Stackable drop generator for an ink-jet printer

Abstract: A stackable drop generator for an ink-jet printer made up of a number of stackable elements (30, 40) in the form of flat plates each comprising a pressure chamber (31, 41), a supply chamber (32, 42) and a piezo-element (33, 43) for forming a pressure wave in the ink in the pressure chamber (31, 41), and in which the elements are so disposed on either side of a first element that the pressure chambers of said elements are not in line with the pressure chamber of the first element.

Description: The invention relates to a stackable drop generator for an ink-jet printer made up of a number of stackable elements each in the form of a single flat plate each comprising: a pressure chamber and an ink supply chamber communicating therewith, a piezo-element for forming a pressure wave in the ink in the pressure chamber, a nozzle with an inlet which leads into the pressure chamber and with an outlet through which ink drops can be ejected from the pressure chamber, openings which are in line with openings in each other element and through which fixing means can be disposed in order to enable the elements to be accurately stacked. A drop generator of this kind is known from U.S. Patent 4 385 304. The ink chambers of the adjacent elements are sealed by electrode plates of a thickness of about 0.075 mm. A seal of this thickness offers a good solution to preventing cross-talk for the pressure waves in two adjacent pressure chambers, but stack density decreases greatly as a result so that the resulting drop generator makes prints with a relatively low resolution. The object of the invention is to provide a stackable drop generator without these and other disadvantages. According to the invention this object is attained in a stackable drop generator in accordance with the preamble in that the elements are so disposed on either side of a first element that the pressure chambers of these elements are not in line with the pressure chamber of the first element, and in that the sidewalls of each element are used as a seal for the adjacent pressure chambers. Consequently, the pressure waves in a pressure chamber have no influence on the other pressure chambers, so that only very thin sealing plates if any, are required between the various elements and the drop generator stack density increases greatly as a result. In one embodiment of a stackable drop generator according to the invention, each group of identical elements comprises an ink supply chamber not communicating with a supply chamber of the elements of another group, each element of a group having at least one passage opening in line with the supply chamber or chambers of the elements of the other groups. Consequently, the resulting drop generator can spray inks of different colours simultaneously in order to produce coloured prints on a receiving sheet. These and other advantages will be explained hereinafter with reference to the accompanying drawings wherein: Fig. 1 illustrates an element for a drop generator according to the invention, Fig. 2 illustrates another element for a drop generator according to the invention, Fig. 3a shows two elements fixed on one another in a drop generator according to the invention, Fig. 3b is a side view of the elements of Fig. 3a, Fig. 4 shows other elements of a drop generator according to the invention, Figs. 5a and 5b diagrammatically illustrate a drop generator viewed in the direction of the nozzles, Fig. 6 shows another element of a drop generator according to the invention, Fig. 7 is a diagrammatic view in the direction of the nozzles of a drop generator according to the invention, and Fig. 8 shows elements for making colour prints. Referring to Fig. 1, an element 50 in the form of a flat metal plate measuring about 15 x 15 mm and 0.1 mm thick is provided with four openings 17. A supply chamber 52 and a pressure chamber 51 are also provided in this element. A narrow opening 56 is provided between the supply chamber 52 and the pressure chamber 51 to allow ink to flow from supply chamber 52 to pressure chamber 51. A recess in which a piezo-element 53 is secured by a glue connection is also provided in the element 50 in communication with the pressure chamber 51. The inlet of nozzle 55 leads into the pressure chamber 51. The piezo-element which is about 0.08 mm thick, has evaporation-applied electrodes (not shown) on both externally facing sides. One electrode is connected to element 50 and the other electrode has a thin connecting foil which is led out via cavity 57 in the element 50. At the places where the connecting foil is pressed against the electrode the foil is corrugated to some extent so that only a few places make contact. By stacking the elements and pressing them on one another the foil will form a kind of spring contact, the total thickness of the assembly made up of the piezo-element 53, electrodes and contact foils having a thickness which corresponds exactly to the thickness of the element 50. The application of voltage to the piezo-element 53 causes a pressure wave to form in known manner in the direction of arrow 54 in the ink present in the pressure chamber 51, so that a drop of ink is ejected through nozzle 55. The openings in the element 50 can be accurately formed by spark erosion. Nozzle 55 is formed by a channel disposed in one side of the element 50. The dimensions of this channel can be selected as required. The channel is preferably 50 µm deep. The channel forming the nozzle 55 may be provided both in the front and in the rear of the element. A channel of this kind is particularly easy to make and keep clean. Because not the entire thickness of the element is drilled, extra rigidity is obtained for the thin element 50. The opening 56 may have the same shape as the nozzle 55. Fig. 2 is a top plan view of an element 10 having approximately the same external dimensions and construction as element 50 in Fig. 1. Element 10 comprises an ink supply chamber 12 communicating with the pressure chamber 11 via an opening 16. The piezo-element 13 when actuated can in the manner described eject a drop of ink through the nozzle 15. To form a drop generator the element 10 is applied against an element 20 (Figs. 3a and 3b). Fig. 3b is a side view of Fig. 3a. The element 10 is situated beneath the element 20 in Fig. 3a. The element 10 is shown in broken lines. Fixing elements in the form of screws or the like are inserted through the openings 17. In this way the pressure chamber 11 is situated against the flat rear of element 20 and element 20 thus forms an ink-sealing side wall for the chambers 11 and 12 and for the nozzle 15. Similarly, the flat top of element 10 forms a seal for the chambers 21 and 22 of element 20. By stacking a large number of alternate elements 10 and 20, a stacked drop generator is obtained in which all the side edges of the chambers and the side edges of the nozzles are sealed off by the flat sides of the adjoining elements. The drop generator described is made up of two groups of identical elements (10 and 20), in which two elements of a group are always separated by an element of the other group. In order to be able to provide an entire group of elements 10 or 20 with ink, passage openings 18, 28 respectively are provided in elements 10 and 20 respectively. Thus all the pressure chambers 11 can be provided with ink via the side edges of the drop generator by way of supply chambers 12 and passage openings 28. Similarly, the pressure chambers 21 can be provided with ink by way of the supply chambers 22 and passage openings 18. To obtain an even better seal between the elements, a very thin foil (± 5 µm) can be provided between each two elements, with the openings 12, 18 or 22 and 28 being formed therein. Another method of obtaining a good seal is to punch out the chambers in the elements, after which small upright edges (of a size of about 10µm) are formed on either side of the element around the chambers by means of mould pressing. Sealing is obtained by locally exceeding the surface pressure. The lay-out of element 10 is so selected that element 20 is obtained by turning this element over. With this drop generator one group (type) of elements is sufficient, provided they are mounted in the correct direction. Since the piezo-elements 13, 23 and the pressure chambers 11, 21 nowhere overlap, minimum cross-talk occurs between the two pressure chambers 11, 21. It has, however, been found that the piezo-elements may overlap one another in order still to obtain good cross-talk suppression. A condition for this, however, is that the pressure chambers should not overlap, i.e. the pressure chambers of adjacent elements must be not in line. This feature has been used in a drop generator according to the invention made up of elements 30 and 40 as shown in Fig. 4. In this, a pressure chamber 31, nozzle 35, supply chamber 32, piezo-element 33 and passage opening 38 are provided in a first group of elements 30 as shown in the drawing. On analogy with Fig. 3a, this element is shown in broken lines beneath a second element 40 forming a part of a second group of elements 40. Element 40 also contains a supply chamber 42, pressure chamber 41, nozzle 45, piezo-element 43 and a passage opening 48. The piezo-elements 33 and 43 overlap, but the pressure chambers 31 and 41 do not overlap. Thus good cross-talk attenuation is obtained while the elements can be made separately smaller than, for example, the elements 10 and 20 in Figs. 2 and 3. It is also possible to give up this small reduction, for example, to enable a larger piezo-element 33, 43 to be provided in the elements, so that the pressure waves in the ink chamber can be larger or so that a lower control voltage can be used for an identical pressure wave. When stacked, the supply chambers 32 and 42 in Fig. 4 are separated from one another, for example to enable two colours of ink to be sprayed by the drop generator. This means that each group of identical elements contains an ink supply chamber which has no communication with a supply chamber of the elements of another group. Each element of a group then has passage openings which, after stacking, are in line with the supply chambers of the elements of another group. It is, of course, also possible to supply identical inks to these supply chambers. When only one colour of ink is to be sprayed, the lay-out of, for example, supply chamber 42 of element 40 can be so selected that when stacked with an element 30 it is exactly in line with the supply chamber 32 of the element 30. If two inks of different colours are to be sprayed with a stacked drop generator as shown in Fig. 4, then the coloured drops will not fall exactly on one another, but next to one another, on a sheet of paper moving past the nozzles. This is shown in Fig. 5a, in which a number of elements are disposed next to one another and which shows a front view of the nozzles. In the elements 30 and 40 the nozzles are all disposed on the right-hand side of the element. Beneath the row of elements the drops ar shown as obtained on a sheet of paper if ink 58 is supplied to elements 30 and ink 59 to elements 40. This is not an optimal result, particularly for producing mixed colours. Fig. 5b shows a better solution for this. Here the nozzles 35 in the elements 30 disposed on the right and the nozzles 45 in the elements 40 on the left. The drops from adjacent elements 30 and 40 will largely overlap (mixed drops). A disadvantage that occurs in these conditions is that the space between two mixed drops is increased. This disadvantage can be largely obviated by spraying larger drops. Fig. 6 shows another solution for making mixed drops. In this, two separate pressure chambers 61, 65, supply chambers 62, 66 and piezo-elements 63, 67, are provided in an element 60. The nozzle 64 has a channel on the right of the elements 60 and nozzle 68 has a channel on the left of element 60. The mixed drops sprayed with this element will have approximately the appearance shown in Fig. 5b. When element 60 (Fig. 7) is stacked with an element 70 of comparable construction but in which the pressure chambers are at a lower level than the pressure chambers 61, 65 in element 60, as is essential according to the invention, then, on analogy with Figs. 5a and 5b, good overlapping of the drops is obtained and the distance between the mixed drops is also greatly reduced in comparison with Fig. 5b. Fig. 8 shows two elements 72, 92 for making a stackable drop generator with which it is possible to produce full-colour prints. The element 72 of a first group of elements comprises four supply chambers 73-76, four pressure chambers 77-80, four piezo-elements 81-84 and four nozzles 85-88. Similarly, element 92 of a second group of elements comprises four supply chambers 93-96 which are exactly in line with the supply chambers 73-76 of element 72. Element 92 also comprises four pressure chambers 97-100, four piezo-elements 101-104, and four nozzles 105-108. According to the invention, the pressure chambers of two neighbouring elements 72 and 92 are not on the same line. To make full-colour prints, the supply chambers 73 and 93 are filled with ink in the color cyan, supply chambers 74 and 94 with magenta ink, supply chambers 75 and 95 with yellow ink and supply chambers 76 and 96 with black ink. The nozzles of each element 72, 92 are disposed on the right of the elements. They can also be offset per element, for example the nozzles, 85, 87 and 105, 107 may be disposed on the right and the nozzles 86, 88 and 106, 108 on the left. It is clear that an ink-jet printer provided with a stackable drop generator according to the invention must be so controlled as to give image-wise prints. For this purpose, a receiving sheet is taken past the drop generator at a uniform speed. The image signals originating, for example, from a document are converted into actuation signals for the various piezo-elements, so that the drops are ejected from the nozzles. Since the nozzles, as considered in the direction of transit of a receiving sheet, are situated consecutively in two or more rows, the image signal originating from one scan line on the document will in known manner be split into signals which are fed directly to the first row and signals which are fed to the second row with some delay. The delay can be produced easily by temporarily storing the signals in a shift register and feeding them at the correct time to the piezo-elements of the second row by means of clock signals derived from the movement of the receiving sheet. The invention is not limited to the embodiments described. The skilled addressee will be able to derive several variants therefrom, but they will all come under the scope of the following claims.

Claims: A stackable drop generator for an ink-jet printer made up of a number of stackable elements (30, 40) each in the form of a single flat plate each comprising: a pressure chamber (31, 41) and an ink supply chamber (32, 42) communicating therewith, a piezo-element (33, 43) for forming a pressure wave in the ink in the pressure chamber (31, 41), a nozzle (35, 45) with an inlet which leads into the pressure chamber (31, 41) and with an outlet through which ink drops can be ejected from the pressure chamber, openings (17) which are in line with openings (17) in each other element (30, 40) and through which fixing means can be disposed in order to enable the elements to be accurately stacked, characterised in that elements (30) are so disposed on either side of a first element (40) that the pressure chambers (35) of these elements (30) are not in line with the pressure chamber (45) of the first element (40), and in that the sidewalls of each element (30, 40) are used as a seal for the adjacent pressure chambers (45, 35). A stackable drop generator according to claim 1, characterised in that it is made up of a number of groups (n) of identical elements, in which two elements of a group at least are separated by an element of another group. A stackable drop generator according to claim 2, characterised in that each group of identical elements comprises an ink supply chamber (32) not communicating with a supply chamber (42) of the elements of another group, and in which each element of a group has at least one passage opening (38, 48) in line with the supply chamber or chambers of the elements of the other groups. A stackable drop generator according to claim 1, 2 or 3, characterised in that each element (60) comprises at least two separate pressure chambers (61, 65) piezo-elements (63, 67) and nozzles (64, 68). A stackable drop generator according to claim 1, 2, 3 or 4, characterised in that the nozzle (15, 25) is formed by a channel provided in one side of the element. A stackable drop generator according to any one of the preceding claims, characterised in that a thin insulating foil is disposed between two elements and has recesses for the openings, for the supply chambers and for the passage openings. A stackable drop generator according to any one of the preceding claims, characterised in that the elements are provided with upright edges around the chambers and sealing is obtained by the surface pressure being locally exceeded. An ink-jet printer provided with a stackable drop generator according to any one of the preceding claims.

Inventors: WITTEVEEN BONTKO, WITTEVEEN, BONTKO
Applicants: OCE NEDERLAND BV, OCE-NEDERLAND B.V.
Application year: 1990
Main classification: B41J2
IPC codes: B41J2, G01D15