Incerti G.

A problem that frequently happens during the use of high speed manipulators is the one related with the vibrations of the end effector; this phenomenon, essentially due to the elasticity of the mechanical components, worsens the dynamic performances and the positioning precision of the machine. The approach proposed in the paper for solving this problem can be summarized by the following points: a) Development of a mathematical model, that allows to reproduce, with a sufficient accuracy, the vibrations arising during the operation of an industrial manipulator. b) For each DOF of the manipulator, definition of a parametric motion profile, whose shape can be modified by varying the values of some coefficients, but always respecting the constraints related with the motion time and the displacement to perform; the parameters that define the shape of each profile are selected so as to reduce the vibrations of the mechanism gripper at the end of the motion time (overshooting). c) Definition of a performance index (related to the amplitude of the residual vibration), whose value must be minimized. d) Simulation of the dynamic behaviour of the mechanism for different acceleration profiles, until the desired target is achieved; the criterion used for the selection of the parameters that define each profile is dependent on the particular algorithm employed for the optimization process. The optimized motion laws can be easily transferred into the mechanism controller: it is sufficient to modify only the numerical tables that define the reference profiles in a ROM memory. The proposed method can be applied to assembly robots, that do not require to follow a particular trajectory by the end effector, but only a point to point movement in a prefixed time, which is consistent with the requirements of the manufacturing cycle and with the working speed of the machine.