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Soft contact manipulation of a rigid objectusing multibond graph

Rathee Raul, Narwal Anil Kumar, Vaz Anand

Computer Assisted Methods in Engineering and Science

2021

Vol. 28, no. 4

321--349

Dexterous manipulation of a rigid object using artificial soft fingers is not easy to achieve.Instantaneous contact areas and the distribution of contact forces at the interfaces changedynamically during the soft contact manipulation of the object. A bond graph modelfor dynamics of the soft contact manipulation of a rigid object using two soft pads is developed. A cylindrical disc is used as the rigid object to be manipulated between two softsilicon rubber pads considered in place of soft fingertips, one above and the other below.The disc is grasped and rolled between the two pads so its center follows a desired horizontal displacement trajectory. A closed-loop feedback control system generates the requiredforce to grasp and control the instantaneous position of the disc’s center. The model determines the instantaneous contact forces required for the desired manipulation. Simulationresults validate the model.

Dynamic optimal grasping of a circular object with gravity using robotic soft-fingertips

García-Rodríguez R., Segovia-Palacios V., Parra-Vega V., Villalva-Lucio M.

International Journal of Applied Mathematics and Computer Science

2016

Vol. 26, no. 2

309--323

Object manipulation usually requires dexterity, encoded as the ability to roll, which is very difficult to achieve with robotic hands based on point contact models (subject to holonomic constraints). As an alternative for dexterous manipulation, deformable contact with hemispherical shape fingertips has been proposed to yield naturally a rolling constraint. It entails dexterity at the expense of dealing with normal and tangential forces, as well as more elaborated models and control schemes. Furthermore, the essential feature of the quality of grasp can be addressed with this type of robot hands, but it has been overlooked for deformable contact. In this paper, a passivity-based controller that considers an optimal grasping measure is proposed for robotic hands with hemispherical deformable fingertips, to manipulate circular dynamic objects. Optimal grasping that minimizes the contact wrenches is achieved through fingertip rolling until normal forces pass through the center of mass of the object, aligning the relative angle between these normal forces. The case of a circular object is developed in detail, though our proposal can be extended to objects with an arbitrary shape that admit a local decomposition by a circular curvature. Simulation and experimental results show convergence under various conditions, wherein rolling and tangent forces become instrumental to achieve such a quality of grasp.