking in a shaft's circumferential groove are always designed as open or slotted rings, because only an open ring allows a retaining ring to be installed in the circumferential groove of a cylindrical shaft. The open area or gap of the retaining ring is necessary to expand the retaining ring and move it axially over a portion of the cylindrical shaft so that it can be placed in the circumferential groove.

[0012] The invention takes advantage of the fact that the extended section of the wave generator has an elliptical cross-section. This makes it possible to place a closed retaining ring in the retaining ring groove. This is done by deforming the closed retaining ring into an elliptical shape and sliding it axially over the extended section until it can engage in the retaining ring groove. The retaining ring is so elastic that the described deformation during installation of the retaining ring does not cause any plastic, i.e., permanent, deformation. When engaged, the retaining ring returns to its original, unstressed shape. This allows the closed retaining ring to be installed quickly and easily. Advantageously, the retaining ring can also be mounted on the wave generator at the same time as, or together with, the radially flexible rolling bearing.

[0013] Compared to slotted or open retaining rings, the closed retaining ring has the advantage that it does not expand significantly during operation, even at high speeds, and consequently cannot escape from the retaining ring groove. Furthermore, with a closed retaining ring, due to the even mass distribution over the entire circumference, no significant imbalances occur even at high speeds, as is the case with open retaining rings with a separation point or a lock. Furthermore, the closed retaining ring minimizes the risk of the retaining ring being undesirably rotated along with another component in its rotational movement and consequently escaping from the retaining ring groove. The latter can happen with conventional retaining rings that are attached to another component at their separation point or a lock and are therefore rotated along with the component.

[0014] The retaining ring preferably has a circular shape. This means that the retaining ring is circular in its unstressed state. For installation on the shaft generator, the retaining ring can be elastically deformed so that it can be placed in the retaining ring groove. A circular retaining ring is inexpensive to manufacture because it can be produced in large quantities and with minimal waste from a preformed tube. The required elasticity of the retaining ring can be ensured by a suitable selection of the material and dimensions of the retaining ring.

[0015] The retaining ring groove is preferably machined according to a circular basic shape. The retaining ring groove can be manufactured as a so-called plunge groove. The preferably circular basic shape is easily manufactured as a plunge groove. This can be done on any machine tool on which the workpiece, in this case the wave generator, is rotatably clamped. The groove base can be cylindrical or conical.

[0016] Due to the elliptical cross-sectional shape of the extension section, the retaining ring groove, which is manufactured according to a circular shape, is not necessarily formed over the entire circumference. Depending on the dimensions of the elliptical cross-section and the depth of the retaining ring groove, the retaining ring groove can only be formed in the areas around the two main axes of the ellipse. Therefore, according to the invention, the retaining ring groove is not formed in a completely circular shape, but rather in the form of two groove sections. The two groove sections are arranged opposite each other on the circumference of the extension section of the wave generator.

[0017] To simplify the production of the wave generator, it is preferably provided that the direction of the main axes of the elliptical cross-section of the bearing seat and the extension section coincide. Particularly preferably, the extension section has the same elliptical cross-section as the bearing seat. In this way, the bearing seat and the extension section can be manufactured with the same outer contour in a single process step. The subsequent machining of the retaining ring groove determines the respective axial dimensions of the bearing seat and the extension section. The bearing seat extends in the axial direction from the retaining ring groove to an opposite mechanical stop for the radially flexible rolling bearing.

[0018] According to one embodiment, an insertion chamfer adjoins the side of the extension section facing away from the bearing seat. The insertion chamfer is therefore arranged on the side of the extension section from which the radially flexible rolling bearing and the retaining ring are mounted. Preferably, the insertion chamfer also has an elliptical cross-section that smoothly transitions into the elliptical cross-section of the extension section. In this way, the radially flexible rolling bearing and the retaining ring can be pulled onto the extension section via the insertion chamfer, with the two parts being deformed into an elliptical shape by the applied axially directed press-on force. Thus, no special tools or further measures are required to deform the radially flexible rolling bearing and the retaining ring for assembly.

[0019] In one design, the lead-in chamfer can follow the elliptical shape of the extension section. Another design provides for the lead-in chamfer to have a circular shape, which allows for easy production, for example, on a lathe.

[0020] The present invention further comprises a stress wave transmission with a wave generator arrangement as described above.

[0021] In the following, the invention and its advantages are explained in more detail with reference to the embodiments shown in the attached figures.

[0022] It shows Fig. 1 shows a section of a stress wave transmission with a wave generator arrangement according to the invention in a sectional view and Fig. 2 a wave generator arrangement according to the invention with a radially flexible rolling bearing in a perspective exploded view.

[0023] The Fig. 1, a section of the stress wave gear unit 1 comprises a wave generator 2, an elastically deformable flexspline 7, and a rigid circular spline 9. The circular spline 9 and the flexspline 7 are rotatably mounted relative to each other by means of a main bearing 16. The essentially rotationally symmetrical stress wave gear unit 1 has a central rotation axis 17 around which the wave generator 2 and the flexspline 7 rotate at different speeds during operation. The directional terms used in this document, such as radial, axial, and circumferential, refer to the rotation axis 17 unless expressly stated otherwise.

[0024] The circular spline 9 has a circular cross-section internal toothing 10, which partially meshes with an external toothing 8 arranged on the flex spline 7. The flex spline 7 and the rigid circular spline 9 are rotatable relative to each other.

[0025] The wave generator 2 has a bearing seat 3 with an elliptical cross-section, which is arranged at least partially within the flexspline 7. Via its elliptical bearing seat 3 and via a radially flexible roller bearing 4 arranged on this bearing seat 3, the wave generator 2 deforms at least the end of the flexspline 7 with the external toothing 8 into an at least approximately elliptical shape, so that its external toothing 8 engages with the internal toothing 10 of the rigid circular spline 9 at two engagement areas. The radially flexible roller bearing 4 is thus arranged between the wave generator 2 and the flexspline 7. A bearing outer ring 6 of the radially flexible roller bearing 4 is arranged at one axial end of the flexspline 7 on its inner circumference. The external toothing 8 is located on the outer circumference of the same end of the flexspline 7.

[0026] By turning, i.e. rotating the wave generator 2 about the rotation axis 17, the meshing between the external gearing 8 and the internal gearing 10 shifts in the circumferential direction. The internal gearing 10 has fewer teeth than the external gearing 8. For example, the internal gearing 10 has two fewer teeth than the external gearing 8. Due to the different numbers of teeth between the external gearing 8 and the internal gearing 10, when driven by the wave generator 2, a relative movement with a high transmission ratio results between the wave generator 2 and the flexspline 7. When the wave generator 2 rotates, the external gearing 8 is essentially supported on the two meshing areas in the internal gearing 10 and is rotated by two teeth relative to the internal gearing 10 for every full revolution of the wave generator 2.

[0027] An inner bearing ring 5 of the radially flexible rolling bearing 4 is arranged on the elliptical bearing seat 3. The inner bearing ring 5 and the outer bearing ring 6 of the radially flexible rolling bearing 4 have a thin cross-section and thus a relatively high degree of flexibility or elasticity. The radially flexible rolling bearing 4 is mounted on the elliptical bearing seat 3, whereby the radially flexible rolling bearing 4 also assumes an elliptical shape. The deformation of the bearing rings 5 ​​and 6 during mounting onto the elliptical bearing seat 3 causes the bearing rings 5 ​​and 6 to be elastically deformed.

[0028] For axial securing of the bearing inner ring 5 on the bearing seat 3, a retaining ring 12 is provided, which is engaged in a retaining ring groove 13. The design of the retaining ring 12 and the retaining ring groove 13 are shown in the Fig.2. The retaining ring 12 is designed as a closed ring. This means that it has no separation point. Therefore, even at high speeds, it cannot expand significantly and subsequently escape from the retaining ring groove 13. Furthermore, in contrast to open retaining rings, a closed ring does not cause any significant imbalance even at high speeds, since its mass is evenly distributed over its entire circumference.

[0029] The wave generator 2 has a bearing seat 3 with an elliptical cross-section, which extends in the axial direction from the retaining ring groove 13 to the end stop 15. The extension section 11 of the wave generator 2 extends from the retaining ring groove 13 in the opposite axial direction. Since the extension section 11 in this exemplary embodiment has the same elliptical cross-sectional shape as the bearing seat 3, it is essentially an extension of the bearing seat 3. In this way, the bearing seat 3 and the extension section 11 can be manufactured together in a single process step.

[0030] The retaining ring groove 13 is formed in the form of two groove sections 13a and 13b, which are arranged on the elliptical circumference of the extension section 11. The two groove sections 13a and 13b are arranged opposite each other on the circumference, thereby ensuring a secure hold of the retaining ring 12 and the radially flexible rolling bearing 4 in the axial direction.

[0031] The end stop 15 is formed by a disk-shaped part extending in the radial direction at one axial end of the wave generator 2. At the end of the wave generator 2 opposite the end stop 15 in the axial direction, the wave generator has an insertion bevel 14. The insertion bevel 14 facilitates the installation of the radially flexible rolling bearing 4 and the retaining ring 13 on the wave generator. The radially flexible rolling bearing 4 and the retaining ring 13 can be easily pushed onto the extension section 11 and the bearing seat 3 in the axial direction using the insertion bevel 14. Reference symbol 1 stress wave gear 2 wave generators 3 bearing seat 4 radially flexible rolling bearings 5 Bearing inner ring 6 Bearing outer ring 7 Flexspline 8 External gearing 9 Circular spline 10 Internal gearing 11 Extension section 12 Retaining ring 13 Retaining ring groove 13a Groove section 13b Groove section 14 Insertion chamfer 15 End stop 16 main bearings 17 Rotation axis

Claims

[1] Wave generator arrangement for a stress wave transmission (1), with a wave generator (2) which comprises a bearing seat (3) of elliptical cross-section for a radially flexible rolling bearing (4) and an extension section (11) of elliptical cross-section, wherein the extension section (11) extends from the bearing seat (3) in the axial direction, wherein the wave generator arrangement comprises a retaining ring (12) for axially securing the radially flexible rolling bearing (4), and wherein a retaining ring groove (13) arranged on the extension section (11) is provided for receiving the retaining ring (12), characterized by that the retaining ring (12) is a closed ring, and that the retaining ring groove (13) is designed in the form of two groove sections (13a, 13b) which are arranged opposite one another on the circumference of the extension section (11). [2] Wave generator arrangement according to claim 1, characterized bythat the retaining ring (12) has a circular shape. [3] Wave generator arrangement according to claim 1 or 2, characterized by that the retaining ring groove (13) is manufactured according to a circular basic shape. [4] Wave generator arrangement according to one of the preceding claims, characterized by that the direction of the main axes of the elliptical cross-section of the bearing seat (3) and the extension section (11) coincide. [5] Wave generator arrangement according to claim 4, characterized by that the extension section (11) has the same cross-section as the bearing seat (3) at least over parts of its axial extent. [6] Wave generator arrangement according to one of the preceding claims, characterized by that an insertion chamfer (14) is connected to the side of the extension section (11) facing away from the bearing seat (3). [7] Wave generator arrangement according to claim 6, characterized bythat an elliptical cross-section of the insertion bevel (14) continuously merges into the elliptical cross-section of the extension section (11). [8] Stress wave transmission (1) with a wave generator arrangement according to one of the preceding claims.

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