Two-Fingered Grasp of Cylindrical Objects in Planar Motion
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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This thesis will develop analytic expressions which model the equilibrium requirements of a grasp by two robotic fingers on a nominally-loaded cylindrical object confined to planar motion. It will derive analytic expressions to evaluate the ability of a grasp to tolerate changes in the external load magnitude, direction, and moment without loss of equilibrium. The gripper fingers are each assumed to be two-link serial mechanisms with revolute joints. The contact of each finger on the object is taken as a point contact with friction. The resulting analytic expressions are based on the static equilibrium requirements and include consideration of constraints on Coulomb friction forces, unisense normal forces, object crush limits, and finger joint torque limits. Plotting the expressions yields new graphical insight into the consequences of employing various fingertip spacings and squeeze force levels when grasping cylindrical objects in planar motion. The analytic equations indicate the range of variation in external load configuration which can be tolerated by a selected grasp without violating any of the aforementioned grasp constraints. Variations in the magnitude, direction, and moment of the external load configuration are considered. The derived analytic expressions can be used as the foundation for developing simplified grasping algorithms.