Question: Your company is seeking proposals for an automated storage/retrieval system that will have a throughput rate of 300 storage/retrieval transactions/hr during the one 8-hr shift/day. The request for proposals indicates that the number of single command cycles is expected to be four times the number of dual command cycles. The first proposal received is from a vendor who specifies the following; ten aisles, each aisle 150 ft long and 50 ft high; horizontal and vertical Leeds of the S/R machine = 200 ft/min and 66.67 ft/min, respectively; and pick-and-deposit time = 0.3 min. As the responsible engineer for the project, you must analyze the proposal and make recommendations accordingly. One of the difficulties you see in the pro-posed AS/RS is the large number of S/R machines that would he required-one for each of the ten aisles. This makes the proposed system very expensive.
Your recommendation is to reduce the number of aisles from ten to six and to select an S/R machine with horizontal and vertical speeds of 300 ft/min and 100 ft/min, respectively. Although each high-speed machine is slightly more expensive than the slower model, reducing the number of machines from ten to six will significantly reduce total cost. Also, fewer aisles will reduce the cost of the rack structure, even though each aisle will be somewhat larger since total storage capacity must remain the same. The problem is that throughput rate will be adversely affected.
(a) Determine the throughput rate of the proposed ten-aisle AS/RS and calculate its utilization relative to the specified 300 transactions/hr.
(b) Determine the length and height of a six-aisle AS/RS whose storage capacity would be the same as the proposed ten-aisle system.
(c) Determine the throughput rate of the six-aisle AS/RS and calculate its utilization relative to the specified 300 transactions/hr.
(d) Gwen the dilemma now confronting you, what other alternatives would you analyze and what recommendations would you make to improve the design of the system?