JP5803459B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with a recording head for discharging droplets.

  As an image forming apparatus such as a printer, a facsimile, a copying apparatus, a plotter, and a complex machine of these, for example, a liquid discharge recording type image forming apparatus using a recording head composed of a liquid discharge head (droplet discharge head) for discharging droplets Inkjet recording apparatuses are known.

  In such an image forming apparatus, a head tank that supplies liquid to the recording head is provided, and an ink cartridge that is a main tank that is detachably (replaceable) attached to the apparatus main body side is connected to the head tank via a supply tube and the like. A system for supplying a liquid is known.

  By the way, in the liquid discharge head, when bubbles flow into the head, the discharge direction of the discharged liquid droplet is bent, or the required amount of liquid droplets cannot be discharged, or the discharge itself becomes impossible. Defects occur.

  Therefore, in order to maintain and recover the performance of the head, for example, a suction method in which the nozzle surface of the head is sealed with a suction cap to which suction means is connected, and liquid is sucked and discharged from the nozzle, or liquid pressurized to the head The air bubbles and other foreign matters in the head are discharged from the nozzle together with the liquid by a pressurizing method in which the gas is supplied and discharged from the nozzle, or a suction pressurizing method using these in combination.

  Conventionally, for example, a pressure pump that pressurizes an ink tank (main tank) connected to a head via a buffer tank (head tank), and a suction cap connected to a suction pump, There is one that discharges liquid from a head by performing suction by a suction pump (Patent Document 1).

Japanese Unexamined Patent Publication No. 4-70353

  By the way, as a head tank, a bendable film-like member that forms a part of the wall surface of the liquid container that contains the liquid, and a direction opposite to the direction in which the film-like member bends due to a decrease in the remaining amount of liquid. In the case of adopting a configuration having a negative pressure generating means including a spring that acts on a restoring force, when trying to pressurize the inside of the head tank, it is necessary to increase the free length of the spring, which increases the size of the head tank. There are challenges.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the bubble discharge performance without increasing the size of the head tank.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having nozzles for discharging droplets;
A head tank for supplying liquid to the recording head;
A replaceable main tank for storing liquid to be supplied to the recording head;
Liquid feeding means for feeding the liquid from the main tank to the head tank;
A suction cap to which suction means is connected and seals the nozzle surface of the recording head;
A buffer tank having a smaller capacity than the head tank, connected to the head tank,
The head tank is
A bendable film-like member that forms a part of the wall surface of the liquid container that contains the liquid, and a restoring force acting in a direction opposite to the direction in which the film-like member bends due to a decrease in the remaining amount of liquid. And a negative pressure generating means including
The buffer tank is
A tank case that forms a buffer chamber communicating with the liquid storage portion of the head tank via a flow path;
A wall member which is movably provided in the tank case and forms a part of the wall surface of the buffer chamber;
A spring that applies a restoring force in a reverse direction when the wall member moves in a direction in which the capacity of the buffer chamber increases,
The spring constant of the spring of the buffer tank has a size not <br/> configuration than the spring constant of the spring of the head tank.

  According to the image forming apparatus of the present invention, it is possible to improve the bubble discharge performance without increasing the size of the head tank.

FIG. 3 is a side explanatory view illustrating a mechanism unit of an example of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. It is a typical plane explanatory view showing an example of a head tank. FIG. 4 is a schematic front explanatory view of FIG. 3. FIG. 2 is a schematic explanatory diagram for explaining an ink supply / discharge system according to the first embodiment of the present invention. It is typical explanatory drawing which shows an example of the buffer tank of the embodiment. It is a schematic block explanatory drawing explaining the control part of the apparatus. It is a flowchart with which it uses for description of control of the bubble discharge | emission operation | movement in the embodiment. FIG. 6 is a schematic explanatory diagram for explaining another first example of the head arrangement in the same embodiment. It is a typical explanatory view explaining other 2nd examples similarly. It is a typical explanatory view explaining an example of a liquid feed pump of the embodiment. FIG. 10 is a schematic explanatory diagram for explaining a first example of an ink supply / discharge system according to a second embodiment of the present invention. FIG. 6 is a schematic explanatory diagram for explaining a second example of the ink supply / discharge system. It is a flowchart with which it uses for description of control of the bubble discharge | emission operation | movement in the embodiment. FIG. 10 is a schematic explanatory diagram for explaining an ink supply / discharge system according to a third embodiment of the present invention. It is a typical explanatory view explaining the liquid level detection of the head tank in the embodiment. It is a flowchart with which it uses for description of control of the bubble discharge | emission operation | movement in the embodiment. FIG. 6 is a schematic explanatory diagram for explaining another first example of the head arrangement and the buffer tank arrangement in the embodiment. It is a typical explanatory view similarly used for explanation of other 2nd examples. It is typical plane explanatory drawing with which it uses for description of the head tank in 4th Embodiment of this invention. It is typical explanatory drawing with which it uses for description of the ink supply / discharge system in 5th Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall configuration of the image forming apparatus, and FIG. 2 is an explanatory plan view of a main part of the apparatus.

  This image forming apparatus is a serial type ink jet recording apparatus, and a carriage 33 is slidable in a main scanning direction by main and sub guide rods 31 and 32 which are guide members horizontally mounted on the left and right side plates 21A and 21B of the apparatus main body 1. It is held and moved and scanned in the carriage main scanning direction via a timing belt by a main scanning motor described later.

  The carriage 33 is provided with recording heads 34a and 34b composed of liquid ejection heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (K). The “recording head 34” is arranged in a sub-scanning direction orthogonal to the main scanning direction, and the ink droplet ejection direction is directed downward.

  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.

  Further, the carriage 33 is equipped with head tanks 35a and 35b (referred to as “head tank 35” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 34. In the head tank 35, ink cartridges 10y, 10m, 10c, and 10k, which are main tanks of the respective colors that are detachably attached to the cartridge loading unit 4, are supplied from the ink pumps 24 through the supply tubes 36 of the respective colors. Of ink is replenished.

  On the other hand, as a paper feeding unit for feeding the papers 42 stacked on the paper stacking unit (pressure plate) 41 of the paper feeding tray 2, a half-moon roller (feeding) that separates and feeds the papers 42 one by one from the paper stacking unit 41. A separation pad 44 made of a material having a large friction coefficient is provided facing the paper roller 43) and the paper feed roller 43, and the separation pad 44 is urged toward the paper feed roller 43 side.

  In order to feed the paper 42 fed from the paper feeding unit to the lower side of the recording head 34, a guide member 45 for guiding the paper 42, a counter roller 46, a transport guide member 47, and a tip pressure roller. And a holding belt 48 which is a conveying means for electrostatically attracting the fed paper 42 and conveying it at a position facing the recording head 34.

  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). Further, a charging roller 56 that is 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 transport belt 51 and to rotate following the rotation of the transport belt 51. The transport belt 51 rotates in the belt transport direction when the transport roller 52 is rotationally driven through timing by a sub-scanning motor described later.

  Further, as a paper discharge unit 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 that is a paper discharge roller. And a paper discharge tray 3 below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the conveyance belt 51, reverses it, and feeds it again between the counter roller 46 and the conveyance 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 nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction. The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a and 82b (hereinafter referred to as “caps 82” when not distinguished from each other) for capping the nozzle surfaces of the recording head 34, and nozzle surfaces. A wiper member (wiper blade) 83 for wiping the recording medium, an empty discharge receiver 84 for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and a carriage And a carriage lock 87 for locking 33. A waste liquid tank 100 for storing waste liquid generated by the maintenance recovery operation is mounted on the lower side of the head maintenance recovery mechanism 81 in a replaceable manner with respect to the apparatus main body.

  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, and the idle discharge receiver 88 includes an opening 89 along the nozzle row direction of the recording head 34.

  In this image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feed tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide 45, and includes the transport belt 51 and the counter. It is sandwiched between the rollers 46 and conveyed, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the 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 a sub-scanning direction that is a circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the paper 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 51.

  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 finished and the paper 42 is discharged onto the paper discharge tray 3.

  When performing the maintenance and recovery of the nozzles of the recording head 34, the nozzle 33 performs the suction from the nozzles by moving the carriage 33 to a position facing the maintenance and recovery mechanism 81 which is the home position and performing capping by the cap member 82. By performing a maintenance and recovery operation such as idle ejection for ejecting droplets that do not contribute to image formation, image formation by stable droplet ejection can be performed.

  Next, an example of the head tank 35 will be described with reference to FIGS. 3 is a schematic top view for one head of the head tank, and FIG. 4 is a schematic front view for one head of the head tank.

  The head tank 35 has a tank case 201 that forms a liquid storage portion 202 that is open at one side for holding liquid. The opening of the tank case 201 is a film-like member 203 that can be bent. It is sealed. A spring 204 as an elastic member is disposed in the tank case 201, and a restoring force is applied in a direction opposite to the direction in which the film-like member 203 bends as the remaining liquid amount decreases. This constitutes a negative pressure generating means for generating a negative pressure when the remaining amount of liquid in the tank case 201 decreases.

  Further, a detection filler 205 that is a displacement member is provided outside the tank case 201 so that one end of the detection filler 205 can be swayed by the shaft 206. The detection filler 205 is fixed to the film-like member 203 by adhesion or the like, and is given a momentum toward the tank case 201 by a spring (not shown).

  As a result, the detection filler 205 is displaced in conjunction with the movement of the film-like member 203. Therefore, the amount of displacement of the detection filler 205 is detected by the sensor 301 comprising an optical sensor arranged on the apparatus main body side, whereby the inside of the head tank 35 is detected. The remaining amount of ink can be detected.

  In addition, a supply port 209 for supplying ink from the ink cartridge 10 is connected to the supply tube 36 at the upper part of the tank case 201. In addition, an air release mechanism 207 that opens the inside of the head tank 35 to the atmosphere is provided on the side of the tank case 201. The atmosphere release mechanism 207 includes a valve body 207b that opens and closes an atmosphere release path 207a that communicates with the inside of the head tank 35, a spring 207c that urges the valve body 207b to a closed state, and the like. The solenoid valve 302 is opened by pushing the valve body 207b, and the inside of the head tank 35 is opened to the atmosphere (a state communicating with the atmosphere).

  Electrode pins 208a and 208b for detecting the remaining amount of ink in the head tank 35 are attached. Since the ink has electrical conductivity, when the ink reaches the electrode pins 208a and 208b, a current flows between the electrode pins 208a and 208b, and the resistance value of the two changes. That is, it can be detected that the air amount in the head tank 35 has become a predetermined amount or more, or that the remaining amount of liquid in the head tank 35 has become a predetermined amount or less.

  Next, the ink supply / discharge system according to the first embodiment of the present invention will be described with reference to FIG.

  First, ink is supplied from the ink cartridge (main tank) 10 to the head tank 35 through a supply tube 36 by a liquid supply pump 241 which is a liquid supply means of the supply pump unit 24. The liquid feed pump 241 is a reversible pump configured by a tube pump or the like, and includes a liquid feed operation for supplying ink from the ink cartridge 10 to the head tank 35 and a reverse feed for returning ink from the head tank 35 to the ink cartridge 10. It is possible to perform actions.

  Further, the maintenance / recovery mechanism 81 has the suction cap 82a for capping the nozzle surface of the recording head 34 and the suction pump 812 as suction means connected to the suction cap 82a as described above, and is capped with the cap 82a. By driving the suction pump 812, the ink in the head tank 35 can be sucked by sucking ink from the nozzles through the suction tube 811 (referred to as head suction or nozzle suction). The sucked waste ink is discharged to the waste liquid tank 100.

  An air release solenoid 302 that opens and closes the air release mechanism 207 of the head tank 35 is disposed on the apparatus main body side, and the air release mechanism 207 can be opened by operating the air release solenoid 302. Further, a sensor 301 including an optical sensor for detecting the detection filler 205 of the head tank 35 is provided on the apparatus main body side.

  The head tank 35 is connected to a buffer tank 90 according to the present invention that communicates only with the bottom side of the liquid storage unit 202 in the head tank 35 and is closed from outside air.

  Here, an example of the buffer tank will be described with reference to FIG. FIG. 6 is a schematic sectional explanatory view of the buffer tank.

  The buffer tank 90 is provided in a tank case 900 that forms a buffer chamber 902 that communicates with the liquid storage portion 202 of the head tank 35 via a flow path 901, and is movably provided in the tank case 900. A wall member 903 that forms a wall surface, a spring 904 that applies a restoring force in the reverse direction when the wall member 903 moves in a direction in which the capacity of the buffer chamber 902 increases, and detection means that detects the pressure in the buffer chamber 902 And a pressure sensor 905.

  By forming the tank case 900 integrally with the tank case 201 of the head tank 35, the flow path 901 and the buffer chamber 902 are isolated from the atmosphere. Further, the flow path 901 communicates with the liquid storage unit 202 on the bottom side of the head tank 35.

  The spring constant of the spring 904 of the buffer tank 90 is set larger than the spring constant of the negative pressure generating spring 204 in the head tank 35.

  In the buffer tank 90 configured as described above, the liquid (ink) flows from the head tank 35 into the buffer chamber 902 via the flow path 901, whereby the wall member 903 increases the volume of the buffer chamber 902 (see FIG. 6, the wall member 903 receives a force in the reverse direction (arrow B direction) by the spring 904 and works to return the volume of the buffer chamber 902 to its original state.

  Here, since the spring constant of the spring 904 is larger than the spring constant of the spring 204 of the head tank 35, the spring 204 mainly expands and contracts when the pressure in the head tank 35 is atmospheric pressure or negative pressure. Therefore, the spring 904 does not operate, and the volume of the buffer chamber 902 hardly changes. That is, the wall member 903 hardly moves.

  On the other hand, when the ink is pressurized and supplied into the head tank 35, the ink flows into the buffer tank 90, so that the wall member 903 is pushed in the direction in which the volume of the buffer chamber 902 increases, and the spring 904 As a result of the restoring force acting on the wall member 903 and being pushed back in the reverse direction, the ink in the head tank 35 is pressurized.

  At this time, since the film-like member 203 is already stretched and does not move, the internal pressure of the head tank 35 cannot detect pressure change or volume change by the movement of the film-like member 203, that is, the movement of the detection filler 205. Therefore, a pressure sensor 905 for detecting the pressure in the buffer chamber 902 of the buffer tank 90 is provided so that the internal pressure of the head tank 90 can be detected.

  Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. In addition, the figure is a block explanatory drawing of the control part.

  The control unit 500 includes a CPU 501 that controls the entire apparatus, a program that includes a program that causes the CPU 501 to execute control according to the present invention, a ROM 502 that stores other fixed data, a RAM 503 that temporarily stores image data and the like, A rewritable non-volatile memory 504 for holding data while the power of the apparatus is cut off, image processing for performing various signal processing and rearrangement on image data, and other input / output for controlling the entire apparatus And an ASIC 505 for processing signals.

  Further, a print control unit 508 including a data transfer unit for driving and controlling the recording head 34 and a driving signal generating unit, a head driver (driver IC) 509 for driving the recording head 34 provided on the carriage 33 side, An AC bias is applied to the charging roller 56, a main scanning motor 554 that moves and scans the carriage 33, a sub-scanning motor 555 that rotates the conveyance belt 51, a motor drive unit 510 that drives the maintenance / recovery motor 556 of the maintenance / recovery mechanism 81. An AC bias supply unit 511 to supply, a solenoid drive unit 512 that drives an atmosphere release solenoid 302 that opens and closes the atmosphere release mechanism 207 of the head tank 35, a pump drive unit 516 that drives the liquid feed pump 241, and the ink cartridge 10. Provided non-volatile memory (in this case, EEPROM) 521 And a like cartridge communication unit 522 performs communication for reading and writing of data against.

  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, an imaging device such as a digital camera, and the like. From the host 600 side via the cable or network via the I / F 506.

  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 is 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 34 that is input serially, and drops droplets on the print head 34. The recording head 34 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 driving pulse constituting the driving signal, for example, dots having different sizes such as a large droplet, a medium droplet, and a small droplet can be sorted.

  The I / O unit 513 acquires information from various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, a print control unit 508, a motor drive unit 510, and an AC bias supply unit. Used to control 511. The sensor group 515 includes an optical sensor 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, an interlock switch for detecting opening and closing of the cover, and the like. The I / O unit 513 can process various sensor information.

  The sensor group 515 input to the I / O unit 513 includes a sensor 301 for detecting the detection filler 205 of the head tank 35, signals of the detection electrode pins 208a and 208b, and a signal of the pressure sensor 905 of the buffer tank 90. Etc. are also input.

  In addition, the control unit 500 includes time measuring means 520 that measures time.

  Next, control of the bubble discharge operation in the first embodiment of the present invention will be described with reference to the flowchart of FIG.

  In this bubble discharge operation (bubble removal operation), a liquid supply operation and a suction operation are performed. First, the nozzle surface of the recording head 34 is capped (sealed) with the suction cap 82a. As a result, after that, when the head tank 35 is pressurized, it becomes possible to process the waste ink discharged from the nozzles in the suction cap 82a, and by pressing the nozzle surface with the suction cap 82a, It is possible to prevent the nozzle surface from being peeled off when the surface is pressurized.

  Thereafter, bubble removal is started, the liquid feed pump 241 is driven to rotate forward, and ink is supplied to the head tank 35. At this time, the ink is pressurized and supplied into the head tank 35 by supplying more ink than the full tank position of the head tank 35.

  As a result, ink flows from the head tank 35 into the buffer chamber 902 of the buffer tank 90, and the wall member 903 is pushed by the spring 94, so that the inside of the buffer chamber 902 of the buffer tank 90 and the liquid storage portion 202 in the head tank 35. Is pressurized.

  In this case, the pressure in the head tank 35 is equal to the pressure in the buffer chamber 902 of the buffer tank 90 and can be monitored by a pressure sensor 905 provided in the buffer tank 90.

  Therefore, it is determined whether or not the internal pressure (pressure value) of the head tank 35 detected by the pressure sensor 905 has reached a preset supply end threshold (first predetermined value). When the pressure value of the head tank 35 reaches the supply end threshold, the operation of the liquid feed pump 241 is stopped and the liquid supply operation is finished. The supply end threshold is set such that the ink flow rate discharged from the nozzles by pressurizing the recording head 34 does not exceed the ink flow rate that can be sucked by the suction pump 812.

  Next, the suction pump 812 is operated to make the sealed space formed between the suction cap 82a and the nozzle surface have a negative pressure, thereby performing head suction for sucking and discharging ink from the nozzle, and sucking ink from the nozzle. It is discharged into the cap 82a.

  When the head suction is started, the inside of the head tank 35 is at a positive pressure, so that the expansion of the bubbles due to the suction can be prevented, the bubbles can be contracted, and the flow path in the recording head 34 can be easily passed. Further, by keeping the inside of the head tank 35 at a positive pressure, the flow rate at the time of ink suction can be increased and the force for flowing the bubbles can be increased, so that the bubble discharge performance is improved.

  Here, the pressure in the head tank 35 decreases as the head suction is performed.

  Therefore, it is determined whether or not the internal pressure (pressure value) of the head tank 35 detected by the pressure sensor 905 has reached a preset suction end threshold (second predetermined value). Then, when the pressure value of the head tank 35 reaches the suction end threshold, the operation of the suction pump 812 is stopped and the suction operation is finished. This suction end threshold is set so that the head tank 35 becomes overnegative pressure and bubbles are not sucked from the nozzle.

  Then, the bubble removal operation is terminated, and a normal negative pressure is formed in the head tank 35 by the negative pressure forming operation.

  As described above, if the bubbles are removed only by the suction operation, the bubbles expand due to the suction and are caught in the ink flow path of the head. It can make it easier to pass inside. Further, by setting the inside of the head tank to a positive pressure, the ink flow rate at the time of sucking the head can be increased and the force for flowing the bubbles can be increased, so that the bubble discharge performance can be improved.

  Here, when the pressure supply of the ink to the head tank is performed by the liquid feed pump, a gas press-fitting device such as a pressure pump for pressurizing the main tank becomes unnecessary.

  However, as described above, when a configuration in which a negative pressure is generated by the deformation of a flexible film-like member and a spring (controlling the internal pressure of the head tank) is adopted as the head tank, ink supply by a liquid feed pump In order to pressurize the inside of the head tank, it is necessary to make the spring in the head tank longer than the free length, and as a result, the head tank becomes large.

  Therefore, in the present embodiment, pressurization in the head tank is performed by liquid feeding by a liquid feeding pump and a buffer tank (pressurizing unit) connected to the head tank. The buffer tank has a spring that applies a restoring force in the reverse direction when the wall member is about to move in the direction in which the volume in the buffer chamber increases, so that the liquid storage portion in the buffer chamber and the head tank The pressure can be applied to the ink.

  Therefore, if more ink is delivered by the liquid feed pump than the head tank is full, the ink will flow into the buffer tank and the volume of the buffer chamber will increase, but the volume will be restored. The inside of the head tank is pressurized by the force

  In this way, by providing the buffer tank as described above, rather than increasing the size of the head tank, the inside of the head tank can be pressurized without increasing the size of the head tank, and the bubble discharge performance by pressurization and suction Can be improved.

  Next, another example of the arrangement of the recording head in the first embodiment of the present invention will be described with reference to FIGS.

  First, in the first example shown in FIG. 9, the recording head 34 is arranged in a state in which droplets are ejected in the horizontal direction on a sheet conveyed in the vertical direction. In the second example shown in FIG. 10, the recording head 34 is disposed in a state in which droplets are ejected upward in the vertical direction, and image formation is performed from below on a sheet conveyed in the horizontal direction. is there.

  Even with these head arrangements, it is possible to prevent the head from being soiled by dripping by capping with the suction cap 82a during the above-described bubble removal operation.

  Next, the liquid feed pump 241 used in the first embodiment of the present invention will be described with reference to FIG.

  In the present embodiment, a tube pump that does not have a state where the flow path is not closed is used as the liquid feeding pump 241. For example, as shown in FIG. 11, the liquid feed pump 241 includes a plurality of (three in this example) rollers 712 provided on a rotating member 711 that is rotated by a shaft 710, and rotates the rotating member 711. This is a tube pump that can perform liquid feeding and reverse feeding by handling the supply tube 36 with the roller 712. Since any roller 712 always presses and crushes the supply tube 36, the flow path is not closed. The state cannot be taken.

  Therefore, even when the liquid feed pump 241 is stopped, the liquid cannot freely flow through the pump 241.

  In this embodiment, the head tank 35 is pressurized by the liquid feeding operation of the liquid feeding pump 241, but the flow path in the pump 241 is closed even after the liquid feeding operation is finished and the pump 241 is stopped. Ink does not flow back through the pump 241. Instead of this tube pump, another non-backflow pump may be used.

  Next, a different example of the second embodiment of the present invention will be described with reference to FIGS. 12 and 13 are schematic explanatory views of the ink supply / discharge system in the same embodiment.

  In the present embodiment, a pump that cannot close the flow path when stopped is used as the liquid feeding pump 241. Therefore, when the pump 241 is stopped, the ink can freely flow. When the liquid feed pump 241 is stopped after pressurization, the ink may flow backward from the head tank 35 to the main tank 10.

  Therefore, in the first example of FIG. 12, when the main tank 10 is the upstream side and the head tank 35 is the downstream side, an electromagnetic valve 242 that opens and closes the flow path is provided on the downstream side of the liquid feed pump 241. By controlling the opening and closing of the electromagnetic valve 242, the pressure is not released from the head tank 35 to the main tank 10 after pressurization.

  In the second example of FIG. 13, when the main tank 10 is on the upstream side and the head tank 35 is on the downstream side, an electromagnetic valve 243 that opens and closes the flow path is provided on the upstream side of the liquid feed pump 241. By controlling the opening and closing of the electromagnetic valve 242, the pressure is not released from the head tank 35 to the main tank 10 after pressurization.

  Next, control of the bubble discharge operation in the second embodiment of the present invention will be described with reference to the flowchart of FIG.

  Here, in the control of the bubble discharge operation of the first embodiment described with reference to FIG. 8, before starting the operation of the liquid feed pump 241, the above-described electromagnetic valve 242 or 243 is opened and the main tank 10 to the head tank 35. The process of opening the flow path to is performed. Further, after the operation of the liquid feed pump 241 is stopped, the above-described electromagnetic valve 242 or 243 is closed to close the flow path from the main tank 10 to the head tank 35. Others are the same as in FIG.

  Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 15 is an explanatory diagram of an ink supply / discharge system in the embodiment.

  First, in the first and second embodiments, the buffer chamber 902 of the buffer tank 90 is arranged so as to continue to the bottom side in the head tank 35. This is because if air enters the buffer chamber 902 of the buffer tank 90 during pressurization, the air volume in the head tank 35 decreases, the liquid level rises, and as a result, ink may enter the atmosphere release mechanism 207. This is to prevent this.

  On the other hand, in the present embodiment, the buffer chamber 902 of the buffer tank 90 is arranged so as to continue to the upper side of the liquid storage portion 202 of the head tank 35 via the flow path 901.

  In this case, air or liquid enters the buffer chamber 902 of the buffer tank 90 from the head tank 35. As described above, when air enters the buffer tank 90 during pressurization, the air volume in the head tank 35 decreases, the liquid level rises, and as a result, the liquid may enter the atmosphere release mechanism 207. For this reason, in the present embodiment, the bubble discharge operation as described below is controlled.

  First, the liquid level detection of the head tank 35 will be described with reference to FIG.

  As described above, the head tank 35 is provided with the electrode pins 208a and 208b. Here, as shown in FIG. 16 (a), when the ink 300 is in contact with two electrode pins 208a and 208b (shown by 208), a current flows and the liquid level is detected. As shown, since the current does not flow when the ink 300 is not in contact with the two electrode pins 208a and 208b (shown by 208), the liquid level is not detected.

  Next, control of the bubble discharge operation in the third embodiment of the present invention will be described with reference to the flowchart of FIG.

  In this bubble discharge operation (bubble removal operation), a liquid supply operation and a suction operation, and an open / close operation of the air release mechanism are performed. First, the nozzle surface of the recording head 34 is capped (sealed) with the suction cap 82a.

  Thereafter, bubble removal is started and the air release mechanism 207 is opened. By opening the air release mechanism 207, the air enters the head tank 35 that was at a negative pressure. When air enters and the film-like member 203 swells more than the negative pressure, the liquid level is lowered and the electrode pin 208 does not detect the liquid level. In this state, the atmosphere release mechanism 207 is closed.

  Then, the liquid feed pump 241 is driven to rotate forward to supply liquid to the head tank 35. At this time, more liquid is supplied than the full tank position of the head tank 35.

  As a result, the liquid flows from the head tank 35 into the buffer tank 90, and the wall member 903 is pushed by the spring 94, whereby the buffer chamber 902 and the inside of the liquid storage unit 202 in the head tank 35 are pressurized.

  At this time, it is determined whether or not the electrode pin 208 has detected the liquid level. If the liquid level rises and the electrode pin 208 detects the liquid level, the liquid feed pump 241 is stopped at that time. By stopping the supply operation, liquid can be prevented from entering the air release mechanism 207 beforehand.

  When the electrode pin 208 has not detected the liquid level, whether the internal pressure (pressure value) of the head tank 35 detected by the pressure sensor 905 has reached a preset supply end threshold, as in the above embodiment. Determine whether or not. When the pressure value of the head tank 35 reaches the supply end threshold, the operation of the liquid feed pump 241 is stopped and the liquid supply operation is finished.

  Next, the suction pump 812 is operated to perform head suction, and the liquid is sucked and discharged from the nozzle.

  Here, since the pressure in the head tank 35 decreases as head suction is performed, it is determined whether or not the internal pressure (pressure value) of the head tank 35 detected by the pressure sensor 905 has reached a preset suction end threshold value. To do. Then, when the pressure value of the head tank 35 reaches the suction end threshold, the operation of the suction pump 812 is stopped and the suction operation is finished.

  Then, the bubble removal operation is terminated, and a normal negative pressure is formed in the head tank 35 by the negative pressure forming operation.

  Next, the head arrangement (droplet ejection direction) and the installation position of the buffer tank in this embodiment will be described with reference to FIGS.

  First, as shown in FIG. 18, when the recording head 34 is arranged so as to eject liquid droplets in the horizontal direction, bubbles in the head tank 35 enter the nozzles above the head 34 and the nozzles are missing. (Discharge failure) may occur. If bubbles enter the buffer chamber 902, the volume of the buffer tank 90 is reduced when the head is sucked, bubbles enter the head tank 35 from the buffer chamber 902, and the bubbles enter the nozzles of the head 34, causing the nozzles to drop out. It becomes.

  Therefore, as shown in FIG. 9 described above, it is preferable that the buffer tank 90 be installed below the lowest nozzle in the nozzle row of the recording head 34 so as to prevent bubbles from entering.

  On the other hand, when the buffer tank 90 cannot be passed through the lower portion of the head tank 35 due to a layout problem or the like, the buffer chamber 902 of the buffer tank 90 is set as shown in FIG. The buffer tank 90 is disposed so that the flow path 901 is inclined obliquely downward while being communicated with the liquid storage unit 202 at the upper part of the head tank 35.

  As a result, even when the buffer tank 90 is passed through the upper portion of the head tank 35, it is possible to reduce the risk of bubbles entering the buffer tank 90 from the head tank 35.

  Next, as shown in FIG. 19, when the recording head 34 is arranged so as to eject droplets upward in the vertical direction, bubbles in the head tank 35 enter the nozzles of the head 34 above. There is a risk of nozzle omission (discharge failure).

  Therefore, as shown in FIG. 10 described above, it is preferable that the buffer tank 90 be installed below the nozzle row of the recording head 34 so as to prevent bubbles from entering.

  On the other hand, when the buffer tank 90 cannot be passed under the head tank 35 due to a layout problem or the like, as shown in FIG. 19, the buffer chamber 902 of the buffer tank 90 is set as shown in FIG. The buffer tank 90 is disposed so that the flow path 901 is inclined obliquely downward while being communicated with the liquid container 202 at the upper part of the head tank 35.

  As a result, even when the buffer tank 90 is passed through the upper portion of the head tank 35, it is possible to reduce the risk of bubbles entering the buffer tank 90 from the head tank 35.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. In addition, FIG. 20 is explanatory drawing with which it uses for description of the pressure detection method of the buffer tank in the embodiment.

  Here, the rod member 906 is provided so as to interlock with the wall member 903 of the buffer tank 90. The rod member 906 can expand the detection filler 205 in conjunction with the movement of the wall member 903. Even when the head tank 35 is full and the film-like member 203 is stretched, the pressure can be detected by the position of the detection filler 205 that moves in conjunction with the wall member 903 of the buffer tank 90.

  The wall member 903 tends to be pushed back by a force that is obtained by multiplying the displacement amount of the wall member 903 moved by the liquid inflow by the spring 904 by the spring constant of the spring 904. Therefore, since the internal pressure of the buffer tank 90, that is, the internal pressure of the head tank 35 is proportional to the displacement of the detection filler 205, the pressure value can be calculated by detecting the position of the detection filler 205 with the sensor 301.

  The orientation of the head tank 35 is not limited to the state shown in the figure, and the shape of the rod member 906 is not particularly limited. Furthermore, a filler that is linked to the wall member can be newly provided and read by an existing or new sensor.

  Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 21 is an explanatory diagram of an ink supply / discharge system in the embodiment.

  In the present embodiment, the pressurized supply and the suction discharge are performed in parallel.

  Here, the ink flow rate sent by the liquid feed pump 241 is Q1, the ink flow rate pushed out from the nozzle surface by the positive pressure of the head tank 35 is Q2, and the ink flow rate sucked by the suction pump 812 is Q3. It is assumed that the head suction is performed by the suction pump 812 simultaneously with the ink supply.

  In this case, unless Q3 ≧ Q2, the ink will eventually overflow from the suction cap 82a. Even if Q3 <Q2 temporarily, the suction amount of the suction pump 812 and the pressure in the head tank 35 are controlled so that Q3 ≧ Q2.

  Next, unless Q2 ≧ Q1, the ink flows too much into the head tank 35, the internal pressure of the head tank 35 increases too much, and the flow rate Q2 eventually exceeds the flow rate Q3. Even if Q2 <Q1 temporarily, the suction amount of the suction pump 812 and the pressure in the head tank 35 are controlled so that Q2 ≧ Q1.

  The flow rates Q1 to Q3 described above may be directly measured, but may be calculated from the number of rotations of the drive motors of the pumps 241 and 814, the pressure of the head tank 35, the position of the filler 205, and the like.

  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.

10 Ink cartridge (main tank)
33 Carriage 34, 34a, 34b Recording head (liquid ejection head)
35 Head tank 36 Supply tube 81 Maintenance / recovery mechanism 82a Suction cap 90 Buffer tank 241 Liquid feed pump 500 Control unit

Claims (8)

A recording head having nozzles for discharging droplets;
A head tank for supplying liquid to the recording head;
A replaceable main tank for storing liquid to be supplied to the recording head;
Liquid feeding means for feeding the liquid from the main tank to the head tank;
A suction cap to which suction means is connected and seals the nozzle surface of the recording head;
A buffer tank having a smaller capacity than the head tank, connected to the head tank,
The head tank is
A bendable film-like member that forms a part of the wall surface of the liquid container that contains the liquid, and a restoring force acting in a direction opposite to the direction in which the film-like member bends due to a decrease in the remaining amount of liquid. And a negative pressure generating means including
The buffer tank is
A tank case that forms a buffer chamber communicating with the liquid storage portion of the head tank via a flow path;
A wall member which is movably provided in the tank case and forms a part of the wall surface of the buffer chamber;
A spring that applies a restoring force in a reverse direction when the wall member moves in a direction in which the capacity of the buffer chamber increases,
The spring constant of the spring of the buffer tank, the image forming apparatus characterized have a size <br/> than the spring constant of the spring of the head tank. The image forming apparatus according to claim 1 , wherein the flow path of the buffer tank communicates with the liquid container on a bottom side of the head tank. The image forming apparatus according to claim 1 , wherein the flow path of the buffer tank communicates with the liquid storage unit on an upper side of the head tank.   The image forming apparatus according to claim 3, wherein the flow path of the buffer tank is inclined obliquely downward.   The image forming apparatus according to claim 1, further comprising a detecting unit that detects a pressure in the buffer tank.   The liquid supply pump pressurizes and supplies the liquid to the head tank, and the suction cap sucks and discharges the liquid from the nozzles of the recording head when performing the maintenance and recovery operation of the recording head. The image forming apparatus according to any one of 1 to 5.   When the pressure in the head tank becomes equal to or higher than a first predetermined value during the pressure supply, the pressure supply operation is stopped, and when the pressure in the head tank becomes equal to or lower than a second predetermined value during the suction and discharge The image forming apparatus according to claim 6, wherein the suction / discharge operation is stopped.   The image forming apparatus according to claim 6, wherein the pressure supply and the suction discharge are performed in parallel.

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