  Safety is one of the most fundamental aspects of robotics, especially when it
comes to collaborative robots (cobots) that are expected to physically interact
with humans. Although a large body of literature has focused on safety-related
aspects for fixed-based cobots, a low effort has been put into developing
collaborative mobile manipulators. In response to this need, this work presents
MOCA-S, i.e., Sensitive Mobile Collaborative Robotic Assistant, that integrates
a low-cost, capacitive tactile cover to measure interaction forces applied to
the robot base. The tactile cover comprises a set of 11 capacitive large-area
tactile sensors distributed as a 1-D tactile array around the base.
Characterization of the tactile sensors with different materials is included.
Moreover, two expanded whole-body controllers that exploit the platform's
tactile cover and the loco-manipulation features are proposed. These
controllers are tested in two experiments, demonstrating the potential of
MOCA-S for safe physical Human-Robot Interaction (pHRI). Finally, an experiment
is carried out in which an undesired collision occurs between MOCA-S and a
human during a loco-manipulation task. The results demonstrate the intrinsic
safety of MOCA-S and the proposed controllers, suggesting a new step towards
creating safe mobile manipulators.
