Design and analysis of a compliant grasper for handling live objects

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Yin, Xuecheng
Lee, Kok-Meng
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This thesis presents the development of a model for analyzing the design of an automated live-bird transfer system (LBTS) developed at Georgia Tech. One of the most fundamental tasks in the automated transferring is to design and control a grasping system that is capable of accommodating a specified range of objects without causing damage. However, unlike grasping in robotic research that focuses on dexterous manipulation of a single object, repetitive transfer of live objects in a production line requires continuous grasping at high-speed. This thesis research investigates the use of rotating fingers (capable of undergoing large deflections) to cradle live birds on a moving conveyor for subsequent handling. As compared to fingers with multiple active joints, flexible fingers have many merits, for they are lightweight and have no relative individually moving parts. Their ability to accommodate a limited range of varying sizes, shapes, and the natural reactions of some objects makes rubber fingers an attractive candidate for use as graspers in a high-speed production setting. However, the advantages of flexible fingers are seldom exploited for grasping because of the complex analysis involved in the design. In order to reduce the number of birds and hardware/software design configurations to be tested, a good understanding of the object dynamics throughout the grasping process is necessary. In this thesis, a quasi-static model has been developed for predicting the contact force between a moving object and a rotating finger. The model has been validated with the experimentally measured data and the computed results using finite element (FE) methods. Finally, an illustrative application of the validated model has been demonstrated in the design of a rotating hand used in the automated LBTS. As illustrated in the simulation results, the computed contact forces can be used as a basis for predicting potential bruises on the bird that may be caused by the rotating fingers. The analytical model presented in this paper provides a rational basis for optimizing the design of the grasping system and developing a controller for a high-speed transfer system. It is expected that the analysis presented here can be readily extended to other dynamic systems involving the use of flexible beams.
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