WO2022012712A1

WO2022012712A1 - Harmonic drive for a robot, and robot comprising a harmonic drive

Info

Publication number: WO2022012712A1
Application number: PCT/DE2021/100520
Authority: WO
Inventors: Uwe Junginger; Oliver Boersch; Tomas Smetana
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2020-07-16
Filing date: 2021-06-17
Publication date: 2022-01-20
Also published as: CN116194689A; JP2023533358A; DE102020118797A1; KR20230022301A

Abstract

The invention relates to a harmonic drive (1) for a robot (12), said harmonic drive comprising: a flexible ring element (3) which can be deformed peripherally in a radial direction by a wave generator (2) and has external toothing (3a); and a rigid ring element (4) which has internal toothing (4a), wherein the external toothing (3a) of the flexible ring element (3) meshes with the internal toothing (4a) of the rigid ring element (4) in order to transmit a torque at at least one tooth engagement region (5a, 5b), wherein the wave generator (2) has a non-circular bearing element (6) comprising rolling elements (7), an inner ring (8) having a first raceway (8a) for the rolling elements (7), and an outer ring (9) having a second raceway (9a) for the rolling elements (7), wherein at least part of the bearing element (6) projects axially into the flexible ring element (3), and wherein the inner ring (8) is connected to a shaft (16) for conjoint rotation therewith, wherein the bearing element (6) is designed as a single-row cylindrical roller bearing, wherein at least part of the second raceway (9a) for the rolling elements (7) is convexly curved radially in the direction of the rolling elements (7) on an inner peripheral surface of the outer ring (9). The invention also relates to a robot (12) comprising such a harmonic drive (1).

Description

Corrugated gear for a robot and robot with a corrugated gear

The invention relates to a harmonic drive for a robot, comprising a flexible annular element with external teeth, which can be deformed circumferentially in the radial direction by a wave generator, and a rigid annular element with internal teeth. The flexible ring element meshes with the rigid ring element to transmit torque. Furthermore, the invention also relates to a robot with a harmonic drive.

DE 102018 123915 A1 discloses a harmonic drive, comprising a flexible annular element with external teeth, which can be deformed locally and radially by a wave generator, and a rigid annular element with internal teeth. The outer toothing of the flexible ring element is available for the transmission of a torque on at least one toothed meshing area with the inner toothing of the rigid ring element in toothed engagement. The wave generator comprises an out-of-round trained tes bearing element consisting of an inner ring, an outer ring and radially there between arranged rolling elements. The bearing element is designed as a spherical roller bearing and the inner ring is non-rotatably connected to a shaft. The outer ring and the flexible ring element are two separate components that are connected to one another in a rotationally fixed manner.

The object of the invention is to develop an alternative harmonic drive, in particular for a robot. Furthermore, the harmonic drive should have a long service life. The object is achieved by the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims, the description and the figures.

A strain wave gearing according to the invention for a robot comprises a flexible ring element that can be deformed in the radial direction by a wave generator and has external teeth and a rigid ring element with internal teeth, the external teeth of the flexible ring element for transmitting a torque on at least one toothed meshing area with the internal teeth of the rigid ring element is in tooth engagement, with the wave generator having an out-of-round detes bearing element, comprising rolling elements, an inner ring with a first raceway for the rolling elements and an outer ring with a second raceway for the rolling elements, the bearing element at least partially protruding axially into the flexible ring element, and the inner ring being non-rotatably connected to a shaft, wherein the bearing element is designed as a single-row cylindrical roller bearing, wherein the second raceway for the rolling bodies is curved at least partially convexly on an inner peripheral surface of the outer ring radially in the direction of the rolling bodies.

The wave generator, also known as wave generator, is in operative connection with the shaft, the shaft preferably being driven by an electric machine in order to cause the wave generator to rotate. For example, the wave generator, in particular the inner ring of the bearing element, has an elliptical or oval cross-sectional shape. The inner ring and the shaft are preferably two separate components, with the inner ring being pressed onto the shaft, for example, in order to implement a non-rotatable connection. Alternatively, it is conceivable to form the inner ring and the shaft in one piece. The wave generator is the drive unit of the wave gear and, in the case of a two-part configuration of the shaft and the inner ring, is preferably pressed into the flexible or elastically deformable ring element together with the bearing element. For example, the shaft is formed as a hollow shaft. Alternatively, the shaft can also be designed as a solid shaft.

The flexible ring element is also called Flexspline and is a high-strength and torsion-resistant sleeve element. It is designed so flexibly that it can at least partially axially accommodate the wave generator with the bearing element, and is locally deformable depending on the outer shape of the wave generator. In particular, the outer shape of the wave generator is formed by the outer ring. The rolling elements of the bearing element come into contact with the outer peripheral surface of the inner ring, with the first raceway for the rolling elements being formed on the outer peripheral surface of the inner ring. Furthermore, the rolling elements of the bearing element come to rest on the inner peripheral surface of the outer ring, with the second raceway for the rolling elements being formed on the inner peripheral surface of the outer ring. The fle xible ring element has at least one open axial side for receiving the wave generator with the bearing element, wherein the inner peripheral surface of the flexible Ring element is set up in operation of the wave generator for non-rotatably receiving the outer peripheral surface of the outer ring of the bearing element.

The outer ring can be connected to the flexible ring element in a rotationally fixed or initially rotatable manner, whereby the term "initially rotatable" means that the outer ring has no direct anti-rotation device with respect to the flexible ring element during assembly of the bearing element in the flexible ring element. However, after an elastic deformation of the flexible ring element, the outer ring can no longer twist into the elliptical or oval shape and is therefore non-rotatable in relation to the flexible ring element.

During operation, the wave generator is rotated, as a result of which the inner ring of the bearing element is rotated relative to the flexible ring element and the outer ring of the bearing element that is rotationally fixed therein. The flexible ring element is elastically deformed in the same way as the direction of rotation and the speed of rotation of the wave generator. In other words, the shaft generator is set in rotation during operation of the shaft gear, which causes the flexible ring element to undergo circumferential deformation.

Preferably, the external toothing of the flexible ring element for the transmission of a torque, based on the axis of rotation of the wave generator, is at two symmetrically opposite toothed meshing areas at least partially with the internal toothing of the rigid ring element in toothed meshing. As a result, a uniform application of force or transmission of force can be implemented and the harmonic drive can be designed to save space.

The rigid ring element, also known as a circular spline, is a torsion-resistant, rigid ring whose inner teeth have more teeth than the outer teeth of the flexible ring element. In particular, the rigid ring element is formed out as a ring gear. The rotation of the wave generator causes permanent, circumferential meshing of the flexible ring member and the rigid ring member. In other words, the opposing tooth meshing areas move continuously around the axis of rotation of the wave generator or in the circumferential direction during the rotation of the wave generator. Since the flexible ring element has fewer teeth than the rigid ring element, a rotation of the wave generator causes a relative movement of the flexible ring element to the rigid ring element. The rolling elements of the single-row cylindrical roller bearing roll off between the inner ring and the outer ring.

The rolling elements designed as cylindrical rollers can, in conjunction with the at least partially convex second raceway on the outer ring, particularly advantageously compensate for tilting movements in the bearing element and thus also in the wave generator. An at least partially convex second raceway on the outer ring means that the inner peripheral surface of the outer ring, which is provided as the outer raceway for the rolling elements, has a convex curvature radially inward toward the rolling elements. In particular, this convex curvature extends not only partially, but completely along the second track for the rolling elements. Hertzian pressures can be set, and in particular reduced, via the radius or degree of curvature of the convex-shaped second raceway on the outer ring, which extends the service life of the harmonic drive. Furthermore, assembly of the wave generator is simplified compared to a wave generator with a ball bearing, particularly when the number of cylindrical rollers is increased and the diameter of the cylindrical rollers is reduced.

According to a preferred embodiment of the invention, the inner ring of the bearing element has a first rim, with the shaft having a second rim. A first or second rim is to be understood as meaning an essentially radially outwardly formed formation on the inner ring or on the shaft, which is designed to allow the rolling elements to come into contact axially, i.e. on the face side, and thereby to adjust the axial position of the rolling elements limit.

The outer ring of the bearing element preferably has a third rim and a fourth rim. A third or fourth rim is to be understood as meaning a protrusion on the outer ring which is essentially radially inward and which is intended to allow the rolling elements to come into contact axially, ie on the face side, and thereby to limit the axial position of the rolling elements. According to a further preferred embodiment of the invention, the flexible ring element and the outer ring of the bearing element are designed in one piece. In other words, the flexible ring element and the outer ring are monolithic, with the external toothing and the second raceway for the rolling elements being formed in one piece on one component, namely the flexible ring element. The outer ring is thus integrated into the flexible ring element and combines the gearing functions for the rigid ring element on the outer peripheral surface of the flexible ring element with the running track functions for the rolling elements on the inner peripheral surface of the flexible ring element. Because a separate outer ring does not exist, there is no clearance fit between the outer ring and the flexible ring element, which results in the stiffness of the strain wave gearing remaining constant, thereby increasing the precision and efficiency of the strain wave gearing.

The inner ring of the bearing element preferably has a first rim and a second rim. A first or second rim is to be understood as meaning an essentially radially outwardly formed formation on the inner ring, which is aimed at enabling the rolling elements to run axially, ie on the face side, and thereby to limit the axial position of the rolling elements.

According to a preferred embodiment of the invention, the rolling elements are guided in a cage. The cage is preferably made of a polymer material. This in particular reduces the wear on the rolling elements.

The second raceway for the rolling bodies is preferably formed in a region of the outer ring which is arranged radially opposite and essentially centrally to the outer toothing on the flexible ring element. In other words, the rolling elements roll in the axial direction in the center of the external teeth on the flexible ring element. This results in a particularly clean and efficient meshing of teeth.

The invention also relates to a robot comprising a corrugated gear according to the invention. In particular, strain wave gearing according to the invention is arranged in a joint for a robot arm and acts at least indirectly between two robot arm segments. Further measures improving the invention are presented in more detail below together with the description of two preferred exemplary embodiments of the invention with reference to the figures. while showing

FIG. 1a shows a simplified schematic sectional view of a harmonic drive according to the invention, shown in half, according to a first exemplary embodiment,

FIG. 1b shows a simplified schematic partial longitudinal section of the corrugated drive according to FIG. 1a,

FIG. 2a shows a simplified schematic sectional view of a harmonic drive according to the invention, shown in half, according to a second exemplary embodiment,

FIG. 2b shows a simplified schematic partial longitudinal section view of the corrugated drive according to FIG. 2a, and

FIG. 3 shows a simplified schematic representation of a robot, shown only partially, with a harmonic drive according to the invention.

Figures 1a and 1b show a first embodiment of the invention. According to Figures 1a and 1b, a harmonic drive 1 according to the invention, only half of which is shown here, comprises a wave generator 2 with a bearing element 6 designed as a single-row cylindrical roller bearing. The bearing element 6 has an inner ring 8, an outer ring 9 and a large number of spatially arranged in between and spaced out from each other rolling elements 7. The wall thickness of the inner ring 8 is exaggerated. The rolling bodies 7 are spaced apart in a cage 10, wherein the cage 10 is made of a polymer material. The inner ring 8 has a first raceway 8a for the rolling bodies 7 on the outer peripheral surface. The outer ring 9 has a second raceway 9a for the rolling bodies 7 on the inner peripheral surface, the second raceway 9a being convexly curved radially in the direction of the rolling bodies 7, so that the maximum wall thickness of the outer rings 9 is substantially axially central to the rolling elements 7 due to the curvature. The inner ring 8 of the bearing element 6 has a first rim 8b, the shaft 16 having a second rim 16a. The first rim 8b serves as an axial contact surface for the rolling elements 7, the second rim 16a serving as an axial contact surface for the rolling elements 7 and as an axial stop for the inner ring 8. The outer ring 9 of the bearing element 6 has a third rim 9b and a fourth rim 9c, which are each provided as an axial contact surface for the rolling elements 7. The wave generator 2 also includes a shaft 16 onto which the inner ring 8 is shrunk to form a non-rotatable connection, wherein the wave generator 2 via the shaft 16 of a - electric motor in a rotational movement can be set - not shown here. In the present case, the shaft 16 is designed as a hollow shaft.

The inner ring 8 and the outer ring 9 of the bearing element 6 presently have an elliptical outer geometry, the outer peripheral surface of the outer ring 9 coming to rest on an inner peripheral surface of a flexible ring element 3 in a rotationally fixed manner. Before the bearing element 6 is installed, the outer ring 9 has an essentially round outer geometry, which, however, deforms elastically into the elliptical outer geometry during installation, depending on the outer geometry of the inner ring 8 . The wave generator 2 or the bearing element 6 is pressed into the flexible ring element 3 so that the wave generator 2 with the bearing element 6 protrudes into the flexible ring element 3 . Here, the flexible ring element 3 assumes the elliptical shape of the wave generator 2 . During operation of the harmonic drive 1, the Wellge generator 2 is set in a rotational movement, with the outer ring 9 and the fle xible ring element 3 deform locally radially. In other words, the rotation of the wave generator 2 about an axis of rotation 11 causes the flexible ring element 3 and the outer ring 9 to be circumferentially deformed.

FIG. 1a also shows that the flexible annular element 3 has external teeth 3a, which are in toothed engagement with internal teeth 4a of a rigid annular element 4 of the harmonic drive 1 for the purpose of transmitting torque. Since the flexible ring element 3 adapts to the elliptical shape of the wave generator 1, the flexible ring element 3 with its external teeth 3a is in two symmetrically opposite toothed engagement areas 5a, 5b with the internal teeth 4a of the rigid ring element 4 in toothed engagement. According to FIG. 1b, the bearing element 6 projects completely into the flexible ring element 3 in the axial direction. Furthermore, the second raceway 9a for the rolling bodies 7 is formed in a region of the outer ring 9 which is arranged radially opposite and centrally in the axial direction to the outer teeth 3a on the flexible ring element 3 . In FIG. 1b, the rigid ring element 4 has not been shown for the sake of simplicity. Furthermore, the wall thickness of the flexible ring element 3 is exaggerated.

Figures 2a and 2b show a second embodiment of the invention. According to FIGS. 2a and 2b, a wave gear mechanism 1 according to the invention comprises a wave generator 2, which has a bearing element 6 with an inner ring 8 and with a plurality of rolling elements 7. The wall thickness of the inner ring 8 is exaggerated. The rolling bodies 7 are spaced apart in a cage 10, wherein the cage 10 is made of a polymer material. The bearing element 6 is designed as a row of cylindrical roller bearings, so that the rolling bodies 7 are designed as cylindrical rollers. The inner ring 8 has a first raceway 8a for the rolling bodies 7 . The first raceway 8a is formed circumferentially on the outer peripheral surface of the inner ring 8 . Consequently, the rolling elements 7 roll on the outer peripheral surface of the inner ring 8 . Furthermore, the inner ring 8 of the bearing element 6 has a first rim 8b and a second rim 8c. The two rims 8b, 8c serve as axial stop surfaces for the rolling elements 7. The wave generator 2 also includes a shaft 16, onto which the inner ring 8 is shrunk to form a non-rotatable connection, the wave generator 2 being connected via the shaft 16 by one - here not shown - electric motor can be set into a rotational movement. In the present case, the shaft 16 is designed as a hollow shaft. Furthermore, harmonic drive 1 has a flexible annular element 3 with external teeth 3a, which can be continuously deformed in the radial direction by wave generator 2, and a rigid annular element 4 with internal teeth 4a. The external toothing 3a of the flexible ring element 3 is available for the transmission of a torque, based on an axis of rotation 11 of the wave generator 2, two symmetrically opposite toothed meshing areas 5a, 5b with the internal toothed opening 4a of the rigid ring element 4 in toothed engagement. The rigid ring element 4 is designed as a ring gear. According to the second exemplary embodiment of the invention, the flexible ring element 3 and the outer ring 9 of the bearing element 6 are designed in one piece. In the present case, the outer ring 9 is integrated into the flexible ring element 3 and therefore no longer exists as a separate component. The flexible ring element 3 bundles the toothing functions for the rigid ring element 4 on the outer peripheral surface of the flexible ring element 3 with the raceway functions for the rolling elements 7 on the inner peripheral surface of the fle xible ring element 3. A second raceway 3b for the rolling elements 7 is formed on the flexible ring element 3 . The second raceway 9b, which is formed by the integration of the outer ring 9 on the flexible ring element 3, is convexly curved radially in the direction of the rolling elements 7, so that the maximum wall thickness of the flexible ring element 3 is essentially axially centered to the rolling elements due to the curvature bodies is 7.

The flexible ring element 3 is formed in one piece with the external teeth 3a and the second raceway 3b. Consequently, the rolling elements 7 roll off directly on the inner peripheral surface of the flexible ring element 3 . The rolling elements 7 follow the exzentri's shape of the first raceway 3a and thereby deform the flexible ring element 3 with the external teeth 3a. Due to the slightly different number of teeth between the external toothing 3a of the flexible ring element 3a and the internal toothing 4a of the rigid ring element 4, there is a high transmission ratio between the shaft 16 and the rigid ring element 4.

According to FIG. 2b, the bearing element 6 projects completely into the flexible ring element 3 in the axial direction. Furthermore, the second raceway 3b for the rolling elements 7 is formed in a region of the flexible ring element 3 which is arranged radially oppositely and centrally in the axial direction to the external toothing 3a. In FIG. 2b, the rigid ring element 4 is not shown for the sake of simplicity. Furthermore, the wall thickness of the flexible ring element 3 is exaggerated.

FIG. 3 shows a section of a robot 12. A joint 13 is arranged between a first robot arm segment 12a and a second robot arm segment 12b, which joint connects the two robot arm segments 12a, 12b to one another in an articulated manner. To change the position of the two robot arm segments 12a, 12b relative to one another the robot 12 has a drive unit 14, comprising an electric motor 15 and a harmonic drive 1 according to the invention.

Reference character list

1 wave gear

2 wave generator

3 flexible ring element

3a External toothing on the flexible ring element

3b second track on the flexible ring element

4 rigid ring element

4a internal toothing on the rigid ring element

5a, 5b meshing area 6 bearing element

7 rolling elements

8 inner ring

8a first track on the inner ring

8b first flange on the inner ring

8c second rim on the inner ring

9 outer ring

9a second track on the outer ring

9b third flange on the outer ring

9c fourth rim on the outer ring

10 cage 11 axis of rotation 12 robot 12a first robot arm segment 12b second robot arm segment

13 joint

14 drive unit

15 electric motor

16 shaft 16a second board on the shaft

Claims

patent claims

1. Wave gear (1) for a robot (12), comprising a shaft generator (2) circumferentially deformable in the radial direction, flexible ring element (3) with egg ner external teeth (3a) and a rigid ring element (4) with internal teeth tion (4a), wherein the external toothing (3a) of the flexible annular element (3) is in toothed engagement with the internal toothing (4a) of the rigid annular element (4) for the transmission of a torque in at least one toothed engagement region (5a, 5b), the wave generator (2) has an out-of-round bearing element (6), comprising rolling bodies (7), an inner ring (8) with a first raceway (8a) for the rolling bodies (7) and an outer ring (9) with a second raceway (9a) for the rolling bodies (7), the bearing element (6) at least partially protruding axially into the flexible ring element (3), and the inner ring (8) being non-rotatably connected to a shaft (16), characterized in that the bearing element (6) as a single row cylindrical roller bearing is formed, wherein the second raceway (9a) for the rolling elements (7) on an inner peripheral surface of the outer ring (9) radially in the direction of the rolling elements (7) is at least partially convex.

2. Harmonic transmission (1) according to claim 1, characterized in that the inner ring (8) of the bearing element (6) has a first rim (8b), the shaft (16) having a second rim (16a).

3. Harmonic transmission (1) according to one of the preceding claims, characterized in that the outer ring (9) of the bearing element (6) has a third board (9b) and a fourth board (9c).

4. harmonic drive (1) according to claim 1, characterized in that the flexible ring element (3) and the outer ring (9) of the bearing element (6) are integrally formed.

5. harmonic drive (1) according to claim 4, characterized in that the inner ring (8) of the bearing element (6) has a first board (8b) and a second board (8c).

6. harmonic drive (1) according to any one of the preceding claims, characterized in that the rolling elements (7) of the bearing element (6) in one

Cage (10) are performed.

7. harmonic drive (1) according to claim 6, characterized in that the cage (10) of the bearing element (6) is formed from a polymer material Po.

8. Harmonic drive (1) according to one of the preceding claims, characterized in that the second raceway (9a) for the rolling elements (7) is formed in a region of the outer ring (9) which is radially opposite and essentially central to the external toothing ( 3a) is arranged on the flexible ring element (3).

9. Harmonic drive (1) according to one of the preceding claims, characterized in that the external teeth (3a) of the flexible ring element (3) for the transmission of a torque, based on the axis of rotation (11) of the wave generator (2), two symmetrically opposite Tooth engagement areas (5a, 5b) are at least partially in mesh with the internal teeth (4a) of the rigid ring element (4).

10. Robot (12) comprising a harmonic drive (1) according to any one of the preceding claims.