Force application adjusting mechanism for adjusting pressure of radial abutting spring

Abstract

The invention discloses a force application adjusting mechanism for adjusting the pressure of a radial abutting spring, which comprises a nut sleeve, two ends of the inner ring of the nut sleeve are respectively provided with a section of symmetrical internal thread and are respectively matched on an adjusting ring which is circumferentially arranged at intervals, and the outer surface of the adjusting ring is provided with an external thread which is matched with the internal thread of a nut. The force application adjusting mechanism further comprises an adjusting ring rotation stopping structure used for preventing the adjusting ring from rotating, the force application adjusting mechanism further comprises a spring seat which abuts against the outer end of the spring in the radial direction, and the upper side and the lower side of the outer end of the spring seat are each slidably connected with an obliquely-arranged adjusting baffle in an abutting mode. The outer ends of the two adjusting baffles are close to each other, the inner ends of the two adjusting baffles are opened to form a transverse splayed shape, the inner ends of the two adjusting baffles are rotatably connected with the corresponding adjusting rings at the upper end and the lower end, and the outer ends of the adjusting baffles are rotatably connected with a retainer. The device has the advantages that the adjusting range is continuous and controllable, large-range adjustment can be achieved with small energy loss, and the device is extremely stable and reliable.

Description

[0001] This application is a divisional application of the patent application No. 202310327105.7, filed on March 30, 2023, entitled "A Linear Variable Stiffness Joint". Technical Field

[0002] This invention relates to a linear variable stiffness joint, and more specifically to a force adjustment mechanism for adjusting the radial contact spring pressure. Background Technology

[0003] In the process of fracture fixation, it is usually necessary to place an external fixator or fixation device on the patient to avoid secondary injury and better promote normal healing of the fracture site. In the early days when medical technology was not advanced, splints or plaster casts were usually used to fix the fracture site. These fixation methods were too rigid and not conducive to the later growth and recovery of the fracture site.

[0004] Foreign patents such as US6030386, US8439914, and WO2011163406, as well as Chinese patent CN201810623485.8, have all proposed a type of six-axis parallel external fixation device. This device consists of six branches (support arms) with identical topological structures and two fixation rings. The surgeon uses metal wires (Kirschner wires) to fix the two fixation rings to the bone fragments at both ends of the fracture. The six branches are connected to the two fixation rings via hinges at both ends. By adjusting the length of the six branches in a specific pattern, six degrees of freedom relative motion between the two fixation rings can be generated, which can precisely correct spatial deformities of the fracture and achieve fracture reduction. After fracture reduction, maintaining the length of the branches, the six-axis parallel external fixation device maintains the relative stability of the fracture ends. Therefore, this type of six-axis parallel external fixation device has both the functions of reduction and fixation of fracture ends and has broad application prospects.

[0005] However, existing six-axis parallel external fixation devices still rely on rigid adjustment of the branches, meaning the branches remain rigid before and after adjustment. In reality, bone growth and density change during the early and late stages of fracture healing, leading to different requirements for the rigidity and flexibility of the fixation support. Therefore, existing six-axis parallel external fixation devices cannot adequately meet the needs of fracture healing and are detrimental to recovery. It is necessary to consider designing an axially adjustable joint component to better assist fracture healing.

[0006] Furthermore, variable stiffness devices are now widely used in various fields, with different fields having different requirements. For example, in the automotive industry, adjusting the stiffness of the car suspension can improve environmental adaptability and ride comfort. In robotics, robotic arms need high stiffness to ensure positional accuracy, while also requiring a certain degree of compliance to ensure safe interaction, and the stiffness needs to be continuously adjusted according to the load mass. In aerospace, high-precision, high-stability remote sensing satellites require variable stiffness devices to suppress on-orbit vibrations caused by moving parts such as momentum wheels, CMGs (Control Moment Gyroscopes), and refrigerators. The wider the stiffness range of the variable stiffness device, the better the vibration suppression effect, and the more conducive it is to achieving the high precision and stability of the system. Additionally, when variable stiffness devices and the isolated equipment experience the active phase of launch, the dynamic response is amplified at the resonant frequency. Higher stiffness of the variable stiffness device reduces the impact of resonance amplification, thus better ensuring the performance and safety of the variable stiffness device and the isolated equipment.

[0007] Therefore, the applications of variable stiffness devices are becoming increasingly diverse. However, existing variable stiffness devices have limited stiffness variations, complex structures, and large drive units, making them difficult to integrate into robots or vibration isolation devices for instruments, and thus unable to better meet the needs of the aforementioned applications. Summary of the Invention

[0008] To address the shortcomings of the prior art, the technical problem to be solved by this invention is: how to provide a linear variable stiffness joint that is easy to adjust, has a large adjustable range, good stability, and good safety; this invention also provides a force adjustment mechanism for adjusting the radial contact spring pressure in the linear variable stiffness joint, making its adjustment range continuously controllable, achieving a large range of adjustment with minimal energy loss, and being extremely stable and reliable.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A linear variable stiffness joint includes a first connecting plate and a second connecting plate arranged coaxially opposite each other. The first connecting plate has a connecting shaft arranged axially at one end opposite the second connecting plate. A plurality of helical abutment springs are evenly distributed circumferentially at the outer end of the connecting shaft. The abutment springs are arranged diametrically and their inner ends abut against the connecting shaft. Their outer ends are connected to the second connecting plate through a force adjustment mechanism.

[0010] In this way, when the variable stiffness joint is in use, the first connecting plate and the second connecting plate can each be installed on a part of the support arm, so that the two parts of the support arm are connected as a whole by the first connecting plate and the second connecting plate. During use, the force adjustment mechanism applies force to the abutment spring, and the magnitude of the abutment force of the abutment spring on the connecting shaft is adjusted, thereby realizing the adjustment of the axial stiffness of the support arm. This has the characteristics of simple structure and good stability.

[0011] Furthermore, the first connecting disc is fixedly connected to the connecting shaft at its center position via a connecting shaft fixing bolt.

[0012] This facilitates the design of the structure and the installation and disassembly of components.

[0013] Furthermore, the outer peripheral surface of the connecting shaft facing the abutting spring has an outward mounting protrusion, and the outer end of the mounting protrusion is provided with a spring mounting groove, and the inner end of the abutting spring abuts against the inner end of the spring mounting groove.

[0014] This better ensures the stability and reliability of spring installation, guarantees that the force applied by the spring is directly opposite the axis, and ensures the stability and reliability of stiffness adjustment.

[0015] Furthermore, the force adjustment mechanism includes a nut sleeve, with symmetrical internal threads at both ends of the inner ring of the nut sleeve, which respectively engage with an adjusting ring spaced circumferentially. The outer surface of the adjusting ring has external threads that engage with the internal threads of the nut. The second connecting plate is also provided with an adjusting ring anti-rotation structure to prevent the adjusting ring from rotating. The force adjustment mechanism also includes a spring seat disposed at the outer end of the spring. The upper and lower sides of the outer end of the spring seat are slidably abutted by an obliquely arranged adjusting baffle. The outer ends of the two adjusting baffles are close to each other and the inner ends are open in a horizontal V-shape. The inner ends of the two adjusting baffles and the corresponding adjusting rings at the upper and lower ends are rotatably connected. The outer ends of the adjusting baffles and a retainer relatively fixed on the second connecting plate are rotatably connected.

[0016] In this way, during use, simply rotating the nut sleeve drives the two adjusting rings to move linearly in the same or opposite directions, which in turn moves the inner end of the adjusting baffle along the axial direction of the joint, changing the tilt angle of the adjusting baffle. This, in turn, compresses or releases the abutment spring, increasing or decreasing the radial pressure of the abutment spring on the connecting shaft, thereby adjusting the axial mobility of the connecting shaft, i.e., adjusting the axial stiffness of the joint. This method, using a lead screw and nut drive combined with a slant plate compression transmission to adjust the spring clamping force and thus the axial stiffness, has the following advantages: First, the overall structure is compact, and the force transmission is stable and reliable. The applied force is transformed from circumferential rotational motion through multiple force transmissions and conversions before being converted into radial motion force, resulting in good self-locking properties and preventing easy instability. Second, the multiple force transmissions and conversions (especially the slant plate's engagement with the inclined plane to convert the direction of force transmission) result in a very large transmission ratio, allowing for a large stiffness adjustment effect with a small input, making the adjustable range of axial stiffness very large. Furthermore, by pre-setting the initial tilt angle of the adjusting baffle, the control and adjustment of the required precision can be easily achieved. The smaller the tilt angle of the adjusting baffle, the greater the stiffness variation can be achieved with a smaller adjustment distance. Finally, and importantly, this structure relies on the radial compression of the connecting shaft by a spring to achieve axial stiffness adjustment. Therefore, changes in the axial load on the connecting disc during adjustment have minimal impact on the magnitude of the spring's radial compression force, resulting in excellent stability and reliability. Thus, this force adjustment mechanism can achieve a wide range of continuously controllable stiffness variations, achieving broad stiffness adjustment with minimal energy loss, and is extremely stable and reliable.

[0017] Furthermore, a roller is provided at the outer end of the spring seat along the joint axis. The axis of the roller is perpendicular to the axis of the spring. The outer circumferential side of the roller is in contact with the adjusting baffle.

[0018] In this way, the rolling action of the rollers can better achieve the transmission of force between the inclined adjustment baffle and the abutment spring, ensuring better reliability.

[0019] Furthermore, a threaded adjustment hole is provided at the middle of the outer end of the spring seat, directly opposite the spring. An adjustment bolt is installed in the threaded adjustment hole, and the front end of the adjustment bolt abuts against the end of the spring.

[0020] In this way, the preload of the adjusting spring can be easily changed by adjusting the bolt when needed.

[0021] Furthermore, the inner end of the spring seat extends forward to form a load-bearing sleeve, which abuts against the outer end of the spring located inside the load-bearing sleeve. The load-bearing sleeve has a mating section that is slidably inserted into a spring mounting groove on the connecting shaft.

[0022] In this structure, the front section of the bearing sleeve is inserted into the spring mounting groove, forming a small gap between the outer wall of the fitting section and the inner wall of the spring mounting groove. This creates a crucial effect: if a sudden, large axial force is generated between the first and second connecting discs due to an accident (such as a fall or collision), the resulting axial movement of the first and second connecting discs allows the spring mounting groove to directly engage with the bearing sleeve fitting section, causing the entire spring seat to move in the same direction. This presses the outer end of the spring seat against the corresponding adjusting baffle, which in turn compresses the spring seat inward. This, in turn, causes the spring to clamp the connecting shaft, thereby increasing the axial stiffness and enabling it to withstand or offset some of the axial force generated by the accident. This achieves an adaptive emergency protection effect, reducing or avoiding safety risks caused by accidents. Furthermore, the thread between the nut sleeve and the adjusting ring is a self-locking thread, further ensuring the realization of the aforementioned adaptive emergency protection effect.

[0023] Furthermore, the retainer is cylindrical in shape and coaxially spaced inside the nut sleeve. An adjustment baffle mounting window is opened in the middle of the retainer, and the outer end of the adjustment baffle is rotatably mounted on the adjustment baffle mounting window. Both ends of the outer circumference of the retainer have an inwardly recessed limiting groove. Each end of the inner cavity of the nut sleeve has a threaded ring fixed inward. The internal threads at both ends of the nut sleeve are set on the inner ring surface of the threaded ring. The threaded ring is rotatably engaged and limited in the limiting groove. Multiple clearance windows are also opened in the limiting groove of the retainer. Multiple outwardly distributed mounting protrusions are evenly distributed on the outer surface of the adjusting ring. The external threads on the adjusting ring are set on the outer end surface of the mounting protrusions. The mounting protrusions pass through the clearance windows and are threadedly engaged with the outer end of the threaded ring. The two sides of the mounting protrusions and the two sides of the clearance windows are attached to form the anti-rotation structure of the adjusting ring.

[0024] In this way, the entire structure is ingenious, compact, stable and reliable, avoiding mutual interference of motion and ensuring the stability of motion and force transmission.

[0025] Alternatively, the outer surface of the nut sleeve is evenly provided with axial vertical grooves and rotation scales. This facilitates manual rotation of the nut sleeve to adjust its stiffness.

[0026] Alternatively, a nut adjusting motor is also installed on the second connecting plate, and the nut adjusting motor is connected to the nut sleeve drive.

[0027] This allows for convenient electric control adjustment of stiffness via a motor that adjusts the nut. In practice, the nut adjusting motor is connected to a computer, enabling automatic control based on preset programs and instructions.

[0028] In summary, the joint of the present invention has the advantages of convenient adjustment, large adjustable range, good stability, and good safety. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of an external fixation and retention system that uses the structure of the present invention in an embodiment.

[0030] Figure 2 for Figure 1 A structural diagram in use.

[0031] Figure 3 for Figure 1 A schematic diagram of the structure of a single support arm.

[0032] Figure 4 for Figure 3 sectional view of .

[0033] Figure 5 for Figure 3 A schematic diagram of a single variable stiffness joint.

[0034] Figure 6 for Figure 5 A sectional view of [the object].

[0035] Figure 7 for Figure 5 A schematic diagram after removing the nut sleeve.

[0036] Figure 8 for Figure 5 The diagram shows the structure after removing the cage, the upper half of the first connecting plate, and the second connecting plate.

[0037] Figure 9 for Figure 8 A schematic diagram of the three-dimensional structure.

[0038] Figure 10 for Figure 8 A schematic diagram of the structure of the separate connecting shaft and spring seat.

[0039] Figure 11 for Figure 10 sectional view of . Detailed Implementation

[0040] The present invention will be further described below with reference to an external fixation and retention system using the structure of the present invention. This external fixation and retention system belongs to the field of medical devices, but the specific application of the present invention is not limited to this field.

[0041] For specific implementation, please refer to Figures 1-11 A bone external fixation auxiliary retention system employing the structure of the present invention (see: Figure 1-4It includes two oppositely arranged fixing rings 4, and the fixing rings 4 are provided with a number of mounting holes to form a bone pin mounting structure. Multiple support arms 2 are also hinged between the two fixing rings. Each support arm 2 is also equipped with a variable stiffness joint 5 that can adjust the axial stiffness of the support arm.

[0042] Therefore, when using the device of this scheme, please refer to... Figure 2 Two fixation rings are fixed to both ends of the fracture site 1. The pin seats of the bone pins (Kirschner wires) are fixed to the fixation rings through the bone pin mounting structure. Then, the two fixation rings are fixedly connected to the bone fragments at both ends of the fracture site by the bone pins. The support arm can then provide fixation and support to both ends of the fracture site, avoiding secondary damage during the healing process. In this design, a variable stiffness joint is also installed on the support arm to adjust the axial stiffness of the support arm. Therefore, during use, the axial stiffness of the support arm can be adjusted to different stages of fracture healing. In the early stage, a higher stiffness can be maintained to keep the fracture ends fixed and grow rapidly. In the later stage, the stiffness can be reduced and the flexibility increased so that the support does not absorb all the energy during rehabilitation training, thus preventing stress shielding and allowing the newly grown bone to have more room to move, which better promotes bone healing and is more conducive to its healthy growth. Therefore, this design can better meet the requirements of different stages of fracture healing and is more conducive to fracture rehabilitation and growth. The fixation rings are provided with several mounting holes to form the bone pin mounting structure. In this way, the outer end of the bone pin can be fixed to a bone pin mounting base, which can be fixed to the fixing ring by bolts passing through the mounting hole. The structure is simple, easy to install, and allows for easy adjustment of the installation position of the bone pin in case of fracture.

[0043] The support arm 2 is also equipped with an axial length adjustment structure.

[0044] In this way, the length of each support arm can be adjusted as needed during the use of the equipment for fixation and during the rehabilitation of the fracture site, so as to better keep the two ends of the fracture in the correct posture position.

[0045] There are 6 support arms 2, which are diagonally staggered so that one end of each pair of adjacent support arms is close together and the other end is separated, forming a V-shape or inverted V-shape. The positions where each pair of support arms is connected on the fixing ring are evenly distributed circumferentially.

[0046] In this way, the six branches formed by the six support arms, together with the two fixed rings, can form a spatial parallel external fixed support with three rotational degrees of freedom and three translational degrees of freedom. This allows for easy adjustment of the three rotational and three translational degrees of freedom by adjusting the axial length of each support arm, thereby enabling spatial angle adjustment of any position of the fixed rings. In practice, the spatial angle adjustment process can be calculated using computer-aided methods, which is existing technology and will not be detailed here.

[0047] The fixing ring 4 is circular in shape and has three protruding connecting parts 6 evenly distributed around its perimeter. The ends of each pair of adjacent support arms 2 are connected to the connecting parts 6, and the connecting parts 6 of the two fixing rings 4 are offset by 60 degrees.

[0048] This ensures that the connection and installation of the support arm will not affect the area and structure where the bone pins are installed.

[0049] The two ends of the support arm 2 are respectively hinged by a Hooke hinge 3 and a fixing ring.

[0050] This allows the Hooke hinge to rotate in two directions, making it convenient and reliable for adjustment.

[0051] The axial length adjustment structure includes two halves that are axially connected to form the main body of the support arm. One half is the force-applying half 7, and the other half is the force-receiving half 8. A lead screw 9 is provided at the end of the force-applying half 7, extending outward along the axial direction. The rear end of the lead screw 9 is rotatably mounted on the force-applying half 7 and connected to the axial adjustment motor 10 on the force-applying half. The front end of the lead screw 9 is screwed through an adjusting nut 11 fixed at the end of the force-receiving half and is located in a lead screw holding cavity 12 inside the force-receiving half 8.

[0052] In this way, the lead screw can be driven to rotate by the axial adjustment motor. Due to the threaded engagement between the adjusting nut and the lead screw, and the fact that the adjusting nut is fixed to the force-bearing half and restricted from circumferential rotation by the Hooke's joint at the end, a lead screw-nut transmission pair can be formed, driving the force-bearing half to achieve axial extension and retraction adjustment. It features a simple structure and stable and reliable adjustment.

[0053] The lead screw holding cavity 12 has an inner cavity that is attached to the outer periphery of the lead screw 9.

[0054] This allows for better circumferential control of the lead screw, preventing wobbling that could affect fracture fixation; and better ensures stable and reliable readings from the pressure sensor.

[0055] The lead screw retaining cavity 12 has a pre-tightening chamber located on the outer periphery of the lead screw at its outer end. The pre-tightening chamber shell 13 is rigidly connected to the adjusting nut. The pre-tightening chamber has a spiral pre-tightening spring 14 movably sleeved on the lead screw. One end of the pre-tightening spring 14 abuts against a boss that protrudes outward from the circumference of the lead screw, and the other end abuts against one end of the inner cavity of the pre-tightening chamber.

[0056] This allows the lead screw and nut to be subjected to an axial preload by the preload spring, preventing axial wobble caused by thread clearance and thus affecting the fracture fixation effect; at the same time, it better ensures the stability and reliability of the pressure sensor's detection values.

[0057] The boss on the lead screw is formed by a preload nut 15 located in the preload chamber and threaded onto the lead screw.

[0058] This not only facilitates the setting and installation of the boss, but also allows for further adjustment of the preload nut's position on the lead screw to change the magnitude of the preload force, achieving a better preload effect without affecting the lead screw nut's own transmission.

[0059] The pre-tightening chamber shell 13 is a cylindrical component that is mounted and fixed on the force-bearing end half, and the adjusting nut is fixed to the outer end of the cylindrical component.

[0060] This makes the installation and setup of the structure more convenient.

[0061] The support arm 2 is also equipped with a pressure sensor 16 that detects its axial force.

[0062] This facilitates the detection of the axial force on the support arm, providing information for adjustment and feedback control.

[0063] The pressure sensor 16 is installed between the end of the force-bearing half and the corresponding Hooke's joint, making it easy to install.

[0064] This also includes a computer (not shown in the computer structure diagram), one end of which is connected to a pressure sensor, and the other end is connected to an axial adjustment motor. This computer-aided calculation and control greatly reduces the computational difficulty of manual operation and improves the ease of use of the equipment.

[0065] The computer includes a fracture simulation module, a control center, and an adjustment output control module connected in sequence. The control center includes an adjustment parameter calculation module. The computer also has a human-machine interface (HMI) connected to the fracture simulation module, the adjustment parameter calculation module, and the adjustment output control module. The fracture simulation module can calculate and simulate the bone structure of the fractured area using imported multi-angle X-ray images (the calculation method is existing technology and will not be detailed here), obtaining bone deformity parameters. The adjustment parameter calculation module can calculate the equipment installation posture based on the obtained fracture structure and bone deformity parameters (including the deformation of the fractured bone), combined with data and / or manual judgment. The adjustment parameter calculation module can also determine the parameters to be adjusted based on the fracture structure and bone deformity parameters, combined with feedback signals from pressure sensors after equipment installation. The adjustment output control module converts the parameters to be adjusted into output control signals and sends them to the axial adjustment motor. The HMI is used to input operation commands and display the obtained graphics and output commands. This facilitates automated detection and adjustment calculations via computer assistance, better supporting the device's fixation and orthopedic operation. During device use, the computer can monitor pressure sensor data feedback in real time to determine whether adjustment of the support arm's axial length is necessary to ensure effective fracture healing.

[0066] The computer control center also includes a support arm stiffness timing adjustment module. This module is connected to a pressure sensor, a human-machine interface (HMI), and an adjustment output control module, which in turn is connected to the variable stiffness joint. The support arm stiffness timing adjustment module generates a variable stiffness joint adjustment signal based on the adjustment parameters (time and stiffness) input through the HMI and the signal detected by the pressure sensor. This signal is then output to the variable stiffness joint via the adjustment output control module to achieve control and adjustment. This allows for better use of the computer system to perform auxiliary calculations and control of the support arm stiffness adjustment operation. The specific stiffness and flexibility ranges of the variable stiffness joint can be obtained through calculation, experimentation, and the experience of medical professionals.

[0067] This allows for better adjustment of the stiffness of the support arm, thus better preventing secondary damage to the fracture site during rehabilitation and promoting better recovery.

[0068] In this embodiment, see Figure 5-11The variable stiffness joint 5 includes a first connecting plate 21 and a second connecting plate 22 arranged coaxially opposite each other. A connecting shaft 23 is arranged axially at one end of the first connecting plate 21 facing the second connecting plate. A plurality of helical abutment springs 24 are evenly distributed circumferentially at the outer end of the connecting shaft 23. The abutment springs 24 are arranged diametrically and their inner ends abut against the connecting shaft 23. Their outer ends are connected to the second connecting plate 22 through a force adjustment mechanism.

[0069] In this variable stiffness joint, the first and second connecting discs are each mounted on a portion of the support arm, connecting the two portions of the support arm into a single unit. During use, the force adjustment mechanism applies force to the abutment spring, adjusting the abutment force of the spring against the connecting shaft, thereby achieving adjustment of the axial stiffness. This design eliminates the need for a constant power supply, resulting in a simple structure and low cost.

[0070] The connecting shaft 23 has an outward mounting protrusion 25 on its outer peripheral surface opposite the position of the abutting spring 24. The outer end of the mounting protrusion 25 is provided with a spring mounting groove, and the inner end of the abutting spring abuts against the inner end of the spring mounting groove.

[0071] This better ensures the stability and reliability of spring installation, guarantees that the force applied by the spring is directly opposite the axis, and ensures the stability and reliability of stiffness adjustment.

[0072] The first connecting plate 21 is fixedly connected to the connecting shaft 23 at the axial center position by a connecting shaft fixing bolt.

[0073] This facilitates the design of the structure and the installation and disassembly of components.

[0074] The force adjustment mechanism includes a nut sleeve 26, with symmetrical internal threads at both ends of the inner ring of the nut sleeve 26, which respectively engage with an adjusting ring 27 spaced circumferentially. The outer surface of the adjusting ring 27 has external threads that engage with the internal threads of the nut. The second connecting plate 22 is also provided with an adjusting ring anti-rotation structure to prevent the adjusting ring from rotating. The force adjustment mechanism also includes a spring seat 28 disposed at the outer end of the spring. The upper and lower sides of the outer end of the spring seat 28 are slidably abutted by an obliquely arranged adjusting baffle 29. The outer ends of the two adjusting baffles 29 are close to each other and the inner ends are open in a horizontal V-shape. The inner ends of the two adjusting baffles 29 are rotatably connected to the corresponding adjusting rings 27 at the upper and lower ends. The outer ends of the adjusting baffles 29 are rotatably connected to a retainer 30 that is relatively fixed on the second connecting plate.

[0075] In this way, during use, simply rotating the nut sleeve drives the two adjusting rings to move linearly in the same or opposite directions, which in turn moves the inner end of the adjusting baffle along the axial direction of the joint, changing the tilt angle of the adjusting baffle. This, in turn, compresses or releases the abutment spring, increasing or decreasing the radial pressure of the abutment spring on the connecting shaft, thereby adjusting the axial mobility of the connecting shaft, i.e., adjusting the axial stiffness of the joint. This method, using a lead screw and nut drive combined with a slant plate compression transmission to adjust the spring clamping force and thus the axial stiffness, has the following advantages: First, the overall structure is compact, and the force transmission is stable and reliable. The applied force is transformed from circumferential rotational motion through multiple force transmissions and conversions before being converted into radial motion force, resulting in good self-locking properties and preventing easy instability. Second, the multiple force transmissions and conversions (especially the slant plate's engagement with the inclined plane to convert the direction of force transmission) result in a very large transmission ratio, allowing for a large stiffness adjustment effect with a small input, making the adjustable range of axial stiffness very large. Furthermore, by pre-setting the initial tilt angle of the adjusting baffle, the control and adjustment of the required precision can be easily achieved. The smaller the tilt angle of the adjusting baffle, the greater the stiffness variation can be achieved with a smaller adjustment distance. Finally, and importantly, this structure relies on the radial compression of the connecting shaft by a spring to achieve axial stiffness adjustment. Therefore, changes in the axial load on the connecting disc during adjustment have minimal impact on the magnitude of the spring's radial compression force, resulting in excellent stability and reliability. Thus, this force adjustment mechanism can achieve a wide range of continuously controllable stiffness variations, achieving broad stiffness adjustment with minimal energy loss, and is extremely stable and reliable.

[0076] The outer end of the spring seat 28 is provided with a roller 31 along the joint axis. The axis of the roller 31 is perpendicular to the axis of the spring. The outer circumferential side of the roller is in contact with the adjusting baffle 29.

[0077] In this way, the rolling action of the rollers can better achieve the transmission of force between the inclined adjustment baffle and the abutment spring, ensuring better reliability.

[0078] Among them, a threaded adjustment hole is provided at the middle position of the outer end of the spring seat 28, which is directly opposite the spring. An adjustment bolt 32 is installed in the threaded adjustment hole, and the front end of the adjustment bolt 32 abuts against the end of the spring.

[0079] In this way, the preload of the adjusting spring can be easily changed by adjusting the bolt when needed.

[0080] The inner end of the spring seat 28 extends forward to form a bearing sleeve 33, which abuts against the outer end of the spring 24 located inside the bearing sleeve 33. The bearing sleeve 33 has a mating section that can be slidably inserted into a spring mounting groove on the connecting shaft.

[0081] In this structure, the front section of the bearing sleeve is inserted into the spring mounting groove, forming a small gap between the outer wall of the fitting section and the inner wall of the spring mounting groove. This creates a crucial effect: if a sudden, large axial force is generated between the first and second connecting discs due to an accident (such as a fall or collision), the resulting axial movement of the first and second connecting discs allows the spring mounting groove to directly engage with the bearing sleeve fitting section, causing the entire spring seat to move in the same direction. This presses the outer end of the spring seat against the corresponding adjusting baffle, which in turn compresses the spring seat inward. This, in turn, causes the spring to clamp the connecting shaft, thereby increasing the axial stiffness and enabling it to withstand or offset some of the axial force generated by the accident. This achieves an adaptive emergency protection effect, reducing or avoiding safety risks caused by accidents. The thread between the nut sleeve and the adjusting ring is a self-locking thread, further ensuring the realization of the aforementioned adaptive emergency protection effect.

[0082] The retainer 30 is cylindrical in shape and coaxially spaced inside the nut sleeve 26. An adjustment baffle mounting window 35 is provided in the middle of the retainer 30, and the outer end of the adjustment baffle 29 is rotatably mounted on the adjustment baffle mounting window 35. Both ends of the outer circumference of the retainer 30 have an inwardly recessed limiting groove. A threaded ring 36 is fixed inwardly at each end of the inner cavity of the nut sleeve 26. The internal threads at both ends of the nut sleeve are located on the inner surface of the threaded ring 36. The threaded ring 36 is rotatably engaged and limited within the limiting groove. Multiple clearance windows 37 are also provided within the limiting groove of the retainer. Multiple outwardly distributed mounting protrusions 38 are evenly distributed on the outer surface of the adjusting ring 27. The external threads on the adjusting ring 27 are located on the outer end surface of the mounting protrusions 38. The mounting protrusions 38 pass through the clearance windows 37 and engage with the outer end of the threaded ring 36. The two sides of the mounting protrusions 38 and the two sides of the clearance windows 37 are attached to form the adjusting ring anti-rotation structure.

[0083] In this way, the entire structure is ingenious, compact, stable and reliable, avoiding mutual interference of motion and ensuring the stability of motion and force transmission.

[0084] Alternatively, the outer surface of the nut sleeve 26 is evenly provided with axial vertical grooves and rotation scales. This facilitates manual rotation of the nut sleeve to adjust its stiffness.

[0085] Alternatively, a nut adjusting motor is also installed on the second connecting plate, and the nut adjusting motor is connected to the nut sleeve drive (not shown in the figure).

[0086] This allows for convenient electric control adjustment of stiffness via a motor that adjusts the nut. In practice, the nut adjusting motor is connected to a computer, enabling automatic control based on preset programs and instructions.

[0087] In implementation, the variable stiffness joint can also be another structure implemented using magnetorheological fluid technology. The variable stiffness joint includes a first cylinder and a second cylinder. The open end of the first cylinder is retractably inserted into the open end of the second cylinder to form a closed chamber (the other ends of the first sleeve and the second sleeve are each installed on a part of the support arm, so that the two parts of the support arm are connected as a whole by the first cylinder and the second sleeve). The outer wall of the first cylinder and the inner wall of the second cylinder are fitted together and a dynamic sealing structure is provided between them. The front half of the open end of the first cylinder has a relief groove along the axial direction. The relief groove is located in the closed chamber. The closed chamber is also provided with a plurality of partitions arranged radially and spaced apart along the axial direction. Some partitions are fixed on the inner wall of the first cylinder, and other partitions pass through the relief groove and are fixed on the inner wall of the second cylinder. The partitions fixed to the first cylinder and the partitions fixed to the second cylinder are staggered and spaced apart. The closed chamber is also filled with magnetorheological fluid. A magnetic field generation control device is also provided inside the first cylinder and the second cylinder near the closed chamber.

[0088] In this way, when the variable stiffness joint of this structure is in use, the magnetic field generating control device is connected to a computer. The computer can control and adjust the magnitude of the magnetic field according to a preset program and instructions, thereby changing the viscosity and hardness of the magnetorheological fluid. This allows for the adjustment and control of the axial stiffness between the first cylinder and the second sleeve. This variable stiffness joint design has the advantages of simple structure and convenient control and adjustment. However, its drawbacks include the need to maintain the magnetic field in a stable state for a long period, resulting in significant power consumption and susceptibility to control instability due to power fluctuations.

Claims

1. A force adjustment mechanism for adjusting the pressure of a radially abutting spring, characterized in that, The device includes a nut sleeve, with symmetrical internal threads at both ends of the inner ring of the nut sleeve, which respectively engage with circumferentially spaced adjusting rings. The outer surface of the adjusting rings has external threads that engage with the internal threads of the nut. It also includes an adjusting ring anti-rotation structure to prevent the adjusting rings from rotating. The force adjustment mechanism also includes a spring seat located radially abutting the outer end of a spring. The upper and lower sides of the outer end of the spring seat each slidably abut against an obliquely arranged adjusting baffle. The outer ends of the two adjusting baffles are close together and their inner ends are open in a transverse V-shape. The inner ends of the two adjusting baffles and the corresponding adjusting rings at the upper and lower ends are rotatably connected. The outer ends of the adjusting baffles and a retainer are rotatably connected.

2. The force adjustment mechanism for adjusting the radial contact spring pressure as described in claim 1, characterized in that, A roller is provided at the outer end of the spring seat along the joint axis. The direction of the roller's axis is perpendicular to the direction of the spring's axis. The outer circumferential side of the roller is in contact with the adjusting baffle.

3. The force adjustment mechanism for adjusting the radial abutment spring pressure as described in claim 1, characterized in that, A threaded adjustment hole is provided at the middle of the outer end of the spring seat, directly opposite the spring. An adjustment bolt is installed in the threaded adjustment hole, and the front end of the adjustment bolt abuts against the end of the spring.

4. The force adjustment mechanism for adjusting the radial contact spring pressure as described in claim 1, characterized in that, The inner end of the spring seat extends forward to form a load-bearing sleeve, which abuts against the outer end of the spring located inside the load-bearing sleeve. The load-bearing sleeve has a mating section that can be slidably inserted into a spring mounting groove on the connecting shaft.

5. The force adjustment mechanism for adjusting the radial contact spring pressure as described in claim 1, characterized in that, The retainer is cylindrical in shape and coaxially spaced inside the nut sleeve. An adjustment baffle mounting window is opened in the middle of the retainer, and the outer end of the adjustment baffle is rotatably mounted on the adjustment baffle mounting window. Both ends of the outer circumference of the retainer have an inwardly recessed limiting groove. A threaded ring is fixed inwardly at each end of the inner cavity of the nut sleeve. The internal threads at both ends of the nut sleeve are located on the inner surface of the threaded rings, which are rotatably engaged and limited within the limiting grooves. Multiple clearance windows are also provided within the limiting grooves of the retainer. Multiple outwardly extending mounting protrusions are evenly distributed on the outer surface of the adjusting ring. The external threads on the adjusting ring are located on the outer end surface of the mounting protrusions. The mounting protrusions pass through the clearance windows and engage with the outer thread of the threaded ring. The two sides of the mounting protrusions and the two sides of the clearance windows abut against each other to form the anti-rotation structure of the adjusting ring.

6. The force adjustment mechanism for adjusting the radial abutment spring pressure as described in claim 5, characterized in that, The outer surface of the nut sleeve is evenly provided with axial vertical grooves and rotation scale.

7. The force adjustment mechanism for adjusting the radial abutment spring pressure as described in claim 5, characterized in that, It is also equipped with a nut adjusting motor, which is connected to the nut sleeve drive.

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