Actuator for a robot arm segment and robots with such an actuator

Abstract

The invention relates to an actuator (14) for a robot arm segment (12a) of a robot (12), comprising an electric drive unit (15) and a drive-effectively connected gearbox (1) which are arranged in a stationary housing (2a, 2b), wherein the gearbox (1) has a flange-shaped ring gear (3) designed as an output shaft with several threaded bolts (4) arranged thereon, which are configured as an interface for a second robot arm segment (12b) connectable thereto. The invention further relates to a robot (12) with such an actuator (14).

Description

[0001] The invention relates to an actuator for a robot arm segment of a robot. Furthermore, the invention relates to a robot, in particular a robot arm segment, with such an actuator.

[0002] For example, EP 3 208 054 A2 discloses a robot joint drive comprising a stationary housing, an output part rotatable relative to the stationary housing, an electric drive motor, and a gearbox, wherein a drive shaft of the electric drive motor is coupled via the gearbox to an output shaft of the rotatable output part in order to rotate the output part relative to the stationary housing. A sensor element is arranged at a free end of the output shaft extending from the output part into the gearbox. Furthermore, an encoder is provided which determines the rotational position of the output shaft by means of the sensor element.

[0003] The object of the invention is to provide an alternative actuator for a robot arm segment. In particular, the actuator should be compact and cost-effective. The weight of the actuator should also be reduced. This object is achieved by the subject matter of claim 1. Preferred embodiments are described in the dependent claims, the description, and the figures.

[0004] An actuator according to the invention for a robot arm segment of a robot comprises an electric drive unit and a drive-effectively connected gearbox, which are arranged in a stationary housing. The gearbox has a flange-shaped ring gear designed as an output shaft with several threaded bolts arranged on it, which serve as an interface for a second robot arm segment connectable to it. The two robot arm segments are thus connected to each other via a joint in which the actuator is integrated.

[0005] The electric drive unit comprises an electric machine configured as a drive motor, with a rotor and a stator, as well as a braking device, in particular a holding brake, that can be connected to the rotor. Furthermore, an encoder and a control unit can be integrated into the electric drive unit. The drive unit is connected to the gearbox via a drive shaft, the gearbox having an output shaft designed as a ring gear with threaded studs arranged on it. The threaded studs form an interface for a second robot arm segment that can be connected to it and is rotatable relative to the actuator housing and thus to the first robot arm segment.

[0006] For example, the transmission is designed as a wave gear. The wave gear comprises a flexible ring element, in particular a collar sleeve, which is deformable in the radial direction by a wave generator and has external teeth, and the ring gear, designed as a rigid ring element with internal teeth. The external teeth of the flexible ring element mesh with the internal teeth of the ring gear at at least one tooth engagement area to transmit torque. The wave generator has a non-circular bearing element comprising an inner ring, an outer ring, and rolling elements arranged between them. The bearing element projects axially, at least partially, into the flexible ring element, with the inner ring being rotationally fixed to the drive shaft.

[0007] The flexible ring element, also called a flexspline, is a high-strength and torsionally rigid collar sleeve that is fixed to the housing, for example, by being bolted to it. It is designed to be flexible enough to accommodate the shaft generator with the bearing element, at least partially axially, and to be locally deformable depending on the shaft generator's outer shape. In particular, the shaft generator's outer shape is determined by the inner ring and formed on the outer ring. The rolling elements of the bearing element contact the outer circumferential surface of the inner ring, with a first raceway for the rolling elements formed on the outer circumferential surface of the inner ring. Furthermore, the rolling elements of the bearing element contact the inner circumferential surface of the outer ring, with a second raceway for the rolling elements formed on the inner circumferential surface of the outer ring.Preferably, the rolling elements are guided in a cage, the cage being preferably made of a polymer material to reduce wear on the rolling elements. The flexible ring element has at least one open axial side for receiving the shaft generator with the bearing element, wherein the inner circumferential surface of the flexible ring element is configured to receive the outer circumferential surface of the outer ring of the bearing element during operation of the shaft generator.

[0008] During operation, the wave generator rotates, causing the inner ring of the bearing element to twist relative to the flexible ring element and the outer ring of the bearing element housed within it. The flexible ring element deforms elastically in accordance with the direction and speed of rotation of the wave generator. Thus, during operation of the wave gear, the wave generator is set into a rotational motion, which causes the flexible ring element to undergo circumferential deformation. Preferably, the external teeth of the flexible ring element, for transmitting torque, engage at least partially with the internal teeth of the ring gear in two symmetrically opposed tooth engagement areas relative to the axis of rotation of the wave generator. This allows for uniform force application and transmission, and the wave gear can be designed to be space-saving.

[0009] The ring gear, also called a circular spline, is a torsionally rigid ring whose internal teeth have more teeth than the external teeth of the flexible ring element. The rotation of the shaft generator causes a continuous, circular meshing of the teeth between the flexible ring element and the ring gear. In other words, the opposing tooth meshing areas move continuously around the shaft generator's axis of rotation, i.e., in the circumferential direction, as the shaft generator rotates. Since the flexible ring element has fewer teeth than the ring gear, rotation of the shaft generator causes a relative movement of the flexible ring element to the ring gear. This results in the rolling elements of the bearing element rolling between the inner and outer rings. For example, the ring gear can be made from a sheet metal part. This reduces not only manufacturing costs but also weight and production time.

[0010] According to one embodiment, the gearbox has a support ring rotatably mounted in the housing via a rolling bearing and which accommodates the flange-shaped ring gear. For example, the rolling bearing is designed as a double-row angular contact ball bearing. The rolling bearing is arranged on an outer circumference of the support ring, with the ring gear being arranged on an inner circumference of the support ring. The support ring is designed not only to accommodate and center the rolling bearing and the ring gear, but also to provide threaded studs and an output geometry for centering and mounting the second robot arm segment. For example, the support ring has only simple geometries, in particular no threads or teeth, and is therefore cost-effective to manufacture.Preferably, the support ring is only subjected to compressive stress, which allows the use of materials such as aluminum, magnesium, or reinforced plastics for its manufacture, thus saving weight. According to one embodiment, the support ring is made of a light metal, particularly a non-ferrous metal. According to an alternative embodiment, the support ring is made of a composite material, particularly a fiber-reinforced plastic.

[0011] According to one embodiment, the flange-shaped internal gear has a radially extending collar. Preferably, the collar abuts the carrier ring and the rolling bearing at their end faces and has openings for receiving the threaded bolts. For example, the threaded bolts are pressed into the openings and guided axially through the carrier ring. The second robot arm segment can be screwed onto the threaded bolts, which have a thread on their outer circumference, using nuts provided for this purpose. For example, the threaded bolts are at least partially or completely manufactured by a forming process, which can further reduce manufacturing costs. According to one embodiment, the threaded bolts are drawn into punched holes in the collar of the internal gear and fit into through holes provided for this purpose in the carrier ring. By selecting external threads, the required installation space for the carrier ring can be kept as small as possible.

[0012] According to one embodiment, the rolling bearing is fixed to an inner circumference of the housing by means of a screw-in ring. The screw-in ring thus has an external thread that engages with an internal thread on the housing. The preload of the rolling bearing can be adjusted via the screw-in ring. According to an alternative embodiment, the rolling bearing is fixed to an inner circumference of the housing by means of a retaining ring and a preload spring. For example, the preload spring is designed as a disc spring and is arranged axially between the outer ring of the rolling bearing and the retaining ring, which is located in a groove provided for this purpose on an inner circumferential surface of the housing.

[0013] The invention also relates to a robot comprising an actuator according to the invention. In particular, the actuator according to the invention is arranged in a joint for a robot arm and acts at least indirectly between two robot arm segments. Preferably, the robot is designed as a cobot or humanoid robot. A cobot, short for "collaborative robot," is a robot designed to work in close cooperation with humans. Unlike industrial robots, which often operate in enclosed areas and require strict safety measures, cobots are designed to operate safely and efficiently directly alongside human workers. Cobots support human workers in repetitive or ergonomically demanding tasks, thus contributing to improved working conditions and increased production quality.A humanoid robot is a robot that exhibits human-like characteristics and a human-like appearance. Humanoid robots are designed to mimic human shape, movements, and even behaviors.

[0014] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to the figures. Fig. 1 a simplified schematic representation of a robot only partially shown with an actuator according to the invention, Fig. 2 a simplified sectional view of the actuator according to the invention in a first embodiment and Fig. 3 a simplified sectional view of the actuator according to the invention in a second embodiment.

[0015] Fig. Figure 1 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, connecting the two robot arm segments 12a and 12b. To change the position of the two robot arm segments 12a and 12b relative to each other, the robot 12 has an actuator 14 according to the invention, which comprises an electric drive unit 15 and a gearbox 1.

[0016] Fig. Figure 2 shows a longitudinal section of actuator 14. Fig. Figure 1, where only a section of the first robot arm segment 12a is shown. The actuator 14 comprises the electric drive unit 15 and the drive-effectively connected gearbox 1, designed as a wave gear, which are arranged in a stationary, two-part housing 2a, 2b. The drive unit 15 and the gearbox 1 are arranged coaxially. The two housing parts of the two-part housing 2a, 2b are rotationally fixed to each other and sealed by a sealing ring 11. Alternatively, the two-part housing 2a, 2b can also be designed as a single piece. The housing 2a, 2b provides the internal interfaces for the functional elements of the actuator 14 and the external interfaces for integration into a higher-level assembly.

[0017] The electric drive unit 15, in particular a rotor shaft of the electric motor (not shown in detail here), is connected via a drive shaft 16, which can rotate about an axis of rotation 22, to an inner ring 17 of a wave generator, the drive shaft 16 being rotatably mounted on the housing 2a via a bearing 21. The wave generator further comprises several rolling elements 18 and an outer ring 19, the inner ring 17, the rolling elements 18, and the outer ring 19 forming a non-circular bearing element. The wave generator interacts with a flexible ring element 20, which is rotationally fixed to the housing 2a by means of screws. The flexible ring element 20 is designed as a collar sleeve and has external teeth that mesh with the internal teeth of a ring gear 3, which is designed as a rigid ring element, at two opposing tooth engagement areas to transmit a torque.

[0018] During operation of the electric motor, the shaft generator is rotated via the drive shaft 16, causing the inner ring 17 of the bearing element to rotate relative to the flexible ring element 20 and the outer ring 19 of the bearing element housed within it. The flexible ring element 20 deforms elastically in accordance with the direction and speed of rotation of the shaft generator. The rotational movement of the shaft generator causes the flexible ring element 20 to undergo circumferential deformation, generating a continuous, rotating tooth engagement between the flexible ring element 20 and the ring gear 3. The opposing tooth engagement areas move continuously in the circumferential direction around the axis of rotation of the shaft generator during its rotation. Since the flexible ring element 20 has fewer teeth than the ring gear 3, rotation of the shaft generator results in a relative movement of the flexible ring element 20 to the ring gear 3.

[0019] The ring gear 3 is flange-shaped, serves as the output shaft of the actuator 14, and is connected to several threaded bolts 4 arranged on it, which serve as an interface for a second robot arm segment that can be connected to it. In particular, the flange-shaped ring gear 3 is made of a metal sheet and has a radially extending collar 7 with openings for receiving the threaded bolts 4. Here, the threaded bolts 4 are pressed into the openings on the collar 7 of the ring gear 3. Furthermore, the gearbox 1 has a support ring 5, which is rotatably mounted on an outer circumference in the housing 2b via a rolling bearing 6 designed as a double-row angular contact ball bearing and receives the flange-shaped ring gear 3 on an inner circumference. The collar 7 abuts the end face of the support ring 5 and the rolling bearing 6, in particular the inner ring of the rolling bearing 6. The threaded bolts 4 extend axially through the support ring 5.In this case, the support ring 5 is made of a non-ferrous metal. Alternatively, the support ring 5 can be made of a composite material, as it is primarily subjected to compressive stress. The threaded bolts 4 are preferably manufactured by a forming process. This saves space, weight, and costs. The rolling bearing 6 is fixed to an inner circumference of the housing 2b by means of a screw-in ring 8 with an external thread. The screw-in ring 8 presses on the outer ring of the rolling bearing 6. The inner ring of the rolling bearing 6 is fixed between a circumferential flange on the support ring 5 and the collar 7 on the ring gear 3.

[0020] Fig. Figure 3 shows a second embodiment of an actuator 14 according to the invention, wherein this embodiment is identical to the embodiment according to the invention except for the fixing of the rolling bearing 6 to the housing 2b. Fig.2 corresponds to the reference made to it. In the present case, the rolling bearing 6 is not fixed to an inner circumference of the housing 2b by means of a screw-in ring, but by means of a retaining ring 9 and a preload spring 10, wherein the preload spring 10 is arranged axially between the outer ring of the rolling bearing 6 and the retaining ring 9. The retaining ring 9 is arranged in a groove on the housing 2b. Reference symbol list 1 gearbox 2a Housing 2b Housing 3. Ring gear 4 threaded bolts 5 carrier ring 6 rolling bearings 7th Federation 8 Screw-in ring 9 retaining ring 10 Preload spring 11 Sealing ring 12 robots 12a Robot arm segment 12b Robot arm segment 13 joint 14 Actuator 15 Drive unit 16 Drive shaft 17 inner ring 18 rolling elements 19 Outer ring 20 flexible ring element 21 warehouses 22 axis of rotation QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 208 054 A2

[0002]

Claims

Actuator (14) for a robot arm segment (12a) of a robot (12), comprising an electric drive unit (15) and a drive-effectively connected gearbox (1) which are arranged in a stationary housing (2a, 2b), wherein the gearbox (1) has a flange-shaped ring gear (3) designed as an output shaft with several threaded bolts (4) arranged thereon, which are configured as an interface for a second robot arm segment (12b) which can be connected thereto. Actuator (14) according to claim 1, characterized in that the flange-shaped ring gear (3) is formed from a metal sheet. Actuator (14) according to one of the preceding claims, characterized in that the transmission (1) has a support ring (5) which is rotatably mounted in the housing (2a, 2b) via a rolling bearing (6) and accommodates the flange-shaped ring gear (3). Actuator (14) according to claim 3, characterized in that the flange-shaped ring gear (3) has a radially extending collar (7) which comes into contact with the carrier ring (5) and the rolling bearing (6) at its end face and has openings for receiving the threaded bolts (4). Actuator (14) according to claim 3 or 4, characterized in that the carrier ring (5) is made of a light metal. Actuator (14) according to claim 3 or 4, characterized in that the support ring (5) is made of a composite material. Actuator (14) according to one of the preceding claims, characterized in that the rolling bearing (6) is fixed to an inner circumference of the housing (2b) via a screw-in ring (8). Actuator (14) according to one of claims 1 to 6, characterized in that the rolling bearing (6) is fixed to an inner circumference of the housing (2b) via a retaining ring (9) and a preload spring (10). Robot (12) comprising an actuator (14) according to any of the preceding claims.

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