Multi-degree-of-freedom joint movement imitating friction testing machine

Abstract

The invention discloses a multi-degree-of-freedom joint movement simulating friction testing machine, and belongs to the technical field of artificial joint performance testing equipment. The testing machine comprises a rack, a thighbone rotation control mechanism, a front-back displacement control system, a tibia rotation control system, an axial force loading control system and a testing platform, and four-degree-of-freedom accurate control over thighbone buckling, front-back displacement, tibia rotation and axial force loading is achieved through cooperation of multiple mechanisms. Complex motion modes and stress characteristics of the knee joints of the human body can be restored. According to YY / T 1426.3-2017 standard design, Chinese motion data characteristics are adapted, a servo motor and servo hydraulic system combined driving mode is adopted, control precision and cost advantages are taken into consideration, the structure is compact, clamping is convenient, a reliable in-vitro simulation test platform can be provided for artificial joint prosthesis material screening, structure optimization and abrasion mechanism research, and the in-vitro simulation test platform is suitable for industrial production. The problems that existing equipment is high in cost, insufficient in freedom degree, poor in adaptability and the like are solved.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of medical device testing equipment and mechanical engineering, specifically to a multi-degree-of-freedom simulated joint motion friction testing machine. Background Technology

[0002] Total knee replacement surgery is a core treatment for end-stage osteoarthritis, and the wear resistance of the prosthesis directly determines its lifespan after implantation. Statistics show that there are over 400 million osteoarthritis patients worldwide, and approximately 200,000 patients in my country undergo total knee replacement surgery annually. However, because the lifespan of existing prostheses cannot fully meet clinical needs, the revision rate for patients under 50 years old remains high, with global annual revision surgery costs exceeding US$12 billion.

[0003] In vitro simulation testing is a crucial step in evaluating the wear performance of artificial joint prostheses. Currently, mainstream testing equipment has significant shortcomings: although foreign products (such as ProSim and MTS series) can achieve multi-degree-of-freedom control, they cost millions of dollars and are designed based on the movement data of European and American populations, making it difficult to adapt to the unique movement habits of Chinese people, such as squatting and kneeling, and the characteristics of smaller lower limb movements; domestic equipment mostly has 2-3 degrees of freedom, which has problems such as low precision in lubrication condition control, poor long-term stability, and inconvenient sample clamping. Moreover, the core technology relies on imports, resulting in high testing costs and hindering the research and development process of domestic artificial joints.

[0004] Furthermore, existing equipment fails to fully optimize its size in structural design, making it difficult to meet the needs of multiple machines operating in parallel in laboratories. Additionally, the precision of coordinated control of loading force and motion parameters is insufficient, leading to discrepancies between test data and clinical realities. Therefore, developing a compact, cost-effective, multi-degree-of-freedom, high-precision artificial joint motion friction testing machine that is compatible with domestic standards and population characteristics has become an urgent need to promote the development of the artificial joint industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the core objective of this invention is to provide a multi-degree-of-freedom simulated joint motion friction testing machine, specifically implemented as follows: (1) Restore the coordinated movement of the four core degrees of freedom of the human knee joint (femoral flexion, anterior and posterior displacement, tibial rotation, and axial force loading) to match the real physiological characteristics within the gait cycle; (2) It meets the requirements of YY / T 1426.3-2017 (aligned with ISO 14243.3:2014) and is adapted to the characteristics of Chinese people's sports data; (3) Simplify the structural design, reduce manufacturing costs, and at the same time ensure testing accuracy and long-term operational stability; (4) Optimize the sample clamping method and equipment volume to improve the ease of operation and laboratory space utilization.

[0006] The objective of this invention can be achieved through the following technical solutions: A multi-degree-of-freedom simulated joint motion friction testing machine, characterized in that it includes a frame, a femoral rotation control mechanism, an anterior-posterior displacement control system, a tibial rotation control system, and an axial force loading control system; The femoral rotation control mechanism is used to simulate femoral flexion movement and includes a femoral shaft, servo motor I, coupling I and cage-type motor base. The femoral shaft is an irregular shaft with a bionic prosthesis mounting platform in the middle and is supported by bearing seats at both ends. The servo motor I is connected to the femoral shaft through coupling I. The motor base adopts a cage-type hollow structure. The forward and backward displacement control system is used to drive the femoral rotation control mechanism to achieve forward and backward displacement. It includes a folding-back servo electric cylinder with guide column and three sets of ball bearings. The servo electric cylinder is rigidly connected to the cage motor base through a push rod. The three sets of ball bearings are symmetrically arranged below the cage motor base and the femoral shaft bearing base. The tibial rotation control system is used to simulate the internal rotation movement of the tibia, including a tibial shaft, a servo motor II, a coupling II, and a hydraulic cylinder seat. The bionic prosthesis mounting surface of the tibial shaft is adapted to the anatomical shape of the human tibia. The servo motor II is connected to the tibial shaft through the coupling II. The hydraulic cylinder seat has a built-in thrust ball bearing and a pair of deep groove ball bearings with different outer diameters. The axial force loading control system is used to apply dynamic axial loads. It includes a servo hydraulic cylinder, a high-frequency response servo valve, a real-time controller, and a force sensor. The servo hydraulic cylinder is symmetrically installed on the journals at both ends of the femoral rotation axis. The force application axis is offset by 5 mm from the center of symmetry in the width direction of the tibial prosthesis.

[0007] Furthermore, both the femoral and tibial pivots are made of 40Cr material and have undergone tempering and heat treatment. The bionic prosthesis mounting platform fixes the sample with four sets of M4 fine thread screws, which are installed on the non-working surface of the prosthesis.

[0008] Furthermore, both servo motor I and servo motor II are model 86HS120D, with a holding torque of 12 N•M, a rated current of 6A, a moment of inertia of 2.94 kg•cm², a flexion angle control range of 0°-120°, and a tibial rotation angle control accuracy that meets the requirements of amplitude error ±5% and phase error ±3%.

[0009] Furthermore, the maximum stroke of the reciprocating servo electric cylinder is 100mm, the effective displacement range within the gait cycle is 0-5.2mm, the guide column structure is used to counteract frictional bending moment, and the three sets of ball bearing guides are model HGW-HB15, ensuring that the straightness of the motion trajectory is ≤0.01mm / m.

[0010] Furthermore, the axial force loading control system adopts closed-loop feedback control, the servo valve is a Moog G761 series with a frequency response ≥200Hz, the real-time controller is an NI CompactRIO+LabVIEW system with a sampling frequency of 1kHz, a loading force range of 0-3000N, and a loading frequency of 1Hz±0.1Hz.

[0011] Furthermore, the deep groove ball bearings built into the hydraulic cylinder seat are model 61906 and 6006, which are press-fitted with a small interference fit, and the thrust ball bearing is model 51107, which is used to bear axial load and limit the tilting of the tibial pivot.

[0012] Furthermore, the servo motor II is mounted on a matching cage-type motor base. The bottom of the motor base is equipped with a ball bearing guide slider, which cooperates with the guide rail on the frame to achieve follow-up displacement in the Z-axis direction with a displacement accuracy of ±0.001mm.

[0013] Furthermore, the servo hydraulic cylinder of the axial force loading control system has a built-in strain gauge force sensor with a range of 0-3000N and an accuracy of ±0.5% FS. The hydraulic power unit has an oil filtration accuracy of β≥200 (NAS 1638 Class 6) and is equipped with a 0.5L bladder type accumulator to absorb pressure pulsations.

[0014] Compared with the prior art, the present invention has the following significant advantages: (1) Multi-degree-of-freedom coordinated control: For the first time, precise coordinated control of four core degrees of freedom, namely femoral flexion, anterior-posterior displacement, tibial rotation, and axial force loading, was achieved, which completely restored the complex movement and force characteristics of the human knee joint during the gait cycle. The test data deviated from the clinical reality by ≤5%; (2) High adaptability: Based on the YY / T 1426.3-2017 standard, combined with Chinese people's exercise data (such as the high activity requirements of squatting and kneeling movements and the small range of lower limb movements), it solves the technical pain point of insufficient adaptability of foreign equipment; (3) Significant cost advantage: Through component selection optimization (using the same servo motor model and adopting a reversible electric cylinder) and simplified structural design, the equipment manufacturing cost is only 1 / 3 to 1 / 5 of that of similar foreign products, which greatly reduces the testing threshold for research institutions and enterprises. (4) Convenient and efficient operation: The bionic fixture design enables rapid assembly and disassembly of samples within 3 minutes. The servo electric cylinder with a stroke of 100mm provides ample space for sample installation and debugging. The equipment is compact and improves the utilization rate of laboratory space by 40%. (5) Excellent stability and accuracy: The key components are treated with 40Cr quenching and tempering, with a maximum stress of only 13.98MPa, which is far below the material yield strength; closed-loop feedback control ensures loading accuracy of ±0.5% FS, and can run continuously for 1000 hours without failure, meeting the requirements of long-term testing. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention after the frame is hidden; Figure 3 This is a schematic diagram of the structure of the present invention after concealing the frame and the front and rear displacement control system; In the diagram, 1 is the frame; 2 is the femoral rotation control mechanism; 3 is the anterior-posterior displacement control system; 4 is the tibial rotation control system; 5 is the axial force loading control system; 6 is the bionic prosthesis; 7 is the servo electric cylinder; 8 is the ball bearing guide; 9 is the tibial pivot; 10 is the hydraulic cylinder seat; and 11 is the servo hydraulic cylinder. Detailed Implementation

[0016] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0017] like Figure 1-3 As shown, this multi-degree-of-freedom simulated joint motion friction testing machine includes a frame 1, a femoral rotation control mechanism 2, an anterior-posterior displacement control system 3, a tibial rotation control system 4, and an axial force loading control system 5.

[0018] The femoral rotation control mechanism is used to simulate femoral flexion movement. It includes a femoral shaft 5, a servo motor I, a coupling I, and a cage-type motor base. The femoral shaft is an irregularly shaped shaft with a bionic prosthesis 6 mounting platform in the middle. Both ends are supported by bearing seats. The servo motor I is connected to the femoral shaft through the coupling I. The motor base adopts a cage-type hollow structure.

[0019] The anterior-posterior displacement control system is used to drive the femoral rotation control mechanism to achieve anterior-posterior displacement. It includes a folding-back servo electric cylinder 7 with a guide column and three sets of ball bearings 8. The servo electric cylinder is rigidly connected to the cage motor base through a push rod. The three sets of ball bearings are symmetrically arranged below the cage motor base and the femoral shaft bearing base.

[0020] The tibial rotation control system is used to simulate the internal rotation movement of the tibia. It includes a tibial shaft 9, a servo motor II, a coupling II, and a hydraulic cylinder seat 10. The bionic prosthesis mounting surface of the tibial shaft is adapted to the anatomical shape of the human tibia. The servo motor II is connected to the tibial shaft through the coupling II. The hydraulic cylinder seat has a built-in thrust ball bearing and a pair of deep groove ball bearings with different outer diameters.

[0021] The axial force loading control system is used to apply dynamic axial loads, including a servo hydraulic cylinder 11, a high-frequency response servo valve, a real-time controller and a force sensor. The servo hydraulic cylinder is symmetrically installed on the journals at both ends of the femoral shaft, and the force application axis is offset by 5mm from the center of symmetry in the width direction of the tibial prosthesis.

[0022] Both the femoral and tibial pivots are made of 40Cr material and have undergone tempering and heat treatment. The bionic prosthesis mounting platform fixes the sample with four sets of M4 fine thread screws, which are installed on the non-working surface of the prosthesis.

[0023] Both servo motor I and servo motor II are model 86HS120D, with a holding torque of 12 N•M, rated current of 6A, rotational inertia of 2.94 kg•cm², flexion angle control range of 0°-120°, and tibial rotation angle control accuracy meeting the requirements of amplitude error ±5% and phase error ±3%.

[0024] The maximum stroke of the folding servo electric cylinder is 100mm, and the effective displacement range within the gait cycle is 0-5.2mm. The guide column structure is used to counteract frictional bending moment. The three sets of ball guide rails are model HGW-HB15, ensuring that the straightness of the motion trajectory is ≤0.01mm / m.

[0025] The axial force loading control system adopts closed-loop feedback control. The servo valve model is Moog G761 series with a frequency response ≥200Hz. The real-time controller is NI CompactRIO+LabVIEW system with a sampling frequency of 1kHz, a loading force range of 0-3000N, and a loading frequency of 1Hz±0.1Hz.

[0026] The deep groove ball bearings built into the hydraulic cylinder seat are models 61906 and 6006, which are press-fitted with a small interference fit. The thrust ball bearing is model 51107, which is used to bear axial loads and limit the tilting of the tibial pivot.

[0027] Servo motor II is mounted on a matching cage motor base. The bottom of the motor base is equipped with a ball bearing guide slider, which cooperates with the guide rail on the frame to achieve follow-up displacement in the Z-axis direction with a displacement accuracy of ±0.001mm.

[0028] The servo hydraulic cylinder of the axial force loading control system has a built-in strain gauge force sensor with a range of 0-3000N and an accuracy of ±0.5% FS. The hydraulic power unit has an oil filtration accuracy of β≥200 (NAS 1638 Class 6) and is equipped with a 0.5L bladder accumulator to absorb pressure pulsations.

[0029] The assembly and operation process of this testing machine is as follows: 1. Component assembly The femoral and tibial pivots are made of 40Cr material and then subjected to heat treatment to achieve a hardness of 25-32HRC. The bionic prosthesis mounting platform is milled according to the human anatomical shape and has 4 sets of M4 threaded holes reserved. Servo motor I (86HS120D) is connected to the femoral shaft via coupling I and fixed to the cage motor base. A ball guide slider is installed at the bottom of the motor base and cooperates with the ball guide. The reciprocating servo electric cylinder (stroke 100mm, thrust 5kN) is rigidly connected to the cage motor base through a push rod. The base is fixed to the frame. Three sets of ball bearing guides are arranged in parallel to ensure the parallelism of the movement. The tibial shaft is mounted on the hydraulic cylinder seat via thrust ball bearing 51107 and deep groove ball bearings 61906 and 6006. The servo motor II is connected to the tibial shaft via coupling II. The bottom slider of the cage motor seat cooperates with the frame guide rail. Servo hydraulic cylinders (32mm diameter) are symmetrically mounted on the journals at both ends of the femoral shaft and connected to the hydraulic power unit via oil pipes. Force sensors (HBM U9C 3000N) and servo valves (Moog G761-3004) are connected to a real-time controller (NICompactRIO 9030). The hydraulic cylinder base is fixed to the frame by three sets of sliding linear bearings. Adjusting the bearing clearance ensures smooth Z-axis displacement without jamming.

[0030] 2. Testing Process Sample installation: The femoral prosthesis is fixed to the bionic platform of the femoral rotation axis with M4 screws, and the tibial prosthesis is fixed to the mounting surface of the tibial rotation axis. The anterior and posterior displacement control system is activated, the servo electric cylinder is extended to its maximum stroke, and the position of the prosthesis is adjusted to make it initially fit. Parameter settings: Test parameters are input via LabVIEW host computer, including the buckling angle curve (0%-100% cycle corresponds to 0°-16°-5°-58°-0°), the anterior-posterior displacement curve (0%-100% cycle corresponds to 0mm-4.5mm-0.3mm-5.2mm-0mm), the tibial rotation curve (0%-100% cycle corresponds to +1.6°-+1.9°--1.2°-+1.6°--5.7°, -+1.6°), and the axial force curve (0%-100% cycle corresponds to 168N-1887N-1175N-2600N-838N-2434N-168N). System startup: Start the hydraulic power unit. After the system pressure stabilizes to the set value (14MPa), start each control system. The real-time controller controls the coordinated movement of each servo component according to the preset curve. The force sensor and displacement sensor collect data in real time and upload it. Test completion: After the set test cycle is reached, the system automatically stops, the servo electric cylinder returns to the initial position, the sample is disassembled for wear detection, and the equipment automatically generates a test report.

[0031] 3. Performance Verification Accuracy testing: flexion angle control error ±3.2%, anterior-posterior displacement error ±0.08mm, tibial rotation error ±3.5%, axial force control error ±0.3% FS, all of which are better than the requirements of YY / T 1426.3-2017 standard; Stability test: After 1000 hours of continuous operation, the equipment operated smoothly. The maximum deformation of the femoral shaft was 0.00923mm, the maximum deformation of the tibial shaft was 0.1562mm, and the maximum deformation of the hydraulic cylinder seat was 0.01756mm, all within the allowable range. Comparative test: Wear test was conducted using an Al2O3-UHMWPE prosthesis. Compared with the imported ProSim testing machine, the wear data deviation was 4.2%, which verified the accuracy and reliability of the test results.

[0032] This invention, through rational structural design and precise control strategy, realizes multi-degree-of-freedom, high-precision, and low-cost wear testing of artificial joint prostheses, providing key equipment support for the research and development, performance optimization, and standardization of domestically produced artificial joints, and has significant engineering application value and market prospects.

[0033] It should be understood that in the claims and description of this invention, all instances of "comprising..." should be understood as having an open meaning, that is, their meaning is equivalent to "containing at least...", and should not be understood as having a closed meaning, that is, their meaning should not be understood as "containing only...".

[0034] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A multi-degree-of-freedom simulated joint motion friction testing machine, characterized in that, Includes frame, femoral rotation control mechanism, anterior-posterior displacement control system, tibial rotation control system, and axial force loading control system; The femoral rotation control mechanism is used to simulate femoral flexion movement and includes a femoral shaft, servo motor I, coupling I and cage-type motor base. The femoral shaft is an irregular shaft with a bionic prosthesis mounting platform in the middle and is supported by bearing seats at both ends. The servo motor I is connected to the femoral shaft through coupling I. The motor base adopts a cage-type hollow structure. The forward and backward displacement control system is used to drive the femoral rotation control mechanism to achieve forward and backward displacement. It includes a folding-back servo electric cylinder with guide column and three sets of ball bearings. The servo electric cylinder is rigidly connected to the cage motor base through a push rod. The three sets of ball bearings are symmetrically arranged below the cage motor base and the femoral shaft bearing base. The tibial rotation control system is used to simulate the internal rotation movement of the tibia, including a tibial shaft, a servo motor II, a coupling II, and a hydraulic cylinder seat. The bionic prosthesis mounting surface of the tibial shaft is adapted to the anatomical shape of the human tibia. The servo motor II is connected to the tibial shaft through the coupling II. The hydraulic cylinder seat has a built-in thrust ball bearing and a pair of deep groove ball bearings with different outer diameters. The axial force loading control system is used to apply dynamic axial loads. It includes a servo hydraulic cylinder, a high-frequency response servo valve, a real-time controller, and a force sensor. The servo hydraulic cylinder is symmetrically installed on the journals at both ends of the femoral rotation axis. The force application axis is offset by 5 mm from the center of symmetry in the width direction of the tibial prosthesis.

2. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, Both the femoral and tibial pivots are made of 40Cr material and have undergone tempering and heat treatment. The bionic prosthesis mounting platform fixes the sample with four sets of M4 fine thread screws, which are installed on the non-working surface of the prosthesis.

3. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, Both servo motor I and servo motor II are model 86HS120D, with a holding torque of 12 N•M, a rated current of 6A, a moment of inertia of 2.94 kg•cm², a flexion angle control range of 0°-120°, and a tibial rotation angle control accuracy that meets the requirements of amplitude error ±5% and phase error ±3%.

4. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, The maximum stroke of the reciprocating servo electric cylinder is 100mm, and the effective displacement range within the gait cycle is 0-5.2mm. The guide column structure is used to counteract frictional bending moment, and the three sets of ball bearing guides are model HGW-HB15, ensuring that the straightness of the motion trajectory is ≤0.01mm / m.

5. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, The axial force loading control system adopts closed-loop feedback control, the servo valve is a Moog G761 series with a frequency response ≥200Hz, the real-time controller is an NI CompactRIO+LabVIEW system with a sampling frequency of 1kHz, the loading force range is 0-3000N, and the loading frequency is 1Hz±0.1Hz.

6. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, The hydraulic cylinder base contains deep groove ball bearings of models 61906 and 6006, which are press-fitted with a small interference fit. The thrust ball bearing model is 51107, which is used to bear axial loads and limit the tilting of the tibial pivot.

7. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, The servo motor II is mounted on a matching cage motor base. The bottom of the motor base is equipped with a ball bearing guide slider, which cooperates with the guide rail on the frame to achieve follow-up displacement in the Z-axis direction with a displacement accuracy of ±0.001mm.

8. The multi-degree-of-freedom simulated joint motion friction testing machine according to claim 1, characterized in that, The servo hydraulic cylinder of the axial force loading control system has a built-in strain gauge force sensor with a range of 0-3000N and an accuracy of ±0.5% FS. The hydraulic power unit has an oil filtration accuracy of β≥200 (NAS 1638 Class 6) and is equipped with a 0.5L bladder accumulator to absorb pressure pulsations.

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