Vacuum or mechanics: how the load decides what holds it

First: can it be done positively?

Before talking about cups or jaws, another question belongs at the start: does the part have a rim, a hole, a contour you can reach under? Positive locking holds without force, does not fail on pressure loss and is independent of whether the surface is oily, dusty or damp. Where it is possible it is the safe and usually the cheaper route – and it is regularly overlooked because cups and jaws are the more obvious images.

Vacuum: taking the surface

Suction cups are the right choice for large, thin and surface-critical parts: sheets, panels, panes, cartons. They spread the load, leave no pressure marks and need no alignment. Sizing depends on more than area: lip material, surface roughness, oil film, temperature and porosity all affect holding force. Oily sheet and open-pored wood demand a markedly higher safety factor than the data sheet suggests.

• Several cups against sagging of long parts
• Soft lips for unevenness, hard ones for shear
• Reservoir and check valve are mandatory, not accessories
• Cup positions from the drawing, not by eye

Clamping: taking the edge

Clamping jaws are robust, tolerate positional variation and work where no closed surface exists – on castings, profiles, containers, rolls. The price is surface pressure: every jaw leaves a mark if material and contact area do not suit. The answer is rarely less force but more area and a softer pad. Sizing is against the friction coefficient and every acceleration in the sequence, not against weight alone.

Magnets: the special case with clear limits

Magnetic grippers are fast, simple and need no access from two sides. But they work only on ferromagnetic materials, and their holding force collapses as soon as an air gap, rust, paint or scale comes between. Permanent magnets are safer than electromagnets because they do not let go on power loss – in return they need a mechanical release that costs force.

The mistake that costs most

It is called: one gripper for everything. When five part families run across one station, the idea of a universal tool with adjustable axes, exchangeable inserts and scales soon appears. The result is expensive, heavy, slow to change over and worse at every single task than a simple tool. Two or three simple grippers with a quick changer are almost always the better answer – even if they look less elegant on the quotation line.