Thermal ribbon cassette for thermal printing device

Abstract: The thermal ribbon cassette is attachable to a thermal printing apparatus, the cassette housing is formed by a forward section (13) attached to a rear wall (15) to define a chamber (17). A supply spool (25) is rotatively mounted to the forward section and the rear wall in the chamber. The supply spool has an ink transfer ribbon (48) continuously wrapped there around and a number of interrupters (47) continuously formed around the edge of the spool. A drag spring (45) is mounted to the rear wall and biased against the interrupters for providing a rotational drag force. The take-up spool (27) is rotatively mounted to the forward section and the rear wall in the chamber, the ink transfer ribbon has one end fixably mounted to the take-up spool and a portion extending through slots in the housing such that a portion of the ink transfer ribbon extends externally to said chamber. A locking gear (29) arrangement is provided for preventing rotation of the take-up spool except in a forward direction.

Description: The present invention relates to a thermal ribbon cassette for attachment to a thermal printing apparatus, comprising a housing formed by a forward section attached to a rear wall to define a chamber; a supply spool rotatably mounted on said forward section and said rear wall and located in said chamber, said supply spool having an ink transfer ribbon continuously wrapped therearound and a plurality of interrupters disposed therearound; a drag spring mounted to said rear wall and biased against said interrupters for providing a rotational drag force on said supply spool; and a take-up spool rotatably mounted on said forward section and said rear wall and located in said chamber; said ink transfer ribbon having one end fixedly mounted to said take-up spool and having a portion extending through slots in said housing such that a portion of said ink transfer ribbon extends external to said chamber. Such a cassette is disclosed in US 4 730 780 A. The cassette as defined above may be used in thermal printing digital postage meters. US Patent No. 5,300,953 A entitled THERMAL RIBBON CASSETTE TENSION CONTROL FOR A THERMAL POSTAGE METER describes a thermal printing cassette particularly suited for application with a digital thermal printing postage meter system. In an empirical evaluation of the thermal printing cassette described in US Patent No. 5,300,953 A it has been determined that thermal transfer ribbon cassettes exhibited non-linear torque requirements for the cassette drive system as described in US Patent No. 5,300,953 A over the change in radius of the cassette supply spool. This was considered disadvantageous. JP 63 283 976 A describes an ink ribbon cassette having a take-up spool whose rotation is prevented except in a forward direction, in which two gears, one of which is transversely displaced to engage a locking pin when the take-up spool is rotated in the reverse direction, are maintained in continuous engagement by a spring pressing said one gear against the other. It is an aim of the invention to provide a thermal ribbon cassette having means for preventing rotation of a take-up spook except in the forward direction, in which two gears, one of which is transversely displaced to engage a locking pin when a take-up spool of the cassette is rotated in the reverse direction, can be maintained in continuous engagement. According to the invention, there is provided a thermal ribbon cassette as initially defined, characterised bymeans for preventing rotation of said take-up spool except in a forward direction, said rotation preventing means comprising said rear wall having a locking pin in said chamber, a first gear rotatably and transversely mounted in said chamber, said take-up spool having a second gear formed thereon in constant mesh with said first gear such that rotation of said take-up spool in the forward direction causes said first gear to transversely displace away from said locking pin and such that rotation of said take-up spool in a reverse direction causes said first gear to engage said locking pin; and a guide formed on said rear wall and arranged for acting on said first gear, for maintaining the same in continuous engagement with said second gear. Two support posts may be formed on the internal surface of the backing wall for securing the drag leaf spring in the area of the supply spool for engaging a continuous series of the interrupters formed on the supply spool to provide a constant drag to the supply spool. Also, a locking leaf spring may be secured between two other support posts which is located to intrude between two adjacent interrupters to prevent rotation of the supply spool. An aperture, aligned to the locking spring, will receive a release pin when the cassette is placed in position on a printing apparatus, to deflect the locking spring away from the interrupters allowing the supply spool to rotate. It will be appreciated that the thermal ribbon cassette defined above can provide an improved thermal transfer ribbon having a simpler construction whereby a more linear torque response can be obtained as the radius of the supply spool varies. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an exploded view of an example of a thermal ribbon cassette in accordance with the present invention; Figure 2 is a front view of the thermal ribbon cassette of Figure 1; Figure 3 is a sectional view of the thermal ribbon cassette along the line 3-3 of Figure 2; and Figure 4 is a frontal view of thermal ribbon cassette drag and locking mechanism and a sectional view of the supply and take-up spools. Referring to the figures, the thermal ribbon cassette, generally indicated by 11, is comprised of a housing having a formed forward section 13 and a formed rear wall section 15 which define a chamber 17. The interior of the rear wall section 15 includes formed hubs 21 and 23 for rotatively supporting a supply spool 25 and a take-up spool 27, respectively. Formed on the interior wall of the rear wall section 15 is a hub 26 which carries a locking gear 29. The locking gear 29 is positioned around the hub 26 to receive the hub 26 within an oversized aperture 31. As a result the locking gear 29 can rotate around the hub 26 and transversely float relative to the hub. The motion of the locking gear 29 causes the locking gear 29 to be positioned in a first position which engages a formed locking pin 33 or a second position which disengages the locking gear 29 from the locking pin 33. The locking gear 29 is maintained in continuous engagement with a gear 35 formed on the take-up spool 27, by a guide 75 formed on the rear wall section 15 and arranged for acting on the locking gear 29. When the spool 27 is rotated in the forward direction, the locking gear 29 is caused by gear 35 to transversely displace to be disengaged from the locking pin 33. However, if the take-up spool 27 is rotated in the reverse direction, the locking gear 29 is brought into engaging contact with the locking pin 33 which, because of engagement between gear 29 and 35, prevents the take-up spool 27 from rotating in the reverse direction. Formed on the internal surface of the backing wall are two securing posts 41 and 43 for securing a drag leaf spring 45 in the area of the hub 21. The drag leaf spring 45 is positioned between the post 41 and 43 such that one end of the drag leaf spring 45 is biased to engage interrupters 47 which are continously formed around the base of the supply spool 25. The interaction between the interrupters 47 and the leaf spring 45 provide a constant drag to the supply spool 25. The drag force prevents the unraveling of the thermal transfer tape 48 secured around the supply spool 25 by any suitable means. Also secured between two other formed securing posts 51 and 53 is a locking spring 55. The locking leaf spring 55 is secured between the posts 51 and 53 in such a way as to cause one end of the locking leaf spring 55 to intrude between the two adjacent interrupters 47, thereby preventing rotation of the supply spool 25. Aligned to the locking leaf spring 55 is an aperture 57 which when the cassette is placed in position will receive a release pin 59 which will deflect the locking leaf spring 55 away from and out from between the interrupters 47. When assembled, the cassette 11, the thermal transfer ribbon 48 is secured around the supply spool 25 utilizing any suitable conventional method, and the outer end of the ribbon 48 is secured to the take-up spool 27 by any suitable conventional method. The leaf springs 45 and 55 are then positioned between respective posts 41, 43 and 51, 53. The supply spool 25 is then positioned on the hub 21 such that the interrupters 47 traverse through a formed channel 61, and the drag spring 45 and locking springs are positioned relative to the interrupters 47 as described. The gear 29 and the gear 35 are located to be in constant mesh with each other. The forward section 13 and a formed rear wall section 15 are then secured together by any suitable means sucy by screws threadably extending through post 63-63', 64-64', 65-65' and 66-66' locating the spools 25 and 27 in the defined chamber 17. The thermal ribbon 48 is positioned such that a portion of the thermal ribbon 48 extends through slots 71 and 73 to enable a portion of the thermal ribbon to be outward of the cassette. The rear wall section 15 includes an aperture 70 formed therein to allow the introduction of a sensor (not shown).

Claims: A thermal ribbon cassette (11) for attachment to a thermal printing apparatus, comprising: a housing formed by a forward section (13) attached to a rear wall (15) to define a chamber (17); a supply spool (25) rotatably mounted on said forward section (13) and said rear wall (15) and located in said chamber (17), said supply spool having an ink transfer ribbon (48) continuously wrapped therearound and a plurality of interrupters (47) disposed therearound; a drag spring (45) mounted to said rear wall (15) and biased against said interrupters (47) for providing a rotational drag force on said supply spool (25); and a take-up spool (27) rotatably mounted on said forward section (13) and said rear wall (15) and located in said chamber (17); said ink transfer ribbon (48) having one end fixedly mounted to said take-up spool (27) and having a portion extending through slots (71,73) in said housing such that a portion of said ink transfer ribbon (48) extends external to said chamber (17); characterised by means (29,33,35) for preventing rotation of said take-up spool (27) except in a forward direction, said rotation preventing means comprising said rear wall having a locking pin (33) in said chamber (17), a first gear (29) rotatably and transversely mounted in said chamber (17), said take-up spool (27) having a second gear (35) formed thereon in constant mesh with said first gear (29) such that rotation of said take-up spool (27) in the forward direction causes said first gear (29) to transversely displace away from said locking pin (33) and such that rotation of said take-up spool (27) in a reverse direction causes said first gear (29) to engage said locking pin (33); and a guide (75) formed on said rear wall and arranged for acting on said first gear (29), for maintaining the same in continuous engagement with said second gear (35). A thermal ribbon cassette as claimed in Claim 1, further comprising locking means for preventing rotation of said supply spool (25) unless said thermal ribbon cassette (11) is attached to said printing apparatus. A thermal ribbon cassette as claimed in Claim 2, wherein said locking means comprises a leaf spring (55) fixably mounted at a point along its length such that one end of said leaf spring (55) is interposed between adjacent interrupters (47), said rear wall (15) having an aperture (57) located in the proximity of said leaf spring (55) such that a release pin (59) formed on said printing apparatus when projected in said aperture (57) causes said leaf spring (55) to deflect causing said one end of said leaf spring (55) to displace away from said interrupters (47) of said supply spool (25). Thermal printing apparatus comprising a thermal ribbon cassette according to any one of the preceding claims. A digital postage meter comprising thermal printing apparatus according to Claim 4.

Inventors: MANNA ROBERT E, MANNA, ROBERT E.
Applicants: PITNEY BOWES INC, PITNEY BOWES, INC.
Application year: 1995
Main classification: B41J33
IPC codes: B41J33