Industrial robots cannot be discussed without referringto their application fields. Industrial robots have becomewidespread since the 1970s when they were first introduced 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 production of automobiles and other products with unified specifications, 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].