We have proposed "Attentive Workbench (AWB)," a new cell production system in which an intelligent system supports human workers. Recognizing worker's condition and intention, the system supports workers from both physical and information aspects. This paper deals with physical assembly support using self-moving parts trays. The system delivers necessary assembly parts to workers and clears finished products quickly. On transporting large products, multiple trays are subjected to form a rigid body working as a large single tray. In order to realize this arrangement of trays in real-time, a planning method based on the priority scheme and heuristic rule is proposed. The present method is evaluated through simulations. A demonstration of assembly support using real self-moving trays are shown.