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: This paper addresses the problem of computing stable grasps of three-dimensional polyhedral objects. We consider the case of a hand equipped with four hard fingers and assume point contact with friction. We prove new necessary and sufficient conditions for equilibrium and force closure, and present a geometric characterization of all possible types of four-finger equilibrium grasps. We then focus on concurrent grasps, for which the lines of action of the four contact forces all intersect in a point. In this case, the equilibrium conditions are linear in the unknown grasp parameters, which reduces the problem of computing the stable grasp regions in configuration space to the problem of constructing the eight-dimensional projection of an eleven-dimensional polytope. We present two projection methods: the first one uses a simple Gaussian elimination approach, while the second one relies on a novel output-sensitive contour-tracking algorithm. Finally, we use linear optimization within t...

Abstract not found

This paper addresses the problem of grasping and manipulating three-dimensional objects with a reconfigurable gripper that consists of two parallel plates whose distance can be adjusted by a computer-controlled actuator. The bottom plate is a bare plane, and the top plate carries a rectangular grid of actuated pins that can translate in discrete increments under computer control. We propose to use this gripper to immobilize objects through frictionless contacts with three of the pins and the bottom plate, and to manipulate an object within a grasp by planning the sequence of pin configurations that will bring this object to a desired position and orientation. A detailed analysis of the problem geometry in configuration space is used to devise simple and efficient algorithms for grasp and manipulation planning. The proposed approach has been implemented and preliminary simulation experiments are discussed. 1

This thesis is about force controlled compliant robot motion, with the emphasis on: 1) mod- elling of arbitrary and time-varying contact situations between a rigid manipulated object and rigid objects in its environment, 2) motion specification in terms of allowed velocities and ac- celerations for the manipulated object, maintaining the contact with the physical constraints but without generating too large contact forces, and 3) on-line identification of uncertainties in the instantaneous geometric parameters of the motion constraint model, i.e., the position of the contact points, the direction of the contact normal, and the local curvature parameters. Requirements for generality, simplicity and robustness have guided the research work.

This paper addresses the problem of grasping and manipulating three-dimensional objects with a reconfigurable gripper equipped with two parallel plates whose distance can be adjusted by a computercontrolled actuator. The bottom plate is a bare plane, and the top one carries a rectangular grid of actuated pins that can translate in discrete increments under computer control. We propose to use this gripper to immobilize objects through frictionless contacts with three of the pins and the bottom plate, and to manipulate an object within a grasp by planning the sequence of pin configurations that will bring this object to a desired position and orientation. A detailed analysis of the problem geometry in configuration space was used in [44] to devise simple and efficient algorithms for grasp and manipulation planning. We have constructed a prototype of the gripper and this paper presents our experiments.

A new discrete event controller synthesis methodology for the successful convergence of assembly tasks is presented. The modelling of an assembly process as a hybrid dynamic system has been shown to be a very effective strategy to incorporate both the continuous and discrete natures of the interaction between the workpiece and its environment. Prior works have presented controller synthesis methodologies for velocity- controlled systems [8] and here we follow a similar structure for force-controlled systems. Force control is a natural paradigm for assembly as it is fundamentally compliant. Compliance reduces sensitivity to positioning errors, which are the most common source of failure in assembly. A non-trivial example is given which demonstrates the effectiveness of this method.

This paper addresses the problem of using three disc-shaped robots to manipulate a polygonal object in the plane in the presence of obstacles. The proposed approach is based on the computation of maximal discs (dubbed maximum independent capture discs, or MICaDs) where the robots can move independently while preventing the object from escaping their grasp. It is shown that, in the absence of obstacles, it is always possible to bring a polygonal object from any configuration to any other one with robot motions constrained to lie in a set of overlapping MICaDs. This approach is generalized to the case where obstacles are present by decomposing the corresponding motion planning task into (1) the construction of a collision-free path for a modified form of the object, and (2) the execution of this path by a sequence of simultaneous and independent robot motions within overlapping MICaDs. The proposed algorithm is guaranteed to generate a valid plan provided a collision-free path exists for the modified form of the object. It has been implemented and experiments with Nomadic Scout mobile robots are presented.

................................................................................................................... vi INTRODUCTION........................................................................................................... 1 Problem Statement ......................................................................................................1 Project Background .....................................................................................................2 History of Vehicles Automated at CIMAR...............................................................2 Evolution of the NTV's Architecture .......................................................................5 Research Motivation....................................................................................................7 Research Objective ......................................................................................................9 REVIEW OF THE LITERATURE......................................

this paper is organized as follows. Previous work in fixture and grasp planning is reviewed in Section 2. Our approach is described in Section 3: sufficient conditions for immobility and stability are derived in Section 3.1; they are used in Section 3.2 to design an efficient algorithm for enumerating all immobilizing stable fixtures of a given polyhedral object using the