BIZOMAT MAKEOS · Pneumatics
Vacuum Gripper Sizing (Cups, Diameter, Holding and Evacuation Time)
Will these suction cups hold the part through the move, what cup size or count would, and how quickly does the system pull down to working vacuum?
Sizing of a vacuum gripper: holding force per cup and in total, the force needed with acceleration, orientation and safety factor (as the vacuum cup tool), the cup diameter needed at the cup count and the cup count needed at the cup diameter, and the time to evacuate the cups and lines to the working vacuum at the pump or ejector flow, against your cycle allowance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cup diameter | mm | Effective diameter of each cup. |
| Number of cups | Number of cups. | |
| Working vacuum | kPa | Vacuum below atmospheric that the system holds. |
| Part mass | kg | Mass of the part. |
| Acceleration of the move | m/s² | Largest acceleration during the move. |
| Cup orientation | choice | Whether the cups face down (lifting) or sideways (holding by friction). |
| Friction coefficient (cup to part) | Friction between cup and part for vertical cups. | |
| Safety factor | Safety factor you require (often 2 horizontal, 4 vertical). | |
| Volume of cups and lines | L | Internal volume of the cups, hoses and manifold to evacuate. |
| Vacuum generator suction flow | L/min | Suction flow of the pump or ejector at free air. |
| Evacuation time allowed | s | Time you allow to reach working vacuum. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Cup diameter
- What it is
- The effective sealing diameter of each suction cup, the circle over which the vacuum acts on the part.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Holding force rises with the square of the diameter.
- Get it right
- Use the effective diameter from the cup catalogue; the lip outside diameter overstates the area.
What this means: Number of cups
- What it is
- How many suction cups share the load on the part.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 200. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total holding force rises in direct proportion.
- Get it right
- The tool assumes every cup seals and carries an equal share; place the cups so they do.
What this means: Working vacuum
- What it is
- The working vacuum at the cups: how far below atmospheric pressure the generator holds them.
- Units and format
- Enter a number in kPa: kilopascals. The form accepts 5 kPa to 95 kPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 kPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Holding force rises in proportion; evacuation time rises steeply as it approaches full vacuum.
- Get it right
- Vacuum below atmosphere (gauge), not absolute pressure.
What this means: Part mass
- What it is
- The mass of the part being picked and moved by the gripper.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Acceleration of the move
- What it is
- The largest acceleration the handling device gives the part during the move. It is added to gravity in the holding check.
- Units and format
- Enter a number in m/s²: metres per second squared. The form accepts 0 m/s² to 100 m/s². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 m/s² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Include emergency stop deceleration if it can be harsher than normal motion.
What this means: Cup orientation
- What it is
- Whether the cups grip from above so the load pulls straight off the cup face, or grip a vertical face so the load acts in shear and must be held by friction.
- Units and format
- Choose one of 2 options from the list: Cups horizontal (lifting); Cups vertical (shear on the cups).
- Example
- The form opens with “Cups horizontal (lifting)” selected as a worked example. Choose the option that matches your case.
- Get it right
- With vertical cups the required force is divided by the friction coefficient, so it is much larger.
What this means: Friction coefficient (cup to part)
- What it is
- The friction coefficient between the cup material and the part surface. It is used only when the cups are vertical and the load acts in shear.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 1.5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- For vertical cups the required force is divided by it.
- Get it right
- Oily, wet or dusty surfaces lower it; get a value for your surface from the cup supplier.
What this means: Safety factor
- What it is
- The factor by which the holding force must exceed the weight and inertia load, covering leaks, wear and surface variation.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 6. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The required force rises in direct proportion.
- Get it right
- Follow your cup supplier’s or company’s requirement.
What this means: Volume of cups and lines
- What it is
- The internal volume to be evacuated: the cups plus the hoses and fittings between them and the vacuum generator.
- Units and format
- Enter a number in L: litres. The form accepts 0.000001 L to 1000 L. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 L as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Evacuation time rises in direct proportion.
What this means: Vacuum generator suction flow
- What it is
- The suction flow the vacuum generator or pump draws, from its data sheet.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 100000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Evacuation time falls in inverse proportion.
- Get it right
- The tool assumes this flow holds through the whole pump-down; real generators lose flow as vacuum deepens, so use a mean value.
What this means: Evacuation time allowed
- What it is
- The longest time the cycle allows for the cups to reach working vacuum before the part is lifted.
- Units and format
- Enter a number in s: seconds. The form accepts 0.000001 s to 600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Force per cup = vacuum × π D² ÷ 4; force needed = m (g + a) × SF, divided by μ for vertical cups (as the vacuum cup tool).
- Cup diameter needed = √[4 F ÷ (π × vacuum × n)]; cups needed = F ÷ force per cup (rounded up).
- Evacuation time ≈ V ÷ Q × ln[p_atm ÷ (p_atm − vacuum)].
- Example: 4 cups of 40 mm hold 301.59 N against 148.07 N; the system pulls down in 0.26906 s.
Limitations
- Flat, sealed surfaces; porous or curved parts leak and need larger flow.
- Ideal pump-down at constant flow; real generators lose flow as vacuum rises.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a gripper for sheet, cartons or panels
- Check a gripper for faster robot moves
- Size the vacuum generator for the cycle time
Who it is for
- Automation engineers
- Machine designers
- Robotics engineers
What you get
- Holding force and force needed
- Cup diameter and count needed
- Evacuation time
Interpreting the result
- Vertical cups need about twice the holding force of horizontal ones for the same part.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3032–3041. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Count the air and what it costs
What it covers: Calculate a cylinder's free air per cycle and per year, convert it to kilowatt-hours and dollars, and compare it with leaks, open blowing and vacuum ejectors that cost far more.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Vacuum Gripper Sizing (Cups, Diameter, Holding and Evacuation Time) calculator