Gripping technology

Gripping technology is the part of a handling device that actually touches the load. A manipulator, balancer or lifting axis carries and guides – but whether the task succeeds is decided at the interface with the part: how quickly it is picked up, whether it holds in every position, whether the surface stays intact, and how much payload remains once the gripper is deducted.

Unlike in robotics, a person guides the load here. The gripper therefore has to do more than hold: it must be operable with one hand, leave the part visible and show clearly whether it is closed.

Every gripper holds in one of two ways: by force or by shape. Suction cups, clamping jaws and magnets hold by force – they need a holding force greater than anything that could release the load. Mounts that reach under a rim, into a bore or around a contour hold by shape; they hold even without energy.

In practice the two are combined: pick up by force because it is quick, and secure by shape as soon as the load is rotated, tilted or joined.

Selection starts with the part and the sequence, not with a catalogue.

The gripper hangs at the end of the arm and counts fully towards the load. On a jib-type device its weight acts at the full lever arm; every kilogram of gripper is a kilogram less payload. Just as important is the position of the combined centre of gravity of gripper and part: if it is not below the suspension, the load hangs at an angle – differently when empty and when loaded.

Gripper design therefore belongs at the start of sizing. Choosing the device first and designing the gripper afterwards often ends with a payload that is no longer sufficient.

Most grippers do not fail on holding force in the normal case but on the boundary conditions.