It is a disk cam mechanism of translation follower.

Turn grey disk cam to open or close the aperture.

Fixed green disk has a hexagon slot.

Each blade (follower) slides along one side of the hexagon.

Instead of the hexagon 6 symmetrical suitable curves are possible.

The mechanism can be used for control valves:

Egger Iris® Diaphragm Control Valve - For a precise and energy saving flow control