TECHNICAL FIELD

The invention relates to an arrangement in typewriters and the like, where a printing ribbon is led over at least three leading means having cylindrical leading surfaces, for eliminating stresses in the transverse direction of the ribbon when the ribbon is displaced transverse its direction of travel at the printing location.

BACKGROUND ART

Typewriters, line printers and such printing apparatus are usually provided with ribbons which, by the action of the writing means, apply pigment to the medium , on which the pigment is to be printed. Ribbon with black and red pigment has been used for a long time. Demands for the availability of printing with several colours has led to wider ribbons then previously, where the pigments are disposed as bands along the ribbon. For writing with a given colour, the ribbon is raised or lowered in relation to the printing means at the printing location. The ribbon is led from a storage place to the printing location and from there back again to the storage space with the aid of guide means keeping the ribbon in position at right angles to its direction of travel, and leading means with the aid of which the direction of the ribbon is changed. To avoid shear stresses in the transverse direction of the ribbon, the cylindrical surfaces of the leading means engaging the ribbon must be oriented at right- angles to the envisaged plane in which the ribbon is led.

A known method of solving the problem mentioned is to turn the ribbon magazine with guiding and leading means about an axis in the plane of the magazine. for writing at different ribbon levels- Other ways are to Lead the ribbon over a plurality of leading rollers mounted on pivotable arms, or to form the leading means with concave or convex contours. All these solutions result in mechanicaLly complicated arrangements.

DISCLOSURE OF INVENTION

The present invention solves the mentioned difficulties by having the leading means, with the aid of which the direction of the ribbon is changed, pivotably such that forces in the transverse direction of the ribbon are eliminated.

The invention is characterized by the disclosures in the following claims.

DESCRIPTION OF FIGURES

The invention will now be described in detail in conjunc¬ tion with the accompanying drawings, whereon Figure 1 schematically illustrates the parts of a typewriter which are of interest for explaining the invention. Figure 2 is a side view of the ribbon path, Figures

3 and 4 illustrate different embodiments of the leading means for altering the direction of travel of the ribbon.

MODE FOR CARRYING OUT THE INVENTION

Figure 1 schematically illustrates the parts of a typewriter of interest for explaining the invention.

A ribbon magazine 1, known per se, with ribbon storage 10,

feed wheels 8 and ribbon brake 9 is provided with two leading means 2 implemented in accordance with the invention. Two further leading means 3, implemented in accordance with the invention, lead the ribbon between the paper 5 and the writing means 6 of the typewriter parallel to a platen 4. The means 3 are raisable and lowerable in relation to the writing means 6 such as to enable the use of different bands, e.g. different colours, in the transverse direction of the ribbon.

Figure 3 illustrates one embodiment of the leading means, which is cylindrical and provided with a longitu- dinaL slot 26.. The latter has parallel walls and sloping bottom surfaces such that its depth is least haflway between the end surfaces of the cylinder. The angle a formed by the sloping bottom surfaces to each other shall be greater than the turning angle b (Figure 2) within which the plane P of the ribbon is intended to move. The leading means coacts with a plate 25 arranged between two end plates 22 and 23 such that the intersection line 24 between the sloping bottom surfaces of the slot 26 constitutes an axis against the plate 25 and about which the leading means may be pivoted. The end surfaces of the leading means are cylindri ca lly formed, with the axis 24 as central axis. This results in that the position of the axis in relation to the end plates 22 and 23 is retained when the leading means is pivoted.

Figure 4 illustraes another embodiment of the leading means. Here also, the device 31 is cylindrical and provided with a longitudinal slot 32. The essential difference between it and the embodiment illustrated in figure 3 is that the leading means is pivoted about a pin 27 fixed to a rod 29 in the slot 32. In this

o Pi

embodiment, the leading means is also provided with an upper and lower flange 28 for guiding the ribbon. Of course, the leading means according to figure 3 may also be provided with flanges for guiding the ribbon in its transverse direction, just as well as the leading means of figure 4 may lack such flanges. With the magazine 1 in a stationary position in the typewriter, the ribbon is led in a plane P (figure 2) which pivots about an axis 7 in raising or lowering the ribbon at the printing location. The axis 7 is at the center line of the ribbon where ^* the ribbon leaves the magazine. For enabling such pivoting of the ribbon plane P without getting shear stresses in the ribbon, the axes of the leading means 2 and 3 are mounted in the plane P of the ribbon path, and are parallel to the axis 7. Due to the tension in the ribbon, the leading means will thus automat cally adjust themselves such that a generatrix of the cylind¬ rical surface over which the ribbon runs will be at right angles to the plane P of the ribbon path. This means that bending moments acting on the ribbon between leading means 2 and 3 are translated into turning moments between one leading means 2 and the feed wheels 8 as weLL as between the other leading means 2 and the ribbon brake 9.