Articulated arm

An articulated arm consists of two arm sections connected by a joint. The first section pivots about the pillar or suspension, the second about the joint in the middle – both pivot axes are vertical. At the end of the second section sits the lifting unit: a chain hoist, a rope unit or a lifting axis.

The arm itself thus moves the load horizontally, the lifting unit vertically. With a rigid lifting unit the result is a manipulator that guides the load; with a rope, a device with long reach and long stroke.

Extended, the arm reaches the circle whose radius is the sum of both section lengths. Folded, it also reaches points close to the pillar. A straight slewing jib can only do that with a trolley running on it – and it reaches each point only along the straight line from the pillar.

This is the advantage of the articulated arm: it reaches around obstacles. If a guard door, a machine enclosure or a rack is in the way, the arm folds past it. Slewing limiters at the joints prevent it from hitting walls or machines.

The operator moves load and arm by hand. How easily depends on the bearings of the joints and the mass of the arm. Alignment is decisive too: if the pivot axes are not plumb, the arm drifts to the lowest point on its own. A properly aligned pillar is therefore a prerequisite, not a refinement.

Adjustable brakes at the joints hold the arm in position and damp the movement so that it does not run on after being released.

The greatest moment acts on the extended arm. It is made up of load, gripper and lifting unit times outreach, plus the self-weight of the arm. This moment passes through pillar and base plate into the floor, or through the suspension into the ceiling – where it has to be verified.

Deflection grows with outreach as well. It shows when the load is taken up and the tip of the arm yields slightly. Anyone who wants to join accurately therefore sizes for the reach actually needed, not for the largest possible.