Modelling of an lower-extremity prostheses and its ankle trajectory control

Abstract

In this survey, solid work model and strength analysis of lower-extremity prostheses with ankle trajectory control depending on hip angle measurement as reference motion, is introduced. After modelling and designing of certain prosthesis and its parts, strength analysis under various pedestal loads are given, to ensure optimal and convenient prostheses. A mathematical model for bipedal walking is then executed as a combination of two serial manipulators, each having two revolute joints, in other words, having two degrees of freedom. Inverse kinematics analysis and recursive Newton–Euler computation methods are given to obtain the dynamic equations, which describe the motion of the walking system. For desired walking characteristics, hip and ankle trajectories are derived. As ankle joint actuator in the system a permanent magnet direct current (DC) servo-motor with position feedback and its state space representation is given. By using the hip trajectory as reference the relevant angular position of ankle joint is calculated and is realised via DC motor. With this novel method besides ankle joint even the knee joint positions in the case of upper knee amputees can be determined for various gait instants. With these calculated values optimal ankle and knee trajectories can be realised via DC Servo motors. Thus best gait conditions for relevant prostheses and patients can be determined and evaluated. For future works this kind of a method may be very efficient solution in tracking problem of bipedal walking with under knee prostheses to obtain a quasi-natural walking.