Ink jet printer

Abstract: The ink jet printer comprises an entrance (11), a printing area (10) with a printhead (15) and an outlet (12). A rotating roller (23) and a back-up cunter-rollers (27) pressed resiliently against the rotating roller (23), and a fixed crosspiece (35) aligned with the circumference of the rotating roller (23), are mounted upstream of the printing area (10). A driving roller (41) provided with points (43) and cooperating with counter-rollers (46) is arranged at the outlet of the printing area and made rotate so as to tauten the sheet to be printed in the printing area (10). The rollers (23,41) and the fixed crosspiece (35) arranged beside the printhead define a reference level creating a predetermined gap (h) with the front surface (20) of the printhead. The latter is thus at a constant distance from the surface of the sheet to be printed, regardless of thickness of the material to be printed, without having to make any provision for an adjusting mechanism. This produces a very precise, reliable printer, at a low cost price.

Description: Field of the Invention - This invention concerns an ink jet printer comprising a printing area in which a printhead is designed to print a flat material moved according to a feeding direction from a printer entrance through the printing area to an outlet and means for adjusting the distance separating the front surface of the printhead from the said flat material. Related Technological Art - In numerous types of printer, and particularly in ink jet printers, it is important that the distance from the front surface of the printhead to the material to be printed is adjusted as precisely as possible, for example by having a constant value of 1.3 mm whatever the material used. However, thickness of the latter may differ considerably, which makes it necessary first and foremost to have measuring means to determine this thickness, and secondly adjusting mechanisms by means of which the printhead can be moved perpendicular to the material to be printed, or, alternately, the supports of the latter can be moved so as to always have the same relative distance. These means and mechanisms considerably increase the cost price of printers; in addition they are difficult to construct and are often lacking in precision. EP-A-0 519 495 and EP-A-0 334 548 disclose a printer according to the preamble of claim 1. In particular, the European Patent Application EP-A-0 519 495 discloses a gap regulating member having an upper surface guiding an ink jet head and a lower surface guiding a recording medium at a defined distance from the head, and the European Patent Application EP-A-0 334 548 discloses a skid-like spacer riding upon the printed surface in order to maintain a preselected spacing between the print head and the printed surface. However these solutions involve the disadvantage of having a mechanical contact between the regulating member or the spacer and the print head. Summary of the Invention - This invention is designed to overcome these drawbacks and to produce a printer where the printhead - material to be printed distance is perfectly constant and which is easy to construct at a moderate cost price. The invention is defined in the annexed set of claims. Accordingly, the support member(s) for the material to be printed is (are) arranged near the printhead and cooperate with the surface to be printed to form a reference level which does not change, regardless of thickness of the material to be printed, whether thin sheet, cardboard sheet, envelope, etc. Considering that it is not necessary to provide means for measuring thickness, nor mechanisms for adjusting height, construction of the printer is greatly simplified, cost price is reduced, operation is reliable and operating life longer. To advantage, the support member consists of at least a first rotating member (i.e. a continuous roller, a cylinder or a segmented roller) mounted on a shaft rotating around a fixed axis, or of a fixed crosspiece. Characteristics such as these grant precise and reliable construction and movement. Preferably, the support member cooperates with a second rotating member (i.e. again a continuous roller, a cylinder or a segmented roller), resiliently pressing against the support member, or with at least a first resilient pressure pad. According to a preferred embodiment, the printer comprises at least a third rotating member (i.e. again a continuous roller, a cylinder or a segmented roller), arranged downstream of the printhead and rotating around a second fixes axis, intended for cooperating with the surface of the flat material facing the printhead to define with the support member the said reference level, and cooperating with a fourth rotating member (i.e. again a continuous roller, a cylinder or a segmented roller), resiliently pressing against it, or with at least a second resilient pressure pad. This provides particularly reliable operation and a construction that is simple. To advantage, the first and the third rotating members are driven to rotate and the tangential speed on the circumference of the third rotating member is from 0.1 to 1.0% greater than that of the first rotating member. The material to be printed is thus perfectly taut and aligned, and its surface to be printed is at one with the reference level defined before, thereby ensuring printing of great quality and precision. The printer can advantageously comprise a second support member consisting of a fixed crosspiece arranged between the first rotating member and the printhead and whose surface facing the flat material is aligned with the circumference of the first rotating member so as to define the said reference level. These characteristics allow even greater printing quality to be achieved and additionally facilitate the paper entrance and outlet. Other advantages are apparent from the features described in the associated claims and from the description relating the invention in greater detail, in conjunction with a drawing schematically depicting one embodiment by way of example. BRIEF DESCRIPTION OF THE DRAWING The sole figure is a side view in partial section of this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the figure, the ink jet printer comprises a frame 14, a printing area 10 situated between an entrance 11 for the flat materials 18 to be printed and an outlet 12. In the printing area 10, a carriage 16 with a printhead 15 is slidingly fitted on a shaft 17 and rests with a projection 25 on a fixed crosspiece 26. It may be moved according to a direction perpendicular to a direction of feeding 19 of the flat materials 18. The latter may be sheets of paper ranging from a light to a heavy weight, cardboard paper, envelopes, etc., so their thickness may vary to a considerable extent. The ink jet printer further comprises a first support member 22 cooperating with a surface of the flat material 18 facing the printhead 15. This first support member 22 comprises a roller 23 (which can be a continuous cylinder or a segmented roller), the shaft 24 of which is rotatable around a fixed axis. Back-up counter-rollers 27 are mounted on pivoting levers 28 and resiliently pressed by springs 29 against the first support member 22 which is arranged in the upstream vicinity of the printhead 15. A first fixed support member 32 is arranged between the roller 23 and the printhead 15 and comprises a fixed crosspiece 35 in the form of a profiled part, the lower surface of which is aligned with the circumference of the roller 23. The pivoting levers 28 are provided at their top part with a blade of a plastic material 36, for example Mylar™, 0.12 mm thick. The blade 36 is attached to the lever 28 and presses resiliently with a distal part against a surface of the flat material 18 opposite to the surface to be printed, so as to press the flat material 18 against the fixed crosspiece 35. The fixed crosspiece 35 and the blade 36 thus ensure in combination precise alignment during introduction of the flat material 18, and also that the material 18 is held in position at page bottom, when the material 18 is no longer held by the roller 23 and the counter-rollers 27. The printer comprises downstream of the printhead 15 a mechanism 40 intended for tautening the material 18 to be printed in the printing area 10. The mechanism 40 comprises a roller 41, arranged on a shaft 42 rotatable around a fixed axis. The roller 41 is fitted with fine points 43 intended for cooperating with the flat material 18. Counter-rollers 46 are resiliently pressed by springs 47 against the roller 41. The latter and the roller 23 are made rotate by a motor not shown. The tangential displacement speed of the roller 41 is slightly greater than that of the roller 23 so that the material 18 is tautened in the printing area. A tangential speed difference of between 0.1 and 1.0% is particularly advantageous. The flat material 18 is introduced through the entrance 11 where it slides on a surface 50 of the frame 14, and where it is guided by a guiding element 51 before being gripped between the roller 23 and the counter-rollers 27. The upper surface of the flat material 18 to be printed thereafter always adopts the same position and height with respect to the printhead 15, regardless of the thickness of the material 18, in order to define a reference level creating a predetermined gap h with the front surface 20 of the printhead 15. The position of the counter-rollers 27 consequently varies in function of thickness of the flat material 18. The flat material 18 is then pressed by the plastic blade 36 against the fixed crosspiece 35, perfectly aligned with the circumference of the roller 23. During introduction, the flat material 18 is thus guided by the frist support member 22 and the first fixed support member 32 until it comes between the roller 41 and the counter-rollers 46, in order to be tautened in the printing area 10. The gap of distance h between the surface of the flat material 18 to be printed and the front surface 20 of the printhead 15 is also constant for all the materials to be printed, however thick they may be. This perfectly adjusted gap is obtained by the support members 22, 32 and the roller 41 and through the effect of the tension exerted on the flat material 18 in the printing area 10. It is clear that the embodiment described in the foregoing possesses no limiting traits and that all the changes desired may be made to the interior of the frame as defined in claim 1. In particular, the rotating members 23, 27, 41 and 46 could consist of continuous rollers or cylinders or discontinuous rollers arranged on a common shaft. The roller 23 could be replaced by a fixed support in the form of a crosspiece. The rollers 23 and 41 need not necessarily be driven; the printer in this case would comprise additional driving members. The rollers 27 and 46 could be replaced by resilient support pads. The printhead 15 and fixed support members could be arranged under the material 18 to be printed, in which case printing would take place upwards. Instead of being horizontal, the reference level could be inclined, or even vertical.

Claims: An ink jet printer comprising: a printing area (10) wherein a printhead (15) is liable to print a flat material (18) moved according to a feeding direction (19) from an entrance (11) of the printer through the printing area (10) to an outlet (12); adjusting means for adjusting a gap (h) separating a front surface (20) of the printhead from said flat material (18), said adjusting means comprising a support member (22, 32) cooperating with a surface of the flat material (18) facing the printhead (15) in order to define a reference level creating the predetermined gap (h) with the front surface (20) of the printhead (15); and a mechanism (40) for tautening the flat material (18) in the printing area (10) so as to position it in a plane passing through the said reference level, characterized in that said support member comprises a first roller (23) rotatable around a first fixed axis, and in that said mechanism for tautening comprises a second roller (41) rotatable around a second fixed axis, said first roller, said second roller and said printhead being located on the same side of said flat material, whereby said first axis and said second axis are at a fixed position with respect to said printhead (15) and said gap (h) remains constant for all materials to be printed. A printer according to claim 1, characterized in that said first roller (23) is fitted on a shaft (24) rotatable around said first axis. A printer according to claim 1, characterized in that said support member (32) comprises a fixed crosspiece (35). A printer according to claim 3, characterized in that it comprises an elastic blade (36) arranged opposite the fixed crosspiece (35) so as to press the flat material (18) against the fixed crosspiece (35). A printer according to claim 2, characterized in that said support member (22) cooperates with a first rotating member (27) resiliently pressed against the support member (22). A printer according to claim 2, characterized in that said support member (22) cooperates with a resilient support pad. A printer according to any one of the previous claims, characterized in that said second roller (41) is arranged downstream of the printhead (15), is fitted on a shaft (42) rotatable around a fixed axis, is provided for cooperating with the surface of the flat material (18) facing the printhead (15) in order to define with said first support member (22) said reference level, and cooperates with a second rotating member (46) resiliently pressed against it. A printer according to any one of the previous claims, characterized in that said second roller (41) is arranged downstream of the printhead (15), is fitted on a shaft (42) rotatable around a fixed axis, is provided for cooperating with the surface of the flat material (18) facing the printhead (15) in order to define with said first support member (22) said reference level, and cooperates with a resilient support pad. A printer according to claim 7 or 8, characterized in that said second roller (41) is made rotate by a driving mechanism and is provided on its circumference with fine points (43) cooperating with the flat material (18), so as to constitute the mechanism (40) designed to tauten the flat material (18) in the printing area. A printer according to claim 7 or 8, characterized in that the first roller (23) and the second roller (41) are made rotate and that a tangential speed on the circumference of said second roller (41) is between 0.1 and 1.0% greater than a tangential speed on the circumference of the first roller (23).

Inventors: BIZZINI CHRISTOPHE, TABASSO ALAIN, ZOGANAS GEORGES, BIZZINI, CHRISTOPHE, TABASSO, ALAIN, ZOGANAS, GEORGES
Applicants: OLIVETTI TECNOST, OLIVETTI TECNOST S.P.A.
Application year: 1997
Main classification: B41J25
IPC codes: B41J25, B41J2, B41J13, B41J11