Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-07-06
2002-10-22
Gordon, Raquel (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
Reexamination Certificate
active
06467901
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for printing a print carrier in a printing region using a stationary ink-jet printing head and with a print carrier moved downstream in the Z-direction of the printing region. The invention is employed in fully electronic digital printing devices in which recording carriers have variable dimensions (i.e. thickness and size). It is particularly suitable for use in voucher printers, franking machines, addressing machines and other mail processing appliances with a transport and printing device for mail items.
German Patent DE 25 01 035 C2 discloses a printing drum with a single ink-jet printing head. The printing drum has a transport function and a printing function, and therefore the ink-jet printing head cannot print the entire printing region. Variable information can be printed only by the ink-jet printing head. Regions in which the printing information cannot, in principle, be changed therefore remain in the printing image.
Modern franking machines, such as, for example, the thermotransfer franking machine known from U.S. Pat. No. 4,746,234, employ fully electronic digital printing devices. It is consequently possible, in principle, to print any desired texts, codes and special characters in the franking-stamp printing region and any desired advertising block print or one assigned to a cost center. A franking machine, for example T1000 from the applicant Francotyp-Postalia AG & Co., is controlled by a microprocessor control surrounded by a secured housing which has an orifice for feeding a letter. Whenever a letter is fed, a mechanical letter sensor (microswitch) transmits a print demand signal to the microprocessor which generates a printing image and, after billing the mailing value to be franked, triggers printing. The franking imprint contains previously entered and stored mail information for transporting the letter.
U.S. Pat. No. 5,467,709 discloses a printing device for an ink-jet franking machine, a franking print being printed onto a mail item by an ink-jet printing head during approximately horizontal letter transport. For printing, the ink-jet printing head is disposed in a stationary manner in a recess behind a guide plate. A rotating transport belt serves as a transport device and is likewise disposed at the side of the guide plate. A back-pressure device with a plurality of rollers is disposed on the other side, opposite the guide plate, so that a fed mail item is clamped between the rollers of the back-pressure device and the rotating transport belt. However, the configuration cannot prevent the print carriers from running askew. Even an insufficiently tensioned transport belt or a not exactly parallel alignment of the axes of those rollers on which the transport belt rotates gives rise to the above-mentioned risk. Due to the multiplicity of rollers of the back-pressure device, the latter is dynamically redundant.
German Patent DE 196 05 015 C1, corresponding to U.S. Pat. No. 5,949,444, has already proposed a version of a printing device of a JETMAIL ink-jet franking machine of the applicant Francotyp-Postalia AG & Co., which, in the case of nonhorizontal approximately vertical letter transport, executes a franking print by an ink-jet printing head which is disposed in a stationary manner in a recess behind a guide plate. A rotating transport belt serves as a transport device, with pressure elements for the mail items (letters with a thickness of up to 20 mm, DIN B
4
format) or for franking strips that are configured to be capable of being glued onto packets of any thickness. The print carrier (letter, packet, franking strip) is clamped between the pressure element and the guide plate.
The transport and printing device is disposed in the base and is controlled by a meter. A trigger sensor for the printing process is disposed in the base, just in front of the ink-jet printing head recess, for detecting the start of a letter and cooperates with an incremental generator on the drive of the transport belt. By use of a transmitted-light barrier as a trigger sensor (Published, European Patent Application EP 0 901 108 A2), the leading edge of even especially thick mail items is detected unequivocally. Moreover, optical sensors for detecting the build-up of mail items are employed in the base of the JETMAIL. An automatic feed and a dynamic balance are disposed in the CONDORD franking system upstream of the JETMAIL franking machine, thus allowing genuine mixed-mail processing for mail items of widely differing formats, thicknesses and weights. At very high printing speeds, it becomes increasingly more difficult to print a stamping print of relatively high quality that allows mechanical evaluation with a high degree of reliability. A rotating transport belt should therefore have no stretching, even under mechanical and thermal load, and the pressure elements should not allow any slip during the transport of the mail items. Only transport and printing devices that are of complicated constructions and are cost-intensive have hitherto satisfied these requirements.
There have also already been proposed more simply constructed transport and drive devices without back-pressure device (German Patent DE 196 05 014 C1) or with a back-pressure device (International Patent Disclosure WO 99/44174) in the vicinity of the printing region of at least one ink-jet printing head. In International Patent Disclosure WO 99/44174, the latter is disposed downstream of a pair of draw-in rollers in the transport direction, the upper roller being driven and the lower back-pressure roller being sprung. A further pair of rollers downstream of the ink-jet printing head, near the ejection, likewise exerts a force on the print carrier. The printing region is at a distance from the force transmission region of one of the pairs of rollers of more than one radius of the respectively driven roller. Although, in principle, the printing information can be changed in all regions as a result of digital printing, the print is nevertheless of lower quality, the higher the selected transport speed. In particular, when two ink-jet printing heads are employed, an offset may occur in the printing image (correspondence error) along a printing length in the transport direction, thus making the mechanical evaluation of the printing image more difficult. The force action of the further pair of rollers downstream of the ink-jet printing head, near the ejection, leads to a different path length and therefore, in the case of two ink-jet printing heads offset to one another, to the correspondence error in the printing image. The print quality demanded within the framework of current programs of the mail service providers, for example the information-based Indicia program of the USPS, could therefore be achieved only at the expense of a low printing speed. Another disadvantage is the small thickness of the print carriers that can be printed by such a simply constructed printing device.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device for printing a print carrier which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which makes it possible, even at very high printing speeds, to have a print of higher quality. Printing is to take place directly onto print carriers that have a thickness of up to 10 mm.
With the foregoing and other objects in view there is provided, in accordance with the invention, a printing device containing a driven transport drum and a non-driven back-pressure device resilient in a Y-direction and disposed opposite the driven transport drum. The driven transport drum and the non-driven back-pressure device define a force transmission region there-between and exert a transport force on a print carrier in the force transmission region. An ink-jet printing head is disposed axially relative to the driven transport drum in an X-direction. The print carrier is printed on in a printing region by the ink-jet printing head and the print carrier
Francotyp-Postalia AG & Co. KG
Gordon Raquel
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
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