Punch assembly having a positive punch retraction mechanism for an internal drum imagesetter

Abstract

A punch assembly is provided with a positive retraction mechanism to remove the punch from the media to be punched, thereby preventing binding of the punch in the media. The punch assembly includes a driving mechanism to provide a driving force on the punch and a positive retraction mechanism disposed to provide a retraction force on the punch operative sequentially following operation of the driving mechanism. The punch assembly, which is of a smaller size and more economical to manufacture, is particularly useful with an imagesetter of a prepress printing system. The punch may be mounted in a cantilever manner to punch the opening as close to the edge of the media as possible without interfering with the laser beam of the imaging assembly. In this maimer, the area of media available for imaging may be maximized and media waste minimized. Additionally, a shaft support mechanism is provided for the shaft upon which the retraction mechanism for each punch is mounted. When the punches advance into the media, an oppositely directed force is placed on the shaft. The shaft support mechanism supports the shaft when it is so loaded by the punches, thereby minimizing deflection of the shaft and allowing use of a smaller diameter shaft. Other equipment, such as take-up rollers which are used to transfer the media may also be fixed to the punch assembly. Similarly, a cutter assembly which cuts sheets of the media may also be fixed to the punch assembly.