Patent Publication Number: US-7896453-B2

Title: Recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2006-093903, filed on Mar. 30, 2006, the entire subject matter of which is incorporated herein by reference. 
     FIELD 
     Aspects of the present invention relate to a recording apparatus, and more particularly to a recording apparatus provided with a DC/DC converter. 
     BACKGROUND 
     In the related art recording apparatuses for discharging ink from a recording head driven by a head driving circuit to record an image on a recording medium have been known. The recording apparatus is provided with a DC/DC converter that converts a DC voltage input from a main power supply into another DC voltage and outputs the converted another DC voltage to the head driving circuit as a power supply. 
     In addition, a DC/DC converter including an FET (field effect transistor), a temperature sensor provided around the FET, and a temperature monitoring circuit that outputs a signal for stopping a control operation of the FET in response to an output from the temperature sensor when the temperature sensor detects an abnormal increase in temperature has been known. 
     However, in the above-mentioned technique, when the temperature of the FET becomes greater than a predetermined temperature representing an abnormal temperature-increasing state, the control operation of the FET stops. Therefore, it is possible to control an increase in the temperature of the FET. However, in this case, the operational range of the DC/DC converter is narrowed. Thus, an increase in the driving efficiency of the DC/DC converter is needed. 
     SUMMARY 
     One aspect of the invention may provide a recording apparatus including a head that discharges ink; a head driving circuit that drives the head; a switching signal generating unit that generates and outputs a switching signal; a first switch that is turned on or off based on the switching signal; and a second switch that is turned on or off based on the switching signal. A first DC voltage is converted into a second DC voltage by switching between the first switch and the second switch, and the second DC voltage is supplied to the head driving circuit. The recording apparatus further includes a temperature detector that detects a temperature of the head or ink of the head; and a controller that controls the switching signal generating unit to generate the switching signal. The controller controls the switching signal generating unit to output the switching signal to the first switch when the detected temperature is less than a first predetermined temperature and to output the switching signal to the second switch when the detected temperature is equal to or greater than the first predetermined temperature. 
     Another aspect of the invention may provide a recording apparatus including a head that discharges ink; a head driving circuit that drives the head; a switching signal generating unit that generates a switching signal; a first switch that is turned on or off based on the switching signal; and a second switch that is turned on or off based on the switching signal. A first DC voltage is converted into a second DC voltage by switching between the first switch and the second switch, and the second DC voltage is supplied to the head driving circuit. The recording apparatus further includes a temperature detector that detects a temperature of the ink; a voltage detector that detects the second DC voltage and a controller that controls the switching signal generating unit to generate the switching signal. The controller controls the switching signal generating unit to output the switching signal to the first switch when the detected ink temperature is greater than or equal to a predetermined temperature, and if the ink temperature is less than the predetermined temperature the controller controls the switching signal generating unit to output the switching signal to the second switch when the detected second DC voltage is less than the predetermined voltage and to output the switching signal to the first switch when the detected second DC voltage is equal to or greater than the predetermined voltage. 
     In a further aspect, a recording apparatus may be provided including a head that discharges ink, a head driving circuit that drives the head, a switching signal generating unit that generates and outputs a switching signal, a first switch that is turned on or off based on the switching signal, and a second switch that is turned on or off based on the switching signal. A first DC voltage may be converted into a second DC voltage by switching one of the first switch and the second switch based on the switching signal, and the second DC voltage can be supplied to the head driving circuit. The recording apparatus further includes a voltage detector that detects the second DC voltage, and a controller that controls the switching signal generating unit to generate the switching signal to output the switching signal to the first switch when the detected second DC voltage is less than a predetermined voltage and to output the switching signal to the second switch when the detected second DC voltage is equal to or greater than the predetermined voltage. 
     In another aspect, a method for controlling discharge of ink from a head in a recording apparatus including detecting temperature of the head or ink in the head, generating a first switching signal when the detected temperature is less than a first predetermined temperature, and generating a second switching signal when the detected temperature is equal to or greater than the first predetermined temperature. Also, the method includes converting a first DC voltage into a second DC voltage in response to the generation of one of the first switching signal and the second switching signal, and supplying the second DC voltage to drive a head driving circuit which drives the head to discharge ink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a color ink jet printer, which is a recording apparatus according to aspects of the invention; 
         FIG. 2  is a block diagram schematically illustrating the electric circuit structure of the color ink jet printer; 
         FIG. 3  is a flowchart illustrating a printing process; and 
         FIG. 4  is a graph illustrating a head voltage set according to the temperature of ink. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary aspects of the invention will be described with reference to the accompanying drawings.  FIG. 1  is a perspective view illustrating a color ink jet printer  1  serving as a recording apparatus according to illustrative of the invention.  FIG. 2  is a block diagram schematically illustrating the electric circuit structure of the color ink jet printer. The color ink jet printer  1  includes, for example, four color ink cartridges  61  having cyan (C), magenta (M), yellow (Y), and black (Bk) ink contained therein, an ink jet head  6  for printing an image on a recording sheet P, a carriage  64  having the ink cartridges  61  and the ink jet head  6  mounted thereon, a driving unit  65  that moves the carriage  64  in the direction of arrow A (main scanning direction), a support member  66  that is provided so as to extend in the direction A in which the carriage  64  is moved and to be opposite to the ink jet head  6 , and a purge device  67  configured to clear the ink jet head  6  under certain predetermined conditions such as when ink blocks the ink jet head  6 . 
     The driving unit  65  includes a carriage shaft  71  that is provided below the carriage  64  so as to extend in parallel to the support member  66 , a guide plate  72  that is provided above the carriage  64  so as to extend in parallel to the carriage shaft  71 , two pulleys  73  and  74  that are provided at both sides of the carriage shaft  71  between the carriage shaft  71  and the guide plate  72 , an endless belt  75  that is wound around the two pulleys  73  and  74 . When one pulley  73  rotates in the forward or reverse direction by the driving of a carriage (CR) motor  16 , the rotation of the pulley  73  in the forward or reverse direction causes the carriage  64  connected to the endless belt  75  to move in the direction of arrow A, which is the main scanning direction, along the carriage shaft  71  and the guide plate  72 . 
     Nozzles (not shown) corresponding to four color inks, that is, C, M, Y, and Bk inks, are provided on the lower surface  6   a  of the ink jet head  6  in a direction B in which the recording sheet P is carried (sub-scanning direction B). In addition, the number of nozzles and the pitch among the nozzles in the arrangement direction depend on, for example, the resolution of an image to be printed. Further, the number of rows of nozzles may increase or decrease according to the number of types of color ink. 
     The recording sheet P is fed from a sheet feeding cassette (not shown) of the color ink jet printer  1  and is then carried by a feed roller (not shown) in the direction of arrow B (sub-scanning direction which is orthogonal to the main scanning direction A) between the lower surface  6   a  of the ink jet head  6  and the support member  66 . Then, ink is discharged from the nozzles onto the recording sheet P to have an image printed thereon, and is then discharged from the ink jet printer  1 . In  FIG. 1 , mechanisms for feeding and discharging the recording sheet P are not shown. 
     The purge device  67  for cleaning the ink jet head  6  having an ink discharge failure is provided on the side of the support member  66  in the direction in which the carriage  64  moves. The ink discharge failure of the ink jet head  6  occurs due to, for example, bubbles in ink or an increase in the viscosity of the ink. The purge device  67  is provided to clean the ink jet head  6  and return the ink jet head  6  from an ink discharge failure state to a normal ink discharge state. 
     The purge device  67  is provided so as to face the ink jet head  6  when a head unit  63  is disposed at a purge position at which it may be cleaned, and includes a cap  81 , a pump  82 , a cam  83 , and an ink containing portion  84 . The cap  81  closely adheres to the bottom surface  6   a  of the ink jet head  6 , and then the pump  82  sucks defective ink, such as ink having bubbles, from the inside of the ink jet head  6 . The cam  83  of the pump  82  rotates to move a piston in the pump  82 , thereby sucking the defective ink from the ink jet head  6 . The suction of defective ink causes the ink discharge failure of the ink jet head  6  to be cleaned and repaired. The defective ink sucked out of the ink jet head  6  is put in the ink containing portion  84 . 
     A wiper member  86  capable of moving relative to the ink jet head  6  is provided on one side of the purge cap  81  facing the support member  66 , and a cap  85  is provided opposite to the wiper member  86  with the purge cap interposed therebetween. The wiper member  86  is formed of an elastic material, such as ethylene propylene rubber, in a plate shape, and one end of the wiper member  86  is inserted into a wiper holder  90 , so that the wiper member  86  is supported by the wiper holder  90 . The wiper member  86  is provided so as to protrude toward the ink jet head  6 , and wipe out ink remaining on the lower surface  6   a  of the ink jet head  6  by the movement of the carriage  64 . The cap  85  covers the nozzles formed in the ink jet head  6  to prevent the evaporation of ink. 
     Next, the electric circuit structure of the color ink jet printer  1  will be described with reference to  FIG. 2 .  FIG. 2  is a block diagram schematically illustrating the electric circuit structure of the color ink jet printer  1 . 
     The color ink jet printer  1  includes an ASIC  21  and a complex IC  20 . The ASIC  21  is provided with a input/output (I/O) port  30 , CPU  32 , which is a one-chip arithmetic device, a RAM  34 , an A/D converter  36 , a serial control circuit  37  that generates serial signals, and a PWM control circuit  38  that generates PWM signals. These components are connected to one another through a bus line  31 . In addition, an EEPROM  35  and a ROM  33  having various control programs and fixed value data stored therein are connected to the bus line  31 . 
     The CPU  32  generates a printing timing signal and a reset signal according to a control program previously stored in the ROM  33 . The generated signals are serially transmitted through the serial control circuit  37 . A head driver temperature detecting thermistor  49  and an ink temperature detecting thermistor  50 , and an output terminal of an inductor  45  are connected to the A/D converter  36 . The head driver temperature detecting thermistor  49  detects the temperature of a head driver  47 . The ink temperature detecting thermistor  50  detects the temperature of ink contained in the ink cartridge  61  (see  FIG. 1 ). Analog data of the detected temperature or an output voltage from the inductor  45  is converted into digital data by the A/D converter  36 . 
     The serial control circuit  37  is connected to a register  40  through a clock signal line CLK, a data signal line DATA, and a strobe signal line STB. The PWM control circuit  38  is connected to a DC/DC control circuit  41  through a D/A converter  39 . A PWM signal, serving as a reference voltage, generated by the PWM control circuit  38  is converted into an analog signal by the D/A converter  39  and is then output to the DC/DC control circuit  41 . Then, the DC/DC control circuit  41  generates a voltage to be output to a head driver  47  on the basis of the reference voltage. The ROM  33  stores a printing control program  33   a  for executing a printing process shown in  FIG. 3 . The EEPROM  35  stores a table having the relationship between the ink temperature and the head voltage shown in  FIG. 4  recorded therein. 
     The register  40  and the DC/DC control circuit  41  are realized on the single complex IC  20 . The DC/DC control circuit  41  generates a switching signal for converting a DC voltage input from a main power supply into another DC voltage, and is connected to a gate of a MOS-FET  42  (hereinafter, referred to as an ‘internal MOS 42’) on the complex IC  20  and a gate of a MOS-FET  43  (hereinafter, referred to as an ‘external MOS 43’) attached outside the complex IC  20 . Sources of the internal MOS  42  and the external MOS  43  are connected to a main power supply  48  through a resistor  51 . A drain of the internal MOS  42  and a drain of the external MOS  43  are connected to the head driver  47  through the inductor  45 . A diode  44  is connected to an input terminal of the inductor  45 , and a capacitor  46  is connected to an output terminal of the inductor  45 . A comparator  53  is connected between the input and output terminals of the resistor  51  to detect an overcurrent. The comparator  53  compares the power supply voltage supplied from main power supply  48  to the input terminal of the resistor  51  with the voltage at the output terminal of the resistor  51 . If an overcurrent is detected then an overcurrent detection signal is sent to the I/O port  30  of the ASIC  21 , which passes the signal on to the CPU  32 . In response to the overcurrent detection signal, the CPU  32  sends a control signal via the serial control circuit  37  to the register  40 , which generates and transmits an OFF signal to the DC/DC converter  41  to turn off the internal MOS  42  and the external MOS  43 . In an alternative aspect, the overcurrent detection signal may be sent directly to the register  40 , which can generate and transmit an OFF signal to the DC/DC converter  41  to turn off the internal MOS  42  and the external MOS  43 . 
     The DC/DC control circuit  41 , the internal MOS  42  (first switch), the external MOS  43  (second switch), the resistor  51 , the comparator  53  for detecting an overcurrent, the inductor  45 , the diode  44 , and the capacitor  46  form a step-down switching DC/DC converter. A DC voltage of the main power supply  48  is converted into another DC voltage by the step-down switching DC/DC converter and is then output to the head driver  47 . 
     The DC/DC control circuit  41  is connected to the register  40 , and includes a mode switch (not shown) that performs switching based on the serial signal transmitted from the register  40 . The output of the switching signal generated by the DC/DC control circuit  41  to the internal MOS  42  or the external MOS  43  is determined by the switching operation of the mode switch. 
     In this structure, the internal MOS  42  and the external MOS  43  are connected to the common resistor  51 , which makes it possible to use a common part and thus to reduce manufacturing costs even when two switching elements, that is, the internal MOS  42  and the external MOS  43 , are provided. In addition, the common resistor  51  is attached outside the complex IC  20  that has the internal MOS  42  thereon and is coated with a metallic material, which makes it possible to for the comparator  53  to detect an overcurrent more accurately than a structure in which a common resistor and comparator are formed of a semiconductor and is realized on the complex IC  20 . 
     Next, a printing process will be described with reference to  FIG. 3 .  FIG. 3  is a flowchart illustrating the printing process. In the printing process, the output of the switching signal to the internal MOS  42  or the external MOS  43  is determined to perform printing. The printing process is performed by the CPU  32  according to the printing control program  33   a  stored in the ROM  33 . 
     In the printing process, first, the ink temperature detecting thermistor  50  detects the temperature of ink (S 301 ), and a head voltage Vc is set according to the detected ink temperature (S 302 ). For example, the relationship between the temperature of ink and the head voltage Vc is that shown in  FIG. 4 . That is, as the temperature of ink increases, the head voltage Vc is lowered. 
     When the head voltage Vc is set, the actual head voltage Vdc is detected (S 303 ). Then, it is determined whether the detected head voltage Vdc is equal to the head voltage Vc set in step S 302  (S 304 ). When the head voltage Vdc is not equal to the head voltage Vc (S 304 : No), the head voltage Vc set in step S 302  is adjusted (S 313 ). Then, the process is repeated from step S 302 . 
     On the other hand, when the detected head voltage Vdc is equal to the head voltage Vc set in step S 302  (S 304 : Yes), the head driver temperature detecting thermistor  49  detects the temperature Tc of the head driver  47  (S 305 ). It is determined whether the temperature Tc of the head driver  47  is less than a predetermined threshold value Tα (for example, 60° C.) (S 306 ). When the temperature Tc of the head driver  47  is less than the predetermined threshold value Tα (S 306 : Yes), it is determined whether the head voltage Vc set in step S 302  is less than a predetermined threshold value Vα (for example, 20 V) (S 307 ). When the head voltage Vc is less than the predetermined threshold value Vα (S 307 : Yes), the switching element outputting the switching signal is set as the internal MOS  42  (S 308 ), and printing is performed (S 309 ). In this way, the printing process is completed. 
     It an alternative aspect S 307  may be omitted from the process in  FIG. 3 , such that if the temperature Tc is less than the predetermined threshold temperature Tα, then control can proceed directly from S 306  to S 308 . In still another alternative aspect, S 306 , S 310  and S 312  may be omitted such that after S 305 , control proceeds directly to S 307 . 
     That is, when the temperature Tc of the head driver  47  is less than the predetermined threshold value Tα, the switching signal is output to the internal MOS  42 . The structure in which the internal MOS  42  performs the switching operation has a higher response performance than the structure in which the external MOS  43  performs the switching operation. Therefore, when the internal MOS  42  performs the switching operation, it is possible to improve the driving efficiency. 
     When the head voltage Vc set in step S 302  is less than the predetermined threshold value Vα, the switching signal is output to the internal MOS  42 . When the head voltage Vc is less than the predetermined threshold value Vα, power consumption and the amount of heat generated are reduced. Therefore, the structure in which the internal MOS  42  performs the switching operation has a higher response performance than the structure in which the external MOS  43  performs the switching operation. Thus, when the internal MOS  42  performs the switching operation, it is possible to improve the driving efficiency. 
     On the other hand, in step S 306 , when the temperature Tc of the head driver  47  is not less than the predetermined threshold value Tα (S 306 : No), it is determined whether the temperature Tc of the head driver  47  is less than a predetermined threshold value Tβ (for example, 90° C.) that is greater than the predetermined threshold value Tα (S 310 ). When it is determined that the temperature Tc of the head driver  47  is less than the predetermined threshold value Tβ (S 310 : Yes), the switching element outputting the switching signal is set as the external MOS  43  (S 311 ), and printing is performed (S 309 ). In this way, the printing process is completed. 
     That is, when the temperature Tc of the head driver  47  is greater than the predetermined threshold value Tα, the switching signal is output to the external MOS  43 . When the temperature Tc of the head driver  47  is greater than the predetermined threshold value Tα, the external MOS  43  performs the switching operation, which makes it possible to increase the amount of heat dissipated and prevent an increase in temperature due to the generation of heat. 
     When it is determined in step S 310  that the temperature Tc of the head driver  47  is not less than the predetermined threshold value Tβ (S 310 : No), a method of discharging ink slower, for example twice as long as the normal discharge period, is set as an ink discharging method (S 312 ). Then, the switching element outputting the switching signal is set as the external MOS  43  (S 311 ), and printing is performed (S 309 ). In this way, the printing process is completed. 
     That is, when it is determined that the temperature Tc of the head driver  47  is not less than the predetermined threshold value Tβ, the method of discharging ink at a slower rate for one line is set as an ink discharging method. The method of discharging ink slower (e.g., twice as along as the regular or standard discharge method) to print one line generates a smaller amount of heat than a method of discharging ink at the standard rate to print one line, and thus can prevent an increase in temperature due to the generation of heat. 
     When it is determined in step S 307  that the head voltage Vc set in step S 302  is not less than the predetermined threshold value Vα (S 307 : No), the switching element outputting the switching signal is set as the external MOS  43  (S 311 ), and printing is performed (S 309 ). In this way, the printing process is completed. 
     That is, when the head voltage Vc set in step S 302  is not less than the predetermined threshold value Vα, the switching signal is output to the external MOS  43 . When the head voltage Vc set in step S 302  is greater than the predetermined threshold value Vα, power consumption and the amount of heat generated increase. Therefore, the structure in which the external MOS  43  performs the switching operation dissipates a larger amount of heat than the structure in which the internal MOS  42  performs the switching operation. Thus, when the external MOS  43  performs the switching operation, it is possible to prevent an increase in temperature due to the generation of heat. 
     Although the exemplary aspects of the invention have been described above, the invention is not limited thereto. For example, various modifications and changes the invention can be made without departing from the scope and spirit of the invention. 
     For example, in the above-described aspects, the use of the internal MOS  42  or the external MOS  43  depends on the set head voltage Vc, but the invention is not limited thereto. For example, the following structure may be used: environmental temperature (for example, outdoor air temperature, temperature in an apparatus, and ink temperature) is measured, and the use of the internal MOS  42  or the external MOS  43  is determined on the basis of the measured environmental temperature. For example, when the environmental temperature is greater than a predetermined threshold temperature, the internal MOS  42  may be used. On the other hand, when environmental temperature is less than the predetermined threshold temperature, the external MOS  43  may be used. 
     In this case, when the environmental temperature is not less than the predetermined threshold temperature, power consumption and the amount of heat generated decrease. Therefore, the structure in which the first switch performs the switching operation has a higher response performance than the structure in which the second switch performs the switching operation. Thus, when the first switch performs the switching operation, it is possible to improve the driving efficiency. On the other hand, when the environmental temperature is less than the predetermined threshold temperature, power consumption and the amount of heat generated increase. Therefore, the structure in which the second switch performs the switching operation can dissipate a larger amount of heat than the structure in which the first switch performs the switching operation, and thus can prevent an increase in temperature due to the generation of heat.