JP2009172967A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein the surface level of ink liquid cannot be detected accurately when an ink used is not the prearranged one. <P>SOLUTION: This image forming device is equipped with: a recording head 1 for discharging droplets from nozzles; a sub-tank 2 for supplying the ink to the recording head 1; a main tank 3 for detachably installing the ink to the sub-tank 2;a first detecting means 21 for detecting the electrical characteristics of the ink in the main tank 3; a second detecting means 31 for detecting the electrical characteristics of the ink in the sub-tank 2; and a controller 42, which detects the ink level height in the sub-tank 2 based on the value of the voltage obtained from the electrical characteristics detected with the second detecting means 31 and the predetermined value of voltage, and sets the predetermined value of voltage in response to the electrical characteristics of the ink detected with the first detecting means 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 and a sub tank that supplies ink to the recording head.

  As an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, a plotter, and a complex machine of these, for example, an ink jet recording apparatus is known as an image forming apparatus of a liquid discharge recording method using a recording head for discharging ink droplets. . This liquid discharge recording type image forming apparatus ejects ink droplets from a recording head onto a conveyed paper to form an image (recording, printing, printing, and printing are also used synonymously). Serial type image forming device that forms an image by ejecting droplets while the recording head moves in the main scanning direction, and a line type that forms images by ejecting droplets without the recording head moving There is a line type image forming apparatus using a head.

  In the present application, “image forming apparatus” means an apparatus for forming an image by landing ink on a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. "Image formation" is not only the application of images with meanings such as characters and figures to the medium, but also the addition of images with no meaning such as patterns to the medium (simply applying droplets to the medium) Also means landing). The “ink” is not limited to the ink, but is used as a general term for all liquids that can perform image formation, such as a recording liquid, a fixing processing liquid, and a liquid. The term “paper” is not limited to paper, but includes the above-described OHP sheet, cloth, and the like, and means that ink droplets adhere to the recording medium, recording medium, recording paper, recording It is used as a general term for what includes what is called paper.

  In such an ink jet recording type image forming apparatus, a sub-tank (also referred to as a head tank or a buffer tank), which is a small-capacity liquid container for supplying ink to a recording head, is mounted on a carriage and has a large capacity. An apparatus is known in which a main tank (also referred to as a main cartridge or an ink cartridge) is detachably installed on the apparatus main body side, and ink is supplied (supplemented supply) to the sub tank from the main tank on the apparatus main body side. .

Further, the liquid level position of the ink in the sub tank needs to be controlled within a predetermined range in order to make the negative pressure constant. As a method for detecting the position (corresponding to the remaining amount) of the ink liquid surface in the sub tank, as described in Patent Document 1, a plurality of electrode pins are arranged in the ink, and a plurality of electrode pins are arranged. It is known to perform detection using the fact that the voltage between them changes depending on the presence or absence of ink.
JP 2005-161834 A

In Patent Document 2, a change in voltage is detected from a change in resistance value of ink and compared with a set value voltage. When the amount of change in voltage exceeds the set voltage, it is determined that the ink has ended, or the set voltage can be changed arbitrarily. In addition, it is described that the set voltage is changed during the printing operation and the maintenance operation, and the set voltage is changed depending on the temperature.
Japanese Patent No. 2842371

  By the way, in the supply device that supplies ink to the recording head in the sub tank system as described above, when the ink stored in the main tank is different from the originally planned ink, the electric resistance value of the ink is different. If the liquid level and remaining amount of the sub tank are detected based on the electrical resistance value of the ink, there is a problem that the liquid level and remaining amount of the ink in the sub tank cannot be accurately detected.

  Instead of the sub tank method, a method of supplying ink directly from the ink cartridge to the recording head is adopted, and the ink liquid level of the ink cartridge (which corresponds to the remaining amount of ink) is based on the electric resistance value of the ink. A similar problem arises when detection is performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable accurate detection of the ink liquid level even when the ink used is different from the intended ink.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head for discharging droplets from the nozzles;
A sub tank for supplying ink to the recording head;
A main tank that is detachably mounted to supply ink to the sub tank;
First detection means for detecting electrical characteristics of the ink in the main tank;
Second detection means for detecting electrical characteristics of the ink in the sub-tank;
Liquid level detection means for detecting the ink liquid level in the sub tank based on a voltage value obtained from the electrical characteristics detected by the second detection means and a predetermined voltage value;
And a means for setting the predetermined voltage value according to the electrical characteristics of the ink detected by the first detection means.

  Here, a voltage value obtained from the electrical characteristics of the ink detected by the first detection means when the main tank is mounted is stored as an initial voltage value, and the predetermined value is determined according to the stored initial voltage value. The voltage value can be set. In this case, whether or not the main tank is empty based on the initial voltage value and the voltage value obtained from the electrical characteristics of the ink detected by the first detection means when the main tank is empty. And means for not supplying ink from the main tank to the sub-tank when the main tank is empty.

  Further, based on the voltage value obtained from the electrical characteristics of the ink detected by the first detection means and the voltage value obtained from the electrical characteristics of the ink detected by the second detection means, the sub tank and the When it is determined that the ink in the main tank is empty, printing can be stopped.

  According to the image forming apparatus of the present invention, the predetermined voltage value for detecting the ink liquid level height is changed based on the detection result of the electrical characteristics of the ink in the main tank. Even when the ink to be printed is different from the scheduled ink, the ink liquid level can be accurately detected accurately.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic explanatory view for explaining the embodiment.
The image forming apparatus includes a recording head 1 that discharges droplets from nozzles, a sub tank 2 that supplies ink 10 to the recording head, a main tank 3 that is detachably attached to supply ink 10 to the sub tank 2, And a control means 4 for controlling each part.

  Ink is supplied from the sub tank 2 to the recording head 1 via the supply path 11, and a negative pressure on the recording head 1 is applied due to a water head difference between the liquid level (ink liquid level) of the ink 10 in the sub tank 2 and the recording head 1. generate. Ink is supplied from the main tank 3 to the sub tank 2 through the supply path 12, and the supply path 12 is provided with a valve 13. By opening the valve 13, a water head difference from the main tank 3 to the sub tank 2 is provided. Ink is supplied.

  The sub tank 2 is provided with a second detection means 21 composed of three electrode pins 21a, 21b, 21c for detecting the ink liquid level. The second detection means 21 detects a change in resistance value when the ink 10 is present between the three electrode pins 21a, 21b, and 21c as a voltage value change, thereby detecting the three electrode pins 21a, 21b, The upper limit position and the lower limit position of the height of the ink liquid level are detected by the combination of conduction in 21c. The sub tank 2 is provided with an air release hole 22.

  The main tank 3 is provided with first detection means 31 composed of electrode pins 31 a and 31 b for detecting the electric resistance value of the ink 10. The first detection means 31 detects the electric characteristic (electric resistance value or electric capacity) of the ink 10 interposed between the electrode pins 31a and 31b as a voltage value. The main tank 3 accommodates an ink bag 30 filled with ink 10, and a first detection means 31 is disposed on the bottom of the ink bag 30, and the first detection means 31 is filled in the ink bag 30. The electrical characteristics (electrical resistance value or electrical capacity) of the ink being detected are detected. Here, the first detection means 31 is composed of conductive electrode pins 31a and 32b. However, an arrangement in which two conductor patterns are arranged on a flexible printed board is arranged on the bottom surface of the bag. You can also.

  The control means 4 includes a detection circuit 41, a controller 42 that also serves as first and second detection means, liquid level detection means, and setting means for controlling the entire apparatus, and a nonvolatile memory 43. The detection circuit 41 detects the electrical characteristics of the ink between the electrode pins 31a and 31b of the first detection means 31 of the main tank 3 by converting them into voltages, and the electrode pins 21a of the second detection means 21 of the sub tank 2 The electrical characteristics of the ink between 21b and 21c are detected by converting them into voltages.

  The controller 42 stores the initial voltage value corresponding to the electrical characteristics detected by the first detection means 31 of the main tank 3 obtained from the detection circuit 41 when the main tank 31 is mounted in the nonvolatile memory 43. Then, the controller 42 compares the voltage corresponding to the electrical characteristics detected by the second detection means 21 of the sub tank 2 obtained from the detection circuit 41 with a set voltage that is a predetermined voltage, so that the ink liquid in the sub tank 2 is obtained. The height of the surface is detected. When the detected voltage is a set voltage (predetermined voltage), 13 is opened and closed. Further, the controller 42 sets a set voltage (predetermined voltage) according to the initial voltage stored in the nonvolatile memory 43.

  The sub tank 2 is shown as having a structure for supplying ink to one recording head 1. However, in the case of a line type recording head in which a plurality of heads are arranged, a plurality of recording heads are provided from one sub tank 2. It can be configured to supply ink. The second detection means 21 of the sub tank 2 is configured to detect the lower limit and upper limit of the ink level with three electrode pins, but detects the lower limit and upper limit of the ink level with two electrode pins. It can also be configured.

In the embodiment configured as described above, a method for detecting the ink liquid surface height by detecting the electrical characteristics of the ink in the sub tank 2 will be described with reference to FIGS.
There are inks having an electrical resistance value and inks having an electrical capacity depending on the characteristics of the ink. Here, an ink having an electrical resistance value will be described.
When the liquid level of the ink 10 in the sub tank 2 is lower than the height h1 shown in FIG. 2B, the resistance value between the electrode pins 21a and 21b and between 21b and 21c is shown in FIG. 2A. Becomes infinite (open state), and when the height is h1, the electrical resistance value between the electrode pins 21a and 21b becomes the resistance value r1. Further, as the liquid level rises, the electrical resistance value between the electrode pins 21a and 21b decreases according to the area in contact with the ink. When the liquid level is height h2, the electrical resistance value between the electrode pins 21b and 21c becomes the resistance value r1, and when the liquid level rises further, the electrical resistance value between the electrode pins 21b and 21c comes into contact with the ink. It goes down according to the area.

  Accordingly, the electrode pins 21a, 21b, 21c as the second detection means 21 are arranged in the sub tank 2, and the electric resistance value between the electrode pins 21a, 21b and between the electrode pins 21b, 21c is detected. It is possible to detect the liquid level of the ink inside.

  Here, when the sub tank 2 is filled with ink up to the upper limit position, as shown in FIG. 3A, the electrode pins 21a, 21b, and 21c are in contact with the ink. Since it is in contact with the ink, as described above, the electrode pins 21a and 21b are connected by the electrical characteristics of the ink. Further, the electrode pins 21b and 21c are also connected due to the electrical characteristics of the ink.

  When the ink is consumed and the ink level drops to the position shown in FIG. 3B, the electrode pins 21a and 21b and the electrode pins 21b and 21c are in an open (unconnected) state. If the electrical characteristic indicates a resistance value, the value is inversely proportional to the area in contact with the ink.

  Accordingly, the ink liquid level height of the sub tank 2 can be controlled within the liquid level height control range shown in FIG. 3A by adopting a circuit configuration capable of detecting the electrical characteristics between the two electrode pins. it can.

An example of the detection circuit 41 will be described with reference to the block explanatory diagram of FIG.
The detection circuit 41 includes a detector selection unit 41A composed of an AND gate, an AC coupling unit 41B composed of a capacitor, a voltage dividing resistor unit 41C composed of a resistor, a peak hold circuit 41D, and an A / D converter 41E. Is done.

  The selection signals S1 to S3 in the detector selection unit 41A are signals output from the controller 42. When the selection signal S1 becomes active, the DC component of the clock signal is removed by the AC coupling unit 41B, and the signal is supplied to the electrode pin 21c of the second detection unit 21 through the resistance of the voltage dividing resistor unit 41C. A voltage divided by the resistance of the voltage dividing resistor 41 and the electrical resistance of the ink between the electrode pins 21b and 21c is input through the diode of the peak hold circuit 41D. The voltage output from the peak hold circuit 41D is digitized by the A / D converter 41E, and the value is read by the controller.

  Thus, by activating the selection signal S1, a voltage value corresponding to the electrical resistance value can be obtained from the electrical resistance detected by the electrode pins 21b and 21c of the second detection means 21. .

  Similarly, by making the selection signal S2 active, a voltage value corresponding to the electrical resistance value can be obtained from the electrical resistance detected by the electrode pins 21a and 21b of the second detection means 21.

  Further, by making the selection signal S3 active, a voltage value corresponding to the electrical resistance value can be obtained from the electrical resistance detected by the electrode pins 31a and 31b of the first detection means 31 of the main tank 3. it can.

  In addition, with respect to ink having an electrical capacity as an electrical characteristic of the ink, a voltage corresponding to the electrical capacity can be obtained by the above-described detection circuit. When the ink has an electric resistance, the voltage divided by the voltage dividing resistor and the electric resistance is input to the peak hold circuit 41D, whereas when the ink has an electric capacity, the voltage dividing resistor and the electric voltage are electrically A voltage attenuated by the frequency transfer characteristic due to the capacitance is input to the peak hold circuit 41D, and a voltage corresponding to the electrical capacitance can be obtained.

Next, the fact that the detection result of the liquid level changes when the electrical resistance value of the ink varies will be described with reference to FIG.
FIG. 5 shows the relationship between the liquid level and the electrical resistance value when the electrical resistance value of the ink varies. If the electrical resistance value changes like a virtual line, if the determination value when determining the liquid level height h1 is determined by the electrical resistance value rs, the liquid level height is determined to be h11. Therefore, the ink level in the sub tank 2 cannot be detected correctly.

  Therefore, in the present invention, the sub tank 2 is corrected by correcting the determination value (predetermined voltage value) for determining the liquid level of the sub tank 3 based on the voltage value obtained from the electrical characteristics of the ink in the main tank 2. Even when the electrical characteristics of the ink in the main tank 3 for supplying ink change, the liquid level of the sub tank 3 can be accurately determined.

Regarding this point, refer to FIG. 6 showing the relationship between the ink level of the main tank 3 and the detection voltage and the relationship of the detection voltage to the level of the sub tank 2 when detected by the detection circuit 41 shown in FIG. To explain.
First, the relationship between the voltage detected by the first detection means 31 and the detection circuit 41 of the main tank 3 and the ink level in the main tank 3 is as shown in FIG. Since the electrical resistance value of the ink is inversely proportional to the contact area between the electrode pins 31a and 31b and the ink, the voltage Vr is detected from the full state to almost empty. When the ink is completely emptied and the electrode pins 31a and 31b are not connected by the ink, the voltage Vc / 2 is detected.

  The relationship between the voltage detected by the second detection means 21 and the detection circuit 41 of the sub tank 2 and the ink level in the sub tank 2 is as shown in FIG. When the ink in the sub tank 3 is empty, since the electrode pins 21a and 21b are in an open state, a voltage of Vc / 2 is detected from the electrode pins 21a and 21b (shown by a solid line). Similarly, since the electrode pins 21b and 21c are in an open state, a voltage of Vc / 2 is detected from the electrode pins 21b and 21c (illustrated phantom line is shown).

  Here, as indicated by a solid line in FIG. 6A, when the ink level in the sub tank 3 reaches the height h1, the electrode pins 21a and 21b are conducted through the ink. For this reason, the detected voltage decreases. Thereafter, the voltage decreases in inverse proportion to the contact area between the electrode pins 21a and 21b and the liquid level. As indicated by the phantom line in FIG. 5A, when the liquid level reaches the height h2, the voltage drops because the electrode pins 21b and 21c are conducted through the ink, and then the contact area between the electrode pin 21c and the ink is reduced. The voltage decreases in inverse proportion.

  Therefore, when the detection voltage value from the first detection means 21 of the sub tank 2 is determined, for example, if “Vr + (Vc / 2−Vr) / 2” is set as the determination value, the liquid level heights h1 and h2 of the ink are set. The position can be detected, and even if the electrical characteristics of the ink are changed by exchanging the main tank 3, the positions of the ink liquid surface heights h1 and h2 can be accurately detected. Here, in the detection circuit 41 described above, the forward voltage of the diode is set to 0 V for simple consideration. Vr is a voltage value detected by the first detecting means 31 when the main tank 3 is full.

Next, ink supply control in this embodiment will be described with reference to the flowcharts shown in FIGS.
First, when the ink supply control is started, it is determined whether or not the main tank 3 is mounted. When the main tank 3 is mounted, it is obtained from the first detection means 31 of the main tank 3 stored in the nonvolatile memory 43. A determination value Vr, which is a predetermined voltage, is calculated (set) from the obtained voltage value V1.

  Then, the voltage value V 1 obtained through the detection circuit 41 is read from the electrical characteristics of the ink detected by the first detection means 31. Thereafter, the voltage value V <b> 2 is detected through the detection circuit 41 from the electrical characteristics detected by the electrode pins 21 a and 22 b of the second detection means 21. Further, the voltage value V3 is detected through the detection circuit 41 from the electrical characteristics detected by the electrode pins 22b and 22c of the second detection means 21.

  Next, the voltage value Ve obtained through the detection circuit 41 based on the electrical characteristics of the ink detected by the first detection means 31 when the ink tank 3 is empty is compared with the detected voltage value V1, and V1 < It is determined whether or not Ve. At this time, if V1 <Ve, the ink tank 3 is not empty, so the determination value Vr is compared with the voltage values V2 and V3 detected by the second detection means 21 of the sub tank 2.

  That is, first, it is determined whether or not V2 ≦ Vr and V3> Vr (this is referred to as “condition 1”). If the condition 1 is satisfied, the ink in the main tank 3 is not empty and the sub tank 2 is not empty. Since the ink liquid level is within the control range as described above, the process returns to the process of calculating the determination value Vr.

  When the condition is not 1, it is determined whether or not V2> Vr and V3> Vr (referred to as “condition 2”). When the condition is 2, the ink in the main tank 3 is not empty, Since the ink level in the sub tank 2 is below the lower limit of the control range, the valve 13 is opened, ink supply (replenishment) from the ink tank 3 to the sub tank 2 is started, and the process returns to the process of calculating the determination value Vr. .

  In contrast, when the condition is not 2, it is determined whether V <Vr and V3 ≦ Vr (this is referred to as “condition 3”). If the condition is 3, the ink level in the sub tank 2 is determined. Is equal to or greater than the upper limit of the control range, and after the valve 13 is closed, the process returns to the process of calculating the determination value Vr if the condition 3 is not satisfied.

  On the other hand, if V1 <Ve, that is, if V1 ≧ Ve, the ink tank 3 is empty, so the determination value Vr is compared with the voltage values V2, V3 detected by the second detection means 21 of the sub tank 2. Then, it is determined whether or not V2 ≦ Vr and V3> Vr (this is referred to as “condition 4”). When the condition 4 is satisfied, the ink in the main tank 3 is empty and the ink liquid in the sub tank 2 is satisfied. Since the surface height is within the control range, the valve 13 is closed and the user is notified of a replacement request for the main tank 3 through the interface with the host side (PC).

  When the condition 4 is not satisfied, it is determined whether or not V2 ≦ Vr and V3> Vr (this is referred to as “condition 5”). When the condition 5 is satisfied, the ink in the main tank 3 is empty, and the sub tank 2 is below the lower limit of the control range, so that the operation of ejecting or sucking ink from the recording head 1 such as the printing operation and the maintenance recovery operation is prohibited, and the interface with the host side (PC) The main tank replacement request is notified to the user through and the system waits until the main tank 3 is replaced. After the main tank 3 is replaced, the process returns to the determination value Vr calculation process.

  Further, when it is not condition 5, that is, when none of the conditions 1 to 5 is satisfied, it is determined that an error has occurred because the condition does not actually occur, and the user is informed that an error has occurred through the interface with the host side (PC). Notify and stop all operations.

Next, the main tank mounting process will be described with reference to the flowchart shown in FIG.
When the main tank is mounted from the state where the main tank is not mounted, or when the main tank is replaced and mounted due to a main tank replacement request or the like, this main tank mounting process is entered.
The voltage value V1 is detected through the detection circuit 41 from the electrical characteristics of the ink in the main tank 3 detected by the first detection means 31, and is detected by the first detection means 31 when the ink tank 3 is empty. The voltage value Ve obtained through the detection circuit 41 based on the electrical characteristics of the ink is compared with the detected voltage value V1, and it is determined whether or not V1 <Ve.

  At this time, if V1 <Ve, the detected voltage value V1 is stored (stored) in the nonvolatile memory 43. On the other hand, if V1 <Ve, it is determined that the user has mistakenly installed the main tank 3 with empty ink, or the electrical characteristics of the ink in the main tank 3 are not suitable for this image forming apparatus. Therefore, the user is notified of an erroneous mounting of the main tank and a request to replace the main tank through the interface with the host side (PC).

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 11 is a schematic explanatory view for explaining the embodiment.
Here, the ink is supplied from the main tank 3 to the sub tank 2 by the pump 14. The pump 14 is driven by the control unit 4, and the ink is supplied from the main tank 3 to the sub tank 2 by driving the pump 14.

  The controller 42 of the control means 4 monitors the voltage detected by the second detection means 21 and the detection circuit 41, drives the pump 14 when the detected voltage value is a predetermined voltage value, and the pump 14 is driven. Since the ink flows from the main tank 3 to the sub tank 2 and the ink level in the sub tank 2 rises, the driving of the pump 14 is stopped when the voltage value detected by the second detection means 21 reaches a predetermined voltage value. .

  Since other configurations and operations are the same as those in the first embodiment, the description thereof is omitted.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a schematic explanatory view for explaining the embodiment.
Here, the recording head 1 and the sub tank 2 are integrated. The sub tank 2 includes a second detection unit 21 that detects the height of the ink level in the sub tank 2, an air release hole 22, a negative pressure generation unit 5 that generates a negative pressure in the ink in the sub tank 2, and a negative pressure. An air release valve 24 is provided for opening and closing the air release hole 22 of the sub tank 2 when pressure is generated. The negative pressure generating means 5 generates negative pressure by drawing ink in the sub tank 2 into the negative pressure generating means 5 at a constant pressure. Since there is an upper limit and a lower limit for the pull-in amount, a sensor for detecting the upper limit and the lower limit is provided, although not shown.

  The controller 42 of the control means 4 opens the air release valve 24 when the sub tank 2 is initially filled with ink. At this time, the negative pressure generating means is in the maximum ink drawing state. In this state, the pump 14 is driven to supply ink from the main tank 3 to the sub tank 2. At the same time, the voltage value detected by the second detection means 21 and the detection circuit 41 in the control means 4 is monitored, and the driving of the pump 14 is stopped when the voltage value reaches a predetermined voltage value. At this time, the predetermined voltage value is calculated based on the initial voltage value stored in the nonvolatile memory 43. After the sub tank 2 is filled with ink, the air release valve 24 is closed.

  Regarding the ink consumption due to printing, the sensor in the negative pressure generating means is monitored, and when the pull-in amount reaches the lower limit, the pump 14 is driven to fill the ink up to the upper limit of the pull-in amount.

  Since other constituent operations are the same as those in the first embodiment, the description thereof is omitted.

  In each of the above embodiments, the first tank is provided with the first detection unit. However, the sub tank itself may have the first detection unit. In this case, the sub-tank includes two detection means for detecting the liquid level for detecting the electrical characteristics of the ink and detection means for setting the voltage value for detecting the electrical characteristics of the ink. Detection means (corresponding to the first detection means in each of the above embodiments) can be provided on the side surface or bottom surface of the sub tank.

In this case, the mounting structure of the electrode pins constituting the voltage value setting detecting means will be described with reference to the cross-sectional explanatory view of FIG.
Here, the holding pins 50 on the recording head 1 side hold the electrode pins 51 a and 51 b constituting the voltage value setting detecting means and the ink supply pin 52, and the electrode pins 51 a and 51 b are respectively provided on the bottom surface of the sub tank 2. , Sealing members 53 and 54 are provided for sealing in a state where the ink supply pin 52 penetrates.

Next, an example of an image forming apparatus to which the present invention is applied will be described with reference to FIGS. FIG. 13 is a schematic configuration diagram for explaining the overall configuration of the mechanism section of the apparatus, and FIG. 14 is an explanatory plan view of the main part of the mechanism section.
This image forming apparatus is a serial type image forming apparatus, and a carriage 233 is slidably held in the main scanning direction by main and sub guide rods 231 and 232 which are guide members horizontally mounted on the left and right side plates 201A and 201B. The main scanning motor that does not perform moving scanning in the direction indicated by the arrow (carriage main scanning direction) via the timing belt.

  The carriage 233 includes recording heads 234a and 234b (which are liquid ejection heads for ejecting ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K)). “Recording head 234”) is arranged in a sub-scanning direction orthogonal to the main scanning direction with a nozzle row composed of a plurality of nozzles, and the ink droplet ejection direction is directed downward.

  Each of the recording heads 234 has two nozzle rows. One nozzle row of the recording head 234a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 234b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets.

  The carriage 233 is equipped with sub-tanks 235a and 235b (referred to as “sub-thunk 35” when not distinguished) for supplying ink of each color corresponding to the nozzle rows of the recording head 234. The sub tank 235 is supplied with ink of each color from ink cartridges 210k, 210c, 210m, and 210y, which are main tanks of the respective colors, through the supply tubes 36 of the respective colors.

  On the other hand, as a paper feeding unit for feeding the paper 242 stacked on the paper stacking unit (pressure plate) 241 of the paper feed tray 202, a half-moon roller (feeding) that separates and feeds the paper 242 one by one from the paper stacking unit 241. A separation pad 244 made of a material having a large coefficient of friction is provided opposite to the sheet roller 243 and the sheet feeding roller 243, and the separation pad 244 is urged toward the sheet feeding roller 243 side.

  In order to feed the sheet 242 fed from the sheet feeding unit to the lower side of the recording head 234, a guide member 245 for guiding the sheet 242, a counter roller 246, a conveyance guide member 247, and a tip pressure roller. And a conveying belt 251 which is a conveying means for electrostatically attracting the fed paper 242 and conveying it at a position facing the recording head 234.

  The conveyor belt 251 is an endless belt, and is configured to wrap around the conveyor roller 252 and the tension roller 253 so as to circulate in the belt conveyance direction (sub-scanning direction). In addition, a charging roller 256 that is a charging unit for charging the surface of the transport belt 251 is provided. The charging roller 256 is disposed so as to come into contact with the surface layer of the conveyor belt 251 and to rotate following the rotation of the conveyor belt 251. The transport belt 251 rotates in the belt transport direction when the transport roller 252 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 242 recorded by the recording head 234, a separation claw 261 for separating the paper 242 from the transport belt 251, a paper discharge roller 262, and a paper discharge roller 263 are provided. A paper discharge tray 203 is provided below the paper discharge roller 262.

  A double-sided unit 271 is detachably attached to the back surface of the apparatus main body. The duplex unit 271 takes in the paper 242 returned by the reverse rotation of the transport belt 251, reverses it, and feeds it again between the counter roller 246 and the transport belt 251. The upper surface of the duplex unit 271 is a manual feed tray 272.

  Further, a maintenance / recovery mechanism 281 for maintaining and recovering the nozzle state of the recording head 234 is disposed in a non-printing area on one side in the scanning direction of the carriage 233. The maintenance / recovery mechanism 281 includes cap members (hereinafter referred to as “caps”) 282a and 282b (hereinafter referred to as “caps 282” when not distinguished) for capping each nozzle surface of the recording head 234, and nozzle surfaces. A wiper blade 283 that is a blade member for wiping the ink, and an empty discharge receiver 284 that receives liquid droplets for discharging the liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. ing.

  In addition, in the non-printing area on the other side in the scanning direction of the carriage 233, the liquid that receives liquid droplets when performing idle ejection that ejects liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An ink recovery unit (empty discharge receiver) 288 that is a recovery container is disposed, and the ink recovery unit 288 includes an opening 289 along the nozzle row direction of the recording head 234 and the like.

  In this image forming apparatus configured as described above, the sheets 242 are separated and fed one by one from the sheet feeding tray 202, and the sheet 242 fed substantially vertically upward is guided by the guide 245, and is conveyed to the conveyor belt 251 and the counter. It is sandwiched between the rollers 246 and conveyed, and further, the leading end is guided by the conveying guide 237 and pressed against the conveying belt 251 by the leading end pressing roller 249, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 256, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 251 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 242 is fed onto the conveyance belt 251 charged alternately with plus and minus, the sheet 242 is attracted to the conveyance belt 251, and the sheet 242 is conveyed in the sub scanning direction by the circumferential movement of the conveyance belt 251.

  Therefore, by driving the recording head 234 according to the image signal while moving the carriage 233, ink droplets are ejected onto the stopped paper 242 to record one line, and after the paper 242 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 242 has reached the recording area, the recording operation is finished and the paper 242 is discharged onto the paper discharge tray 203.

Next, another example of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 15 is a schematic side view for explaining the overall configuration of the image forming apparatus.
This image forming apparatus is a line type image forming apparatus, and a plurality of line type recording heads 310y that discharge inks that are liquids of black (K), cyan (C), magenta (M), and yellow (Y). , 310m, 310c, 310k (hereinafter, when the colors are not distinguished, the symbols without the sub-codes y, m, c, k are used. The same applies to the other members). The head unit 301 is integrally held. The head unit 301 is arranged to be movable in the paper feeding direction (the arrow direction in FIG. 15).

  As shown in FIGS. 16 and 17, each recording head 310 has ten heads 401 </ b> A to 401 </ b> J arranged in two rows in a staggered manner on a head support member 400. Each head 401 has a nozzle surface 404 in which nozzle rows 403 in which a plurality of nozzles 402 for discharging droplets are arranged side by side are arranged in two rows in a staggered manner.

  An ink supply device that supplies ink of each color to each recording head 310 of the head unit 301 includes a main tank unit 302 including a replaceable main tank (ink cartridge) 320 that stores ink of each color, and the main tank 320. And a sub tank unit 303 including a sub tank 330 that supplies ink to the recording head 310 via a supply tube (supply path) 331. A water head difference is provided between the sub tank 330 and the recording head 310 of the head unit 301 to generate a required negative pressure in the recording head 310.

  A paper transport mechanism 306 that transports the paper 305 fed from the paper feeder 304 facing the head unit 301 is disposed below the head unit 301. The paper transport mechanism 306 includes a transport belt 361 in which a plurality of suction holes are formed by perforating processing for sucking and transporting the paper 305, transport rollers 362 and 363 around the transport belt 361, and a transport belt 361 (not shown). Includes a platen member for maintaining appropriate flatness, a suction fan 365 for sucking air from the suction holes of the transport belt 361 and sucking the paper 305 onto the transport belt 361, and the like. Note that the suction of the sheet is not limited to suction, but may be configured to be held by electrostatic suction or adhesion.

  In addition, a conveyance guide plate 307 is disposed on the downstream side of the conveyance belt 361 so as to be openable and closable, and a paper discharge table 308 is disposed on the downstream side of the conveyance guide plate 307. A maintenance / recovery mechanism (cleaning unit) 309 that performs maintenance / recovery of the recording head 310 is disposed below the conveyance guide plate 307.

  In this image forming apparatus, an image is recorded by the recording head 310 while adsorbing and conveying the sheet 305 fed from the sheet feeding device 304 onto the conveyance belt 361, and discharged from the conveyance guide plate 307 to the sheet discharge tray 308. To do.

It is typical explanatory drawing explaining 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the method of detecting the electrical property of the ink of a subtank, and detecting the liquid level height of an ink. It is explanatory drawing similarly used for description of the liquid level height control range. It is block explanatory drawing which shows an example of a detection circuit. It is explanatory drawing with which it uses for description of the dispersion | variation in the electrical resistance value of ink, and the dispersion | variation in the detection result of a liquid level height. It is explanatory drawing with which it uses for description of the relationship of the detection voltage with respect to the liquid level height of the ink level of a main tank, and the liquid level of a sub tank. It is a flowchart with which it uses for description of ink supply control. FIG. 6 is a flowchart for explaining ink supply control in the same manner. It is a flowchart with which it uses for description of a main tank mounting process. It is typical explanatory drawing explaining 2nd Embodiment of this invention. It is typical explanatory drawing explaining 3rd Embodiment of this invention. It is typical sectional explanatory drawing with which it uses for description of the mounting structure of the electrode pin which comprises a 1st detection means. 1 is a schematic configuration diagram illustrating an overall configuration of a mechanism unit in 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 schematic side view for explaining the overall configuration of another example of the image forming apparatus according to the present invention. FIG. 6 is a plan view of the recording head. It is a plane explanatory view similarly used for description of the head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Recording head 2 ... Sub tank 3 ... Main tank 4 ... Control means 21 ... 1st detection means 31 ... 2nd detection means 41 ... Detection circuit

Claims (4)

A recording head for discharging droplets from the nozzles;
A sub tank for supplying ink to the recording head;
A main tank that is detachably mounted to supply ink to the sub tank;
First detection means for detecting electrical characteristics of the ink in the main tank;
Second detection means for detecting electrical characteristics of the ink in the sub-tank;
Liquid level detection means for detecting the ink liquid level height in the sub tank based on a voltage value obtained from the electrical characteristics detected by the second detection means and a predetermined voltage value;
An image forming apparatus comprising: a means for setting the predetermined voltage value according to the electrical characteristics of the ink detected by the first detection means.   The image forming apparatus according to claim 1, wherein a voltage value obtained from an electrical characteristic of the ink detected by the first detection unit when the main tank is mounted is stored as an initial voltage value, and the stored initial value is stored. An image forming apparatus, wherein the predetermined voltage value is set according to a voltage value.   The image forming apparatus according to claim 2, wherein the main voltage is based on the initial voltage value and a voltage value obtained from an electrical characteristic of the ink detected by the first detection unit when the main tank is empty. An image forming apparatus comprising: means for determining whether or not a tank is empty; and no ink is supplied from the main tank to the sub-tank when the main tank is empty.   4. The image forming apparatus according to claim 1, wherein a voltage value obtained from an electrical characteristic of the ink detected by the first detection unit and an electrical value of the ink detected by the second detection unit are defined. An image forming apparatus, wherein printing is stopped when it is determined that ink in the sub tank and the main tank is empty based on a voltage value obtained from characteristics.

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