High Level Palletizer Retrofit

Many plants run a layer-forming palletizer that was installed a long time ago and still does its job. The frame is sound, the layer table moves, and operators know its habits. What ages faster is everything around the steel: the controller, the drives, the sensors, the guarding, and the paperwork. A palletizer retrofit deals with that gap, and it usually begins with an honest question about whether the machine should be kept at all. This guide covers how older layer-forming machines work, what to inspect, where maintenance effort pays off, how to approach controls and safety upgrades, how to weigh retrofit against replacement, and what to check when buying a used machine. It is a companion to the guide on selecting a new high level palletizer, and it sits within the wider palletizing section.

How older layer-forming palletizers work

This is general background, not a description of one model. For a deeper treatment of the machine itself, see the high level palletizer guide. Machines that form whole layers before loading the pallet follow a common sequence.

1. Cases arrive on a conveyor, usually from a case sealer or a wrapping station. A case switch or gapping section sets spacing so the machine can sense each case.
2. Many patterns need some cases rotated 90 degrees. A turner, often a pair of belts running at different speeds or a mechanical arm, rotates cases in line without stopping the flow.
3. Cases are grouped into rows. A lane divider or slat mechanism sends cases into parallel lanes, and a stopper or pusher collects the row.
4. Rows are pushed together on a layer table until a full layer matches the programmed pattern. Patterns with voids for stability can be built by moving the plate that supports the layer in sections.
5. The completed layer is moved over the pallet. On a high level machine, a bi-parting plate or sweep carries the layer out while the pallet hoist brings the pallet into position, and the layer is released onto the load.
6. A pallet dispenser supplies empty pallets and a discharge conveyor carries finished loads away. Tier sheets, if used, are placed between layers by a separate head.
7. A PLC sequences the motions, stores the pattern recipes, and handles faults. Operator panels let staff select a recipe at changeover.

Used-equipment listings for older units, such as FLI-series machines, typically describe features like a PLC, case switch, and metering belt, so those are the parts to ask about first.

In-line and right-angle arrangements

Layer-forming palletizers are commonly built in two arrangements. In an in-line arrangement, cases keep moving in the same direction from infeed to layer table, which suits fast lines that need a straight conveyor path. In a right-angle arrangement, the layer table sits at a right angle to the infeed, which can fit a tighter floor plan and lets the machine form rows from slower product streams. The arrangement affects speed, floor space, and where operators can reach, and it limits what a retrofit can change.

Vendors have never used the labels “low level,” “mid level,” and “high level” in exactly the same way. Treat the label as a rough description, and look at where the cases enter and where the layer is formed.

What to inspect on an older machine

An inspection turns a vague feeling that the machine is getting old into a list that can be priced. Do it with the machine stopped, locked out, and guarded as required, and bring someone who knows the controls as well as someone who knows the mechanics. Photograph everything and keep the notes, because they become the scope of any retrofit or the argument for replacement.

Start with the structure. Look for cracks at welds, loose anchor bolts, rust that has eaten into sections, and any sign that the frame has been modified without drawings. A frame that has sagged or racked under load is a strong reason to lean toward replacement.

The hoist carries the pallet and the growing load, so inspect its chains, sprockets, guides, and brakes with particular care. Check chain stretch, uneven wear on sprockets, and any noise or jerking during travel, and confirm that overtravel limits and mechanical stops work as designed. On the layer table and transfer, examine the plates, the bi-parting or sweep mechanism, rails, and bearings. Layers that arrive crooked or rows that do not close tightly often trace back to worn guides or loose adjustments, not to the controls.

Upstream of that, check belts, rollers, guide rails, diverters, and stoppers on the infeed, turner, and row-forming sections. Uneven wear can point to misalignment upstream. In the pneumatics, look for leaking fittings, hardened hoses, worn cylinders, and valves that stick. Air leaks are easy to fix and often responsible for intermittent faults.

Photoeyes, proximity switches, and flexing cables fail more often than large mechanical assemblies, so look for cracked insulation, repeated taped repairs, and cable tracks with fatigue. Inside the electrical cabinet, look for dust, heat damage, loose terminals, discolored wiring, and undocumented jumpers, and compare what is there with the drawings. Differences usually point to past modifications that nobody recorded. Note the model numbers, ages, and condition of drives and motors, and record nameplate data for each one, because that list tells you which parts can still be bought and which cannot.

Collect the electrical drawings, mechanical drawings, manuals, spare parts lists, and the PLC program, and test that the program backup actually restores. Many delays in older plants trace back to missing schematics or a program that exists only on one aging laptop.

Walk the perimeter and every access point of the safeguarding. Check that doors are interlocked, that interlocks cannot be defeated with a piece of tape or a spare key, and that light curtains and gates still do what they are meant to do. Look for bypasses and ask who installed them and why.

Finally, consider pallet and product condition. A machine can look worse than it is when it is being fed damaged or mixed pallets, so check pallet quality at the supplier before blaming the palletizer.

Maintenance priorities

When the budget is limited, spend it in this order: safety first, then the parts whose failure stops the line, then the parts whose failure is hard to repair.

Interlock switches, guard doors, emergency stops, and light curtains deserve regular functional tests, with the results written down. A device that no one has tested in years should be treated as unproven.

Back up the software and store it off site. Save the PLC program, HMI project, drive parameters, and any recipe files, store copies away from the plant, and test the restore procedure. This one low-cost task prevents the most painful kind of downtime.

Make a list of controllers, drives, servo amplifiers, communication modules, and operator panels, and mark each as available, limited, or discontinued. Then decide which discontinued parts to stock as spares and which to replace on a schedule. Waiting for a failure is the most expensive way to find out a part is gone.

Belts, chains, bearings, guide rails, and cylinders wear at predictable rates when the machine is run consistently. Keep a small stock of the common types, and replace in sets where uneven wear would cause trouble. Keep cabinet filters clean, make sure cooling fans run, and keep dust out of electrical enclosures, because heat shortens the life of drives and power supplies.

Operators who understand what a normal cycle looks like catch problems earlier, and maintenance staff need a clear procedure for jam clearing and changeovers that does not rely on defeating a guard. A simple log of stops, causes, and repairs shows which problems recur. After a few months, it often points to the real cause, whether that is a pallet issue, a worn guide, or a sensor in a bad spot.

Controls and safety upgrades

Controls and safety are the most common reasons to retrofit, and they are also where the work needs the most care. Every item below should begin with a risk assessment and end with documented validation.

PLC and HMI migration

An older PLC may still run reliably, but its programming software, memory cards, and communication modules can be hard to find, and fewer technicians know the platform. Migration means moving the logic to a current controller family. It can be a straightforward translation or a rewrite, depending on how the original program is structured and documented.

Questions to settle before starting:

• Who owns the existing program, and is the source available with comments?
• Will the sequence stay the same, or is the plan to improve it?
• Which sensors, valves, and drives connect to the controller, and can they be reused?
• Is a new operator interface part of the scope, and how many recipes must be stored?
• How will the changeover from old to new be tested, and how long can the line be down?

A new HMI can add fault messages that tell operators exactly which sensor is blocked, storage for more patterns, and simple recipe selection. Those features reduce downtime without touching the mechanics. Drives and motors can be handled in the same project, particularly when a discontinued drive is the reason for the work.

Safety-rated controls

Older machines often use standard relays or standard PLC outputs for functions that today would be handled by safety-rated components. Safety-related control functions are commonly designed to ISO 13849-1, which defines performance levels. A safety-knowledge overview from a sensor maker explains how the required level follows from the risk and how the design must meet it. In practice, that means safety relays or a safety controller, dual-channel inputs on interlocks and emergency stops, monitored outputs, and a defined stopping behavior.

Keep the safety function separate from the standard control program: it should not depend on the same logic that runs the cycle. Confirm the edition of each standard that applies to your project, since several have been revised in recent years.

Guarding and interlocks

Check that every point of access is protected: fixed guards where access is not needed, interlocked doors where it is, and light curtains or area scanners at pallet entry and exit. Interlocks should be of a type that is hard to defeat, and the stopping time of moving parts, including the hoist and layer table, should be compared against the distance to the hazard. If a person can reach a moving part before it stops, the guard is in the wrong place or the stopping system is too slow.

Pay attention to the tasks that cause the most injuries: clearing jams, changing over, and cleaning. If those tasks require operators to reach into the machine, the guarding should allow it safely, for example through a controlled-entry system that stops motion and prevents an unexpected restart.

Risk assessment

A risk assessment covers normal operation, jam clearing, changeover, cleaning, maintenance, and fault recovery. It identifies the hazards, estimates the risk, and decides what protective measures are needed. For machines modified several times over the years, it should also search for undocumented bypasses and temporary fixes that became permanent. An A3 article on robot safety standards notes that those standards address the whole application, including the end-effector, workpiece, and peripheral equipment, and the same thinking applies to palletizers: the assessment is about the complete installation, not one component. If a robot is added to a retrofitted line, the robotic safety standards enter the picture as well.

Lockout and tagout

Each energy source on the machine needs a clear isolation point: electrical, pneumatic, hydraulic, and gravity. The U.S. rule on the control of hazardous energy, 29 CFR 1910.147, sets out the requirements for energy-control procedures, devices, training, and periodic inspection. On a high level palletizer, pay particular attention to stored energy, such as a suspended layer, a raised hoist, a charged air line, or a drive that holds charge. The upgrade should make isolation points obvious and labeled, and the written procedure should match the machine as modified, not as originally built.

Retrofit vs. replace

The choice rarely comes down to one factor. The table compares the usual drivers.

Use the table as a conversation starter, not a score. The deciding factor is often the first one: if the frame is sound, a retrofit can extend the life of the machine for years. If it is not, no controls upgrade will fix it. Be careful about hidden scope too. A retrofit that begins as a controller swap can grow to include drives, wiring, guarding, sensors, and a new interface once the cabinet is opened. Ask for a fixed scope with a list of exclusions, and compare it against a new quote on the same basis, including installation, commissioning, training, and warranty.

The palletizer cost guide explains the factors that move a quote, and the guide to how to choose a palletizer helps define the requirements that a retrofit or a new machine must meet. Pallet-related handling problems may sit upstream, so the pallet handling application page is worth a look if pallet quality is behind your stoppages.

Buying a used high level palletizer

A used machine can be a sensible choice, especially for a stable product and a plant with maintenance skills. It can also mean buying somebody else’s problems, so treat the purchase as a project, not a bargain.

Checklist before you commit:

• Confirm the machine type and where the layer is formed, and that it fits your building height, infeed height, and floor plan.
• Ask for a power-on demonstration with the product and pattern you plan to run, not only a demonstration with empty cycles.
• Request the PLC program, HMI project, drive parameters, and backups, and confirm that you can open them.
• Request electrical and mechanical drawings, manuals, and the parts list.
• Ask for the service history, the reason for sale, and any known faults.
• Check the controller, drive, and operator panel models against what is still available.
• Inspect the hoist, chains, layer table, and frame using the checklist above.
• Evaluate the safeguarding and the safety circuits against current practice, and price the upgrade.
• Confirm what is included: pallet dispenser, sheet placer, infeed conveyors, discharge conveyors, and any lifts.
• Ask who handles disassembly, rigging, transport, reinstallation, and commissioning, and who is responsible if something is damaged.
• Verify the electrical supply requirements and whether your plant can provide them.
• Confirm warranty terms, or the absence of any, in writing.
• Budget for guarding updates, a controls review, spare parts, and training.

The listing price rarely includes those last items. A listing that shows a machine with a PLC, case switch, and metering belt tells you what the machine has, but not how well it runs, how it is documented, or how it will meet current safety expectations. The commissioning and acceptance checklist covers questions to ask any equipment supplier and applies to used machines as well. When the palletizer is part of a bigger project, see the guidance on turnkey lines.

Modern alternatives

Layer-forming machines of this type still have a place. Current conventional palletizers refine the same idea with servo-driven axes, faster changeover, recipe management, and remote diagnostics, and they remain a natural fit for lines that run a few patterns at high rates. If the existing machine has done its job for years and the product mix has not changed, a new conventional machine can be a like-for-like replacement with better controls and safety built in.

When a plant handles many case sizes, mixed pallets, or frequent changeovers, robotic palletizers offer flexibility through programmable gripper motions, usually at a lower peak rate and with a smaller footprint. They bring their own safeguarding requirements, since the robot standards apply to the whole cell. A robot can also be a reasonable answer when the old frame is sound but the product range has outgrown the layer table, because the cell can be placed in the same area after the old machine is removed.

Whichever route you take, define the requirements first: cases, patterns, rate, pallet types, safety expectations, and the maintenance skills in the plant. Then compare a retrofit scope, a used machine, and a new machine on the same basis.