Design and control of a novel variable stiffness soft arm

Abstract

Soft robot arms possess such characteristics as light weight, simple structure and good adaptability to the
\nenvironment, among others. On the other hand, robust control of soft robot arms presents many difficulties. Based
\non these reasons, this paper presents a novel design and modelling of a fuzzy active disturbance rejection control
\n(FADRC) controller for a soft PAM arm. The soft arm comprises three contractile and one extensor PAMs, which
\ncan vary its stiffness independently of its position in space. Force analysis for the soft arm is conducted, and stiffness
\nmodel of the arm is established based on the relational model of contractile and extensor PAM. The accuracy of
\nstiffness model for the soft arm was verified through experiments. Associated to this, a controller based on the fuzzy
\nadaptive theory and ADRC, FADRC, has been designed to control the arm. The fuzzy adaptive theory is used to
\nadjust the parameters of the ADRC, the control algorithm has the ability to control stiffness and position of the soft
\narm. In this paper, FADRC was further verified through comparative experiments on the soft arm. This paper
\nreinforces the hypothesis that FADRC control, as an algorithm, indeed possesses good robustness and adaptive
\nabilities.<br/>
\n<br/>Key words: soft robot, variable stiffness, PAM, stiffness modelling, FADRC