Research And Development Of An In-vitro Knee Joint Biomechanical Test Bench

The experimental test system of knee joint specimen is the key equipment to study the biomechanical characteristics of knee joint in sports medicine laboratory.By installing the knee specimen on the test equipment,the changes of biomechanical parameters were measured after simulating the muscle loading and the external loads on the knee joint.The experimental results can quantitatively evaluate the function of knee joint and guide the clinical surgery strategy.At present,there is no design research for this biomechanical experimental system of knee joint specimens in China.Based on the theory of knee anatomy and mechanical design,this paper develops the biomechanical experimental test bench of knee specimen for ACL biomechanical research,and verifies the performance of this test bench through experiments,the main work contents and achievements are as follows:1)Using QFD method,user demand of this test bench was determined by means of literature retrieval and visit investigation,and the design requirements were deduced,the relationship matrix between user demand and design requirements was established,and the importance of each design requirement was established.According to the design requirements,carry out detailed solution design and mechanical structure design.Including specimen installation solution design,knee flexion angle adjustment solution design,bionic muscle loading solution design,tibial module design.A new measurement method of tibial posture is proposed,which solves the problem of uncertainty of tibial posture caused by the change of joint rotation axis.A new external loading method is proposed to realize the measurement of multiDOF coupling motion of tibia caused by the pathological shift of joint rotating axis.The method of gravity compensation by installing a spring on Z-axis guide rail is put forward to eliminate the influence of the weight of the tibial module on the experiment and to improve the loading accuracy of the internal and external torque.The static analysis of this test bench was carried out to determine the ultimate working load,and the finite element simulation and strength check of the key components were carried out to ensure the rigidity of this test bench.Compared with the traditional robot test system,this test bench has a more compact structure,lower cost and more reliable measurement results.2)According to the functional requirements,the hardware system of the measurement and control system is established around industrial computer.Taking the electric proportional valve as the actuator,the mono-axis force sensor is the feedback element,the PID algorithm is used,the 8-way force closed-loop valve control system is established,and the segmented PID algorithm is used to achieve fast response for the pneumatic loop with directional valve.Data acquisition and processing of the anterior translation of the tibia,of the tibia posture angle,of the six-dimensional reaction force,of the proximal femur,of the ACL strain,all biomechanical parameters were transmitted to the industrial computer through the bus protocol,after processing,these data are stored and displayed.Based on LabVIEW software,the software operation platform of this test bench is developed,which satisfies the functions of the user to set the force control parameters,force load state switching operation,and realize the visualization,calibration and data export of the measurement parameters.3)In order to test the performance of this test bench,a knee specimen was used in this experiment to verify function of this test bench.Firstly,the static and dynamic closed-loop muscle loading are loaded,the overshoot,steady state error and adjustment time of the control system under static loading are analyzed,and the phase lag time and maximum error of the control system under dynamic loading are analyzed.The standard deviation(SD)and the root mean square error(RMSE)between the measured values of the load force of multiple repetitive experiments are calculated,accuracy and repeatability of static and dynamic force loading are evaluated.The experimental conditions in the peer research results were repeated on this test bench,and the results showed same trend,and the standard deviation(SD)of the data was smaller than peer work,showing better repeatability.The destructive test of the Anterior Lateral Ligament(ALL)was carried out on the specimen,and the results of the measurement parameters successfully verified the theory of ALL physiological function.The experimental results show that force loading system designed in this paper has high precision,good repeatability,and biomechanical parameter measurement system has good repeatability and high reliability.