Patent Grant
8465132
The present application claims priority under 35 U.S.C §119 based on Japanese Patent Application No. 2009-203073 filed Sep. 2, 2009, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly to an image forming apparatus having a recording head discharging liquid droplets.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a multi function peripheral thereof and the like, there has been known an inkjet recording apparatus and the like employing a liquid discharging recording method using a recording head that discharges ink droplets. In the image forming apparatus employing the liquid discharging recording method, an image is formed by discharging ink droplets from a recording head onto a fed sheet. Herein, the term “forming” is a synonym of the terms recording typing, imaging, and printing. The image forming apparatus employing the liquid discharging recording method includes a serial-type image forming apparatus and a line-type image forming apparatus. In the serial-type image forming apparatus, an image is formed by discharging ink droplets from the recording head while the recording head moves in the main scanning direction. On the other hand, in the line-type image forming apparatus, an image is formed by discharging ink droplets from the line-type recording head while the recording head does not change its position.
Herein, the term “image forming apparatus” refers to an apparatus (including a simple liquid discharging apparatus) forming an image by discharging ink onto a medium including paper, thread, fiber, textile, leather, metal, plastic, glass, wood, ceramic and the like. Further, this term “image forming apparatus” refers to a simple liquid discharging apparatus as well. The term “image forming” refers to not only forming a meaningful image such as characters, figures, and the like on a medium but also forming a meaningless image such as a pattern and the like on a medium (including simply discharging droplets onto a medium by an apparatus such as so-called a droplet discharging apparatus or a liquid discharging apparatus). Further, the term “ink” is collectively used to refer to not only any material called “ink” but also any liquid for forming an image which may be called recording liquid, fixing processing liquid, liquid, a DNA sample, a patterning material or the like. Further, the term “sheet” is not limited to a material made of paper, and is collectively used to refer to any material called a medium to be recorded, a recording medium, recording paper, recording sheet, and the like to which ink (ink droplets) is adhered, the material including an OHP sheet, fabric and the like.
As a liquid discharging head (droplet discharging head) to be used as the recording head, there have been known a piezoelectric type head and a thermal-type head. In the piezoelectric type head, liquid droplets are discharged by increasing the pressure by changing a volume in the liquid chamber by displacing a vibration plate using a piezoelectric actuator or the like. On the other hand, in the thermal-type head, the liquid droplets are discharged by increasing the pressure in the liquid chamber by generating bubbles by heating a heating element in the liquid chamber by supplying a current to the heating element.
Regarding the image forming apparatus employing such a liquid discharging method, there has been a demand for the increase of the image forming speed. To that end, a method is widely used in which ink is supplied from the ink cartridge (main tank) to a sub tank (which may also be called a head tank or a buffer tank) via a tube, the ink cartridge (main tank) having a large capacity and being installed to be fixed to the apparatus body, the sub tank being disposed on the recording head. By using this method (tube-supply method) using the tube to supply ink, it becomes possible to reduce the size and weight of the carriage section, thereby enabling greatly reducing the size of the structure and driving mechanism of the apparatus.
In the tube-supply method, the ink to be consumed by the recording head for forming an image is supplied from the ink cartridge to the recording head via the tube. In this case, when a flexible and thin tube is used, the fluid resistance when ink flows in the tube is increased, which may cause an ink discharge failure in which necessary ink may not be sufficiently supplied to maintain the discharge stability of the ink. Especially, in a large-scale apparatus for printing a recording medium having a wide width, the length of the tube becomes longer. As a result, the fluid resistance of the tube is accordingly increased. Similarly, when fast printing is performed and when the ink having high viscosity is discharged, the fluid resistance is also increased. As a result, a failure of supplying ink to the recording head may occur.
To overcome such failure, as Japanese Patent No. 3606282 (Patent Document 1) discloses, there is a conventionally known technique in which a pressure applied to the ink in the ink cartridge is maintained, and a differential pressure valve is disposed on the ink supply upstream side of the recording head, so that the ink is supplied when the negative pressure of the sub tank is greater than a predetermined pressure.
Further, as disclosed in Japanese Patent Application Publication No. 2005-342960 (Patent Document 2), the ink supply pressure is positively controlled by using a pump to feed the ink to the negative pressure chamber where a negative pressure is generated using a spring, the negative pressure room being disposed on the upstream side of the recording head. Further, as disclosed in Japanese Patent Application Publication No. 5-504308 (Patent Document 3), a pump is similarly used to positively control the pressure without providing a negative pressure chamber.
On the other hand, to obtain the negative pressure with a simple configuration, the ink cartridge communicated with air is communicated with the recording head via a tube, and the ink cartridge is simply disposed below the recording head. By doing this, negative pressure can be obtained by the water head difference.
By using this method, more stable negative pressure can be obtained with much simpler configuration when compared with a method in which a pressure is always applied by using a negative pressure associated valve or a method in which the negative pressure chamber is disposed and the pump is used to supply liquid. However, in this method using the water head difference, the pressure loss due to the tube resistance may become a problem
There is a known method of resolving the pressure loss problem in the ink supply system obtaining negative pressure using the water head difference. In this method, for example, as disclosed in Japanese Patent Application Publication No. 2004-351845 (Patent Document 4), a pump is provided in the tube between the recording head and the ink cartridge and a bypass flow path connecting the upstream side and the downstream side of the pump is provided. Further, a valve is provided in the bypass flow path, and the opening of the valve is appropriately controlled depending on the printing state, so that a desired pressure can be maintained.
However, in the method disclosed in Patent Document 1, the problem of shortage of refill supplies as described above may be resolved. However, the mechanism of controlling the negative pressure is complicated and the demand for the sealing characteristics of the negative pressure associated valve is very high. In addition, the pressure is always required to be applied. Because of this feature, the demand for the sealing characteristics of all the connecting sections in the ink supply flow path is high, and in case of trouble, ink may spout out.
In the method disclosed in Patent Documents 2 and 3, the pump is used to positively control the pressure. Therefore, it is required to accurately control the liquid feeding flow rate by using the pump in response to the consumption flow rate of ink and the like. To that end, for example, it may become necessary to perform a feedback control using the pressure of the negative pressure chamber. Further, for example, when this method is applied to an image forming apparatus using a plurality of different color ink, it is required to separately control the pump for each color ink. As a result, the control may become complicated and the size of the apparatus may be increased.
Also in the method disclosed in Patent Document 4, when this method is applied to an image forming apparatus using a plurality of different color ink, it is required to control the pumps for the respective color inks. As a result, the size of the apparatus may be increased.
The present invention is made in light of the above circumstances, and may become possible to maintain the negative pressure of the recording head in an appropriate range with a simple configuration and simple control and discharge liquid having high viscosity in high speed while reducing discharge failure.
According to an aspect of the present invention, an image forming apparatus includes a recording head having a nozzle for discharging droplets of liquid, a first fluid flow path supplying the liquid to the recording head, a liquid tank storing the liquid, a second fluid flow path being in fluid communication with the liquid tank, a pressure adjusting valve allowing the first fluid flow path and the second fluid flow path to be in fluid communication with each other, and a third fluid flow path having a liquid feeding unit, the third fluid flow path allowing either the second fluid flow path or the liquid tank and the pressure adjusting valve to be in fluid communication with each other. Further, the pressure adjusting valve include a tube member defining an internal fluid flow path of the pressure adjusting valve, a movable member movably disposed in the internal fluid flow path, a first throttling part disposed on a side of the first fluid flow path, and a second throttling part disposed on a side of the second fluid flow path. Further, the second throttling part is formed as a gap between an internal wall of the tube member and the movable member; a length of the gap varies in response to a flow rate of the liquid flowing in the first fluid flow path; an internal fluid resistance of the pressure adjusting valve varies in response to the flow rate of the liquid flowing in the first fluid flow path; the third fluid flow path is in fluid communication with the internal fluid flow path through a part of the pressure adjusting valve, the part being disposed between the first throttling part and the second throttling part; and, when the liquid is discharged from the nozzle, the liquid is fed from the liquid tank to the recording head by the liquid feeding unit in a state where the recording head is in fluid communication with the liquid tank via the pressure adjusting valve.
Other objects, features, and advantages of the present invention will become more apparent from the following description when read in conjunction with the accompanying drawings, in which:
In the following, embodiments of the present inventions are described with reference to the accompanying drawings.
First, an inkjet recording apparatus as an image forming apparatus according to an embodiment of the present invention is described with reference to
As illustrated in
On the carriage 4, one or more recording heads 10 are mounted discharging, for example, black (K), cyan (C), magenta (M), and yellow (Y) ink droplets. The recording heads 10 have plural ink discharging ports (nozzles) arranged in the direction crossing the main scanning direction so that ink discharging direction is in the downward direction.
Herein, as illustrated in
There are various types of the recording heads. For example, in one method employed by the recording head, the pressure for discharging ink is obtained by deforming a vibration plate using a piezoelectric device or electrostatic force. The recording head employing any other method may also be used in the image forming apparatus according to an embodiment of the present invention.
However, some recording heads using the thermal method employ an edge shooter method in which the relationship between the ink flowing direction and the center axis direction is different from that in the side shooter method. When this edge shooter method is used, the heating body 14 may be gradually destroyed due to the impact generated during bubble collapse. This phenomenon is called a cavitation phenomenon. On the contrary, the side shooter method has the following advantages when compared with the edge shooter method due to the structural difference. In the side shooter method, when bubbles expand and reach the nozzle 15, the bubbles reach air also. Therefore, the bubbles are not shrunk due to the temperature decrease. As a result, the lifetime of the recording head may become longer. Further, the energy from the heating body 14 can be effectively converted into kinetic energy used for forming and discharging ink droplets. Further, the meniscus can be recovered faster due to ink supply. Because of the advantages, the recording head of the inkjet recording apparatus according to an embodiment of the present invention employs the side shooter method.
On the other hand, under the carriage 4, a sheet 20 on which an image is to be formed by the recording head 10 is fed in the direction (sub scanning direction) orthogonal to the main scanning direction. As illustrated in
During that period, the scanning of the carriage 4 in the main scanning direction and the ink discharge from the recording head 10 is synchronized with each other at appropriate timings based on an image data to be printed. By doing this, one band of image is formed on the sheet 20. After one band of the image forming is completed, the sheet 20 is fed in the sub scanning direction by a predetermined distance. Then the same image forming operation is repeated until the entire page of the image forming operation is completed.
On the other hand, a sub tank (buffer tank, head tank) 30 and the recording head 10 are integrally connected to each other so that the sub tank 30 is disposed on the recording head 10. Herein, the state expressed by the term “integrally (connected)” includes a state that the recording head 10 and the sub tank 30 are connected with a tube and the like, and both of the recording head 10 and the sub tank 30 are mounted on the carriage 4.
Each color ink is supplied from an ink cartridge (main tank) 76 to the sub tank 30 via a liquid supply tube 71. The ink cartridge (main tank) 76 is a liquid tank of the present invention containing each color ink and is removably attached to a cartridge holder 77 disposed on one end in the main scanning direction of the apparatus main body. The liquid supply tube 71 is a tube member forming a part of the ink supply path from the ink cartridge (main tank) 76 and forming (serving as) a first flow path.
On the other end in the main scanning direction of the apparatus main body, a maintenance-and-recovery mechanism 51 is disposed that maintains and recovers the recording head 10. As illustrated in
Next, an ink supply system according to an embodiment of the present invention that can be used in the above inkjet recording apparatus is described with reference to
Further, one end of the liquid (ink) supply tube 71 is connected to the sub tank 30. The other end of the liquid (ink) supply tube 71 is connected to the cartridge holder 77 mounted to the apparatus main body as illustrated in
Further, as illustrated in
Next, an exemplary configuration and operations of the ink supply system according to the first embodiment of the present invention is described with reference to
As illustrated in
Herein, the flow path resistance varying unit 83 has characteristics in which the flow path resistance of the flow path resistance varying unit 83 varies depending on the flowing direction and the flow rate of the fluid flowing in the flow path resistance varying unit 83.
As illustrated in
As described above, the valve body 88 is movably disposed in the tube member 87. Depending on the state of the fluid flowing in the tube member 87, the valve body 88 changes its position in the tube member 87 to the position (lower dead point) indicated in
By disposing the valve body 88 in the tube member 87, in the internal flow path 87a, a first gap is formed between an outer circumference surface of the valve body top part 88t and an inner wall surface of the tube member 87. Hereinafter, a part having the first gap may be called a first throttling part 181. Further, in the internal flow path 87a, a second gap is formed between an upper surface (side) of the valve body bottom part 88b and a lower surface (side) of the separation wall 89. Hereinafter, a part having the second gap may be called a second throttling part 182. As described above, depending on the state of the fluid flowing in the tube member 87, the valve body 88 changes its position in the tube member 87. For example, depending on the flow rate of the fluid flowing in the first flow path (liquid (ink) supply tube) 71, the valve body 88 changes its position in the tube member 87. Then, when the valve body 88 changes its position in the tube member 87, the second throttling part (second gap) 182 varies accordingly. Namely, in this case, a throttle value (indicating the degree of throttle) of the second throttling part (second gap) 182 also varies accordingly.
Further, the tube member 87 includes a transverse hole (port) 86c formed from a part of the inner wall surface of the tube member 87, the part facing the valve body middle part 88m. Namely, the transverse hole (port) 86c is disposed between the first throttling part 181 and the second throttling part 182. Further, the transverse hole (port) 86c is connected to the third flow path 61 to serve as a part of the third flow path.
Referring back to
Next, an initial ink filling operation using the above ink supply path is described with reference to the flowchart of
After determining that the ink cartridge (main tank) 76 is attached, the nozzle surface of the recording head 10 is capped with the cap member 52 of the maintenance-and-recovery mechanism 51 (capping condition). During the capping condition, the suction pump 53 is driven to suction air inside the ink supply path through the nozzle of the recording head 10 (start nozzle suction). This nozzle suction is continued until a predetermined time period has elapsed since the start of the nozzle suction. By performing the nozzle suction for the predetermined time period, ink in the ink cartridge (main tank) 76 reaches the first flow path (liquid (ink) supply tube) 71.
After that, when determining that a predetermined time period has elapsed since the start of the nozzle suction (when timer is up), the motor 82 is driven to drive the pump (assist pump) 78. At this timing, the ink supply path is formed as illustrated in
After that, when determining that a predetermined time period has elapsed (when timer is up), both the suction pump 53 and the pump (assist pump) 78 are stopped. At this timing, the entire ink supply path is filled with ink.
After that, the cap member 52 of the maintenance-and-recovery mechanism 51 is released (separated) from the nozzle surface of the recording head 10 (capping condition is released), and the nozzle surface of the recording head 10 is wiped by a wiper member (not shown) of the maintenance-and-recovery mechanism 51. Then, the recording head 10 is driven to discharge a predetermined number of droplets which do not contribute to forming any meaningful image from the nozzle (preliminary discharge of recording head). By doing this, a desired meniscus is formed on the nozzle surface.
Then, the nozzle surface of the recording head 10 is capped with the cap member 52 of the maintenance-and-recovery mechanism 51 (head capping).
By doing in this way, the initial ink filling operation is finished. According to the flowchart of
Next, a printing operation is described with reference to the flowchart of
After a print job signal is received, a temperature in the apparatus is detected by a temperature sensor 27 (
Then, based on the detected (estimated) ink temperature, a flow rate to be fed by the pump (assist pump) 78 is determined, so that the pump (assist pump) 78 is driven to feed the determined flow rate. After that, the cap member 52 of the maintenance-and-recovery mechanism 51 is released (separated) from the nozzle surface of the recording head 10 (capping condition is released). Then, the recording head 10 is driven to discharge a predetermined number of droplets from the nozzle (preliminary discharge of recording head). After that, printing is started.
During that time, the pump (assist pump) 78 is being driven. Therefore, even when ink having high viscosity is used in a system having a long liquid (ink) supply tube (first flow path) 71, it may become possible to adequately reduce the pressure loss in ink supply paths. As a result, it may become possible to perform good printing while preventing the ink supply shortage.
After the printing operation is finished, the carriage 4 is returned to its predetermined position (home position) in the apparatus. Then, the nozzle surface of the recording head 10 is capped with the cap member 52 of the maintenance-and-recovery mechanism 51 (head capping). Then, the pump (assist pump) 78 is stopped.
Herein alternatively, the pump (assist pump) 78 may be stopped immediately after the printing operation is finished. Further, in the above description, the flow rate to be fed by the pump (assist pump) 78 is controlled based on the temperature. However alternatively, regardless of the temperature, depending on the requirement of ink supply or the like, the ink may be fed based on the flow rate that is determined as the flow rate that may not cause the ink supply shortage at the lowest possible temperature.
In such a printing operation, in a case where the viscosity of ink to be discharged is high or where the fluid resistance of the liquid (ink) supply tube (first flow path) 71 is high, when, for example, the tube is thin or long, or an flow rate of discharged ink is large, the ink supply shortage may occur due to the fluid resistance of the ink supply paths. More specifically, major parts responsible for impeding the ink supply in the ink supply system are the liquid (ink) supply tube (first flow path) 71, the filter 109, and a joint section 89 (
For example, in a case where an image forming apparatus having a wide width has the diameter and the length of the liquid (ink) supply tube (first flow path) 71 of 2.8 mm and 2,500 mm, respectively, when ink having high viscosity of 16 cP is discharged, the fluid resistance of the liquid (ink) supply tube (first flow path) 71 becomes 2.7e10 [Pa·s/m3]. Further, in this embodiment, it is assumed that the fluid resistances of the filter 109 and the joint section 89 are 1e10 [Pa·s/m3] and 2e9 [Pa·s/m3], respectively.
In this case, it is assumed that the limit value of the pressure loss so as to stably discharge ink from the recording head 10 is 2.5 kPa. When ink is continuously discharged from all the nozzles, the flow rate of discharged ink is 0.1 cc/s. Then, the pressure loss is 6.9 kPa. Further, when there is no pressure control unit 81, the pressure loss is 3.94 kPa. Therefore, an ink supply system simply utilizing the water head difference may not naturally supply ink.
As described above, when the pressure loss is increased due to the fluid resistances in the ink supply system and refilling shortage occurs, the pump (assist pump) 78 is then driven to feed ink from the third flow path 43 (61 and 62) in the Qa direction. Herein, a symbol “Qa” denotes an assist flow rate or a fluid (ink) flow for assist. However, for explanatory purposes, the symbol “Qa” is also used as a sign of an arrow. By feeding fluid (ink) by the pump (assist pump) 78, the ink supply shortage may be compensated (refill assist).
Next, how to assist the ink feeding in the ink supply system is described with reference to
First, in the state of
On the other hand,
According to this embodiment of the present invention, the larger the pressure loss becomes in response to the increase of the discharged flow rate from the recording head 10, the narrower the second gap “Gb” between the valve body bottom part 88b and the separation wall 89 becomes. In other words, in this case, the throttle value of the second throttling part 182 becomes accordingly larger. Further, in this case, the effect of the assist pressure generated by the pump (assist pump) 78 is accordingly increased. Therefore, it may become possible to realize the automatic ink supply having a simple configuration without performing conventional complicated control of the flow rate adjustment valve using an actuator.
In the configuration according to this embodiment of the present invention, the fluid resistance at the second throttling part 182 having the second gap “Gb” varies inversely with the fourth power of the second gap “Gb” between the valve body bottom part 88b and the separation wall 89. Because of this feature, in this ink supply system in which the second gap varies directly depending on the movement of the valve body 88, it may become possible to obtain good responsiveness when generating the assist pressure to reduce the pressure loss in the ink supply system.
Further, in this ink supply system, there are protrusions 68 partially formed on the upper surface (side) of the valve body bottom part 88b. Because of the protrusions 68, even when the valve body 88 is in contact with the separation wall 89 due to inertia of the movement or the like, a flow path corresponding to the height of the protrusions 68 is secured. Namely, it becomes possible to prevent the case where the second gap “Gb” becomes zero (0), the ink flow path is fully blocked, and the negative pressure at the recording head 10 is suddenly increased. Alternatively, the protrusions 68 may be disposed on the lower surface (side) of the separation wall 89 facing the upper surface (side) of the valve body bottom part 88b. Even if the protrusions 68 are disposed in this way, the same effect may be obtained.
Further alternatively, as illustrated in
Further, as described above, the image forming apparatus according to this embodiment of the present invention may discharge four color inks for color printing. To that end, there are provided four separate ink supply systems each having the configuration as illustrated in
When an image is formed by discharging plural colors, the flow rates of color inks discharged from the recording heads 10 may vary depending on an image to be formed. For example, there may be a case where ink is discharged from all nozzles of a certain recording head but no ink is discharged from any nozzle of another recording head. Even in this case, in the ink supply system according to this embodiment of the present invention, the fluid resistances of the flow path resistance varying units 83 automatically vary in response to the flow rate of the color inks discharged from the respective recording heads 10. Because of this feature, it is not necessary to control the pumps (assist pumps) 78 in response to the flow rate of ink discharged from the respective recording heads 10. Namely, as control of the ink supply system according to this embodiment of the present invention, less assist (pressure) is automatically provided (generated) for the recording head requiring less assist (pressure) due to small flow rate of ink discharged from the recording head. On the other hand, greater assist (pressure) is also automatically provided (generated) for the recording head 10 requiring greater assist (pressure) due to large flow rate of ink discharged.
As described above, according to this embodiment of the present invention, even in a system having plural ink supply systems due to, for example, the use of plural color inks for color printing, it may be possible to collectively control all the pumps of the respective ink supply systems with only one actuator. Because of this feature, the configuration of the apparatus and the control method may be simplified, and the cost and the size of the apparatus may be accordingly reduced.
Generally, the viscosity of fluid varies depending on the fluid temperature. Therefore, it is preferable to control the pump (assist pump) 78 to determine the flow rate of fluid (ink) fed (assisted) by the pump (assist pump) 78 based on feedback control using a temperature value such as an ambient temperature value or an inside temperature value of the apparatus measured using the temperature sensor 27 in
Further, a pressure sensor may be installed in the ink supply path, so that the pressure change is measured when a predetermined flow rate of ink is discharged from the recording head 10. Based on the measurement result, the viscosity of the fluid (ink) corresponding to the pressure loss due to the fluid (ink) may be detected. Then, based on the detected viscosity value, a parameter for controlling the pump (assist pump) 78 may be changed, thereby enabling using various liquids having different viscosities. Further, the parameter for controlling the pump (assist pump) 78 may be input by a user while the user monitors the discharge condition. In this case, the mechanism of detecting the fluid viscosity may be omitted, thereby simplifying the configuration of the apparatus.
Next, an ink supply system according to a second embodiment of the present invention is described with reference to
First, the ink cartridge (main tank) 76 includes a bag member 93 made of a flexible material that can be flexibly deformed when ink is consumed. In this case, for example, the shape of the bag member 93 is changed from the state of
By having the configuration of the ink cartridge (main tank) 76, the ink supply system becomes a sealed system. Therefore, it may become easier to stably maintain the quality of the fluid (ink) to be supplied to the recording head 10. Further, the negative pressure at the recording head 10 is maintained by the height difference between the recording head 10 and the ink cartridge (main tank) 76. Because of this feature, a stable negative pressure may be obtained.
Further, as schematically illustrated in
In this ink supply system, when the valve body 88 changes its position (up and down direction) in the flow path resistance varying unit 83, the throttle value of the second throttling part 182 between the valve body bottom part 88b and the separation wall 89 of the tube member 87 accordingly changes. When the throttle value of the second throttling part 182 changes, the fluid resistance of the flow path resistance varying unit 83 accordingly changes. By changing the fluid resistance of the flow path resistance varying unit 83, the pressure value (assist pressure) to cancel the negative pressure value is adjusted. In this case, a force moving the valve body 88 is generated (determined) due to the throttle of the through holes 84 which is serving as the first throttling part. By forming the first throttling part by using the through holes 84 of the valve body top part 88t, it may become easier to accurately form the first throttling part. As result, it may become possible to obtain stable throttle characteristics.
Further, as described above, four through holes 84 are symmetrically disposed with respect to the circumferential direction (rotational direction) of the valve body 88. However alternatively, the diameter of the through holes 84 may become smaller and the number of the through holes 84 may be increased. Otherwise, the diameter of the through holes 84 may become larger and the number of the through holes 84 may be decreased. However, it is preferable that the through holes 84 be symmetrically disposed with respect to the circumferential direction (rotational direction) of the valve body 88 so that the valve body 88 can be moved straightly along the axis direction.
Similar to the above first embodiment of the present invention, in this second embodiment, when the valve body 88 moves, the second gap between the valve body bottom part 88b and the separation wall 89 of the tube member 87 accordingly changed in a range between “Gb1” (
Further, similar to the above first embodiment of the present invention, in the configuration according to this second embodiment, the fluid resistance at the second throttling part 182 having the second gap varies inversely with the fourth power of the second gap between the valve body bottom part 88b and the separation wall 89. Because of this feature, in this ink supply system in which the second gap varies directly depending on the movement of the valve body 88, it may become possible to obtain good responsiveness when generating the assist pressure to reduce the pressure loss in the ink supply system.
Further, in this ink supply system, there are protrusions 68 partially formed on the upper surface (side) of the valve body bottom part 88b. Because of the protrusions 68, even when the valve body 88 is in contact with the separation wall 89 due to inertia of the movement or the like, a flow path corresponding to the height of the protrusions 68 is ensured. Namely, it becomes possible to prevent the case where the second gap “Gb” becomes zero (0), the ink flow path is fully blocked, and the negative pressure at the recording head 10 is suddenly increased.
Further, the protrusions 68 are integrally formed with the valve body middle part 88m (smaller radius part). Because of this feature, it may become easier to perform mold design when the valve body 88 is formed by molding. Further, it may become possible to enhance the bending stiffness of the valve body middle part 88m and strength of the valve body 88.
Further, in this second embodiment of the present invention, as illustrated in
Next, an ink supply system according to a third embodiment of the present invention is described with reference to
First, the ink cartridge (main tank) 76 includes the bag member 93 made of a flexible material that can be flexibly deformed as ink therein is consumed (e.g., the shape is changed from the state of
By having this configuration, the ink cartridge (main tank) 76 may spontaneously generate negative pressure. Therefore, for example, as illustrated in
As illustrated in
Further, plural grooves 66 are formed on the upper surface (side) of the valve body bottom part 88b facing the separation wall 89 in a manner such that the grooves 66 extend radially from the center axis of the valve body 88. Further, a concave-convex structure is formed on the lower surface (side) of the separation wall 89 facing the valve body bottom part 88b in a manner such that the convex parts 65 faces the corresponding grooves 66 as illustrated in
By having the concave-convex structures on the upper surface of the valve body bottom part 88b and the lower surface of the separation wall 89 so that the valve body bottom part 88b is engaged with the separation wall 89 with gaps therebetween as illustrated in
Further, the second throttling part 182 having the gap “Gb1” between the valve body bottom part 88b and the separation wall 89 is formed (inclined) in a manner such that the side of the first flow path 71 (center side of the valve body bottom part 88b) is above (higher than) the side of the second flow path 60 (outer periphery side of the valve body bottom part 88b) in the vertical direction. By having this inclined structure of the second throttling part 182, even when an air bubble is fed from the side of the ink cartridge (main tank) 76 into the flow path resistance varying unit 83 (pressure adjusting valve) via the port 86b, the air bubble may be easily removed from the flow path resistance varying unit 83 (pressure adjusting valve) because the air bubble automatically moves upward due to its buoyancy force. As a result, it may become possible to easily prevent the air bubble from remaining in the flow path resistance varying unit 83 (pressure adjusting valve).
Further, in this embodiment, as illustrated in
Next, a flow path resistance varying unit 83 used in an ink supply system according to a fourth embodiment of the present invention is described with reference to
In this flow path resistance varying unit 83, the valve body 88 is a rotating body and plural concentric grooves 66 are formed on the upper surface of the valve body bottom part 88b, the upper surface facing the lower surface of the separation wall 89. A concave-convex structure is formed on the lower surface of the separation wall 89, the lower surface facing the upper surface of the valve body bottom part 88b. Further, the convex parts 65 of the concave-convex structure are disposed so as to face respective grooves 66, so that, when the valve body 88 moves upward, the convex parts 65 and the respective grooves 66 are engaged with each other as illustrated in
By having the concave-convex structures on the upper surface of the valve body bottom part 88b and the lower surface of the separation wall 89 so that the valve body bottom part 88b is engaged with the separation wall 89 with gaps therebetween as illustrated in
Further, by having the concentrically formed concave-convex structure, when the valve body bottom part 88b and the separation wall 89 are engaged with each other as illustrated in
Further, because of the concentric concave-convex structures, by making the gap “Gt2” in
In this case, when the convex parts 65 of the separation wall 89 and the respective grooves 66 of the valve body bottom part 88b have the tapered surfaces as illustrated in
Further, in the above descriptions, the operations and effects of the present invention are described based on an example where different color ink are supplied to the respective recording heads. However, the present invention is not limited to this configuration. For example, the present invention may also be applied to cases where the same color ink is supplied to plural recording heads and where differently processed inks (not different color inks) are supplied to the respective recording heads. Further, the present invention may also be applied to a liquid (ink) supply system having a recording head(s) including plural nozzle rows so that different types of fluid are discharged from a single recording head. Further, the present invention is not limited to an image forming apparatus discharging narrowly-defined ink. The present invention may also be applied to a liquid discharging apparatus (described as the “image forming apparatus” in this description of the present invention) discharging various liquids.
According to an embodiment of the present invention, an image forming apparatus includes a recording head having a nozzle for discharging droplets of liquid, a first fluid flow path supplying the liquid to the recording head, a liquid tank storing the liquid, a second fluid flow path being in fluid communication with the liquid tank, a pressure adjusting valve allowing the first fluid flow path and the second fluid flow path to be in fluid communication with each other, and a third fluid flow path having a liquid feeding unit, the third fluid flow path allowing either the second fluid flow path or the liquid tank and the pressure adjusting valve to be in fluid communication with each other. Further, the pressure adjusting valve includes a tube member defining an internal fluid flow path of the pressure adjusting valve, a movable member movably disposed in the internal fluid flow path, a first throttling part disposed on a side of the first fluid flow path, and a second throttling part disposed on a side of the second fluid flow path. Further, the second throttling part is formed as a gap between an internal wall of the tube member and the movable member; a length of the gap varies in response to a flow rate of the liquid flowing in the first fluid flow path; an internal fluid resistance of the pressure adjusting valve varies in response to the flow rate of the liquid flowing in the first fluid flow path; the third fluid flow path is in fluid communication with the internal fluid flow path through a part of the pressure adjusting valve, the part being disposed between the first throttling part and the second throttling part; and, when the liquid is discharged from the nozzle, the liquid is fed from the liquid tank to the recording head by the liquid feeding unit in a state where the recording head is in fluid communication with the liquid tank via the pressure adjusting valve.
Further, an anti-blocking unit may be provided on at least one of the internal wall of the tube member and the movable member of the pressure adjusting valve and preventing the internal fluid flow path from being blocked.
The anti-blocking unit may be one or more protrusions or grooves.
Further, the movable member may include a first pressure generation part forming the first throttling part, a second pressure generation part forming the second throttling part, and an intermediate part allowing the first pressure generation part and the second pressure generation part to be connected with each other via the intermediate part. Further the one or more protrusions may be formed on the intermediate part.
Further, at least one of the first pressure generation part, the second pressure generation part, and the intermediate part may have a sliding part sliding above the internal wall of the tube member.
Further, the movable member may have a through hole so that the first fluid flow path and the third fluid flow path are in fluid communication with each other.
Further, the through hole includes plural through holes, and the plural through holes may be symmetrically disposed with respect to the circumferential direction on a surface of the valve body, the surface facing the side of the first fluid flow path.
Further, in a part of the gap forming the second throttling part, a rib may be formed on one of the internal wall of the tube member and the movable member and a concave part may be formed on the other one of the internal wall of the tube member and the movable member so that the rib is engaged with the concave part.
Further, the movable member may be rotatably disposed in the internal fluid flow path, and the rib and the concave part may be concentrically formed.
Further, in a part of the gap forming the second throttling part, the side of the first fluid flow path may be higher than the side of the second fluid flow path in the vertical direction.
Further, the image forming apparatus may include plural liquid feeding units corresponding to liquid of different colors. Further the recording head may discharge different color droplets or include plural nozzle rows discharging liquid droplets of different colors, and the plural liquid feeding units may be driven by a common actuator.
In an image forming apparatus according to an embodiment of the present invention, when liquid droplets are discharged from the nozzle of the recording head, the liquid is fed from the liquid tank to the recording head by the liquid feeding unit in a state where the recording head is in fluid communication with the liquid tank via the pressure adjusting valve. In this case, the internal fluid resistance of the pressure adjusting valve varies in response to the flow rate of the liquid. By having this configuration, an assist pressure in response to the discharge flow rate from the recording head can be automatically and adequately determined and the determined assist pressure is applied to the recording head. Therefore, it may become possible to prevent the ink supply shortage due to the use of a longer tube member, increase of discharge flow rate, increase the viscosity of liquid to be discharged and the like, and also reduce the discharge failure. Further, in the pressure adjusting valve, the internal fluid resistance is generated in a gap between the tube member and the movable member and the gap (length of gap) varies in response to the discharge flow rate from the recording head. By having this configuration, the pressure control (adjustment) having good responsiveness may be performed.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
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