Vacuum Gripper Selection Guide — Cup Types, Sizing and Failure Modes

Quick reference

Vacuum grippers work by creating a pressure differential between atmospheric pressure and the evacuated cup interior; the force is F = Pressure × Area
Required holding force = m × (g + a) × safety factor — always apply a safety factor of at least 2.0 for industrial applications
Cup choice: flat cups for rigid flat surfaces; bellows cups for uneven or oily surfaces; oval cups for narrow or elongated parts
NBR rubber for dry surfaces; silicone for food contact or high-temperature; EPDM for oily surfaces
Use the free vacuum gripper sizing calculator to get cup area and count in seconds

How vacuum grippers work

A vacuum gripper creates a low-pressure zone inside a suction cup pressed against a part surface. Atmospheric pressure (approximately 1,013 mbar at sea level) acts on the outside of the cup and presses the part against it. The holding force is:

          F (N) = Vacuum pressure (Pa) × Cup area (m²)
        

At 650 mbar vacuum (65,000 Pa) and a Ø50mm cup (area = 0.00196 m²):

          F = 65,000 × 0.00196 = 127 N (≈ 13 kg force)
        

The vacuum source — either a venturi generator (air-powered) or a vacuum pump (electric) — removes air from inside the cup and maintains the pressure differential during the pick-and-place cycle. A check valve prevents drop-off if the vacuum source fails momentarily.

Suction cup types

Cup type	Best for	Avoid on	Height compensation
Flat (single-lip)	Rigid, flat, smooth surfaces: glass, sheet metal, smooth plastics, smooth cardboard	Curved, uneven, or flexible surfaces	None — requires consistent Z positioning
Flat (multi-lip / ribbed)	Cardboard, textured surfaces — lips conform to minor surface variation	Highly curved parts	Minor
Bellows (1.5- or 2.5-fold)	Uneven surfaces, parts at varying heights, warped sheets, oily surfaces, fragile parts	Very fast cycles (slower cup response)	15–60 mm depending on fold count
Oval / rectangular	Narrow parts (profiles, pipes, boards), limited space between pick points	Parts requiring rotational stability (oval cups allow rotation)	Same as equivalent round cup
Deep bellows (3.5-fold)	Very uneven surfaces; parts at highly variable heights; glass with significant bow	High-speed applications	Up to 80+ mm

Suction cup materials

Material	Temp range	Best for	Avoid
NBR (Nitrile Butadiene Rubber)	−10°C to +70°C	General industrial; dry clean surfaces; standard machine tending	Oily surfaces, high temperatures, food contact
Silicone	−40°C to +180°C	Food contact (FDA-compliant grades); high temperature; clean rooms	Mineral oils; ketones
EPDM	−30°C to +120°C	Oily machined parts; light coolant exposure; outdoor use	Mineral oils (moderate resistance only)
Polyurethane (PU)	−10°C to +60°C	Abrasion-resistant; rough surfaces; high cycle count	Hot parts; solvent exposure
Neoprene (CR)	−20°C to +90°C	Outdoor or weather-exposed; ozone resistance	Aromatics, ketones
HNBR (Hydrogenated NBR)	−30°C to +150°C	Oily parts at elevated temperature; engine components	Aromatic hydrocarbons

Sizing: formula and worked example

The standard sizing method (per Schmalz and SMC vacuum engineering guidelines):

Step 1: Calculate required holding force

          F_required = m × (g + a) × SF

          where: m = part mass (kg), g = 9.81 m/s², a = robot max acceleration (m/s²), SF = safety factor (≥2.0)

Step 2: Calculate required cup area

          A_required (mm²) = F_required ÷ (vacuum_level_mbar × 0.1)

          [Note: 1 mbar = 100 Pa; F/P = A → A(m²) = F(N) / P(Pa); convert to mm²]

Worked example

Scenario: Picking a 4 kg sheet metal blank. Robot max acceleration: 4 m/s². Surface: clean, flat, dry mild steel. Using 650 mbar vacuum. Safety factor 2.0.

          F_required = 4 × (9.81 + 4) × 2.0 = 4 × 13.81 × 2.0 = 110.5 N

          A_required = 110.5 ÷ (650 × 0.001) = 110.5 ÷ 0.65 = 170 cm²

          Using Ø60mm cups (area = 28.3 cm² each):

          Cups needed = 170 ÷ 28.3 = 6.0 → 6 × Ø60mm cups

          Alternatively, using Ø80mm cups (area = 50.3 cm² each):

          Cups needed = 170 ÷ 50.3 = 3.4 → 4 × Ø80mm cups

Run this calculation for your specific part using the free vacuum gripper sizing calculator — it handles horizontal, vertical, and overhead orientations automatically.

Vertical and overhead orientation adjustments

The formula above applies to horizontal pick-up (cup faces down, part hangs below). For vertical pick-up (cup on side, shear force), friction between cup and part resists the weight — use a higher safety factor (2.5–3.0) and ensure the cup material has adequate friction against the part surface. For overhead pick-up (cup faces up, part is above the robot), gravity assists detachment — apply an additional 10% to the required force and use a safety factor of 2.5 minimum.

Vacuum source types

Type	How it works	Typical vacuum	Pros	Cons
Venturi generator (ejector)	Compressed air flows through a nozzle, creating a low-pressure zone via Bernoulli effect	550–750 mbar	Simple; fast response; no moving parts; easy to integrate	Consumes compressed air continuously; noisy; lower vacuum than pump
Electric vacuum pump	Motor-driven pump evacuates the cup circuit	700–950 mbar	Higher vacuum; no compressed air needed; energy-efficient	Larger; slower response; more complex integration
Electric venturi (integrated)	Small electric vacuum module integrated into the gripper (e.g., Schmalz ECBPi, Piab Kenos)	600–850 mbar	No compressed air; fast; compact; suitable for cobots with no air supply	Higher unit cost; battery-limited for cordless applications

For cobots without a compressed air supply (electric-only deployments), electric venturi modules or small electric vacuum pumps are the standard solution. Schmalz, Piab, and SMC all offer cobot-compatible electric vacuum modules.

Common failure modes

1. Cup seal failure (most common)

Cause: Worn cup lip, cut or cracked cup, contamination on the part surface (oil, chips, dust), or cup landing on a part edge or gap.
Fix: Establish a cup inspection and replacement schedule — bellows cups typically last 500,000–2,000,000 cycles depending on material and part surface; flat cups last longer on clean surfaces. Add cup wear monitoring (vacuum pressure sensor with threshold alarm).

2. Insufficient cup area

Cause: Undersized design — commonly caused by sizing for static weight only and omitting robot acceleration, or using an inadequate safety factor.
Fix: Re-size using the full dynamic force formula. Add cups or upgrade to larger cups. Check if vacuum level is actually being achieved (see failure mode 4).

3. Vacuum loss during cycle

Cause: No check valve in the circuit; venturi generator loses supply pressure; leak in tubing or fittings.
Fix: Install a vacuum check valve in the cup circuit. Monitor supply pressure at the venturi. Pressure-test all fittings at commissioning. Use vacuum hold time measurement to detect leaks.

4. Porous or textured part surface

Cause: The part material allows air to bleed through (cardboard, foam, fabric, porous castings) or the surface texture prevents an effective seal.
Fix: For slightly porous surfaces (e.g., corrugated cardboard), use a high-flow venturi that can compensate for leakage. For highly porous surfaces, vacuum grippers do not work — use mechanical grippers or soft grippers instead.

5. Cable and tubing fatigue

Cause: Robot wrist flexes thousands of times per hour; poorly routed tubing fatigue-cracks at bend points.
Fix: Use correctly rated flexible tubing (polyurethane or nylon) with appropriate bend radius. Route tubing through energy chains designed for robotic motion. Inspect regularly — tubing failure is a predictable wear item.

When not to use a vacuum gripper

Highly porous surfaces: Open-cell foam, loose woven fabric, uncoated MDF, rough castings — vacuum cannot maintain a seal
Very oily parts: Heavy cutting oil on machined parts can pool in the cup seat and break the seal; use mechanical grippers for oily finished parts
Flexible or floppy parts: Thin sheet metal that deflects under vacuum, flexible packaging, limp fabric — the part deforms under the vacuum force
Very rough surfaces: Grit-blasted, heavily textured, or profiled surfaces prevent cup sealing
Parts with through-holes in the pickup area: Vacuum bleeds through holes in the part
Parts at high temperature: Above ~80°C, standard NBR cups degrade rapidly; use silicone cups for temperatures up to 180°C, and check that the vacuum system tolerates the temperature

For these cases, consider mechanical grippers, magnetic grippers (for ferrous metals), or soft grippers for irregular shapes.

Frequently asked questions

How many suction cups should I use?

Use the minimum number that satisfies the force requirement with your chosen cup size, then verify that the cup placement provides stable support across the part without tipping. For rectangular sheet parts, four-cup arrangements (one near each corner) provide stability against tipping. Two cups work for small, rigid parts. For very large or flexible sheets, more cups distributed across the surface prevent deflection. Also consider serviceability — fewer cups means less to inspect and replace.

What vacuum level should I target?

60–70% vacuum (600–700 mbar) is the typical target for standard industrial venturi systems. This is achievable with most standard ejectors and is sufficient for most pick-and-place applications on non-porous surfaces. Higher vacuum (700–900 mbar) is available from electric pumps and improves holding force for a given cup area — useful for heavier parts or where space constrains cup count. Do not design for more vacuum than your source reliably achieves; always confirm achievable vacuum under loaded conditions, not just at the generator outlet.

How do I handle parts with slight surface variation?

Use bellows cups — their accordion structure compensates for surface height variation (15–60 mm depending on fold count) and conforms to slight surface curvature. Bellows cups also apply lower initial contact force, making them better for fragile or marked surfaces. The trade-off is slightly slower vacuum buildup time compared to flat cups. For parts varying ±5 mm in flatness, a 1.5-fold bellows cup is usually sufficient; for ±20 mm variation, use a 2.5-fold bellows cup.

Can I use one vacuum generator for multiple cups?

Yes, and it is standard practice. A single venturi generator or vacuum pump is usually connected to a manifold that distributes vacuum to all cups on the gripper. The key consideration: all cups must be sealed simultaneously for the circuit to reach target vacuum. If one cup fails to seal (cup lands on a gap, hole, or contamination), the entire circuit loses vacuum. For applications where partial cup loss is a risk, use individual cup vacuum circuits with independent sensors — more complex but more robust.

Sources

Schmalz vacuum technology selection guide, schmalz.com, accessed September 2026
SMC vacuum gripper engineering handbook, smcusa.com, accessed September 2026
Piab vacuum solutions catalogue 2025, piab.com, accessed September 2026
Festo vacuum technology guide, festo.com, accessed September 2026