Abstract:
An inkjet pen including an ink reservoir for storing ink and providing ink for jetting. A port, located on top of the ink reservoir, fluid-communicated with the ambient air, is used for adjusting the air pressure inside the reservoir. A valve, operated by a spring or a resilient element, normally seals the port, while occasionally opening the port to introduce air into the reservoir when the ink level is low and the underpressure rises. In other embodiments, an elastic bag is included in the reservoir that has an opening communicated with the ambient air through a second port formed on top of the reservoir. The elastic bag expands in response to the increasing underpressure generated in the reservoir when ink is being used. The bag expansion actuates the opening of the valve so as to regulate the underpressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a mechanism for regulating the ink pressure within an ink reservoir of an inkjet pen. The mechanism automatically regulates the underpressure inside the inkjet pen to prevent the ink from leaking.  
           [0003]    2. Related Art  
           [0004]    Common inkjet printers apply ink pens that include ink reservoirs and print heads. The print head controls ink drops jetting from the ink reservoir. Two common methods for inkjet control are the thermal bubble system and the piezoelectric system. Although conventional print heads are effective for jetting ink drops from pen reservoirs, they need extra mechanisms for preventing ink from leaking out of the print heads when the print heads are inactive. These mechanisms generally provide slight underpressure at the print heads to prevent ink leakage from the pens whenever the print heads are inactive. The term “underpressure” used herein means a partial vacuum (less pressure than the ambient air) within the pen reservoir that prevents flow of ink through the print head. The underpressure at the print head must be strong enough at all times for preventing ink leakage. However, the underpressure must not be so strong that the print head is unable to overcome the underpressure to jet ink drops, the size of the ink drops and the print quality are influenced, or the printing totally fails.  
           [0005]    In order to maintain normal functions, the underpressure at the print head must be regulated within an operating range. In other words, the pressure in the ink reservoir must always be lower than the ambient pressure to prevent ink leakage, but not be too low to hinder the inkjet function. To fulfill the aforesaid requirements, many prior methods have been developed. For example, U.S. Pat. No. 4,992,802, “Method and apparatus for extending the environmental operating range of an ink jet print cartridge”, disclosed by Dion et al, applies two pressure control mechanisms for limiting the reservoir underpressure. The first pressure control mechanism limits reservoir underpressure by introducing replacement fluid (i.e. air or ink) thereto. The second pressure control mechanism limits reservoir underpressure by changing the volume thereof. The two pressure control mechanisms cooperate to regulate the underpressure in the reservoir within a desired range. However, the mechanisms of Dion are rather complicated and occupy more space in the reservoir.  
           [0006]    In contrast, a simpler mechanism, disclosed by Pollacek, et al in U.S. Pat. No. 5,040,002, “Regulator for ink-jet pens”, provides a regulator that comprises a seat and associated valve element. The seat is mounted to the body of an inkjet pen reservoir. The seat has a port formed through it. Magnetism is employed to attract the seat and valve element together and thereby close the port and permit underpressure to develop in the reservoir. When the underpressure within the reservoir rises above the level that may cause failure of the inkjet print head, the valve element moves away from the seat to permit air to enter the reservoir, thereby reducing the underpressure to an operable level. However, the magnetic mechanism is influenced when a strong magnetic force is to close to the inkjet pen, for example, during transportation, the underpressure is changed and the function and quality of printing may be influenced.  
           [0007]    Another kind of underpressure regulator includes a flexible bag mounted to a flat curved spring. The elasticity of the spring tends to contract the bag as the bag expands in response to back pressure reduction in the reservoir. As disclosed in U.S. Pat. No. 5,409,134, “Pressure-sensitive accumulator for ink-jet pens” by Cowger, et al, the flexible bag varies its volume between a minimum volume position and a maximum volume position to regulate the inkjet pen reservoir volume and adjust the underpressure so that the underpressure remains within an operating range that is suitable for preventing ink leakage while permitting the print head to continue ejecting ink drops. This kind of regulator, however, encounters the difficulty of exhausting the ink in the reservoir since the flexible bag has an expansion limitation. When the ink in the reservoir is low, the flexible bag has expanded to its limit, and the higher underpressure then causes the inkjet to fail and the rest of the ink cannot be used up. Furthermore, the ideal operative range of underpressure is within negative 2.5 to negative 10 cm water column, or −0.0024 to −0.0097 atmospheric pressure, which is so small that the elasticity of the spring has to be precisely controlled. The elasticity of the spring involves the technical problems of the contents of the material, the heat treatment process, and variations of shape, length and thickness of the spring, which cause instability of the spring characteristics. Consequently, Cowger, et al further discloses in U.S. Pat. No. 5,505,339, “Pressure-sensitive accumulator for ink-jet pens”, some suitable shapes for the spring.  
         SUMMARY OF THE INVENTION  
         [0008]    The primary object of the invention is to provide a reservoir mechanism for an inkjet pen like Pollacek&#39;s, but one that is simpler and is not influenced by external magnetic force.  
           [0009]    The inkjet pen according to the invention includes an ink reservoir for storing ink and providing ink for jetting. The reservoir includes a rigid body for storing ink, a port located on top of the rigid body, fluid-communicated with the ambient air for adjusting the air pressure inside the ink reservoir, and a valve operated by a spring or a resilient element for normally sealing the port but occasionally opening the port to introduce air into the reservoir when the ink level is low and the underpressure rises. In another embodiment, an elastic bag is included in the reservoir and has an opening communicated with the ambient air through a second port formed on top of the reservoir. The elastic bag expands in response to the increasing underpressure generated in the reservoir when ink is being used. The bag expansion actuates the opening of the valve so as to regulate the underpressure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention will become more fully understood from the detailed description given hereinbelow. However, this description is for purposes of illustration only, and thus is not limitative of the invention, wherein:  
         [0011]    [0011]FIG. 1 is an explanatory configuration view of an inkjet pen of the invention, which is not scaled;  
         [0012]    [0012]FIG. 2 is a sectional view of an inkjet pen of the first embodiment of the invention that does not include an air bag;  
         [0013]    [0013]FIGS. 3 and 4 are sectional views of an inkjet pen of the second embodiment of the invention showing an air bag shrunk and expanded respectively;  
         [0014]    [0014]FIGS. 5 and 6 are sectional views of an inkjet pen of the third embodiment of the invention showing a port mechanism being sealed and opened respectively;  
         [0015]    [0015]FIGS. 7 and 8 are sectional views of an inkjet pen of the fourth embodiment of the invention showing a port mechanism being sealed and opened respectively;  
         [0016]    [0016]FIG. 9 is an example of an inkjet pen based on the fourth embodiment of the invention incorporating an ink bag;  
         [0017]    [0017]FIG. 10 is a partial sectional view of port mechanism of an inkjet pen of the fifth embodiment of the invention;  
         [0018]    [0018]FIG. 11 is a sectional view of an inkjet pen of the sixth embodiment of the invention showing the components in positions of normal underpressure within the operating range;  
         [0019]    [0019]FIG. 12 is a sectional view of an inkjet pen of the sixth embodiment of the invention showing the components in positions of higher underpressure outside the operating range;  
         [0020]    [0020]FIG. 13 is a sectional view of an inkjet pen of the seventh embodiment of the invention showing the components in positions of normal underpressure within the operating range;  
         [0021]    [0021]FIG. 14 is a sectional view of an inkjet pen of the seventh embodiment of the invention showing the components in positions of higher underpressure outside the operating range;  
         [0022]    [0022]FIG. 15 is an operational view of an inkjet pen of the seventh embodiment of the invention showing the ambient air entering the inkjet pen when there is higher underpressure;  
         [0023]    [0023]FIG. 16 is a sectional view of an inkjet pen of the eighth embodiment based on the sixth embodiment of the invention incorporating an air bag;  
         [0024]    [0024]FIG. 17 is an operational view of an inkjet pen of the eighth embodiment of the invention showing the ambient air entering the air bag and decreasing the underpressure;  
         [0025]    [0025]FIG. 18 is a sectional and operational view of an inkjet pen of the ninth embodiment based on the seventh embodiment of the invention and incorporating an air bag, in which the ambient air is entering the air bag and decreasing the underpressure. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    FIG. 1  shows a general configuration of an inkjet pen. The inkjet pen includes an ink reservoir  10  and a print head  20 . The print head  20  is composed of several micro vents  21 . A soft electrode band transfers control signals to the print head  20  so that ink drops are controlled to jet from the ink reservoir  10  to the paper (not shown in the drawing) or other objects.  
         [0027]    The driving mechanisms for jetting ink drops are usually the thermal bubble system or the piezoelectric system. Whatever the system is, each micro vent  21  connects with an ink chamber where the driving mechanism functions.  
         [0028]    First Embodiment  
         [0029]    [0029]FIG. 2 is a first embodiment of an inkjet pen according to the invention. The inkjet pen  1  includes an ink reservoir  10  having a rigid body for storing ink and providing ink for jetting. A port  12  is formed on top of the rigid body, communicated with the ambient air, for adjusting the underpressure inside the ink reservoir  10 . The port  12  is sealed from the inside of the reservoir  10  by a needle  13  that is pressed by a pressing spring  14  mounted in a seat  11 . The needle  13  is formed with a cone or round end  1301  for tightly sealing the port  12 . The stem  1302  of the needle  13  is sleeved in the spring  14  and has a flange  1303  touching the spring  14  so as to press and tightly seal the port  12  with the cone or round end  1301 . However, any other shapes of the needle end  1301  can be used as long as the sealing can be achieved. As the ink is used, the underpressure in the cartridge increases, the needle  13  seals the port  12  till the force of the spring  14  cannot overcome the vacuum force of the underpressure, and a certain amount of ambient air will enter the cartridge  20  to decrease the underpressure to within operating range.  
         [0030]    Second Embodiment  
         [0031]    [0031]FIG. 3 is a second embodiment of an inkjet pen according to the invention, which is a modification from the first embodiment of FIG. 2. An air bag  15  is fluid-communicated with the port  12  through a vent  1101  formed on the seat  11 .  
         [0032]    When the ink is being used, the level  31  of the ink decreases and the underpressure in the cartridge  10  increases. However, when the underpresuure is within the operating range, the pressing force provided by the spring  14  is larger than the pressure force of ambient air acting on the needle end  1301  so that the cartridge  10  remains sealed.  
         [0033]    As shown in FIG. 4, after the underpressure reaches an upper limit, the pressure of the ambient air is greater than the pressing force of the spring  14  acting on the needle end  1301 . Hence, the needle  13  is forced to retract and let ambient air flow into the cartridge  10  through the port  12 . The input air blows up the air bag  15 , which further pushes the ink level  31  up and lowers the underpressure to within operating range. After the underpressure decreases, the spring  14  presses the needle  13  back and seals the port  12  again.  
         [0034]    Third Embodiment  
         [0035]    [0035]FIG. 5 is a third embodiment of an inkjet pen according to the invention, which is a modification from the second embodiment of FIG. 3. The needle  13  is now replaced with a spring plate  16  to force the cone-shaped sealing portion  1301  directly. The spring plate  16  forces the sealing portion  1301  to seal the port  12 .  
         [0036]    Same as the aforesaid functions, as shown in FIG. 6, when the ink is being used, the level  31  of the ink decreases and the underpressure in the cartridge  10  increases. After the underpressure reaches an upper limit, the pressure of the ambient air is greater than the pressing force of the spring plate  16  acting on the sealing portion  1301 . Hence, the sealing portion  1301  is forced to retract and let ambient air flow into the cartridge  10  through the port  12 . The input air blows up the air bag  15 , which further pushes the ink level  31  up and lowers the underpressure to within operating range. After the underpressure decreases, the spring plate  16  further presses the sealing portion  1301  back and seals the port  12  again.  
         [0037]    Fourth Embodiment  
         [0038]    [0038]FIG. 7 is a fourth embodiment of an inkjet pen according to the invention, which is a modification from the first embodiment of FIG. 2. The needle is replaced with a spheric element, such as a steel ball  40 , and the spring is replaced with a resilient element, such as an O-ring  41 .  
         [0039]    Same as the aforesaid functions, as shown in FIG. 8, when the ink is being used, the level  31  of the ink decreases and the underpressure in the cartridge  10  increases. After the underpressure reaches an upper limit, the pressure of the ambient air is greater than the pressing force of the resilient element  41  acting on the spheric element  40 . Hence, the spheric element  40  is forced to retract and let ambient air flow into the cartridge  10  through the port  12 . After the underpressure decreases, the resilient element  41  further presses the spheric element  40  back and seals the port  12  again.  
         [0040]    In order to prevent the ink from leaking during idle time, the underpressure in the cartridge has to be higher than −2.5 cm water column but not higher than −10 cm water column. Therefore, in the aforesaid embodiments, the pressing force of the resilient element (the spring  14 , spring plate  16  or O-ring  41 ) to the sealing element (the needle end  1301  or spheric element  40 ) is set to balance with the force of ambient air on the sealing element when the underpressure in the cartridge is about −10 cm water column. Thus, when the underpressure in the cartridge approaches −10 cm water column, the ambient air pushes the sealing element to open the port  12  and enters the cartridge to decrease the underpressure. Finally, before the underpressure decreases to −2.5 cm water column, the pressing force of the resilient element presses the sealing element to seal the port  12  so as to maintain a minimum underpressure for avoiding ink leakage.  
         [0041]    Fifth Embodiment  
         [0042]    [0042]FIG. 10 is a fifth embodiment of an inkjet pen according to the invention showing the port mechanism only. A movable element  51  carrying an O-ring  50  is movably mounted in a seat  11  and forced by a spring  52  to seal the port  12  of the cartridge  10 . When the ink in the cartridge  10  is being used, the underpressure in the cartridge  10  increases. After the underpressure reaches an upper limit, the pressure of the ambient air is greater than the pressing force of the spring  52  acting on the movable element  51 . Hence the movable element  51  with the O-ring  50  is forced to retract and let ambient air flow into the cartridge  10  through the port  12 . After the underpressure decreases, the spring  52  further presses the movable element  51  back and the O-ring seals the port  12  again.  
         [0043]    In each of the aforesaid embodiments, an ink bag  60  can be used in the cartridge  10  in order to prevent air from coming in contact with the ink. Taking the fourth embodiment for example, the ink bag incorporated therein is shown in FIG. 9. When the ink is used for printing, the ink bag  60  gradually shrinks, and the air cavity in the cartridge  10  is gradually increased. As a result, the underpressure continues to increase. When the underpressure reaches an upper limit, the pressure of the ambient air overcomes the pressing force of the resilient element  41  acting on the spheric element  40 . Therefore, the spheric element  40  is retracted to let some ambient air flow into the cartridge  10  through the port  12 . As the air enters, the underpressure in the cartridge decreases to within operating range, and the resilient element  41  further presses the spheric element  40  to seal the port  12 .  
         [0044]    Sixth Embodiment  
         [0045]    [0045]FIG. 11 is a sixth embodiment of an inkjet pen according to the invention. The port mechanism includes a first port  71  and a second port  72 . The first port  71  is selectively sealed and opened by a needle  13 , which is connected to a connecting element  73  mounted in a seat  11 . The connecting element  73  is forced by a pressing spring  732  sleeved in a stem  731  so as to press the needle  13  sealing the first port  71  with the needle end  1301 . The second port  72  is fluid-communicated with a resilient air bag  74  in a manner such that when the ambient air pressure is higher than the air pressure inside the cartridge  10 , the air bag  74  expands. As the air bag  74  expands and touches the connecting member  73 , it starts to overcome the pressing force of the spring  732 , and eventually moves the connecting element  73  and the needle  13  down to open the first port  71 . As shown in FIG. 11, when the ink  30  is being used, the level  31  of the ink  30  in the cartridge  10  decreases and the underpressure in the cartridge  10  increases. However, when the underpresuure is within operating range, the pressing force provided by the spring  732  is larger than the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  74  acting on the connecting member  73  so that the first port  71  remains sealed.  
         [0046]    As shown in FIG. 12, after the underpressure reaches an upper limit, the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  74  acting on the connecting member  73  is greater than the pressing force of the spring  732  acting on the connecting member  73  and the needle  13 . Hence, the needle  13  is forced to retract and let ambient air flow into the cartridge  10  through the port  71  and a vent  1101 . The input air lowers the underpressure. After the underpressure decreases to within operating range, the spring  732  further presses the connecting member  73  and the needle  13  back and seals the port  71  again.  
         [0047]    Seventh Embodiment  
         [0048]    [0048]FIG. 13 is a seventh embodiment of an inkjet pen according to the invention, which is a modification from the sixth embodiment of FIG. 11. Instead of directly connecting the needle  13  with the connecting member  73 , the needle  13  is now flexibly connected to the connecting element  73  through a pressing spring  1304  in order to enhance the sensitivity of movement. The pressing spring  1304  provides a certain force to seal the needle  13  to the port  71 . As shown in FIG. 14, when the ink  30  is being used, the level  31  of the ink in the cartridge  10  decreases and the underpressure in the cartridge  10  increases. However, when the underpresuure is within operating range, the pressing force provided by the springs  732  and  1304  is greater than the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  74  acting on the connecting member  73  so that the first port  71  remains sealed.  
         [0049]    As shown in FIG. 15, after the underpressure reaches an upper limit, the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  74  acting on the connecting member  73  is greater than the composite force of the pressing force of the spring  732  acting on the connecting member  73  and the pressing force of the spring  1304  acting on the needle  13 . Hence, the needle  13  is forced to retract and let ambient air flow into the cartridge  10  through the port  71  and a vent  1101 . The input air lowers the underpressure. After the underpressure decreases to within operating range, the springs  732  and  1304  further press the connecting member  73  and the needle  13  back and seal the port  71  again.  
         [0050]    Eighth Embodiment  
         [0051]    [0051]FIG. 16 is an embodiment of the invention that further includes a resilient air bag  80  as that of the sixth embodiment in order to prevent ambient air from coming in contact with the ink  30 . As shown in FIG. 17, when the ink  30  is being used, the level  31  of the ink in the cartridge  10  decreases and the underpressure in the cartridge  10  increases. After the underpressure reaches an upper limit, the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  80  acting on the connecting member  73  is greater than the pressing force of the spring  732  acting on the connecting member  73  and the needle  13 . Hence, the needle  13  is forced to retract and let ambient air flow into the air bag  80  through the port  71  and a vent  1101 . The input air blows up the air bag  80 , which further pushes the ink level  31  up and lowers the underpressure to within operating range.  
         [0052]    Ninth Embodiment  
         [0053]    [0053]FIG. 18 is an embodiment of the invention that further includes a resilient air bag  90  from the seventh embodiment in order to prevent ambient air from coming in contact with the ink  30 . When the ink  30  is being used, the level  31  of the ink in the cartridge  10  decreases and the underpressure in the cartridge  10  increases. After the underpressure reaches an upper limit, the composite force of the ambient air pressure acting on the needle end  1301  and the expansion force of the air bag  90  acting on the connecting member  73  is greater than the pressing force of the spring  732  acting on the connecting member  73  and the needle  13 . Hence, the needle  13  is forced to retract and let ambient air flow into the air bag  90  through the port  71  and a vent  1101 . The input air blows up the air bag  90 , which further pushes the ink level  31  up and lowers the underpressure to within operating range.  
         [0054]    While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention.