Patent Publication Number: US-2005116987-A1

Title: Method for preventing air from pressing into a print nozzle of an ink container using negative pressure

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to a method for preventing air from pressing into a print nozzle of an ink container, and more particularly, to a method for preventing air from pressing into a print nozzle of an ink container using negative pressure.  
      2. Description of the Prior Art  
      As personal computers become more popular, ink jet printing devices are becoming a common computer output/printing device used by people, families, and companies because a price and quality of the ink jet printers attract customers. However the high level of printing quality also depends on how to preserve the print head effectively.  
      A typical ink jet printing device has a print head that moves along a track, back and forth, to print on a document. The print head usually has at least an ink cartridge, and the ink cartridge includes a housing with an ink reservoir for storing ink and a print head connected to the ink reservoir to control the ink jetting. In a typical ink jet printing device, flow control is usually employed to control the ink jetting out to the document from the ink reservoir. Typical print head flow control mechanisms are divided into two types: thermal-bubbles and pressure-waves. The thermal-bubbles print head includes a thin-film resister. When the resistor is heated, a trace of ink vaporizes immediately, quickly expanding to make ink pass through the print head and print on the document. Although the print head using the flow control can get ink from the ink reservoir and jet ink effectively, the flow control needs a controlling mechanism, so that the print head does not seep ink when not in use. The controlling mechanism usually provides a light negative pressure to prevent ink from seeping onto the print head. The negative pressure is a partial vacuum in the ink cartridge, so that the external atmospheric pressure is slightly higher than the fluid pressure in the ink cartridge. The negative pressure is indicated by a positive value, so an increase in the negative pressure means an increased vacuum of the ink cartridge and a greater difference between the external atmospheric pressure and the fluid pressure in the cartridge. By increasing the negative pressure, ink is prevented from seeping from the print head. Although increasing the negative pressure prevents ink from seeping out of the print head, the negative pressure has an upper limit. If the negative pressure is too high, ink cannot overcome the negative pressure and cannot jet from the print head. Moreover, if the external atmospheric pressure is much greater than the fluid pressure in the cartridge, the external atmospheric pressure will overcome the fluid pressure in the cartridge and the external air will seep into the print head in bubble form. Therefore the ink channel will be clogged and the print quality will be lowered.  
      In addition, the current manufacturers often provide a capping mechanism for the print head to prevent ink from vaporizing. However, if the capping mechanism causes too much negative pressure in the cartridge, there is often unwanted air that is compressed into the print head. Therefore the ink channel will be clogged and the print quality will be lowered.  
     SUMMARY OF INVENTION  
      It is therefore a primary objective of the present invention to provide a method for preventing air from pressing into a print nozzle of an ink container to solve the above-mentioned problems.  
      According to the claimed invention, a method for preventing air from pressing into a print nozzle of an ink container of a printer is proposed. The printer includes a pressure-generating module and a capping module. The method includes generating local pressure nearby the print nozzle of the ink container with the pressure-generating module when the capping module caps the print nozzle and capping the print nozzle with the capping module for separating the print nozzle from the air outside the capping module.  
      According to the claimed invention, a printer includes a housing and an ink container installed inside the housing. The ink container includes a pressure-generating module. The printer also includes a capping module installed inside the housing for capping a print nozzle of the ink container and a control unit for controlling the pressure-generating module to generate local pressure nearby the print nozzle of the ink container when the capping module caps the print nozzle.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a functional block diagram of a printer according to the present invention.  
       FIG. 2  is a diagram of an ink container according to the present invention.  
       FIG. 3  is a sectional drawing of the ink container along the axis  3 - 3 ′.  
       FIG. 4  is a flowchart illustrating that air is prevented from pressing into a print nozzle of the ink container of the printer according to the present invention.  
    
    
     DETAILED DESCRIPTION  
      Please refer to  FIG. 1 .  FIG. 1  is a functional block diagram of a printer  10  according to the present invention. The printer  10  includes a housing  12  and an ink container  14  installed inside the housing  12 . The ink container  12  includes a casing  16 , a pressure-generating module  18 , and a temperature-measuring unit  20 . The pressure-generating module  18  can be a heating module or an electrothermal transducer for transforming electric energy into heat energy, like an electrothermal chip including a thermal resistance. The temperature-measuring unit  20  can measure the heating temperature of the ink container  14  and transmit the heating temperature to the printer  10 . The printer  10  also includes a capping module  22  installed inside the housing  12  for capping a print nozzle of the ink container  14  and a motor  24  for moving the ink container  14  back and forth to print on a document. The motor  24  can be a DC motor. The printer  10  further comprises a control unit  26  for controlling the pressure-generating module  18  to generate local pressure nearby the print nozzle of the ink container  14  according to the heating temperature transmitted from the temperature-measuring unit  20  when the capping module  22  caps the print nozzle.  
      Please refer to  FIG. 2  and  FIG. 3 .  FIG. 2  is a diagram of the ink container  14  according to the present invention.  FIG. 3  is a sectional drawing of the ink container  14  along the axis  3 - 3 ′. The ink container  16  includes the casing  16  for forming an ink reservoir  30  for storing ink  28 . A print head  32  is installed on top of the ink container  14  and connected to the ink reservoir  30  for controlling the ink  28  jetting out to the document from the ink reservoir  30 . The pressure-generating module  18  is installed inside the print head  32 . The ink container  14  also includes a manifold  34 . The print head  32  is connected to the ink reservoir  30  via the manifold  34 . The print head  32  further includes an orifice layer  36 . A plurality of ink chambers  38  is formed between the orifice layer  36  and the pressure-generating module  18 . The pressure-generating module  18  includes a plurality of heating units  40 , and each heating unit  40  is utilized for heating the ink  28  in a corresponding ink chamber  38  to generate bubbles. The orifice layer  36  includes a plurality of print nozzle  42 , and each print nozzle  42  is located in a position corresponding to one heating unit  40 . When the electric current passes through the heating unit  40  so that the heating unit  40  can heat the ink  28  in the ink chamber  38  to generate bubbles, the ink  28  will be jetted from the print nozzle  42 .  
      Please refer to  FIG. 4 .  FIG. 4  is a flowchart illustrating that air is prevented from pressing into the print nozzle  42  of the ink container  14  of the printer  10  according to the present invention. The method includes: 
          Step  100 : The control unit  26  generates a capping signal and sends the capping signal to the motor  24  and the pressure-generating module  18  of the ink container  14 . Proceed to step  102  and step  104 ;     Step  102 : Move the ink container  14  to a position corresponding to the capping module  22  so that the capping module  22  can cap the print nozzle  42  of the ink container  14 . Go to step  106 ;     Step  104 : The pressure-generating module  18  generates local pressure nearby the print nozzle  42  of the ink container  14  when the capping module  22  caps the print nozzle  42  of the ink container  14 . Go to step  108 ;     Step  106 : The capping module  22  finishes capping the print nozzle  42  of the ink container  14  for separating the print nozzle  42  from air outside the capping module  22 ; and     Step  108 : Finish the capping action.        

      The detailed description is as follows. When the ink container  14  finishes the printing job, the ink container  14  will be back to an original location that is usually located on either side of the printer  10 . At this time the capping module  22  will cap the print nozzle  42  of the ink container  14  to prevent the ink  28  from vaporizing from the print nozzle  42 . The control unit  26  of the printer  10  will generate a capping signal and send the capping signal to the motor  24  and the pressure-generating module  18  of the ink container  14 . When the motor  24  receives the capping signal, the motor  24  will move the ink container  14  to a position corresponding to the capping module  22  so that the capping module  22  can cap the print nozzle  42  of the ink container  14 . Simultaneously the pressure-generating module  18  will generate local pressure nearby the print nozzle  42  of the ink container  14 . The method of generating local pressure can be that the heating unit  40  heats the ink  28  nearby to increase the temperature. The working principle is according to the ideal gas equation PV=nRT (P: gas pressure; V: gas volume; n: mole number of gas; R: Avogadro&#39;s number; T: temperature of gas). When the air nearby the print nozzle  42  is heated for increasing its temperature, the pressure of the air nearby the print nozzle  42  will be increased for generating local pressure. The increasing pressure can resist the capping pressure of the capping module  22 , so the air outside the capping module  22  can be prevented from pressing into the print nozzle  42  of the ink container  14 . Therefore there is less air clogging in the ink channel of the print nozzle  42 . The print quality will be increased because the accuracy of the jetting direction and the success rate of jetting the ink  28  from the print nozzle  42  are increased and the size of jetting bubbles can be controlled effectively.  
      Besides the method mentioned above, the ink  28  nearby the heating unit  40  can be heated by the heating unit  40  to raise the temperature nearby the print nozzle  42  of the ink container  14 , and some ink  28  can be jetted from the print nozzle  42  for generating local pressure. Therefore not only will the pressure of the air nearby the print nozzle  42  be increased for generating local pressure, but also a hydraulic pressure will be generated nearby the print nozzle  42  of the ink container  14  for preventing the air outside the capping module  22  from pressing into the print nozzle  42  of the ink container  14 . The hydraulic pressure is generated from the ink inside the print nozzle  42 . So when the ink  28  is jetted outside the print nozzle  42 , the original bubbles inside the print nozzle  42  will be jetted outside the print nozzle  42  too. The operating mechanism of the pressure-generating module  18  is not limited to the heating mechanism mentioned above. The pressure-generating module  18  also can be a piezoelectricity transducer for transforming electric energy into mechanical energy so as to pressurize ink inside the ink channel of the ink container  14  and air nearby the print nozzle  42 . For example, the pressure-generating module  18  can be made of piezoelectricity material for transforming electric energy into energy of deformation so as to pressurize ink inside the ink channel of the ink container  14  and air nearby the print nozzle  42  when the energy of deformation stored in the piezoelectricity material is released.  
      When the pressure-generating module  18  generates local pressure nearby the print nozzle  42  of the ink container  14 , the ink container  14  will move to the position corresponding to the capping module  22  and then the capping module  22  will finish capping the print nozzle  42  of the ink container  14  for separating the print nozzle  42  from air outside the capping module  22 . Therefore it can prevent dirt outside from entering the print nozzle  42  and prevent the ink  28  from vaporizing from the print nozzle  42 . Thus the capping job is finished.  
      In contrast to the prior art, the printer  10  according to the present invention can utilize the pressure-generating module  18  to generate local pressure nearby the print nozzle  42  of the ink container  14  for preventing unwanted air outside from pressing into the print nozzle  42  of the ink container  14  and for preventing the ink channel from becoming clogged by bubbles when the capping module  22  caps the print nozzle  42  of the ink container  14 . Furthermore, compared with the prior method of preventing outside air from pressing into the print nozzle  42 , utilizing the heating mechanism for generating local pressure according to the present invention can allow the present invention to be implemented under the current structure of present ink jet printing devices. The present invention also can be applied to other image printing devices in ink jet printing technology, like fax machines or multi-function products. Any method for preventing air from pressing into the print nozzle  42  of the ink container  14  using negative pressure is all within the scope of the present invention.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the method and the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.