Patent Publication Number: US-7896472-B2

Title: Recording-head driving device for driving recording head

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2006-308503, which was filed on Nov. 15, 2006, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in to a recording-head driving device for driving a recording head. 
     2. Discussion of Related Art 
     In a conventionally known inkjet-type recording apparatus, there has been provided a recording head including a plurality of actuator sections each provided for performing a recording operation on a recording medium. As an example of the inkjet-type recording apparatus, there has been known an apparatus, as disclosed in, for example, a Patent Document 1 (JP-A-2005-193497, in particular, paragraph 0047, 0048 and FIG. 4), which includes a wiring board for supplying a drive signal to each of the plurality of actuator sections. In the disclosed apparatus, one drive-circuit unit (i.e., drive IC) is mounted on the wiring board. 
     In recent years, there has been increased a demand that the recording head is provided with a large number of the actuator sections. Such a demand causes increase in size of the drive-circuit unit that has wires for connecting the actuator sections and the drive-circuit unit, and also increase in density of wires (or reduction on pitch of the wires). Due to required limitations with respect to the density (or reduction) of the wires and characteristic of the drive-circuit unit, there has been proposed a recording apparatus, as disclosed in the above-identified Patent Document 1, in which two recording heads are provided to be connected to respective two wiring boards such that two drive-circuit units are disposed on the respective two wiring boards. 
     SUMMARY OF THE INVENTION 
     In the above-described recording apparatus disclosed in the Patent Document 1 in which the two wiring boards are respectively routed from the respective two recording heads in respective opposite directions, a large space is required for disposing the wiring boards, thereby increasing a size of the recording apparatus. Further, it is cumbersome to connect the wiring boards to a body-side control device. If the two recording heads are provided by a single piece unit with the two drive-circuit units which are disposed on a single wiring board that extends from the single piece unit, an amount of heat generated in each of o drive-circuit units are increased so that operations of the actuator sections could be negatively affected by the increased amount of the generated heat. 
     The present invention has been developed in view of the background discussed above. It is therefore an object of the present invention to provide a recording-head driving device in which two drive-circuit units are provided in one wiring board so that the number of wires connected to each of the drive-circuit units can be decreased, which arrangements effective to reduce negative influence on operation of each actuator section and to facilitate routing of the wiring board. 
     To solve the above-described problem, the present invention provides a recording-head driving device for driving a recording head which includes a plurality of actuator sections each provided for performing a recording operation on a recording medium. Further, the recording-head driving device includes: a wiring board which is elongated in a longitudinal direction and which is to be connected, at a connected portion near to one of longitudinally opposite ends thereof, to the plurality of actuator sections of the recording head; two drive-circuit units mounted on respective mount portions of the wiring board such that the connected portion of the wiring board at which the wiring board is connected to the plurality of actuator sections is interposed between the mount portions, in the longitudinal direction. More specifically, the wiring board includes: (a) a plurality of wires a part of which connects one of the two drive-circuit units and a part of the plurality of actuator sections, for supplying a drive signal from the one of the two drive-circuit units to the part of the plurality of actuator sections, and the rest of which connects the other of the two drive-circuit units and the rest of the plurality of actuator sections, for supplying a drive signal from the other of the two drive-circuit units to the rest of the plurality of actuator sections; and (b) a plurality of input terminals which are electrically connected to the two drive-circuit units and are provided on the other of the longitudinally opposite ends of the wiring board. 
     In this recording-head driving device according to the present invention, the two drive-circuit units are provided, whereby the number of the plurality of wires connected to each of the two drive-circuit units can be decreased, a load imposed on each of the two drive-circuit units can be reduced and a layout of the plurality of wires can be simplified. Further, although each of the two drive-circuit units is a source of heat generation, an influence of the heat generation is not increased even if the two drive-circuit units are provided because the two drive-circuit units are away or distant from each other, with the plurality of actuator sections being interposed therebetween. Further, since the two drive-circuit units are disposed such that an area where the plurality of actuator sections are arranged is interposed between the two drive-circuit units in the direction in which the wiring board is elongated (i.e., in a longitudinal direction of the wiring board), the heat is conducted to this area from both sides of the wiring board in the longitudinal direction thereof. Therefore, a variation of temperature distribution can be reduced. Accordingly, a variation of temperature in the plurality of actuator sections due to the heat generation of the drive-circuit units can be decreased. Further, as described above, since two drive-circuit units are mounted on one wiring board, the wiring board can be routed in only one direction, thereby facilitating the routing of the wiring board in the recording apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and optional objects, features, and advantages of the present invention will be better understood by reading the following detailed description of preferred embodiments of the invention when considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view explaining a relationship among an ink-channel unit, an actuator unit and a flexible wiring board in an ink-jet recording apparatus using a recording-head driving device as an embodiment of the present invention; 
         FIG. 2  is a schematic plan view showing the flexible wiring board as one example of the embodiment; 
         FIG. 3  is a cross-sectional view showing a relationship among a drive IC, wires and an individual electrode in the wiring board; 
         FIG. 4  is a schematic plan view showing a flexible wiring board as a second example of the embodiment; 
         FIG. 5  is a schematic plan view showing a flexible wiring board as a third example of the embodiment; and 
         FIG. 6  is a cross-sectional view showing a relationship among a drive IC, wires and a base film in a wiring board as a forth example of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, there will be described a preferred embodiment of the present invention by reference to the drawings. It is noted that, in this embodiment, there is adopted an inkjet recording head for color recording. 
       FIG. 1  is a perspective view showing a situation in which a flexible wiring board is superposed on and bonded to an upper surface of the recording head, according to the present invention. 
     As shown in  FIG. 1 , a recording head  1  includes an ink-channel unit  2  and an actuator unit  3  which are superposed on the ink-channel unit  2 . The ink-channel unit  2  includes a plurality of nozzles each opening in a lower surface of the ink-channel unit  2  and a plurality of ink channels respectively corresponding the plurality of nozzles. The actuator unit  3  includes a plurality of actuator sections (not shown) each corresponds to one of the ink channels. As generally known, a piezoelectric element or a heater for boiling an ink can be adopted as each of the actuator sections. Further, on an upper surface of the actuator unit  3 , there are provided a plurality of individual electrodes  12   a  for selectively applying an electric voltage to the respective actuator sections and a common electrode  12   b  commonly connected to all of the actuator sections. The recording head  1  is mounted on a carriage that is reciprocated in a direction X (i.e., in a main-scanning direction) perpendicular to a direction Y (i.e., a sub-scanning direction) in which a recording sheet (i.e., a recording medium) is carried. The recording head  1  performs a recording operation on the recording sheet by ejecting the ink via the plurality of nozzles, owing to the actuator sections each being driven. 
     On the upper surface of the actuator unit  3 , there is provided a flexible wiring board  4  for supplying a drive signal to each of the actuator sections. The flexible wiring board  4  has an elongated shape which is elongated in the direction X on the actuator unit  3 . On the flexible wiring board  4 , there are mounted two drive-circuit units, i.e., a first drive IC  5  and a second drive IC  6  so as to be arranged in parallel to each other in the longitudinal direction of the flexible wiring board  4  with a space left between the first and the second drive ICs  5 ,  6 . 
     As shown in  FIGS. 2 and 3 , in the flexible wiring board  4 , there are provided a plurality of wires  11  for supplying the drive signals to the actuator sections. Each of the wires  11  has, in one of opposite end portions thereof, a first terminal portion  11   a  to be connected to a corresponding one of the individual electrodes  12   a  for driving a corresponding one of the actuator sections. That is, the flexible wiring board  4  is connected, at a connected portion thereof, to the actuator sections. In the connected portion, the first terminal portion  11   a  is provided. The first and the second drive ICs  5 ,  6  are disposed such that an area of the flexible wiring board  4  in which the plurality of first terminal portions  11   a  are arranged is interposed between the first and the second drive ICs  5 ,  6  in the longitudinal direction of the flexible wiring board  4 . Further, each of the wires  11  has, in the other of opposite end portions thereof, a second terminal portion  11   b  to which a corresponding one of output terminals  5   a ,  6   a  respectively provided in the first and the second drive ICs  5 ,  6  for outputting the drive signals is connected. Connection terminals  5   b ,  5   c  provided in the first drive IC  5  are respectively connected to wires  21 ,  22  (i.e., a pair of wires). Also, connection terminals  6   b ,  6   c  provided in the second drive IC  6  are respectively connected to the wires  21 ,  22 . A base film  14  and a cover layer  15  constitute the flexible wiring board  4 . 
     The first drive IC  5  supplies drive signals to a part of the first terminal portions  11   a  which are near to the first drive IC  5 . The second drive IC  6  supplies drive signals to rest of the first terminal portions  11   a  which are near to the second drive IC  6 . That is, the first and the second drive ICs  5 ,  6  cooperatively take charge of supplying the drive signals to all of the first terminal portions  11   a.    
     One of opposite end portions of the flexible wiring board  4  in the longitudinal direction thereof which is nearer to the first drive IC  5  is extended in a direction opposite to the first terminal portions  11   a . On this extended end portion of the flexible wiring board  4 , input terminals  13  are arranged in a widthwise direction of the flexible wiring board  4 . 
     There are provided, for supplying input signals to both of the first and the second drive ICs  5 ,  6 , terminals  13   a  which constitute a part of the input terminals  13  and which are disposed at an intermediate portion (in the above-described extended end portion) of the flexible wiring board  4  in the widthwise direction thereof. Further, there are provided, for supplying the drive voltage for driving the actuator sections to both of the first and the second drive ICs  5 ,  6 , terminals  13   b ,  13   b ,  13   c  which constitute a part of the input terminals  13  and which are disposed at the respective opposite side end portions (in the above-described extended end portion) of the flexible wiring board  4  opposite to each other in the widthwise direction thereof. Further, terminals  13   d ,  13   d  which constitute a part of the input terminals  13  and which are respectively disposed outside of the terminals  13   b ,  13   b  are connected to the common electrode  12   b  provided on the upper surface of the actuator unit  3 . These terminals  13   a ,  13   b ,  13   c ,  13   d  are arranged in the widthwise direction of the flexible wiring board  4 . 
     The wire  21 , as one of the pair of wires  21 ,  22  for supplying the drive voltage to the first and the second drive ICs  5 ,  6 , has first portions  21   a ,  21   a  (i.e., a pair of portions) extending along the respective widthwise opposite side end portions of the flexible wiring board  4 , such that the first terminal portions  11   a  are interposed between the first portions  21   a ,  21   a . The first portions  21   a ,  21   a  are connected to each other via a second portion  21   b  extending in a direction perpendicular to a direction in which the first portions  21   a ,  21   a  extend, in a vicinity of the other of the opposite end portions of the flexible wiring board  4  that is opposite to the input terminals  13 . That is, the wire  21  is formed into a loop by the first portions  21   a ,  21   a  and the second portion  21   b . In other words, the first and second portions  21   a ,  21   b  cooperate to provide the wire  21  with substantially U-shape as its entire shape. The second portion  21   b  extends below the second drive IC  6 . 
     A branch wire  21   c  to be connected to the first drive IC  5  is branched from the wire  21  formed into the loop. The branch wire  21   c  has an open or free distal end at which the branch wire  21   c  is not electrically connected to any conductive objects. Inside of the wire  21  formed into the loop, in one of opposite side end portions of the flexible wiring board  4  in the widthwise direction thereof, there is provided the wire  22  as the other of the pair of wires  21 ,  22 . The wire  22  has a wire portion  22   a  extending in parallel with the first portions  21   a  of the wire  21 . A first branch wire  22   b  is branched from a distal end of the wire portion  22   a , in a vicinity of the other of the opposite end portions of the flexible wiring board  4 . The first branch wire  22   b  has a distal end that is open or free and extends below the second drive IC  6 . Further, in the wire  22 , a second branch wire  22   c  is branched from an intermediate portion of the wire portion  22   a . The second branch wire  22   c  has a distal end that is open or free and extends below the first drive IC  5 . 
     Each of the first and the second drive ICs  5 ,  6  is mounted on the flexible wiring board  4 , such that the connection terminals  5   c ,  6   c  (that are provided in a side of the flexible wiring board  4  to which the drive voltage is supplied) are respectively connected to the first and the second branch wires  22   b ,  22   c  of the wire  22 , and such that the connection terminals  5   b ,  6   b  (that are provided in a side of the flexible wiring board  4  which is to be connected to the ground) are respectively connected to the branch wire  21   c  and the second portion  21   b  of the wire  21 . 
     On the flexible wiring board  4 , outside the first portions  21   a ,  21   a  of the wire  21 , there are respectively provided wires (not shown) for connecting or interconnecting the respective terminals  13   d ,  13   d  and the common electrode  12   b  provided on the upper surface of the actuator unit  3 . 
     Further, on the flexible wiring board  4 , there are provided input-signal wires (not shown) for connecting the terminals  13   a  provided in the widthwise intermediate portion of the flexible wiring board  4  and the first and the second terminals  5 ,  6 . The input-signal wires includes first input-signal wires interconnecting the terminals  13   a  and respective input terminals of the first drive IC  5  and second input-signal wires interconnecting the terminals  13   a  and respective input terminals of the second drive IC  6 . The first input-signal wires extend almost in straight. The second input-signal wires extend in non-straight rather than in straight. Specifically described, the second input-signal wires passes through a space defined between the wire portion  22   a  and the free distal end of the branch wire  21   c , a space defined between the branch wire  21   c  and the second branch wire  22   c , a space defined between one of the first wire portions  21   a  and the free distal end of the second branch wire  22   c , and a space defined between the one of the first wire portions  21   a  and the first terminal portion  11   a , so as to reach the input terminals provided in a portion of lower surface of the second drive IC  6  that is located between the branch wire  22   b  an the second portion  21   b.    
     The input terminals  13  are electrically connected to a control device provided in a body of the recording apparatus. The control device is configured to generate input signals and drive voltages that are supplied to the input terminals  13 . 
     The input signals inputted to the terminal  13   a  provided in the intermediate portion are serially inputted to the first and the second drive ICs  5 ,  6 . In each of the first and the second drive ICs  5 ,  6 , the input signals are converted into parallel signals corresponding to an arrangement of the first terminal portions  11   a , then converted into the drive signals having a voltage corresponding to the drive voltage inputted from the wire  22 . The converted drive signals are supplied to the respective individual electrodes  12   a  via the respective wires  11 , thereby driving the respective actuator sections. The drive circuits provided in each of the first and the second drive ICs  5 ,  6  for generating respective drive signals to be supplied to the respective actuator sections are independent of each other, such that each of the drive circuits serves for a corresponding one of the actuator sections. The drive voltage is supplied, via the wire  22 , to the respective drive circuits which are connected to the ground via the wire  21 . The drive signals are outputted from the respective drive circuits via the respective wires  11 . 
     The wire  21  to be connected to the ground is formed in the loop shape, which makes it possible to decrease a resistance difference between opposite end portions and an intermediate portion of the second portion  21   b . As a result, in a plurality of positions to which the respective drive circuits of the drive IC  6  are connected, it is possible to reduce variation of an electric potential difference between the second portion  21   b  of the wire  21  and the first branch wire  22   b  of the wire  22  for supplying the drive voltage, so that the respective drive circuits of the drive IC  6  can be almost equally operated. The arrangement may be modified such that the drive voltage may be supplied from the wire  21  formed in the loop shape, while the wire  22  is connected to the ground. In this modified arrangement, voltage drop is decreased in the opposite end portions and the intermediate portion of the second portion  21  of the wire  21  from which the drive voltage is supplied, so that the drive circuits of drive IC  6  can be almost equally operated. 
     The recording head  1  in the above-described embodiment has the plurality of nozzles arranged in rows that respectively correspond to four different color inks. The rows are arranged in parallel to the first and the second drive ICs  5 ,  6 , namely, the respective rows of the first terminal portions  11   a  (shown in  FIG. 2 ) are arranged in parallel to the first and the second drive ICs  5 ,  6 . However, the voltage drop may be occurred due to an increase of the resistance in accordance with an increase of lengths of the first and the second branch wires  22   b ,  22   c , at the respective distal ends thereof (see S 1 , S 3  shown in  FIG. 2 ). Further, the electric potential difference may be decreased between the distal end of the branch wire  21   c  to be connected to the ground (see S 2  shown in  FIG. 2 ) and the second branch wire  22   c  for supplying the drive voltage. In these cases, specific ones of the wires  11  for supplying the drive signals to specific ones of the actuator sections which are used or operated at a relatively low frequency may be connected to a portion of each of the first and the second drive ICs  5 ,  6  in which the voltage drop is occurred or the electric potential difference is decreased, thereby avoiding a recording failure due to the voltage drop or the decrease of the electric potential difference. For instance, the specific ones of the actuator sections may be provided by those serving for yellow-color ink, cyan-color ink and magenta-color ink and so on which are used at the relatively low frequency as compared to the black ink. 
     In the above-described embodiment, the wire  21 , as the one of the pair of wires  21 ,  22  for supplying the drive voltage to the actuator sections, is formed into the loop form in the vicinity of the above-described other of the opposite end portions of the flexible wiring board  4  (that is opposite to the input terminals  13 ). However, the present embodiment is not limited to details of the above-described example. The embodiment according to the present invention encompasses the following examples: 
     (i) As shown in  FIG. 4 , there may be respectively provided, in opposite side end portions of flexible wiring board  4 ′, a pair of wires  21 ′,  22 ′ for supplying the drive voltage (for driving the actuator sections) to both of the first and the second drive ICs  5 ,  6  (each as the drive circuit units). Further, there may be provided two first branch wires  21   e ,  21   f  to be respectively connected to the second and the first drive ICs  6 ,  5  and two second branch wires  22   e ,  22   f  to be respectively connected to the second and the first drive ICs  6 ,  5 . The two first branch wires  21   e ,  21   f  are branched from the wire  21 ′ (i.e., one of the pair of wires). Each of the two first branch wires  21   e ,  21   f  has a free distal end. The two second branch wires  22   e ,  22   f  are branched from the wire  22 ′ (i.e., the other of the pair of wires). Each of the two second branch wires  22   e ,  22   f  has a free distal end. 
     (ii) The first and second drive ICs  5 ,  6  do not necessarily have to extend in the direction perpendicular to the longitudinal direction of a flexible wiring board  4  (i.e., the direction Y shown in  FIG. 1 ). For example, as first and second drive ICs  5 ′,  6 ′ provided on a flexible wiring board  4 ″ that is shown in  FIG. 5 , the first and the second drive ICs  5 ,  6  may extend in the longitudinal direction of the flexible wiring board  4  (i.e., the direction X shown in  FIG. 1 ). 
     (iii) In the above-described embodiment, the first and the second drive ICs  5 ,  6  and the wires  11  are respectively provided in opposite sides of the base film  14  which is interposed therebetween. However, as shown in  FIG. 6 , the first and the second drive ICs  5 ,  6  and the wires  11  may be provided in the same side as one of the opposite sides of the base film  14 . 
     The present invention can be adopted to various recording-head driving devices such as a thermal head, other than the ink-jet recording head. It is to be understood that the invention is not limited to the details of the illustrated embodiments, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the invention defined in the attached claims.