Abstract. We review recent advances in rectification control of artificial microswimmers, also known as Janus particles, diffusing along narrow, periodically corrugated channels. The swimmer self-propulsion mechanism is modeled so as to incorporate a nonzero torque (propulsion chirality). We first summarize the effects of chirality on the autonomous current of microswimmers freely diffusing in channels of different geometries. In particular, left-right and upside-down asymmetric channels are shown to exhibit different transport properties. We then report new results on the dependence of the diffusivity of chiral microswimmers on the channel geometry and their own self-propulsion mechanism. The self-propulsion torque turns out to play a key role as a transport control parameter.

No abstract

Previous researches of robot motion planning are based on known and static environmental model. However, there are uncertainty and emergency in the real world. In order to build robust robotic system that is able to interact with its environment and makes appropriate real-time reaction to deal with unexpected situations, we present an emergency -tolerant topological motion planning method mainly for manipulators in an assembly workspace. The term "emergency-tolerant" means that the robot can reach its goal by avoiding unexpected obstacles. Since the model of an assembly workspace can be approximately known in advance and the workspace will not dynamically change, our method is actually helpful for building practical intelligent assembly robots.Our discussion is based on the topological motion planning method, which first partitions the Configuration Space into several connected blocks and constructs a Characteristic Network (CN), then searches for a path in CN. The partition of C-Space in topological method is accurate and complete, which is especially suitable for guiding the robot handling the emergency.The partition of C-Space is usually time consuming and is often performed offline. When emergency occurs, no deliberation is possible. Instead, rapid reaction toward the goal is rieeded for the robot. Therefore the process is not a simple repeat of the off-line planning but a rapid local adjustment or/and global replanning.The main future of our method is as follows. If unexpected obstacles are met when the robot moves along original planned path, the robot first locates it corresponding connected block in CN according to its current geometry position. Under the guidance of the information contained in CN it tries to reach the next block while avoiding the obstacles within the current block. If this succeeds, the robot continues its motion. Otherwise the connectivity between the two successive blocks is cut off and a new path is searched for in CN. We call the above two processes local adjustment and global replannhg, respectively. If the workspace changes greatly, then the local adjustment becomes very difficult. But when only some episodic emergency occurs, in the assembly environment, the method is effective and efficient.Based on the method we developed, we implemented such a planning system for a manipulator arm (PUMA 560). We mount the infrared proximity sensors on the arm as its sensitive skin. We use big boxes and human as the unexpected obstacles. The many experiments show that the method we developed to deal with emergency is real-time, robust and efficient.