Wave gear with dry running

Abstract

Wave gear with a drive component (2), a wheel (6) provided with internal teeth (5) and an elastic transmission component (4) arranged in the wheel (6) and provided with external teeth (3), wherein the transmission component (4) is fitted onto the drive component (2) and is elliptically deformed by the drive component (2) such that the external teeth (3) of the transmission component (4) engage with the internal teeth (5) of the wheel (6) in opposite regions of a major ellipse axis, wherein the transmission component (2) is cup-shaped and tapers conically from a first cup end (7) having the external teeth (3) to a second cup end (8), and wherein the drive component (2) engages a bearing (9) on the transmission component (4) in the region of the major ellipse axis, characterized in thatthat the contour (11) of the internal toothing (5) of the wheel (6) and the contour (10) of the external toothing (3) of the transmission component (4) are designed such that the area for torque transmission in normal operation is arranged at the tooth head (12) of the contour (10) of the external toothing (3) of the transmission component (4), so that there is no contact between the two contours (10, 11) in the root area (14) of the contour (10) of the external toothing (3), wherein the contour (11) of the internal toothing (5) of the wheel (6) and the contour (10) of the external toothing (3) of the transmission component (4) are designed such that an area for torque transmission in overload operation is arranged at the tooth head (13) of the contour (10) of the external toothing (3) of the transmission component (4), so that there is no contact between the two contours (10,11) in the foot area (14) of the contour (10) of the external toothing (3) and the teeth of the external toothing (3) of the transmission component (4) which engage with the internal toothing (5) of the wheel (6) bear the load over their entire height.

Description

[0001] The invention relates to a wave gear according to the preamble of claim 1.

[0002] Such wave gears are used in a variety of ways in many technological fields. Regarding the functionality of such wave gears, the Harmonic Drive® gear, which belongs to the group of wave gears, serves as an example, and its operation is described below. is described at http: / / harmonicdrive.de / technologie / harmonic-drive-wellgetriebe / .

[0003] The drive component, designed as an elliptical wave generator, deforms the transmission component, designed as an externally toothed flexspline, via a ball bearing. This transmission component engages with the internally toothed, circular spline gear in the areas opposite the major axis of the ellipse. As the wave generator rotates, the major axis of the ellipse shifts, thus changing the tooth engagement area. Since the flexspline of the Harmonic Drive® gearbox has two fewer teeth than the circular spline, a relative movement of one tooth occurs between the flexspline and circular spline during half a revolution of the wave generator, and two teeth during a full revolution. When the circular spline is fixed, the flexspline rotates as the output element in the opposite direction to the drive. The circular spline can be fixed in a bearing ring.

[0004] From DE 10 2004 034 823 A1, a shaft drive device is known which comprises a rigid internal gear, a flexible external gear, and a shaft generator. The tooth profiles of the two gears are initially defined by a basic rack profile. The lower parts of the tooth root regions of these tooth profiles are modified by curves with pressure angles such that these are smaller than the standard pressure angle of the basic rack profile.

[0005] DD 244 796 A1 discloses a gearing on shaft drives, in particular with a cup-shaped elastic wheel, wherein the cup-shaped, cylindrical, elastic wheel has a conical tooth ring such that the contact line of the tooth pair in the area of ​​the large generator axis runs parallel to the head edges corresponding to this operating position at constant tooth heights when the tooth pair is fully engaged.

[0006] From DE 10 2008 044 109 A1 a wave gear for an actuator with an eccentric drive core driven by a servo motor is known, which elastically deforms a radially flexible rolling bushing in a radial direction, wherein an external toothing on an outer surface of the radially flexible rolling bushing partially engages with a rigid internal toothing of a support ring in continuous alternation.

[0007] A particular advantage of Harmonic Drive® gearboxes is that they exhibit no backlash increase in the gear teeth throughout their entire service life and possess outstanding positioning accuracy of less than one arc minute and repeatability of only a few arc seconds. Furthermore, Harmonic Drive® gearboxes are significantly more compact and lighter than conventional gearboxes, making them ideal for use in robotics, prosthetics, and similar technical fields where rotary motion must be achieved in the smallest possible space. Because power transmission occurs over a large tooth engagement area, Harmonic Drive® gearboxes can transmit higher torques than conventional gearboxes. With just three components, reduction ratios from 30:1 to 320:1 are achieved in a single stage. Under nominal operating conditions, efficiencies of up to 85% are attained. Harmonic Drive® gearboxes are non-self-locking and do not exhibit stick-slip behavior.Furthermore, Harmonic Drive® gearboxes exhibit high torsional stiffness with a nearly linear characteristic curve across the entire torque range. In addition, Harmonic Drive® gearboxes offer the option of a central hollow shaft. Cables, shafts, laser beams, etc., can thus be easily routed through the hollow shaft. Harmonic Drive® gearboxes are characterized by high reliability and a long service life, achieving significantly higher MTBF values ​​than other gearbox types.

[0008] However, a specific design for dry running is not currently established for this type of wave gear. Therefore, wave gears, which are normally equipped with grease lubrication, are also used for operation with tribologically active coatings when necessary. To nevertheless extend the possible service life, these wave gears are designed with backlash, unlike grease-lubricated versions. This backlash is achieved by a profile or contour shift of the internal teeth of the gear or the circular spline.However, this profile or contour shift is designed in such a way that even after the coating is applied, a permanent play in the meshing of the external teeth of the transmission component or the flex spline and the internal teeth of the wheel or the circular spline cannot be ruled out. Therefore, with this procedure, preloading of the wave gear after its assembly cannot be guaranteed.

[0009] It is therefore an object of the invention to further develop a wave gear of the type mentioned above in such a way that a preload of the assembled gear is also ensured for dry running in wave gears. However, this is done without sacrificing essential advantageous product features of grease-lubricated wave gears, such as zero backlash and high overload capacity.

[0010] This problem is solved by a wave gear with the features of claim 1. Advantageous embodiments of the invention are found in the dependent claims.

[0011] The wave gear according to the invention essentially consists of a drive component, a wheel with internal teeth, and an elastic transmission component arranged in the wheel and provided with external teeth. The transmission component is mounted onto the drive component and is deformed elliptically by the drive component such that the external teeth of the transmission component engage with, or mesh with, the internal teeth of the wheel in opposite regions of a major ellipse axis. The transmission component is cup-shaped and tapers conically from a first end of the cup, which has the external teeth, to a second end. The drive component engages with a bearing on the transmission component in the region of the major ellipse axis.According to a first alternative of the invention, the bearing lies outside a projection of the internal teeth of the wheel perpendicular to the direction of the axis of rotation of the wave gear. According to a second alternative of the invention, or in addition to the first alternative, the contour of the internal teeth of the wheel and the contour of the external teeth of the transmission component are designed such that the area for torque transmission in normal operation is arranged at the tooth tip of the contour of the external teeth of the transmission component, so that there is no contact between the two contours in the root area of ​​the external teeth.

[0012] By positioning the bearing outside the projection of the wheel's internal teeth perpendicular to the axis of rotation of the wave gear (as in a first, unloaded alternative), the radial stiffness of the wave gear is reduced, particularly in the contact area between the wheel's internal teeth and the transmission component's external teeth. This advantage of the invention is primarily achieved by allowing the drive component to be positioned significantly deeper within the cup-shaped transmission component compared to standard wave gears. This results in the transmission component bending back in the area of ​​the external teeth when the wheel is mounted onto this transmission component. Consequently, contact forces are generated in the teeth of the transmission component and the wheel's internal teeth, even when no external torque is applied to the wave gear.As a result of the drive component being positioned lower within the cup-shaped transmission component, the leverage ratios within the wave gear change. Specifically, because the bearing on which the drive component is supported against the transmission component is positioned lower within the cup-shaped transmission component, the forces generated by the bending of the transmission component in the gear teeth are reduced compared to prior art wave gears, even with unchanged radial deformation of the transmission component.

[0013] It is particularly advantageous if not only the bearing, but the entire drive component, is located outside the projection of the internal teeth of the wheel perpendicular to the direction of the axis of rotation of the wave gear.

[0014] According to a first embodiment of the invention, the transmission component has a wall thickness and, in the unassembled state, an inner diameter in the area of ​​the external teeth, wherein the ratio of the inner diameter to the wall thickness is less than 0.007. This design of the transmission component further increases the effect of reducing the radial stiffness of the wave gear, particularly in the contact area between the external teeth of the transmission component and the internal teeth of the wheel. It should be noted that the wall thickness of the transmission component also includes the thickness of the tooth root ring of the transmission component. The external teeth of the transmission component are arranged in the area of ​​this tooth root ring.

[0015] These modifications according to the invention reduce the contact pressure resulting from the gear preload, particularly in the meshing of the external teeth of the transmission component and the internal teeth of the gear. Due to the reduced radial stiffness, the dependence of the contact pressures on manufacturing tolerances and / or deviations is also reduced. Since the achievable service life is significantly determined by the contact pressures in this meshing, this leads to an increase in service life and a reduction in the dependence between manufacturing accuracy and service life. According to the invention, the wave gear is equipped with both zero backlash and high overload capacity.

[0016] According to a second claimed alternative, the object of the invention can also be achieved solely by modifying the tooth profile of the external teeth of the transmission component and the internal teeth of the gear. For this purpose, the contour of the internal teeth of the gear and the contour of the external teeth of the transmission component are designed such that the area for torque transmission during normal operation is located at the tooth tip of the contour of the external teeth of the transmission component. This prevents contact between the two contours in the root region of the external teeth of the transmission component. As a result, the area used to transmit the low operating torque during normal operation is shifted closer to the tooth tip of the external teeth of the transmission component.The contour of the internal gear teeth of the wheel is designed such that, in the area of ​​the tooth root of the external gear teeth of the transmission component, there is no contact during tooth engagement in normal operation. This results in a significant reduction of the friction path between the external gear teeth of the transmission component and the internal gear teeth of the wheel.

[0017] Contact between the tooth flanks of the internal gearing of the wheel and the external gearing of the transmission component at the base of the transmission component's external gearing only occurs after the transmission component's external gearing is fully engaged in the gap of the wheel's internal gearing. This only happens, however, under a high external load, particularly an overload, which causes a correspondingly large bending of the teeth of the transmission component's external gearing in the engagement area. This ensures a minimal friction path during normal operation under normal loads, while according to the invention, in the case of an overload, the teeth of the transmission component's external gearing, which engage with the wheel's internal gearing, bear the load over their entire height.

[0018] For this purpose, it is provided that the contour of the internal toothing of the wheel and the contour of the external toothing of the transmission component are designed in such a way that the area for torque transmission in overload operation is arranged at the tooth head of the contour of the external toothing of the transmission component, so that there is contact between the two contours in the foot area of ​​the contour of the external toothing in overload operation.

[0019] To further optimize friction, the contour of the external teeth of the transmission component and / or the contour of the internal teeth of the gear are designed such that the tooth tip of the respective contour is flattened. This prevents the corresponding tooth tips from making an additional, unnecessary contribution to friction.

[0020] According to the invention, it can of course also be provided that the internal teeth of the transmission component and / or the external teeth of the wheel are provided with a tribologically effective coating, at least in the area of ​​their tooth flanks that are in contact during the operation of the wave gear.

[0021] For example, diamond-like carbon layers can be used as tribologically effective coatings.

[0022] With regard to further optimization of the friction conditions of the wave gear, it has proven advantageous to have a pressure angle α of greater than or equal to 25°.

[0023] The invention is also intended to provide independent protection for a gearbox installation kit with a previously described wave gear.

[0024] Further objectives, advantages, features, and applications of the present invention will become apparent from the following description of exemplary embodiments with reference to the figures. All features described and / or illustrated, individually or in any meaningful combination, constitute the subject matter of the present invention, even independently of their compilation in the claims or their cross-reference.

[0025] They show: Fig. 1 An embodiment of the wave gear according to the invention in an assembled state in a top view along an axis of rotation of the wave gear, Fig. 2 a detailed representation of a cross-section of a wave gear according to the state of the art in the area of ​​a gear tooth, Fig. 3 a detailed representation of a cross-section of a wave gear according to the invention in the area of ​​a toothing, Fig. 4 a detailed representation of a cross-section of the contours of the meshing gears of the wave gear according to the invention in a load case, Fig. 5: a detailed representation of a cross-section of the contours of the meshing teeth of the wave gear according to the invention in a different load case.

[0026] In the Fig. Figure 1 shows an embodiment of the wave gear according to the invention in its assembled state, shown in a top view along a rotational axis 1 of the wave gear. A transmission component 4, designed as a flexspline, is mounted on a drive component 2, which is designed as an elliptical wave generator and is supported on a hollow shaft 15. The transmission component 4 is also elliptically deformed by the elliptical drive component 2. The elliptically deformed transmission component 4 engages with an external tooth 3 in the regions opposite the major axis of the ellipse with an internal tooth 5 of a gear 6 designed as a circular spline. In the top view according to Figure 1, the transmission component 4 is also elliptically deformed by the drive component 2. Fig. 1 The wave gear according to the invention does not differ essentially from wave gears known from the prior art.

[0027] In the Fig. 2 and Fig. Figure 3 shows detailed cross-sectional views of a wave gear in the area of ​​the toothing of the external toothing 3 of the transmission component 4 and the internal toothing 5 of the wheel 6. This shows Fig. 2 a wave gear known from the prior art, while Fig. Figure 3 shows an embodiment of a wave gear according to the invention.

[0028] The two wave gears of the Fig. 2 and Fig. The three components essentially have the same wheel 6, which is provided with internal teeth 5. The internal teeth 5 of the wheel 6 are located in the region of the major axis of the ellipse, which is in the Fig. 2 and Fig. Figure 3 shows the transmission component 2 engaging with the external teeth 3 of the transmission component 4, which in this case is cup-shaped and has a first end 7 and a second end 8. The transmission component 2 tapers from the first end 7 to the second end 8, so that the major axis of the ellipse decreases from the first end 7 to the second end 8.

[0029] In the two wave gears of the Fig. 2 and Fig. In the cup-shaped transmission component 4, a drive component 2 is inserted, which deforms the transmission component 4 elliptically. The drive component 2 can be designed as an elliptical disk, which sits on a hollow shaft 15 (not shown here) and is driven via it.

[0030] The wave gear according to the invention of the Fig. 3 now exhibits two significant differences compared to the wave gear of the Fig. 2 from the state of the art.

[0031] Firstly, the wall thickness t2 of the wave gear is different compared to the wall thickness t1 of the wave gear known from the prior art according to Fig. 2 is significantly reduced. The wall thickness is determined by the ratio of the wall thickness t2 to the inner diameter of the transmission component 4 in the unassembled state, which should not exceed 0.007, while the ratio of wall thickness t1 of the wave gear known from the prior art according to Fig. 2 and the inner diameter of the transmission component there does not usually fall below a value of 0.01.

[0032] The other essential difference between the wave gear according to the invention and those of the prior art is that the drive component 2 is inserted into the cup-shaped transmission component 4 in such a way that the bearing 9, on which the drive component 2 is mounted on the transmission component 4, lies outside a projection of the internal teeth 5 of the wheel 6 perpendicular to the direction of rotation of the axis of rotation 1 of the wave gear. Fig. 3 clearly shows that the drive component 2 differs from the prior art according to Fig. The drive component 2 is displaced by a distance v towards the second end 8 of the transmission component 4 in the known arrangement. This deeper placement of the drive component 2 in the cup-shaped transmission component 4 changes the lever ratios in the transmission. Whereas in the wave gear known from the prior art according to Fig. 2 the length l1 is the length l gesof the lever in the transmission according to the invention Fig. 3. As a result of the displacement of the drive component 2 by the distance v in the transmission component 4, the total length l is increased by the value l2. ges The length of the lever is therefore calculated as the length l1 plus the length l2.

[0033] As a result of this special arrangement of the drive component 2 in the transmission component 4, the lever force F3 in the transmission according to the invention is lower compared to the corresponding lever force F1 in the transmission known from the prior art according to Fig. 2, which arise from the re-bending of the transmission component 4 in the area of ​​the meshing of the external teeth 3 of the transmission component 4 and the internal teeth 5 of the gear 6, are significantly reduced. However, the force F4 that the drive component 2 exerts on the transmission component 4 in the area of ​​the bearing 9 remains essentially unchanged compared to the corresponding force F2 in the prior art gearbox. This effect on the forces is further enhanced by the previously described reduction in the wall thickness t2 of the transmission component. Here, the wall thickness t2 refers to the total thickness of the transmission component 4 in the cup area, including the area of ​​the base ring on which the external teeth 3 of the transmission component 4 are located.

[0034] In the Fig. Figure 4 shows a detailed cross-sectional view of the contours 10 and 11 of the teeth of the external gear 3 of the transmission component 4 and the internal gear 5 of the gear 6 in a meshed position during normal operation. The contour 10 of the tooth of the external gear 3 of the transmission component 4 rests against the contour 11 of a tooth of the internal gear 5 of the gear 6 in its head region 12 and forms a pressure angle α in this region, which is approximately 25°.

[0035] In the area of ​​the tooth head 13 of the tooth of the internal gear 5 of the gear 6, the contour 10 of the tooth of the external gear 3 of the transmission component 4 has no contact in its root area 14 during normal operation. This arrangement of the contours 10 and 11 of the teeth of the external gear 3 of the transmission component 4 and the internal gear 5 of the gear 6 results in a significant reduction of the friction path in the mesh between the external gear 3 and the internal gear 5. Contact between the two contours 10 and 11 in the root area 14 of the contour 10 of a tooth of the external gear 3 occurs – as shown in Fig.Figure 5 shows that this occurs only after the tooth has fully engaged in the gap between two teeth of the internal toothing 3 of the gear 6 and a high external load is applied. However, this load only becomes noticeable in the case of overload through a correspondingly large bending of the tooth of the external toothing 3. In this case, the external toothing 3 of the tooth now makes contact over a region 17 that extends over both its tooth head 12 and its tooth root 14. This ensures minimal friction with no backlash during normal operation, while according to the invention, in the case of overload, the teeth of the external toothing 3 and the internal toothing 5 bear the load without backlash over their entire height.

Claims

[1] Wave gear with a drive component (2), a wheel (6) provided with internal teeth (5) and an elastic transmission component (4) arranged in the wheel (6) and provided with external teeth (3), wherein the transmission component (4) is fitted onto the drive component (2) and is elliptically deformed by the drive component (2) such that the external teeth (3) of the transmission component (4) engage with the internal teeth (5) of the wheel (6) in opposite regions of a major ellipse axis, wherein the transmission component (2) is cup-shaped and tapers conically from a first cup end (7) having the external teeth (3) to a second cup end (8), and wherein the drive component (2) engages the transmission component (4) at a bearing (9) in the region of the major ellipse axis. characterized by, that the contour (11) of the internal toothing (5) of the wheel (6) and the contour (10) of the external toothing (3) of the transmission component (4) are designed such that the area for torque transmission in normal operation is arranged at the tooth head (12) of the contour (10) of the external toothing (3) of the transmission component (4), so that there is no contact between the two contours (10, 11) in the root area (14) of the contour (10) of the external toothing (3), wherein the contour (11) of the internal toothing (5) of the wheel (6) and the contour (10) of the external toothing (3) of the transmission component (4) are designed such that an area for torque transmission in overload operation is arranged at the tooth head (13) of the contour (10) of the external toothing (3) of the transmission component (4), so that there is no contact between the two contours (10,11) in the foot area (14) of the contour (10) of the external toothing (3) and the teeth of the external toothing (3) of the transmission component (4) which engage with the internal toothing (5) of the wheel (6) bear the load over their entire height. [2] Wave gear according to claim 1, characterized by , that the transmission component (4) has a wall thickness (t2) and, in the unassembled state, an inner diameter (d) in the area of ​​the external toothing (3), wherein the ratio of the wall thickness (t2) to the inner diameter (d) is less than 0.

007. [3] Wave gear according to one of the preceding claims, characterized by , that the contour (10) of the external toothing (3) of the transmission component (4) and / or the contour (11) of the internal toothing (5) of the wheel (6) is / are designed such that the tooth head (12, 13) of the respective contour (10, 11) is flattened. [4] Wave gear according to one of the preceding claims, characterized by, that the internal toothing (5) of the wheel (6) and / or the external toothing (3) of the transmission component (4) is provided with a tribologically effective coating at least in the area of ​​their tooth flanks which are in contact during the operation of the wave gear. [5] Wave gear according to claim 4, characterized by , that a tungsten carbide-reinforced molybdenum disulfide (MoS2 / WC) is used as a tribologically effective coating. [6] Wave gear according to one of the preceding claims, characterized by , that an angle of action (α) of greater than or equal to 25° is given.

Images