Dexterous grippers: between simple industrial grippers and complex robotic hands

This thesis addresses the issue of introducing dexterity, namely the ability to manipulate objects in hand, into simple mechanical grippers. Among the many possibilities to give dexterity to a gripping device we opted to intervene at the finger-pad surface since it is the part of the end effector directly in contact with the object to be manipulated. The first contribution is the development of an under-actuated gripper with Active Surfaces on the inner side of the fingers which allow to in-hand manipulate the grasped objects. The gripper, named Velvet Fingers, was designed from the theoretical concepts, manufactured, assembled and then turned into an applicative scenario. A second main contribution of this thesis, carried out in collaboration with AASS Research Center, of the University of \"Orebro (Sweden), is a grasp execution routine using the Active Surfaces of the Velvet Fingers to achieve a robust power grasp starting from an initial fingertip grasp. This routine is very useful and effective in cluttered environment where an initial fingertip grasp is much more likely to be feasible than a bulky power grasp. The third main contribution is the development of a small gripper for small household objects such as cans, small bottles, little boxes, tennis balls etc. This gripper, named Velvet-II, is able to perform in-hand manipulation tasks, to elicit information from the grasped object, namely the contact point location and the components of the grasping forces and to detect incipient slippage between the gripper and the object. Within a collaboration with AASS Research Center the gripper has been employed on a robotic platform for autonomous picking and palletizing

Verso un microgripper di silicio: prove sperimentali, modellazione e progettazione

Sommario Verso un microgripper di silicio: prove sperimentali, modellazione e progettazione. Questo lavoro di tesi è focalizzato su microgripper meccanici a due dita. Si è in primo luogo svolto un lavoro di caratterizzazione a fatica di un microgripper in acciaio armonico realizzato presso il Dipartimento di Ingegneria Meccanica e Nucleare sezione Produzione. Al fine di miniaturizzare ulteriormente il microgripper si è iniziata la caratterizzazione del silicio, materiale che sta assumendo sempre maggior importanza non solo per prodotti elettronici, ma anche per microprodotti elettromeccanici. Si sono quindi realizzati strumenti sia FEM sia analitici per lo studio delle deformazioni di un microgripper piano in silicio. Presso il Laboratorio di Tecnologie Microelettroniche e Microsistemi del Dipartimento di Ingegneria dell’Informazione è in corso la messa a punto di una tecnica di fabbricazione di microstrutture in silicio che comporta la formazione di una distribuzione ordinata di microfori diretti secondo lo spessore. Il microgripper così realizzato risulta perciò completamente microforato e di questo se ne sono valutati gli effetti sulla risposta elastica del microgripper stesso. Particolarmente importante per un gripper meccanico è poi il controllo della forza di presa, per cui se ne sono fatte alcune simulazioni e studiato le deformazioni correlate. Toward a silicon microgripper: experimental tests, modellation and design. Abstract This work is focused on two fingers mechanical microgrippers. At the beginning we have developed a work of characterization of the behavior at fatigue of an harmonic steel microgripper made at the Department of Mechanical and Nuclear Engineering section Production. In order to miniaturize further the microgripper we started characterizing the silicon, a material which is assuming always more importance not only for electronic devices, but also for electromechanical microproducts. Therefore we have carried out the instruments, whether FEM or analytic, for the analysis of the strain of a plane silicon microgripper. At Microelectronic Technologies and Microsystems Lab of the Department of Information Engineering, the manufacturing process for achieving a thick silicon microstructure is in progress. The final structure is formed by a tidy pattern of microholes in the direction of the thickness. The microgripper, obtained through such process, is totally microholed and so it is necessary to evaluate its effects on the elastic response of the microgripper itself. The grasping force control is especially important for a mechanical gripper, therefore we simulated and analised the correlated strain

Implementation and Control of the Velvet Fingers: a Dexterous Gripper with Active Surfaces

Since the introduction of the first prototypes of robotic end-effectors showing manipulation capabilities, much research focused on the design and control of robot hand and grippers. While many studies focus on enhancing the sensing capabilities and motion agility, a less explored topic is the engineering of the surfaces that enable the hand to contact the object. In this paper we present the prototype of the Velvet Fingers smart gripper, a novel concept of end-effector combining the simple mechanics and control of under-actuated devices together with high manipulation possibilities, usually offered only by dexterous robotic hands. This enhancement is obtained thanks to active surfaces, i.e. engineered contact surfaces able to emulate different levels of friction and to apply tangential thrusts to the contacted object. Through the paper particular attention is dedicated to the mechanical implementation, sense drive and control electronics of the device; some analysis on the control algorithms are reported. Finally, the capabilities of the prototype are showed through preliminary grasps and manipulation experiment

Design of an under-actuated wrist based on adaptive synergies

An effective robotic wrist represents a key enabling element in robotic manipulation, especially in prosthetics. In this paper, we propose an under-actuated wrist system, which is also adaptable and allows to implement different under-actuation schemes. Our approach leverages upon the idea of soft synergies - in particular the design method of adaptive synergies - as it derives from the field of robot hand design. First we introduce the design principle and its implementation and function in a configurable test bench prototype, which can be used to demonstrate the feasibility of our idea. Furthermore, we report on results from preliminary experiments with humans, aiming to identify the most probable wrist pose during the pre-grasp phase in activities of daily living. Based on these outcomes, we calibrate our wrist prototype accordingly and demonstrate its effectiveness to accomplish grasping and manipulation tasks

The Next Step in Robot Commissioning : Autonomous Picking and Palletizing

So far, autonomous order picking (commissioning) systems have not been able to meet the stringent demands regarding speed, safety, and accuracy of real-world warehouse automation, resulting in reliance on human workers. In this letter, we target the next step in autonomous robot commissioning: automatizing the currently manual order picking procedure. To this end, we investigate the use case of autonomous picking and palletizing with a dedicated research platform and discuss lessons learned during testing in simplified warehouse settings. The main theoretical contribution is a novel grasp representation scheme which allows for redundancy in the gripper pose placement. This redundancy is exploited by a local, prioritized kinematic controller which generates reactive manipulator motions on-the-fly. We validated our grasping approach by means of a large set of experiments, which yielded an average grasp acquisition time of 23.5 s at a success rate of 94.7%. Our system is able to autonomously carry out simple order picking tasks in a humansafe manner, and as such serves as an initial step toward future commercial-scale in-house logistics automation solutions

Sensitive Active Surfaces on the Velvet II Dexterous Gripper

The Velvet Fingers [1] is a dexterous under-actuated gripper for unstructured industrial environments. It offers enhanced manipulability by means of Active Surfaces (AS) on its fingers, i. e., surfaces able to emulate different levels of friction and to apply tangential thrusts to the contacted object. The usefulness of the AS (implemented by controlled conveyor belts) is discussed in [2]. Although their benefits are substantial, their main limitations are the lack of force feedback and missing information of the contact point location, as well as limitations on the fictitious friction range

The Grasp Acquisition Strategy of the Velvet II

In this work we exploit the combined effects of the underactuation and the active surfaces of the Velvet II dexterous gripper. The aim is to achieve a firm enveloping grasp, starting from an initial pinch grasp. The pull-in grasping strategy described here turns out to be very useful in untidy environments where the scene is populated by many objects in a cluttered disposition. In this context, a nimble fingertip grasp is more likely to be feasible than a robust enveloping gras

Improving Grasp Robustness via In-Hand Manipulation with Active Surfaces

EU-FP7 RobLo