JP5223780B2 - Image forming apparatus - Google Patents

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.

Japanese Patent No. 3606282 JP 2005-342960 A Japanese Patent Publication No. 5-504308 JP 2004-351845 A

  However, although the technique disclosed in Patent Document 1 solves the above-mentioned problem of insufficient refill, the mechanism for controlling the negative pressure is complicated, and the sealing performance of the negative pressure interlocking valve is highly required. There is a problem. 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.

  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. The purpose is to be able to.

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. And
The fluid resistance between the pressure regulating valve and the branch portion is larger than the fluid resistance between the branch portion and the liquid tank.

  Here, it can be set as the structure provided with the buffer tank in the said branch part.

  Further, a variable resistance valve may be provided between the pressure regulating valve and the branch portion, and the variable resistance valve may have a configuration in which fluid resistance increases as the flow rate of liquid from the pressure regulating valve to the branch portion increases.

An image forming apparatus according to the present invention includes:
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 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 fifth flow path that directly communicates the liquid tank 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. And
The second channel and the fifth channel are connected to the liquid tank at a spaced position.

An image forming apparatus according to the present invention includes:
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 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 fifth flow path that directly communicates the liquid tank 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. And
A partition portion is provided between communication portions of the second flow channel and the fifth flow channel with the liquid tank.

  Here, the second flow path includes a variable resistance valve in which fluid resistance changes, and the variable resistance valve is configured such that when the flow rate of the liquid from the pressure regulating valve to the liquid tank exceeds a set value. Alternatively, the fluid resistance can be increased according to the flow rate of the liquid from the pressure regulating valve to the liquid tank.

  Moreover, it can be set as the structure provided with the bypass flow path which bypasses the said resistance variable valve.

  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 reduce the discharge failure by avoiding the 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 liquid, etc. Since the fluid resistance of the liquid delivery device is larger than the fluid resistance between the branch and the liquid tank, the liquid delivery device sucks out the liquid from the pressure adjustment valve when the liquid delivery amount by the liquid delivery device is increased. Reduce By suppressing bets it can be performed more efficiently pressure drop reduction. Thereby, the negative pressure of the head can be maintained in an appropriate range with a simple configuration and control, and even a highly viscous liquid can be discharged at high speed without causing defective discharge.

  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. Therefore, it is possible to reduce the discharge failure by avoiding the 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 liquid, etc., and further the communication with the liquid tank and the pressure regulating valve. And a fifth flow channel that directly communicates between the liquid tank and the liquid feeding means, and the second flow channel and the fifth flow channel are connected to the liquid tank at spaced positions. Therefore, the amount of liquid delivered by the liquid delivery means When pressurized, suppressing a decrease in the assist efficiency liquid feeding means so as to suck liquid from reliably liquid tank rather than a pressure regulating valve, it is possible to perform more efficiently the pressure drop reduction. Thereby, the negative pressure of the head can be maintained in an appropriate range with a simple configuration and control, and even a highly viscous liquid can be discharged at high speed without causing defective discharge.

  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. Therefore, it is possible to reduce the discharge failure by avoiding the 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 liquid, etc., and further the communication with the liquid tank and the pressure regulating valve. A second flow path, a fifth flow path that directly communicates the liquid tank and the liquid feeding means, and the second flow path and the fifth flow path between the communication portions of the respective liquid tanks. Because it has a configuration with a partition When increasing the amount of liquid delivered by the liquid delivery means, the liquid delivery means reliably sucks out liquid from the liquid tank instead of the pressure adjustment valve to suppress the drop in assist efficiency and reduce pressure loss more efficiently. Can do. Thereby, the negative pressure of the head can be maintained in an appropriate range with a simple configuration and control, and even a highly viscous liquid can be discharged at high speed without causing defective discharge.

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 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. FIG. 5 is a schematic explanatory diagram for explaining fluid resistance between a flow path resistance variable unit and an ink cartridge and a branching portion. It is explanatory drawing of the ink supply system in 2nd Embodiment of this invention. It is typical explanatory drawing with which it uses for description of the branch part of the embodiment. It is explanatory drawing of the ink supply system in 3rd Embodiment of this invention. It is a typical explanatory view showing an example of a variable throttle valve of the embodiment. It is a typical explanatory view showing other examples of a restrictor variable valve similarly. It is explanatory drawing of the ink supply system in 4th Embodiment of this invention. It is a typical explanatory view showing the state of the variable throttle valve for explanation of the operation of the embodiment. It is explanatory drawing of the ink supply system in 5th Embodiment of this invention. It is explanatory drawing of the ink supply system in 6th Embodiment of this invention. It is explanatory drawing of the ink supply system in 7th Embodiment of this invention.

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, the recording head 10 includes a heating element substrate 12 and a liquid chamber forming member 13 as shown in FIG. 4, and a common channel 17 and liquid chambers (individually separated through an ink supply path formed in the base member 19. The ink sequentially supplied to the (flow 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.

  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 cap 52 for capping the nozzle surface of the recording head 10, a suction pump 53 for sucking the inside of the cap 52, a discharge path 54 for discharging the waste liquid of ink sucked by the suction pump 53, and the like. 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.

  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 diagram of the ink supply system, and FIG. 10 is an explanatory diagram showing an example of the variable flow path resistance 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) has a third flow path 61 that communicates with the pump 78, and a fourth flow path 62 that communicates the branch portion 63 and the pump 78.

  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.

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. 11, the assist pump (pump 78) is continuously driven until the nozzle suction is stopped. However, the above-described bypass path (from the branching portion 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. 11, since the pump 78 is driven also 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. 13 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. 13 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.

  Thus, in this ink supply system, the pressure increasing effect is determined by the shape of the narrow gap Gb1 and the flow rate of the liquid flowing through this portion. When the amount of ink consumed from the recording head 10 by high-speed recording increases, the force for lifting the valve body 88 increases, and finally when the limit point at which the valve body 88 can move in the tube member 87 is reached, the length of the gap Gb1 is increased. Since the distance does not change, the assist action is saturated. Therefore, if the flow rate to the recording head 10 further increases, a pressure loss corresponding to the increased amount occurs, and in some cases insufficient refilling occurs.

In this case, in order to cope with the condition that the valve body 88 reaches the top dead center, it is conceivable to increase the flow rate of the liquid indicated by the arrow D in FIG. Here, the conditions of the flow path for efficiently obtaining the pressure increasing effect by increasing the pump flow rate will be described with reference to FIG.
FIG. 14 is a schematic explanatory diagram of piping from the ink cartridge 76 to the variable flow path resistance unit 83. FIG. 14A shows the branching section 63 from the variable flow path resistance unit 83 in the second flow path 60. When the fluid resistance of the valve-side flow path 60a is made smaller than the fluid resistance of the cartridge-side flow path 60b from the branching portion 63 to the ink cartridge 76 (the flow path 60a is illustrated relatively thickly). FIG. On the other hand, FIG. 14B is a diagram showing a case where the fluid resistance of the valve side channel 60a is larger than the fluid resistance of the cartridge side channel 60b (the channel 60b is shown relatively thick). .

  As described above, when the flow rate of the pump 78 is increased in order to increase the assist pressure (pressure increase) generated in the variable flow path resistance unit 83, first, under the conditions of FIG. Since the resistance is smaller than the fluid resistance of the cartridge side channel 60b, the pump 78 can easily suck out ink from the valve side channel 60a. As a result, the ink flowing into the flow path resistance variable unit 83 by the pump 78 is used as the ink sucked by the pump 78 indicated by the arrow E, and the flow rate indicated by the arrow F is insufficient, so that a sufficient assist pressure cannot be generated. .

  On the other hand, as shown in FIG. 14B, when the fluid resistance of the valve-side channel 60a is larger than the fluid resistance of the cartridge-side channel 60b, the pump 78 can easily suck out ink from the cartridge-side channel 60b. Therefore, the ink flowing into the variable flow path resistance unit 83 by the pump 78 is preferentially supplied from the ink cartridge 76 as indicated by the arrow H, and the overflow from the variable flow resistance unit 83 flows as indicated by the arrow G. Therefore, unlike the configuration of FIG. 14A, there is no problem of insufficient refill when the pump flow rate is increased, and the assist pressure can be increased efficiently.

  That is, by setting the fluid resistance between the pressure regulating valve and the branching portion to be larger than the fluid resistance between the branching portion and the liquid tank (configuration in FIG. 14B), the liquid feeding amount by the liquid feeding means can be reduced. In the case of increase, it is possible to suppress the pressure loss more efficiently by suppressing the liquid feeding means from sucking out the liquid from the pressure regulating valve and lowering the assist efficiency.

Next, an ink supply system according to a second embodiment of the present invention will be described with reference to FIG. FIG. 15 is a schematic explanatory diagram showing the overall configuration of the ink supply system.
Here, the buffer tank 150 is provided in the branch part 63. The operation of this embodiment will be described in comparison with the first embodiment described above.

  FIG. 16A shows an explanatory diagram of the ink flow of the branching portion 63 in the configuration in the first embodiment described above (the configuration in FIG. 9). As shown in FIG. 16A, when the flow paths 60a, 60b, 62 are close to each other at one point, the fluid resistance of the valve-side flow path 60a is larger than the fluid resistance of the cartridge-side flow path 60b. However, when the flow rate Qa of the fourth flow path 62 is increased, the suction flow velocity at the branch portion 63 is increased, and the ink is easily pulled from the valve side flow path 60a.

  Thus, as in the second embodiment (configuration of FIG. 15), when the branching portion 63 is provided with a large capacity portion such as the buffer tank 150, the ink flow is as shown in FIG. That is, by separating the flow paths 60a, 60b, and 62 and providing a relatively large volume therebetween, the flow is decelerated in the buffer tank 150 even if the flow rate Qa of the fourth flow path 62 increases. Therefore, a flow determined by the relationship between the fluid resistances of the valve-side channel 60a and the cartridge-side channel 60b can be stably formed.

Next, an ink supply system according to a third embodiment of the present invention will be described with reference to FIG. FIG. 17 is a schematic explanatory view showing the overall configuration of the ink supply system.
Here, a variable throttle valve 151 whose fluid resistance changes is disposed in the valve-side flow path 60 a between the flow path resistance variable unit 83 and the branching portion 63.

  For example, as shown in FIG. 18A, the variable throttle valve 151 is provided with a deformable beam 152 in a part of a flow path 153 formed therein. The end of the beam 152 is inclined toward the flow path resistance variable unit 83 side, and the flow path is narrowed to the gap d1. Here, under the condition that the flow in the direction indicated by the arrow J in FIG. 18A is weak, the aperture opening of the aperture variable valve 152 is the gap d1, but the flow rate of the ink flowing inside increases, and FIG. When the flow in the direction is strong as shown by the arrow K as shown in b), the beam 152 is bent and the aperture of the diaphragm is narrowed to the gap D2 (d2 <d1).

  Therefore, when the flow rate from the pump 78 is increased in order to prevent insufficient refill by providing the variable throttle valve 151 in the valve side flow path 60a between the variable flow path resistance unit 83 and the branching portion 63, the variable throttle can be obtained. The valve 151 increases the fluid resistance of the valve-side channel 60a, and the assist efficiency can be prevented from being lowered due to the pump 78 sucking out ink from the valve-side channel 60a.

  The throttle variable valve 151 is not limited to that shown in FIG. 18 because it has only to have a characteristic that the fluid resistance increases when the flow rate of the flow from the flow path resistance variable unit 83 toward the branch portion 63 increases. For example, as shown in FIG. 19, a spring 156 and a valve body 155 are provided in the flow path 154, and the gap through which the valve body 155 moves up and down according to the ink flow rate indicated by arrows J and K is a gap g1. A configuration that changes within a range of ~ g2 can also be used.

  As described above, a variable resistance valve is provided between the pressure regulating valve and the branch portion, and the resistance variable valve has a characteristic that the fluid resistance increases as the flow rate of the liquid from the pressure regulating valve to the branch portion increases. When increasing the amount of liquid delivered by the liquid delivery means in order to generate pressure, it is possible to make it difficult for the liquid delivery means to suck out the liquid from the pressure adjustment valve by the action of the resistance variable valve. Decreasing the assist efficiency due to the increase can be suppressed, and the pressure loss can be reduced more efficiently.

Next, an ink supply system according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 20 is a schematic explanatory diagram showing the overall configuration of the ink supply system.
Here, similarly to the third embodiment, the variable throttle valve 151 is disposed in the valve-side flow path 60 a between the variable flow resistance unit 83 and the branching portion 63, and further communicates with both ends of the variable throttle valve 151. A bypass channel 165 is provided. The bypass channel 165 is set to have a resistance corresponding to the maximum fluid resistance value that can be obtained by the variable channel resistance unit 83. Note that the throttle variable valve 151 is configured as shown in FIG.

  Accordingly, as shown in FIG. 19, under the condition that the gaps g1 and g2 formed by the valve body 156 of the variable throttle valve 151 are secured to some extent, the ink flows through the gaps g1 and g2 and generates an assist pressure. Further, when the ink flow rate increases, as shown in FIG. 21, the valve element 156 completely closes the flow path by the ink flow rate in the direction indicated by the arrow L. Even in such a state, since the bypass channel 165 is provided in this embodiment, the ink can flow through the bypass channel 165.

  In this way, even if the flow path in the variable flow path resistance unit 83 is completely blocked, the ink cartridge 76 and the recording head 10 are kept in communication with each other by the bypass flow path 165, and thus stable while utilizing the water head difference between the two. Pressure control can be realized. Moreover, the selection range of the throttle variable valve 151 can be expanded by providing the bypass flow path.

  In other words, by providing a bypass flow path for the variable resistance valve, when the resistance variable valve is used to suppress a decrease in assist efficiency, the variable flow valve can be surely liquidated by the bypass flow path, even when the variable resistance valve is closed. The tank and the pressure adjusting valve can be communicated with each other, the pressure of the recording head can be stabilized, and the design conditions of the resistance variable valve can be expanded.

Next, an ink supply system according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 22 is a schematic explanatory diagram showing the overall configuration of the ink supply system.
Here, the ink cartridge 76 and the pump 78 are in direct communication with each other through the fifth flow path 64. With such a configuration, the pump 78 can more reliably suck ink from the ink cartridge 76.

  In this case, if the second flow path 60 and the fifth flow path 64 are provided in the proximity positions in the ink cartridge 76, the pump 78 is driven to directly suck ink from the second flow path 60, thereby providing the assist effect described above. It is easy for problems to be reduced. Therefore, it is preferable that the second flow path 60 and the fifth flow path 64 are located at positions where the suction port portions are separated from each other. As the configuration of separating, not only the positions of the suction port portions of the second flow channel 60 and the fifth flow channel 64 are separated, but either a configuration in which both are provided on different wall surfaces of the ink cartridge 76, or one of them is provided. Further, a configuration (an example in FIG. 22) that communicates with the inner side of the ink cartridge 76 can be employed.

  In this way, by having a fifth flow path that directly communicates the liquid tank and the liquid feeding means, the second flow path and the fifth flow path are connected to the liquid tank at spaced positions. When the amount of liquid fed by the liquid feeding means is increased, the liquid feeding means reliably sucks the liquid from the liquid tank instead of the pressure adjustment valve, thereby suppressing the reduction in assist efficiency and reducing pressure loss more efficiently. be able to.

Next, an ink supply system according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 23 is a schematic explanatory diagram showing the overall configuration of the ink supply system.
Here, as in the fifth embodiment, the ink cartridge 76 and the pump 78 are directly communicated with each other through the fifth flow path 64, and the suction openings of the second flow path 60 and the fifth flow path 64 are close to each other. And a partition portion 66 is provided between each of them. As a result, even if the suction ports of the second flow path 60 and the fifth flow path 64 are close to each other, ink is discharged from the second flow path 60 by driving the pump 78, as in the fifth embodiment. Direct suction can be prevented, and assist efficiency can be improved reliably.

  In this way, the fifth tank has a fifth flow path that directly communicates the liquid tank and the liquid feeding means, and the partition portion is provided between the communication sections of the second flow path and the respective liquid tanks of the fifth flow path. By using the configuration, when increasing the amount of liquid fed by the liquid feeding means, the liquid feeding means reliably sucks the liquid from the liquid tank instead of the pressure adjustment valve, and suppresses the decrease in assist efficiency. Pressure loss can be reduced more efficiently.

Next, an ink supply system according to a seventh embodiment of the present invention will be described with reference to FIG. FIG. 24 is a schematic explanatory diagram showing the overall configuration of the ink supply system.
In this embodiment, a pump 78 is directly connected to the ink cartridge 76 as in the fifth and sixth embodiments, and a throttle variable valve 151 and a bypass channel 165 are provided as in the fourth embodiment. It is configured.

  Also in this embodiment, the same effect as the fourth embodiment can be obtained. Here, in the ink cartridge 76, the communication portion (joint 89a) with the pump 78 and the communication portion (joint 89b) with the flow path resistance variable unit 83 are spaced apart in the horizontal direction. This makes it difficult for the pump 78 to directly suck ink from the variable flow path resistance unit 83.

  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 Variable throttle valve 165 Bypass flow path

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 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. And
The image forming apparatus according to claim 1, wherein a fluid resistance between the pressure regulating valve and the branch portion is larger than a fluid resistance between the branch portion and the liquid tank.   The image forming apparatus according to claim 1, wherein a buffer tank is provided in the branch portion.   The resistance variable valve is provided between the pressure regulating valve and the branch portion, and the resistance resistance of the resistance variable valve increases when a flow rate of liquid from the pressure regulating valve to the branch portion increases. The image forming apparatus according to 1 or 2. 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 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 fifth flow path that directly communicates the liquid tank 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. And
The image forming apparatus, wherein the second flow path and the fifth flow path are connected to the liquid tank at a spaced position. 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 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 fifth flow path that directly communicates the liquid tank 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. And
An image forming apparatus, wherein a partition portion is provided between communication portions of each of the second flow path and the fifth flow path with the liquid tank.   The second flow path includes a variable resistance valve that changes a fluid resistance, and the variable resistance valve is configured such that when the flow rate of the liquid from the pressure regulating valve to the liquid tank exceeds a set value, or 6. The image forming apparatus according to claim 4, wherein a fluid resistance increases in accordance with a flow rate of the liquid from the pressure regulating valve to the liquid tank.   The image forming apparatus according to claim 3, further comprising a bypass flow path that bypasses the variable resistance valve.

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