Dead weight

Dead weight is the mass of everything hanging between the hoisting unit and the workpiece: gripper, spreader beam, rotary and tilting unit, adapter, hoses, control handle. It hangs from the unit on every lift, with a workpiece and without. Because it contributes nothing to the transport, it is called dead load.

For sizing, net payload equals rated capacity minus dead weight. A unit with 125 kg rated capacity and a 28 kg gripper lifts workpieces up to 97 kg – not up to 125.

The enquiry states the workpiece weight because it is known. The load handling attachment does not exist yet at that point. Its weight only results from the design – and grows with every requirement: rotating, tilting, several workpiece sizes, protection against dropping.

As a rough guide, simple hooks and loops weigh a few kilograms; mechanical grippers with a rotary function and vacuum beams with several suction pads weigh many times that. Only the figure from the gripper design is reliable; until then a generous estimate is used.

In the tilting moment it counts with its distance from the axis of rotation – and the gripper sits at the far end. On a balancer it has to be compensated: the unit keeps two states in equilibrium, the empty gripper and the gripper with a workpiece. The heavier the gripper relative to the load, the more mass the operator moves on every empty run.

The structure itself also has a dead weight. It loads track, ceiling or foundation permanently and belongs in the load data for the building.

Every kilogram on the gripper counts twice: it is missing from the net payload and it is moved twice in every cycle.

A load handling attachment is marked with its working load limit. If its dead weight makes up a notable share of that limit, EN 13155 also requires the dead weight to be stated. This allows a check at the workstation that hoisting unit, attachment and workpiece fit together.