FIELD OF THE INVENTION

The present invention relates to a device for the feeding of a printing ribbon, comprising a pair of reciprocally meshed gears and driven by a driving shaft, and in which device the printing ribbon is interposed between the engaged teeth of the pair of gears and therefore the printing ribbon is obliged to assume a configuration having windings which follow the profile of the engaged teeth of the pair of gears.

BACKGROUND OF THE INVENTION

From the Italian Patent No. 1,211,410 issued to the Applicant on

18th October 1989, a device of this type is known, which is mounted within a cartridge and which is particularly suitable to allow the printing ribbon to advance towards a magazine, within which the same ribbon is randomly arranged in the form of turns. This device is not always capable to supply the printing ribbon with a constant and sufficient traction force, necessary to allow the ribbon to advance in a regular and uniform way, for overcoming all the frictions that the same ribbon meets in its path, and consequently this device is affected with ribbon slidings with respect to the ribbon driving gears. This inconvenience may mainly happen in the so-called high capacity cartridges, in which either the printing ribbon length to draw, or the friction force opposing to the feeding of the same ribbon, are higher than the usual.

SUMMARY OF THE INVENTION

The technical problem that the present invention aims to solve is that of realizing a device for the feeding of a printing ribbon, the feeding device being fit to generate a force suitable to allow the printing ribbon to advance in a regular way and without slidings, even in the more critical conditions with

regards to the feeding force. This technical problem is solved by the feeding device according to the present invention, which is characterized in that a third gear is engaged with a first gear of the pair of gears and in that the printing ribbon is also interposed between the first gear and the third gear and in that the printing ribbon is obliged by these latter to assume a further configuration having windings which correspond to the profile of the engaged teeth of the first gear and of the third gear.

According another feature, the device according to the present invention is characterized in that the first and the further configurations have different developments between them, which correspond to the different diametral pitches of the second and of the third gears respectively, and in that, with respect to the ribbon feeding sense, the configuration with windings having a greater development is arranged successively to the configuration with windings having a lower development.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will be clear by the following disclosure, given by way of non-limiting example, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a device for the feeding of a printing ribbon according to the invention; and

Fig. 2 is a partial plan view of the device of Fig. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to Figs. 1 and 2 a feeding device 11 for a printing ribbon 12, according to the present invention, comprises a pair of gears 13 and 14 with a plurality of teeth 15, respectively 16, reciprocally engaging, and a driving shaft

17 fixed to the gear 14 and suitable to receive , in a known manner, the rotary

motion from a motor member, for example from a printing carriage, not shown in the drawings.

The printing ribbon 12, of a known type, for example made by inked web, is interposed between the gears 13 and 14 and is obliged, in a portion 18 thereof, to assume a first configuration having windings which follow the form of the teeth 15 and 16 engaged by the gears 13 and14. A third gear 20 is provided with teeth 21 , has a diametral pitch greater than the diametral pitch of the gear 14, and is meshed with the gear 13. The ribbon 12 is also interposed between the teeth 15 and 21 of the gears 13 and 20, in such a way as to assume a second configuration with windings 22.

The gears 14 and 20 are arranged angularly staggered with respect to the central gear 13, defining in such a way an intermediate area 27 between the configurations with windings 18 and 22, in which area the ribbon 12 winds round the same gear 13 for a short portion, standing on the ends of the teeth 15. A post 23 is arranged near the driving gear 14 for driving towards it the ribbon 12.

The gears 13 and 14 are preferably mounted with the rotation axis fixed, while the gear 20 is free to move in radial sense with respect to the gear 13. Resilient means, for example formed by a traction spring 25, press the gear 20 against the gear 13 with a predetermined force F and, consequently, the resilient means press the ribbon 12 between the engaged teeth 15 and 21 of the corresponding gears 13 and 20, so obliging the ribbon 12 to follow the path with the windings 22. The traction spring 25 urges always the gear 20 against the gear 13, avoiding oscillations of the axis of the gear 20 with respect to the axis of the gear 13, in such a way to prevent the ribbon 12 to slide with respect to them.

The developments of the configurations with windings 18 and 22 are determined by the profile of the teeth 15 and 16 reciprocally engaged, and respectively by the profile of the teeth 15 and 21 reciprocally engaged. The

diametral pitch of the gear 20 is greater than the diametral pitch of the gear 14, and therefore the development of the configuration with windings 22 is greater than the development of the configuration with windings 18.

The functioning of the device according to the present invention is the following.

The driving shaft 17 is made to rotate in the clockwise sense, for permitting the gears 14, 13 and 20 to rotate according to the rotation directions of the arrows 26. The pairs of gears 13-14 and 13-10 allow the ribbon 12 to advance according to the direction indicated by the arrow 24 and permit to the ribbon portion, which is in contact with the intermediate area 27 of the gear 13 and is included between the configurations 18 and 22, to be constantly tight, preventing the same ribbon 12 to have slackenings or to form undesired bends.

In particular the configuration 22, in consequence of its greater development with respect to the configuration 18, is able both to draw all the ribbon quantity which exits from the configuration 18, and to impart a further driving force to the ribbon 12.

In a preferred embodiment, the gear 14 has twelve teeth while the gears 13 and 20 have each thirty teeth. In this case, assuming that these latter shall be pressed one against the other by an appropriate value of the force F of the spring 25, the device 11 permits to obtain a feeding force of the ribbon 12 higher than 2.000 grams, whilst in the known devices such force is considerably lower.

It is clear that the device of this invention, in the preferred embodiment above disclosed, may be subject to several modifications and/or addition of parts, without departing from the scope of the invention.