Crown extruder with four nozzles is design idea of Cem Schnitzler inspired by microscope rotating lenses. It enables you to use different nozzle diameters for different purposes, ie.: very small nozzle for precision and large one for speed and rougher infills. It would be interesting to see it developed and tested.
Crown extruder project homepage:
http://crownextruder.wordpress.com/
Crown extruder project homepage:
http://crownextruder.wordpress.com/