An ink jet printer mechanism is a non-impact printing device which forms characters and other images ejecting ink droplets, in a controllable manner, from a print head. The ink jet mechanisms can be used in different devices, such as printers, plotters, facsimile machines, copiers and the like. For the sake of convenience reference shall hereinafter be made solely to large format ink jet printers or plotters, to illustrate the concepts of the present invention.
The printhead of a machine of the kind mentioned ejects ink through multiple nozzles as minuscule droplets, which "fly" over a short space and strike a printing media. Different nozzles are used for different colours. Ink jet printers usually print within a range of 180 to 2400 or more dots per inch. The ink thus deposited on the media is immediately dried after being deposited to form the desired printed images.
There are several types of ink jet printheads, for example, thermal print heads and piezoelectric ones. By way of example, in a thermal ink jet printhead, the ink droplets are ejected from individual nozzles by localized heating. Each of the nozzles has a small heating element. An electric current is made to pass through the element to heat it. This causes a tiny volume of ink to be heated by the heating element and vaporized instantaneously. On vaporization the ink is ejected through the nozzle. An exciter circuit is connected to individual heating elements to supply energy impulses and, in this way, to deposit in a controlled way droplets proceeding from associated individual nozzles onto the media. These exciter circuits respond to character generators or other imaging circuits to activate selected nozzles of the printhead to form the desired images on the media.
The ink nozzles customarily form part of an ink cartridge, disposable or otherwise, and the printhead of a printer of the kind to which the invention refers can have cartridges mounted for different ink colours, for example, cyan, magenta, yellow and black. These are arranged in the carriage in such a way that their nozzle sections are to be found very close to the surface of the support platen of the media, but separated therefrom, for the purpose of allowing the passage of said media between them. The carriage moves the printhead back and forth through the printing zone in one direction, called the scan direction, the location of the carriage in the printing zone being constantly controlled thanks to codifying means which control an actuating motor, for example a stepping motor.
In machines of this type there is generally used, as media, a band of paper of large width, for example D and E size, arranged in rolls of up to 90 m. in length. A 90 m. roll of E size paper can weigh almost 8 kg., so precautions should be taken at the time of handling it.
Such handling is even more difficult if we consider that the face of the media band on which the printing is performed is the external face and that a large part of the media used in a machine of the kind to which the invention refers have a coated surface which is sensitive to contact with the operator's hands, such that the operator should as much as possible avoid touching said printing surface during operation while, at the same time, keeping it clean and away from objects that could harm or scratch the media surface.
Moreover, for certain printing tasks the operator may have to utilize media in the form of large cut sheets, for example in A, B, C, D and E formats, as well as in formats utilized in Architecture. Such pre-cut sheets can easily spoil during handling, especially the larger sized ones. Care should be taken when removing the media from the packet and during its insertion and adjustment in the printer and, furthermore, care should be taken to touch the media only at the edges, to avoid harming or soiling the area on which the printing has to take place.
Once the printing task concludes, the machine automatically cuts the media (this does not occur in the case of printing on individual sheets) and the media, in one or the other case, is allowed to drop on to the output tray, with the possibility of the ink still not having dried completely with the resulting risks this entails, i.e., that the printed work may be spoilt during initial handling of the media.
In the prior art printing machines of different types are already known (impact or ink jet, for example) which are capable of printing both on continuous media and on cut sheets. A known machine of this type makes use of a "parking" facility of the continuous paper while operating with cut sheets fed manually.
For example, from U.S. Pat. No. 5,544,966 a printer is known which, provided with at least one tractor for continuous paper, allows the use of cut sheets to print while the continuous paper is "parked" outside the printing area. This machine achieves this interchangeable feeding by the provision of, at least, two different pathways for paper input (continuous and cut sheets), a third pathway being foreseeable for the input of continuous paper, likewise with the intervention of a tractor (the one cited or another additional one) for paper.
In the first place the printer to which said document of the prior art refers, is of small format and provided with tractors for the input of paper, which can be fed into it in continuous band, folded zig-zag, with the usual perforations in the margins or in the form of loose sheets, of small format.
In the second place, in said printer of the prior art is necessary to change the turning direction of the main roller to take the continuous medium towards a parking position, beyond the printing area and out of contact with said main roller prior to being able to feed cut sheets.
Large-format printers are also known, to allow parking of a print medium supplied starting from a roll and feeding in, in its place, a cut sheet to perform a printing operation on it. These prior art printers have two superimposed openings for input of the printing medium: one for the supply starting from a roll and another for the supply as cut sheet. However, the said two superimposed openings give way to a single advance path of the printer medium.
In machines of this type, when a user wishes to perform a printing task on a cut sheet in a printer loaded with continuous medium, the printer has to be requested, in the first place and by pressing a control panel button, to withdraw the continuous medium from the printing area, making it recede separating it from the main feeder roller and parking it, by a deviator which completely withdraws it from the main advance roller. In the second place, the user has to manually insert the medium in cut sheet form into the suitable opening, operation of which is bothersome, since the manipulation of said cut sheet is difficult, owing to its extreme width and, in particular, because of the close arrangement of said two input openings (which are, moreover, hidden from the operator's view), the most likely result being that the cut sheet will be fed into the wrong opening, already occupied by the parked continuous medium. Finally, by means of another push-button in the control panel, the user has to make the machine load the paper in sheet form until the printing area.
Moreover, the input path of the means in sheet form is practically mutual with that of feed in of the medium in cut sheet form and it is not possible to supply said cut sheet simultaneously with removal of the medium fed in starting from a roll.