JP2010264636A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to maintain a stable negative pressure by a simple configuration in an ink supply system using a tube and to avoid insufficient refilling, so that the discharge capability of air bubbles, foreign substances, and the like is not enough in the maintenance recovery operation. <P>SOLUTION: An image forming apparatus includes a first channel 41 which supplies ink to a recording head 10, a second channel 42 which communicates with an ink cartridge 76, a channel resistance variable unit 83 which makes the first channel 41 and the second channel 42 communicate, and further a third channel 43 with a pump 78 which makes the second channel 42 and the channel resistance variable unit 83 communicate with each other. When liquid droplets are ejected from nozzles, the liquid is sent by the pump 78 from the ink cartridge 76 to the recording head 10 in a state that the recording head 10 and the ink cartridge 76 communicate via the channel resistance variable unit 83. When the maintenance recovery operation of the recording head 10 is carried out, the interior of a cap 52a is made to a negative pressure by a suction pump 53, and thereafter the pump 78 is driven to send the liquid. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a recording head for discharging droplets.

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, and a complex machine of these, for example, an ink jet recording apparatus is known as an image forming apparatus of a liquid discharge recording method using a recording head for discharging ink droplets. . This liquid discharge recording type image forming apparatus ejects ink droplets from a recording head onto a conveyed paper to form an image (recording, printing, printing, and printing are also used synonymously). Serial type image forming device that forms an image by ejecting droplets while the recording head moves in the main scanning direction, and a line type that forms images by ejecting droplets without the recording head moving There is a line type image forming apparatus using a head.

  In the present application, an “image forming apparatus” is an apparatus that forms an image by landing ink on a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics (simple liquid ejection apparatus) In addition, “image formation” not only gives an image having a meaning such as a character or a figure to a medium but also gives an image having no meaning such as a pattern to the medium. It also means (including what is simply referred to as a droplet discharge device or a liquid discharge device). In addition, the term “ink” is not limited to what is referred to as ink, but can be used for image formation such as recording liquid, fixing processing liquid, liquid, DNA sample, patterning material, resin, and the like. It is used as a general term for liquids. The term “paper” is not limited to paper, but includes the above-described OHP sheet, cloth, and the like, and means that ink droplets adhere to the recording medium, recording medium, recording paper, recording It is used as a general term for what includes what is called paper.

  As a liquid discharge head (droplet discharge head) used as a recording head, a piezoelectric head or the like is used to displace a diaphragm and change the volume in the liquid chamber to increase the pressure to discharge the liquid droplet. There is known a thermal type head in which a heating element that generates heat is provided, the pressure in the liquid chamber is increased by bubbles generated by the heat generation of the heating element, and droplets are discharged.

  In such a liquid ejection type image forming apparatus, it is particularly desired to improve the image forming throughput, that is, to increase the image forming speed. From the large-capacity ink cartridge (main tank) installed on the main body through the tube. A system is used in which ink is supplied to sub-tanks (including head tanks and buffer tanks) above the recording head. By adopting a method for supplying ink using such a tube (tube supply method), the carriage portion can be reduced in weight and size, and the apparatus including the structure system and the drive system can be significantly reduced in size.

  By the way, in the tube supply method, ink consumed from the recording head in image formation is supplied from the ink cartridge to the recording head through the tube. For example, when a thin flexible tube is used, the tube is Since the fluid resistance when the ink flows is large, the ink supply is not in time for ink ejection, resulting in ejection failure. In particular, in a large machine that prints on a wide recording medium, the tube inevitably becomes long and the fluid resistance of the tube increases. Also, when printing at high speed or ejecting highly viscous ink, fluid resistance increases, and insufficient ink supply to the recording head becomes a problem.

  Therefore, conventionally, while maintaining the ink in the ink cartridge in a pressurized state, a differential pressure valve is provided on the upstream side of the ink supply of the head so that the ink is supplied when the negative pressure in the sub tank is greater than a predetermined pressure ( Patent Document 1), which supplies ink with a pump to a negative pressure chamber that obtains a negative pressure by a spring upstream of the head and actively controls the ink supply pressure (Patent Document 2), is disclosed in Patent Document 3 As described above, there is known a system (Patent Document 3) that does not have a negative pressure chamber but similarly positively controls pressure by a pump.

  On the other hand, as a method of obtaining a negative pressure with a simple configuration, an ink cartridge communicated with the atmosphere and a recording head are connected by a tube, and the ink cartridge is simply disposed below the recording head, so that the negative pressure can be reduced by a water head difference. There are ways to get.

  In this method, a more stable negative pressure can be obtained while having an overwhelmingly simple configuration as compared to a method of constantly pressurizing using a negative pressure interlocking valve or a method of providing a negative pressure chamber and feeding liquid by a pump. However, this water head method has a problem of pressure loss due to the tube resistance described above.

  As a technique for solving this pressure loss with an ink supply system that obtains a negative pressure due to this water head difference, for example, a pump is provided in a tube that connects the head and the ink cartridge, and a bypass path that connects the upstream side and the downstream side of the pump is provided. In addition, there is known a configuration in which a valve is provided in the bypass path, and an opening degree of the valve provided in the bypass path is appropriately controlled by printing to maintain a desired pressure (Patent Document 4).

  Further, in such an image forming apparatus, an apparatus (maintenance / recovery mechanism) that maintains and recovers the performance of the recording head that ejects ink is indispensable, and as one of its functions, bubbles, foreign matter, and thickening inside the head. It is required to discharge ink and the like from the nozzles to reduce ejection defects.

  Conventionally, as a method of sucking and discharging ink from a nozzle, the nozzle surface is capped and suction is performed by a suction means (Patent Document 5), and ink is pressurized and supplied to the head to discharge the ink from the nozzle. And the like (Patent Documents 6 and 7), and the combination of pressurization and suction (Patent Document 8) are known.

Japanese Patent No. 3606282 JP 2005-342960 A Japanese Patent Publication No. 5-504308 JP 2004-351845 A JP 2004-284084 A JP 2007-185905 A JP 2006-150745 A JP 2002-178537 A

  First, regarding the insufficient supply of ink to the recording head, the technique disclosed in Patent Document 1 solves the above-described problem of insufficient refill, but the mechanism for controlling the negative pressure is complicated, and the negative pressure interlocking valve There is a problem that a high sealing performance is required. In addition, since the pressure is constantly applied, airtightness of all the connecting portions in the ink supply path is also highly required, and in the event of a failure, there is a risk that ink may be ejected.

  Further, in the techniques disclosed in Patent Documents 2 and 3, since the pressure is positively controlled by the pump, it is necessary to accurately control the pumped liquid amount according to the ink consumption amount. Feedback control using the pressure in the chamber is required. For example, when applied to an image forming apparatus using a plurality of types of inks having different colors, it is required to control the pump for each color type, and there is a problem in that the control is complicated and the apparatus becomes large.

  Further, even in the technique disclosed in Patent Document 4, when applied to an image forming apparatus using a plurality of types of inks having different colors, it is required to control a pump for each color type, which increases the size of the apparatus. is there.

  On the other hand, regarding the maintenance and recovery of the recording head, in the configuration in which ink is sucked and discharged from the nozzle as in the technique disclosed in Patent Document 5, the flow velocity in the vicinity of the nozzle can be increased, which is effective for discharging foreign matter. In order to further improve the discharge performance, the cap structure must be able to withstand a high negative pressure, which makes it difficult to improve the discharge performance. In addition, when the inside of the cap is opened to the atmospheric pressure, there is a problem that ink and bubbles around the nozzle easily flow back into the nozzle, and it is necessary to take measures to prevent a discharge failure due to the ink.

  Further, as in the technique disclosed in Patent Document 6, in the configuration in which the ink in the head is rapidly pressurized by the pressurizing force of the pressurizing unit and the ink is pressurized and discharged, the configuration of the pressurizing chamber is complicated. In order to further improve the discharge performance, the sealing performance (pressure resistance) of the entire ink supply path is required, and there is a problem that the cost of the entire apparatus increases. Further, as in the technique disclosed in Patent Document 7, in the configuration in which the internal pressure of the buffer tank is pre-pressurized to a predetermined pressure in advance by the pre-loading unit, and then the ink is supplied, the configuration including the pre-loading unit is complicated. There is a similar problem of ensuring the breakdown voltage and ensuring the breakdown voltage.

  Further, in the configuration in which suction and pressurization are combined as in the technique disclosed in Patent Document 8, high discharge performance can be obtained by the differential pressure between pressurization and suction, but the discharge efficiency with respect to the ink consumption is greatly increased. It is difficult to improve.

  The present invention has been made in view of the above problems, and when supplying a plurality of different types of ink by an ink supply method using a tube, the configuration is simple, a stable negative pressure is maintained, and the speed is further increased. An object is to prevent a shortage of refill even when a long tube is formed or a high ink viscosity, and to further improve the discharge of bubbles or foreign matters in the head.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having nozzles for discharging droplets;
A liquid tank for storing liquid to be supplied to the recording head;
A first flow path for supplying the liquid to the recording head;
A second flow path communicating with the liquid tank;
A pressure regulating valve that connects the first flow path and the second flow path, and an internal flow path resistance changes according to a flow rate of the liquid flowing through the first flow path;
A third flow path communicating the second flow path or the liquid tank and the pressure regulating valve;
Liquid feeding means provided in the third flow path;
When ejecting droplets from the nozzle, the liquid is fed from the liquid tank to the recording head by the liquid feeding means in a state where the recording head and the liquid tank are in communication with each other via the pressure adjusting valve. Means to
A cap for capping the nozzle surface of the recording head;
Suction means connected to the cap;
The suction means is driven in a state in which the nozzle surface of the recording head is capped with the cap to make negative pressure in the cap internal space between the cap and the nozzle surface. In this state, the liquid is supplied by the liquid feeding means. And a means for feeding a liquid from the liquid tank to the recording head.

  Here, the pressure regulating valve has a configuration in which an increase rate of the fluid resistance is increased when the change in the flow rate of the liquid is equal to or higher than the threshold value with respect to an increase rate of the fluid resistance when the change is less than a predetermined threshold value. And can.

  In addition, a means for detecting the pressure in the cap may be provided, and the liquid may be sent from the liquid tank to the recording head until the pressure in the cap becomes a positive pressure or higher.

  In addition, a means for detecting the pressure in the cap may be provided, and liquid feeding from the liquid tank to the recording head may be stopped before the pressure in the cap becomes positive.

  In addition, liquid feeding from the liquid tank to the recording head can be performed during a liquid feeding time that is determined in advance corresponding to the driving time of the suction unit.

  In this case, the liquid feeding time can be configured to be a time during which the pressure in the cap becomes equal to or higher than the positive pressure.

  Further, the liquid feeding time can be configured to be a time during which the pressure in the cap stays below a positive pressure.

  According to the image forming apparatus of the present invention, when droplets are ejected from the nozzles of the recording head, the recording head and the liquid tank are connected via the pressure adjustment valve whose internal flow path resistance changes according to the flow rate of the flowing liquid. Since the liquid is fed from the liquid tank to the recording head while in communication, the appropriate assist pressure is automatically adjusted according to the discharge amount of the recording head and applied to the recording head. In addition, it is possible to avoid shortage of refill due to the lengthening of the tube member, the increase of the discharge flow rate, the increase in the viscosity of the discharge ink, and the suction means in a state where the nozzle surface of the recording head is capped with a cap. The cap interior space between the cap and the nozzle surface is driven to a negative pressure, and in this state, the liquid is fed from the liquid tank to the recording head by the liquid feeding means. And it is possible to discharge the liquid from the nozzle to increase the internal flow rate, thereby improving the discharge of air bubbles or foreign matters.

1 is a schematic front explanatory view showing an ink jet recording apparatus as an image forming apparatus according to an embodiment of the present invention. It is a schematic plane explanatory drawing similarly. It is a schematic side surface explanatory drawing similarly. FIG. 2 is an enlarged explanatory view of a main part for explaining a recording head of the same apparatus. It is typical sectional explanatory drawing of the sub tank of the ink supply system (ink supply system) of the apparatus. It is explanatory drawing of a cartridge holder part similarly. It is explanatory drawing of a pump unit similarly. It is explanatory drawing of a pressure control unit similarly. It is explanatory drawing of an ink supply system similarly. It is explanatory drawing which shows the flow-path resistance variable unit of a pressure control unit. It is a block explanatory drawing explaining the outline | summary of the control part of the apparatus. It is a flowchart with which it uses for description of the maintenance recovery operation | movement which concerns on 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the change of the pressure in a cap, and the stop timing of an assist pump. It is a flowchart with which it uses for description of the maintenance recovery operation | movement which concerns on 2nd Embodiment of this invention. It is a flowchart with which it uses for description of the maintenance recovery operation | movement which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows an example of the table of the relationship of the suction drive time and liquid feeding drive time with which it uses for description of the embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings. An ink jet recording apparatus as an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 is a schematic front view of the recording apparatus, FIG. 2 is a schematic plan view, and FIG. 3 is a schematic side view.
The ink jet recording apparatus includes a guide rod 2 that is a guide member horizontally mounted on the left and right side plates 1L and 1R provided upright on the main body frame 1, and a guide rail attached to a rear frame 1B that is horizontally mounted on the main body frame 1. 3, the carriage 4 is slidably held in the main scanning direction (guide rod longitudinal direction), and the carriage 4 is moved and scanned in the longitudinal direction (main scanning direction) of the guide rod 2 by a main scanning motor and a timing belt (not shown). To do.

  The carriage 4 includes, for example, recording heads 10K, 10C, 10M, and 10Y (hereinafter, different colors) that eject ink droplets of black (K), cyan (C), magenta (M), and yellow (Y). If not, it is referred to as “recording head 10. Other members are also the same.) The recording head 10 has a plurality of ink ejection openings (nozzles) arranged in a direction crossing the main scanning direction to eject ink droplets. Wearing the direction downward.

  Here, for example, as shown in FIG. 4, the recording head 10 includes a heating element substrate 12 and a liquid chamber forming member 13, and a common channel 17 and a liquid chamber (individual flow) are formed from the channels formed in the head base member 19. The ink sequentially supplied to the (path) 16 is ejected as droplets. This recording head 10 is of a thermal type that obtains a discharge pressure by boiling the ink film by driving the heat generating element 14, and the direction of ink flow to the discharge energy acting part (heat generating part) in the liquid chamber 16 and the nozzles. This is a side shooter type configuration in which the opening center axis of 15 is a right angle.

  As the recording head, there are various methods such as a method in which the diaphragm is deformed by using a piezoelectric element, and the diaphragm is deformed by an electrostatic force to obtain a discharge pressure. The present invention can be applied to such an image forming apparatus.

  On the other hand, below the carriage 4, a sheet 20 on which an image is formed by the recording head 10 is conveyed in a direction perpendicular to the main scanning direction (sub-scanning direction). As shown in FIG. 3, the paper 20 is sandwiched between a transport roller 21 and a pressing roller 22, transported to an image forming area (printing unit) by the recording head 10, sent onto a printing guide member 23, and discharged. A pair of rollers 24 feeds in the paper discharge direction.

  At this time, the scanning of the carriage 4 in the main scanning direction and the ink ejection from the recording head 10 are synchronized at an appropriate timing based on the image data, and an image for one band is formed on the paper 20. After image formation for one band is completed, a predetermined amount of paper 20 is fed in the sub-scanning direction, and the same recording operation as described above is performed. These operations are repeated to form an image for one page.

  On the other hand, a sub tank (buffer tank, head tank) 30 in which an ink chamber for temporarily storing ink to be ejected is formed is integrally connected to the upper portion of the recording head 10. Here, “integral” includes that the recording head 10 and the sub-tank 30 are connected by a tube, a pipe, and the like, both of which are mounted on the carriage 4 together.

  The sub tank 30 is an ink cartridge (main tank) which is a liquid tank according to the present invention and contains ink of each color which is detachably attached to a cartridge holder 77 provided on one end side in the main scanning direction on the apparatus main body side. The ink of each color is supplied from a liquid supply tube 41 which is a tube member forming a part of the ink supply path from 76 and forming a first flow path.

  A maintenance / recovery mechanism 51 that performs maintenance / recovery of the recording head 10 is disposed on the other end side in the main scanning direction of the apparatus main body. The maintenance / recovery mechanism 51 includes a suction and moisturizing cap 52a and a moisturizing cap 52b for capping the nozzle surface of the recording head 10, a suction pump 53 as a suction means for sucking the inside of the cap 52b, and a suction pump 53. The waste liquid discharged from the discharge path 54 is discharged to a waste liquid tank 56 disposed on the main body frame 1 side, including a discharge path 54 for discharging the sucked ink waste liquid (waste ink).

  Next, an ink supply system (ink supply system) applied to the ink jet recording apparatus will be described with reference to FIGS. 5 is a schematic cross-sectional explanatory view of the sub tank of the ink supply system, FIG. 6 is also an explanatory view of the cartridge holder portion, FIG. 7 is also an explanatory view of the pump unit, and FIG. 8 is an explanatory view of the pressure control unit. FIG. 9 is an explanatory view showing an example of the flow path resistance variable unit.

  First, the sub tank 30 is provided with a flexible rubber member 102 formed in a convex shape toward the outside at a part of the opening of the tank case 101 forming the ink chamber 103. A filter 109 is provided in the vicinity of the connection portion with the recording head 10, and is configured to supply the recording head 10 with ink that has been filtered to remove foreign matters.

  One end of an ink supply tube 41 is connected to the sub tank 30. The other end of the ink supply tube 41 is connected to a cartridge holder 77 that is stationary as shown in FIGS.

  The cartridge holder 77 is connected to an ink cartridge 76, a pump unit 80 that is a liquid feeding means, and a pressure control unit 81.

  As shown in FIG. 6, branch flow paths 74 and flow paths 70 and 79 are formed in the cartridge holder 77 corresponding to each color ink, and pump connection ports 73 a and 73 b communicating with the pump unit 80. Pressure control ports 72a, 72b, 72c communicating with the pressure control unit 81 are provided. The pump connection port 73a and the pressure control port 72c communicate with each other through the internal flow path 70.

  As shown in FIG. 7, the pump unit 80 includes ports 85a and 85b that communicate with the pump connection ports 73a and 73b of the cartridge holder 77, respectively, and a pump 78 that communicates with these ports 85a and 85b. As the pump 78, various pumps such as a tubing pump, a diaphragm pump, and a gear pump can be applied. The pump unit 80 of FIG. 7 includes four pumps 78K, 78C, 78M, and 78Y corresponding to the four colors of ink. However, these four pumps are driven by one motor 82 in conjunction with each other. It is said.

  As shown in FIG. 8, the pressure control unit 81 includes ports 86a, 86b, 86c that communicate with the pressure control ports 72a, 72b, 72c of the cartridge holder 77, respectively, and pressure adjustments that communicate with these ports 86a, 86b, 86c. A variable flow path resistance unit 83 that is a valve is provided.

Next, the overall configuration and operation of the ink supply / discharge system will be described with reference to the schematic configuration diagram shown in FIG. FIG. 9 shows only main components connected to one liquid discharge head (recording head) 10 so that the operation and action of the ink supply / discharge system can be easily understood.
First, the ink supply system will be described. The ink cartridge 76 that stores ink to be supplied to the recording head 10, the liquid supply tube 41 that is a first flow path for supplying ink to the recording head 10, and the ink cartridge 76 are communicated. A pressure control unit 81 including a second flow path 42, a liquid supply tube 41 that is the first flow path, and a flow resistance variable unit 83 that is a pressure adjusting valve that communicates the second flow path 42; The second flow path 42 and the pressure control unit 81 are in communication with each other, and the third flow path 43 and the pump 78 of the pump unit 80 that is a liquid feeding means provided in the third flow path 43 are provided.

  Here, the flow path resistance variable unit 83 has a characteristic that the flow path resistance changes depending on the flow direction and flow rate of the liquid flowing inside. For example, as shown in FIG. 10, the variable flow path resistance unit 83 includes a pipe member 87 that is a flow path forming member, and a valve body 88 that is a movable member that is movably accommodated in the pipe member 87 in a free state. have.

  The pipe member 87 has a port 86a for connecting the liquid supply tube 41 serving as the first flow path, a port 86b for connecting the second flow path 42, and a port 86c for connecting the third flow path 43. is doing. The valve body 88 is a stepped shaft-shaped member having step portions having different diameters in the liquid flow direction, and has at least three step portion elements of an upper portion 88t, a central portion 88m, and a lower portion 88b. The diameter is smaller than the lower part 88b. The valve body 88 is movable inside the pipe member 87, and takes the position shown in FIG. 10A, the position shown in FIG. 10B, or an intermediate position depending on the state of the internal flow. .

  Here, a first throttle portion 181 on the first flow path side is formed between the upper portion 88t of the valve body 88 and the flow path portion 87a of the pipe member 87, and the lower portion 88b of the valve body 88 and the pipe member 87 A second throttle portion 182 is formed between the flow passage portion 87b and the valve body 88 moves according to the state of the internal flow as described above, so that the throttle amount of the second throttle portion 182 is reduced. Change.

  The pipe member 87 has a horizontal hole (a part of the third flow path 43 between the position of the central portion 88m of the valve body 88, that is, between the first throttle portion 181 and the second throttle portion 182). Port) 86c is formed.

  Returning to FIG. 9, the ink cartridge 76 is provided with an air communication portion 90, and the liquid level in the ink cartridge 76 is disposed at a position lower than the nozzle surface of the recording head 10. As a result, in a state where ink is filled in the entire ink supply path, the recording head 10 is held at a negative pressure due to the water head difference h between the liquid levels of the recording head 10 and the ink cartridge 76, so that the recording head is stable. Ink droplet ejection can be performed from 10.

  As described above, when the viscosity of the ink to be ejected is large, the fluid resistance of the liquid supply tube 41 is large, for example, when the tube is thin or long, or when the ink ejection flow rate is large, the ink supply path Pressure loss due to fluid resistance increases and ink supply cannot keep up (insufficient refill occurs). Specifically, the main elements that become the ink supply resistance in the ink supply system include the liquid supply tube 41, the filter 109, and the joint 89 (see FIG. 9).

  In this way, when the pressure loss increases due to the resistance of the ink supply system and the refill is insufficient, the pump 78 is driven to draw ink from the third flow path 43 by the arrow Qa (Qa is the assist flow rate or the flow of the assist liquid). However, it is also used as an arrow sign for convenience.) The liquid supply of the pump 78 can compensate for the insufficient supply of ink (refill assist).

  FIG. 11 shows an example of the relationship between the discharge flow rate of the recording head 10, the liquid feed amount (assist flow rate) of the pump 78, and the pressure of the recording head 10. FIG. 11 shows a change in pressure loss of the ink supply system with respect to the head discharge flow rate when the assist flow rate is 0 to 2 cc / s. As described above, when the assist flow rate is “0”, the pressure loss of the head is about 7 kPa, and ink cannot be continuously ejected, resulting in ejection failure. However, by assisting with the pump 78, the pressure loss is 1 kPa. It becomes the following grade and can be continuously discharged.

Here, the assist principle in the present ink supply / discharge system will be described with reference to FIG.
FIG. 10A shows a state where the droplet resistance is not discharged from the recording head 10 or the state of the variable flow path resistance unit 83 under a condition where the discharge flow rate is small. In this state, the valve body 88 is on the port 86b side. As shown in FIG. 10A, the gap Gb between the pipe member 87 and the lower part 88b of the valve body 88 is larger than the gap Gt between the pipe member 87 and the upper part 88t of the valve body 88, and further, the tip of the port 86a. 9 includes the liquid supply tube 41 and the filter 109 having a large fluid resistance, as shown in FIG. 9, the ink fed by the pump 78 indicated by the arrow Qa flows toward the port 86b where it easily flows (arrow C). Therefore, the ink flow generated by the pump 78 only circulates in the loop path formed by the pump unit 80 and the flow path resistance variable unit 83 in FIG. 9, and has almost no influence on the pressure of the recording head 10. Absent.

  On the other hand, FIG. 10B shows the state of the variable flow path resistance unit 83 under the condition that the discharge flow rate of the recording head 10 is large. By setting the gap Gt between the pipe member 87 and the upper portion 88t of the valve body 88 to be narrow, the valve body 88 is pulled toward the port 86a by the ink flow caused by the droplet discharge from the recording head 10 indicated by the arrow Qh. Moves (moves upward in the figure). Thereby, the lower part 88b of the valve body 88 moves to the small diameter part (flow-path part 87b: 2nd narrowing part 182) of the pipe member 87, and the gap between the pipe member 87 and the lower part 88b of the valve body 88 is a small gap. Gb1. As shown by the arrow Qa, the ink fed by the pump 78 tends to flow through this narrow gap Gb1 (arrow D), and pressure is generated. This pressure can reduce the pressure loss that occurs when the ink flows through the recording head 10, and can provide a large flow of ink.

  In this variable flow path resistance unit 83, the direction of ink flow between the peripheral surface of the lower portion 88b of the valve body 88 and the flow path portion 87b of the tube member 87 under conditions where the discharge flow rate of the recording head 10 increases and the pressure loss increases. , The length of the narrow portion Gb1 between the lower portion 88b of the valve body 88 and the pipe member 87 is increased, and the length of the pump 88 is increased by the pump (assist pump) 78. Increase pressure effect. Thereby, there is no trouble of controlling the flow rate adjustment valve with another actuator or the like as in the prior art, and stable ink supply can be realized automatically with a simple configuration.

  Since this image forming apparatus ejects four colors of ink, four ink supply systems having the configuration shown in FIG. 9 are provided for each color. In correspondence with each color pump 78, four actuators such as motors for driving the pump 78 can be individually provided, and the motor can be individually controlled according to the ink discharge amount of each recording head 10. As shown in FIG. 7 described above, only one motor (actuator) 82 may be provided in common for the number of pumps 78 (78K, 78C, 78M, 78Y) of the number of colors.

  When an image is formed by ejecting ink droplets of a plurality of colors, the amount of ink ejected from each recording head 10 varies. For example, a certain head ejects ink from all nozzles, The head may be in a non-ejection state. Even in such a case, in the ink supply system of the present invention, the fluid resistance of the flow path resistance variable unit 83 is automatically changed according to the discharge flow rate of the recording head 10, so that it corresponds to the discharge flow rate of each head. It is not necessary to control the pump.

  That is, control is performed automatically for a head that has a low discharge flow rate and does not require assistance, and that gives a large assist to a head that has a high discharge flow rate and requires assistance.

  Even in a system having a plurality of ink supply systems such as having a plurality of inks as described above, the pumps of all the ink supply systems can be driven together by a single actuator, which simplifies the configuration and control of the apparatus and reduces the cost. A small device can be realized.

  Next, the maintenance / recovery mechanism 51 constituting the ink discharge system will be described. As described above, the cap 52a for capping the nozzle surface 10a (see FIG. 4) of the recording head 10 and the suction means connected to the cap 52a. The suction pump 53 is driven in a state where the nozzle surface 10a of the recording head 10 is capped, and the space in the cap 52a is made negative, and ink can be discharged from the nozzle 15 into the cap 52a. . The waste ink discharged into the cap 52a is discharged to the waste liquid tank 56.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. FIG. 11 is an explanatory block diagram of the entire control unit.
The control unit 500 temporarily stores a CPU 501 also serving as a means for controlling the assist operation and the maintenance / recovery operation for controlling the entire apparatus, a ROM 502 for storing programs executed by the CPU 501 and other fixed data, and image data. RAM 503 for storing, rewritable nonvolatile memory 504 for holding data even while the power of the apparatus is shut off, image processing for performing various signal processing and rearrangement on image data, and other control of the entire apparatus And an ASIC 505 for processing input / output signals.

  In addition, a print control unit 508 for driving and controlling the recording head 34 according to print data, a head driver (driver IC) 509 for driving the recording head 10 provided on the carriage 4 side, and moving and scanning the carriage 4. A main scanning motor 551 for rotating, a sub-scanning motor 552 for rotationally driving the transport 21 for transporting the paper 20, a cap lifting mechanism 513 for lifting and lowering the caps 52a and 52ab of the maintenance / recovery mechanism 51 and a wiper member (not shown) A motor driving unit 512 for driving 512, a pump driving unit 511 for driving the suction pump 53 and the assisting pump 73 of the maintenance and recovery mechanism 51, and the like.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side, an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, and the like. From the host 600 side via the cable or network via the I / F 506.

  The CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints the image data. The data is transferred from the unit 508 to the head driver 509. Note that generation of dot pattern data for image output is performed by the printer driver 601 on the host 600 side.

  The print control unit 508 transfers the print data described above as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transfer of the print data and confirmation of the transfer to the head driver 509. The head driver 509 drives the heating element 14 based on print data corresponding to one line of the recording head 10 input serially.

  The I / O unit 515 acquires information from various sensor groups 516 mounted on the apparatus, extracts information necessary for controlling the printer, and uses it to control the print control unit 508 and the motor drive unit 510. . The sensor group 515 includes an optical sensor for detecting the position of the paper, a thermistor for monitoring the temperature in the machine, a sensor for monitoring the voltage of the charging belt, an interlock switch for detecting opening and closing of the cover, and the like. The I / O unit 515 can process various sensor information. Further, a detection signal from a temperature / humidity sensor that detects environmental conditions (temperature and humidity) and a detection signal from a full tank detection sensor that detects a full tank in the waste liquid tank 56 are also input.

Next, a first embodiment of the present invention in this image forming apparatus will be described with reference to the flowchart shown in FIG.
First, it is determined whether or not the ink cartridge 76 is attached to the cartridge holder 77. When the ink cartridge 76 is not attached, a cartridge attachment request is displayed on the operation panel 514.

  When the ink cartridge 76 is mounted, the maintenance / recovery motor 512 is driven to raise the cap 52a of the maintenance / recovery mechanism 51, thereby capping the nozzle surface 10a of the recording head 10. Then, the suction pump 53 is driven to make the inside of the cap 52a have a negative pressure, and ink suction / discharge from the nozzle 15 is started.

  As a result, the flow rate of the tube 41 in the ink supply path increases, the valve body 88 of the pressure control unit 81 rises, and the valve body 88 rises to a moving range that can be raised by a rapid flow rate change and stops. At this time, in the pressure control unit 81, since the relationship of ink discharge> supply is established, the pressure rapidly increases. As a result, the pressure loss rapidly increases, and the ink discharge from the nozzles 15 of the recording head 10 decreases rapidly, so the negative pressure in the cap 82a increases rapidly.

  When the assist pump 78 is driven and ink is supplied to the pressure adjustment unit 81 when the predetermined suction amount is reached, ink is supplied to the recording head 10 at a stretch and the ink is discharged from the nozzle 15. The

  Then, when the predetermined liquid feeding amount is reached, the suction pump 53 is stopped to stop the nozzle suction, and the assist pump 78 is stopped. Then, the cap lifting mechanism 513 is operated to record the cap 82a. The nozzle 10 is separated from the nozzle surface 10 a of the head 10 (capping is released), the nozzle surface is wiped by a wiper member (not shown) of the maintenance / recovery mechanism 51, and droplets that do not contribute to image formation (empty discharge) are discharged from the recording head 10. After that, the caps 82a and 82b are raised to cap the nozzle surface 10a of the recording head 10, and the recovery operation is completed.

The change in the cap internal pressure and the drive stop timing of the assist pump will be described with reference to FIG.
By starting the suction by driving the suction pump 53 at time t0 in FIG. 13, the pressure in the cap decreases (negative pressure increases), and the pressure in the cap starts from time t1 when the valve element 88 hits the upper surface and stops. Decreases rapidly (negative pressure increases). That is, in the pressure adjustment unit 81, the increase rate of the fluid resistance when the change in the flow rate of the liquid is greater than or equal to the threshold with respect to the increase rate of the fluid resistance when the change is less than the predetermined threshold. As a result, the amount of ink discharged into the cap due to the suction pressure is reduced, and the pressure in the cap is rapidly reduced (the negative pressure is increased), so that the flow velocity in the nozzle of the head is increased and the discharge of foreign matters and the like is improved.

  Since the ink is supplied to the recording head 10 by starting driving the assist pump 78 at time t2, the pressure in the cap rises, and the assist pump 78 is stopped at time t3. The timing at which the assist pump 78 is stopped (time point t3) is the time when the cap internal pressure becomes equal to or higher than the positive pressure (that is, the liquid is supplied until that time: indicated by a solid line in FIG. 13), or the cap internal pressure is positive. It can be any one of the time points before the pressure is reached (that is, the liquid feeding is stopped at that time point: indicated by a broken line in FIG. 13).

  In this way, the suction means is driven in a state where the nozzle surface of the recording head is capped with the cap, and the internal space between the cap and the nozzle surface is made negative pressure. In this state, the liquid is supplied from the liquid tank by the liquid feeding means. By feeding the liquid to the recording head, it is possible to increase the flow rate of the liquid inside the recording head and discharge it, thereby improving the ability to discharge bubbles and foreign matters.

Next, a second embodiment of the present invention will be described with reference to the flowchart shown in FIG.
In this example, although not shown, a means for detecting the pressure of the cap 52a is provided. In the first embodiment, the nozzle surface 10a of the recording head 10 is capped, the suction pump 53 is driven, the inside of the cap 52a is set to a negative pressure, and the suction and discharge of ink from the nozzle 15 is started. When the first predetermined value is reached, the assist pump 78 is driven to supply ink to the pressure adjusting unit 81, and when the cap internal pressure reaches the second predetermined value, the suction pump 53 is driven. The nozzle suction is stopped and the assist pump 78 is stopped.

  Here, the second predetermined value can be a value at which the pressure in the cap 82a becomes positive. In this case, the pressure in the cap changes as shown by the solid line from time t2 to time t3 in FIG. In this case, it is possible to prevent ink from flowing back into the head from the nozzle side.

  The second predetermined value can be a value before the pressure in the cap 82a becomes positive. In this case, the pressure in the cap changes from the time point t2 to t3 in FIG. The predetermined value at this time is a negative pressure value (less than the positive pressure) that does not cause a back flow of ink into the head. In this case, the ink can be fed from the nozzle side to a negative pressure state close to the positive pressure where the ink does not flow back into the head, and further unnecessary ink feeding can be suppressed.

Next, a third embodiment of the present invention will be described with reference to a flowchart shown in FIG.
First, in this embodiment, a table in which negative pressure driving time (suction pump driving time) and liquid feeding time (assist pump driving time) are associated with each other is stored and held in a storage unit such as an internal ROM. Here, the time is stored as the count value of the internal counter. For example, in the example shown in FIG. 16, the “suction recovery operation 1” is a liquid supply time (count value) when the drive stop timing of the assist pump 78 becomes a positive pressure in the cap. “2” is the liquid feeding time (count value) when the drive stop timing of the assist pump 78 is before the cap internal pressure becomes positive. Specifically, the negative pressure value in the cap is equivalent to −10 kPa at the count value “500” of the cap suction drive time, and the pressure in the cap is positive by driving the assist pump 78 for a time equivalent to the count value “250”. Then, by driving the assist pump 78 for a time corresponding to the count value “200”, the liquid feeding is stopped before the pressure inside the cap becomes positive (negative pressure value−0.1 kPa).

  Therefore, in the first embodiment, the nozzle surface 10a of the recording head 10 is capped, the suction pump 53 is driven, the inside of the cap 52a is set to a negative pressure, and ink suction and discharge from the nozzle 15 is started. When the count value is counted up, the assist pump 78 is driven to supply ink to the pressure adjustment unit 81. When the count value is counted up corresponding to the liquid feed pump drive time, the suction pump 53 is driven. Is stopped, nozzle suction is stopped, and driving of the assist pump 78 is stopped.

  Thus, the drive control is simplified by managing the drive time of the suction means and the liquid feed time of the liquid feed means by time.

  In the above description, the operation and effect of the present invention have been described with an example in which different color inks are supplied to a plurality of heads. However, when the same color ink is supplied to a plurality of heads, it is not a color. The same can be applied to the case where inks having different prescriptions are supplied to a plurality of heads. Further, the present invention can also be applied to an ink supply system in a case where a liquid discharge head having a plurality of nozzle rows in one head discharges different types of liquid from one head. Further, the present invention is not limited to an image forming apparatus that discharges ink in a narrow sense, and can also be applied to a liquid discharging apparatus that discharges various liquids (included in the “image forming apparatus” in the present invention). .

4 Carriage 10 Recording head 30 Sub tank 41 Ink supply tube (first flow path)
42 Second channel 43 Third channel 51 Maintenance / recovery mechanism 52a Cap for suction and moisture retention 52b Cap for moisture retention 53 Suction pump (suction means)
76 Ink cartridge (Main tank: Liquid tank)
77 Cartridge holder 78 Pump (Assist pump)
80 pump unit 81 pressure control unit 83 fluid resistance control unit 87 pipe member (flow path forming member)
88 Disc

Claims (7)

A recording head having nozzles for discharging droplets;
A liquid tank for storing liquid to be supplied to the recording head;
A first flow path for supplying the liquid to the recording head;
A second flow path communicating with the liquid tank;
A pressure regulating valve that connects the first flow path and the second flow path, and an internal flow path resistance changes according to a flow rate of the liquid flowing through the first flow path;
A third flow path communicating the second flow path or the liquid tank and the pressure regulating valve;
Liquid feeding means provided in the third flow path;
When ejecting droplets from the nozzle, the liquid is fed from the liquid tank to the recording head by the liquid feeding means in a state where the recording head and the liquid tank are in communication with each other via the pressure adjusting valve. Means to
A cap for capping the nozzle surface of the recording head;
Suction means connected to the cap;
The suction means is driven in a state in which the nozzle surface of the recording head is capped with the cap to make negative pressure in the cap internal space between the cap and the nozzle surface. In this state, the liquid is supplied by the liquid feeding means. An image forming apparatus comprising: a liquid tank that sends liquid to the recording head.   The pressure regulating valve is characterized in that an increase rate of the fluid resistance when the fluid flow rate change is greater than or equal to the threshold with respect to an increase rate of the fluid resistance when the change in the flow rate of the liquid is less than a predetermined threshold. The image forming apparatus according to claim 1.   3. The apparatus according to claim 1, further comprising a means for detecting a pressure in the cap, wherein the liquid is fed from the liquid tank to the recording head until the pressure in the cap becomes a positive pressure or higher. Image forming apparatus.   3. The apparatus according to claim 1, further comprising: a unit that detects a pressure in the cap, wherein the liquid feeding from the liquid tank to the recording head is stopped before the pressure in the cap becomes a positive pressure. Image forming apparatus.   3. The image forming apparatus according to claim 1, wherein liquid feeding from the liquid tank to the recording head is performed for a liquid feeding time that is determined in advance corresponding to a driving time of the suction unit.   The image forming apparatus according to claim 5, wherein the liquid feeding time is a time during which the pressure in the cap becomes a positive pressure or more.   The image forming apparatus according to claim 5, wherein the liquid feeding time is a time during which the pressure in the cap stays below a positive pressure.

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