Grasping
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Grasping Gualtiero Fantoni and Marco Santochi Department of Civil and Industrial Engineering, University of PisaLargo Lucio Lazzarino, Pisa, Italy
and industrial grippers were oriented to achieve different goals, nowadays the gap is reduced and it is often difficult to distinguish a simplified robotic human-like hand from a complex industrial gripper (Krüger et al. 2009).
Theory and Application Synonyms Gripping
Definition Grasping is defined as a series of handling operations which provide forces and torques necessary to get and maintain the part in a relative position and orientation with respect to the grasping device (e.g., tweezers for small parts or vacuum cups for flat and nonporous objects). The end effector that exerts the grasping is called “gripper” and it is also used in cases of holding rather than actual grasping (Monkman et al. 2007). Extended Definition Nowadays several factors such as the increasing cost of human labor, the spread of automation and the decreasing cost of robotic systems have pushed both industry to the adoption of grasping systems to automate many production processes in different fields. While in the past robot hands
Gripper Selection The design of a gripper depends on the object characteristics (porosity, roughness, water sensitiveness, stiffness, and electrical conductivity) but it is also affected by the task characteristics as the position to be reached and the orientation of the target releasing point (derived from previous phase as feeding) and by handling performances (accelerations, precision in positioning and releasing difficulties). Several grasping principles based on different physical effects (Fig. 1) have been successfully used in different applications. Some principles can be applied only at the microscale (e.g., acoustic levitation or laser tweezers), while others proposed for microhandling are now expanding beyond that field (e.g., van der Waals forces) (van Brussel et al. 2000). Mechanical grippers are based on friction or on form closure, but also intrusive grippers belong to that class. They are the most widespread. Suction based grippers and magnetic grippers dominate metal sheet handling in the automotive field.
# CIRP 2017 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_16832-1
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Grasping
Grasping, Fig. 1 Grasping principles (Figure a reproduced with permission of IFIP)
While Bernoulli grippers, even if also they exploit negative pressure, are now receiving more attention since they handle parts in a contactless way. Electrostatic grippers are based on charge difference (sometimes induced by the gripper itself) between the gripper and the part, while van der Waals grippers are based on the low force (electrostatic forces) due to the atomic attraction between the molecules of the gripper and those of the object. Capillary grippers use the surface tension of a liquid meniscus between the gripper and the part, such a small liquid quantity is frozen in cryogenic gri
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