A palletising vacuum gripper requires a rated holding force of at least twice the case weight after losses from porosity, leakage, acceleration and cup geometry are included.
Select the gripper from the product and process
Start with case mass, lifting surface, dimensions, centre of gravity and required cycle time. Confirm that the cobot payload covers the combined mass of the product, EOAT, hoses, fittings and any retained items during multi-pick operation.
Measure the usable contact area rather than the total top face. Tape seams, labels, straps, creases and damaged cardboard reduce the area available for stable cup placement.
Record the product variants scheduled on the cell. A gripper covering every stock keeping unit without manual adjustment reduces changeover time, but additional cups increase EOAT mass and compressed air demand.
Apply a safety factor of 2 to cup sizing
Calculate case weight from mass using `F = m × g`, where `g = 9.81 m/s²`. Multiply this force by a minimum safety factor of 2 for a horizontal lifting face.
Calculate theoretical cup force using `F = ΔP × A`. Vacuum differential `ΔP` is measured in pascals, while cup area `A` is measured in square metres.
Apply correction factors for cup effectiveness, leakage and acceleration after calculating theoretical force. Manufacturer data provides rated lifting force at stated vacuum levels, so final selection uses the supplier's tested figure rather than diameter alone.
Worked cup sizing calculation
A sealed case has a mass of 15 kg and is lifted from its horizontal top face. Its weight is `15 × 9.81 = 147.15 N`, giving a required holding force of `147.15 × 2 = 294.3 N`.
Four cups divide the requirement into `294.3 ÷ 4 = 73.6 N` per cup. At a vacuum differential of 60 kPa, the ideal area required per cup is `73.6 ÷ 60,000 = 0.001227 m²`.
The equivalent ideal circular diameter is `√(4A ÷ π)`, which gives 39.5 mm. Applying a 0.7 effectiveness factor raises the required nominal diameter to approximately 47 mm, so four 50 mm cups form the starting selection.
Confirm the result against the cup manufacturer's force table at 60 kPa. Increase cup count or diameter when corrugation, print texture, tape, rapid acceleration or uneven loading reduces actual grip.
Match cup design to the lifting surface
| Product surface | Vacuum behaviour | Cup or gripper starting point | Main verification |
|---|---|---|---|
| Sealed coated carton | Low leakage | Flat cups with individual check valves | Panel stiffness and tape position |
| Corrugated cardboard | Moderate leakage through board and seams | Soft-lip cups or foam area gripper | Vacuum recovery under representative porosity |
| Shrink-wrapped case | Usually sealed but flexible | Bellows cups with rounded contact edges | Film stretch, wrinkles and puncture risk |
| Open tray | Limited contact area | Multiple small cups or mechanical side grip | Rim strength and product retention |
| Woven or paper sack | High leakage and changing shape | Bag gripper with high-flow vacuum | Fill distribution and material permeability |
| Rigid plastic tote | Low leakage on smooth areas | Flat cups or mechanical gripper | Moulded ribs, lid security and static charge |
Corrugated cardboard varies by flute, recycled fibre content, coating and humidity. Test production samples from each supplier because a sealed trial carton does not represent every batch.
Shrink wrap can form a seal while stretching away from the product. Bellows cups accommodate height variation, but excessive compliance allows the load to swing during fast horizontal moves.
Sacks present both leakage and shape variation. A dedicated bag gripper spreads contact over a larger area and supplies higher flow than isolated cups.
Choose cup count and layout
Use at least three contact points when case stiffness and available area permit. A symmetrical pattern controls rotation and distributes force across weak cardboard panels.
Place cups around the product's centre of gravity rather than around the geometric centre alone. Offset contents such as bottles, pouches or metal components shift the load and increase peel force on one side.
Fit individual non-return valves when uncovered cups occur across different case sizes. The valves isolate open flow paths and preserve vacuum at cups contacting the product.
A foam area gripper suits variable carton positions and multiple footprints. Its higher leakage flow and larger mass require checks against cobot payload, reach and duty cycle.
Compare venturi and electric vacuum pumps
| Criterion | Venturi generator | Electric vacuum pump |
|---|---|---|
| Energy source | Compressed air | Electrical supply |
| Response | Fast when mounted near cups | Depends on pump volume and hose length |
| Leakage handling | High flow available with correct ejector | Defined by pump flow curve |
| Operating cost | Driven by air consumption and compressor efficiency | Driven by motor power and run time |
| Installation | Compact with valves and silencers | Requires pump mounting and filtration |
| Noise | Exhaust noise requires silencing | Motor and pump noise |
| Best fit | Intermittent gripping and short lines | Long holds or sites limiting compressed air use |
A venturi generator has no moving parts at the EOAT and provides rapid evacuation when mounted close to the cups. Its compressed air demand continues whenever the ejector remains energised unless an air-saving circuit isolates the vacuum.
Calculate annual compressed air consumption from ejector flow, active seconds per cycle, cycles per hour and operating hours. Compare that volume with the site's measured cost per normal cubic metre rather than treating compressed air as free.
An electric pump avoids continuous ejector air use and suits longer hold periods. Size its flow against real leakage, reservoir volume and the maximum permitted grip acquisition time.
Account for cup wear and maintenance
Inspect cup lips each shift for cuts, flattening, contamination and permanent deformation. Replace cups when measured holding performance falls below the validated threshold, not only after a fixed calendar interval.
A practical initial replacement interval is 250,000 cycles for clean sealed cartons, followed by adjustment from inspection records. Abrasive cardboard dust, hot products, oils and sharp film edges shorten this interval.
Log vacuum level and evacuation time through the robot or PLC. Rising evacuation time identifies leaks, blocked filters and worn cups before dropped-product faults occur.
Design multi-pick tooling around payload and pattern
Multi-pick EOAT lifts two or more cases per cycle to reduce robot travel per placed unit. The total retained mass must remain inside the cobot payload rating throughout the full reach and lifting-column position.
Each product requires independent vacuum confirmation when one failed pick cannot be detected from a shared pressure signal. Zoned valves also release cases separately for staggered pallet patterns.
Compare the theoretical gain with the complete palletising cycle-time calculation. Conveyor accumulation, layer pattern and vacuum acquisition often set the practical output limit.
Use mechanical or bag gripping when vacuum is unsuitable
Choose a mechanical gripper when the product has reliable side faces, severe top leakage, exposed contents or insufficient cup area. Clamps also retain products during a vacuum supply loss, subject to jaw force and friction validation.
Choose a bag gripper for porous sacks, loose fill and surfaces that change shape during lifting. These tools combine large contact areas, high vacuum flow and product-support features.
Compare gripping technologies using representative products at maximum acceleration. The broader vacuum versus mechanical gripper guide covers retention, marking and changeover criteria.
Validate the EOAT within the complete palletising cell
Gripper selection affects cobot payload, reach, cycle time, utilities and safeguarding. A 7 kg EOAT handling a 15 kg case creates a 22 kg static payload before hoses, retained packaging and dynamic loads are counted.
Mounting a vacuum generator on the wrist shortens evacuation lines but adds moving mass. Locating it on the frame reduces EOAT mass while increasing hose volume and response time.
The risk assessment must cover dropped products, stored vacuum energy, loss of compressed air, sharp tooling edges and access beneath suspended loads. PUWER applies to work equipment used in Great Britain, while machinery conformity requirements determine UKCA or CE marking for the completed installation and destination market.
Validate the gripper with the lightest, heaviest, most porous and most distorted products. Testing must include maximum reach, highest acceleration, emergency stop behaviour and the lowest permitted supply pressure.
Document cup specification, vacuum threshold, evacuation timeout, filter grade, inspection frequency and replacement trigger. These values form part of the operating standard and preventative maintenance schedule for the cobot palletising solution.
A final acceptance test records successful picks, rejected picks, dropped loads and achieved cycle time over a defined production run. Use at least one complete pallet for every representative product and pattern included in the cell specification.
Quick selection sequence
1. Record maximum case mass, dimensions, centre of gravity and top-surface construction.
2. Multiply case weight by a safety factor of 2.
3. Divide required force across cups that fit clear contact zones.
4. Correct theoretical force for porosity, leakage, cup effectiveness and acceleration.
5. Select cup material and geometry from temperature, texture and product compliance.
6. Compare venturi air cost with electric pump energy and maintenance.
7. Verify EOAT plus product mass against cobot payload across the programmed reach.
8. Test every representative product at production speed.
Use pallet pattern software to confirm whether separate release zones or multi-pick spacing are required. Pattern data also identifies orientation changes that alter cup placement relative to the centre of gravity.
Information to give an integrator
Provide product drawings, mass ranges, physical samples and photographs of acceptable packaging variation. State hourly throughput, shift pattern, conveyor presentation, pallet dimensions and maximum stack height.
Include site compressed air pressure, measured flow capacity and air-quality standard. Record available electrical supply, environmental temperature, dust exposure and washdown requirements.
The integrator uses this information to test vacuum acquisition, retained force and release time. A complete specification also supports a defensible risk assessment and an accurate UK palletising cost estimate.
Frequently asked questions
Is a safety factor of 2 always sufficient?
A factor of 2 is the minimum starting point for a horizontal suction face under controlled handling. Vertical gripping, rapid acceleration, uneven loading or safety-critical retention requires a higher factor based on tested dynamic loads and manufacturer guidance.
How many cups does a carton require?
Use enough cups to deliver the calculated holding force and stabilise the panel. Three or four cups provide rotational control for many rectangular cartons, while weak panels require more distributed contact points.
What vacuum level suits cardboard cases?
The correct level comes from cup force data and leakage testing. Higher flow often improves porous-cardboard performance more effectively than increasing peak vacuum.
How often are vacuum cups replaced?
Start inspection from the first shift and trend evacuation time over production cycles. An initial planning value of 250,000 cycles suits clean sealed cartons, but observed wear and validated holding force set the actual interval.
Does multi-pick always increase throughput?
Multi-pick reduces robot journeys per case when conveyor accumulation and pallet pattern support grouped handling. Increased EOAT mass, longer acquisition time and separate release movements can remove the expected cycle-time gain.
When does a lifting column affect gripper choice?
A lifting column changes hose routing, maximum reach and dynamic behaviour across pallet height. Review the seventh-axis lifting column guide when stack height exceeds the cobot's usable vertical envelope.
