Thermodynamic analysis of a mechatronic pneumatically driven spherical joint

Jointed-member robotic devices (Arthrobots) can benefit from the pneumatic tug-and-twist technology. In particular, two crossed Twistor-pairs provide a flexural spherical joint in the form of a Twistor gimbal-drive. Previous papers have shown that the performance characteristics of both Tuggers and Twistors may be derived from a unique appropriate enthalpy function, which results in open-loop proportional control. This paper develops the Twistor enthalpy H(P, α) based upon independent volume and torque measurements, which fully accounts for pressure-dependent Twistor´s stretch and Coulomb torque. This function then provides model equations for mechatronic computer-control of the final spherical joint