Printer with interchangeable paper-feed modules

Abstract

A data printer having removable, and interchangeable, paper-feed modules, such as may embody a tractor or pin-feed-type paper-feed mechanism. The interchangeable modules each have guide ways which cooperate with and move along complementary guideways supported by the printer main frame to guide the selected module into place and seat it in a particularly defined position. A mechanical latch locks the seated module to maintain it in place. The paper-feed mechanism of each module is driven by a rotatable member, with the power train including a motor-driven worm mounted on the printer and a mating worm-gear carried on the removable paper-feed module. The worm is mounted in an upright position, and the worm-gear moves into mating relation with the worm by travelling an upright path, but with a small acute angle between such paths. The worm and worm-gear have a tooth or thread profile with a rounded nose section. BACKGROUND OF THE INVENTION In the use of data printers generally, and particularly in those of sufficiently simple design to be economically feasible for purchase or lease by an average-size business enterprise, which may require a printer capability to complement a data entry terminal, it is often desired to use a variety of different types of business forms as the printing medium. However, such forms are usually so different in nature that they will not fit the same paper-feed mechanism, frequently a tractor, or sometimes a pin-feed mechanism. Nonetheless, in the past, printers have mainly had only a single type of permanently-mounted paper drive, and the needed flexibility to accommodate differently-sized forms has not been available, largely because of the difficulties in obtaining paper-feed module interchangeability while maintaining the needed structural integrity and operational consistency. This is particularly true because the most common type of such printer is an impact device having a reversing or reciprocating carriage of some type, which is subject to substantial vibration and shock during use, which tends to shake, weaken and loosen all but extremely rigid and permanently-anchored components. Thus, the need has been present for some time for greater flexibility in such printers, in the way of convertible or interchangeable paper-feed mechanisms, but this need has of yet remained largely unfilled. BRIEF SUMMARY OF THE INVENTION The present invention answers the foregoing need and provides a data printer structure by which ready removeability and complete interchangeability is achieved for the paper-feed apparatus, by means of interchangeable paper-feed modules, each carrying a different type of paper-feed mechanism, as well as preferably carrying its own platen, which is thus changed with the paper-feed module. The printer has an outer housing and a support structure or frame within the housing, for the printer mechanism. This support frame defines or carries a mounting bed for the paper-feed modules. The modules preferably comprise a pair of side plates with at least one interconnecting support member and a paper-feed apparatus mounted between the side plates, such apparatus including a platen, which may or may not be rotatable, and a rotatable element with associated means for engaging paper stock and moving the same lengthwise. The rotatable element comprise a rotary drive element which when the module is seated on the printer frame engages a complementary motor-driven member mounted on such frame. Seating of the module is achieved by complementary guideways cooperating between the module and the printer frame, by which the module may be slid upon a guide into accurately indexed position, where an interlock will hold it securely in position. Most preferably, the printer-mounted power drive comprises a motor-driven worm which is oriented generally vertically, and the paper-feed module has a mating worm-gear which is moved into a position engaging the worm by the guided seating movement of the paper-feed module, which preferably is along a path disposed at a small acute angle relative to the worm axis. Both the worm thread and the worm gear teeth should have a profile with a curved outer tip, so that as the paper feed module is moved toward and into its seated position the worm gear moves toward and engages the worm, with the rounded tips of the engaging gear teeth and worm thread sliding off one another in the event of interfering alignment, to prevent tooth breakage. The many advantages of the invention, together with its objectives, will become more apparent from a study of the ensuing Specification and the attached drawings.

Dependencies are inferred from the claim text.