GB2243579A - Distributing wear of ink ribbons by transverse oscillations - Google Patents

Abstract

A ribbon transport mechanism includes a printing position and a ribbon guide (13) arranged and adapted to impart to a ribbon (9) a lateral snaking or serpentine movement as the ribbon (9) moves longitudinally. The arrangement is such that, in successive passes of the ribbon (9) through the printing position, different regions of the ribbon width will be presented to the printing means (12). As described, the mechanism for imparting the oscillations is a roller (13) mounted on the ribbon cartridge; which roller has its rotation axis showed with respect to its cylindrical axis so that it wobbles. Preferably the ink ribbon is a multicolour ribbon having a plurality of side by side stripes of different colour, and the recording instrument with which it cooperates is a chart recorder. <IMAGE>

Description

CARTRI DGE This invention relates to mechanisms for the transport of ink transfer ribbons and the like; the invention is applicable particularly but not exclusively to ink ribbon cartridges containing endless ribbons.

In use, ink from the ribbon is impressed by a printing device onto paper or another medium, and the ink ribbon is moved longitudinally so that a fresh region is exposed to the printing device as printing proceeds.

The printing device may for example be a daisy wheel, dot matrix printing head, a printing pin or a transverse array of printing pins for example for printing continuous or broken lines on a chart. In each case, only part of the width of the ribbon is used at each impression. To discard the ribbon after a single printing pass along its length is wasteful. Also, in some applications it is not possible, in particular in the case of chart recorders and other devices which operate automatically and unattended over periods of time. It is therefore desirable that ribbons be re-used.

However this leads to the problem that if the region of the width of the ribbon which has already been used passes again under the printing device, the printed Image will be less intense, and with successive re-uses, the print quality will deteriorate quite rapidly. This problem is acute in the case of endless ribbon cartridges for chart recorders and the like, where lines are to be printed by one or more pins.

An object of the present invention is to increase the number of times a ribbon can be re-used before the print quality deteriorates to an unacceptable level.

According to the present invention, a ribbon transport mechanism includes at least one ribbon guide adjacent the printing position, arranged and adapted to impart to the ribbon a lateral snaking or serpentine movement as the ribbon moves longitudinally, whereby in successive passes of the ribbon through the printing position, different regions of the ribbon width will be presented to the printing means.

The ribbon guide may for example be a roller extending across the width of the ribbon, the geometrical axis of the roller being oblique relative to its axis of rotation.

Alternatively, the ribbon guide may oscillate bodily in a direction generally parallel to the width of the ribbon, and may for example comprise a guide roller oscillating in this manner, and/or edge guides oscillating in the said manner.

The use of a roller as or actuating the ribbon guide has the advantage that the transverse motion is derived automatically from the longitudinal motion of the ribbon, and furthermore will be relatively random, at least on the scale of the ribbon length, so that successive passes of the ribbon are extremely unlikely to present the same region of the width of the ribbon to the printing means.

The amplitude of the lateral serpentine movement of the ribbon can be selected to suit the characteristics of the printing device.

If the ribbon guide comprises a roller, the surface of the roller may be provided with projections or recesses, for example circumferential ribs or grooves, in order to improve frictional grip between the roller and ribbon so that the ribbon is reliably entrained in the longitudinal direction of the roller. Alternatively or in addition, the roller may be provided with end flanges for engaging the edges of the ribbon.

The invention will be furthor described with reference to the accompanying drawings in which: Figure 1 is a side view, partly cut away, of an endless ink ribbon cartridge for use in a chart recorder and a print head, Figure 2 is an underneath plan view of the cartridge and print head, and Figure 3 is an enlarged detail of Figure 2 and schematically shows a ribbon guide roller of the cartridge.

Figure 1 shows, in side elevation, an inked ribbon cartridge for a chart recorder. The cartridge comprises a body 1, usually of plastics material. The body has a cover or lid 2. Within the body is accommodated an endless loop of inked ribbon 9. The bulk of this ribbon is stored in a folded form in a chamber 14 within one end of the body. The ribbon extends along a path defined by a drive wheel or roller 3 and pinch wheel or roller 4, and guide pins or rollers 6, 13. The body is formed with a recess 15 and a portion of the ribbon path extends across the mouth of this recess, being thereby exposed.

A spring 7 applies pressure to the ink ribbon perpendicular to its width so as to tension the ribbon, before it reaches the exposed region at the mouth of the recess 15. A spring 8 urges the rubber pinch wheel 4 against the rubber drive wheel 3 so that the ribbon is frictionally gripped between these wheels and can be drawn by them across the mouth of the recess 15 and then returned to the storage chamber 14. Conventional strippers 5 are provided to prevent the ribbon from continuing around the rollers i.e. it is stripped off.

In use, the cartridge is mounted in a chart recorder or other printing device, so that a print head 12 is inside the recess 15 and the drive wheel 3 is in engagement with a driving mechanism of the chart recorder, for rotating the drive wheel to transport ribbon. A platen 10 faces the print head, with the exposed portion of the ribbon and a web of paper 11 between the print head and the platen.

The print head is a needle printing head comprising an array of individual needles spaced across the width of the ribbon. Correspondingly the ribbon has discrete colour bands, for example 6 in number, aligned with individual needles of the print head so that the print head can print lines of different colours on the paper web 11 passing over the platen 10.

In a conventional cartridge, the ribbon moves in a straight line and therefore each print needle will operate on essentially the same part of the width of the ribbon during successive passes of the endless ribbon.

The life of the ribbon is measured by the number of dots that the print head can apply before the ink fades to an unacceptable level. This will happen relatively quickly if each needle always strikes essentially the same part of the width of its associated colour band of the ribbon.

To increase the life of the ribbon, the roller 13 immediately following the print head (alternatively, a roller immediately preceding the position of the print head) is designed to cause the ribbon to move sideways across its width so that the print head needle will not always strike the ribbon in a continuous straight line along the length of the ribbon, but instead, different portions of the width of each colour band will be presented to the respective needles on successive passes under the needles. By this means, effectively the entire width of each colour band, can, over a period of time, be brought under the respective needle, with a corresponding increase in the ribbon life.

In the embodiment illustrated by Figure 2, the roller 13 rotates on or about a spindle 16 mounted in the cartridge body, with the spindle axis parallel to the plane of the ribbon and perpendicui.aL to t longitudinal direction of the ribbon. The geometrical axis 17 of the roller does not coincide with the axis 18 of the spindle but makes a small angle with it. As the ribbon passes over the roller, friction between the ribbon and roller will cause the roller to rotate about the axis 18. Because the roller axis is oblique to the rotation axis, the roller will effectively "wobble" as it rotates and will cause the ribbon contacting it to oscillate sideways in the direction of the width of the ribbon.This sideways oscillation or snaking movement of the ribbon will of course be reproduced, with somewhat smaller amplitude, at the printing position, as the ribbon extends without impedance or locating means between the printing position and the "wobbly" roller 13.

The roller may have end flanges 19 to enhance the effect of the roller in entraining the ribbon in its sideways movement. Alternatively or in addition the roller may have circumferential grooves or ribs, preferably with relatively sharp edges to grip the ribbon.

The amplitude of the sideways oscillation or snaking movement is typically of the order of 1 mm. Typically, the diameter of a printing needle is 0. 35 mm and the width of a colour band is 3 mm.

It will be understood that adequate friction between t ribbon and roller is essential for rotating the roller to generate the sideways oscillation. The roller may therefore also be roughened in a manner enhancing friction in the longitudinal direction of the ribbon, for example by having longitudinal ribs or grooves.

Thus, for example, the roller surface may have a checker pattern of ribs or grooves, or even individual projecting points or teeth to enhance friction between it and the ribbon.

Claims (8)

Claims

1. A ribbon transport mechanism comprising at least one ribbon guide adjacent a printing position, the ribbon guide or guides being arranged and adapted to impart to a ribbon a lateral snaking or serpentine movement as the ribbon moves longitudinally, whereby in successive passes of the ribbon through the printing position, different regions of the ribbon width will be presented to a printing means.

2. A ribbon transport mechanism according to claim 1, wherein the said ribbon guide comprises a roller arranged to extend across the width the said ribbon, the geometrical axis of the roller being oblique relative to its axis of rotation.

3. A ribbon transport mechanism according to claim 1, wherein the ribbon guide is arranged to oscillate bodily in a direction generally parallel to the width of the ribbon.

4. A ribbon transport mechanism according to claim 3, wherein the said ribbon guide comprises a guide roller and/or guides arranged to oscillate in said manner.

5. A ribbon transport mechanism according to claim 2, wherein the said roller is provided with projections or recesses, in order to improve frictional grip between the roller and the ribbon, so as to encourage entrainment of the ribbon in the longitudinal direction of the roller.

6. A ribbon transport mechanism according to claim 5, wherein the said projections or recesses are circumferential ribs or grooves.

7. A ribbon transport mechanism according to claim 2 or 5, wherein the said roller is further provided with end flanges for engaging the edges of the ribbon.

8. A ribbon transport mechanism substantially as described herein with reference to the accompanying drawings.