Generation of monitoring signal in safety confirmation type contact sensor using ultrasonicwave propagating in viscoelastic tube

In a pHRI, physical contact between humans and robots may happen occasionally or on purpose. Extensive efforts have been made to develop safety measures reducing human injury and improving human safety. Contact sensor is a fundamental requirement for those robots to sense the contact with humans and to take appropriate safety measures. In this paper, we propose a safety confirmation type wide-range detectable contact sensor that detects an ultrasonic wave propagating through a viscoelastic tube. The proposed sensor generates ultrasonic waves from a transmitter installed at the end of a long and slender viscoelastic tube, and detects the waves as safety monitoring signals by a receiver located at the other end. For all cases where safety monitoring signals is not detected, such as an abnormal state of ultrasonic wave and sensor elements failure, it does not transmit safety. An estimation equation related to the propagating sound pressure and time of an ultrasonic wave in the silicon tube was derived through experimental investigation on the propagation characteristics in a straight and a curved tube. It was confirmed that a safety monitoring signal was successively generated in an arbitrary curved tube by setting an appropriate safety threshold which was calculated using the estimation equation.