Caractérisation, modélisation et contrôle vibratoire d’une articulation rotoïde flexible, dédiée à un système robotique

Abstract

This thesis presents a characterization, modeling and experimental research work on vibration control of a flexible robotic system. Within the scope of this work, we build a one degree of freedom experimental set-up in order to characterize different components of a joint and design control algorithms for minimizing the vibration. The ultimate goal is to generalize the proposed approach for implementation in the next generation of the SCOMPI robot at IREQ Hydro-Québec’s research institute. Characterization of stiffness, hysteresis effect, friction and kinematic error of the harmonic drive was performed and a mathematical model (Simulink) taking into accounts the nonlinearities inherent to the harmonic drive was developed. The experimental set-up was a single-arm robot with a rotational joint including two rotating encoders; one on the motor at the input and another one on the at output link. Since the measurement difference between the two encoders is used to evaluate the vibrational behaviour of the test rig, the accuracy of encoders is critical. Therefore, a laser tracker was used to characterize the error of the output encoder. The results showed that the error was repeatable and it is thus possible to compensate it in real-time. This correction allowed reaching an accuracy of 50 μrad (8 time better then without). Four Rosette strain gauges were fixed on the flexible spline of the harmonic drive to determine its torsion. To reduce the torque ripple (about 2% of the maximum torque of the harmonic drive), a real-time correcting function was applied. It was therefore possible to reduce the error down to 0.3% of the full scale error. The torque sensor was also used to replace the reading of the output rotating encoders and experimental results were found very well matching. Vibration control was performed implementing two strategies, namely the singular perturbation and feed-forward control. Simulation results showed a considerable suppression of vibration response compared to a common rigid control for the two types of control schemes implemented. However, experimental results showed a considerable suppression of vibration response only with the feed-forward approach while the singular perturbation methodology generated too much torque ripple to the motor. Feedforward controller can quickly stabilize the link for the same response time as with the rigid control algorithm.

Date	26 Apr 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Zhaoheng Liu (Supervisor) & Pascal Bigras (Co-supervisor)