JP4421379B2 - Remaining amount detection device - Google Patents

Description

  The present invention relates to a remaining amount detection device that detects the remaining amount of recording paper stored in a paper feed tray of an image forming apparatus.

  In a conventional image forming apparatus, a technique using a variable resistor and a reed switch is known as a technique for detecting the remaining amount of recording paper stored in a paper feed tray. The paper feed tray is provided with a placement plate on which the recording paper is placed, and this placement plate is urged toward the upper surface side of the paper feed tray by a spring disposed on the bottom surface of the paper feed tray, It is arranged to move to the bottom side of the paper feed tray according to the number of stacked sheets.

  In the method using a variable resistor, the contact point of the variable resistor moves in conjunction with the movement of the mounting plate, and the remaining amount of recording paper is detected by capturing the change in resistance value as a change in voltage. In the method using the reed switch, a plurality of magnets are attached to the moving position of the mounting plate, and a plurality of reed switches that are turned on by a magnetic field from the magnet are provided at positions corresponding to the respective magnets. The remaining amount of recording paper is detected depending on which reed switch is turned on with the movement of. Also known is a method in which the configuration is the same as the method using a reed switch and a Hall element is used instead of the reed switch.

Further, in Patent Document 1, a magnetic output unit that generates a magnetic field in accordance with a drive current output from a driver and an induction coil formed on a sensor base mounted on a mounting plate (movable plate) are spaced at a predetermined interval. An invention is disclosed in which the remaining amount of recording paper is detected by detecting a change in the strength of the magnetic field of the magnetic output unit by moving the placing plate that is disposed and moves up and down according to the remaining amount of paper. .
JP 7-61646 A

  However, in the method using the variable resistor, the contact point is worn down over time and the resistance value is distorted, and contact failure of the contact point occurs due to dust such as toner and paper dust, and the remaining amount detection accuracy gradually increases. There was a problem of declining. Also, in the method using a reed switch or a hall element, the magnet and the hall element cannot be arranged with a sufficient space due to the problem of installation space, and a sufficient dynamic range and resolution cannot be obtained. There is a problem that the remaining amount of recording paper cannot be detected well.

  Furthermore, in the method of Patent Document 1, it is necessary to provide a power supply line for supplying power from the apparatus main body to the induction coil. In addition to an increase in the number of components, the power supply line is cut off. There is a possibility that trouble occurs, or that contact between the power supply line and the paper feed tray may cause contact failure due to dust such as toner or paper dust.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a remaining amount detecting device that detects the remaining amount of recording paper with high resolution without providing a power supply line for supplying power from a power source to the paper feed tray from the apparatus main body. Is to provide.

A remaining amount detecting device according to the present invention is a remaining amount detecting device that detects the remaining amount of recording paper stored in a paper feeding tray of an image forming apparatus, and is disposed in the paper feeding tray, and a recording paper is loaded thereon. A recording sheet on the basis of a mounting plate to be placed, a remaining amount sensor disposed in the main body of the image forming apparatus so as to face the mounting plate, and an electric signal output from the remaining amount sensor Detecting means for detecting the remaining amount of the recording paper, wherein the mounting plate includes a conductive plate, and the distance to the remaining amount sensor varies according to the number of recording sheets deposited, and the remaining amount sensor An eddy current is generated in the conductive plate by induction, and an electric signal having a level corresponding to the distance between the remaining amount sensor and the conductive plate is generated based on the magnetic field generated by the eddy current, and the detection means outputs rotatably is arranged with respect to the conductive plate, the mounting plate When the recording paper is placed on the mounting plate, it is almost flush with the mounting surface of the mounting plate, and when there is no recording paper placed on the mounting plate Rotate and close to the remaining amount sensor .

  The remaining amount sensor includes a differential transformer including a primary side drive coil, a secondary side reference coil, and a detection coil. The reference coil and the drive coil are sequentially arranged from the mounting plate side. Preferably, the detection coil is disposed, and a difference between an electromotive force generated in the reference coil and an electromotive force generated in the detection coil is output as the electric signal.

  The mounting plate includes a first plane parallel to a sensor surface of the remaining amount sensor and a second plane inclined downward by a predetermined angle with respect to the first plane. Is disposed in the vicinity of a boundary line between the first plane and the second plane so as to face the second plane, and the conductive plate includes the first plane and the second plane. In the hole formed in the mounting plate so as to include a plane boundary line, when the recording sheet placed on the mounting plate is removed by being rotatably fitted around the boundary line as an axis, the first It is preferable that the size of the first plane side is larger than the size of the second plane side so that the conductive plate on the second plane side is close to the remaining amount sensor.

  The remaining amount sensor includes: an amplifying unit that cuts a DC component of the electric signal output from the differential transformer and amplifies the AC component; and a DC converting unit that converts the amplified electric signal into a DC electric signal. And the detection means includes an analog-digital conversion means for converting an electrical signal converted into a direct current from an analog signal into a digital signal, and a storage means for preliminarily storing the number of recording sheets according to the value of the digital signal. And a central processing unit which receives the digital signal and determines the remaining amount of recording paper by referring to the storage means.

  Moreover, it is preferable that the detection means further includes a low-pass filter that removes a high-frequency component of the electrical signal output from the DC conversion means and outputs the high-frequency component to the analog-digital conversion means.

  Moreover, it is preferable that the said electrically conductive plate is comprised by affixing the aluminum tape on the surface.

According to the first aspect of the present invention, an eddy current is generated by electromagnetic induction on the conductive plate of the mounting plate whose distance to the remaining amount sensor varies according to the number of recording papers to be deposited. Based on the generated magnetic field, an electric signal of a level corresponding to the distance between the conductive plate and the remaining amount sensor is output, and the remaining amount of the recording paper is detected based on this electric signal. Therefore, the remaining amount of recording paper can be detected without providing a power supply line for supplying power from the main body on the paper feed tray side. Also, since the remaining amount sensor is arranged in the main body and the conductive plate is arranged on the paper feed tray side, the problem of installation space is alleviated compared to the method using a reed switch or a hall element, and the remaining amount is reduced. A sufficient distance between the sensor and the conductive plate is ensured, and a high dynamic range and high resolution can be realized.
According to the first aspect of the present invention, when the number of recording sheets becomes zero, the conductive plate is close to the remaining amount sensor, so that the electrical signal output from the remaining amount sensor is one recording sheet. Therefore, it can be detected more accurately that the number of recording sheets is zero.

  According to the second aspect of the present invention, an eddy current is generated in the conductive plate due to the influence of the magnetic field generated from the drive coil, and an electromotive force is generated in the detection coil and the reference coil. Here, since the detection coil is arranged on the conductive plate side, the electromotive force fluctuates due to the magnetic field generated by the eddy current, but the reference coil is arranged away from the conductive plate, so The electromotive force is constant without being affected by the generated magnetic field. Since the difference in electromotive force with respect to the detection coil and the reference coil is output as an electrical signal, and the remaining amount is detected based on this electrical signal, the remaining amount of recording paper can be accurately detected.

  According to the fourth aspect of the present invention, the mounting plate includes the first and second planes, the remaining amount sensor is disposed so as to face the second plane, and the conductor plate includes the first and second planes. When the number of sheets of recording paper deposited becomes zero in a hole formed in the mounting plate so as to include the boundary line of the two planes, and the boundary line serves as an axis, and the number of recording sheets deposited becomes zero The size of the first plane side is made larger than the size of the second plane side so that the plane side of the first side is close to the remaining amount sensor. That is, the conductor plate is rotated by its own weight and comes close to the remaining amount sensor. Therefore, the conductor plate can be rotated with a simplified configuration.

  According to the fifth aspect of the present invention, when there is no recording paper placed on the placement plate, the conductive plate is rotated by its own weight so that the second plane side is close to the remaining amount sensor.

  According to the sixth aspect of the present invention, the electrical signal output from the remaining amount sensor is cut in the direct current component, the alternating current component is amplified, converted into a direct current electrical signal, converted into a digital signal, and the central processing unit. Received by. Then, the central processing unit refers to a storage means in which the number of recording sheets corresponding to the value of the digital signal is stored in advance, and the remaining amount of recording sheet is detected from the value of the received digital signal. Therefore, the remaining amount of recording paper can be detected with high accuracy.

  According to the seventh aspect of the present invention, since the electric signal output from the direct current conversion means is removed from the high frequency component and output to the analog / digital conversion means, the detection accuracy of the remaining amount of the recording paper can be further improved. .

  According to the seventh aspect of the present invention, the conductive plate can be configured with a simplified configuration in which the aluminum tape is attached.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic side view mainly showing a mechanical configuration when the remaining amount detection device according to the present invention is applied to a digital multi-function peripheral. The digital multi-function peripheral includes a main unit 200, a sheet post-processing unit 300 disposed on the left side of the main unit 200, an operation unit 400 for a user to input various operation commands and the like, and an upper part of the main unit 200. The document reading unit 500 is disposed, and the document feeding unit 600 is disposed above the document reading unit 500.

  The operation unit 400 includes an operation panel 401, a start key 402, a numeric keypad 403, and the like. The operation panel 401 displays various operation screens and various operation buttons for the user to input various operation commands. The start key 402 is used for the user to input a print execution command and the like, and the ten key 403 is used for inputting the number of copies to be printed.

  The document feeding unit 600 includes a document placement unit 601, a document discharge unit 602, a paper feed roller 603, a document transport unit 604, and the like, and the document reading unit 500 includes a scanner 501 and the like. The paper feed roller 603 feeds out the original set on the original placement unit 601, and the original transport unit 604 transports the fed originals one by one on the scanner 501. The scanner 501 sequentially reads the conveyed document, and the read document is discharged to the document discharge unit 602.

  The main body 200 includes a plurality of paper feed cassettes 201, a plurality of paper feed rollers 202, a transfer roller 203, an intermediate transfer body roller 204, a photosensitive drum 205, an exposure device 206, and development for each color of yellow, magenta, cyan, and black. Devices 207Y, 207M, 207C, and 207K, a fixing roller 208, a discharge port 209, a discharge tray 210, and the like are provided.

  The photosensitive drum 205 is uniformly charged by a charging device (not shown) while rotating in the direction of the arrow. The exposure device 206 converts the modulation signal generated based on the image data of the original read by the original reading unit 500 into a laser beam and outputs it, and forms an electrostatic latent image on the photosensitive drum 205 for each color. The developing devices 207Y, 207M, 207C, and 207K supply each color developer to the photosensitive drum 205 to form a toner image for each color.

  The intermediate transfer roller 204 transfers the color toner images from the photosensitive drum 205, and forms a color toner image on the intermediate transfer roller 204.

  On the other hand, the paper feeding roller 202 pulls out the recording paper from the paper feeding cassette 201 in which the recording paper is stored, and feeds the recording paper to the transfer roller 203. A remaining amount sensor 700 for detecting the remaining amount of recording paper stored in the paper feed cassette 201 is disposed on the main body 200 side and above the center of the paper feed cassette 201. The transfer roller 203 transfers the toner image on the intermediate transfer body roller 204 onto the conveyed recording paper, and the fixing roller 208 heats and fixes the transferred toner image on the recording paper. Thereafter, the recording paper is carried into the paper post-processing unit 300 from the discharge port 209 of the main body unit 200. The recording paper is also discharged to the discharge tray 210 as necessary.

  The paper post-processing unit 300 includes a carry-in port 301, a recording paper transport unit 302, a carry-out port 303, a stack tray 304, and the like. The recording paper transport unit 302 sequentially transports the recording paper carried into the carry-in port 301 from the discharge port 209 and finally ejects the recording paper from the carry-out port 303 to the stack tray 304. The stack tray 304 is configured to move up and down in the direction of the arrow in accordance with the number of recording sheets stacked from the carry-out port 303.

  FIG. 2 is a diagram schematically showing the appearance of the paper feed cassette 201. The paper feed cassette 201 includes a housing 220, a placement plate 230, an elastic body 240, and a conductor plate 250. The housing 220 is a substantially rectangular parallelepiped member having an open top surface, and recording paper is fed from the open surface. The mounting plate 230 has a substantially square shape when viewed from the side, is composed of a rectangular member when viewed from the top, and is disposed in the housing 220 so that the left surface 230a is substantially horizontal with respect to the ground. ing. A rectangular hole 230d is formed in an intersection line 230c between the left surface 230a and the right surface 230b in the center in the width direction (Y direction) of the mounting plate 230.

  An elastic body 240 is provided between the back side of the left surface 230 a and the bottom surface of the housing 220. The elastic body 240 uses a spring or the like, and urges the mounting plate 230 upward (+ Z direction). In addition, grooves 221 and 221 are provided in parallel to the Z-axis direction on the distal end side in the X-axis direction of the right surface 230b on the side wall of the housing 220. Further, convex portions 231 protruding in the Y-axis direction are provided on both side surfaces of the right surface 230b, and the two convex portions 231 are fitted into the opposing grooves 221 so as to be slidable in the Z direction. . Accordingly, as the number of recording sheets deposited on the loading plate 230 increases, the loading plate 230 moves downward (−Z direction), and as the number of recording sheets decreases, the loading plate 230 moves upward. Move in the direction (+ Z direction).

  In the hole 230d, a conductor plate 250 made of a member having a square shape in a side view and a rectangular shape in a top view is disposed so as to be continuous with the recording paper placement surface of the placement plate 230. The conductor plate 250 is made of a conductor by affixing an aluminum tape on the surface. In addition, as a structure of the conductor plate 250, it may replace with the said structure and may comprise the whole conductors, such as aluminum and iron, or magnetic bodies, such as a ferrite. In the conductor plate 250, the length of the side H1 in the X direction of the left surface 250a is longer than the length of the side H2 in the X direction of the right surface 250b. In addition, the conductor plate 250 is rotatably connected to the mounting plate 230 through the shaft 250d along an intersection line 250c between the left surface 250a and the right surface 250b. When the number of recording sheets deposited on the mounting plate 250 is one or more, the left surface 250a of the conductor plate 250 is connected to the left surface 230a of the mounting plate 230 due to the weight of the recording paper. When the number of sheets of recording paper deposited on the conductive plate 250 becomes zero, the length of the side H1 and the side H2 is set so that the right surface 250b side rotates in the + Z direction due to its own weight. The remaining amount sensor 700 is disposed above the conductor plate 250.

  The remaining amount sensor 700 includes a differential transformer T1 including a drive coil L1, a detection coil L2, and a reference coil L3. FIG. 3 is a diagram showing the arrangement relationship of the drive coil L1, the detection coil L2, and the reference coil L3. FIG. 4 is a diagram showing the configuration of the remaining amount sensor 700. As shown in FIG. 3, the drive coil L1 to the reference coil L3 are arranged in the order of the detection coil L2, the drive coil L1, and the reference coil L3 from the conductor plate 250 side. Specifically, these three coils L1 to L3 are wound around the peripheral surface of one cylindrical core with a predetermined number of turns.

  As shown in FIG. 4, the drive coil L1 is driven by the drive voltage V1 from the oscillator OSC. The detection coil L2 and the reference coil L3 are magnetically connected to the drive coil L1, and when the drive coil L1 is driven, a magnetic flux φ1 is generated, and this magnetic flux φ1 penetrates the detection coil L2 and the reference coil L3, thereby detecting A voltage V2 and a reference voltage V3 are generated. Further, the detection coil L2 and the reference coil L3 are wound so that the detection voltage V2 and the reference voltage V3 are in opposite phases, and output a voltage difference between the two voltages V2 and V3 as the output voltage VO.

  When the drive voltage V1 is applied to the drive coil L1 by the oscillator OSC, a magnetic flux φ1 is generated (FIG. 3), and this magnetic flux φ1 generates an eddy current in the conductor plate 250, and this eddy current generates a magnetic flux φ2. Therefore, when the conductor plate 250 is positioned away from the detection coil L2, no eddy current is generated, the magnitudes of the detection voltage V2 and the reference voltage V3 are equal, and the output voltage VO is the reference voltage V3—the detection voltage V2. = 0V. On the other hand, when the conductor plate 250 approaches the detection coil L2, the magnetic flux φ2 increases, and the detection voltage V2 increases due to the influence. When this increase is ΔV2, the output voltage VO is expressed as VO = V3− (V2 + ΔV2). Here, since the reference coil L3 is arranged as shown in FIG. 3, it is not affected by the magnetic flux φ2, and the reference voltage V3 is constant. Therefore, the output voltage VO is VO = ΔV2.

  FIG. 5 is a diagram showing an electrical configuration of the digital multi-function peripheral shown in FIG. As shown in FIG. 5, the digital multi-function peripheral includes a control unit 10, an operation unit 400, a printing unit 30, a document reading unit 500, and a remaining amount sensor 700. The remaining amount sensor 700 includes a differential transformer T1 shown in FIGS. 3 and 4, an oscillator OSC connected to the drive coil L1 of the differential transformer T1, and an AC amplifier circuit 701 connected to one end of the detection coil L2. And a detection circuit 702 connected to the next stage of the AC amplification circuit 701.

  The oscillator OSC is composed of a Colpitts oscillation circuit including an npn bipolar transistor Q1. One end of the drive coil L1 is connected to the collector of the transistor Q1, and a capacitor C1 is connected between the collector and emitter. The emitter of the transistor Q1 is connected to a capacitor C2 and a resistor R2 each having one end grounded. The base of the transistor Q1 is connected to a capacitor C3 and a resistor R1 each having one end grounded, and the other end of the drive coil L1 is connected via the resistor R3. Instead of the Colpitts oscillation circuit, another oscillation circuit such as a Hartley oscillation circuit or an LC oscillation circuit may be employed.

  The AC amplifier circuit 701 includes an npn bipolar transistor Q2. A power supply unit Vcc is connected to the collector of the transistor Q2 via a collector resistor R6, and an emitter resistor R7 and a capacitor C5 each having one end grounded are connected to the emitter. A resistor R4 is connected between the base and collector of the transistor Q2. Further, a resistor R5 having one end grounded is connected to the base of the transistor Q2, and a detection coil L2 is connected via a capacitor C4.

  The detection circuit 702 includes two capacitors C5 and C6, two diodes D1 and D2, and a resistor R8. Capacitor C5 has one end connected to the collector of transistor Q2 and the other end connected to the anode of diode D1. The diode D2 has an anode grounded and a cathode connected to the anode of the diode D1. One end of the capacitor C6 is grounded, and the other end is connected to the cathode of the diode D1. The resistor R8 has one end connected to the cathode of the diode D1 and the other end grounded.

  The control unit 10 includes a CPU 11, a storage unit 12, and a low pass filter 13. The low-pass filter 13 includes an integration circuit including an operational amplifier OP. The inverting input terminal (−) of the operational amplifier OP is connected to the cathode of the diode D1 through the resistor R9 and to the power supply unit Vcc through the resistor R10. The non-inverting input terminal (+) of the operational amplifier OP is grounded through the resistor R11. A resistor R12 and a capacitor C7 connected in parallel to the resistor R12 are connected between the inverting input terminal (−) and the output terminal of the operational amplifier OP. A CPU 11 is connected to the output terminal of the operational amplifier. The CPU 11 includes an A / D conversion unit that converts an analog electrical signal output from the low-pass filter 13 into a digital electrical signal.

  The storage unit 12 is connected to the CPU 11 via the bus line BL, and stores a sheet number specifying table for specifying the number of recording sheets stored in the sheet feeding cassette 201. FIG. 6 is a diagram showing an example of the number specifying table. The number specification table is composed of fields of input value and address. The column of input values is composed of a total of 11 classes of first to eleventh classes defined by predetermined threshold values V0 to V10 (however, V0> V1>...> V10). The address column is composed of addresses M1 to M11 corresponding to the first to eleventh classes. Data indicating that the remaining number of recording sheets is 0, 10, 20,..., 100 is stored in the addresses M1 to M11 of the storage unit 12, respectively.

  The CPU 11 is connected to the operation unit 400, the printing unit 30, and the document reading unit 500 via the bus line BL. The printing unit 30 includes the transfer roller 203, the intermediate transfer member roller 204, the photosensitive drum 205, and the developing devices 207Y to 207K illustrated in FIG. 1, and an image of the document read by the document reading unit 500 under the control of the CPU 11. Print data on chart paper.

  With the above configuration, the output voltage VO output from the differential transformer T1 is cut in the DC component by the capacitor C4 of the AC amplifier circuit 701, amplified in the AC component, rectified and smoothed by the detection circuit 702, and then the DC voltage This is an electrical signal, high-frequency noise is removed by the low-pass filter 13 and output to the CPU 11.

  Next, the processing of the CPU 11 will be described according to the flowchart shown in FIG. When the CPU 11 receives the electrical signal output from the output terminal of the operational amplifier OP (step S1), the CPU 11 refers to the number specifying table in the storage unit 12 and determines which class of the first to eleventh classes the voltage Vd belongs to. (Step S2). Specifically, the CPU 11 determines that it belongs to the first class when Vd is equal to or higher than V0, and determines that it belongs to the second class when V0> Vd ≧ V1, and the second class when V1> Vd ≧ V2. When V2> Vd ≧ V3, it is determined that it belongs to the fourth class. When V3> Vd ≧ V4, it is determined that it belongs to the fifth class, and when V4> Vd ≧ V5, If V5> Vd ≧ V6, it is determined that it belongs to the seventh class. If V6> Vd ≧ V7, it is determined that it belongs to the eighth class, and V7> Vd ≧ V8. It is determined that it belongs to the ninth class. When V8> Vd ≧ V9, it is determined that it belongs to the tenth class, and when V10> Vd ≧ V11, it is determined that it belongs to the eleventh class.

  Then, the CPU 11 refers to the number specification table, reads data stored at the address corresponding to the class to which the voltage Vd belongs, and determines the remaining number of recording sheets (step S3). Specifically, when the voltage Vd belongs to the first class to the eleventh class, the CPU 11 sets the remaining number of recording sheets to 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, respectively. Judge as a sheet.

  The number specifying table is merely an example, and may be changed as appropriate according to the maximum number of recording sheets stored in the sheet feeding cassette 201. Further, the increment of the remaining number is not limited to 10 units, and may be 1 or more and 9 or less, or 11 or more. The threshold values V0 to V10 are set to appropriate values based on the relationship between the distance between the remaining amount sensor 700 and the conductor plate 250 and the voltage Vd output from the remaining amount sensor 700.

  In step S <b> 4, the CPU 11 displays the determination result on the operation panel 401. Thereby, the user can grasp the remaining amount. With respect to the display mode on the operation panel 401, for example, when the user touches the remaining number confirmation button displayed in advance on the operation panel 401, the remaining number may be displayed on the operation panel 401.

  Note that the flowchart shown in FIG. 7 may be executed at regular time intervals, or may be executed every time a certain number of recording sheets (for example, 1 sheet, 5 sheets, etc.) are used.

  Next, an experiment performed on the remaining amount detection apparatus according to the present invention will be described. FIG. 8A is a table showing experimental results, and FIG. 8B is a graph with respect to the table of FIG. FIG. 9 is an internal side view of the paper feed cassette 201 for explaining this experiment. The table shown in FIG. 8A includes columns for the remaining number of recording sheets and the sensor output voltage. The sensor output voltage is a voltage output from the detection circuit 702 shown in FIG. 5, that is, a voltage with respect to the resistor R5. In FIG. 9, (a) shows a case where 120 sheets of the maximum number of recording sheets are stored in the paper feeding cassette 201, and (b) shows about half of the maximum number of recording sheets stored. (C) shows the case where the number of recording sheets to be stored is zero. In this experiment, a conductive plate 250 made of iron and having a thickness of 1 mm was used. The distance D2 between the upper surface of the paper feed cassette 201 and the remaining amount sensor 700 was 3.5 mm. Further, the number of turns of the drive coil L1 and the reference coil L3 of the detection coil L2 constituting the differential transformer T1 is 100, respectively.

  As shown in FIGS. 9A to 9C, as the number of recording papers P decreases, the loading plate 230 moves in the + Z direction due to the biasing force in the + Z direction by the elastic body 240, and accordingly. It can be seen that the distance D1 between the conductor plate 250 and the remaining amount sensor 700 is small.

  As shown in FIG. 8B, it can be seen that the voltage output from the remaining amount sensor 700 increases with a certain slope as the number of sheets decreases. When the number of recording sheets becomes zero, as shown in FIG. 9C, the placement plate 230 is positioned on the upper surface of the paper feed cassette 201, and the conductor plate 250 is caused by the weight of the left surface 250a. It rotates in the A direction indicated by the arrow, and the right surface 250b comes close to the sensor surface of the remaining amount sensor 700 in parallel. As a result, as shown in FIG. 8A, when the remaining amount of recording paper is one, the voltage output from the remaining amount sensor 700 is 2.648 mV, but when it becomes zero, It becomes 3.392 mV, and it can be seen that the output voltage increases rapidly. Therefore, there is a significant difference in the voltage output from the remaining amount sensor 700 between the case where there is one recording sheet and the case where there are two recording sheets, and it is ensured that the number of recording sheets P has become zero. It becomes possible to detect. Here, when the number of sheets reaches zero, the right surface 250b comes close to the sensor surface of the remaining amount sensor 700 in a substantially parallel state, so that the detection accuracy is improved when the number of sheets is zero.

  As described above, according to the remaining amount detection device, an eddy current is generated in the conductor plate 250 due to the influence of electromagnetic induction, and the magnetic flux φ2 is generated by the eddy current. As the distance D1 between the conductor plate 250 and the remaining amount sensor 700 becomes closer, the magnetic flux passing through the detection coil L2 in the magnetic flux φ2 increases, and the detection voltage V2 induced in the detection coil L2 increases and is output from the differential transformer T1. The voltage VO to be increased increases, and the remaining number of recording sheets can be detected based on this voltage VO. For this reason, it is possible to detect the remaining number of recording sheets without using a component that needs to supply power to the paper feed cassette 201, and wiring for supplying power to the paper feed cassette 201 is provided. There is no need. Further, since the remaining amount sensor 700 is disposed in the main body 200 and the conductor plate 250 is disposed on the sheet feeding cassette 201 side, a sufficient distance D1 between the remaining amount sensor 700 and the conductor plate 250 is ensured. And a high dynamic range and high resolution can be realized.

FIG. 3 is a schematic side view mainly showing a mechanical configuration when the remaining amount detection device according to the present invention is applied to a digital multi-function peripheral. 3 is a diagram schematically showing the appearance of a paper feed cassette. It is drawing which showed the structure of the coil which comprises a remaining amount sensor. It is drawing which showed the arrangement | positioning relationship of a drive coil, a detection coil, and a reference coil. 2 is a diagram showing an electrical configuration of the digital multi-function peripheral shown in FIG. 1. It is drawing which showed an example of the number specification table. It is a flowchart which shows the process of CPU. FIG. 8A is a table showing the results of an experiment performed on the remaining amount detecting device, and FIG. 8B is a graph with respect to the table of FIG. It is an internal side view of the paper feed cassette for demonstrating this experiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control part 12 Memory | storage part 13 Low pass filter 30 Printing part 230 Mounting board 240 Elastic body 250 Conductor board 700 Residual quantity sensor 701 AC amplification circuit 702 Detection circuit L1 Drive coil L2 Reference coil L3 Reference coil

Claims (6)

A remaining amount detection device for detecting the remaining amount of recording paper stored in a paper feed tray of an image forming apparatus,
A placement plate disposed on the paper feed tray and on which recording paper is placed;
A remaining amount sensor disposed in the main body of the image forming apparatus so as to face the mounting plate;
Detecting means for detecting the remaining amount of recording paper based on the electrical signal output from the remaining amount sensor;
The mounting plate includes a conductive plate, and the distance to the remaining amount sensor fluctuates according to the number of recording sheets deposited,
The remaining amount sensor generates an eddy current in the conductive plate by electromagnetic induction, and an electric signal having a level corresponding to a distance between the remaining amount sensor and the conductive plate based on a magnetic field generated by the eddy current. Generate and output to the detection means ,
The conductive plate is disposed so as to be rotatable with respect to the mounting plate. When a recording paper is placed on the mounting plate, the conductive plate is substantially flush with the mounting surface of the mounting plate. A remaining amount detecting apparatus that rotates when the recording sheet placed on the placing plate runs out and approaches the remaining amount sensor .   The remaining amount sensor includes a differential transformer including a primary side drive coil, a secondary side reference coil, and a detection coil, and the reference coil, the drive coil, and 2. The remaining amount detecting device according to claim 1, wherein the detecting coil is provided, and a difference between an electromotive force generated in the reference coil and an electromotive force generated in the detecting coil is output as the electric signal. The mounting plate includes a first plane parallel to a sensor surface of the remaining amount sensor, and a second plane inclined downward by a predetermined angle with respect to the first plane.
The remaining amount sensor is disposed in the vicinity of a boundary line between the first plane and the second plane so as to face the second plane.
The conductive plate is rotatably fitted around the boundary line as an axis in a hole formed in the mounting plate so as to include a boundary line between the first plane and the second plane. When there is no recording paper placed on the plate, the size of the first plane side is the second plane side size so that the second plane side conductive plate is close to the remaining amount sensor. 3. The remaining amount detection device according to claim 1 , wherein the remaining amount detection device is larger than the size. The remaining amount sensor includes an amplifying unit that cuts a DC component of the electric signal output from the differential transformer and amplifies the AC component, and a DC converting unit that converts the amplified electric signal into a DC electric signal. Prepared,
The detection means includes an analog-digital conversion means for converting an electrical signal converted into a direct current from an analog signal into a digital signal, a storage means for storing in advance the number of recording sheets corresponding to the value of the digital signal, and the digital signal receives, by referring to the storage means, the remaining amount detecting apparatus according to any one of claims 1 to 3, characterized in that it comprises a determining central processing unit the remaining amount of the recording paper. 5. The remaining amount detecting apparatus according to claim 4 , wherein the detecting unit further includes a low-pass filter that removes a high-frequency component of the electrical signal output from the DC converting unit and outputs the electrical signal to the analog-to-digital converting unit. The conductive plate is level detecting apparatus according to any one of claims 1 to 5, characterized in that it is constituted by pasting an aluminum tape to the surface.

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