Variable stiffness rotary joint based on a cross-section crimped elastic beam

Abstract

The application discloses a variable stiffness rotary joint based on a cross-section crimping elastic beam, and the crimping elastic beam is driven to convert between a flat cross-section and a circular cross-section through mechanical transmission, the wide-range adjustment of the stiffness of the joint is realized by the significant change of the inertia moment of the cross-section, the parasitic displacement in the adjustment process is avoided, and the self-locking characteristic of the worm gear is used to realize the power loss-free stiffness maintenance. The application realizes a variable stiffness joint with the advantages of compact structure, large adjustment range, no parasitic displacement and self-locking maintenance capacity.

Description

Technical Field

[0001] This invention relates to the technical field of biomimetic robot joint mechanisms, and in particular to a variable stiffness rotary joint based on a cross-sectionally curled elastic beam. Background Technology

[0002] Traditional rigid joints are prone to impact damage when robots come into contact with people or the environment due to their lack of compliance. To solve this problem, variable stiffness joints have emerged, which can adjust the joint stiffness in real time according to task requirements while ensuring torque output.

[0003] Existing variable stiffness joints mainly adopt the following technical approaches: 1. Drive method: Two motors are used to drive the elastic element in opposition, and the stiffness is adjusted by changing the preload. However, this method has the drawbacks of high energy consumption and complex control. 2. Changing the transmission ratio: The effective transmission ratio is changed by altering the force transmission path through mechanical structure, but the mechanism is complex and bulky; 3. Change the effective length of the elastic body or the pre-deformation method: The stiffness can be adjusted by changing the effective working length of the spring or by introducing pre-compression or pre-tension, but the adjustment range is limited and parasitic displacement is often accompanied during the adjustment process.

[0004] The aforementioned solutions generally suffer from drawbacks such as a small stiffness adjustment range, undesirable motion during adjustment, and the need for continuous energy consumption to maintain stiffness. Therefore, there is an urgent need for a variable stiffness joint that is compact, has a large adjustment range, is free of parasitic displacement, and possesses self-locking capabilities. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a variable stiffness rotary joint based on a cross-section curling elastic beam. The curling elastic beam is driven by mechanical transmission to switch between a flat cross-section and a circular arc cross-section. The joint stiffness can be adjusted over a wide range by utilizing the significant change in the moment of inertia of the cross-section, while avoiding parasitic displacement during the adjustment process. Furthermore, the self-locking characteristics of the worm gear are used to achieve zero-power stiffness maintenance.

[0006] The objective of this invention is achieved through the following technical solution: a variable stiffness rotary joint based on a cross-section curled elastic beam, comprising an input end assembly and an output end assembly. The output end assembly and the input end assembly are coaxially rotatably connected, forming the rotating body of the joint. The input end assembly includes an input end base and a stiffness adjustment mechanism. The stiffness adjustment mechanism includes a stiffness adjustment motor, a large gear, a small gear, a worm, a worm wheel, a transmission rod, a compliant rotary connecting rod, and a curled elastic beam. The fixed end of the stiffness adjustment motor passes through the output end assembly and is mounted on the input end base. The output end of the stiffness adjustment motor is connected to the large gear. Multiple small gears are evenly distributed along the circumference of the large gear and mesh with it. Each small gear... Each component is equipped with a worm gear, one end of which is coaxially mounted with a pinion, and the other end of which is mounted on the input end base. The worm gear meshes with the worm gear, forming a worm gear pair with self-locking characteristics. One end of the transmission rod is connected to the center of the worm gear and forms a synchronous transmission with the worm gear. The other end of the transmission rod is connected to the rotation center of the compliant rotating link. The compliant rotating link has at least two pairs of left-right arranged support arms, and the root of each support arm is provided with a compliant hinge. All support arms can rotate around the rotation center within a preset angle range. Each pair of support arms is hinged to a flexible elastic beam, and all flexible elastic beams are arranged radially along the center of the input end base. The flexible elastic beams are mounted on the input end base.

[0007] Furthermore, the input terminal assembly includes an input terminal housing; the input terminal housing is connected to the input terminal base, and the upper surface of the input terminal housing has a pre-set joint motor mating hole.

[0008] Furthermore, the joint includes a bearing; the output assembly is coaxially rotatably connected to the center of the input base via the bearing.

[0009] Furthermore, the center of the input end base is equipped with an intermediate support with a reserved bearing mounting position. A cylindrical support is formed on the outer side of the intermediate support. The cylindrical support has multiple transmission rod mounting holes for the transmission rod to pass through. The inner wall of the cylindrical support has multiple mounting seats for mounting a flexible beam.

[0010] Furthermore, one end of the rollable elastic beam is connected to the mounting base, and the rollable elastic beam is provided with a sliding groove. The length direction of the sliding groove is consistent with the length direction of the rollable elastic beam. The sliding groove is connected to the intermediate support through a pin to form a sliding groove-pin mating structure, which is used to release the radial displacement of the rollable elastic beam caused by rolling and joint rotation.

[0011] Furthermore, the flexible elastic beam is made of a metal material with a high elastic limit, including spring steel or beryllium bronze, and the thickness of the flexible elastic beam is 0.3mm~1.0mm and the width is 30mm.

[0012] Furthermore, the flexible beam can be rolled into a circular arc cross-section, the central angle of which ranges from 60° to 180°.

[0013] Furthermore, the stiffness adjustment motor is installed inside the bearing, and the output end of the stiffness adjustment motor is connected to the large gear through a gear flange.

[0014] Furthermore, the compliant rotating connecting rod and the flexible elastic beam are installed inside the cylindrical support, the large gear and the small gear are installed above the cylindrical support, the worm and the worm wheel are installed on the outside of the cylindrical support, and the transmission rod passes through the transmission rod mounting hole.

[0015] Furthermore, there are four small gears.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Wide range of stiffness adjustment: By utilizing the configuration change of the flexible beam from a flat rectangle to a circular arc section, the moment of inertia of the section is increased.

[0017] 2. No parasitic displacement: The curling process mainly changes the cross-sectional shape. The neutral axis of the curlable elastic beam remains basically straight. When adjusting the stiffness, it hardly causes relative rotation between the input and output ends, thus avoiding the problem of zero-position drift.

[0018] 3. Self-locking and zero-power maintenance: Using worm gear transmission, the current stiffness state can be locked after adjustment without continuous power supply, which significantly reduces energy consumption; when the robot loses power or stops in an emergency, the stiffness will not be suddenly lost, ensuring high safety.

[0019] 4. Multi-group synchronous adjustment and symmetrical load bearing: A large gear synchronously drives four small gears to achieve synchronous bending adjustment of four sets of elastic beams; the four pairs of elastic beams are evenly distributed along the circumference, and the torque transmission is uniform and symmetrical, without the problem of off-center load.

[0020] 5. Radial displacement release and deformation coordination: The flexible elastic beam is connected to the output end through the cooperation of the slide and the pin, which effectively releases radial displacement and ensures that the curling deformation and the joint rotation deformation do not interfere with each other. The joint stiffness is determined only by the bending stiffness of the elastic beam.

[0021] 6. Compact structure and high integration: The drive, transmission, elastomer and adjustment mechanism are integrated in the cylindrical space, which makes high space utilization. Attached Figure Description

[0022] Figure 1 This is an isometric view of the overall assembly of the present invention.

[0023] Figure 2This is a schematic diagram of the mounting structure of the large gear, small gear, worm, worm wheel, output end assembly, and input end base.

[0024] Figure 3 This is a front view of the mounting structure of the large gear, small gear, worm, worm wheel, output end assembly, and input end base.

[0025] Figure 4 This is a schematic diagram of the installation structure of the pinion, worm gear, worm wheel, transmission rod, compliant rotating connecting rod, flexible elastic beam, and input end base.

[0026] Figure 5 This is a schematic diagram of the installation structure of four pairs of flexible beams and compliant rotating links.

[0027] Figure 6 This is a top view of the mounting structure of the flexible beam, the compliant rotating link, and the input end base.

[0028] Explanation of the labels in the diagram: 1-Input end base; 2-Input end housing; 3-Output end base; 4-Bearing; 5-Stiffness adjustment motor; 6-Large gear; 7-Small gear; 8-Worm; 9-Worm wheel; 10-Transmission rod; 11-Compliant rotating connecting rod; 12-Compliant hinge; 13-Flexible elastic beam; 14-Support; 15-Pin; 16-Slide groove; 17-Intermediate support; 18-Fixing boss; 19-Gear flange. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. Example 1

[0030] See Figures 1 to 6 As shown, this embodiment provides a variable stiffness rotary joint based on a cross-sectional curled elastic beam, including an input end assembly and an output end assembly.

[0031] The input assembly includes an input housing 2, an input base 1, and a stiffness adjustment mechanism. The input housing 2 is connected to the input base 1 via screw holes on its inner wall. The upper surface of the input housing 2 has a pre-set joint motor mating hole for connecting an external drive motor. The output assembly includes an output base 3, which is coaxially rotatably connected to the center hole of the input base 1 via a bearing 4, forming the rotating body of the joint.

[0032] The stiffness adjustment mechanism includes a stiffness adjustment motor 5, a large gear 6, four small gears 7, four worm gears 8, four worm wheels 9, a transmission rod 10, a compliant rotating connecting rod 11, and four pairs of flexible elastic beams 13.

[0033] Center drive and synchronous transmission: The stiffness adjustment motor 5 passes through the inner hole of the output end base 3 and is fixed to the input end base 1. The output shaft of the stiffness adjustment motor 5 is connected to a large gear 6 via a gear flange 19. The large gear 6 is located in the central area of ​​the input end base 1. Four small gears 7 are evenly distributed along the circumference of the large gear 6, and all four small gears 7 mesh with the large gear 6 simultaneously. When the large gear 6 rotates, it synchronously drives the four small gears 7 to rotate, ensuring the synchronicity of the four sets of adjustment mechanisms.

[0034] Worm gear drive: Each pinion 7 is coaxially coupled to a worm 8, with no relative circumferential rotation between the worm 8 and the pinion 7. The two ends of the worm 8 are hinged to fixed bosses 18 formed around the input end base 1 via bearings. Each worm 8 is coupled to a corresponding worm wheel 9, which is hinged to the outer wall of the input end base 1. The worm wheel 9 and the worm 8 form a worm gear pair with self-locking characteristics, meaning that the worm wheel 9 can only be driven by the worm 8, and cannot be driven in the opposite direction.

[0035] Compliant connecting rod and transmission rod: A transmission rod 10 passes through the center of each worm gear 9. The transmission rod 10 is coaxial with the worm gear 9 and can rotate synchronously. A compliant rotating connecting rod 11 is fixedly connected to the upper end of the transmission rod 10. The compliant rotating connecting rod 11 has four arms, and each arm has a compliant hinge 12 at its root. The arm can rotate within a certain angle range around the rotation center of the compliant hinge 12.

[0036] Arrangement and connection of the rollable elastic beams: Four pairs of rollable elastic beams 13 are evenly distributed along the circumference and radially arranged along the center of the input end base, with adjacent pairs forming a 90° angle. Each rollable elastic beam can be rolled into a circular arc cross-section, the central angle of which ranges from 60° to 180°. The rollable elastic beams are made of a high elastic limit metal material, including spring steel or beryllium bronze, and the thickness of the rollable elastic beam is 0.3mm to 1.0mm, and the width is 30mm.

[0037] One end of each flexible beam 13 is fixed to a support 14 on the inner wall of the input end base 1 via a screw hole on the center line. This fixing method uses a single row of center screws, allowing the flexible beam to bend and deform freely in the width direction. At the same time, the inner side of each flexible beam 13 is provided with two hinge holes, which are respectively connected to the hinge holes at the ends of a pair of support arms of the compliant rotating connecting rod 11 via pin engagement.

[0038] Each rollable elastic beam 13 is provided with a groove 16, which is connected to the intermediate support 17 of the output end base 3 via a pin 15. The pin 15 can slide within the groove 16 along the length of the rollable elastic beam 13. This groove-pin mating structure can release the radial displacement of the rollable elastic beam 13 caused by rolling and joint rotation without hindering the roll and bending deformation of the rollable elastic beam 13. This ensures that the stiffness of the variable stiffness rotary joint during rotation is determined only by the bending stiffness of the rollable elastic beam 13, and is not affected by the additional stiffness caused by radial constraints.

[0039] The working process of the variable stiffness rotary joint based on the cross-section curled elastic beam provided in this embodiment is as follows: Low stiffness state (compliant mode): The stiffness adjustment motor 5 is not working or drives the compliant rotating link 11 to the initial position, and the flexible beam 13 is in a flat cross-section state. At this time, when the joint is subjected to an external torque, the flexible beam 13 can bend and deform more easily around the radial axis, and relative rotation can occur between the input end component and the output end component. The joint exhibits low stiffness, which is suitable for human-computer interaction or collision absorption scenarios.

[0040] Stiffness adjustment process: When joint stiffness needs to be increased, the stiffness adjustment motor 5 rotates forward, driving the large gear 6 to rotate. The large gear 6 synchronously drives the four small gears 7 and the four coaxial worm gears 8 to rotate. The worm gears 8 drive the worm wheel 9 to rotate, and the worm wheel 9 drives the compliant rotating link 11 to rotate synchronously through the transmission rod 10. Since the end of the support arm of the compliant rotating link 11 is connected to the two hinged feet at the upper end of the flexible elastic beam 13, when the support arm rotates around the rotation center of the compliant hinge 12, it applies a curling torque along the width direction to the flexible elastic beam 13. Under the action of the curling torque, the cross section of the flexible elastic beam 13 gradually curls from a flat rectangle to a circular arc cross section. As the curling angle increases, the moment of inertia of the circular arc cross section increases significantly, and the stiffness of the flexible elastic beam 13 against bending around the radial axis is greatly improved. Since the four pairs of flexible elastic beams 13 are arranged in parallel and adjusted synchronously, the equivalent rotational stiffness of the entire joint is increased accordingly.

[0041] High stiffness state (load-bearing mode): When the flexible beam 13 is rolled to a set angle (e.g., a central angle of 120°), the stiffness adjustment motor 5 stops. Due to the self-locking characteristic of the worm gear pair, the worm wheel 9 cannot drive the worm 8 in reverse, the position of the compliant rotating link 11 is locked, and the flexible beam 13 remains in the rolled state. At this time, the joint has high stiffness and can withstand a large load, making it suitable for precise trajectory tracking or heavy-duty operation.

[0042] Stiffness reduction process: When it is necessary to reduce the joint stiffness, the stiffness adjustment motor 5 reverses, and the compliant rotating link 11 rotates in the opposite direction, releasing the curling constraint on the rollable elastic beam 13. Under the action of its own elastic restoring force, the rollable elastic beam 13 unfolds and returns to its flat cross-section state, thus reducing the joint stiffness.

[0043] End constraint release and deformation coordination: When the joint rotates and the input and output components generate relative displacement, the lower end of the rollable elastic beam 13 will generate radial displacement. The mating structure of the groove 16 and the pin 15 allows this radial displacement to be released freely, avoiding additional constraint reaction force on the output base 3. At the same time, the upper end of the rollable elastic beam 13 is fixed by a central screw and hinged at both sides. The central screw provides axial positioning, and the hinged points on both sides transmit the roll-up torque. This "one-point fixing + two-point driving" layout ensures reliable installation of the rollable elastic beam 13 and avoids excessive constraint on the roll-up deformation. Example 2

[0044] The variable stiffness rotary joint based on a cross-section curling elastic beam provided in this embodiment differs from that in Embodiment 1 in that it includes a mechanical limiting structure, which is disposed on the compliant rotary four-arm connecting rod or the curling elastic beam, to limit the maximum curling angle of the curling elastic beam and prevent the elastic beam from entering a reverse steady state or forming a closed cylinder. Example 3

[0045] The variable stiffness rotary joint based on a cross-section curling elastic beam provided in this embodiment has an outer diameter of 150 mm and an axial height of 50 mm. The input base 1 and output base 3 are made of aluminum alloy. Four pairs (eight in total) of curlable elastic beams 13 are evenly distributed along the circumference. The curlable elastic beams 13 are made of beryllium bronze C17200 material with a thickness of 0.5 mm, a width of 20 mm, and a length of 45 mm. The stiffness adjustment motor 5 is a miniature DC geared motor with a rated torque of 0.15 N·m. The large gear 6 has a module of 1.0 and 60 teeth; the small gear 7 has a module of 1.0 and 15 teeth, with a single-stage transmission ratio of 4:1. The worm gear 8 has a module of 0.5, and the worm wheel 9 has 30 teeth, with a worm-wheel transmission ratio of 30:1. The total transmission ratio is 120:1, which can amplify the motor torque to 18 N·m, sufficient to overcome the curling resistance of the curlable elastic beams 13.

[0046] The compliant rotating link 11 is machined from a single piece of aluminum alloy, and the compliant hinge 12 is formed by local thinning to create an elastic hinge, allowing the support arm to rotate within a range of ±15°. The maximum bending angle of the flexible beam 13 is limited to 120° (central angle).

[0047] Experiments showed that when the flexible beam 13 was fully unfolded, the joint rotational stiffness was approximately 8 N·m / rad; when it was rolled up to 120°, the joint rotational stiffness increased to approximately 200 N·m / rad, with a stiffness adjustment factor of approximately 25 times. During the adjustment process, the parasitic rotation angle between the input and output ends was less than 0.3°.

[0048] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any changes made in accordance with the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A variable stiffness rotary joint based on a cross-sectionally curled elastic beam, comprising an input end assembly and an output end assembly, wherein the output end assembly and the input end assembly form a coaxial rotatable connection, constituting the rotating body of the joint, characterized in that: The input terminal assembly includes an input terminal base and a stiffness adjustment mechanism. The stiffness adjustment mechanism includes a stiffness adjustment motor, a large gear, a small gear, a worm, a worm wheel, a transmission rod, a compliant rotating connecting rod, and a flexible elastic beam. The fixed end of the stiffness adjustment motor passes through the output terminal assembly and is mounted on the input terminal base. The output end of the stiffness adjustment motor is connected to the large gear. Multiple small gears are evenly distributed along the circumference of the large gear and mesh with it. Each small gear is equipped with a worm, one end of which is coaxially mounted with the small gear, and the other end of which is mounted on the input terminal base. Above, the turbine and worm gear mesh together to form a worm gear pair with self-locking characteristics; one end of the transmission rod is connected to the center of the turbine and forms synchronous transmission with the turbine, and the other end of the transmission rod is connected to the rotation center of the compliant rotating link; the compliant rotating link has at least two pairs of left and right arranged support arms, and the root of the support arms is provided with a compliant hinge, and all support arms can rotate around the rotation center within a preset angle range; each pair of support arms is hinged to a flexible elastic beam, and all flexible elastic beams are arranged radially along the center of the input end base, and the flexible elastic beams are mounted on the input end base.

2. The variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 1, characterized in that: The input terminal assembly includes an input terminal housing; the input terminal housing is connected to the input terminal base, and the upper surface of the input terminal housing has a pre-set joint motor mating hole.

3. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 1, characterized in that: Includes bearings; the output assembly is coaxially rotatably connected to the center of the input base via the bearings.

4. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 3, characterized in that: The input end base has a central support with a reserved bearing mounting position. A cylindrical support is formed on the outer side of the central support. The cylindrical support has multiple transmission rod mounting holes for the transmission rod to pass through. The inner wall of the cylindrical support has multiple mounting seats for mounting a flexible beam.

5. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 4, characterized in that: One end of the rollable elastic beam is connected to the mounting base. The rollable elastic beam is provided with a sliding groove. The length direction of the sliding groove is consistent with the length direction of the rollable elastic beam. The sliding groove is connected to the intermediate support through a pin to form a sliding groove-pin mating structure, which is used to release the radial displacement of the rollable elastic beam caused by rolling and joint rotation.

6. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 1, characterized in that: The flexible beam is made of a metal material with a high elastic limit, including spring steel or beryllium bronze. The thickness of the flexible beam is 0.3mm to 1.0mm and the width is 30mm.

7. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 1, characterized in that: The flexible beam can be rolled into a circular arc cross-section, the central angle of which ranges from 60° to 180°.

8. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 3, characterized in that: The stiffness adjustment motor is installed inside the bearing, and the output end of the stiffness adjustment motor is connected to the large gear through a gear flange.

9. A variable stiffness rotary joint based on a cross-sectional curling elastic beam according to claim 4, characterized in that: The compliant rotating connecting rod and the flexible elastic beam are installed inside the cylindrical support, the large gear and the small gear are installed above the cylindrical support, the worm and the worm wheel are installed on the outside of the cylindrical support, and the transmission rod passes through the transmission rod mounting hole.

10. A variable stiffness rotary joint based on a cross-sectional curled elastic beam according to claim 1, characterized in that: There are four small gears.

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