## Modeling and grasping of thin deformable objects

 dc.contributor.advisor Yan-bin Jia dc.contributor.author Tian, Jiang dc.contributor.department Computer Science dc.date 2018-08-11T09:07:36.000 dc.date.accessioned 2020-06-30T02:36:12Z dc.date.available 2020-06-30T02:36:12Z dc.date.copyright Fri Jan 01 00:00:00 UTC 2010 dc.date.embargo 2013-06-05 dc.date.issued 2010-01-01 dc.description.abstract

Deformable modeling of thin shell-like and other objects have potential application in robot grasping, medical robotics, home robots, and so on. The ability to manipulate electrical and optical cables, rubber toys, plastic bottles, ropes, biological tissues, and organs is an important feature of robot intelligence. However, grasping of deformable objects has remained an underdeveloped research area. When a robot hand applies force to grasp a soft object, deformation will result in the enlarging of the finger contact regions and the rotation of the contact normals, which in turn will result in a changing wrench space. The varying geometry can be determined by either solving a high order differential equation or

minimizing potential energy. Efficient and accurate modeling of deformations is crucial for grasp analysis. It helps us predict whether a grasp will be successful from its finger placement and exerted force, and subsequently helps us design a grasping strategy.

The first part of this thesis extends 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 the 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 and the results generated by two commercial softwares ABAQUS and ANSYS. Our method achieves a convergence rate an 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.

The second part numerically studies two-finger grasping of deformable curve-like objects under frictional contacts. The action is like squeezing. Deformation is modeled by a degenerate version of the thin shell theory. Several differences from rigid body grasping are shown. First, under a squeeze, the friction cone at each finger contact rotates in a direction that depends on the deformable object's global geometry, which implies that modeling is necessary for grasp prediction. Second, the magnitude of the grasping force has to be above certain threshold to achieve equilibrium. Third, the set of feasible finger placements may increase significantly compared to that for a rigid object of the same shape. Finally, the ability to resist disturbance is bounded in the sense that

increasing the magnitude of an external force may result in the breaking of the grasp.

dc.format.mimetype application/pdf dc.identifier archive/lib.dr.iastate.edu/etd/11512/ dc.identifier.articleid 3256 dc.identifier.contextkey 2808454 dc.identifier.doi https://doi.org/10.31274/etd-180810-2585 dc.identifier.s3bucket isulib-bepress-aws-west dc.identifier.submissionpath etd/11512 dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/25718 dc.language.iso en dc.source.bitstream archive/lib.dr.iastate.edu/etd/11512/Tian_iastate_0097E_11229.pdf|||Fri Jan 14 18:52:11 UTC 2022 dc.subject.disciplines Computer Sciences dc.title Modeling and grasping of thin deformable objects dc.type article dc.type.genre dissertation dspace.entity.type Publication relation.isOrgUnitOfPublication f7be4eb9-d1d0-4081-859b-b15cee251456 thesis.degree.level dissertation thesis.degree.name Doctor of Philosophy
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