Abstract:
A pressure control device for regulating the ink pressure of a multi-reservoir ink cartridge. The pressure regulator employs an external spring or springs plate assembly mounted between two neighboring ink reservoirs. The external surfaces of the spring or assembly are attached to the respective side face of the reservoirs. Each ink reservoir has at least a side face formed from a flexible non-elastic material. When all of the ink reservoirs are full, the spring or assembly is in a relaxed state. By withdrawing a small quantity of ink from each ink reservoir, atmospheric pressure exerts forces on the ink reservoirs leading to a small contraction. The resulting distortion of the spring or assembly produces a force that resists further contraction of the reservoirs. Since the pressures inside the reservoirs are smaller than external atmospheric pressure, a back-pressure that prevents any leakage of ink from the reservoirs is created. In addition, a pressure plate can be added to the spring means to squeeze the ink out of the reservoir more evenly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 88115623, filed Sep. 10, 1999. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a pressure control device. More particularly, the present invention relates to a pressure control device for controlling the flow of ink from the ink reservoir of an ink cartridge. 
     2. Description of Related Art 
     Most conventional inkjet printers employ a jet nozzle to deliver ink to paper. The ink required by the print head is usually supplied from an ink reservoir within an ink cartridge. To direct the ink from the reservoir to the print head so that printing can be carried out smoothly, the How of ink must be regulated. Although regulating the flow of ink can guarantee a spray of fine ink drops, some mechanism must be present to prevent ink from leaking from the cartridge when the print head is not printing. 
     To prevent ink leakage, two self-adjusting mechanisms have been developed so far. The first method is the placement of some polymer foam inside the ink reservoir. Utilizing the capillary action of narrow spacing within the foam, leakage is prevented. However, storage capacity for this kind of ink reservoir is rather limited. The second method is to set up a sub-atmospheric or negative pressure inside the ink reservoir when the print head is not in use. A negative pressure is created when the ink reservoir is in a partial vacuum so that its internal pressure is lower than external atmospheric pressure. Hence, an increase in negative pressure means that the degree of vacuum inside the reservoir is increased. By setting up a negative pressure inside the ink reservoir, seepage of ink from the print head virtually stops. 
     Although the presence of a negative pressure inside the ink reservoir may suppress ink leakage from the print head, too much negative pressure will also prevent ink drops from getting out of the print head during printing. Moreover, if the external pressure changes, the negative pressure inside the reservoir needs to be changed correspondingly. For example, if there is a drop in the external pressure, the negative pressure must drop correspondingly in order to prevent the leakage of ink from the print head. 
     In 1980, Epson developed a type of ink reservoir described in U.S. Pat. No. 4,422,084. The invention uses organic polypropylene to form the ink reservoir. Negative pressure inside the ink reservoir is regulated by a set of springs both inside and/or outside the reservoir. However, using this type of pressure control mechanism, a portion of the ink inside the reservoir cannot be used. Furthermore, the ink reservoir is detached from the cartridge of the print head. 
     In 1982, Hewlett Packard has developed a type of ink reservoir for print heads described in U.S. Pat. No. 4,509.062. The invention relies on non-linear springs and a rubber bladder for maintaining a negative pressure inside the ink reservoir. One end of the spring is fixed upon a supporting structure while the other end is attached to the rubber bladder. However, due to the springs and other support structures, the volume of ink held by each reservoir in a multi-reservoir ink cartridge, for color printing especially, is severely limited. 
     In 1992, Hewlett Packard has developed another type of ink reservoir described in U.S. Pat. No. 5,757.706. A spring formed by a pair of thin plates is placed inside the ink reservoir. Through the forces exerted by the spring plates on two non-elastic soft walls of the reservoir, a suitable negative pressure is created. However, since the spring plates are enclosed inside the ink reservoir, the spring plates are likely to react chemically with the ink. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a pressure control device for controlling the flow of ink from a print head cartridge. A negative pressure of suitable magnitude is formed inside the ink reservoirs where the ink is stored. Therefore, ink drops can exit the reservoir during a normal printing operation and cannot leak out from the reservoir when the printing stops. Furthermore, because the pressure control device enables the ink reservoirs to be fully compressed, even the last few drops of ink inside the ink reservoir can be used. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a pressure control device suitable for a multi-reservoir ink cartridge. The pressure control device employs an external traction spring means between the ink reservoirs of the cartridge. Each ink reservoir has at least a side surface formed from a flexible non-elastic material. When the ink reservoirs are full, the traction spring means is in a relaxed state. By withdrawing a small quantity of ink from each ink reservoir, atmospheric pressure exerts a force on the ink reservoirs leading to a small contraction. The resulting distortion of the traction spring means produces a force that resists further contraction of the reservoirs. Since the pressures inside the reservoirs are smaller than external atmospheric pressure, a back-pressure that prevents any ink from leaking out of the reservoirs is created. Through proper design of the traction spring means loading and elasticity of the ink reservoirs, a suitable ink jet is formed during normal printing operation. In addition, a pressure plate can be added to the traction spring means to squeeze ink from the reservoir more evenly. Hence, the back-pressure of each ink reservoir can be more effectively controlled and every drop of ink inside each ink reservoir can be fully utilized. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings. 
     FIG. 1 is a sketch showing the cartridge of a conventional inkjet print head; 
     FIG. 2A is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to a first embodiment of this invention when the ink reservoirs are full; 
     FIG. 2B is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to the first embodiment of this invention when the ink reservoirs are rather empty. 
     FIG. 2C is a schematic cross-sectional view showing an alternative pressure control device inside an inkjet cartridge also according to the first embodiment of this invention when the ink reservoirs are full; 
     FIG. 2D is a schematic cross-sectional view showing the alternative pressure control device inside an inkjet cartridge also according to the first embodiment of this invention when the ink reservoirs are rather empty: 
     FIG. 3A is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to a second embodiment of this invention when the ink reservoirs are full; 
     FIG. 3B is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to the second embodiment of this invention when the ink reservoirs are rather empty; 
     FIG. 3C is a schematic cross-sectional view showing an alternative pressure control device inside an inkjet cartridge also according to the second embodiment of this invention when the ink reservoirs are full; and 
     FIG. 3D is a schematic cross-sectional view showing the alternative pressure control device inside an inkjet cartridge also according to the second embodiment of this invention when the ink reservoirs are rather empty. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     FIG. 1 is a sketch showing the cartridge of a conventional inkjet print head. As shown in FIG. 1, the ink cartridge  100  can be divided into two major sections: a cartridge body  102  and a cartridge nose  104 . Ink for printing is stored inside the cartridge body  102 . The cartridge nose  104 , on the other hand, includes filters, ink channels (not shown in the figure) and banks of jet nozzles  106 . Since the cartridge nose  104  only occupies a small volume, back-pressure regulation has to be conducted inside the cartridge body  102 . 
     The pressure control device of this invention is installed inside an ink cartridge similar to the one shown in FIG.  1 . FIG. 2A is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to a first embodiment of this invention when the ink reservoirs are full. FIG. 2B is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to the first embodiment of this invention when the ink reservoirs are rather empty. In fact, FIGS. 2A and 2B are cross-sectional views of a cartridge body, very similar to the cartridge body  102 , along a plane perpendicular to the viewing direction  108  in FIG.  1 . 
     As shown in FIG.  2 A. the pressure regulator  200  includes traction spring means  210  and ink reservoirs  206 . The ink cartridge body  202  has a first sidewall  204   a  and a second sidewall  204   b  that are parallel to each other. The cartridge body  202  also has a plurality of reservoirs  206  running parallel to the first sidewall  204   a  and the second sidewall  204   b . Each ink reservoir  206  includes at least a side face  208   c  formed from a flexible non-elastic material. The flexible non-elastic material includes aluminum foil and plastic sheeting. The first ink reservoir  206   a  is attached to the first sidewall  204   a while the second ink reservoir  206   b  is attached to the second sidewall  204   b.    
     A first side face  208   a  of the first ink reservoir  206   a  is attached to the first sidewall  204   a . Similarly, a second side face  208   b  of the second ink reservoir  206   b  is attached to the second sidewall  204   b . The traction spring means  210  is inserted between the ink reservoirs  206   a  and  206   b . The sides of the traction spring means  210  are attached to the central portion of the side faces  208   c  of the ink reservoirs  206   a  and  206   b , respectively. The traction spring means  210  comprises of two spring, plates  212  running almost parallel to the first sidewall  204   a  and the second sidewall  204   b  between two ink reservoirs  206   a  and  206   b . The front ends and the back ends of the spring, plates  212  are bonded together to form a spring, plate assembly. Material for forming the spring plates  212  includes metal, plastic, bamboo or wooden sheet. The exterior surfaces  214  of the assembled spring plates  212  are attached to the side face  208   c  of the first reservoir  206   a  and the second reservoir  206   b , respectively. 
     As shown in FIGS. 2A and 2B, the arrows show the direction towards which ink flows from the reservoirs  206   a  and  206   b  to the cartridge nose section (label  104  in FIG.  1 ). Ultimately, ink will be ejected through ink nozzles (label  106  in FIG. 1) during a printing operation. 
     When the reservoirs  206   a  and  206   b  of the cartridge body  202  are full of ink as shown in FIG. 2A, the spring plates  212  of the traction spring means  210  are in the most relaxed position. Since the ink reservoirs  206  are completely sealed, the ink reservoirs  206  shrink a little due to atmospheric pressure after a small amount of ink is removed. Hence, the spring plates  212  mounted next to the reservoirs  206  will deform slightly. A restorative or traction force resisting the shrinking of the reservoirs  206  results from the deformation of the spring plates  212 . Consequently, a negative pressure is created so that the pressure inside the reservoirs  206  is smaller than external atmospheric pressure. The negative pressure inside the reservoirs  206  prevents the ink from leaking out of the reservoirs  206  after printing stops. 
     After the cartridge has been in use for some time, some of the ink inside the reservoirs  206  is ,one as shown in FIG.  2 B. Hence, the degree of vacuum inside the reservoirs  206  increases and the reservoirs contract. The pressure inside the ink reservoirs  206  remains below atmospheric pressure due to the presence of a restorative force provided by the deformation of the spring plates  212 . 
     However, if the negative pressure inside the ink reservoirs  206  is too large, or in other words, if the difference in pressure between inside and outside is great atmospheric pressure may prevent ink from exiting through the nozzles during printing. Hence, negative pressure inside the ink reservoirs  206  must be carefully controlled so that ink can flow smoothly throughout the working life of the cartridge. Since the restorative force generated by the spring plates  212  is little affected by deformation the negative pressures inside the respective ink reservoirs  206  can be maintained within defined limits throughout the working life. Hence, the difficulties in ejecting ink from the nozzle during a printing operation are avoided. In other words the ink does not leak from the ink reservoir when the print head is not working but can still get out from the ink reservoirs during a normal printing operation. 
     FIG. 2C is a schematic cross-sectional view showing an alternative pressure control device inside an inkjet cartridge also according to the first embodiment of this invention when the ink reservoirs are full. FIG. 2D is a schematic cross-sectional view showing the alternative pressure control device inside an inkjet cartridge also according to the first embodiment of this invention when the ink reservoirs are rather empty. FIGS. 2C and 2D are cross-sectional views of a cartridge body, very similar to the cartridge body  102 , along a plane perpendicular to the viewing direction  108  in FIG.  1 . Since FIGS. 2C and 2D are very similar to FIGS. 2A and 2B, identical elements are labeled identically. In this alternative arrangement the spring plates  212  are replaced by springs  216 . The ends of the springs  216  are attached to the side faces  208   c  of neighboring ink reservoirs  206  near the central area of the cartridge. The springs  216  serve a similar function as the spring plate  212 . In addition the springs  216  can be linear or non-linear springs. 
     When the inkjet cartridge is in use during printing, ink inside the ink reservoir gradually reduces. To maintain a constant back-pressure inside the ink reservoir throughout its working life, especially when most of the ink has been used, a flat plate can be installed on one side of the spring means. The spring plate or spring is attached directly to the flat plate instead of the ink reservoir, and so a uniform pressure is exerted on the ink reservoir. Furthermore, the ink reservoirs can be completely compressed with the spring plates, so all the ink inside the reservoir can be fully used. 
     FIG. 3A is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to a second embodiment of this invention when the ink reservoirs are full. FIG. 3B is a schematic cross-sectional view showing the pressure control device inside an inkjet cartridge according to the second embodiment of this invention when the ink reservoirs are rather empty. The second embodiment is very similar to the first embodiment. In fact, FIGS. 3A and 3B are cross-sectional views of a cartridge body, very similar to the cartridge body  102  along a plane perpendicular to the viewing direction  108  in FIG.  1 . The arrows in FIGS. 3A and 3B show the direction in which ink flows from the reservoirs  206   a  and  206   b  to the cartridge nose section (label  104  in FIG.  1 ). 
     As shown in FIG. 3A, the ink reservoirs  306  inside the cartridge body  302  are almost completely filled so that only a slight back-pressure is established. The pressure regulator  300  includes traction spring, means ( 130   a ,  310   b  and  310   c ) and ink reservoirs ( 306   a  and  306   b ). The cartridge body  302  has a first sidewall  304   a  and a second sidewall  304   b  that are parallel to each other. A plurality of reservoirs  306  are fitted inside the cartridge body  302  that also runs parallel to the first sidewall  304   a  and the second sidewall  304   b , respectively. Each ink reservoir  306  has at least one side face  308  formed using flexible non-elastic material. The flexible non-elastic material includes aluminum foil and plastic sheet. The first ink reservoir  306   a  is attached to the first sidewall  304   a  while the second ink reservoir  306   b  attached to the second sidewall  304   b.    
     The first traction spring means  310   a  is between the first sidewall  304   a  and the first reservoir  306   a ; the second traction spring means  310   b  is between the second sidewall  304   b  and the second reservoir  306   b ; and the third traction spring means  310   c  is between the two reservoirs  306   a  and  306   b . The first spring means  310   a  includes a first spring plate assembly  312   a  and a first pressure plate  318   a . The first spring plate assembly  312   a  is comprised of two spring plates with their front ends and their back ends bonded together. One side of the spring plate assembly  312   a  is attached to the first sidewall  304   a . The first pressure plate  318   a  is between the first spring plate assembly  312   a  and the first reservoir  306   a . One surface of the pressure plate  318   a  is attached to a spring plate of the spring plate assembly  312   a  while the other surface is attached to a side face of the first reservoir  306   a.    
     The second traction spring means  310   b  is structurally identical to the first traction spring means  310   a . The second traction spring means includes a second spring plate assembly  312   b  and a second pressure plate  318   b . The second spring plate assembly  312   b  is in contact with the second sidewall  304   b . The second pressure plate  318   b  is between the second spring plate assembly  312   b  and the second reservoir  306   b . One surface of the second pressure plate  318   b  is attached to a spring plate of the second spring plate assembly  312   b  while the other surface is attached to a side face of the second reservoir  306   b.    
     The third traction spring means  310   c  includes a third spring plate assembly  312   c  and a pair of pressure plates  308   c . The pair of pressure plates  318   c  is parallel to the reservoirs  306   a  and  306   b , respectively. Each pressure plate  318   c  is attached to one side face of the reservoirs  306 . The third spring plate assembly  312   c  is comprised of two spring, plates  314  with their front ends and their back ends bonded together. Each spring plate  314  is in contact with the central area of a pressure plate  318   c . Material for forming the spring plates  314   c  includes metals, plastic, bamboo, or wood. In addition springs can be used instead of the spring plate assemblies  312   a ,  312   b  an d  312   c.    
     The pressure regulator  300  in this second embodiment of the invention operates in a similar manner as in the first embodiment. The main difference lies in their structures. In this embodiment, a first traction spring means  310   a  is mounted between the first sidewall  304   a  and the first reservoir  306   a  while a second traction spring means  310   b  is mounted between the second sidewall  304   b  and the s econd reservoir  306   b . In addition, a third traction spring means  310   c  is mounted between the two reservoirs  306   a  and  306   b . Furthermore, each of the traction spring means  310   a  and  310   b  has a pressure plate while the traction spring means  310   c  has two additional pressure plates attached. 
     As shown in FIG. 3B, after the cartridge has been in use for some time, most of the ink inside the reservoirs  306  is gone as shown in FIG.  3 B. Hence the degree of vacuum inside the reservoirs  206  will increase and the reservoirs  306  will contract. Through the interaction between various traction spring means ( 312   a ,  312   b  and  312   c ) and reservoirs  306   a  and  306   b  inside the pressure regulator  300 , a uniform pressure is exerted on the side faces  308  of the reservoirs  306   a  and  306   b . Even when most of the ink inside the reservoirs  306  is gone, a constant back-pressure can still be maintained. Consequently, all the ink inside a reservoir can be fully used because large back-pressure is avoided. 
     FIG. 3C is a schematic cross-sectional view showing an alternative pressure control device inside an inkjet cartridge also according to the second embodiment of this invention when the ink reservoirs are full. FIG. 3D is a schematic cross-sectional view showing the alternative pressure control device inside an inkjet cartridge also according to the second embodiment of this invention when the ink reservoirs are rather empty. FIGS. 3C and 3D are cross-sectional views of a cartridge body very similar to the cartridge body  102  along a plane perpendicular to the viewing direction  108  in FIG.  1 . Since FIGS. 3C and 3D are very similar to FIGS. 3A and 3B, identical elements are labeled identically. In this alternative arrangement, the spring plates are replaced by springs. 
     As shown in FIGS. 3C and 3D, a first spring  316   a  is inserted into the space between the first sidewall  304   a  and the first pressure plate  318   a . The ends of the first spring  316   a  are attached to the central section of the first sidewall  304   a  and the first pressure plate  318   a , respectively. Similarly, a second spring  316   b  is inserted into the space between the second sidewall  304   b  and the second pressure plate  318   b . The ends of the second spring  316   b  are attached to the central section of the second sidewall  304   b and the second pressure plate  318   b , respectively. A third spring  316   c  is inserted into the space between the neighboring reservoirs  306   a  and  306   b . The ends of the third spring  316   c  are attached to the central section of two similar pressure plates  318   c . The springs  316   a ,  316   b  and  316   c  within various spring means ( 310   a ′,  310   b ′ and  310   c ′) have functions identical to the aforementioned spring plates  314 . In addition, the springs ( 316   a ,  316   b  and  316   c ) can be linear or non-linear springs as in the first embodiment of this invention. 
     In the aforementioned embodiments, two ink reservoirs are enclosed in the cartridge body. However, the pressure regulator of this invention can also be applied to a cartridge having two or more reservoirs. Since a traction spring means such as a spring is inserted between every pair of neighboring reservoirs, back-pressure inside each of the reservoir will be identical. Consequently, minor deviation of the dimensions of the traction spring means can be tolerated. Hence, the traction spring means can have a larger manufacturing tolerance than other conventional internal spring systems. 
     In addition, the spring plates used in the first embodiment can be replaced by other types of linear or non-linear springs. The ink reservoir preferably has a width smaller than 18 mm so that the back-pressure variation inside the ink reservoir is always contained within acceptable limits throughout the cartridge&#39;s working life. 
     In this invention, the spring plates or springs together with the pressure plates that constitute the traction spring means are all installed outside the reservoirs. Since these artifacts are not in contact with any ink, there is no need to worry about possible chemical reaction with ink or cleanliness of these artifacts. Hence, materials such as metal, plastic, bamboo or wood can all be used to form the spring plates and the pressure plates. 
     In summary, the pressure regulator of this invention is formed by assembling a set of springs or a set of spring plate assemblies, pressure plates and reservoirs together inside an inkjet cartridge. The number of necessary components is relative small and easy to assemble. Besides the prevention of ink from leaking from the cartridge, the pressure regulator permits printing to carry on until the last few drops of ink inside the reservoir are also used. In brief, the characteristics of this invention includes: 
     1. Since the traction spring means are installed outside the reservoir, there are fewer concerns regarding the type of material and the cleanliness of the material forming the traction spring means. 
     2. Using a set of springs or spring plates together with pressure plates, the pressure regulator permits the entire package of ink inside the reservoir to be fully used. 
     3. All the reservoirs inside the same cartridge body have identical back-pressure. 
     4. A larger deviation in manufacturing dimensions of the traction spring means can be tolerated. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.