Research On Kinematics Of Cat Lower Limbs And Bionic Walking Legs Based On 3D Dynamic X-ray

With the rapid development of bionic technology,bionic quadruped robots replace or assist humans in dangerous work,which greatly increases human work safety and reduces work intensity.Because the quadruped walking robot has strong terrain adaptability,good motion stability,and simple mechanical structure compared with other multi-legged robots,it has become a compelling research field.At present,the mechanical leg mechanisms of most quadruped robots are mostly rigid hinged connections,and friction and impact between rigid bodies are inevitable.The flexibility of the mechanical legs is insufficient,and they are prone to impact damage under high-speed motion.In nature,four-legged animals that can run fast and withstand significant impacts without damage to the leg and foot system may provide new inspiration for the solution of the problem.This topic selects cats that have significant movement flexibility and flexibility compared with other animals.-Domestic cats are the experimental subjects.The bionic prototype selects its leg musculoskeletal system,combined with the use of two-plane three-dimensional dynamic X-ray motion capture technology to test and analyze its three-dimensional motion adjustment laws of lower limb joints at four different motion speeds.On this basis,the integrated modeling of the flexible unit(cartilage between muscles,ligaments and bones)and rigid bones of the lower limb joint system was carried out,and the functional principle of rigid-flexible coupling was simulated and analyzed;a rigid-flexible coupled bionic walking leg was designed,Combined with multi-body mechanics simulation,analyzed the influence of the stiffness of the bionic flexible ligament,the position of the connection point of the bionic patellar ligament and the bionic muscle on the change of the joint angle of the walking leg.The main work and conclusions of this paper are as follows:(1)When a cat is exercising,its knee joints of the lower limbs are adjusted adaptively according to the change of movement speed.The cat's knee joints sequentially present flexion-extension-flexion-extension,internal rotation-internal rotation rotation-external rotation-internal rotation,varus-inversion rotation-eversion-inversion movement and internal movement-external movement-inward movement-The regular movement of outward movement,the separation-convergence-separation-convergence movement between the femur and tibia occurs in sequence.The knee joint in the ground contact period first undergoes small flexion,internal rotation,varus,knee joint internal movement,and femoral tibia up and down Separation,the knee joint produces small extensions,internal rotation rotation,varus,external movement and up and down convergence of the femur and tibia,and then enters the swing phase,the knee joint angle reaches the maximum flexion,external rotation,varus,internal movement and the femur and tibia up and down separation,The hind limbs begin to fall,and the knee joints begin to stretch,internally rotate,flip and move the tibia,and then move the femur and tibia up and down until the sole of the foot touches the ground again.With the increase of speed,the cat's lower limb contact period is significantly reduced,from about 55% of the original gait cycle at 0.8km/h to about 35% at 1.4km/h.(2)The flexible ligaments and muscular system of the knee joint make the stress distribution on the rigid bones tend to be uniform,and at the same time improve the bending resistance of the bones.Under the same load boundary conditions,different muscles around the knee joint have different effects on the bone stress distribution,which may be closely related to the distribution pattern,shape and size of the muscle itself.The change of the elastic modulus of muscle has a more significant effect on the balanced distribution of the axial stress of the femur and tibia,while the effect on the distribution of the axial stress of the tibia and the femur is not obvious.(3)When the elastic modulus of the bionic flexible ligament is about 1-200 MPa,the flexion angle of the knee joint of the rigid-flexible coupling bionic walking leg changes less and less,and when the elastic modulus of the bionic flexible ligament is greater than 200 MPa,the rigid-flexible coupling bionic walking leg The effect of joint angle flexion is not obvious.The change of the connection position between the bionic muscle and the calf bone component has an impact on the knee flexion angle of the walking leg.When the connection point of the bionic muscle gradually moved away from the end of the calf bone component,the angle of the knee joint showed a trend of first increasing and then decreasing,indicating that different connection point positions of the bionic muscle have different effects on the angle of the joint.When the connection point is about 20% away from the end of the calf component,the knee flexion angle of the walking leg changes the most.