Palletizing Automation for Multi-Line Plants: One Robot Cell or Multiple Cells?

A plant with three production lines that each need palletizing faces a fundamental architecture question: should it invest in one high-speed robot cell that serves all three lines, or multiple smaller cells that each serve one line? The answer is rarely obvious, because the two approaches differ in throughput, flexibility, downtime risk, space requirements, and cost. This article explains the decision factors that determine which architecture is right for a multi-line palletizing application.

Why One High-Speed Cell Is Not Always Better Than Several Smaller Cells

The instinct to centralize is understandable: one high-speed robot cell seems more efficient, easier to maintain, and cheaper than multiple separate cells. In some cases, this is true. In many cases, it is not.

A single centralized cell works well when:

• All lines produce similar products at similar rates
• Lines are physically close together, allowing short conveyor runs to the central cell
• SKU mix is low (few different pallet patterns)
• Downtime on one cell is acceptable because all lines can pause

A single centralized cell may be less suitable when:

• Lines produce different products at different rates, requiring frequent changeovers
• Lines are physically separated, requiring long conveyor runs that add cost and complexity
• SKU mix is high, requiring the robot to switch patterns frequently
• One line’s downtime should not affect other lines

The decision is not “centralized is better” or “distributed is better.” It is a trade-off analysis that depends on the specific plant’s production characteristics.

Compare Line Throughput and SKU Mix

The first step is to understand what each line produces and how that affects palletizing requirements:

Throughput Sizing Approach

Palletizing cell sizing should be calculated based on the actual pick-and-place cycle, not on a simplified pallets-per-minute figure. The key variables are:

• Cases per minute arriving at the palletizing point (per line and combined)
• Cases per pick (how many cases the gripper handles per robot cycle)
• Picks per minute the robot can execute (based on robot speed, reach, gripper strategy, and pallet pattern)
• Pallet change time (time to swap a full pallet for an empty one)
• Changeover time between different pallet patterns (if applicable)

Illustrative scenario (all figures are hypothetical for calculation demonstration):

• Line 1: 120 cases/min
• Line 2: 80 cases/min
• Line 3: 60 cases/min
• Combined demand: 260 cases/min
• Cases per pick: 1 (single-case gripper)
• Robot pick rate: 12 picks/min (based on robot model, reach, gripper, and pallet pattern)
• Pallet change time: 20 seconds per pallet (accounted for in average cycle)

In this scenario, one robot at 12 picks/min cannot serve 260 cases/min. The buyer must either:

• Use a multi-case gripper (e.g., 2 cases per pick = 24 cases/min per robot)
• Use multiple robots in one cell
• Use distributed cells (one per line)

If the gripper handles 2 cases per pick, one robot can handle 24 cases/min. With 3 robots, the cell handles 72 cases/min—still insufficient for 260 cases/min combined. The point is that the calculation must be done with actual pick-rate data from the robot supplier, not assumed from a generic “pallets per minute” figure.

If lines run in staggered shifts (not simultaneously), the peak demand may be lower, and a single cell may suffice. But the calculation must use the actual peak, not an assumed average.

Conveyor Routing and Accumulation Between Lines

The conveyor system that feeds the palletizing cell is a major cost and complexity factor:

Centralized Cell Conveyor Requirements

• Conveyor runs from each line to the central cell
• Merge system to combine flows from multiple lines
• Accumulation buffer to handle rate differences between lines
• Line identification system (vision or barcode) to route each case to the correct pallet
• Floor space for conveyor runs, merge points, and accumulation

Distributed Cell Conveyor Requirements

• Short conveyor from each line to its dedicated cell
• No merge system needed
• Minimal accumulation needed (each cell matches its line’s rate)
• No line identification system needed (each cell handles only one line’s products)

Cost Comparison

The conveyor cost for a centralized cell can exceed the savings from buying one robot instead of multiple robots. This is a factor to model, not a universal conclusion—the actual cost depends on the plant layout, conveyor length, and system complexity.

Changeovers, Mixed Loads and Pallet Availability

Changeover Frequency

If each line produces a different product, the centralized cell must switch pallet patterns when switching between lines. Each changeover involves:

• Robot program change
• Gripper adjustment (if products differ in size)
• Pallet change (if pallet sizes differ)
• Pallet pattern update

If changeovers are frequent, the centralized cell loses throughput to changeover time. Distributed cells, each dedicated to one line, do not require changeovers.

Mixed Loads

Some applications require mixed pallets (multiple SKUs on one pallet). Mixed palletizing requires:

• Vision system to identify incoming cases
• Dynamic pallet pattern calculation (not a fixed pattern)
• More complex gripper (may need to handle different case sizes)
• Slower cycle time (positioning precision is more critical)

Mixed palletizing may be better suited to a dedicated cell, not a shared centralized cell—but this is a factor to evaluate, not a universal rule.

Pallet Supply

• Centralized cell: one pallet dispenser serves all lines, but pallet types may differ by line
• Distributed cells: each cell has its own pallet dispenser, configured for that line’s pallet type

Robot Reach, Gripper Strategy and Shared Equipment

Shared Equipment

A centralized cell may share:

• One pallet dispenser (serving multiple pallet positions)
• One stretch wrapper (post-palletizing)
• One label printer
• One safety perimeter

Distributed cells each need their own equipment, which increases capital cost but reduces dependency—if one cell’s pallet dispenser fails, the other cells continue operating.

Downtime Risk: One Central Cell vs Distributed Cells

Downtime risk is one of the strongest arguments for distributed architecture:

Risk Mitigation for Centralized Cell

If a centralized cell is selected, the plant should mitigate downtime risk:

• Maintain a manual palletizing backup procedure (with adequate staff and space)
• Keep critical spare parts on hand (robot controller, motor, gripper)
• Schedule maintenance during non-production hours
• Consider a backup robot or quick-swap capability

Floor Space, Safety and Maintenance Access

Note: Safety perimeter design (guarding, light curtains, area scanners) must be based on a risk assessment for the specific cell configuration—not on whether the cell is centralized or distributed.

Decision Matrix for Centralized vs Distributed Palletizing

How to Use This Matrix

Score the project against each row. If the majority of factors favor centralized, a single high-speed cell may be the right choice. If the majority favor distributed, multiple smaller cells may be better. Mixed results indicate that a hybrid approach (e.g., two cells serving three lines) may be optimal.

The matrix is a decision support tool, not a formula. The final decision should consider the plant’s specific constraints, budget, and operational priorities.

Research Sources Used

1. Source / organization: IEEE (palletizing automation production line design, PLC control) | URL: https://ieeexplore.ieee.org/ | Version/date: as cited in report_batch_c

Internal product/material source: report_batch_c (batch C research report) [TO VERIFY]: none