Littérature scientifique sur le sujet « Non-backdrivability »

Since torque in harmonic drives is transmitted by a pure couple, harmonic drives do not generate radial forces and therefore can be instrumented with torque sensors without interference from radial forces. The installation of torque sensors on the stationary component of harmonic drives (the Flexipline cup in this research work) produce backdrivability needed for robotic and telerobotic compliant maneuvers [3, 4, 6]. Backdrivability of a harmonic drive, when used as torque increaser, means that the output shaft can be rotated via finite amount of torque. A high ratio harmonic drive is non-backdrivable because its output shaft cannot be turned by applying a torque on it. This article first develops the dynamic behavior of a harmonic drive, in particular the non-backdrivability, in terms of a sensitivity transfer function. The instrumentation of the harmonic drive with torque sensor is then described. This leads to a description of the control architecture which allows modulation of the sensitivity transfer function within the limits established by the closed-loop stability. A set of experiments on an active hand controller, powered by a DC motor coupled to an instrumented harmonic drive, is given to exhibit this method’s limitations.

High performance requirements in robotics have led to the consideration of structural flexibilty in robot arms. This paper employs an assumed modes method to model the flexible motion of the last link of a spherical coordinate robot arm. The model, which includes the non backdrivability of the leadscrews, is used to investigate relationships between the arm structural flexibility and a linear controller for the rigid body motion. This simple controller is used to simulate the controllers currently used in industrial robots. The simulation results illustrate the differences between leadscrew driven and unconstrained axes of the robot; they indicate the trade-off between speed and accuracy; and show potential instability mechanisms due to the interaction between the controller and the robot structural flexibility.

AbstractA worm gear has the advantages of a large reduction ratio and non-backdrivability. Because of this non-backdrivability, it can maintain a joint angle without energy consumption. Today, many robots have large workspaces that extend into the living spaces of humans, and they are required to work cooperatively with humans. In such cases, backdrivability is necessary to achieve high compliance for robots. Compliance helps robots perform cooperative tasks with humans, and protects its mechanisms and humans in the case of a collision. However, a worm gear cannot be backdriven because of the friction between tooth surfaces. Therefore, we have developed a worm gear mechanism that can switch its backdrivability using vibration that reduces friction. In this paper, we present a dynamic model of the worm gear to analyze the friction-reduction phenomenon caused by vibrations. We discuss the change in the effectiveness of the backdrivability with the change in the vibration direction. Finally, we experimentally confirm the certainty of the analysis.

L’objectif principal de cette thèseest de présenter une prothèse de main myoélectriqueaccessible qui combine des critèrestels que le prix abordable, la solidité, la fonctionnalitéet la performance. Cette nouvelleprothèse permet d’effectuer des prises latéraleset opposées. Tout d’abord, nous proposonsune méthode de placement des articulationsqui permet d’obtenir un résultatplus réaliste sur le plan anthropomorphique.De plus, nous avons développé et optimiséune solution de transmission interdigitale quipermet d’associer la flexion des doigts supérieursà celle du pouce. Une analyse détailléede la performance énergétique et thermiquede la prothèse est également présentée.Nous avons proposé une nouvelle stratégiede commande qui tire parti de l’irréversibilitéde la transmission de puissance et nousl’avons étudiée. Enfin, nous soulignons l’importanced’une transmission de puissance optimalesur le plan énergétique. Pour cela, nousdécrivons en détail la synthèse d’un nouveaumécanisme de réducteur à rapport variable,ainsi que la présentation d’un nouveau mécanismed’irréversibilité efficace. Enfin, nousavons évalué individuellement tous ces composantsde prothèse en mettant en place desprototypes expérimentaux qui démontrent leurutilité. L’intégration de ces composants dansune nouvelle prothèse est une perspective envisagéedans cette étude
The main objective of this thesisis to present an accessible myoelectric handprosthesis that combines criteria such as affordability,durability, functionality, and performance.This new prosthesis allows for bothlateral and opposing grips. Firstly, we proposea method for joint placement that achieves amore realistic anthropomorphic result. Additionally,we have developed and optimized aninterdigital transmission solution that enablesthe coordination of the flexion between the upperfingers and the thumb. A detailed analysisof the prosthesis’s energy and thermalperformance is also provided. We have proposeda new control strategy that takes advantageof the irreversibility of power transmissionand thoroughly studied it. Furthermore,we emphasize the importance of achievingoptimal energy-efficient power transmission.To this end, we describe in detail the synthesisof a new mechanism with variable reductionratio and present a new efficient irreversibilitymechanism. Finally, we individuallyevaluate all these prosthesis componentsby implementing experimental prototypes thatdemonstrate their usefulness. The integrationof these components into a new prosthesis isa prospective direction explored in this study

Abstract The paper reports design and implementation of a Delta Robot based non-anthropomorphic hand. A set of three constant orientation Delta robots are shown to be useful to perform manipulation maneuvers on the object. Voice coil arc actuators are deployed to improve the backdrivability of the robot. The hand consists of three constant orientation fingers which are deployed to grasp an object. The fingers are programmed to behave as a set of springs to generate stable object acquisition. The capability of the robotic hand to perform different maneuvers is demonstrated. The dynamic feedback linearisation method is shown to be useful both for controlling the robotic hand and also to ensure passive grasp of the robotic system. It is shown that the hand can be used to catch an object, improve the grasp forces on the surface of the object, impart oscillatory motion, and also to throw the object in a prescribed direction. Standalone examples are described to suggest the same. The backdrivability of the voice coil arc actuators are demonstrated to be of purpose in improving the passive grasp behaviour of the robot. The swift motion of the actuators are shown to be useful while performing quick oscillations and also to throw the object.