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Fundamentals_of_Robotic_Mechanical_Systems Part 2

Tham khảo tài liệu 'fundamentals_of_robotic_mechanical_systems part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 12 1. An Overview of Robotic Mechanical Systems FIGURE 1.8. The four-fingered hydraulically actuated TU Munich Hand courtesy of Prof. F. Pfeiffer. others. Of these the Utah MIT Hand Jacobsen et al. 1984 1986 is commercially available. It consists of four fingers one of which is opposed to the other three and hence plays the role of the human thumb. Each finger consists in turn of four phalanges coupled by revolute joints each of these is driven by two tendons that can deliver force only when in tension each being actuated independently. The TU Munich Hand shown in Fig. 1.8 is designed with four identical fingers laid out symmetrically on a hand palm. This hand is hydraulically actuated and provided with a very high payload-to-weight ratio. Indeed each finger weighs only 1.470 N but can exert a force of up to 30 N. We outline below some problems and research trends in the area of dextrous hands. A key issue here is the programming of the motions of the fingers which is a much more complicated task than the programming of a six-axis manipulator. In this regard Liu et al. 1989 introduced a task-analysis approach meant to program robotic hand motions at a higher level. They use a heuristic knowledge-based approach. From an analysis of the various modes of grasping they conclude that the requirements for grasping tasks are i stability ii manipulability Hi torquability and iv radial rotatability. Stability is defined as a measure of the tendency of an object to return to its original position after disturbances. Manipu-lability as understood in this context is the ability to impart motion to the object while keeping the fingers in contact with the object. Torquability or tangential rotatability is the ability to rotate the long axis of an object here the authors must assume that the manipulated objects are 1.6 Walking Machines 13 convex and can be approximated by three-axis ellipsoids thereby distinguishing between a longest and a shortest axis with a minimum force for a