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L. Biagiotti
" Advanced Robotic Hands: Design and Control Aspects"
Type PhD Thesis
Author(s) L. Biagiotti
Title Advanced Robotic Hands: Design and Control Aspects
Editor University of Bologna
Keywords Robot Hands, Control
In last decades, there has been a growing interest towards the development of advanced robotic hands, that is robotic end-effectors able to reproduce the functional capabilities (and in some cases the structure) of the human hand. The applications of such devices can be various: when the goal is to perform, by means of a robotic system, activities which foresee physical interactions (e.g. grasping and manipulation of some objects) with an unstructured environment, the use of an advanced end-effector is necessary. A typical application field is those of space activities, where robotic systems aim to replace human beings in the accomplishment of tasks, which are too dangerous, time consuming or simply annoying. However, despite the wide potential applications of these devices, no real examples can be found and their use remains limited to research laboratories. As a matter of fact the high-level capabilities of dexterous hands to perform manipulation tasks imply, as a side-effect, high complexity of their mechanical structure, their sensory equipment and the control strategies. This is mainly due to technological limits: the human hand is the ideal target of each researcher in the field of dexterous manipulation but the tools (actuators, sensors...) currently available are still far from their biological models (muscles, receptors...). The structural complexity of dexterous robotic hands leads to high costs and very poor reliability of the developed prototypes. Therefore an important requirement to encourage the diffusion of such devices will be their general simplification. Several are the ways to achieve this simplification. Obviously, technological improvements (concerning actuators, materials, sensors...) can allow an improvement of the overall system. The implementation of suitable control strategies can help to manage the complexity of such devices. The adoption of new design criteria (which are currently tied to the traditional robotics) can lead to simplified mechanical structures. But, in general, the problem of complexity has been not faced by the designers of dexterous robotic hands, whose target is to prove the effectiveness of a particular structure, rather than to make an “usable” device. Moreover, often the attention is mainly devoted to the physical design and development of the robotic hands, rather than to control problems tied to these devices. It is widespread the (wrong) idea that the control must be added (and hence designed) in a second phase. Therefore, some impressive examples of dexterous robotic hands are indeed able to perform only simple manipulation tasks, since the control is not adequate. Conversely, there are some devices which are purposely designed to validate control algorithms for dexterous manipulation, but usually they have simple structures and they can not be defined hands. The thesis have been structured in the following way: - In Chapter 2, starting from a review of some noticeable robotic hands developed over the last three decades, the state of art in robotic manipulation is analyzed with the purpose of emphasizing trends and open problems that currently characterize this research field. - In Chapter 3, a robotic gripper purposely designed for space applications is presented. Despite a trends towards anthropomorphic hands has been recognized, the design of this device aims to demonstrate the effectiveness of a not-anthropomorphic structure to perform complex operations. - The research activity, reported in Chapter 4, aims to validate the use of a new sensing element for mechanical “strain” in the robotic field. In particular, this new transducer (directly built on a deformable substrate) could replace traditional strain-gauge technology in force/torque sensors manufacturing, encouraging a deeper integration between mechanical and electronic part. The final result will be a general simplification and a considerable reduction of the dimensions of force sensors, which could be easily integrated in those structures where the available room is very narrow, such as the fingers of a robotic hand. - Chapter 5 presents the development of a controller able to drive a complex robotic system, such as a multifingered robotic hand, during the interaction with the environment in order to perform grasp and manipulation tasks. In particular a suitable strategy has been recognized in the impedance controller approach, which has been adapted to solve specific problems of dexterous robotic end-effectors. The achieved control algorithm has been implemented and experimentally validated on the DLR Hand II. - Chapter 6 describes the development, from the early idea to a working prototype, of a new kind of articulated robotic fingers, that is the basic element which will form a new hand for dexterous manipulation. This research summarizes in real terms the idea developed over this thesis and in this sense it is the right conclusion of the overall work; in particular it shows how, by means of a proper integration between the design of the physical structure (mechanical frame as well as sensory equipment) and the choice of the control strategies, it is possible to achieve a general simplification of robotic devices for dexterous manipulation.
Document 21a5.Document.pdf (4430054 bytes)
Year 2003

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