Date of Award
Master of Science
Many peg-hole-insertion strategies have been developed for autonomous assembly tasks. Unfortunately, none of them appear applicable to the simple task of mounting a screwdriver, which has a thin tip, onto a screw, whose small head and narrow drive significantly limit the work space. The task has thus remained a challenging test for a robot's dexterity. In this thesis, we have developed a mounting strategy for a robotic arm that proceeds in two phases: a) screwdriver tip localization relative to the screw's drive via sliding and b) tip insertion into the slot via rotation. During the entire operation, the contact between the screwdriver's tip and the screw head is maintained with a sequence of three hybrid controllers.
The hybrid controller has two goals---motion tracking and force regulating. As long as these two goals are not mutually exclusive, they can be decoupled in some way. In this thesis, we make use of the smooth and invertible mapping from the joint space to the task space to decouple the two control goals and design controllers separately. The traditional motion controller in the task space is used for motion control, while the force controller is designed through manipulating the desired trajectory to regulate the force indirectly.
Two case studies---contour tracking/polishing surfaces and grabbing boxes with two robotic arms---are presented to show the efficacy of the hybrid controller, and simulations with physics engines are carried out to validate the efficacy of the proposed method. The mounting strategy using hybrid control is simulated on the same platform for demonstration as well.
Xie, Shengwen, "Mounting a screwdriver onto a screw using hybrid control" (2020). Graduate Theses and Dissertations. 18429.