Chain conveyor load handling devices sit in a different design class from telescopic forks on pallet stacker cranes: the chain conveyor is a power-driven pallet-moving surface used to discharge a unit load from the crane onto an in-line chain conveyor, whereas the telescopic fork is a passive extension arm that slides the pallet off the mast into the rack or onto a static pick station [S1].
Both attachment families are mounted on a single-mast or twin-mast stacker crane and share the same aisle rail geometry, WMS/WCS layer and safety stack, but their throughput profile, payload envelope and storage-depth flexibility diverge sharply above 1,000 kg or 20 m lift [S3][S4].
Function and integration into the AS/RS
Chain-conveyor load handling attachments on pallet stacker cranes carry a section of motorised chain track built into the load plate, so the crane deposits a pallet into the attachment and the chain drive then indexes the pallet out onto a downstream conveyor or order-picking lane [S1]. The geometry eliminates the forklift-style back-out manoeuvre in the picking aisle and lets the stacker crane hand off a load without lowering the mast to a transfer cart.
Telescopic forks on a pallet stacker crane are extendable fork arms that carry the pallet only during the in/out stroke; once the pallet is in the rack pocket or on a pick station, the forks retract into the mast. The cradle is rated for pallet weights up to roughly 1,500 kg on single-mast pallet stacker cranes and for cold-store operation down to -30 °C on heavy-duty designs [S1][S7].
Payload, lift height and speed envelope
Single-deep telescopic forks on standard pallet stacker cranes are widely rated for unit loads up to 1,500 kg with the mast working at heights between roughly 23 m and 30 m; the MIAS PAL 23 design travels at up to 240 m/min and lifts at 120 m/min, with a 20 % weight reduction over the prior mast series [S1][S2]. Double-deep and triple-deep telescopic forks trade payload for storage density: single-mast stacker cranes for pallets max out at 1.65 t in single-deep configuration and drop to 1.1 t in double-deep across the MT-1 to MT-5 model range, with a 148 ft (45 m) maximum height on the tallest MT-5 frame [S3].
Chain-conveyor attachments are sized to the same 1,500 kg envelope but add a powered chain deck, so the crane's effective cycle is governed by the slower of the mast travel/hoist profile and the chain index time, which is typically in the 3-6 s range per pallet transfer on European AS/RS builds [S1]. Telescopic forks have no extra powered stage between rack pocket and pick station, so for storage-and-retrieval cycles without conveyor hand-off they preserve the crane's full 217 ft/min (66 m/min) lift and 722 ft/min (220 m/min) travel capability [S3].
Storage depth and aisle density
Telescopic forks win on rack depth flexibility: single-, double- and triple-deep variants exist on a common mast, so a single crane can serve deep lanes for slow movers and shallow lanes for fast movers, with the double-deep MIAS design dating from the late 1970s [S1][S2]. The Interlake Mecalux MT-1 to MT-5 range shows this clearly, with max height dropping from 59 ft single-deep to 51 ft double-deep on the MT-1, and from 148 ft to 108 ft on the MT-4, because the deeper fork extension forces a lighter unit load (1.65 t down to 1.1 t) at the top of the mast [S3].
Chain-conveyor attachments are depth-neutral but aisle-restrictive: they only make sense in a distribution-centre cell with a downstream material handling conveyor, typically a chain or roller line that matches the attachment's chain pitch. In a pure high-bay storage aisle with no picking conveyor, the chain-conveyor attachment adds dead weight, motor load and a failure mode (chain stretch, sprocket wear) for no throughput benefit [S1][S6].
Decision matrix: when each attachment fits
Use a telescopic fork when the cell is a high-bay storage aisle, the WMS drives direct-to-rack put-away, the load is below 1,500 kg per pallet, and storage depth spans single to triple deep; this is the default for roughly 90 % of greenfield pallet AS/RS in ambient and cold (down to -30 °C) operation [S1][S3][S7].
Use a chain-conveyor load handling device when the stacker crane terminates at an order-picking zone and the downstream flow is a live chain conveyor or a shuttle, the pick face is one-pallet-deep, and the WMS is sequencing orders into a goods-to-picker lane; MIAS lists this combination as a stock product for distribution-centre cells [S1]. Avoid chain-conveyor attachments on heavy-duty cranes rated above 1,500 kg, where the chain deck drive, sprocket and motor become a maintenance liability and the telescopic fork's positive-locking double-row gear train is a more proven powertrain [S1][S7].
Operating envelope and environmental limits
Standard pallet stacker cranes with telescopic forks operate from -22 °F (-30 °C) to 104 °F (40 °C) in Interlake Mecalux's MT-series, with travel accelerations up to 2 ft/s² (0.6 m/s²) and lift accelerations up to 2 ft/s²; cold-store variants extend the lower bound with low-temperature grease, sealed bearings and anti-condensation heaters on the mast electrical cabinet [S3][S7].
Chain-conveyor attachments introduce an additional environmental constraint: the chain and sprocket set needs lubrication (or sealed-for-life lube on stainless chain) and is sensitive to dust, cardboard fibre and shrink-wrap debris from order picking, so the picking zone typically requires a guarded chain deck with side skirts and a cleaning brush. Syncore/Dambach pairs these attachments with the warehouse control system so the WMS can slow the chain index when load sensing detects an off-centre pallet, protecting the sprocket from side load [S4][S6].
Reliability, retrofit and lifecycle signals
MIAS has sold telescopic forks continuously since the 1960s and frames the design as "tried and tested a thousand times over" with low maintenance thanks to a positive-locking, double-row stationary gear, while Syncore highlights stepwise retrofits (extra drive units, toothed rack mechanisms) that raise throughput without replacing the stacker crane [S1][S4].
For chain-conveyor load handling devices, the lifecycle signal to watch is chain pitch wear and sprocket tooth profile: a typical European pallet AS/RS chain deck on a 1,500 kg-rated attachment runs 8-12 million cycles between chain replacements in mixed-load operation, and 15-20 million cycles in food/beverage cells with clean pallets; the telescopic fork's gear-driven extension in the same duty class regularly exceeds 20 million cycles before a bearing swap [S1][S7]. The retrofit market is also relevant for design decisions: a telescopic fork retrofit on a DAMBACH or Syncore stacker crane is a bolt-on change with no rack-side modification, while retrofitting a chain-conveyor attachment requires the downstream conveyor to be commissioned in the same outage window, so chain-conveyor swaps are typically scoped at greenfield or full-rack-rebuild projects [S4][S6].
For a high-density 25 m cold-store build with 1,200 kg Euro pallets, spec a double-deep telescopic fork on a single-mast crane with the -30 °C lube package; for a 12 m ambient distribution-centre cell with order picking onto a live chain line, spec a chain-conveyor load handling device matched to the downstream conveyor chain pitch. The first signal to track over the next planning cycle is whether vendors publish 2026-vintage cycle-life data for chain-conveyor attachments above 1,200 kg, because the current public envelope tops out at the 1,500 kg MIAS pallet-class figure and any lift above that will force a heavier chain and a re-rated sprocket [S1][S2][S7].
For related coverage, see #40 vs #60 vs #80 roller chain pitch, dimensions, and sizing rules.