A new close-loop control method for an inspection robot equipped with electropermanent-magnets

Since the industrial age began, increasing numbers of manufacturing plants have been set up to serve economic growth demand. More bridges were built simultaneously to connect cities and to make transportation more convenient. As these facilities have aged, regular maintenance has increased. The limb mechanism project we started almost 20 years ago was to deliver new types of inspection and maintenance to industrial fields. Our first prototype, a six-limb robot called Asterisk, included such capabilities as walking on ceilings, climbing and descending stairs and ladders, walking tightropes, and transversing rough terrain. Asterisk’s latest version uses electromagnets to work in antigravity environments such as steel structures. Unfortunately, this presented a major danger, requiring that we replace electromagnets with electropermanentmagnets (EPMs). Limitations on EPMs, however, required a new control strategy. We propose and compare three control methods – open-loop control, closed-loop control using torque feedback, and closed-loop control using angle feedback – in the sections that follow. Our objective is to determine the best control for inspection robots having electropermanent magnets but not using additional sensors.