The Palletizer That Dropped the Boxes
We built a palletizer (a robot, article 52, stacks boxes on a pallet). On the floor, the robot dropped boxes (it missed the pallet). The problem: the pallet’s position (the pallet is placed by a fork truck, not exactly). The robot’s program (the stacking) assumed the pallet was at the exact position. The fork truck placed the pallet off (by 50 mm). The robot missed. We added a vision (article 193) or a sensor (to find the pallet). We used a photo-eye (to detect the pallet’s edge). The robot adjusted (it found the pallet). The boxes stacked. The mistake was assuming the pallet was exactly positioned (without a sensor to find it).
Palletizing layout finds the pallet (and stacks). This article covers the design.
The Palletizer
A palletizer (robot or gantry) stacks boxes on a pallet. The boxes come (from a conveyor, article 121). The robot picks a box, places it on the pallet (in a pattern). The stack builds (layers).
Step 1: The Pallet Position (Find It)
The pallet is placed (by a fork truck) — not exactly. The robot must find the pallet (its position). Options:
- Photo-eye (article 108): A sensor detects the pallet’s edge (the robot homes to it). Simple. But if the pallet is rotated (not aligned), the sensor misses.
- Vision (article 193): A camera finds the pallet (and its rotation). Accurate. Expensive.
- Fixed nest (a slot): The pallet sits in a fixed nest (it’s positioned). Simple. But the fork truck must place it in the nest (operation).
The palletizer rule: Find the pallet (don’t assume). The robot that dropped boxes assumed the pallet was exact. Use a photo-eye (or vision) to find it. The pallet is placed by a fork truck (not exact). The robot adjusts.
Step 2: The Stacking Pattern
The boxes stack in a pattern (layer 1, layer 2, …). The pattern (the box orientation, the offset) is programmed. The robot places each box (in the pattern). The pattern is tight (the boxes interlock, stable). For a tall stack (10 layers), the pattern must be stable (no lean).
Step 3: The Pallet Height (Sensors)
As the stack builds, the height grows. The robot must know the current height (to place the next layer). A height sensor (a photo-eye, or a laser) measures the stack’s height. The robot adjusts (it lowers to the right height).
Step 4: The Layer Pad (Sheet)
Between layers, a sheet (a cardboard pad) is placed (to separate the layers). The palletizer picks a sheet (from a magazine) and places it. The sheet dispenser (a feeder) holds the sheets.
| Step | Method |
|---|---|
| Find the pallet | Photo-eye (or vision, article 193) |
| Stack the boxes | Pattern (programmed) |
| Measure height | Height sensor |
| Layer pad | Sheet dispenser |
A Palletizer Checklist
- How does the robot find the pallet? (Sensor?)
- Is the pattern programmed? (Boxes?)
- Is the height measured? (Sensor?)
- Is there a layer pad? (Dispenser?)
- Is the stack stable? (No lean?)
- Is the robot rated? (Payload? Article 52?)
- Is the cycle OK? (Takt? Article 191?)
- Is the pallet exchanged? (Fork truck?)
- Is the safety fence? (Article 74?)
- Does it drop boxes? (Test?)
The Bottom Line
Palletizing layout finds the pallet (and stacks). The robot that dropped boxes assumed the pallet was exact. Use a sensor (or vision). Program the pattern. Measure the height. The palletizer that stacked boxes wasn’t the exact-position robot — it found the pallet.
