  The collaborative robot market is flourishing as there is a trend towards
simplification, modularity, and increased flexibility on the production line.
But when humans and robots are collaborating in a shared environment, the
safety of humans should be a priority. We introduce a novel wearable robotic
system to enhance safety during Human-Robot Interaction (HRI). The proposed
wearable robot is designed to hold a fiducial marker and maintain its
visibility to a motion capture system, which, in turn, localizes the user's
hand with good accuracy and low latency and provides vibrotactile feedback to
the user's wrist. The vibrotactile feedback guides the user's hand movement
during collaborative tasks in order to increase safety and enhance
collaboration efficiency. A user study was conducted to assess the recognition
and discriminability of ten designed vibration patterns applied to the upper
(dorsal) and the down (volar) parts of the user's wrist. The results show that
the pattern recognition rate on the volar side was higher, with an average of
75.64% among all users. Four patterns with a high recognition rate were chosen
to be incorporated into our system. A second experiment was carried out to
evaluate users' response to the chosen patterns in real-world collaborative
tasks. Results show that all participants responded to the patterns correctly,
and the average response time for the patterns was between 0.24 and 2.41
seconds.
