# Holding and break-away forces on suction cups

How are the holding force and break-away force calculated?
In order to determine the required holding force, you need the calculated mass, the system acceleration and the friction coefficient.

The holding force required depends on the load situation. Below are the three main load situations:

• Case 1: suction cup in horizontal position, movement in vertical direction (best case)
• Case 2: suction cup in horizontal position, movement in horizontal direction
• Case 3: suction cup in vertical position, movement in vertical direction (worst case)

With most pick and place cycles you will find many different movement situations. The worst case with the greatest theoretical holding force must always be used for the following calculations.

The workpiece weight and acceleration are required in order to calculate the holding force.

Case 1: suction cup in horizontal position, movement in vertical direction (most favourable case)

Case 2: suction cup in horizontal position, movement in horizontal direction

Case 3: suction cup in vertical position, movement in horizontal direction
(least favourable case)

• FH = Theoretical holding force of the suction gripper [N]
• m = Mass (kg)
• g = Acceleration due to gravity (9.81 m/s²)
• a = Acceleration of the system (m/s²) Attention: note the emergency off acceleration
• S = Safety factor (at least 1.5 with linear movement, at least 2 for rotary movement)
• µ = Friction value

Please note: the following values are average values and should be verified for the workpiece in question.
Empirical friction value (surface)

• Oily µ = 0.1
• Wet µ = 0.2…0.3
• Rough µ = 0.6
• Wood µ = 0.5
• Metal µ = 0.5
• Glass µ = 0.5
• Stone µ = 0.5

Empirical acceleration values

• Electric spindle 6 m/s²
• Electric toothed belt: 20 m/s²
• Servopneumatic: 25 m/s²
• Pneumatic: 30 m/s²
• Pneumatic rotary drive: 40 m/s²