Web and Sheet Paper Feed Mechanism for Printers

1. Field of the Invention

This invention relates to printer mechanisms and more particularly to a paper transport system for printer mechanisms.

2. Prior Art

Printers, such as the type used in connection with electronic data processing systems or so-called hard copy printers, and particularly matrix printers, are normally utilized in connection with continuous form paper and therefore are provided with motor driven transport devices for moving the continuous form paper past a printing station area. Such transport devices frequently consist of two pin belt tractors which are displaceable along a guide strip and received around drive shafts. The guide strip extends transversely of the direction of movement of the paper past the printing station area as do the drive shafts. By making the tractor assemblies movable, it is possible to accommodate varying widths of paper. Such transport devices are disclosed, for example, in German OS No. 28 27 125.

Since such printers are often desired to be used in connection with single sheets of paper, or in connection with multi-sheet form paper, such as carbon copy sets, it has been known to design the tractor transport mechanism so as to be removable from the remainder of the printer. In such cases, the transport device, including the paper tractors and the allocated motor drive, are removable from the main portion of the printer and are then replaced by means specifically designed for single sheets, such as platen assemblies.

When such prior art printers are used in connection with multiple form sets, a problem arises in that the individual copies of the multiple form set may shift relative to one another, so that non-aligned printing will be reproduced on underlying form sheets. Moreover, in systems that require an exchange of different mechanisms, one for tractor transport of continuous paper forms, such as side margin perforated papers, and one for single sheet or multi-carboned forms, change over is cumbersome and it is necessary for storage space to be provided adjacent the printer for storage of the non-presently used mechanism. Of course, additionally, removal and exchange provide opportunities for mechanism damage.

It would therefore be an advance in the art to design a paper transport assembly for printers such that the assembly is readily utilizable with minor modifications for both transporting individual sheets and continuous paper and which is utilizable in a standard format fashion which minimizes the misalignment of multiple form sets.

It is a principal object of this invention to provide a transport mechanism for line-at-a-time printers, which includes paper tractors for use with continuous form paper, the paper tractors being movable along a guide member normal to the path of movement of the paper to accommodate various width papers and which further includes attachable means for properly guiding single sheet paper independent of the tractor drive without removal of the tractor drive.

A transport mechanism for continuous form paper can be converted to a transport mechanism for single sheets or for form sets by means of two channel defining side elements consisting of injection molded members which are attachable to the guide strip guiding the paper tractors of the pin belt tractor mechanism when the tractor mechanism is in a perpendicular position with respect to the printer.

To facilitate such a conversion, the transport means for the continuous form paper is pivotably fastened to the printer in the illustrated preferred embodiment. This allows the tractor transport assembly to operate both in a horizontal position when desired and in a vertical position vis-a-vis the print station area. When in a vertical position, attachment of single sheet guiding elements will not only be facilitated but, further, the single sheet paper will be advantageously moved vertically past the print position. Also, when printing on continuous or single multi-form sets with the single sheet feed guiding elements, the vertical positioning will assure that no relative offset of the copies with respect to one another will occur.

In a further embodiment of the invention, paper transport shafts carrying paper transport pinch rollers can be provided positioned below the printing area to provide an under roll intake. Such under roll intakes are favored, for example, for transporting continuous multi-form and single sheets. By means of an appropriate drive coupling, the drive of the paper transport under roll shafts can drive from the motor allocated to the pin belt tractors.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 is a schematic perspective view, with portions broken away to show underlying portions of a matrix printer equipped with the paper transport mechanism of this invention.

FIG. 2 is a schematic sectional view of the printer of FIG. 1 illustrating the paper transport mechanism.

FIG. 3 is a fragmentary partial side schematic view of the drive mechanism for the paper transport mechanism.

FIG. 4 is a schematic side view of a guiding element.

FIGS. 5 and 6 are diagrammatic schematic views of the printer of this invention equipped with paper transport mechanism of this invention showing paper flow paths.

FIG. 1 schematically illustrates a printer of the type utilizable both in connection with continuous form margin perforated paper and single sheet paper, as well as multi-copy sets. The printer includes a dot matrix printhead 10 which is movable from side to side of the printer to form a line of print. The print head 10 is moved by motor 11.

When printing on continuous form paper, the paper is moved past the print station by a tractor transport mechanism consisting of pin belt tractor assemblies 12. The tractor assemblies 12 are mounted on shafts 16 which may carry gear wheel shieves for movement of the tractor belt. A transverse bar 14 is provided for guidance of the pin belt tractor assemblies 12 and the tractor assemblies are movable towards and away from one another along the guide bar 14.

As illustrated in FIG. 1, the entire tractor assembly is pivotable from the vertical position illustrated to a horizontal position. The drive to the tractor shafts is by means of motor 15 which may drive a gear train to one of the shafts. In the horizontal position, the position of the motor 15, which is disposed at one lateral side of the tractor transport mechanism would be illustrated by the broken lines at the end of the curved arrow.

Printing is accomplished by placing a piece of paper between the dot matrix printer head assembly 10 and an opposed backup or beam member 13. It is therefore the function of the paper transport mechanisms to move the paper, line by line, between the print head 10 and the beam 13.

Preferably, when using continuous form paper, the transport mechanism can be in its horizontal position. In such instance, the paper may enter from the rear of the printer, pass between a clamp element and the pin belt on the underside of the pin belt tractor, then around the beam 13, then between a clamp member and the pin belt on the top side of the pin belt tractor and back toward the rear of the printer. The pin belt tractors being movable in reverse directions can cause the paper to be advanced or retracted as necessary.

However, since single sheets are generally not provided with margin perforations engageable by the pin belt, it is generally preferable to feed the single sheets in a substantially vertical position and to positively feed them by means of pinch rollers. In order to facilitate both vertical feeding and positive pinch roller feeding, the tractor transport mechanism, including the guide bore bar 15, is pivotable to a vertical position. Guide elements 18 and 19 provided with clips 17, can then be clipped onto the guide bar 14. The guide elements 18 and 19 are laterally displaceable along the guide bar 14 and are designed symmetrical relative to one another, providing somewhat U-shaped cross-sectional channels having their open ends facing towards one another substantially as shown in FIG. 2. The guiding elements may be somewhat funnel shaped in cross-section having a relatively large top opening decreasing in depth to a main channel lower portion. The front face of the guide elements may be provided with recesses which contain spring biased pressure rolls 21. The pressure rolls can be aligned with opposed rolls 24 carried on one of the shafts 16. In order to accommodate different size widths, the rolls 24 can be longitudinally movable along the shaft 16. The rolls 24 are thereby powered rolls powered by rotation of the shaft 16 under influence of the motor 15 with the opposed spring rolls 21 functioning to provide a pressure roll set to press a single sheet 23 introduced between the guiding elements against the drive rollers 24 for controlled movement.

The overall paper transport channel is designed such that when in the vertical position, as illustrated in FIG. 5, the paper passage channel lies directly over the print position. As a result of such a design of the paper transport channel, the paper, whether single sheet or continuous form paper, is conducted vertically past the print position. Thus, no offset will occur in multi-copy sets. In addition, such a design promotes and facilitates proper feed of the paper in both feed directions.

By utilization of this transport mechanism, various operating modes are possible. As shown in FIG. 5, continuous form paper 25 can be moved both forward and backward around the print beam 13 under influence of the tractors 12. Such back and forth movement is advantageous, for example, when filling out forms. Additionally, a single sheet 23 can be also moved back and forth in the vertical direction when the guiding elements are in position.

When employing multiple sets and label carriers, it is advantageous to provide an additional guidance within the printer to provide a paper feed from below. To this end, and under roll entry can be provided in the bottom of the printer and opposed pressure rollers 26, consisting of two paper transport shafts and associated rollers, can be provided below the printing area. As shown in FIG. 3, the shafts 26, or one of them, can be commonly driven from the motor 15 by means of a gear train which may employ a drive belt 27. The rollers 26 can operate in conjunction with the rollers 20, 21 or independently thereof. When used in conjunction with the rollers 20, 21, due to the spacing of the paper across the print head and the relatively short spacing distance between the drive rollers 20, 21, and the rollers 26, an up and down movement of the paper is greatly facilitated. Additionally, it will be appreciated that due to the vertical movement, a misalignment of copy sets in multi-form sets, whether single or continuous form, is avoided. Of course, as shown in FIG. 6, it is possible to employ only the rollers 20, 21 and to bypass the rollers 26 while still using the bottom entry if desired.

An advantage of this invention is the provision of a single drive motor 15 operating all of the paper transport mechanisms, the pin belt tractors 12, the single sheet pressure rollers 20, 21, and the bottom entry rollers 26. Moreover, because the motor is disposed laterally of the mechanism, it can be dimensioned substantially as large as desired.

Although the teachings of my invention have herein been discussed with reference to specific theories and embodiments, it is to be understood that these are by way of illustration only and that others may wish to utilize my invention in different designs or applications.