Wave gear for a robot and robot with a wave gear

Abstract

The invention relates to a wave gear (1) for a robot (12), comprising a flexible ring element (3) with external teeth, which can be deformed in the radial direction by a wave generator (2), and a ring gear (4) designed as a rigid ring element with internal teeth, wherein the external teeth of the flexible ring element (3) mesh with the internal teeth of the ring gear (4) in at least one tooth engagement region for transmitting a torque, wherein the wave generator (2) has a non-circular bearing element (6) comprising an inner ring (8), an outer ring (9) and rolling elements (7) arranged therebetween, wherein the bearing element (6) projects at least partially axially into the flexible ring element (3), wherein the inner ring (8) is connected in a rotationally fixed manner to a drive shaft (10), wherein the ring gear (4) is designed as an output shaft,wherein the bearing element (6) is designed as a single-row roller bearing with spherical rolling elements (7) and a respective spherical raceway for the rolling elements (7) on the inner ring (8) and on the outer ring (9), wherein means for axially displacing the rolling elements (7) relative to the flexible ring element (3) act at least indirectly on the bearing element (6) in order to adjust at least one tooth engagement region of the flexible ring element (3) on the ring gear (4).

Description

[0001] The invention relates to a wave gear for a robot or an application with similar requirements, comprising a flexible ring element with external teeth that can be deformed radially by a wave generator, and a rigid ring 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 wave gear.

[0002] DE 10 2018 123 915 A1 discloses a wave gear comprising a flexible ring element with external teeth, which can be locally radially deformed by a wave generator, and a rigid ring element with internal teeth. The external teeth of the flexible ring element mesh with the internal teeth of the rigid ring element to transmit torque at at least one tooth engagement area. The wave generator comprises a non-circular bearing element consisting of an inner ring, an outer ring, and rolling elements arranged radially therebetween. The bearing element is designed as a spherical roller bearing, and the inner ring is connected to a shaft in a rotationally fixed manner. The outer ring and the flexible ring element are two separate components that are connected to one another in a rotationally fixed manner.

[0003] EP 4 080 088 A1 describes a stress wave transmission with a wave generator that is rotatably mounted relative to a flexspline by means of a radially flexible rolling bearing. The rolling elements are not balls, and their rolling surfaces do not have a cylindrical portion along their axial length. The bearing's running surfaces are curved in a cross-sectional plane along the axial direction and have a lesser curvature in the cross-sectional plane along the axial direction than the rolling surfaces of the rolling elements.

[0004] DE 10 2022 111 705 A1 describes a stress wave transmission with a circular spline (ring gear), a flexspline, and a wave generator. The wave generator is arranged so that it can be axially displaced relative to the flexspline.

[0005] The object of the invention is to develop a strain wave gear for a robot in which, after assembly of the strain wave gear, the stiffness of the strain wave gear can be easily adjusted. This 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.

[0006] A wave gear according to the invention for a robot comprises a flexible ring element with external teeth, which can be deformed in the radial direction by a wave generator, and a ring gear designed as a rigid ring element with internal teeth, wherein the external teeth of the flexible ring element mesh with the internal teeth of the ring gear at least in one tooth engagement area to transmit a torque, wherein the wave generator has a non-circular bearing element, comprising an inner ring, an outer ring and rolling elements arranged therebetween, wherein the bearing element projects at least partially axially into the flexible ring element, wherein the inner ring is connected in a rotationally fixed manner to a drive shaft, wherein the ring gear is designed as an output shaft,wherein the bearing element is designed as a single-row roller bearing with spherical rolling elements and a respective spherical raceway for the rolling elements on the inner ring and on the outer ring, wherein means for axially displacing the rolling elements relative to the flexible ring element act at least indirectly on the bearing element in order to adjust at least one tooth engagement area of ​​the flexible ring element on the ring gear.

[0007] Roller bearings are rolling bearings with cylindrical, needle, tapered, or spherical rollers as rolling elements. For example, the roller bearing is designed as a spherical roller bearing or a spherical roller bearing. The roller bearing absorbs not only radial forces but also axial forces. The means for axially displacing the rolling elements relative to the flexible ring element adjusts the axial position of the fulcrum of the flexible ring element. In particular, this changes the angle and degree of rebound of the flexible ring element, adjusting the contact pressure of the gearing between the flexible ring element and the ring gear. The spherical rolling elements and the spherical raceways for the rolling elements on the inner and outer rings enable the outer ring to tilt when the rolling elements are axially displaced relative to the flexible ring element.

[0008] Preferably, the respective raceway for the rolling elements is concavely curved radially in the direction of the rolling elements, at least partially or completely, i.e., over the entire axial length of the inner ring and the outer ring. In particular, the rolling elements have an oval, in particular elliptical longitudinal section. Due to the axial displacement of the rolling elements relative to the flexible ring element, the flexible ring element is radially pressed open, i.e., the diameter in the non-circular area is increased such that the flexible ring element is pressed more deeply into the toothing on the ring gear. This increases rigidity, with geometric tolerances being compensated for by the preloaded rolling elements. Alternatively, the means for axially displacing the rolling elements can also be used to reduce rigidity, thereby simultaneously reducing wear and precision.

[0009] The wave generator is operatively connected to the drive shaft, wherein the drive shaft is driven, preferably by an electric motor, in order to set the wave generator in rotation. 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 drive shaft are preferably two separate components, wherein the inner ring is pressed, glued, or screwed onto the drive shaft to create a rotationally fixed connection. Alternatively, it is conceivable to form the inner ring and the drive shaft in one piece. The wave generator is the drive unit of the harmonic drive and, in the case of a two-part design of the drive shaft and the inner ring, is preferably pressed into the flexible or elastically deformable ring element together with the bearing element.For example, the drive shaft is designed as a hollow shaft. Alternatively, the drive shaft can also be designed as a solid shaft.

[0010] The flexible ring element is also called a flexspline and is a high-strength and torsionally rigid sleeve element. It is designed to be flexible enough to at least partially axially accommodate the wave generator with the bearing element, while being locally deformable depending on the external shape of the wave generator. In particular, the external 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 a 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 into contact with the inner peripheral surface of the outer ring, with a second raceway for the rolling elements being formed on the inner peripheral surface of the outer ring. The rolling elements are preferably guided in a cage, with the cage preferably being made of a polymer material in order to reduce wear on the rolling elements.For example, the rolling elements of the bearing element are arranged in a ring-guided cage. Thus, the cage is guided on the inner ring and / or the outer ring. This particularly improves the guidance of the rolling elements. The flexible ring element has at least one open axial side for accommodating the wave generator with the bearing element, wherein the inner circumferential surface of the flexible ring element is configured to non-rotatably receive the outer circumferential surface of the outer ring of the bearing element during operation of the wave generator.

[0011] During operation, the wave generator rotates, causing the inner ring of the bearing element to rotate relative to the flexible ring element and the outer ring of the bearing element, which is non-rotatably received therein. The flexible ring element deforms elastically in line with the direction and speed of rotation of the wave generator. As a result, the wave generator is set into a rotational movement during operation of the wave gear, which causes the flexible ring element to undergo circumferential deformation. To transmit torque, the external toothing of the flexible ring element is preferably in tooth engagement at least partially with the internal toothing of the ring gear in two symmetrically opposite tooth engagement areas relative to the axis of rotation of the wave generator. This enables uniform force introduction and force transmission, and the wave gear can be designed in a space-saving manner.

[0012] The ring gear, also called a circular spline, is a torsionally rigid, ring whose internal toothing has more teeth than the external toothing of the flexible ring element. The rotation of the wave generator causes a permanent circumferential tooth engagement between the flexible ring element and the ring gear. In other words, the opposing tooth engagement 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 ring gear, rotation of the wave generator causes the flexible ring element to move relative to the ring gear. This causes the rolling elements of the bearing element to roll between the inner and outer rings. For example, the ring gear is indirectly connected to an output shaft in a rotationally fixed manner via a ring gear carrier. For example, the ring gear carrier and the ring gear are bolted together.The output shaft can be designed as an output shaft flange. In particular, the output shaft can be directly connected to the ring gear in a rotationally fixed manner.

[0013] According to a preferred embodiment of the invention, a ring element is axially displaceably mounted on the drive shaft and, for axial displacement of the inner ring, comes into contact at least indirectly with the inner ring at its end face, with a spring element preloading the inner ring against the ring element. Thus, the ring element presses axially against the inner ring and, through this, also against the spring element in order to displace the inner ring and thus also the rolling elements relative to the flexible ring element. Thus, the ring element is arranged on one end face of the inner ring, with the spring element being arranged on the opposite end face of the inner ring. For example, the spring element is designed as a wave spring.Preferably, the ring element is designed as a threaded ring with an internal thread, with a cooperating external thread being formed on the drive shaft, so that axial displacement of the ring element on the drive shaft occurs by screwing the ring element to the drive shaft. Since the inner ring is connected to the drive shaft in a rotationally fixed manner, the ring element exhibits no relative movement to the inner ring after the preload of the bearing element has been adjusted.

[0014] According to a further preferred embodiment of the invention, a ring element is axially displaceably received on the ring gear and, for axial displacement of the outer ring, comes into contact at least indirectly at the end face of the outer ring. In particular, the ring element is designed as a threaded ring with an external thread, wherein a cooperating internal thread is formed on the ring gear, so that an axial displacement of the ring element on the ring gear occurs through rotation of the ring element. During operation of the wave generator, a relative movement occurs between the ring gear and the outer ring. In order to reduce wear between the ring element and the outer ring and to increase the efficiency of the wave gear, it is proposed to arrange a friction-reducing contact element, which is designed for end face contact with the outer ring, on the ring element. In particular, the friction-reducing contact element is integrated into the ring element.For example, the friction-reducing contact element is designed as a coating or ball. For example, the ball is mounted on a spring.

[0015] The invention also relates to a robot comprising a strain wave gear according to the invention. In particular, the strain wave gear according to the invention is arranged in a joint for a robot arm and acts at least indirectly between two robot arm segments.

[0016] Further measures improving the invention are described in more detail below together with the description of preferred embodiments of the invention with reference to the figures. Fig. 1 a simplified schematic sectional view of a section of the wave gear according to the invention according to a first embodiment, Fig. 2 a simplified schematic sectional view of a section of the wave gear according to the invention according to a second embodiment, Fig. 3 a simplified schematic representation of a partially shown robot with a wave gear according to the invention.

[0017] In Fig. 1 shows a section of a wave gear 1 according to the invention. The wave gear 1 comprises a flexible ring element 3 which can be deformed radially by a wave generator 2. The flexible ring element 3 has external teeth. The external teeth of the flexible ring element 3 mesh with the internal teeth of a ring gear 4, which is designed as a rigid ring element, to transmit torque at two opposite tooth engagement areas. The wave generator 2 comprises a non-circular bearing element 6 with an inner ring 8, an outer ring 9 and rolling elements 7 arranged therebetween. The inner ring 8 is connected in a rotationally fixed manner to a drive shaft 10, wherein the drive shaft 10 is drivingly connected to an electrical machine (not shown in detail). The bearing element 6 partially projects axially into the flexible ring element 3.

[0018] During operation of the electric machine, the wave generator 2 is rotated via the drive shaft 10, whereby the inner ring 8 of the bearing element 6 is rotated relative to the flexible ring element 3 and the outer ring 9 of the bearing element 6, which is non-rotatably received therein. The flexible ring element 3 deforms elastically in accordance with the direction of rotation and the rotational speed of the wave generator 2. The rotational movement of the wave generator 2 causes the flexible ring element 3 to undergo circumferential deformation, thereby creating a permanent circumferential tooth engagement between the flexible ring element 3 and the ring gear 4. The opposing tooth engagement regions move continuously in the circumferential direction around the rotational axis of the wave generator 2 during rotation of the wave generator 2. Since the flexible ring element 3 has fewer teeth than the ring gear 4, rotation of the wave generator 2 causes a relative movement of the flexible ring element 3 to the ring gear 4.

[0019] The ring gear 4 is configured for output and, for this purpose, is non-rotatably connected to an output shaft (not shown in detail) via a screw connection (not shown in detail). Furthermore, the ring gear 4 is non-rotatably connected to an inner ring 21 of a double-row needle bearing 20 via the same screw connection. The double-row needle bearing 20 further comprises a first and a second outer ring, which are non-rotatably connected to a housing (not shown in detail) via a screw connection (not shown in detail). The double-row needle bearing 20 is sealed at least against grease leakage by means of a seal 24 arranged between the first outer ring 22 and the inner ring 21.

[0020] Furthermore, the wave gear 1 has means for axially displacing the rolling elements 7 relative to the flexible ring element 3, wherein the means acts at least indirectly on the bearing element 6 in order to change at least one tooth engagement area of ​​the flexible ring element 3 on the ring gear 4. The bearing element 6 of the wave generator 2 is designed as a single-row roller bearing with spherical rolling elements 7 and a respective spherical raceway for the rolling elements 7 on the inner ring 8 and the outer ring 9. In the present case, the respective raceway for the rolling elements 7 is concavely curved radially in the direction of the rolling elements 7 on the inner ring 8 and the outer ring 9, wherein the rolling elements 7 have an oval longitudinal section. Furthermore, in the present case, a ring element 5 is axially displaceably received on the drive shaft 10 and comes into contact with the inner ring 8 at its end face. A spring element 5 designed as a wave spring.1, which is arranged axially between a shaft shoulder on the drive shaft 10 and the inner ring 8, preloads the inner ring 8 against the ring element 5. The ring element 5 is designed as a threaded ring with an internal thread, with a cooperating external thread being formed on the drive shaft 10. An axial displacement of the ring element 5 on the drive shaft 10 is achieved in a simple manner by screwing the ring element 5 to the drive shaft 10, whereby the ring element 5 then presses on the inner ring 8 and displaces the rolling elements 7 relative to the flexible ring element 3. This results in an adjustment of the axial position of the fulcrum of the flexible ring element 3. In particular, this changes the angle and degree of rebound of the flexible ring element 3, whereby the contact pressure of the toothing between the flexible ring element 3 and the ring gear 4 is adjusted.

[0021] The spherically shaped rolling elements 7 and the spherically shaped raceways for the rolling elements 7 on the inner ring 8 and on the outer ring 9 enable tilting of the outer ring 9 upon axial displacement of the rolling elements 7 relative to the flexible ring element 3. The ring element 5 on the drive shaft 10 enables variable stiffness adjustment of the strain wave gear 1 after assembly. By varying the preload of the strain wave gear 1, different pairings can be compensated for or completely replaced, so that the strain wave gear can be manufactured within a narrower stiffness tolerance range without increasing assembly costs. Partially worn strain wave gears can thus be stiffened in-situ. Furthermore, the stiffness can be reduced in a targeted manner, for example to increase efficiency or achieve smoother running.

[0022] According to a second embodiment of the strain wave gear 1, the ring element 5, which is designed as a means for the indirect axial displacement of the rolling elements 7 relative to the flexible ring element 3, is not mounted on the drive shaft 10, but is mounted axially displaceably on the ring gear 4. The ring element 5 is provided here for the axial displacement of the outer ring 9 and comes into contact with the outer ring 9 via a friction-reducing spherical contact element 5.2 integrated into the ring element 5. The ring element 5 is designed as a threaded ring with an external thread, with a cooperating internal thread formed on the ring gear 4. Axial displacement of the ring element 5 on the ring gear 4 occurs through rotation of the ring element 5. Furthermore, the rolling elements 7 of the bearing element 6 are arranged in a ring-guided cage 6.1 to improve guidance and reduce wear.Otherwise, the second embodiment of the strain wave gear 1 corresponds to the first embodiment of the strain wave gear 1 to which reference is made.

[0023] Fig. Figure 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 connects the two robot arm segments 12a, 12b in an articulated manner. To change the position of the two robot arm segments 12a, 12b relative to each other, the robot 12 has a drive unit 14 comprising an electric motor 15 and a strain wave gear 1 according to the invention. List of reference symbols 1 wave gear 2 wave generators 3 flexible ring element 4 ring gear 5 ring element 5.1 Spring element 5.2 Investment element 6 bearing element 6.1 ring-guided cage 7 rolling elements 8 inner ring 9 Outer ring 10 Drive shaft 12 robots 12a first robot arm segment 12b second robot arm segment 13 Joint 14 Drive unit 15 Electric motor 20 double row needle bearing 21 Inner ring of the double-row needle bearing 22 first outer ring of the double row needle bearing 23 second outer ring of the double-row needle bearing 24 Seal

Claims

[1] Wave gear (1) for a robot (12), comprising a flexible ring element (3) with external teeth, which can be deformed in the radial direction by a wave generator (2), and a ring gear (4) designed as a rigid ring element with internal teeth, wherein the external teeth of the flexible ring element (3) mesh with the internal teeth of the ring gear (4) in at least one tooth engagement region for transmitting a torque, wherein the wave generator (2) has a non-circular bearing element (6) comprising an inner ring (8), an outer ring (9) and rolling elements (7) arranged therebetween, wherein the bearing element (6) projects at least partially axially into the flexible ring element (3), wherein the inner ring (8) is connected in a rotationally fixed manner to a drive shaft (10), wherein the ring gear (4) is designed as an output shaft,wherein the bearing element (6) is designed as a single-row roller bearing with spherical rolling elements (7) and a respective spherical raceway for the rolling elements (7) on the inner ring (8) and on the outer ring (9), , characterized by that means for axially displacing the rolling elements (7) relative to the flexible ring element (3) act at least indirectly on the bearing element (6) in order to adjust at least one tooth engagement region of the flexible ring element (3) on the ring gear (4). [2] Wave gear (1) according to claim 1, characterized by that a ring element (5) is received axially displaceably on the drive shaft (10) and comes into contact at least indirectly on the end face of the inner ring (8) for the axial displacement of the inner ring (8), wherein a spring element (5.1) prestresses the inner ring (8) against the ring element (5). [3] Wave gear (1) according to claim 2, characterized bythat the ring element (5) is designed as a threaded ring with an internal thread, wherein a cooperating external thread is formed on the drive shaft (10), so that an axial displacement of the ring element (5) on the drive shaft (10) takes place by screwing the ring element (5) onto the drive shaft (10). [4] Wave gear (1) according to claim 1, characterized by that a ring element (5) is received axially displaceably on the ring gear (4) and comes into contact at least indirectly on the end face of the outer ring (9) for the axial displacement of the outer ring (9). [5] Wave gear (1) according to claim 4, characterized by that the ring element (5) is designed as a threaded ring with an external thread, wherein a cooperating internal thread is formed on the ring gear (4) so ​​that an axial displacement of the ring element (5) on the ring gear (4) takes place by rotation of the ring element (5). [6] Wave gear (1) according to claim 4 or 5, characterized bythat the ring element (5) has a friction-reducing contact element (5.2) which is designed to bear against the outer ring (9) at the front. [7] Wave gear (1) according to one of the preceding claims, characterized by that the rolling elements (7) of the bearing element (6) are arranged in a ring-guided cage (6.1). [8] Wave gear (1) according to one of the preceding claims, characterized by that the respective raceway for the rolling elements (7) is formed radially in the direction of the rolling elements (7) at least partially concavely curved on the inner ring (8) and on the outer ring (9). [9] Wave gear (1) according to one of the preceding claims, characterized by that the rolling elements (7) have an oval longitudinal section. [10] Robot (12) comprising a wave gear (1) according to one of the preceding claims.

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