Turning device

A turning device is a complete lifting attachment for a turning task: it picks up the part, rotates it about a horizontal axis – usually by 90 or 180 degrees – and sets it down in the new position. The rotation unit is only one element; the gripper that holds the part at every angle and the matching to the centre of gravity are the others.

Turning takes place in the air on the hoist or manipulator. Stationary turners, on which the part is set down and rotated, are a different matter.

If the axis of rotation is not at the centre of gravity, a moment of weight force times offset acts. During rotation the horizontal distance of the centre of gravity from the axis changes – and reverses sign as it passes the vertical. The load that had to be raised a moment ago now pulls onwards by itself: it swings through.

This is exactly what makes tipping parts over an edge on the floor so dangerous. A turning device avoids the swing-through by placing the axis through the centre of gravity, by damping the motion or by using a self-locking drive.

A grip that is secure in the starting position may hold by friction alone after 90 degrees and not at all after 180. The principle for turning is therefore: grip by shape or secure by positive locking. The mount has to carry the part in every position between start and finish, even if compressed air or power fails.

The starting point is the mass, dimensions and centre of gravity of the part and its start and end positions. From these follow the position of the axis, the greatest moment over the angle of rotation and the swept space: a part rotating about its centre needs a circle with half its diagonal as radius – which must be clear of operator, fixture and floor.

With part families the centre of gravity moves. The axis is then made adjustable, or a drive is provided that holds the residual moment safely.

Turning tasks are often underestimated because the part is “only” to be rotated.