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Title: Planning dextrous robot hand grasps from range data, using preshapes and digit trajectories
Author: Wren, David Owen
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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In this thesis a grasp metric based on stability and kinematic feasibility is introduced. The preshaping paradigm is extended to include consideration of the trajectories that the digits take during closure from preshape to final grasp. The resulting grasp strategy is dependent upon task requirements and is designed for a set of "ideal" object-hand configurations. The grasp strategy couples the degrees of freedom of the dextrous hand in an anthropomorphic manner; the resulting reduction in degrees of freedom makes the grasp planning less complex. Grasp strategies are fitted to real objects by optimisation of the grasp metric; this corresponds to fitting the real object-hand configurations as close to the ideal as possible. First, the preshape aperture, which defines the positions of the fingertips in the preshape, is found by optimisation of an approximation to the grasp metric (which makes simplifying assumptions about the digit trajectories and hand kinematics). Second, the full preshape kinematics and digit closure trajectories are calculated to optimise the full grasp metric. Grasps are planned on object descriptions built from laser striper range data from two viewpoints. A surface description of the object is used to prune the space of possible contact sites and to allow the accurate estimation of surface normals, which is required by the grasp metric to estimate the amount of friction required. A voxel description, built by ray-casting, is used to check for collisions between the object and the robot hand using an approximation to the Euclidean distance transform. Results are shown in simulation for a 3-digit hand model, designed to be like a simplified human hand in terms of its size and functionality. There are clear extensions of the method to any dextrous hand with a single thumb opposing multiple fingers and several different hand models that could be used are described. Grasps are planned on a wide variety of curved and polyhedral objects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available