Patent Publication Number: US-6712438-B2

Title: Ink-jet printer and method of driving head thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 2002-7007, filed Feb. 7, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet printer, and more particularly, to an ink-jet printer capable of preventing a malfunction of a head driving unit, which occurs when ink is simultaneously discharged from a plurality of nozzles. 
     2. Description of the Related Art 
     Usually, a printer using one of a wire dot method, a heat transfer method, and an ink jet method of forming an image on a recording medium, such as printing paper or an OHP (over head project) film, uses a recording head. 
     The recording head of an ink-jet printer using one of the above methods has a plurality of nozzles being formed with minute discharging holes to eject ink. The ink in the nozzles is heated and expanded by heating elements disposed in corresponding ones of the nozzles and is ejected outside of the nozzles and stuck on the recording medium. 
     Accordingly, the ink-jet printer forms the image on the recording medium by ejecting the ink through the nozzles by selectively heating the nozzles in the recording head corresponding to the image to be recorded. 
     As shown in FIG. 1, a general ink-jet printer  200  includes an interface  210  receiving printing data and a control command from a host  100 , an input unit  230  allowing a user to input a selection command, a storage unit  250  storing a program for driving and controlling each part of the ink jet printer  200  and the printing data, a printing unit  270  performing a printing operation, and a controller  290  controlling the entire system of the ink-jet printer  200  in accordance with the program. 
     A nozzle selection data signal is transmitted to a head driving device  271  of the printing unit  270  in order to drive selected ones of a plurality of nozzles of the recording head  273  in response to the printing data. 
     As shown in FIG. 2, the head driving device  271  includes a first data unit  21  and a second data unit  23  receiving the nozzle selection data signal having an ADDR (address) data signal ADDR and a P (primitive) data signal P_Data, a signal supply  27  having AND gates, and a nozzle driving unit  29  driving the selected nozzle among the plurality of nozzles to discharge the ink. 
     For example, in a case of the recording head having an n×m number of nozzles, the ADDR data signal ADDR is a data signal to select one of n number of fire groups A 1 -An each having an m number of nozzles, and the P data signal P_Data is a data signal to select a predetermined number of nozzles among the m number of nozzles in a corresponding one of the fire groups A 1 -An. 
     In other words, when the ADDR data signal ADDR and the P_data signal P_Data have 10 bits, then one fire group is selected among the 10 fire groups A 1 -A 10  in response to corresponding one of the 10-bits of the ADDR data signal ADDR, and the number of the nozzles capable of simultaneously discharging the ink in response to the P data signal P-Data in the fire groups A 1 -A 10  is 10. In other words, the entire number of nozzles of the recording head is 10×10=100. 
     Hereinbelow, a general operation of the head driving device  271  according to the input data signals will be described by referring to FIGS. 3A-3F. 
     The ADDR data signal Addr_ 1  and the P_data signal Data_a of the nozzle selection data signal are synchronized with a clock signal CLOCK, shifted to each bit shift register, and stored in each latch. 
     Then, when a load signal LOAD is input, the ADDR data signal Addr_ 1  and the P_data signal Data_a stored in each of the bit shift register are latched. 
     After that, when a fire strobe signal STRB_ 1  to discharge the ink in the nozzles by heating the heating element is input from the controller  290  to the signal supply  27 , next ADDR data signal Addr_ 2  and next P data signal Data_b are stored in respective one of the n-bit shift register and the m-bit shift resistor. 
     Therefore, the latched data signals Addr_ 1  and Data_a and the strobe signal STRB_ 1  are input into the signal supply  27  having the n×m number of AND gates to drive the nozzle driving unit  29 . 
     In other words, a transistor (or FET) of the nozzle driving unit  29  is turned on in response to an output signal of the AND gate corresponding to the selected nozzle among the n×m number of AND gates of the signal supply  27 . 
     Therefore, an electric current flows as a driving voltage is supplied to each heating element connected with the turned on transistor (or FET) among the n×m number of transistors (or FET) to eject the ink through the selected nozzle. 
     As described above, to discharge the ink from the plurality of nozzles, a large amount of electric current is required. 
     Recently, the number of nozzles simultaneously discharging the ink in order to perform a high density and printing speed has been increased. Accordingly, a high electric current flows to a power supply terminal Vp of the recording head  273  of the printing unit  270 . 
     As shown in FIGS. 4A-4G, the high electric current flowing to the power supply terminal Vp in order to drive the plurality of the nozzles causes a noise signal to be input to an input signal line (P_data, ADDR). Because the high electric current flows to the recording head  273  within a relatively short period of time, the power supply terminal Vp becomes unstable, and as a result, the noise signal is produced. 
     Therefore, there is a problem of a malfunction in controlling the nozzles as the noise signal is input into the head driving device together with the data signals. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome the above and other problems of the related art. Accordingly, it is the object of the present invention to provide an ink-jet printer capable of preventing a malfunction of a head driving device, which is generated when the ink is simultaneously discharged from a plurality of nozzles. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     An ink-jet printer is provided in order to achieve the above and other objects and includes a nozzle driving unit driving a plurality of nozzles to discharge ink, a signal supply supplying a driving signal to the nozzle driving unit, a shift register storing the nozzle selection signal to select a nozzle in response to a recording image after the nozzle selection signal is synchronized with a clock signal, a counter counting an input number of the clock signal and deciding whether to operate the shift register, and a controller inputting a discharge signal to discharge the ink into the signal supply when the shift register is disabled. 
     The counter compares a set-up value set up in accordance with a predetermined bit number of the nozzle selection data signal and the input number of the clock signal. When the input number is over the set-up value, the shift register is disabled. 
     On the other hand, a method of driving a head of an ink-jet printer according to an aspect of the present invention includes inputting a nozzle selection data signal to select a nozzle among a plurality of nozzles into a shift register when the nozzle selection data signal is synchronized with a clock signal, disabling the shift register when an input number is above a predetermined value after counting the input number of the clock signal, latching the nozzle selection data signal stored in the shift register, and inputting a discharge signal to discharge ink from the selected nozzle based on the latched nozzle selection data signal. 
     The latching of the nozzle selection data signal includes resetting a counter counting the input number of clock signals . Therefore, noise generated in the data signal by the discharge signal is eliminated as the discharge signal is input after the nozzle selection data signal is stored into the shift register. Thus a malfunction of head driving device can be prevented. 
     Moreover, even though the noise signal is generated in the data signal, the malfunction of the head driving device caused by the noise signal can be prevented since the data signal as much as the corresponding bit is input into the shift register by the counter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a block diagram showing a conventional ink-jet printer; 
     FIG. 2 is a block diagram showing a head driving device of the ink-jet printer of FIG. 1; 
     FIGS. 3A-3F are timing charts of input signals of the head driving device of FIG. 2; 
     FIGS. 4A-4G are views showing a driving voltage Vph wave form and a noise phenomenon generated in the input signals of the head driving device of FIG. 2; 
     FIG. 5 is a block diagram showing a head driving device of an ink-jet printer according to an embodiment of the present invention; 
     FIGS. 6A-6F are timing charts of input signals of the head driving device of FIG. 5; and 
     FIG. 7 is a flow chart showing a method of driving the head driving device of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention be referring to the figures. 
     Herein below, the present invention will be described in greater detail by referring to the appended drawings. 
     Referring to FIG. 5, in an ink-jet printer according to an embodiment of the present invention, a head driving device  371  corresponds to the head driving device  271  of FIG.  1  and driving a recording head  273  of FIG. 1 with n×m number of nozzles will be described. Here, n is the number of fire groups, and m is the number of the nozzles in each fire group. Same reference numerals have been given to the same elements as those described in FIGS. 1-4G. 
     The head driving device  371  includes a first data unit  31  and a second data unit  33  synchronizing an n bit ADDR data signal and an m bit P data signal P_Data, which are nozzle selection data signals to select respective nozzles of the recording head  273  in response to an image to be recorded, with a clock signal CLOCK and temporarily storing the nozzle selection data signals, n-bit and m-bit counters  35 ,  35 ′ controlling the ADDR data signal and the P data signal P_Data by counting the clock signal CLOCK, a signal supply  37  having AND gates and a nozzle driving unit  39  driving the nozzle selected from the n×m number of nozzles in response to the ADDR data signal and the P data signal P_Data to discharge the ink through the selected nozzle. 
     The first data unit  31  has an n-bit shift register to shift the n-bit ADDR data signal, such as Addr_ 1 , Addr_ 2 , Addr_ 3 , by synchronizing with the clock signal CLOCK and storing the n-bit ADDR data signal, and an n-bit latch to temporarily latch the n bit ADDR data signal when a load signal LOAD is input. 
     The first data unit  31  also has the n-bit counter  35 . The n-bit counter  35  enables the n bit shift register to store up to the ADDR data signal until an nth clock signal is counted, and disables the n-bit shift register not to store an n+1th ADDR data signal when an n+1th clock signal is counted. On the other hand, when the load signal LOAD is input, the n-bit counter  35  is reset. 
     The second data unit  33  has an m-bit shift register to store the m-bit P data signal P_Data, such as Data_a, Data_b, and Data_c, after shifting the m bit P data signal P_Data by synchronizing with the clock signal CLOCK, and an m bit latch to temporarily latch the m bit P data signal P_Data when the load signal LOAD is input. 
     Moreover, the second data unit  33  also has the m-bit counter  35 ′. The m-bit counter  35 ′ enables the m-bit shift register to store up to an mth P data signal P_Data until an mth clock signal CLOCK is counted, and disables the m-bit shift register not to store an mth P data signal P_Data when an m+1th clock signal CLOCK is counted. On the other hand, when the load signal LOAD is input, the m-bit counter  35  is reset. 
     Each of the bit counters  35  and  35 ′ can be disposed in the respective n-bit and m-bit shift registers as described above, or separately disposed outside the respective n-bit and m-bit shift registers. 
     When the data signals ADDR and P_Data are completely input into each of the n-bit and m-bit shift registers and when the n-bit and m-bit shift registers are disabled, a controller  290  inputs a strobe signal STRB, which is a discharge signal to discharge the ink, into the head driving device  271 . 
     The signal supply  37  has a combination of the AND gates (1, 2, . . . m×n ) corresponding to the n×m number of nozzles. When the load signal LOAD is input, the data signals ADDR and P_Data, which are temporarily latched to each latch, are input into corresponding AND gate of the signal supply  37 . At this time, an AND gate corresponding to a selected nozzle among the n×m numbers of AND gates outputs an output signal in response to each of the input data signals ADDR and P_Data. 
     Corresponding one of n×m numbers of transistors (or FET) of the nozzle driving unit  39  is operated by the output signal of the AND gate. 
     In other words, the electric current is flown to a heating element R of the selected nozzle as a transistor (or FET) corresponding to the selected nozzle among the n×m numbers of the transistors (or FET) is turned on. Therefore, the ink in the selected nozzle is discharged as heat is generated by the heating element R. 
     A driving method of the head driving device  271  according to the embodiment of the present invention will be described referring to FIGS. 6A-6F and  7 . 
     Firstly, the ADDR data signal Addr_ 1  and P data signal Data_a of the nozzle selection data signals corresponding to a recording image and the clock signal CLOCK, which is a synchronized signal, are input in operation S 10 . 
     The ADDR data signal Addr- 1  and the P data signal Data_a are synchronized with the clock signal CLOCK and respectively stored in the n-bit and m-bit shift registers after being shifted in operation S 20 . 
     For example, 10 bits of ADDR data signal Addr- 1 , synchronized with the clock signal CLOCK are input and stored in a corresponding ones of 10 shift registers of 10-bit shift register in operation S 20 . At this time, 10 bits counter  35  has a set-up value of 10, which is the bit number of the ADDR data signal Addr- 1 . Accordingly, the 10-bit counter  35  compares a clock signal frequency of the input clock signal CLOCK and the set-up vale in operation S 30 . 
     The 10-bit counter  35  allows the input ADDR data signal Addr- 1  to be stored into the 10 bit shift register  31  by synchronizing with the clock signal CLOCK until a 10 th  clock signal and the set-up value are counted in operation S 20  . After that, 10 bit shift register  31  is disabled so as not to store a certain data signal when an 11 th  clock signal CLOCK is counted in operation S 40 . 
     Then, when the load signal LOAD is input, each bit counter  35  and  35 ′ is reset, and at the same time, the ADDR data signal Addr- 1  and the n- bit and m-bit shift registers are latched in corresponding n-bit and m-bit latches in operation S 50 . 
     When a strobe signal STRB_ 1  to discharge the ink is input from the controller  290  in operation S 60 , the strobe signal STRB_ 1  and each of the latched data signal Addr- 1  and Data_a are input to corresponding the input terminals of the AND gate of the signal supply  37 . 
     Here, a strobe signal STRB_ 0  is a previous discharge signal with respect to a previously selected nozzle of a previously selected fire group of the recording head  273 . 
     An output signal of each AND gate becomes high only when all input signals of input terminals of the AND gate are high due to the characteristic of the AND gate, thus only the AND gate having all high input signals outputs the high output signal. 
     The transistor (or FET) of the nozzle driving unit  39  corresponding to the high output signal of the AND gate is turned on. Therefore, as a driving voltage Vph is supplied to each transistor (or FET), the electric current is flown to the heating element K of the selected nozzle, and the ink is discharged from the selected nozzle. 
     In other words, the controller  290  determines whether the ADDR data signal Addr- 1  and the P data signal Data_a are completely stored in the n-bit and m-bit shift registers, and then inputs the strobe signal STRB_ 1 . Therefore, the noise presented in the ADDR data signals Addr- 1  and the P-data signal Data_a or Addr_ 2  and Data_b by inputting the strobe signal STRB_ 1  can be prevented. 
     Moreover, even though the noise signal is presented in the data signals ADDR —1  and Data_a, the noise signal is not input into the shift register by the counters  35  and  35 ′, thus the nozzle driving unit  39  is not affected after that. 
     Accordingly, the malfunction of the head driving device  271 , which is generated when the ink is discharged simultaneously from the plurality of nozzles of the recording head  273 , can be prevented. 
     According to the present invention, the noise flow generated in the data signal by the strobe signal can be eliminated since the strobe signal is input after the nozzle selection data signal is stored into the shift register. 
     In addition, even though there is a noise signal in the data signal, the malfunction of the head driving device  371  can be prevented by inputting the data signal as much as the amount of the corresponding bit into the shift register by the counter. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.