Design and control of a pneumatic-driven biomimetic knee joint for biped robot

This paper presents the design and control of a biomimetic knee joint for biped robots. The robotic knee joint driven by pneumatic artificial muscles is designed by imitating the structure of the human knee. It has desirable characteristics similar with human knee joint including joint compliance, changeable instantaneous center of rotation, as well as large range of joint motion. In order to model and compensate the length/pressure hysteresis of pneumatic artificial muscles in the position control, a novel method termed as direct inverse hysteresis modeling approach is introduced. Other than deriving from the forward hysteresis model, the inversion of the length/pressure hysteresis is directly modeled by a modified Prandtl-Ishlinskii model which has two newly-designed play operators. Then a cascade position controller with forward hysteresis compensation is proposed for the knee joint. The mechanical structure and control scheme of the knee joint are validated by experiments.