Grippers and lifting devices: the choice that decides everything

All gripping technology comes down to four working principles. Vacuum holds via air pressure on a tight surface – fast, distributed and gentle, but dependent on surface quality and tightness. Friction via clamps holds from the side – insensitive to surfaces, but with a contact pressure that can deform delicate parts. Form fit uses the geometry of the part – the safest variant, but tied to the part. And the mandrel or hook uses an existing opening – simple and rugged wherever reels, spools and coils are involved.

Vacuum grippers are rightly the most common lifting device in material handling: pick-up takes fractions of a second and the force is distributed. Limits show on porous surfaces such as raw chipboard or recycled board, with moisture from chilled areas, with wrinkled film and with strongly curved parts. The answer then is not more vacuum but more suction area, a more powerful pump – or a different principle. We therefore always test on actual production parts, not on laboratory samples.

As long as a load is only lifted vertically, friction is enough. As soon as it is rotated, tipped or joined against resistance, the force directions change – and a friction grip can slip. The design rule is therefore: where the load tilts, rotates or joins, it is gripped or secured by form fit. That is not a precaution but the result of the risk assessment.

Lifting devices not permanently attached to the lifting equipment – beams, tongs, vacuum lifters, C-hooks – fall under the harmonised standard EN 13155. It sets requirements for safety factors, behaviour on loss of energy and marking. In practice: a vacuum lifter must hold the load on power failure or set it down under control, and the rated capacity must be permanently marked on the device. Permanently attached grippers on a manipulator, by contrast, are treated as part of the machine and covered in its risk assessment.

Every kilogram of gripper is a kilogram less useful load – and it acts at the full lever arm. A form gripper with rotary axis, clamping and sensors can weigh 30 kilograms; on a 125-kilogram unit a quarter of the payload is gone before the first part is attached. That is why gripper design belongs at the start of the sizing, not at the end. Aluminium instead of steel, turned instead of milled parts, sensors only where they are needed – those are the levers.

Where several part variants run, a gripper change system is almost always the right choice. It costs design effort once and then saves a complete unit with every new variant. What matters is generous sizing of the interface: media, signals and a spare channel. Specify the interface too tightly and by the third gripper you have a problem that can only be solved by replacing all the existing ones.