Conjugate Surface Measurement Of Knee Joint Based On Compliant Sensor

In exoskeleton research,it is a significant requirement in structure design that the motion of the device should flexibly couple with the human joint motion.Any interference or resistance would result in joint injury.As a result,understanding the biological conjugate surface during the knee joint motion is the foundation to design an exoskeleton robot which could function harmonious with human motion.However,its complex nonlinear geometry,complicated joint motion and constant moving rotation center make it a challenge to measure its exact articular surface.The thesis takes knee joint as the research object.It takes the mathematical account of the conjugate surface of the knee joint as the relative motion of tibia and femur.A new method for equivalent knee joint conjugate surface modeling has been presented.The basic idea is to back analysis the relative motion of tibia and femur and reconstruct the equivalent joint conjugate surface by examining deformation of the compliant exoskeleton which would deform along with joint motion.Based on the 3D large deformable soft beam model,the relation among strain,curvature and deformation has been deduced.With mode superposition principle,a method which measures the strains of limited points to reconstruct the joint motion has been proposed.And a compliant exoskeleton embedded with a strain sensor has been designed.A simulation has been run on ABAQUS software platform to verify the accuracy of the soft beam deformation theory model.The static and dynamic measurement error has been calibrated through experiments.The results prove the high measurement accuracy of the sensor in static and dynamic measuring and it shows that the results could well reflect the relative motion of the knee joint.All these experiments prove the feasibility to measure the joint conjugate surface via this approach.At last,the equivalent conjugate surface of knee joint without weight bearing has been reconstructed when the experimenter is in his sitting posture through a compliant exoskeleton measuring the free flexion motion of knee joint.The repetitve results have shown the stability of the constructed result,which could serve as the design principle of the joint kinematic pair design.