Modelling and experimental validation of a planar 2-dof cobot as a differential-algebraic equation system

Cobots are passive robots designed to work in a cooperative way with human operators. In human-cobot collaboration, the human operator provides the necessary force to perform the movement of the system and the cobot provides a virtual guiding surface. This paper presents the modelling and experimental validation of a planar two degree of freedom (2-dof) cobot with differential gear trains in serial configuration as a differential-algebraic equation system, where the dynamic model of a conventional 2-dof robot considering the force exerted by the human operator represents the set of differential equations and the kinematic model of the differential gear train represents the algebraic constraint. For simulation results, the force exerted by the human operator is decomposed into its cartesian components and considered as the output of a PD controller. The presented model allows the constraint to which the system is subject be fulfiled in tighter tolerances. Moreover, to validate the proposed model, a comparison between both experimental and simulation results is presented.