Natural Motion of the RR-4R-R Manipulator: Effects of Trajectory Types and Parameters

In robotics, it is possible to exploit the Natural Motion, or Free Vibration Response, of a manipulator equipped with elastic elements to reduce the energy consumption in cyclic motions, such as pick-and-place tasks. In [1], this approach has been applied to the RR-4R-R manipulator, a SCARA-like robot in which the vertical prismatic joint is replaced with a four-bar mechanism lying in a vertical plane, to facilitate the introduction of balancing elastic elements. While exact elastic balancing of the vertical four-bar provides indifferent equilibrium, suitable for slow movements, a linear elastic balancing obtained by linear torsional springs gives rise to a Natural Motion, which can be exploited to reduce energy consumption in fast cyclic motions, in which inertial forces become prevalent. The threshold of convenience between Exact Balancing (EB) and Natural Balancing (NB) has been evaluated for the RR-4R-R robot by means of a multibody model in [1] in terms of Integral Control Effort (ICE) and maximum values of the actuation torques. A wider simulation campaign has been carried out, with different trajectory types and parameters, and also considering the influence of finite stop phases, to assess the proposed architecture's energy-saving effectiveness more exhaustively.