Conveyor and sorting systems form the fixed transport backbone of most large fulfilment centres. They move cartons, totes, and polybags between receiving docks, storage areas, picking stations, packing lines, and outbound shipping lanes — at speeds that would be impossible for a mobile fleet alone.
The simplest and most common type. A continuous belt driven by rollers transports items along a fixed path.
Gravity rollers — slope-fed, no motor; used in picking lanes and packing stations to allow cartons to flow forward as items are removed.
Powered roller (MDR — Motor Driven Roller) — each roller zone has its own small motor; enables zero-pressure accumulation, where items queue without crashing into each other.
Used primarily for apparel on hangers. Garments travel on hooks or carriers along an overhead track, enabling high-density sortation and order grouping without floor space consumption.
These are the highest-speed, highest-accuracy sortation technologies:
Tilt-tray sorter:
Carriers with a flat tray travel in a closed loop. At the assigned sort destination, the tray tips to one side, sliding the item into a chute.
Cross-belt sorter:
Each carrier has its own short belt conveyor running perpendicular to the loop direction. At the sort point, the belt activates and ejects the item laterally.
A flat conveyor bed with diagonally-oriented shoes (slats) that slide laterally to divert items to angled take-away lanes. Gentler than tilt-tray, handles heavier cartons.
Point-of-diversion modules installed inline. A set of rollers or wheels rises up through the conveyor surface at an angle, redirecting an item 30° or 90°.
Every conveyor network includes scan tunnels — arched frames containing multiple barcode cameras or RFID antenna that read every passing item from all angles simultaneously. The scan result tells the sorter controller where to direct the item.
Items from multiple upstream sources (picking stations, AS/RS outputs, returns processing) must merge onto the main sortation loop without collisions. Induction is the controlled process of placing items onto the sorter at correct spacing (gap control).
Conveyors include buffer loops and accumulation zones to smooth flow between fast upstream processes (picking) and slower downstream processes (packing). Zero-pressure accumulation (ZPA) via MDR ensures items queue without damage.
| Sorter type | Lines/hour | Load capacity | Typical use |
|---|---|---|---|
| Tilt-tray | 6,000–12,000 | up to 5 kg | Flat/polybag e-com |
| Cross-belt | 8,000–20,000 | up to 35 kg | General parcel |
| Sliding shoe | 4,000–9,000 | up to 50 kg | Heavy carton |
| Bomb bay (pocket sorter) | 15,000–30,000 | <2 kg | Polybag / apparel |
Conveyor and sorter systems are controlled by a Warehouse Control System (WCS) or Warehouse Execution System (WES), which receives sort orders from the WMS and translates them into real-time divert commands. Modern WES platforms also route work to AMRs and robotic systems from the same layer, creating a unified execution orchestration layer.