Ink Ribbon Cassette With Slidable Ribbon Guide

The present invention relates generally to printers and, more particularly, to printers using an ink ribbon cassette in which an ink ribbon is positioned to face a printing head within the range of reciprocation of the printing head.

An ink ribbon cassette of the prior art has a pair of arms integrally extending from opposite end portions thereof, the cassette case being longer than the reciprocating range of the printing head. Ribbon take-out and take-in slits are formed in the ends of the respective arms for exposing a portion of an ink ribbon contained within the cassette. Thus, the printing head and the ink ribbon are positioned to face each other within the range of reciprocation of the printing head while exposing the ink ribbon to the outside between the ribbon take-out and take-in slits.

In case, however, such a prior art ribbon cassette is used in a printer having a long range of reciprocation of the printing head, the cassette case has to be elongated. This, in turn, enlarges the distance between the ribbon take-out and take-in slits so that the ink ribbon portion exposed between the ribbon take-out and take-in slits becomes slackened. The slackening of the exposed ink ribbon portion alters the facing positional relationship between the printing head and the ink ribbon. This is disadvantageous in that the printing head and the ink ribbon fail to accurately face each other. In the prior art, this disadvantage is coped with by enlarging the width of the ink ribbon which has the drawback of increasing the thickness of the ribbon cassette. This disadvantage is especially serious in the case of using a multi-color ink ribbon having a plurality of lengthwise extending color bands. When using a multi-color ink ribbon, a color band switching device is used to shift the ribbon so that different color bands face the printing head, and the positional relationship between each color band and the printing head is displaced as the ribbon slackens thereby making it difficult if not impossible to perform the desired multi-color printing operation. For making multi-color prints of high quality, strict alignment of the positions of the ink ribbon and printing head is indispensable.

It is, therefore, an object of the present invention to provide an ink ribbon cassette which overcomes the disadvantages of the prior art devices.

It is another object of the present invention to provide an ink ribbon cassette which maintains a constant positional relationship between the facing positions of the printing head and the ink ribbon to make prints of high quality even in case the ribbon take-out and take-in slits are spaced a long distance apart.

The above and other objects are achieved by means of a cassette case charged with an ink ribbon and having a pair of arms integrally extending from opposite end portions thereof and opened at their leading ends to form ribbon take-out and take-in slits between which the ink ribbon is exposed to the outside. The cassette case is provided with a ribbon guide slidably supported on a guide shaft and disposed to move vertically with respect to a horizontally reciprocable printing head and to move horizontally together with the printing head. The ribbon guide is provided with restricting means for allowing the exposed portion of the ink ribbon to slide lengthwise therethrough in the vicinity of the tip of the printing head while restricting vertical movement of the exposed portion of the ink ribbon with respect to the cassette case. The exposed portion of the ink ribbon is forced without fail to face the printing head at a predetermined positional relationship via the restricting means.

FIG. 1A is a front elevational view of an ink ribbon cassette according to the present invention and FIG. 1B is a front elevational view of a printing head showing the positional relationship between the cassette and printing head;

FIG. 2 is a top plan view, partly cut away, showing the ink ribbon cassette mounted on the printing head;

FIG. 3 is a partial cross-sectional view taken along line 3--3 of FIG. 1A;

FIG. 4 is a partially cut-away top plan view of the printing head; and

FIG. 5 is a side elevational view of the printing head.

The present invention will be described hereinafter in conjunction with one embodiment thereof with reference to the accompanying drawings.

As shown in FIGS. 1A and 2, a cassette case 1 has a pair of arms 2 and 3 extending integrally from opposite end portions of the cassette case 1 to form a ribbon take-in slit 2a and a ribbon take-out slit 3a. The arms 2 and 3 are formed with upwardly extending projections 2b and 3b which have openings 2c and 3c therein for receiving and supporting a guide shaft 4 which extends parallel to the direction of movement of a rigid printing head 8. A ribbon guide 5 is slidably supported on the guide shaft 4 by means of a mount portion 5a which is slidably mounted on the guide shaft 4.

The mount portion 5a has a pair of legs 51 and 52 which depend downwardly in spaced-apart relation and which define therebetween a predetermined gap. The legs 51 and 52 are formed at their lower end portions with lateral engagement projections 51a and 52a. From the legs 51 and 52, there extend forward engagement arms 53 and 54 of generally C-shaped section (as shown in FIG. 3) which slidably engage with the exposed portion 6A of an ink ribbon 6. The engagement arms 53 and 54 are formed at their upper and lower end portions with retaining claws 53a and 54a, and 53b and 54b, respectively, which slidably engage with the upper and lower edges of the exposed ribbon portion 6A. The retaining claws 53a , 54a, 53b and 54b jointly constitute restricting means for restricting vertical movement of the exposed ribbon portion 6A with respect to the cassette case 1. Thin elastic plates 7a and 7b are inserted between the retaining claws 53a and 53b and between the retaining claws 54a, and 54b, respectively, for ensuring the sliding engagement of the ink ribbon 6 with the ribbon guide 5.

The ink ribbon 6 comprises a multi-color printing endless ink ribbon composed of a plurality of colored ink bands 6a, 6b, 6c and 6d which extend lengthwise of the ink ribbon 6 in parallel relation and which are impregnated with ink of different colors, respectively. The endless ink ribbon 6 is fed lengthwise in the longitudinal direction by means of a drive roller la disposed in the cassette case 1 by the action of a ribbon feeder (not shown) disposed in a printer body (not shown). The remaining portion of the ink ribbon 6 other than the exposed portion 6A extending between the ribbon take-out and take-in slits 3a and 2a is stored in zigzag form in the cassette case 1, as shown in FIG. 2.

The printing head 8 is slidably supported on print guide 10a and 10b via a carriage 9. The printing head 8 includes a print wire guide 8a which is formed at its opposite side walls with vertical engagement grooves 8b and 8c as best seen in FIGS. 4 and 5. The engagement grooves 8b and 8c are dimensioned to slidably receive therein the lateral engagement projections 51a and 52a of the ribbon guide legs 51 and 52. By such a construction, the ribbon guide 5 together with the exposed ribbon portion 6A can be displaced vertically relative to the printing head 8 and, during such vertical displacement, the engagement projections 51a and 52a vertically slide in the vertical engagement grooves 8b and 8c of the wire guide 8a. The print wire guide 8a has an array of printing wires 11 slidably inserted therein to undergo selective actuation to strike the ink ribbon 6 in a manner well known in the art. The printing head 8 further includes a pair of vertical ribs 8d and 8e which slidably engage with the sides of the ribbon guide legs 51 and 52, and a front cover 8f.

During use, the cassette case 1 is removably mounted on a conventional color band switching device (not shown) of the printer (not shown). As shown in FIG. 1, the ribbon guide 5 is mounted vertically movably on the printing head 8 by bringing the engagement projections 51a and 52a of the ribbon guide 5 into sliding engagement with the engagement grooves 8b and 8c of the printing head 8, respectively, and by sliding the ribbon guide 5 downwardly. In this manner, the ribbon guide 5 is carried integrally with the printing head 8 and slides along the guide shaft 4 via the mount portion 5a, and the ribbon guide 5 can move in sliding engagement with the exposed portion 6A of the ink ribbon 6 at a constant vertical position with respect to the cassette case 1 while restricting movement of the exposed ribbon portion 6A in the vertical direction. As a result, the exposed portion 6A of the ink ribbon 6 will not become slack, even if the distance between the ribbon take-in and take-out slits 2a and 3a is made long, so that the ink ribbon 6 always faces the printing head 8 with a predetermined positional relationship.

During multi-color printing operations, the cassette case 1 is vertically displaced a predetermined distance by the color band switching device (not shown) so as to selectively bring one of the color bands 6a, 6b, 6c and 6d into a suitable position to face the printing wires 11 in accordance with the color to be printed. At this time, as the ribbon guide 5 is slidably supported on the guide shaft 4 so as to move in accordance with the vertical movements of the cassette case 1, the ribbon guide 5 effectively restricts vertical movement of the ink ribbon 6 relative to the cassette case 1 while holding the longitudinal position of the ink ribbon 6 relative to the cassette case 1. By such a construction, the ink ribbon 6 accurately follows the vertical movements of the cassette case 1 so that a predetermined color band accurately faces the printing wires 11 of the printing head 8 in the predetermined positional relationship.

According to the present invention, the positional relationship between the printing head and the exposed portion of the ink ribbon remains constant for each color band, even in case the distance between the ribbon take-out and take-in slits is long, so that the printing head and the exposed ribbon portion always face one another in an accurate positional relationship. As a result, the ribbon cassette can be made thinner without enlarging the width of the ink ribbon more than necessary. Moreover, the positional adjustment of the ink ribbon during assembly is facilitated thereby improving the working efficiency and reducing the production cost.