An image forming apparatus for forming an image on a recording medium has an image forming system for forming an image on the recording medium, a second image forming system for forming an image on the recording medium based on an image forming method different from that for the first image forming system,...http://www.google.com.au/patents/US5570451?utm_source=gb-gplus-sharePatent US5570451 - Image forming apparatus including plural image forming means and plural recording medium transport passages
