Tutorial on Embodiment

3.3.2. Cheap grasping with a universal gripper*


As our everyday experience con­firms, a multifingered hand is an extremely dexterous manipulator. However, from a robotic perspective, this approach is highly complex from a hardware as well as software point of view. Brown et al. (2010) have therefore devised a gripper that utilizes a completely different strategy. Individual fingers are replaced by a single mass of granular material (e.g., ground coffee). The prin­ciple of operation is illustrated in Fig. 3.3.2.1., D. The ‘bag' containing granular material is pressed onto an object, flows around it, and conforms to its shape. Then, a vacuum pump is used to evacuate air from the gripper, which makes the granular material jam and stabilize the grasp. The gripper conforms to arbitrary shapes passively, that is without any sensory feedback, thanks to its morphological properties only (see Video 3.3.2.1). Brown et al. identify three mechanism that contribute to the gripping: (i) geometric constraints from interlocking between gripper and object surfaces; (ii) static friction from normal stresses at contact; and (iii) an additional suction effect, if the gripper membrane can seal off a portion of the object's surface. The properties of the gripper can be changed by using a different granular material. Objects of various shapes (see Fig. 3.3.2.1., E) as well as hardness (from steel springs to raw eggs) can be gripped. An additional advantage is that the orientation of objects that are picked up and placed again does not change.

 

Fig. 3.3.2.1. Jamming-based grippers for picking up a wide range of objects without the need for active feedback. (A) Attached to a fixed-base robot arm. (B) Picking up a shock absorber coil. (C) View from the underside. (D) Schematic of operation. (E) Holding force Fh for several three-dimensional-printed test shapes (the diameter of the sphere shown on the very left, 2r = 25.4 mm, can be used for size comparison). The thin disk could not be picked up at all (from Brown et al., 2010, courtesy John Amend of Cornell University).

Video 3.3.2.1. Universal robotic gripper based on the jamming of granular material


* adapted from Hoffmann and Pfeifer, 2011

References

Brown, E.; Rodenberg, N.; Amend, J.; Mozeika, A.; Steltz, E.; Zakin, M. R.; Lipson, H. & Jaeger, H. M. (2010), 'From the Cover: Universal robotic gripper based on the jamming of granular material.', Proc Natl Acad Sci U S A 107(44), 18809--18814.
Hoffmann, M. & Pfeifer, R. (2011), The implications of embodiment for behavior and cognition: animal and robotic case studies, in W. Tschacher & C. Bergomi, ed., The Implications of Embodiment: Cognition and Communication, Exeter: Imprint Academic, pp.31-58.

 

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