  Robots have been brought to work close to humans in many scenarios. For
coexistence and collaboration, robots should be safe and pleasant for humans to
interact with. To this end, the robots could be both physically soft with
multimodal sensing/perception, so that the robots could have better awareness
of the surrounding environment, as well as to respond properly to humans'
action/intention. This paper introduces a novel soft robotic link, named
ProTac, that possesses multiple sensing modes: tactile and proximity sensing,
based on computer vision and a functional material. These modalities come from
a layered structure of a soft transparent silicon skin, a polymer dispersed
liquid crystal (PDLC) film, and reflective markers. Here, the PDLC film can
switch actively between the opaque and the transparent state, from which the
tactile sensing and proximity sensing can be obtained by using cameras solely
built inside the ProTac link. In this paper, inference algorithms for tactile
proximity perception are introduced. Evaluation results of two sensing
modalities demonstrated that, with a simple activation strategy, ProTac link
could effectively perceive useful information from both approaching and
in-contact obstacles. The proposed sensing device is expected to bring in
ultimate solutions for design of robots with softness, whole-body and
multimodal sensing, and safety control strategies.
