A Depalletising Vacuum Example for Cartons

A carton depalletiser can look straightforward until the first mixed pallet reaches the line. Cartons may be dusty, slightly bowed, taped unevenly or produced from porous board, and each condition changes how a vacuum gripper performs. This depalletising vacuum example shows how to specify a practical end-of-arm system for lifting single cartons from a pallet and placing them onto a conveyor.

The figures below are an engineering starting point, not a substitute for testing on the actual pack. Board grade, surface finish, carton stiffness, lift speed and the condition of the pallet load all affect the final selection.

Depalletising vacuum example: single carton handling

Assume an automated cell must remove corrugated cartons measuring 600 x 400 x 300 mm from a pallet. The cartons weigh up to 10 kg, arrive with their top faces exposed after outer stretch film removal, and are transferred at a moderate cycle rate to a takeaway conveyor. The robot approaches vertically, lifts each case, travels clear of the pallet, then releases it in a controlled position.

A suitable starting arrangement is a gripper plate with four 60 mm bellows vacuum cups, mounted on spring compensators. The cups are placed well inside the carton edges, broadly around the strongest areas of the top panel. The compensators allow each cup to land despite minor height differences, carton bowing or a pallet that is not perfectly level.

At a vacuum level of approximately -60 kPa, a 60 mm diameter cup has a theoretical holding force of around 170 N on an airtight surface. Four cups therefore provide roughly 680 N before allowances. That theoretical figure is not the load rating. Corrugated board leaks air, surface contact is rarely perfect, and acceleration during robot movement adds force. A sensible safety factor, combined with realistic testing, is essential.

For a 10 kg carton, four cups of this size can provide a workable basis where the carton top is reasonably flat and firm. If the board is more porous or the carton is prone to top-panel collapse, increasing cup diameter is not automatically the answer. Larger cups need more clear area and can distort weaker board. A wider gripper with additional cups, or foam sealing cups that tolerate leakage, may be the better solution.

Why four cups instead of one large cup?

A single central cup concentrates the load and leaves no redundancy. If the carton top includes a tape seam, printed varnish, dust or a shallow depression, that one sealing point can fail. Four independently supported cups spread the load and maintain contact when one area is less favourable.

The trade-off is airflow demand. More cups mean more potential leakage paths, particularly when lifting porous cartons. The vacuum source must therefore be selected for both vacuum level and evacuation flow, not on nominal vacuum pressure alone.

Selecting cups for the carton surface

For clean, reasonably smooth carton tops, standard bellows cups in nitrile or a similar general-purpose elastomer are often appropriate. Bellows help the gripper settle onto uneven cartons and reduce the risk that one cup takes the full load before the others engage.

Where cartons are dusty, recycled, highly porous or slightly irregular, foam-lipped cups can offer more reliable sealing. Their sealing face follows the board texture better than a conventional flat lip. However, foam cups generally consume more air and wear differently, so they need inspection as part of planned maintenance.

Cup material also depends on the operating environment. Food packaging areas may require materials and construction suited to the site’s hygiene regime. Cold stores, high temperatures, oils, inks and cleaning chemicals can all shorten cup life if the elastomer is poorly matched. A low initial cup price is quickly lost if production staff are replacing seals every week.

Cup holders should include spring compensators rather than rigid mounts where carton heights vary. A compensator stroke only needs to accommodate the real variation, but it must provide enough movement for all cups to seal before the robot starts lifting. Excessive stroke can add unwanted bounce at high cycle rates.

Size the vacuum source for leakage, not just lifting force

In this depalletising vacuum example, the cup array may require a vacuum generator or pump capable of reaching the target vacuum quickly while compensating for normal board leakage. This is where many systems underperform. A generator can achieve a strong vacuum on a blanked-off test port yet still struggle when four cups contact porous cartons.

Start by defining the required pickup time. If the robot allows 0.3 seconds between contacting the carton and lifting, the vacuum system must evacuate cup volume, hose volume and any small reservoir within that window. It must then maintain a safe holding level throughout acceleration, transfer and placement.

A central vacuum pump with a local reservoir can suit multiple handling stations or longer duty cycles. A pneumatic vacuum generator close to the gripper can reduce response time and simplify a compact robotic tool. Neither approach is universally better. Compressed-air cost, duty cycle, available utilities, noise limits and the number of simultaneous picks should determine the choice.

Use generous hose bore where flow is needed, and keep the hose run between source and cups as short as practical. Undersized tubing is a common restriction that cannot be corrected by fitting a larger generator upstream. Filters should protect valves and generators from board dust, but they also need accessible service intervals. A blocked filter can appear as an intermittent gripping fault.

Control logic that protects the cycle

The gripper should not lift merely because a valve has opened. A vacuum switch should confirm that vacuum has reached the agreed pickup threshold before the robot leaves the carton. The threshold must be proven during trials with the worst acceptable carton condition, not with a pristine sample.

A practical sequence is simple. The robot moves into position, lowers until the cups contact the carton, opens the vacuum valve and waits for confirmation. Once the vacuum switch changes state, the robot lifts and transfers the carton. At the placement point, vacuum is switched off and a controlled blow-off pulse breaks the seal cleanly.

Blow-off pressure must be modest and correctly timed. Too little can leave a cup clinging to the carton and delay release. Too much can disturb lightweight cartons or create unnecessary noise and air consumption. On high-speed lines, a separate release circuit and adjustable flow control provide more repeatable results than relying on a general air blast.

For higher-risk loads, add fault handling rather than treating the vacuum switch as a basic on/off signal. If pickup confirmation is not achieved within the allowed time, the robot should retract safely, flag the fault and avoid dragging a partly gripped carton across the pallet. If vacuum drops during travel, the cell response must reflect the risk assessment, the load path and the installed guarding.

Layout details that decide whether it works

The cup pattern must account for pallet geometry. As cartons are removed from the outer rows, the robot needs clearance from adjacent cases and pallet boards. A gripper that works on the centre of a test pallet may strike a neighbouring carton at the edge positions.

Layer sheets create another consideration. A thin slip sheet can lift with the carton if it is exposed around the case or if the top carton has a poor seal. Depending on the pallet format, the cell may need a layer-sheet removal method, a separator check or a gripper design that avoids contact with sheet edges.

Mixed pallets require further sensing. If carton heights, widths or top layouts vary, the robot needs reliable product data or vision guidance before it commits to a pick point. Vacuum handling is forgiving of modest variation, but it cannot compensate for a cup pattern placed over a void, a handle opening or a carton that is not where the programme expects.

Test the worst carton, not the ideal one

Before releasing a system into production, test it with cartons taken from the difficult end of normal supply: dusty stock, recycled-board cases, uneven tape, low-fill cartons, damp packaging where relevant, and cartons from the bottom and top layers of a pallet. Run the intended acceleration and deceleration profile, not a slow demonstration cycle.

Check for cup marks, top-panel deflection and movement during transfer. A carton that remains attached is not necessarily acceptable if the cups are crushing its contents or damaging printed presentation. Also measure recovery after a deliberate missed seal. The cell should identify the failed pick predictably and return to operation without creating a pallet collapse risk.

Vacuum Technologies Shop can help match cups, compensators, valves, switches, filters and vacuum generation to the actual carton and cycle requirement. Providing carton dimensions, maximum mass, surface condition, required cycle time and available utilities makes the selection process far more accurate.

The most dependable depalletising gripper is rarely the one with the highest stated vacuum figure. It is the one that maintains a verified grip on the least favourable acceptable carton, releases cleanly at the right point and remains easy for the maintenance team to inspect and service.