Industrial robots cannot be discussed without referringto their application fields. Industrial robots have becomewidespread since the 1970s when they were first intro-duced in factories for transportation and welding tasks.Industrial robots with a teaching playback function canrepeat with high speed and accuracy any task once it hasbeen taught to them by humans. The teaching playbackfunction, which works effectively for the mass produc-tion of automobiles and other products with unified spec-ifications, has continuously supported factory automationfrom the 1980s high-growth period of Japan until now.According to the International Federation of Robotics(IFR) survey, about 250,000 industrial robot units wereput into operation in the world in 2015 [b]