Multibody modelling of N DOF robot arm assigned to milling manufacturing. Dynamic analysis and position errors evaluation

Nowadays, with the large use of robot manipulators in the most different fields of industrial production, two main aims must be commonly reached: robot dynamic behavior improvement and end-effector position errors reduction. For a N DOF robot arm, in case of specific applications such as milling manufacturing, one of the main source of end-effector position errors can be identified with joint compliances. This aspect, well known in literature, has been confirmed by experimental tests and measurements carried out on a specific robot assigned to non-standard milling manufacturing of marble objects (sculptures realization). To approach and analyze this issue the authors chose the multibody simulation environment. Hence, the authors developed a parametric modelling procedure that, by determining the robot characteristics through CAD model and technical data sheet investigation, provides reliable multibody dynamic models of generic N DOF robot arms. In this modelling approach the robot geometry construction is based on a standard strategy typical of this research field (i. e. Denavit-Hartenberg, Veitschegger-Wu). The developed procedure enables to obtain robot representation at various complexity levels according to the number of modelled robot components and actuation typology (Motion laws defined both in displacement or applied torque). Eventually, for a specific test case, the authors were able to correctly simulate the robot dynamic behavior, as it was demonstrated by numerical/experimental comparison. In this way the influence of the joint compliance behavior and actuator rotational inertia effects on end-effector position accuracy was analyzed.