Wave generator
By designing a wave generator with an oval or elliptical inner and outer ring, the balls at four contact points are used to contact the raceway, the problems of high load and high failure risk of wave generators in strained wave gear transmission are solved, and the operation effect of high accuracy and low failure is achieved.
Patent Information
- Application Number
- CN202280101181.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-08
- Publication Date
- 2025-05-27
AI Technical Summary
The wave generators in existing strained wave gear transmissions are constantly deformed, resulting in high loads, high risk of failure and high energy loss.
Design a wave generator with the inner and outer rings of ovate or elliptical, and the ball contacts the raceway at four contact points, ensuring that each ball always has four contact points with the raceway, dispersing contact pressure and reducing wear and friction.
Through the design of four contact points, contact pressure and sliding are reduced, bending stiffness and load distribution uniformity are improved, wear and fault risks are reduced, and high operating accuracy and low fault risks are achieved.
Smart Images
Figure CN120051646A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a wave generator for a strain wave gearing having an oval inner ring and an oval outer ring according to claim 1. Furthermore, the present invention relates to a strain wave gearing having such a wave generator according to claim 9. Background Art
[0002] A strain wave gearing, also known as a harmonic gearing, is a high-precision gear device which can be used, for example, in joints of articulated robots. The strain wave gearing consists of a wave generator which is arranged in an elastically deformable cup or bushing or even an elastically deformable cylinder (so-called "flexspline"), which in turn is surrounded by a cylindrical outer ring (so-called "circular spline"). The bushing has external teeth and can be elastically deformed into an oval shape such that the external teeth of the bushing engage with the internal teeth of the cylindrical outer ring at two opposite points. The ovality of the bushing is produced by the oval shape of the wave generator. The wave generator or shaft generator represents a bearing having an oval or elliptical shape instead of a circular shape.
[0003] Due to the continuous deformation of the bearing or the wave generator, in particular the outer ring in contact with the oval bushing experiences dynamically changing deformations at all points on this outer ring. The rings of the wave generator thus are subjected to high loads, which increases the risk of failure and the need for very high material grades. At the same time, the bearing must be operated under preloading to ensure a minimum rotational difference between the inner ring of the wave generator which is driven from the outside and the outer ring of the wave generator for driving the oval bushing.
[0004] So far, deep groove ball bearings have generally been used for the wave generator. However, centrifugal forces cause an increase in sliding. Since there are only two contact points between the balls and the raceways, this can lead to high contact pressures. The two contact points between the balls and the raceways change with the loading direction, which results in a dynamic change in the rotational axis of the balls and thus in high and non-constant sliding and thus in high energy losses. Summary of the Invention
[0005] Therefore, it is an object of the present invention to provide a wave generator which avoids the above-mentioned disadvantages and allows high running accuracy and a low risk of failure.
[0006] This object is achieved by a wave generator according to claim 1 and a strain wave gearing having such a wave generator according to claim 9.
[0007] The wave generator includes an oval or elliptical inner ring and an oval or elliptical outer ring. Balls are arranged between the two rings and roll on raceways arranged on the two rings.
[0008] To allow for smaller sliding and friction losses, as well as higher bending stiffness and lower maximum contact pressure with the raceways, each ball has four contact points with the raceways. This means that each ball has a total of four contact points, i.e., two contact points with each ring. At the contact points, the corresponding raceway and ball have the same tangent, and the radius of curvature (i.e., the distance between the center of the curvature circle of the raceway and the contact point) is perpendicular to this tangent. Compared with the deep groove ball bearings currently in use, these four contact points distribute the contact pressure, thereby reducing the contact stress, and further reducing wear, friction, and other surface damages.
[0009] Conventional four-point contact ball bearings, which can be used as deep groove ball bearings in the wave generator and also have four contact points, but these are only theoretically existent. In operation, only two of the four theoretical contact points are effective, which results in high contact pressure at these two effective contact points. In contrast, in the wave generator proposed herein, the four contact points are always effective, which means that the contact pressure is better distributed. Since the normal direction of the contact points is not aligned with the axial or radial axis, the conventional four-point contact ball bearings have reduced contact stiffness in both the axial and radial directions. In addition, such bearings require high axial and / or radial preloading in order to be able to support radial loads.
[0010] To achieve this, the wave generator is divided in cross-section by the axis of rotation of the balls and the axis perpendicular to the axis of rotation of the balls into four quadrants arranged in a clockwise direction. The axis of rotation of the balls is regarded here as the imaginary axis of rotation in the stationary state. In operation, the axis of rotation of the balls is not fixed, but can move or shift.
[0011] The raceways of the elliptical outer ring are located in the first and second quadrants, and the raceways of the elliptical inner ring are located in the third and fourth quadrants. The center of the radius of curvature of the raceway in the first quadrant is in the third quadrant, the center of the radius of curvature of the raceway in the second quadrant is in the fourth quadrant, the center of the radius of curvature of the raceway in the third quadrant is in the first quadrant, and the center of the radius of curvature of the raceway in the fourth quadrant is in the second quadrant. Each of the four contact points of the balls is located in one of the four quadrants. This special arrangement ensures that each ball always has four contact points with its raceways, and these contact points remain unchanged even under loading. In conventional four-point contact ball bearings, during the loading operation, only two or at most three contact points are loaded. The four contact points thus result in a lower contact pressure for each contact point with the balls, which can, for example, reduce the wear of the wave generator, while being able to withstand radial and axial loads due to the arrangement of the contact points.
[0012] In addition to reducing the contact pressure, the kinematics achieved by the four contact points also reduce the sliding of the balls in the wave generator. This allows for a higher preload in the wave generator while allowing for higher running accuracy without increasing the loads on the elliptical inner ring or the elliptical outer ring. Alternatively, the preload and running accuracy can be maintained at the current level, but with the advantage of a lower risk of ring failure.
[0013] According to one embodiment, the intersection of the two curvature radii of the raceway of the elliptical inner ring lies on an axis perpendicular to the axis of rotation of the balls, and the intersection of the two curvature radii of the raceway of the elliptical outer ring also lies on an axis perpendicular to the axis of rotation of the balls. These axes can also be a common axis, in particular an axis perpendicular to the axis of rotation and passing through the center of the balls. Additionally, the intersection points can lie on the axis of rotation. Each raceway thus has two curvature radii whose centers do not coincide, such that each raceway consists of two sections between which there is a transition. The transition between the two raceways or the contact line of the two raceways lies in a plane passing through the center of the balls and perpendicular to the imaginary axis of rotation of the balls. These two curvature radii and their particular arrangement ensure that the balls always have four contact points with the raceways. The two curvature radii can be different or the same.
[0014] According to a further embodiment, the curvature radii are the same. This results in a symmetric distribution of the curvature radii and their centers in the four quadrants. This symmetric arrangement distributes the load evenly among the four contact points between the balls and the raceways.
[0015] According to a further embodiment, the contact points are arranged offset from the axis perpendicular to the axis of rotation of the balls. This means that the contact points are preferably not located on the axis of rotation of the balls, but on an axis perpendicular to the axis of rotation of the balls. In this way, it is possible to prevent the wave generator from behaving like a conventional deep groove ball bearing with only two contact points, which would reduce the radial or axial stiffness. Additionally, compared to a conventional deep groove ball bearing having one contact point on each raceway, the radial or axial load can be supported by the wave generator in a defined manner directly from the start of loading. In the same way, compared to a ball bearing having one contact point on one of the axes as well, the axial or radial load can be supported directly from the start of loading in a defined manner.
[0016] According to a further embodiment, the contact points are arranged in the range of ±20°, preferably ±10°, around an axis perpendicular to the axis of rotation of the balls. Depending on the application, the contact points between the balls and the raceways can vary within this range. Due to this arrangement, the four contact points result in a special kinematics of the balls, since the axis of rotation of the balls always remains perpendicular to the axis around which the contact points are arranged even during loading.
[0017] According to one embodiment, the curvature radius is a variable radius. This means that the corresponding raceway can be an arc segment, but can generally also be an ellipse or an oval.
[0018] The oval inner ring and / or the oval outer ring can each be formed as a split ring, providing a preloading mechanism to control the contact point between the balls and the raceways. By preloading the corresponding ring, the preloading of the contact point can be adjusted by regulating the gap between the parts of the split ring.
[0019] This has the advantage that the preloading required in the wave generator can be easily achieved by installing a split inner ring or outer ring with appropriate preloading, which was not possible in previous wave generators. For example, during assembly, first the outer ring with the rolling elements, i.e., the balls, is installed, and then the first part of the split inner ring is installed. Then the correct preloading can be measured and the second part of the split inner ring can be installed accordingly. If a split outer ring is used, the assembly is carried out in the same way. Compared with previous wave generators, due to the four contact points, the load can be better distributed in a simple and convenient way, and the required preloading can also be introduced into the wave generator in a simple way.
[0020] In particular, the wave generator described herein provides good radial load stiffness and reduced wear behavior due to little sliding behavior.
[0021] According to another aspect, a strain wave gear transmission including the wave generator as described above is provided. The strain wave gear transmission further includes a deformable ring, also referred to as a flexible spline, arranged around the wave generator, which can be a cylindrical bushing or cylinder with external teeth, and a rigid cylindrical outer ring with internal teeth, also referred to as a circular spline. The teeth of the deformable ring and the cylindrical outer ring are configured to mesh with each other. When the wave generator is driven and rotates within the deformable ring, the deformable ring elastically elliptically deforms by contacting the wave generator according to its elliptical shape. Thus, the external teeth of the deformable ring mesh with the internal teeth of the cylindrical outer ring at two opposite points.
[0022] For example, such a strain wave gear transmission can be used in robots that require very precise control of the motion sequence and joints using bearings. The wave generator can be used, for example, in robotic applications to connect successive arms or arm components.
[0023] Further advantages and advantageous embodiments are given in the description, the drawings, and the claims. In particular, the combination of features given in the description and the drawings is purely exemplary, so these features can also exist alone or in other combinations.
[0024] Hereinafter, the present invention will be described in more detail with reference to the exemplary embodiments shown in the drawings. In this case, the exemplary embodiments and the combinations shown in the exemplary embodiments are purely exemplary and are not intended to limit the scope of protection of the present invention. This is only defined by the appended claims. Description of the Drawings
[0025] The accompanying drawings show:
[0026] Figure 1 is a schematic view of a strain wave gear drive having a wave generator;
[0027] Figure 2 is Figure 1 a schematic cross-sectional view of a first embodiment of the wave generator of;
[0028] Figure 3 is Figure 1 a schematic cross-sectional view of a second embodiment of the wave generator of, having an open inner ring; and
[0029] Figure 4 is Figure 1 a schematic cross-sectional view of a third embodiment of the wave generator of, having an open outer ring.
[0030] Hereinafter, identical or functionally equivalent elements are denoted by the same reference numerals. Detailed Description of the Invention
[0031] Figure 1 Shows a strain wave gear drive 20 having a wave generator 1 disposed in an elastically deformable ring 22. The ring 22 can be a cup-shaped member or a bushing, i.e., it can be closed on one side. Alternatively, the ring can be a toothed cylinder without a bottom, as in the case of a cup-shaped member or a bushing. The ring 22 is in turn surrounded by a rigid cylindrical outer ring 26. The ring 22 has external teeth 26 and is elastically deformable into an oval or elliptical shape.
[0032] The wave generator 1 consists of an elliptical inner ring 2 and an elliptical outer ring 4, between which balls 6 are arranged. When the wave generator rotates, the ring 22 (e.g., a bushing) is elastically deformed into an ellipse according to the elliptical shape of the outer ring 4 in contact with the ring 22. In this way, the external teeth 24 of the ring 22 come into contact with and engage the internal teeth 28 of the cylindrical outer ring 26 at two opposite positions.
[0033] Due to the continuous deformation of the wave generator 1, especially the outer ring 4 in contact with the ring 22 undergoes dynamic alternating deformation at all positions of the ring 4. The rings 2, 4 of the wave generator are thus exposed to high loads, which increases the risk of failure and the requirement for very high material quality. At the same time, the wave generator 1 must operate under preloading to ensure a minimum rotational difference between the externally driven inner ring 2 of the wave generator 1 and the outer ring 4 of the wave generator 1 for driving the elliptical ring 22. To achieve this, the wave generator 1 is used as described below.
[0034] Figure 2 Shows a wave generator 1 having an elliptical inner ring 2 and an elliptical outer ring 4. Balls 6 are arranged as rolling elements between the rings 2, 4. The balls 6 roll on raceways 8 arranged on the rings 2, 4.
[0035] In Figure 2 the wave generator 1 shown, the raceway 8 can be hypothetically divided into four quadrants I, II, III, and IV. The division into four quadrants I, II, III, and IV is formed by the axis of rotation A of the balls R and an axis A R perpendicular to the axis of rotation A S . The raceway of the outer ring 4 is formed by two sections 8-I and 8-II and is located in the first and second quadrants I and II, and the raceway of the inner ring 2 is formed by two raceway sections 8-III and 8-IV and is located in the third and fourth quadrants III and IV.
[0036] The balls 6 are in contact with the raceways 8-I and 8-II at two contact points P-I and P-II located in two contact zones 10-I and 10-II, and are in contact with the raceways 8-III and 8-IV at two contact points P-III and P-IV located in contact zones 10-III and 10-IV. To ensure that the balls 6 contact the raceway 8 at the contact points P-I, P-II, P-III, and P-IV, the raceway 8 has a special design: the center M-I of the radius of curvature R-I of the raceway section 8-I is located in the third quadrant III, the center M-II of the radius of curvature R-II of the raceway section 8-II is located in the fourth quadrant IV, the center M-III of the radius of curvature R-III of the raceway section 8-III is located in the first quadrant I, and the center M-IV of the radius of curvature R-IV of the raceway section 8-IV is located in the second quadrant II.
[0037] In Figure 2 the embodiment shown, the intersection of the radii of curvature R-I and R-II of the first and second quadrants I and II is located on the axis A S , and the intersection of the radii of curvature R-III and R-IV of the third and fourth quadrants III and IV is also located on the axis A S . However, the intersection may not be located on the axis A S . The radius of curvature R is here understood as the radius defining the curvature, i.e., the distance between the raceway 8 and the center M. In particular, as Figure 1 shown, the line passing through M-I and M-III intersects the line passing through M-II and M-IV at the intersection point S. In the case shown here, the intersection point S is simultaneously located at the intersection of the axis of rotation A R and the axis A S , but this is not mandatory. This specific design of the radius of curvature R of the raceway 8 ensures that the balls 6 contact the raceway 8 at the contact points P-I, P-II, P-III, and P-IV. The contact points P-I, P-II, P-III, and P-IV are located in the contact zone 10 and are within a range of ±20°, especially ±10°, around the axis A S .
[0038] To ensure that the wave generator 1 cannot adapt only to axial or radial loads, the contact points P-I, P-II, P-III, P-IV are always offset from the axis A S . In this way, the balls 6 always have four contact points P-I, P-II, P-III, P-IV with the raceways 8, which are located in the contact zones 10-I, 10-II, 10-III and 10-IV respectively, thus achieving good radial load stiffness and good load and pressure distribution, and thus achieving low wear behavior.
[0039] As Figure 3 and 4 shown, the wave generator 1 can be further configured to achieve. It should be noted that in all embodiments, the rotational axis A R is parallel to the rotational axis A of the wave generator 1 L arranged. In this case, the axis A around which the contact zones 10-I, 10-II, 10-III and 10-IV are arranged S is perpendicular to the rotational axis A of the wave generator 1 L .
[0040] As Figure 3 shown, the wave generator 1 can be formed with open inner rings 2, 2'. This has the advantage that the preloading required in the wave generator 1 can be introduced into the wave generator 1 in a simple manner. For example, this can be done during installation, first installing the first part 2 of the inner ring without paying attention to the preloading, and then installing the second part 2' of the inner ring, where the preloading is measured and adjusted by installing the inner ring 2'.
[0041] In this case, for example, a preloading mechanism, such as a threaded connection, can be used, which acts in the direction of line 14. The preloading mechanism is used to control the contact points P-I, P-II, P-III, P-IV or the contact zones 10 between the balls 6 and the raceways 8 during the installation of the inner ring 2', and if necessary, adjust them afterwards. By preloading the rings 2, 2', the preloading of the contact points P-I, P-II, P-III, P-IV can be adjusted by adjusting the gap between the parts of the open rings 2, 2'.
[0042] Alternatively, the outer ring 4 can also be open, as Figure 4As shown. In this case, the outer ring includes a first part 4 and a second part 4'. As described for the open inner rings 2, 2', the open outer rings 4, 4' can also be used to adjust and set the required preload in the wave generator 1 along line 14. A preloading mechanism can also be used, which sets the required preload during the installation of the second part 4' after the installation of the first part 4. Compared with the previous wave generators designed without open rings, the wave generator 1 proposed here thus not only offers the advantage of better load distribution due to the four contact points, but also the additional advantage of easier setting of the required preload.
[0043] Due to the lower friction or reduced sliding behavior, the wave generators described herein can also achieve good radial and axial load stiffness and low wear behavior, respectively.
[0044] List of reference numerals
[0045] 1 Wave generator
[0046] 2, 2' Oval inner rings
[0047] 4, 4' Oval outer rings
[0048] 6 Balls
[0049] 8 Raceways
[0050] 10 Contact zones
[0051] 14 Preloading mechanism
[0052] 20 Strain wave gear drive
[0053] 22 Rings
[0054] 24 External teeth
[0055] 26 Cylindrical outer ring
[0056] 28 Internal teeth
[0057] I, II, III, IV Quadrants
[0058] A L Axis of rotation of the wave generator
[0059] A R Axis of rotation of the ball
[0060] A S Axis perpendicular to the axis of rotation of the ball
[0061] Center of the radius of curvature M
[0062] P Contact point
[0063] R Radius of curvature
[0064] S Intersection point
Claims
1. A wave generator (1) for a strain wave gear transmission (20), the wave generator (1) comprising an elliptical inner ring (2) and an elliptical outer ring (4), wherein balls are arranged between the elliptical inner ring (2) and the elliptical outer ring (4), and wherein the balls (6) roll on raceways (8) arranged on the elliptical inner ring (2) and the elliptical outer ring (4). Characterized in that The wave generator (1) is centered in cross section around the rotation axis (A) of the ball (6). R ) and the rotation axis (A) of the ball (6) R )Vertical axis (A S ) is imaginarily divided into four quadrants (I, II, III, IV) arranged clockwise, wherein the ball (6) has four contact points (PI, P-II, P-III, P-IV) with the raceway (8), and wherein each contact point (PI, P-II, P-III, P-IV) is located in one of the four quadrants (I, II, III, IV), wherein the raceway (8) of the elliptical outer ring (4) is located in the first and second quadrants (I, II), and the raceway (8) of the elliptical inner ring (2) is located in the third and fourth quadrants (III, IV), wherein the first quadrant The center (MI) of the radius of curvature (RI) of the raceway (8-I) of (I) is located in the third quadrant (III), wherein the center (M-II) of the radius of curvature (R-II) of the raceway (8-II) of the second quadrant (II) is located in the fourth quadrant (IV), wherein the center (M-III) of the radius of curvature (R-III) of the raceway (8-III) of the third quadrant (III) is located in the first quadrant (I), and wherein the center (M-IV) of the radius of curvature (R-IV) of the raceway (8-IV) of the fourth quadrant (IV) is located in the second quadrant (II).
2. The wave generator according to claim 1, wherein The intersection point of the two curvature radii (R-III, R-IV) of the raceway (8-III, 8-IV) of the elliptical inner ring (2) lies on an axis perpendicular to the rotation axis (A R ) of the ball (6), and wherein the intersection point of the two curvature radii (R-I, R-II) of the raceway (8-I, 8-II) of the elliptical outer ring (4) lies on an axis perpendicular to the rotation axis (A R ) of the ball (6).
3. The wave generator according to claim 1 or 2, wherein the radius of curvature (R-I, R-II, R-III, R-IV) is the same.
4. The wave generator according to any one of the preceding claims, wherein The contact points (P-I, P-II, P-III, P-IV) are arranged to be offset from an axis (A R ) perpendicular to the rotation axis (A S ) of the ball (6).
5. The wave generator according to claim 4, wherein The contact points (P-I, P-II, P-III, P-IV) of the ball (6) with the raceway (8) are arranged within a range of ±20°, preferably ±10°, about an axis (A R ) perpendicular to the axis of rotation (A S ) of the ball (6).
6. The wave generator according to any one of the preceding claims, wherein the radius of curvature (R-I, R-II, R-III, R-IV) of the raceway (8) is a variable radius.
7. The wave generator according to any one of the preceding claims, wherein the elliptical inner ring (2) and / or the elliptical outer ring (4) is formed as an open ring, and a preloading mechanism is provided to control the contact points (P-I, P-II, P-III, P-IV) between the balls (6) and the raceways (8).
8. The wave generator according to any one of the preceding claims, wherein The axis of rotation (A R ) of the ball (6) is perpendicular to the axis of rotation (A L ) of the wave generator (1).
9. A strain wave gear transmission (20) comprising a wave generator (1) according to any one of the preceding claims, a deformable cylindrical ring (22) having external teeth (24) arranged around the wave generator (1), and a rigid cylindrical outer ring (26) having internal teeth (28), wherein the teeth (24, 28) of the cylindrical ring (22) and the cylindrical outer ring (26) are configured to mesh with each other.