Crossed-Boson-Exchange Contribution and Bethe-Salpeter Equation

The gap between the print head and the printing surface or platen in a printer is extremely critical in certain types of printers. Where printers are required to accept print media of various thickness (single or multipart paper), an adjust mechanism is required to optimize the print gap. A problem arises thereafter whenever ribbon has to be changed or new paper fed into the printer, since the print head must be retracted from its optimum gap position for ease of operation. The present invention provides for automatically resetting the print head to its predetermined previous gap spacing following movement of the print head away from the printing surface for servicing such as paper loading on ribbon replacement. This is accomplished by providing a lever, adapted to move the print head away from the printing surface, with a cam face for mating with a cam follower carried by a gap adjustment arm pivoted for movement in fixed distance increments about a pivot point. The movable arm serves as a memory for recording the previous print head gap spacing as well as providing extremely fine control for moving the print head in fine, fixed distance increments corresponding to the incremental distance movements of the movable arm.