  Multiple levels of safety measures are required by multiple interaction modes
which collaborative robots need to perform industrial tasks with human
co-workers. We develop three independent modules to account for safety in
different types of human-robot interaction: vision-based safety monitoring
pauses robot when human is present in a shared space; contact-based safety
monitoring pauses robot when unexpected contact happens between human and
robot; hierarchical intention tracking keeps robot in a safe distance from
human when human and robot work independently, and switches robot to compliant
mode when human intends to guide robot. We discuss the prospect of future
research in development and integration of multi-level safety modules. We focus
on how to provide safety guarantees for collaborative robot solutions with
human behavior modeling.
