Photocopying apparatus with vacuum means

Claim 1

Apparatus for making a photocopy of a master transparency, comprising: a vacuum chamber formed of first and second cooperating wall assemblies that are separable to permit access into said chamber, said first wall assembly including a light transparent window therein, means within the vacuum chamber on said first wall assembly for holding a master transparency in a manner to form a compartment therebehind but in front of said window that is sealed from the rest of said vacuum chamber at least when the pressure in said master compartment is less than that on the opposite side of said master transparency, means within the vacuum chamber on said second wall assembly for holding a photocopy sheet in a manner forming a compartment therebehind that is vacuum sealed from the rest of said vacuum chamber at least when the pressure in said photocopy compartment is less than that on the opposite side of said photocopy sheet, the volume of said photocopy compartment being much less than the volume of said master chamber, said photocopy holding means being slidable in said second wall assembly to a first extreme position to urge the master and photocopy against each other when said first and second walls are connected together to form said vacuum chamber, said photocopy holding means also being movable to a second extreme position providing a space between said master and photocopy, means including a pneumatic system for moving said photocopy holding means back and forth between its said extreme positions, a first vacuum line communicating through said second wall assembly into said photocopy compartment, a second vacuum line communicating through said first wall assembly into the master compartment, said second vacuum line joining said first vacuum line to form a common line, a compensating chamber positioned in said first vacuum line and having a volume sufficient to make about the same the total volumes of each of said vacuum lines including their respective compartments, a vacuum source, a vacuum valve operably connected to said common vacuum line in a manner to selectively connect said common line to said vacuum source or to vent said common line to the atmosphere, means responsive to pressure in said common vacuum line falling to a predetermined level far below normal atmospheric pressure for automatically causing said pneumatic system to move said photocopy holder to its said first extreme position wherein said master and photocopy are mechanically urged against said one another, and means sensing the movement of said photocopy holding means to its said first extreme position for automatically switching said vacuum valve to open the common vacuum line to the atmosphere, whereby the master transparency and the photocopy sheet are automatically positioned for exposure once an operator has initiated connection of the common line to the vacuum pump by operation of said vacuum valve.