Impact of speed on the performance of vehicle-free transport

Automated material handling systems (AMHS) are the backbone of a 300 mm fab. Today´s AMHS is required to support dynamic movement demands ranging from 1,000 to as high as 10,000 moves per hour. The volume and volatility of demand is driving AMHS teams worldwide to look toward new vehicle-free transport systems (VFT). VFT methods, such as conveyors, move the FOUP directly, so capacity is not limited by vehicles and FOUPs do not need to wait for a vehicle to be dispatched, allowing for more consistent delivery times. In this paper the authors examine the correlation between speed and delivery performance of vehicle-free transport in various configurations. Criteria are established to assure adequate performance for the requirements of typical and hot lots. Detailed simulation models of real factory applications are evaluated to predict the capacity, average and peak delivery times. The analysis calculates the speed required for VFT to be an optimized solution for today´s high volume and tomorrow´s 450 mm manufacturing.