Patent Publication Number: US-8974026-B2

Title: Liquid droplet ejection head, control device, control method, and manufacturing method of the same, and recording medium of the same methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based on and claims the benefit of priority under 35 U.S.C. §119 of Japanese Patent Application No. 2013-131882 filed Jun. 24, 2013, the entire contents of which are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a control device of a liquid droplet ejection head, and a control method and a manufacturing method of the liquid droplet ejection head. 
     2. Description of the Related Art 
     To form an image (print characters or print an image) on a surface of a recording medium, a liquid droplet ejection head may be used. Herein, the term “liquid droplet ejection head” refers to a device or the like that ejects (discharges) liquid droplets (e.g., ink droplets) through a plurality of respective ejection openings (nozzles) by applying a pressure to the liquid. Further, some liquid droplet ejection heads may detect a temperature thereof and control the ejection operation based on the detected temperature. 
     Japanese Laid-open Patent Publication No. H02-289354 discloses a technique of a liquid injection recording head (liquid droplet ejection head) in which an electro-thermal conversion body, which generates thermal energy to be used for ejecting liquid therefrom and a temperature detection device, which detects a temperature of the electro-thermal conversion body, are mounted on the same supporting body. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a control device of controlling an operation of a liquid droplet ejection head includes a head substrate having a plurality of ejection openings; a head controller applying a drive voltage to the head substrate to control an operation of ejecting liquid droplets from the ejection openings; a relay substrate electrically connecting the head substrate and the head controller to each other; a main-body controller controlling an operation of the head controller; and a voltage conversion circuit disposed in the relay substrate. 
     Further, the voltage conversion circuit converts a resistance value, which changes in accordance with a temperature of the head substrate, into an output voltage, the relay substrate inputs the output voltage into the main-body controller, and the main-body controller detects the temperature based on the output voltage input to the main-body controller and determines the drive voltage based on the temperature detected by the main-body controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following description when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic top view of an example liquid droplet ejection head according to an embodiment of the present invention; 
         FIG. 2  is a functional block diagram of an example configuration of the liquid droplet ejection head according to an embodiment; 
         FIG. 3  is a schematic circuit diagram of an example temperature detection unit (voltage conversion circuit) of the liquid droplet ejection head according to an embodiment; 
         FIG. 4  is a graph illustrating an example of a correction value of the liquid droplet ejection head according to an embodiment; 
         FIG. 5  is a graph illustrating another example of the correction value of the liquid droplet ejection head according to an embodiment; 
         FIG. 6  is a graph illustrating an example of a detection result (output voltage) of the temperature detection unit (voltage conversion circuit) of the liquid droplet ejection head according to an embodiment; and 
         FIG. 7  is a graph illustrating another example of the detection result (output voltage) of the temperature detection unit (voltage conversion circuit) of the liquid droplet ejection head according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the related technologies of the liquid droplet ejection head, in order to improve quality of an image to be formed, it is desired to more accurately control the liquid droplet ejection operation (discharge operation) of the liquid droplet ejection head. Along with the desire for the accurate control of the ejection operation, it is also desired to more accurately detect the temperature of the liquid droplet ejection head (hereinafter may be simplified as “head”). 
     However, in the related technologies (e.g., Japanese Laid-open Patent Publication No. H02-289354) of the liquid droplet ejection head, an overall resistance value is detected of the liquid droplet ejection head and the transmission path (e.g., the Flexible Flat Cable (FFC)) between the temperature detection device and the control section. Due to this, the detection value may include an error. 
     Namely, in this case, if, for example, the wiring distance of the transmission path is long, the impedance of the transmission path is high, or the transmission path is subject to influence of disturbance (e.g., noise), it may become difficult to accurately detect the temperature. 
     The present invention is made in light of this problem, and may provide a control device of a liquid droplet ejection head, a liquid droplet ejection head, a control method of the liquid droplet ejection head, and a manufacturing method of the liquid droplet ejection head in which it becomes possible to highly accurately detect the temperature based on an output voltage that changes in accordance with a temperature change. 
     With the descriptions below of a liquid droplet ejection head that ejects liquid as liquid droplets from the ejection openings (nozzles) thereof, non-limiting example embodiments of the present invention are described. Here, it should be noted that the present invention is applied to not only the liquid droplet ejection head described below but also, for example, a copier, a multifunction peripheral, a printer, a scanner, a plotter, a facsimile machine, and other image forming means (i.e., device, apparatus, unit, system, etc.) that form an image on a surface of a recording medium. Herein, the term “form an image on a surface of a recording medium” includes printing, imaging, and recording an image and printing characters. 
     Further, besides the liquid droplet ejection head described below, the present invention may also be applied to a forming unit that forms a three-dimensional shape (e.g., three-dimensional (3D) forming device). Here, the term “forming a three-dimensional shape” includes the forming of a DNA sample, a resist, a pattern material, and an object having a fine shape such as wires. 
     Further, in the following descriptions, the same or relevant reference numerals may be used throughout the figures to describe the same or equivalent members and parts. Further, the figures are not intended to illustrate the relative ratio between members or parts. Therefore, it becomes possible for a person skilled in the art to determine the specific sizes of the members and parts in the figures based on a non-limiting embodiment described below. 
     With reference to a liquid droplet ejection head according to an embodiment, the present invention is described in the following order. 
     1. Configuration of the liquid droplet ejection head 
     2. Control device of the liquid droplet ejection head 
     3. Example temperature detection unit 
     4. Control method of the liquid droplet ejection head 
     5. Manufacturing method of the liquid droplet 
     ejection head 
     6. Program and recording medium 
     1. Configuration of the Liquid Droplet Ejection Head 
     With reference to  FIG. 1 , an example of the liquid droplet ejection head according to an embodiment is described. Here,  FIG. 1  is a schematic top view of an example configuration of a liquid droplet ejection head  100  (i.e., a surface to eject liquid droplets) according to an embodiment of the present invention. It should be noted that the liquid droplet ejection head according to the present invention is not limited to this configuration. 
     As illustrated in  FIG. 1 , the liquid droplet ejection head  100  includes rows (four rows in this embodiment)  10   na ,  10   nb ,  10   nc , and  10   nd , each having a plurality of ejection openings (hereinafter may be “ejection-opening rows  10   na ,  10   nb ,  10   nc , and  10   nd ”) to eject liquid droplets from a head substrate  10 HP. For example, the four rows of ejection openings ( 10   na ,  10   nb ,  10   nc , and  10   nd ) may be eject black (K), yellow (Y), magenta (M), and cyan (C) color liquid droplets, respectively. 
     The liquid droplet ejection head  100  further includes drive Integrated Circuits (ICs)  10 ICa,  10 ICb,  10 ICc, and  10 ICd that control the operations of ejecting liquid droplets from the ejection-opening rows  10   na ,  10   nb ,  10   nc , and  10   nd , respectively. Here, when a thermal ejection method is used, the drive ICs  10 ICa,  10 ICb,  10 ICc, and  10 ICd control respective power levels supplied to a thermal source (head substrate  10 HP). 
     The liquid droplet ejection head  100  according to this embodiment causes the drive ICs  10 Ica,  10 ICb,  10 ICc, and  10 ICd to control the ejection of respective liquid droplets from the ejection openings of the head substrate  10 HP so that the liquid droplets are ejected at desired timings from desired ejection openings. 
     The liquid droplet ejection head  100  further includes a temperature detection unit (i.e., a voltage conversion circuit  12 S described below) provided on a surface of a relay substrate  12  (described below with reference to  FIG. 2 ) on the side contacting the head substrate  10 HP. Here, the temperature detection unit (the voltage conversion circuit  12 S) refers to a circuit to change an output voltage (hereinafter “output voltage “Vs””) in accordance with a resistance value that changes in association with a change of the temperature of the head substrate  10 HP. 
     Namely, the liquid droplet ejection head  100  according to this embodiment detects the temperature of the head substrate  10 HP as a temperature of a head unit by using the temperature detection unit (the voltage conversion circuit  12 S). A specific example of the temperature detection unit (the voltage conversion circuit  12 S) is described in the section “3. Example temperature detection unit” below. 
     The liquid droplet ejection head  100  according to this embodiment or a device including the liquid droplet ejection head  100  may further include an operation section (e.g., operation buttons, an operation panel, a touch panel, etc.) (not shown). Here, the term “operation buttons” refer to, for example, buttons to input operating conditions by an operator (or user). The term “operation panel” refers to, for example, a panel (e.g., a Liquid Crystal Display (LCD), a Light-Emitting Diode (LED), etc.) to display an operating state or an operation result of the liquid droplet ejection head  100 . 
     When the liquid droplet ejection head  100  is driven (i.e., when liquid droplets are ejected), the temperature of the head unit (including the head substrate  10 HP) and the temperature of liquid (“ink temperature”) in the head unit are increased by heat generation due to electric resistance and friction resistance of a piezoelectric element, heat generation due to electric resistance of wiring patterns, etc., and heat generation of the drive ICs and the like. 
     Namely, due to the temperature increase of the liquid (ink), the viscosity of the liquid (ink) is decreased while the liquid droplet ejection head  100  is driven. In this case, if the ejection operation of the liquid droplet ejection head  100  is controlled with the same drive waveform between before and after the temperature increase, the shape, the volume, etc., of the ejected ink droplets change due to the change of the viscosity of the liquid (ink). As a result, the ejection characteristics i.e., print quality) may be degraded (impaired). 
     The liquid droplet ejection head  100  according to this embodiment detects the temperature of the head unit (including the head substrate  10 HP) based on the output voltage “Vs” output from the temperature detection unit (the voltage conversion circuit  12 S). Further, the liquid droplet ejection head  100  according to this embodiment appropriately changes (selects) a drive voltage (drive waveform) based on the detected temperature to realize (obtain) desired ejection characteristics (print quality). A specific example of the liquid droplet ejection operation of the liquid droplet ejection head  100  is described in the section “4. Control method of the liquid droplet ejection head” below. 
     2. Control Device of the Liquid Droplet Ejection Head 
     With reference to  FIG. 2 , a control device  10  of the liquid droplet ejection head  100  according to this embodiment is described.  FIG. 2  is a schematic functional block diagram of an example configuration of the liquid droplet ejection head according to an embodiment. It should be noted that the functions of the liquid droplet ejection head  100  in the present invention are not limited to the functions described in  FIG. 2 . 
     As illustrated in  FIG. 2 , the liquid droplet ejection head  100  includes the control device  10 . Here, the control device  10  refers to a device that sends instructions to the elements of the liquid droplet ejection head  100  to control the operations of the elements. Further, as illustrated in  FIG. 2 , in the following descriptions, a combination including the head substrate  10 HP and the relay substrate  12  is called a head unit  100 U. Further, a main-body control section (main-body controller)  10 C and a head control section (head controller)  13  are mounted on a main-body control substrate  100 C. 
     The control device  10  in this embodiment includes the head control section  13 , which applies a drive voltage to the head substrate  10 HP, the main-body control section  10 C, which controls the operations of the head control section  13 , and the relay substrate  12  that electrically connects the head substrate  10 HP and the head control section  13  to each other. Here, the main-body control section  10 C and the head substrate  10 HP are connected to each other via a Flexible Printed Circuit (FPC). 
     The main-body control section  10 C is electrically connected to the head control section  13 . The main-body control section  10 C controls the operations of the head unit  100 U (head control section  13 ) and the like based on the operating conditions which are input to the liquid droplet ejection head  100 . The main-body control section  10 C inputs (transmits) the information indicating, for example, the drive voltage (drive waveform) to the head control section  13 . 
     Further, the main-body control section  10  according to an embodiment detects the temperature of the head unit  100 U (head substrate  10 HP) based on the output voltage “Vs” which is output from the relay substrate  12  (i.e., the temperature detection unit described below). The main-body control section  10 C inputs (receives) the output voltage “Vs”, which is illustrated, for example, in line “La” of  FIG. 6  described blow, from the relay substrate  12 . Namely, main-body control section  10 C inputs (receives) the output voltage “Vs” which changes in accordance with the temperature of the head substrate  10 HP. 
     In this case, the main-body control section  10 C stores in advance the relationship data between the output voltage “Vs” which is input to the main-body control section  10 C (the vertical axis of  FIG. 6 ) and the temperature of the head unit  100 U (head substrate  10 HP) (the horizontal axis of  FIG. 6 ). The main-body control section  10 C detects the temperature of the head unit  100 U (head substrate  10 HP) based on the input (received) value of the output voltage “Vs”. 
     Further, since the main-body control section  100  can detect the temperature of the head unit  100 U (head substrate  10 HP), the main-body control section  10 C sets (selects) an appropriate drive voltage (drive waveform) based on the detected temperature. By doing this, it becomes possible for the liquid droplet ejection head  100  (the main-body control section  10 C) to realize (set) desired ejection characteristics (i.e., print quality) based on the temperature of the head unit  100 U (head substrate  10 HP). 
     Further, for example, the main-body control section  10 C may use a program (e.g., a control program, an application program, etc.) stored in advance to control the operations of the elements of the liquid droplet ejection head  100  (such as the head unit  100 U, etc.). Further, for example, the main-body control section  10 C may further use the information which is input by a user via the operation section to control the operations of the elements of the liquid droplet ejection head  100 . 
     The relay substrate  12  is provided (used) to electrically connect the main-body control substrate  100 C and the head unit  100 U to each other. Also, the relay substrate  12  is provided (used) to electrically connect the head control section  13  and the head substrate  10 HP to each other. 
     The relay substrate  12  according to an embodiment further includes the temperature detection unit (i.e., the voltage conversion circuit  12 S of  FIG. 3  described below) to detect the temperature of the head unit  100 U (the head substrate  10 HP in this embodiment). The relay substrate  12  inputs (transmits) the detection result, which is detected by the temperature detection unit, (i.e., the output voltage “Vs” from the voltage conversion circuit  12 S) into the main-body control section  10 C (the main-body control substrate  100 C). 
     By doing this, in the liquid droplet ejection head  100  according to this embodiment, it becomes possible to detect the temperature of the head unit  100 U (the head substrate  10 HP) based on the detection result, which is detected by the temperature detection unit, (i.e., the output voltage “Vs” from the voltage conversion circuit  120 ). 
     Further, in the liquid droplet ejection head  100  according to this embodiment, since the temperature of the head unit  100 U can be detected based on the detection result which is detected by the temperature detection unit, it is not necessary to mount an element (part) dedicated to detecting the temperature such as a thermistor or the like. 
     Further, in the liquid droplet ejection head  100  according to this embodiment, since it is not necessary to mount an element (part) dedicated to detect the temperature such as a thermistor or the like, it becomes possible to effectively reduce the size and the cost of the liquid droplet ejection head  100 . An example of the temperature detection unit (the voltage conversion circuit  12 S) is described in the section “3. Example temperature detection unit” below. 
     Further, the relay substrate  12  may further include a storage section (not shown). When the relay substrate  12  includes the storage section, the relay substrate  12  may store the detection result which is detected by the temperature detection unit (e.g., a correction value, etc.). Further, in a case where the relay substrate  12  includes the storage section, the relay substrate  12  may store in advance a value of a voltage which is output from the voltage conversion circuit  12 S (an example of the temperature detection unit) when, for example, the temperature of the head substrate  10 HP is at a predetermined temperature “Ts” (hereinafter, the voltage may be referred to as a “reference voltage”). 
     By storing the detection result and/or the reference voltage in the storage section in advance, it becomes possible for the liquid droplet ejection head  100  (the main-body control section  10 C) to read the detection result and/or the value of the reference voltage stored in the storage section of the relay substrate  12  of the head unit  100 U when, for example the head unit  100 U is exchanged. Further, the liquid droplet ejection head  100  (the main-body control section  10 C) may store the detection result and/or the value of the reference voltage into the storage section of the relay substrate  12  of the head unit  100 U when, for example, the liquid droplet ejection head  100  is manufactured. 
     Here, the predetermined temperature “Ts” may be defined as the temperature which is determined based on the resistance values of the voltage conversion circuit  12 S and a transmission path  11  (see  FIG. 2 ) and other specifications of the liquid droplet ejection head  100 . Further, the predetermined temperature “Ts” may be defined as the temperature which is set in the “5. Manufacturing method of the liquid droplet ejection head” described below (for example, when heat is applied while the head control section  13  and the relay substrate  12  are sealed). 
     Further, the predetermined temperature “Ts” may be defined as the temperature of the head unit  1000  when it is desired to correct (adjust), for example, the variation of the resistance values of the wires in the liquid droplet ejection head  100  when the liquid droplet ejection head  100  is manufactured and the variation of the resistance value(s) of the voltage conversion circuit  12 S. 
     The relay substrate  12  may further include an analog-to-digital (A/D) conversion circuit (not shown). Namely, when the relay substrate  12  includes the A/D conversion circuit, the relay substrate  12  may convert the output voltage “Vs”, which is output from the voltage conversion circuit  12 S (temperature detection unit), into digital data. 
     Further, when the relay substrate  12  includes the A/D conversion circuit, the relay substrate  12  may input (transmit) the digital data converted by the A/D conversion circuit into the main-body control section  10 C (the main-body control substrate  100 C). Namely, since the liquid droplet ejection head  100  can convert the value of the output voltage “Vs” which is output from the voltage conversion circuit  12 S into the digital data, the liquid droplet ejection head  100  can reduce the risk that disturbance (e.g., noise) is included into the detection result (and output voltage “Vs”). 
     Especially, since the liquid droplet ejection head  100  can transmit a digital signal (digital data) where the risk to receive the influence of disturbance can be reduced without transmitting an analog signal to the transmission path  11  (the FFC, etc.) which is subject to, for example, the influence of disturbance, it becomes possible to improve the accuracy of the detected temperature. 
     The head control section  13  is a substrate (base board) which is electrically connected to the head substrate  10 HP via the relay substrate  12 . Further, the head control section  13  controls the ejection operation of the head substrate  10 HP based on the information which is input from the main-body control section  10 C. 
     Specifically, the head control section  13  generates drive voltages to be applied to the head substrate  10 HP, by using the drive ICs  10 ICa,  10 ICb,  10 ICc, and  10 ICd of  FIG. 1 , based on the information related to the drive waveform which is input from the main-body control section  10 C, and applies the generated drive voltages to the head substrate  10 HP. By doing this, the head control section  13  can control the operation of ejecting droplets from the openings of the head substrate  10 HP (i.e., the ejection operation). 
     3. Example Temperature Detection Unit 
     An example of the temperature detection unit of the liquid droplet ejection head  100  according to an embodiment is described with reference to  FIG. 3 .  FIG. 3  illustrates an example of the voltage conversion circuit  12 S as the temperature detection unit used in the liquid droplet ejection head  100 . In  FIG. 3 , for example, the input voltage “Vcc” may be 3.3 V and the resistances of the voltage dividing resistors “R 0 ”, “R 1 ”, “R 2 ”, “R 3 ”, and “R 4 ” may be 100 Ω, 1 kΩ, 47 kΩ, 3.3 kΩ, and 150Ω, respectively. It should be noted that the temperature detection unit according to the present invention is not limited to the voltage conversion circuit  12 S illustrated in  FIG. 13 . 
     As illustrated in  FIG. 3 , the temperature detection unit (the voltage conversion circuit  12 S) of the liquid droplet ejection head  100  includes a resistor  12 Rs whose resistance value changes in accordance with the temperature change. Further, the temperature detection unit converts the input voltage “Vcc” into the output voltage “Vs” (“Vout” in  FIG. 3 ) and outputs the output voltage “Vs” (“Vout”). Namely, the temperature detection unit uses the resistor  12 Rs whose resistance value changes in accordance with the temperature change and outputs the output voltage “Vs” (“Vout”) which corresponds to the temperature change (resistance value change). 
     More specifically, as illustrated in  FIG. 3 , the voltage conversion circuit  12 S (temperature detection unit) applies the input voltage “Vcc” to the resistor  12 Rs, whose resistance value changes in accordance with the temperature change, and the voltage dividing resistor “R 0 ”. When the temperature changes (i.e., when the resistance value of the resistor  12 Rs changes), the voltage conversion circuit  12 S uses a comparator 12Cmp (see  FIG. 3 ) to convert the changed amount of the resistance value of the resistor  12 Rs due to the temperature change into a change amount of a voltage value. 
     Then, the voltage conversion circuit  12 S uses an amplifier 12Amp to amplify the change amount of the voltage value by comparing the output voltage of the comparator 12Cmp with a voltage which is determined based on the input voltage “Vcc” and the voltage dividing resistors “R 3 ” and “R 4 ”. Then, the voltage conversion circuit  12 S outputs the amplified voltage (the change amount of the voltage) as the output voltage “Vs” (“Vout”) which corresponds to the temperature change. 
     The temperature detection unit according to an embodiment (i.e., the voltage conversion circuit  12 S) outputs the output voltage “Vs” to the main-body control section  10 C via the transmission path  11 . In this case, for example, as illustrated in the line “La” of  FIG. 6 , the temperature detection unit outputs the output voltage “Vs” (the vertical axis) corresponding to the temperature “Th” of the head unit  100 U (the horizontal axis). Here, when the temperature detection unit includes the A/D conversion circuit, the temperature detection unit may converts the output voltage “Vs” into digital data. 
     4. Control Method of the Liquid Droplet Ejection Head 
     Next, an example operation of ejecting liquid droplets (push-pull operation in a piezoelectric method) by the liquid droplet ejection head  100  according to an embodiment is described. Here, it should be noted that the operation of ejecting liquid droplets by the liquid droplet ejection head  100  according to the present invention is not limited to the operations described below. 
     Namely, for example, the operation of ejecting liquid droplets (push-pull operation in a piezoelectric method) by the liquid droplet ejection head  100  according to an embodiment may be based on a method in which a heat generation resistor is used to heat liquid to generate bubbles therein (so-called thermal type) (see, for example, Japanese Laid-open Patent publication No. S61-59911), or a method in which an electrostatic force is used to apply a pressure onto the liquid (so-called electrostatic type) (see, for example, Japanese Laid-open Patent publication No. H06-71882). 
     Based on the information input by a user via the operation section or the like, the main-body control section  10 C (see  FIG. 2 ) of the liquid droplet ejection head  100  starts the operation of ejecting liquid droplets. Namely, based in the input information, the main-body control section  10 C outputs the information of the drive waveform(s) (drive voltage(s)) into the head control section  13  ( FIG. 2 ). 
     Next, the head control section  13  uses the drive ICs  10 ICa,  10 ICb,  10 ICc, and  10 ICd ( FIG. 1 ) to generate respective drive voltages corresponding to the drive waveform(s) and applies the generated drive voltage(s) to the head substrate  10 HP. Base on this operation, the head substrate  10 HP ejects liquid droplets through the ejection openings (nozzles) in accordance with the input drive waveform(s). 
     Specifically, as the drive voltage to be applied, first, the head control section  13  reduces the voltage applied to the head substrate  10 HP to be less than a reference potential (voltage) to shrink (retract) the piezoelectric element in the head substrate  10 HP. In this case, due to the shrinkage of the piezoelectric element, the volume (capacity) of a liquid chamber in the head substrate  10 HP is increased (expanded). By doing this, it becomes possible for the head control section  13  to supply liquid (e.g., ink) to refill the liquid chamber of the head substrate  10 HP. 
     Next, the head control section  13  increases the voltage applied to the head substrate  10 HP to be greater than the reference potential to expand (project) the piezoelectric element of the head substrate  10 HP. In this case, due to the expansion of the piezoelectric element, the volume (capacity) of a liquid chamber in the head substrate  10 HP is reduced (shrunk). By doing this, it becomes possible for the head control section  13  to apply pressure to liquid in the liquid chamber, so as to eject (inject) liquid in the liquid chamber through the ejection openings (nozzles). 
     After that, the head control section  13  sets the voltage applying to the piezoelectric element back to the reference potential to return (restore) the piezoelectric element back to the original position (state). In this case, the head substrate  10 HP reduces the pressure in the liquid chamber due to the expansion of the liquid chamber, so as to supply liquid (e.g., ink) to refill the liquid chamber. Next, the head control section  13  repeats the operation of ejecting liquid droplets based on the information related to the drive waveform(s) (drive voltage(s)) input from the main-body control section  10 C. 
     The liquid droplet ejection head  100  (the main-body control substrate  100 C) according to an embodiment detects the temperature of the head unit  100 U ( FIG. 2 ) by using the temperature detection unit and controls the ejection operation based on the detected temperature while driving (i.e., while ejecting liquid droplets). Namely, the main-body control section  10 C (the main-body control substrate  100 C) detects the temperature of the head substrate  10 HP (the head unit  100 U) based on the output voltage “Vs” output from the voltage conversion circuit  12 S (the temperature detection unit), and appropriately changes (selects) the drive voltage (the drive waveform) based on the detected temperature. 
     Specifically, first, as a voltage conversion step, the liquid droplet ejection head  100  uses the voltage conversion circuit  12 S disposed in the relay substrate  12  to convert the resistance value, which changes in accordance with the temperature of the head substrate  10 HP, into the output voltage “Vs”. Then, as a voltage input step, the liquid droplet ejection head  100  uses the relay substrate  12  to input (transmit) the output voltage “Vs” into the main-body control section  10 C via the transmission path  11 . Next, as a temperature detection step, the liquid droplet ejection head  100  uses the main-body control section  10 C to detect the temperature of the head unit  100 U (the head substrate  10 HP) based on the input (received) output voltage “Vs”. 
     Here, the main-body control section  10 C stores in advance the relationship between the output voltage “Vs” to be input (received) and the temperature “Th” of the head unit  100 U. Therefore, it becomes possible for the main-body control section  10 C to identify the temperature corresponding to the input (received) output voltage “Vs”, and detect the identified temperature as the temperature of the head unit  1000  (the head substrate  10 HP). 
     After that, as a head drive step, the liquid droplet ejection head  100  uses the main-body control section  10 C to determine (select) the drive voltage adapted to the detected temperature. Further, the liquid droplet ejection head  100  uses the head control section  13  (the drive Its  10 ICa,  10 ICb,  10 ICc, and  10 ICd) to apply the determined drive voltage(s) to the head substrate  10 HP, so as to eject liquid droplets from the ejection openings (nozzles) of the head substrate  10 HP. 
     By doing as described above, (the main-body control section  10 C of) the liquid droplet ejection head  100  can realize desired ejection characteristics (print quality) in accordance with the temperature “Th” of the head unit  100 U. (The main-body control section  10 C of) the liquid droplet ejection head  100  can realize desired ejection characteristics (print quality) in accordance with, for example, the temperature of the head substrate  10 HP, the temperature (viscosity) of liquid (ink), etc. 
     When the relay substrate  12  in the liquid droplet ejection head  100  includes the storage section, by comparing the detection result (e.g., the reference potential at the predetermined temperature “Ts”) and the output voltage “Vs” stored in the storage section in advance, the temperature “Th” of the head unit  100 U may be determined. Further, when the relay substrate  12  in the liquid droplet ejection head  100  includes the storage section, the temperature “Th” of the head unit  100 U may be estimated by further using drive history stored in the storage section. 
     5. Manufacturing Method of the Liquid Droplet Ejection Head 
     In the liquid droplet ejection head  100  according to an embodiment, the head unit  100 U ( FIG. 2 ) is manufactured by stacking (laminating) the head substrate  10 HP and the relay substrate  12 . Further, the liquid droplet ejection head  100  according to an embodiment is manufactured by electrically connecting the head unit  100 U (the relay substrate  12  and the head substrate  10 HP) and the main-body control substrate  100 C (the main-body control section  10 C and the head control section  13 ) to each other via the transmission path  11  ( FIG. 2 ). 
     In a method of manufacturing the liquid droplet ejection head  100 , as the head substrate  10 HP, for example, a silicon substrate, a substrate made of a polyphenylene sulphite (PPS), thermal hardening resin, synthetic resin, engineering plastic, etc., may be used. When the head substrate  10 HP is made of a silicon substrate, the liquid chamber and the ejection openings can be formed by anisotropic etching using alkaline etching solution such as calcium hydroxide solution (KOH). Further, the wirings and the circuits of the head substrate  10 HP may be formed by using, for example, a photolithography technique, an electroforming process, or a Chemical Vapor Deposition (CVD) method. 
     In a method of manufacturing the liquid droplet ejection head  100 , as the relay substrate  12 , for example, a silicon substrate, a substrate made of a polyphenylene sulphite (PPS), thermal hardening resin, synthetic resin, engineering plastic, etc. may be used. Further, in the relay substrate  12  according to an embodiment, the temperature detection unit (e.g., the voltage conversion circuit  12 S in  FIG. 3 ) is disposed (formed) (voltage conversion circuit forming step). The temperature detection unit (e.g., the voltage conversion circuit  12 S) may be disposed (formed) on the surface of the relay substrate  12  by using, for example, a photolithography technique, an electroforming process, or a Chemical Vapor Deposition (CVD) method. 
     In a method of manufacturing the liquid droplet ejection head  100 , as the main-body control substrate  100 C, an arithmetic processing unit including known Central Processing Unit (CPU), memories (Read Only Memory (ROM) and Random Access Memory (RAM)), etc., may be used. Here, the CPU reads an Operating System (OS) and a program from a storage device (e.g., the ROM) and performs logical operations, etc., to control elements and calculate data, process data, etc. The ROM stores a control program, operating conditions, etc. The RAM is used as a working area (a cache memory, a work area) to temporarily store data which are necessary for executing a program. 
     In a method of manufacturing the liquid droplet ejection head  100 , as the transmission path  11 , a belt-like cable coated with a resin film may be used. In a method of manufacturing the liquid droplet ejection head  100 , as the transmission path  11 , an FFC may be used where a plurality of conductive wires are bundled in a belt form and coated with a resin film. 
     With reference to  FIGS. 4 and 5 , a correction value calculation step is described of calculating a correction value which is to be used for detecting the temperature “Th” of the head unit  100 U in an adjusting step in a manufacturing method of the liquid droplet ejection head  100 . Namely, a step (an adjustment step) is described of cancelling a temperature measurement error due to impedance of the transmission path  11  between the head unit  100 U and the main-body control substrate  100 C and correcting the variation of the wiring resistance of the head unit  100 U and the variation of the parts of the temperature detection unit.  FIGS. 4 and 5  illustrates one example of the correction value to be used by the liquid droplet ejection head  100 . 
     As illustrated in  FIG. 4 , in the liquid droplet ejection head  100 , the value of the output voltage “Vs” varies due to variation of parts in the temperature detection unit (the voltage conversion circuit  12 S). The voltage “Lm” in  FIG. 4  refers to the output voltage “Vs” when, for example, it is assumed that the resistance tolerance (variation of the parts) of the voltage conversion circuit  12 S is 0.050 and errors are summed only in the direction of increasing the error amount. 
     On the other hand, the voltage “Lo” in  FIG. 4  refers to the output voltage “Vs” when, for example, the resistance value of the voltage conversion circuit  12 S does not include an error. In comparison between the voltages “Lm” and “Lo” in  FIG. 4 , even when the output voltage of the voltage conversion circuit  12 S is the same, there is approximately 0.7 degrees (see “ΔT” in  FIG. 4 ) of difference therebetween due to the resistance tolerance (variation of the parts) of the voltage conversion circuit  12 S. 
     To take the difference in consideration, in a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, the variation of (the part of) the voltage conversion circuit  12 S is regarded as the variation of the wiring resistance (e.g., the impedance of the transmission path  11 ), and the correction value to correct the voltage “Lm” to the voltage “L25” in  FIG. 4  is calculated. 
     Namely, in a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, a single correction value is calculated by further using the resistance value (impedance) of the transmission path  11  electrically connecting between the main-body control substrate  100 C and the relay substrate  12  (the head unit  100 U) without separating the variation of the parts of the voltage conversion circuit  12 S and the variation of the wiring resistance. 
     In a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, in a step of heating the head unit  100 U (e.g., in heating when the relay substrate  12  is sealed), the correction value may be calculated based on the output voltage “Vs” of the temperature detection unit. As the heat step in the method of manufacturing the liquid droplet ejection head  100 , for example, as illustrated in  FIG. 5 , the head unit  100 U is heated at a temperature in a range from 37 to 40° C. 
     In this case, the correction value may be calculated by comparing the voltage “Lm”, which is output when the head unit  100 U is heated as the heat process in the method of manufacturing the liquid droplet election head  100  (when the resistance value of the voltage conversion circuit  12 S includes an error), and the voltage “Lo” (when the resistance value of the voltage conversion circuit  12 S does not include an error). 
     By doing this, in the method of manufacturing the liquid droplet ejection head  100 , it becomes possible to measure (calculate) the correction value without adding a heat process to calculate the correction value. Namely, it becomes possible to reduce the manufacturing cost of the liquid droplet ejection head  100 . 
     Further,  FIG. 6  illustrates an example output voltage of the temperature detection unit in the liquid droplet ejection head  100 . Here, the voltage “La” in  FIG. 6  is one example of the output voltage of the voltage conversion circuit  12 S according to an embodiment (when the voltage conversion circuit  12 S is mounted on the relay substrate  12 ). On the other hand, the voltage “Lb” in  FIG. 6  is another example of the output voltage of the voltage conversion circuit  12 S according to an embodiment (when the voltage conversion circuit  12 S is not mounted on the relay substrate  12 ). 
     As illustrated in  FIG. 6 , the change amount in the voltage “Lb” relative to the temperature change (when the voltage conversion circuit  12 S is not mounted on the relay substrate  12 ) is (relatively small). Due to this, the voltage “Lb” is subject to influence of noise. On the other hand, the change amount in the voltage “La” relative to the temperature change (when the voltage conversion circuit  12 S is mounted on the relay substrate  12 ) is greater than that in the voltage “Lb”. 
     Namely, by mounting the voltage conversion circuit  12 S on the relay substrate  12 , it becomes possible to increase the change amount of the voltage (increase the absolute value of the inclination of the voltage in the graph) so as to be less subject to (reduce) the influence of noise. 
       FIG. 7  illustrates the output voltages “Vs” when the wiring resistance of the temperature detection unit (the voltage conversion circuit  12 S) in the liquid droplet ejection head  100  is set to 90 Ω, 100Ω, and 110Ω. In  FIG. 7 , the lines “L(90)”, “L(100)”, and “L(110)” denote the cases where the wiring resistances are 90 Ω, 100Ω, and 110Ω, respectively. Here, the wiring resistance varies depending on variation in the film pressure of the wirings and in etching process in manufacturing the liquid droplet ejection head  100 . 
     As illustrated in  FIG. 7 , in comparison among the cases of the lines “L(90)”, “L(100)”, and “L(110)”, there exist a difference of more than 40° C. even at the same output voltage. Namely, it is desired to correct the relationship between the temperature “Th” of the head unit  100 U and the output voltage “Vs” in accordance with the variation of the wiring resistance in manufacturing the liquid droplet ejection head  100 . 
     Here, the wiring resistance “R” can be calculated based on the following formula (1):
 
 R= 100+ AT   formula (1)
 
     Where, the symbol “A” denotes a temperature coefficient, and the symbol “T” denotes a detected temperature. 
     When the wiring resistance of the voltage conversion circuit  12 S varies due to a diameter of the wirings, the temperature coefficient “A” is not changed. Due to this, when a resistance change rate is given as “X”, the wiring resistance “R” can be expressed in the following formula (2):
 
 R=X (100+ AT )  formula (2)
 
     Namely, in a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, the resistance change rate “X” is calculated, so that the correction is done in a whole temperature range by using the calculated resistance change rate “X”. In a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, for example, at an ordinary temperature such as around 25° C., the temperature “Th” of the head unit  100 U and the output voltage “Vs” are measured. Then, the wiring resistance in this case is calculated and a ratio to a target value is calculated, so that the output voltage “Vs” in a range from 0 to 40° C. is corrected based on the calculated ratio. By doing this, in the method of manufacturing the liquid droplet ejection head  100 , it becomes possible to detect the temperature “Th” of the head unit  100 U. 
     As described above, in a method of manufacturing (a step of adjusting) the liquid droplet ejection head  100  according to an embodiment, it becomes possible to reduce an error in temperature detection (temperature measurement error) due to the impedance of the transmission path  11  between the head unit  100 U and the main-body control substrate  100 C. Further, in a method of manufacturing (a step of adjusting) the liquid droplet ejection head  100  according to an embodiment, it becomes possible to correct the variation of the wiring resistance in the head unit  100 U and the variation of the parts in the temperature detection unit. 
     Namely, in a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, in the adjustment step, it becomes possible to correct (1) the variation of the wiring resistance of the transmission path  11 , etc., (2) the variation of the temperature detection unit (the voltage conversion circuit  12 S), and (3) the variation of the wiring resistance inside the main-body control substrate  100 C (the main-body control section  10 C, etc.). 
     Based on the above, in a method of manufacturing the liquid droplet ejection head  100  according to an embodiment, it becomes possible to adjust (correct) the above variations (1) through (3) in a single adjustment process. Therefore, it becomes possible to reduce the manufacturing cost of the liquid droplet ejection head  100 . 
     6. Program and Recording Medium 
     A program “Pr” according to an embodiment causes a computer to execute the method of controlling an operation of a liquid droplet ejection head including a head substrate having a plurality of ejection openings, a head controller applying a drive voltage to the head substrate, a relay substrate electrically connecting the head substrate and the head controller to each other, and a main-body controller electrically connected to the relay substrate, the method including a voltage conversion step of converting, by a voltage conversion circuit disposed in the relay substrate, a resistance value, which changes in accordance with a temperature of the head substrate, into an output voltage; a voltage input step of inputting, by the relay substrate, the output voltage into the main-body controller; a temperature detection step of detecting, by the main-body controller, the temperature based on the output voltage input to the main-body controller; and a head drive step of determining, by the main-body controller, the drive voltage based on the detected temperature and applying the drive voltage to the head substrate to eject liquid droplets from the ejection openings. 
     By executing the method, the same effect as that in “4. Control method of the liquid droplet ejection head” can be obtained. 
     Another program “Pr” according to an embodiment causes a computer to execute the method of manufacturing a liquid droplet ejection head including a head substrate having a plurality of ejection openings, a head controller applying a drive voltage to the head substrate, a relay substrate electrically connecting the head substrate and the head controller to each other, and a main-body controller electrically connected to the relay substrate, the method including a voltage conversion circuit allocation step of allocating a voltage conversion circuit, whose resistance value changes in accordance with a temperature of the head substrate, in the relay substrate; and a correction value calculation step of calculating a correction value associating the temperature of the head substrate with the resistance value of the voltage conversion circuit. Here, in the correction value calculation step, a resistance value of a transmission path, which electrically connects the main-body controller and the relay substrate to each other, is further used to calculate the correction value. 
     By executing the method, the same effect as that in “5. Manufacturing method of the liquid droplet ejection head” can be obtained. 
     According to an embodiment, it is possible to provide a (non-transitory and computer-readable) recording medium “Md” storing the above program “Pr”. As the recording medium “Md” storing the above program “Pr”, a Flexible Disk (PD), a Compact Disk-ROM (CD-ROM), a CD Recordable (CD-R), a Digital Versatile Disk (DVD), other computer-readable media, a semiconductor memory such as a flash memory, a RAM, a ROM, etc., a memory card, a Hard Disk Drive (HDD) or any other computer-readable object may be used. 
     Here, it is assumed that the recording medium “Md” storing the above program “Pr” includes a server capable of transmitting the program “Pr” via a network and a volatile memory in a computer system as a client of the server. Here, the “network” refers to, for example, a network such as the Internet and a communication line such as a telephone line. 
     Here, the “volatile memory” refers to, for example, a Dynamic Random Access Memory (DRAM). Further, the program “Pr” stored in the recording medium “Md” may include a so-called differential file which can achieve the functions upon being combined with a program already recorded in a computer system. 
     According to an embodiment of the present invention, there is provided a method of controlling an operation of a liquid droplet ejection head including a head substrate having a plurality of ejection openings, a head controller applying a drive voltage to the head substrate, a relay substrate electrically connecting the head substrate and the head controller to each other, and a main-body controller electrically connected to the relay substrate, the method including a voltage conversion step of converting, by a voltage conversion circuit disposed in the relay substrate, a resistance value, which changes in accordance with a temperature of the head substrate, into an output voltage; a voltage input step of inputting, by the relay substrate, the output voltage into the main-body controller; a temperature detection step of detecting, by the main-body controller, the temperature based on the output voltage input to the main-body controller; and a head drive step of determining, by the main-body controller, the drive voltage based on the detected temperature and applying the drive voltage to the head substrate to eject liquid droplets from the ejection openings. 
     Further, according to an embodiment of the present invention, there is provided a method of manufacturing a liquid droplet ejection head including a head substrate having a plurality of ejection openings, a head controller applying a drive voltage to the head substrate, a relay substrate electrically connecting the head substrate and the head controller to each other, and a main-body controller electrically connected to the relay substrate, the method including a voltage conversion circuit allocation step of allocating a voltage conversion circuit, whose resistance value changes in accordance with a temperature of the head substrate, in the relay substrate; and a correction value calculation step of calculating a correction value associating the temperature of the head substrate with the resistance value of the voltage conversion circuit. Further, in the correction value calculation step, a resistance value of a transmission path, which electrically connects the main-body controller and the relay substrate to each other, is further used to calculate the correction value. 
     Further, according to an embodiment of the present invention, there is provided a program causing a computer to execute the above method of controlling an operation of a liquid droplet ejection head or the above method of manufacturing a liquid droplet ejection head. 
     Further, according to an embodiment of the present invention, there is provided a recording medium storing the above program. 
     In a control device of controlling an operation of a liquid droplet ejection head and a method of controlling an operation of a liquid droplet ejection head or a method of manufacturing a liquid droplet ejection head according to an embodiment of the present invention, it becomes possible to detect the temperature based on the output voltage which varies depending on the temperature change or detecting the temperature based on the output voltage. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.