A Model-Free Approach for Accurate Joint Motion Control in Humanoid Locomotion

A new model-free approach to precisely control humanoid robot joints is presented in this article. An input&-output online identification procedure will permit to compensate neglected or uncertain dynamics, such as, on the one hand, transmission and compliance nonlinear effects, and, on the other hand, network transmission delays. Robustness toparameter variations will be analyzed and compared to other advanced PID-based controllers. Simulations will show that not only good tracking quality can be obtained with this novel technique, but also that it provides a very robust behavior to the closed-loop system. Furthermore, a locomotion task will be tested in a complete humanoid simulatorto highlight the suitability of this control approach for such complex systems.This work has been supported by the CAM Project S2009/DPI-1559/ROBOCITY2030 II, developed by the research team RoboticsLab at the University Carlos III of Madrid.Publicad

Nonlinear robust control of functional electrical stimulation system for paraplegia

The study was directed towards enhancing Functional Electrical Stimulation (FES) for sit-to-stand movement restoration in paraplegia subjects. The scarcity of FES assistive devices was due to the inability of the developed equipment to attain clinical acceptance. Applications of control systems have shown fruitful results. And based on the literature, further improvements in model, trajectory and control systems are needed. Model with a higher level of accuracy and continuous as well as bump-free trajectories are essential ingredients for better control systems. The control systems can be enhanced by giving considering to changes in mass of the subject, disturbance rejection and stability. Hence, the comprehensive control scheme is necessary for this application as well as a better model and trajectory. In modelling an additional joint has been considered to improve the accuracy. In trajectory planning, the six-order polynomial has been used to refine the desired trajectory. The comprehensive control systems have been designed with consideration of robustness, disturbance rejection, and stability. Three nonlinear control approaches have been investigated; the Sliding Mode Control (SMC), Feedback Linearisation Control (FLC), and Back-Stepping Control (BSC). Results reveal improvements in the accuracy of the kinematic model by 24%, and the dynamic model by 47%. The trajectory planning parameters are continuous, and not susceptible to jerks or spikes. Execution time enhanced by 11%, the upper and lower terminal velocities improved by 16.9% and 20.9% respectively. The system response without disturbance shows good results with the SMC, FLC, and BSC. Revelations by robustness examination also maintain remarkable enhancements in the parameters with both 53% and 126% mass. The results for disturbance rejection examinations with fatigue, spasm, tremor, and combined disturbance effects showed sustenance of refinement in the response parameters. Therefore, indicating improvements despite the changes to the system. The BSC showed the best performance, followed by the FLC, and the SMC. Hence, the BSC is recommended for such systems

Modélisation et compensation des déficiences linéaires et non linéaires dans les transmissions électromécaniques des robots humanoïdes

Walking robots need precise control for legs articulations because it influence their equilibrium. It is necessary to compensate vibrational effects caused by imperfections in their articulations, like elasticities, mechanical backlashes, frictions and structural deformations and those appearing during shocks with the ground or when forces become significant. Our approach consists in correcting the inputs of the robot control system in a robust way according to variations of functional conditions and robot parameters. To reach this objective, we use adaptive and learning control methods, nonlinear oscillators.The research problematic, objectives, and state of the art are presented in the chapter 1. As it’s necessary to know exact torques of a robot, we present in the chapter 2 an approach of polyarticulated multi-masses systems modeling that takes into account its control system, mechanical transmissions and nonlinearities of transmissions. Experimental validations are carried on the biped robot ROBIAN. The chapter 3 explains the instrumentation of the non-direct articulation accelerations measurement method based on distributed accelerometer measurements on the body of the robot. The chapter 4 concerns experimental validation of compensation and control methods for ROBIAN for different kinds of flexion/extension movements.Les robots marcheurs demandent un contrôle articulaire des jambes précis car cela influence leur équilibre. Il est important de compenser les effets vibratoires provoqués par les imperfections dans leurs articulations comme les élasticités, les jeux mécaniques, les frottements, les déformations structurelles et celles qui apparaissent lors des chocs contre le sol ou lorsque les efforts deviennent importants.Notre démarche consiste à ajouter une correction dans les boucles d’asservissement articulaires du robot qui améliore la robustesse par rapport aux changements des conditions du fonctionnement et aux paramètres du robot. Pour atteindre cet objectif, nous comparons différentes méthodes dont celles de contrôle par adaptation et par apprentissage, à base d’oscillateurs non linéaires.Dans le chapitre 1, la problématique et les objectifs de la recherche, l’état de l’art sont présentés. Dans le but de connaitre les couples articulaires exacts d’un robot, le chapitre 2 présente la modélisation des systèmes polyarticulés multimasses avec système d’asservissement, les transmissions prenant en compte les non linéarités articulaires. La validation expérimentale est donnée pour le robot bipède ROBIAN. Le chapitre 3 explique le système d’instrumentation de mesure indirecte à base d’accéléromètres permettant de calculer des accélérations articulaires à partir des mesures réparties sur le corps d’un robot marcheur. Le chapitre 4 concerne la validation expérimentale des méthodes de compensation et de contrôle sur ROBIAN