Actuator for a robot arm segment, and robot comprising an actuator of this kind

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 transmission (1) which can be drivingly connected thereto, which are arranged in a stationary housing (2a), wherein: a wrap spring (3) is arranged in the power flow between the electric drive unit (15) and the transmission (1); and the wrap spring (3) is designed to transmit a drive torque from the drive unit (15) to the transmission (1) and for the purpose of torque reaction support, with the torque being directed from the transmission (1) to the drive unit (15), on a cylindrical friction surface (4). The invention also relates to a robot (12) comprising an actuator (14) of this kind.

Description

[0001] Actuator for a robot arm sequence and robot with such an actuator

[0002] 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.

[0003] For example, DE 10 2019 112 023 A1 discloses a braking device for a drive unit of a joint between two segments of a robot arm. The braking device comprises a brake activation device and a locking element, wherein the brake activation device is configured to engage the locking element with a rotor of the drive unit when required, in order to stop rotation of the rotor. The locking element is configured as a bolt and the braking element as a brake star with webs that provide a defined contact surface for the bolt.

[0004] Furthermore, DE 10 2010 022 891 A1 discloses a coiling spring mechanism comprising a coiling spring with a coiling section and two spring leg ends angled substantially radially inwards or outwards from the coiling section, and a closing element rotatable relative to the coiling spring, which, when rotated, acts on a spring leg end to tension the coiling spring in a positive locking contact with a friction element associated with the coiling spring.

[0005] US Patent 2024 O 188 984 A1 describes an orthopedic rotary tool comprising a motor, a first and a second clutch, a rotating mass, and an output anvil. The motor and the first clutch drive a first drive path that rotates the output anvil at a certain speed. Selectively, the motor and the second clutch can activate a second drive path that moves the rotating mass to the output anvil and increases the speed of the anvil.

[0006] DE 10 2018 119 906 A1 describes a drive arrangement for a vehicle functional part.

[0007] In this design, a drive shaft, via a gear assembly, moves an adjusting element from a closed to an open position. A coil spring assembly, consisting of two coil spring elements acting in opposite directions, is arranged on the gear output side in the area of ​​the adjusting element.

[0008] The object of the invention is to provide an alternative actuator for a robot arm segment. In particular, the actuator is to be equipped with a compact and cost-effective brake. Preferably, the weight and complexity of the actuator's brake are to 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.

[0009] An actuator according to the invention for a robot arm segment of a robot comprises an electric drive unit and a gearbox that can be effectively connected to it for drive purposes. The drive unit and the gearbox are arranged in a stationary housing. A coil spring is arranged in the power flow between the electric drive unit and the gearbox. The coil spring is configured to transmit a drive torque from the drive unit to the gearbox and to support a torque directed from the gearbox to the drive unit against a cylindrical friction surface. The gearbox can be connected to another robot arm segment via an output shaft. The two robot arm segments are thus connected to each other via a joint in which the actuator is integrated.

[0010] The electric drive unit comprises an electric machine configured as a drive motor, with a rotor and a stator. Furthermore, an encoder and a control unit can be integrated into the electric drive unit. The coil spring acts not only as a torque transmission device but also as a brake when the torque is transmitted not from the drive motor to the gearbox, but from the gearbox to the drive motor. For this purpose, the coil spring has a coiled section and two spring legs angled radially outwards or inwards from the coiled section. When a drive torque is introduced from the drive unit into the coil spring via one of the spring legs, the coil spring deforms in such a way that the frictional torque between the coil spring and the cylindrical friction surface is reduced, in particular minimized, thereby allowing the drive torque to be transmitted to the gearbox via the coil spring.When a torque is introduced from the gearbox into the coil spring via one of the spring legs, the coil spring deforms in such a way that a frictional torque between the coil spring and the cylindrical friction surface is increased to a maximum value, thereby generating a braking torque.

[0011] According to one embodiment, the coil spring interacts with an opening contour on a motor shaft to transmit the drive torque from the motor shaft to the gearbox, the opening contour being arranged on the motor shaft between two legs of the coil spring. For example, the opening contour is designed as a circular segment on the motor shaft of the electric machine.

[0012] According to one embodiment, the coil spring interacts with a closing contour on a transmission shaft to support the torque from the transmission shaft against the cylindrical friction surface, the closing contour being arranged on the transmission shaft between two legs of the coil spring. For example, the closing contour is designed as a circular segment on the transmission shaft, particularly on a transmission input shaft.

[0013] Preferably, the motor shaft, the transmission shaft, and the coil spring are arranged coaxially and at least partially axially overlapping each other. This allows for significant space savings.

[0014] 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 a 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 transmission input shaft.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. The flexible ring element is designed to accommodate the shaft generator and bearing element, at least partially axially, and is 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.

[0015] During operation of the wave gear, 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, the wave generator is set into a rotational motion during operation of the wave gear, which causes the flexible ring element to undergo circumferential deformation. Preferably, the external teeth of the flexible ring element, which transmit 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 enables a space-saving design of the wave gear.

[0016] 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 axis of rotation of the shaft generator, 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.

[0017] According to the invention, the coiling spring is arranged with a circumferential surface of the coiling spring on a circumferential surface of a stationary element, wherein this circumferential surface of the stationary element forms the cylindrical friction surface.

[0018] According to one embodiment, the coil spring is arranged with an inner circumferential surface against an outer circumferential surface of a stationary element, this outer circumferential surface forming the cylindrical friction surface. For example, the stationary element is rotationally fixed, particularly as a single piece, to a housing or a housing cover. When a drive torque is introduced from the drive unit into the coil spring via one of the spring legs in the circumferential direction, the diameter of the coil spring increases, so that the friction torque between the coil spring and the cylindrical friction surface arranged on the inner circumference of the coil spring decreases, in particular becomes minimal, thereby allowing the drive torque to be transmitted to the gearbox via the coil spring.When a torque is introduced from the gearbox into the coil spring via one of the spring legs in the circumferential direction, the diameter of the coil spring is reduced, so that a frictional torque between the coil spring and the cylindrical friction surface arranged on the inner circumference of the coil spring increases, in particular becomes maximal, thereby generating a braking torque so that the coil spring blocks rotation.

[0019] According to an alternative embodiment, the coil spring is arranged with an outer circumferential surface on an inner circumferential surface of a stationary element, this inner circumferential surface forming the cylindrical friction surface. For example, the stationary element is rotationally fixed, in particular as a single piece, to a housing or a housing cover. When a drive torque is introduced from the drive unit into the coil spring via one of the spring legs, the diameter of the coil spring is reduced, so that the friction torque between the coil spring and the cylindrical friction surface arranged on the outer circumference of the coil spring decreases, in particular becomes minimal, thereby allowing the drive torque to be transmitted to the gearbox via the coil spring.When a torque is introduced from the gearbox into the coil spring via one of the spring legs, the diameter of the coil spring is increased, so that a frictional torque between the coil spring and the cylindrical friction surface arranged on the outer circumference of the coil spring increases, in particular becomes maximum, thereby generating a braking torque so that the coil spring blocks rotation.

[0020] According to one embodiment, the coil spring is arranged in an annular groove formed as an axial recess. Preferably, the annular groove is formed in a housing cover that is rotationally fixed to the housing. For example, the motor shaft and the transmission shaft are at least partially arranged in the annular groove, in particular the opening and closing contours that interact with the coil spring.

[0021] 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 in such a way that they can mimic human shape, movements, and even behaviors. 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.

[0022] Figure 1 is a highly simplified schematic representation of a robot, only partially depicted, with an actuator according to the invention.

[0023] Figure 2 shows a highly simplified representation of the actuator according to the invention in a first embodiment,

[0024] Figure 3 shows a simplified sectional view of the actuator according to a second embodiment of the invention.

[0025] Figure 4 shows a further simplified sectional view of the actuator according to the invention in the second embodiment,

[0026] Figure 5 shows a simplified sectional view of the actuator according to the invention in a third embodiment and

[0027] Figure 6 shows a further simplified sectional view of the actuator according to the invention in the third embodiment.

[0028] 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.

[0029] Figure 2 shows a highly schematic representation of the actuator 14 from Figure 1. The actuator 14 comprises an electric drive unit 15 with a housing-mounted stator 17 and a rotor 16, as well as a drive-effectively connectable gearbox 1, which are arranged in a stationary housing 2a. Furthermore, the actuator 14 includes a coil spring 3, which is arranged in the power flow between the electric drive unit 15 and the gearbox 1. The coil spring 3 is configured to transmit a drive torque from the drive unit 15 to the gearbox 1 and to support a torque directed from the gearbox 1 to the drive unit 15 against a cylindrical friction surface 4. Thus, the transmission of torque from the gearbox 1 to the drive unit 15 is prevented by the coil spring 3. For example, the gearbox 1 is designed as a wave gear.

[0030] The coil spring 3 has a coiled section and two spring legs radially angled from the coiled section and interacts with an opening contour 5 on a motor shaft 6 designed as a rotor shaft to transmit the drive torque from the motor shaft 6 to the gearbox 1. The motor shaft 6, the gearbox shaft 8, and the coil spring 3 are arranged coaxially and at least partially axially overlapping with each other and rotate together about a rotational axis 11 in drive mode. Furthermore, the coil spring 3 interacts with a closing contour 7 on a gearbox shaft 8 designed as a gearbox input shaft to support the torque from the gearbox shaft 8 against the cylindrical friction surface 4. In this case, the coil spring 3 is arranged with an inner circumferential surface against an outer circumferential surface of a stationary element designed as a housing cover 2b, which is rotationally fixed to the housing 2a.Thus, the outer circumferential surface of the stationary element forms the cylindrical friction surface 4, on which the coil spring 3 generates the braking torque when an external torque is introduced into the gearbox 1 via an output shaft 10 of the gearbox 1 and directed towards the drive unit 15.

[0031] Figure 3 shows a longitudinal section of the actuator 14 according to a second embodiment. As can be seen particularly well in Figure 3, the actuator 14 is very compact. The drive unit 15, designed as an electric machine, and the transmission 1, designed as a wave gear, are arranged coaxially and axially adjacent to each other. The coil spring 3 interacts with an opening contour 5 shown in Figure 4 on a motor shaft 6 to transmit the drive torque from the motor shaft 6 to the transmission 1. Figure 4 shows a section along a section line 30 shown in Figure 3. Furthermore, the coil spring 3 interacts with a closing contour 7 shown in Figure 4 on the transmission shaft 8 to support the torque from the transmission shaft 8 against the cylindrical friction surface 4, independent of the direction of rotation.As can be seen from Figure 3, the coil spring 3 is arranged in an annular groove 9 formed as an axial recess, the annular groove 9 being formed in a housing cover 2b which is rotationally fixed to the housing 2a. The coil spring 3 is arranged with an inner circumferential surface against an outer circumferential surface in the annular groove 9 of the housing cover 2b, this outer circumferential surface forming the cylindrical friction surface 4.

[0032] When the electric drive unit 15 drives the motor shaft 6, the drive power is introduced into the gearbox 1 via the coil spring 3 and the gearbox shaft 8, which is configured as the gearbox input shaft. The motor shaft 6, the gearbox shaft 8, and the coil spring 3 rotate together about a pivot axis 11. The motor shaft 6 is rotatably mounted on the housing cover 2b via a bearing 24. The gearbox shaft 8 is rotationally fixed to an inner ring 21 of a wave generator, in particular by bolting, and the gearbox shaft 8 is rotatably mounted on the housing 2a via a bearing 22. The wave generator further comprises several rolling elements 18 and an outer ring 19, the inner ring 21, 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 bolting.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, designed as a rigid ring element, at two opposing tooth engagement areas to transmit torque. The ring gear is rotatably mounted in the housing 2a via a rolling bearing 23 and serves as the output shaft 10 of the actuator 14. For example, the ring gear can be connected, at least indirectly, to a shaft of another robot arm segment.

[0033] During operation of the electric drive unit 15, the shaft generator is rotated via the transmission shaft 8, causing the inner ring 21 of the bearing element to rotate relative to the flexible ring element 20 and the outer ring 19 of the bearing element, which is fixedly mounted therein. 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 continuous deformation, resulting in a continuous tooth engagement between the flexible ring element 20 and the ring gear. The opposing tooth engagement areas move continuously circumferentially 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, rotation of the shaft generator causes a relative movement of the flexible ring element 20 to the ring gear.

[0034] Figures 5 and 6 show a third embodiment of an actuator 14 according to the invention, wherein this embodiment corresponds to the embodiment according to Figures 3 and 4, to which reference is made, except for the design and arrangement of the coil spring 3 and the design of the opening contour 5 on the motor shaft 6 and the closing contour 7 on the transmission shaft 8. Figure 5 shows a section along a section line 40 shown in Figure 6. The coil spring 3 is arranged with an outer circumferential surface on an inner circumferential surface of the housing cover 2b, this inner circumferential surface forming the cylindrical friction surface 4. Since the coil spring 3 is arranged on the inner circumferential surface of the housing cover 2b, expansion of the coil spring 3 when actuated by the closing contour 7 on the transmission shaft 8 leads to the locking of the transmission shaft 8.In contrast, the coil spring 3 is arranged on an outer circumferential surface of the housing cover 2b, so that when the coil spring 3 is actuated by the opening contour 5 on the motor shaft 6, it expands to transmit a drive torque from the drive unit 15 to the gearbox 1.

[0035] In all embodiments, the coil spring 3 forms a passive brake when the torque is directed from the gearbox 1 to the drive unit 15. The passive brake requires neither electrical, hydraulic, nor pneumatic actuating elements, nor a control unit for active brake application. Thus, the respective actuator 14 is equipped with a compact and cost-effective brake. (List of reference symbols)

[0036] I Gearbox

[0037] 2a Housing

[0038] 2b Housing cover

[0039] 3 coil spring

[0040] 4 cylindrical friction surfaces

[0041] 5 Opener contour

[0042] 6 Motor shaft

[0043] 7 Closer contour

[0044] 8 Gear shaft

[0045] 9 ring groove

[0046] 10 Output shaft

[0047] II axis of rotation

[0048] 12 robots

[0049] 12a Robot arm segment

[0050] 12b Robot arm segment

[0051] 13 joint

[0052] 14 Actuator

[0053] 15 Drive unit

[0054] 16 Rotor

[0055] 17 Stator

[0056] 18 rolling elements

[0057] 19 Outer ring

[0058] 20 flexible ring elements

[0059] 21 inner ring

[0060] 22 warehouses

[0061] 23 warehouses

[0062] 24 warehouses

[0063] 30 Section line

[0064] 40 Section line

Claims

Patent claims 1. Actuator (14) for a robot arm segment (12a) of a robot (12), comprising an electric drive unit (15) and a drive-effectively connectable gearbox (1) thereto, which are arranged in a stationary housing (2a), wherein a coil spring (3) is arranged in the power flow between the electric drive unit (15) and the gearbox (1), wherein the coil spring (3) is configured to transmit a drive torque from the drive unit (15) to the gearbox (1) and to support a torque directed from the gearbox (1) to the drive unit (15) on a cylindrical friction surface (4), characterized in that the coil spring (3) is arranged with a circumferential surface of the coil spring (3) on a circumferential surface of a stationary element, wherein this circumferential surface of the stationary element forms the cylindrical friction surface (4).

2. Actuator (14) according to claim 1 , characterized in that the coil spring (3) interacts with an opening contour (5) on a motor shaft (6) to transmit the drive torque from the motor shaft (6) to the gearbox (1 ).

3. Actuator (14) according to one of the preceding claims, characterized in that the coil spring (3) interacts with a closing contour (7) on a transmission shaft (8) to support the torque from the transmission shaft (8) on the cylindrical friction surface (4).

4. Actuator (14) according to claims 2 and 3, characterized in that the motor shaft (6), the transmission shaft (8) and the coil spring (3) are arranged coaxially and at least partially axially overlapping each other.

5. Actuator (14) according to one of the preceding claims, characterized in that the transmission (1 ) is designed as a wave transmission.

6. Actuator (14) according to one of the preceding claims, characterized in that the coil spring (3) is arranged with an inner circumferential surface on an outer circumferential surface of a stationary element, wherein this outer circumferential surface forms the cylindrical friction surface (4).

7. Actuator (14) according to one of claims 1 to 5, characterized in that the coil spring (3) is arranged with an outer circumferential surface on an inner circumferential surface of a stationary element, wherein this inner circumferential surface forms the cylindrical friction surface (4).

8. Actuator (14) according to one of the preceding claims, characterized in that the coil spring (3) is arranged in an annular groove (9) designed as an axial recess.

9. Actuator (14) according to claim 8, characterized in that the annular groove (9) is formed in a housing cover (2b) which is rotationally fixed to the housing (2a).

10. Robot (12) comprising an actuator (14) according to any of the preceding claims.

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