JP2008137176A - Inkjet image forming device and its recovery method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovery method which enables a reliable recovery action by preventing an inconvenience due to inks discharged to a cap. <P>SOLUTION: Ink discharged from an ink discharge opening of a recording head 22K temporarily gathers in the cap 52 but flows into a buffer tank 92, passing through an ink channel 86, an air release valve 88 and an ink channel 90. The ink flowing into the buffer tank 92 is held in a position where its balance is kept by a fall and prevented from flowing back to the cap 52. Since an air communication pipe 94 is arranged in the upper wall of the buffer tank 92, pressure in the buffer tank 92 never increases. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet image forming apparatus that discharges ink onto a recording medium to form an image, and a recovery method, and particularly to an ink jet image forming apparatus having a long recording head and a recovery suitable for the ink jet image forming apparatus. Regarding the method.

  2. Description of the Related Art Inkjet image forming apparatuses that form an image by ejecting ink onto a recording medium from a recording head on which a large number of ink ejection openings from which ink is ejected are widely used. When the recording head of this ink jet image forming apparatus is continuously operated for recording (ie, ink is continuously ejected), ink droplets adhere and grow near the nozzles of the recording head. There is a possibility that the viscosity of the droplets will increase and the sound ink ejection performance will be hindered. In addition, if air bubbles enter the nozzles of the recording head, the ink ejection state from the ink ejection port may become unstable, and ejection defects such as deviation (bias) in the ejection direction or non-ejection may occur. .

  In order to prevent such troubles, in the inkjet image forming apparatus, the suction pump is operated with the cap closely attached to the recording head to generate a negative pressure in the cap, and the ink is sucked from the nozzle of the recording head. And a method of forcibly discharging ink from the nozzles of the recording head using a pressure pump (pressure recovery).

  Furthermore, during non-recording, in order to prevent the standby nozzle from drying and thickening the ink, in order to stabilize the operation of performing ejection at a regular interval (standby preliminary ejection) and the state of the meniscus generated in the nozzles In addition, an operation of performing discharge immediately before printing (pre-printing pre-printing) is employed.

  The cap mentioned above has a function to cover and protect the surface (face surface) on which the ink discharge port of the recording head is formed during non-recording, mainly in the case of suction recovery, a negative pressure generating source (suction pump, etc.), a tube, etc. In the case of performing a function as a suction cap for sucking thickened ink in the ink discharge port (inside the nozzle) or air bubbles, and when recovering pressure, the ink discharged from the nozzle It has a function for temporarily storing.

  The cap is provided with an air communication port, and this air communication port communicates the inside of the cap with the air when the cap is brought into close contact with the face surface (see, for example, Patent Document 1). This atmospheric communication port prevents the meniscus from retreating when the ink discharge port is pressurized.

At the time of suction recovery, it is connected to the suction pump etc. that communicates with the atmosphere even when capping, so the space inside the cap of the suction cap must communicate with the atmosphere via a tube etc. even when capping. It becomes. Further, when pressure recovery is performed in the capping state, the cap is communicated with the atmosphere in order to suppress an increase in pressure in the cap.
Japanese Patent Laid-Open No. 2000-2111164

  In each of the recovery operations described above, particularly in the case of an inkjet image forming apparatus using a long head, when pressure recovery is performed, the amount of ink discharged from the nozzle is larger than in the case of suction recovery, There is a risk that the pressure inside the cap rises rapidly and the ink is scattered outside the cap. Similarly, during pre-discharge during standby or before printing, there is a risk that the pressure in the cap increases and print quality is lowered. In order to avoid such a situation, it is conceivable to perform ejection or pressure recovery after moving the recording head slightly upward from the capping position to release the inside of the cap to the atmosphere. However, in this method, there is a possibility that mist generated when ink is ejected is discharged to the outside of the apparatus, or ink pushed out by pressurization is scattered outside the cap.

  Furthermore, when performing pressure recovery, particularly in recovery that requires discharging a large amount of ink from the nozzle, the pressure operation at the capping position and the suction operation for removing the ink in the cap can be performed simultaneously. Necessary. However, it is difficult to control the amount of waste liquid from the nozzle, and variations may occur, which may impair image quality.

  In the configuration in which the atmosphere communication means is provided in the cap, the opening of the atmosphere communication means communicating with the atmosphere inside the cap and the opening of the ink communication means communicating with the suction pump are provided on the bottom surface inside the cap. For this reason, when ink is sucked from the recording head during suction recovery, the ink that has flowed into the cap may also flow into the atmosphere communicating means. As described above, when ink enters the tube used for the air communication means, the ink attached to the inner wall surface of the tube is not easily sucked and discharged even when the suction pump is driven. If the ink in the tube is not discharged and a part of it remains, the water evaporates from the remaining ink and the ink concentration increases, causing tube clogging or ink with increased viscosity in the discharge operation. There are cases where nozzles are clogged by adhering to the recording head.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an inkjet image forming apparatus and a recovery method capable of preventing a disadvantage caused by ink discharged to a cap and performing a highly reliable recovery operation.

In order to achieve the above object, an inkjet image forming apparatus of the present invention includes a cap that covers a face surface of a recording head having a face surface on which an ink discharge port for discharging ink is formed, and the inside of the cap is opened to the atmosphere. An ink jet type image forming apparatus for forming an image by discharging ink from the ink discharge port onto a recording medium.
(1) The present invention is characterized in that a buffer tank is provided between the cap and the atmosphere communication means for storing ink discharged from the cap.

here,
(2) The buffer tank is connected to the cap by an ink flow path through which ink flows.
(3) The atmospheric communication means may be a cylindrical one fixed to the upper wall of the buffer tank.

further,
(4) The buffer tank may have an ink liquid level that reaches the same height as the lower end of the atmospheric communication means or a position lower than the lower end.

Furthermore,
(5) The buffer tank may be arranged at a position where the liquid level of the ink stored in the buffer tank is lower than the liquid level of the ink stored in the cap.

Furthermore,
(6) An openable / closable valve attached to the ink flow path may be provided.

Furthermore,
(7) A pump for sucking and discharging ink stored in the buffer tank may be provided.

The recovery method of the present invention for achieving the above object forms an image by ejecting ink from the ink ejection port of the recording head to the recording medium while supplying ink to the recording head from the sub tank in which the ink is stored In the ink jet type image forming apparatus, the ink discharge port is closed with a cap and pressure is applied to the ink in the recording head to discharge the ink from the ink discharge port, thereby changing the ink discharge state from the ink discharge port. In the recovery method to recover to the initial state,
(8) A buffer tank for storing the ink discharged from the cap is disposed at a position lower than the cap,
(9) The ink discharge port is closed with the cap and pressure is applied to the ink in the recording head to discharge the ink from the ink discharge port, temporarily store it in the cap, and discharge it to the buffer tank. It is characterized by this.

here,
(10) When the pressure is applied to the ink in the recording head by closing the ink discharge port with the cap, bubbles may be removed from the ink flow path from the sub tank to the recording head.

further,
(11) The ink stored in the buffer tank may be moved to the sub tank.

  According to the present invention, the ink discharged from the ink discharge port and stored in the cap can be quickly discharged to the buffer tank. Therefore, it is possible to prevent a trouble at the time of recovery such that a large amount of ink is stored in the cap and the ink adheres to the ink discharge port or scatters outside, and a highly reliable recovery operation can be executed.

  The present invention has been realized in an inkjet image forming apparatus in which long recording heads are arranged in the recording medium conveyance direction.

  With reference to FIG. 1, a printer as an example of an ink jet image forming apparatus of the present invention will be described.

  FIG. 1 is a front view schematically showing a printer which is an example of an ink jet image forming apparatus of the present invention.

  The printer 10 is connected to a host PC (personal computer) 12 (see FIG. 2) that sends image information to the printer 10. In the printer 10, four (four) recording heads 22K, 22C, 22M, and 22Y are arranged side by side in the conveyance direction (arrow A direction) of the recording medium (roll paper in this case). The four recording heads 22K, 22C, 22M, and 22Y eject black, cyan, magenta, and yellow inks, respectively. These four recording heads 22K, 22C, 22M, and 22Y are so-called line heads, and extend in a direction orthogonal to the paper surface of FIG. 1 (a direction orthogonal to the arrow A direction). The lengths of these four recording heads 22K, 22C, 22M, and 22Y are slightly longer than the maximum width (the length in the direction perpendicular to the paper surface of FIG. 1) of the recording media that can be printed by the printer 10. Further, these four recording heads 22K, 22C, 22M, and 22Y are fixed and do not move during image formation (are in a non-moving state).

  A recovery unit 40 is incorporated in the printer 10 so that ink can be stably ejected from the four recording heads 22K, 22C, 22M, and 22Y. By the recovery unit 40, the ink ejection state from the recording heads 22K, 22C, 22M, and 22Y is restored to the initial ink ejection state. The recovery unit 40 includes a capping mechanism 50 that removes ink from the ink discharge port formation surfaces (face surfaces) 22Ks, 22Cs, 22Ms, and 22Ys of the four recording heads 22K, 22C, 22M, and 22Y during the recovery operation. ing. The capping mechanism 50 is provided independently for each of the recording heads 22K, 22C, 22M, and 22Y. In the example of FIG. 1, six colors (that is, six capping mechanisms 50) are shown. The color component is a preliminary mechanism when the recording head is added. The capping mechanism 50 includes a known wiper blade, a blade holding member, a cap, and the like.

  The roll paper P is supplied from the roll paper supply unit 24 and is transported in the direction of arrow A by the transport mechanism 26 incorporated in the printer 10. The transport mechanism 26 includes a transport belt 26a for loading and transporting the roll paper P, a transport motor 26b for rotating the transport belt 26a, and a roller 26c for applying tension to the transport belt 26a.

  When forming an image on the roll paper P, after the recording start position of the roll paper P being conveyed reaches below the black recording head 22K, the recording head is based on the recording data (image information). Black ink is selectively ejected from 22K. Similarly, each color ink is ejected in the order of the recording head 22C, the recording head 22M, and the recording head 22Y to form a color image on the roll paper P. The printer 10 includes main tanks 28K, 28C, 28M, and 28Y for storing ink supplied to the recording heads 22K, 22C, 22M, and 22Y, and the recording heads 22K, 22C, and 22M, in addition to the components and members described above. , 22Y are provided with various pumps (not shown) for supplying ink and performing a recovery operation.

  The electrical system of the printer 10 will be described with reference to FIG.

  FIG. 2 is a block diagram showing an electrical system of the printer of FIG.

  Recording data and commands transmitted from the host PC 12 are received by the CPU 100 via the interface controller 102. The CPU 100 is an arithmetic processing unit that performs overall control such as reception of recording data of the printer 10, recording operation, handling of the roll paper P, and the like. After analyzing the received command, the CPU 100 renders the image data of each color component of the recording data by developing a bitmap on the image memory 106. As an operation process before recording, a capping motor 122 and a head up / down motor (head motor) 118 are driven via an input / output port (I / O) 114 and a motor driving unit 116, and the recording heads 22K, 22C, and 22M are driven. , 22Y is moved away from the capping mechanism 50 to the recording position (image forming position).

  Subsequently, the roll paper is driven by driving the input / output port 114, the roll motor 124 that feeds the roll paper P through the motor driving unit 116, the transport motor 120 that transports the roll paper P at a low speed, and the like. P is conveyed to the recording position. The leading edge detection sensor 111 for determining the timing (recording timing) at which ink starts to be ejected onto the roll paper P conveyed at a constant speed detects the leading edge position of the roll paper P. Thereafter, in synchronization with the conveyance of the roll paper P, the CPU 100 sequentially reads out the corresponding color recording data from the image memory 106, and controls the recording heads 22K, 22C, 22M, and 22Y to read the read data. Transfer via the circuit 112.

  The operation of the CPU 100 is executed based on a processing program stored in the program ROM 104. The program ROM 104 stores processing programs and tables corresponding to the control flow. A work RAM 108 is used as a working memory. During the cleaning and recovery operations of the recording heads 22K, 22C, 22M, and 22Y, the CPU 100 drives a pump motor (not shown) via the input / output port 114 and the motor driving unit 116 to pressurize and suck ink. Control.

  With reference to FIG. 3, the recovery unit provided in the printer 10 will be described.

  FIG. 3 is a schematic diagram illustrating a recovery unit that is on standby. In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

  The four recording heads 22K, 22C, 22M, and 22Y are integrally held by the head holder 22. During the standby of the printer 10, the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys of the recording heads 22K, 22C, 22M, and 22Y are covered with caps 52 of the respective capping mechanisms 50. The four caps 52 are fixed on a recovery rod 54 extending in the direction of arrow A, move up and down together with the recovery rod 54, and move in the direction of arrow A and in the opposite direction. Inside the four caps 52, ink guides 51 for guiding the ink discharged from the nozzles of the recording heads 22K, 22C, 22M, and 22Y to the lower side of the cap 52 are arranged. Under each cap 52, a hole is formed for allowing the ink guided by the ink guide 51 to flow to the recovery rod 54.

  A flexible wiper blade 60 made of an elastic body is fixed on the recovery rod 54. The wiper blade 60 is fixed to a holding portion 62 fixed to the upper surface of the recovery rod 54. With the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys of the recording heads 22K, 22C, 22M, and 22Y positioned at the cleaning position away from the cap 52, the recovery rod 54 is in the direction opposite to the arrow A direction. , The wiper blade 60 moves while being bent in contact with the face surfaces 22Ks, 22Cs, 22Ms, 22Ys. Thereby, since the ink and paper dust adhering to the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys are wiped off by the wiper blade 60, the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys are cleaned.

  With reference to FIG. 4, the flow of ink relating to the recording head 22K will be described. The ink flow of the other recording heads 22C, 22M, and 22Y is the same as that of the recording head 22K.

  FIG. 4 is a schematic diagram showing the flow of ink related to the recording head 22K.

  Ink necessary for recording is fed from the removable main tank 28K to the sub tank 27K and stored therein. The ink in the main tank 28K is stored in, for example, a pack-like container (ink tank) that contracts as it is sucked out. In the sub tank 27K, an ink liquid level sensor 27KE composed of electrodes is inserted and installed. The ink liquid level sensor 27KE includes the position of the ink liquid level when the ink is full and the ink empty ( The presence or absence of ink is detected by detecting the position of the ink liquid level in the (Empty) state.

  Ink is transported to each part by two pumps, a pressure pump 70 and a suction pump 72. The pressurizing pump 70 is driven simultaneously with each station (four ink supply paths corresponding to the four recording heads 22K, 22C, 22M, and 22Y) by a pressurizing pump motor (not shown). On the other hand, the suction pump 72 is driven by a suction pump motor (not shown), and each suction pump at each station is driven by an electromagnetic clutch (not shown) provided in the middle of the transmission mechanism to the suction pump of each station. It can be selectively driven.

  Further, both the pressurizing pump 70 and the suction pump 72 are provided with one-way valves on the upstream side (suction side) and the downstream side (discharge side), and are configured so that they cannot flow backward. The ink discharged from the ink discharge port of the recording head 22K is caught (received) by the cap 52. A recycle filter 76 and a recycle valve (open / close valve) 78 are attached to the ink flow path (tube) 74 between the cap 52 and the suction pump 72, and the ink flow between the main tank 28 </ b> K and the suction pump 72. A supply valve (open / close valve) 82 and a filter 84 are attached to the passage (tube) 80.

  The recycle valve 78 and the supply valve 82 are driven by a driving device (not shown) so that the open / close state is switched simultaneously at each station. However, the open / close state of the recycle valve 78 and the supply valve 82 is maintained in the opposite state, and when one is in an open state (distribution state), the other is controlled to be in a sealed state. By switching this timely, when the suction pump 72 is driven, either the ink suction from the cap 52 or the ink suction from the main tank 28K is selectively performed.

  An ink flow path 86 is connected to the bottom of the cap 52, and an atmosphere release valve 88 is attached to the ink flow path 86. A portion of the ink flow path 86 that is slightly downstream (lower part) from the air release valve 88 is branched into an ink flow path 74 and an ink flow path 90. The ink flow path 74 is connected to the suction pump 72 as described above. The ink flow path 90 is connected to the bottom of the buffer tank 92 in which the ink discharged from the cap 52 is stored. A cylindrical atmosphere communication pipe 94 communicating with the atmosphere is fixed to the upper wall of the buffer tank 92. Therefore, the cap 52 is connected to the atmosphere communication pipe 94 via the ink flow paths 86 and 90 and the buffer tank 92.

  In the buffer tank 92, the highest ink level reaches the same height as the lower end of the atmosphere communication pipe 94 or a position lower than the lower end. The buffer tank 92 is disposed at a position where the highest liquid level of the ink stored in the buffer tank 92 is lower than the highest liquid level of the ink stored in the cap 52.

  One end of an ink flow path 96 connected to the recording head 22K is connected to the upper wall of the sub tank 27K, and an open / close valve 98 is attached to the ink flow path 96. The pressurizing pump 70 is connected to the recording head 22 </ b> K by the ink flow path 71.

  With reference to FIG. 5, the procedure for recovering the pressure of the recording head will be described.

  FIG. 5 is a flowchart showing a procedure for recovering the pressure of the recording head.

  In order to recover the pressure of the recording head, first, the recycle valve 78 and the on-off valve 98 are closed (S501), and the air release stool 88 is opened (S502). Subsequently, the pressure pump 70 is driven to apply pressure to the ink in the recording head 22K (pressurize the ink) (S503). By this pressurization, bubbles existing in the recording head 22K and in the ink flow path 71 from the sub tank 27K to the recording head 22K are discharged together with the ink from the ink discharge port of the recording head 22K and removed.

  The ink discharged from the ink discharge port of the recording head 22K is temporarily stored in the cap 52, but flows into the buffer tank 92 through the ink flow path 86, the air release valve 88, and the ink flow path 90. Since the ink that has flowed into the buffer tank 92 is held at a position where the balance can be maintained due to the difference in water head, it is prevented from flowing back into the cap 52. Further, since the atmosphere communication pipe 94 is disposed on the upper wall of the buffer tank 92, the pressure in the buffer tank 92 does not increase.

  The pressurization pump 70 is driven for a predetermined time and then stopped (S504), the recycle valve 78 is opened, and the air release valve 88 is closed (S505). In this state, the suction pump 72 is driven (S506). By this driving, the ink stored in the buffer tank 92 is returned to the sub tank 27K. After the suction pump 72 is driven for a certain time and then stopped, the recycle valve 78 is closed (S507). As described above, since a large amount of ink is not stored in the cap 52, inconvenience due to the ink discharged from the intended port can be prevented, and a highly reliable recovery operation can be executed.

1 is a front view schematically showing a printer which is an example of an inkjet image forming apparatus of the present invention. FIG. 2 is a block diagram illustrating an electrical system of the printer of FIG. 1. It is a schematic diagram which shows the recovery unit in standby. It is a schematic diagram showing the flow of ink relating to the recording head 22K. FIG. 5 is a flowchart showing a procedure for recovering pressure of a recording head.

Explanation of symbols

10 Printer 22K Recording head 27K Sub tank 28K Main tank 70 Pressure pump 72 Suction pump 88 Atmospheric release valve 92 Buffer tank 94 Atmospheric communication pipe

Claims (9)

A cap that covers the face surface of the recording head having a face surface on which an ink discharge port for discharging ink is formed; and an atmosphere communication means for opening the inside of the cap to the atmosphere. In an inkjet image forming apparatus that forms an image by ejecting ink,
An ink-jet image forming apparatus comprising a buffer tank for storing ink discharged from the cap and disposed between the cap and the air communication means. The buffer tank is connected to the cap by an ink flow path through which ink flows,
2. An ink jet image forming apparatus according to claim 1, wherein the air communication means is a cylindrical member fixed to the upper wall of the buffer tank. 3. The ink jet type image forming apparatus according to claim 1, wherein the buffer tank has an ink liquid level that reaches the same height as the lower end of the atmosphere communication means or a position lower than the lower end. . The buffer tank is disposed at a position where the liquid level of the ink stored in the buffer tank is lower than the liquid level of the ink stored in the cap. Or an inkjet type image forming apparatus according to 3; The inkjet image forming apparatus according to claim 1, further comprising an openable / closable valve attached to the ink flow path. The inkjet image forming apparatus according to claim 1, further comprising a pump that sucks and discharges ink stored in the buffer tank. In an ink jet type image forming apparatus that forms an image by discharging ink from an ink discharge port of a recording head to a recording medium while supplying the ink to the recording head from a sub tank in which the ink is stored, the ink discharge port is closed with a cap In the recovery method, the ink is discharged from the ink discharge port by applying pressure to the ink in the recording head to restore the ink discharge state from the ink discharge port to the initial state.
A buffer tank for storing ink discharged from the cap is disposed at a position lower than the cap,
The ink discharge port is closed by the cap, and pressure is applied to the ink in the recording head to discharge the ink from the ink discharge port, temporarily store the ink in the cap, and discharge the ink to the buffer tank. And recovery method. The air bubble is removed from an ink flow path from the sub tank to the recording head when the ink ejection port is closed with the cap and pressure is applied to the ink in the recording head. Recovery method. 9. The recovery method according to claim 7, wherein the ink stored in the buffer tank is moved to the sub tank.

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