Selecting and applying the optimal material handling equipment, including an automated storage and retrieval system – AS-RS, is a critical part of distribution center design. Industry trends towards shortening order fulfillment cycle time, reducing labor, reducing space footprint, and minimizing on-hand inventory, all point towards increased use of automated storage and retrieval systems (AS-RS) approaches.
Assuming all other things equal, a critical factor for an automated storage and retrieval system is the relationship between the quantity of unique storage positions and the transaction rate for storage and retrieval. For instance consider the requirements of the following hypothetical operations:
Touch-all ratio (hours)
The touch-all factor is the ratio of slots to transaction rate and can be interpreted literally as the amount of time it would take to touch each of the required slots at the required transaction rate.
Typically, the number of unique slots is closely related to the number of SKUs supported by the operation, and the transaction rate is related to the overall throughput of the operation measured in pick lines per hour. For the sake of this discussion, let’s assume that the product for each operation is similar and can be stored in totes with sufficient quantity per segment to support about one month of demand.
System 1 might be well served by a mini-load crane-per-aisle automated storage and retrieval system or AS-RS, or a bank of carousels with a high-speed stationary inserter/extractor per axle. These are high density solutions with noteworthy latency for insertion and extraction. Their somewhat leisurely pace is well suited to the long (but appropriate) touch-all factor.
On the other hand, System 2 has a very short touch-all requirement. This might be best satisfied using high-performance multi-level shuttle technology. The mini-load multi-level shuttle automated storage and retrieval system or AS-RS has an input/extractor device for each level of shelving. They all operate on multiple levels in multiple aisles at the same time, thereby achieving a much higher performance level.
The importance of understanding these differences in requirements and their influence on equipment selection is that each of these options has a different price point. There is actually a range of solutions with different price/performance positions. Carousels and the mini-load crane automated storage and retrieval system fall at the low-price end of the range; The multi-level mini-load shuttle automated storage and retrieval system falls at the high-price end.
Using a multi-level shuttle automated storage and retrieval system to resolve the requirements of System 1 would be like using a bazooka to hunt mosquitos; And yet, you will find this equipment being applied to that application time-and-time again by suppliers who only have that option available to them. On the flip side of that, you would need a highly distorted carousel or mini-load crane automated storage and retrieval system to meet the requirements of system 2; Multi-level shuttles would likely hit their sweet-spot for storage and throughput, and be at a price point that better supports the return on investment (ROI).
A manufacturer or distributor is likely to propose a design that draws on the narrow equipment solution set that they represent. On the other hand, a sophisticated systems integrator will have the knowledge and expertise to draw from a broader equipment solution set from multiple manufacturers. They will use a variety of data analysis tools to choose and validate an optimal equipment selection and fulfillment center design. Aligning with the proper integrator is crucial to your success.