Station 2 of 6 Load and stack
How to Integrate Bread Trays with Conveyor and Automated Handling Systems
Contents: 6 sections
Fix the tray before you engineer the line. Conveyor guides, transfers, sensors and stackers are set to a tray’s dimensions, so the tray model and its dimensional tolerances are inputs to the design, not something to check after installation. Get the tolerances in writing, run a sample at line speed on the actual equipment, and keep uncontrolled variation in tray dimensions off the line. One model per line is the simplest way to do that; where a line has to run more than one model, set it up and test it for each model and switch guides and settings between them on a written procedure.
Why does the tray matter more on an automated line?
Because a machine does not adjust to the tray the way a person does. On a manual line, a worker absorbs a slightly wider tray, a rounder corner or a warped floor without thinking about it. A guide rail set for one width, a photo-eye set for one edge height or a stacker set for one rim profile does not. A mixed fleet, or trays from different generations of the same model, puts that variation on the line.
Tray makers treat this as a design input. ORBIS says its NPL660B tray “can be integrated with automated systems” and lists “Automation compatible features” without spelling them out; the same page asks: “Please fill out the Request a Quote form for dimensional tolerances if you are designing automation to interface with trays” (ORBIS, NPL660B). In other words, the tolerances your line needs are available on request, and the request is yours to make before the line is built.
What should you ask the tray maker?
Start with the equipment maker: if it has already run a tray model on the same machine, ask for that model and the test results. Then send the tray maker these questions for the exact model you plan to run, and keep the answers with the line’s design file:
| Ask for | Why the line needs it |
|---|---|
| Outside length, width and height, with tolerances | Guide spacing, transfer widths and stacker settings are set from these |
| Whether the tolerances hold across production lots, and how they are checked | Trays bought next year have to run on the same settings |
| Corner and edge profile | Square or sharp edges can catch on guides and transfer frames |
| Bottom profile, sent with your roller spacing | The bottom has to cross roller gaps and transfers without rocking or catching |
| Locating features, ribs or flats for guides and stops | Features that position the tray reduce the work the line has to do |
| Position of holes, vents and recesses, sent with your sensor positions | An opening where a sensor looks can read as a missing or misplaced tray |
| Loaded weight with your heaviest product | Conveyor and stacker ratings are set against it |
| Whether the model is expected to stay in production | A discontinued tray forces a line change |
Sources for the table: the list is ours, built from the tolerance request on the ORBIS page cited above and the fit checks on the accessories page; it is not a maker’s list.
Ask for a dimensional drawing as well as the numbers. Laying it over your sensor and guide positions shows conflicts before any steel is cut. The measured outside dimensions of common models, which differ from their size names, are in published dimensions for current tray models.
What does the conveyor side need to get right?
The same variables, from the equipment side:
- Guide spacing. Wide enough that the tray never drags, narrow enough that it cannot wander. Guides with curved or angled lead-ins correct position gradually instead of stopping the tray against an edge.
- Transfers. The gap between two conveyor sections is where a tray is least supported. Keep it smaller than the tray’s bottom features can bridge, and check it with a loaded tray.
- Speed matching. A tray moving from a slow section onto a fast one, or the reverse, takes a jolt. Match speeds at transfers or ramp them.
- Sensors. Position them against the tray drawing, and keep lenses clean; dust on a lens and a hole in a tray can produce the same false read.
- Sanitation. Conveyors in product-contact areas have to be cleanable to the same standard as other food-contact equipment in your plant.
How do you trace a jam or misfeed?
By where and when it happens, not by how many times:
- It follows one tray model or one purchase lot. The trays vary from what the line was set for. Measure them against the drawing.
- It follows older trays. Wear or warping has changed the tray. Pull the trays that jam and run the rock and lock tests on them.
- It happens at one transfer, whatever the tray. The gap, the speed change or the guide at that point is the cause.
- Sensors fault at random. Check the lenses first, then whether the fault lines up with a hole or recess in the tray passing the sensor.
Record each jam with the tray model, the location on the line and the time. With those three fields, each jam can be sorted into one of the four.
Can you automate with the trays you already have?
Sometimes, and the test decides. Measure a sample of your current trays across ages and purchase lots. If they fall within a range the equipment maker can accept, adjustable guides can take them. If they do not, you have three routes:
- Standardize the trays on that line. Dedicate one tray model to the automated line and keep other models off it. This removes the variation instead of working around it.
- Adjustable guides and settings. They cope with more than one model, at the cost of changeovers and more adjustment to maintain.
- Adaptors. A fixture that gives an old tray the geometry the line needs. It adds a part that has to be tracked, cleaned and replaced, so treat it as a bridge during a changeover, not a permanent fix.
Whichever route you take, trays bought later have to match what the line is set for; how to keep dollies, racks and trays matched as a fleet changes is covered in keeping a compatibility record for trays and accessories.
What do you decide before you buy the equipment?
The tray model the line will run, with its tolerances in writing and a sample that has passed a run at line speed on the maker’s test rig or your own line. If you cannot name that tray yet, the line is not ready to be specified. For tray problems away from the line, start from the troubleshooting table for tray problems.