Plate changers of this type include as individualizing means a friction roll engaging the uppermost plate in a stack of plates, with the plates being individualized by the friction roll being rotated at appropriate times to push the top plate from the stack into guide means comprising rolls and guide rails or vanes to guide the offset plate through an etchant or fixing bath container removably mounted in the offset printing machine and from the container directly onto the form cylinder. After having been fixed, the plate is retained on the form cylinder by known means such as suitable grippers so that printing may start right after the fixing treatment. As soon as the printing plate is to be changed, the grippers are suitably controlled to open and the plate is conveyed from the form cylinder to a used-plate depository.
In plate changing apparatus of this type, the stacking table for the supply of plates, the fixing bath container and the form cylinder are sequentially arranged substantially in a row so that the system has a relatively great overall length. In the case of small-size offset printers, these space requirements may constitute a substantial disadvantage, and individualization, or removal of individual plates frequently is unsatisfactory. Furthermore, as the individualizing means engages each plate on the side bearing the graphic information, visible traces may be left on the finished printed product.
It is, therefore, an object of the present invention to improve printing plate changing apparatus of the kind described above so that the plate changing mechanism will be much more compact and save space, to have as low a number of parts as possible, and to realize improved reliability with respect to plate individualization. Further, the present invention allows for a more careful handling of the printing surface of such plates.