Apparatus for the transport of paper in printers
FIELD OF THE INVENTION 
     The present invention relates to apparatus for the transport of paper in printers such, for example, as dot matrix printers. It is more particularly directed to apparatus for controlled selection of either individual sheets or endless webs, for transport through the printer, by varying the positions of paper path-defining friction rollers and associated elements. 
     BACKGROUND OF THE INVENTION 
     Printers capable of transporting and handling multiple kinds of paper--such, for example, as single sheets on the one hand and endless webs on the other--and controllable for selectively switching between single sheet and endless web modes of operation, are known in the art. These arrangements are particularly useful and desirable when printing is to be effected on different kinds of paper being fed to a printer and the paper type currently not in use must be parked or maintained in a waiting or standby position. 
     An example of such an arrangement is disclosed in European Patent No. EP 0 186 132. The printing device disclosed therein includes a printing station past which individual sheets and endless webs to be printed are transported. A pair of friction rollers are disposed upstream of or prior to the printing station, in the direction of paper transport, for transporting or moving both individual sheets and endless webs. The apparatus includes a single feed channel formed of curved guides for individual sheets, and a feed channel for endless webs. This heretofore known arrangement requires that individual sheets be introduced into the printer only from the operator&#39;s side of the printer, while endless webs are fed from the back or rear side of the device. In addition, the apparatus does not enable the use of a drivable tractor of the customary flip-type construction, allowing sufficient room or space for accommodating only a so-called porcupine wheel for effecting endless web transport. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a printer which incorporates separate feed channels for individual or single sheets and for endless webs of paper, the feed channels having only a single common pair of friction rollers arranged downstream of the printing station in the direction of paper transport so as to provide for a constant friction-driven transport of printer paper, whether of individual sheets or endless webs, while minimizing the duplication of or requirement for additional parts. 
     This and other objects are achieved in accordance with the invention by providing a printer having a printing station and a rotatable guide roll arranged upstream of or prior to the printing station, in the direction of paper transport, the guide roll having a length sufficient to extend for at least the full width of the paper upon which printing is to be effected. Associated with the guide roll are first and second groups of friction rollers which are movable, between first and second positions, respectively, into and out of surface-to-surface contact with the guide roll periphery and which are circumferentially spaced apart from each other about the guide roll. A feed channel for single sheets is thus formed by the combination of the guide roll and the first group of friction rollers in their first or contact position, and by the guide roll and second group of friction rollers in their first or raised or contact position; a feed channel for endless webs, on the other hand, is formed when the first group of friction rollers is moved to its second position and the second group of friction rollers is lowered to its second position, the endless webs being driven or transported forward by the combination of a conventional push tractor and a friction drive, common to both the single sheet and endless web modes of operation, arranged upstream of the printing station. There is in this manner provided a functional separation of feed channels for individual sheets and for endless webs whereby individual sheets can be selectively fed and transported through the printer from either the bottom of the printer or from the top by at least one group of friction rollers, and endless webs--with the first and second groups of friction rollers moved to their second positions--are transported by the push tractor to and beyond the printing station. This clear separation of the feed-channel functions for single sheets and for endless webs, through the provision of distinct functional elements for the separable forming of feed channels for individual sheets and for endless webs, assures improved disturbance-free introduction of multiple kinds of paper while providing a waiting or standby or parked position for that type of paper temporarily not in use. 
     This arrangement is furthermore advantageous for providing both a feed channel from below and another from above for single or individual sheets. And by providing the guide roll with a larger diameter than the friction rollers of the first and second groups, the positions of the feed channels are structurally determined for enhanced utility and operation. 
     The first group of friction rollers are provided with hubs and support springs connected thereto, with the ends of the support springs opposite the hubs resting on or proximate the printer base plate against cam projections of a first switch shaft. The first switch shaft is rotatable for varying the position of its cam projections and thereby effecting movement of the first group of friction rollers between their first and second positions. 
     The second group of friction rollers is mounted on one or a multiplicity of coaxial shaft sections or lengths which are, in turn, supported on a plurality of leaf springs. Each leaf spring rests, at one end, on a stationary support bearing and, at its other end, on a cam projection of a second switch shaft. The second switch shaft is also rotatable for varying the position of its cam projections and thereby effectuating movement of the second group of friction rollers between their first and second positions. 
     The first and second switch shafts extend substantially parallel to the shafts of the first and second friction roller groups and carry, in addition to the aforementioned cam projections, pairs of eccentric pins located at the switch shaft ends. These eccentric pins engage at least one push rod common to both switch shafts and supported for longitudinal sliding movement on the printer base plate. A gear wheel is mounted for axial displacement under the urgency of a spring on a tractor shaft which is rotatable for driving the endless web push tractor, the gear wheel meshing in its engaged position with the pinion of an operable electric drive motor. A coupling shaft extends substantially perpendicular to the tractor shaft and bears radial projections which lie against the front face of the tractor shaft-carried gear wheel. A pinion is secured to the end of the coupling shaft and engages a spur gearing on the longitudinally-movable push rod. These elements cooperate to effectuate switching of the paper feeding mode, i.e. between the individual sheet and endless web modes of printer operation. 
     The coupling shaft is additionally provided with a hand-operable knob for enabling manual switching between the two operating modes. Mode switching can also be carried out, however, in a more automated fashion since the pinion which is secured to the end of the coupling shaft is disposed for engagement with an output gear of a transmission unit powered by a geared electrically-driven motor. 
     In an advantageous alternative embodiment of the invention, the primary difference with respect to the first-disclosed apparatus is that the first group of friction rollers is disposed for movability so as to provide a variable force with which the friction rollers are applied or held or directed against the guide roll. That is, movement of the first group of friction rollers from their first to their second positions, so as to switch the printer from its single sheet to its endless web mode of operation, results in a variable reduction in the urgency with which the first friction rollers are maintained in contact with the guide roll surface. This functionality is in contradistinction to the first-disclosed embodiment of the invention wherein movement of the first group of friction rollers from its first to its second position results in the friction rollers being displaced away from and out of direct contact or abutment with the guide roll surface. 
     Thus, in this alternate embodiment, the support springs of the first group of friction rollers are integrally secured at their ends opposite the hubs and rollers to at least one base plate member that carries a spring pin. A compression spring is seated on or about the spring pin and is captured between the base plate member and the printer base plate. This arrangement structurally provides the variable force with which the first friction rollers are maintained in surface-to-surface contact with the guide roll. 
     Other objects and features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
     FIG. 1 is a vertical cross-sectional side view through a preferred embodiment of an apparatus in accordance with the present invention and depicting its operation in single sheet feed mode; 
     FIG. 2 is a vertical cross-sectional side view similar to that shown in FIG. 1 and depicting operation in endless sheet feed mode; 
     FIG. 3 is a top view taken along the lines III--III in FIG. 1; 
     FIG. 4 is a transverse sectional view through the two parallel switch shafts in single sheet feed mode, as in FIG. 1; 
     FIG. 5 is a top plan view of the transverse section of FIG. 4; 
     FIG. 6 is a transverse sectional view through the two parallel switch shafts in endless web feed mode, as in FIG. 2; 
     FIG. 7 is a top plan view of the transverse section of FIG. 6; and 
     FIG. 8 is a vertical cross-sectional side view generally corresponding to FIG. 1 of an apparatus constructed in accordance with an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The inventive apparatus for the transport of paper in printers permits the user-selectable feeding of individual or single sheets 1, either from the top or the bottom of the printer, and the feeding of endless webs 2 from the back or rear 3 of the printer. 
     For this purpose, there are formed feed channels 4 and 5 for individual or single sheets 1 and a feed channel 6 for endless webs 2. A rotatable guide roll 7 extends along the entire width of the paper on which printing is to occur and, in addition, along the full length of groups of friction rollers which, as hereinafter described, cooperate with the guide roll to form the feed channels and enable the feeding of the paper. As seen in FIG. 1, the feed channel 4 for single sheets 1 is formed by the combination of the guide roll 7 and a first group of friction rollers 8, and the feed channel 5 for single sheets is formed of the combination of the guide roll and a second group of friction rollers 9. In front or upstream of the feed channel 5, in the direction of paper movement, a feed shaft 11 including guide ribs 10 is disposed for receiving and guiding single sheets 1 into the feed channel 5. Upon lowering of the second group of friction rollers 9 so as to carry them from their first to their second positions, the functionally-independent feed channel 6 for endless webs 2 is defined, the webs 2 being pushed or driven or transported into the feed channel 6 by a push tractor 12 that is freely accessible from above the same. 
     Each of the components of the apparatus thus far described are located in front or upstream, as seen in the paper transport direction 13, of a printing station 14 at which characters and/or symbols are imprinted on the transported paper substrate. The printing station is more particularly formed of a dot matrix-needle printing head 15 and a printing backing or member or abutment 16. Both single sheets 1 and endless webs 2 are transported in the paper movement direction 13 by a friction drive 17 disposed behind or downstream of the printing station 14. The friction drive 17 may, by way of example, comprise a pair of friction rollers as shown in FIGS. 1 and 2, or a single friction roller together with an associated application arm 17a as illustrated by dotted lines in the same Figures. 
     In order to suitably form the paper feed channels, the guide roll 7 is preferably provided with a larger diameter than the friction rollers 8, 9 of the first and second groups, respectively. Specific structural details of the apparatus may, of course, be varied through appropriate selection of the diameter of the guide roll 7. 
     Details of that portion of the apparatus by which the printer is switchable between its single sheet and endless web feeding modes will now be described. These structural elements cooperate to alternately form the feed channels 4, 5 or the feed channel 6 for single sheet and endless web paper feeding, respectively. Thus, in switching from the single sheet to the endless web mode of operation, the first and second groups of friction rollers 8, 9 are moved from their first to their second positions. More particularly, the first group of friction rollers 8 is moved from a first position (FIG. 1) in which the rollers 8 are disposed in surface-to-surface abutment or contact with the guide roll 7, so as to define the single sheet feed channel 4, to a second position (FIG. 2) in which the rollers 8 are displaced away from or out of contact with the guide roll. The second group of friction rollers 9, in switching from the single sheet to the endless web feeding modes of operation, is lowered from the first position (FIG. 1) in which the single sheet feed channel 5 is defined to the second position (FIG. 2) in which the endless web feed channel 6 is formed. 
     The printer base plate 18, which may also include integral or attached or associated side walls (not shown), carries or supports the shafts 8a of the friction rollers 8 and the substantially parallel-extending shafts of the rotatable guide rolls 7. First and second switch shafts 21, 22--which carry radial cam projections 19, 20, respectively--also extend substantially parallel to the guide roll shaft and the friction roller shafts 8a. The switch shafts 21, 22 are supported, preferably at multiple points, for rotation on the printer base plate 18. 
     The friction roller shafts 8a are provided with hubs 23 to which spaced apart support springs 24 are secured. A cam projection 19 lies against the end 24a of each support spring 24. 
     The second group of friction rollers 9 is mounted, in the disclosed embodiment of the invention, on a plurality of coaxial partial shafts or shaft sections 25, the shafts 25 being supported on a multiplicity of spaced apart leaf springs 26. Each leaf spring 26 has a first end 26a which rests on a fixed support bearing 27 and a second end 26b that is supported atop one of the cams 20 of the second switch shaft 22. 
     As seen in FIGS. 4 to 7, each of the switch shafts 21, 22 carries, at least at its end 28, a pair of eccentric pins 29, 30. These pins 29, 30 engage one or a plurality of push rods 31 that are supported for longitudinal sliding movement in and along a guide defined in the printer base plate 18. The eccentric pin 29, in conjunction with the push rod 31, forms a link bracket, the first switch shaft end 28 being rotatable about a central shaft 32 of the pin 29. The second eccentric pin 30 is movable in and along a free groove 33 of the push rod 31. 
     Upon displacement of the push rod 31 to the right, as seen in FIGS. 4 and 5, the first switch shaft 21 rotates clockwise (in the Figures) about its axis. This results in a corresponding clockwise rotation of the cam projections 19 whereby the first group of friction rollers 8 is displaced into surface-to-surface contact with the guide rolls 7 to form the feed channel 4--i.e. into the single sheet feed mode of operation (FIG. 1). At the same time, the end 28 of the second switch shaft 22 also undergoes a clockwise rotation, carrying therewith its cam projections 20 whereby the leaf springs 26 are raised to their FIG. 1 position. As the springs 28 are raised, they carry the shafts 9a of the second group of friction rollers 9 whereby the rollers 9 are placed in surface-to-surface abutment with the guide rolls 7 to thereby form or define the single sheet mode feed channel 5 (FIG. 1). Thus, rightward displacement of the push rod 31 forms the feed channels 4, 5 and thereby places the apparatus in its single sheet feed mode of operation. 
     Upon leftward displacement of the one or plural push rods 31, as shown in FIGS. 6 and 7, the end 28 of the first switch shaft 21 undergoes a counterclockwise rotation whereby the eccentric pin 30 enters and moves along the groove 33. In the course of this rotation, all of the cam projections 19 are carried through a corresponding clockwise rotation whereby the support springs 24 displace the friction roller shafts 8a to the left in FIG. 1; the first group of friction rollers 8 is thereby carried or moved out of surface-to-surface contact with the guide roll 7, thus eliminating the single sheet feed channel 4. Leftward displacement of the push rod(s) 31 correspondingly effects a counterclockwise rotation of the second switch shaft 22 and its cam projections 20, by which the leaf springs 26 are lowered from their FIG. 1 to their FIG. 2 position. Lowering of the springs 26 carries with them the friction roller shafts 9a, whereby the second group of friction rollers 9 are correspondingly lowered so as to eliminate the single sheet feed channel 5 and form or establish or define the endless web feed channel 6. Accordingly, leftward displacement of the one or plural push rods 31 operatively switches or transforms the printer apparatus from its single sheet to its endless web feed mode of operation. 
     The selectable or controllable switching of the apparatus between the single sheet feed and endless web feed modes of operation can be carried out either manually or in an automated manner. The push tractor 12 is operatively driven by a tractor shaft 34, the shaft 34 being operatively rotated by an electric motor (not shown) that carries or otherwise rotates a pinion 35. A gear wheel 36 is supported for axial displacement, under the urgency of a spring 39, on the tractor drive shaft 34. In its engaged state, illustrated in FIGS. 6 and 7, the gear wheel 36 meshes with the motor-driven pinion 35 so that the tractor shaft 34 is then rotatably driven for feeding an endless web 2. 
     A coupling shaft 37 which extends substantially perpendicular to the tractor drive shaft 34 carries, on its shaft 37a, cams 38 which, in their FIG. 5 position, rest against one face or side 36a of the tractor gear wheel 36. The spring 39 urges the gear wheel 36 toward the shaft 37a until the wheel 36 rests against a movement-limiting safety disk 47. A pinion 41 mounted on the end 40 of the coupling shaft 37 engages a spur gearing 42 which is defined as a part of the push rod 31. In addition, a manually-rotatable or hand knob 43 is carried on the upper, free end 37b of the coupling shaft 37 (FIG. 6). The setting of the selected paper feed mode of operation can accordingly be carried out through rotation of the hand knob 43, by which the coupling shaft 37 is rotatable between the positions shown in FIGS. 4 and 5, on the one hand, and FIGS. 6 and 7, on the other. FIGS. 6 and 7 depict the endless web feeding mode of operation wherein the cams 38 are rendered inactive so as to permit the gear wheel 36 to engage the pinion 35 and thereby transfer the pinion rotation to the tractor shaft 34 for operating the push tractor 12 and thereby advancing the endless web 2. The disengaged position of the gear wheel 36, seen in FIGS. 4 and 5, accordingly corresponds to the single sheet feed mode of operation. 
     Automated switching of the operative mode is effected by the geared electric motor 46. The motor 46 is connected to a transmission unit 45 having an output gear wheel 44. The gear wheel 44 engages the pinion 41 secured to the end 40 of the coupling shaft 37. The alternative selection of the single sheet or the endless web feed modes of operation can therefore be carried out by controlled operation of the electric motor 46 to bidirectionally rotate the output gear wheel 44. 
     The operation of this first and currently preferred embodiment of the inventive apparatus for selectively switching between single sheet and endless web modes of paper feeding should now be apparent. In the first position of the friction rollers 8,9--corresponding to the single sheet feed mode--both the first and second groups of friction rollers 8,9 are maintained in surface-to-surface contact with the rotatable guide rolls 7 so as to frictionally contact the single sheets being fed through the printer and thereby exert a pressing force on the paper. When the friction rollers 8, 9 are moved to their respective second positions, however, this pressing force of the friction rollers against the guide rolls 7 and on the endless web 2 being fed through the printer is immediately reduced to zero or substantially zero by the leftward (in FIG. 1) displacement of the first group of friction rollers 8 and the lowering of the second group of friction rollers 9. Thus, in moving from single sheet to endless web feeding modes, the single sheet feed channels 4 and 5 are eliminated and only the endless web feed channel 6 is present for receiving the endless web 2. 
     An alternative embodiment of the apparatus of the invention is illustrated in FIG. 8. In most respects, the various elements which cooperatively form this alternate embodiment are and function in a manner identical to the corresponding elements of the first-disclosed and currently preferred form of the invention shown in FIGS. 1 to 7. The primary difference, as can be seen in FIG. 8, lies in the elements associated with and the manner of operative displacement of the first group of friction rollers 8. In particular, the friction rollers 8 are arranged for applying a variable pressure against the guide rolls 7. 
     Thus, associated with the first group of friction rollers 8 are supporting springs 24. In a preferred form of this alternate embodiment, each of the supporting springs 24 is integrally or unitarily connected, at one of its ends, to the friction roller shafts 8a and, at its other end 24a, to a base plate member 24b. The spring 24, base plate 24b and friction roller shaft 8a may all advantageously be fabricated of a single piece of flexibly resilient plastic material. The base plate member 24b carries an integral spring pin 48 about which a compression spring 49 is supportingly receivable with the spring extending between the plate member 24b and the printer base plate 18. In this manner, the plate member 24b is urged under the spring force to the right (in FIG. 8) whereby the friction rollers 8 are pressed with a selectable force against the guide roll 7. The compression spring 49 is of such a nature that, depending upon the rotative position of the first switch shaft 21 and its cam projections 19, either a greater or a lesser setting force acts on the first group of friction rollers 8 for urging the rollers 8 into surface-to-surface contact with the guide roll 7. Thus, in the second or endless web feed mode of operation the first group of friction rollers 8 are sufficiently displaced from their first or single sheet feed positions only so as to apply a reduced pressing force of the rollers 8 against the guide rolls 7 and thereby enable the feeding of endless webs 2 between the friction rolls 8 and the guide roll 7. 
     While there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the apparatus illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.