EP0051694B1 - Ribbon guide in longitudinal direction - Google Patents

Description

The invention relates to a device for guiding a ribbon which is moved in the longitudinal direction, in particular an ink ribbon which is deflected, for example in front of the printing position of a printing unit, the ribbon being guided over a guide edge which is concavely transverse to the feed direction.

For guiding and deflecting a belt that is moved in the longitudinal direction, cylindrical pins are usually used, over which the belt is pulled, with simultaneous deflection by an angle determined by the further belt guide. In order to prevent the tape from running off the pin, the pins have often been provided with disk-shaped flanges at the ends or, as is known from DE-A-2 529 875, arranged laterally next to the pins perpendicular to the axis of their guide pins. However, these measures have the disadvantage that the tape runs onto the flange or the guide pins when transverse forces occur and the tape edge is exposed to increased wear, and that there is also the risk that the tape tilts over at one edge, that is, folded.

In order to improve these conditions, in particular in order to achieve a gentle centering, variously the deflection pins have been designed with a concave or convex surface, ie spherical or with a reduced diameter towards the center of the pin; however, the success was not satisfactory, because it was not possible to prevent the tape from running onto the flanges and tipping over. A similar design is known from US-A-4 114751, in which the ribbon roll is designed with a stepped spherical surface, namely asymmetrically, with the aim that, when wear occurs in an edge zone of the tape, the area of the tape which is not affected by wear is centered , so a certain correction occurs automatically with respect to the transverse position of the belt.

Another measure, as is also known from DE-A-2 529 875, is to guide the guide pins or rollers with corrugated or, as in the IBM Technical Disclosure Bulletin, Volume 22, No. 4, page 1315 , shown, with a toothed surface. This design should specifically take into account the requirements for the management of ribbons in printing units; Because with color ribbons there is the peculiarity that they are generally only affected by the printing types in the central area and are therefore stretched more and more in this area after a long period of operation.

This peculiarity when using ribbons for a long time has the consequence that the ribbon tension in the longitudinal direction of the ribbon becomes inconsistent, namely in the printing area is considerably less than in the edge areas, so that forces act across the feed direction of the ribbon and "buckling" of the ribbon takes place. The ink ribbon is deflected laterally when the transverse forces that occur cannot be compensated. Further influences on the behavior of a longitudinally moving belt also result from fluctuations in the operating conditions, e.g. B. Changes in ambient temperature and humidity.

A solution to the problem of the centering of ink ribbons shows a concave guide surface or edge over which the ribbon is guided before it gets between the drive rollers again. This training is described in the IBM Technical Disclosure Bulletin, Volume 19, No. 2, pages 621/22.

Sufficient centering of the band at the deflection position can be achieved in part with the known band guide arrangements, but at the same time there is the risk that the band stretched in the longitudinal direction as a result of the uneven loading in certain areas, in particular in the central area, will wrinkle in the longitudinal direction and thereby possibly even become unusable , so that in any case the print quality is impaired or even the machine has to be switched off and the belt has to be replaced.

The invention has for its object to provide a tape guiding device which, at the same time as the centering, also smoothes the tape and maintains it functional, even if it shows considerable signs of wear and, in particular, deformation after a long period of use. This object has been achieved in a device of the type described in the introduction with a concave guide edge in that a convex guide surface is arranged immediately after the concave guide edge.

The advantages that can be achieved with the device according to the invention are that, with a precisely defined tape guide, better utilization of the life of a tape is achieved, that no information loss can occur with a tape for recording or processing information, since the tape does not tip over, and that Furthermore, lower demands are placed on the manufacturing tolerances, since reliable guidance of the belt is guaranteed even after a longer service life.

The use of the device according to the invention is not limited to the guidance of color ribbons, but is also suitable for ribbons of other types and uses. This also applies in particular to those ligaments in which experience has shown that, as a result of prolonged use, certain changes in the ligament occur over time, which primarily includes stretching in certain areas, with the resulting internal tensions, which affect the behavior of the belt with regard to its function in the transport and guide elements. In this case, the advantages of the device according to the invention can be used for tapes constructed on the basis of plastics as well as for tapes made of textile fabrics. The use of the proposed device is also not restricted to relatively narrow ribbons, but is also possible with color blankets, such as those used in line printing units, in which the problems indicated above occur in the same way.

Various, particularly expedient embodiments of the invention are contained in the subclaims. The concave guide edge and the convex guide surface are advantageously integrated into a common guide element. Furthermore, the concave guide edge can be formed in a simple manner by penetrating the convex guide surface from a body with a convex surface, namely, for example, from a cylinder or a single-shell hyperboloid.

Particularly good guiding properties for strips are obtained if the convex guiding surface of the device according to the invention is designed as part of an ellipsoid cut off on both sides. If the tape to be guided is a ribbon that is operated with a change of direction, for example a ribbon that can be moved back and forth between two spools, the spools alternately serving as supply spools and as take-up spools, the guide element on both sides of the convex guide surface can be in seen the running directions of the belt, each with a concave leading edge. In this case, the device according to the invention is freely pivotable about an axis arranged transversely to the tape running directions and its pivoting movement is limited by two stop elements. With each change in the direction of the strip, the leading edge arranged in front of the guide surface reaches its operative position centering the strip.

• Fig. 1 eine schaubildliche Ansicht eines Druckwerks mit einem von einer Vorratsspule vor die Druckzeile geführten und zu einer Aufnahmespule bewegten Farbband,
• Fig.2 ein Führungselement zur Umlenkung des Farbbandes gemäß Fig. 1 in vergrößerter schaubildlicher Darstellung, in der Ausführungsform für einen Ein-Richtungs-Farbbandvorschub,
• Fig.3 ein Führungselement zur Umlenkung des Farbbandes gemäß Fig. 1 in vergrößerter schaubildlicher Darstellung, in der Ausführungsform für einen Zwei-Richtungs-Farbbandvorschub,
• Fig. 4 eine Draufsicht auf das Druckwerk gemäß Fig. 1, mit je einem Führungselement zu beiden Seiten der Druckzeile in der Ausführung für einen Zwei-Richtungs-Farbbandvorschub,
• Fig. 5a eine vergrößerte Draufsicht auf ein Führungselement nach Fig.4 in der Position beim Farbbandantrieb in der ersten Richtung, und
• Fig. 5b eine vergrößerte Draufsicht auf ein Führungselement nach Fig. 4 in der Position beim Farbbandantrieb in der zweiten Richtung.

The invention is described below with reference to the drawings in one embodiment. It shows

• 1 is a perspective view of a printing unit with an ink ribbon guided by a supply spool in front of the printing line and moved to a take-up spool,
• 2 shows a guide element for deflecting the ink ribbon according to FIG. 1 in an enlarged diagrammatic representation, in the embodiment for a unidirectional ink ribbon feed,
• 3 shows a guide element for deflecting the ink ribbon according to FIG. 1 in an enlarged diagrammatic illustration, in the embodiment for a two-direction ink ribbon feed,
• 4 shows a top view of the printing unit according to FIG. 1, with a guide element on each side of the printing line in the version for a two-direction ribbon feed,
• 5a is an enlarged top view of a guide element according to FIG. 4 in the position in the ribbon drive in the first direction, and
• Fig. 5b is an enlarged plan view of a guide element according to Fig. 4 in the position in the ribbon drive in the second direction.

In the printing unit shown in FIG. 1, an endless type chain 2 is guided around two rollers 4, 6 and is driven by one of the rollers 4, 6 by means of a toothing. The rollers 4, 6 are mounted in a housing 8 which protects the type chain 2 and at the same time serves as a pressure abutment.

In front of the type chain 2 are the pressure hammers 12 which can be pivoted about the axis 10 against the types and which are actuated by a plunger 14 by (not shown) electromagnets. In front of the front surface of the printing hammers 12, the paper 16 to be printed is passed through the printing station, where it is unrolled from a supply roll 18 by a paper feed (not shown). An ink ribbon 20 runs between the paper 16 and the type chain 2 in the print line and is guided from a supply spool 22 to a take-up spool 24. The supply spool 22 sits on a shaft 26 which is connected to a stepper motor 30. In a corresponding manner, the take-up spool 24 is seated on a shaft 28 which is coupled to a stepper motor 32. The terms “supply spool” and “take-up spool” apply as long as the ink ribbon 20 is transported from the spool 22 in the direction to the right onto the spool 24, the stepping motor 32 alone being effective. As soon as the ink ribbon 20 has been unwound from the spool 22, the direction is reversed and, driven by the stepping motor 30, the spool 22 now becomes the take-up spool and the spool 24 becomes the supply spool. The reversal during the respective change of direction is carried out by a sensing device, not shown.

The printer shown in FIG. 1 is a back-side printer in which the types, viewed from the impact side of the print hammers 12, are printed on the back of the paper 16. For the ribbon guide described below, however, it does not matter whether it is a back-side printer or a front-side printer in which the types are posted from the front of the paper for printing.

As FIG. 1 further shows, the ink ribbon 20 is guided by the spool 22 over a guide pin 34 and then deflected into its alignment with the printing line via a guide element 38 mounted on a bearing axis 36 (cf. also FIG. 4). In a corresponding symmetrical arrangement there are likewise on the right side of the printing station a guide element 38 fastened on a bearing axis 36 and subsequently a guide pin 34, via which elements the ink ribbon 20 is guided onto the take-up spool 24. 4, in Supplement to Fig. 1, makes it clear that one of the guide elements 38 has the function of both deflecting the ribbon fed from the respective supply reel by the required angle and centering it so that it reaches the printing station in a precise alignment. In contrast, the guide pins 34 only serve to compensate for the different tape winding diameters of the coils, such that the deflection angle in the guide elements 38 is constant, regardless of the respective outer diameter of the tape winding of the associated coil.

The formation of different guide elements is shown in more detail in FIGS. 2 and 3. The guide element 37 according to FIG. 2 is provided for a printing unit in which the ink ribbon is always guided through the printing position in the same direction. This applies, for example, to printing units with an ink ribbon cassette with a storage chamber, through which an endless ink ribbon is transported by means of drive rollers or transport rollers in a uniform feed direction. The ink ribbon transport direction is indicated in Fig. 2 by an arrow.

The guide element 37 according to FIG. 2 consists of a convex guide surface 40 which is delimited on one side by a substantially straight guide edge 40a and on the opposite side by a concave guide edge 42. The guide edge 42 can be formed, for example, by penetrating the convex guide surface 40 from a body with a convex surface, for example a single-shell hyperboloid. A guide bearing 44 with a bore 45 is also formed on the guide surface 40 in the central region of the surface and is fastened in the frame (not shown) by means of a guide shaft 46 running through the bore 45. At the upper end of the guide shaft 46 there is a head 46a which is designed, for example, as a screw head. The guide element 37 is fixed immovably in the machine, namely by tightening the guide shaft 46 on the hexagon head 46a, but can be adjusted in its angular position by temporarily loosening it in order to be able to adapt the guide edge 42 to the feed angle of the ribbon.

The guide element 38 according to FIG. 3 has a convex guide surface 41, on which a guide bearing 44 with a bore 45 is also integrally formed. The guide element 38 differs from the guide element 37 according to FIG. 2 in that it is delimited not only on one side, but on both opposite sides by a concave guide edge 42a, 42b, and in that the bearing axis is through the bore 45 of the guide bearing 44 48 (see FIG. 1), around which the guide bearing 38 is pivotally mounted. As already explained in connection with FIG. 2, each of the guide edges 42a, b can be formed by penetration of the guide surface 41 by a single-shell hyperboloid or another body with a convex surface. The two tape feed directions are shown in Fig. 3 by a double arrow.

In both versions of the guide elements 37 and 38 according to FIGS. 2 and 3, the course of the band to be guided is indicated by edges drawn in broken lines. The pivot axis 50 of the guide elements 37 and 38, which is characterized by the bores 45, lies with respect to the guide surface 40 and 41 such that the points formed by the pivot axis 50 each have approximately the same distance from the individual points of the guide surface 40 and 41 in the corresponding radial plane to have. In other words: If the guide surfaces 40, 41 had the shape of a cylinder segment, the pivot axis 50 would lie exactly in the central axis of this cylinder, so that the position of the guide surfaces 40, 41 would not change with respect to the pivot point if the guide elements were pivoted. Regardless of the actual shape of the guide surfaces 40, 41 deviating from a cylinder segment, the position of the pivot axis 50 determined by the bores 45 in the guide bearings 44 is selected accordingly so that the pivoting movement of the guide surfaces 40, 41 minimizes the change in position in the radial direction Experienced. It is pointed out that in the designs of the guide elements according to FIGS. 3 and 3, matching parts are identified by the same reference numerals.

5a and 5b there are stop pins 52 and 54 on both sides of the guide bearing 44 of the guide element 38, which limit the pivoting movement of the guide element 38 when the tape feed direction changes. 5 a shows the position of the guide element 38 during a feed movement of the ink ribbon 20 to the left (see arrow), the guide element 38 bearing with the corresponding surface of the guide bearing 44 on the stop pin 52, which, like the bearing axis 36, is in a (not shown) frame plate of the printing unit is fixed. If the tape feed direction is switched because the tape supply has run out of the supply reel, the guide element 38 is pivoted counterclockwise due to the force exerted by the deflection by means of the ink ribbon 20 on the guide surface 41 until the opposite surface of the guide bearing 44 abuts the stop pin 54 and prevents further pivoting movement.

As a result of the pivoting movement of the guide element 38 as a function of the tape feed direction, the guide edge 42a or 42b lying at the tape inlet becomes effective, so that the ink ribbon 20 is centered on the guide surface 41 before it runs up. Here, the leading edge 42a or b on the opposite set side of the guide surface 41 swung out of the guideway of the belt, as can be seen from FIGS. 5a and 5b. In each of the two operating states, the ink ribbon 20 thus first comes into the effective range of one of the guide edges 42a or 42b before it runs onto the guide surface 41 and is smoothed there to prevent it from turning over or forming wrinkles.

Claims (7)

1. Device for guiding a ribbon moved in a longitudinal direction, in particular an ink ribbon, which is deflected to be, for example, in front of the print position of a printer, with a concave guide edge (42), characterized in that immediately adjacent to the concave guide edge (42) in the ribbon guide path a convex guide face (40; 41) is arranged.

2. Device according to claim 1, characterized in that the concave guide edge (42) and the convex guide face (40, 41) are integrated in a common guide element (37; 38).

3. Device according to claim 2, characterized in that the concave guide edge (42) is formed by penetrating the convex guide face (40; 41) by a body with a convex surface.

4. Device according to claim 3, characterized in that the concave guide edge (42) is formed by penetrating the convex guide face (40; 41) by a cylinder.

5. Device according to claim 3, characterized in that the concave guide edge (42) is formed by penetrating the convex guide face (40; 41) by a one-sheet hyperboloid.

6. Device according to claims 1 to 5, characterized in that the convex guide face (40; 41) is designed as part of an ellipsoid cut at both ends.

7. Device according to claims 1 to 6, characterized in that on either side of the convex guide face (41), viewed in the direction of ribbon movement, the guide element (38) has one concave guide edge (42a, 42b) each and in the directions of ribbon movement, limited by two stopper elements (52, 54), is freely pivotable about an axis (36), arranged transversely to said directions of ribbon movement, such that each time the ribbon is reversed, the guide edge (42a or 42b) located in front of the guide face is caused to assume a position in which it centers the ribbon running onto the guide face (41).

Images