Crossing a step of a robust power assist cart taking tumble prevention of conveyed objects into account

Abstract

Owing to the aging of societies, the research and development of power-assist systems that increase human-operational forces have become popular. However, a power-assist system is a typical human-machine system. Therefore, the design and use of such a system should take into account the safety of both the operator and the conveyed objects. Some of the authors have already studied on power-assist systems, using an assist-control system design consisting of an impedance controller, a disturbance-accommodating optimal controller, a disturbance observer, and a reaction-force controller. However, unintentional input forces acting on a power-assist system may cause reckless motion and severe accidents in actual use. Therefore, we discuss the use of a robust control method to prevent this abrupt motion by substituting a frequency-shaped disturbance-accommodating optimal controller (FSDAOC) for the original optimal controller. The FSDAOC enables us to eliminate high-frequency-range motion by its frequency-shaping characteristic. The objective of this study is to assess the effectiveness of the FSDAOC-based method in enabling a power-assist cart to cope with the unexpected input forces caused by crossing a step without its load tumbling. We verified the effectiveness experimentally and found that our method had a tumble-prevention rate of 80%, which was an improvement over the 23% of the previous method.

Keywords

• power assist
• impedance control
• shock
• optimal control
• frequency-shaping
• tumble prevention