阅读说明：本技术 液面检测装置及图像形成装置 (Liquid level detection device and image forming apparatus ) 是由 河合寿二 于 2021-03-23 设计创作，主要内容包括：本发明提供一种液面检测装置及图像形成装置。液面检测装置包含电极衬垫、线圈、存储器、检测控制电路。电极衬垫安装于图像形成装置的盒的外侧面。线圈与电极衬垫连接。存储器存储初始值。检测控制电路求出包含线圈和带电极衬垫的盒在内的第一谐振电路的静电电容(第一静电电容)。在求液位值的情况下,检测控制电路从第一静电电容减去误差值而求出第一修正电容,并基于第一修正电容和初始值来求出液位值。(The invention provides a liquid level detection device and an image forming apparatus. The liquid level detection device comprises an electrode pad, a coil, a memory and a detection control circuit. The electrode pad is attached to an outer surface of a cartridge of the image forming apparatus. The coil is connected to the electrode pad. The memory stores initial values. The detection control circuit determines the capacitance (first capacitance) of a first resonance circuit including the coil and the case with the electrode pad. When the level value is obtained, the detection control circuit obtains a first correction capacitance by subtracting the error value from the first capacitance, and obtains the level value based on the first correction capacitance and the initial value.)

1. A liquid level detection device is mounted on an image forming apparatus, and includes:

an electrode pad attached to an outer side surface of a cartridge that is provided in the image forming apparatus and that contains a liquid;

a coil connected to the electrode pad and forming a part of a first resonant circuit;

a memory that nonvolatilely stores an initial value; and

a detection control circuit that recognizes a resonance frequency of the first resonance circuit using the cartridge having the electrode pad mounted thereon as a capacitor and obtains a first capacitance that is a capacitance of the first resonance circuit based on the recognized resonance frequency,

in the case where the initial value is stored in the memory,

the detection control circuit obtains the first capacitance before installation in the image forming apparatus,

the memory stores the first electrostatic capacitance obtained as the initial value,

in the case where the error value is stored in the memory,

the detection control circuit finds the first capacitance after being installed in the image forming apparatus,

the memory stores the error value based on a difference between the initial value and the first electrostatic capacitance found after installation to the image forming apparatus,

when a liquid level value that is a value indicating the height of the liquid surface of the liquid in the height direction of the electrode pad is obtained,

the detection control circuit obtains the first capacitance, obtains a first correction capacitance by subtracting the error value from the first capacitance obtained, and obtains the level value based on the first correction capacitance and the initial value.

2. The liquid level detection device according to claim 1,

the liquid level detection device comprises a detection substrate,

the detection substrate includes the memory, the detection control circuit, and the coil, and is connected to the electrode pad through a signal line.

3. The liquid level detection device according to claim 1 or 2,

the memory stores an initial null value and an initial upper value as the initial values,

the initial null value is a value obtained by measurement before installation to the image forming apparatus and is the first electrostatic capacitance in the absence of the liquid,

the initial upper end value is a value obtained by measurement before installation in the image forming apparatus, and is the first electrostatic capacitance when the height of the liquid surface is the same as the height of the upper end of the electrode pad,

the detection control circuit calculates the level value by calculating (A-B)/(C-B) when A is set to the first correction capacitor, B is set to the initial null value, and C is set to the initial upper end value.

4. The liquid level detection device according to claim 1 or 2,

the memory stores an initial null value that is,

the initial null value is a value obtained by measurement before installation to the image forming apparatus, is the first electrostatic capacitance in the absence of the liquid,

the detection control circuit obtains, as the error value, a value obtained by subtracting the initial null value from the first capacitance obtained after the mounting to the image forming apparatus when the liquid is not present.

5. The liquid level detection device according to claim 1 or 2,

comprising a second resonance circuit connected to said detection control circuit and not to said electrode pad and comprising a capacitor,

the detection control circuit identifies a resonance frequency of the second resonance circuit and obtains a second capacitance that is a capacitance of the second resonance circuit based on the identified resonance frequency of the second resonance circuit,

the memory stores a temperature correction electrostatic capacitance in a nonvolatile manner,

when the temperature correction electrostatic capacitance is stored in the memory,

the detection control circuit obtains the second capacitance before being mounted on the image forming apparatus,

the memory stores the second capacitance obtained as the temperature correction capacitance,

in the case of finding the level value,

the detection control circuit

Determining the second capacitance after the mounting to the image forming apparatus,

obtaining a second correction capacitance in which the first correction capacitance is corrected by performing a predetermined calculation based on the temperature correction electrostatic capacitance and the second electrostatic capacitance obtained after the temperature correction electrostatic capacitance is mounted on the image forming apparatus,

the level value is found based on the second correction capacitance and the initial value.

6. The liquid level detection device according to claim 5,

comprises a substrate for detection,

the detection substrate includes the memory, the detection control circuit, the coil, and the second resonance circuit, and is connected to the electrode pad through a signal line.

7. The liquid level detection device according to claim 5,

the memory stores an initial null value and an initial upper value as the initial values,

the initial null value is a value obtained by measurement before installation to the image forming apparatus and is the first electrostatic capacitance in the absence of the liquid,

the initial upper end value is a value obtained by measurement before installation in the image forming apparatus, and is the first electrostatic capacitance when the height of the liquid surface is the same as the height of the upper end of the electrode pad,

the detection control circuit calculates the level value by calculating (D-E)/(F-E) when D is the second correction capacitor, E is the initial null value, and F is the initial upper value.

8. The liquid level detection device according to claim 5,

the detection control circuit performs an operation of multiplying the ratio by the first correction capacitance as the predetermined operation,

the ratio is a value obtained by dividing the temperature correction electrostatic capacitance by the second electrostatic capacitance obtained when the level value is obtained.

9. An image forming apparatus, comprising:

the liquid level detection device according to claim 1 or 2; and

an image forming section for performing printing based on the liquid,

the liquid is an ink that is capable of,

the cartridge is a container that houses the ink agent.

10. The image forming apparatus according to claim 9,

a notification unit that notifies based on the level value,

the notification unit notifies a first message that the cartridge should be replaced when the level value is equal to or higher than a predetermined first threshold value.

Technical Field

The present invention relates to a liquid level detection device that recognizes a current capacitance based on a resonance frequency and obtains a value indicating a liquid level height. The present invention also relates to an image forming apparatus including the liquid level detection device.

Disclosure of Invention

Technical problem to be solved

In the case of detecting the height of the liquid surface (liquid level) in the container or the cartridge, an electrostatic capacitance sensor may be used. Generally, an electrostatic capacitance sensor includes a pair of electrodes. The pair of electrodes functions as a capacitor. For example, the pair of electrodes is provided in the container so that the long sides thereof extend in the vertical direction. The more liquid in the container, the more amount of liquid between the electrodes. The dielectric constant between the electrodes varies depending on the height of the liquid in the container. The electrostatic capacitance varies depending on the degree of immersion of each electrode in the liquid.

There is known a device for detecting the liquid level based on a change in electrostatic capacitance as follows. Specifically, there is known a liquid level detection device including a liquid level sensor having a cylindrical external electrode inserted into a liquid and an internal electrode provided with an insulating gap therebetween, the liquid level sensor applying an alternating voltage between the external electrode and the internal electrode of the liquid level sensor, detecting a capacitance between the external electrode and the internal electrode based on the applied voltage, and detecting a liquid level based on the detected capacitance.

The type of liquid processing is included in the image forming apparatus. For example, there is an image forming apparatus that performs printing using an ink. It is conceivable to assemble the liquid level detection apparatus in such an image forming apparatus. In order to accurately detect the height of the liquid level, the liquid level detection device may include: a sensor that detects that the liquid level reaches an upper limit (upper end), a sensor that detects the current electrostatic capacitance between the electrodes, and a sensor that detects that the liquid level is at a lower limit (no liquid). By using these three types of sensors, the capacitance at the lower limit, the capacitance at the upper limit, and the current capacitance between the electrodes can be accurately grasped. Thus, it is possible to determine which liquid level (height) the current liquid level is at between the minimum liquid level and the maximum liquid level, which is between the lower limit and the upper limit.

However, if at least three kinds of sensors are provided, the manufacturing cost of the liquid level detection device increases. In order to suppress the cost, a sensor (electrode) that measures only the current electrostatic capacitance between electrodes may be considered. For example, the capacitance at the lower limit of the liquid surface and the capacitance at the upper limit of the liquid surface are written in the memory. The data of the memory can be used when measuring the liquid level. However, when the respective capacitances are written in the memory, or when the liquid level detection device is actually mounted in the image forming apparatus, the detection environment (measurement condition) of the liquid level detection device changes. For example, the stray capacitance between a circuit for calculating the electrostatic capacitance and an electrode (capacitor) varies.

Therefore, the electrostatic capacitance written in the memory may be inappropriate. As a result, the height of the liquid surface may not be accurately detected. In the known liquid level detection device, writing of data into the memory is not described.

In view of the above-described problems, the present invention provides a liquid level detection device including a memory for storing data for detecting a liquid level height, which is mounted on an image forming apparatus, and which can reduce an error caused by a change in a detection environment and accurately detect the height of a liquid level.

(II) technical scheme

In order to achieve the above object, a liquid level detection device according to the present invention is mounted on an image forming apparatus. The liquid level detection device comprises an electrode pad, a coil, a memory and a detection control circuit. The electrode pad is attached to an outer side surface of a cartridge that is provided in the image forming apparatus and that contains liquid. The coil is connected to the electrode pad and is part of a first resonant circuit. The memory non-volatilely stores an initial value. The detection control circuit identifies a resonance frequency of the first resonance circuit that uses the cartridge mounted with the electrode pad as a capacitor. The detection control circuit obtains a first capacitance that is a capacitance of the first resonance circuit based on the identified resonance frequency. When the initial value is stored in the memory, the detection control circuit determines the first capacitance before the image forming apparatus is mounted. The memory stores the first capacitance obtained as the initial value. When the error value is stored in the memory, the detection control circuit determines the first electrostatic capacitance after the image forming apparatus is mounted. The memory stores the error value based on a difference between the initial value and the first electrostatic capacitance found after installation to the image forming apparatus. When a level value that is a value indicating a height of the liquid level of the liquid in a height direction of the electrode pad is obtained, the detection control circuit obtains the first capacitance, obtains a first correction capacitance by subtracting the error value from the obtained first capacitance, and obtains the level value based on the first correction capacitance and the initial value.

(III) advantageous effects

According to the liquid level detection device of the present invention, when the liquid level detection device including the memory for storing the data for height detection is mounted on the image forming apparatus, it is possible to reduce an error due to a change in the detection environment. The height of the liquid level can be accurately detected. Further features or advantages of the invention may become more apparent from the embodiments shown below.

Drawings

Fig. 1 is a diagram showing an example of an image forming apparatus according to an embodiment.

Fig. 2 is a diagram showing an example of the image forming apparatus according to the embodiment.

Fig. 3 is a diagram showing an example of the maintenance unit according to the embodiment.

FIG. 4 is a diagram showing an example of the liquid level detection device according to the embodiment.

Fig. 5 is a diagram showing an example of a flow of writing an initial value into a memory in the liquid level detection device according to the embodiment.

Fig. 6 is a diagram showing an example of the difference in capacitance obtained in the liquid level detection device according to the embodiment.

Fig. 7 is a diagram showing an example of a flow of recording an error value in the liquid level detection device according to the embodiment.

Fig. 8 is a diagram showing an example of a flow of calculating a liquid level value in the liquid level detection device according to the embodiment.

Fig. 9 illustrates an example of notification in the image forming apparatus according to the embodiment.

Detailed Description

The liquid level detection device 9 according to the embodiment of the present invention and the image forming apparatus 100 including the liquid level detection device 9 will be described below with reference to fig. 1 to 9. The image forming apparatus 100 performs printing using an ink. The image forming apparatus 100 described below is a printer. Further, the image forming apparatus 100 may be a multifunction peripheral.

(overview of image Forming apparatus 100)

First, an image forming apparatus 100 according to an embodiment is schematically described with reference to fig. 1 and 2. The image forming apparatus 100 prints on paper. The image forming apparatus 100 includes: the control unit 1, the storage unit 2, the engine control unit 3a, the video control unit 3b, the operation panel 4, the paper feed unit 5, the paper feed unit 6, the image forming unit 7, the ink supply unit 8, and the liquid level detection device 9. The control unit 1, the engine control unit 3a, and the video control unit 3b are, for example, boards including a control circuit and an arithmetic circuit.

The control unit 1 issues an operation command to each unit of the image forming apparatus 100. The control unit 1 manages print jobs. When executing a print job, the control portion 1 issues a paper feed and paper conveyance instruction to the engine control portion 3 a. The engine control unit 3a controls the operations of the paper feed unit 5 and the paper transport unit 6, triggered by the command. When the print job is executed, the control section 1 generates image data for ink ejection. The control section 1 transmits a print command and ink-ejection image data to the video control section 3 b. The video control section 3b ejects the ink from the line head 70 based on the ink-ejection image data.

The control unit 1 is a board including a control circuit 10, an image processing circuit 11, and a communication circuit unit 12. The control circuit 10 is, for example, a CPU. The control circuit 10 performs arithmetic and processing based on the control program and the control data stored in the storage unit 2. The storage unit 2 includes a nonvolatile storage device such as a ROM and a storage device (HDD, flash ROM), and a RAM. The image processing circuit 11 performs image processing on image data used for printing (image data for printing), and generates image data for ink ejection.

The communication circuit unit 12 includes: a communication connector, a communication control circuit, and a communication memory. The communication memory stores communication software. The communication circuit unit 12 communicates with the computer 200. The computer 200 is, for example, a PC or a server. The control section 1 receives print job data from the computer 200. The print job data includes: print settings and print contents. For example, the print job data contains data described by a page description language. The control unit 1 (image processing circuit 11) analyzes the received (input) print job data. The control unit 1 generates raster data (image data for printing) based on the analysis result of the print job data.

The engine control unit 3a includes, for example, an engine control circuit and an engine memory. The engine control circuit is, for example, a CPU. The engine memory stores programs and data related to paper feed control and paper conveyance control.

The video control unit 3b is a substrate or a chip. The video control unit 3b includes a video control circuit and an image memory. The video control circuit performs image processing and controls the ink ejection from the line head 70. The image memory is a memory for storing image data for ink ejection and data necessary for image processing and ink ejection. The image memory is, for example, a DRAM.

The operation panel 4 includes a display panel 41 and a touch panel 42. The control unit 1 displays a setting screen or information on the display panel 41. The display panel 41 displays operation images such as keys, buttons, and labels. The touch panel 42 detects a touch operation to the display panel 41. The control unit 1 recognizes the operation image on which the operation is performed based on the output of the touch panel 42. The control unit 1 recognizes a setting operation performed by a user.

The paper feed unit 5 stores a bundle of paper sheets. The paper feed section 5 includes a paper feed roller 51. The sheet feed roller 51 contacts the sheet set in the sheet feed portion 5. A paper feed motor (not shown) for rotating the paper feed roller 51 is provided. When executing a print job, the engine control portion 3a rotates the paper feed motor and rotates the paper feed roller 51. Thereby, the sheet is sent out from the sheet feeding portion 5 to the sheet conveying portion 6 (first conveying portion 6 a).

The paper conveying section 6 conveys paper. The paper conveying unit 6 includes a first conveying unit 6a and a second conveying unit 6 b. The first conveying unit 6a conveys the sheet fed from the sheet feeding unit 5 to the image forming unit 7. The second conveying unit 6b conveys the sheet having passed through the image forming unit 7 (line head 70) to the discharge tray 101. A post-processing device (optional device, not shown) can be attached to a side surface (left side in fig. 1) of the image forming apparatus 100.

As shown in fig. 1, the first conveying section 6a includes a conveying unit 60 and a first conveying roller pair 61. The first conveying roller pair 61 is provided in plurality. In order to rotate each first conveying roller pair 61, a first conveying motor 62 is provided. When executing the print job, the engine control portion 3a rotates the first conveyance motor 62. The conveying unit 60 includes a conveying belt 63, a driving roller 64, and a plurality of driven rollers 65. The conveying belt 63 is wound around a driving roller 64 and a driven roller 65. To rotate the drive roller 64, a belt motor 66 is provided. When executing a print job, the engine control unit 3a rotates the belt motor 66 and causes the conveyor belt 63 to circulate. Further, for example, a plurality of holes are opened in the conveyor belt 63. An adsorption device (not shown) for sucking air from the hole is also provided. The paper position on the tape can be fixed by suction.

The second transfer portion 6b includes a plurality of second conveying roller pairs 67. In order to rotate each second conveying roller pair 67, a second conveying motor 68 is provided. When executing the print job, the engine control portion 3a rotates the second conveyance motor 68.

The image forming section 7 prints on the transported paper. The image forming unit 7 ejects ink to the transported paper. As shown in fig. 1, the image forming section 7 includes four line inkjet heads 70. The line head 70Bk ejects black ink. The line head 70Y ejects yellow ink. The line head 70C ejects ink agent of cyan. The line head 70M ejects magenta ink. The respective rows of inkjet heads 70 are fixed. Each line of inkjet heads 70 is disposed above the conveying unit 60 (conveying belt 63). A certain gap is provided between each line of the inkjet heads 70 (nozzles on the lower surface) and the conveyor belt 63. The paper passes through the gap.

The line head 70 includes a plurality of nozzles. The nozzles are arranged in a direction (main scanning direction) perpendicular to the sheet conveying direction (in fig. 1, a direction perpendicular to the sheet surface). The nozzle faces downward. The openings of the nozzles face the conveyor belt 63. The control section 1 supplies image data for ink ejection used for printing to the video control section 3 b. The video control section 3b causes the line head 70 to eject the ink from the nozzles onto the paper being conveyed, based on the image data for ink ejection. The ink is made to adhere to the conveyed paper to record (form) an image.

The ink supply portion 8 includes an ink cartridge 81 and an ink supply tube 82. The ink cartridge 81 stores ink for supplying the line head 70. The ink cartridges 81 are respectively provided with four colors. The ink supply tube 82 connects the line head 70 of the color corresponding to the ink cartridge 81. The ink is supplied to the line head 70 through an ink supply tube 82.

(maintenance unit 7a)

Next, an example of the maintenance unit 7a according to the embodiment will be described with reference to fig. 1 and 3. The image forming apparatus 100 does not always print a real image. During printing, nozzles that do not eject ink sometimes appear in the fixed line head 70. In the nozzle, the components (solvent) of the ink agent volatilize (evaporate). In a nozzle that does not eject the ink for a long time, the viscosity of the ink increases due to volatilization of the components. Ink having a high viscosity is difficult to eject. If the viscosity continues to rise, it eventually plugs the nozzle.

Therefore, the control unit 1 causes the image forming unit 7 (line head 70) to perform the cleaning process every time a certain time elapses after the start of printing. The cleaning process is a process of discharging the ink agent from the line head 70 in order to prevent clogging. The cleaning process is a maintenance process. Printing is interrupted during the cleaning process. In the cleaning process, the engine control portion 3a does not feed and convey the paper.

In order to perform maintenance on the line head 70, the image forming apparatus 100 includes a maintenance unit 7 a. As shown in fig. 1, the maintenance unit 7a is disposed below the line head 70. As shown in fig. 3, the maintenance unit 7a includes a first moving mechanism 71, a second moving mechanism 72, and a tray unit 73.

The tray unit 73 contains an ink-receiving tray 74. The ink agent receiving tray 74 is a tray that receives and collects the ink agent discharged from the line head 70 (nozzles). For example, an ink agent discharge hole is provided in the center of the ink agent receiving tray 74. The ink-receiving tray 74 has its surface on which ink falls inclined so that the ink flows toward the ink discharge hole. Below the ink discharge hole, a waste ink tank 75 (corresponding to a tank) is provided. The waste ink cartridge 75 receives the ink agent that is discharged and falls from the ink agent discharge hole. In other words, the waste ink cartridge 75 recovers the discharged ink as the waste ink.

The first moving mechanism 71 moves the conveyance unit 60 in the horizontal direction (the direction perpendicular to the paper surface in fig. 1). When printing is performed, the first movement mechanism 71 disposes the conveyance unit 60 below the line head 70. When performing the cleaning process, the control unit 1 causes the first movement mechanism 71 to move the conveyance unit 60 to the retracted position. The retracted position of the conveyance unit 60 is a position shifted from below the line head 70.

The second moving mechanism 72 moves the tray unit 73 in the up-down direction (vertical direction). When the cleaning process is performed, the transport unit 60 is moved to the retracted position, and then the controller 1 raises the tray unit 73 by the second moving mechanism 72. Thereby, the tray unit 73 moves toward the lower surface of the line head 70. The second moving mechanism 72 moves the tray unit 73 to a position below the inkjet head 70. When the cleaning process is finished, the control section 1 causes the second moving mechanism 72 to lower the tray unit 73 to the lower limit position. After the lowering, the control section 1 causes the first movement mechanism 71 to move the conveyance unit 60 downward of the line head 70.

The first and second moving mechanisms 71 and 72 include mechanical members such as a motor, a gear, a belt, a pulley, a belt, and a wire rod to move the unit and the tray. The control unit 1 controls the rotation of the motor and controls the movement of the maintenance unit 7 a. The image forming apparatus 100 also includes a pump 76 for performing the cleaning process. When the cleaning process is performed, the control unit 1 operates the pump 76. The pump 76 is a device that applies pressure to the ink in the direction of feeding the ink jet heads 70 to the respective lines. As a result, the ink oozes out from all the nozzles. The ink is extruded from each nozzle. By applying this pressure, the ink agent having an increased viscosity can be extruded to the outside of the nozzle.

The control unit 1 performs the cleaning process at predetermined execution intervals. The execution interval is, for example, any time between several minutes and 60 minutes. The operation panel 4 may receive setting of an execution interval. In this case, the control section 1 performs the cleaning process for all the line heads 70 of the four colors at the set execution interval. When the execution interval has elapsed since the start of the print job or from the previous cleaning process, the control section 1 temporarily suspends printing, performs the cleaning process, and resumes printing after the cleaning process.

(liquid level detecting device 9)

Next, an example of the liquid level detection device 9 according to the embodiment will be described with reference to fig. 4. The liquid level detection device 9 includes: detection control circuit 90, coil L1 (part of first resonant circuit 91), second resonant circuit 92, electrode pad 93 (part of first resonant circuit 91), and memory 94. For example, the detection control circuit 90 is an IC designed to be able to detect a resonance frequency and a capacitance. The memory 94 is a non-volatile storage device. For example, the memory 94 is an EEPROM. The memory 94 nonvolatilely stores a plurality of initial values. The initial value includes data for determining the capacitance of the waste ink cartridge 75 by identifying the resonance frequencies of the first resonance circuit 91 and the second resonance circuit 92, and determining a liquid level value indicating the height of the liquid level in the waste ink cartridge 75 (details will be described later).

The liquid level detection device 9 includes a detection substrate 95. The detection substrate 95 is provided with: detection control circuit 90, coil L1, second resonant circuit 92, memory 94.

A waste ink tank 75 is provided in the image forming apparatus 100. Fig. 4 shows an example in which the waste toner box 75 is provided on a frame F1 in the image forming apparatus 100. For example, the frame F1 is made of metal and has conductivity. For example, the frame F1 is made of iron. Since the waste toner box 75 is used as a capacitor of the first resonance circuit 91, the electrode pad 93 is mounted (attached) to the waste toner box 75. The waste ink tank 75 can be replaced (removable). When the waste ink cartridge 75 is replaced, the electrode pad 93 is removed from the old waste ink cartridge 75. When a new waste toner box 75 is set, the electrode pad 93 is mounted in the new waste toner box 75.

The electrode pad 93 is attached to any one surface of the waste ink tank 75 other than the bottom surface (the surface in contact with the frame F1). The flat surface of the electrode pad 93 contacts and adheres to the side surface of the waste-ink tank 75. The electrode pad 93 is attached to the outside (outer surface) of the waste-ink cartridge 75. Therefore, the electrode pad 93 does not contact the ink. Fig. 4 shows an example in which the electrode pad 93 is attached to the side surface of the waste ink tank 75. In the example of fig. 4, the longitudinal direction of the electrode pad 93 is parallel to the height direction of the waste-ink cartridge 75 provided in the image forming apparatus 100.

The waste ink tank 75 itself is made of resin. The material of the waste ink tank 75 is insulating in order to function as a capacitor. The length of the long side of the electrode pad 93 is the same as or shorter than the height (length in the vertical direction) of the waste-ink cartridge 75. When the waste toner box 75 is mounted, the position of the electrode pad 93 may be fixed so as to contact the waste toner box 75 at a predetermined position.

The electrode pad 93 may have adhesiveness. A mark may be added to the waste toner box 75 so that the mounting position of the electrode pad 93 is constant. The mark can be any one of labeling, imprinting and coating. The mark may have the same size and the same shape as the attachment surface of the electrode pad 93, or may be a line indicating the upper end position of the electrode pad 93.

The electrode pad 93 is connected to one end of the coil L1 via a signal line 96. One end of the coil L1 is also connected to the first terminal 90a of the detection control circuit 90. The other end of the coil L1 is connected to a second terminal 90b of the detection control circuit 90. The first resonant circuit 91 includes: a coil L1, an electrode pad 93, and a waste toner box 75 as a capacitor. The first resonant circuit 91 is an LC resonant circuit. The liquid level detection device 9 recognizes the resonance frequency of the first resonance circuit 91 using the waste ink cartridge 75 as a capacitor in order to determine the capacitance of the first resonance circuit 91 (waste ink cartridge 75).

The detection control circuit 90 inputs a signal to the first resonance circuit 91 (coil L1) using the first terminal 90a and the second terminal 90 b. For example, the detection control circuit 90 applies an alternating voltage. The detection control circuit 90 changes the frequency and monitors the current flowing in the first resonance circuit 91. The detection control circuit 90 recognizes the frequency at which the current reaches the maximum as the resonance frequency of the first resonance circuit 91.

The second resonant circuit 92 includes a coil L2 and a capacitor C2. The second resonant circuit 92 is connected to the detection control circuit 90. One end of the coil L2, one end of the capacitor C2, and the third terminal 90C of the detection control circuit 90 are connected. The other end of the coil L2, the other end of the capacitor C2, and the fourth terminal 90d of the detection control circuit 90 are connected. The second resonance circuit 92 is not connected to the electrode pad 93.

The detection control circuit 90 inputs a signal to the second resonance circuit 92 (coil L2) using the third terminal 90c and the fourth terminal 90 d. For example, the detection control circuit 90 applies an alternating voltage. The detection control circuit 90 changes the frequency and monitors the current flowing in the second resonance circuit 92. The detection control circuit 90 recognizes the frequency at which the current reaches the maximum as the resonance frequency of the second resonance circuit 92.

(detection of a value indicating the level height of the liquid)

The detection of the value indicating the liquid level height of the liquid by the liquid level detection device 9 according to the embodiment will be described with reference to fig. 4. The liquid level detection device 9 is attached to the image forming apparatus 100. The electrode pad 93 is attached to the waste ink tank 75. The flat surface of the electrode pad 93 contacts the waste ink tank 75. The liquid level detector 9 determines a liquid level value. The liquid level value is a value indicating the height of the liquid level of the liquid (waste ink agent) in the waste ink cartridge 75.

Specifically, the detection control circuit 90 calculates the level value by the following calculation (equation 1).

(formula 1) liquid level value (current electrostatic capacitance-initial null 97)/(initial upper end value 98-initial null 97)

According to formula 1, it can be seen that: the liquid level value is a value indicating the position (height) at which% of the liquid level is located in a range in which the upper end of the attached electrode pad 93 is set to 100% and no liquid is set to 0%. The detection control circuit 90 calculates the ratio as a level value. Further, when a negative value is calculated, the detection control circuit 90 treats it as 0%.

The initial null 97 is the electrostatic capacitance of the waste ink tank 75 when there is no liquid (empty) obtained by measurement before installation to the image forming apparatus 100. The initial upper end value 98 is the electrostatic capacitance of the waste ink tank 75 when the liquid reaches the upper end (when it is determined that the liquid reaches the upper end), which is obtained by measurement before installation in the image forming apparatus 100. These initial values (initial null 97 and initial upper end 98) are written in the memory 94 in a nonvolatile manner.

The raw material of the waste ink tank 75 is an insulating resin (plastic). The waste toner box 75 is in contact with the frame F1 (on the lower side in the example of fig. 4). Therefore, the waste toner box 75 is grounded. The electrode pad 93 and the frame F1 in contact with the waste-ink tank 75 function as electrodes. The waste toner box 75 charges the space between the electrode pad 93 and the frame F1. That is, the waste toner box 75 can be treated as a capacitor due to the electrode pads 93 and the waste toner box 75 that is grounded.

When the waste ink cartridge 75 is empty, the waste ink cartridge 75 becomes a capacitor using insulating resin and air as dielectrics. When the waste ink enters the waste ink tank 75, the waste ink tank 75 becomes a capacitor using insulating resin, liquid (waste ink agent), and air as dielectrics. The dielectric constant of the waste toner box 75 changes in accordance with the height of the liquid surface of the waste toner. The waste ink agent of the present embodiment has a higher dielectric constant than air. Therefore, the higher the liquid surface, the larger the electrostatic capacitance of the waste-ink cartridge 75.

The detection control circuit 90 identifies the resonance frequency of the first resonance circuit 91. The detection control circuit 90 determines the capacitance (first capacitance) of the first resonance circuit 91 (the current waste toner box 75) based on the identified resonance frequency. If the equation for the resonant frequency Alternatively, when the resonance condition XL ═ XC (2 pi fL ═ 1/2 pi fC) is adjusted, C ═ 1/(4 pi fC) can be obtained²f²L). The detection control circuit 90 substitutes f for the resonance frequency and L for the inductance value of the coil L1 of the first resonance circuit 91 to determine the capacitance of the first resonance circuit 91. The memory 94 nonvolatilely stores the inductance value of the coil L1.

(writing of initial value)

Next, an example of a flow of writing an initial value into the memory 94 in the liquid level detection device 9 according to the embodiment will be described with reference to fig. 5. The liquid level detection device 9 is attached to the image forming apparatus 100. The liquid level detection device 9 can be said to be one component (unit) incorporated into the image forming apparatus 100. The liquid level detection device 9 (combination of the detection substrate 95 and the electrode pad 93) is produced at a different place. The produced liquid level detection device 9 is carried into a manufacturing and assembling factory of the image forming apparatus 100, and is mounted (assembled) on the image forming apparatus 100.

During production of the liquid level detection device 9, the initial value is written in the memory 94. The initial value is data for obtaining a first capacitance which is a capacitance of the first resonant circuit 91. The initial values include the initial null 97 and the initial upper value 98 described above. The initial value may include the temperature correction capacitor 99. The temperature correction capacitance 99 is the capacitance of the capacitor C2 of the second resonant circuit 92 when the initial value is stored.

Before writing the initial values, the inductance values of the coil L1 and the coil L2 of the liquid level detection device 9 are written in the memory 94 in advance in a nonvolatile manner. This is because it is necessary to determine the first electrostatic capacitance. The inductance values of coil L1 and coil L2 were determined during the design phase. Therefore, the memory 94 may also store design values. In addition, the inductance values of the coil L1 and the coil L2 may also be measured with a device. The measurement results may also be stored in the memory 94.

In the case where the initial value is stored during the production, the liquid level detection device 9 is provided in the jig for writing the initial value. The state of being mounted on the image forming apparatus 100 is simulated and reproduced. In addition, for example, the jig may include a setting computer. The liquid level detection device 9 is provided in the jig, and the setting computer is connected to the detection control circuit 90 through a communication line. This enables the setting computer to issue a command to the detection control circuit 90.

Fig. 5 is started in a state where the liquid level detection device 9 is provided in the jig. First, the detection control circuit 90 obtains an initial null value 97 (step # 11). For example, the setting computer issues a command to obtain the initial null value 97. Triggered by this instruction, the detection control circuit 90 executes step # 11.

Specifically, when obtaining the initial null 97, the operator can attach (can touch) the electrode pad 93 to the empty waste-ink cartridge 75. Further, since the first capacitance in the empty state can be recognized, the measurement can be performed in a state where the electrode pad 93 is not attached to the waste ink cartridge 75. After that, the detection control circuit 90 changes the frequency and applies an alternating voltage to identify the resonance frequency of the first resonance circuit 91. The detection control circuit 90 determines the first capacitance in the empty state as the initial empty value 97 based on the identified resonance frequency and the inductance value of the coil L1.

Next, the detection control circuit 90 obtains an initial upper end value 98 (step # 12). For example, the setting computer issues a command to obtain the initial upper value 98. Triggered by this instruction, the detection control circuit 90 executes step # 12.

Specifically, when the initial upper value 98 is obtained, the operator can attach the electrode pad 93 to the waste ink tank 75 filled with the waste ink agent. The operator mounts (brings into contact with) the electrode pad 93 to the waste-ink tank 75 in such a manner that the liquid surface coincides with the upper end of the electrode pad 93. After that, the detection control circuit 90 applies an alternating voltage and recognizes the resonance frequency of the first resonance circuit 91. The detection control circuit 90 determines the first electrostatic capacitance in the state where the waste toner cartridge 75 is filled with the waste toner as an initial upper end value 98 based on the identified resonance frequency and the inductance value of the coil L1.

Next, the detection control circuit 90 obtains the temperature correction electrostatic capacity 99 (step # 13). For example, the setting computer issues a command to obtain the temperature correction electrostatic capacity 99. Triggered by this command, the detection control circuit 90 executes step # 13. Specifically, when the temperature correction capacitor 99 is obtained, the detection control circuit 90 applies an ac voltage to the second resonant circuit 92 and recognizes the resonant frequency of the second resonant circuit 92. The detection control circuit 90 determines a second capacitance, which is the capacitance of the second resonant circuit 92, as the temperature correction capacitance 99 based on the identified resonant frequency and the inductance value of the coil L2.

The detection control circuit 90 writes the initial value in the memory 94 (step # 14). Thus, the memory 94 nonvolatilely stores the initial values and the inductance values of the coils L1 as data for detecting the liquid level. The initial values are the initial null 97, the initial upper end 98, and the temperature correction capacitance 99 obtained. The detection control circuit 90 ENDs the process of writing the initial value (END).

(entry of error value 910)

Next, an example of the recording error value 910 in the liquid level detection device 9 according to the embodiment will be described with reference to fig. 6 and 7. The liquid level detection device 9 is attached to the image forming apparatus 100. The actual machine and the jig of the image forming apparatus 100 are different in environment for detecting (measuring) the resonance frequency and the electrostatic capacitance. There is a difference in the detection conditions (measurement conditions). Therefore, even if the liquid surface height of the waste ink cartridge 75 is the same, the first capacitance (capacitance of the first resonance circuit 91) determined by the detection control circuit 90 differs. The reason for this difference may be considered several. One of the reasons why the stray capacitance C0 (see fig. 4) from the detection substrate 95 to the electrode pad 93 differs between the jig and the actual image forming apparatus 100.

Fig. 6 is a graph showing an example of the difference in the first capacitance due to the difference in the detection environment. Fig. 6 shows an example of a case where the first capacitance obtained (measured) when actually mounted on the image forming apparatus 100 is large. In addition, the first capacitance obtained when actually mounted in the image forming apparatus 100 may be small.

The liquid level detector 9 determines a liquid level value using the initial value. If the difference in the first electrostatic capacitance due to the difference in the detection environment is large before and after installation in the image forming apparatus 100, the height of the liquid level cannot be accurately detected. Therefore, in the image forming apparatus 100, when the level value is obtained, the obtained first capacitance is corrected. For correction, error value 910 is stored in memory 94. Entry (storage) of the error value 910 may be performed after the liquid level detection device 9 is mounted to the image forming apparatus 100. Error value 910 may be recorded as one of the steps in manufacturing and assembling image forming apparatus 100, or error value 910 may be recorded as one of the inspections before shipping image forming apparatus 100.

The beginning of fig. 7 is the time at which entry of error value 910 begins. At the timing of fig. 7, the liquid level detection device 9 has been mounted to the image forming apparatus 100. The start of fig. 7 is, for example, when the operation panel 4 receives a command to register the error value 910 in a state where the liquid level detection device 9 is installed in the image forming apparatus 100. The operator issues an entry instruction to the operation panel 4. The control unit 1 is communicably connected to a detection control circuit 90 (see fig. 4). Control unit 1 sends an instruction to start recording error value 910 to detection control circuit 90. Upon receiving the instruction, the detection control circuit 90 starts the process of storing the error value 910.

First, the detection control circuit 90 obtains a first capacitance after being attached to the image forming apparatus 100 (in a state of being attached to the image forming apparatus 100) (step # 21). Specifically, the detection control circuit 90 applies an alternating voltage, and recognizes the resonance frequency of the first resonance circuit 91. The detection control circuit 90 determines the first capacitance based on the identified resonance frequency and the inductance value of the coil L1.

Further, when error value 910 is entered, waste toner box 75 may or may not be installed in image forming apparatus 100. In the case where the waste ink cartridge 75 is installed, the waste ink cartridge 75 that is not filled with liquid (empty) is used. It is preferable that the state is the same as that when the initial null value 97 is obtained. For example, when the capacitance of the waste ink tank 75 is measured when there is no liquid (when empty) to obtain the initial empty value 97, it is preferable to mount the electrode pad 93 to the waste ink tank 75 that is not filled with liquid (empty).

Next, the detection control circuit 90 obtains an error value 910 based on the first capacitance obtained in step #21 (step # 22). Then, the detection control circuit 90 stores (writes) the obtained error value 910 in the memory 94 (step #23 → end). Thus, memory 94 again non-volatilely stores error value 910.

A graph shown in the graph of fig. 6 shows a change in the first electrostatic capacitance with respect to the liquid level height of the waste ink agent. Although the detection environment changes, the compositions of the detection control circuit 90, the coil L1, and the ink agent do not change. Therefore, the inclination of the curve and the shape of the curve do not change significantly when the image forming apparatus 100 is attached to the jig or when the image forming apparatus is attached.

A waste ink box 75 filled with waste ink can be used when entering error value 910. However, it takes time and labor to prepare the waste ink cartridge 75 in which the waste ink agent is filled up to the upper end of the electrode pad 93. In addition, after entering error value 910, waste toner cartridge 75 must be replaced. Therefore, in the image forming apparatus 100, the following values are taken as the error value 910, that is: a value obtained by subtracting the initial null value 97 from the first electrostatic capacitance when there is no liquid (the first electrostatic capacitance obtained in step #21) obtained by measurement after installation to the image forming apparatus 100.

(calculation of level value)

Next, an example of a flow of calculating the liquid level value by the liquid level detection device 9 according to the embodiment will be described with reference to fig. 8. The start of fig. 8 is a timing to start calculating the liquid level value of the waste-ink tank 75. At the start of fig. 8, the liquid level detection device 9 is also attached to the image forming apparatus 100. The control unit 1 sends an instruction to start calculating the level value to the detection control circuit 90. The detection control circuit 90 receives the instruction and starts the calculation process of the level value.

When the image forming apparatus 100 is started up by turning on the main power supply, the control unit 1 may transmit an instruction to start the calculation to the detection control circuit 90. When the cleaning process is executed, the control unit 1 may transmit an instruction to start the calculation to the detection control circuit 90. When printing is started, the control unit 1 may transmit a command to start calculation to the detection control circuit 90. When the printing is finished, the control unit 1 may transmit a command to start the calculation to the detection control circuit 90. The controller 1 may send a command to start the calculation to the detection control circuit 90 when opening and closing the cover that is opened when the waste ink cartridge 75 is replaced.

First, the detection control circuit 90 obtains a first capacitance (step # 31). Specifically, the detection control circuit 90 applies an alternating voltage, and recognizes the resonance frequency of the first resonance circuit 91. The detection control circuit 90 determines the first capacitance (the capacitance of the first resonance circuit 91 and the capacitance of the waste ink tank 75) based on the identified resonance frequency and the inductance value of the coil L1.

Next, the detection control circuit 90 obtains a value obtained by subtracting the error value 910 from the obtained first capacitance as a first correction capacitance (step # 32). The first correction capacitance is a value obtained by correcting the first capacitance obtained in step #31 by the error value 910 in order to reduce the influence of the detection environment change.

When the first electrostatic capacitance obtained when error value 910 is entered (after installation to image forming apparatus 100) is larger than initial null value 97 (see fig. 6), error value 910 is a positive value. Therefore, the first electrostatic capacitance is reduced by the correction of step # 32. On the other hand, when the first electrostatic capacitance obtained when error value 910 is entered is smaller than initial null value 97, error value 910 is a negative value. In this case, the first electrostatic capacitance is increased by the correction of step # 32.

Next, the detection control circuit 90 obtains the second capacitance (step # 33). Specifically, the detection control circuit 90 applies an alternating voltage, and identifies the resonance frequency of the second resonance circuit 92. The detection control circuit 90 determines the second capacitance (capacitance of the second resonant circuit 92) based on the identified resonant frequency and the inductance value of the coil L2.

The electrostatic capacitance of the capacitor changes according to the temperature. Here, the second resonant circuit 92 is not connected to a circuit other than the detection control circuit 90. When the second capacitance obtained differs from the temperature correction capacitance 99, it is considered that the reason is a temperature difference between the time when the initial value is entered and the current time. The first resonant circuit 91 also has the influence of a temperature difference. Therefore, the detection control circuit 90 performs a predetermined calculation based on the temperature correction capacitor 99 and the obtained second capacitor, and obtains a second correction capacitor in which the first correction capacitor is corrected.

Specifically, the detection control circuit 90 obtains a ratio (step #34) using the second capacitance temperature correction capacitance 99 obtained in step #33 (ratio temperature correction capacitance 99/second capacitance). Then, the detection control circuit 90 multiplies the obtained ratio by the first correction capacitance to obtain a second correction capacitance (step # 35). Since the correction is performed based on the ratio, the electrostatic capacitance of the capacitor C2 of the second resonance circuit 92 can be smaller than that of the first resonance circuit 91. A small and inexpensive capacitor can be used.

If the temperatures of first resonant circuit 91 and second resonant circuit 92 both rise, the capacitance increases. When the current second capacitance is larger than the temperature correction capacitance 99 (capacitance when the jig is used), the current temperature is higher than that when the temperature correction capacitance 99 is set. The ratio obtained by the above calculation is less than 1. Therefore, the correction is performed in a direction to decrease the capacitance in step # 34.

On the other hand, when the current second capacitance is 99 hours smaller than the temperature correction capacitance, the current temperature is lower than when the initial value is set. The ratio obtained by the above calculation exceeds 1. The correction is performed in a direction to increase the capacitance in step # 34.

Then, the detection control circuit 90 obtains a level value based on the initial value (initial null value 97, initial upper end value 98), the first correction capacitance, or the second correction capacitance (step # 36). The detection control circuit 90 may find the level value based on the first correction capacitance. The detection control circuit 90 may obtain the level value based on the second correction capacitor.

When the first correction capacitor is used, the level value is obtained without performing temperature-dependent correction. When the second correction capacitor is used, the level value is obtained by performing temperature-dependent correction. The operation panel 4 can accept selection of which of the first correction capacitor and the second correction capacitor is used. The detection control circuit 90 uses the selected correction capacitor to determine the level value. In the case where the second correction capacitor is not used, the detection control circuit 90 may skip steps #33 to # 35.

A detection method when the first correction capacitor is used will be described. A is set as the first correction capacitor, B is set as the initial null 97, and C is set as the initial upper value 98. The detection control circuit 90 performs the calculation of (A-B)/(C-B). The detection control circuit 90 calculates a ratio as a liquid level value (liquid level height of the liquid).

Next, a detection method when the second correction capacitor is used will be described. D is set as the second correction capacitor, E is set as the initial null 97, and F is set as the initial upper end 98. The detection control circuit 90 performs the calculation of (D-E)/(F-E). The detection control circuit 90 calculates the ratio as a level value. Further, B and E may be the same value. In addition, C and F may be the same value.

Then, the detection control circuit 90 notifies the control unit 1 of the level value (step #37 → end). The higher the position of the liquid surface in the waste ink cartridge 75, the closer the obtained ratio (liquid level value) is to 1. The lower the position of the liquid surface in the waste ink cartridge 75, the closer the obtained ratio is to 0. That is, the controller 1 can recognize how much waste ink agent is accumulated based on the magnitude of the liquid level value.

(Notification based on detection result)

Next, an example of notification in the image forming apparatus 100 according to the embodiment will be described with reference to fig. 9. The control unit 1 receives a value (level value) indicating the level height from the liquid level detection device 9 (detection control circuit 90). The control section 1 can recognize whether the waste ink cartridge 75 reaches the replacement period based on the liquid level value. In addition, it is also possible to identify whether or not to continue accumulating the ink as the risk of overflowing the ink from the waste ink tank 75 increases. The control unit 1 notifies the user of the level value transmitted from the liquid level detection device 9. An example of the notification flow is described below with reference to fig. 9. The start of fig. 9 is when the liquid level value is received from the liquid level detection device 9 (detection control circuit 90).

The control unit 1 checks whether or not the level value is equal to or higher than the first threshold value (step # 41). The first threshold value is a value for determining whether the waste ink agent is accumulated to such an extent that printing needs to be stopped. If printing is performed in an excessively accumulated state, the waste ink may overflow. In addition, the possibility of overflowing the waste ink agent when the waste ink cartridge 75 is removed for replacement is also increased. The first threshold value may be predefined. For example, the storage unit 2 (storage device) stores the first threshold in a nonvolatile manner. For example, the first threshold may be any value in the range of 80 to 100%.

When the level value is equal to or higher than the first threshold value (yes in step #41), the control unit 1 causes the notification unit to notify the first message (step # 42). The first message is a message notifying that the waste ink tank 75 should be replaced and that printing cannot be performed before the waste ink tank 75 is replaced. The notification unit is one or both of the display panel 41 and the communication circuit unit 12. The control unit 1 may cause the display panel 41 to display the first message. Further, the control unit 1 may cause the communication circuit unit 12 to transmit data including the first message to the computer 200 of the administrator of the image forming apparatus 100.

In this case, the control unit 1 sets the image forming apparatus 100 to the print prohibition mode in which the print job cannot be started (step #43 → end). Specifically, even if a command to start a print job is issued, the paper feed unit 5, the paper transport unit 6, and the image forming unit 7 are not operated.

In the case where the user wants to release the print prohibition mode, the user has to replace the waste ink tank 75. For example, a sensor is provided that detects opening and closing of the cover that is opened when the waste toner box 75 is removed. When the cover is opened or closed, the control unit 1 causes the liquid level detection device 9 to determine the liquid level value. When the newly notified level value is smaller than the first threshold value, the control section 1 releases the print prohibition mode.

When the level value is smaller than the first threshold value (no in step #41), the control unit 1 checks whether or not the level value is equal to or larger than the second threshold value (step # 44). The second threshold value is a value for determining whether or not a message urging replacement of the container (waste ink cartridge 75) is displayed. The second threshold value may be predefined. For example, the storage unit 2 (storage device) stores the second threshold in a nonvolatile manner. For example, the second threshold may be any value in the range of 40 to 70%. The second threshold is smaller than the first threshold.

When the level value is equal to or higher than the second threshold value (yes in step #44), the control unit 1 causes the notification unit including the second message to notify (step # 45). After step #45, or when the level value is smaller than the second threshold value (no in step #44), the control unit 1 ENDs the process of this flow (END). The second message is a message informing that the waste toner box 75 should be replaced, or that the replacement period is approaching. The control unit 1 may cause the display panel 41 to display the second message. Further, the control unit 1 may cause the communication circuit unit 12 to transmit data including the second message to the computer 200 of the administrator of the image forming apparatus 100.

Thus, the liquid level detection device 9 of the embodiment is attached to the image forming apparatus 100. The liquid level detection device 9 includes an electrode pad 93, a coil L1, a memory 94, and a detection control circuit 90. The electrode pad 93 is attached to an outer side surface of a cartridge that is provided in the image forming apparatus 100 and that contains liquid. The coil L1 is connected to the electrode pad 93 and is part of the first resonant circuit 91. The memory 94 nonvolatilely stores the initial value. The detection control circuit 90 recognizes the resonance frequency of the first resonance circuit 91 using the case mounted with the electrode pad 93 as a capacitor. The detection control circuit 90 determines a first capacitance, which is a capacitance of the first resonant circuit 91, based on the identified resonant frequency. When the initial value is stored in the memory 94, the detection control circuit 90 determines the first capacitance before mounting the image forming apparatus 100. The memory 94 stores the obtained first capacitance as an initial value. When error value 910 is stored in memory 94, detection control circuit 90 obtains the first capacitance after installation in image forming apparatus 100, and obtains error value 910 based on the difference between the initial value and the first capacitance obtained after installation in image forming apparatus 100. The memory 94 stores the found error value 910 in the memory 94. When a level value, which is a value indicating the height of the liquid surface of the liquid in the height direction of the electrode pad 93, is obtained, the detection control circuit 90 may obtain a first capacitance, subtract the error value 910 from the obtained first capacitance to obtain a first correction capacitance, and obtain the level value based on the first correction capacitance and the initial value. The cartridge is, for example, a waste ink cartridge 75.

In the determination of the level value, the first electrostatic capacitance can be corrected based on the error value 910. In other words, the capacitance obtained by measurement after installation in the image forming apparatus 100 can be corrected so as to be the first capacitance obtained in the measurement environment when the initial value is set. The value (level value) indicating the height of the liquid level can be accurately obtained based on the corrected first capacitance (first correction capacitance) and the initial value. In addition, an electrode pad 93 is mounted on the outside of the replaceable cartridge. Since the electrode pad 93 is independent from the cartridge, the manufacturing cost of the cartridge can be suppressed. In addition, since the electrode pad 93 is not in contact with the liquid, the electrode pad 93 is not contaminated.

The memory 94 stores an initial null value 97 and an initial upper end value 98 as initial values. The initial null 97 is a value obtained by measurement before installation to the image forming apparatus 100, and is a first electrostatic capacitance when there is no liquid. The initial upper end value 98 is a value obtained by measurement before installation to the image forming apparatus 100, and is a first electrostatic capacitance when the height of the liquid surface is the same as the upper end of the electrode pad 93. When a is set as the first correction capacitor, B is set as the initial null value 97, and C is set as the initial upper value 98, the detection control circuit 90 calculates (a-B)/(C-B) to obtain the level value. It is possible to detect what proportion the current liquid level reaches within the range from no liquid to the height corresponding to the initial upper end value 98.

Memory 94 stores an initial null 97. Memory 94 stores as error value 910 the following values: a value obtained by subtracting the initial null value 97 from the first electrostatic capacitance obtained when there is no liquid after the image forming apparatus 100 is mounted. The difference between the first capacitance in the state where no liquid is present when the initial value is stored and the first capacitance in the state where no liquid is present after the image forming apparatus 100 is attached can be set as the error value 910. The first electrostatic capacitance can be appropriately corrected.

The liquid level detection device 9 includes a second resonance circuit 92, the second resonance circuit 92 being connected to the detection control circuit 90 and not to the electrode pad 93, and including a capacitor C2. The detection control circuit 90 recognizes the resonance frequency of the second resonance circuit 92, and obtains the second capacitance, which is the capacitance of the second resonance circuit 92, based on the recognized resonance frequency of the second resonance circuit 92. The memory 94 stores the temperature correction capacitor 99 in a nonvolatile manner. When the temperature correction capacitor 99 is stored in the memory 94, the detection control circuit 90 determines the second capacitor before mounting it to the image forming apparatus 100. The memory 94 stores the obtained second capacitance as the temperature correction capacitance 99. In the case of obtaining the level value, the detection control circuit 90 may obtain the second capacitance after being attached to the image forming apparatus 100, obtain the second correction capacitance in which the first correction capacitance is corrected by performing a predetermined operation based on the temperature correction capacitance 99 and the second capacitance obtained after being attached to the image forming apparatus 100, and obtain the level value based on the second correction capacitance and the initial value. The electrostatic capacitance of the capacitor changes according to the temperature. The obtained capacitance (first capacitance, first correction capacitance) can be corrected to eliminate the influence of the temperature difference between when the initial value is stored and when the level value is obtained. Since the influence of the temperature difference is reduced, the height of the current liquid level can be accurately detected.

The liquid level detection device 9 includes a detection substrate 95. The detection substrate 95 includes a memory 94, a detection control circuit 90, a coil L1, and a second resonance circuit 92, and is connected to the electrode pad 93 via a signal line 96. The liquid level detection devices 9 can be integrated on one substrate. Memory 94, detection control circuit 90, coil L1, and second resonant circuit 92 can be mounted on image forming apparatus 100 together only by mounting the substrate.

The memory 94 stores an initial null value 97 and an initial upper end value 98 as initial values. When D is set as the second correction capacitor, E is set as the initial null value 97, and F is set as the initial upper value 98, the detection control circuit 90 can calculate the level value by performing the calculation of (D-E)/(F-E). It is possible to detect what proportion the current liquid level reaches within the range from the height corresponding to the initial null value 97 to the height corresponding to the initial upper end value 98.

As a predetermined operation, the detection control circuit 90 performs an operation of multiplying the ratio by the first correction capacitance. The ratio is a value obtained by using the second capacitance temperature correction capacitance 99 obtained when the level value is obtained. The rate of change in capacitance due to the temperature difference can be determined. The obtained change rate is multiplied by the first correction capacitance, and a first capacitance (second correction capacitance) in which the influence of the temperature difference is eliminated can be obtained.

The liquid is an ink. The cartridge is a container that stores ink (waste ink). The image forming apparatus 100 includes an image forming unit 7 for printing with an ink and a liquid level detecting device 9. The height of the liquid level of the ink agent contained in the cartridge can be accurately detected.

The image forming apparatus 100 includes a notification unit that notifies and a control unit 1. When the detected liquid level is higher than or equal to a predetermined threshold, the control unit 1 causes the notification unit to notify the necessity of replacing the cartridge. The user can be notified (warned) that the amount of ink in the cartridge is increased. Specifically, the notification unit performs notification based on the magnitude of the level value. The notification unit is one or both of the display panel 41 and the communication circuit unit 12. The notification unit notifies a first message that the cartridge (waste ink cartridge 75) should be replaced when the liquid level value is equal to or higher than a predetermined first threshold value. When the level value is less than the first threshold value but not less than a predetermined second threshold value, the notification unit notifies a second message that the cartridge should be replaced or the replacement period is approaching.

The embodiments of the present invention have been described above, but the scope of the present invention is not limited to the above, and various modifications can be made without departing from the scope of the present invention.

For example, an example in which the liquid level detection device is applied to the waste ink tank is described. However, the liquid level detection device 9 may be applied to the ink agent cartridge 81 that supplies the ink agent to each line of the inkjet heads. In this case, the level value is a value representing the remaining amount of ink of the ink cartridge 81.