Performance-based design synthesis and analysis of a 6-4 UPS parallel mechanism based virtual biomechanical shoulder robot model

The human shoulder complex provides a broad range of motions for the upper arm and existing in-silico musculoskeletal models can be used to study the associated kinematic parameters. These models are also quite useful in the design of suitable control systems for rehabilitation robots. However, to save the time consumed in the control-related computations, normally these musculoskeletal models are required to be simplified compromising their versatility. In this article, a Virtual 6-4 Parallel Biomechanical Shoulder Robot Model (VBSRM) is proposed to be used as a musculoskeletal model for a shoulder rehabilitation robot. The kinematic model of the proposed VBSRM is developed and validated by a case study. A singularity analysis of the robot’s Jacobian matrix was carried out to avoid a possible singular VBSRM design. Wrench analysis and structural design analysis were conducted to obtain actuator forces and dynamic stiffness behavior of the VBSRM respectively. Finally, an optimal design of the parallel mechanism of the VBSRM was obtained using genetic algorithm (GA), while establishing a tradeoff between various performance indices. This optimal design is that used to evaluate the workspace of the proposed VBSRM. This optimal design can further be used in studying the dynamics of the proposed VBSRM and shoulder functioning evaluations.