JP2013103485A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To equalize liquid ejection for improvement in image quality in an image forming apparatus in which nozzles are arrayed in a row along the direction of gravitational force.SOLUTION: The image forming apparatus includes a recording head 24 arranged such that a liquid droplet is ejected from a nozzle 205 in a horizontal direction. The image forming apparatus is provided with: a sub tank to which ink is supplied from a main tank, and connected to, via a liquid storage part 231 of a head tank 29 and a supply tube 306, a supply port 208 leading to an upper part of a common liquid chamber 207 of the recording head 24, and also to, via a return path 236 of the head tank 29 and a return tube 308, a return port 209 leading to a lower part of the common liquid chamber 207; and a return pump disposed in the return tube 308. The return pump is driven when the recording head 24 ejects a liquid droplet to thereby cause the ink in the common liquid chamber 207 to flow from the upper part to the lower part of the common liquid chamber 207.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a recording head that discharges droplets in a horizontal direction.

  As an image forming apparatus such as a printer, a facsimile, a copying machine, a plotter, or a complex machine of these, for example, a liquid discharge recording type image forming apparatus using a liquid discharge head (droplet discharge head) for discharging droplets as a recording head For example, an ink jet recording apparatus is known.

  As a liquid ejection type image forming apparatus, a configuration including a recording head that transports a recording medium in a horizontal direction and ejects liquid droplets downward in the vertical direction with respect to the recording medium (this is called a “vertical printing system”). .) And a configuration including a recording head that transports a recording medium in a vertical direction and discharges liquid droplets toward the recording medium in a horizontal direction (this is referred to as a “horizontal printing method”). Is known (Patent Documents 1 and 2).

  Here, the vertical printing type image forming apparatus has an advantage that the influence of individual pixels on the image can be minimized because the droplet discharge direction is the gravitational direction. In this case, so-called face-down paper discharge can be easily performed with the printing surface of the recording medium facing down, or a recording head can be placed opposite to both sides of the paper to print on both sides simultaneously. Also has the advantage of being easy to do.

Japanese Patent No. 4186557 JP 09-254401 A

  In the horizontal printing type image forming apparatus described above, the nozzle rows are arranged in a direction along the direction of gravity due to the discharge of liquid droplets in the horizontal direction, so that a difference in height occurs in the position of the nozzles. It will be. Along with this difference in height, the hydrostatic pressure of each nozzle is different, so that there is a problem that the droplet discharge state is not uniform, the dot diameter is not uniform, and the landing position is shifted.

  The present invention has been made in view of the above-described problems, and an object thereof is to make the droplet discharge state uniform and improve the image quality.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A nozzle row in which a plurality of nozzles for discharging droplets are arranged; a plurality of individual liquid chambers through which the plurality of nozzles communicate; and a common liquid chamber for supplying a liquid to the plurality of individual liquid chambers. A recording head arranged so as to discharge in the horizontal direction;
An ink tank containing the liquid to be supplied to the recording head;
Liquid feeding means for circulating the liquid between the ink tank and the recording head,
The liquid feeding means is connected to the upper end side and the lower end side of the common liquid chamber of the recording head,
Control for driving the liquid feeding means to cause the liquid in the common liquid chamber to flow from the upper end side to the lower end side of the common liquid chamber when droplets are ejected from the recording head. It was set as the structure which has a means.

  According to the image forming apparatus of the present invention, it is possible to make the droplet discharge state uniform and improve the image quality.

FIG. 2 is a side explanatory view of a mechanism unit of the image forming apparatus according to the first embodiment of the present invention. It is explanatory drawing which looked at FIG. 1 from the arrow A direction. It is explanatory drawing of the nozzle surface of a recording head. FIG. 2 is an explanatory cross-sectional view illustrating an example of the same recording head. It is explanatory drawing of the ink supply circulation system in the same apparatus. FIG. 4 is a cross-sectional explanatory view of a recording head and a head tank portion. FIG. 7 is a cross-sectional explanatory view taken along line BB in FIG. 6. It is block explanatory drawing of a control part. FIG. 6 is a cross-sectional explanatory view of a recording head and a head tank portion in a second embodiment of the present invention. FIG. 10 is a cross-sectional explanatory view taken along line CC in FIG. 9. FIG. 10 is a cross-sectional explanatory view of a recording head and a head tank portion in a third embodiment of the present invention. FIG. 10 is a cross-sectional explanatory view of a recording head and a head tank portion in a fourth embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view of a mechanism portion of the image forming apparatus, and FIG. 2 is an explanatory view of FIG.

  This image forming apparatus is a serial type image forming apparatus, and has an image forming unit 2, a transport mechanism unit 5 and the like inside the apparatus main body, and can stack sheets 10 as recording media on the lower side of the apparatus main body. A paper feed tray (including a paper feed cassette and used in the meaning of a paper feed unit) 4 is provided, the paper 10 fed from the paper feed tray 4 is taken in, and the paper 10 is moved vertically by the transport mechanism unit 5 ( The image forming unit 2 discharges droplets in the horizontal direction and records a required image while intermittently transporting the sheet 10 in the direction along the vertical direction). The paper 10 is conveyed upward and discharged to a paper discharge tray 7 provided on the upper side of the apparatus main body.

  Also, when performing double-sided printing, after the printing on one side (front side) is completed, the paper 10 is taken into the reversing unit 8 from the paper discharge unit 6 and reversed while being conveyed in the reverse direction (downward) by the transport mechanism unit 5. Then, the other side (back side) is sent again to the transport mechanism as a printable side, and the paper 10 is discharged to the discharge tray 7 after the other side (back side) printing is completed.

  Here, the image forming unit 2 movably holds a carriage 23 on which the recording head 24 is mounted with a main guide member 21 and a sub-guide member 22 spanned between the left and right side plates 101L and 101R, and a main scanning motor 25. Thus, the moving scanning is performed in the main scanning direction via the timing belt 28 passed between the driving pulley 26 and the driven pulley 27.

  The carriage 23 has recording heads 24a and 24b composed of liquid ejection heads for ejecting ink droplets of each color of yellow (Y), magenta (M), cyan (C), and black (K). As shown, the recording head 24 is arranged in a sub-scanning direction perpendicular to the main scanning direction, and the droplet discharge direction is mounted in the horizontal direction. That is, a horizontal printing method is employed in which a nozzle surface on which nozzles for discharging droplets are formed is arranged in the vertical direction and includes a recording head 24 that discharges droplets in the horizontal direction.

  Here, for example, as shown in FIG. 3, the recording head 24 has two nozzle rows Na and Nb in which nozzles 205 for discharging a plurality of liquid droplets are arranged, and one nozzle of the recording head 24a. Row Na is a yellow (Y) droplet, the other nozzle row Nb is a magenta (Y) droplet, one nozzle row Na of the recording head 24b is a black (K) droplet, and the other nozzle row. Nb ejects cyan (C) droplets, respectively.

  For example, as shown in FIG. 4, the recording head 24 includes a heating element substrate 202 and a liquid chamber forming member 203, and the liquid supplied to the common liquid chamber 207 is guided to the individual liquid chamber 206, and the heating element is formed. A thermal type is used in which the liquid boils when 204 is driven, and droplets are ejected from the nozzle 205.

  As the recording head, there are various methods such as a method in which the diaphragm is deformed by using a piezoelectric element, and the diaphragm is deformed by an electrostatic force to obtain a discharge pressure. The present invention can be applied to such an image forming apparatus.

  The carriage 23 is mounted with a head tank 29 for supplying ink of each color corresponding to each nozzle row Na, Nb of the recording head 24. As will be described later, ink as liquid is supplied to the head tank 29 via a sub tank which is an ink tank to which liquid from each color ink cartridge (main tank) is detachably attached to the apparatus main body. Is done.

  Further, an encoder scale 121 formed with a predetermined pattern is stretched between both side plates 101L and 101R along the main scanning direction of the carriage 23, and an encoder composed of a transmissive photosensor that reads the pattern of the encoder scale 121 is read on the carriage 23. A sensor 122 is provided, and the encoder scale 121 and the encoder sensor 122 constitute a linear encoder (main scanning encoder) 123 that detects the movement of the carriage 23.

  Further, a maintenance / recovery mechanism 9 for maintaining and recovering the state of the nozzle 205 of the recording head 24 is disposed in a non-printing area on one side of the carriage 23 in the scanning direction. The maintenance / recovery mechanism 9 includes a suction cap 92a and a cap 92b for capping each nozzle surface 124 (see FIG. 3) of the recording head 24 at the frame 90 (referred to as “cap 92” when not distinguished). , A wiper member (wiper blade) 93 that moves in the direction of the arrow and wipes the nozzle surface 124 is held, and preliminary discharge that discharges droplets that do not contribute to recording in order to discharge thickened ink ( An empty discharge receiver 94 for receiving droplets when performing (empty discharge) is provided. A suction pump 96 as suction means is connected to the suction cap 92 a, and the suction pump 96 communicates with a waste liquid tank 97. The suction cap 92a is provided with an openable and closable atmospheric release valve 98 that opens the sealed space formed when the nozzle surface of the recording head 24 is capped with the suction cap 92a.

  The paper 10 in the paper feed tray 4 is separated one by one by a paper feed roller (half-moon roller) 43 and a separation pad 44 and fed into the apparatus main body, and conveyed along the conveyance guide member 45 by the conveyance mechanism unit 5. It is fed between the belt 51 and the presser roller 48 and is attracted to the transport belt 51 and transported.

  The conveyance mechanism unit 5 includes an endless conveyance belt 51 that is stretched between a conveyance roller 52 that is a driving roller and a driven roller 53, a charging roller 54 that charges the conveyance belt 51, and the image forming unit 2. And a platen member 55 that maintains the flatness of the conveyor belt 51 at a portion facing the plate.

  The conveyance belt 51 rotates in the belt conveyance direction (sub-scanning direction, paper conveyance direction) when the conveyance roller 52 is rotationally driven by the sub-scanning motor 151 via the timing belt 152 and the timing pulley 153. In this conveyance belt 51, the area from the conveyance roller 52 that adsorbs the paper 10 facing the image forming unit 2 to the driven roller 53 is a normal conveyance portion 51a, and the area from the driven roller 53 to the conveyance roller 52 is reversely conveyed. This is referred to as a portion 51b.

  In addition, a code wheel 154 is attached to the shaft 52 a of the transport roller 52, and an encoder sensor 155 including a transmission type photo sensor for detecting a pattern formed on the code wheel 154 is provided. The code wheel 154 and the encoder sensor 155 A rotary encoder (sub-scanning encoder) 156 that detects the amount and position of movement of the conveyor belt 51 is configured.

  The paper discharge unit 6 includes a paper discharge guide member 61, a paper discharge conveyance roller 62 and a spur 63, a paper discharge roller 64 and a spur 65, and the paper 10 on which an image is formed is discharged to the paper discharge roller 64 and the spur 65. The paper is discharged face-down onto the paper discharge tray 7 from the middle.

  The reversing unit 8 reverses the paper 10 partially discharged to the paper discharge tray 7 by the switchback method and feeds the paper 10 between the conveyance belt 51 and the presser roller 48. A claw 81, a reverse guide member 82, a reverse roller 83 and a spur 84 as a reverse roller, a conveyance auxiliary roller 85 facing the driven roller 53, a reverse conveyance portion 51b of the conveyance belt 51, and a reverse conveyance of the conveyance belt 51 A detour guide member 86 for guiding the sheet 10 separated from the portion 51 b between the conveyance belt 51 and the pressing roller 48 by detouring the charging roller 54 is provided.

  In this image forming apparatus configured as described above, the paper 10 is separated and fed from the paper feed tray 4 one by one, and the paper 10 is electrostatically attracted to the charged transport belt 51, and the transport belt 51 is moved by the circular movement. The paper 10 is conveyed in the vertical direction. Therefore, by driving the recording head 24 according to the image signal while moving the carriage 23, ink droplets are ejected onto the stopped paper 10 to record one line, and after the paper 10 is conveyed by a predetermined amount, The next line is recorded, and the sheet 10 for which recording has been completed is discharged to the discharge tray 7.

  When performing maintenance and recovery of the nozzles of the recording head 24, the carriage 23 is moved to a position opposite to the maintenance and recovery mechanism 9 as the home position, and the suction cap 92a is capped to perform suction and discharge from the nozzles 205. By performing a maintenance and recovery operation such as nozzle suction and idle ejection for ejecting droplets that do not contribute to image formation, image formation by stable droplet ejection can be performed.

  In the case of performing duplex printing, the first surface printing performs the operation as described above, and when the rear end of the paper 10 passes through the reversing part branch (switching claw 81), the paper discharge roller 64 is driven in reverse. The sheet 10 is switched back, guided to the reversing guide member 82 side, conveyed between the reversing roller 83 and the spur 84, and the sheet 10 is sent between the reverse conveying portion 51 b of the conveying belt 51 and the conveying auxiliary roller 85. It is.

  As a result, the sheet 10 is attracted to the transport belt 51, transported by the circular movement of the transport belt 51, separated from the transport belt 51 on the transport roller 52 side, and guided by the detour guide member 86 (via the detour path). Then, the second side printing is performed by feeding again between the normal conveyance portion 51a of the conveyance belt 51 and the pressing roller 48 and being adsorbed by the conveyance belt 51, and again adsorbed and conveyed to the image forming area by the recording head 24. After that, the paper is discharged to the paper discharge tray 7.

  Next, an ink circulation system in this image forming apparatus will be described with reference to the explanatory diagram of FIG.

  The main tank 301 contains ink 300 that is a liquid supplied to the recording head 24. The ink 300 in the main tank 301 is sent by a supply pump 302 to a sub tank 303 that is an ink tank that is placed on the apparatus main body.

  The sub-tank 303 communicates with the atmosphere through an air communication port 304 provided at the top, the liquid level inside is maintained below the recording head 24, and the hydrostatic pressure of the recording head 24 is set to a predetermined negative pressure. keeping.

  The sub tank 303 is provided with a liquid level detecting means 305 for detecting the liquid level. When it is detected that the liquid level has dropped, the supply pump 302 is operated to supply ink from the main tank 301. To be replenished. Here, as the liquid level detection means 305, an electrode pair is used and the liquid level is detected by a change in electrical resistance between them, but a float sensor or a method for optically detecting the liquid level is also possible. Can be used.

  The sub tank 303 is connected to the head tank 29 via the supply tube 306. The sub tank 303 is connected to the head tank 29 via a circulation pump 307 and a return tube 308.

  From the head tank 29, ink is supplied into the common liquid chamber 207 from the upper end side of the common liquid chamber 207 of the recording head 24, and is supplied to the return tube 308 from the lower end side of the common liquid chamber 207 through the return path in the head tank 29. Ink is discharged.

  Thus, by driving the circulation pump 307, the ink 300 is supplied from the sub tank 303 into the common liquid chamber 207 of the recording head 24 via the supply tube 306 and the head tank 29, and from the common liquid chamber 207 of the recording head 24. The ink 300 is circulated by returning the ink 300 to the sub tank 303 via the head tank 29 and the return tube 308.

  Next, details of the recording head and the head tank will be described with reference to FIGS. 6 is a cross-sectional explanatory view of the recording head and the head tank portion, and FIG. 7 is a cross-sectional explanatory view taken along line BB in FIG.

  The recording head 24 is provided with a supply port (supply port) 208 that communicates with the upper end of the common liquid chamber 207 and a return port (return port) 209 that communicates with the lower end of the common liquid chamber 207. . The common liquid chamber 207 has a constant cross-sectional area in a direction orthogonal to the nozzle arrangement direction (vertical direction).

  The head tank 29 has a tank case 230 in which a liquid storage portion 231 is formed, and a deflectable film member 232 that forms a wall surface of the liquid storage portion 231 is provided in a part of the tank case 230. It has been. In addition, a spring 233 that pushes the film member 232 outward (in a direction in which the volume of the liquid storage portion 231 is expanded) is provided in the liquid storage portion 231 with a restoring force. Further, a filter member 234 is provided in the liquid storage portion 231.

  The ink 300 is supplied to the liquid storage portion 231 of the head tank 29 connected to the supply tube 306. The liquid storage portion 231 of the head tank 29 communicates with the supply port 208 at the upper end of the common liquid chamber 207 of the recording head 24 through the supply port 235 on the downstream side of the filter member 234.

  The head tank 29 is provided with a return path 236 that communicates with the return port 209 at the lower end of the common liquid chamber 207 of the recording head 24, and a return tube 308 is connected to the return path 236.

  Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.

  The control unit 500 includes a CPU 501 also serving as a control unit according to the present invention that controls the entire apparatus, various programs including programs necessary for control according to the present invention to be executed by the CPU 501, and a ROM 502 that stores other fixed data. , A RAM 503 for temporarily storing image data, a rewritable nonvolatile memory 504 for retaining data even when the apparatus is powered off, and an image process for performing various signal processing, rearrangement, etc. on the image data And an ASIC 505 for processing input / output signals for controlling the entire apparatus.

  Also, a print control unit 508 including a data transfer unit for driving and controlling the recording head 24 and a driving signal generating unit, a head driver (driver IC) 509 for driving the recording head 24 provided on the carriage 23 side, A main scanning motor 25 that moves and scans the carriage 23, motor driving units 510 and 511 for driving a sub-scanning motor 151 that moves the conveyor belt 51 in a circular manner, an AC bias supply unit 512 that supplies an AC bias to the charging roller 54, and the like It has.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side, an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera. Or the like from the host 600 side via the cable or network.

  The CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints the image data. The data is transferred from the unit 508 to the head driver 509. Note that generation of dot pattern data for image output can be performed by the printer driver 601 on the host 600 side.

  The print control unit 508 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 509. Including a D / A converter for D / A converting D / A conversion of drive pulse pattern data stored in the ROM, a voltage signal amplifier, a current amplifier, and the like, and a drive signal or a plurality of drive pulses Is output to the head driver 509.

  The head driver 509 selectively selects a drive pulse that constitutes a drive signal provided from the print control unit 508 based on image data corresponding to one line of the print head 24 that is input serially, and drops droplets of the print head 24. The recording head 24 is driven by applying it to a driving element (for example, a piezoelectric element) that generates energy to be discharged. At this time, by selecting a drive pulse that constitutes a drive signal, for example, droplets having different droplet sizes, such as large droplets, medium droplets, and small droplets, can be ejected to print different sizes of dots.

  The I / O unit 513 acquires information from the main scanning encoder 123, the sub-scanning encoder 156, and various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, and print control unit 508. And used to control the motor drive units 510 and 511 and the AC bias supply unit 512. The sensor group 515 includes an optical sensor (paper sensor) provided on the carriage 23 for detecting the position of the paper, a thermistor for monitoring the temperature and humidity in the machine, a sensor for monitoring the voltage of the charging belt, and a cover. There are interlock switches for detecting opening and closing, and the I / O unit 513 can process various sensor information.

  For example, the CPU 501 detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 122 constituting the main scanning encoder 123, and a speed target value and a position target obtained from a previously stored speed / position profile. A drive output value (control value) for the main scanning motor 25 is calculated based on the value and the main scanning motor 25 is driven via the motor driving unit 510. Similarly, a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 155 constituting the sub-scanning encoder 156, a speed target value and a position target value obtained from a previously stored speed / position profile, and Based on this, a drive output value (control value) for the sub-scanning motor 151 is calculated, and the sub-scanning motor 151 is driven via the motor driving unit 511.

  Further, the control unit 500 drives and controls the cap moving mechanism 531 that moves the cap 92 forward and backward with respect to the nozzle surface of the recording head 24 via the maintenance / recovery driving unit 534, and the wiper moving mechanism 532 that moves the wiper member 94. And the suction pump 96 and the air release valve 98 are driven and controlled, and the maintenance and recovery operation is controlled.

  In addition, the control unit 500 performs drive control of the supply pump 302 and the circulation pump 307 via the supply system drive unit 535. At this time, the detection result of the remaining amount of liquid in the sub tank 303 by the liquid level detection means 305 of the sub tank 303 or the detection result of the ink temperature detected by the temperature sensor included in the sensor group 515 is used.

  Next, ink circulation control in this image forming apparatus will be described.

  As described above, in this image forming apparatus, ink droplets are ejected from the recording head 24 in the horizontal direction to form an image. Therefore, since a plurality of nozzles 205 provided in the recording head 24 are arranged in the direction of gravity (vertical direction), as shown in FIG. If the hydrostatic pressure of each nozzle 205 varies with the height difference h, the discharge state of the droplets does not become uniform.

  Therefore, in this embodiment, as indicated by an arrow Q in FIG. 6, the hydrostatic pressure of each nozzle 205 of the recording head 24 is adjusted to be equal by circulating ink. That is, when forming an image by ejecting liquid droplets from the recording head 24, the circulation pump 307 is driven to circulate the ink between the sub tank 303 and the recording head 24.

  At this time, an ink flow in the direction from the upper end side to the lower end side is generated in the common liquid chamber 207 of the recording head 24. That is, the direction of the ink flow is made to go from the upper nozzle 205 of the recording head 24 toward the lower nozzle 205.

  As a result, in the common liquid chamber 207 where the ink flows, the pressure is reduced on the downstream side rather than on the upstream side, so that this pressure difference is made equal to the water head difference in the arrangement of the nozzles 205. As a result, the pressures of all the nozzles 205 become equal, and variations in droplet ejection characteristics between channels (between nozzles) can be reduced.

  Here, in order to make the water head difference between the nozzles 205 the same, as shown in FIG. 6, the height difference from the uppermost nozzle 205 to the lowermost nozzle 205 is h, and the uppermost nozzle 205. When the fluid resistance in the portion of the common liquid chamber 207 between the lowermost nozzle 205 and R is R, the flow rate Q of the ink circulation is preferably Q = h / R.

  In this embodiment, since the head difference of each nozzle 205 is adjusted using pressure loss due to ink circulation, the fluid resistance R of the common liquid chamber 207 is at least the nozzle 205 for ejecting ink and the individual liquid chamber 206. It is preferable that it is constant in the vicinity of.

  Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is an explanatory sectional view of the recording head and the head tank portion in the same embodiment, and FIG. 10 is an explanatory sectional view taken along the line CC of FIG.

  In this embodiment, the filter member 234 is disposed in the common liquid chamber 207 of the recording head 24, and the common liquid chamber 207 is divided into a filter upstream chamber 207b and a filter downstream chamber 207a. Here, the filter downstream chamber 207 a communicates with the individual liquid chamber 206, and the filter upstream chamber 207 b communicates with the supply port 208 and the return port 209.

  With this configuration, the ink flow formed by the circulation pump 307 is almost only in the filter upstream chamber 207b. As a result, even when the liquid feed of the circulation pump 307 varies, the filter member 234 mainly cuts high-frequency pressure fluctuations, so that the pressure of the nozzle 205 can be further stabilized. Further, the circulation pump 307 may be one that generates pulsation, and a simple pump can be used.

  Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a cross-sectional explanatory view of a recording head and a head tank portion in the same embodiment.

  In the present embodiment, in the first embodiment, the head tank 29 is provided with a temperature sensor 246 that detects the temperature of the ink in the liquid container 231.

  Ink generally changes in viscosity with temperature, but when the viscosity changes, the pressure loss when flowing through the common liquid chamber 207 also changes. Specifically, when the viscosity is small, the pressure difference in the common liquid chamber 207 generated by the ink circulation is smaller than the water head difference, and the lower nozzle 205 has a lower negative pressure than the upper nozzle 205. Become. On the contrary, if the viscosity is large, the pressure difference in the common liquid chamber 207 generated by the ink circulation becomes larger than the water head difference, and the lower nozzle 205 has a higher negative pressure than the upper nozzle 205.

  Therefore, the temperature of the ink in the head tank 29 is detected by the temperature sensor 246, and the control unit 500 controls the flow rate Q that circulates according to the detected ink temperature, so that the temperature and viscosity of the ink are not affected. The pressure difference formed by the circulation can be made equal to the water head difference at each nozzle position (vertical direction position), and the pressures of all the nozzles 205 can be made the same.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 12 is a cross-sectional explanatory view of a recording head and a head tank portion in the same embodiment.

  In the present embodiment, in the second embodiment, the top surface 245 in the liquid storage portion 231 of the head tank 29 is an inclined surface in a direction descending from the inflow port portion 237 connecting the supply tube 306 toward the supply port 235. Yes. In this embodiment, as the circulation pump 307, a tube pump, a gear pump, or the like capable of feeding liquid in both directions (reversible pump) is used.

  With this configuration, the discharge performance of the bubbles 400 that have entered the common liquid chamber 207 is improved.

  That is, in the ink jet recording apparatus, bubbles accumulate in the recording head 24 over time, and when a certain amount or more of air accumulates, it causes ejection failure. The air in the individual liquid chamber 206 and the nozzle 205 can be easily discharged by sucking from the nozzle 205, but the air in the common liquid chamber 207 has a large volume in the common liquid chamber 207. From 205, it is difficult to discharge.

  Here, in the image forming apparatus according to the present embodiment, since the plurality of nozzles 205 are arranged in the gravity direction (vertical direction) as described above, the upper part of the common liquid chamber 207 (supply port 208). Air (bubbles 400) is collected in the vicinity.

  As described above, since ink is circulated in the direction of arrow Q during printing, bubbles with small buoyancy ride on the ink flow and enter the individual liquid chamber 206 to cause ejection failure or adhere to the filter member 234. This may cause problems such as increasing fluid resistance.

  Therefore, in the present embodiment, when printing is not performed, the control unit 500 drives the reversible circulation pump 307 in the reverse direction so that the lower end (feedback) of the common liquid chamber 207 is placed in the common liquid chamber 207 of the recording head 24. Ink is circulated so as to generate a flow in the direction of arrow S from the port 209) side to the upper end (supply port 208) side.

  As a result, the air (bubbles 400) in the common liquid chamber 207 enters the supply tube 306 along the top surface 245 which is an inclined surface in the head tank 29, and is discharged from the air communication port 304 of the sub tank 303.

  As described above, when printing is not performed, the ink is circulated in the opposite direction to that during printing, so that the air in the common liquid chamber can be easily discharged, and the ejection stability of the recording head can be improved.

  In the present application, the “paper” is not limited to paper, but includes OHP, cloth, glass, a substrate, etc., and means a material to which ink droplets or other liquids can be attached. , Recording media, recording paper, recording paper, and the like. In addition, image formation, recording, printing, printing, and printing are all synonymous.

  The “image forming apparatus” means an apparatus that forms an image by discharging liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. “Formation” means not only giving an image having a meaning such as a character or a figure to a medium but also giving an image having no meaning such as a pattern to the medium (simply causing a droplet to land on the medium). ) Also means.

  The “ink” is not limited to an ink unless otherwise specified, but includes any liquid that can form an image, such as a recording liquid, a fixing processing liquid, or a liquid. Used generically, for example, includes DNA samples, resists, pattern materials, resins, and the like.

  In addition, the “image” is not limited to a planar image, and includes an image given to a three-dimensionally formed image and an image formed by three-dimensionally modeling a solid itself.

  Further, the image forming apparatus includes both a serial type image forming apparatus and a line type image forming apparatus, unless otherwise limited.

2 Image forming section 4 Paper feeding section 5 Transport mechanism section 6 Paper discharge section 7 Paper discharge tray 8 Reversing section 9 Maintenance recovery mechanism 10 Paper (recording medium)
23 Carriage 24 Recording head 29 Head tank 51 Conveying belt 205 Nozzle 207 Common liquid chamber 300 Ink 301 Ink cartridge (main tank)
302 Supply pump 303 Sub tank 306 Supply tube 307 Circulation pump 308 Return tube 500 Control unit

Claims (6)

A nozzle row in which a plurality of nozzles for discharging droplets are arranged; a plurality of individual liquid chambers through which the plurality of nozzles communicate; and a common liquid chamber for supplying a liquid to the plurality of individual liquid chambers. A recording head arranged so as to discharge in the horizontal direction;
An ink tank containing the liquid to be supplied to the recording head;
Liquid feeding means for circulating the liquid between the ink tank and the recording head,
The liquid feeding means is connected to the upper end side and the lower end side of the common liquid chamber of the recording head,
Control for driving the liquid feeding means to cause the liquid in the common liquid chamber to flow from the upper end side to the lower end side of the common liquid chamber when droplets are ejected from the recording head. An image forming apparatus comprising: means.   The flow rate Q of the liquid flow generated in the common liquid chamber is Q = h / R, where h is the height difference from the upper end to the lower end of the common liquid chamber and R is the fluid resistance. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 1, wherein the common liquid chamber has a constant cross-sectional area in a direction perpendicular to a liquid flow direction in the liquid flow direction.   4. The filter according to claim 1, further comprising a filter member configured to filter liquid foreign matter between the common liquid chamber and the individual liquid chamber, and generating a liquid flow upstream of the filter member. An image forming apparatus according to claim 1. Temperature detecting means for detecting the temperature of the liquid;
5. The image formation according to claim 1, wherein the control unit changes a flow rate of the liquid in the common liquid chamber according to a temperature of the liquid detected by the temperature detection unit. apparatus. The liquid feeding means can feed liquid in both directions,
The control means controls the liquid in the common liquid chamber to flow from the lower end side to the upper end side of the common liquid chamber when droplets are not ejected from the recording head. The image forming apparatus according to claim 1.

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