INK METERING DEVICE AND INK JET PRINTHEAD PROVIDED WITH SUCH AN INK METERING DEVICE

Abstract: An ink metering device for an ink jet printhead comprises a number of joined-together plates (21, 22) and an actuator. At least one ink supply, an internal filter element (23), one or more nozzles (25), an ink channel (26-27) from the ink supply to the said nozzle or nozzles (25) are provided in the plates. According to the invention, the inlet side of the filter element (23) and the outlet side of the nozzles (25) are provided, at a distance from one another, in the same plate (21).

Description: Short title: Ink metering device and ink jet printhead provided with such an ink metering device. Ink metering device for an ink jet printhead, which device comprises an assembly of joined-together plates and an actuator, a diaphragm plate of the assembly comprising an internal filter element and one or more nozzles arranged at a distance therefrom, and the assembly of joined-together plates furthermore being provided with an ink supply and an ink channel from the ink supply to the one or more nozzles. An ink metering unit of this kind, in particular a method for fabricating an ink jet printhead having an integral filter, is known from the United States patent 5,141,596. This known ink jet printhead comprises a channel plate with internal filter, which filter is formed by openings in the top surface of the channel plate. The filter openings open out into a recess which forms an ink reservoir. This ink reservoir is connected to nozzles via channels. The nozzles are situated in a front surface of the channel plate. Furthermore, the printhead comprises a heating plate and, if desired, a thick film layer provided with a pattern. Etching techniques, in particular anisotropic etching, are used to produce the channel plate, and an etch stop layer is required, which layer is formed by implantation of boron ions. The various components of the channel plate, namely integral filter and nozzles, cannot be produced simultaneously, but rather have to be made successively. Another embodiment of an ink metering unit is known from EP-A-0, 678, 387. In this known ink metering unit too, a filter and nozzles are arranged at a distance from one another in the same plate of an assembly of plates . The nozzles and the openings in the filter are formed by etching recesses and grooves in the surface of the plate which are covered by a cover plate. The described structure of grooves and further components can be produced in a single step by means of anisotropic etching. Yet another ink metering unit is known from United States patent 5,489,930. This known ink metering unit - 2 - comprises a number of assembled plates, whic^-J-'comprise a plate with one or more nozzles for spraying an ink jet or a jet of small ink droplets onto a substrate which is to be printed on, an ink source for supplying ink, as well as an ink flow path from the ink source to the nozzles. A filter element is integrated in this known ink metering unit, which filter element comprises two plates which are each provided with small openings and are aligned in such a manner that the openings only partially overlap one another. A metering device of this kind is used in an ink jet printhead which, in addition to this device, comprises a charging electrode for charging the ink drops, as well as a pair of deflecting electrodes for deflecting the charged ink drops, and a drop collector for collecting drops which are not to reach the substrate to be printed on. In still further metering devices for ink printheads which are known in the prior art, a tapering channel is formed in their housing. A piece of porous filter material which filters the incoming ink is pressed into the wide side of this channel. It is necessary to filter ink since contaminants in the ink, as well as dirt from the assembly comprising the printhead and metering device, may block the nozzles. Furthermore, dirt may have an adverse effect on the spraying direction. Both in this known device with porous filter material and the device according to the abovementioned United States patent 5,489,930, it is impossible, or at least not fully possible, to check that the assembled device is clean, because, on the one hand, the porous filter material covers a number of parts of the ink channel and thus makes inspection impossible and, on the other hand, because the integrated filter layers are disposed between various other layers and thus make the filter openings invisible. Also, the nature of the porous filter material means that it is impossible to be certain of the maximum dimensions of particles allowed through. Also, additional contamination may arise as a result of the positioning and presence of a filter of this nature. Furthermore, owing to the large number of components, these known devices are complicated and time- - 3 - consuming to assemble. In addition, the known devices have structural drawbacks as a result of the selected arrangement of internal filter elements and the one or more nozzles. The ink metering device cannot easily be accommodated in the housing of the ink jet printhead, because the position of the connections for the ink supply and the position of the nozzles do not allow this. It is thus impossible to obtain a compact structure of an ink jet printhead with ink metering device. One object of the present invention is to provide an ink metering device for an ink jet printhead in which the position of the ink supply and the nozzles is such that the ink metering device can easily be accommodated in the housing of an ink jet printhead. A further object of the present invention is to provide an ink metering device for an ink jet printhead in which the purity and cleanness after assembly and during maintenance are easier to check and ensure. A further object of the invention is to reduce the number of plates to be assembled when producing an ink metering device of this nature. The ink metering device of the type described above, according to the invention, is characterized in that the inlet side of the filter element and the outlet side of the one or more nozzles are provided, at a distance from one another, in the same face of the diaphragm plate. By providing the inlet side of the filter element and the outlet side of the nozzle in the same face (front face) of the ink metering device, it is possible for all connections to the ink metering unit, such as hoses for supplying ink and the like, to be on the same side of the ink metering unit as the nozzles. The result of this is that the ink metering unit can easily be positioned in the housing of the ink jet printhead. The nozzles or nozzle are always accommodated in the outer- most flat plate, since the ink has to exit through this plate. In the ink metering device according to the invention, the filter element is also accommodated in the said outermost plate, so that this element is easy to inspect. A further advantage is that the number of manufacturing steps is - 4 - reduced by the fact that the filter element and the nozzles are produced in the same plate, simultaneously and using the same techniques . According to a preferred embodiment of the ink metering device, this device is composed of 2 plates. In this case, the ink metering device comprises a first plate, which is provided with the filter element and the nozzle or nozzles, as well as a second plate, which contains the ink channel structure which connects the filter element and the nozzle or nozzles to the first plate. The filter element preferably comprises a number of small passage openings or slots, so that their dimensions can easily be checked visually from the outside using light. To achieve a good filtering action, these openings and slots are advantageously arranged in a defined pattern. Non-limiting examples of such patterns comprise a circular part with a plurality of longitudinal slots of different lengths, if desired with different orientations, round holes of equal or unequal sizes, or slots of equal lengths or slots positioned in one or more circles. According to a preferred embodiment of the metering device according to the invention, the nozzles and the filter element are provided in the diaphragm plate, which is attached to a support plate, in which support plate an ink channel is provided which connects the filter element and the nozzles to one another. This channel may be arranged as a surface structure in the support plate, making it easier to check and clean. Since some techniques are unable to produce the openings or grooves in the filter element with sufficient fineness, the support plate advantageously comprises a filter chamber which is aligned with the filter element and in which further filtering takes place. According to a particular embodiment, the filter chamber comprises a first subchamber, which is in communication with the filter element of the diaphragm plate, and a second subchamber, which opens out into the ink channel, as well as a partition between these chambers, provided with passage openings for ink. Advantageously, the - 5 - second subchamber surrounds the first subchamber. Furthermore, the partition advantageously comprises a partition wall in which the passage openings are provided in the top side (the side facing towards the diaphragm plate) , i.e., when the support plate is considered on its own, a number of small grooves. In order to obtain a sufficiently large flow-through surface, the wall is an undulating wall, i.e. wavy, toothed, provided with rectangular projections, etc., in which a large number of passage openings are provided. The invention also relates to an ink jet printhead which is provided with an ink metering device according to the invention. One of the additional advantages of the device according to the invention is that the ink supply can easily be accommodated in the housing of the ink jet printhead - for the filtering takes place in the plate containing nozzles - so that no additional lines (hoses) are required for it and all the connections to the ink metering unit can be provided on one side. As a result of which the ink metering device can easily be positioned in the housing of the printhead. The metering device and the printhead according to the invention can be produced in a customary way by joining together separate plates in which the various components are formed. These plates may themselves also be produced using standard techniques, such as electroforming, etching, etc. The invention is explained below with reference to the drawing, in which: Fig. 1 shows an ink metering unit according to the prior art ; Fig. 2 shows a diagrammatic, perspective view of an embodiment of an ink metering device according to the invention; Fig. 3 shows three structures of a first filter element which can be used in the device according to the invention; Fig. 4 shows a preferred embodiment of an additional filter element which can be used in the device according to the invention; Fig. 5 shows a detail of the filter element in - 6 - accordance with Fig. 4; and Fig. 6 shows an embodiment of a printhead according to the invention. Fig. 1 shows an embodiment of an ink metering device according to the prior art which is known per se . This device comprises a housing 1 with a tapering ink channel 2. A piece of porous material 3 is positioned in the wide side of the ink channel 2. This material functions as a filter for incoming ink. A support 4, in which there is a groove 5, is adhesively bonded to the other end of the channel 2. This groove 5 is covered with a nickel diaphragm 6 in which a large number of nozzles are arranged in a row. One or more actuators 7 is/are attached to the opposite side of the support 4. With the aid of these actuators 7, the ink jets supplied are made to vibrate and are thus broken up into a series of ink drops. As has already been mentioned above, it is not possible to check the functioning of the internal filter 3 in this known metering device, and neither is the device including filter easy to clean. An embodiment of an ink metering device according to the invention is shown in Fig. 2. The ink metering device - denoted overall by reference numeral 20 - comprises a diaphragm plate 21 and a support plate 22. The diaphragm plate 21 is provided with a filter element 23 in the form of a number of continuous openings 24 which are grouped together in a circular area. Furthermore, the diaphragm plate 21 comprises a series of nozzles 25 which are positioned at a distance from the filter element 23. The inlet side of the filter element 23 and the outlet side of the nozzles 25 are situated on the same side, i.e. the front face, of the diaphragm plate 21, so that an ink supply (not shown) can easily be connected to the filter element 23. Ink which passes through the openings 24 flows to the nozzles 25 via a channel structure in the support plate 22. This channel structure is a surface structure, i.e. it does not comprise any through openings. The aligned channel structure comprises a filter chamber 26 which is connected to the openings 24 and in which a second filtering step is carried out. An example thereof is explained in more detail below with reference to - 7 - Figs. 4 and 5. The filter chamber 26 is in communication with the nozzles 25 via a channel 27, a further chamber 28 and a second channel 29. This means that the filter element 23 of the diaphragm plate 21 is positioned above the filter chamber 26 of the support plate 22 and the nozzles 25 are positioned above the second channel 29. The remaining parts of the channel structure in the support plate 22 are covered by the diaphragm plate 21. This positioning of the plates can be achieved in a simple manner. An actuator (not shown) is disposed at the level of the second chamber 28 in order to cause the ink to vibrate. The presence of chamber 28 provides a large surface area for this operation. If the actuator is sufficiently strong, there is no need for the chamber 28 to be provided. Fig. 3 shows three examples of different patterns for the filter element 23. In Fig. 3a, the filter element is composed of elongate slots 31 of unequal lengths and different orientations, which are disposed in a circular area 32. Fig. 3b shows radially directed slots 33 which are disposed on the circumference of an imaginary circle. The embodiment shown in Fig. 3c shows radially directed slots 34 and 35 which are disposed in two concentric circles. The width of the slots 31 lies, for example, in the range from 1- 25 μm. Figs. 4 and 5 show the fine filter chamber 26 in more detail. The filter chamber 26 comprises a first subchamber 41 and a second subchamber 42. The first chamber 41 is in communication with the coarse filter element 23, while the second filter chamber 42 opens out into the channel 27. The two filter chambers are separated by partition wall 43, an "undulating" wall section 44 being provided in the top side. Small openings 45 (1-5 μm) , which carry out the actual fine filtering action, are provided in this wall section 44. As can be seen from these figures, the entire structure is built up from the bottom upwards, so that it is easy to check and clean. It is easy to visually determine the dimensions of the openings in the coarse filter 23 and the fine filter 26. It will be understood that the metering device according to the invention is in no way limited to the - 8 - embodiment shown. The presence of the second chamber 28 is not required, as has already been indicated above, so that the channel structure in the support plate comprises a continuous groove to which a diaphragm plate and an actuator are adhesively bonded. Also, a straight channel structure is not necessary. Other forms of the chambers in the support plate include rectangular, square, elliptical, etc. Fig. 6 shows an embodiment of an ink printhead according to the invention which comprises an ink metering device 61 according to the invention. For each ink jet 62 of the device 61, there is also a charging electrode 63 for charging the ink jet 62 which has been broken up into drops, depending on the printing pattern which is to be printed, and there is also a pair of deflecting electrodes 64 for each printhead, in order to deflect charged ink drops and position the ink drops on a substrate which is not shown. A drop collector 65 collects drops which are not to be used for printing.

Claims: - 9 - CLAIMS 1. Ink metering device for an ink jet printhead, which device comprises an assembly of joined-together plates and an actuator, a diaphragm plate of the assembly comprising an internal filter element and one or more nozzles arranged at a distance therefrom, and the assembly of joined-together plates furthermore being provided with an ink supply and an ink channel from the ink supply to the one or more nozzles, characterized in that the inlet side of the filter element (23) and the outlet side of the one or more nozzles (25) are provided, at a distance from one another, in the same face of the diaphragm plate (21) . 2. Ink metering device according to claim 1, characterized in that the filter element (23) comprises a number of small openings (24) or slots (31; 33; 34, 35) . 3. Ink metering device according to claim 2, characterized in that the said openings or grooves are arranged in a defined pattern. 4. Ink metering device according to one of the preceding claims, characterized in that the ink metering device is composed of two plates. 5. Ink metering device according to one of the preceding claims, characterized in that the diaphragm plate (21) is attached to a support plate (22) , in which support plate (22) the ink channel (26-29) is provided. 6. Ink metering device according to claim 5, characterized in that the support plate (22) comprises an ink chamber (26) which is aligned with the said filter element (23) and is in communication, via the said ink channel (27- 29) , with the said nozzles (25) . 7. Ink metering device according to claim 6, characterized in that the ink chamber (26) comprises a first subchamber (41) which is in communication with the filter element (23) of the diaphragm plate (21) , as well as a second subchamber (42) which opens out into the said ink channel (27-29) , and a partition which is provided with passage openings for the passage of ink from the first subchamber to the second subchamber (45) . - 10 - 8. Ink metering device according to claim 7, characterized in that the second subchamber (42) surrounds the first subchamber (41) . 9. Ink metering device according to claim 7 or 8 , characterized in that the partition comprises a partition wall (43, 44) which, on the side facing towards the diaphragm plate, is provided with the said passage openings (45) . 10. Ink metering device according to one of the preceding claims 7-9, characterized in that the partition wall (43, 44) has an undulating form. 11. Ink jet printhead provided with an ink metering device according to one of the preceding claims .

Inventors: KRUIJS FRANCISCUS WILHELMUS JO, VAN DE KRUIJS, FRANCISCUS, WILHELMUS, JOHANNA, GERARDUS
Applicants: KRUIJS FRANCISCUS WILHELMUS JO, STORK DIGITAL IMAGING B V, STORK DIGITAL IMAGING B.V., VAN DE KRUIJS, FRANCISCUS, WILHELMUS, JOHANNA, GERARDUS
Application year: 1999
Main classification: B41J2
IPC codes: B41J2