Patent Publication Number: US-2011057975-A1

Title: Recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 12/549,226 filed Aug. 27, 2009, which is a Divisional of U.S. patent application Ser. No. 11/686,117 filed Mar. 14, 2007, issued U.S. Pat. No. 7,600,841, which claims priority from Japanese Patent Application No. 2006-071128 filed Mar. 15, 2006, the entire contents of each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording apparatus for recording an image on a recording medium. 
     2. Description of the Related Art 
     A thermal printer and an inkjet recording apparatus, which records characters and images by ejecting ink onto a recording medium, such as recording paper, are well known as a recording apparatus. An inkjet recording apparatus, which is typically used as an information outputting unit of a printer, a copier, or a facsimile machine, performs recording by ejecting ink while moving a relative position between a recording medium and an inkjet recording head. The image quality of a recording result of the inkjet recording apparatus depends on control of a relative velocity between the inkjet recording head and the recording medium, control of an ejection timing associated therewith, and stability of power supply to the recording head. 
     Ink jet recording apparatuses are broadly divided into a so-called serial type and full-line type. The serial-type recording apparatus performs recording by ejecting ink while moving an inkjet recording head and is commonly and widely used. 
     The ink ejecting recording head can eject ink by the operation of a piezoelectric element, the momentary surface boiling of ink, or some other operation. A recording head that ejects ink by boiling of ink supplies ejection energy by boiling ink adjacent to a heater in the vicinity of an ink path adjacent to an ink nozzle by energization of the heater. 
     In order to maintain satisfactory image quality, it is important to generate uniform ink droplets by continuous stable supply of energy required for ejecting ink and by maintaining the same conditions for ink ejection. However, in recording operations, a duty ratio varies with image data, and thus the number of heaters simultaneously energized varies. Therefore, driving conditions vary depending on effects of voltage variations caused by the difference between output currents of a power source, the difference between drop voltages caused by the resistive component in a transmission system, and some other factor. 
     Ink ejection control described above is carried out in a range that satisfies a stable ejection condition by use of high accuracy of an output voltage of a power source or a transmission system that has a structure with lower loss. A DC/DC converter that supplies the recording head with power is described below. 
       FIG. 10  illustrates a block diagram of a voltage control system including a DC/DC converter in the related art. A DC/DC-converter input voltage Vin supplied from a power-source unit (not shown) is input to a switching element  201 . The input voltage Vin is output from the switching element  201  and a diode  209  as a direct-current output converted via an inductor  202  and a capacitor  204 . The output is supplied as an output voltage VH to a recording head being a load. The switching element  201  is connected to a capacitor  203  at its input side and to the capacitor  204  at its output side via the inductor  202 . The inductor  202  and the capacitor  204  constitute a smoothing circuit  205 . The output voltage signal VH detected from an output terminal of the smoothing circuit  205  is subjected to direct-current voltage division by a resistor R 1  and a resistor R 3  in a voltage control circuit  206 , is input to an error amplifier  207  included in the voltage control circuit  206 , and is feedback-controlled. 
     An output signal from the error amplifier  207 , which receives a Vcc potential from a reference voltage  212  and a feedback output voltage signal VH, is an output signal of the voltage control circuit  206  and performs pulse-width modulation (PWM) control and constant voltage control on the switching element  201  via a PWM comparator circuit  208 . A resistor R 5  and a capacitor Cl connected to an inversion terminal and an output terminal of the error amplifier  207 , respectively, constitutes an example of a phase compensation circuit for adjusting stability and responsivity of an output voltage. 
     As described above, power is supplied such that feedback is controlled so that a stable output voltage is supplied so as to accommodate variations in output current caused by variations in the number of nozzles simultaneously driven on a recording head being a load. 
     The recent improvement in semiconductor processes enables the switching speed of a DC/DC converter to be driven at the megahertz level. Additionally, the responsivity of feedback control found in current-mode control is becoming high, like the advent of a control IC that achieves high responsivity on the order of microseconds, so it becomes possible to accurately supply power. 
     For an inkjet recording head, the performance of ink ejection is apt to depend on the temperature of the recording head. In particular, in a thermal inkjet recording apparatus, since ink droplets are ejected from nozzles by film boiling of ink caused by energization of heater resistors of the recording head, the temperature of the recording head during printing varies constantly. 
     In particular, when a larger number of sheets are printed continuously or a high-duty image is printed, the frequency of foaming of ink in the recording head increases and the number of ink ejection operations is high, and thus the temperature of the recording head gradually rises. 
     For the performance of ink ejection with respect to temperature, at low temperatures, the viscosity of ink is high and thus it is difficult to eject, and at high temperatures, the viscosity of ink is low and thus the amount of ink ejected from nozzles increases. Therefore, a defect of ink ejection, such as an increased diameter of a dot of a pixel formed on a recording medium, occurs. 
     Japanese Patent Laid-Open No. 10-119273 describes correction of energy for heat generation with respect to variations in the temperature of a recording head by controlling a driving pulse width. 
     However, if the temperature of the recording head itself continues rising by continuous recording operations, control of only the driving pulse width may not suppress an increase in the amount of ink ejection. That is, under present circumstances, it is difficult to perform control of reducing the amount of ink ejection by only pulse-width control. 
     SUMMARY OF THE INVENTION 
     The present invention provides a recording apparatus capable of recording a high-quality image through stabilization of the amount of ink ejection effected by modulation of not only a driving pulse but also a driving voltage in consideration of the temperature of a recording head. 
     An aspect of the present invention provides a recording apparatus for performing recording by scanning a recording head. The recording apparatus includes an acquisition unit configured to acquire temperature information of the recording head, a generation unit configured to generate a signal that indicates outputting of an output voltage based on the temperature information, a voltage control unit configured to control a voltage to be output to the recording head based on the signal, and a control unit configured to simultaneously perform preliminary ejection processing in an interval between a previous scan and a next scan of the recording head and output processing of the signal. 
     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 block diagram of a recording apparatus according to an exemplary embodiment of the present invention. 
         FIG. 2  is a diagram of a DC/DC converter according to the exemplary embodiment. 
         FIG. 3  is a graph of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIG. 4  is a schematic diagram for describing a timing of temperature detection and a timing of modulation of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIG. 5  is a sequence diagram for describing a timing of temperature detection and a timing of modulation of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIG. 6  is a flowchart for describing a timing of temperature detection and a timing of modulation of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIG. 7  is another flowchart for describing a timing of temperature detection and a timing of modulation of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIGS. 8A to 8E  are illustrations for describing a timing of modulation of an output voltage of the DC/DC converter according to the exemplary embodiment. 
         FIG. 9  is a perspective view of the recording apparatus according to the exemplary embodiment. 
         FIG. 10  is a diagram of a known DC/DC converter. 
         FIG. 11  is a diagram of a timing of activation of the DC/DC converter. 
         FIGS. 12A and 12B  are diagrams of a timing of VH modulation during a recording operation. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the present invention are described below with reference to the drawings. In the exemplary embodiments described below, an inkjet recording apparatus is described by way of example. 
     As illustrated in  FIG. 9 , the recording apparatus according to an exemplary embodiment performs recording on a recording sheet by using a recording head  2  composed of a black (Bk) head unit  2 - 1 , a yellow (Y) head unit  2 - 2 , a magenta (M) head unit  2 - 3 , and a cyan (C) head unit  2 - 4 . These four head units and a DC/DC converter  50  (not shown in  FIG. 1 ) are mounted on a carriage  3 . 
     The carriage  3  is attached to part of a driving belt  4  for transmitting a driving force of a carriage drive motor  5  and moves along a guide shaft  6 . This structure enables the recording head  2  to perform scan recording on a recording sheet and to form an image on the recording sheet. 
     By use of a signal of a carriage encoder  403  (not shown) arranged in parallel with the guide shaft  6 , moving and stopping of the recording head  2  and a recording position are controlled. 
     The inkjet recording head units  2 - 1  to  2 - 4  each include a plurality of head nozzles for ejecting ink at an ejection surface facing a recording surface of the recording sheet. The nozzles have the form of a thin pipe and are arranged in parallel. The inkjet recording head units  2 - 1  to  2 - 4  each further include a heater in the proximity of the nozzles. The heater provides ejection energy to ink supplied from integral ink tanks  1 - 1  to  1 - 4 . 
     The nozzles of the inkjet recording head units  2 - 1  to  2 - 4  are aligned so as to be substantially perpendicular to the direction of scanning of the carriage  3 . The four recording head units  2 - 1  to  2 - 4  are arranged along the direction of scanning of the carriage  3 . 
     The inkjet recording apparatus described above converts data into recording data corresponding to the recording head  2  on the basis of data such as an image information control command input from an external host device and the like. The recording data is transferred to the recording head  2  while the carriage  3  performs scanning, and the recording head  2  ejects ink at a necessary timing, so that an image is formed on the recording sheet. 
     The carriage  3  is connected to a main substrate with a flexible cable  11  and receives various signals and power necessary for the sensor and the DC/DC converter  50 . 
       FIG. 1  is a block diagram illustrating a first exemplary embodiment. A main substrate  30  includes an application-specific integrated circuit (ASIC)  31 , a read-only memory (ROM)  32 , a random-access memory (RAM)  33 , both of which function as a storing unit, an interface circuit  34 , and a driver reset circuit  35 . The interface circuit  34  receives data and a command from a host device  51 . The driver reset circuit  35  drives the drive motor  5  and a paper feed motor  10 . The ASIC  31  includes a central processing unit (CPU) and a plurality of control blocks (not shown). Examples of the control blocks include an ejection control unit for the recording head  2 , a drive control unit for the motors, and a control unit for controlling a power source. 
     The drive motor  5  can be, for example, a stepping motor or a DC motor. The ASIC  31  transmits a signal for the drive motor  5  to the driver reset circuit  35  to move the carriage  3  and at the same time keeps track of the present position of the carriage  3 , which mounts the recording head  2 , by managing the number of operation signals from a datum point in the direction of scanning and a signal from the carriage encoder  403 . 
     When the carriage  3  moves and reaches a position at which the mounted recording head units  2 - 1  to  2 - 4  are to eject ink, the ASIC  31  controls the recording head units  2 - 1  to  2 - 4  to eject ink. 
     Although only management of a driving pulse of the drive motor  5  would allow a print position in the direction of scanning to be detected, the recording apparatus according to the present embodiment includes the dedicated carriage encoder  403  to detect the position of the carriage  3  more accurately and uses a signal from the carriage encoder  403  to detect the position of the carriage. 
     The ASIC  31  controls operation of the inkjet recording apparatus in accordance with a program previously stored in the ROM  32  or a control command input from the host device  51  via the interface circuit  34 . The ROM  32  holds a program used for causing the ASIC  31  to operate and various table data required for control of the recording head  2 . 
     The interface circuit  34  functions as an interface used when a control command and control data are exchanged between the host device  51  and the inkjet recording apparatus. 
     The RAM  33  contains a work area used during computation of the ASIC  31  or a temporary storage area for recording data and control code input from the host device  51  via the interface circuit  34 . A print buffer, which stores bit data corresponding to nozzles of the recording head  2  developed from the recording data, is present in the RAM  33 . 
     A power-source unit  9  supplies a Vcc voltage to the main substrate  30 , supplies a VM voltage to the driver reset circuit  35 , the paper feed motor  10 , and the drive motor  5 , and supplies a VHin voltage to a DC/DC converter  50 . 
     The DC/DC converter  50  performs control of changing the value of the VH voltage to be supplied to the recording head  2  according to a DCHRG signal and a voltage setting signal C from the ASIC  31 . The reference voltage Vcc for the DC/DC converter  50  is turned on or off by use of a Vcc_ENB signal. The VH modulation DC/DC converter  50  is turned on or off by use of a VH_ENB signal. 
     A temperature detecting unit  36  is adjacent to the nozzle heater of each of the inkjet recording head units  2 - 1  to  2 - 4  and detects the temperature of the nozzle heater of each of the inkjet recording head units  2 - 1  to  2 - 4 . The temperature detecting unit  36  detects the temperature of the recording head  2 . The temperature of the recording head  2  is transmitted to the ASIC  31  via an A/D converter (not shown) after being converted from an analog value to a digital value by the A/D converter. 
     A rise in the temperature of the recording head  2  increases the temperature of ink present in an ink channel inside the recording head prior to foaming and ejected. As a result, the temperature difference ΔT between the ejection temperature of ink in the recording head  2  and the temperature of film boiling of ink varies depending on the temperature of the recording head  2 . Thus, if the temperature of ink prior to foaming varies, ink foaming energy required for ink ejection varies. Therefore, energy adjustment is necessary for stable ink ejection. 
     The ink foaming energy is adjusted by changing the value of an output voltage of the DC/DC converter  50  by AV to optimally adjust energy for ink foaming caused by the temperature difference ΔT. Additionally, in order to perform accurate and stable foaming, the value of the output voltage of the DC/DC converter  50  is corrected so as to be changed by change of the amount of ejection to the amount of electric power with respect to a change in the temperature of the recording head  2 . 
     The actual DC/DC converter  50  is described below with reference to  FIGS. 2 and 3 .  FIG. 2  is a circuit diagram for describing an example of the structure of the DC/DC converter  50 . In the present embodiment, a DC/DC-converter input voltage Vin supplied from a power-source unit (not shown) is input to a switching element Q 101 . The switching element Q 101  is connected to a capacitor C 005  at its input side and to the capacitor C 101  at its output side via the inductor L 101 . 
     The Vcc_ENB signal is a signal that turns on or off a reference-voltage circuit  212 . The reference-voltage circuit  212  is operated by the Vcc_ENB signal having an H level and supplies a reference voltage for a DC/DC control circuit (DC/DC control IC) via a D/A converter  211  and resistors R 4  and R 5 . The Vcc_ENB signal having an L level turns off the reference-voltage circuit  212 . 
     The VH_ENB signal is supplied to the DC/DC control IC and turns on or off the operation of the DC/DC converter  50 . The VH_ENB signal having an H level turns on the DC/DC converter  50 . The VH_ENB signal having an L level turns off the DC/DC converter  50 . 
     To modulate an output voltage VH, the DC/DC converter  50  according to the present embodiment adds a current to a division point of the output voltage VH by the D/A converter  211 . The reference-voltage circuit  212  outputs a Vcc potential to the D/A converter  211  when the Vcc_ENB signal output from the ASIC  31  is at the H level. At this time, the Vcc potential is also supplied to an error amplifier  207  of the DC/DC control IC via the resistors R 4  and R 5 . 
     The D/A converter  211  receives a reference voltage Vcc generated by the reference-voltage circuit  212  and outputs an output voltage V A  corresponding to a control signal (digital signal) C output from the ASIC  31 . 
     Therefore, a current I 2  corresponding to the output voltage V A  is added to a division point of resistors R 1  and R 3  via a resistor R 2 . For example, if the control signal C is an 8-bit digital signal, the output of the D/A converter  211  can be adjusted in 256 levels. In this case, the output voltage V A  of the D/A converter  211  is represented by the following expression: 
     
       
         
           
             VA 
             = 
             
               
                 Vcc 
                 
                   2 
                   8 
                 
               
               × 
               Xbit 
             
           
         
       
     
     where Vcc denotes an input voltage of the D/A converter  211  and Xbit denotes a value of the 8-bit control signal C. By addition of the current I 2  corresponding to the output voltage V A  to the division point of the resistors R 1  and R 3 , the output voltage VH is changed in the following manner. 
     A voltage VH 1  to be input to a noninverting terminal of the error amplifier  207  is controlled so as to eliminate the error between the voltage VH 1  and a reference voltage Vref to be input to an inverting terminal of the error amplifier  207 . Therefore, currents I 1 , I 2 , and I 3  passing through the resistors R 1 , R 2 , and R 3 , respectively, are represented by the following expressions: 
     
       
         
           
             
               I 
               1 
             
             = 
             
               
                 VH 
                 - 
                 
                   V 
                    
                   
                       
                   
                    
                   ref 
                 
               
               
                 R 
                  
                 
                     
                 
                  
                 1 
               
             
           
         
       
       
         
           
             
               I 
               2 
             
             = 
             
               
                 VA 
                 - 
                 Vref 
               
               
                 R 
                  
                 
                     
                 
                  
                 2 
               
             
           
         
       
       
         
           
             
               I 
               3 
             
             = 
             
               Vref 
               
                 R 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
     By applvina Kirchhoff&#39;s current law: 
     
       
         
           
             
               
                 I 
                 1 
               
               + 
               
                 I 
                 2 
               
             
             = 
             
               I 
               3 
             
           
         
       
       
         
           
             
               
                 
                   
                     VH 
                      
                     
                         
                     
                      
                     1 
                   
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     ref 
                   
                 
                 
                   R 
                    
                   
                       
                   
                    
                   1 
                 
               
               + 
               
                 
                   VA 
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     ref 
                   
                 
                 
                   R 
                    
                   
                       
                   
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                   2 
                 
               
             
             = 
             
               
                 V 
                  
                 
                     
                 
                  
                 ref 
               
               
                 R 
                  
                 
                     
                 
                  
                 3 
               
             
           
         
       
     
     Hence, the output voltage VH is represented by the following expressions: 
     
       
         
           
             
               VH 
               - 
               
                 V 
                  
                 
                     
                 
                  
                 ref 
               
             
             = 
             
               R 
                
               
                   
               
                
               1 
                
               
                 { 
                 
                   
                     Vref 
                     
                       R 
                        
                       
                           
                       
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                       3 
                     
                   
                   - 
                   
                     
                       ( 
                       
                         VA 
                         - 
                         Vref 
                       
                       ) 
                     
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
                 } 
               
             
           
         
       
       
         
           
             VH 
             = 
             
               
                 V 
                  
                 
                     
                 
                  
                 ref 
               
               + 
               
                 R 
                  
                 
                     
                 
                  
                 1 
                  
                 
                   { 
                   
                     
                       Vref 
                       
                         R 
                          
                         
                             
                         
                          
                         3 
                       
                     
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                         Vref 
                         - 
                         VA 
                       
                       
                         R 
                          
                         
                             
                         
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                         2 
                       
                     
                   
                   } 
                 
               
             
           
         
       
     
     In this way, the output voltage VH can be changed by changing the value of the output voltage V A  of the D/A converter  211 . 
     A discharge circuit  301  includes a MOS-FET Q 102 , which functions as a switching element, and a resistor R 6  for restricting a discharge current. The discharge circuit  301  removes a charge from a capacitor C 101  when the DC/DC converter  50  is turned off. The discharge circuit  301  removes a charge from the capacitor C 101  when the output voltage VH is modulated. 
     A DCHRG signal is a signal that turns on or off the discharge circuit  301  of the DC/DC converter  50  and is supplied to a gate of the switching element Q 102 . When the DCHRG signal is at an H level, the switching element Q 102  is turned on. When the DCHRG signal is at an L level, the switching element Q 102  is turned off. 
       FIG. 3  shows a relationship between a selected value of an 8-bit control signal C and an output voltage VH. In the present embodiment, as the value of the control signal C increases, the output voltage V A  of the D/A converter  211  increases and a current I 2  after passing through the resistor R 2  increases. Since the relationship among current values is I 1 +I 2 =I 3 , an increase in current I 2  reduces a current I 1  after passing through the resistor R 1 . A reduction in current I 1  reduces the output voltage VH. That is, feedback control in this circuit structure is that an increase in current I 2  after passing through the resistor R 2  reduces the output voltage VH. 
     A timing of acquisition of temperature data and a timing of changing the voltage during printer operation are described with reference to  FIGS. 4 and 5 . 
       FIG. 4  illustrates an operation of the carriage  3  with respect to a recording medium and is a schematic diagram of a timing of detection of temperature data of the recording head  2 . 
       FIG. 5  schematically illustrates a series of printer operations and illustrates a sequence of signals during the operations. 
     Each of a period (timing) A and a period (timing) B illustrated in  FIG. 4  is a period during which ink is not being ejected. The period A and the period B illustrated in  FIG. 4  correspond to a period A and a period B illustrated in  FIG. 5 , respectively. 
     Although a rise in the temperature of the recording head  2  increases the amount of ink ejection, the increase in the amount of ink ejection can be suppressed by increasing a driving voltage and shortening a pulse width. Therefore, the amount of ink ejection can be stabilized by increasing the VH voltage of the DC/DC converter  50  when the temperature of the recording head  2  rises and by reducing the VH voltage of the DC/DC converter  50  when the temperature of the recording head  2  declines. 
     Control of a pulse width is a known technique, so the description thereof is omitted. Modulation of a driving voltage of the recording head  2  is described below. 
     In  FIGS. 4 and 5 , the carriage  3  performs reciprocating motion, in which moving (scanning) from a point “a”, which is also a home position of the carriage  3 , to a point “b” with respect to a recording medium  401  and moving (scanning) from the point b to the point a, with respect to the recording medium  401 . The carriage  3  forms an image on the recording medium  401  while performing the reciprocating motion in conjunction with conveyance of the recording medium  401 . 
     The carriage  3  ejects ink to an end of a maximum recording-medium width of the apparatus to form an image. Therefore, the carriage  3  moves from a range A to a range B illustrated in  FIG. 4 . Each of the ranges A and B is an acceleration/deceleration range for turning the reciprocating motion of the carriage  3  to the opposite direction and a stop range. In the ranges A and B, the recording head  2  on the carriage  3  does not eject ink onto the recording medium  401 . 
     When the carriage  3  moves directly above the recording medium  401 , the carriage  3  is in a uniform speed range, in which an image is formed by ejection of ink and control of a relative speed between the carriage  3  and the recording medium  401  by conveyance of the recording medium  401 . 
     In  FIG. 4 , since the recording head  2  performs ejection of ink a plurality of times while the carriage  3  moves from the point a (its home position) to the point b, the temperature of the recording head  2  gradually rises. The temperature of the recording head  2  when the carriage  3  has moved from the point a (its home position) to the point b, the temperature of the recording head  2  at the points a and b (or the points b and a) after the reciprocating motion is repeated a plurality of times, and the temperature of the recording head  2  when the carriage  3  returns to the point a (its home position) after an image is formed on a single recording medium increase substantially proportional to a print time, i.e., different from the temperature of the recording head  2  at the start of printing. 
     The increase in the temperature of the recording head  2  is not very sharp, but, if a high-duty image, which requires an increased number of ink ejection from the recording head  2 , is formed or if an image is repeatedly formed on a plurality of recording media, the temperature of the recording head  2  gradually rises. In this case, image quality may be different for every recording medium or may be different according to the location where ink is ejected on a recording medium, so it is difficult to provide stable image quality. 
     A sequence of a series of recording operations and signals are described below with reference to  FIG. 5 .  FIG. 5  illustrates that the power is turned on, recording is performed, and the status shifts to a standby mode. In  FIG. 5 , time progresses from left to right. Between a scan in the forward direction and a scan in the return direction, a recording sheet (recording medium) is conveyed. 
       FIG. 11  is a diagram that enlarges a timing of a VH activation illustrated in  FIG. 5  in terms of time.  FIGS. 12A and 12B  are diagrams each enlarging a timing of VH modulation operation in a section of a 2  in  FIG. 5  in terms of time. In the a 2  section, as illustrated in  FIG. 12A , the voltage VH is enhanced. When the temperature of the recording head  2  rises, the amount of ink ejection increases. In the a 2  section, the voltage VH is enhanced in order to suppress the increase in the amount of ink ejection. 
     On the other hand, for example, if the temperature of the recording head  2  declines, the amount of ink ejection decreases. In the a 2  section, in order to suppress the reduction in the amount of ink ejection, the voltage VH is reduced.  FIG. 12B  illustrates the processing for reducing the voltage VH. 
     In  FIG. 12A , for example, after the temperature is detected at T 0 , T 1 , and T 2 , on the basis of the results of the temperature detection, a control signal C that indicates a target voltage is output. Therefore, the voltage VH can be increased to a desired voltage. 
     In  FIG. 12B , on the basis of the results of the temperature detection, a control signal C that indicates a target voltage is output, and, additionally, an indication signal DCHRG for discharge is output. Therefore, the voltage VH can be reduced to a desired voltage. In  FIG. 12B , although a timing of temperature detection is omitted, the temperature detection is performed, as in the case of  FIG. 12A . 
     A section of (c) in  FIG. 5  represents that the printer is in a print standby mode (prior to a soft power on) or the power source is in an off state. In this section, an output VH of the DC/DC converter  50  is 0 volt by the L level of the Vcc_ENB signal and the VH_ENB signal and the H level of the DCHRG signal. 
     The temperature of the recording head  2  is measured by a temperature sensor, such as a diode sensor, in units of, for example, 10 ms. The diode sensor is disposed on a heater board (base member) on which the heaters are mounted. It is difficult for a temperature sensor, such as the diode sensor, to accurately measure the temperature while the heaters of the recording head  2  are being driven because of superimposition of noise caused by effects of a driving signal. 
     More specifically, the temperature is measured as a value that is approximately 20° C. higher than a value that would be detected when the heaters are not driven because of superimposition of a noise component caused by a driving signal. It has been found that, since the temperature of the recording head during printing rises on the order of a few seconds to several tens of seconds or declines on the order of several tens of seconds to a few minutes, the temperature of the recording head  2  detected on the order of milliseconds does not vary significantly. 
     As a result, the difference in temperature data between a head-temperature datum detected at a timing and a head-temperature datum detected at a next timing is managed by a digital filter disposed in the ASIC. If a sharp change in temperature is detected in a short period of time, the detected temperature data is cancelled as data on which a noise component is superimposed. Alternatively, the data is processed as data that has no temperature change (e.g., 1° C. or less). 
     When, at a timing of (d) in  FIG. 5 , the soft power on is activated or the power is switched on, the Vcc_ENB signal and the VH_ENB signal shift from the L level to the H level and the DCHRG signal shifts from the H level to the L level. Therefore, the control IC of the DC/DC converter  50  is activated, the discharge circuit, which has caused the output voltage to be 0 V, is brought in an off operation, and the DC/DC converter  50  is activated. At this time, data is not output to the D/A converter  211 , and thus the output of the DC/DC converter  50  rises to a predetermined voltage value (VHmax) during the activation. When the soft power on is activated or the power is switched on, then the temperature of the recording head is detected in units of, for example, 10 ms. 
     The ASIC  31  acquires a base temperature T 0  of the recording head within 0.3 seconds after the activation of the DC/DC converter  50  and then refers to a table (not shown) of the recording head  2  temperature to the set voltage. The ASIC  31  transmits a voltage control signal C to the D/A converter  211 . The D/A converter  211  outputs an output voltage V A  according to the value of the voltage control signal C. The switching element Q 102  in the discharge circuit  301  is turned on in response to the DCHRG signal transmitted from a controller for a fixed period of time after the ASIC  31  transmits the voltage control signal C. At this time, a charge flows as a discharge current from the capacitor C 101  via the resistor R 6 . 
     If the value of the voltage VH decreases from VHmax to VHx, a period of time during which the discharge circuit  301  is in the on state is represented by the following expression: 
     
       
         
           
             ton 
             = 
             
               
                 - 
                 R 
               
                
               
                   
               
                
               6 
               × 
               C 
                
               
                   
               
                
               101 
               × 
               ln 
                
               
                 
                   VH 
                    
                   
                       
                   
                    
                   x 
                 
                 
                   VH 
                    
                   
                       
                   
                    
                   max 
                 
               
             
           
         
       
     
     where C 101  represents an output capacitance of the capacitor C 101  in the DC/DC converter  50  and R 6  represents a resistance of the resistor R 6 . In  FIG. 5 , the period of time during which the discharge circuit  301  is in the on state is in a range of 8 ms to 29 ms. 
     This processing causes the voltage of the capacitor C 101  (VH voltage) to decrease to a second voltage value (preset voltage value) determined from the base temperature T 0  of the recording head  2 . 
     In the present embodiment, the amount of electric energy applied on the capacitor C 101  by the voltage setting signal C is larger than the amount of electric energy discharged by the discharge circuit  301 . Therefore, discharge processing of the discharge circuit  301  is always performed at a timing set by the voltage setting signal C, so that the output voltage VH is increased or reduced. 
     As described above, the VH voltage has a set value set by a set voltage of the D/A converter  211 . The output voltage VH in a short period of time is adjusted by a combination of feedback control in the power-source circuit (DC/DC converter  50 ) and discharge processing. 
     Another method for adjusting the level of the output voltage VH is to operate the discharge circuit  301  at a timing set by the voltage control signal C only when the output voltage VH is to be reduced. 
     Processing of ejecting ink from the recording head  2  includes preliminary ejection (processing) for ejecting ink on a regular basis to prevent the nozzle from clogging and main ejection (processing) for ejecting ink to form an image. 
     The main ejection is performed when the carriage  3  is positioned directly above the recording medium, whereas the preliminary ejection is performed when the carriage  3  is not positioned directly above the recording medium but is at its home position. 
     The temperature of the recording head  2  gradually rises when recording operation continues. In the sections A and B illustrated in  FIGS. 4 and 5 , since only the preliminary ejection is performed, a rise in the temperature is mild. 
     Data detected by the temperature sensor during the main ejection, in which ink is ejected onto the recording medium, contains a superimposed noise component. Therefore, temperature information of the recording head  2  is cancelled by a digital filter or some other member. 
     Temperature data (information on temperature) is acquired in a fixed period of time (0.2 s) in the ranges A and B, where the reciprocating motion is turned from the forward direction (forward scan) to the return direction (return scan), outside the printing area, the ranges A and B being an acceleration/deceleration range of the carriage. 
     The temperature data is digitized by the A/D converter (not shown) in order to be processed by the ASIC  31  on the main substrate  30 . By use of the digitized information, information on the set voltage of the DC/DC converter  50  held in the ROM  32  is referred to. The information on the set voltage read from the ROM  32  is output from the ASIC  31  toward the DC/DC converter  50 . 
     In the information on the set voltage held in the ROM  32 , information on the nozzle rank is a parameter. Therefore, even if there are variations in the ejection characteristics of the nozzles of the recording head  2 , accurate correction can be performed. 
     The voltage VH of the DC/DC converter  50  is controlled in such a way that the voltage VH is modulated when the temperature of the recording head  2  changes by a predetermined fixed value of ±ΔT° C. (e.g., 5° C.) or more relative to the base temperature T 0 . If the temperature does not change by ±ΔT or more relative to the base temperature T 0 , the VH modulation operation is not performed, and the DC/DC converter  50  is driven with the unmodulated VH voltage. 
     In an example illustrated in  FIG. 5 , when print data is sent to the recording head  2  and printing starts, the temperature of the recording head  1  gradually rises. At a timing of temperature detection of T n-1 , a rise in the temperature is predetermined +ΔT° C. (5° C. in an example illustrated in  FIG. 4 ) relative to the base temperature T 0  After a timing of temperature detection of the recording head  2  of T n-1 , predetermined-VH-voltage mapping information for the temperature of the recording head  2  to the set voltage of the DC/DC converter  50  is referred to, the voltage control signal C is transmitted to the D/A converter  211 , and then the DCHRG signal is transmitted to the discharge circuit  301 . 
     By this series of operations, after a temperature detection timing of T n-1 , a section a 2  in  FIG. 5 , which is an interval between an operation in the return direction and that in the forward direction, the VH modulation control is performed. In  FIG. 5 , a period of time during which the voltage VH is modulated is in a range of 2 ms to 10 ms. This period of time is determined from the time required for response to a feedback loop of the DC/DC converter  50  in the case in which the voltage VH rises from VHx 1  to VHx. In an example illustrated in  FIG. 5 , a width of voltage modulation from VHx 1  to VHx is 1.5 V, and the modulation is performed within 2 ms. 
     In the case in which, at a timing of T n-1 , the temperature changes by predetermined ±ΔT° C. or more relative to the base temperature T 0  and the voltage VH is modulated, the base temperature information stored in the controller is rewritten to temperature information at T n-1 as new base information, and the next VH modulation is performed for a temperature change of ±ΔT or more relative to the temperature at T n-1 . 
     In  FIG. 5 , in the standby state after a status of being ready to record (e.g., 1 minute), while preliminary ejection is performed at fixed time intervals (e.g., 2 second intervals), the recording head  2  awaits the start of printing at its home position. Since only the preliminary ejection from the recording head  2  is performed in the standby state, although a change is small, the temperature of the recording head  2  gradually decreases. 
     In  FIG. 5 , the temperature detected at a timing of T m-1  changes by −ΔT relative to that at T n-1 , at which the previous VH modulation was performed. Therefore, at a temperature detection timing of T m-1 , the VH modulation control is performed. 
     Since the temperature of the recording head  2  at a temperature detection timing of T m-1  changes by −ΔT° C. relative to the base temperature at T n-1 , after a temperature detection timing of T m-1 , predetermined-VH-voltage mapping information for the temperature of the recording head to the set voltage of the DC/DC converter  50  is referred to, the voltage control signal C is transmitted to the D/A converter  211 , and then the DCHRG signal is transmitted to the discharge circuit  301 . 
     By this series of operations, after a temperature detection timing of T m-1  in  FIG. 5 , in an interval between preliminary ejections, the VH modulation control is performed. 
     If the value of the voltage VH decreases from VHx to VHx 1 , a period of time during which the voltage is modulated after T m-1  is represented by the following expression: 
     
       
         
           
             ton 
             = 
             
               
                 - 
                 R 
               
                
               
                   
               
                
               6 
               × 
               C 
                
               
                   
               
                
               101 
               × 
               ln 
                
               
                 
                   VH 
                    
                   
                       
                   
                    
                   x 
                    
                   
                       
                   
                    
                   1 
                 
                 
                   VH 
                    
                   
                       
                   
                    
                   x 
                 
               
             
           
         
       
     
     where C 101  represents an output capacitance of the capacitor C 101  in the DC/DC converter  50  and R 6  represents a resistance of the resistor R 6 . In  FIG. 5 , a width of voltage modulation from VHx to VHx 1  is −1.5 V, and the modulation is performed within a range of 2 ms to 10 ms. 
     In the present embodiment, the modulation of the voltage VH is completed before the recording head  2  starts a printing operation both for modulation of increasing voltage VH and modulation of reducing the voltage VH. This is because, if printing starts before the completion of the VH modulation operation, the amount of ink ejection would vary, and the image quality would be degraded. As a result, a period of time during which the discharge circuit  301  performs discharge for a width of voltage modulation (control width) is shorter than a pause period of recording (pause timing), which is an interval between a scan and a next scan. 
     In  FIG. 5 , if print data has not been received from the host device  51  for a fixed period of time (e.g.,  2  minutes), a capping operation is performed as an operation of the recording apparatus, the VH_ENB signal changes from the H level to the L level, the DCHRG signal changes from the L level to the H level, and the DC/DC converter  50  stops operating. As a result, the VH voltage has a value of 0 V. 
     In  FIG. 5 , the DC/DC converter  50  is activated without transmission of data of the D/A converter  211 . After that, the temperature of the recording head  2  T 0  is referred to, the DC/DC converter  50  is controlled with a voltage value corresponding to the referred temperature. However, these operations may be reversed. That is, the temperature of the recording head  2  T 0  may be read before the activation of the DC/DC converter  50 , and data corresponding to the temperature is output to the D/A converter  211  at the activation. 
       FIG. 6  is a flowchart for describing a timing of temperature detection and a timing of VH modulation control at the activation. 
       FIG. 11  is a diagram that enlarges a timing of an activation illustrated in  FIG. 5 .  FIG. 11  also illustrates waveforms of VHin, Vcc_ENB, and Vcc signals. 
     Turning to  FIG. 6 , in step SO, the power of the recording apparatus is turned on (or soft power on is activated). Then, in step S 1 , the Vcc_ENB signal is turned on, thereby shifting the Vcc voltage to be supplied to the D/A converter  211  to the H level. 
     In step S 2 , the VH_ENB signal of the DC/DC converter  50  is shifted to the H level. Then, in step S 3 , the DCHRG signal is shifted to the L level. Therefore, the level of the voltage VH of the DC/DC converter  50  is shifted to VHmax (first voltage). 
     In step S 4 , the base temperature T 0  of the recording head  2  is acquired. Next, in step S 5 , the base temperature T 0  is stored in the RAM. In step S 6 , a table of the head rank and the temperature is referred to. In step S 7 , the referred voltage set value is transmitted to the D/A converter  211  in the form of a digital signal. 
     Flow proceeds to step S 8 , where a predetermined time period is waited, so that the output of the D/A converter  211  is changed by this waiting. When the predetermined time period has been exceeded, in step S 9 , the DCHRG signal is shifted to the H level, thereby causing the discharge circuit to operate. Next, in step S 10 , if it is determined that the DCHRG signal has been output for more than a fixed time period, the DCHRG signal is shifted to the L level in step S 11 , thereby stopping conduction of the discharge circuit. Then, in step S 12 , the VH voltage changes to a preset voltage (second voltage), and the printer is in a standby state.  FIG. 7  is a flowchart for describing a timing of temperature detection and a timing of VH modulation control during printing. First, printing starts (step S 13 ). Then, as a sequence of VH modulation (step S 14 ), the temperature of the recording head  2  is acquired by the ASIC at fixed intervals (step  24 ). In steps S 25  and S 26 , the acquired temperature is compared with the base temperature T 0 . Here, temperature data acquired during printing is processed as data that has no temperature change or is canceled by a digital filter because a noise component is superimposed thereon and the detected temperature is higher than the actual temperature. After scanning in the forward direction in step S 15 , flow proceeds to step S 16 , where it is determined whether preliminary ejection is to be performed. If, in step S 16 , it is determined that preliminary ejection is to be performed (YES), flow proceeds to step S 17 , where the preliminary ejection is performed. If, in step S 16 , it is determined that preliminary ejection is not to be performed (NO), flow proceeds to step S 18 . After scanning in the return direction in step S 19 , flow proceeds to step S 20 , where it is determined whether preliminary ejection is to be performed. If, in step S 20 , it is determined that preliminary ejection is to be performed (YES), flow proceeds to step S 21 , where the preliminary ejection is performed. If, in step S 20 , it is determined that preliminary ejection is not to be performed (NO), flow proceeds to step S 22 . 
     Therefore, in an interval between a scan in the forward direction (step S 15 ) and a scan in the return direction (step S 19 ), at which the recording head does not perform a print operation, or in an interval between a scan in the return direction and a scan in the forward direction, the temperature of the recording head  2  is reflected and the VH modulation control is performed. That is, the VH modulation control is performed in a period of time (timing) corresponding to an acceleration/deceleration range and a stop range, at which printing performed by the reciprocating motion of the recording head  2  is not performed. 
     The execution of the VH modulation control is determined by whether the difference between the temperature of the recording head  2  acquired in step S 24  and the base temperature T 0  is equal to or larger than a predetermined value. In  FIG. 7 , a change of 5° C. relative to the base temperature T 0  is detected (steps S 25  and S 26 ). If a change is 5° C. or more (YES in step S 25 ), the base temperature is updated from T 0  to T n-1  (step S 27 ). If a change is −5° C. or more (YES in step S 26 ), the base temperature is updated from T 0  to T n-1  (step S 27 ). In other words, when −5° C&lt;T n-1 −T 0 &lt;5° C., processing of steps S 27  through S 30  is omitted. The table of the head rank to the temperature is referred to for the updated temperature (step S 28 ). Then, a digital signal is transmitted to the D/A converter (step S 29 ). The DCHRG signal is transmitted (step S 30 ). After that, flow proceeds to step S 31 , where the processing is completed. The VH modulation operation is thus performed. In step S 23 , it is determined whether the recording operation is to be completed. If, in step S 23 , it is determined that the recording operation is not to be completed (NO), flow returns to step S 15 . If, in step S 23 , it is determined that the recording operation is to be completed (YES), flow proceeds to step S 32 . In the present embodiment, the DCHRG signal is output without exception. However, the DCHRG signal may be output only when the recording-head driving voltage VH is caused to be reduced. 
     By this series of operations, using temperature information detected at a timing at which the recording head  2  does not eject ink, the recording-head driving voltage VH is also modulated at a timing at which the recording head  2  does not eject ink. 
     The temperature data is processed by the digital filter in the ASIC. Additionally, the VH modulation control can be performed more precisely by use of information from the carriage encoder  403 , which detects the position of the recording head  2 . The more precise VH modulation control in an acceleration range, a deceleration range, and a stop range in the reciprocating motion of the head carriage unit is described below with reference to  FIGS. 8A to 8E . 
     In sections A or B illustrated in  FIG. 5 , preliminary ejection may or may not be performed. A timing of the preliminary ejection and a timing of the VH modulation control can be varied depending on printing conditions (conditions for printing operation or recording mode). 
       FIGS. 8A to 8E  are schematic diagrams illustrating the preliminary ejection and the VH modulation operation in acceleration and deceleration ranges and a stop range during a printing operation of the head carriage unit. More specifically, in  FIGS. 8A to 8E , time progresses from left to right. In other words, after the recording head performs a previous scan, the recording head stops. Subsequently, the recording head performs a next scan. 
       FIG. 8A  shows a case in which preliminary ejection is not performed in an acceleration range, a deceleration range, and a stop range of the head carriage unit. In the acceleration range, the deceleration range, or the stop range, the temperature of the recording head  2  is acquired and the VH modulation control is performed. In this drawing, the VH modulation control is performed in the stop range. However, the VH modulation control may be performed in the acceleration range or the deceleration range. If the VH modulation control is performed in an acceleration range, which is immediately before the next main ejection, newer temperature information of the recording head  2  can be reflected, and thus recording with a more accurate amount of ink ejection can be realized. 
       FIGS. 8B to 8E  illustrate cases in which the preliminary ejection is performed in a stop range of the recording head  2  (head carriage unit).  FIG. 8B  illustrates a sequence (control) in which the VH modulation control is performed after the preliminary ejection. The temperature of the recording head  2  acquired after the preliminary ejection is reflected on the VH modulation control. If the nozzles of the recording head  2  are less prone to being clogged, the VH modulation control is performed before recording on a priority basis. 
       FIG. 8C  illustrates a sequence (control) in which the VH modulation control is performed before the preliminary ejection. In other words,  FIG. 8C  illustrates a sequence (control) in which the preliminary ejection is performed after the VH modulation control. Before a timing of the preliminary ejection, a VH voltage value on which the temperature of the recording head  2  has been reflected is modulated. This process can reliably avoid clogging of the nozzles of the recording head  2  before printing. In other words, the amount of energy required for the preliminary ejection can be adjusted by adjustment of the VH voltage. 
     In the case of  FIG. 8B , the energy of the preliminary ejection may be adjusted by control of a pulse width. In the case of  FIG. 8C , the pulse width control can be omitted from the ASIC of the controller. Therefore, a load imposed on the controller can be reduced. 
       FIG. 8D  illustrates a case in which a timing of the preliminary ejection overlaps a timing of the VH modulation control. In this case, the preliminary ejection and the VH modulation control are simultaneously performed. As in the case of  FIG. 8C , the temperature information of the recording head  2  can be acquired before the preliminary ejection, so the accurate VH modulation control can be performed. 
     Since the operation of the discharge circuit and the preliminary ejection overlap one another, power consumed by the preliminary ejection processing is employed as a discharge current of output of the DC/DC converter  50 . As a result, the time required for the VH modulation can be reduced. 
       FIG. 8E  illustrates a modification of  FIG. 8D  and illustrates a case in which the preliminary ejection overlaps the latter half of the VH modulation control. That is, after the discharge circuit starts operating in the VH modulation control, the preliminary ejection starts. 
     VH modulation control that uses position information from the carriage encoder  403  can perform modulation every one scan of the head carriage unit, not for a change of a predetermined fixed value of ±ΔT° C. In this case, more precise VH modulation control can be realized. 
     Processing occurring when the recording head  2  does not move has been described with reference to  FIGS. 8A to 8E . However, the present invention is not limited to these examples. For example, in  FIG. 8A , even in a deceleration range, the temperature of the recording head  2  may be acquired and the voltage modulation processing may be performed as long as the recording head  2  finishes ink ejection. Alternatively, for example, even in an acceleration range, the temperature of the recording head  2  may be acquired and the voltage modulation processing may be performed as long as a period of time during which the recording head  2  does not start ink ejection is maintained. 
     Alternatively, in  FIG. 8B , even in a deceleration range, the preliminary ejection to a preliminary ejection area may be performed, and, thereafter, the temperature of the recording head  2  may be acquired and the voltage modulation processing may be performed as long as the recording head  2  finishes ink ejection. Alternatively, for example, even in an acceleration range, the temperature of the recording head  2  may be acquired and the voltage modulation processing may be performed as long as a period of time during which the recording head  2  does not start ink ejection is maintained. 
     Alternatively, in  FIG. 8C , even in a deceleration range, the temperature of the recording head  2  may be acquired, and, thereafter, the voltage modulation processing and the preliminary ejection to a preliminary ejection area may be performed as long as the recording head  2  finishes ink ejection. Alternatively, for example, even in an acceleration range, the temperature of the recording head  2  may be acquired and the voltage modulation processing may be performed as long as a period of time during which the recording head  2  does not start ink ejection is maintained. A parameter for time is not limited to the above-described values. 
     As described above, even when the temperature of the recording head  2  varies, the voltage for driving the recording head  2  can be adjusted at a timing at which the recording head  2  does not perform a printing operation. Therefore, the amount of ink ejected from the recording head  2  can be stabilized and image recording with high image quality can be realized. 
     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 modifications, equivalent structures and functions.