EP0195981B1 - Printing mechanism with a printing head movable in print line direction and a print hammer bar as platen backing - Google Patents

Description

The invention relates to a printing unit of the type mentioned in the preamble of claim 1 and claim 4.

In such printing units, the recording medium is generally transported in line jumps by the transport device perpendicular to the line direction and printed line by line by the print head. The print heads of modern printing units, for example needle print heads or ink mosaic print heads that can be moved in the line direction or thermal print bars that are immobile in the line direction, must be kept with great accuracy at a very short distance from the recording medium during the printing process or must be held against the recording medium with a certain pressure force. In order to ensure the exact distance or pressure even in the case of recording media of different thicknesses, it is already known to determine the thickness of the recording media by means of a sensor arrangement and to control the distance of the print head from the platen by the sensor arrangement. Typical application examples for printing units of the generic type are the printing units of receipt printers in cash registers, which have to process shingled receipts in the transport direction, and of printers for printing savings bank books or the like. It should be noted at this point that the platen has any suitable shape and can be designed, for example, as a bar with a flat writing surface or as a rotatable pressure roller.

A construction is already known in which the sensor arrangement is formed by a sensor roller or roller arranged on a swivel frame, which is formed by spring means is placed against the recording medium resting on the pressure bar fixedly arranged in the printer housing (DE-PS 22 48 262). A guide bar extending parallel to the line direction is fastened to the swivel arm, against which the print head, which is movable perpendicular to the writing plane, rests resiliently via guide rollers. This device is used only to control the distance between the print head and the print bar. You must also be equipped with means, not shown, for lifting the sensor rollers and the print head. In addition, a device for transporting the recording medium must be provided regardless of the components described in DE-PS 22 48 262. This generally comprises transport rollers connected to a drive, counter-pressure rollers and means for placing the transport rollers against the recording medium and for lifting the transport rollers when a recording medium is to be inserted.

The structure of the known device is very complex since, in addition to the indispensable transport system with its drive and adjustment devices, it has an independent sensor arrangement, which in turn has a number of movably mounted components and means for actuating the sensor arrangement. Another disadvantage of the known construction is seen in the fact that the transfer of the position of the sensor roller to the print head takes place via a series of bearing points which are moved when the sensor arrangement is put on or taken off and which are subject to particularly high wear. This wear manifests itself in an increasing misalignment of the printhead in the course of the use of the printing unit, so that a regular readjustment or a regular exchange of parts of the sensor arrangement is necessary.

US-A-4,227,819 already shows a printing unit of the type mentioned in the preamble of the new claim 1, in which a Platen and a drivable transport roller are arranged on a common carrier and can be adjusted together into their respective operating positions by means of a single drive. Both the platen and the transport roller are resiliently mounted on the common carrier. The carrier 66 is adjusted between an inoperative position and a fixed predetermined operating position by an adjustment drive 120, 124, the transport roller first coming into contact with the counter roller 112 and then the platen against the stop at stops which are firmly aligned with the printhead.

Accordingly, there is no controlled delivery of the carrier depending on the thickness of the print carrier. Both the transport roller and the pressure counter bearing are largely resiliently placed against the counter roller or the stops. A major disadvantage of the known construction is seen in the fact that the platen jams the printing medium between itself and the stops during the printing process. For the further transport of the print carrier, it must be released, i.e. the carrier must be adjusted in the direction of its non-operational position so that it takes the platen with it and lifts it from the stops so that the print carrier can move freely.

IBM Technical Disclosure Bulletin Vol. 25, No. 10, page 5188 shows a solution in which, similar to DE 22 48 262, a feeler roller scans the thickness of the print carrier and adjusts the counter-bearing relative to the print head fixed perpendicular to the print carrier via a lever arrangement. Here, too, the feeler roller and lever arrangement is provided in addition to the transport rollers, so that this construction is also complex and expensive.

WO 85/04840, which falls under Art. 54 (3) EPC, shows an arrangement in which the transport roller and the platen are also arranged on a common carrier. In contrast to the present invention, the thrust bearing is not fixedly mounted on the carrier, but can deflect downward against the force of springs. For the printing process, the carrier is pivoted by means of an adjusting device until the transport roller rests on the counter roller. The platen resiliently presses the print carrier against a lower surface of the print head by means of the springs. In this construction, too, the carrier must be lifted for the purpose of transporting the printing medium to such an extent that the printing medium is no longer clamped between the platen and the underside of the print head. There is also no regulation of the distance between the platen and the print head as a function of the thickness of the print carrier.

The object on which the invention is based is seen in creating a printing unit in which the distance between the print head and print carriers of different thicknesses can be precisely adjusted, in particular fixed stops associated with the print head and serving as spacers, which periodically retract the platen during Make print carrier transport necessary, should be avoided.

This object is achieved by the features contained in claim 1 and in claim 4.

Both alternative solutions solve this task with technical means that are partly the same but sometimes different. In both solutions, the platen is fixed on the carrier, so that a certain setting of the carrier also a certain setting of the Platen and thus a certain distance of this platen corresponds to the printhead. In both solutions, this fact is used for the regulation of the printing gap, in that the carrier is set during the printing process depending on the thickness of the material to be printed in a position in which there is a certain printing gap between the print head and the material lying on the platen. In the first alternative, this is achieved by using a limit switch which is actuated by the transport roller axis and regulates a predetermined pressure gap. A major advantage of this first alternative is that the pressure of the transport roller is regulated independently of the thickness of the material to be printed.

In the second alternative, the correct pressure gap is reached immediately when the transport roller is in contact with the counter roller; the compression of the resilient transmission means taking place according to this system only serves to generate a pressure for the transport roller. The advantage of this configuration is seen in its special structural simplicity, but the pressure depends on the thickness of the material to be printed.

The printhead, the precise arrangement of which is particularly important, does not perform an infeed or lift movement perpendicular to the writing plane. In the case of print heads that can be moved in the line direction, for example, they can only be mounted so that they can move in this direction, which can be accomplished in a simple manner with robust and precise longitudinal guides. A cross slide-like arrangement according to one of the known constructions with the accuracy problems that occur is not necessary. The control of the distance or pressure between the print head and the platen is rather carried out by delivering the platen perpendicular to Writing plane, whereby the movable mounting of the platen can also be very simple, since this also only carries out a movement in one direction. The transport rollers are also mounted on the support bearing the platen, so that only a single adjustment drive is required for the delivery and lifting of the platen and the transport rollers relative to the recording medium. After the transport rollers have been placed on the recording medium, the resilient transmission means are tensioned by further delivery of the carrier until the correct distance of the print head with respect to the recording medium is reached in the first alternative, or until the transport rollers are sufficiently pressed against the second alternative.

In the construction according to the invention, the transport device can at the same time take on the task of a thickness sensing device, since the transport roller interacts with one (or more) counter-rollers precisely aligned with the print head and, in this way, also causes the print platen to be precisely aligned with the print head due to the mechanical coupling via the common carrier . Since only one roller system is suitable for the transport and for sensing the strength of the record carrier or document; While separate pressure systems must also be provided in the case of separate transport and feeler rollers, a single pressure system is sufficient in the present invention.

In the solution according to claim 1, the adjustment drive of the carrier is designed as a positioning drive, a limit switch which can be actuated by the displaceable transport roller axis being arranged on the carrier and which controls the positioning drive in such a way that the displaceable transport roller axis assumes a desired position relative to the carrier, in which the pressure spring is one certain spring force corresponding to the desired pressure force. When inserting the document the adjustment drive of the carrier receives the command to deliver it. The limit switch has a position that corresponds to the delivery command of the adjustment drive. When the transport roller comes to rest against the document, it is displaced relative to the feed direction relative to the carrier, the pressure spring being tensioned and the limit switch being opened relative to the carrier at a specific desired position of the transport roller, so that the adjustment drive stops. In the event of deviations from the target position, the adjustment drive is controlled via the limit switch in order to restore this target position. In order to improve the resolution of the control, it is further provided according to the invention that the displaceable transport roller axis drives a translation lever which is pivotably mounted on the carrier and increases the displacement movement of the transport roller axis, the output end of which actuates the limit switch and is acted upon by the pressure spring.

In the other embodiment of the invention according to claim 4, the transport roller is arranged in a fixed position on the carrier, the adjusting drive of the carrier being designed as a linear adjusting drive, each with a disengaged position and a switching position corresponding to the engaging position, and with a resilient transmission device between the adjusting drive and the carrier is provided which enables an overstroke of the adjustment drive which goes beyond the stroke corresponding to the engagement position. If, when the carrier is delivered, the transport roller lies against the document and the pressure bar has reached its writing position, the adjustment drive carries out its overstroke and thereby tensions the resilient transmission device, the spring force achieved thereby determining the pressure force of the transport roller.

The carrier is designed, for example, as a frame which is adjustably mounted on the printer housing via a parallel link arrangement. The transport drive connected to the transport roller can be arranged in the printer housing, the drive connection being designed, for example, as a cardan shaft because of the relative movement between the transport roller and the transport drive; In a preferred embodiment of the invention, however, the transport drive is also arranged on the carrier, it being possible for the drive connection between the transport roller and the transport drive to be rigid.

Fig. 1

schematisch ein Druckwerk in einer Seitenansicht mit abgehobenem Träger und Druckbalken in einem für das Einlegen eines Aufzeichnungsträgers bereiten Zustand;

Fig. 2

eine Ansicht gemäß Fig. 1 mit zugestelltem Träger;

Fig. 3 und 4

jeweils eine Einzelheit eines Druckwerkes gemäß den Fig. 1 oder 2;

Fig. 5

eine Einzelheit zur Verstellung des Trägers gemäß den Fig. 1 bis 4;

Fig. 6 und 7

jeweils eine Einzelheit aus Fig. 5 in vergrößerter Darstellung;

Fig. 8

eine Einzelheit zur Verstellung des Trägers gemäß den Fig. 5 bis 7;

Fig. 9

schematisch einen Verstellantrieb für den Träger gemäß Fig. 8, mit einem Positionierantrieb;

Fig. 10

eine Darstellung gemäß Fig. 9 mit einem linearen, zwei Schaltstellungen aufweisenden Verstellantrieb;

Fig. 11

schematisch Transportrollen und damit zusammenwirkende Andruckrollen in einer Vorderansicht;

Fig. 12

schematisch einen Träger mit Transportrollen und außerhalb des Trägers angeordnetem Transportantrieb;

Fig. 13

schematisch einen Träger mit Transportrollen und auf dem Träger angeordnetem Transportantrieb.

Further features and advantages of the invention result from the patent claims, the drawing and the description of the drawing. Several embodiments of the invention are shown in the drawing and described in more detail below.
Show it:

Fig. 1

schematically shows a printing unit in a side view with the carrier raised and the printing bar in a state ready for inserting a recording medium;

Fig. 2

a view of Figure 1 with the carrier delivered.

3 and 4

in each case a detail of a printing unit according to FIGS. 1 or 2;

Fig. 5

a detail for adjusting the carrier according to Figures 1 to 4.

6 and 7

each a detail of Figure 5 in an enlarged view.

Fig. 8

a detail for adjusting the carrier according to FIGS. 5 to 7;

Fig. 9

schematically an adjustment drive for the carrier according to FIG 8, with a positioning drive.

Fig. 10

a representation according to FIG 9 with a linear, two switching positions adjusting drive.

Fig. 11

schematically transport rollers and interacting pressure rollers in a front view;

Fig. 12

schematically a carrier with transport rollers and transport drive arranged outside the carrier;

Fig. 13

schematically a carrier with transport rollers and a transport drive arranged on the carrier.

The printing unit 2 shown schematically in FIG. 1 is arranged in a printer housing 4. It comprises a print head 6, a pressure beam 8 serving as a pressure counter bearing, one or more transport rollers 10 lying next to one another for further transport of the recording medium 12 in the direction of the arrow 14 and counter rollers 16 serving as counter bearings for the transport rollers 10. The pressure beam 8 and the transport rollers 10 are in one Carrier 18 arranged, which is adjustably mounted in the printer housing 4 in the direction of arrow 20. The for storage and adjustment of the carrier 18 in the direction of The means provided for by arrow 20 are described further below.

As can be seen in FIG. 1, the transport roller axis 22 is not mounted directly on the carrier 18, but rather on a transmission lever 24, which in turn is pivotably mounted on the carrier 18 about the axis 26. In this way, the transport roller axis 22 on an arc around the axis 26, i. H. thus essentially shift in a direction corresponding to the adjustment direction 20 of the carrier 18 relative to the carrier 18. The free end of the translation lever 24 is acted upon by a pressure spring 28, which this end in the pressure direction, i. H. so loaded in the direction of arrow 30.

A limit switch 32 with three contact blades 34, 35, 36; the middle contact lamella 35 can be moved from an upper switching position shown in FIG. 1 via a neutral position into a lower switching position shown in FIG. 2 by an actuating projection 38 formed on the transmission lever 24. The upper switch position according to FIG. 1 activates the adjustment drive for the carrier 18 in the pressing direction 30, the lower switch position according to FIG. 2 activates it in the opposite direction; the adjustment drive is not activated in the intermediate neutral position.

The function of the printing unit is explained below with reference to FIGS. 1 and 2. The one shown in Fig. 1 When the carrier 18 is in the lowered position, the printing unit is in a state ready for inserting the recording medium 12. The record carrier 12 is inserted between the print head 6 and the print bar 8 until it abuts a stop 40. A suitable sensor detects that a recording medium 12 has been inserted and activates the adjustment drive for the support 18. Since the limit switch 32 has a switch position which corresponds to an actuation of the adjustment drive in the sense of an infeed of the support 18 in the direction of arrow 30, it moves the carrier 18 upwards and places the recording medium 12 against the counter rollers 16. When the carrier 18 moves further in the direction of the arrow 30, the transport roller axis 22 is displaced downward relative to the carrier 18 against the force of the pressure spring 28. At a predetermined compression of the pressure spring 28, in which it applies the desired pressure force, the contact plate 35 is lifted by the actuating extension 38 from the contact plate 34, so that the adjustment drive stops. In this position, in which the desired pressure force of the transport rollers is reached, the pressure bar 8 has at the same time its correct writing distance from the print head 6, so that the printing unit is ready for writing.

Simultaneously with the readiness to write, the transport drive for the transport rollers 10 and the print head 6 are activated in a known manner, so that the recording medium 12 z. B. line by line is described. During the infeed movement of the carrier 18, the stop 40 has been moved from its operating position shown in FIG. 1 to the inoperative position shown in FIG. 2, as will be explained in more detail further below.

The transport rollers 10 simultaneously fulfill the task of determining the thickness of the recording medium 12 and of controlling the print distance between the print head 6 and the print bar 8. If the recording medium 12 z. B. has a decreasing strength with increasing feed movement, as is often the case with till receipts or the like, then the transport rollers 10 shift when reaching each step relative to the carrier 18 by an amount corresponding to the step height. The actuation extension 38 stands out from the central contact plate 35, which comes into contact with the upper contact plate 34, so that the adjustment drive of the carrier 18 moves the latter upwards until the limit switch 32 returns to its neutral position. If the thickness of the document increases, the transport rollers 10 move downwards relative to the carrier 18, the middle and lower contact lamella 35 and 36 coming into contact, so that the carrier 18 is adjusted downward until the limit switch 32 is again its Neutral position, while the transport roller 10 has its correct pressure, the pressure bar 8 has its correct writing distance to the print head 6.

3 and 4 show the printing unit 2 schematically in a sectional view, in which the stop 40 can be seen in its two possible positions. The stop 40 consists of a stop plate 42 which is approximately perpendicular to the writing plane and is mounted in the printer housing 4 so as to be pivotable about an axis 46 via an arm 44 which is at right angles thereto. A tension spring 48 acts on the arm 44, the free end of which is firmly connected to the carrier 18 at an attachment point 50. The fastening point 50 is in the lowered position of the carrier 18 according to FIG. 3 somewhat below the axis 46, so that the stop 40 is held in the operating position shown. When the carrier 18 is moved in the direction of the arrow 30, the fastening point 50 also moves upward, so that the stop 40 is tilted to the left when a certain dead center is exceeded, the stop plate 42 withdrawing from the writing plane defined by the recording medium 12 and enables the further transport of the record carrier. When the carrier 18 is lowered, the stop 40 snaps back into its operating position.

The mounting of the carrier 18, which can be adjusted in the direction of the arrow 20, is carried out via a parallel link arrangement according to FIG. In Fig. 5 is only the locking bar facing the viewer 52 shown. Two link arms 56 are pivotally connected to the adjusting bolt 52 at pivot points 58. The other ends of the link arms 56 are pivotally connected to the carrier 18 at pivot points 60. Two further link arms 62 are pivotally connected to the adjusting bolt 52 at pivot points 64. The other ends of the link arms 62 are pivotable and vertically displaceable with the pivot points 66 in the printer housing and in the carrier 18 in corresponding, overlapping guide slots 68, 70. When the adjustment bolt 52 is moved to the right (in FIG. 5), the carrier 18 is moved upwards, and when the adjustment bolt 52 is moved to the left, it is adjusted accordingly downwards.

The operation of the parallel link arrangement is explained in more detail with reference to FIGS. 6 and 7. In Fig. 7, the two link arms 56 and 62 are shown in a position which corresponds to the position shown in FIG. 5. The carrier 18 is in its lower position, in which the transport rollers are disengaged, the print bar is removed from the print head. When the adjustment bolt 52 moves to the right (in FIG. 7), the pivot points 58, 64 which are firmly connected to the adjustment bolt 52 are moved into the positions 58 ′, 64 ′ shown in FIG. 6.

Since the fulcrum 58 cannot deflect in the vertical direction, the fulcrum 60 is shifted upward by the amount a, taking the carrier 18 firmly connected to the fulcrum 60. The slot 68 formed in the printer housing allows only a vertical one Displacement of the fulcrum 66. Since the carrier 18 can also only perform a vertical movement with respect to the fulcrum 66 via the slot 70 formed therein, the carrier 18 is lifted vertically upwards without any lateral movement.

Fig. 8 again shows the printing unit 2 with the printer housing 4, the carrier 18 adjustable therein in the direction of the arrow 20, the transport rollers 10 arranged on the carrier and the pressure bar 8, further with the print head 6 and the counter rollers 16. In addition, the Viewers facing horizontally displaceable adjustment bolts 52 can be seen. The horizontal adjustment of the adjustment bolt 52 takes place via a driver 72 engaging in it (see FIGS. 8 and 9), which engages in a recess 74 formed in the adjustment bolt 52.

9 shows an adjustment drive 76, which is designed as a so-called positioning drive. It comprises an electric motor 78 which can run in both directions of rotation and drives a threaded spindle 80. A spindle nut 82 is arranged on the threaded spindle 80 and can be adjusted by the threaded spindle 80 in the direction of the arrow 84. The spindle nut 82 is connected to the driver 72. The adjustment drive 76 is used in connection with the arrangement of the transport rollers 10 described in FIGS. 1 and 2. It is controlled by the limit switch 32 in the manner described above, so that the carrier 18 is raised or lowered depending on the direction of rotation of the electric motor 78.

10 shows an adjustment drive 86 which is designed as a linear adjustment drive with two switching positions. It essentially comprises a one-armed lever 88, which is designed as a U-shaped bracket in the exemplary embodiment shown and which is mounted with its lower end pivotably about the axis 90 in the printer housing. The lever 88 carries the driver 72, which adjusts the locking bar 52 in the direction of the arrow 92. The lever 88 is pivoted by a magnetic switch 94 in two switching positions, which correspond to the disengaged position or the engaged position of the transport rollers. The actuating member 96 is connected to a U-shaped bracket 98 which is displaceably guided in the switching direction of the magnetic switch 94 on a transverse axis 100 arranged on the lever 88. A compression spring 102 is arranged between the base leg of the bracket 98 and the axis 100. When the magnetic switch 94 picks up, it takes the lever 88 with it via the bracket 98 and in this way actuates the adjusting bolt 52 and the carrier 18 until the transport rollers abut against the counter roller 16 or the recording medium 12 arranged therebetween Actuating element 96, the intermediate spring 102 is tensioned and determines with its spring force the pressing force of the transport rollers. The reset takes place, for example, by a return spring acting on a suitable point, for example on the adjustment bolt 52, as was not shown in more detail.

11 schematically shows the arrangement of two transport rollers arranged on a transport roller axis 122 110. The transport roller axis is, for example, as described with reference to FIGS. 1 and 2, with one end 104 fixed but pivotally mounted in the printer housing, while the other end 106 is slidably mounted in the direction of arrow 108 against the force of a pressure spring 128. The counter rollers 116 are arranged on a common pendulum yoke 112, which is also pivotable about a pendulum axis 114 in the pivot plane of the transport roller axis 122. In this way, there is always a uniform pressure force of both transport rollers 110 on the recording medium 12 resting against the counter rollers 116, since the pendulum yoke 112 adapts to the respective pivoting angle position of the transport roller axis.

12 schematically shows the carrier 18 with transport rollers 210 arranged thereon. The transport roller axis 222 is mounted in the carrier 18 and can be adjusted with it in the direction of the arrow 212. The drive motor 214 is fixed in the pressure housing 4. Between the drive motor 214 and the transport roller axis 222, a cardan shaft 216 is provided, which enables the height adjustment of the carrier 18 with an existing drive connection.

13 shows a carrier 18 on which a transport roller axis 322 with two transport rollers 310 is arranged. The carrier is in turn adjustable in the direction of arrow 312 in the printer housing 4. In the present exemplary embodiment, the drive motor 314 is likewise arranged on the carrier 18 and is adjusted with it. The drive connection between the drive motor 314 and the transport roller axis 322 can accordingly be rigid.

The device for regulating the pressure of the transport rollers on the counter rollers, as described above, can also be used for regulating the pressure of the print carrier against a thermal writing strip.

Claims (9)

1. A line printing unit, comprising a printing abutment (8) and at least one transport roller (10) which are disposed beneath a printing medium plane on a common carrier (18) adjustable relatively to the printing medium plane, and comprising a print head (6) co-operating with the printing abutment (8) and a backing roller (16) co-operating with the transport roller, which print head and backing roller are fixed above the printing medium plane, the transport roller (10) being disposed on the carrier (18) on a spindle (22) which is mounted for displacement in a direction corresponding substantially to the direction of displacement of the carrier (18) and which is loaded by a biasing spring (28) in the blasing direction, characterised in that the printing abutment (8) is fixed on the carrier (18) and in that a limit switch (32) adapted to be actuated by the displaceable transport roller spindle (22) is disposed on the carrier (18) and so controls a positioning drive (76) connected to the carrier (18) that after the transport roller (10) has engaged the backing roller (16) the transport roller spindle (22) occupies relatively to the carrier (18) a set position in which the biasing spring (28) has a specific compression.
2. A printing unit according to claim 1, characterised in that the displaceable transport roller spindle (22) is mounted on a transmission lever (24) which is pivotally mounted on the carrier (18) and which increases the displacement movement of the transport roller spindle (22), the transmission lever drive end actuating the limit switch (32) and being subjected to the action of the blasing spring (28).
3. A printing unit according to claim 1 or 2, characterised in that only one end (106) of the transport roller spindle (122) is mounted to be displaceable while the other end (104) is mounted to be stationary but pivotally on the carrier (18), in that the transport roller spindle (122) carries two spaced transport rollers (110) which co-operate with two respectively associated backing rollers (116) disposed on a common pendulum yoke (112) mounted to pivot in the pivot plane of the transport roller spindle (122) about a pendulum axis (114) disposed between the backing rollers (116).
4. A line printing unit, comprising a printing abutment and at least one transport roller (10) which are disposed beneath a printing medium plane on a common carrier (18) adjustable relatively to the printing medium plane, and comprising a print head co-operating with the printing abutment and a backing roller (18) co-operating with the transport roller (10), which print head and backing roller are fixed above the printing medium plane, the transport roller (10) being fixed on the carrier (18) and a resilient transmission means (98, 100, 102) being disposed between the carrier and an adjustment drive (94) for the carrier (18), and the printing abutment (8) being fixed on the carrier (18) and the adjustment of the printing abutment (8) relatively to the transport roller (10) being so selected that when the transport roller (10) engages the backing roller or a printing medium (12) disposed between them a predetermined distance is left between the print head and the printing abutment (8) or the printing medium (12).
5. A printing unit according to claim 4, characterised in that the resillient transmission means comprises a one-arm lever (88) which is mounted by one end pivotally in the printer housing and on which the adjustment member (96) of the adjustment drive (86) acts via an intermediate spring.
6. A printing unit according to any one of claims 1 to 5, characterised in that the carrier (18) is in the form of a frame which is mounted on the printer housing (4) so as to be adjustable by way of a parallel link arrangement (65, 62).
7. A printing unit according to any one of claims 1 to 6, characterised in that the printer housing (4) contains a stop (40) which is substantially perpendicular to the printing plane, extends in the line direction, and is mounted adjustably between an operative position projecting into the path of the printing medium (12) and a withdrawn inoperative position, and in that the stop (40) is so drivingly connected to the carrier that during the adjustment movement of the carrier (18) in the biasing direction the stop (40) moves into its inoperative position, while on the adjustment movement in opposition to the biasing direction it passes into its operative position.
8. A printing unit according to any one of claims 2 to 7, characterised in that the transport roller (10) disposed on the carrier (18) is connected to a transport drive (314), the latter being rigidly drivingly connected on the carrier (18).
9. A printing unit according to any one of claims 2 to 7, characterised in that the transport roller (10) disposed on the carrier (18) is connected to a transport drive (314), the latter being disposed in the printer housing (4) and being connected to the transport roller (210) via a cardan shaft (216).

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