Direct drive actuator for robotic finger joint

Abstract

The application provides a direct drive actuator for a robot finger joint, and belongs to the technical field of robot accessories. The direct drive actuator for the robot finger joint comprises an outer rotor motor including an outer rotor, a harmonic reducer including a flexible bearing, a flexible gear and a steel gear, and a damping assembly including a rigid constraint ring and a damping rubber ring. The outer ring surface of the rigid constraint ring is matched with and fixedly connected to the inner ring of the flexible bearing. The inner ring surface of the rigid constraint ring is circular. The outer ring surface of the damping rubber ring is fixedly connected to the inner ring surface of the rigid constraint ring. The inner ring surface of the damping rubber ring is fixedly connected to the outer peripheral surface of the outer rotor. The inner ring surface of the rigid constraint ring is provided with main ribs at both ends in the long axis direction and both ends in the short axis direction. The main ribs are raised along the radial direction and are recessed in the inner ring surface of the damping rubber ring. The direct drive actuator for the robot finger joint can effectively prevent the deformation of the outer rotor as a wave generator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of robot accessory, and particularly relates to a direct drive actuator for robot finger joint. BACKGROUND

[0002] A harmonic reducer is a high-precision, compact wave generator transmission device, mainly including a wave generator, a flexible bearing, a flexspline and a rigid spline. The harmonic reducer has the advantages of high reduction ratio, high precision, low backlash, small size and the like, and is therefore widely applied to industrial robots, especially small motion points such as finger joints.

[0003] Generally, a robot joint adopts a servo motor or a brushless direct current motor in cooperation with a harmonic reducer, a rotating shaft of the motor is connected with a wave generator of the harmonic reducer to form a direct drive, a steel wheel of the harmonic reducer is generally fixed on a joint base or a shell, a flexspline is taken as an output, and the flexspline is connected with a rotating shaft of the robot joint through a flange or a hollow structure to realize driving.

[0004] In order to better adapt to the design requirements of robot miniaturization, a technology of directly taking an outer rotor of a motor as a wave generator of a harmonic reducer appears. In order to serve as the wave generator of the harmonic reducer, the outer rotor needs to be provided with an elliptical shape, and the outer rotor will be subjected to a circumferential shear force during rotation. Since the outer rotor is a thin-walled cylindrical component, and a magnet is arranged on the inner side of the outer rotor (generally, the magnet is pasted on the outer rotor through epoxy), the circumferential shear force will cause fatigue deformation of the outer rotor, and even cause the magnet to fall off. SUMMARY

[0005] An object of the present application is to provide a direct drive actuator for robot finger joint, which can effectively prevent deformation of an outer rotor serving as a wave generator.

[0006] A further object of the present application is to realize overload protection of a damping assembly.

[0007] In particular, the present application provides a direct drive actuator for robot finger joint, comprising:

[0008] An outer rotor motor comprising an outer rotor;

[0009] A harmonic reducer comprising a flexible bearing, a flexspline and a steel wheel;

[0010] The damping assembly comprises a rigid constraint ring and a damping rubber ring, the outer ring surface of the rigid constraint ring is matched and fixedly connected with the inner ring of the flexible bearing, the inner ring surface of the rigid constraint ring is circular, the outer ring surface of the damping rubber ring is fixedly connected with the inner ring surface of the rigid constraint ring, the inner ring surface of the damping rubber ring is fixedly connected with the outer peripheral surface of the outer rotor, and the inner ring surface of the rigid constraint ring is provided with main ribs at both ends in the long axis direction and both ends in the short axis direction.

[0011] Optionally, the damping rubber ring has a loss factor of any one of 0.2-0.5, a thermal conductivity greater than 3 W / m·K, and a shear modulus of any one of 0.5 MPa-2.5 MPa in the working temperature range.

[0012] Optionally, the rigid constraint ring is further provided with auxiliary ribs between adjacent main ribs, the auxiliary ribs have a height less than that of the main ribs, the outer peripheral surface of the outer rotor is provided with a limiting protrusion, and the limiting protrusion has an overlapping part with the auxiliary ribs in the radial direction and a preset gap in the circumferential direction.

[0013] Optionally, the surface of the limiting protrusion is provided with an elastic rubber sleeve.

[0014] Optionally, the preset gap dt is determined according to the following formula:

[0015] dt=d0+ds+dr;

[0016] wherein d0 is a minimum safety gap, ds is a gap error caused by manufacturing and assembly processes, and dr is a gap change amount caused by thermal expansion of the rigid constraint ring and the limiting protrusion.

[0017] Optionally, dr is determined according to the following formula:

[0018] ;

[0019] wherein r2 is the distance between the top end of the auxiliary rib and the center of the outer rotor, Δα is the difference between the thermal expansion coefficients of the limiting protrusion and the rigid constraint ring, and ΔT is the maximum working temperature difference.

[0020] Optionally, a plurality of auxiliary ribs are arranged between adjacent main ribs, and the plurality of auxiliary ribs are uniformly distributed in an arc range with a central angle of 20°-30°.

[0021] Optionally, the duty cycle of the plurality of auxiliary ribs in the arc range is any one of 70%-80%.

[0022] Optionally, the main rib comprises a vertical part extending in the radial direction and a brim part extending in the circumferential direction and connected to the inner annular surface of the rigid constraint ring and the vertical part respectively.

[0023] Optionally, the size of the main rib, the thickness of the damping rubber ring, and the position, number and size of the auxiliary rib are determined according to modal margin requirements and damping effectiveness requirements.

[0024] The modal margin requirements include that the ratio of the difference between the second-order elliptical modal frequency of the damping assembly and 2 times the fundamental frequency of the outer rotor motor and the fundamental frequency is greater than a ratio threshold value.

[0025] The damping effectiveness requirements include that the average shear strain of the damping rubber ring is less than a first strain threshold value, and the maximum shear strain of the damping rubber ring is less than a second strain threshold value.

[0026] According to an aspect of the present application, by adding a damping assembly between the outer rotor and the flexible bearing, the damping rubber ring of the damping assembly can convert the circumferential shear force applied by the flexible bearing into heat through its deformation, so that the outer rotor only bears a smaller contact pressure, thereby playing a role in protecting the outer rotor. Further, the setting of the main rib on the rigid constraint ring can improve the elliptical stiffness of the damping assembly, which is not easy to deform, thereby improving the shape accuracy and ensuring the accuracy of the motion transmission.

[0027] Further, the "T"-shaped main rib increases the bending stiffness of the root, can better disperse stress, and increases the area of the bonding surface of the main rib and the rigid constraint ring and the outer skin, which can reduce local stress, thereby better maintaining the elliptical stiffness and facilitating heat dissipation.

[0028] Further, the brim part and the inner annular surface of the rigid constraint ring are provided with a fillet, which can significantly reduce the stress concentration coefficient and facilitate the distribution of the damping rubber ring in this area.

[0029] According to another aspect of the present application, the auxiliary rib is further provided between adjacent main ribs, which can increase the stiffness at this position, avoid the deformation of bulging or collapsing, and make the stiffness of the rigid constraint ring smoothly transition to avoid local distortion.

[0030] Further, the auxiliary rib is arranged between the main ribs, i.e. in the gentle area which is not easy to deform, and the outer rotor is provided with a limiting protrusion corresponding to the auxiliary rib, which can be blocked by the corresponding limiting protrusion when the circumferential displacement of the top end of the auxiliary rib exceeds a certain threshold value due to the circumferential shear force, thereby playing a role in limiting the shear deformation amount, i.e. preventing excessive deformation of the rigid constraint ring, thereby playing a role in overload protection of the damping assembly.

[0031] Furthermore, the aforementioned preset gap setting ensures that the secondary rib and the limiting protrusion do not contact each other under normal working conditions, thus guaranteeing a safe distance and controlling the degree of overload protection. For example, when setting the aforementioned minimum safe gap, it is determined based on the sliding amount of the secondary rib corresponding to overload protection. The larger the minimum safe gap, the greater the distance that the rigid constraint ring is allowed to move circumferentially, which means that a greater degree of deformation can be accepted.

[0032] Furthermore, by setting a set of secondary ribs between two adjacent main ribs, and by setting a reasonable distribution area and duty cycle, the stability of the stiffness of the area can be guaranteed, while avoiding excessive stiffness increase that would lead to excessive constraint. Attached Figure Description

[0033] Figure 1 A schematic diagram of a direct-drive actuator for a robot finger joint according to an embodiment of the present invention is shown;

[0034] Figure 2 A schematic cross-sectional view of the damping assembly and outer rotor of a direct-drive actuator for a robot finger joint according to an embodiment of the present invention is shown.

[0035] Figure 3 A schematic cross-sectional view of a damping component of a direct-drive actuator for a robot finger joint according to another embodiment of the present invention is shown;

[0036] Figure 4 The present invention is shown Figure 3 A magnified view of a section at point A in the middle;

[0037] Figure 5 The present invention is shown Figure 3 A magnified view of a section at point B in the middle;

[0038] Figure 6 A schematic diagram of the assembly structure of the motor shaft and the outer rotor of a direct-drive actuator for a robot finger joint according to an embodiment of the present invention is shown.

[0039] 100-Direct drive actuator for robot finger joints, 10-External rotor motor, 11-External rotor, 12-Motor base, 13-Motor shaft, 14-First bearing, 15-Motor winding, 16-Motor magnet, 20-Harmonic reducer, 21-Flexible bearing, 22-Flexible wheel, 23-Steel wheel, 24-Second bearing, 30-Damping assembly, 31-Rigid constraint ring, 32-Damping rubber ring, 311-Main rib, 312-Secondary rib, 111-Limiting protrusion, 112-Elastic rubber sleeve, 301-Vertical part, 302-Brim part, 303-Rounded. Detailed Implementation

[0040] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0041] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps is not limited to the steps listed, but may optionally include steps not listed, or may optionally include other steps inherent to such process, method, product, or apparatus.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] Figure 1 A schematic diagram of the structure of a direct-drive actuator 100 for a robot finger joint according to an embodiment of the present invention is shown. Figure 2 A schematic cross-sectional view of the damping assembly 30 and the outer rotor 11 of a direct-drive actuator 100 for a robot finger joint according to an embodiment of the present invention is shown. Figure 1 As shown, in one embodiment, the direct-drive actuator 100 for a robot finger joint includes an external rotor motor 10, a harmonic reducer 20, and a damping assembly 30. The external rotor motor 10 includes an external rotor 11. Generally, the external rotor motor 10 also includes a motor base 12 and a motor shaft 13. The motor shaft 13 and the external rotor 11 form an anti-rotation connection. The motor shaft 13 is supported on the fixedly mounted motor base 12 by a first bearing 14, which is typically a deep groove ball bearing. Here, a motor winding 15 is provided at the motor base 12, and a motor magnet 16 is fixed to the external rotor 11 opposite to the motor winding 15. The working principle of the external rotor motor 10 is a conventional technique in the art and will not be described in detail here. The harmonic reducer 20 includes a flexible bearing 21, a flexible wheel 22, and a steel wheel 23. A second bearing 24 is provided between the flexible wheel 22 and the steel wheel 23. The second bearing 24 can be a four-point angular contact bearing; that is, the harmonic reducer 20 in this embodiment does not include a wave generator. Figure 2As shown, the damping assembly 30 comprises a rigid constraint ring 31 and a damping rubber ring 32, the outer ring surface of the rigid constraint ring 31 is matched and fixedly connected with the inner ring of the flexible bearing 21, the inner ring surface of the rigid constraint ring 31 is circular, the outer ring surface of the damping rubber ring 32 is fixedly connected with the inner ring surface of the rigid constraint ring 31, and the inner ring surface of the damping rubber ring 32 is fixedly connected with the outer peripheral surface of the outer rotor 11. That is, in the embodiment, the outer ring surface of the rigid constraint ring 31 is elliptical as the peripheral surface of the wave generator, and the inner ring surface and the outer ring surface of the damping rubber ring 32 are both circular, so that the outer rotor 11 does not need to be changed in shape and still maintains a circular shape.

[0044] In the embodiment, by additionally arranging the damping assembly 30 between the outer rotor 11 and the flexible bearing 21, the damping rubber ring 32 of the damping assembly 30 can convert the circumferential shear force applied by the flexible bearing 21 to heat through its deformation, so that the outer rotor 11 only bears a smaller contact pressure, thereby playing a role in protecting the outer rotor 11. Further, the elliptical stiffness of the damping assembly 30 in shape can be improved by arranging the main ribs 311 on the rigid constraint ring 31, so that the deformation of the shape is not easy to occur, thereby improving the shape accuracy and ensuring the accuracy of the motion transmission.

[0045] In one embodiment, the loss factor of the damping rubber ring 32 in the working temperature range is any value in 0.2-0.5, for example, the loss factor is 0.2, 0.25, 0.35, 0.4 or 0.5; the thermal conductivity is greater than 3 W / m·K, and the shear modulus is any value in 0.5 MPa-2.5 MPa, for example, the shear modulus is 0.5 MPa, 1 MPa, 2 MPa or 2.5 MPa. The working temperature range here can be a temperature range of 40-90°C, i.e. the general working temperature of the robot joint. According to the above performance, the material of the damping rubber ring 32 is selected to ensure the ability of absorbing shear force and rapid heat conduction while avoiding excessive deformation of the damping rubber ring 32.

[0046] Figure 3 A schematic cross-sectional view of the damping assembly 30 of the direct drive actuator 100 for a robot finger joint according to another embodiment of the application is shown. Figure 4 A schematic cross-sectional view of the damping assembly 30 of the direct drive actuator 100 for a robot finger joint according to another embodiment of the application is shown. Figure 3 A partial enlarged view of part A in the embodiment of the application is shown. Figure 3 And 4As shown, in a further embodiment, the main rib 311 comprises a vertical portion 301 extending in the radial direction and a brim portion 302 extending in the circumferential direction and connected to the inner annular surface of the rigid constraint ring 31 and the vertical portion 301 respectively.

[0047] The "T" shaped main rib 311 in this embodiment increases the bending stiffness of the root portion, better disperses stress, and increases the area of the bonding surface between the main rib 311, the rigid constraint ring 31 and the outer skin, which reduces local stress, better maintains the elliptical stiffness, and facilitates heat dissipation.

[0048] Further, a fillet 303 is provided between the brim portion 302 and the inner annular surface of the rigid constraint ring 31, which significantly reduces the stress concentration coefficient and facilitates the distribution of the damping rubber ring 32 in this area.

[0049] Figure 5 A partial enlarged view according to the present application is shown in B. Figure 3 A partial enlarged view according to the present application is shown in B. Figure 6 A schematic diagram of the assembly structure of the motor shaft 13 and the outer rotor 11 of the direct drive actuator 100 for a robot finger joint according to an embodiment of the present application is shown. As shown in Figure 2 As shown in FIG. 5, in another embodiment, the rigid constraint ring 31 is further provided with a secondary rib 312 between adjacent main ribs 311. The number of secondary ribs 312 between adjacent main ribs 311 can be one or more, which is not limited herein. The secondary rib 312 can be arranged at a position between two main ribs 311, for example Figure 2 When the number of secondary ribs 312 is one, the included angle P between the secondary rib 312 and the main rib 311 is 45 degrees. When the number of adjacent secondary ribs 312 is more than one, the plurality of secondary ribs 312 between adjacent main ribs 311 are referred to as a group of secondary ribs (for example Figure 3 In region B, all secondary ribs 312 constitute a group of secondary ribs), the above-mentioned included angle can be considered as the included angle between the secondary rib 312 in the middle position of the group of secondary ribs and the main rib 311. The height of the secondary rib 312 is less than the height of the main rib 311, where the height of the secondary rib 312 refers to the dimension in the radial direction. A limiting protrusion 111 is arranged at the outer circumferential surface of the outer rotor 11 (see also Figure 6The limiting protrusion 111 can be directly machined on the outer rotor 11, or can be a component subsequently installed on the outer rotor 11, such as a fastener assembled on the outer rotor 11, the arc surface portion protruding from the outer ring surface of the outer rotor 11 serving as the limiting protrusion 111. Here, the shape of the limiting protrusion 111 is preferably a spherical surface, an arc surface or other gentle curved surface, so as to facilitate smooth installation of the damping assembly 30. The limiting protrusion 111 has an overlapping portion with the secondary rib 312 in the radial direction and a predetermined gap dx in the circumferential direction. The surface of the limiting protrusion 111 is provided with an elastic rubber sleeve 112, which can be made of silicone, PU or PTEE, and can be sleeved or coated on the limiting protrusion 111, as long as it can play a certain buffering and isolation role. The predetermined gap dt is determined according to the following formula (1):

[0050] ;

[0051] wherein d0 is the minimum safety gap, which can be set according to experience, ds is the gap error caused by the manufacturing and assembly process, and dr is the gap change amount caused by the thermal expansion of the rigid restraint ring 31 and the limiting protrusion 111, wherein dr can be calculated according to the following formula (2):

[0052] ;

[0053] wherein r2 is the distance between the top end of the secondary rib 312 and the center of the outer rotor 11, Δα is the difference between the thermal expansion coefficients of the limiting protrusion 111 and the rigid restraint ring 31, and ΔT is the maximum working temperature difference.

[0054] In the present embodiment, the secondary rib 312 is further arranged between adjacent primary ribs 311, which can increase the rigidity at this position, avoid deformation such as bulging or collapse, and smoothly transition the rigidity of the rigid restraint ring 31 to avoid local distortion.

[0055] Further, the secondary rib 312 is arranged between the primary ribs 311, i.e. in a gentle area that is not prone to deformation, and the limiting protrusion 111 corresponding to the secondary rib 312 is arranged on the outer rotor 11, which can be blocked by the corresponding limiting protrusion 111 when the top end of the secondary rib 312 is subjected to a circumferential displacement exceeding a certain threshold value due to the circumferential shear force, thereby playing a role in limiting the shear deformation amount, i.e. preventing excessive deformation of the rigid restraint ring 31, thereby playing a role in overload protection of the damping assembly 30.

[0056] Further, the setting of the preset gap can ensure that the sub-ribs 312 and the limiting protrusions 111 are not in contact under normal working conditions, i.e., a safety distance is ensured, and the degree of overload protection is also controlled. For example, when setting the minimum safety gap, according to the corresponding sub-rib 312 slip amount of the overload protection, the greater the minimum safety gap, the greater the distance allowed for the circumferential movement of the rigid restraint ring 31, i.e., a greater degree of deformation can be accepted.

[0057] Further, the elastic rubber sleeve 112 provided at the limiting protrusion 111 has a buffering and damping effect, avoiding hard collision between the limiting protrusion 111 and the sub-rib 312.

[0058] In a further embodiment, a group of sub-ribs 312 is provided between adjacent main ribs 311, and each sub-rib 312 of each group of sub-ribs 312 is uniformly distributed within an arc range with a central angle q of 20-30°, for example, the plurality of sub-ribs 312 are uniformly distributed within an arc range with a central angle q of 20°, 25° or 30°. The duty cycle of the plurality of sub-ribs 312 in each group of sub-ribs 312 within the arc range is any value in 70-80%, where the duty cycle is understood as the ratio of the arc length L1 of the sub-rib 312 to the arc length L2 between adjacent two sub-ribs 312 in the circumferential direction.

[0059] This embodiment can ensure the stability of the stiffness in the region by providing a group of sub-ribs 312 between adjacent two main ribs 311, and by setting a reasonable distribution area and duty cycle, while avoiding excessive stiffness that leads to excessive constraint.

[0060] Further, a certain distance, for example, a spacing of 0.3-0.5 mm, is provided between the two ends of the main ribs 311 and the sub-ribs 312 in the axial direction and the two end faces of the rigid restraint ring 31, avoiding stress concentration at the end of the rigid restraint ring 31, and improving the volume of the damping rubber ring 32, which is beneficial to the improvement of damping performance.

[0061] In an embodiment, the rigid restraint ring 31, the main ribs 311 and the sub-ribs 312 are made of 7075-T6 aluminum alloy. The main ribs 311 and the sub-ribs 312 are formed by machining the aluminum alloy material. The damping rubber ring 32 is made of heat-conducting epoxy damping glue, for example, 3MDP490 or LOCTITE EA9394 mixed with heat-conducting fillers to form the material of the damping rubber ring 32.

[0062] The damping ring 32 can be filled with heat-conducting epoxy damping glue between the outer rotor 11 and the rigid constraint ring 31 after the relative positions of the two are fixed by a tool, and formed after curing, or the heat-conducting epoxy damping glue can be coated and cured to form on the rigid constraint ring 31 first, and then coated on the inner ring surface of the damping ring 32, and then bonded to the outer surface of the outer rotor 11 at a certain pressure, for example, cured at a pressure of 0.1-0.3 MPa to achieve firm bonding with the outer rotor 11. Of course, the surface of the rigid constraint ring 31 and the outer rotor 11 can also be treated before the heat-conducting epoxy damping glue is coated, such as sandblasting and IPA degreasing treatment, so that the glue is more firmly bonded to the rigid constraint ring 31 and the outer rotor 11. Of course, in other embodiments, the damping ring 32 can also be a separately manufactured product, which is assembled to the rigid constraint ring 31, for example, by a key and slot fitting assembly method, or a fastener, interference pressure connection method, etc., which is not limited here, as long as the damping ring 32 can be effectively fixed.

[0063] In one embodiment, the size of the main rib 311, the thickness of the damping ring 32, and the position, number and size of the secondary rib 312 are determined according to the modal margin requirement and the damping effectiveness requirement.

[0064] The modal margin requirement is shown in the following formula (3):

[0065]

[0066] Where f2 is the second-order elliptical modal frequency of the damping assembly 30, fd is the fundamental frequency of the outer rotor motor 10, and f0 is a ratio threshold.

[0067] Here, f0 can be set according to requirements, for example, set to 25%, so that the second-order elliptical modal frequency of the damping assembly 30 can maintain a bandwidth spacing of 25% with the main excitation frequency (since the main excitation of the harmonic reducer 20 is 2 times the fundamental frequency of the outer rotor motor 10), preventing excessive deformation due to resonance of the damping assembly 30.

[0068] The damping effectiveness requirement includes that the average shear strain of the damping ring 32 is less than a first strain threshold, and the maximum shear strain of the damping ring 32 is less than a second strain threshold. The first strain threshold can be set to 0.2, and the second strain threshold can be set to 0.5.

[0069] As shown in FIG. 6, the damping ring 32 is provided with a plurality of secondary ribs 312, and the secondary ribs 312 are arranged in a plurality of rows along the circumferential direction of the damping ring 32. Figure 2 ​As shown, the relative displacement of the damping rubber ring 32 at the point P2 on the outer ring surface at an angle of θ relative to the point P1 on the inner ring surface is S(θ), and the shear strain is S(θ) / dj, where dj is the thickness of the damping rubber ring 32. The average shear strain can be obtained by performing an arithmetic average on the shear strain, and the maximum shear strain is the maximum value of the shear strain at each position in the circumferential direction. Generally, the above can be obtained by simulation using software such as Abaqus or ANSYS.

[0070] When performing optimization design, some size data that are strongly related to the modal margin requirement and the damping effectiveness requirement can be selected for optimization, such as the radial height of the main rib 311, the circumferential width of the brim, the thickness of the damping rubber ring 32, and the duty cycle of the auxiliary rib 312. The constraint conditions include that the thickness of the damping rubber ring 32 covering the top end of the main rib 311 is greater than or equal to 0.25 mm, and the radius of the fillet 303 between the brim 302 and the inner ring surface of the rigid restraint ring 31 is greater than 0.5 mm.

[0071] The higher the radial height of the main rib 311, the greater the radial stiffness at the major and minor axes, and the second-order elliptical modal frequency is significantly improved. For example, the radial height of the main rib 311 can be set in the range of 0.9 mm-1.2 mm.

[0072] The increase in the circumferential width of the brim can effectively improve the bending resistance of the main rib 311 and further improve the second-order elliptical modal frequency. For example, the circumferential width of the brim can be set in the range of 1.8 mm-2.2 mm.

[0073] The increase in the thickness of the damping rubber ring 32 can effectively improve the damping performance and reduce the average shear strain and the maximum shear strain. For example, the thickness of the damping rubber ring 32 can be set in the range of 0.35 mm-0.45 mm.

[0074] The smaller the duty cycle of the auxiliary rib 312, the greater the effective damping area, but too small duty cycle will result in a decrease in the stiffness of the rigid restraint ring 31. Therefore, a reasonable duty cycle also has an important influence on the damping effectiveness requirement and the modal margin requirement. For example, the duty cycle can be set in the range of 0.7-0.8.

[0075] By changing the above design variables, setting the constraint conditions and optimization target requirements, a damping assembly 30 with good modal and damping performance can be obtained. The optimization process can be realized by using existing finite element software such as ANSYS software.

[0076] The above is only some specific embodiments of the present application, and any improvement made on the basis of the concept of the present application is considered to be within the scope of protection of the present application.

Claims

1. A direct drive actuator for a robotic finger joint, characterized by, The application relates to an outer rotor motor, a harmonic reducer and a damping assembly. The outer rotor motor comprises an outer rotor. The harmonic reducer comprises a flexible bearing, a flexible gear and a steel gear. The damping assembly comprises a rigid restraint ring and a damping rubber ring. The outer ring surface of the rigid restraint ring is matched and fixedly connected with the inner ring of the flexible bearing. The inner ring surface of the rigid restraint ring is circular. The outer ring surface of the damping rubber ring is fixedly connected with the inner ring surface of the rigid restraint ring. The inner ring surface of the damping rubber ring is fixedly connected with the outer peripheral surface of the outer rotor. The inner ring surface of the rigid restraint ring is provided with main ribs at both ends in the long axis direction and both ends in the short axis direction.

2. The direct drive actuator for a robotic finger joint of claim 1, wherein, The damping rubber ring has a loss factor of any one of 0.2-0.5 and a thermal conductivity greater than 0.5 MPa-2.5 MPa in the working temperature range.

3. The direct drive actuator for a robotic finger joint of claim 1, wherein, The main ribs are raised along the radial direction and are sunken in the inner ring surface of the damping rubber ring. ； The rigid restraint ring is further provided with auxiliary ribs between adjacent main ribs.

4. The direct drive actuator for a robotic finger joint of any of claims 1-3, wherein, The height of the auxiliary ribs is smaller than that of the main ribs.

5. The direct drive actuator for a robotic finger joint of claim 4, wherein, The outer peripheral surface of the outer rotor is provided with a limiting protrusion.

6. The direct drive actuator for a robotic finger joint of claim 1, wherein, The limiting protrusion and the auxiliary ribs have an overlapping part in the radial direction and a preset gap in the circumferential direction.

7. The direct drive actuator for a robotic finger joint of claim 5, wherein, The surface of the limiting protrusion is provided with an elastic rubber sleeve. The preset gap dt is determined according to the following formula: dt=d0+ds+dr. Wherein, d0 is the minimum safety gap, ds is the gap error caused by the manufacturing and assembling process, and dr is the gap change caused by the thermal expansion of the rigid restraint ring and the limiting protrusion. dr is determined according to the following formula: Wherein, r2 is the distance between the top end of the auxiliary rib and the center of the outer rotor, Delta alpha is the difference between the thermal expansion coefficients of the limiting protrusion and the rigid restraint ring, and Delta T is the maximum working temperature difference. A plurality of auxiliary ribs are arranged between adjacent main ribs. The plurality of auxiliary ribs are uniformly distributed in an arc range with a central angle of 20-30 degrees. The duty ratio of the plurality of auxiliary ribs in the arc range is any value in the range of 70-80%. The main rib comprises a vertical part and a brim part. The vertical part extends along the radial direction. The brim part extends along the circumferential direction and is connected with the inner ring surface of the rigid restraint ring and the vertical part on both sides. The size of the main rib, the thickness of the damping rubber ring, the position, quantity and size of the auxiliary rib are determined according to the modal margin requirement and the damping effectiveness requirement. The modal margin requirement comprises that the ratio between the difference between the second-order elliptical modal frequency of the damping assembly and 2 times the fundamental frequency of the outer rotor motor and the fundamental frequency is greater than a ratio threshold value. The damping effectiveness requirement comprises that the average shear strain of the damping rubber ring is less than a first strain threshold value, and the maximum shear strain of the damping rubber ring is less than a second strain threshold value.

Images