Design, Modelling, and Experimental Validation of a Soft Continuum Wrist Section Developed for a Prosthetic Hand

Soft continuum sections are widely used in robotic mechanisms for achieving dexterous motions. However, most available designs of soft continuum sections cannot support payload during a motion. This paper presents a development of a novel soft robotic wrist section for a prosthetic hand named ‘PRISMA Hand II’. Our research focuses on various phases of development of a soft continuum wrist section, that can support a substantial payload and maintain postures of the hand. Mechanical design, fabrication, and modelling strategies adopted for developing the wrist section are described. The design of the wrist section is constructed by assembling springs, discs, and tendons. The numbers and dimensions of springs and discs are optimised using static structural analysis. Kinematic modelling and dynamic modelling of the wrist section are carried out using Geometric Variable Strain (GVS) approach based on Cosserat rod theory and a generalised coordinate method respectively. The geometric formulations involved in Cosserat rod theory guaranteed accurate and quick computations considering deformation parameters. Dynamic modelling approach also enhanced the performance of the wrist section reducing errors and computational time during real time implementations. This paper also discusses about a dynamic model based controller strategy for the wrist section and advantages of the proposed controller are proved using a comparative study with a kinematic model based PID controller. Experimental validations of motions of the fabricated wrist section employing the dynamic controller are also included in the paper.