A linear variable stiffness joint

Abstract

The present invention discloses a linear variable-stiffness joint comprising a first connecting plate and a second connecting plate disposed coaxially opposite each other. The joint is characterized in that a connecting shaft is axially disposed at one end of the first connecting plate facing the second connecting plate, and a plurality of spiral abutment springs are evenly distributed circumferentially at the outer end of the connecting shaft. The abutment springs are arranged diametrically with their inner ends abutting the connecting shaft, and their outer ends connected to the second connecting plate via a force adjustment mechanism. The joint of the present invention has the advantages of easy adjustment, a wide adjustable range, good stability, and excellent safety.

Description

Technical Field

[0001] The invention relates to a joint component, in particular to a linear variable-rigidity joint. Background Art

[0002] During fracture fixation, an external fixator or device is often placed outside the patient's body to prevent secondary injury and promote proper healing. In the early days of less advanced medical technology, fractures were often fixed with splints or plaster casts. These methods are too rigid and hinder subsequent growth and recovery.

[0003] International patents such as US6030386, US8439914, and WO2011163406, as well as Chinese patent CN201810623485.8, propose a six-axis parallel external fixation device. This device consists of six topologically identical branches (support arms) and two fixation rings. The doctor uses metal bone pins (Kirschner wires) to secure the two fixation rings to the bone fragments at either end of the patient's fracture. The six branches are connected to the two fixation rings via hinges at either end. Regularly adjusting the lengths of the six branches generates six degrees of freedom relative motion between the two fixation rings, precisely correcting the spatial deformity of the fracture and achieving fracture reduction. After fracture reduction, the branch lengths are maintained, and 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 combines the functions of reducing and fixing the fracture ends, and has broad application prospects.

[0004] However, this existing six-axis parallel external bone fixation device still uses rigid adjustment to adjust the branches, that is, the front and rear branches are adjusted to maintain a constant rigidity. However, in reality, bone growth and bone density will change in the early and late stages of fracture healing, resulting in different requirements for the rigidity and flexibility of the fixation support. Therefore, this type of existing six-axis parallel external bone fixation device still cannot better meet the needs of fracture growth and healing, and is not conducive to the recovery of the fracture. It is necessary to consider designing a joint component with adjustable axial stiffness to better assist fracture healing.

[0005] Furthermore, variable stiffness devices are now widely used in various fields, and the requirements for these devices vary across different sectors. For example, in the automotive sector, adjusting the stiffness of a vehicle's suspension is required to improve environmental adaptability and ride comfort. In robotics, robotic arms require high stiffness to ensure positioning accuracy, while also maintaining a certain degree of compliance to ensure safe interaction, and the stiffness must be continuously adjusted based on the mass of the payload. In aerospace, high-precision and high-stability remote sensing satellites require variable stiffness devices to suppress on-orbit vibrations caused by moving components such as momentum wheels, CMGs (Control Moment Gyros), and refrigerators. The wider the stiffness range of a variable stiffness device, the better the vibration suppression effect, and the more conducive it is to achieving high-precision and high-stability system specifications. Furthermore, when a variable stiffness device and the equipment being isolated experience an active-segment launch environment, the dynamic response is amplified at the resonant frequency. Higher stiffness in the variable stiffness device minimizes the impact of this resonant amplification, thus enhancing the performance and safety of the device and the equipment being isolated.

[0006] Therefore, the demand for variable stiffness devices is becoming increasingly widespread. However, existing variable stiffness devices have a small stiffness change, a complex structure, and a large drive mechanism. They are not easy to integrate into robots or vibration isolation devices for instruments, making it difficult to better meet the needs of these applications. Summary of the Invention

[0007] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present 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.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A linear variable stiffness joint comprises a first connecting plate and a second connecting plate arranged coaxially opposite to each other, characterized in that a connecting shaft is axially arranged at one end of the first connecting plate facing the second connecting plate, and a plurality of spiral abutment springs are evenly distributed circumferentially at the outer end of the connecting shaft, the abutment springs are arranged along the diameter direction and the inner ends abut on the connecting shaft, and the outer ends are connected to the second connecting plate through a force adjustment mechanism.

[0010] Thus, when the variable stiffness joint is in use, the first connecting plate and the second connecting plate can be mounted on a portion of the support arm, so that the two portions of the support arm are connected as a whole by the first connecting plate and the second connecting plate. When in use, the force adjustment mechanism applies force to the abutment spring to adjust the abutment force of the abutment spring on the connecting shaft, thereby adjusting the axial stiffness of the support arm. This has the characteristics of simple structure and good stability.

[0011] Furthermore, the axial center position of the first connecting disk is fixedly connected and installed with the connecting shaft through a connecting shaft fixing bolt.

[0012] This makes it easier to set up the structure and install and disassemble components.

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

[0014] In this way, the stability and reliability of the spring installation can be better guaranteed, the direction of the spring force application can be guaranteed to be directly opposite to the axis center line, and the stability and reliability of the stiffness adjustment can be guaranteed.

[0015] Furthermore, the force adjustment mechanism includes a nut sleeve, and the two ends of the inner ring of the nut sleeve are respectively provided with a symmetrical internal thread and respectively engaged with an adjusting ring arranged at a circumferential interval. The outer surface of the adjusting ring has an external thread and the internal thread of the nut is matched. The second connecting disk is also provided with an adjusting ring anti-rotation structure for preventing the adjusting ring from rotating. The force adjustment mechanism also includes a spring seat arranged to abut the outer end of the spring, and the upper and lower sides of the outer end of the spring seat are each slidably abutted with an obliquely arranged adjustment baffle, the outer ends of the two adjustment baffles are close to each other and the inner ends are opened in a horizontal figure eight shape, the inner ends of the two adjustment baffles are rotatably connected to the corresponding adjustment rings at the upper and lower ends, and the outer end of the adjustment baffle is rotatably connected to a retaining frame relatively fixed on the second connecting disk.

[0016] In this way, during use, simply rotating the nut sleeve drives the two adjustment rings to move linearly in the same or opposite directions, thereby driving the inner end of the adjustment baffle to move axially along the joint, changing the inclination angle of the adjustment baffle, and thereby compressing or relaxing the abutment spring, causing the abutment spring to increase or decrease the radial pressure on the connecting shaft, thereby adjusting the axial mobility of the connecting shaft, that is, adjusting the axial stiffness of the joint. This method, which uses a screw-nut transmission combined with a swash plate extrusion-fit transmission to adjust the spring compression force and, consequently, the axial stiffness, has the following advantages. First, the overall structure is compact, and force transmission is stable and reliable. Force is converted from circumferential rotational motion through multiple force transmissions and conversions before being converted into radial force, resulting in excellent self-locking properties and preventing instability. Second, the multiple force transmissions and conversions (particularly the swash plate's inclined surface's conversion of force direction) result in a very large transmission ratio, enabling a large stiffness adjustment effect with a relatively small input, resulting in a very wide adjustable range of axial stiffness. In addition, the initial tilt angle of the adjustment baffle can be adjusted in advance, and the control adjustment of the conversion of the adjustment accuracy requirements can be easily realized. The smaller the tilt angle of the adjustment baffle, the smaller the adjustment distance can be used to achieve a greater stiffness change adjustment. Finally, a very important point is that in this structure, the axial stiffness adjustment is achieved by the radial compression of the connecting shaft by the spring. Therefore, when the axial bearing force of the connecting disk changes during the adjustment process, it basically does not affect the change in the size of the radial compression force of the spring, so it can have good stability and reliability. Therefore, the force adjustment mechanism can adjust to achieve a wide range of continuously controllable stiffness changes, achieve a wide range of stiffness adjustment with less energy loss, and is extremely stable and reliable.

[0017] Furthermore, a roller is provided at the outer end of the spring seat along the axial direction of the joint, the axis direction of the roller is perpendicular to the axis direction of the abutting spring, and the circumferential outer side of the roller is abutted and matched with the adjustment baffle.

[0018] In this way, the rolling cooperation of the roller can better realize the transmission of force between the oblique adjustment baffle and the abutment spring, thereby ensuring better reliability.

[0019] Furthermore, a threaded adjustment hole is provided at the middle position of the outer end of the spring seat facing the spring, and an adjustment bolt is installed in the threaded adjustment hole, and the front end of the adjustment bolt abuts against the end of the abutting spring.

[0020] In this way, the size of the preload force of the adjustment spring can be conveniently changed by adjusting the bolt when necessary.

[0021] Furthermore, the inner end of the spring seat extends forward to form a bearing sleeve, and the outer end of the abutting spring is located in the bearing sleeve. The bearing sleeve has a matching section that can be slidably inserted into the spring installation groove on the connecting shaft.

[0022] In this structure, the front mating section of the load-bearing sleeve is inserted into the spring mounting groove, creating a small gap between the outer wall of the mating section and the inner wall of the spring mounting groove. This creates a very important advantage. If a large axial force is suddenly generated between the first and second connecting plates due to an accident (such as a fall or collision), the first and second connecting plates will experience significant axial movement. This will cause the spring mounting groove to directly drive the entire spring seat in the same direction through the mating section of the load-bearing sleeve. This, in turn, compresses the outer end of the spring seat against the corresponding adjustment baffle. The adjustment baffle on that side can compress the spring seat inward, causing the spring to squeeze the connecting shaft and clamp it, correspondingly increasing the axial stiffness and enabling it to withstand or offset some of the axial force generated by the accident. This achieves the device's adaptive emergency protection effect, reducing or avoiding safety risks caused by accidents. Furthermore, the thread between the nut sleeve and the adjustment ring is self-locking, further ensuring the realization of the aforementioned adaptive emergency protection effect.

[0023] Furthermore, the retaining frame is cylindrical as a whole and is coaxially spaced apart on the inner side of the nut sleeve. An adjusting baffle installation window is provided in the middle of the retaining frame, and the outer end of the adjusting baffle can be rotatably installed on the adjusting baffle installation window; both ends of the outer circumference of the retaining frame have a circle of inwardly concave limiting grooves, and both ends of the inner cavity of the nut sleeve are fixed inward with a threaded ring, and the internal threads at both ends of the nut sleeve are provided on the inner ring surface of the threaded ring, and the threaded ring can be rotatably clamped and limited in the limiting groove. A plurality of clearance windows are also provided in the limiting groove of the retaining frame, and a plurality of outward mounting protrusions are evenly distributed on the outer surface of the adjusting ring. The external thread on the adjusting ring is provided on the outer end surface of the mounting protrusion, and the mounting protrusion passes through the clearance window and cooperates with the outer end thread of the threaded ring. The two sides of the mounting protrusion and the two sides of the clearance window are attached to form the adjusting ring anti-rotation structure.

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

[0025] As an option, the outer surface of the nut sleeve is evenly distributed with vertical grooves and rotation scales along the axial direction, so as to facilitate manual force application to rotate the nut sleeve for stiffness adjustment.

[0026] As another option, a nut adjusting motor is further installed on the second connecting plate, and the nut adjusting motor is transmission-connected to the nut sleeve.

[0027] In this way, it is convenient to realize electric control and adjustment of stiffness by controlling the nut adjustment motor. When implemented, the nut adjustment motor is connected to a computer and automatic control can be realized according to 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 FIG. 1 is a schematic structural diagram of an external bone fixation auxiliary retention system using the structure of the present invention in an embodiment.

[0030] Figure 2 for Figure 1 Schematic diagram of the structure in use.

[0031] Figure 3 for Figure 1 Schematic diagram of the structure of the separate support arm.

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

[0033] Figure 5 for Figure 3 Schematic diagram of the structure of a single variable stiffness joint.

[0034] Figure 6 for Figure 5 Cross-sectional view of .

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

[0036] Figure 8 for Figure 5 Schematic diagram of the structure after removing the retaining frame, the upper half of the first connecting plate and the second connecting plate.

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

[0038] Figure 10 for Figure 8 Schematic diagram of the structure in which the shaft and spring seat are connected separately.

[0039] Figure 11 for Figure 10 sectional view of . DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with an external bone fixation auxiliary retention system adopting the structure of the present invention. The external bone fixation auxiliary 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, see Figures 1-11 :A bone external fixation auxiliary holding system using the structure of the present invention, (see Figure 1-4) includes two relatively arranged fixing rings 4, and a plurality of mounting holes are provided on the fixing rings 4 to form a bone needle mounting structure. A plurality of support arms 2 are hingedly provided between the two fixing rings, wherein each support arm 2 is also provided with a variable stiffness joint 5 capable of adjusting the axial stiffness of the support arm.

[0042] Thus, when the device of this solution is used, see Figure 2 Two fixing rings are fixed to the ends of the fracture site 1. The needle holders of the bone pins (Kirschner wires) are fixed to the fixing rings via the bone pin mounting structure. The two fixing rings are then fixedly connected to the bone fragments at both ends of the patient's fracture via the bone pins. This allows the support arm to provide fixed support at both ends of the fracture site, preventing secondary damage during the healing process. This solution also features a variable stiffness joint on the support arm that adjusts the axial stiffness of the support arm. Therefore, during use, the support arm can be adjusted to different axial stiffnesses at different stages of fracture healing. This allows for early adjustments to maintain a high stiffness, ensuring that both ends of the fracture remain fixed and grow rapidly. Later, the stiffness can be adjusted to increase flexibility, preventing the brace from absorbing all energy during rehabilitation training and causing stress shielding. This allows for greater mobility of the newly grown bone, promoting better bone healing and promoting healthy growth. Therefore, this solution can better meet the requirements of different fracture healing stages and facilitate recovery and growth. The fixing rings are provided with several mounting holes to form the bone pin mounting structure. In this way, the outer end of the bone needle can be fixed to a bone needle mounting seat, and the bone needle mounting seat can be fixed to the fixing ring by means of bolts passing through the mounting holes. The structure is simple, the installation is convenient, and the installation position of the fracture can be easily adjusted.

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

[0044] In this way, the length of each support arm can be adjusted as needed during the use and fixation of the device and the recovery of the fracture, so that the two ends of the fracture can be better kept in the correct posture position.

[0045] There are six support arms 2, which are staggered obliquely so that one end of each adjacent two support arms are close together and the other end is separated to form a V-shape or an inverted V-shape. The connection positions of each two support arms on the fixing ring are evenly distributed along the circumference.

[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 fixation bracket with three rotational degrees of freedom and three translational degrees of freedom. This allows the three rotational degrees of freedom and three translational degrees of freedom to be easily achieved by adjusting the axial length of each support arm, thereby enabling spatial angle adjustment at any position of the fixed ring. In practice, the spatial angle adjustment process can be performed through computer-assisted calculation, the specific details of which are existing technologies and will not be detailed here.

[0047] The fixing ring 4 is in an annular shape as a whole and has three protruding connecting parts 6 evenly distributed around the periphery. The ends of each two adjacent groups of support arms 2 are connected to the connecting parts 6, and the connecting parts 6 of the two fixing rings 4 are staggered by 60 degrees.

[0048] In this way, the connection and installation of the support arm will not affect the area and structure where the bone needle is installed.

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

[0050] In this way, the Hooke hinge can realize hinged rotation in two directions, which is convenient and reliable to adjust.

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

[0052] In this way, the axial adjustment motor can drive the screw to rotate. Due to the threaded fit of the adjustment nut and the fact that the adjustment nut is fixed to the load-bearing half and is restricted from circumferential rotation by the Hooke's hinge at the end, a screw-nut transmission pair can be formed, driving the load-bearing half to achieve axial telescopic adjustment. This has the characteristics of simple structure and stable and reliable adjustment.

[0053] The screw holding cavity 12 has an inner cavity that is arranged in contact with the outer circumference of the screw 9 .

[0054] In this way, the circumferential limit of the lead screw can be better maintained to avoid shaking that affects the fracture fixation effect; and the detection value of the pressure sensor can be better guaranteed to be stable and reliable.

[0055] Among them, the outer end of the screw holding cavity 12 also has a pre-tightening chamber located on the outer periphery of the screw, the pre-tightening chamber shell 13 is rigidly connected to the adjusting nut, and the pre-tightening chamber has a spiral pre-tightening spring 14 movably sleeved on the screw, one end of the pre-tightening spring 14 abuts against a boss protruding outward from the circumference of the screw, and the other end abuts against one end of the inner cavity of the pre-tightening chamber.

[0056] In this way, the preload spring can apply an axial preload force between the lead screw and the nut, avoiding axial shaking caused by thread gap and affecting the fracture fixation effect; at the same time, better ensuring the stability and reliability of the detection value of the pressure sensor.

[0057] The boss on the lead screw is formed by a pre-tightening nut 15 located in the pre-tightening chamber and threadedly screwed onto the lead screw.

[0058] This not only facilitates the setting and installation of the boss, but also allows the size of the pre-tightening force to be changed by adjusting the position of the pre-tightening nut on the screw, so that it can achieve a better pre-tightening effect without affecting the transmission of the screw nut itself.

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

[0060] This makes it easier to install the structure.

[0061] The support arm 2 is also provided with a pressure sensor 16 for detecting the axial force thereof.

[0062] In this way, it is convenient to detect the axial force of the support arm, which serves as the information basis for adjusting the feedback control.

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

[0064] The system also includes a computer (not shown in the diagram), one end of which is connected to the pressure sensor and the other to the axial adjustment motor. This computer system, aided by calculations and control, significantly reduces the computational complexity of manual operation and improves the ease of use of the device.

[0065] Among them, the computer is provided with a fracture pattern simulation module, a control center and an adjustment output control module connected in sequence, and the control center includes an adjustment parameter calculation module; the computer also has a human-machine operation graphical interface connected to the fracture pattern simulation module, the adjustment parameter calculation module and the adjustment output control module respectively; the fracture pattern simulation module can calculate and simulate the bone structure pattern of the fracture part by importing multi-angle X-rays of the fracture part (the calculation and simulation method is existing technology and is not described in detail here) to obtain bone deformity parameters; the adjustment parameter calculation module can calculate the equipment installation posture pattern based on the obtained fracture part structure pattern and bone deformity parameters (including the deformation of the bone fracture part), combined with data and / or manual judgment; the adjustment parameter calculation module can also obtain the parameters that need to be adjusted based on the fracture part structure pattern and bone deformity parameters combined with the pressure sensor detection feedback signal after the equipment is installed; the adjustment output control module is used to convert the parameters that need to be adjusted into output control signals and send them to the axial adjustment motor; the human-machine operation graphical interface is used to input operation instructions and display the obtained graphics and output instructions. This facilitates computer-assisted automatic detection and adjustment calculations, better assisting in the device's fixation and correction operations. During use, the computer can monitor the pressure sensor data feedback in real time to determine whether the axial length of the support arm needs to be adjusted to ensure the healing effect of the fracture.

[0066] The computer's control center also includes a support arm stiffness timing adjustment module, which is connected to the pressure sensor, the human-machine graphical interface, and the adjustment output control module. The adjustment output control module is connected to the variable stiffness joint. The support arm stiffness timing adjustment module can generate a variable stiffness joint adjustment signal through the (time and stiffness) adjustment parameter instructions input from the human-machine graphical interface and the signal detected by the pressure sensor, and output the signal to the variable stiffness joint through the adjustment output control module to achieve control and adjustment. In this way, the computer system can be better utilized to achieve auxiliary calculation and control of the support arm stiffness adjustment operation in the equipment. The specific numerical range of the stiffness and flexibility of the variable stiffness joint can be obtained through calculation, experimentation, and doctor's experience.

[0067] In this way, the stiffness of the support arm can be better adjusted to better avoid secondary damage to the fracture during the rehabilitation process, which is more conducive to the recovery of the fracture.

[0068] In this embodiment, see Figure 5-11The variable stiffness joint 5 includes a first connecting plate 21 and a second connecting plate 22 that are coaxially arranged opposite to each other. A connecting shaft 23 is axially arranged at one end of the first connecting plate 21 facing the second connecting plate. A plurality of spiral abutment springs 24 are evenly distributed along the circumference at the outer end of the connecting shaft 23. The abutment spring 24 is arranged along the diameter direction and the inner end abuts on the connecting shaft 23. The outer end is connected to the second connecting plate 22 through a force adjustment mechanism.

[0069] In this way, the first and second connecting plates in the variable stiffness joint are each mounted on a portion of the support arm, so that the two portions of the support arm are connected as a whole by the first and second connecting plates. During use, the force adjustment mechanism applies force to the abutment spring, adjusting the abutment force of the abutment spring on the connecting shaft, thereby adjusting the axial stiffness. This eliminates the need for a long-term power supply, simplifies the structure, and reduces costs.

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

[0071] In this way, the stability and reliability of the spring installation can be better guaranteed, the direction of the spring force application can be guaranteed to be directly opposite to the axis center line, and the stability and reliability of the stiffness adjustment can be guaranteed.

[0072] The axial center position of the first connecting plate 21 is fixedly connected and installed with the connecting shaft 23 through a connecting shaft fixing bolt.

[0073] This makes it easier to set up the structure and install and disassemble components.

[0074] Among them, the force adjustment mechanism includes a nut sleeve 26, and the two ends of the inner ring of the nut sleeve 26 are respectively provided with a symmetrical internal thread and are respectively matched with an adjusting ring 27 arranged at a circumferential interval. The outer surface of the adjusting ring 27 has an external thread and the internal thread of the nut is matched. The second connecting disk 22 is also provided with an adjusting ring anti-rotation structure for preventing the adjusting ring from rotating. The force adjustment mechanism also includes a spring seat 28 arranged at the outer end of the abutting spring, and the upper and lower sides of the outer end of the spring seat 28 are each slidably abutted with an obliquely arranged adjustment baffle 29. The outer ends of the two adjusting baffles 29 are close to each other and the inner ends are opened in a horizontal figure eight shape. The inner ends of the two adjusting baffles 29 are rotatably connected to the adjusting rings 27 corresponding to the upper and lower ends, and the outer end of the adjusting baffle 29 is rotatably connected to a retaining frame 30 relatively fixed on the second connecting disk.

[0075] In this way, during use, simply rotating the nut sleeve drives the two adjustment rings to move linearly in the same or opposite directions, thereby driving the inner end of the adjustment baffle to move axially along the joint, changing the inclination angle of the adjustment baffle, and thereby compressing or relaxing the abutment spring, causing the abutment spring to increase or decrease the radial pressure on the connecting shaft, thereby adjusting the axial mobility of the connecting shaft, that is, adjusting the axial stiffness of the joint. This method, which uses a screw-nut transmission combined with a swash plate extrusion-fit transmission to adjust the spring compression force and, consequently, the axial stiffness, has the following advantages. First, the overall structure is compact, and force transmission is stable and reliable. Force is converted from circumferential rotational motion through multiple force transmissions and conversions before being converted into radial force, resulting in excellent self-locking properties and preventing instability. Second, the multiple force transmissions and conversions (particularly the swash plate's inclined surface's conversion of force direction) result in a very large transmission ratio, enabling a large stiffness adjustment effect with a relatively small input, resulting in a very wide adjustable range of axial stiffness. In addition, the initial tilt angle of the adjustment baffle can be adjusted in advance, and the control adjustment of the conversion of the adjustment accuracy requirements can be easily realized. The smaller the tilt angle of the adjustment baffle, the smaller the adjustment distance can be used to achieve a greater stiffness change adjustment. Finally, a very important point is that in this structure, the axial stiffness adjustment is achieved by the radial compression of the connecting shaft by the spring. Therefore, when the axial bearing force of the connecting disk changes during the adjustment process, it basically does not affect the change in the size of the radial compression force of the spring, so it can have good stability and reliability. Therefore, the force adjustment mechanism can adjust to achieve a wide range of continuously controllable stiffness changes, achieve a wide range of stiffness adjustment with less 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 axial direction of the joint. The axis of the roller 31 is perpendicular to the axis of the abutting spring. The circumferential outer side of the roller is abutted against the adjustment baffle 29.

[0077] In this way, the rolling cooperation of the roller can better realize the transmission of force between the oblique adjustment baffle and the abutment spring, thereby ensuring better reliability.

[0078] A threaded adjustment hole is provided at the middle of the outer end of the spring seat 28 facing the spring, and an adjustment bolt 32 is installed in the threaded adjustment hole. The front end of the adjustment bolt 32 abuts against the end of the abutting spring.

[0079] In this way, the size of the preload force of the adjustment spring can be conveniently changed by adjusting the bolt when necessary.

[0080] The inner end of the spring seat 28 extends forward to form a bearing sleeve 33, and the outer end of the abutment spring 24 is located in the bearing sleeve 33. The bearing sleeve 33 has a matching section that can be slidably inserted into the spring installation groove on the connecting shaft.

[0081] In this structure, the front mating section of the load-bearing sleeve is inserted into the spring mounting groove, creating a small gap between the outer wall of the mating section and the inner wall of the spring mounting groove. This creates a very important advantage. If a large axial force is suddenly generated between the first and second connecting plates due to an accident (such as a fall or collision), the first and second connecting plates will experience significant axial movement. This will cause the spring mounting groove to directly drive the entire spring seat in the same direction through the mating section of the load-bearing sleeve. This, in turn, compresses the outer end of the spring seat against the corresponding adjustment baffle. The adjustment baffle on that side can compress the spring seat inward, causing the spring to squeeze the connecting shaft and clamp it, correspondingly increasing the axial stiffness and enabling it to withstand or offset some of the axial force generated by the accident. This achieves the device's adaptive emergency protection effect, reducing or avoiding safety risks caused by accidents. The threads between the nut sleeve and the adjustment ring are self-locking, further ensuring the realization of this adaptive emergency protection effect.

[0082] The cam 36 is a screw threaded part 36 which is fixed to the inner surface of the cam 36 so that the cam 36 can rotate and rotate relative to the cam 36 to stop the rotation of the cam 36.

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

[0084] As an option, the outer surface of the nut sleeve 26 is evenly distributed with vertical grooves and rotation scales along the axial direction. This makes it convenient to manually apply force to rotate the nut sleeve for rigidity adjustment.

[0085] As another option, a nut adjusting motor is further mounted on the second connecting plate, and the nut adjusting motor is drivingly connected to the nut sleeve (not shown in the figure).

[0086] In this way, it is convenient to realize electric control and adjustment of stiffness by controlling the nut adjustment motor. When implemented, the nut adjustment motor is connected to a computer and automatic control can be realized according to preset programs and instructions.

[0087] During 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 can be retracted and 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. A clearance groove is provided in the axial direction at the front half of the open end of the first cylinder. The clearance groove is located in the closed chamber. A plurality of partitions arranged at intervals along the axial direction are also provided in the closed chamber. Some of the partitions are fixed on the inner wall of the first cylinder, and the other part of the partitions are fixed on the inner wall of the second cylinder through the clearance groove. The partitions fixed to the first cylinder and the partitions fixed to the second cylinder are staggered and arranged at intervals. The closed chamber is also filled with magnetorheological fluid. A magnetic field generation control device is also provided near the closed chamber inside the first cylinder and the second cylinder.

[0088] In this way, when the variable stiffness joint of this structure is used, the magnetic field generating control device is connected to the computer. The computer can control the magnetic field generating control device to adjust the size of the magnetic field according to the preset program and instructions, thereby changing the viscosity and hardness of the magnetorheological fluid. In this way, the axial stiffness between the first cylinder and the second sleeve can be adjusted and controlled. The variable stiffness joint of this solution has the advantages of simple structure and convenient control and adjustment, but the disadvantage is that it is necessary to keep the magnetic field generating control device in a stable state for a long time, which consumes a lot of electricity and energy, and is prone to control instability due to power fluctuations and other reasons.

Claims

1. A linear variable stiffness joint, comprising a first connecting plate and a second connecting plate coaxially arranged opposite to each other, characterized in that: A connecting shaft is axially provided at one end of the first connecting disk facing the second connecting disk, and a plurality of spiral abutment springs are evenly distributed along the circumference at the outer end of the connecting shaft. The abutment springs are arranged in the diameter direction and the inner ends abut on the connecting shaft, and the outer ends are connected to the second connecting disk via a force adjustment mechanism. The outer peripheral surface of the connecting shaft facing the abutment spring position has an outward mounting protrusion, the outer end of the mounting protrusion is correspondingly provided with a spring mounting groove, and the inner end of the abutment spring abuts against the inner end of the spring mounting groove; The force adjustment mechanism includes a nut sleeve, and each of the two ends of the inner ring of the nut sleeve is provided with a symmetrical internal thread and respectively engaged with an adjusting ring arranged at a circumferential interval. The outer surface of the adjusting ring has an external thread and the internal thread of the nut is matched. The second connecting disk is also provided with an adjusting ring anti-rotation structure for preventing the adjusting ring from rotating. The force adjustment mechanism also includes a spring seat arranged to abut the outer end of the spring, and the upper and lower sides of the outer end of the spring seat are each slidably abutted with an obliquely arranged adjusting baffle, the outer ends of the two adjusting baffles are close to each other and the inner ends are opened in a horizontal figure eight shape, the inner ends of the two adjusting baffles are rotatably connected to the adjusting rings corresponding to the upper and lower ends, and the outer end of the adjusting baffle is rotatably connected to a retaining frame relatively fixed on the second connecting disk.

2. The linear variable stiffness joint according to claim 1, characterized in that: The axis center position of the first connecting disk is fixedly connected and installed with the connecting shaft through a connecting shaft fixing bolt.

3. The linear variable stiffness joint according to claim 1, wherein: A roller is provided at the outer end of the spring seat along the axial direction of the joint, the axis centerline direction of the roller is perpendicular to the axis centerline direction of the abutting spring, and the circumferential outer side of the roller is abutted and matched with the adjusting baffle.

4. The linear variable stiffness joint according to claim 1, wherein: A threaded adjustment hole is provided at the middle position of the outer end of the spring seat, facing 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 abutting spring.

5. The linear variable stiffness joint according to claim 1, wherein: The inner end of the spring seat extends forward to form a bearing sleeve, and the outer end of the abutting spring is located in the bearing sleeve. The bearing sleeve has a matching section that can be slidably inserted into the spring installation groove on the connecting shaft.

6. The linear variable stiffness joint according to claim 1, wherein: The retaining frame is cylindrical as a whole and is coaxially spaced and arranged on the inner side of the nut sleeve. An adjusting baffle installation window is provided in the middle of the retaining frame, and the outer end of the adjusting baffle can be rotatably installed on the adjusting baffle installation window; the two ends of the outer circumference of the retaining frame have a circle of inwardly concave limiting grooves, and the two ends of the inner cavity of the nut sleeve are each fixed inward with a threaded ring, and the internal threads at both ends of the nut sleeve are set on the inner ring surface of the threaded ring, and the threaded ring can be rotatably clamped and limited in the limiting groove, and a plurality of clearance windows are also provided in the limiting groove of the retaining frame, and a plurality of outward mounting protrusions are evenly distributed on the outer surface of the adjusting ring, and the external thread on the adjusting ring is set on the outer end surface of the mounting protrusion, and the mounting protrusion passes through the clearance window and cooperates with the outer end thread of the threaded ring. The two sides of the mounting protrusion and the two sides of the clearance window are attached to form the adjusting ring anti-rotation structure.

7. The linear variable stiffness joint according to claim 6, characterized in that: The outer surface of the nut sleeve is evenly distributed with vertical grooves and rotation scales along the axial direction.

8. The linear variable stiffness joint according to claim 6, wherein: A nut adjusting motor is also installed on the second connecting plate, and the nut adjusting motor is transmission-connected to the nut sleeve.

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