Computer science colloquia: Yan-Bin Jia
| Date/Time: | Thursday, 02 Sep 2010 at 3:40 pm |
|---|---|
| Location: | B29 Atanasoff |
| Cost: | free |
| Phone: | 515-294-6516 |
| Channel: | College of Liberal Arts and Sciences |
| Categories: | Lectures |
| Actions: | Download iCal/vCal | Email Reminder |
The robot hand applying force on a deformable object will result in a changing wrench space due to the varying shape and normal of the contact area. Design and analysis of a manipulation strategy thus depend on reliable modeling of the object's deformations as actions are performed. We consider modeling of shell-like objects in particular. The classical shell theory assumes a parameterization along the two lines of curvatures on the middle surface of a shell, and is not immediately applicable to an arbitrary parameterization.
In this talk, we first extend the linear and nonlinear shell theories to describe extensional, shearing and bending strains in terms of geometric invariants including the principal curvatures and vectors, and their related directional and covariant derivatives. To our knowledge, this is the first non-parametric formulation of thin shell strains. A computational procedure for the strain energy is then offered for general parametric shells. In practice, a shell deformation is conveniently represented by a subdivision surface. We compare the results via potential energy minimization over a couple of benchmark problems with their analytical solutions as well as numerical ones generated by two commercial software packages ABAQUS and ANSYS. Our method achieves a convergence rate one order of magnitude higher. Experimental validation involves regular and freeform shell-like objects (of various materials) grasped by a robot hand, with the results compared against scanned 3-D data (accuracy 0.127mm). Grasped objects often undergo sizable shape changes, for which a much higher modeling accuracy can be achieved using the nonlinear elasticity theory than its linear counterpart.