JP5210599B2 - Image recording device - Google Patents

Description

The present invention relates to an image recording equipment to remove bubbles in Lee ink supply path.

  As a conventional inkjet image recording apparatus, for example, a recording medium such as recording paper or OHP paper is transported by a recording medium transporting means, and ink is ejected from a plurality of nozzles provided in the recording head. It is known to form an image of image quality. In such an image forming apparatus, if air bubbles are stagnated in a part of the ink supply path for supplying ink to the recording head, the ink ejection failure or the ink ejection direction is bent, resulting in a decrease in image quality. Invite.

  As a method for solving such a problem, the following Patent Document 1 is disclosed. The droplet discharge device of Patent Document 1 includes a recording head, a reservoir tank that stores ink to be supplied to the recording head, and a first ink channel and a second ink channel that communicate the recording head and the reservoir tank. In addition, by providing a pump in the first ink flow path, the ink can be circulated between the recording head and the reservoir tank. Further, the first ink flow path is formed with a bypass flow path having an open valve that bypasses the upstream side in the circulation direction and the downstream side in the circulation direction with the pump interposed therebetween.

The bubble removing method of the droplet discharge apparatus configured as described above removes bubbles in the ink flow path by controlling on / off of the driving of the pump and opening / closing of the opening / closing valve.
JP 2007-69419 A

  However, in Patent Document 1, it is necessary to form a bypass channel in order to remove bubbles in the ink supply path. For this reason, not only the ink supply path becomes complicated, but also an on-off valve must be provided in the bypass flow path, which is disadvantageous in terms of cost.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an image recording apparatus capable of removing bubbles in an ink supply path with a simple configuration and a maintenance method thereof.

That is, an image recording apparatus according to the present invention includes an image recording unit having a recording head that discharges ink from a nozzle to record an image on a recording medium, and a position above the nozzle surface of the recording head on which the nozzle is formed in the direction of gravity. An upper tank that stores the ink to be supplied to the recording head, a first valve that is provided in the upper tank and communicates with or shuts off the atmosphere in the upper tank, and the recording A lower tank that is disposed below the nozzle surface of the head on which the nozzle is formed and that is not ejected by the recording head, is provided in the lower tank, and communicates with the atmosphere in the lower tank. Or a second valve for shutting off, a pressure adjusting unit provided in the lower tank for adjusting the pressure in the lower tank, and stored in the lower tank A pump for sending ink to the upper tank; and an ink circulation system for flowing the ink from the upper tank in the order of the image recording unit and the lower tank, and returning the ink to the upper tank again. In the mode of circulating the ink, in order to perform image recording by the image recording unit, the first valve is opened and the second valve is kept closed, and the nozzle of the recording head is used. A first circulation mode in which the pressure in the lower tank is maintained at a constant negative pressure by the pressure adjusting unit so that the pressure becomes a pressure at which the ink can be discharged, and bubbles stagnating in the ink circulation system are removed. Therefore, in the first circulation mode state, at least an opening / closing operation for opening / closing the first valve, an opening / closing operation for opening / closing the second valve, or the pressure adjusting unit. Having a second circulation mode in which any one of the operation of the variable operation for varying the pressure in the lower tank.

According to the present invention, it is possible to provide an image recording equipment capable of removing bubbles in the ink supply path with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, a first embodiment of the present invention will be described with reference to FIGS.

  In the following description, in the drawing, the conveyance direction of the recording medium is the X-axis direction or the sub-scanning direction, and the direction orthogonal to the conveyance direction is the Y-axis direction, the main scanning direction, or the width direction of the recording medium. . In addition, a direction orthogonal to the X-axis and Y-axis directions is defined as a Z-axis direction or a vertical direction.

  FIG. 1 is a schematic sectional view of an image recording apparatus in the first embodiment of the present invention.

  In FIG. 1, an image recording apparatus 10 includes a paper feeding unit 11, a paper transport unit 12, an image forming unit 13, a paper discharge unit 14, a maintenance unit 15, an ink bottle unit 16, an upper tank 17, a lower tank 18, and a circulation. A pump 19, a waste liquid bottle 20, and a control unit 21 are included. The image recording apparatus 10 forms an ink circulation system in which ink is circulated by an image forming unit 13, an upper tank 17, a lower tank 18, a circulation pump 19, and an ink circulation path connecting the respective.

  First, conveyance of the recording medium and image recording will be described.

  The paper feed unit 11 includes a paper feed stand 25 and a pickup roller 26.

  For example, cut sheets as recording media are stacked on the paper feed tray 11. The pickup roller 26 picks up the recording media stacked on the paper feed tray 11 one by one and conveys the recording medium to the paper conveying unit 12.

  The paper transport unit 12 includes a registration roller 29, a roller 30, a transport belt 31, a platen 32, and a suction fan 33.

  The registration roller 29 corrects the conveyance posture of the recording medium conveyed by the pickup roller 26 and adjusts the timing to convey the recording medium to the conveyance belt 31. The conveyor belt 31 is formed in an endless belt shape and is provided with a large number of holes. The conveyor belt 31 is held in a state where tension is applied by, for example, three rollers 30. Note that a conveyance motor 80 described later is connected to at least one of the rollers 30, and the conveyance belt 31 moves by driving the conveyance motor 80.

  A platen 32 and a suction fan 33 are provided below the conveyor belt 31. The platen 32 is processed so that at least a region facing the image forming unit 13 is a flat surface, and a large number of holes are formed. The suction fan 33 sucks air from the many holes of the conveying belt 31 through the many holes of the platen 32. As a result, the recording medium conveyed from the registration roller 29 is attracted onto the conveyance belt 31 and conveyed downstream at a predetermined conveyance speed.

  The image forming unit 13 is provided to face the paper conveying unit 12. The image forming unit 13 includes head units 35, 36, 37, and 38 that discharge black (K), cyan (C), magenta (M), and yellow (Y) inks. The unit 35, the head unit 36 are referred to as a C color head unit 36, the head unit 37 is referred to as an M color head unit 37, and the head unit 38 is referred to as a Y color head unit 38), and ink of each color is distributed to the head units 35 to 38. Distribution tanks 40, 41, 42, 43 (hereinafter, distribution tank 40 is K color distribution tank 40, distribution tank 41 is C color distribution tank 41, distribution tank 42 is M color distribution tank 42, and distribution tank 43 is Y color distribution tank. 43) and recovery tanks 76, 7 for recovering ink that has not been ejected from the head units 35, 36, 37, 38. 78, 79 (hereinafter, the recovery tank 76 is referred to as a K color recovery tank 76, the recovery tank 77 is referred to as a C color recovery tank 77, the recovery tank 78 is referred to as an M color recovery tank 78, and the recovery tank 79 is referred to as a Y color recovery tank 79). The head unit holding member 44 holds at least each of the head units 35 to 38.

  Each head unit 35, 36, 37, 38 is held by a head unit holding member 44 so as to be equal to or larger than the width of the recording medium in a direction orthogonal to the transport direction. In the present embodiment, each head unit 35, 36, 37, 38 is configured to have a width equal to or greater than the width of the recording medium by arranging six short recording heads in a staggered manner.

  2A and 2B show a configuration of a short recording head, in which FIG. 2A is an external perspective view, FIG. 2B is a perspective view showing a nozzle surface, and FIG. 2C is a cross-sectional view. 2 shows only one short recording head of the K-color head unit 35, but the other short recording heads and the other head units 36, 37, and 38 have the same configuration. The description will be omitted as referring to the K-color head unit 35.

  The short head includes a nozzle plate 46 on which nozzles 45 are formed, and a mask plate 47 for protecting the nozzle plate 46. As shown in FIG. 2C, the structure in the vicinity of the nozzle 45 of this short recording head is composed of a channel 49, a piezoelectric element 50, and a nozzle plate 46. By energizing the piezoelectric element 50, the internal volume of the channel 49 varies, and the ink 51 in the channel 49 is ejected from the nozzle 45.

  Each distribution tank 40, 41, 42, 43 is provided to supply ink of a predetermined color to each head unit 35, 36, 37, 38. In other words, in this embodiment, each of the distribution tanks 40, 41, 42, and 43 distributes a predetermined color of ink to six short recording heads.

  The collection tanks 76, 77, 78, and 79 are provided to collect ink that has not been ejected from the head units 35, 36, 37, and 38. That is, in the present embodiment, the collection tanks 76, 77, 78, and 79 collect the ink that has not been ejected from the six short recording heads in one place for each color.

  In the image forming unit 13 configured as described above, when a recording medium is conveyed under the K color head unit 35, the C color head unit 36, the M color head unit 37, and the Y color head unit 38, each short recording is performed. Ink is ejected from the head, and an image is formed on the recording medium.

  The recording medium on which the image is formed by the image forming unit 13 is discharged to a paper discharge stand 54 by a paper discharge roller 53 of the paper discharge unit 14.

  Next, maintenance of each head unit will be described.

  The maintenance unit 15 generates a negative pressure in the suction unit and a known suction unit and wipe blade corresponding to the K color head unit 35, the C color head unit 36, the M color head unit 37, and the Y color head unit 38, respectively. And a negative pressure source 56 connected through a tube (not shown) for maintenance.

  During image formation, as shown in FIG. 1, the maintenance unit 15 is retracted between the head units. On the other hand, at the time of maintenance, as shown in FIG. 3, the paper transport unit 12 is lowered and the maintenance unit 15 is also lowered by a moving mechanism (not shown). Then, the maintenance unit 15 is moved to a maintenance position facing each head unit. Thereafter, the paper transport unit 12 and the maintenance unit 15 are raised again in the Z-axis direction, and maintenance is performed. The surplus ink that has come out during the maintenance is collected into the waste liquid bottle 20 by the negative pressure source 56.

  Next, ink supply to the image forming unit will be described.

  The configuration for supplying ink to the image forming unit 13 includes an ink bottle unit 16, a lower tank 18, an upper tank 17, and a circulation pump 19.

  The ink bottle unit 16 includes a K ink bottle 60, a C ink bottle 61, an M ink bottle 62, and a Y ink bottle 63 for each color. Each ink bottle 60, 61, 62, 63 is connected to the lower tank 18 via a tube (not shown). The lower tank 18 includes a K lower tank 65, a C lower tank 66, an M lower tank 67, and a Y lower tank 68 that store ink supplied from the ink bottle unit 16. The lower tank 18 is connected to a negative pressure adjusting unit 70 for adjusting the pressure in each of the lower tanks 65 to 68 and causing each head unit 35 to 38 to form an appropriate meniscus. The ink in each of the lower tanks 65 to 68 is supplied to the upper tank 17 by a circulation pump 19 via a tube (not shown).

  The upper tank 17 includes a K upper tank 71, a C upper tank 72, an M upper tank 73, and a Y upper tank 74 that store ink supplied from the lower tank 18. The ink in each upper tank 71-74 is supplied to each distribution tank 40-43 via the tube which is not shown in figure, and ink is supplied to each head unit 35-38 from each distribution tank 40-43. The ink that has not been ejected by the head units 35 to 38 is temporarily collected by the collection tanks 76 to 79, and returns from the collection tanks 76 to 79 to the lower tanks 65 to 68.

  Next, the configuration of the control system of the thus configured image recording apparatus will be described with reference to the block diagram of FIG.

  At least the circulation pump 19, the suction fan 33, the conveyance motor 80, the image data receiving unit 83, the moving motor 89, and the suction pump 90 as the negative pressure source 56 are connected to the control unit 21, and via the head driver 81. The head 82 is connected to a solenoid valve 86 and a pressure bellows 87 via a timer 85. The control unit 21 controls the entire control operation of the image recording apparatus 10. The paper supply unit 11, the paper transport unit 12, the image forming unit 13, the paper discharge unit 14, the maintenance unit 15, and the upper tank 17. The lower tank 18 and the circulation pump 19 are controlled, respectively, and control for removing bubbles in the ink circulation path, which will be described later, is performed.

  The circulation pump 19, which will be described in detail later, constitutes a part of the ink circulation system, and is provided for supplying predetermined ink from the lower tank 18 to the upper tank 17. The suction fan 33 is provided for adsorbing the recording medium to the transport belt 31, and the transport motor 80 is connected to at least one of the rollers 30 in order to move the transport belt 31 in a predetermined direction. Driving means.

  The head 82 corresponds to the short recording head of each of the color head units 35 to 38 described above, and is based on data with a waveform sent from the image data receiving unit 83 by the control unit 21 via the head driver 81. Thus, a predetermined voltage, pulse width, and waveform are applied.

  The timer 85 measures the opening / closing timing of the electromagnetic valve 86 and the operation timing of the pressure bellows 87, as will be described in detail later.

  The moving motor 89 is a motor for moving the maintenance unit 15 and the paper transport unit 12 described above. Furthermore, the suction pump 90 is a pump for sucking excess ink remaining on the nozzle surface.

  Next, the ink path of the first embodiment will be described in detail.

  FIG. 5 is a schematic diagram showing the ink path of K ink. In the present embodiment, a circulation path for circulating ink between the K lower tank 65 and the K color head unit 35 is formed.

  In addition, since the same ink path | route is comprised also about other inks, description here is abbreviate | omitted as referring to K ink.

  In FIG. 5, the K ink bottle 60 is always open to the atmosphere via the filter 93. The K ink bottle 60 is connected to the K lower tank 65 via a tube having an electromagnetic valve 86a as an ink supply valve. Then, the K ink in the K ink bottle 60 is supplied to the K lower tank 65 by opening and closing the electromagnetic valve 86a as necessary.

  The circulation path is a first ink path that connects the K lower tank 65 and the K upper tank 71 via the K upper tank 71 and the K distribution tank 40 in order to supply the ink in the K lower tank 65 to the K color head unit. 105, and a second ink path 102 that connects the K color head unit 35 and the K lower tank 65 in order to return the K ink that has not been ejected by the K color head unit 35 to the K lower tank 65. ing. The first ink path 105 connects the K upper tank 71 and the K color head unit 35 via the K distribution tank 40 and the third ink path 103 connecting the K upper tank 71 and the K lower tank 65. The fourth ink path 104 is configured.

  Details of the circulation path will be described. The K ink in the K lower tank 65 is supplied to the K upper tank 71 through the third ink path 103 to which the circulation pump 19 is connected. Here, the K lower tank 65 is disposed to be lower than the nozzle surface of the K color head unit 35 in the direction of gravity. This is because the electromagnetic valve 86b is closed and the electromagnetic valve 86c is opened when the ink is not circulated, but the pressure applied to the nozzle 45 of the K-color head unit 35 at this time is held at a slight negative pressure. It is. By disposing the ink in this way, the K ink does not drip from the nozzle 45 even when the ink is not circulated.

  A negative pressure adjusting unit 70 is connected to the K lower tank 65 via a tube. The negative pressure adjusting unit 70 includes a pressure cavernose 87, a weight 96, a support body 97, an air chamber 98, and an electromagnetic valve 86c that allows the air chamber 98 to be opened to the atmosphere. Has been.

  The pressure bellows 87 is composed of an elastic member having a bellows-like elasticity, and the pressure bellows 87 expands and contracts when the weight 96 is moved (moved up and down) in the direction of arrow A by the support 97. The negative pressure adjusting unit 70 adjusts the pressure (negative pressure) in the air chamber 98 by expanding and contracting the pressure cavernose 87 by the support body 97 with the electromagnetic valve 86c closed. That is, since the negative pressure adjusting unit 70 communicates with the K lower tank 65 via the tube, the pressure (negative pressure) in the K lower tank 65 is adjusted.

  In the K upper tank 71 to which the K ink in the K lower tank 65 is supplied by the circulation pump 19, the liquid level sensor 100 for monitoring the amount of K ink in the K upper tank 71 and the K upper tank 71 can be opened to the atmosphere. An electromagnetic valve 86b is provided. The K upper tank 71 is arranged to be above the nozzle surface of the K-color head unit 35 in the direction of gravity. For this reason, the K ink in the K upper tank 71 flows down to the K color distribution tank 40 through the fourth ink path 104 due to its own weight (natural fall) and the negative pressure of the K lower tank 65. Then, K ink is supplied from the K color distribution tank 40 to each short recording head of the K color head unit 35. The K ink that has not been ejected from the K head unit 35 flows down to the K lower tank 65 via the K color recovery tank 76 and the second ink path 102.

  In this way, in this embodiment, the K ink is circulated from the K lower tank 65 → K upper tank 71 → K color distribution tank 40 → K color head unit 35 → K color collection tank 76 → K lower tank 65. An ink circulation system is configured.

  Next, an ink circulation method of the ink circulation system configured as described above will be described with reference to the flowchart of FIG.

  When this sequence is started, first, the circulation pump 19 is turned on (ON) and driven in step S1. Next, in step S2, the electromagnetic valve 86b is opened, and in the subsequent step S3, the electromagnetic valve 86c is closed. Further, in step S 4, the pressure body 87 is extended by moving the support body 97 downward, and the pressure in the K lower tank 65 is made negative through the air chamber 98. This state is referred to as pressure bellows ON. At this time, the pressure in the vicinity of the nozzle 45 of the K color head unit 35 is a combined pressure of the positive pressure from the K upper tank 71 and the negative pressure in the K lower tank 65, but the pressure in the vicinity of the nozzle 45 becomes a slight negative pressure. Have been adjusted so that. That is, the absolute value of the negative pressure in the K lower tank 65 is adjusted to be larger than the absolute value of the positive pressure in the K upper tank 71. In the present embodiment, the pressure in the vicinity of the nozzle 45 is set to be −0.5 to −2.5 kPa. In addition, although it is possible to eject ink within the above pressure range, it is desirable that the pressure is set to -1.5 kPa.

  Further, the pressure cavernose 87 holds the pressure in the K lower tank 65 constant by the weight 96. In order to stabilize the pressure in the vicinity of the nozzle 45, a geared pump with little pulsation is adopted as the circulation pump 19 in this embodiment. As a result, the ink flows in the direction indicated by arrows B and C without dripping from the nozzle 45, and ink circulation is performed in step S5. When ink is ejected from the K-color head unit 35 by image formation and ink in the ink circulation path is consumed, the liquid level sensor 100 of the K upper tank 71 is turned off. At this time, the electromagnetic valve 86a is opened and ink is supplied from the K ink bottle 60 into the ink circulation path until the liquid level sensor 100 is turned on. In this way, at the time of image formation, a predetermined amount of ink is always filled in the ink circulation path.

  When the ink circulation is stopped, the circulation pump 19 is stopped in step S6. Next, in step S7, the electromagnetic valve 86b is closed, and in step S8, the electromagnetic valve 86c is opened. Then, the pressure bellows 87 is pushed up by moving the support body 97 upward in step S9. This state is referred to as a pressure bellows OFF. Then, the process exits this sequence and shifts to a standby state.

  Next, the maintenance operation of each head unit will be described in detail.

  Each head unit is maintained by the following method after a predetermined time has elapsed or when a predetermined number of images have been formed. In the present embodiment, the pressure purge method is employed for maintenance of each head unit.

  Specifically, in a non-circulation state, that is, when the electromagnetic valve 86b is closed and the electromagnetic valve 86c is open, the pressure bellows 87 is stretched. Then, when the electromagnetic valve 86 c is closed, the pressure bellows 87 is pushed up by the support body 97. As a result, the pressure in the K lower tank 65 and the second ink path 102 is made positive, and the ink is pushed out from the K color head unit 35. The pushed ink is collected by the maintenance unit 15 and is flowed to the waste liquid bottle 20. That is, the nozzle surface of the pushed ink is wiped by the wipe blade, and excess ink remaining on the nozzle surface is sucked by the suction portion communicating with the suction pump 90 as the negative pressure source 56. The sucked excess ink is collected into the waste liquid bottle 20 through a tube (not shown).

  Here, when the ink is circulated by the ink circulation system as described above, bubbles may stagnate in part of the ink circulation path (first, second, and third ink circulation paths). In such a case, bubbles in the ink circulation path are removed by the following method. Unlike the above-described maintenance method for each head unit, this bubble removal method is performed without extruding ink.

  FIG. 7 is a flowchart for explaining the operation of the circulating maintenance for removing bubbles without pushing out such ink.

  When this sequence is started, first, in the case of a non-circulation state, a transition is made to a circulation state. Specifically, the same operation as in steps S1 to S4 is performed, and the circulation pump 19 is turned on in step S11. Next, in step S12, the electromagnetic valve 86b is opened, and in step S13, the electromagnetic valve 86c is closed.

  In step S14, the pressure bellows 87 is turned ON to generate a negative pressure in the K lower tank 65 to circulate ink. In this state, the pressure near the nozzle 45 is adjusted to about -1.5 kPa. In the case of removing bubbles from the circulating state, the above steps S11 to S14 are omitted, and the following steps are started.

  Next, in step S15, the electromagnetic valve 86b is closed, and after being held for a desired time by the timer 85, the process proceeds to step S16, and the electromagnetic valve 86b is opened again. In step S17, it is determined whether the opening / closing operation of the electromagnetic valve 86b has been performed a desired number of times, and the processing operations in steps S15 to S17 are repeated until the number of times is reached. FIG. 8 is a diagram showing a timing chart of the opening / closing time of the electromagnetic valve 86b. In this embodiment, as shown in FIG. 8, the opening time T1 and the closing time T2 of the electromagnetic valve 86b are each 0.2 seconds. When the electromagnetic valve 86b is closed during ink circulation, the pressure of the circulation pump 19 is applied to the K color head unit 35 via the K upper tank 71 and the K color distribution tank 40, and the positive pressure applied to the vicinity of the nozzle 45 is increased. growing. For this reason, pressure fluctuations can be generated in the ink circulation system by repeating the opening and closing operation of the electromagnetic valve 86b. Thereby, bubbles stagnated in a part of the ink circulation path can be removed. Thus, since the pressure fluctuation can be generated in the ink circulation system by the opening / closing operation of the electromagnetic valve 86b, the electromagnetic valve 86b also functions as a pressure adjusting mechanism for adjusting the pressure in the ink circulation system.

  At this time, the opening / closing operation of the electromagnetic valve 86b is controlled so that ink does not spill from the nozzle 45. In the present embodiment, during normal circulation, the combined pressure of the positive pressure of the K upper tank 71 and the negative pressure of the K lower tank 65 is set to −1.5 kPa. Therefore, when the opening / closing operation of the electromagnetic valve 86b is repeated, the nozzle 45 The opening / closing operation is controlled so that the combined pressure applied in the vicinity is equal to the atmospheric pressure or is a pressure between the atmospheric pressure and the negative pressure −1.5 kPa.

  If the opening / closing operation of the electromagnetic valve 86b is performed a desired number of times in step S17, the process proceeds to step S18, and the circulation pump 19 is turned off. Next, in step S19, the electromagnetic valve 86b is closed, and in step S20, the electromagnetic valve 86c is opened. After that, when the pressure bellows 87 is turned off in step S21, the non-circulating state is set and this sequence is completed. When the circulating state is maintained, the above steps S18 to S21 may be omitted and the process may proceed to image formation. If the pressure in the vicinity of the nozzle is not the desired pressure by opening and closing the electromagnetic valve 86b a predetermined number of times, the negative pressure adjusting unit 70 re-adjusts the pressure in the vicinity of the nozzle. Note that the following method may be used when bubbles are removed from the ink circulation path.

  9 and 10 are timing charts showing the driving waveform of the head.

  FIG. 9 shows an ejection drive waveform for ejecting ink. T3 is a time period for discharging one drop of the ink 51 from the nozzle 45. First, the drive voltage V1 is applied and held for the drive time T4. Next, the release voltage V2 is applied and held for the release time T6. Thereafter, the voltage is set to 0 V and held for the rest time T5. Then, ink is ejected from the nozzle 45 when the release voltage V2 is applied.

  FIG. 10 shows a non-ejection drive waveform that does not eject ink. T7 is the same time as T3. First, the drive voltage V3 is applied and held for the drive time T8. Next, the release voltage V4 is applied and held for the release time T10. Thereafter, the voltage is set to 0 V and held for the rest time T9. By setting the drive time T8 and the release time T10 to ¼ or less of the drive time T4 and the release time T6 of the ejection drive waveform, the wave timing in the head is shifted so that ink is not ejected from the nozzles 45.

  By using such a drive waveform, a result that ink is not ejected is obtained from experiments. Further, since the voltage application time is shortened, even if the same voltage as the ejection drive waveform or a higher voltage is applied, the ink from the nozzles is not ejected, and ink mist can be prevented from being generated. A non-ejection drive voltage higher than the ejection drive voltage at the time of printing may be set according to the withstand voltage of the head and the capacity of the drive circuit, and the voltage application time for non-ejection may be set.

  By applying such a non-ejection drive waveform when the electromagnetic valve 86b is opened and closed, bubbles near the nozzle 45 can be efficiently removed. In addition to air bubbles, it is also possible to reliably replace ink thickened by evaporation or the like in the vicinity of the nozzle 45 with normal ink.

  As described above, according to the first embodiment, by opening and closing the electromagnetic valve 86b, which is an air release valve provided in the upper tank, while circulating ink, the atmospheric pressure is equal to or larger than the atmospheric pressure in the circulation path. Pulsates in the range of pressure lower than atmospheric pressure. Thereby, the air bubbles stagnating in a part of the circulation path can be removed. As a result, it is possible to prevent ink ejection failure or bending in the ink ejection direction, and to provide a highly reliable image recording apparatus.

  Further, when the ink is circulated in the ink circulation path, the electromagnetic valve 86b can maintain the pressure in the vicinity of the nozzle always at a desired pressure by opening to the atmosphere by the negative pressure from the lower tank 18. Since the pulsation can be given to the ink circulation path by performing the opening / closing operation, the ink circulation path can be simplified and can be designed at a low cost.

  Further, by applying a non-ejection drive waveform to the head during the opening / closing operation of the electromagnetic valve 86b, bubbles near the nozzle 45 can be more efficiently removed, and the thickened ink near the nozzle 45 can be removed with normal ink. Can be definitely replaced. Thereby, an image recording apparatus with higher reliability can be provided.

  Next, a first modification of the first embodiment will be described.

  A first modification of the first embodiment of the present invention will be described with reference to the timing charts of FIGS.

  In the first embodiment described above, the opening / closing time of the electromagnetic valve 86b is constant, but a further effect can be obtained by changing the opening / closing time. For example, as shown in the timing chart of FIG. 11, the first opening time T1 is set to 0.2 seconds, the second opening time T11 is set to 0.1 seconds, and this is repeated a predetermined number of times. Also, as shown in the timing chart of FIG. 12, the first closing time T2 is set to 0.2 seconds, the second closing time T12 is set to 0.1 seconds, and this is repeated a predetermined number of times. As a result, pressure fluctuations (pulsations) are generated in the circulation path. Note that, also in this modification, pulsation is applied in a pressure range equal to or lower than the atmospheric pressure. As described above, by combining the opening / closing time of the electromagnetic valve 86b provided in the upper tank 71 during the ink circulation with two or more kinds, it is possible to more effectively remove bubbles staying in the ink path. .

  Next, a second modification of the first embodiment will be described.

  In the first embodiment described above, the pressure fluctuation in the circulation path is caused by opening and closing the electromagnetic valve 86b as a pressure adjusting mechanism. In this second modification, instead of opening and closing the electromagnetic valve 86b. Bubbles are removed by moving the pressure bellows 87 up and down. That is, when the pressure bellows 87 is pushed up (shrinks), the pressure of the head shifts to the atmospheric pressure side, so that the pressure bellows 87 may be expanded and contracted at the timing shown in FIGS. In this modification as well, a pressure fluctuation is given in a range of pressure that is equal to or lower than the atmospheric pressure. Even in this case, an effect equivalent to that of the first embodiment described above can be obtained.

  Next, a third modification of the first embodiment will be described.

In the first embodiment described above, the pressure fluctuation in the circulation path is caused by opening and closing the electromagnetic valve 86b as a pressure adjusting mechanism. However, in this third modification, instead of opening and closing the electromagnetic valve 86b. Bubbles are removed by opening and closing an electromagnetic valve 86c as an air release valve. That is, when the electromagnetic valve 86c is opened, the pressure of the head shifts to the atmospheric pressure side, so that the electromagnetic valve 86c is opened and closed at the timing shown in FIGS. In this modification as well, a pressure fluctuation is given in a range of pressure that is equal to or lower than the atmospheric pressure. Even in this case, an effect equivalent to that of the first embodiment described above can be obtained.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  In the first embodiment described above, an image recording apparatus that circulates ink during image formation has been described. However, this second embodiment is an example of an image recording apparatus that does not circulate ink during image formation.

  In the second embodiment, the same parts as those in the first embodiment shown in FIGS. 1 to 10 are denoted by the same reference numerals, and only the configuration and operation of the different parts will be described. .

  FIG. 13 is a schematic diagram showing an ink path of K ink in the second embodiment of the present invention.

  In addition, since the same ink path | route is comprised also about other inks, description here is abbreviate | omitted as referring to K ink.

  In FIG. 13, this image recording apparatus includes a K upper tank 71 having an electromagnetic valve 86b, a K lower tank 65 having an electromagnetic valve 86c, and a negative electrode of the image recording apparatus of the first embodiment shown in FIG. Instead of the pressure adjusting unit 70, a sub tank 110 having an electromagnetic valve 111 as an atmospheric release valve disposed below the nozzle surface of the K-color head unit 35 in the gravity direction is provided. In addition, a first ink path 105 that connects the K-color head unit 35 and the sub tank 110 is provided in order to remove bubbles remaining in at least a part of the ink path. Also in this embodiment, the K color head unit has a width equal to or larger than the width of the recording medium by arranging six short recording heads in a staggered manner in a direction orthogonal to the conveying direction of the recording medium to be used. It is configured.

  In such a configuration, during printing or standby, the electromagnetic valve 111 of the sub tank 110 is opened, and the pressure near the nozzle 45 is caused by the negative pressure (water head pressure) between the K-color head unit 35 and the sub tank 110. Is retained. In this embodiment, the negative pressure adjusting unit 70 is not provided, but the negative pressure adjusting unit 70 may be provided to adjust the pressure in the vicinity of the nozzle 45. In addition, when air bubbles are removed from the ink path, the K ink in the sub tank 110 is supplied from the circulation pump 19, the first ink path 105, the K color collection tank 76, the K color head unit 35, the K color distribution tank 40, and the second ink. An ink circulation system that returns to the sub tank 110 via the path 102 is configured.

  When removing bubbles in the ink path, the electromagnetic valve 111 is first closed. Then, the circulation pump 19 is driven to start the circulation of K ink. In this state, the pressure fluctuation is generated in the ink circulation system by repeating the opening / closing operation of the electromagnetic valve 111. This pressure fluctuation is given within a range between atmospheric pressure and a predetermined negative pressure. Thus, the electromagnetic valve 111 can not only form an appropriate meniscus for the nozzle 45 of the K-color head unit 35, but can also cause pressure fluctuations in the ink circulation system by the opening and closing operation of the electromagnetic valve 111. Also, it functions as a pressure adjusting mechanism for adjusting the pressure in the ink circulation system. Therefore, the bubbles staying in the ink path can be removed as in the first embodiment described above. Further, similarly to the first embodiment described above, in this embodiment, the non-ejection drive waveform is applied during the opening / closing operation of the electromagnetic valve 111, so that bubbles near the nozzle 45 can be more efficiently removed. In addition to being able to be removed, it is possible to reliably replace the thickened ink in the vicinity of the nozzle 45 with normal ink.

  As described above, the embodiments of the present invention have been described. In the present invention, the line head type image recording apparatus in which the head is fixed to the head holding member has been described. However, the present invention is not limited thereto, and the head is moved in the main scanning direction. The present invention can also be applied to a serial type image recording apparatus that performs image formation. Further, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  Further, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention Can be extracted as an invention.

1 is a schematic cross-sectional view of an image recording apparatus in a first embodiment of the present invention. 1A and 1B show a configuration of a short recording head, in which FIG. 1A is an external perspective view, FIG. 1B is a perspective view showing a nozzle surface, and FIG. FIG. 2 is a schematic cross-sectional view during maintenance of the image recording apparatus in the first embodiment of the present invention. FIG. 2 is a block configuration diagram illustrating a configuration of a control system of the image recording apparatus having the configuration of FIG. 1. It is the schematic diagram which showed the ink path | route of K ink. 6 is a flowchart for explaining an operation of circulation maintenance when ink is circulated in the first embodiment. 5 is a flowchart for explaining an operation of circulation maintenance for removing bubbles without pushing out ink in the first embodiment. It is a timing chart for demonstrating the opening / closing time of the solenoid valve in 1st Embodiment. 6 is a timing chart showing an ejection driving waveform for ejecting ink. 6 is a timing chart illustrating a non-ejection drive waveform that does not eject ink. It is a timing chart for demonstrating the opening / closing time of a solenoid valve in the 1st modification of the 1st Embodiment of this invention. It is another timing chart for demonstrating the opening / closing time of a solenoid valve in the 1st modification of the 1st Embodiment of this invention. It is the schematic diagram which showed the circulation path | route of K ink in the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Image recording device, 11 ... Paper feed part, 12 ... Paper conveyance part, 13 ... Image formation part, 14 ... Paper discharge part, 15 ... Maintenance unit, 16 ... Ink bottle unit, 17 ... Upper tank, 18 ... Lower tank 19 ... circulation pump, 20 ... waste bottle, 21 ... control unit, 26 ... pickup roller, 29 ... registration roller, 30 ... roller, 31 ... conveyor belt, 32 ... platen, 33 ... suction fan, 35 ... head unit (K) Color head unit) 36 ... Head unit (C color head unit), 37 ... Head unit (M color head unit), 38 ... Head unit (Y color head unit), 40 ... Distribution tank (K color distribution tank), 41 ... Distribution tank (C color distribution tank), 42 ... Distribution tank (M color distribution tank), 43 ... Distribution tank (Y color distribution tank), 44 ... F 45 ... Nozzle, 46 ... Nozzle plate, 56 ... Negative pressure source, 60 ... K ink bottle, 61 ... C ink bottle, 62 ... M ink bottle, 63 ... Y ink bottle, 65 ... K lower tank, 66 ... C lower tank, 67 ... M lower tank, 68 ... Y lower tank, 70 ... negative pressure adjusting section, 71 ... K upper tank, 72 ... C upper tank, 73 ... M upper tank, 74 ... Y upper tank, 76 ... Collection tank (K color collection tank), 77 ... Collection tank (C color collection tank), 78 ... Collection tank (M color collection tank), 79 ... Collection tank (Y color collection tank), 80 ... Conveyance motor, 81 ... Head Driver, 82 ... Head, 83 ... Image data receiver, 85 ... Timer, 86, 86a, 86b, 86c ... Solenoid valve, 87 ... Pressure bellows, 89 ... Moving motor, 90 ... Suction pump, 93 ... Filter, 97 ... support, 98 ... air chamber 100 ... liquid level sensor, 102 ... second ink passage, 103 ... third ink path, 104 ... fourth ink passage, 105 ... first ink path.

Claims (7)

An image recording unit having a recording head for recording an image on a recording medium by discharging ink from a nozzle;
An upper tank that is disposed above the nozzle surface on which the nozzles of the recording head are formed in the gravity direction and stores the ink to be supplied to the recording head;
A first valve provided in the upper tank, for communicating with or blocking the atmosphere in the upper tank;
A lower tank that is disposed below the nozzle surface on which the nozzles of the recording head are formed in the direction of gravity and stores the ink that has not been ejected by the recording head;
A second valve provided in the lower tank for communicating with or blocking the atmosphere in the lower tank;
A pressure adjusting unit provided in the lower tank for adjusting the pressure in the lower tank;
A pump for sending the ink stored in the lower tank to the upper tank; and an ink circulation system for flowing the ink from the upper tank in the order of the image recording unit and the lower tank and returning the ink to the upper tank again. ,
The mode for circulating the ink in the ink circulation system is:
In order to perform image recording by the image recording unit, the first valve is opened and the second valve is kept closed, and the pressure applied to the nozzles of the recording head can eject the ink. A first circulation mode in which the pressure in the lower tank is maintained at a constant negative pressure by the pressure adjusting unit so as to obtain a proper pressure;
In order to remove bubbles stagnating in the ink circulation system, in the first circulation mode state, at least an opening / closing operation for opening / closing the first valve, or an opening / closing operation for opening / closing the second valve, or And a second circulation mode in which any one of variable operations for varying the pressure in the lower tank by the pressure adjusting unit is performed.   In the second circulation mode, at least an opening / closing operation for opening / closing the first valve, an opening / closing operation for opening / closing the second valve, or a variable operation for varying the pressure in the lower tank by the pressure adjusting unit. 2. The image recording apparatus according to claim 1, wherein when performing any one of the operations, a pressure applied to the nozzle of the recording head varies within a range between an atmospheric pressure and a predetermined negative pressure.   The image recording apparatus according to claim 2, wherein the predetermined negative pressure is a pressure applied to the nozzles of the recording head in the first circulation mode. In the second circulation mode, the opening and closing operation of the first valve is repeated a plurality of times, and the time for opening the first valve and the time for closing the first valve are the same time. The time for setting or opening the first valve and the time for closing the first valve are set to different times. 5. The image recording apparatus described.   In the second circulation mode, the opening and closing operation of the second valve is repeated a plurality of times, and the time for opening the second valve and the time for closing the second valve are the same time. The time for setting or opening the second valve and the time for closing the second valve are set to different times. 5. The image recording apparatus described.   The pressure adjusting unit includes an expandable / contractible member that communicates with an air portion of the lower tank and has a space formed therein, and expands / contracts the expandable member a plurality of times in the second circulation mode. The image recording apparatus according to claim 1, wherein the image recording apparatus is an image recording apparatus.   7. The image recording apparatus according to claim 1, wherein when the ink is not circulated in the ink circulation system, the first valve is closed and the second valve is kept open. The image recording apparatus according to any one of the above.

Images