A Bioinspired Stiffness Tunable Sucker for Passive Adaptation and Firm Attachment to Angular Substrates

The ability to adapt and conform to angular and uneven surfaces improves the suction cup's performance in grasping and manipulation. However, in most cases, the adaptation costs lack of required stiffness for manipulation after surface attachment; thus, the ideal scenario is to have compliance during adaptation and stiffness after attachment to the surface. Nevertheless, most stiffness modulation techniques in suction cups require additional actuation. This article presents a new stiffness tunable suction cup that adapts to steep angular surfaces. Using granular jamming as a vacuum driven stiffness modulation provides a sensorless for activating the mechanism. Thus, the design is composed of a conventional active suction pad connected to a granular stalk, emulating a hinge behavior that is compliant during adaptation and has high stiffness after attachment is ensured. During the experiment, the suction cup can adapt to angles up to 85 degrees with force lower than 0.5 N. We also investigated the effect of granular stalk's length on the adaptation and how this design performs compared to passive adaptation without stiffness modulation.