Showing papers by "Paolo Rocco published in 2002"

Modelling Flexible Manipulators With Motors at the Joints

Abstract: A computationally efficient recursive model of a flexible manipulator with motors at the joints is described in this paper. The model adopts a mixed Eulerian and Lagrangian formulation of the equations of a flexible body and exploits the chained structure of the equations for a serial manipulator. The dynamic effects of the motors at the joints, including gyroscopic terms, are fully taken into account. Symbolic manipulation is used in a newly developed package, whose performance in detailed reproduction of the dynamic effects due to the interplay between the motors and the flexible links is assessed through simulation. A comparison between the complete model and a simplified one, where the motors are considered as simple inertias rotating around their own axis, has been carried out, using both a time domain analysis and a frequency domain analysis, in order to show the relevance of gyroscopic effects in modelling flexible robots.

Limitations in control of elastic servos with co-located sensors

Abstract: Performance limitations of elastic servomechanisms where only the motor position is measured emerge considering also the load position behavior. Limitations inherent to PID control, the most common solution in commercial products are dealt with first. The authors explicitly relate a bound of the H/sub /spl infin// norm of the motor position setpoint to load position transfer function to the motor position loop bandwidth and to the other servo design parameters. Then they show that introducing the torque disturbance observer the load oscillates almost freely at the locked frequency, when excited either from the setpoint or from a torque disturbance at the load side. Finally, they point out that even a very general two-way control structure, combining a feedforward action and an observer based algebraic feedback, cannot improve sensibly the performance achieved with the PID controller.

Modeling and experimental analysis of the vibrations in hard disk drives

Abstract: A combined methodology, based on dynamic modeling and experimental measures, is used to study the vibrations in hard disk drives, in a frequency range up to 1 kHz. A lumped parameter model of the disks/spindle assembly is developed, where only the disk modes coupled with the spindle motion are retained. The proposed model has been validated by comparison with experimental results. Using the model, the sources of axial and radial vibrations measured in a single plate commercial hard disk drive have been explained. Among them are the disk structural resonances, due to compliances in bearings and disks, displacements of the center of mass from the rotation axis and unbalanced magnetic forces. On the other hand, no evidence has been found of the influence of torque disturbances on the measured vibrations.

Simulating permanent magnet brushless motors in DYMOLA

Abstract: Multi-domain dynamic simulation is becoming an is- sue in the design of high performance mechatronic systems, where advances are foreseen only if the mu- tual interaction of different parts of the system is well understood. The modelling environment provided by DYMOLA with Modelica language proved to be ideal for studying the mutual effects of mechanics, elec- tronics and control in a brushless motor, whose model has been conceived as one of the building blocks of a wider project, aimed at simulating a complete machin- ing centre. Details on the model of the brushless motor as well as on its simulation are given in the present pa- per.