JP2011000831A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of maintaining the negative pressure of a head in a proper range by the control of a simple constitution, and capable of discharging even a high viscosity liquid at high speed without making a discharge fault occur.SOLUTION: The image forming device has a flow channel resistance variable unit 83 and a pump 78 for feeding ink to the flow channel resistance variable unit 83. The flow channel resistance in the flow channel resistance variable unit 83 changes according to an ink flowing quantity flowing through a first flow channel 71. The flow channel resistance variable unit 83 feeds ink from an ink cartridge 76 to a recording head 10 by the pump 78 when the recording head 10 is in communication with the ink cartridge 76 via the flow channel resistance variable unit. A flow quantity adjusting valve 300 is arranged between the flow channel resistance variable unit 83 and the branched part 63. When performing maintaining and restoring operations for discharging foreign matters such as air bubbles, a flow quantity from the flow channel resistance variable unit 83 to a branched part 63 side is limited and ink is fed at high velocity to the first flow channel 71.

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 called ink, but is any liquid that can form an image, such as a recording liquid, a fixing liquid, a liquid, a DNA sample, or a patterning material. Used as a general term. 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, as disclosed in Patent Document 1, conventionally, the ink in the ink cartridge is held in a pressurized state, and a differential pressure valve is provided on the upstream side of the ink supply of the head so that the negative pressure in the sub tank is a predetermined pressure. It is known to supply ink when it is larger.

  Also, as disclosed in Patent Document 2, the ink supply pressure is positively controlled by pumping ink to a negative pressure chamber that obtains a negative pressure by a spring upstream of the head, Patent Document 3 discloses As disclosed, there is also known a system that does not have a negative pressure chamber, but similarly positively controls the 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 by the water head difference, for example, as disclosed in Patent Document 4, a pump is provided in a tube that connects a head and an ink cartridge, and further, It is known that a bypass path connecting the upstream side and the downstream side is provided, and a valve is provided in this bypass path, and the opening of the valve provided in the bypass path is appropriately controlled by printing to maintain a desired pressure. Yes.

  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. What is performed (Patent Documents 6, 7, and 8), and what performs pressurization and suction in combination (Patent Document 9) 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 Japanese Patent Laid-Open No. 3-184872 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 the ink is circulated between the recording head and the ink tank as in the technique disclosed in Patent Document 8, there is a problem that the head connection portion and the supply system become complicated because two connecting portions with the head are required. is there.

  Further, in the configuration in which suction and pressurization are combined as in the technique disclosed in Patent Document 9, high discharge performance can be obtained by the differential pressure between pressurization and suction, but the discharge efficiency with respect to ink consumption is greatly increased. It is difficult to improve.

  The present invention has been made in view of the above problems, and can maintain the negative pressure of the head within an appropriate range with a simple configuration and control, and can discharge a high-viscosity liquid at high speed without causing defective discharge. Another object is to improve the discharge performance of bubbles and 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 channel having a branch part in the middle and communicating with the liquid tank;
A pressure regulating valve for communicating the first flow path and the second flow path;
Liquid feeding means for feeding the liquid to the pressure regulating valve;
A third flow path communicating the pressure regulating valve and the liquid feeding means;
A fourth flow path communicating the branch portion and the liquid feeding means,
The pressure regulating valve has an internal channel resistance that changes according to the flow rate of the liquid flowing through the first channel,
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. An image forming apparatus that
A flow rate adjusting means for adjusting a flow rate between the pressure regulating valve and the branch portion;
A means for supplying liquid from the liquid supply means in a state in which the flow rate from the pressure adjustment valve to the branch portion is restricted by the flow rate adjustment valve when maintaining and recovering the recording head. It was.

  Here, the flow rate adjusting means may be an on-off valve.

  The flow rate adjusting means may be a valve whose fluid resistance increases according to the flow rate.

  And a cap for capping the nozzle surface of the recording head; and a suction means connected to the cap, and when performing the maintenance recovery, the suction means in a state where the nozzle surface of the recording head is capped by the cap. Is driven to create a negative pressure in the space in the cap between the cap and the nozzle surface, and the liquid can be sucked from the nozzles of the recording head.

  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 avoids the shortage of refilling due to the lengthening of the tube member, the increase in the discharge flow rate, the increase in the viscosity of the discharge liquid, etc. With this liquid, it is possible to discharge at high speed without causing defective discharge, and the flow control valve restricts the flow from the pressure adjustment valve to the branch when maintaining and recovering the recording head. so Since a configuration to perform the liquid supply from the liquid means and it is possible to discharge the liquid from the nozzle to increase the internal flow velocity head, it is possible to discharge the foreign matters such as bubbles efficiently.

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 the ink supply system in 1st Embodiment of this invention. It is explanatory drawing which shows the flow-path resistance variable unit in the embodiment. It is block explanatory drawing which shows the outline | summary of the control part of the apparatus. It is a flowchart with which it uses for description of initial filling operation | movement. It is a flowchart with which it uses for description of printing operation. It is explanatory drawing which similarly shows an example of the relationship between head discharge flow volume, head pressure loss, and assist flow volume. It is a flowchart with which it uses for description of an example of a maintenance recovery operation | movement. It is explanatory drawing with which it uses for description of the flow volume change of the 1st flow path at the time of the maintenance recovery operation | movement. It is a flowchart with which it uses for description of the other example of a maintenance recovery operation | movement.

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.

  For example, one or a plurality of recording heads 10 that eject ink droplets of black (K), cyan (C), magenta (M), and yellow (Y) are mounted on the carriage 4. The ink discharge ports (nozzles) are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet discharge direction facing downward.

  Here, as shown in FIG. 4, the recording head 10 includes a heating element substrate 12 and a liquid chamber forming member 13, and droplets of ink that are sequentially supplied to the common channel 17 and the liquid chamber (individual channel) 16. Discharge as 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.

  In addition, among thermal heads, there is an edge shooter method in which the discharge direction is different. In this edge shooter method, the heating element 14 is gradually destroyed by an impact when bubbles disappear, so-called cavitation. There is a problem with the phenomenon. On the other hand, in the side shooter method described above, bubbles grow, and when the bubbles reach the nozzle 15, the bubbles communicate with the atmosphere, and the bubbles do not contract due to a temperature drop. Therefore, there is an advantage that the life of the recording head is long. Further, there is a structural advantage that the energy from the heating element 14 can be more efficiently converted into the formation of ink droplets and the kinetic energy of the flight, and the meniscus can be quickly returned by supplying ink. Therefore, the ink jet recording apparatus employs a side shooter type recording head.

  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. Ink of each color is supplied from a liquid supply tube 71 that is a tube member that forms a part of the ink supply path from 76 and forms 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). Further, as shown in FIG. 9 described later, the maintenance / recovery mechanism 51 is provided with a wiper member 57 for wiping the nozzle surface of the recording head 10 by a wiping unit 58 so as to be able to advance and retreat with respect to the nozzle surface. ing.

  Next, an ink supply system (ink supply system) according to the first embodiment of the present invention 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 71 is connected to the sub tank 30. The other end of the ink supply tube 71 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, internal flow paths 70, 74, and 79 are formed in the cartridge holder 77 corresponding to each color ink, and pump connection ports 73 a and 73 b that communicate with the pump unit 80, and pressure control Pressure control ports 72a, 72b, 72c communicating with the 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 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 system can be easily understood.
This ink supply system is also referred to as an ink cartridge 76 for storing ink to be supplied to the recording head 10 and a liquid supply tube (hereinafter referred to as “first flow path”) as a first flow path for supplying ink to the recording head 10. .) 71, a second flow path 60 having a branching portion 63 in the middle and communicating with the ink cartridge 76, and a flow that is a pressure adjusting valve for communicating the first flow path 71 and the second flow path 60. A pressure control unit 81 including a variable path resistance unit 83; a pump unit 80 including a pump 78 which is a liquid feeding means for sending ink to a pressure adjusting valve (variable flow path resistance unit 83); and a pressure adjusting valve (variable flow resistance). The unit 83) and the third flow path 61 that communicates with the pump 78, the fourth flow path 62 that communicates the branch part 63 and the pump 78, and the branch part 63 and the variable flow path resistance unit 83. Flow And a flow regulating valve 300 is a regulating means.

  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 includes a port 86a that connects the first flow path (liquid supply tube) 71, a port 86b that connects the flow path 60a branched by the branch portion 63 of the second flow path 60, and a third flow. And a port 86c for connecting the path 61. 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.

On the other hand, as described above, the maintenance / recovery mechanism 51 constituting the ink discharge system includes a cap 52a for capping the nozzle surface 10a (see FIG. 4) of the recording head 10, and a suction pump as a suction unit connected to the cap 52a. 53, 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 the 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.
Further, as shown in FIG. 9 described later, the maintenance / recovery mechanism 51 is provided with a wiper member 57 for wiping the nozzle surface of the recording head 10 by a wiping unit 58 so as to be able to advance and retreat with respect to the nozzle surface. ing.

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 rotating and driving the transport 21 for transporting the paper 20, a maintenance / recovery motor 512 for operating a cap lifting / lowering mechanism 513 for lifting / lowering the caps 52a and 52b of the maintenance / recovery mechanism 51 And a pump / valve drive unit 511 for driving the flow rate adjusting valve 300, 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, the ink initial filling operation using the ink supply system will be described with reference to the flowchart of FIG.
After confirming that the ink cartridge 76 has been installed, the nozzle surface of the recording head 10 is capped with the cap 52 of the maintenance unit 51. In this capped state, the suction pump 53 is driven to suck air in the ink supply system path through the nozzles of the recording head 10 (nozzle suction start). The nozzle suction is performed until a predetermined time has elapsed from the start of nozzle suction. By performing suction for a predetermined time, the ink in the ink cartridge 76 reaches the first flow path (liquid supply tube) 71.

  Thereafter, when a predetermined time has elapsed from the start of nozzle suction (when the timer counts up), the motor 82 is driven to drive the pump (assist pump) 78. At this time, since the ink supply path is formed as shown in FIG. 9, the pump 78 is driven to feed the liquid flow resistance variable unit 83 to the arrow Qa side, and the bypass path to which the pump 78 is connected. Air in a certain third flow path 61 is pushed out to the flow resistance variable unit 83 side and is replaced with ink.

  Thereafter, when the predetermined time has elapsed (when the timer has counted up), both the suction pump 53 and the pump 78 are stopped. At this stage, the entire ink supply path can be filled with ink.

  Thereafter, the capping by the cap 52 of the maintenance unit 51 is released, the nozzle surface of the recording head 10 is wiped by a wiper member (not shown) provided in the maintenance unit 51, and the recording head 10 is driven so that predetermined drops that do not contribute to image formation A desired meniscus can be formed on the nozzle by discharging a number of ink droplets from the nozzle (head empty discharge).

  In this way, the initial filling of ink is completed. In the flow chart shown in FIG. 12, the assist pump (pump 78) is continuously driven until the nozzle suction is stopped, but the above-described bypass path (from the branch part 63 to the fourth flow path 62, the third flow path). The initial filling can be performed even if the ink replacement in the path 61 and the horizontal hole 86c is stopped as soon as it is completed. However, in the example shown in FIG. 12, since the pump 78 is driven even when the liquid supply tube 71 and the recording head 10 are filled, the initial filling can be completed in a shorter time.

Next, the printing operation will be described with reference to the flowchart shown in FIG.
After receiving the print job signal, first, the temperature sensor 27 detects the temperature inside the apparatus (inside the apparatus) to estimate the ink temperature. Although the temperature sensor 27 is mounted on the carriage 4 (see FIG. 2), it may be provided at another location such as an ink cartridge portion or a recording head portion. Alternatively, the ink temperature may be directly detected by providing the ink supply path.

  Then, based on the temperature of the ink, the flow rate of liquid fed by the assist pump 78 is determined, and the pump 78 is driven. Thereafter, the cap 52 covering the nozzle surface of the recording head 10 is separated from the nozzle surface (capping is released), and after a predetermined number of drops are ejected, printing is started.

  At this time, since the assist pump 78 is driven, even when a high-viscosity ink is used in a system with a long liquid supply tube 71, the pressure loss accompanying the ink supply can be appropriately reduced, resulting in an insufficient supply of ink. Good printing can be performed without any problem.

  After printing, the carriage 4 is stopped at a predetermined position (home position) of the apparatus, and the nozzle surface of the recording head 10 is capped with a cap 52. Thereafter, the assist pump 78 is stopped.

  Here, the assist pump 78 may be stopped immediately after the end of printing. Further, although the liquid supply amount of the assist pump 78 is controlled based on the temperature, depending on the conditions such as the ink supply specification, all the temperatures can be obtained with the liquid supply amount that does not cause supply shortage in the ink supply in the lowest temperature environment. It is also possible to send liquids under conditions.

  When performing such a printing operation, when the viscosity of the ejected ink is large, the fluid resistance of the liquid supply tube 71 is large, for example, when the tube is thin or long, or when the ink discharge flow rate is large, A situation occurs in which the ink supply cannot catch up due to the fluid resistance of the ink supply path. Specifically, the main elements that become the ink supply resistance in the ink supply system include the liquid supply tube 71, the filter 109, and the joint 89 (see FIG. 9).

For example, when a high-viscosity ink of 16 cP is ejected in a wide image forming apparatus including a long tube having a diameter of 2.8 mm and a length of 2500 mm, the liquid supply tube 71 has a fluid resistance of 2 0.7e10 [Pa · s / m ³ ]. In this embodiment, the fluid resistance of the filter 109 and the joint 89 is 1e10 [Pa · s / m ³ ] and 2e9 [Pa · s / m ³ ], respectively.

  Here, when the limit value of the pressure loss that enables stable ejection from the recording head 10 is 2.5 kPa, and ink is ejected continuously from all the nozzles, the ejection flow rate is 0.1 cc / s. The pressure loss at that time is 6.9 kPa. Even in the absence of the pressure control unit 81, the pressure is 3.94 kPa, so that it cannot be naturally supplied by a simple water head difference ink supply system.

  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. 14 shows an example of the relationship between the discharge flow rate of the recording head 10, the liquid feeding amount (assist flow rate) of the pump 78, and the pressure of the recording head 10. FIG. 14 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 0.2 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 of the ink supply system will be described with reference to FIG. 10 described above.
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 71 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 that is easy to flow (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.

Next, an example of the operation of discharging foreign matters such as bubbles and thickened ink in the maintenance / recovery operation will be described with reference to the flowchart of FIG.
It is confirmed whether or not the ink cartridge 76 has been installed. When it is confirmed that the ink cartridge 76 has been installed, the assist pump 78 starts to be driven and ink feeding to the fluid resistance variable unit 83 is started. At this time, as described above, the ink sent to the variable fluid resistance unit 83 flows separately on the first flow path 71 side and the second flow path 60 side (period during liquid supply in FIG. 16). ).

  Thereafter, when the flow rate adjusting valve 300 is controlled to limit the ink flow rate to the second flow path 60, the amount of liquid flowing into the first flow path 71 increases momentarily, and the ink flow rate inside the recording head 10 increases. .

  When the flow rate to the first flow path 71 increases in this way, the valve body 88 in the flow path resistance variable unit 83 rises upward and stops (time point t1 in FIG. 16). That is, when the valve body 88 rises to a moving range that can be raised by a rapid change in the flow velocity and stops, the flow rate of ink to the first flow path 71 is reduced (period of flow rate reduction in FIG. 16).

  Then, after a predetermined time has elapsed from the start of the flow restriction by the flow adjustment valve 300 (after counting up), the restriction of the flow by the flow adjustment valve 300 is canceled to restore the flow, and the drive of the assist pump 78 is stopped ( Time t2 in FIG.

  Thereafter, the nozzle surface 10a of the recording head 10 is wiped and cleaned by the wiper member 57, and after the idle discharge from the recording head 10, the recording head 10 is capped by the cap 52 and the recovery operation is finished.

  In this way, by instantaneously feeding ink to the first flow path, a discharge operation (recovery operation) with an increased flow velocity inside the head can be performed, and foreign matters such as bubbles in the head can be efficiently removed. Can be removed.

  In this case, the flow rate adjusting valve 300 can be constituted by an on-off valve, and the on-off valve is closed to restrict the flow rate.

  Further, an assist pump 78 that can change the amount of liquid to be fed is used so that the flow rate Q per unit time can be fed at the operation of the flow rate Q1 and the flow rate Q2 (Q1 <Q2). In the discharge operation, there are two types of discharge: a first discharge operation (liquid feeding at a flow rate Q1) with a small amount of liquid consumption and a second discharge operation (liquid feeding at a flow rate Q2) with a high consumption amount and a high discharge performance. It is also possible to perform the operation selectively or in a superimposed manner.

  Further, the flow rate adjusting valve 300 may be configured by a valve whose fluid resistance changes in accordance with the flow rate and whose fluid resistance increases as the flow rate increases. Thus, when the discharge operation of the flow rate Q1 and the discharge operation of the flow rate Q2 can be performed as described above, the fluid resistance automatically increases when the discharge operation by the flow rate Q2 is performed. Without controlling the operation of 300 from the outside, the liquid flow rate to the first flow path 71 can be temporarily increased, and the discharge performance can be efficiently implemented.

Next, another example of the maintenance / recovery operation will be described with reference to the flowchart of FIG.
As in the example of FIG. 15, it is confirmed whether or not the ink cartridge 76 has been installed. When the installation of the ink cartridge 76 is confirmed, the assist pump 78 starts to be driven and the fluid resistance variable unit 83 is Ink feeding starts. At this time, as described above, the ink fed to the variable fluid resistance unit 83 flows separately on the first flow path 71 side and the second flow path 60 side.

  Thereafter, when the flow rate adjusting valve 300 is controlled to limit the ink flow rate to the second flow path 60, the amount of liquid flowing into the first flow path 71 increases momentarily, and the ink flow rate inside the recording head 10 increases. .

  In a state where the flow rate is maximized (until the valve body 88 rises to the top and stops), the cap 82a of the maintenance / recovery mechanism 51 is raised to cap the nozzle surface 10a of the recording head 10, and the suction pump The ink suction operation from the nozzle 15 is started by driving 53 to make the inside of the cap 82a have a negative pressure. Accordingly, the ink flow rate in the recording head 10 can be increased by the pressurization by the assist pump 78 and the suction pressure of the suction pump 53, and the bubbles in the recording head 10 can be discharged more efficiently.

  Then, after a predetermined time has elapsed (after counting up), the suction operation is stopped, the flow rate restriction by the flow rate adjustment valve 300 is released, the flow rate is recovered, and the drive of the assist pump 78 is stopped.

  Then, after releasing the capping, the nozzle surface 10a of the recording head 10 is wiped and cleaned by the wiper member 57, and after the idle discharge from the recording head 10, the recording head 10 is capped by the cap 52 to perform the recovery operation. finish.

  In this way, by performing the suction operation from the recording head 10 together, foreign matters such as bubbles and thickened ink remaining in the head can be more effectively discharged.

  In the above description, the operation and the like have been described using the ink cartridge 76 having the atmosphere opening portion 90. However, the present invention similarly applies to the case where an ink cartridge using a bag containing ink is used. Applicable.

  Further, 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. However, when ink of the same color is supplied to a plurality of heads, inks having different prescriptions instead of colors are used. The same can be applied to the case of supplying to a plurality of heads. 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 Subtank 60 Second Channel 61 Third Channel 62 Fourth Channel 63 Branching Section 64 Fifth Channel 71 Liquid Supply Tube (First Channel)
76 Ink cartridge (Main tank: Liquid tank)
77 Cartridge holder 78 Pump (Assist pump)
80 Pump unit 81 Pressure control unit 83 Fluid resistance variable unit 87 Pipe member (flow path forming member)
88 Valve body 151 Restriction variable valve 165 Bypass flow path 300 Flow rate adjustment valve

Claims (4)

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 channel having a branch part in the middle and communicating with the liquid tank;
A pressure regulating valve for communicating the first flow path and the second flow path;
Liquid feeding means for feeding the liquid to the pressure regulating valve;
A third flow path communicating the pressure regulating valve and the liquid feeding means;
A fourth flow path communicating the branch portion and the liquid feeding means,
The pressure regulating valve has an internal channel resistance that changes according to the flow rate of the liquid flowing through the first channel,
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. An image forming apparatus that
A flow rate adjusting means for adjusting a flow rate between the pressure regulating valve and the branch portion;
Means for causing liquid feeding from the liquid feeding means in a state in which the flow rate from the pressure regulating valve to the branch portion is restricted by the flow regulating valve when maintaining and recovering the recording head. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the flow rate adjusting unit is an on-off valve.   The image forming apparatus according to claim 1, wherein the flow rate adjusting unit is a valve whose fluid resistance increases in accordance with the flow rate.   A cap for capping the nozzle surface of the recording head; and a suction unit connected to the cap, and when performing the maintenance recovery, the suction unit is driven with the nozzle surface of the recording head capped by the cap. 4. The image formation according to claim 1, wherein an operation of sucking a liquid from a nozzle of the recording head is performed by setting a negative pressure in a space in the cap between the cap and the nozzle surface. apparatus.

Images