Lazy VS-control strategy for passive walking

New control strategy called ´lazy control´ is proposed. This concept has its origin in Sliding-Sector Variable Structure Systems (SS-VSS). In SS-VSS system, the state is carried by specified variable-structure input (VS-input) law to a stable region which is called a ´sliding sector´, and after reaching into the sector the system is stabilized with zero-input. In this paper we apply this scheme to active control of passive walking. Passive walking motion emerges autonomously on slight incline slope, and don´t need external power except a potential-energy. The limit cycle is stable locally, but the stable region is narrow. It is shown that lazy control enhances the stability by minimum attention to the system, i.e. the walker can walk by itself as long as the own stability is valid without external input, and is helped to recover the stable motion only when the walker might not be able to walk by itself. The effectiveness is demonstrated by simulation