Comparison of interfacing mechanics for soft robotic grippers

Soft robots and soft robotic gripping as an idea dates back to the 1980s and has received significant attention around the early 2000s. The goal is to design and manufacture robotic systems which, in contrast to classical “hard” robots, possess a large amount of passive degrees of freedom in terms of movement and/or deformation. Being “soft” in that sense enables the system to reliably deal with unknown variables present in many cases during its use, for example due to the unexpected shape of an object being gripped, or due to the length and narrowness of an accessway it is supposed to traverse. Soft gripping, more specifically, strives to simplify the gripping process via usage of soft or stiff but self-compliant materials and mechanisms. In recent years, a range of approaches has been presented, differing in their core principle, actuation method and other characteristics. In many cases, however, it stands to reason that soft grippers would benefit from specialized interfacing mechanisms that translate their closing force and conformability to increased contact area, friction, or/and adhesion with the object, in order to realize their full potential. Numerous examples from nature exploit such interfacing structures to adapt themselves to a range of grasping scenarios. While grasping structures, for example in spiders or insects, differ in their morphology, their functional principles can be assigned to few categories. Extraction of their working principles allows for their abstraction and possible biomimetic adoption into technical environments. This work aims to establish a qualitative guideline to estimate the effects of different types of bionic interface-enhancements for gripping applications. Three relatively common biological interfacing principles (hairy pads, smooth soft pads and friction-increasing pads) were exploratorily compared based on artificial variants in their performance-enhancing effect in gripping scenarios. As a testing platform, the TriTrap gripper was used – a biomimetic gripper inspired from insect tarsal chains. The qualitative results show that in the vast majority of cases, the gripping interfaces significantly improve performance, with friction pads proving to be especially effective. Soft smooth as well as hairy pads also increased performance, but exhibited clear weaknesses that are discussed in detail.