An ink ribbon cassette

Abstract: An inked ribbon cassette comprising an ink supply felt (16), a first gear (11) arranged in contact with the felt (16) and a second gear (12) in engagement with the first gear (11). An ink ribbon (1) is pinched between the first (11) and the second (12) gears and is driven by them upon their rotation. Accordingly, ink is transferred from the felt (16) to the first gear (11), and in turn, from the first gear (11) to the ink ribbon (1). There are grooves (13) in the first gear (11) for containing any excess ink which is transferred from the ink supply means (16) to the first gear (11). The grooves (13) are preferably provided by deepening the bottom lands (11b) of the first gear (11) by increasing the depth of the teeth (11a) of the first gear (11).

Description: The present invention relates to an ink ribbon cassette used in a printer, a typewriter or the like. Several types of ink ribbon cassettes are used in many printers and typewriters. In thermal type printers, one-time disposable ink ribbon cassettes are generally used. In impact dot type printers, one type of ink ribbon cassette includes a relatively long, for example, 10 to 60 meters, endless ink ribbon in the cassette, and another type of ink ribbon cassette includes a relatively short, for example, 0.5 to 1 meters, endless ink ribbon in the cassette. In the latter case, an ink supply means is incorporated in the cassette and the ink ribbon is repeatedly used with the supply of ink thereon. For example, Japanese Unexamined Patent Publication (Kokai) No. 63-182174 discloses an ink ribbon cassette in which an inking roller having ink absorbed therein and an ink transferring roller is provided in the cassette to supply ink onto the ink ribbon. Japanese Unexamined Patent Publication (Kokai) No. 1-198379 discloses an ink ribbon cassette in which an inking roller is also shown in Fig. 3 in this publication. Also, Figs. 1 and 2 of this publication show a pair of gears between which the ink ribbon is pinched and fed. An ink belt is provided in Fig. 1 therein, which is driven by one of the gears to supply ink to the ink ribbon. Recently, an ink ribbon cassette comprising a pair of gears between which an ink ribbon 101 is pinched and fed, and ink is transferred from one of the gears to the ink ribbon, as showm in Fig. 7 attached hereto. The upper gear, for example, which transfers ink to the ink ribbon 101, is in contact with an ink supply means having ink absorbed therein, for example, a felt containing ink therein. Therefore, ink absorbed in the felt is scraped off by the upper gear gradually, and transferred to the ink ribbon 101 via the upper gear. US-A-4,747,111 discloses a cartridge for an inked ribbon in which the ribbon passes between a pair of gears to transfer ink from one of the gears to the ink ribbon. A problem of the above described prior art is that a concentration of ink in the ink ribbon varies due to occasional excessive supply of ink. For example, when the temperature around the felt is relatively high, the viscosity of ink in the felt becomes low and ink flows easily in the felt so that excessive ink is transferred to the ink transferring gear. Also, when the ink ribbon is idle fed and the printing head does not print letters, ink in that portion of the ink ribbon is not consumed and thereafter ink is further supplied by the ink transferring gear, resulting in an excessive ink supply. When excessive ink supply occurs, ink is filled in the spaces between adjacent teeth of the ink transferring gear and a large amount of ink is transferred to the ink ribbon locally to cause a variation of ink concentration in the ink ribbon and thereby deteriorate the quality of the typing. The object of the present invention is to solve the above described problem and to provide an ink ribbon cassette in which ink is generally and uniformly supplied to an ink ribbon and a variation of ink concentration is mitigated. According to the present invention an ink ribbon cassette comprising an ink supply means having ink absorbed therein, a first rotatable gear having teeth and bottom lands between adjacent teeth, arranged in contact with the ink supply means; a second rotatable gear arranged in engagement with the first gear; and, an ink ribbon pinched between the first and the second gears and driven along a path by the rotation of the first and the second gears; is characterized in that at least one groove is arranged in the first gear for containing ink when an excess of ink is transferred from the ink supply means to the first gear, wherein the groove is provided by increasing the depth of the bottom lands between adjacent teeth, to a depth greater than that of a standard gear. With this arrangement, when excessive ink is transferred to the ink transferring gear, due to a temperature change or idle feeding of the ink ribbon, it adheres to the first gear and only the portion of ink adhered at the tooth surfaces of the first gear is transferred to the ink ribbon. The excessive ink is contained in the at least one groove in the first gear and not transferred to the ink ribbon. Therefore, ink is uniformly distributed on the ink ribbon. The present invention will become more apparent from the following description of the preferred embodiments, with reference to the accompanying drawings, in which: Fig. 1 is a partially cross-sectional view of an ink ribbon cassette according to the embodiment of the present invention, and showing a portion of Fig. 2 in a larger scale; Fig. 2 is a cross-sectional view of the ink ribbon cassette according to the embodiment of the present invention; Fig. 3 is a detailed view of the upper gear of Fig. 1; Fig. 4 is a detailed view of the lower gear of Fig. 1; Fig. 5 is a view showing the upper and lower gears in engagement with each other; Fig. 6 is a detailed view of the upper gear of Fig. 3; and Fig. 7 is a view of a prior art. Figures 1 and 2 show an ink ribbon cassette used in an impact dot printer. The ink ribbon cassette comprises a cassette case 2 having a ribbon chamber 2a and opposite parallel arms 3 extending from the ribbon chamber 2a. A head access opening 4 is provided at the ends of the arms 3. An ink ribbon 1 is a continuous and endless ribbon made of fabric, which is accommodated in the ribbon chamber 2a of the cassette case 2 in serpentine form and runs within a passage formed in the arms 3. The ink ribbon 1 is revealed at the head access opening 4 where a printing head (not shown) acts on the ink ribbon 1. The cassette case 2 includes an ink supply chamber 6 where a felt 6a having ink fully absorbed is arranged. A strip of ink supply felt 16 extends from the ink supply chamber 6. A pair of gears 11 and 12 are arranged in the ribbon chamber 2a and below the ink supply felt 16. The upper gear 11 is arranged in contact with the ink supply felt 16 and has a support shaft 14 driven for rotation by a motor not shown. The lower gear 12 has a support shaft 15 that is carried by a bracket 19. The bracket 19 is pivotally mounted to the cassette case 2 and biased by a relatively weak spring 18 so that the lower gear 12 is lightly engaged with and driven by the upper gear 11. The ink ribbon 1 is pinched between the upper and the lower gears 11 and 12 and driven by the upper and the lower gears 11 and 12 upon rotation thereof for traveling along the above described path, as shown by the arrows. As will be clear, the upper gear 11 scrapes ink in the ink supply felt 16 and transfers ink to the ink ribbon 1. Thus, the ink ribbon 1 can be used repeatedly, and it is possible for the ink ribbon 1 to be relatively short for example, 0.5 to 1 meters. The upper and the lower gears 11 and 12 have teeth 11a and 12a and bottom land 11b and 12b, respectively. The upper gear 11 also has grooves 13 for containing ink therein when ink is excessively transferred from the ink supply felt 16 to the upper gear 11. In the preferred embodiment, the grooves 13 are arranged in the bottom lands 11b of the upper gear 11. The teeth 12a of the lower gear 12 are formed in a standard involute tooth profile. The teeth 11a of the upper gear 11 are formed by a standard involute tooth profile 11c and a further tooth profile 11d contiguous to the standard involute tooth profile 11c, as shown in Fig. 6. The further tooth profile 11d is preferably a straight line and a portion of the further tooth profile 11d constitutes the groove 13. The whole depth of the tooth is the sum of addendum "a" and dedendum "b", as shown in Fig. 5. Therefore, the whole depth of the upper gear 11 is greater than a whole depth of a standard gear. In the preferred embodiment, the whole depth of the upper gear 11 is 2L when a whole depth of a standard gear is H, as shown in Fig. 6. The groove 13 has a depth in correspondence with a subtraction of the whole depth of a standard gear from the whole depth of the upper gear 11 and accordingly, the depth of the grooves 13 of the upper gear 11 is L. Preferably, the depth of the grooves 13 is within a range from 0.5 to 1.5 times the whole depth of a standard gear (i.e., the whole depth is within a range from 1.5L to 2.5L). In operation, the upper gear 11 and the lower gear 12 feed the ink ribbon 1, and simultaneously the upper gear 11 transfers ink to the ink ribbon 1. Thus, the ink ribbon 1 can be used repeatedly. There may be cases where excessive ink is supplied to the ink ribbon 1. For example, when the temperature around the ink supply felt 16 is relatively high and the viscosity of the ink in the ink supply felt 16 becomes low, ink flows easily in the ink supply felt 16 so that excessive ink is transferred from the ink supply felt 16 to the upper gear 11. Alternately, when the ink ribbon 1 is idle fed and the printing head does not print letters, ink in that portion of the ink ribbon 1 is not consumed and thereafter ink is further supplied by the upper gear 11 to the ink ribbon 1. In such cases, ink is adhered to the whole portion of teeth 11a of the upper gear 11 and only a portion of ink adhered at the tooth surfaces of the upper gear 11 is transferred to the ink ribbon 1. The excessive ink is contained in the grooves 13 in the upper gear 11 and this ink is not transferred to the ink ribbon 1. Therefore, ink is uniformly distributed on the ink ribbon 1. It has been found that ink contained in the grooves 13 does not drop on the ink ribbon 1 and does not cause a variation of ink concentration in the ink ribbon 1. Thus the quality of the typing or printing is ensured. It is believed that ink contained in the grooves 13 may adequately evaporate and the quality of the typing or printing is ensured during continuous use of the printer. Figures 3 and 4 show a detailed embodiment of the upper and the lower gears 11 and 12, respectively, which have the following dimensions, where Dp is a diameter of a pitch circle, d, is a diameter of a root circle, "m" is a module, and N is a number of teeth. UPPER GEAR 11 LOWER GEAR 12 Dp 13.8 (mm) 13.8 (mm) d r 13.05 (mm) 12.45 (mm) m 0.3 0.3 N 46 46 Figure 3 also shows a width C of the groove 13 in the upper gear 11 and a diameter d c at which a standard involute tooth profile 11c and a straight tooth profile 11d merges (and from which the groove 13 is formed by a straight line). In this example, the value of "C" is 0.4 mm and the value of d c is 13.5 mm. It should be noted that the number of teeth thereof is large with respect to the size of the upper gear 11 and the provision of the grooves 13 in this condition.

Claims: An inked ribbon cassette comprising: ink supply means (6, 16) having ink absorbed therein; a first rotatable gear (11) having teeth (11a) and bottom lands (11b) between adjacent teeth (11a), arranged in contact with the ink supply means (6, 16); a second rotatable gear (12) arranged in engagement with the first gear (11); and, an ink ribbon (1) pinched between the first (11) and the second (12) gears and driven along a path by the rotation of the first (11) and the second (12) gears; characterized in that at least one groove (13) is arranged in the first gear (11) for containing ink when an excess of ink is transferred from the ink supply means (6, 16) to the first gear (11), wherein the groove (13) is provided by increasing the depth of the bottom lands (11b) between adjacent teeth (11a), to a depth greater than that of a standard gear. An inked ribbon cassette according to claim 1, wherein the depth of the groove (13) of the first gear is within a range from 0.5 to 1.5 times the depth of a standard gear. An inked ribbon cassette according to claim 1 or 2, wherein the second gear (12) has teeth (12a), and each of the teeth (11a) of the first gear (11) has a first part of its tooth profile adapted for engagement with the teeth (12a) of the second gear (12), and a second part of its tooth profile contiguous to the first part of its tooth profile, the second part of its tooth profile being arranged such that it does not substantially contact the teeth (12a) of the second gear (12) and the second part of its tooth profile constitutes a groove (13) for containing ink. An inked ribbon cassette according to claim 3, wherein the first part of the tooth profile of the first gear (11) comprises an involute curve and the second part of the tooth profile comprises a curve other than an involute curve. An inked ribbon cassette according to claim 3 or 4, wherein the second part of the tooth profile of the first gear (11) comprises a linear line. An inked ribbon cassette according to any one of the preceding claims, wherein the first gear (11) has teeth (11a) with a first depth and the second gear (12) has a teeth (12a) with a second depth, the first depth being greater than the second depth.

Inventors: KUBOTA MASAYUKI, OHTA HIROKI, SEKIOKA CHIAKI, SUGIE MASARU, SUZAWA HIROMICHI, KUBOTA, MASAYUKI, OHTA, HIROKI, SEKIOKA, CHIAKI, SUGIE, MASARU, SUZAWA, HIROMICHI
Applicants: FUJITSU ISOTEC LTD, FUJITSU ISOTEC LIMITED
Application year: 1991
Main classification: B41J31
IPC codes: B41J31, B41J32