JP6314632B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus such as a printer, a facsimile machine, a plotter, a copier, or a multi-function machine having a plurality of functions provided with a droplet discharge head for discharging droplets.

As an image forming apparatus such as a printer, a facsimile machine, a plotter, a copying machine, or a multi-function machine having a plurality of functions, for example, a liquid discharge recording type image formation using a recording head composed of a droplet discharge head for discharging ink droplets. As an apparatus, an ink jet recording apparatus or the like is known.
This liquid discharge recording type image forming apparatus forms an image by discharging ink droplets from a recording head onto a conveyed sheet. This image forming apparatus includes a serial type image forming apparatus that forms an image by ejecting liquid droplets while the recording head moves in the main scanning direction, and an image by ejecting liquid droplets without moving the recording head. There is a line type image forming apparatus using a line type head to be formed. Here, the object on which image formation is performed is not limited to paper, but includes OHP and the like, which means that ink droplets, other liquids, and the like can be attached. Also called paper, recording paper, and the like. In addition, image formation also includes recording, printing, printing, and printing as synonyms.

  In the present application, the “image forming apparatus” of the liquid discharge recording method is an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or the like. Means. In addition, “image formation” not only applies an image having a meaning such as a character or a figure to a medium but also applies an image having no meaning such as a pattern to the medium (simply applying a droplet to the medium). It also means to land on. “Ink” is not limited to ink, but is used as a general term for all liquids capable of image formation, such as recording liquid, fixing processing liquid, and liquid. DNA samples, resists, pattern materials, resins and the like are also included. The term “image” is not limited to a two-dimensional image, but also includes an image given to a three-dimensionally formed image, and an image formed by three-dimensionally modeling a solid itself.

  In general, a droplet discharge head has a plurality of nozzles having nozzle holes for discharging liquid as droplets from a discharge surface. Further, in the droplet discharge head, individual liquid chambers communicating with the respective nozzle holes are provided. The droplet discharge head generates a pressure in the individual liquid chamber using the pressure generating means, and discharges the droplet by instantaneously pushing out the liquid filled in the individual liquid chamber from the nozzle hole. As the pressure generating means, an electromechanical conversion element such as a piezoelectric element or an electrothermal conversion element such as a heater is employed. Each individual liquid chamber communicates with the common liquid chamber via the supply path, and the liquid is distributed from the common liquid chamber to the individual liquid chamber. The common liquid chamber is connected to and communicated with a head tank called a sub tank which is a liquid supply source via a supply port. The liquid in the head tank is supplied to the common liquid chamber via the supply port, and is further distributed and supplied from the common liquid chamber to each individual liquid chamber.

  If air bubbles are mixed in the common liquid chamber, the bubbles enter the individual liquid chamber along the flow of liquid from the supply port of the common liquid chamber to the nozzle during printing or the like, which causes discharge failure. However, gases such as air are dissolved (meaning that they are dissolved) in the liquid. It is known as a physical law that the amount of dissolved gas is larger when the temperature is lower and smaller when the temperature is higher. Here, if the liquid in which the gas is dissolved is changed from a low temperature state to a high temperature, the gas that cannot be completely dissolved becomes bubbles and bubbles are generated. Also, bubbles generated upstream of the common liquid chamber enter the common liquid chamber along the flow of liquid supply.

  In this way, bubbles generated in the common liquid chamber emerge from the liquid and accumulate on the upper wall of the common liquid chamber. When the accumulated bubbles enter the individual liquid chamber due to the flow in the common liquid chamber generated by printing, it becomes impossible to discharge the liquid from the nozzle hole, which causes discharge failure.

  Therefore, in the prior art, when bubbles are generated in the common liquid chamber or upstream of the common liquid chamber in the droplet discharge head, the two patterns are discharged from the nozzle or circulated back to the upstream side of the nozzle. Countermeasures have been taken (see, for example, Patent Documents 1 and 2).

  However, in the technologies up to now, including the above-mentioned Patent Documents 1 and 2, the bubbles are unintentionally intruded from the common liquid chamber to the individual liquid chamber when the operation is not to discharge the bubbles. There was a problem of becoming.

  The present invention has been made in view of the above-described circumstances, and prevents the occurrence of defective discharge by preventing the bubbles from entering the individual liquid chambers unintentionally when the operation is not performed to discharge the bubbles. The purpose is to prevent. In other words, an object of the present invention is to provide an image forming apparatus capable of reliably discharging bubbles by allowing bubbles to enter the individual liquid chamber only from the liquid discharging operation.

  In order to achieve the above object, the present invention provides a plurality of nozzles that discharge droplets, individual liquid chambers that are in communication with the nozzles and filled with a liquid that is supplied to the nozzles, and each of the individual liquid chambers. Pressure generating means for generating a pressure for discharging the liquid from the corresponding nozzle, a common liquid chamber for supplying the liquid to the individual liquid chambers, and the individual liquid chambers on the upper wall surface constituting the common liquid chamber. At least one first step formed on the upstream side of the liquid supply path, which captures and holds bubbles rising to the upstream side, and creates a concave air pocket; and the downstream side of the liquid supply path in the first step A second step that is larger than the first step that forms a concave air pocket that captures and holds the bubbles that float to the upstream side, and the liquid at the first and second steps. Downstream of supply path A droplet discharge head having a third step that is formed on the upper wall surface of the upper wall less than the number of first steps and is equivalent to the size of the first step, and a first that discharges liquid from the nozzle. An image forming apparatus having a maintenance unit and a second maintenance unit that discharges more liquid from the nozzle than the amount of liquid discharged by the first maintenance unit. The bubbles present in the first step flow downstream of the liquid supply path from the first step, and the bubbles present in the second step flow downstream of the liquid supply path from the second step. And the bubbles present in the second step are configured to flow from the second step to the downstream side of the liquid supply path when the liquid is discharged by the second maintenance means. An image forming apparatus is.

  According to the present invention, with the above-described configuration, bubbles can be surely discharged by allowing bubbles to enter the individual liquid chamber from the common liquid chamber only during the liquid discharging operation. Thereby, when it is not the operation | movement which discharges | emits a bubble, since a bubble is not made to invade into an individual liquid chamber from a common liquid chamber, generation | occurrence | production of discharge failure can be prevented beforehand.

1 is a schematic side view illustrating an outline of a mechanism unit of an image forming apparatus according to an embodiment of the present disclosure. FIG. 2 is a plan view of a main part of the image forming apparatus in FIG. 1. FIG. 6 is a schematic explanatory diagram illustrating a configuration / operation when a carriage moves to a maintenance / recovery mechanism. FIG. 4 is a cross-sectional view taken along a direction orthogonal to the nozzle arrangement direction of the recording head. FIG. 2 is a schematic plan view showing an internal configuration of a recording head. FIG. 3 is a schematic cross-sectional view along the nozzle arrangement direction of the recording head. FIG. 7 is a schematic enlarged sectional view showing the individual liquid chamber and the common liquid chamber in an enlarged manner by removing and breaking the upper portion of FIG. 6. (A), (b), (c) is a graph explaining the method of changing the ink discharge amount of the first maintenance and the second maintenance. (A) is a cross-sectional view of a main part of a recording head showing a conventional example, and (b) is a cross-sectional view in which a main part of the recording head showing Example 1 is partially broken and omitted. It is explanatory drawing explaining the discharge transition state of a bubble by the 1st and 2nd maintenance implemented in Example 1. FIG. (A) is a cross-sectional view in which a main part of the recording head showing the first modification is partially broken and omitted, and (b) is a force acting on air bubbles according to the degree of inclination of the inclined surfaces of the first and second steps. It is a figure explaining. FIG. 10 is a block diagram illustrating a control configuration of main parts of a second embodiment. It is a diagram explaining the control content of Example 2. FIG. 10 is a cross-sectional view in which a main part of a recording head showing Example 3 is partially broken and omitted.

  Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In the embodiment and each example, components (members and components) having the same function and shape are described once by giving the same reference numerals after having been described once unless there is a possibility of confusion. Omitted. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate.

With reference to FIGS. 1 and 2, an overall configuration of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic side view showing an outline of a mechanism part of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view of a main part of the image forming apparatus of FIG.
An image forming apparatus 100 shown in FIG. 1 is a serial type ink jet recording apparatus. The main mechanism of the image forming apparatus 100 includes an image forming unit 93 having a carriage 33 and the like, a paper feeding unit 94 having a paper feeding cassette 90 and a feeding unit, a transport belt 51, various transport members, and the like. There is a paper discharge unit 96 including a transport unit 95, a paper discharge roller 62, a paper discharge tray 91, and the like.

  As shown in FIG. 2, side plates 37 </ b> A and 37 </ b> B are fixed and arranged on the left and right sides of the apparatus main body 99. The main and slave guide rods 31 and 32 are laid across the side plates 37A and 37B. By these guide rods 31, 32, the carriage 33 is slidably held in the main scanning direction (meaning that it slides in contact). The carriage 33 is moved and scanned in the arrow direction (carriage main scanning direction) via a timing belt (not shown) to which the carriage 33 is fixed by the main scanning motor 54 shown in FIG.

  The carriage 33 includes a recording head 34a as an image forming unit, which includes a droplet discharge head for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). 34b (referred to as “recording head 34” when not distinguished) is mounted. In the recording head 34, a nozzle row composed of a plurality of nozzles is arranged in the sub-scanning direction orthogonal to the main scanning direction, and the carriage 33 moves the recording head 34 so that the ink droplet ejection direction from the nozzles is downward. Wearing.

  Each of the recording heads 34 has two nozzle rows. One nozzle row of the recording head 34a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 34b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets.

  The carriage 33 is equipped with sub tanks 35a and 35b (referred to as “sub tank 35” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 34. From the ink cartridges 65y, 65m, 65c, and 65k of the respective colors that are detachably attached to the cartridge loading unit 92, the sub tank 35 is connected to the sub tank 35 through the supply tubes 36 of the respective colors by a pump unit that includes the supply pump 38 shown in FIG. Thus, ink of each color is supplied. Note that the ink cartridges 65y, 65m, 65c, and 65k of the respective colors are referred to as “ink cartridges 65” when not distinguished from each other. Each color supply tube 36 serves as an ink supply path for each color.

  On the other hand, the paper feed cassette 90 places the paper 42 and feeds the paper 42 to a paper feed roller 43 provided on the apparatus main body 99 side (position state shown in FIG. 1) and the feed position. A bottom plate 41 that can swing between the lowered position and the lowered position is provided. In order to feed the paper 42 stacked on the bottom plate 41 of the paper feed cassette 90, the paper 42 on the bottom plate 41 is opposed to the paper feed roller 43 and the paper feed roller 43 for separating and feeding the paper 42 one by one. A separation pad 44 is provided as separation means made of a material having a large friction coefficient. The separation pad 44 is urged (means that force is applied) toward the paper feed roller 43 by an urging means such as a spring (not shown).

  In order to send the paper 42 fed from the paper feed cassette 90 to the lower side of the recording head 34, a transport unit 95 is arranged. The transport unit 95 electrostatically attracts the guide member 45 that guides the paper 42, the counter roller 46, the transport guide member 47, the pressing member 48 having the tip pressure roller 49, and the fed paper 42 to the recording head 34. A transport belt 51 is provided for transporting at opposing positions.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 and circulate in the belt transport direction (sub-scanning direction). A charging roller 56 as a charging unit for charging the surface of the transport belt 51 is provided. The charging roller 56 is disposed so as to come into contact with the surface layer of the conveyor belt 51 and to rotate by following the rotation of the conveyor belt 51 (which means that the conveyor belt 51 moves circularly in the forward and reverse directions). The conveyance belt 51 rotates in the belt conveyance direction when a conveyance roller 52 is rotationally driven by a sub-scanning motor (not shown) via a timing belt (not shown).

  As a paper discharge unit 96 for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying belt 51, a paper discharge roller 62, and a spur 63 as a paper discharge roller, , And a paper discharge tray 91 disposed below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus main body 99. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the transport belt 51, reverses it, and feeds it again between the counter roller 46 and the transport belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, a maintenance / recovery mechanism 81 for maintaining and recovering the state of the nozzles of the recording head 34 is disposed in a non-printing area on one side in the scanning direction of the carriage 33. The maintenance and recovery mechanism 81 includes cap members 82a and 82b (referred to as “cap member 82” when not distinguished), a wiper member 83, an idle discharge receiver 84, a carriage lock 87, and the like. The cap member 82 is for capping each nozzle surface of the recording head 34, and the wiper member 83 is a wiper blade for wiping the nozzle surface. The idle discharge receptacle 84 receives droplets when idle ejection is performed to eject droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the carriage lock 87 is maintained by the maintenance / recovery mechanism 81. This is for locking the carriage 33 so that the recovery operation can be performed.

  A non-replaceable first waste liquid tank 85 is provided below the maintenance / recovery mechanism 81 to accommodate waste liquid generated from the idle discharge receptacle 84 due to idle discharge with respect to the idle discharge receptacle 84 and cleaning of the wiper member 83 in the maintenance / recovery operation. I have. Further, on the side of the maintenance / recovery mechanism 81, a second waste liquid tank 86 that can be replaced from the front side of the apparatus main body is provided below the cartridge loading section 92.

  Further, in the non-printing area on the other side of the carriage 33 in the scanning direction, there is an empty space for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 88 is disposed. The idle discharge receiver 88 includes an opening 89 along the nozzle row direction of the recording head 34.

  In the image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding cassette 90, and the sheets 42 fed substantially vertically upward are guided by the guide member 45, and the transport belt 51. And the counter roller 46. The sheet 42 thus conveyed is further guided at the leading end by a conveying guide member 47 and pressed against the conveying belt 51 by a leading end pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated with respect to the charging roller 56, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 51 alternates, that is, in the sub-scanning direction that is the circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the sheet 42 is electrostatically attracted to the conveyance belt 51, and the sheet 42 is moved in the sub-scanning direction by the circular movement of the conveyance belt 51. Be transported.

  Therefore, by driving the recording head 34 according to the image signal while moving the carriage 33, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is terminated and the paper 42 is discharged onto the paper discharge tray 91.

Then, when performing maintenance / recovery of nozzles (not shown) of the recording head 34, the carriage 33 is moved to a position facing the maintenance / recovery mechanism 81 which is the home position. Then, by performing maintenance and recovery operations such as nozzle suction for performing capping by the cap member 82 to perform suction from the nozzles, and idle discharge for discharging liquid droplets that do not contribute to image formation, image formation by stable liquid droplet ejection is performed. It can be performed.
Further, a maintenance / recovery mechanism 81 for maintaining and recovering the state of the nozzles of the recording head 34 is disposed in a non-printing area on one side in the scanning direction of the carriage 33. The maintenance and recovery mechanism 81 includes cap members 82a and 82b (referred to as “cap member 82” when not distinguished), a wiper member 83, an idle discharge receiver 84, a carriage lock 87, and the like. The cap member 82 is for capping each nozzle surface (not shown) of the recording head 34, and the wiper member 83 is made of a wiper blade for wiping the nozzle surface. The idle discharge receptacle 84 receives droplets when idle ejection is performed to eject droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the carriage lock 87 is maintained by the maintenance / recovery mechanism 81. This is for locking the carriage 33 so that the recovery operation can be performed.

With reference to FIG. 3, the configuration and operation of the carriage 33 and the maintenance / recovery mechanism 81 will be supplementarily described. FIG. 3 is a schematic explanatory view for explaining the configuration and operation when the carriage 33 moves to the maintenance / recovery mechanism 81. As described with reference to FIG. 2, supply for supplying ink of each color from the ink cartridge 65 serving as the main tank to the sub tank 35 disposed in the carriage 33 is provided in the supply tube 36 serving as the ink supply path. A pump 38 is connected. The supply pump 38 is, for example, a tubing pump, and can send and suck ink by forward and reverse operations.
In order to prevent the ink stored in the sub tank 35 from leaking from the recording head 34 which is a liquid droplet ejection head, a mechanism (not shown) that places the sub tank 35 in a negative pressure state may be provided.

The sub tank 35 is provided with an air passage 39 and an air release valve 40 for discharging air accumulated in the sub tank 35 by air permeation or the like. The accumulated air is discharged by supplying ink to the sub-tank 35 while the air release valve 40 is opened. If ink is supplied while the atmosphere is released, the inside of the sub tank 35 is in the atmospheric pressure state. Therefore, after the atmosphere release valve 40 is closed, the supply pump 38 is reversed to suck the ink from the recording head 34. It is necessary to discharge the ink and create a negative pressure in the sub tank 35.
The carriage 33 is provided with an encoder sensor 66. By reading the encoder sheet 67 provided on the apparatus main body 99 side, the position of the carriage 33 in the main scanning direction can be detected.

  As shown in FIG. 3, the cap member 82 of the maintenance / recovery mechanism 81 for capping each nozzle hole (not shown) of the recording head 34 and the nozzle surface (not shown) can move relatively. It is configured to be possible. By pressing the cap member 82 against the nozzle surface, the nozzle holes of the recording head 34 can be capped. At least one of the cap members 82 communicates with a maintenance pump 68 that sucks liquid or gas. Accordingly, the maintenance pump 68 is driven and sucked in a state where the nozzle surface and the cap member 82 are in contact with each other, thereby making the inside of the cap member 82 have a negative pressure, and the ink (recording liquid) is discharged from the nozzle hole to the first waste liquid. It can be discharged into the tank 85. “Abutting” means contacting in the abutted state.

  The maintenance / recovery mechanism 81 configured as described above sucks and discharges ink from the nozzle surface using the maintenance pump 68 in order to maintain the discharge state of the nozzles, so that the foreign matter (thickened viscosity) clogged in the nozzle holes. Maintenance / recovery operation for discharging air bubbles and ink together with ink. Thereafter, by wiping the nozzle surface with a wiper, an ink meniscus is created in the nozzle hole, and the ink can be ejected normally.

At least two types of maintenance / recovery operations are set. One is a cleaning operation, and the other is refreshing for recovering the ejection state when many ejection failures due to missing nozzles occur.
In order to maintain the normal discharge state, a cleaning operation is performed. The cleaning operation recovers the discharge state by sucking a certain amount of ink from the nozzle hole while the air release valve 40 is closed and discharging foreign matter from the nozzle hole together with the ink. After sucking and moving the cap member 82 and the nozzle surface relatively, a meniscus is generated by wiping the nozzle surface with a wiper.

  As described above, the pressure feeding mechanism 60 that pressurizes the ink of the ink cartridge 65 serving as the main tank and supplies the ink to the recording head 34 via the sub tank 35 is mainly configured by the supply pump 38 and the supply tube 36. A suction mechanism 64 that communicates with the cap member 82 for covering and capping the plurality of nozzles and discharges ink from the plurality of nozzles by setting the inside of the cap member 82 to a negative pressure is constituted by the cap member 82 and the maintenance pump 68. Mainly composed. The supply pump 38 and the maintenance pump 68 described above may use the same drive source.

The detailed configuration of the recording head 34 will be described with reference to FIGS. FIG. 4 is a cross-sectional view taken along a direction orthogonal to the nozzle arrangement direction of the recording head 34. FIG. 5 is a schematic plan view showing the internal configuration of the recording head 34. 6 is a schematic cross-sectional view taken along the nozzle arrangement direction of the recording head 34. FIG. 7 is a schematic view showing the individual liquid chamber 6 and the common liquid chamber 10 in an enlarged manner by removing the upper portion of FIG. FIG.
As shown in FIG. 4, the recording head 34 includes a flow path plate 2, also called a flow path substrate or a liquid chamber substrate, a vibration plate member 3 bonded to the upper surface of the flow path plate 2, and a lower surface of the flow path plate 2. And a joined nozzle plate 1. As a result, a plurality of nozzles 4 that eject droplets communicate with each other through individual nozzle channels 5 and serve as individual flow chambers 6 serving as individual flow paths, and a fluid resistance unit that supplies ink to the individual liquid chambers 6. A communication portion 8 communicating with the individual liquid chamber 6 through the passage 7 and the supply passage 7 is formed. Then, a filter portion is provided in the supply port 9 a formed in the diaphragm member 3, and ink is supplied to the communication portion 8 from the common liquid chamber 10 formed in the frame member 17 described later. The individual liquid chamber is also simply referred to as a liquid chamber or a pressurized liquid chamber, a pressure chamber, a pressurized chamber, a flow path, and the like.

  The channel plate 2 is formed by, for example, subjecting a single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 5, the individual liquid chamber 6 is formed with recesses and holes. The flow path plate 2 is not limited to a single crystal silicon substrate, and other stainless steel substrates or photosensitive resins can be used. For example, it can be formed by etching a SUS substrate with an acidic etchant or machining such as punching (press). A space between the individual liquid chambers 6 of the flow path plate 2 is a liquid chamber interval wall 6A.

  The diaphragm member 3 is formed of a first layer 3A, a second layer 3B, and a third layer 3C. And this diaphragm member 3 has each vibration area | region (diaphragm part) 3a formed in the 1st layer 3A which forms the wall surface corresponding to each separate liquid chamber 6. As shown in FIG. In this vibration region 3a, an island-shaped convex portion 3b formed of the first layer 3A and the second layer 3B is provided on the outer surface (the surface opposite to the individual liquid chamber 6). A piezoelectric actuator 20 including an electromechanical conversion element as pressure generating means (actuator means, driving means) for deforming the vibration region 3a is disposed on the island-shaped convex portion 3b.

The piezoelectric actuator 20 has two laminated piezoelectric members 12 bonded with adhesive under the base member 13. In the laminated piezoelectric member 12, grooves are formed by half-cut dicing, and a required number of piezoelectric element columns (appearing in a cross section orthogonal to FIG. 4) are formed in a comb-like shape at a predetermined interval with respect to one piezoelectric member 12. Forming.
The lower end surface (joint surface) of the drive piezoelectric element column 12 </ b> A is joined to the island-shaped protrusion 3 b of the diaphragm member 3. In this embodiment, the length of the drive piezoelectric element column 12A in the longitudinal direction of the liquid chamber is longer than the length of the island-shaped convex portion 3b of the diaphragm member 3 in the longitudinal direction of the liquid chamber.

  Here, the piezoelectric member 12 is formed by alternately stacking the piezoelectric material layers 21 and the internal electrodes 22A and 22B, and the internal electrodes 22A and 22B are respectively substantially perpendicular to the end face, that is, the diaphragm member 3 of the piezoelectric member 12. Pull out to the side. Displacement in the stacking direction is generated by connecting the external electrodes 23 and 24 as end electrodes formed on the side surfaces and applying a voltage between the external electrodes 23 and 24. Here, one external electrode 23 is used as an individual external electrode (individual electrode), and the other external electrode 24 is used as a common external electrode (common electrode).

  The piezoelectric member 12 is connected to an FPC 15 as a flexible wiring member (flexible wiring board) for giving a driving signal to the driving piezoelectric element column 12A. Although not shown, the FPC 15 includes a driver IC (drive circuit) that gives a drive waveform to the drive piezoelectric element column 12A.

  The nozzle plate 1 is formed from a nickel (Ni) metal plate, and is formed by an electroforming method (electroforming). From a metal such as stainless steel, a resin such as a polyimide resin film, silicon, and a combination thereof. Can also be used. In this nozzle plate 1, nozzles 4 that are nozzle holes having a diameter of 10 to 35 μm are formed corresponding to the individual liquid chambers 6 and bonded to the flow path plate 2 with an adhesive. A water repellent layer is provided on the droplet discharge side surface (surface in the discharge direction: discharge surface or surface opposite to the individual liquid chamber 6 side) of the nozzle plate 1.

  Further, a frame member 17 formed by injection molding with an epoxy resin or polyphenylene sulfite is joined to the outer peripheral side of the piezoelectric actuator 20 composed of the piezoelectric member 12, the base member 13, the FPC 15, and the like. In the frame member 17, the common liquid chamber 10 described above is formed, and further, a supply port (not shown) for supplying ink to the common liquid chamber 10 from the outside is formed. This supply port is not shown. It is connected to an ink supply source such as a sub tank or an ink cartridge.

  In the recording head 34 configured in this manner, for example, when driven by a punching method, a driving pulse voltage of 20 to 50 V is selectively applied to the driving piezoelectric element column 12A according to an image recorded from a control unit (not shown). Apply. Then, the driving piezoelectric element column 12A to which the pulse voltage is applied is displaced to deform the vibration region 3a of the vibration plate member 3 in the direction of the nozzle plate 1, and the inside of the individual liquid chamber 6 due to the change in volume (volume) of the individual liquid chamber 6 By pressurizing this liquid, ink droplets are ejected from the nozzles 4 of the nozzle plate 1. As the ink is ejected, the pressure in the individual liquid chamber 6 decreases, and a slight negative pressure is generated in the individual liquid chamber 6 due to the inertia of the liquid flow at this time. Under this state, by turning off the voltage application to the drive piezoelectric element column 12A, the vibration region 3a of the diaphragm member 3 returns to the original position, and the individual liquid chamber 6 becomes the original shape. Further, negative pressure is generated. At this time, ink is filled from the common liquid chamber 10 into the individual liquid chamber 6, and ink droplets are ejected from the nozzles 4 in response to the next drive pulse application.

  As shown in FIGS. 6 and 7, the recording head 34 has a plurality of nozzles 4 that eject ink as droplets from the ejection surface. An individual liquid chamber 6 communicating with each nozzle 4 is formed in the recording head 34. The recording head 34 generates a pressure in the individual liquid chamber 6 by using the piezoelectric actuator 20 which is a pressure generating means, and instantaneously pushes out the ink filled in the individual liquid chamber 6 from the nozzle 4 to thereby generate droplets. Discharge. Each individual liquid chamber 6 communicates with the common liquid chamber 10 via an ink supply path X as a liquid supply path, and ink is distributed from the common liquid chamber 10 to the individual liquid chamber 6. . The common liquid chamber 10 has a supply port 25, and the ink in the sub tank 35 passes through the filter unit 26 and is supplied to the common liquid chamber 10 from the supply port 25.

  As shown in FIGS. 3 and 6, the sub tank 35 is configured to communicate with the atmosphere release valve 40 and the atmosphere via the air path 39. As shown in FIGS. 6 and 7, the ink 69 inside the sub tank 35 is provided. Is in contact with air in the sub tank 35. For this reason, air dissolves in the ink 69 inside the sub tank 35. The melted air thus causes bubbles 70 to be generated in the recording head 34 due to an increase in the temperature of the recording head 34 due to printing. The generated bubble 70 flows downstream of the ink supply path X indicated by the arrow, enters the nozzle 4 from the individual liquid chamber 6 and causes discharge failure. Hereinafter, for simplification of each drawing, the bubble 70 and the like are enlarged and exaggerated to show only one or several, and the downstream side of the ink supply path X may be illustrated outside the common liquid chamber 10.

  An embodiment for preventing the occurrence of defective discharge by preventing the bubbles 70 from entering the nozzle 4 (individual liquid chamber 6) unintentionally when the generated bubbles 70 are not discharged will be described below. .

  Although the description will be mixed, the first maintenance and the second maintenance unique to the present invention will be described. The first and second maintenance is set in addition to the maintenance and recovery operation. The first maintenance means for discharging ink from the nozzles 4 of the recording head 34 and the second maintenance means for discharging more ink from the nozzles 4 than the amount of ink discharged by the first maintenance means include the pressure feeding mechanism 60 and / or The suction mechanism 64 is configured. In other words, ink discharge by the first and second maintenance means is performed by the pressure feeding mechanism 60 and / or the suction mechanism 64 (Claim 4). Hereinafter, the ink discharge operation performed by the first maintenance unit is simply referred to as first maintenance, and the ink discharge operation performed by the second maintenance unit is simply referred to as second maintenance.

The first and second maintenance is performed by suction using the maintenance pump 68 of the suction mechanism 64 and pressurization using the supply pump 38 of the pressure feed mechanism 60. A plurality of methods for differentiating the ink discharge amount between the first maintenance and the second maintenance can be considered as combinations shown in FIG. In the graphs of FIGS. 8A, 8B, and 8C, the horizontal axis represents time (t), and the vertical axis represents the strength (magnitude) of the pump signal. Yes.
As shown in FIG. 8 (a), there is a method in which the suction time of the second maintenance is set longer than the suction time of the first maintenance under the same condition of the strength of the suction / maintenance pump signal (pump output). It is done. Further, as shown in FIG. 8B, a method of setting the second maintenance pump signal (pump output) stronger than the first maintenance suction / maintenance pump signal (pump output) (suction / maintenance pump signal: Signal that affects the rotation speed of the maintenance pump). Furthermore, as shown in FIG. 8C, by the pressurization that sets the pump signal (pump output) of the second maintenance stronger than the strength (pump output) of the pressurization / supply pump signal of the first maintenance. You may carry out by the method. Of course, the first maintenance and the second maintenance may be realized by an operation combining suction and pressurization.

[Conventional example]
With reference to FIG. 9A, a conventional recording head 134 will be described. FIG. 9A is a cross-sectional view of a main part of a recording head 134 showing a conventional example. As shown in FIG. 9A, in the recording head 134 of the conventional example, the upper wall surface 117a of the frame member 117 constituting the common liquid chamber 110 has a flat surface without a step shape that creates an air reservoir. Yes. Therefore, a large amount of ink needs to be discharged in order to discharge the bubbles 70 generated in the above-described process. On the other hand, in later-described embodiments including the first embodiment of the present invention shown in FIGS. 9B and 10, as will be described in detail later, the bubbles 70 are generated with a much smaller ink discharge amount. It is possible to discharge out of the recording head 34, and the bubble discharge performance is remarkably improved.

[Example 1]
Embodiment 1 of the present invention will be described with reference to FIGS. 9B and 10 (claims 2 and 4). FIG. 9B is a cross-sectional view in which the main part of the recording head showing the first embodiment of the present invention is partly broken and omitted, and FIG. 10 is a diagram illustrating how bubbles are removed by the first and second maintenance performed in the first embodiment. It is explanatory drawing explaining a discharge transition state. For simplification of each drawing, the first and second steps shown in FIGS. 9B and 10 and the like including the bubble 70 are enlarged and exaggerated.
As shown in FIG. 9B, the recording head 34 of Example 1 has at least one first step 75 formed on the upstream side of the ink supply path X in the upper wall surface 17 a constituting the common liquid chamber 10. And a second step 78 formed on the most downstream side of the ink supply path X.

  In the first step 75, a downward concave portion that captures and holds the bubble 70 that occurs in the above-described manner and floats upstream of the ink supply path X, that is, backflows upstream of the ink supply path X in the common liquid chamber 10. A shaped air reservoir S1 is formed. In the first embodiment, a plurality of n first steps 75 are formed. In FIG. 9 (b), a plurality of n first steps 75 are indicated by 75-n including two of which the shapes are actually shown, and the other first steps 75 are omitted. Yes.

  The second step 78 (made by the air reservoir S2) is formed in a larger shape than the first step 75 (made by the air reservoir S1). In other words, the second step 78 closest to the individual liquid chamber 6 is wider than the distance between the other first steps 75 and is deep enough not to reach the individual liquid chamber 6 in the first maintenance. It is formed in a concave shape (air reservoir S2). The second step 78 is formed with a downward concave air reservoir S2 that captures and holds the air bubble 70 that occurs in the above-described manner and floats to the upstream side of the ink supply path X. With this configuration, air bubbles do not accidentally enter the individual liquid chamber 6 when not intended, as has been a problem in the past.

Here, a supplementary explanation will be given on the upper wall surface 17a constituting the common liquid chamber 10. The distance between the individual liquid chamber 6 and the supply port 25 (see FIGS. 6 and 7 and the like) of the common liquid chamber 10 (the distance in the left-right direction in the drawing along the ink supply path X) differs depending on the individual liquid chamber 6. For this reason, when ink is ejected and consumed in the individual liquid chamber 6 in the vicinity of the common liquid chamber supply port, the flow rate decreases as the distance from the supply port 25 increases, and the supply of ink to the individual liquid chamber 6 cannot be made in time. In order to stably supply ink to the individual liquid chamber 6 that is at a distance from the supply port 25, it is desirable that the cross-sectional area is reduced and the flow rate is increased as the distance from the supply port 25 is increased. Therefore, in the first embodiment shown in FIG. 9B, the upper wall surface 17a of the common liquid chamber 10 is inclined so as to gradually decrease from the upstream side to the downstream side of the ink supply path X as the distance from the supply port 25 increases. In this case, the inclined surface is inclined to the left. With this configuration, the cross-sectional area of the common liquid chamber 10 is reduced as the distance from the supply port 25 increases. The first step 75 and the second step 78 are formed in consideration of the generation, growth and movement of the bubbles 70, and from the technical matters described in FIG. It is desirable to be the upper wall surface 17a of the inclined surface of the common liquid chamber 10 along the above.
Note that the upper wall surface 117a of the individual liquid chamber 110 of the conventional example shown in FIG. 9A is also from the upstream side to the downstream side of the ink supply path X, similarly to the upper wall surface 17a of the first embodiment shown in FIG. 9B. The inclined surface is inclined so as to be gradually lowered toward the side (inclined to the left in the figure).

Hereafter, in each figure which shows the below-mentioned Example, the air reservoir S1 formed in the 1st level | step difference 75 and the air pocket S2 formed in the 1st level | step difference 78 are illustration for the simplification of a figure. Omitted and shown only in FIG.
The plurality of n first steps 75 (air reservoirs created) are all drawn in the same shape in the following drawings, but are smaller than the second step 78 (air reservoir S2 created). Different shapes may be used.

  The shape of the first step 75 and the second step 78 is limited to a shape that has a cross-sectional shape as shown in FIG. 9B and that forms the substantially triangular air reservoirs S1 and S2 that are open at the bottom. I can't. That is, the shape may be a slightly deformed shape, a groove shape, a semicircular shape, or a semielliptical shape as long as it captures and holds the bubbles 70 that float to the upstream side of the ink supply path X. The shape of the first step 75 and the second step 78 shown in FIG. 9 (b) is a shape for moving bubbles in consideration of buoyancy as compared with other shapes, as described in FIG. It is considered excellent. Recently, due to advances in semiconductor processes and micro electro mechanical systems (MEMS), the shape of the first step 75 and the second step 78, including laser processing, can be manufactured compared to the case of forming a groove shape. Is also relatively easy.

  The size and dimensions of the first step 75 and the second step 78 are not particularly specified, but may be any size and dimension that can exhibit the above basic functions. In setting and designing the size / dimension, it is preferable to design the optimum size / dimension range after observing the growth of bubbles in the liquid ink and conducting a test or the like.

With reference to FIG. 10, the operation of the first embodiment executed by the image forming apparatus 100 including the recording head 34 will be described. In FIG. 10, one second step 78 (hereinafter also simply referred to as “step 78”) formed on the most downstream side of the ink supply path X, and the first step formed on the upstream side of the ink supply path X. A case will be described in which there are four steps 75 (hereinafter also simply referred to as “steps 75”), for a total of five steps.
FIG. 10A shows a bubble 70 that emerges upstream of the ink supply path X generated in the above-described manner. Here, when the first maintenance as described with reference to FIG. 8 is performed once, as shown in FIG. 10B, the air bubble 70 rides on the flow of discharged ink and is downstream of the ink supply path X. To the position indicated by the broken line. Thereafter, the journey 70 that has advanced to the position indicated by the broken line is trapped and held in an air pocket (not shown) of the first step 75-1 by the buoyancy of the bubble 70 itself.

  Further, when the first maintenance is performed three times (four times in total), the same process as described above is followed, and as shown in FIG. Are trapped and held in an air pocket (not shown). In this way, each time the first maintenance is performed, the bubble 70 advances to the downstream side of the one-stage ink supply path X. Without such a configuration, the bubble 70 floats to the top by its buoyancy, and the common liquid chamber 10 becomes full of bubbles, leading to a problem that cannot be recovered.

  When the first maintenance is performed once (five times in total) from the state shown in FIG. 10C, as shown in FIG. It rides and flows to the most downstream side of the ink supply path X, and is trapped and held in an air reservoir (not shown) of the second step 78. From the ink discharge performance of the first maintenance described above, the amount of ink discharged is small in the first maintenance no matter how many times the first maintenance is performed. For this reason, the bubbles 70 do not advance downstream until the state shown in FIG. 10D, and do not accidentally enter the individual liquid chamber 6 when not intended. Therefore, no discharge failure is caused.

  The bubble 70 in the state shown in FIG. 10D (the state accumulated in the air reservoir of the second step 78) performs the second maintenance, and the second maintenance has an ink discharge amount. Therefore, the liquid is discharged from the nozzle 4 through the individual liquid chamber 6.

  As described above, the air bubbles 70 existing in the first step 75 flow to the downstream side of the ink supply path X from the first step 75 due to the ink discharge by the first maintenance, and enter the second step 78. The existing bubbles 70 are configured not to flow from the second step 78 to the downstream side of the ink supply path X. In addition, the air bubbles 70 existing in the second step 78 flow to the downstream side of the ink supply path X from the second step 78 by discharging the ink by the second maintenance.

  In the first embodiment, the description of the control configuration and operation timing in which the first and second maintenance are performed is omitted, but for example, almost the same as the control configuration in FIG. 12 (only the temperature sensor 59 is unnecessary in the first embodiment). It is executed at an appropriate timing under the command of the control means 50.

  As described above, according to the first embodiment, bubbles can be surely discharged by allowing bubbles to enter the individual liquid chamber from the common liquid chamber only during the ink discharging operation. Thereby, when it is not the operation | movement which discharges | emits a bubble, since a bubble is not made to invade into an individual liquid chamber from a common liquid chamber, generation | occurrence | production of discharge failure can be prevented beforehand. In other words, according to the examples described later including the first embodiment, both the improvement of nozzle stability (hardness of nozzle down) and the improvement of nozzle recoverability (hardness of maintenance) are improved. Both have been achieved.

[Modification 1]
A first modification of the first embodiment will be described with reference to FIG. 11 (Claim 3). FIG. 11A is a cross-sectional view in which the main part of the recording head of the first modification is partially broken and omitted, and FIG. 11B is a bubble related to the degree of inclination of the inclined surfaces of the first and second steps. It is a figure explaining the force which acts on.
In the first modification, as shown in FIGS. 11A and 11B, the inclined surface 78a of the second step 78 on the downstream side of the ink supply path X is compared with the first embodiment. The difference is that the degree of inclination is steeper than that of the inclined surface 75a of the step 75. Modification 1 other than this difference is the same as the first embodiment.

  As shown in FIG. 11B, on the second step 78 side, a component force 78F2 that is a component of the force against the discharge force is generated by the buoyancy 78F1 acting on the bubble 70 in contact with the inclined surface 78a. On the other hand, on the first step 75 side, a force component / component force 75F2 that resists the discharge force is generated by the buoyancy 75F1 acting on the bubble 70 in contact with the inclined surface 75a. As is apparent from the figure, the component force 78F2 that is a component of the force resisting the discharge force on the second step 78 side is larger than the component / component force 75F2 of the force that resists the discharge force on the first step 75 side. (78F2> 75F2). As a result, it is possible to prevent bubbles from entering the individual liquid chamber unintentionally during the first maintenance.

[Example 2]
A second embodiment of the present invention will be described with reference to FIGS. 12 and 13 (claims 4, 5 and 6). FIG. 12 is a block diagram illustrating a control configuration of a main part of the second embodiment. FIG. 13 is a diagram for explaining the control contents of the second embodiment.
Compared with the above embodiment and Example 1, Example 2 uses a temperature sensor 59 that detects the temperature of the recording head 34 as shown in FIG. The main difference is that the control means 50 for controlling the second maintenance means is used. The temperature sensor 59 is composed of, for example, a thermocouple, and is disposed in the vicinity of the recording head 34 shown in FIG. 1, and functions as a head temperature detection unit that detects the temperature of the recording head 34. The control means 50 controls the first and second maintenance means to execute ink discharge when the temperature of the recording head 34 detected by the temperature sensor 59 exceeds a preset threshold value related to the rising temperature difference. It has a function to control.

  The control means 50 has a function of controlling the operation of the supply pump 38 and / or the maintenance pump 68, which are the first and second maintenance means, based on information (data signal) from the temperature sensor 59 shown in FIG. . Further, the control means 50 controls the drive of the main scanning motor 54 based on information (data signal) from the encoder sensor 66 shown in FIG. 12, thereby moving and stopping the carriage 33 shown in FIG. Is controlling.

As shown in FIG. 12, the control unit 50 includes a CPU 50a, an unillustrated I / O (input / output) port, a ROM 50b including a PROM, a RAM 50c, a timer 50d, and the like, and these are connected by a signal bus. It has a microcomputer. The CPU 50a has an arithmetic function and a control function for performing the above-described control executed by the control means 50. The ROM 50b contains a program for demonstrating the arithmetic function and control function of the CPU 50a, and related data for demonstrating the arithmetic function and control function of the CPU 50a (for example, a calculation formula for obtaining a threshold value related to the rising temperature difference). Stored in advance.
The RAM 50c is backed up by, for example, a battery, and can store and hold the temperature of the recording head 34 detected by the temperature sensor 59 at any time, and can also store various data on / off signals and the like at any time via the CPU 50a. Have The timer 50d is backed up by a battery or the like, for example, and functions as a timing unit that measures and holds the time shown in FIG.

As described above, when the temperature of the ink, which is a liquid, is raised, air dissolved in the ink is generated as bubbles. Since the amount of generated bubbles varies depending on the increased temperature difference, the first and second maintenance operations are performed on the basis of the temperature increase detected and measured by the temperature sensor 59, so that the nozzle 4 of the recording head 34 is applied to the nozzle 4. The bubble entry prevention performance is significantly increased. Therefore, in the second embodiment, as shown in FIG. 13, the temperature change of the recording head 34 is monitored by the temperature sensor 59 constantly or at any time, and the first temperature difference is exceeded when the rising temperature difference exceeds a preset temperature difference threshold. The determination that the maintenance or the second maintenance is performed is executed.
In addition, regarding the discharge of bubbles generated due to an increase in the temperature of the ink, it is discharged without any problem in the same process and progress as in the first embodiment.

  As described above, according to the second embodiment, the bubbles generated when the temperature of the recording head rises can be surely discharged with good timing.

In addition to the second embodiment described above, the following configuration may be used. That is, there are a plurality of first steps 75, and when the control means 50 exceeds the threshold value related to the temperature rise difference, the first maintenance means executes ink discharge as many times as the number of the first steps. Then, the second maintenance unit may perform ink discharge.
If comprised as mentioned above, the bubble discharge | emission property can be improved more by implementing 2nd maintenance in the state which advances to the level | step difference of the discharge side a little after bubble generation and is easy to discharge.

[Example 3]
A third embodiment of the present invention will be described with reference to FIG. FIG. 14 is a cross-sectional view of a main part of the recording head showing the third embodiment.
In the third embodiment illustrated in FIG. 14, the second step 78 is not located on the most downstream side of the ink supply path X, and the first step 75 has a smaller number of steps than the first step 75 formed on the upstream side of the ink supply path X. A third step 76 equivalent to the size of the step 75 is arranged on the most downstream side of the ink supply path X. The first and / or second maintenance of the third embodiment is performed in the same manner as the first embodiment.

The number of steps of the third step 76 disposed on the most downstream side of the ink supply path X from the second step 78 is larger than the number of steps of the first step 75 disposed on the upstream side of the second step 78. The smaller one is more effective from the viewpoint of bubble discharge efficiency during the bubble discharge operation.
According to the third embodiment, it is needless to say that the same effects as those of the first embodiment can be obtained from the technical contents detailed in the first embodiment.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments and examples described above, and is described in the claims unless specifically limited by the above description. Various modifications and changes can be made within the scope of the present invention. For example, the above embodiment, Examples 1 to 3 and Modification 1 may be appropriately combined.

  For example, the image forming apparatus to which the present invention is applied is not limited to the type of image forming apparatus described above, and may be another type of image forming apparatus. In other words, the image forming apparatus to which the present invention is applied may be a copier, a single facsimile, or a complex machine of these, or a complex machine such as a monochrome machine related thereto. In addition, the image forming apparatus to which the present invention is applied may be an image forming apparatus used for forming an electric circuit or an image forming apparatus used for forming a predetermined image in the biotechnology field. The pressure generation means is not limited to the electromechanical conversion element such as the piezoelectric element of the above embodiment, but may be an electrothermal conversion element such as a heater.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 1 Nozzle plate 2 Flow path plate 3 Vibration plate member 4 Nozzle 5 Nozzle communication path 6 Individual liquid chamber 7 Supply path 10 Common liquid chamber 12 Piezoelectric member 13 Base member 17 Frame member 17a Upper wall surface of common liquid chamber 20 Piezoelectric actuator (pressure generation) means)
25 Supply port 26 Filter unit 34 Recording head (an example of a droplet discharge head)
35 Sub tank 36 Supply tube 38 Supply pump 50 Control means 59 Temperature sensor (an example of head temperature detection means)
60 Pressure feeding mechanism (an example of first and / or second maintenance means)
64 Suction mechanism (an example of first and / or second maintenance means)
65 Ink cartridge (example of main tank)
70 Air bubbles 75 First step 75a Inclined surface of the first step 76 Third step 78 Second step 78a Inclined surface of the second step 81 Maintenance recovery mechanism 82 Cap member 100 Image forming apparatus S1, S2 Air pool X Ink supply path (liquid supply path)

Japanese Patent Laid-Open No. 10-024572 JP 2004-358737 A

Claims (6)

A plurality of nozzles for discharging droplets;
An individual liquid chamber filled with a liquid that communicates with each nozzle and is supplied to the nozzle;
Pressure generating means for generating a pressure for discharging the liquid in each individual liquid chamber from the corresponding nozzle;
A common liquid chamber for supplying a liquid to each of the individual liquid chambers;
At least one first air reservoir is formed on the upper wall surface constituting the common liquid chamber on the upstream side of the liquid supply path to the individual liquid chambers, and forms a concave air pocket that captures and holds the bubbles rising to the upstream side. 1 step and
A second step that is formed on the upper wall surface on the downstream side of the liquid supply path in the first step and is larger than the first step that forms a recess-like air pocket that captures and holds the bubbles that float to the upstream side. When,
A third step that is formed on the upper wall surface on the most downstream side of the liquid supply path in the first and second steps, less than the number of the first steps, and is equivalent to the size of the first step. A droplet discharge head;
First maintenance means for discharging liquid from the nozzle;
Second maintenance means for discharging more liquid from the nozzle than the amount of liquid discharged by the first maintenance means;
An image forming apparatus having
Due to the liquid discharge by the first maintenance means, the bubbles existing in the first step flow to the downstream side of the liquid supply path from the first step, and the bubbles existing in the second step become the second It is configured not to flow from the step to the downstream side of the liquid supply path, and the bubbles present in the second step due to the liquid discharge by the second maintenance means are downstream of the liquid supply path from the second step. An image forming apparatus configured to flow to the side. A plurality of nozzles for discharging droplets;
An individual liquid chamber filled with a liquid that communicates with each nozzle and is supplied to the nozzle;
Pressure generating means for generating a pressure for discharging the liquid in each individual liquid chamber from the corresponding nozzle;
A common liquid chamber for supplying a liquid to each of the individual liquid chambers;
At least one first air reservoir is formed on the upper wall surface constituting the common liquid chamber on the upstream side of the liquid supply path to the individual liquid chambers, and forms a concave air pocket that captures and holds the bubbles rising to the upstream side. 1 step and
A second step larger than the first step is formed on the upper wall surface on the most downstream side of the liquid supply path in the first step and creates a concave air pocket that captures and holds the bubbles rising to the upstream side. A droplet discharge head comprising a step, and
First maintenance means for discharging liquid from the nozzle;
Second maintenance means for discharging more liquid from the nozzle than the amount of liquid discharged by the first maintenance means;
An image forming apparatus having
Due to the liquid discharge by the first maintenance means, the bubbles existing in the first step flow to the downstream side of the liquid supply path from the first step, and the bubbles existing in the second step become the second It is configured not to flow from the step to the downstream side of the liquid supply path, and the bubbles present in the second step due to the liquid discharge by the second maintenance means are downstream of the liquid supply path from the second step. An image forming apparatus configured to flow to the side. The image forming apparatus according to claim 1 or 2,
The first and second steps each have an inclined surface that decreases from the upstream side to the downstream side of the liquid supply path,
2. The image forming apparatus according to claim 1, wherein the inclined surface of the second step has a steeper degree than that of the first step. The image forming apparatus according to any one of claims 1 to 3,
A sub-tank for storing liquid to be supplied to the droplet discharge head, a pressure feeding mechanism for pressurizing and supplying liquid from a main tank for storing liquid to be supplied to the sub-tank to the sub-tank, and for covering and capping the plurality of nozzles Any one of a suction member that discharges liquid from the plurality of nozzles by communicating with the cap member and making the inside of the cap member negative pressure,
The liquid discharge by the first and second maintenance means is performed by the pressure feeding mechanism and / or the suction mechanism. The image forming apparatus according to any one of claims 1 to 4,
Head temperature detecting means for detecting the temperature of the droplet discharge head;
When the temperature of the droplet discharge head detected by the head temperature detection unit exceeds a preset threshold value related to the rising temperature difference, the first and second maintenance units are configured to execute the liquid discharge. Control means for controlling;
An image forming apparatus comprising: The image forming apparatus according to claim 5.
The control means controls the first maintenance means to perform the liquid discharge as many times as the number of the first steps when the threshold value related to the rising temperature difference is exceeded, and then the second maintenance means An image forming apparatus, wherein a maintenance unit controls the liquid discharge.

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