Abstract:
An inkjet recording head and an inkjet recording apparatus capable of mounting the inkjet recording head. The inkjet recording head includes a plurality of electrothermal conversion members, a plurality of driving elements, a plurality of discharge openings, a common wiring, an ink path, and an ink supply opening. Each electrothermal conversion member includes a heating resistor and a pair of electrodes. Each driving element is electrically connected to one of the pair of electrodes of its associated electrothermal conversion member. The common wiring is electrically connected to the other of the pair of electrodes of each electrothermal conversion member. The heating resistors are disposed along the ink supply opening in the longitudinal direction thereof such that their shortest distances from the ink supply opening differ based on the time-sharing driving timings. The wiring resistance values of at least one electrode of each of the pairs of electrodes are substantially the same for all of the electrothermal conversion members. The inkjet recording apparatus is capable of mounting the inkjet head and includes a carriage capable of scanning in a direction of arrangement of the heating resistors and in a direction perpendicular to the direction of arrangement, while the carriage carries the head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inkjet recording head which ejects ink from an orifice in the form of ink droplets, and an inkjet apparatus using the inkjet recording head. More particularly, the present invention relates to an inkjet recording head which ejects ink in a direction perpendicular to a substrate, is provided with heaters that are driven in a time-sharing fashion, and causes the ink to land on the proper location on the recording medium by shifting the position of the heater and the corresponding discharge opening, since the time-sharing driving causes the location where the ink lands to be shifted; and an inkjet apparatus using the inkjet recording head. 
     2. Description of the Related Art 
     An inkjet recording method, disclosed for example in Japanese Patent Laid-Open No. 54-51837, is different from other inkjet recording methods in that the action of thermal energy on ink is used as the driving force for discharging ink droplets. More specifically, in the recording method of the aforementioned disclosure, heating the ink produces air bubbles therein that form the ink into ink droplets that are discharged from an orifice (discharge opening) at the front end of the recording head and adhere onto a recording medium, whereby information is recorded on the recording medium. 
     In general, the recording head used in this recording method includes an ink discharge section, a heating resistor (heater), an upper protective layer, and a lower protective layer. The ink discharge section has an orifice for discharging ink, and an ink path communicating with the orifice and forming part of a heat-acting section, where thermal energy acts upon ink in order to discharge ink in the form of droplets. The heating resistor serves as an electrothermal conversion member that is a means which produces thermal energy. The upper protective layer protects the heater from ink, while the lower layer accumulates heat. 
     In order to take full advantage of the characteristics of the above-described head, it is necessary to use a larger number of heaters, which are disposed close together in a high-density arrangement for high-speed operation. 
     A larger number of heaters results in a larger number of electrical connections with an external wiring plate. In addition, when the heaters are disposed close together in a high-density arrangement, the pitch between the heater electrodes becomes smaller, which makes it impossible to make electrical connections using ordinary electrical connection methods, such as wire bonding. 
     In Japanese Patent Laid-Open No. 57-72867, this problem is overcome by forming a driving element on a substrate. 
     Japanese Patent Laid-Open No. 59-95154 discloses a recording head of the type that discharges ink in a direction perpendicular to a heat-acting portion surface by adhering an orifice plate to a substrate. 
     In general, when such a head has a large number of heaters, the heaters are driven in a time-sharing fashion in order to lower the peak voltage that occurs when all of the heaters are driven. 
     When the heaters are driven in a time-sharing fashion, however, a voltage is applied to heaters at different times, so that the discharge timing differs, causing ink to land on the recording paper in a zigzag fashion. 
     To overcome such a problem in the recording head of the above-described type, a proposal has been made to shift the positions of the heaters in accordance with the timing of the time-sharing driving. 
     FIG. 5 is a view showing the vicinity of the heaters  202 - 1  and  202 - 2  in a conventional recording head. As shown in FIG. 5, when the driving elements  205  are arranged side by side and a common electrode is formed on the driving elements, the resistance of a selection electrode varies with the position of the heater, since a shift in the heater position changes the separation distances between the heater and the driving element wiring. 
     In addition, since the distance between the heater and the common electrode changes, the resistance value of the wiring between the heater and the common electrode changes. 
     Further, the aforementioned pattern has the following two problems. The first problem is that the wirings, which pass between the heaters, get in the way when the heaters are disposed very close together in a high-density arrangement. In addition, it becomes difficult to operate the heaters at a high frequency, since they can be less freely arranged in the lateral direction. The second problem is that a folded electrode, provided between the heater and the ink supply opening  208 , increases the distance between the heater and the ink supply opening and thus increases the flow resistance between the heater and the ink supply opening. This deteriorates the discharge frequency characteristics, so that discharge cannot be performed at a high frequency. 
     Accordingly, in order to overcome the above-described problem, a proposal was made to form the pattern without the folded electrodes between the heaters  202 - 1  and  202 - 2  and the ink supply opening  208 , as shown in FIG.  6 . 
     In such a pattern, however, shifting the heater position causes the distances between the heaters and the driving elements  205  to become different, as well as the distances between the heaters and the common electrode to be different, thereby causing the resistance values of the individual selection wirings of the heaters, as well as the resistance values of the wirings between the heaters to be different. Therefore, a different voltage is applied to the heaters, which results in poor printing performance. In the worst case, ink cannot be discharged, depending on the heater position. 
     Accordingly, with the pattern shown in FIG. 6, it is necessary to design the electrodes and the driving elements such that a fixed voltage is applied to the heaters, in accordance with their positions. In particular, it is necessary to give good consideration to the method of correcting the resistances, since the wiring resistances can only be corrected within a narrow space between the driving elements and the heaters, when forming a driving element to the substrate. 
     Accordingly, an object of the present invention is to provide an inkjet recording head which can provide a constant discharge performance, without variations in the print quality, by applying a fixed voltage to each of the shifted heaters. In the inkjet recording head, ink is discharged perpendicular to the substrate, and heaters that are driven in a time-sharing fashion are provided. The time-sharing driving causes the landing location of the ink on the recording medium to be shifted. Thus, the ink is made to land on the proper location by shifting the location of the heaters and the corresponding discharging openings. 
     SUMMARY OF THE INVENTION 
     To this end, according to the present invention, there is provided an inkjet recording head, comprising: a plurality of electrothermal conversion members, each member including a heating resistor used for discharging ink and a pair of electrodes electrically connected to the heating resistor; a plurality of driving elements, each element being electrically connected to one of the pair of electrodes of its associated electrothermal conversion member in order to drive its associated heating resistor; a common wiring electrically connected to the other of the pair of electrodes of each of the plurality of electrothermal conversion members; a plurality of discharge openings used for discharging ink, which are provided upwardly of the heating resistors in correspondence with their respective heating resistors; an ink path which communicates with the discharge openings; and a slot-shaped ink supply opening for supplying the ink to the ink path. In the inkjet recording head, the plurality of heating resistors are disposed along the ink supply opening in the longitudinal direction thereof such that the shortest distances of the plurality of heating resistors from the ink supply opening differ based on the time-sharing driving timings of the heating resistors. In addition, the wiring resistance values of at least one electrode of each of the pairs of electrodes are substantially the same for all of the electrothermal conversion members. 
     According to the present invention, a structure may be adopted that allows a fixed voltage to be applied to each of the heaters by changing at least the width of the individual selection electrode wiring with respect to each heater and the width of the wiring between each heater and the common electrode. 
     In addition, according to the present invention, a structure may be adopted that allows a fixed voltage to be applied to each of the heaters by changing at least the connecting locations of the driving element wiring and the individual electrode wiring for each heater and the connecting locations of the wirings between each heater and the common electrode. 
     Further, according to the present invention, a structure may be adopted that allows a fixed voltage to be applied to each of the heaters by changing the position of the driving element with respect to each heater. 
     Still further, according to the present invention, a structure may be adopted that allows a fixed voltage to be applied to each of the heaters by correcting the resistances of the electrical power wirings used to apply electrical power to the driving elements, in relation to each of the heaters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a detailed view of the vicinity of the heaters in Embodiment 1 in accordance with the present invention. 
     FIG. 2 is a detailed view of the vicinity of the heaters in Embodiment 2 in accordance with the present invention. 
     FIG. 3 is a detailed view of the vicinity of the heaters in Embodiment 3 in accordance with the present invention. 
     FIG. 4 is a detailed view of the vicinity of the heaters in Embodiment 4 in accordance with the present invention. 
     FIG. 5 is a detailed view of the vicinity of the conventional heaters. 
     FIG. 6 is a detailed view of the vicinity of the conventional heaters of another embodiment. 
     FIG. 7 is a schematic perspective view of an inkjet recording head of the present invention. 
     FIG. 8 is a sectional view of the main portion of the inkjet recording head taken along line A-A′ of FIG.  7 . 
     FIG. 9 is a view showing the form of each ink path and the arrangement of the heaters in the inkjet recording head of FIG.  7 . 
     FIG. 10 is a schematic perspective view of an inkjet recording apparatus to which an inkjet recording head can be mounted in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As described above, a fixed voltage can be applied to each of the shifted heaters by a structure that allows the electrode wiring width to be changed in accordance with the position of the heater so as to fix the value of the wiring resistance. 
     More specifically, the heater is made thicker when there is a large separation distance between the heater and the connecting section with the driving element wiring, or a large separation distance between the heater and a common electrode, whereas the heater is made thinner when either of these separation distances are small. 
     When the wiring width is to be changed, either the electrode between the heater and the driving element wiring, or the electrode between the heater and the common electrode, or both may be changed in width. 
     In addition, a fixed voltage can be applied to the heaters by fixing the separation distance between the heater to the connecting location with the driving element wiring, or fixing the separation distance between the heater and the connecting location of the common electrode wiring. This method is used, when the electrode between the heater and the driving element or the distance between the heater and the common electrode is on the whole short, or when resistance value corrections cannot be conducted therebetween, or when wiring corrections cannot be done in accordance with the design, since the wiring over-etch amount is not constant, or when the distance between the connecting location with the driving element wiring and the heater is fixed in order to prevent ink from coming into contact with the connecting location. 
     Since the driving element electrodes can be made wider, the resistance values are substantially unchanged, even when the distances between the connecting locations and the driving elements differ. 
     The common electrode has a large width, even when the connecting location of the wiring between the heater and the common electrode changes. 
     To change the connecting location, either the separation distance between the heater and the connecting location with the driving element, or the distance between the heater and the common electrode, or both may be changed. 
     The problem of different resistance values due to different separation distances between the connecting location of the driving element wiring and the driving element can be overcome by shifting the position of the driving element. 
     When it is difficult to shift the driving element, such as when it is difficult to route the logic wiring, a fixed voltage can be applied to the heaters by correcting the resistance value of an electrical power wiring used to input electrical power to the driving element. 
     The resistance value can be corrected by correcting the width of the wiring between the driving element and the electrical power wiring or by fixing the distance between the connecting location and the driving element. 
     The various methods, which have been discussed for achieving the object, may be used singly or in combination. It is preferable that the object is achieved by an optimum combination when the positioning the heaters. 
     A description will now be given of the preferred embodiments. 
     Embodiment 1 
     FIG. 7 is a perspective view of an inkjet recording head of the present embodiment. 
     The inkjet recording head of the present invention is a bubble jet type head which discharges ink in a direction perpendicular to a heater by the pressure of high-pressure air bubbles produced by applying voltage in the form of pulses to the heater formed on a substrate. In FIG. 7, reference numeral  301  denotes a silicon (Si) substrate, reference numeral  302  denotes a layer forming an ink path wall, and reference numeral  303  denotes an orifice plate with discharge openings. Reference numeral  304  denotes an L-shaped aluminum (Al) base plate, with one side of the L-shaped face joined to the substrate  301 . Reference numeral  305  denotes a tank which contains ink. 
     Reference numeral  306  denotes a flexible cable, reference numeral  307  denotes a bonding wire for connecting a wiring on the substrate  301  and the flexible cable  306 , and reference numeral  308  denotes an electrical contact for electrical connection with the apparatus body side of a printer carriage carrying the head. 
     Reference numerals n 1  to n 32  denote discharge openings in the orifice plate  303 , which are arranged in two rows, with the rows displaced by ½ the pitch of the discharge openings. That is, the discharge openings n 1  to n 32  are arranged in a zigzag fashion. The head is carried by the carriage of a printer to be described later and discharges ink as the head moves in the direction of arrow x of FIG.  7 . 
     FIG. 8 is a sectional view showing the main portion of the inkjet recording head taken along line A-A′ of FIG.  7 . 
     From an ink tank  305 , ink flows through a hole  310  in a base plate  304 , through a hole  108  (hereinafter referred to as “ink supply opening”) in the Si substrate  101 , through an ink path  312  to a chamber including a heater, and is discharged from each discharge opening nk (k=1, 2, . . . , 32). In FIG. 8, reference character hk (k=1, 2, . . . , 32) denotes a heater formed on the Si substrate  301 . The heaters, provided in correspondence with the discharge openings, are disposed directly below their corresponding discharge openings such that the center of each heater is aligned with the center of its associated discharge opening. 
     FIG. 9 is a view showing the shape of each ink path  312  and the arrangement of each heater hk in its associated ink path. 
     In FIG. 9, the relative positions of the heaters hk correspond to the relative positions of the discharge openings nk. The heaters h 1  to h 16  are displaced with respect to the heaters h 17  to h 32  by ½ the pitch of the discharge openings, as mentioned above. 
     The head has  32  heaters that are driven  16  times, the timings of which are previously set based on the time-sharing for an equal number of heaters. Therefore, a maximum of two heaters are driven at the same timing in accordance with the discharge data. In the present embodiment, the phrase “distance from an edge of an ink supply opening” refers to the distance from the left edge of the ink supply opening when speaking of the left row heaters, while the same phrase refers to the distance from the right edge of the ink supply opening when speaking of the right row heaters. 
     In the inkjet recording head of the present embodiment, the two heaters driven at the same timing always causes the ink to land on locations separated by a 10-dot pitch in the main scanning direction, or in the direction of carriage movement. 
     FIG. 1 is a detailed plan view showing the vicinity of the heaters in Embodiment 1 in accordance with the present invention. Reference numeral  101  denotes a substrate, reference numerals  102  denote heaters, reference numeral  103  denotes a selection electrode, reference numeral  104  denotes a wiring electrode between the heaters and a common electrode, reference numeral  105  denotes a driving element, reference numeral  106  denotes a driving element wiring, reference numeral  107  denotes the common electrode, and reference numeral  108  denotes an ink supply opening. 
     In preparing the recording head of the present embodiment, the driving elements and logic elements are formed on the silicon substrate by the bi-CMOS process. 
     The pitch of the driving element is the same as the pitch of the heater, which is 300 dpi. 
     In the final step of preparing the driving element, the wiring electrodes of the driving elements are prepared using Al—Cu material that is formed into a thickness of 1.0 μm, followed by patterning and preparation of an inter-layer insulating layer formed from SiO 2  material that is formed into a thickness of 1.5 μm. 
     Then, a 20 μm×20 μm through hole  109  is etched in a location of each inter-layer protective layer where the driving element wiring and an individual electrode of the heater are connected together. 
     The heater is formed from TaN material that is formed into a thickness of 0.1 μm. 
     On the heater is formed an electrode layer formed from Al material that is formed into a thickness of 0.6 μm, followed by patterning using photolithography, as shown in FIG.  1 . 
     Each heater is 30 μm×30 μm large. 
     As shown in FIG. 1, the heater  102 - 1  and the heater  102 - 2  are disposed at different distances from the ink supply opening  108 . 
     The distance A between a heater side end of the through hole  109  that is a connecting portion with the driving element wiring and an end of the heater electrode is 100 μm for the heater  102 - 1  and 75 μm for the heater  102 - 2 . 
     The distance B between an end of the heater electrode and the common electrode is 150 μm for the heater  102 - 1  and 125 μm for the heater  102 - 2 . 
     Therefore, when the electrode wirings have the same width, the resistance of the electrode wiring for the heater  102 - 1  is 1.25 times the resistance of the electrode wiring for the heater  102 - 2 . Therefore, when the heater wirings are of the same width, the voltage applied to the heaters are different, causing the heaters to have different discharge characteristics, thereby deteriorating printing characteristics. 
     Therefore, in the present embodiment, the resistance of the wirings are corrected by changing the thickness of the wirings. 
     The width of the selection electrode between the heater and the driving element and the width of the wiring electrode between the heater and the common electrode are both 20 μm for the heater  102 - 1  and 16 μm for the heater  102 - 2 . When the thickness of the wiring for the heater  102 - 1  is made 1.25 times the thickness of the wiring for the heater  102 - 2 , the resistance of the wiring for the heater  102 - 2  between the heater side end of the through hole  109 , being a connecting portion with the driving element wiring, and an end of the heater electrode is the same as the resistance of the wiring for the heater  102 - 1  between an end of the heater electrode and the common electrode. 
     In addition, the same voltage is applied to the heaters since the electrode resistance values are the same. 
     Embodiment 2 
     FIG. 2 is a detailed plan view showing the vicinity of the heaters in Embodiment 2 in accordance with the present invention. 
     As with Embodiment 1, driving elements and logic elements are prepared on the silicon substrate by the Bi-CMOS process. 
     The pitch of the driving elements is the same as the pitch of the heaters, which is 300 dpi. 
     In the final step of preparing the driving element, the wiring electrode is formed using Al—Cu material that is formed into a thickness of 1.0 μm, followed by patterning and preparation of an inter-layer insulating layer formed from SiO 2  material that is formed into a thickness of 1.5 μm. 
     Then, a 10 μm×10 μm through hole  109  is etched at a location of each inter-layer protective layer where the driving element wiring and the individual heater electrode are connected together. 
     As shown in FIG. 2, the through holes  109  are formed in correspondence with the positions of the heaters such that the distance between each heater and the through hole  109  is fixed at 50 μm. 
     Each heater is formed from TaN material that is formed into a thickness of 0.1 μm. 
     An electrode layer is formed on each heater, using Al material that is formed into a thickness of 0.6 μm, followed by patterning using photolithography, as shown in FIG.  2 . 
     As shown in FIG. 2, the heaters and the common electrode are connected at a location corresponding to the location of the heaters, such that the distance between each heater and the common electrode is the same at 100 μm. 
     The size of each heater is 30 μm×30 μm. 
     The thicknesses of the electrodes are the same at 20 μm. Accordingly, it is possible to fix the resistance of a wiring for any heater to a certain value, and thus to apply a fixed voltage to any heater. The distance between the heater and the location where it is connected with the driving element wiring as well as the distance between the heater and the common electrode are fixed, so that the wiring resistance for any heater can be fixed, regardless of its position, even when the overetch amount of the electrode layer changes. 
     In addition, since the wiring resistance is not adjusted by the distance between the heater and the driving element electrode, the through hole  109  and the heater can be sufficiently spaced apart, thus allowing the through hole  109  to be covered with organic resin or other nozzle forming material. 
     Embodiment 3 
     FIG. 3 is a detailed plan view of the vicinity of the heaters in Embodiment 3 in accordance with the present invention. 
     In Embodiments 1 and 2, the wirings  106  between the drive elements and the through holes are formed into different lengths, depending on the location of the heaters. Since the wirings extending from the driving elements to the through holes  109  can be made with a larger film thickness and a larger width, the difference in the resistance values of the wirings in Embodiments 1 and 2 was ignored. 
     The wiring resistance values need to be corrected when the heaters are greatly displaced from each other, or when the discharge performance varies greatly according to the voltage applied to the heaters, or when the wiring from the driving element to the through hole  109  cannot be made thicker. This can be done by changing the position of the driving element. 
     A detailed description will now be given of the present embodiment. 
     As with Embodiment 1, drive elements and logic elements are prepared on a silicon substrate by the Bi-CMOS process. 
     The pitch of the driving elements is the same as the pitch of the heaters, which is 300 dpi, with the driving elements being disposed in correspondence with the displacement of the heaters, as shown in FIG.  3 . 
     In the final step of preparing the driving elements, a wiring electrode for each driving element is prepared from Al—Cu material that is formed into a thickness of 1.0 μm, followed by patterning and preparation of an inter-layer insulating layer from SiO 2  material that is formed into a thickness of 1.5 μm. 
     Then, a 20 μm×20 μm through hole  109  is etched in a portion of each inter-layer protective layer where the driving element wiring and an individual electrode of the heater is connected together. 
     As with Embodiment 2, the through holes  109  are formed in correspondence with the locations of the heaters such that the distance A between each heater and the through hole  109  is fixed at 50 μm. The heaters are each formed from TaN material that is formed into a thickness of 0.1 μm. 
     On each heater is formed an electrode layer composed of Al that is formed into a thickness of 0.6 μm, followed by patterning using photolithography techniques, as shown in FIG.  3 . 
     As with Embodiment 2, each heater and the common electrode is connected at a location in correspondence with the location of the heater such that the distance B between each heater and the common electrode is fixed at 100 μm. 
     The size of each heater is 25 μm×50 μm. The electrodes are all 30 μm thick. Accordingly, the wiring resistances and the driving element wirings resistances are fixed for any heater, thus allowing a fixed voltage to be applied to the heaters with high precision. 
     Embodiment 4 
     FIG. 4 is a detailed plan view of the vicinity of the heaters in Embodiment 4 in accordance with the present invention. 
     In the present embodiment, when the position of the driving element cannot be changed due to the routing of a logic wiring or the like in Embodiment 3, a fixed voltage can be applied to the heaters by power wirings  410  for inputting electrical power to their respective driving elements. 
     As shown in FIG. 4, the resistance value of the driving element wiring can be corrected by changing the connecting positions of the power wiring used for inputting electrical power to the driving element. 
     This allows a fixed voltage to be applied to the heaters with high precision, without changing the position of the driving element. 
     FIG. 10 is a schematic perspective view of an inkjet printer which can use the inkjet recording head described above. 
     The inkjet heads of each of the above-described embodiments are provided in correspondence with each of the ink types, yellow (Y), magenta (M), cyan (C), and black (BK). These four inkjet heads and tanks containing ink supplied to each of their respective heads are removably carried by a carriage  12 . The carriage  12  is slidably mounted to a guide shaft  11 , which permits scanning along the guide shaft  11  by a belt  52  run by a motor (not shown). A print medium P is intermittently transported at portions opposing the discharge openings of the inkjet heads during carriage  12  scanning. In other words, the print medium P is intermittently transported by two pairs of conveyor rollers  15  and  16 , and  17  and  18  that are rotated by a motor (not shown) as they nip the print medium P at the aforementioned portions opposing the discharge openings. 
     At the home position of the carriage is provided a recovery unit  19  for performing discharge recovery operations of each of the inkjet heads. 
     As can be understood from the foregoing description, the inkjet recording head of the present invention can constantly provide good ink discharge performance, without variations in the print quality, by the application of a fixed voltage to the heaters that are displaced from each other. In the inkjet recording head, ink is discharged perpendicular to a substrate provided with an ink discharging means, and each of the heaters disposed side by side on the substrate are driven in a time-sharing fashion, which causes the landing location of the ink on the recording medium to be shifted. This is solved by making the ink land on the proper location by shifting the location of the heaters and the corresponding discharging openings. An element for driving each of the heaters is formed on the substrate. 
     According to the present invention, a wiring is made thicker when there is a large separation distance between the heater and the connecting portion with the driving element wiring, or a large separation distance between the heater and the common electrode, and the wiring is made thinner when these separation distances are small. This causes the wiring resistance values to be fixed, thereby permitting a fixed voltage to be applied to the heaters. 
     In addition, according to the present invention, it is also possible to apply a fixed voltage to the heaters by fixing the separation distance between the heater to the connecting location with the driving element wiring, or by fixing separation distance between the heater and the connecting location of the common electrode wiring. This method is used, when the electrode between the heater and the driving element or the distance between the heater and the common electrode is on the whole short, or when resistance value corrections cannot be conducted therebetween, or when wiring corrections cannot be done in accordance with the design, since the wiring over-etch amount is not constant, or when the distance between the connecting location with the driving element wiring and the heater is fixed in order to prevent ink from coming into contact with the connecting location. 
     Further, according to the present invention, when there is a difference in the resistance values due to a difference in the separation distances between the connecting locations of the driving element wirings and the driving elements, a fixed voltage can be applied to the heaters by shifting the positions of the driving elements. 
     Still further, according to the present invention, when it is difficult to shift the driving element, such as when it is difficult to route the logic wiring, a fixed voltage can be applied to the heaters by correcting the resistance value of an electrical power wiring used to input electrical power to the driving element.