A Novel 4-DoF Robotic Link Mechanism with E-CoSMo: Kinematics Based Torque Analysis

In this study, a novel four degrees of freedom (DoF) robotic link mechanism and its torque analysis based on extended coaxial spherical joint module (E-CoSMo) are introduced. The E-CoSMo is a previously developed 4-DoF point-centered rotational parallel mechanism with coaxial actuators. The use of the E-CoSMo on robotic system is expected to improve dynamic performance since all actuators are mounted on fixed base. Furthermore, output torque is amplified in a specific axial direction, due to a coaxial parallel mechanism. Torque analysis of the mechanism is derived based on kinematics of a virtual 4-DoF serial linkages and the E-CoSMo. A virtual force-based position control simulation is performed for verifying the torque analysis. Due to the valid torque analysis, the norm of position error is less than 0. 7 mm. It is confirmed that the output torque is amplified compare to actuator torques, which is a special feature of the E-CoSMo. Control experiments using prototype are also carried out to validate the feasibility.