In this paper, an attempt at summarizing the evolution and the state-of-the-art in the field of robot hands is made. In such exposition, a critical evaluation of what in the author's view are the leading ideas and emerging trends, is privileged with respect to exhaustiveness of citations. The survey is focused mainly on three types of functional requirements a machine hand can be assigned in an artificial system, namely, manipulative dexterity, grasp robustness, and human operability. A basic distinction is made between hands designed for mimicking the human anatomy and physiology, and hands designed to meet restricted, practical requirements. In the latter domain, arguments are presented in favor of a "minimalistic" attitude in the design of hands for practical applications, i.e., use the least number of actuators, the simplest set of sensors, etc., for a given task. To achieve this rather obvious engineering goal is a challenge to our community. The paper illustrates some of the ...

Fixturing is a fundamental problem in mechanical assembly. Usually, two and a half dimensional objects can be fixtured in many different ways using a fixture vice, especially if pegs of different radii are available. We present an algorithm which enumerates all force closure fixture vice configurations and corresponding object poses. Automatic fixture design algorithms are essential for planning because optimal fixturing selection for multiple operations requires examining all of the valid configurations. The algorithm runs in O(A) time, where A is the number of configurations which simultaneously contact the object. 1 Introduction The task of immobilizing a workpiece via mechanical devices, commonly called fixturing or workholding, is an essential problem in manufacturing. Machining fixtures must handle very large forces (20KN), whereas assembly fixtures handle smaller forces (50N). Fixture apparatus design is more a craft than a science. Without geometric analysis, a fixturing exp...

We consider the problem of finding optimum force closure grasps of two and three-dimensional objects. Our focus is on grasps which are useful in practice, namely grasps with a small number of fingers, with friction at the contacts. Assuming frictional contact and rounded finger tips---very mild assumptions in practice---we give new upper (and lower) bounds on the number of fingers necessary to achieve force closure grasps of 2-D and 3-D objects. We develop an optimality criterion based on the notion of decoupled wrenches, and use this criterion to derive optimum two and three finger grasps of 2-D objects, and optimum three finger grasps for 3-D objects. We present a simple O(n) algorithm for computing these optimum grasps for convex polygons, a O(n log n) algorithm for non-convex polygons, and an O(n 3 ) algorithm for polyhedra. In studying these optimum grasps, we derive several interesting theoretical results concerning grasp geometry. 1 Introduction The theory of what constitute...

Three important problems in the study of grasping and manipulation by multifingered robotic hands are: (a) Given a grasp characterized by a set of contact points and the associated contact models, determine if the grasp has force closure; (b) If the grasp does not have force closure, determine if the ngers are able to apply a specified resultant wrench on the object; and (c) Compute "optimal" contact forces if the answer to problem (b) is affirmative. In this paper, based on an early result by Buss, Hashimoto and Moore, which transforms the nonlinear friction cone constraints into positive definiteness of certain symmetric matrices, we further cast the friction cone constraints into linear matrix inequalities (LMIs) and formulate all three of the problems stated above as a set of convex optimization problems involving LMIs. The latter problems have been extensively studied in optimization and control community and highly efficient algorithms with polynomial time complexity are now available for their solutions. We perform simulation studies to show the simplicity and efficiency of the LMI formulation to the three problems.

A familiar task in industrial applications is grasping an object to constrain its motions. When the external forces and torques acting on the object are uncertain or varying, form-closure grasps are preferred; these are grasps that constrain all infinitesimal and finite motion of the object. Much of previous work on computing form-closures has involved achieving it with point-contacts; for a planar object, four point-contacts were proven to be necessary and sufficient. Inspired by the intuitive habit of supporting an object against something flat to immobilize it, in this paper we propose a new class of contacts called edge-contacts; these offer a straight-line support against which the object rests. Our first result is that almost any polygonal part can be constrained in form-closure with an edge-contact and two point-contacts. A related problem is that of immobilizing an object with modular fixtures. These typically comprise of a regular lattice of holes on which the object is placed...

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