Effect of the granular material on the maximum holding force of a granular gripper
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ORIGINAL PAPER
Effect of the granular material on the maximum holding force of a granular gripper Julián M. Gómez–Paccapelo1 · Angel A. Santarossa1,3 · H. Daniel Bustos1 · Luis A. Pugnaloni1,2 Received: 8 June 2020 / Accepted: 15 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A granular gripper is a device used to hold objects by taking advantage of the phenomenon of Reynold’s dilatancy. A membrane containing a granular sample is allowed to deform around the object to be held and then vacuum is used to jam the granular material inside the membrane. This allows to hold the object against external forces since deformation of the granular material is prevented by not allowing the system to increase its volume. The maximum holding force supported by the gripper depends on a number of variables. In this work, we show that in the regime of frictional holding (where the gripper does not interlock with the object), the maximum holding force as a function of the penetration of the object in the gripper does not depend on the granular material used to fill the membrane. Results for a variety of granular materials can be collapsed into a single curve if maximum holding force is plotted against the penetration depth achieved. The results suggest that a robotic arm capable of sensing the penetration depth can use this master curve to estimate the maximum holding force at each gripping operation. Keywords Universal gripper · Jamming · Dilatancy
1 Introduction The handling of objects is a regular task in the industry. Holding objects of well defined size, shape and hardness can be done by robotic arms that present a gripper with a matching shape that fits the object to hold (e.g., hooks). Also, magnets can be used with ferromagnetic objects, and suction systems with objects presenting smooth surfaces. However, matching some of the gripping characteristics of the human hand is always desirable. Fingered grippers have been developed systematically over decades to provide a more universal (any shape, size and hardness) gripping ability (for a recent review see Ref. [1]). However, these handlike grippers require complex auxiliary systems to asses * Luis A. Pugnaloni [email protected] 1
Dpto. Física, FCEyN, Universidad Nacional de La Pampa, Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina
2
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
3
Present Address: Institute for Multiscale Simulation, Universität Erlangen-Nürnberg, Cauerstraße 3 91058 Erlangen, Germany
the gripping problem and take multiple decisions on how to handle each finger (time and amplitude of aperture, time of closure, applied pressure to hold, etc.). These auxiliary systems require complex hardware and software. More than 30 years ago, there where new proposals to tackle the gripping problem by using some unique properties of dens granular matter [2–4]. The “granular gripper” consists in a flexible impermeable bag partially filled with a granular
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