I. Introduction
Even a few years ago, manipulators were operated inside a fence and had to be stopped when workers approached them, and had to conform to ISO 10 218 [1]. Thus, there were numerous restrictions on the tasks that robots could perform and the places in which robots could be employed. However, collaborative robots, the so-called Cobot, which allow for complex tasks to be performed by humans and robots working together in the same space, have recently appeared. Accordingly, the demand for safe interaction technologies for human and robot collaborations is increasing in the field of robotics.