Automated Material Handling Systems (AMHS) and Tier Sheet Integration

A tier sheet is a thin layer placed between palletized product layers to protect goods and improve load stability; in AMHS environments it must be engineered for reliable robotic handling.

Definition and role

A tier sheet is a flat sheet of material—commonly fiberboard, coated paperboard, corrugated plastic or composite film—placed between layers of products on a pallet to protect goods, stabilize the stack, and facilitate handling. In Automated Material Handling Systems (AMHS), including AS/RS, robotic palletizers and depalletizers, tier sheets are both a physical protection element and a functional component of the automation workflow: they must be repeatably singulated, sensed, and placed by robotic end-of-arm tooling (EOAT) with millimeter accuracy.

Why AMHS integration changes tier sheet requirements

Unlike manual palletization where human operators can compensate for variability, AMHS depend on consistent, machine-friendly inputs. In automated environments variability in thickness, porosity, edge straightness, or flatness becomes a direct cause of mis-picks, machine stalls, false sensor readings and unplanned downtime. Therefore tier sheets used in these systems require tighter specifications, documented testing, and predictable behavior across environmental ranges.

Key material and physical properties

• Porosity control: For vacuum-based EOAT, the sheet’s porosity must be calibrated so a single sheet can form a reliable seal. Excessive permeability allows vacuum to draw through multiple sheets or fail to generate required hold force; too little permeability prevents consistent suction grip.
• Dimensional stability and flatness: Sheets must resist warping, curling and edge waviness under normal warehouse humidity and temperature ranges. Warped sheets can break optical sensor intent and cause misalignment during deposition.
• Thickness uniformity and tolerances: Consistent thickness within narrow tolerances (often ±0.1–0.3 mm depending on material) ensures predictable stack height and palletizer stroke programming.
• Surface finish and friction: Top and bottom surface friction coefficients affect how reliably sheets slide into position and how product layers interact with the sheet.
• Edge straightness: Clean, square edges support accurate sensing and reduce the chance of skewed placement.
• Static and cleanliness: Anti-static treatments and low-dust surfaces prevent cling and particle contamination that can impair vacuum seals or product surfaces.

Design and manufacturing considerations

Manufacturers supplying tier sheets for AMHS should specify material composition, coating type, porosity metrics (e.g., Gurley seconds or air permeability values), thickness distribution, warp limits and environmental conditioning requirements. Production controls such as calendering for dimensional stability and controlled surface coatings for vacuum sealing are commonly used. Suppliers often produce samples matched to a customer’s EOAT type for factory acceptance testing.

Testing and qualification

Before full-scale deployment, tier sheets should pass a standardized qualification protocol that includes:

1. Environmental conditioning (humidity and temperature cycling) to assess warp and dimensional drift.
2. Vacuum pick-and-hold testing with the actual EOAT to measure hold force, leak rates and single-sheet pick reliability.
3. Dimensional measurement of thickness, flatness and edge tolerance across representative batches.
4. Compatibility testing on downstream equipment (conveyors, stretch wrappers, strapping machines) to ensure the sheet does not interfere with other automation steps.

Integration best practices

• Define detailed tier sheet specifications in procurement contracts and include sample approval clauses.
• Run pilot trials with the target AMHS configuration, including robots, grippers and sensors, before blanket acceptance.
• Tune EOAT parameters (vacuum pressure, dwell time, cup pattern) for the chosen material and thickness range.
• Implement incoming quality inspection for dimensional and porosity checks on production lots.
• Maintain version control on specifications and notify automation teams whenever a material or supplier changes.

Common problems in AMHS integration and mitigation

Frequent issues include double picks (two sheets suctioned at once), failed picks from warped sheets, and placement misalignment. Mitigations include specifying controlled porosity, adding singulation features on feeders, incorporating presence and vacuum-sensor feedback loops, and using pre-conditioning (stack flattening) stations.

Real-world example

A high-volume third-party logistics (3PL) operator deploying robotic palletizers switched from an inexpensive paperboard tier sheet to a slightly thicker, sealed-surface board with specified air permeability. This reduced double-pick incidents by 95% and cut palletizer downtime from repeated jams, justifying the small per-sheet cost increase through productivity gains.

Conclusion

Tier sheets are a small but critical component in AMHS. When specified and tested for automated handling—covering porosity, flatness, thickness uniformity and environmental stability—they enable reliable robotic picks and smooth pallet build processes. Early specification, supplier qualification and joint pilot testing between automation and packaging teams are essential to ensure trouble-free integration.