Performance of autonomous carrier systems in respect of collisions

The economic development challenges the intralogistic in a new way. It gets necessary to distribute goods very fast and with the minimum of costs. The short timespan to amortize a warehouse is highlighted by many previous articles. The nowadays common automated material handling systems are installed permanently. Therefore they can be used for a specific kind of goods and a predefined throughput. This means the facility is usually oversized when it is built and any change of layout or an adaption to other goods is very expensive. One answer to this challenge could be found in the increase of flexibility of the participating intralogistic systems. Some new automated material handling technologies were presented by Furmans [1] and at the CeMat 2011. The difference to the previous used systems is that they are built in modular units. These units were well known as shuttles in or on racks. The newest step is, to bring these shuttles on the shopfloor where they can navigate freely and deliver goods or fulfill other tasks. To distinguish, the automated guided vehicles (AGV) move on predetermined routes, the new shuttles can avoid collisions by using an alternative path without human interaction (compare with [2]). Furthermore they act like autonomous mobile robots, so these vehicles can be called autonomous carriers and the complete system autonomous carrier system. Götting [3] referred to mobile robotics as well.
Previous works deal with the way to calculate the throughput with different approaches. Rajota [4]uses the vehicle travel time to determine the optimal fleet size. Koo [5]presents a method to estimate the fleet size by predicting empty travel and delivery time.
This article gives another perspective to discuss the performance of an autonomous carrier system. Until now throughput is calculated linear to the amount of operating vehicles. The performance is assumed to rise linear with every added vehicle. This is examined and discussed. Reasons for a blocking situation in these systems are given and a prototype of a simulation is presented to calculate the vehicle travel time.