Mobile Fulfillment Verses Carousels

Mobile Fulfillment versus Carousel

Distribution centers handling split-case products have many options for automating some portion of the picking process. Once common approach has been the use of carousels, both horizontal and vertical. This paper will compare the use of traditional carousels to a new approach, mobile fulfillment.

Overview of mobile fulfillment

Kiva Systems has introduced a new approach to order fulfillment, using a fleet of mobile robotic drive units to store, move and sort inventory. Operators stand at stations around the perimeter of the building while inventory is stored on mobile racks, called pods. These pods are arranged in a grid pattern in the interior of the building, and when an operator requires an item for an order, a mobile robot brings the pod containing that item to the worker. Each worker is supported by 5-10 drive units and so is kept continuously busy filling orders. Because the entire inventory is mobile, every worker has access to all products, and so can fill complete orders.

Benefits of carousels

The benefits of carousel over less automated solutions are mainly in the areas of productivity and space utilization. Carousels allow operators to eliminate operator walking and thus increase productivity. Due to the time it takes for a carousel to spin to the correct item, most implementations use multiple (3-4) carousels per operator to minimize operator wait time. In addition, by storing products without requiring aisles for human access, they allow tighter storage, especially of small parts.

Benefits of Mobile Fulfillment versus Carousel

Higher pick rates

Kiva's Mobile Fulfillment System enables significantly faster pick times than carousels by eliminating all operator wait time. In any carousel system there are two potential sources of idle time - all carousels in front of an operator are spinning, and the operator has no available picks from their SKU set. Kiva delivers a new pick face to an operator every six seconds regardless of which SKUs are required; ensuring the operator always has a pick ready. Second, every Kiva operator has access to all the SKUs in the building and so is independent of all other operators. As long as there is work in the building, all operators can be utilized.

Simultaneous pick and replenishment

A carousel station can be used to either pick or replenish but not both at the same time. As a result, any unexpected stockouts create operational confusion as replenishment work happens around the pick worker. With mobile fulfillment, pickers and replenishers operate independently with no loss of productivity.

Lower capital costs

A carousel system requires several carousels per operator as well as a transport method (typically conveyor) to move orders from worker to worker. Add in diverts to control movement of orders and a system to integrate all of this equipment and the capital cost of a carousel-based material handling system can be quite high. Compared to this, a Kiva system is a