JP2013000930A - Liquid ejection apparatus and image forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink ejection apparatus in which influence of pressure increase due to air bubbles caused in a liquid supply route is eliminated, without using a complicated control mechanism and uselessly consuming ink.SOLUTION: The ink ejection apparatus includes: a recording head 1 including nozzles for ejecting liquid droplets; a sub tank 101 for storing the liquid to be supplied to the recording head 1; an ink cartridge 76; a supply tube 16 interconnecting them; and a liquid feed pump 81 interposed in the supply tube 16. The supply tube 16 includes flexible films 202 located opposite a gravitational direction; and springs 201 for energizing the flexible films 202 outward from the inside of the supply tube 16. The liquid is repeatedly fed by the liquid feed pump 81 in both a first liquid feeding direction to feed the liquid from the ink cartridge 76 to the sub tank 101, and a second liquid feeding direction opposite the first liquid feeding direction. The liquid is repeatedly fed while swelling and denting the flexible films 202. The air bubbles are successively moved toward the cartridge 76, and finally, stored in the cartridge 76.

Description

  The present invention relates to a droplet discharge device and an image forming apparatus using the droplet discharge device.

  In recent years, inkjet printers and similar types of printers (hereinafter simply referred to as inkjet printers) have become increasingly diverse as they have increased printing speeds and are widely used not only for home use but also for business purposes. Demand for formation is also increasing. In business applications, in order to print in large quantities, the ink storage capacity of the ink cartridge is increased to reduce the cartridge replacement frequency. For this purpose, a so-called off-carriage method is often used in which an ink cartridge is provided in a printer body and ink is supplied by communicating with a recording head on a carriage through a tube. In this off-carriage method, a buffer called a sub tank is provided immediately before the recording head in order to stably maintain the pressure of the ink supplied to the recording head, and the ink in the sub tank drips from the recording head. In order to prevent this, the pressure is lower than atmospheric pressure, that is, negative pressure.

  In such an ink jet printer, when a used ink cartridge is removed, a small amount of foamy air may enter the tube. Alternatively, if the air permeability of the tube is low, air enters the tube over time. Such air becomes bubbles and stays in the sub tank through the tube as the ink from the recording head is consumed. Incidentally, since the recording head flies ink droplets in the direction of gravity, the ink flow in the sub tank is in the direction of gravity. On the other hand, the bubbles stagnate in the opposite direction of the gravity direction, that is, in the upper part of the sub tank, and do not flow in the direction of the recording head due to the buoyancy of the bubbles themselves. Further, there is a filter between the recording head and the sub tank, and a large pressure difference and flow velocity are required for air bubbles to pass through the filter. Because of this situation, it is not easy to remove the bubbles from the sub tank. When the ink jet printer is placed in a high temperature environment with air bubbles remaining in the sub tank, the air bubbles expand, and the pressure in the sub tank increases accordingly. That is, the negative pressure in the sub tank collapses and normal printing cannot be performed. In order to prevent this, there is a technique for discharging bubbles in the sub tank.

  For example, pressurize the ink in the ink cartridge, provide a valve in the tube between the cartridge and the sub tank, close the valve, cap the nozzle placement surface of the recording head, and discharge the ink by the pump. A so-called choke method is already known in which the air pressure in the sub tank is discharged from the recording head at a stroke by a large pressure difference by lowering the pressure and then opening the valve. In addition, there is already known a method in which a liquid feed pump is provided in a tube communicating between the cartridge and the sub tank, and the bubbles in the sub tank are returned to the cartridge until the telescopic member in the sub tank is contracted by a predetermined amount by reverse rotation of the pump.

  However, in the case of the above-described choke method, bubbles in the sub tank are discharged from the recording head at a stroke due to a large pressure difference, so that there is a problem that ink that does not need to be discharged is wasted. In addition, when the pump between the cartridge and the sub tank is reversed and the bubbles in the sub tank are returned to the cartridge, when a long tube or a tube with a large inner diameter is used, the bubbles will remain in the cartridge even if the pump rotates backward. Before reaching the position, the expansion / contraction member in the sub-tank is contracted by a predetermined amount, resulting in an overnegative pressure and entraining bubbles from the nozzle. Even if the pump is rotated forward and backward in order to prevent overnegative pressure, the bubbles are reciprocated in the tube and the sub tank, and there is a problem that it is difficult to obtain the effect of discharging the bubbles.

For the purpose of providing a liquid ejecting apparatus and an ink storing means in a sub tank that can prevent ejection failure due to bubbles remaining in the liquid ejecting head and reduce the liquid (ink) discard rate, Japanese Patent Application Laid-Open No. 2003-151867 discloses the following. Such a configuration is disclosed.
That is, the ink cartridge and the sub tank are connected with a supply tube, and the supply tube is provided with a tube pump. Inside the sub tank, an expandable / contractible member (bellows), a switch for detecting the displacement of the expandable member, It is comprised from the vertical pipe | tube which supplies ink in a member (bellows). There are two switches in the sub tank and they are arranged up and down. Furthermore, a spring that urges the bellows in the extending direction is provided inside the sub tank. When bubbles (air) accumulate in the storage chamber in the extendable member, the tube pump sends liquid from the sub tank toward the ink cartridge, and moves the bubbles (air) inside to the cartridge. At this time, when the negative pressure in the storage chamber increases and the telescopic member contracts by a predetermined amount, the displacement is detected by a switch. When the switch is detected, the tube pump rotates in the reverse direction, and the ink is fed from the cartridge into the sub tank.

  With this technology, when a tube with a large internal volume (long tube or tube with a large inner diameter) is used, the tube pump rotates backward to return the bubbles in the sub tank to the cartridge, but before the bubbles reach the cartridge. In addition, the elastic member in the sub tank is recessed by a predetermined amount, resulting in an overnegative pressure. When the subtank reaches an overnegative pressure, air bubbles enter from the nozzle, preventing normal discharge. In order to prevent this, even if the rotation direction of the pump is switched before the overnegative pressure is reached, there is a problem that the bubbles are reciprocated in the tube and the sub tank, and the effect of discharging the bubbles cannot be obtained. Furthermore, in this technique, since the expansion / contraction member is included in the sub tank, there is a problem that the assembling property is poor.

  Therefore, the present invention realizes an ink ejection apparatus and an image forming apparatus that can eliminate the effect of pressure increase due to bubbles generated in the supply path without using a complicated control mechanism and wastefully consuming ink. The purpose is to do.

  The liquid droplet ejection apparatus and the image forming apparatus of the present invention include a recording head having a nozzle for ejecting liquid droplets, a sub tank that stores liquid supplied to the recording head, a liquid tank that stores the liquid, and the liquid tank. And a supply channel that communicates between the sub-tanks, and a liquid-feeding unit that is interposed in the supply channel, wherein the liquid-feeding unit includes a first direction from the liquid tank to the sub-tank, and from the sub-tank. The liquid tank can be fed in both directions of the second direction, and the supply channel has at least one flexible membrane on the side opposite to the direction of gravity, and the flexible membrane passes through the supply channel. A spring urging from the inside toward the outside, and when the liquid feeding means feeds the liquid in the first direction, the flexible membrane swells from the outside of the supply flow path, and the liquid feeding means When the liquid is fed in the second direction, Sex film recessed inwardly from an outer side of the supply passage, the liquid feeding means repeats the liquid feed of the first direction to the second direction.

  The liquid droplet ejection apparatus and the image forming apparatus of the present invention include a recording head having a nozzle for ejecting liquid droplets, a sub tank that stores liquid supplied to the recording head, a liquid tank that stores the liquid, and the liquid. A supply flow path communicating between the tank and the sub tank; and a liquid feed means interposed in the supply flow path, wherein the liquid feed means includes a first direction from the liquid tank to the sub tank, and the sub tank. To the liquid tank in the second direction, and the supply flow path is integrated with at least one flexible membrane on the side opposite to the direction of gravity and on the outside of the flexible membrane. And a biasing spring that biases the pressure receiving plate outside the supply flow path. When the liquid feeding means feeds the liquid in the first direction, The flexible membrane swells from the outside of the supply channel. When the liquid feeding means sends the liquid in the second direction, the flexible membrane is recessed inward from the outside of the supply flow path, and the liquid feeding means has the first direction and the first direction. Repeat feeding in the direction of 2.

  According to the present invention, it is possible to remove the influence of pressure increase due to bubbles generated in the supply path with a simple configuration.

1 is a diagram showing an ink jet recording apparatus as an embodiment of an image forming apparatus according to the present invention. Schematic diagram of ink supply system and maintenance / recovery system of the apparatus of FIG. The figure for demonstrating the exhaust_gas | exhaustion operation | movement of the apparatus of FIG. The figure for demonstrating about the installation interval of a bubble reservoir The figure about the pressure in the sub-tank and the liquid feed amount of the liquid feed pump The figure which shows Example 2 of this invention which has provided the film | membrane 2 of the bellows structure instead of the bubble reservoir shown in FIG. The figure which shows Example 3 of this invention which installed the spring inside the tube The figure which shows an example of a structure of the liquid feeding pump which can be used in each Example of this invention The figure which similarly shows an example of a structure of a liquid feeding pump Flowchart for explaining a control sequence that can be employed in each of the above-described embodiments. The figure which shows the structure of the bubble storage part of the further another Example of this invention with which the supply tube was integrally formed for every color kind. The figure which shows the structure provided with the supply tube which connects a subtank, an ink cartridge, and both in the upstream of a recording head in an ink supply direction.

  For this purpose, a liquid supply pump capable of normal rotation and reverse rotation is provided in a supply tube communicating between the sub tank and the ink cartridge, and the supply tube is made of a flexible film material on the opposite side to the direction of gravity. This is achieved by providing the bubble reservoirs at regular intervals and providing the bubble reservoirs with springs that bias the tube from the inside to the outside.

That is, as shown in FIG. 12, on the upstream side of the recording head in the ink supply direction, the sub-tank 101 for storing the liquid to be supplied to the recording head, the ink cartridge 76 that is a liquid tank for storing the liquid, and the supply flow that connects the two A liquid supply tube 16 (hereinafter simply referred to as supply tube 16) serving as a path is provided. Further, a liquid feed pump 81 as a liquid feed means is interposed in the supply tube 16. The supply tube 16 has bubble reservoirs 200 formed at regular intervals in the direction opposite to the direction of gravity (the direction in which buoyancy acts). Further, the bubble reservoir provided in the supply tube 16 is urged by a spring 201 from the inside to the outside of the supply tube 16. In the figure, 8 is a recording material such as paper, 30 is an apparatus main body, 50 is a cap, 51 is a maintenance / recovery pump, 76 is an ink cartridge, and 125 to 127 are conveying rollers.

The behavior is
1) When sending bubbles in the sub tank 101 to the cartridge 76:
The liquid feeding pump 81 moves the air bubbles to the cartridge 76 by repeating the liquid feeding operation in the first direction A direction (forward rotation) and the second direction B direction (reverse rotation). Specifically, first, the liquid feed pump P is driven in the A direction, and the bubbles in the sub tank 101 are moved in the direction of the cartridge 76. When the liquid feed pump 81 is continuously driven in the A direction, the negative pressure in the supply tube 16 increases, the bubble reservoir 200 provided in the tube 16 is recessed by the negative pressure, and is deformed inside the tube. The bubbles move toward the cartridge 76 by the flow created by the liquid feed pump 81P. Then, when the negative pressure in the sub tank 101 becomes smaller than a predetermined value, that is, before the over negative pressure is reached, the liquid feed pump 81 is driven in the B direction. This is because if an overnegative pressure is reached, bubbles will eventually flow in from the nozzle, and the bubbles will enter the sub tank 101 again despite being removed from the sub tank 101. Another reason is that normal discharge cannot be performed by blocking the nozzles with bubbles.
As a result, the pressure in the sub tank 101 and the tube 16 recovers from the negative pressure to the atmospheric pressure direction, and the bubble reservoir 200 swells due to the urging force of the spring 201. The bubbles in the tube 16 return to the sub tank 101 direction when the liquid feed pump 81 is driven in the B direction, but do not reverse any further by entering the nearest bubble reservoir 200. . When the liquid feed pump 81 is driven again in the direction A, the flexible film 202, which is a flexible film, is recessed, the bubble advances in the direction of the cartridge 76, and the negative pressure becomes smaller than a predetermined value. The drive of the pump 81 is switched in the B direction. By repeating this liquid feeding operation, the bubbles can be sequentially moved toward the cartridge 76 and finally stored in the cartridge 76. The bubble reservoirs 200 are provided at regular intervals.
2) When supplying ink:
The liquid feed pump 81 is driven in the B direction (forward rotation), and the ink stored in the cartridge 76 is fed to the sub tank 101.

  With the above operation, bubbles in the tank are exhausted without wasting ink and without complicated assembly of the sub tank 101. That is, the bubbles staying in the sub tank 101 can be transferred to the cartridge 76 without discarding the ink, the pressure increase due to the bubbles can be prevented in a high temperature environment, and the negative pressure in the sub tank 101 is not broken. Furthermore, since complicated components are not required for the sub tank 101, the assemblability is not deteriorated.

<Example 1>
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing an ink jet recording apparatus (hereinafter referred to as an ink jet printer) as an embodiment of an image forming apparatus according to the present invention. 1A shows a front view of the ink jet printer, FIG. 1B shows a right side view, and FIG. 1C shows a plan view. In this printer, a carriage 120 is slidably held in a main scanning direction (longitudinal direction of the guide rod) by a guide rod 122 and a guide rail 128 which are guide members horizontally mounted on the left and right side plates 123L and 123R.

  The carriage 120 is moved and scanned in the longitudinal direction (main scanning direction) of the guide rod 122 by a main scanning motor and a timing belt (not shown). On the carriage 120, the recording head 1 that ejects ink droplets of a plurality of colors (for example, yellow (Y), cyan (C), magenta (M), black (Bk), etc.) crosses the main scanning direction. And are mounted with the ink droplet ejection direction facing downward.

  The recording head 1 is of a thermal type that obtains a discharge pressure by ink film boiling. There are various types of recording heads, such as those that use a piezoelectric element to deform the diaphragm or deform the diaphragm with an electrostatic force to obtain the discharge pressure. can do. A sub tank 101 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 1. The term “integral” as used herein includes not only one that is literally unitary in structure but also one in which the recording head 1 and the sub-tank 101 are connected by a tube, tube, etc., both of which are mounted on the carriage together. It means that.

  A supply tube 16 is connected to the sub tank 101, and the other end of the supply tube 16 is connected to a cartridge holder 77 that is stationary on the main body. Inside the cartridge holder 77 is a liquid feed pump 81 for supplying ink, and the supply tube 16 is connected to the liquid feed pump 81 in the cartridge holder. One end of the liquid feed pump 81 is connected to the ink cartridge 76. Therefore, the recording head 1, the sub tank 101, the liquid feed pump 81, and the ink cartridge 76 are in communication.

  FIG. 2 shows a schematic diagram of an ink supply system and a maintenance recovery system of the apparatus of FIG. The ink cartridge 76 communicates with the liquid feed pump 81 and the sub tank 101 through the supply tube 16. The liquid feed pump 81 supplies the ink stored in the ink cartridge 76 in the direction of arrow A, that is, to the sub tank 101 by the forward rotation operation. On the other hand, the liquid feed pump 81 can feed the fluid in the sub tank 101 to the direction of the arrow B, that is, the ink cartridge 76 by the reverse rotation operation. In FIG. 2, the sub tank 101, the ink cartridge 76, and the supply tube 16 are one type, but there may be a plurality of types depending on the color type of ink to be used.

  The recording head 1 is used for moisture retention and suction for the purpose of sucking ink in the recording head 1 when the nozzle is clogged by removing bubbles from the recording head 1 at the same time as preventing moisture drying of the ink when not ejecting. A cap 50 is provided. When the ink in the recording head 1 is sucked, the cap 50 is capped on the ink discharge surface of the recording head 1, and the ink is guided to the waste liquid tank 52 by the maintenance / recovery pump 51. The cap 50 may serve not only as a suction operation but also as an idle discharge receiver from the recording head 1. The wiper blade 71 is attached to the wiping unit 70, and the wiper blade 71 wipes the ink discharge surface of the recording head 1 after maintenance, thereby adjusting the meniscus of the ink discharge surface.

FIG. 3 is a view for explaining the exhaust operation of the apparatus of FIG. 1, and FIG. 3 (A) shows a state in which bubbles 300 are retained in the sub tank 101 in the supply system.
In this state, when the ink jet printer including the sub tank 101 is placed in a high temperature environment, the bubbles 300 try to expand, but the expansion rate of the bubbles (air) is larger than the expansion rate of the ink in the sub tank 101. Bubbles cannot expand and pressure rises. As a result, the pressure in the sub tank 101 increases and the negative pressure formed in the sub tank 101 is broken. When the negative pressure in the sub tank 101 rises to an atmospheric pressure from a certain range, normal ink ejection cannot be performed. Therefore, when the bubbles 300 stay in the sub tank 101 more than a predetermined amount, it is necessary to discharge the bubbles 300 inside. As a method of discharging the bubbles in the sub tank 101, there is a choke method. Therefore, the ink in the ink cartridge 76 is pressurized, a valve is provided in the supply tube 16, the nozzle arrangement surface of the recording head 1 is capped with the valve closed, and the pressure in the sub tank 101 is lowered by the maintenance / recovery pump 51. Then, by opening the valve thereafter, the bubbles in the sub tank 101 are discharged from the recording head at a stretch by a large pressure difference. In the case of this method, the pressure difference is increased and the flow velocity is increased, so that a large amount of ink that can be used for normal printing is discarded. Therefore, in this embodiment, the bubble reservoir 200 that temporarily stores the bubbles 300 is provided on the side opposite to the gravity direction of the supply tube 16.

  3 (B) and 3 (C) are enlarged views of the bubble reservoir 200 shown in FIG. 3 (A). The bubble reservoir 200 uniformly transmits to the film 202 a flexible film 202 that can be deformed by a pressure difference, a spring 201 that urges the film 202 from the inside of the supply tube 16 to the outside, and a biasing force of the spring. Plate 205 for the purpose.

Next, the exhaust operation of the apparatus of the present embodiment will be described with reference to FIGS. 3 (B) and 3 (C).
When bubbles 300 are mixed in the sub tank 101, the liquid feed pump 81 is driven in the direction of arrow A, opposite to the direction of arrow B for supplying normal ink. By this driving, the negative pressure in the supply tube 16 becomes larger as shown in FIG. 3B, and the flexible film 202 of the bubble reservoir 200 is recessed inside the supply tube 16. In addition, in order for the flexible film 202 to dent reliably, the spring force of the urging spring 201 in the bubble reservoir 200 is greater than the force obtained by the product of the negative pressure in the tube and the area of the flexible film 202. Set smaller.

  By driving the liquid feed pump 81 in the direction of arrow A, the bubbles 300 in the sub tank 101 move in the direction of the cartridge 76 through the supply tube 16. When the liquid feed pump 81 continues to be driven in the direction of arrow A, the pressure in the sub tank 101 continues to decrease, and the negative pressure eventually increases excessively. As a result, air is mixed into the sub tank 101 from the ink discharge nozzles. In order to prevent this, the liquid feed pump 81 is once driven in the arrow B direction. When the liquid feed pump 81 is driven in the arrow B direction, the pressure in the supply tube 16 that has been lowered increases (increases in the atmospheric pressure direction). As a result, as shown in FIG. 3C, the flexible film 202 of the bubble reservoir 200 swells and swells to a position higher than the flow path of the supply tube 16.

  Since the bubble reservoir 200 swells, even if the liquid feed pump is driven in the direction of arrow B, the bubble 300 rises by its own buoyancy at the bubble reservoir 200 as indicated by the dashed arrow. Even if the liquid feed pump 81 is driven in the direction of arrow B and a flow is generated toward the sub tank 101, the bubbles 300 that have risen in the bubble reservoir 200 do not move from the bubble reservoir 200 toward the sub tank 101. This is because the bubble 300 is at a position higher than the flow path of the supply tube 16 due to its own buoyancy, and does not flow down from that position even when the liquid feed pump 81 is driven. That is, the bubble reservoir 200 can trap the bubbles 300 so as not to flow in the direction of arrow A. Therefore, when the liquid feed pump 81 is driven in the direction of the arrow A and the pressure of the ink in the sub tank 101 is lowered to a certain value, it is driven again in the direction of the arrow B, so that it is within a certain range in the sub tank 101. Only the bubbles 300 can be returned to the ink cartridge 76.

  3C, the urging force of the spring 201 can be transmitted to the entire surface of the flexible film 202, so that the plate 205 is sandwiched between the spring 201 and the flexible film 202. It is desirable. The plate 205 may be bonded to the flexible film 202 and operate integrally.

  The ink cartridge 76 may be a flexible bag or a tank on a bottle. However, even if the bubble 300 expands in the cartridge 76, the pressure does not increase extremely, so that a certain volume is required for the bubble reservoir. Alternatively, even if the liquid supply pump 81 is a system in which the supply tube 16 is crushed and the flow path is closed like a tube pump, for example, even if the bubbles returned to the ink cartridge 76 expand and the pressure rises, It is possible to prevent the influence from being transmitted to the sub tank 101.

  As described above, in this embodiment, the air bubbles 300 stored in the sub tank 101 are reliably transported to the ink cartridge without discarding the ink that can be originally used and without requiring complicated components in the sub tank 101. It is possible to prevent an increase in pressure in the sub-tank 101 due to expansion of bubbles.

  In order to detect that the bubble 300 has accumulated in the sub tank 101, it is desirable to attach a sensor to the sub tank 101. For example, as shown in FIG. 3D, there is a method in which the electrode pin 150 is installed and the staying state of the bubble 300 is detected from the change in electrical resistance between the ink and the bubble (air). Note that the detection method is not limited to this method, and it is sufficient that the retention of the bubbles 300 can be detected. If the device for detecting the retention of the bubbles 300 is provided, the bubbles 300 can be returned to the ink cartridge 76 at an appropriate timing, so that the pressure in the sub tank 101 can be maintained. Alternatively, the effect of the present invention can be obtained even if the bubble discharge sequence is automatically activated after a predetermined elapsed time without providing the detection sensor. The top surface of the sub tank 101 that opposes the gravitational direction is preferably provided with an inclination so that the bubbles 300 gather in one place and efficiently flow into the supply tube 16 as shown in FIG.

FIG. 4 is a view for explaining the installation interval of the bubble reservoirs.
When the volume of the sub tank 101 is large or the supply tube is short, it is sufficient that only one bubble reservoir 200 is provided in the supply tube 16. However, since the sub tank 101 of a general serial printer has a small internal volume, bubbles If there is one or a few reservoirs 200 on the supply tube, the liquid feed pump 81 is driven in the direction of arrow A, and before the bubbles 300 reach the bubble reservoir 200, the negative pressure becomes a predetermined value or more. There is a risk that. Therefore, the bubble reservoirs 200 shown in FIG. 4 are provided at regular intervals L so that the negative pressure of the sub tank 101 does not become an overnegative pressure.

  With this configuration, even in the sub-tank 101 having a small volume, the ink cartridge 76 sequentially repeats the driving of the liquid feed pump 81 in the A direction and the B direction in accordance with the above-described principle. Can be returned to. That is, regardless of the volume of the sub tank 101, even if the sub tank 101 is small, the bubbles 300 can be discharged from the sub tank 101 without wasting any ink. Therefore, the effect of the present invention is great. Incidentally, the constant interval L shown in FIG. 4 represents the distance between the bubble reservoirs 200. If the bubble 300 cannot move to the next bubble reservoir 200, the bubble 300 only moves in the supply tube 16 while the liquid feed pump 81 is driven in the direction of the arrow B and the arrow A, and is transferred to the ink cartridge. The exhaust effect to 76 cannot be obtained. Therefore, this fixed interval L ensures that the bubble 300 is in the next bubble reservoir 200 in the direction of the ink cartridge 76 from when the liquid feed pump 81 is driven in the direction of arrow B to when it is driven in the direction of arrow A. Must be designed to reach.

FIG. 5 is a diagram regarding the pressure in the sub tank 101 and the amount of liquid fed by the liquid feed pump, and FIG. 5A shows an example of the sub tank 101.
A flexible film 210 is provided on the side surface of the sub tank 101, and an urging spring 212 for urging the flexible film 210 from the inside of the sub tank 101 to the outside is provided. A negative pressure is formed in the sub tank 101 by the spring force of the biasing spring 212. The filler 211 is in contact with the flexible film 210, and the pressure in the sub tank 101 is set as the displacement of the flexible film 210. Furthermore, the filler 211 is attached to increase the amount of displacement. By detecting the displacement of the filler 211 by the detection unit 213, the pressure in the sub tank 101 can be detected.

  FIG. 5B shows driving of the liquid feed pump 81 with respect to the pressure change in the sub tank 101. The vertical axis indicates the pressure in the sub tank 101, and the range between the upper limit value and the lower limit value is an appropriate negative pressure range of the sub tank. The horizontal axis indicates time. Now, when the liquid feed pump 81 is driven in the direction of arrow B, the volume in the sub tank 101 decreases and the pressure decreases. This pressure is read by the displacement of the filler 211, and the liquid feed pump 81 is driven until the time when the lower limit value is reached (time B in FIG. 5B). An appropriate negative pressure range can be maintained by driving the liquid feed pump 81 while detecting the pressure in the sub tank 101. Thereafter, by driving the liquid feed pump in the direction of arrow A, the pressure in the sub tank 101 is returned to the upper limit value.

  Thus, by detecting the pressure in the sub tank 101 and driving the liquid feed pump until the pressure reaches the lower limit value / upper limit value, it is possible to prevent the proper negative pressure from being broken during the bubble discharging operation. . Furthermore, it is not necessary to form a negative pressure again after the bubble discharging operation. Therefore, such control is effective. Note that the pressure detection in the sub tank 101 shown in FIG. 5A is not limited to the filler 211. For example, a pressure sensor may be incorporated, or the displacement of the flexible film 210 may be detected by an optical sensor. good.

<Example 2>
FIG. 6 is a diagram for explaining another embodiment. In this embodiment, a bellows structure film 207 is provided instead of the bubble reservoir 200 shown in FIG. The flexible film tends to have a bias with respect to the deformation (swelling or shrinking) of the film, and it may be difficult to have a certain deformation behavior. If the manner of deformation changes and the film tilts, it is also conceivable that the bubble 300 cannot be trapped reliably in the bubble reservoir 200. Therefore, in this embodiment, as shown in FIG. 6, a bellows structure film 207 is used instead of the flexible film. By adopting the bellows structure, the deformation becomes constant, the unexpected deformation of the film can be prevented, and the function of bubble accumulation can be surely provided. The material for the bellows structure may be an elastically deformable elastomer instead of a film.

<Example 3>
FIG. 7 is a diagram illustrating still another embodiment of the present invention. 3 has a configuration in which the spring 201 is provided inside the supply tube 16, but in this configuration, the spring is installed inside the tube, and the assemblability may be poor. Therefore, in this embodiment, the spring 201 is installed outside the flexible film 202 as shown in FIG.

  FIG. 7B shows a state in which the liquid feed pump 81 is driven in the direction of arrow B to move the ink in the supply tube 16 toward the sub tank 101. The pressure receiving plate 208 is attached integrally with the flexible film 202, and the spring 202 further urges the pressure receiving plate 208 in the arrow α direction. By this urging force, the flexible film 202 swells and the bubbles 300 can be trapped.

  FIG. 7A shows a state in which the liquid feed pump 81 is driven in the arrow A direction. When driven in the direction of arrow A, the flexible film 202 is recessed, and the pressure receiving plate 208 is also recessed accordingly. As a result, the bubble 300 can move in the cartridge direction without being trapped by the bubble reservoir 200. With the configuration as described above, the same operation as the operation of the bubble reservoir 200 so far can be realized, the spring 201 can be assembled outside the supply tube 16, and the assembly efficiency can be improved.

<Ink cartridge>
FIG. 8 is a diagram for explaining an ink cartridge that can be used in each of the above-described embodiments. The cartridge 76 shown in FIG. 8 is provided with electrode pins 151 for detecting the remaining amount of ink. Furthermore, an air opening 209 is provided in order to lower the liquid level due to ink consumption. The atmosphere opening port 209 is preferably in an elongated shape in order to prevent water evaporation of ink, and is generally provided in a labyrinth shape on the side surface of the cartridge.

  In this embodiment, the air bubbles mixed in the sub tank 101 are returned into the ink cartridge 76, and then the ink and air are separated in the ink cartridge 76. FIG. 8A shows a state where a large amount of ink 500 remains in the ink cartridge 76. When the liquid feed pump 81 is driven in the direction of arrow A and the bubble 300 reaches the ink cartridge 76, the bubble 300 rises to the upper surface of the ink cartridge 76 by buoyancy. Therefore, ink and air are separated.

  FIG. 8B shows a state where the amount of ink is small. When the amount of ink 500 becomes small, the liquid level drops and the lower end of the electrode pin 151 and the liquid level are separated. At this time, it is determined that there is no remaining ink, and the driving of the liquid feed pump 81 is stopped. With the above control operation, when the ink 500 stored in the ink cartridge 76 is exhausted with the number of printed sheets, the liquid feed pump 81 drives the air in the cartridge in the B direction, so that the direction of the supply tube 16 Can be prevented from being sent to.

  The present invention is not limited to the use of the electrode pins 151, and various means and methods can be adopted for detecting the remaining ink amount in the cartridge.

  Further, the electrode pin 152 is attached to detect that the bubble 300 has surely returned to the ink cartridge 76 when returning the bubble 300 from the sub tank 101 in the cartridge direction. Not only the method of detecting the return of the bubble by the signal from the electrode pin 152 but also the remaining number detecting means such as the electrode pin 151 is not provided, and the number of printed sheets is counted, and the ink in the ink cartridge 76 is determined by the counted number. A method of estimating the remaining amount and stopping the driving of the liquid feeding pump 81 from the estimation result can also be adopted.

<Liquid feed pump>
FIG. 9 is a diagram illustrating an example of a configuration of a liquid feeding pump that can be used in each of the above-described embodiments.
In this example, a motor is prepared for each color type as a pump body and an actuator, and is independently controlled. When the bubble 300 in the sub tank 101 is detected by the electrode pin 150 attached to the sub tank 101 shown in FIG. 3D, the motor in FIG. 9 is driven to draw the bubble 300 into the cartridge.

  In addition, it is desirable for the pump to have a characteristic capable of feeding in the forward direction and the reverse direction. In the case where the ink cartridge 76 is an air communication type as shown in FIG. 8, if atmospheric pressure propagates to the sub tank 101, the pressure in the sub tank 101 increases and normal ejection cannot be performed. Therefore, when the ink cartridge is in communication with the atmosphere, the pump 81 is desirably a pump that can block the flow path, such as a tube pump.

<Control sequence>
FIG. 10 is a flowchart for explaining a control sequence that can be employed in each of the above-described embodiments.
The bubble discharge sequence shown in FIG. 3 is executed when the electrode pin 150 of the sub tank 101 shown in FIG. 3D detects air (bubble) (step S1). It is detected from the electrode pin 151 whether the ink 500 remains in the ink cartridge 76 shown (step S2).

  When it is determined from the signal of the electrode pin 151 that the liquid level of the ink 500 is lower than that of the electrode pin 151, that is, that the ink 500 does not remain in the cartridge 76, the ink is displayed to the user on the main body display (not shown). Replacing the cartridge 76 is prompted (step S9). This is to avoid sending air into the supply tube 16 by performing the forward rotation operation of the liquid pump 81 (the operation of feeding the liquid toward the sub tank 101) in the absence of the ink 500. When the ink 500 is present in the ink cartridge 76, the liquid feed pump 81 is reversely rotated (liquid feed toward the ink cartridge) (step S3).

  At this time, as shown in FIG. 5, if the ink pressure in the sub tank 101 is within the lower limit of the appropriate negative pressure range (step S4), the liquid feed pump is detected while detecting the presence or absence of bubbles with the electrode pin 152 in FIG. 81, when the electrode pin 152 detects air bubbles, the liquid feed pump 81 is reversely rotated only during time t [s] to ensure that the air bubbles enter the cartridge 76 (step S5), and time t [ s] After the passage, the liquid feed pump 81 is stopped (step S6). Since the value of the time t varies depending on the flow path and cross-sectional area of the electrode pin 152 and the cartridge 76 and the flow rate of the liquid feeding pump, it is desirable to obtain an optimal value.

When the liquid feed pump 81 rotates in the reverse direction and the electrode pin 152 does not detect bubbles, it can be determined that the bubbles are in the supply tube 16. Therefore, the liquid feed pump 81 is driven until the pressure in the sub tank 101 reaches the lower limit value (steps S3 and S4). When the pressure in the sub tank 101 reaches the lower limit value, the drive of the liquid feed pump 81 is switched to rotate forward (step S7). The liquid feed pump 81 is continuously driven until the pressure in the sub tank 101 reaches the upper limit value (steps S7 and S8), and when the upper limit value is reached, the liquid feed pump 81 is reversely rotated again (step S3). Note that when the liquid feed pump 81 is rotating forward, bubbles do not flow toward the ink cartridge 76. Therefore, at this time, it is not necessary to detect the presence or absence of bubbles in the electrode pin 152 immediately before the ink cartridge 76.
The control flow described above is an example, and the operation of the present invention is not limited to this control flow.

<Example 4>
FIG. 11 is a diagram for explaining still another embodiment of the present invention, and shows the configuration of the bubble reservoir 200 when the supply tube 16 is integrally formed for each color type. The bubble reservoir 200 is formed on the side opposite to the direction of gravity, that is, in the direction in which buoyancy is applied to the bubble 300. If a plurality of supply tubes are formed in a vertical row as in the case of a general inkjet printer, the bubble reservoir 200 cannot be provided. Therefore, as shown in FIG. 7A, the present invention can be applied even if the plurality of supply tubes 16 are integrally formed by arranging the supply tubes 16 obliquely and configuring the bubble reservoirs 200. . As shown in FIG. 7B, the bubble reservoirs 200 can be provided by alternately arranging the supply tubes 16 for each color. Therefore, even when a plurality of supply tubes 16 are integrally formed for each color, this can be implemented.

  The present invention is not limited to the embodiments described above, and many variations are possible by those having ordinary knowledge in the art within the technical idea of the present invention.

1: Recording head 101: Sub tank 16: Liquid supply tube (supply tube)
30: Device main body 50: Cap 51: Maintenance / recovery pump 52: Waste liquid tank 70: Wiping unit 71: Wiper blade 76: Ink cartridge 77: Cartridge holder 81: Liquid feed pump 120: Carriage 122: Guide rods 123L, 123R: Side plate 125 127: Conveying roller 128: Guide rail 150: Electrode pin 200: Bubble reservoir 201: Spring 202: Flexible film 205: Plate 207: Bellows structure film 208: Pressure receiving plate 209: Atmospheric opening 210: Flexible Film 211: Filler 212: Energizing spring 213: Detection unit 300: Bubble 500: Ink L: Space between bubble reservoirs

JP 2007-230041 A

Claims (8)

A recording head having nozzles for discharging droplets;
A sub tank for storing liquid to be supplied to the recording head;
A liquid tank for storing the liquid;
A supply flow path communicating between the liquid tank and the sub tank;
Liquid feeding means interposed in the supply flow path;
With
The liquid feeding means includes a first direction from the liquid tank to the sub tank,
Liquid can be fed in both directions of the second direction from the sub tank to the liquid tank;
The supply channel has at least one flexible membrane on the side opposite to the direction of gravity, and a spring that biases the flexible membrane from the inside to the outside of the supply channel,
When the liquid feeding means sends the liquid in the first direction, the flexible membrane swells from the outside of the supply flow path,
When the liquid feeding means sends the liquid in the second direction, the flexible membrane is recessed more inside than the outer side of the supply flow path, and the liquid feeding means has the first direction and the second direction. A droplet discharge device characterized by repeating liquid feeding in a direction.   The droplet discharge device according to claim 1, further comprising a plate that operates integrally with the flexible membrane between the flexible membrane and the spring.   The droplet discharge device according to claim 1, wherein the flexible film and the spring are provided at a constant interval between the sub tank and the liquid tank.   4. The volume of the liquid fed by the liquid feeding means in the second direction is a volume until the pressure in the sub tank drops to a predetermined value. 5. The liquid droplet ejection apparatus described.   The droplet discharge device according to claim 1, wherein the flexible film has a bellows structure. A recording head having nozzles for discharging droplets;
A sub tank for storing liquid to be supplied to the recording head;
A liquid tank for storing the liquid;
A supply flow path communicating between the liquid tank and the sub tank;
Liquid feeding means interposed in the supply flow path;
With
The liquid feeding means includes a first direction from the liquid tank to the sub tank,
Liquid can be fed in both directions of the second direction from the sub tank to the liquid tank;
The supply flow path has at least one flexible membrane on the side opposite to the direction of gravity, and a pressure receiving plate attached integrally to the outside of the flexible membrane, and further, the outside of the supply flow channel A biasing spring for biasing the pressure receiving plate;
When the liquid feeding means sends the liquid in the first direction, the flexible membrane swells from the outside of the supply flow path,
When the liquid feeding means sends the liquid in the second direction, the flexible membrane is recessed more inside than the outer side of the supply flow path, and the liquid feeding means has the first direction and the second direction. A droplet discharge device characterized by repeating liquid feeding in a direction.   The droplet according to any one of claims 1 to 6, wherein the supply path is configured integrally with a plurality of paths, and a side opposite to the gravity direction of each supply path does not overlap with another supply path. Discharge device. An image forming apparatus comprising: means for recording an image on a recording medium; and the droplet discharge device according to claim 1.