Question: A unit load automated storage/retrieval system has five aisles. The storage racks are 60 ft high and 280 ft long. The SIR machine travels at a horizontal speed of 200 ft/min and a vertical speed of 80 ft/min. The pick-and-deposit time = 0.30 min. Assume that the number of single command cycles per hour is four times the number of dual command cycles per hour and that the system operates at 80% utilization. A dedicated storage scheme is used for organizing the stock, in which unit loads are separated into two classes, according to activity level.
The more-active stock is stored in the half of the rack system located closest to the input/output station, and the less-active stock is stored in the other half of the rack system (farther away from the input/output station). Within each half of the rack system. random storage is used. The more-active stock accounts for 75% of the transactions, and the less-active stock accounts for the remaining 25% of the transactions. Determine the throughput rate (loads moved per hour into and out of storage) of the AS/RS, basing your computation of cycle times on the same types of assumptions used in the Mill method. Assume that when dual command cycles are performed, the 2 transactions/cycle are both in the same class.