Horizontal carousels are automated storage systems that bring items to a picker instead of making the picker walk through aisles. They use a loop of carriers or bins that rotate horizontally, usually in an oval path, until the needed storage location reaches an operator station. This matters because travel time is often a major source of wasted labor in order picking.
By reducing walking, horizontal carousels can improve speed, accuracy, floor space use, and worker ergonomics.
Key Facts
- Picker travel savings occur because the system follows goods-to-person flow instead of person-to-goods flow.
- Average pick cycle time can be estimated as Tcycle = Trotate + Tpick + Tconfirm.
- Carousel throughput can be estimated as Throughput = picks per cycle / cycle time.
- Storage density increases when aisles are removed or reduced, so more SKUs can fit in the same floor area.
- Batch picking raises efficiency by grouping orders so one carousel visit can support multiple customer orders.
- Pick accuracy improves when lights, screens, scanners, and software confirm item location, quantity, and order match.
Vocabulary
- Horizontal carousel
- A storage machine with carriers that rotate in a horizontal loop to deliver items to a fixed picking station.
- Carrier
- A moving shelf, bin frame, or storage segment attached to the carousel chain or track.
- Goods-to-person
- A warehouse method in which automated equipment brings stored items to a worker instead of the worker traveling to the items.
- SKU
- A stock keeping unit is a unique item type tracked separately in inventory.
- Batch picking
- A picking method where items for several orders are collected during the same work sequence to reduce repeated trips or rotations.
Common Mistakes to Avoid
- Ignoring rotation time, which is wrong because carousel performance depends on how long it takes the requested carrier to reach the operator.
- Storing fast-moving items randomly, which is wrong because high-demand SKUs should be placed to reduce average access time and congestion.
- Measuring only machine speed, which is wrong because real throughput also includes scanning, confirming, packing, replenishment, and operator handling time.
- Overloading carriers beyond design limits, which is wrong because excess weight can damage the drive system, reduce accuracy, and create safety hazards.
Practice Questions
- 1 A carousel averages 18 seconds of rotation time, 12 seconds of picking time, and 5 seconds of confirmation time per line. What is the average cycle time per picked line?
- 2 A station completes 1 pick every 30 seconds on average. How many picks per hour can it complete if it runs continuously with no interruptions?
- 3 A warehouse has many small parts with high order frequency and limited floor space. Explain why a horizontal carousel may be better than conventional shelving, and name one situation where it may not be the best choice.