Optimization of the Design of a Four Bar Mechanism for a Lower Limb Prosthesis Using the Taboo Search Algorithm

In this chapter, the optimization of the design of a four bar mechanism used in polycentric prosthesis with voluntary control is reported. This prosthesis has been used by a male, whose left leg was amputated above the knee. He is 34 years old, weighs 78 kg and is 1.75 m tall. One of the objectives of this optimization was to fulfill the requirements of his anthropometric characteristics. The taboo search algorithm was used for this purpose. In this case, the lengths of the links were determined, following an inverse analysis. The objective function was the minimization of the error between the target trajectory of the instantaneous center of rotation (ICR) and the path followed by ICR of the four bar mechanism. This curve is very important because it is related with the kinematic and the forces that are developed in the gait cycle. Therefore, it is expected that the amputee individual develop a natural gait cycle with this prosthesis. In the final stage, 1,900 iterations were carried out and the lengths of the bars were augmented by 0.01 mm. The lengths of the links of the optimized mechanism are the following: Bar 1 = 43 mm; Bar 2 = 55.5 mm; Bar 3 = 59 mm and Bar 4 = 29 mm. With this information, the prosthesis was manufactured and adapted to the patient.