I've seen one or two DC over the years with an agitator built into the filter which operates when the main blower/sucker switches off and the worst of the accumulated fine dust will drop out. My involvement has been when the control gear has given trouble and users have been mystified by the extra wiring and built in timer associated with the agitator. I've not had a problem with the agitators themselves to sort out.
I don't use it on my system as the filter are horizontal up on the ceiling. They get taken down once every couple of years and cleaned out in the garden - you should hear the birds coughing after that
http://vid115.photobucket.com/albums/n313/9fingersphotos/Mvi_0217.mp4