JP2012081665A - Image processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus that can surely and easily prevent a circuit in an apparatus from being short-circuited and damaged by an input of an excess voltage from a connection apparatus.SOLUTION: An image forming apparatus 10 includes: an I/F circuit 94 for transmitting and receiving a signal to and from the connection apparatus through a USB cable and wires L2-L9; a connection connector 101 for detachably connecting the USB cable and being connected to wires L2-L9; a potential difference detecting circuit 103 for detecting a potential difference between the wire L9 and the wire L5 which are electrically connected to the USB cable when the USB cable is connected to the connection connector 101; a CPU 80 for determining whether a detected potential difference is within a predetermined allowable range; switches SW1-SW4 provided in the middle of the wires L2-L9, which conduct or shut off the wires L2-L9; and a transistor Q1 for controlling the conduction and shutoff of the wires L2-L9 by the switches SW1-SW4 based on a determination result of the CPU 80.

Description

  The present invention relates to an image processing apparatus that transmits / receives a signal to / from an external device via a wiring, and more particularly to a technique for preventing a short circuit breakdown of a circuit due to an input of an overvoltage.

  2. Description of the Related Art Conventionally, an image forming apparatus that transmits and receives signals via an external device such as a PC (Personal Computer) and a USB (Universal Serial Bus (registered trademark)) cable is known. Referring to FIG. 1, a conventional image forming apparatus 1 can send and receive signals to and from PC 2 by being connected to PC 2 via a USB cable (not shown).

  In such an image forming apparatus 1, the following problems may occur when the power supply ground of the PC 2 is miswired. For example, the FG (Frame Ground) terminal connected to the frame (casing) of the PC 2 is not connected to the ground line to be originally connected, but to the ungrounded pole side of the AC (Alternating Current) power source 3. To do. In this case, the frame potential (body potential) of the PC 2 is the same as the potential (230 V) of the Live terminal (hereinafter referred to as “L terminal”). In this state, when the image forming apparatus 1 and the PC 2 are cable-connected, a potential difference is generated between the potential on the image forming apparatus 1 side and the potential on the PC 2 side, and the image forming apparatus 1 is input by the input of an overvoltage from the PC 2. There is a risk that the internal circuit may be short-circuited.

  In order to solve such problems, various techniques have been proposed. For example, Patent Document 1 described below discloses a switching power supply device in which a plurality of electrolytic capacitors are connected in series between positive and negative power supply lines. The potential difference detection circuit provided in the switching power supply device detects the potential difference between the monitoring voltage and the reference voltage, and outputs an abnormality detection signal indicating an abnormality of the electric field capacitor when the potential difference exceeds a predetermined threshold value. Thus, on / off of the two switching elements provided in the circuit is controlled. As a result, the switching power supply disclosed in Patent Document 1 is a safety device that safely stops operation without causing smoke and ignition of the remaining electric field capacitor when one of the series-connected electrolytic capacitors breaks down due to a short circuit. Function as.

JP 2006-304414 A

  The technique disclosed in Patent Document 1 is to stop the operation of the device when the electrolytic capacitor is short-circuited by an input of an overvoltage, and the circuit is destroyed. Therefore, the switching power supply device is used again. I can't.

  In order to prevent short-circuit breakdown of the circuit due to the input of overvoltage, a method for increasing the breakdown voltage of the interface (hereinafter referred to as “I / F”) circuit 4 (see FIG. 1) of the image forming apparatus 1 and the grounding between the devices A method of connecting in advance is conceivable. However, it is very difficult to increase the withstand voltage of an I / F circuit that transmits and receives USB signals and the like at high speed, and it is difficult to realize the former method. In addition, since there is a possibility that some users do not perform ground connection between devices, the latter method is not reliable.

  An object of the present invention is to provide an image processing apparatus that can reliably and easily prevent a circuit in the apparatus from being short-circuited and broken by an input of an overvoltage from a connected device.

  An image processing apparatus according to an aspect of the present invention detachably attaches / detaches a connection device to / from a transmission / reception unit that transmits and receives a signal via a first wiring and a second wiring, and the first wiring connected to the connection device. A connecting means connected to the second wiring, a detecting means for detecting a potential difference between the first wiring and the second wiring when the first wiring is connected to the connecting means, and a detection Provided in the middle of the second wiring that connects the determination means for determining whether the potential difference detected by the means is within a predetermined allowable range and the connection means and the transmission / reception means. Or the switching means to interrupt | block, and the 1st control means which controls conduction | electrical_connection or interruption | blocking of the 2nd wiring by a switching means based on the determination result of a determination means are included.

  In this way, in the image processing apparatus, the potential difference between the first wiring and the second wiring is detected, and based on whether or not the detected potential difference is within a predetermined allowable range, the connection means and the transmission / reception means Is connected or cut off. As a result, when the potential difference is excessive, for example, the connection between the transmitting / receiving means and the connected device can be electrically interrupted without being connected. It is possible to reliably and easily prevent the short circuit from being broken.

  Preferably, the first control unit causes the switching unit to conduct the second wiring when the determination unit determines that the potential difference detected by the detection unit is out of a predetermined allowable range. Let's block without. As a result, when the potential difference is excessive, the transmission / reception means and the connected device can be disconnected more reliably without being connected, so that image processing can be performed by inputting an overvoltage from the connected device. It is possible to more reliably prevent the circuit in the apparatus from being short-circuit broken.

  More preferably, the first control unit causes the switching unit to conduct the second wiring when the determination unit determines that the potential difference detected by the detection unit is within a predetermined allowable range. . Thus, stable signal transmission / reception can be performed without causing a short circuit breakage of a circuit in the image processing apparatus due to an input of an overvoltage from the connected device.

  More preferably, the image processing apparatus further includes a second control unit that causes the switching unit to block the second wiring when the first wiring is not connected to the connection unit. Thus, the second wiring can be prevented from being conducted before the switching control based on the determination result by the determination unit is performed. As a result, it is possible to more reliably prevent the circuit in the image processing apparatus from being short-circuited and broken by the input of the overvoltage from the connected device. Therefore, the circuit in the image processing apparatus can be reliably protected.

  More preferably, the detection means detects a potential difference between the first wiring and the second wiring after a predetermined time has elapsed since the connection of the first wiring to the connection means. Thereby, the potential difference can be detected after the signal input from the connected device is stabilized. As a result, due to the influence of noise and bounce that occurs immediately after the connection of the first wiring, the second wiring becomes conductive even though the potential difference is excessive, or the potential difference is within an allowable range. A malfunction in which the second wiring is interrupted can be prevented. Therefore, it is possible to transmit and receive signals more safely and stably.

  More preferably, the image processing apparatus further includes notification means for notifying the occurrence of an abnormality when the determination means determines that the potential difference detected by the detection means is outside a predetermined allowable range. As a result, the user of the image processing apparatus can easily know that the second wiring is not conductive. As a result, the user can be prompted to confirm the cause of the lack of conduction. Therefore, the user can quickly remove the cause of the lack of conduction.

  More preferably, the image processing apparatus further includes a third circuit that causes the switching means to shut off the second wiring when a predetermined condition indicating that transmission / reception of a signal to / from the connected device is not performed is satisfied. Including control means. As a result, the power supply of the connected device is turned on / off and the AC power source is changed while the second wiring is in a conductive state, so that an overvoltage is input from the connected device and the circuit in the image processing apparatus is short-circuited. It can be prevented from being destroyed. Therefore, the circuit in the image processing apparatus can be more reliably protected.

  More preferably, the first wiring is a GND (Ground) of the connected device, and the second wiring is a GND of the image processing apparatus. As a result, the second wiring can be cut off when the ground of the connected device is abnormal. As a result, it is possible to reliably prevent the circuit in the image processing apparatus from being short-circuited and broken due to the input of the overvoltage from the connected device due to the grounding abnormality.

  According to the present invention, in the image processing apparatus, a potential difference between the first wiring and the second wiring is detected, and transmission / reception is performed with the connection unit based on whether or not the detected potential difference is within a predetermined allowable range. The second wiring connecting the means is turned on or off. As a result, when the potential difference is excessive, for example, the connection between the transmitting / receiving means and the connected device can be electrically interrupted without being connected. It is possible to reliably and easily prevent the short circuit from being broken.

It is a figure for demonstrating the problem which arises in the conventional image forming apparatus. 1 is a diagram schematically illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which shows the structure of the image forming station 22K typically. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus together with a part of hardware. FIG. It is a figure for demonstrating the circuit structure of an electrical potential difference confirmation apparatus. It is a figure which shows the control structure of the computer program for implement | achieving I / F connection control processing in the flowchart format. FIG. 3 is a diagram illustrating an example of a state of an image forming apparatus and a connected device when a USB cable is connected. It is a figure for demonstrating the circuit structure of an electrical potential difference confirmation apparatus.

  In the following description and drawings, the same reference numerals and names are assigned to the same components. Their functions are also the same. Therefore, detailed description thereof will not be repeated each time.

  The image forming apparatus 10 according to the present embodiment is a digital multi-function peripheral that prints a multicolor or single color image on a predetermined sheet (recording paper) in accordance with image data transmitted from an external apparatus. The image forming apparatus 10 is provided with a potential difference confirmation device 93 to be described later in order to prevent a short circuit failure of the circuit due to an input of an overvoltage from an external device.

<Hardware configuration>
-Overall configuration-
Referring to FIG. 2, the image data handled by the image forming apparatus 10 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, the image forming apparatus 10 includes image forming stations 22K, 22C, 22M, and 22Y for forming a black toner image, a cyan toner image, a magenta toner image, and a yellow toner image, respectively. In the following description, the image forming stations 22K, 22C, 22M, and 22Y may be collectively referred to as “image forming station 22”. A detailed configuration of the image forming station 22 will be described later.

  The image forming apparatus 10 further includes a document placing table 12 provided on the image forming apparatus 10, and an automatic document feeder (hereinafter referred to as “ADF (” Automatic Document Feeder) ”) 16) and a document reading unit 14 provided below the document table 12. The document placing table 12 is a plate-like member made of transparent glass for placing a document. The ADF 16 is a device that automatically conveys a document onto the document table 12. The user can manually place the document on the document placing table 12 by opening the ADF 16 in the direction indicated by the arrow M.

  The document reading unit 14 includes a document scanning unit including a light source, a reflection mirror, an optical lens, and a CCD (Charge-Coupled Device) line sensor (all of which are not shown). The document scanning unit obtains a reflected light image by irradiating light from the light source to the image surface of the document placed on the document placing table 12 manually by the user or by the ADF 16. The reflection mirror and the optical lens form the resulting reflected light image on the CCD line sensor. The CCD line sensor sequentially photoelectrically converts the formed reflected light image and outputs it as image data to the image processing unit 90 (see FIG. 4).

  The image processing unit 90 performs image processing including screen processing (gradation processing) on the input image data to create image data of a predetermined gradation, and outputs the image data to the LSU control device 28.

  The image forming apparatus 10 is further provided below the image forming station 22 and is a laser scanner unit (hereinafter referred to as “LSU (Laser Scanner Unit)”) for exposing the image forming station 22 by laser scanning. 24. The LSU 24 includes a laser oscillation unit 26 including a semiconductor laser for oscillating laser light, a polygon mirror for scanning the laser light, and laser light reflected by the polygon mirror on the surface of the photosensitive drum 60 (see FIG. 2). A lens for guiding, an optical element such as a reflection mirror, and image data output from the image processing unit 90 are converted into a laser emission signal, and the operation of the laser oscillation unit 26 is controlled based on the laser emission signal. LSU control device 28 and the like. In this embodiment, the LSU 24 is used as the exposure apparatus. However, for example, a light emitting element such as an EL (Electro Luminescence) or LED (Light Emitting Diode) writing head arranged in an array may be used. Good.

  The image forming apparatus 10 is further provided above the image forming station 22 and an intermediate transfer belt 30 for transferring a single color toner image formed at each of the image forming stations 22 on a recording sheet as a recording medium. And two support rollers 32 </ b> A and 32 </ b> B for supporting the intermediate transfer belt 30 that are provided inside the intermediate transfer belt 30 at an interval in the left-right direction on the paper surface. The intermediate transfer belt 30 is an endless belt-like member that is wound around two support rollers 32A and 32B. The intermediate transfer belt 30 is not particularly limited as long as it is generally used in this field. For example, a film having a thickness of 100 μm to 150 μm can be used. The support roller 32A (on the right side in FIG. 1) is rotatably provided around an axis by a drive unit (not shown), and the intermediate transfer belt 30 is rotated in the direction indicated by the arrow R, that is, in the opposite direction. Rotate clockwise. The support roller 32B (left side in FIG. 1) is provided so as to be able to be driven to rotate by the rotation of the support roller 32A, and applies a certain tension to the intermediate transfer belt 30 so that the intermediate transfer belt 30 does not loosen.

  A transfer roller 34 is provided on the opposite side of the support roller 32A across the intermediate transfer belt 30 so as to make a pair with the support roller 32A. In the following description, upstream and downstream are expressed with reference to the secondary transfer position (transfer nip portion) where the support roller 32A and the transfer roller 34 are in pressure contact with the rotation direction of the intermediate transfer belt 30. The image forming stations 22K, 22C, 22M, and 22Y are arranged in this order from the upstream side toward the downstream side in the rotation direction of the intermediate transfer belt 30 indicated by the arrow R.

  One of the transfer roller 34 and the support roller 32A is preferably made of a hard material such as metal, and the other is preferably an elastic roller made of a soft material such as an elastic rubber roller or a foamed resin roller. Thereby, the transfer nip portion can be obtained constantly. When the sheet (recording paper) is conveyed to the transfer nip portion, a high voltage having a polarity (+) opposite to the toner charging polarity (−) is applied to the transfer roller 34. As a result, the full color toner image formed on the intermediate transfer belt 30 is transferred to a sheet (recording paper).

  The image forming apparatus 10 is further provided inside the intermediate transfer belt 30 so as to face the image forming stations 22K, 22C, 22M, and 22Y. The image forming apparatus 10 is formed by the image forming stations 22K, 22C, 22M, and 22Y. Four intermediate transfer rollers 40 for transferring the monochrome toner image onto the intermediate transfer belt 30 are included. When a high-voltage transfer bias having a polarity opposite to the toner charging polarity (for example, a polarity opposite to the toner charging polarity (-) (+)) is applied from each intermediate transfer roller 40, the image forming station 22K, Each single color toner image formed by 22C, 22M, and 22Y is sequentially transferred onto the intermediate transfer belt 30 to form one full color toner image. The intermediate transfer roller 40 is not particularly limited as long as it is generally used in the field. For example, the intermediate transfer roller 40 is based on a metal shaft such as stainless steel having a diameter of 8 mm to 10 mm, and the surface thereof is a conductive elastic material ( For example, a roller covered with ethylene propylene rubber (EPDM) or foamed urethane or the like can be used. By using such a conductive elastic material, a transfer bias can be uniformly applied to the intermediate transfer belt 30. In the present embodiment, a roller-shaped member is used as the transfer electrode, but a brush-shaped member or the like may be used.

  The image forming apparatus 10 is further provided on the downstream side in the rotation direction of the intermediate transfer belt 30 with respect to the image forming station 22Y, and the transfer described above for transferring the full-color toner image formed on the intermediate transfer belt 30 onto a recording sheet. A roller 34 and a belt cleaning unit 42 provided on the downstream side of the transfer roller 34 in the rotation direction of the intermediate transfer belt 30 and for cleaning the surface of the intermediate transfer belt 30 are included.

  The belt cleaning unit 42 includes a belt cleaning brush 44 and a belt cleaning blade 46 that contact the surface of the intermediate transfer belt 30 in order to remove the toner that remains on the surface of the intermediate transfer belt 30 and causes toner color mixture. . The belt cleaning blade 46 is disposed downstream of the belt cleaning brush 44 in the rotation direction of the intermediate transfer belt 30. A support roller 32B is located on the opposite side of the belt cleaning blade 46 with the intermediate transfer belt 30 in between.

  The image forming apparatus 10 further includes a tray 48 provided below the LSU 24 for accommodating sheets (recording paper) therein, and a pickup roller 53A for transporting the recording paper in the tray 48 to the paper transport path. , A plurality of sets (four sets in the present embodiment) of paper feed roller pairs 54 </ b> A to 54 </ b> D and a registration roller 55. The paper feed roller pairs 54A to 54D are small roller pairs provided along the paper conveyance path, and assist the conveyance of the sheet by promoting it. The pickup roller 53A is provided in the vicinity of the end of the tray 48, picks up sheets one by one from the tray 48, and supplies the sheets to the paper transport path. The registration roller 55 temporarily holds the sheet conveyed on the sheet conveyance path, and conveys the sheet to the transfer roller 34 at a timing when the leading edge of the toner image on the photosensitive drum 60 is aligned with the leading edge of the sheet. The recording paper accommodated in the tray 48 is conveyed to the secondary transfer position (transfer nip portion) by a roller such as the above-described pair of feed rollers 54A to 54D. The conveyance direction of the recording paper (hereinafter referred to as “paper conveyance direction”) is indicated by an arrow F. Note that the sheet used for image formation can also be placed in the manual paper feed cassette 49. A pickup roller 53B provided near the end of the manual sheet feed cassette 49 picks up sheets one by one from the manual sheet feed cassette 49 and supplies them to the sheet conveyance path.

  The image forming apparatus 10 is further provided on the downstream side of the transfer roller 34 with respect to the sheet conveyance direction indicated by an arrow F, and a fixing unit 50 for fixing the full color toner image transferred onto the recording sheet onto the recording sheet. A discharge roller 52 that is provided further downstream of the fixing unit 50 in the sheet conveyance direction and discharges the recording sheet on which a full-color image is formed from the image forming apparatus 10 toward the discharge tray 51. The paper discharge tray 51 is a tray that is provided in the upper part of the image forming apparatus 10 and for collecting printed sheets face down.

  The fixing unit 50 includes a heat roller 50A, a pressure roller 50B, and an external heating belt 50C. The heat roller 50A is a roller-like member provided so as to be rotatable around an axis by a drive unit (not shown). The pressure roller 50B is a roller-like member provided so as to be pressed against the heat roller 50A by a pressure member (not shown). The pressure roller 50B rotates following the rotation of the heat roller 50A. The external heating belt 50C is an endless belt-like member for heating the surface of the heat roller 50A from the outside. A heating member (not shown) such as a halogen lamp for heating the surface of the heat roller 50A is provided inside the heat roller 50A. The heating member and the external heating belt 50C are temperature-controlled by a CPU 80 (see FIG. 4), which will be described later, based on a signal from a temperature detector (not shown) so as to reach a predetermined fixing temperature. Hereinafter, the pressure contact portion between the heat roller 50A and the pressure roller 50B is referred to as a fixing nip portion. The fixing unit 50 heats and melts the toner constituting the toner image and presses the sheet (recording paper) when the sheet (recording paper) onto which the toner image has been transferred in the transfer unit passes through the fixing nip portion. Then, the toner image is thermally fixed on the recording medium to form an image.

  The image forming apparatus 10 further includes an operation panel 92 (see FIG. 4) in which a display device such as a liquid crystal display and an input device such as a touch panel are overlapped. The operation panel 92 receives a user instruction for the operation of the image forming apparatus 10, displays the contents of the instruction, and outputs an instruction signal corresponding to the instruction to a CPU 80 described later.

  In the image forming apparatus 10, the single color toner images formed at the image forming stations 22K, 22C, 22M, and 22Y are sequentially superimposed on the intermediate transfer belt 30 and primarily transferred to form a full color toner image. The full-color toner image formed on the intermediate transfer belt 30 is secondarily transferred onto the recording paper conveyed by the pair of paper feed rollers 54A to 54D at the secondary transfer position (transfer nip portion), and then transferred to the fixing unit 50. Is fixed on the recording paper. The recording paper on which the full color image is formed by the fixing unit 50 is discharged from the image forming apparatus 10 by the paper discharge roller 52. Further, the toner remaining on the surface of the intermediate transfer belt 30 without being transferred to the recording paper after the secondary transfer is removed by the belt cleaning unit 42.

  When performing double-sided printing, when the single-sided printing is completed and the trailing edge of the sheet that has passed through the fixing unit 50 is gripped by the paper discharge roller 52, the paper discharge roller 52 rotates reversely to convey the sheet. Guide to roller pair 54C, 54D. Thereafter, printing is performed on the back surface of the sheet through the registration roller 55, and then the sheet is discharged to the discharge tray 51.

-Configuration of the image forming station 22-
Since the image forming stations 22K, 22C, 22M, and 22Y have the same configuration except that the color of toner stored in the developing tank 68 described later is different, the configuration of the image forming station 22K will be representatively described below. Will be described.

  Referring to FIG. 3, the image forming station 22K includes a photosensitive drum 60, a charger 62 for uniformly charging the surface of the photosensitive drum 60, and an electrostatic latent image formed on the surface of the photosensitive drum 60. A developing unit 64 for forming a visible image, and a photosensitive drum cleaner 66 for removing a residue including toner remaining on the surface of the photosensitive drum 60.

  The photosensitive drum 60 is provided so as to be rotatable around an axis by a drive unit (not shown). The photosensitive drum 60 is rotated in the direction indicated by the arrow Rd, that is, in the clockwise direction by the rotational driving thereof.

  The charger 62, the developing unit 64, and the photosensitive drum cleaner 66 are respectively provided around the photosensitive drum 60 in this order along the rotation direction of the photosensitive drum 60 indicated by an arrow Rd. The developing unit 64 is provided so as to be below the charger 62, and the photosensitive drum cleaner 66 is provided so as to be above the charger 62.

  The charger 62 is a non-contact type scorotron charger, and performs corona discharge on the photosensitive drum 60 to uniformly charge the surface of the photosensitive drum 60 to a predetermined potential. The charger 62 is not limited to the scorotron charger and may be any one that is generally used in this field. For example, a non-contact type corotron charger or a contact type charger using a charging roller or a charging brush can be used. The surface of the photosensitive drum 60 charged to a predetermined potential by the charger 62 is exposed by laser scanning of the laser oscillation unit 26 shown in FIG. 1, so that an electrostatic latent image based on image data is converted into a photosensitive member. It is formed on the surface of the drum 60.

  The developing unit 64 includes a developing tank 68 for storing therein a two-component developer containing toner and a carrier. An opening 70 is provided at a position facing the surface of the photosensitive drum 60 on the side surface of the developing tank 68. It is formed. The developing unit 64 further includes a developing roller 72. The developing roller 72 is provided in the developing tank 68 at a position facing the photosensitive drum 60 through the opening 70 so as to be rotatable around an axis by a driving unit (not shown). The developing roller 72 is provided so as to be separated from the surface of the photosensitive drum 60 by a predetermined gap, and the rotation direction of the developing roller 72 at the closest part to the photosensitive drum 60 is the same as the rotational direction of the photosensitive drum 60. Rotate in the direction. The developing roller 72 carries and conveys a two-component developer on the outer peripheral surface thereof, and supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 60 at the closest part to the photosensitive drum 60. The electrostatic latent image is developed. When supplying the toner, a potential having a polarity opposite to the charging potential of the toner is applied to the surface of the developing roller 72 as a developing bias voltage. As a result, the toner on the surface of the developing roller 72 is smoothly supplied to the electrostatic latent image. The toner stored in the developing tank 68 is supplied from a toner cartridge (not shown) that is detachably mounted in the vicinity of the developing unit 64.

  The photosensitive drum cleaner 66 scrapes off the residue containing toner remaining on the surface of the photosensitive drum 60, holds the residue scraped off by the cleaning blade 77, and prevents its scattering. A waste toner collecting container 78. The cleaning blade 77 is a plate-like member provided so that its longitudinal direction extends along the axial direction of the photosensitive drum 60, and one end portion in the short side direction is a position where the rotational direction of the photosensitive drum 60 is downward. In FIG. 5, the toner is disposed in the waste toner collecting container 78 so as to be bent and pressed in a counter direction (a direction opposite to the rotation direction of the photosensitive drum 60) with respect to the rotation direction of the photosensitive drum 60. By arranging in this way, the residue can be scraped off more easily at one end in the short direction.

  According to the image forming station 22K, the surface of the photosensitive drum 60 that has been uniformly charged by the charger 62 is irradiated with laser light based on image data from the LSU 24 to form an electrostatic latent image. To the formed electrostatic latent image, toner is supplied from the developing unit 64 to form a single color toner image, and the formed toner image is primarily transferred to the intermediate transfer belt 30. After the primary transfer, the residue remaining on the surface of the photosensitive drum 60 is removed by the photosensitive drum cleaner 66. This series of toner image forming operations is repeatedly executed in the image forming stations 22K, 22C, 22M, and 22Y.

<Electrical configuration>
Referring to FIG. 4, image forming apparatus 10 includes a CPU 80. A bus line 81 is connected to the CPU 80, and a ROM (Read-Only Memory) 82, a RAM (Random Access Memory) 83, and an HDD (Hard Disk Drive) 84 are electrically connected to the CPU 80 via the bus line 81. Connected to. The ROM 82 is a read-only memory that stores a computer program (hereinafter simply referred to as “program”) for realizing a general operation of the image forming apparatus 10. The RAM 83 is a temporary storage memory in which the program in the ROM 82 is expanded or used as a working memory when the CPU 80 executes various programs. The HDD 84 is an auxiliary storage device that stores various data such as programs and image data.

  In the present embodiment, the HDD 84 stores a program for realizing a general operation of the image forming apparatus 10 and a program for realizing an I / F connection control process described later. A program structure for realizing the I / F connection control processing in this program will be described later.

  The CPU 80 executes desired processes such as the operation of each unit of the image forming apparatus 10 and communication with an external apparatus by executing the various programs described above. The various programs described above are stored in the ROM 82 or the HDD 84 in advance, and are read from the ROM 82 or the HDD 84 and transferred to the RAM 83 when a desired process is executed. The CPU 80 reads and interprets a program instruction from an address in the RAM 83 specified by a value stored in a register called a program counter (not shown) in the CPU 80. CPU 80 also reads data necessary for the operation from the address specified by the read instruction, and executes an operation corresponding to the instruction on the data. The execution result is also stored in an address specified by an instruction, such as a register in the RAM 83, HDD 84, and CPU 80.

  Further, a NIC (Network Interface Card) 86 is electrically connected to the CPU 80 via the bus line 81. The NIC 86 interfaces with a network 85 made up of a LAN (Local Area Network) line. The image forming apparatus 10 can communicate with an external device such as a PC 87 on the network 85 via the NIC 86.

  Further, the first sub CPU 88, the second sub CPU 89, the image processing unit 90, the image memory 91, and the operation panel 92 described above are electrically connected to the CPU 80 via the bus line 81.

  The first sub CPU 88 controls the operation of the document reading unit 14. The second sub CPU 89 controls the operation of the image forming unit including the image forming station 22, the LSU 24, the transfer unit, the fixing unit 50, and the like. The image memory 91 temporarily stores image data to be printed for each page. In response to an instruction from the CPU 80 or the like, the image memory 91 outputs the stored image data to the image forming unit in synchronization with image formation by the image forming unit.

  The CPU 80 is further electrically connected to the potential difference confirmation device 93 and the I / F circuit 94 via the bus line 81. Hereinafter, the circuit configuration of the potential difference confirmation device 93 will be described with reference to FIG. The potential difference confirmation device 93 includes a connection connector 101, a relay 102, and a potential difference detection circuit 103.

  The connection connector 101 includes a USB (Universal Serial Bus) port. The connection connector 101 detects an input of a specific voltage when an external device is electrically connected via a USB cable during the operation of the image forming apparatus 10. Then, a notification signal indicating that the USB cable is connected is output to the CPU 80 via a wiring (not shown). When the USB is removed, the connection connector 101 detects that a specific voltage is not input. Then, a notification signal indicating that the USB cable is not connected is output to the CPU 80 via a wiring (not shown). Hereinafter, in order to distinguish from an external device on the network 85, the external device connected to the connection connector 101 of the potential difference confirmation device 93 may be referred to as a connected device.

  Relay 102 includes switches SW1 to SW4 and a coil L1. One terminals of the switches SW1 to SW4 are connected to the I / F circuit 94 via wirings L2 to L5, respectively. The other terminals of the switches SW1 to SW4 are connected to the connection connector 101 via wirings L6 to L9, respectively. The wiring L5 is also connected to the GND of the image forming apparatus 10 and one terminal of the coil L1, respectively. The wiring L9 is also connected to the GND of the connected device. A wire L11 connected to the frame of the connected device is connected to the wire L10 branched from the wire L9 and connected to the GND of the connected device. The other terminal of the coil L1 is connected to the collector of a PNP transistor (hereinafter referred to as “PNP transistor”) Q1. The emitter of the PNP transistor Q1 is connected to the power supply VCC supplied from the power supply of the image forming apparatus 10. The base of the PNP transistor Q1 is electrically connected to the CPU 80 of the image forming apparatus 10.

  The PNP transistor Q1 supplies a current to the relay 102 in accordance with a control signal applied to its base. That is, when the control signal output from the CPU 80 instructs the continuity of the switches SW1 to SW4, the transistor Q1 is turned on to pass current. As a result, the coil L1 is excited and the switches SW1 to SW4 are turned on. On the other hand, when the control signal output from the CPU 80 instructs the switch SW1 to SW4 to be cut off, the transistor Q1 is turned off to cut off the current. As a result, the coil L1 is not excited and the switches SW1 to SW4 are cut off. In this way, the CPU 80 controls conduction or interruption of the switches SW1 to SW4 of the relay 102 by switching the state of the transistor Q1 to the on state or the off state. In the present embodiment, it is assumed that the switches SW1 to SW4 are cut off when the image forming apparatus 10 is powered on.

  Here, the GND of the image forming apparatus 10 indicates a logic GND. This logic GND is grounded via inductors I1 and I2. A wiring connected to the frame of the image forming apparatus 10 is connected to the connection point of the inductors I1 and I2. As a result, the frame is also grounded. Thereby, the GND potential of the circuit in the image forming apparatus 10 and the potential of the frame are the same as the ground potential.

  The potential difference detection circuit 103 includes a first potential comparison unit 104 and a second potential comparison unit 105. The first potential comparison unit 104 includes a comparator C1 and resistance elements R1 to R4. One end of the resistance element R2 is connected to the GND of the image forming apparatus 10. The other end of the resistance element R2 is connected to one end of the resistance element R1. The other end of the resistance element R1 is connected to the wiring L10. One end of the resistance element R4 is connected to the GND of the image forming apparatus 10. The other end of the resistance element R4 is connected to one end of the resistance element R3. The other end of the resistance element R3 is connected to the wiring L10. The non-inverting input terminal of the comparator C1 is connected to a connection point between the resistance element R1 and the resistance element R2. The inverting input terminal of the comparator C1 is connected to a connection point between the resistance element R3 and the resistance element R4. The output of the comparator C1 is electrically connected to the CPU 80.

  The comparator C1 uses the resistance elements R3 and R4 to convert the potential difference between the GND of the connection device and the GND of the image forming apparatus 10 by the resistance elements R1 and R2, and the potential difference between the GND of the connection equipment and the GND of the image forming apparatus 10 by the resistance elements R3 and R4. A first comparison signal indicating a difference between the divided voltage and the divided voltage is output to the CPU 80. In the present embodiment, when the GND potential of the connected device is higher than the GND potential of the image forming apparatus 10 by a predetermined value or more, the first comparison signal becomes “H” level. Have been chosen.

  The second potential comparison unit 105 includes a comparator C2 and resistance elements R5 to R8. One end of the resistor element R6 is connected to the GND of the image forming apparatus 10. The other end of the resistance element R6 is connected to one end of the resistance element R5. The other end of the resistance element R5 is connected to the wiring L10. One end of the resistance element R8 is connected to the GND of the image forming apparatus 10. The other end of the resistance element R8 is connected to one end of the resistance element R7. The other end of the resistance element R7 is connected to the wiring L10. The non-inverting input terminal of the comparator C2 is connected to the connection point between the resistance element R7 and the resistance element R8. An inverting input terminal of the comparator C2 is connected to a connection point between the resistance element R5 and the resistance element R6. The output of the comparator C2 is electrically connected to the CPU 80.

  The comparator C2 uses the resistance elements R7 and R8 to convert the potential difference between the GND of the connection device and the GND of the image forming apparatus 10 by using the resistance elements R5 and R6, and the potential difference between the GND of the connection device and the GND of the image forming apparatus 10 by the resistance elements R7 and R8. A second comparison signal indicating a difference between the divided voltage and the divided voltage is output to the CPU 80. In the present embodiment, the resistance values of the resistance elements R5 to R8 are such that when the GND potential of the connected device is lower than the GND potential of the image forming apparatus 10 by a predetermined value or more, the second comparison signal becomes “H” level. Have been chosen.

  As a result, if the difference between the GND potential of the connected device and the GND potential of the image forming apparatus 10 is within a predetermined range, the input to the CPU 80 is “L” level, and if it is outside the predetermined range, it is “H” level.

  When the outputs from the comparators C1 and C2 are at “L” level, the CPU 80 outputs a control signal instructing to turn on the switches SW1 to SW4 to the transistor Q1. When the outputs from the comparators C1 and C2 are at “H” level, the CPU 80 outputs a control signal that instructs the transistor Q1 to shut off the switches SW1 to SW4.

  When the switches SW1 to SW4 are turned on, the I / F circuit 94 performs USB signal transmission / reception and GND connection with the connected device via the wirings L2 to L9. That is, the I / F circuit 94 transmits a first signal to a third signal (indicated by “Signal 1 to Signal 3” in the drawing) that are USB signals to the connected device. The I / F circuit 94 is a first I / F signal to a third I / F signal (“I / F Signal 1 to I / F Signal 3” in the figure) that are USB signals transmitted from the connected device. ).

  In this way, the potential difference confirmation device 93, the I / F circuit 94, and the CPU 80 are in a case where there is no potential difference between the GND of the connected device and the GND of the image forming apparatus 10, that is, the ground of the connected device is normal. Sometimes, communication between the image forming apparatus 10 and the connected device is enabled. On the other hand, when there is a potential difference larger than the allowable range between the GND of the connected device and the GND of the image forming apparatus 10, that is, when the ground of the connected device is abnormal, the connection between the image forming apparatus 10 and the connected device is not performed. Make communication impossible.

  Referring to FIG. 4 again, the CPU 80 is further electrically connected to a DC (Direct Current) power source 95 via the bus line 81. The image forming apparatus 10 can operate each unit by applying a voltage (230 V) from an AC power source 96 via a DC power source 95. The DC power source 95 includes a live (L) side input terminal, a neutral (N) side input terminal, and an FG terminal (all not shown) connected to the frame of the image forming apparatus 10. The live (L) side input terminal is connected to the non-grounded pole side of the AC power source 96. The neutral (N) side input terminal is connected to the ground pole side of the AC power source 96. The FG terminal is grounded by connecting it to the earth line.

<Software configuration>
(I / F connection control processing)
As described above, the program stored in the HDD 84 is programmed to execute the I / F connection control process. The CPU 80 controls the operation of each unit of the image forming apparatus 10 according to the above program, and executes various processes shown below in cooperation with the hardware and the program.

  Referring to FIG. 6, the program for realizing the I / F connection control process is started when the image forming apparatus 10 is turned on, and is ended when the power is turned off. It is assumed that the switches SW1 to SW4 are cut off when the image forming apparatus 10 is turned on (in an initial state).

  This program waits until the USB cable is connected to the connection connector 101 of the potential difference confirmation device 93. When it is determined in step S100 that the USB cable is connected (in the case of YES), that is, the USB Step S101 is executed when a notification signal indicating that the cable is connected is input from the connection connector 101, and waiting until a predetermined time elapses. The predetermined time in step S101 is a time required for the signal input from the connection connector 101 to the potential difference detection circuit 103 to be stabilized, and is determined in advance based on experience values.

  The program further includes a step S102 that is executed when it is determined in step S101 that the predetermined time has elapsed (in the case of YES), and outputs the outputs of the comparators C1 and C2 of the potential difference detection circuit 103. The read value reflects the potential difference between the GND of the connected device and the GND of the image forming apparatus 10.

  This program further determines whether or not the outputs from the comparators C1 and C2 are at the “L” level, so that the potential difference between the GND of the connected device and the GND of the image forming apparatus 10 is within a predetermined allowable range. It includes step S103 for determining whether or not.

  In step S103, this program further determines that the potential difference between the GND of the connected device and the GND of the image forming apparatus 10 is within a predetermined allowable range (in the case of YES), that is, from the comparators C1 and C2. Step S104 is executed when it is determined that the output of “L” is at the “L” level, and a control signal instructing to turn on the switches SW1 to SW4 is output to the transistor Q1 of the potential difference confirmation device 93.

  In step S103, the program further determines that the potential difference between the GND of the connected device and the GND of the image forming apparatus 10 is outside the allowable range (in the case of NO), that is, from the comparators C1 and C2. This step is executed when it is determined that the output is at the “H” level, and includes a step S105 in which an error message indicating that a connection error has occurred is displayed on the operation panel 92. After the process of step S105, control returns to step S101.

  This program further waits until the USB cable is disconnected from the connection connector 101 of the potential difference confirmation device 93. If it is determined in step S106 that the USB cable is disconnected (in the case of YES), that is, the USB This is executed when a notification signal indicating that the cable is not connected is input from the connection connector 101, and outputs a control signal that instructs the transistor Q1 of the potential difference confirmation device 93 to shut off the switches SW1 to SW4. Step S107 is included. After the process of step S107, control returns to step S100.

  When the USB cable is disconnected from the connection connector 101 with the switches SW1 to SW4 of the potential difference confirmation device 93 being cut off, this control is started again from step S100.

<Operation>
1 to 7, the image forming apparatus 10 operates as follows. General operations of the image forming apparatus 10 except for the following operations are the same as those of the conventional image forming apparatus. In the following operation, it is assumed that the image forming apparatus 10 is in a state immediately after the power is turned on, and the switches SW1 to SW4 of the potential difference confirmation device 93 are cut off.

  Referring to FIG. 7, the DC power source 110 of the PC 97 is connected to the live (L) side input terminal, the neutral (N) side input terminal, and the frame of the PC 97 similarly to the DC power source 95 of the image forming apparatus 10. FG terminals (none of which is shown) are included. In the DC power source 110, the live (L) side input terminal is connected to the non-grounded pole side of the AC power source 96. The neutral (N) side input terminal is connected to the ground electrode side of the AC power source 96. The FG terminal is not an earth line to be originally connected, but is erroneously connected to the non-grounding electrode side of the AC power source 96. As a result, the frame potential of the PC 97 is the same as the potential of the L terminal.

  In this state, the user connects the connection connector (not shown) of the PC 97 and the connection connector 101 of the potential difference confirmation device 93 with a USB cable. When the USB cable is connected, the connection connector 101 outputs a notification signal indicating that the USB cable is connected to the CPU 80 of the image forming apparatus 10 via a wiring (not shown).

  When the notification signal is input, CPU 80 determines that the USB cable is connected to connection connector 101 (YES in step S100), and waits until a predetermined time has elapsed (step S101). When the predetermined time has elapsed (YES in step S101), that is, when the signal input from connection connector 101 to potential difference detection circuit 103 is stabilized, CPU 80 reads the outputs of comparators C1 and C2 of potential difference detection circuit 103 ( Step S102).

  The CPU 80 determines whether or not the read value is “L” level, thereby determining whether or not the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 is within a predetermined allowable range. (Step S103).

  Here, the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 exceeds the allowable range, and the outputs from the comparators C1 and C2 are at the “H” level. Therefore, the CPU 80 determines that the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 is outside the allowable range (NO in step S103), and an error indicating that a connection error has occurred on the operation panel 92. A message is displayed (step S105). At this time, the transistor Q1 to which the control signal is input remains in the OFF state, the coil L1 is not excited, and the switches SW1 to SW4 remain cut off. After the error message is displayed, the CPU 80 repeats the above operation until it is determined that the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 is within the allowable range.

  The user who confirmed the error message redoes the chassis grounding of the PC 97. That is, the FG terminal is connected to the ground line that should be connected. As a result, the frame potential of the PC 97 becomes the same as the ground potential.

  After displaying the error message, the CPU 80 waits until a predetermined time has elapsed (step S101). When the predetermined time has elapsed (YES in step S101), CPU 80 reads the outputs of comparators C1 and C2 of potential difference detection circuit 103 (step S102).

  The CPU 80 determines whether or not the read value is “L” level, thereby determining whether or not the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 is within a predetermined allowable range. (Step S103).

  At this time, the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 10 is within an allowable range, and the outputs from the comparators C1 and C2 are at the “L” level. Therefore, CPU 80 determines that the potential difference between the GND of PC 97 and the GND of image forming apparatus 10 is within the allowable range (YES in step S103), and switches SW1 to SW4 for transistor Q1 of potential difference confirmation device 93. A control signal instructing conduction is output (step S104). When the control signal is input, the transistor Q1 is turned on. As a result, the coil L1 is excited and the switches SW1 to SW4 are conducted. When the switches SW1 to SW4 are turned on, the I / F circuit 94 starts transmission / reception of the USB signal to / from the PC 97 and conduction of the GND via the wirings L2 to L9. As a result, the image forming apparatus 10 can communicate with the PC 97.

  The user removes the USB cable from the connection connector 101 after performing predetermined communication between the image forming apparatus 10 and the PC 97. When the USB cable is removed, the connection connector 101 outputs a notification signal indicating that the USB cable is not connected to the CPU 80 of the image forming apparatus 10 via a wiring (not shown). When the notification signal is input, CPU 80 determines that the USB cable has been removed (YES in step S106) and instructs control transistor 93 of potential difference confirmation device 93 to shut off switches SW1 to SW4. Is output (step S107). When the control signal is input, the transistor Q1 is turned off. As a result, the coil L1 is not excited and the switches SW1 to SW4 are cut off.

[Second Embodiment]
An image forming apparatus 120 according to the second embodiment of the present invention has a potential difference confirmation device 122 instead of the potential difference confirmation device 93, and a program for realizing the I / F connection control process described above. Is the same as that of the image forming apparatus 10 according to the first embodiment except that is not stored in the HDD 84. Hereinafter, different configurations will be described.

<Circuit Configuration of Potential Difference Confirmation Device 122>
In the present embodiment, the potential difference confirmation device 122 has the same configuration as the potential difference confirmation device 93 according to the above embodiment, except that the connection destination of both terminals of the coil L1 of the relay 102 is different.

  In relay 102, one terminal of coil L1 is connected in common to the outputs of comparators C1 and C2. The other terminal of the coil L1 is connected to a power supply VCC supplied from the power supply of the image forming apparatus 120. The wiring L5 is not connected to one terminal of the coil L1, but is connected to the GND of the image forming apparatus 120.

  The relay 102 turns on or off the switches SW1 to SW4 based on the common output potential of the comparators C1 and C2. That is, in the relay 102, when the voltage potential applied to one terminal of the coil L1 by the comparators C1 and C2 is “L” level, the coil L1 is excited and the switches SW1 to SW4 are turned on. On the other hand, when the voltage potential applied to one terminal of the coil L1 by the comparators C1 and C2 is “H” level, the coil L1 is not excited and the switches SW1 to SW4 are cut off.

  In this way, the potential difference confirmation device 122 and the I / F circuit 94 are not controlled by the CPU 80, and when there is no potential difference between the GND of the connected device and the GND of the image forming device 120, that is, the ground of the connected device is When it is normal, communication between the image forming apparatus 120 and the connected device is enabled. In addition, when there is a potential difference larger than the allowable range between the GND of the connected device and the GND of the image forming apparatus 120, that is, when the ground of the connected device is abnormal, communication between the image forming apparatus 120 and the connected device is disabled. enable.

<Operation>
Referring to FIG. 8, image forming apparatus 120 operates as follows. Except for the following operations, the operation of the image forming apparatus 120 is the same as the operation of the image forming apparatus 10 according to the first embodiment. In the following operation, it is assumed that the image forming apparatus 120 is in a state immediately after the power is turned on, and the switches SW1 to SW4 of the potential difference confirmation device 122 are in an interrupted state.

  Similarly to the DC power source 95 of the image forming apparatus 120, the DC power source 110 of the PC 97 includes a live (L) side input terminal, a neutral (N) side input terminal, and an FG terminal connected to the chassis of the PC 97 (sometimes above). (Not shown). In the DC power source 110, the live (L) side input terminal is connected to the non-grounded pole side of the AC power source 96. The neutral (N) side input terminal is connected to the ground electrode side of the AC power source 96. The FG terminal is not an earth line to be originally connected, but is erroneously connected to the non-grounding electrode side of the AC power source 96. As a result, the frame potential of the PC 97 is the same as the potential of the L terminal.

  In this state, the user connects the connection connector (not shown) of the PC 97 and the connection connector 101 of the potential difference confirmation device 122 with a USB cable. When the USB cable is connected, the common output of the comparators C 1 and C 2 of the potential difference detection circuit 103 is output to one terminal of the coil L 1 of the relay 102.

  Here, the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 120 exceeds the allowable range, and the potential input to one terminal of the coil L1 (common output of the comparators C1 and C2) is “H” level. is there. Therefore, the coil L1 is not excited and the switches SW1 to SW4 remain cut off.

  A user who has confirmed that communication between the PC 97 and the image forming apparatus 120 is in an incapable state performs grounding of the chassis of the PC 97 again. That is, the FG terminal is connected to the ground line that should be connected. As a result, the frame potential of the PC 97 becomes the same as the ground potential.

  At this time, the potential difference between the GND of the PC 97 and the GND of the image forming apparatus 120 is within an allowable range, and the potential applied from one of the comparators C1 and C2 to the one terminal of the coil L1 is at the “L” level. Therefore, the coil L1 is excited and the switches SW1 to SW4 are conducted. When the switches SW1 to SW4 are turned on, the I / F circuit 94 starts transmission / reception of the USB signal to / from the PC 97 and conduction of the GND via the wirings L2 to L9. As a result, the image forming apparatus 120 can communicate with the PC 97.

  The user removes the USB cable from the connection connector 101 after performing predetermined communication between the image forming apparatus 120 and the PC 97. When the USB cable is removed, the connection connector 101 detects that a specific voltage is not input. Then, a signal for blocking the switches SW1 to SW4 is output to the switches SW1 to SW4 via a wiring (not shown), thereby blocking the switches SW1 to SW4. As a result, the image forming apparatus 120 cannot communicate with the PC 97. In this way, the potential difference confirmation device 122 can turn off the switches SW1 to SW4 without being controlled by the CPU 80 when the USB cable is removed.

<Action and effect>
According to the first and second embodiments, the image forming apparatus 10 (or 120) includes the I / F circuit 94 that transmits and receives signals to and from the PC 97 that is a connected device via the USB cable and the wirings L2 to L9. When the USB cable connected to the PC 97 is detachably connected and the connection connector 101 is connected to the wirings L2 to L9, and the USB cable is connected to the connection connector 101, the USB cable is electrically connected. The potential difference detection circuit 103 that detects the potential difference between the wiring L9 and the wiring L5, and the CPU 80 (or coil L1) that determines whether or not the potential difference detected by the potential difference detection circuit 103 is within a predetermined allowable range. Are provided in the middle of the wirings L2 to L9 that connect the connection connector 101 and the I / F circuit 94, and the wirings L2 to L9 are electrically connected or cut off. A pitch SW1 to SW4, based on the determination result of the CPU 80 (or coil L1), comprising the transistor Q1 to control the conduction or blocking of the wiring L2~L9 by switches SW1 to SW4 (or coil L1), the.

  As described above, in the image forming apparatus 10, the potential difference between the wiring L9 and the wiring L5 is detected, and the connection connector 101 and the I / F circuit 94 are determined based on whether or not the detected potential difference is within a predetermined allowable range. Are connected or interrupted. As a result, when the potential difference is excessive, etc., the connection between the I / F circuit 94 and the PC 97 can be cut off electrically, so that the image forming apparatus can be input by the input of the overvoltage from the PC 97. 10 can be surely and easily prevented from being short-circuit broken.

  Further, according to the first and second embodiments, the transistor Q1 (or coil L1) has a potential difference detected by the potential difference detection circuit 103 by the CPU 80 (or coil L1) deviating from a predetermined allowable range. If it is determined that the wirings L2 to L9 are not conducted, the switches SW1 to SW4 are cut off. As a result, when the potential difference is excessive, the connection between the I / F circuit 94 and the PC 97 can be more reliably interrupted without being connected, so that the image is input by the input of the overvoltage from the PC 97. It is possible to prevent the circuit in the forming apparatus 10 from being short-circuit broken.

  According to the first and second embodiments, the transistor Q1 (or coil L1) has a potential difference detected by the potential difference detection circuit 103 by the CPU 80 (or coil L1) within a predetermined allowable range. Are determined, the wirings L2 to L9 are conducted to the switches SW1 to SW4. As a result, stable signal transmission / reception can be performed without causing a short circuit breakage of the circuit in the image forming apparatus 10 due to the input of an overvoltage from the PC 97.

  According to the first and second embodiments, the transistor Q1 (or the connection connector 101) is connected to the connection connector 101 when the USB cable is not connected (for example, when the power is turned on and the USB cable is connected to the connection connector 101). The wirings L2 to L9 are cut off from the switches SW1 to SW4. Accordingly, it is possible to prevent the wirings L2 to L9 from being conducted before the switching control based on the determination result by the CPU 80 (or the coil L1) is performed. As a result, it is possible to more reliably prevent the circuit in the image forming apparatus 10 from being short-circuited and broken due to the input of the overvoltage from the PC 97. Therefore, the circuit in the image forming apparatus 10 can be reliably protected.

  Further, according to the first embodiment, the potential difference detection circuit 103 detects the potential difference between the wiring L9 and the wiring L5 after a predetermined time has elapsed since the USB cable was connected to the connection connector 101. Thus, the potential difference can be detected after the signal input from the PC 97 is stabilized. As a result, due to the influence of noise and bounce that occurs immediately after the connection of the USB cable, the wirings L2 to L9 are conducted even though the potential difference is excessive, or the wiring L2 even though the potential difference is within the allowable range. It is possible to prevent a malfunction that L9 is blocked. Therefore, it is possible to transmit and receive signals more safely and stably.

  Further, according to the first embodiment, the image forming apparatus 10 further determines that the abnormal state is detected when the CPU 80 determines that the potential difference detected by the potential difference detection circuit 103 is outside a predetermined allowable range. An operation panel 92 for notifying occurrence is included. Thereby, the user of the image forming apparatus 10 can easily know that the wirings L2 to L9 are not conducted. As a result, the user can be prompted to confirm the cause of the lack of conduction. Therefore, the user can quickly remove the cause of the lack of conduction. The notification of the occurrence of an abnormality is not limited to the operation panel 92, and may be, for example, an image forming unit. That is, instead of the operation panel 92, the image forming unit may print out an error message indicating a connection error.

  Further, according to the first and second embodiments, the wiring L9 is the GND of the PC 97, and the wiring L5 is the GND of the image forming apparatus 10. As a result, when the grounding of the PC 97 is abnormal, the wirings L2 to L9 can be cut off. As a result, it is possible to reliably prevent the circuit in the image forming apparatus 10 from being short-circuited and broken by the input of the overvoltage from the PC 97 due to the grounding abnormality.

<Modification>
In the first and second embodiments, when the USB cable is disconnected from the connection connector 101, the switches SW1 to SW4 are cut off. However, the present invention is not limited to such an embodiment. . For example, when a predetermined condition indicating that no signal is transmitted to or received from the PC 97 is satisfied, the switches SW1 to SW4 may be cut off by the transistor Q1 or the like according to the control by the CPU 80. The predetermined condition is, for example, a case where a predetermined time has elapsed without transmission / reception of a signal to / from the PC 97, a case where a predetermined switch is turned off, or the like. As a result, when the power of the PC 97 is turned on / off and the AC power is changed while the wirings L2 to L9 are conducted, an overvoltage is input from the PC 97 and the circuit in the image forming apparatus 10 is short-circuited. Can be prevented. Accordingly, the circuit in the image forming apparatus 10 can be more reliably protected.

  Further, according to the first and second embodiments, the potential difference confirmation device 93 (or 122) is configured integrally with the image forming device 10 (or 120), but the present invention is such an embodiment. It is not limited to. For example, the potential difference confirmation device 93 (or 122) and the image forming apparatus 10 (or 120) may be separate devices.

  According to the first and second embodiments, the connection or removal of the USB cable from the connection connector 101 is determined based on whether or not a specific voltage is input. However, the present invention is not limited to such an embodiment. For example, the connection connector 101 may be provided with a switch that is turned on or off in conjunction with the connection or removal of the USB cable, and the determination may be made based on the on / off of the switch.

  Further, according to the first and second embodiments, two comparators (C1, C2) having different polarities are provided. This is because it is difficult to predict whether the potential difference is positive or negative, and it is necessary to cope with both cases. The number of comparators is not limited to the above embodiment.

  The embodiment disclosed herein is merely an example, and the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated by each claim of the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are included. Including.

10,120 Image forming apparatus 80 CPU
92 Operation panel 94 I / F circuit 97 PC
101 connector 103 potential difference detection circuit L1 coil L2 to L9 wiring Q1 transistor SW1 to SW4 switch

Claims (8)

Transmitting and receiving means for transmitting and receiving signals via the connection device and the first wiring and the second wiring;
A connection means for detachably connecting the first wiring connected to the connection device and connected to the second wiring;
Detecting means for detecting a potential difference between the first wiring and the second wiring when the first wiring is connected to the connection means;
Determination means for determining whether or not the potential difference detected by the detection means is within a predetermined allowable range;
Switching means provided in the middle of the second wiring for connecting the connection means and the transmitting / receiving means, and for conducting or blocking the second wiring;
An image processing apparatus including: a first control unit configured to control conduction or blocking of the second wiring by the switching unit based on a determination result of the determination unit.   The first control means connects the second wiring to the switching means when the determination means determines that the potential difference detected by the detection means is out of a predetermined allowable range. The image processing apparatus according to claim 1, wherein the image processing apparatus is cut off without being conducted.   The first control unit conducts the second wiring to the switching unit when the determination unit determines that the potential difference detected by the detection unit is within a predetermined allowable range. The image processing apparatus according to claim 1, wherein:   The image processing apparatus further includes a second control unit that causes the switching unit to block the second wiring when the first wiring is not connected to the connection unit. The image processing apparatus according to claim 3.   The detection unit detects a potential difference between the first wiring and the second wiring after a predetermined time has elapsed since the connection of the first wiring to the connection unit. Item 5. The image processing device according to any one of Items 4 to 5.   The image processing apparatus further includes notification means for notifying the occurrence of an abnormality when the determination means determines that the potential difference detected by the detection means is outside a predetermined allowable range. The image processing apparatus according to any one of claims 1 to 5.   The image processing apparatus is further configured to cause the switching unit to block the second wiring when a predetermined condition indicating that transmission / reception of a signal to / from the connected device is not performed is satisfied. The image processing apparatus according to claim 1, comprising a control unit.   The image processing apparatus according to claim 1, wherein the first wiring is a GND of the connection device, and the second wiring is a GND of the image processing apparatus.

Images