Patent Publication Number: US-8109593-B2

Title: Substrate for inkjet head and inkjet head using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inkjet head for performing print on a print medium by ejecting ink according to an inkjet system and a substrate for the inkjet head. 
     2. Description of the Related Art 
     Depending on various inkjet systems, there are various types of inkjet heads (hereinafter, also referred to as inkjet print heads or print heads) used in printing apparatuses (hereinafter, also referred to as printers) that make print by applying ink onto print media such as printing paper. In one of the systems, an inkjet print head heats ink to form bubbles by using, as an energy generating element (also called a print element), a heater element (also called a heater) configured of a heating resistor that generates heat in response to conduction, and makes print by using pressure generated from the bubbles thus formed. This enables highly fine printing at high speed because it is easy to highly accurately manufacture a substrate for a print head substrate in which a large number of heater elements, wirings and the like are arranged with a high density. Moreover, this leads to achievement of further size reduction of a print head and accordingly a printer using the print head. 
     If all of a large number of heater elements thus arranged are driven at one time, a large amount of current flows into the print head instantaneously. To avoid this situation, several tens to several hundreds of heater elements are divided into several blocks, and the blocks of heater elements are driven at slightly different timings. By reducing the number of heater elements driven at one time as described above, the total amount of instantaneously flowing current is limited to a predetermined low level. Moreover, heater element drive circuits for driving a large number of heater elements are incorporated in the print head. This configuration is intended to prevent an increase in the number of wirings between the print head and a printer in which the print head is mounted. In widely used configurations, these drive circuits are built in a Si (silicon) wafer used as a substrate for forming the heater elements. 
     There are various configurations of the drive circuits. Here, a configuration disclosed in Japanese Patent Laid-Open No. 2002-307685 is described as a typical configuration. 
     The driving of each heater element is controlled in accordance with a block control signal (BLKn) indicating a number of a block to which the heater element belongs, and a print signal (DATA) corresponding to the block control signal (DATA). As the block control signal (BLKn), binary data obtained by encoding a block number are used. Here, a value calculated by dividing the total number of heater elements (T) by the total number of blocks (N) indicates the number of heater elements (M=T/N) drivable at one time in one driving operation. Moreover, one bit of the print data corresponds to one heater element. If the print data are transferred in an amount corresponding to the number of heater elements that are simultaneously driven at one driving operation in a time division driving, M represents the number of bits of the print signals (DATA) for driving the heater elements simultaneously driven in one operation. 
     Moreover, gates and transistors are provided for the number of bits equal to the number of heater elements (T). In addition, a shift register and a latch circuit are provided for the number of bits of the block control signals (BLKn) and the number of bits of the print signals (DATA) for simultaneously driving the heater elements in one driving operation. Data composed of the print signals (DATA) and the block control signals (BLKn) are serially transferred to the shift register from a controller of printer main body. After the print signals (DATA) are aligned in the shift register, the print signals (DATA) are latched by the latch circuits. For each block, drive signals are obtained by decoding the block control signals, and the obtained drive signals and the latched print signals are inputted to the gates. In response to this input, the transistors corresponding to the heater elements of the block are driven. Incidentally, this patent document discloses that a usable type of transistors is a bipolar transistor or a field effect transistor (FET). 
     As for an inkjet print head, the ejection characteristics of ink ejected from ejection openings and the temperature of the substrate for the print head are closely related to each other. For this reason, detecting the substrate temperature plays an important role in the control to obtain stable ejection characteristics. 
     For this purpose, as described in Japanese Patent Laid-Open No. H02-258266 (1990), a conventional inkjet print head is equipped with a temperature sensor built in a substrate for a print head and thus are enabled to read the substrate temperature with high accuracy. This temperature sensor is used to control the ink ejection characteristics that vary due to heat. In addition, using monitor values of the temperature sensor, the inkjet print head forcefully suspends a printing operation for a brief period of time when the substrate temperature rises to an abnormally high degree due to an occurrence of some problem in the substrate. For example, such forceful suspension is performed when the power supply shorts out or when the heater elements are driven under the condition where no ink is left because of any factor (this driving situation is called “blank ejection”). 
     One known temperature sensor has a diode type configuration. Japanese Patent Laid-Open No. 2004-050637 discloses that a diode type of temperature sensor is arranged near a connection terminal (input/output pad) for transmitting and receiving print signals and other signals to and from external units. 
     To meet a recently-increasing demand for printing at even higher speed, the number of ejection openings and heater elements arranged in a print head has been increasing. In other words, a print head is configured to have a larger print swath by increasing the number of ejection openings and heater elements in an arranging direction (increasing a size or length of a print head). In some cases, however, such length increase causes the temperature distribution in the substrate for the print head to largely vary depending on the driving status of respective heater elements corresponding to the contents of print data or a print mode. 
     Since the conventional substrate for the print head is relatively small, the temperature sensor is capable of detecting the temperature with sufficiently high accuracy even when being disposed in a position not very close to an array of heater elements, that is, in a position close to a connection terminal. However, as the size of the print head increases, the distance from the temperature sensor to the array of heater elements, especially the array center, increases, thereby making it more difficult to detect the accurate temperature. 
     As a result, even though it is strongly desirable to dispose the temperature sensor in a position corresponding to the center of the heater element array, the conventional substrate configuration has the following problems. 
     In the conventional substrate configuration, logic circuits for bringing the heater elements into conduction in response to the drive signals, and logic wirings connected to the logic circuits are disposed. Of these, the logic circuits are formed as an “underlying layer” in a base plate made of Si by a semiconductor manufacturing process, and electrodes and the like for the logic circuits are formed by using an underlying wiring layer. On the other hand, the logic wirings are arranged in parallel in number corresponding to the number of heater elements. Accordingly, the number of logic wirings increases as the number of heater elements increases. Because the underlying wiring layer allows size reduction in the width of wirings and the spaces between the wirings, the underlying wiring layer is also used to form the logic wirings. When a functional element such as a diode sensor, for example, is used as the temperature sensor, the functional element is also formed by the semiconductor manufacturing process as in the case of the logic circuits. Thus, the functional element is also formed by using the underlying wiring layer. Instead, the sensor may be formed by using a wiring or the like as a resistor. In this case, the resistance value of the wiring or the like needs to be locally increased to a sufficiently high level for achieving high detection sensitivity. To form such sensor, it is also desirable to use the underlying wiring layer that allows size reduction in the width of lines and the spaces between the lines. 
     As described above, even if the temperature sensor is attempted to be disposed in a position corresponding to the center of the heater element array, the logic circuits and the logic wirings are located around the heater element array and therefore, the temperature sensor is disposed at an outer side of these circuits and wirings. As a result, the substrate size in a width direction is increased by an area of the temperature sensor. Consequently, problems arise that the number of substrates manufactured from a single Si wafer is reduced, thereby increasing costs for the substrates. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the foregoing problems. An object of the present invention is to enable accurate temperature detection even for a long substrate including a large number of heater elements, while preventing an increase in the width of the substrate which would accompany the placement of a temperature sensor. 
     In an aspect of the present invention, there is provided a substrate for an inkjet head comprising: M×N energy generating elements for generating energy utilized to eject ink, arranged in an array, and divided into N blocks for performing time-divisional driving; and M signal lines for selecting energy generating elements to be driven in each of the N blocks, wherein the M signal lines include L signal lines (L&lt;M) and (M−L) signal lines, the L signal lines for selecting, from the energy generating elements, L energy generating elements closest to an one end side of the substrate with respect to an arrangement direction of the energy generating elements, extending in the arrangement direction from a start point that is a portion in the one end side toward another end side of the substrate in the arrangement direction, the (M−L) signal lines for selecting, from the energy generating elements, (M−L) energy generating elements closest to the other end side from the energy generating elements, extending in the arrangement direction from a start point that is a portion at the other end side toward the one end side, wherein a number of the L signal lines crossing an intersecting direction intersecting the arrangement direction and a number of the (M−L) signal lines crossing the intersecting direction are decremented as distances from respective the start points increase, and with the decrement in the numbers of the signal lines, the L signal lines and the M−L signal lines are arranged so that the remaining signal lines are shifted toward the energy generating elements, and wherein a temperature sensor for detecting a temperature of the substrate is provided in an empty area produced by the shift of the signal lines. 
     In another aspect of the present invention, there is provided an inkjet head comprising: a substrate as the above; and a member provided in contact with the substrate, and provided with ejection openings for ejecting ink by action of the energy generated by the energy generating elements. 
     According to the present invention, accurate temperature detection can be performed even for a long substrate including a large number of printing elements and at the same time, an increase in the width of the substrate is prevented even though such increase would otherwise occur due to the placement of a temperature sensor. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view showing one example of a printing apparatus on which a print head according to an embodiment of the present invention is mountable; 
         FIG. 2  is a schematic perspective view showing a configuration example of a print element unit applied to a print head mounted on the printing apparatus in  FIG. 1 ; 
         FIG. 3  is a block diagram showing a configuration example of a drive circuit that is formed on a substrate constituting the print element unit in  FIG. 2 , and includes logic circuits; 
         FIG. 4  is a schematic diagram showing a basic layout in the case where the drive circuit in  FIG. 3  is built in a substrate; 
         FIG. 5  is a schematic diagram according to the first embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors within a region in the layout of  FIG. 4 ; 
         FIG. 6  is a schematic diagram showing a comparative example in relation to the configuration in  FIG. 5 ; 
         FIG. 7  is a schematic diagram according to a modified example of the first embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors within a region in the layout in  FIG. 4 ; 
         FIG. 8  is a schematic diagram according to another modified example of the first embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors within a region in the layout in  FIG. 4 ; 
         FIG. 9  is a schematic diagram according to a second embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors; 
         FIG. 10  is a schematic diagram according to a modified example of the second embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors; 
         FIG. 11  is a schematic diagram according to another modified example of the second embodiment of the present invention and showing a wiring of signal lines for transmitting drive signals and a placement of temperature sensors; 
         FIG. 12  is a schematic cross section view for explaining a configuration example of a substrate and its supporting member to which the second embodiment is effectively applied; 
         FIG. 13  is a schematic plan view showing an example in which the second embodiment is applied to a substrate having the configuration in  FIG. 12 ; 
         FIG. 14  is a schematic plan view showing a configuration example of a temperature sensor in  FIG. 13 ; 
         FIG. 15  is a schematic cross section view for explaining another configuration example of the substrate and its supporting member to which the second embodiment is effectively applied; 
         FIG. 16  is a schematic cross section view taken along the line XVI-XVI in  FIG. 15 ; and 
         FIG. 17  is a schematic plan view of a substrate, and shows a placement of temperature sensors in the configuration in  FIG. 15 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, the present invention will be described in detail with reference to the drawings. 
     1. First Embodiment 
     (1) Printing Apparatus 
       FIG. 1  is a schematic plan view showing one example of a printing apparatus on which a print head according to an embodiment of the present invention is mountable. 
     In the printing apparatus shown in  FIG. 1 , a print head including a print element unit to be described later is configured as a cartridge type print head (hereinafter, referred to as a print head cartridge) in combination with a container containing ink that is detachably or undetachably attached to the print head. The print head cartridge H 1000  is positioned in and thus is removably mounted on a carriage  2 . The carriage  2  is provided with an electric connector for transmitting drive signals and the like to the print element unit through an external signal input terminal on the print head cartridge H 1000 . 
     The carriage  2  is supported as being capable of reciprocating along guide shafts  3 , which are provided to an apparatus body, and which extend in a main-scan direction. The carriage  2  is driven by a main scanning motor  4  through a driving mechanism including a motor pulley  5 , a driven pulley  6 , a timing belt  7  and the like. Also, the position and the movement of the carriage  2  are controlled by the main scanning motor  4  through the driving mechanism. Moreover, a home position sensor  30  is provided to the carriage  2 . In this configuration, the position of the carriage  2  is detected when the home position sensor  30  on the carriage  2  passes by the position of a shielding plate  36 . 
     Print media  8  such as a print sheet or a plastic thin film are supplied separately one by one from an automatic sheet feeder (ASF)  32  by rotating pickup rollers  31  with a driving force of a sheet supply motor  35 . Here, the driving force is transmitted to the pickup rollers  31  through a transmission mechanism such as gears. Then, with rotation of a conveyance roller  9 , the print medium  8  is conveyed (sub-scanned) through a position (printing region) facing an ejection opening forming face of the print head cartridge H 1000 . The conveyance roller  9  is rotated by receiving a driving force transmitted from an LF motor  34  through a transmission mechanism such as gears. At this time, a paper end sensor  33  detects the front end of the print medium  8  to judge whether or not the print medium  8  is fed, and to determine a print start position on the print medium. Moreover, the paper end sensor  33  is used to detect where the rear end of the print medium  8  actually is positioned, and thus the paper end sensor  33  is also used for finally determining the current printing position according to the actual position of the rear end. 
     Incidentally, the print medium  8  is supported on its back side by a platen (not illustrated) so as to form a flat print face in the printing region. On the other hand, the print head cartridge H 1000  mounted on the carriage  2  is held so that the ejection opening forming face thereof is projected downward from the carriage  2  and is located in parallel with the surface of the print medium  8 . Moreover, the print head cartridge H 1000  is mounted on the carriage  2  so that an array direction of ejection openings in the print element unit intersects the main scanning direction of the carriage  2 . 
     (2) Print Element Unit 
       FIG. 2  is a schematic perspective view showing a configuration example of the print element unit applied to the print head cartridge H 1000 . A substrate  1110  constituting the print element unit is formed of Si in a thickness of 0.5 mm to 1 mm, and is provided with an ink supply opening  202  that is a through-hole in a long groove shape and serves as an ink channel. Ink is introduced to this ink supply opening  202 . Two arrays of heater elements  214  serving as ejection energy generating portions are provided, one at either side of the ink supply opening  202 . The arrays are positioned in such a staggered arrangement that the heater elements  214  in one of the arrays are shifted by ½ pitch from those of the other array in a Y direction. Electrodes for electrically connecting the heater elements and the logic circuits to the outside are formed along two sides of the substrate  1110  in a direction crossing the array direction of the heater elements  214  (this will be described later). Moreover, a component  1108  is provided in contact with the substrate  1110 . The component  1108  includes liquid paths formed by ink channel walls  1106 , and ink ejection openings  1107  that communicate with the liquid paths and is used to eject ink to a print medium with the action of thermal energy. 
     Incidentally, as a print element for generating energy used to eject ink, any type of print element is usable, including a heater element that generates thermal energy for heating ink to form bubbles in response to conduction. However, as the type of print element using the heater element receives such a great influence of heat generated during the driving of the heater element, the present invention is preferably applicable to this type of print element. 
     In addition, although  FIG. 2  only schematically shows the heater elements  214  and the ejection openings  1107 , the print element unit may be formed to have  288  heater elements at either side of the ink supply opening  202  in practice. The  288  heater elements are divided by 24 elements into 12 blocks (the dividing number is N=12). Then, the print element unit can be configured such that one of the heater elements of each block (24 heater elements in total) can be driven at one timing (the number of heater elements simultaneously drivable in one driving operation is M=24) 
     (3) Configuration Example of Drive Circuit 
       FIG. 3  is a block diagram showing a configuration example of a drive circuit being formed on the substrate  1110  and including logic circuits. This drive circuit is formed on a silicon (Si) substrate by using film formation techniques and the like. 
     The shown drive circuit is configured to provide print signals D 1  to D 24  and block control signals B 1  to B 4  to the print element unit through shift registers and latch circuits. As shown in  FIG. 3 , a print signal DATA 1  and a print signal DATA 2  are provided from a printer main body, and the print signal DATA 1  includes the print signals D 1  to D 12  whereas the print signal DATA 2  includes the print signals D 13  to D 24  and the block control signals B 1  to B 4 . 
     In  FIG. 3 , reference numeral  103  indicates a 12-bit shift register to which the print signal DATA 1  is serially inputted in synchronization with clock signals CK provided from the printer main body. Reference numeral  104  indicates a 12-bit latch circuit that latches 12 bits of the print signals D 1  to D 12  aligned in the 12-bit shift register  103 , in response to latch signals LATCH provided from the printer main body. Reference numeral  108  indicates a 4-bit shift register to which the print signals DATA 2  is serially inputted in synchronization with the clock signals CK provided by the printer main body. Reference numeral  105  indicates a 12-bit shift register to which the print signals D 13  to D 24  of the print signals DATA 2  shifted and outputted from the shift register  108  are serially inputted in synchronization with the clock signals CK provided by the printer main body. Reference numeral  106  indicates a 12-bit latch circuit that latches 12 bits of the print signals D 13  to D 24  aligned in the 12-bit shift register  105 , in response to the latch signals LATCH provided by the printer main body. 
     Reference numeral  109  indicates a 4-bit latch circuit that latches 4 bits of the block control signals B 1  to B 4  stored in the 4-bit shift register  108 , in response to the latch signals LATCH provided by the printer main body. Reference numeral  107  indicates an AND circuit that calculates the logical AND between an enable signal ENB and each of 24 bits of the print signals latched by the 12-bit latch circuit  104  and the 12-bit latch circuit  106 . 
     Reference numeral  110  indicates a decoder that decodes the block control signals Bi to B 4  provided by the printer main body to generate block selection signals N 1  to N 12 . Reference numerals H 1  to H 288  indicate heater elements. In addition, reference numerals T 1  to T 288  indicate switching transistors for powering on/off the heater elements H 1  to H 288 , respectively. Reference numerals A 1  to A 288  indicate AND circuits connected to the bases of the transistors T 1  to T 288 , respectively. The AND circuits A 1  to A 288  calculate the logical ANDs between each of outputs from the AND circuit  107  based on the print signals D 1  to D 24  inputted by the printer main body, and each of the block selection signals N 1  to N 12  outputted by the decoder  110 . In other words, based on the selections indicated by the block selection signals N 1  to N 12 , the outputs from the AND circuit  107  are provided as the drive signals dl to d 24  to the bases of the transistors T 1  to T 288 , whereby the heater elements H 1  to H 288  are selectively powered on. Here, the timings of driving the heater elements H 1  to H 288  are determined in response to the block selection signals N 1  to N 12 . 
     In this embodiment, the drive signals d 1  to d 24  are signals provided to the respective groups of 12 heater elements arranged continuously in space. On the other hand, the block selection signals N 1  to N 12  are signals that determine which of the 12 heater elements in each of the groups is to be driven. To put it differently, the “block” is not composed of heater elements arranged continuously in space, but is composed of every twelfth heater elements arranged in the whole array. More specifically, the heaters H 1 , H 13 , H 25 , . . . , H 277 , for example, forms one block of heaters to be simultaneously driven. 
     The width of a drive signal (drive pulse width) outputted by the AND circuit  107  is defined by an enable signal ENB inputted to one of input terminals of the AND circuit  107 . Incidentally, in the illustrated example, the enable signal ENB is of negative logic. Thus, the AND circuit  107  is configured to output the drive signal when the logic state of the enable signal ENB is “low.” 
     Moreover, in the configuration shown in  FIG. 3 , the following seven signal lines including a supply line for a power supply voltage (VH) and a signal line of a ground voltage (GNDH) are provided between the drive circuit and the printer main body. Specifically, the seven signal lines are for the print signal DATA 1 , the print signal DATA 2 , the clock signal CK, the enable signal ENB, the latch signal LATCH, the power supply voltage VH and the ground voltage GNDH. 
     Together with the heater elements H 1  to H 288  and the transistors A 1  to A 288  for power on/off control, the drive circuit illustrated in this embodiment is formed on the same substrate (for example, a silicon substrate) by using semiconductor manufacturing processes, thereby forming the substrate for the print head. 
     (4) Layout of Drive Circuit 
       FIG. 4  is a schematic diagram showing a basic layout in the case where the drive circuit is formed on the substrate. The configuration shown in  FIG. 4  includes two of the drive circuits shown in  FIG. 3  arranged approximately in line symmetry with respect to the ink supply opening  202 . Incidentally, in general, multiple drive circuits are formed on one substrate such as a silicon (Si) wafer at one time, and then the substrate  1110  shown in  FIG. 2  is obtained by dividing the substrate into pieces. 
     Reference numerals  221 ,  222 ,  223  and  224  indicate regions where terminals  1105  for connecting signal lines connecting the printer main body and the print element unit are arranged appropriately. These signal lines are for transmitting the print data DATA 1  and DATA 2 , the latch signal LATCH, the clock signal CK, the enable signal ENB, the power supply voltage VH and the ground voltage GNDH to each of the drive circuits provided at both sides of the ink supply opening  202 . Here, the print data DATA 1  are connected to terminals located in the regions  221  and  222 , while the print data DATA 2  are connected to terminals located in the regions  223  and  224 . 
     Reference numerals  219  and  220  indicate regions where the 12-bit shift registers  103  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 . Reference numerals  224  and  225  indicate regions where the 4-bit shift registers  108  and the 12-bit shift registers  105  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 . Reference numerals  217  and  218  indicate regions where the 12-bit latch circuits  104  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 . Reference numerals  226  and  227  indicate regions where the 4-bit latch circuits  109  and the 12-bit latch circuits  106  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 . 
     Reference numerals  215  and  216  indicate regions where the AND circuits  107  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 , and reference numerals  203  and  204  indicate regions where the decoders  110  are formed similarly for the respective drive circuits. Reference numeral  209  and  210  indicate regions where the AND gates A 1  to A 288  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 , and reference numeral  211  and  212  indicate regions where the power transistors T 1  to T 288  are formed similarly for the respective drive circuits. Reference numeral  213  and  214  indicate regions where the heater elements H 1  to H 288  are formed for the respective drive circuits provided at both sides of the ink supply opening  202 , and reference numeral  207  and  208  indicate wiring regions where the signal lines and the like for transmitting various kinds of signals d 1  to d 24 , N 1  to N 12  and B 1  to B 4  are formed similarly for the respective drive circuits. 
     Reference numerals  200  and  201  indicate regions where voltage step-up circuits are formed for enhancing the driving capabilities of the transistors in the respective regions  211  and  212 . The voltage step-up circuit is used to increase the drive voltage of the logic circuit to provide each of the transistors with a gate voltage larger than the drive voltage. Reference numeral  202  indicates a supply opening region for supplying ink to the heater elements H 1  to H 288  from the reverse side of the substrate. Reference numeral  205  and  206  indicate regions each including a set of one heater element, one transistor and one AND gate. Here, the transistor and AND gate are formed corresponding to the heater element. 
     Reference numerals  230  and  231  indicate diode temperature sensors provided at both end sides of the heater element arrays. In this embodiment, a diode temperature sensor is further provided in a position corresponding to the center of each of the heater element arrays, thereby improving the accuracy of temperature detection. In this embodiment for this case, a region for arranging the temperature sensor is secured within each of the regions  207  and  208  in the foregoing drive circuit layout by appropriately arranging wirings of the signal lines for transmitting the drive signals d 1  to d 24  to the respective groups of heater elements. 
       FIG. 5  shows a wiring state of the signal lines for transmitting the drive signals d 1  to d 24  within the regions  207  and  208  in the layout in  FIG. 4  according to the first embodiment of the present invention. 
     Here, reference numeral Wd 1  indicates a signal line for transmitting the drive signal d 1 , and is connected to the heater elements H 1  to H 12  (a group including first to twelfth heater elements from the lowermost side in  FIG. 5 ). Reference numeral Wd 2  indicates a signal line for transmitting the drive signal d 2 , and is connected to the heater elements H 13  to H 24  (a group including thirteenth to twenty-fourth heater elements from the lowermost side in  FIG. 5 , similarly). The connection relationships between the other following-numbered signal lines and heater elements are defined in the same manner as described above. Thus, a signal line Wd 12  is connected to heater elements H 133  to H 144  (a group including 133rd to 144th heater elements from the lowermost side in  FIG. 5 ). 
     Also, reference numeral Wd 24  indicates a signal line for transmitting the drive signal d 24 , and is connected to the heater elements H 288  to H 277  (a group including first to twelfth heater elements from the uppermost side in  FIG. 5 ). Reference numeral Wd 23  indicates a signal line for transmitting the drive signal d 23 , and is connected to the heater elements H 276  to H 255  (a group including thirteenth to twenty-fourth heater elements from the uppermost side in  FIG. 5 , similarly). The connection relationships between the other following-numbered signal lines and heater elements are defined in the same manner as described above. Thus, a signal line Wd 13  is connected to heater elements H 156  to H 145  (a group including 133rd to 144th heater elements from the uppermost side in  FIG. 5 ). 
     In the aforementioned layout, the signal lines Wd 1  to Wd 12  are formed such that the number of signal lines crossing an intersecting direction intersecting (orthogonally intersecting, in this embodiment) a direction in which the heater element are arranged decreases with the decrease in the distance to the center of the heater element array. More specifically, the signal line Wd 1  is not formed out of a region for the first group of 12 heater elements from the lowermost side in  FIG. 5 , the signal line Wd 2  is not formed out of a region for the first and further second groups of 12 heater elements from the lowermost side in  FIG. 5 . Thus, only the signal line Wd 12  is eventually formed in a region for the group of 12 heater elements closest to the center of the heater element array. On the other hand, the number of the signal lines Wd 24  to Wd 13  also decreases with the decrease in the distance to the center of the heater element array. More specifically, the signal line Wd 24  is not formed out of a region for the first group of 12 heater elements from the uppermost side in  FIG. 5 , the signal line Wd 23  is not formed out of a region for the first and further second groups of 12 heater elements from the uppermost side in  FIG. 5 . Thus, only the signal line Wd 13  is eventually formed in a region for the group of 12 heater elements closest to the center of the heater element array. 
     In this embodiment, with attention focused on the foregoing layout, the wiring configuration of the signal lines Wd 1  to Wd 12  and Wd 24  to Wd 13  is appropriately determined as shown in  FIG. 5 . In other words, each of the signal lines is arranged not to linearly extend in a direction along the heater element array. To be more precise, instead of it, the number of signal lines is decremented by one as the distance from each start point of signal lines increases. Here, the start point is located in the proximity of each of both ends of the heater element array in the array direction. Thus, the signal lines are arranged in a staircase pattern in which, with the decrement in the number of signal lines crossing the above intersecting direction, the remaining signal lines are shifted toward the heater element array and thereby come close to the heater element array. 
     In this wiring configuration, each of the regions  207  and  208  includes an empty region, which is surrounded on three sides by the signal lines, around the center of the heater element array. Thus, the diode temperature sensors  232  and  233  are respectively arranged in these regions. Even when the temperature of the print element unit or the print head rises due to heat generated by the heater elements with the progress of a printing operation and the like, this configuration allows accurate detection of the temperature and enables control for obtaining the stable ejection characteristics. 
     Moreover, since the temperature sensor can be arranged within the region  207 , the substrate size does not increase in the width direction (in the lateral direction in  FIGS. 4 and 5 ). This avoids a problem of decreasing the number of substrates manufactured from a single wafer, and thereby prevents an increase in costs for substrates. 
     In contrast, in the case where the wiring configuration of the drive signal lines is not considered at all unlike this embodiment, for example, the signal lines are arranged to linearly extend in the direction along the heater element array, and then respective signal lines are wired so as to bend with respect to respective heater elements, as shown in  FIG. 6 . In such a case, each of the regions  207  and  208  becomes a rectangular region in which the signal lines are wired, along the heater element array. For this reason, when locating the temperature sensors at central portions of the substrate, the respective temperature sensors are inevitably arranged at the outer side of the regions  207  and  208 . That is to say, in this case, the substrate size increases in the width direction, which in turn decreases the number of substrates manufactured from a single wafer and leads to an increase in costs for substrates. 
     (5) Modified Example 
     In the embodiment shown in  FIG. 5 , the signal lines are arranged in the staircase pattern in which, every time the number of signal lines is decremented by one, the remaining signal lines are shifted toward the heater element array and thereby come close to the heater element array. As the wiring configuration, however, any configuration can be employed as long as the configuration certainly provides an area for arranging the temperature sensor in the region  207 . For instance, each of the signal lines may be arranged to linearly extend from the start point in the proximity of one end of the heater element array, to the heater element group to which the signal line is connected, i.e., the signal line may be arranged in a direction of an oblique line in  FIG. 5 . 
     In the foregoing example, the heater element arrays are provided at both sides of the ink supply opening  202  and the temperature sensors are provided to the respective heater element arrays. If temperature detection with desired accuracy is possible, providing of one temperature sensor to only one of the heater element arrays may be sufficient. In addition, the present invention is effectively applicable to even a case where the heater element array is arranged at only one side of the ink supply opening  202 . 
     Moreover, in the foregoing example, the number of heater elements targeted by one temperature sensor for temperature detection is set to  288  and the M=24 print elements are simultaneously can be driven at one driving timing. These heater elements are divided at the center of the array into two groups of 144 heater elements, and drive signals of M/2=12 bits are provided to the two groups, respectively, from opposite side portions of the substrate. However, the number of heater elements arranged and the dividing position of the heater elements may be determined as desired. More specifically, when M signal lines (also referred to as ‘M bits of drive signals’, hereinafter) are divided into L signal lines (also referred to as ‘L bits of drive signals’, hereinafter) for L-bit signal lines for selecting L heater elements, and (M−L) signal lines (also referred to as ‘(M−L) bits of drive signals’, hereinafter) for (M−L)-bit signal lines, M and L do not always have to satisfy L=M−L, i.e., L=M/2. The number L can be appropriately determined as long as a desired level of accuracy is achieved. Alternatively, if M is an odd number, L can be selected so as to satisfy L≈M−L, i.e., L≈M/2. In other words, a temperature sensor can be provided to a position near the center of the heater element array, instead of a position at the exact center of the heater element array, within a range where the temperature sensor can achieve a desired level of accuracy. The “substantial center of an array area” includes such cases. Incidentally, M and L are natural numbers. 
     Moreover, the foregoing example shows that the temperature sensor is configured of a diode, but the present invention is not limited to this. 
     Each of  FIGS. 7 and 8  shows an example in which temperature sensors  234  and  235  are formed by use of a wiring layer. When a temperature sensor is formed by use of a wiring layer, it is desirable to form a sensor wiring with a small width or to form the wiring in a meandering shape as shown in  FIGS. 7 and 8 . The sensor wiring thus formed has higher resistance than other regions. In this case, the temperature detection accuracy is improved, because the higher the resistance, the larger the change in the resistance due to the temperature characteristic. Further, the thickness of the wiring may be reduced instead of, or in addition to, making the width of the wiring thinner. 
     Although various materials are usable for the wiring layer to form the temperature sensor, one of desirable materials is the same material as that used for the wirings of the drive circuit. For example, aluminum is desirable. 
     2. Second Embodiment 
     The foregoing first embodiment provides the description of the configuration in which: the single ink supply opening  202  is provided in the substrate; and the heater elements are arranged at both sides of the ink supply opening  202 . Alternatively, the present invention is also applicable to a substrate provided with two or more ink supply openings. 
       FIG. 9  is a schematic diagram showing a layout of driving circuits and the like on a substrate provided with two ink supply openings according to a second embodiment of the present invention. As similar to the foregoing example, heater elements are arranged at both sides of each of ink supply openings  202   a  and  202   b . Incidentally, the two ink supply openings  202   a  and  202   b  may be provided for a single color ink or may be provided respectively for inks with different tones (colors, densities). 
     A diode temperature sensor is provided in a position corresponding to the substantial center of each of the heater element arrays as in the case of the first embodiment. Incidentally, although  FIG. 9  shows a case where a single temperature sensor  238   d  is provided in common to the heater element array at the left side of the ink supply opening  202   a  and the heater element array at the right side of the ink supply opening  202   b , two temperature sensors may be provided respectively to these two heater element arrays. 
     In addition, although  FIGS. 9 to 11  each illustrate a substrate including two ink supply openings, it is needless to say that the substrate may include three or more ink supply openings. 
     As shown in  FIGS. 10 and 11 , as in the cases shown in  FIGS. 7 and 8  of the modified examples of the first embodiment, respectively, temperature sensors  236   a ,  237   a  and  238   a  may also be formed by use of a wiring layer. 
     The second embodiment or its modified example produces not only the same effect as described above, but also the following advantageous effects. 
     3. Advantageous Effects of Second Embodiment 
     In the foregoing second embodiment, the present invention is applied to the substrate provided with two ink supply openings. Here, when the two ink supply openings are provided for the inks with different tones (colors, densities), each of the openings is formed to pass through the substrate from the obverse surface to the reverse surface. Likewise, when the two ink supply openings are provided for the same ink, each of the openings is formed to pass through the substrate. In the former case, independent ink supply paths for the respective inks are typically formed in a supporting member that is a component of the print head for supporting the substrate. In the latter case, however, the print head may employ a configuration in which an ink supply path of a supporting member for the same ink is connected to an area entirely covering the two ink supply openings that are open to the reverse surface of the substrate, whereby the ink is distributed to each of the ink supply opening. In the latter case, the substrate may possibly be configured so that a reverse surface of the substrate is out of contact with the supporting member, partially at a portion on the opposite side from an area where the heater elements are arranged (hereinafter, this configuration is referred to as “an ink distribution configuration” for convenience). 
     In this ink distribution configuration, the following problems may occur if the print head falls into the state of the so-called “blank ejection” due to ink supply failure attributed to any possible factor. Since most of the thermal energy generated with driving of the heater elements is usually consumed as ink ejection energy, the temperature of the substrate itself gradually increases with an increase of operating time of the print head. In the case of the blank ejection, however, the thermal energy generated by the heater elements remains in the substrate, whereby the substrate is subjected to a sharp rise of the temperature. This is because the thermal energy transmitted from the heater elements to the substrate is not effectively transmitted to the supporting member in the configuration in which the reverse surface of the substrate is out of contact with the supporting member, partially at the portion on the opposite side from the area where the heater elements are arranged. This tendency is especially remarkable in a central portion of the heater element array where the length of a heat transmission route to the supporting member is long. 
     The foregoing second embodiment or its modified example is effectively applicable to even such an ink distribution configuration. The following description shows application examples thereof. 
       FIG. 12  is a schematic cross section view for explaining a configuration of a substrate and its supporting member that employ the ink distribution configuration. As shown in  FIG. 12 , a substrate  1110  includes two ink supply openings that are open on a reverse surface thereof, and is bonded to a supporting member  807  with an adhesive agent  809 , at an area except for a communication portion with an ink supply path  808  to which the two ink supply openings are connected. Thus, a part of the substrate has the heater element array on its obverse surface and has the communication portion with the ink supply path  808  on its reverse surface. In other words, this part is not in contact with the supporting member  807  but faces a hollow portion. 
       FIG. 13  is a schematic plan view showing an example of a substrate in which the second embodiment is applied to such an ink distribution configuration. In the illustrated example, a wiring  810  is provided between the ink supply openings  202   a  and  202   b  to linearly extend from an electrode terminal  1105  disposed at one end of the substrate to an electrode terminal disposed at the other end thereof. When this wiring  810  itself is used to form a temperature sensor, the wiring  810  can be partially formed with a small width at a position XIV corresponding to the substantial center of the heater element array as shown in  FIG. 14 , and thereby can be configured to have higher resistance to achieve temperature detection with high accuracy. Instead, at the position P, the wiring  810  may be formed in the meandering shape, as shown in  FIG. 10  or  11 . Alternatively, as shown in  FIG. 9 , a diode temperature sensor can be inserted into the position P. 
       FIG. 15  is a schematic plan view for explaining another configuration example of a substrate and its supporting member employing the ink distribution configuration, and  FIG. 16  is a schematic cross section view taken along the line XVI-XVI in  FIG. 15 . 
     In this embodiment, the substrate  1110  is configured to have improved heat dissipation property by forming beams  813  partially in the ink supply path  808  in the supporting member  807 , the path  808  communicating with the ink supply openings  202   a  and  202   b . To put it differently, the substrate  1110  is configured to partially have an area in contact with the beams  813 , although the supporting member does not exist in the area in the configuration in  FIG. 12 . Incidentally, a concave portion of each of the beams shown by Q in  FIG. 16  is an engraved portion in a semicircular shape for surely allowing a sufficient amount of ink to flow at locations where the beams are formed. The concave portion may be in any other shape as long as the concave portion surely allows a sufficient amount of ink to flow. 
       FIG. 17  is a schematic plan view of a substrate showing a way of arranging temperature sensors in the foregoing configuration. A broken-line portion  808 A in  FIG. 17  is a communication portion with the ink supply path  808  in the supporting member provided on the reverse surface of the substrate. The substrate  1110  is in contact with the supporting member  807  at the positions where two beams  813  are formed. The beams  813  are provided in the positions evenly dividing the communication portion into three areas. In the illustrated example, a temperature sensor is provided at a position R corresponding to the center of each of the divided areas where the substrate and the supporting member  807  are out of contact with each other. In other words, at this position, the wiring is formed to have a small width or is formed in the meandering shape, or a diode temperature sensor is installed in the wiring. 
     With the configuration in which the reverse surface of the substrate  1110  is in contact with the supporting member  807  through the beams  813  as shown in this embodiment, the heat of the substrate is likely to dissipate toward the supporting member. Thus, the reliability against abnormal temperature rise is improved. In addition, in this embodiment, attention is focused on the areas, i.e., the divided areas, which have low heat transfer property because the reverse surface of the substrate is out of contact with the supporting member. Thus, in these areas, the temperature sensors are formed to achieve further improvement of the reliability against temperature rise. By forming a substrate in the aforementioned configuration, the substrate is prevented from undergoing abnormal temperature rise. Moreover, even if abnormal temperature rise occurs by any chance, the substrate and therefore the print head are prevented from being damaged, on the basis of the detection of the temperature sensors. 
     Incidentally, the number and positions of beams may be determined as desired. Meanwhile, from the viewpoint of abnormal temperature rise detection, it is preferable to dispose a temperature sensor at the position R corresponding to the center of each of the divided areas. In order to achieve even more accurate detection of the temperature in the entire area of the heater element array, it is strongly desirable to dispose a temperature sensor at a position corresponding to the substantial center of the heater element array even through the position is a place where the heat is easily transferred through a beam. For instance, even when a beam is located in a position evenly dividing the area of the heater element array into two areas, it is preferable to dispose temperature sensors not only at positions corresponding to the centers of the respective divided areas, but also at a position corresponding to the substantial center of the entire heater element array, for example, on the obverse side at the position corresponding to the location of the beam. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2008-142677, filed May 30, 2008, which is hereby incorporated by reference herein in its entirety.