Image forming apparatus

Abstract

To provide an image forming apparatus capable of releasing a surge to a ground part even when the surge is input from a body electrode of an apparatus body without arranging a surge countermeasure component in a signal line leading to the body electrode of the apparatus body and a control part.SOLUTION: The printer 1 includes a signal line ground switching circuit 111 controlled by the ASIC81. The cartridge terminals CIC _ Y and the like on the ASIC81 are connected to the main body electrodes 87 via the signal line 105. The side ASIC81 performs transmission and reception of a signal with the memory of the cartridge side IC64 via the signal line 105 when the drum unit 11 is mounted in the main assembly 10. The signal line ground switching circuit 111Y and the like switch whether or not to connect the signal line ASIC81 and the like to the ground portion GND based on signals from the switching terminals SI1 of 105Y.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present application relates to a technique for preventing surges in an image forming apparatus. [Background technology]

[0002] Conventionally, a drum unit that is detachable from the main body of an image forming apparatus is known, which includes a photosensitive drum and an IC chip (see Patent Document 1). The electrical contact surface (corresponding to the contact terminal) of the drum unit is in contact with the main body electrode of the main body when the drum unit is attached to the main body. In conventional image forming devices, to prevent surges from reaching the main electrodes of the device body when the drum unit is removed from the device body, a surge protection component consisting of a capacitor is placed on the signal line leading from the main electrodes of the device body to the control unit, so that even if a surge is input from the main electrodes of the device body, the surge can be dissipated to the ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-028345 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when surge protection components are placed on the signal line between the main electrode of the device main body and the control unit as a countermeasure against surges input from the main electrode of the device main body, the signal sent from the drum unit to the control unit when the drum unit is attached to the device main body is dulled by the surge protection components, resulting in the problem that it takes time for the control unit to detect the signal.

[0005] The present application has been proposed in view of the above-mentioned problems, and aims to provide an image forming apparatus that can dissipate a surge to the ground section even if a surge is input from the main electrode of the apparatus main body, without placing a surge protection component on the signal line leading from the main electrode of the apparatus main body to the control section. [Means for solving the problem]

[0006] In order to achieve the above object, an image forming apparatus according to a first aspect of the present application includes: an apparatus main body; a first toner cartridge having a first photosensitive drum, a first developing roller for carrying a first toner and supplying the first toner to the first photosensitive drum, and a first cartridge control circuit; a drum unit that is attachable to the apparatus main body and has a drum unit contact substrate having a first contact terminal electrically connected to the first cartridge control circuit; a main electrode substrate having a first main body electrode, where the first contact terminal and the first main body electrode come into contact when the drum unit is attached to the apparatus main body; a control unit that is electrically connected to the first main body electrode by a first signal line, where the control unit transmits and receives signals to and from the first cartridge control circuit via the first signal line when the drum unit is attached to the apparatus main body; a ground unit that is electrically grounded; and a first signal line ground switching circuit that switches whether to connect the first signal line to the ground unit based on control by the control unit.

[0007] According to this, when the drum unit is detached from the device main body, the control unit connects the first signal line to the ground portion, and surges input via the first main body electrode can be discharged to the ground portion. This protects the control unit from surges and the like. Furthermore, when the drum unit is attached to the device main body, the control unit can disconnect the ground portion from the first signal line and connect the first main body electrode to the control unit via the first signal line. Because the drum unit and control unit can be connected without using a surge protection component such as a capacitor, the signal input from the drum unit to the control unit can be prevented from becoming corrupted.

[0008] In order to achieve the above object, an image forming apparatus according to a second aspect of the present application includes: an apparatus main body; a first toner cartridge having a first photosensitive drum and a first developing roller for carrying a first toner and supplying the first toner to the first photosensitive drum; an intermediate board on which a sensor is disposed; and a drum unit contact board having a sensor contact terminal electrically connected to the sensor, the drum unit being attachable to the apparatus main body; a main electrode board having a sensor main electrode, the sensor contact terminal and the sensor main electrode board being in contact with each other when the drum unit is attached to the apparatus main body; a control unit electrically connected to the sensor main electrode by a sensor signal line, the control unit receiving a signal from the sensor via the sensor signal line when the drum unit is attached to the apparatus main body; an electrically grounded ground unit; and a sensor signal line ground switching circuit that switches whether to connect the sensor signal line to the ground unit based on the control of the control unit.

[0009] According to this, when the drum unit is removed from the device main body, the control unit connects the sensor signal line to the ground portion, and surges input via the sensor main body electrode can be discharged to the ground portion, thereby protecting the control unit from surges and the like. Furthermore, when the drum unit is attached to the device main body, the control unit can disconnect the ground portion from the sensor signal line and connect the sensor main body electrode to the control unit via the sensor signal line. Because the sensor and control unit can be connected without using a surge protection component such as a capacitor, the signal input from the sensor to the control unit can be prevented from becoming distorted.

[0010] The drum unit may further include a relay board electrically connecting the first contact terminal and the first cartridge control circuit, the relay board having a sensor disposed thereon, the drum unit contact board further including a sensor contact terminal electrically connected to the sensor, the main body electrode board further including a sensor main body electrode, the sensor contact terminal and the sensor main body electrode being in contact with each other when the drum unit is attached to the device main body, and the control unit may further include a sensor signal line ground switching circuit electrically connected to the sensor main body electrode by a sensor signal line, receiving a detection result from the sensor via the sensor signal line when the drum unit is attached to the device main body, and switching whether or not to connect the sensor signal line to the ground section based on the control of the control unit.

[0011] With this, when the drum unit is removed, the sensor signal line and the ground can be connected, and surges input via the sensor main body electrode can be discharged to the ground. Also, when the drum unit is installed, the ground can be disconnected from the sensor signal line, preventing distortion of the signal input from the sensor to the control unit.

[0012] Furthermore, the control unit may have a switching terminal that is electrically connected to the first signal line ground switching circuit and the sensor signal line ground switching circuit, and the first signal line ground switching circuit connects the first signal line to the ground section by a first signal input from the switching terminal, and the sensor signal line ground switching circuit connects the sensor signal line to the ground section by the first signal input from the switching terminal.

[0013] With this, the control unit can control the first signal line ground switching circuit and the sensor signal line ground switching circuit by a signal output from the switching terminal, and can connect the first signal line to the ground section and the sensor signal line to the ground section by outputting the first signal from the switching terminal.

[0014] The drum unit further includes a second toner cartridge having a second photosensitive drum, a second developing roller that carries a second toner and supplies the second toner to the second photosensitive drum, and a second cartridge control circuit; a third toner cartridge having a third photosensitive drum, a third developing roller that carries a third toner and supplies the third toner to the third photosensitive drum, and a third cartridge control circuit; and a fourth toner cartridge having a fourth photosensitive drum, a fourth developing roller that carries a fourth toner and supplies the fourth toner to the fourth photosensitive drum, and a fourth cartridge control circuit. The drum unit contact substrate further includes a second contact terminal electrically connected to the second cartridge control circuit, a third contact terminal electrically connected to the third cartridge control circuit, and a fourth contact terminal electrically connected to the fourth cartridge control circuit. The main body electrode substrate further includes a second main body electrode, a third main body electrode, and a fourth main body electrode. the second contact terminal and the second body electrode are in contact, the third contact terminal and the third body electrode are in contact, and the fourth contact terminal and the fourth body electrode are in contact, and the control unit is further electrically connected by the second body electrode and the second signal line, the third body electrode and the third signal line, and the fourth body electrode and the fourth signal line, respectively, and when the drum unit is attached to the apparatus main body, transmits and receives signals to and from the second cartridge control circuit, the third cartridge control circuit, and the fourth cartridge control circuit via the second signal line, the third signal line, and the fourth signal line, respectively, and may include a second signal line ground switching circuit that switches whether to connect the second signal line to the ground section based on control of the control unit, a third signal line ground switching circuit that switches whether to connect the third signal line to the ground section based on control of the control unit, and a fourth signal line ground switching circuit that switches whether to connect the fourth signal line to the ground section based on control of the control unit.

[0015] With this, when the drum unit is removed from the device main body, the control unit can connect each of the first to fourth signal lines to the ground portion and discharge surges input via the first to fourth main body electrodes to the ground portion. Also, when the drum unit is attached to the device main body, the control unit can disconnect the ground portion from each of the first to fourth signal lines to prevent distortion of signals input from the drum unit to the control unit via each signal line.

[0016] Furthermore, the control unit may have a switching terminal, and the switching terminal is electrically connected to the first signal line ground switching circuit, the second signal line ground switching circuit, the third signal line ground switching circuit, and the fourth signal line ground switching circuit, respectively, the first signal line ground switching circuit connects the first signal line to the ground section by a first signal input from the switching terminal, the second signal line ground switching circuit connects the second signal line to the ground section by the first signal input from the switching terminal, the third signal line ground switching circuit connects the third signal line to the ground section by the first signal input from the switching terminal, and the fourth signal line ground switching circuit connects the fourth signal line to the ground section by the first signal input from the switching terminal.

[0017] With this, the control unit can collectively control the first to fourth signal line ground switching circuits by outputting the first signal from the switching terminal, and can connect the four signal lines to the ground unit. The four signal lines can be collectively switched using the same signal.

[0018] Furthermore, the first cartridge control circuit, the second cartridge control circuit, the third cartridge control circuit, and the fourth cartridge control circuit each have an open collector circuit, and further include a first pull-up resistor connected to the first signal line, a second pull-up resistor connected to the second signal line, a third pull-up resistor connected to the third signal line, a fourth pull-up resistor connected to the fourth signal line, a pull-up power supply, and a pull-up voltage switching circuit that switches, in response to a signal from the control unit, whether or not a pull-up voltage is applied from the pull-up power supply to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor, and when the control unit outputs a first signal from the switching terminal, the pull-up voltage switching circuit does not apply a pull-up voltage to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor, and The configuration may also be such that, when a ground switching circuit connects the first signal line to the ground section, the second signal line ground switching circuit connects the second signal line to the ground section, the third signal line ground switching circuit connects the third signal line to the ground section, and the fourth signal line ground switching circuit connects the fourth signal line to the ground section, and the control unit outputs a second signal different from the first signal from the switching terminal, the pull-up voltage switching circuit applies a pull-up voltage to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor, the first signal line ground switching circuit disconnects the first signal line from the ground section, the second signal line ground switching circuit disconnects the second signal line from the ground section, the third signal line ground switching circuit disconnects the third signal line from the ground section, and the fourth signal line ground switching circuit disconnects the fourth signal line from the ground section.

[0019] This allows the pull-up voltage switching circuit and the first to fourth signal line ground switching circuits to be controlled by the same signal (first signal, second signal).When signal transmission / reception via the first to fourth signal lines is not performed and pull-up voltages are not applied to the first to fourth pull-up resistors from the pull-up power supply, the control unit can output the first signal to control the first to fourth signal line ground switching circuits to connect the first to fourth signal lines to the ground unit. Furthermore, when a pull-up voltage is applied from a pull-up power supply to the first to fourth pull-up resistors to transmit and receive signals via the first to fourth signal lines, the first to fourth signal line ground switching circuits can be controlled to disconnect the first to fourth signal lines from the ground section, thereby enabling the pull-up voltage switching circuit and the first to fourth signal line ground switching circuits to be controlled in synchronization using the same signal.

[0020] The device main body may further include an opening for removing the drum unit, a cover for opening and closing the opening, and a cover sensor for detecting whether the cover is open or closed, and the control unit may be configured to control the first signal line ground switching circuit to connect the first signal line to the ground unit when it detects that the cover is open based on a signal from the cover sensor.

[0021] This allows the first signal line to be connected to the ground when the cover is opened and the drum unit is removed. If a user inserts their hand into the opening and touches the first body electrode, generating static electricity and causing a surge, the surge can be diverted to the ground.

[0022] Furthermore, the sensor may be a temperature detection sensor that outputs a signal corresponding to the temperature inside the image forming apparatus, and the control unit may be configured to control the sensor signal line ground switching circuit to connect the sensor signal line to the ground unit when the temperature cannot be detected based on the signal from the temperature detection sensor.

[0023] According to this, if the temperature cannot be detected based on the signal from the temperature detection sensor, it is possible that the temperature detection sensor has been removed. When the temperature detection sensor is removed, no signal is input from the temperature detection sensor via the sensor signal line. Therefore, by connecting the sensor signal line to the ground based on the fact that the temperature cannot be detected, if the temperature detection sensor is removed and the sensor main body electrode becomes open, the control unit can be protected from a surge input from the sensor main body electrode.

[0024] Furthermore, the sensor may be a temperature detection sensor that outputs a signal corresponding to the temperature inside the image forming apparatus, and when the temperature cannot be detected based on the signal from the temperature detection sensor, the control unit may control the first signal line ground switching circuit to connect the first signal line to the ground section, and may also control the sensor signal line ground switching circuit to connect the sensor signal line to the ground section.

[0025] With this configuration, when the drum unit and the temperature detection sensor are removed, the first signal line ground switching circuit is controlled to connect the first signal line to the ground, and the sensor signal line ground switching circuit is controlled to connect the sensor signal line to the ground, thereby more reliably protecting the control unit from surges.

[0026] The first signal line ground switching circuit may also be configured to include a first semiconductor transistor and a first resistor, an output terminal of the first semiconductor transistor connected to the ground section, a control terminal of the first semiconductor transistor connected to the control section via the first resistor, and an input terminal of the first semiconductor transistor connected to the first signal line.

[0027] With this, the control unit can switch the first semiconductor transistor on and off by changing the signal level of the signal output to the control terminal of the first transistor, and switch the connection between the first signal line and the ground unit.

[0028] In addition, the first cartridge control circuit may have a cartridge memory that stores information related to the first toner cartridge, and the control unit may control the first signal line ground switching circuit to receive the information related to the first toner cartridge from the cartridge memory via the first signal line while the first signal line and the ground unit are disconnected.

[0029] This allows the first signal line to be disconnected from the ground when reading information related to the first toner cartridge from the cartridge memory of the first cartridge control circuit, thereby enabling accurate detection of signals from the cartridge memory.

[0030] Furthermore, the image forming apparatus may further include a fan, and the control unit may control the sensor signal line ground switching circuit to detect the temperature inside the image forming apparatus based on a signal from the temperature detection sensor while the sensor signal line is disconnected from the ground unit, and control the fan based on the detected temperature.

[0031] This allows the sensor signal line to be disconnected from the ground when detecting temperature based on a signal from the temperature detection sensor. By disconnecting the sensor signal line from the ground, the signal from the temperature detection sensor can be detected with high accuracy. This allows for accurate temperature-based fan control. [Effects of the Invention]

[0032] According to the image forming device of the present application, even if a surge is input from the main electrode of the device main body, the surge can be dissipated to the ground section without placing a surge protection component on the signal line leading from the main electrode of the device main body to the control section. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a color laser printer according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram of the control configuration of the color laser printer according to the first embodiment. [Figure 3] FIG. 2 is a perspective view showing the main body connector according to the first embodiment. [Figure 4] FIG. 2 is a perspective view showing the drum unit according to the first embodiment. [Figure 5] FIG. 2 is a perspective view showing a first connector, a drum relay board, and a flat cable according to the first embodiment. [Figure 6] FIG. 2 is a block diagram showing a connection configuration between the apparatus main body and the drum unit according to the first embodiment. [Figure 7] FIG. 10 is a block diagram showing the connection configuration of a main board, a drum unit relay board, and a toner cartridge provided in a printer of a comparative example. [Figure 8] FIG. 2 is a block diagram showing the connection configuration of a main board, a drum unit relay board, and a toner cartridge according to the first embodiment. [Figure 9] FIG. 2 is a block diagram showing the connection configuration of a main board, a drum unit relay board, and a toner cartridge according to the first embodiment. [Figure 10] 4 is a graph showing analog signals (voltages) in a comparative example and the first embodiment. [Figure 11] FIG. 10 is a diagram showing the flow of signals when the drum unit according to the first embodiment is not removed. [Figure 12] FIG. 10 is a diagram showing a state in which a surge is input when the drum unit according to the first embodiment is removed. [Figure 13] 10A and 10B are diagrams illustrating the connection configuration of a main board, a drum unit relay board, and a toner cartridge according to a second embodiment. [Figure 14] 10A and 10B are diagrams illustrating a connection configuration of a main board, a drum unit relay board, and a toner cartridge according to a third embodiment. [Figure 15] 10A and 10B are diagrams illustrating a connection configuration of a main board, a drum unit relay board, and a toner cartridge according to a third embodiment. [Figure 16]10A and 10B are diagrams illustrating a connection configuration of a main board, a drum unit relay board, and a toner cartridge according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0034] (First embodiment) A color laser printer according to a first embodiment, which is an embodiment of an image forming apparatus according to the present invention, will be described below with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view of a color laser printer (hereinafter simply referred to as the "printer") 1 according to the first embodiment, viewed from the right side. FIG. 2 is a block diagram of the control configuration of the printer 1. As shown in FIGS. 1 and 2, the printer 1 includes a main body 10 and a drum unit 11. The printer 1 is an image forming apparatus capable of forming a color image on a sheet S by electrophotography. In the following description, the side of the main body 10 on which a front cover 13 is provided is defined as the front (front) of the printer 1, as shown in FIG. 1, and the front-rear, left-right, and up-down directions will be defined based on the direction as viewed from the front. That is, the left side in FIG. 1 will be referred to as the "front," the right side as the "rear," the upper side as the "upper," the lower side as the "lower," the near side as the "right," and the far side as the "left."

[0035] The device main body 10 includes a sheet supply unit 21, an image forming unit 22, a main body connector 23, a high-voltage power supply board 25 (see FIG. 2), a main board 26 (see FIG. 2), an intermediate discharge roller 27, a discharge roller 28, a low-voltage power supply board 29, a fixing fan 31, a low-pressure fan 32, and a charging fan 33. The device main body 10 is box-shaped and houses the sheet supply unit 21, the image forming unit 22, and the like. The device main body 10 includes an access opening 10A for removing the drum unit 11 and a front cover 13 for opening and closing the access opening 10A. The access opening 10A is provided on the front of the device main body 10 and is a hole that penetrates the device main body 10 in the front-rear direction. The front cover 13 is held by the device main body 10 so as to be rotatable around its lower end and can rotate between a closed position indicated by a solid line and an open position indicated by a two-dot chain line (phantom line). The closed position is a position where the outlet 10A is closed by the front cover 13. The open position is a position where the outlet 10A is open.

[0036] The sheet supply unit 21 includes a sheet tray 35 and a sheet supply mechanism 36. The sheet tray 35 stores sheets S stacked vertically. The sheets S are, for example, standard-sized paper such as A4 size. The sheets S are not limited to paper media such as plain paper or cardboard, and may be other recording media such as overhead projector film. The sheet supply mechanism 36 includes a pickup roller 41, a separation roller 43, a separation pad 44, a conveying roller 45, and a registration roller 46. The pickup roller 41, the separation roller 43, the conveying roller 45, and the registration roller 46 are held by the device main body 10 so as to be rotatable about rotation axes parallel to the left-right direction, and rotate in response to the drive of a main motor (not shown) provided within the device main body 10.

[0037] Pickup roller 41 feeds out sheet S from sheet tray 35. The sheet S fed out by pickup roller 41 is transported along transport path P shown in FIG. 1 to image forming unit 22, and is discharged from image forming unit 22 to discharge tray 15 provided on the top surface of apparatus body 10. Separation roller 43 and separation pad 44 separate sheet S fed out by pickup roller 41 into a single sheet. Transport roller 45 and registration roller 46 transport sheet S to image forming unit 22.

[0038] The image forming section 22 has a laser unit 51, a transfer unit 52, and a fixing device 53. The laser unit 51 is provided in an upper portion of the apparatus main body 10 and has a light-emitting unit that emits laser light, a polygon mirror that polarizes the laser light emitted from the light-emitting unit, and the like. As shown by the dashed-dotted line in FIG. 1, the laser unit 51 irradiates a beam polarized by the polygon mirror toward the photosensitive drum 55 of the drum unit 11, thereby exposing the photosensitive drum 55. The laser unit 51 irradiates the beam to form an electrostatic latent image based on image data on the surface of the photosensitive drum 55.

[0039] The drum unit 11 is detachably attached to the image forming unit 22. The drum unit 11 is detachable from the image forming unit 22 through the access opening 10A when the front cover 13 is in the open position shown by the phantom lines in FIG. 1. The drum unit 11 has a first connector C1, four second connectors C2Y, C2M, C2C, and C2K, four photosensitive drums 55Y, 55M, 55C, and 55K, and four chargers 57. A housing section 10B that houses the drum unit 11 is provided within the device main body 10.

[0040] The main body connector 23 is provided, for example, at a position at the rear and upper part of the storage section 10B. The main body connector 23 is electrically connected to the first connector C1 of the drum unit 11 when the drum unit 11 is attached to the image forming section 22. When the drum unit 11 is removed from the apparatus main body 10, the main body connector 23 is located at the upper part of the back side of the storage section 10B, exposing a main body electrode 87 (described later).

[0041] Four toner cartridges 60Y, 60M, 60C, and 60K can be detachably attached to the drum unit 11. The toner cartridges 60Y, 60M, 60C, and 60K correspond to four colors, yellow (Y), magenta (M), cyan (C), and black (K), respectively, and are attached to the drum unit 11 in that order from the front to the rear of the printer 1. Note that the four toner cartridges 60Y, 60M, 60C, and 60K differ in toner color but otherwise have the same configuration. For this reason, in the following description, the four toner cartridges 60Y, 60M, 60C, and 60K corresponding to each color will be collectively referred to as toner cartridge 60. Similarly to the toner cartridge 60, other components corresponding to the colors yellow, magenta, cyan, and black (such as the photosensitive drum 55, the second connector C2, and the cartridge IC board 63) may be described individually with the letters Y, M, C, and K added after their reference numerals, or may be described collectively without reference numerals.

[0042] The toner cartridge 60 includes a developing roller 61, a cartridge connector 62, and a cartridge IC board 63. The toner cartridges 60Y, 60M, 60C, and 60K contain toner of each color (Y, M, C, and K), and supply the toner to the photosensitive drums 55Y, 55M, 55C, and 55K of each color by rotating the developing roller 61. The four toner cartridges 60 are examples of the first to fourth toner cartridges of the present application, and the toner contained in each of the four toner cartridges 60 are examples of the first to fourth toners of the present application. The cartridge connector 62 is electrically connected to the second connector C2 when the toner cartridge 60 is attached to the drum unit 11. The toner cartridges 60 of each color are connected to the second connectors C2Y, C2M, C2C, and C2K corresponding to the respective colors via the cartridge connector 62. Each of the four second connectors C2Y, C2M, C2C, and C2K is electrically connected to the first connector C1. Therefore, the four toner cartridges 60 are connected to the apparatus main body 10 via the main body connector 23. A cartridge connector 62 and a cartridge IC 64 (see FIG. 6) are mounted on the cartridge IC board 63 of the toner cartridge 60. The cartridge IC 64 of the cartridge IC board 63 is electrically connected to a main board 26 (see FIG. 2) of the apparatus main body 10 (described later) via the cartridge connector 62 and the second connector C2.

[0043] The cartridge IC 64 is, for example, an IC chip, and is equipped with a memory (an example of the cartridge memory of the present application). Information about the toner cartridges 60 of each color is stored in the memory of the cartridge IC 64. The information about the toner cartridges 60 includes, for example, information about the developing roller 61 and information about the lifespan of the toner cartridge 60. The information about the developing roller 61 includes, for example, the manufacturing date and manufacturing location of the developing roller 61, and the maximum number of usable rotations. The information about the lifespan of the toner cartridge 60 includes, for example, the cumulative number of rotations of the developing roller 61 and the cumulative number of pages printed using the toner cartridge 60. The main board 26 can communicate with the cartridge IC 64 when the cartridge connector 62 and the second connector C2 are connected, and the first connector C1 and the main body connector 23 are connected.

[0044] The photosensitive drum 55 is a cylindrical member extending in the left-right direction and is held by the device main body 10 so as to be rotatable about a rotation axis parallel to the left-right direction. Four chargers 57 are provided corresponding to each color. The chargers 57 are provided behind and above the photosensitive drum 55 and are, for example, scorotron-type chargers having a charging wire and a grid. The chargers 57 are connected to the high-voltage power supply board 25 (see FIG. 2), and a voltage is applied to the charging wire from the high-voltage power supply board 25. The main board 26 (see FIG. 2) is connected to the high-voltage power supply board 25 and controls the high-voltage power supply board 25 to change the magnitude of the voltage applied from the high-voltage power supply board 25 to the charging wire of the charger 57. The charger 57 generates a corona discharge by applying a voltage to the charging wire from the high-voltage power supply board 25, thereby uniformly positively charging the surface of the photosensitive drum 55. Note that the device that charges the photosensitive drum 55 is not limited to a scorotron-type charger, and other devices, such as a roller-type charging roller, may also be used. Furthermore, the polarity with which the photosensitive drum 55 is charged is not limited to positive charging, and it may be negative charging.

[0045] The transfer unit 52 is disposed between the sheet tray 35 and the drum unit 11 in the vertical direction, and includes a drive roller 71, a driven roller 72, an endless transfer belt 73, and four transfer rollers 74. The transfer belt 73 is stretched between the drive roller 71 and the driven roller 72, and its upper surface is in contact with the photosensitive drum 55. The four transfer rollers 74 are provided corresponding to each color, and are disposed inside the transfer belt 73 so as to sandwich the transfer belt 73 between themselves and the corresponding photosensitive drum 55. The photosensitive drum 55 is rotated by the rotational driving force transmitted from the main motor, and conveys the sheet S conveyed along the conveyance path P by sandwiching it between itself and the transfer rollers 74.

[0046] In response to a printing operation, the photosensitive drum 55 is positively charged by the charger 57 and then exposed by the laser unit 51, forming an electrostatic latent image. The developing roller 61 supplies toner to the photosensitive drum 55, developing the electrostatic latent image formed on the surface of the photosensitive drum 55 and forming a toner image. The toner carried on the developing roller 61 moves to the electrostatic latent image on the photosensitive drum 55 due to the potential difference between the developing roller 61 and the electrostatic latent image formed on the photosensitive drum 55, forming a toner image. This toner image is transferred to the sheet S by applying a negative voltage to the transfer roller 74 while the photosensitive drum 55 is in contact with the sheet S on the transport path P.

[0047] The fixing device 53 is provided behind the transfer unit 52 within the apparatus main body 10. The sheet S onto which the toner image has been transferred is transported to the fixing device 53. The fixing device 53 has a heating roller 77 that heats the sheet S with a heater, and a pressure roller 78 that sandwiches the sheet S between the heating roller 77. The pressure roller 78 is rotated by the rotational driving force of the main motor, and presses the sheet S against the heating roller 77, thereby pressurizing the sheet S. In this way, the fixing device 53 fixes the toner image onto the sheet S. The intermediate discharge rollers 27 and discharge rollers 28 discharge the sheet S onto which the toner image has been fixed onto the discharge tray 15.

[0048] The low-voltage power supply board 29 may also be equipped with, for example, an AC / DC converter, which converts AC voltage supplied from an AC power supply into DC voltage. The low-voltage power supply board 29 may also be equipped with, for example, a DC / DC converter, which generates a low DC voltage (3.3 V, 5 V, 24 V, etc.) and supplies the generated DC voltage to various parts of the printer 1, such as the image forming unit 22, main board 26, fixing fan 31, low-voltage fan 32, and charging fan 33.

[0049] Fixing fan 31 is provided, for example, at a position behind laser unit 51, and when driven, exhausts air inside apparatus main body 10 to the outside of apparatus main body 10. Low-pressure fan 32 is provided, for example, near low-voltage power supply board 29, and when driven, air-cools low-voltage power supply board 29. Charging fan 33 is provided, for example, at a position close to toner cartridge 60, and when driven, sucks in toner around charger 57 to prevent toner from adhering to charger 57.

[0050] The main board 26 is a control board that controls the printer 1 overall, and as shown in FIG. 2, has an ASIC 81, a ROM 82, a RAM 83, and an EEPROM 84. The ASIC 81 is an Application Specific Integrated Circuit and has a CPU 81A. The ASIC 81 is an example of the control unit of the present application. Note that the control unit of the present application is not limited to an ASIC, and may be another device such as an SoC (System on a Chip).

[0051] The ROM 82 stores various control programs for controlling the printer 1, various setting information, and the like. The RAM 83 is, for example, a DRAM, and is used as a work area for reading out the various control programs and as a storage area for temporarily storing image data based on a print job. The EEPROM 84 is used to store setting values ​​used in various processes. The ASIC 81 is electrically connected to the fixing device 53, high-voltage power supply board 25, low-voltage power supply board 29, charging fan 33, low-pressure fan 32, and fixing fan 31. The CPU 81A executes processing in accordance with the control programs read from the ROM 82 and signals input from various sensors such as the internal temperature sensor 98, and controls each part of the printer 1 while storing the processing results in the RAM 83 and EEPROM 84.

[0052] 2 is an example. For example, the printer 1 may have a non-volatile storage device such as a flash memory, HDD, or SSD. The storage medium for storing the control program may be an external storage medium such as a USB memory, or may be a storage medium such as a CD-ROM or DVD-ROM.

[0053] The main connector 23 is also provided with a main electrode board 85. The ASIC 81 is electrically connected to the main electrode board 85. A plurality of main electrodes 87 shown in FIG. 3 are mounted on the main electrode board 85. As shown in FIG. 3, the main connector 23 holds the main electrode board 85 (see FIG. 2) with the main electrodes 87 exposed. The plurality of main electrodes 87 are, for example, pogo pins, and are attached to the main connector 23 aligned in the left-right direction. The plurality of main electrodes 87 protrude, for example, diagonally downward toward the front side. The main electrodes of the present application are not limited to pogo pins, and may be other terminals or electrodes.

[0054] 4, the drum unit 11 includes a drum frame 91, four photosensitive drums 55, four chargers 57, a drum unit relay board 92, a first connector C1, and four second connectors C2Y, C2M, C2C, and C2K. The four photosensitive drums 55, the four chargers 57, the drum unit relay board 92, the first connector C1, and the four second connectors C2Y, C2M, C2C, and C2K are attached to the drum frame 91. The drum frame 91 is box-shaped with an opening on the top, and the four photosensitive drums 55 and the four chargers 57 are attached to the bottom.

[0055] A first connector C1 and a drum unit relay board 92 are attached to a rear frame 91A provided on the rear side of the drum frame 91. The first connector C1 is attached to the right end of the rear frame 91A. A drum unit contact board 93 (see FIG. 2) is attached to the first connector C1. A plurality of contact terminals 95 shown in FIG. 5 are mounted on the drum unit contact board 93. As shown in FIG. 5, each of the plurality of contact terminals 95 is, for example, a flat electrode. The first connector C1 holds the drum unit contact board 93 with the contact surfaces of the plurality of contact terminals 95 facing diagonally upward toward the rear side. When the drum unit 11 is attached to the device main body 10, the plurality of contact terminals 95 come into contact with and are electrically connected to main body electrodes 87 (see FIG. 3) of the device main body 10. When the drum unit 11 is attached to the device main body 10, the main board 26 is electrically connected to the drum unit relay board 92 and the cartridge IC boards 63 of the four toner cartridges 60 via the main body electrode board 85 and the drum unit contact board 93. Note that the contact terminals of the present application are not limited to flat electrodes, and may be, for example, electrodes shaped to allow the main body electrodes 87 to be inserted therein.

[0056] As shown in FIGS. 5 and 6, a third connector C3 is mounted on the drum unit contact board 93. The third connector C3 is electrically connected to each of the contact terminals 95. The drum unit relay board 92 is attached to the left end of the rear frame 91A shown in FIG. 4. The drum unit relay board 92 is mounted with a fourth connector C4, two fifth connectors C5A and C5B, an EEPROM 97, and an internal temperature sensor 98. The fourth connector C4 is electrically connected to the third connector C3 of the drum unit contact board 93 via a flat cable 99. The flat cable 99 is, for example, a flexible flat cable (FFC). The third connector C3 and the fourth connector C4 may be connected by wiring other than a flexible flat cable. The non-volatile memory included in the drum unit relay board 92 is not limited to the EEPROM 97, and may be a flash memory.

[0057] As shown in FIG. 4, four second connectors C2 are attached to the left frame 91B on the left side of the drum frame 91. The four second connectors C2 are attached to the upper part of the left frame 91B, facing rearward. For example, each of the four second connectors C2 is provided with a pogo pin that contacts and electrically connects with a connection terminal of the cartridge connector 62. The second connectors C2Y, C2M, C2C, and C2K are arranged in this order from front to rear. The drum unit 11 can accommodate four toner cartridges 60 through an opening at the top. When the four toner cartridges 60 are installed in the drum unit 11, the second connectors C2 are connected to the cartridge connector 62 and the toner cartridges 60 are arranged in a line in the front-to-rear direction.

[0058] As shown in FIGS. 5 and 6, the fifth connector C5A is electrically connected to the second connector C2Y via a cable 101Y. The ASIC 81 on the main board 26 is connected to the cartridge IC board 63Y (cartridge IC 64Y) of the toner cartridge 60Y via the main connector 23, the first connector C1, the third connector C3, the fourth connector C4, the fifth connector C5A, and the second connector C2Y. The ASIC 81 reads data from and writes data to the memory of the cartridge IC 64Y. Similarly, the fifth connector C5A is connected to the second connector C2M via a cable 101M. The fifth connector C5B is connected to the second connector C2C via a cable 101C. The fifth connector C5B is also connected to the second connector C2K via a cable 101K.

[0059] The EEPROM 97 also stores information about the drum units 11 for each color. The information about the drum units 11 includes, for example, information about the photosensitive drums 55 and information about the lifespan of the drum units 11. The information about the photosensitive drums 55 includes, for example, the manufacturing date and manufacturing location of the photosensitive drums 55, and the maximum number of rotations that can be performed. The information about the lifespan of the drum units 11 includes, for example, the cumulative number of rotations of the photosensitive drums 55 and the cumulative number of pages printed using the photosensitive drums 55. The EEPROM 97 is electrically connected to the fourth connector C4. The ASIC 81 can communicate with the EEPROM 97 when the first connector C1 and the main body connector 23 are electrically connected when the drum unit 11 is attached to the device main body 10. The ASIC 81 reads data from and writes data to the EEPROM 97 via the main body connector 23.

[0060] The internal temperature sensor 98 is, for example, a thermistor. One end of the internal temperature sensor 98 is connected to the fourth connector C4 and electrically connected to the ASIC 81 on the main board 26 via the fourth connector C4. The internal temperature sensor 98 outputs a signal corresponding to the temperature inside the device main body 10 to the ASIC 81. The other end of the internal temperature sensor 98 is connected to the ground GND of the drum unit relay board 92. The ground GND of the drum unit relay board 92 is connected to the fourth connector C4 via a ground wire (not shown), for example, and is connected to the ground GND of the main board 26 via the fourth connector C4. The ground GND of the main board 26 is electrically grounded and serves as the reference potential of the printer 1. The internal temperature sensor 98 is an example of a temperature detection sensor of the present application. Note that the temperature detection sensor of the present application is not limited to a thermistor, and may be any other sensor capable of detecting temperature, such as a sensor using a thermocouple. Furthermore, the sensor of the present application is not limited to a sensor that detects temperature, but may be another sensor such as a sensor that detects the presence or absence of paper or a sensor that detects received light. The contact terminal 95 connected to the internal temperature sensor 98 is an example of the sensor contact terminal of the present application. The main body electrode 87 connected to the internal temperature sensor 98 is an example of the sensor main body electrode of the present application.

[0061] The ASIC 81 controls the charging fan 33, the low-pressure fan 32, and the fixing fan 31 based on the temperature detected by the internal temperature sensor 98. The printer 1 may be provided with multiple temperature detection sensors used to control the charging fan 33, the low-pressure fan 32, and the fixing fan 31. The ASIC 81 may also control at least one of the charging fan 33, the low-pressure fan 32, and the fixing fan 31 based on the temperature detected by the internal temperature sensor 98 provided on the drum unit relay board 92. The printer 1 may also be configured to include at least one of the charging fan 33, the low-pressure fan 32, and the fixing fan 31. The printer 1 may also be configured to include the internal temperature sensor 98 on a member other than the drum unit relay board 92, for example, on the drum unit contact board 93.

[0062] As shown in FIG. 6 , the ASIC 81 has a power supply terminal V_SUPPLY, four cartridge terminals CIC_Y, CIC_M, CIC_C, and CIC_K, a ROM data terminal E2P_DATA, a ROM clock terminal E2P_CLK, and a temperature sensor terminal ThM. The power supply terminal V_SUPPLY is electrically connected to the main electrode 87 of the main electrode substrate 85 via a power supply line 103 provided in the device main body 10. The power supply terminal V_SUPPLY is connected to a power supply line 104 of the drum unit relay substrate 92 via the drum unit contact substrate 93 and the like. The power supply line 104 is connected to the cartridge ICs 64 of each of the four toner cartridges 60 and the EEPROM 97 of the drum unit relay substrate 92. The ASIC 81 supplies a drive voltage of, for example, 3.3 V to the four cartridge ICs 64 and the EEPROM 97 from the power supply terminal V_SUPPLY.

[0063] The cartridge terminal CIC_Y corresponding to yellow is connected to the main electrode 87 of the main electrode substrate 85 via a signal line 105Y provided in the apparatus main body 10. The cartridge terminal CIC_Y is connected to the cartridge IC 64Y of the toner cartridge 60Y via the drum unit contact substrate 93, etc. The ASIC 81 reads data from and writes data to the cartridge IC 64Y via the cartridge terminal CIC_Y. Similarly, the other three cartridge terminals CIC_M, CIC_C, and CIC_K are connected to the cartridge ICs 64M, 64C, and 64K, respectively, via signal lines 105M, 105C, and 105K.

[0064] The apparatus main body 10 has ground lines 107A and 107B connected to the two ground sections GND of the main board 26, respectively. The ground line 107A is connected to the main body electrode 87 and is connected to each of the cartridge ICs 64Y and 64M via the drum unit contact board 93 and the like. The ground line 107B is connected to the main body electrode 87 and is connected to each of the cartridge ICs 64C and 64K via the drum unit contact board 93 and the like. The four cartridge ICs 64 read from and write to their memories using the reference potential of the ground section GND of the main board 26 as a reference.

[0065] Similarly, the ROM data terminal E2P_DATA is connected to the main body electrode 87 via a signal line 108A, and is connected to the EEPROM 97 via the drum unit contact board 93 etc. The ASIC 81 reads data from the EEPROM 97 and writes data to the EEPROM 97 via the ROM data terminal E2P_DATA.

[0066] The ROM clock terminal E2P_CLK is connected to the main body electrode 87 via a signal line 108B, and is connected to the EEPROM 97 via the drum unit contact board 93, etc. The ASIC 81 outputs a clock signal to the EEPROM 97 via the ROM clock terminal E2P_CLK. This clock signal is a synchronization signal that synchronizes the timing of writing data to or reading data from the EEPROM 97. The device main body 10 also has a ground line 109 connected to the ground section GND of the main board 26. The ground line 109 is connected to the main body electrode 87, and is connected to the ground terminal of the EEPROM 97 via the drum unit contact board 93, etc.

[0067] The temperature sensor terminal ThM is connected to the main body electrode 87 via a sensor signal line 110 provided in the main body 10. The temperature sensor terminal ThM is connected to an internal temperature sensor 98 via the drum unit contact board 93 or the like, and a signal corresponding to the temperature inside the main body 10 is input from the internal temperature sensor 98.

[0068] (Surge protection) Here, there is a risk that a surge may be input to the main body electrode 87 of the main body electrode board 85 to which the drum unit 11 is connected for some reason. For example, in the printer 1 of this embodiment, when the drum unit 11 is removed from the device main body 10, the main body electrode 87 is exposed in the housing section 10B that houses the drum unit 11. Therefore, if a user puts their hand into the housing section 10B and accidentally touches the main body electrode 87, generating static electricity, there is a risk that a surge may be input to the main body electrode 87. The input of a surge from the main body electrode 87 may cause damage to the terminals of the ASIC 81 or the circuits within the ASIC 81.

[0069] Figure 7 shows the connection configuration of the main board 200, drum unit relay board 92, and toner cartridge 60 provided in a printer of the comparative example. Note that Figure 7 omits the illustration of some components, such as toner cartridge 60M. In the following description of the comparative example of Figure 7, the same components as those in the first embodiment are given the same reference numerals, and their description will be omitted as appropriate. In the printer of the comparative example, as a surge countermeasure, capacitors (only CY and CS are shown in Figure 7) are connected to signal line 105 and sensor signal line 110 (hereinafter sometimes referred to as signal lines 105, 110) that connect main body electrode 87 and ASIC 81, respectively.

[0070] 7, a pull-up resistor Rup1 and a capacitor CY are connected to a signal line 105Y connected to a cartridge terminal CIC_Y. The signal line 105Y is connected to a pull-up power supply Vcc1 via the pull-up resistor Rup1. The pull-up voltage of the pull-up power supply Vcc1 is, for example, 3.3 V.

[0071] For example, the cartridge IC 64 is equipped with an open collector circuit (hereinafter referred to as the open collector circuit). By turning on the switch of this open collector circuit, the cartridge IC 64 connects the terminal of the cartridge IC 64 connected to the signal line 105Y to the ground. As a result, a reference potential voltage (e.g., 0 V) ​​is input to the ASIC 81 via the cartridge terminal CIC_Y. By turning off the switch of the open collector circuit, the cartridge IC 64 outputs a high-impedance (Hi-Z) signal from the terminal connected to the signal line 105Y. As a result, a voltage of, for example, 3.3 V is input to the ASIC 81 via the cartridge terminal CIC_Y. The cartridge IC 64Y turns on and off the switch of the open collector circuit according to the bit value indicated by the information related to the toner cartridge 60 stored in the memory, switching between a low-level signal indicating the reference potential and a high-level signal indicating 3.3 V, and transmits the information stored in the memory to the ASIC 81.

[0072] In addition, signal line 105Y is connected to ground GND via capacitor CY. As a result, if a surge is input from main body electrode 87 connected to signal line 105Y while drum unit 11 is removed, the input surge can be discharged by flowing to ground GND via capacitor CY. This protects the terminals of ASIC 81 and the circuits within ASIC 81. Similarly, surge protection can be implemented for other signal lines 105M, 105C, and 105K by connecting capacitors to them.

[0073] The main board 200 also has a sensor signal line 110 connected to the temperature sensor terminal ThM, which is connected to a pull-up resistor Rup2 and a capacitor CS. The sensor signal line 110 is connected to a pull-up power supply Vcc2 via the pull-up resistor Rup2. The pull-up voltage of the pull-up power supply Vcc2 is, for example, 1.8 V. When the drum unit 11 is installed in the device main body 10 and a pull-up voltage is applied from the pull-up power supply Vcc2, a current flows from the pull-up power supply Vcc2 to the ground GND via the internal temperature sensor 98. The voltage of the internal temperature sensor 98, i.e., a voltage corresponding to the temperature inside the device main body 10, is input to the temperature sensor terminal ThM. The ASIC 81 detects the temperature inside the device main body 10 based on the input voltage of the temperature sensor terminal ThM.

[0074] Furthermore, the sensor signal line 110 is connected to the ground GND via a capacitor CS. As a result, if a surge is input from the main body electrode 87 connected to the sensor signal line 110 while the drum unit 11 is removed, the input surge can be discharged to the ground GND via the capacitor CS.

[0075] As described above, surge protection can be implemented by connecting capacitors CY and CS to signal lines 105Y and 110. However, when capacitors CY and CS are connected to signal lines 105Y and 110, the signal sent from drum unit 11 to ASIC 81 when drum unit 11 is attached to device main body 10 is damped by capacitors CY and CS, which causes a problem in that it takes time for ASIC 81 to detect the signal (see FIG. 10).

[0076] In contrast, the main board 26 of this embodiment has a signal line ground switching circuit 111 that switches whether the signal line 105 is connected to the ground section GND based on the control of the ASIC 81. The main board 26 also has a sensor signal line ground switching circuit 115 that switches whether the sensor signal line 110 is connected to the ground section GND based on the control of the ASIC 81. Note that in Fig. 6, the signal line ground switching circuit 111 and the sensor signal line ground switching circuit 115 are shown by dashed lines to avoid cluttering the drawing.

[0077] 8 and 9 show the connection configuration of the main board 26, drum unit relay board 92, and toner cartridge 60 in the first embodiment. As shown in Fig. 8 and 9, the main board 26 has four signal line ground switching circuits 111Y, 111M, 111C, and 111K, a pull-up voltage switching circuit 113, and a sensor signal line ground switching circuit 115.

[0078] The four signal line ground switching circuits 111Y, 111M, 111C, and 111K are identical to one another. Therefore, the following description will mainly focus on the signal line ground switching circuit 111Y corresponding to yellow, and will omit descriptions of the signal line ground switching circuits 111M, 111C, and 111K corresponding to the other colors. The signal line ground switching circuit 111Y includes a transistor TR_Y and a resistor RY1. The transistor TR_Y is an NPN transistor and is connected between the signal line 105Y and the ground GND. The NPN transistor TR_Y is an example of a first semiconductor transistor according to the present application. The semiconductor transistor according to the present application is not limited to a bipolar transistor such as an NPN transistor, but may also be a field-effect transistor (FET). The base of the transistor TR_Y is an example of a control terminal of a semiconductor transistor, and is a terminal for controlling the operation of the semiconductor transistor. If the semiconductor transistor is an FET, the control terminal of the semiconductor transistor corresponds to the gate of the FET. Furthermore, the collector of transistor TR_Y, which is an NPN transistor, is an example of an input terminal of a semiconductor transistor, and is a terminal through which a current or voltage is input to the semiconductor transistor. If the semiconductor transistor is a PNP transistor, the input terminal of the semiconductor transistor corresponds to the emitter of the PNP transistor. If the semiconductor transistor is an N-channel FET, the input terminal of the semiconductor transistor corresponds to the drain of the FET. If the semiconductor transistor is a P-channel FET, the input terminal of the semiconductor transistor corresponds to the source of the FET. Furthermore, the emitter of transistor TR_Y, which is an NPN transistor, is an example of an output terminal of a semiconductor transistor, and is a terminal through which a current or voltage is output from the semiconductor transistor. If the semiconductor transistor is a PNP transistor, the output terminal of the semiconductor transistor corresponds to the collector of the PNP transistor. If the semiconductor transistor is an N-channel FET, the output terminal of the semiconductor transistor corresponds to the source of the FET. If the semiconductor transistor is a P-channel FET, the output terminal of the semiconductor transistor corresponds to the drain of the FET.

[0079] The emitter of the transistor TR_Y is connected to the ground GND. The collector of the transistor TR_Y is connected to the signal line 105Y. The base of the transistor TR_Y is connected to a switching terminal SI1 of the ASIC 81 via a resistor RY1. The ASIC 81 outputs a high-level signal (an example of the first signal of the present application) or a low-level signal (an example of the second signal of the present application) via the switching terminal SI1.

[0080] When the ASIC 81 outputs a high-level signal from the switching terminal SI1, a current flows from the switching terminal SI1 to the ground GND via the base-emitter of the transistor TR_Y. The transistor TR_Y is turned on, allowing a current to flow from the collector to the emitter of the transistor TR_Y. The signal line 105Y is connected to the ground GND.

[0081] Furthermore, when the ASIC 81 outputs a low-level signal from the switching terminal SI1, no current flows from the switching terminal SI1 to the ground GND via the base-emitter of the transistor TR_Y. The transistor TR_Y is turned off, and the signal line 105Y is disconnected from the ground GND.

[0082] The switching terminal SI1 is also connected to the bases of the transistors TR_M, TR_C, and TR_K of the other three signal line ground switching circuits 111M, 111C, and 111K, respectively. Therefore, the ASIC 81 can collectively switch the on / off states of the four transistors TR_Y, TR_M, TR_C, and TR_K by switching the signal output from the switching terminal SI1 between a high-level signal and a low-level signal.

[0083] The pull-up voltage switching circuit 113 also includes a transistor TR1 and a resistor R1. The transistor TR1 is a PNP transistor and is connected between a pull-up power supply Vcc1 and the four signal lines 105. The emitter of the transistor TR1 is connected to the pull-up power supply Vcc1 (for example, a +3.3V power supply). The pull-up power supply Vcc1 connected to the emitter of the transistor TR1 may be the power supply terminal V_SUPPLY of the ASIC 81 shown in FIG. 6. +3.3V is an example of the pull-up voltage in this application.

[0084] The base of transistor TR1 is connected to switching terminal SI1 via resistor R1. The collector of transistor TR1 is connected to four signal lines 105Y, 105M, 105C, and 105K. Signal line 105Y is connected to the collector of transistor TR1 via pull-up resistor RY2. Similarly, signal lines 105M, 105C, and 105K are connected to the collector of transistor TR1 via pull-up resistors RM2, RC2, and RK2, respectively.

[0085] When the ASIC 81 outputs a high-level signal from the switching terminal SI1, no current flows between the emitter and base of the transistor TR1. The transistor TR1 is turned off, and the pull-up voltage (+3.3V) is not applied to the pull-up resistors RY2, RM2, RC2, and RK2 of the four signal lines 105.

[0086] Furthermore, when the ASIC 81 outputs a low-level signal from the switching terminal SI1, current flows from the emitter to the base of the transistor TR1. When the transistor TR1 is turned on, current flows from the pull-up power supply Vcc1 to each of the four pull-up resistors RY2, RM2, RC2, and RK2 via the transistor TR1. A pull-up voltage is applied to each of the four pull-up resistors RY2, RM2, RC2, and RK2 from the pull-up power supply Vcc1.

[0087] 9, the sensor signal line ground switching circuit 115, like the signal line ground switching circuit 111, includes a transistor TR_S and a resistor RS1. The transistor TR_S is an NPN transistor and is connected between the sensor signal line 110 and the ground GND. The emitter of the transistor TR_S is connected to the ground GND, and the collector is connected to the sensor signal line 110. The base of the transistor TR_S is connected to a switching terminal SI2 of the ASIC 81 via the resistor RS1. The sensor signal line 110 is connected to a pull-up power supply Vcc2 via a pull-up resistor RS2.

[0088] The ASIC 81 outputs a low-level signal from the switching terminal SI2 to turn off the transistor TR_S and disconnect the sensor signal line 110 from the ground GND. A pull-up voltage (+1.8 V) is applied to the internal temperature sensor 98 from the pull-up power supply Vcc2 via the pull-up resistor RS2 and the sensor signal line 110. The ASIC 81 also outputs a high-level signal from the switching terminal SI2 to turn on the transistor TR_S and connect the sensor signal line 110 to the ground GND.

[0089] Fig. 10 shows the analog signal (voltage) of the on-board temperature sensor 98 in each of the configuration of the main board 200 of the comparative example shown in Fig. 7 and the configuration of the main board 26 of the first embodiment shown in Figs. 8 and 9. The vertical axis of Fig. 10 represents the voltage value of the analog signal, that is, the input voltage Vin input to the temperature sensor terminal ThM. The horizontal axis represents time. The solid line graph represents the graph of the configuration of the first embodiment, and the dashed line graph represents the graph of the configuration of the comparative example.

[0090] 11, when detecting the temperature using the on-board temperature sensor 98, the ASIC 81 outputs a low-level signal from the switching terminal SI2 to turn off the transistor TR_S. A pull-up voltage (1.8 V) is applied to the on-board temperature sensor 98 from the pull-up power supply Vcc2 via the pull-up resistor RS2 and the sensor signal line 110. An input voltage Vin corresponding to the resistance value of the on-board temperature sensor 98 is input to the temperature sensor terminal ThM.

[0091] As the temperature inside the device main body 10 changes, the resistance value of the on-device temperature sensor 98 changes, which in turn changes the input voltage Vin input to the temperature sensor terminal ThM. For example, if the on-device temperature sensor 98 is a PTC thermistor (Positive Temperature Coefficient), the resistance value of the on-device temperature sensor 98 increases as the temperature inside the device main body 10 increases. If the resistance value of the on-device temperature sensor 98 is Rs and the resistance value of the pull-up resistor RS2 is RS2, the input voltage Vin to the temperature sensor terminal ThM is Vin=Vcc2*(Rs / (Rs+RS2)), and increases as the temperature increases.

[0092] As shown by the dashed line graph in Figure 10, in the configuration of the comparative example, the time required for the input voltage Vin at the temperature sensor terminal ThM to saturate increases as the capacitance of the capacitor CS (see Figure 7) increases. This increases the time required for the ASIC 81 to detect the temperature of the device main body 10 from the input voltage Vin. This makes it necessary to set the time required for the ASIC 81 to detect the temperature longer.

[0093] On the other hand, as shown in Fig. 11, no surge protection component such as a capacitor is connected to the sensor signal line 110 of the first embodiment. Therefore, as shown by the solid line in Fig. 10, the input voltage Vin of the temperature sensor terminal ThM changes more sharply than in the comparative example, and the time required to reach saturation is shortened. This allows the ASIC 81 to shorten the time required to detect the temperature. The same applies when the temperature drops and the input voltage Vin decreases.

[0094] Furthermore, the detection time can be shortened not only for analog signals such as the input voltage Vin, but also for digital signals that change between two signal levels, high and low. As shown in FIG. 11, when the ASIC 81 communicates with the cartridge IC 64, it outputs a low-level signal from the switching terminal SI1 to turn on the transistor TR1 and turn off all four transistors TR_Y, TR_M, TR_C, and TR_K. The cartridge IC 64 connects the signal line 105Y to ground by turning on the switch of the open-collector circuit. This allows the ASIC 81 to input a reference potential voltage via the cartridge terminal CIC_Y. The cartridge IC 64 also outputs a high-impedance signal to the signal line 105Y by turning off the switch of the open-collector circuit. This allows the ASIC 81 to input the pull-up voltage of the pull-up power supply Vcc1 via the cartridge terminal CIC_Y.

[0095] For example, when cartridge IC64Y switches its open-collector circuit from transmitting a reference potential signal to transmitting a high-impedance signal, the signal input to cartridge terminal CIC_Y rises from 0V to +3.3V. In the comparative example, the time required for the input signal to cartridge terminal CIC_Y to saturate at 3.3V increases as the capacitance of capacitor CY (see Figure 7) increases. This increases the time required for ASIC81 to detect a high-level (3.3V) signal. This requires a longer time for ASIC81 to determine whether the signal is high or low.

[0096] 11, no surge protection components such as a capacitor are connected to the signal line 105 of the first embodiment. Therefore, when the input signal to the cartridge terminal CIC_Y rises or falls, the signal changes more sharply than in the comparative example, shortening the time required for saturation. The time required for the ASIC 81 to determine whether the signal is at a high level or a low level can be shortened.

[0097] Furthermore, the ASIC 81 maintains the state shown in FIG. 11 while the drum unit 11 is attached to the device main body 10. Furthermore, as shown in FIG. 12, when the ASIC 81 detects that the drum unit 11 has been removed, it outputs a high-level signal from the switching terminal SI1 to turn off the transistor TR1 and turn on all four transistors TR_Y, TR_M, TR_C, and TR_K. Turning off the transistor TR1 prevents the pull-up voltage from being applied from the pull-up power supply Vcc1 to the four pull-up resistors RY2 and RY3. Turning on the transistors TR_Y, TR_M, TR_C, and TR_K connects the four signal lines 105 to the ground GND. For example, if a user touches the main body electrode 87 with the drum unit 11 removed, generating static electricity and causing a surge to be input from the main body electrode 87 connected to the signal line 105Y, the input surge can be passed to the ground GND via the transistor TR_Y, thereby dissipating the surge. This makes it possible to protect the cartridge terminal CIC_Y and the circuits inside the ASIC 81. Similarly, surge protection can be implemented for the main body electrodes 87 connected to the signal lines 105 of other colors.

[0098] Furthermore, when the ASIC 81 detects that the drum unit 11 has been removed, it outputs a high-level signal from the switching terminal SI2 and turns on the transistor TR_S. This connects the sensor signal line 110 to the ground GND. If a surge is input from the main body electrode 87 to the sensor signal line 110, it can be released to the ground GND via the transistor TR_S. This protects the temperature sensor terminal ThM and other components.

[0099] A method for detecting whether the drum unit 11 has been removed from the printer main body 10 can be to determine the input voltage Vin of the temperature sensor terminal ThM. When the drum unit 11 is installed and the transistor TR_S is turned on, as described above, the input voltage Vin corresponding to the resistance value of the internal temperature sensor 98 is input to the temperature sensor terminal ThM. This allows the ASIC 81 to detect the temperature inside the printer main body 10. On the other hand, when the drum unit 11 is removed, the main body electrode 87 connected to the sensor signal line 110 is open, and the input voltage Vin of 1.8 V is input to the temperature sensor terminal ThM via the pull-up resistor RS2. The ASIC 81 cannot detect the temperature inside the printer main body 10. Therefore, if the input voltage Vin remains at 1.8 V for a predetermined reference time or longer, the ASIC 81 determines that the temperature cannot be detected and that the drum unit 11 has been removed. Alternatively, the printer 1 may be equipped with a sensor for detecting the installation or removal of the drum unit 11. For example, printer 1 may include an optical sensor that outputs a different signal depending on whether drum unit 11 is present in housing 10B, and ASIC 81 may determine whether drum unit 11 has been removed based on the signal from the optical sensor.

[0100] (Regarding signal switching at switching terminals SI1 and SI2) For example, when the drum unit 11 is installed, the ASIC 81 outputs a low-level signal from the switching terminals SI1 and SI2 as shown in Fig. 11. Furthermore, when the ASIC 81 detects that the drum unit 11 has been removed, it outputs a high-level signal from the switching terminals SI1 and SI2 as shown in Fig. 12.

[0101] However, the condition for switching the levels of the signals output from the switching terminals SI1 and SI2 is not limited to the condition that the drum unit 11 is removed. For example, as shown by the dashed line in FIG. 2, the printer 1 may further include a cover sensor 121 that detects whether the front cover 13 (see FIG. 1) is open or closed. The cover sensor 121 is attached to the device main body 10, for example, and electrically connected to the ASIC 81. When the front cover 13 is in the closed position shown by the solid line in FIG. 1, the cover sensor 121 outputs a low-level signal to the ASIC 81. When the front cover 13 is in a position other than the closed position, the cover sensor 121 outputs a high-level signal to the ASIC 81. This allows the ASIC 81 to detect whether the front cover 13 is open based on the signal from the cover sensor 121. When the ASIC 81 receives a high-level signal from the cover sensor 121 and detects that the front cover 13 is open, the ASIC 81 may output a high-level signal from the switching terminals SI1 and SI2 to turn on the transistors TR_Y, TR_S, etc.

[0102] Alternatively, the ASIC 81 may change the level of the signals output from the switching terminals SI1 and SI2 in accordance with the timing of communication with the cartridge IC 64 and the timing of temperature detection by the internal temperature sensor 98. For example, if information such as the number of printed sheets is transmitted from the cartridge IC 64 to the ASIC 81 when the power to the apparatus main body 10 is turned on, the ASIC 81 may output a low-level signal from the switching terminal SI1 in accordance with the timing of power-on. Then, once the ASIC 81 has completed acquiring the information such as the number of printed sheets, the ASIC 81 may output a high-level signal from the switching terminal SI1. Furthermore, if the ASIC 81 updates the information in the cartridge IC 64, such as the number of printed sheets, in response to printing execution, the ASIC 81 may output a low-level signal from the switching terminal SI1 in accordance with the execution of the update communication with the cartridge IC 64, thereby updating the information in the cartridge IC 64. Then, once the update is completed, the ASIC 81 may output a high-level signal from the switching terminal SI1.

[0103] In addition, if ASIC81 outputs a voltage of 3.3V from the power supply terminal V_SUPPLY in response to the start of communication with cartridge IC64 and stops outputting 3.3V in response to the end of communication, it may change the level of the signal output from switching terminal SI1 in response to switching of the output of power supply terminal V_SUPPLY.

[0104] Furthermore, in order to control the fixing fan 31, etc., the ASIC 81 may output a low-level signal from the switching terminal SI2 in accordance with the timing at which the input voltage Vin is input from the internal temperature sensor 98 to detect the temperature. Furthermore, in a state in which the ASIC 81 does not control the fixing fan 31, etc., or in a state in which the internal temperature sensor 98 does not detect the temperature, the ASIC 81 may output a high-level signal from the switching terminal SI2 to turn on the transistor TR_S.

[0105] As described above, the first embodiment provides the following effects. (1) The printer 1 of this embodiment includes an ASIC 81 and a signal line ground switching circuit 111 controlled by the ASIC 81. The ASIC 81 is electrically connected to the main body electrode 87 via a signal line 105, and transmits and receives signals to and from the cartridge IC 64 via the signal line 105 when the drum unit 11 is attached to the device main body 10. The signal line ground switching circuit 111 switches whether or not to connect the signal line 105 to the ground GND based on the control of the ASIC 81.

[0106] According to this, when the drum unit 11 is removed from the device main body 10, the ASIC 81 connects the signal line 105 to the ground section GND, and can discharge surges input via the main body electrode 87 to the ground section GND. Furthermore, when the drum unit 11 is attached to the device main body 10, the ASIC 81 can disconnect the ground GND from the signal line 105 and connect the drum unit 11 and ASIC 81 without passing through a surge protection component such as a capacitor. This prevents the signal input from the drum unit 11 to the ASIC 81 from becoming dull.

[0107] (2) The printer 1 also includes a sensor signal line ground switching circuit 115 controlled by the ASIC 81. The ASIC 81 is electrically connected to the main body electrode 87 via a sensor signal line 110, and receives a signal from the internal temperature sensor 98 via the sensor signal line 110 when the drum unit 11 is attached to the device main body 10. The sensor signal line ground switching circuit 115 switches whether or not the sensor signal line 110 is connected to the ground GND, based on the control of the ASIC 81.

[0108] According to this, when the drum unit 11 is removed from the device main body 10, the ASIC 81 connects the sensor signal line 110 to the ground section GND, and can discharge surges input via the main body electrode 87 to the ground section GND. Furthermore, when the drum unit 11 is attached to the apparatus main body 10, the ASIC 81 can connect the internal temperature sensor 98 to the ASIC 81 without passing through a surge protection component such as a capacitor by disconnecting the ground GND from the sensor signal line 110. This prevents the signal input from the internal temperature sensor 98 to the ASIC 81 from becoming dull.

[0109] (3) The ASIC 81 also has switching terminals SI1 and SI2. The signal line ground switching circuit 111 connects the signal line 105 to the ground GND in response to a high-level signal (an example of the first signal of the present application) input from the switching terminal SI1. The sensor signal line ground switching circuit 115 connects the sensor signal line 110 to the ground GND in response to a high-level signal input from the switching terminal SI2. According to this, the ASIC 81 can connect the signal line 105 to the ground GND and can connect the sensor signal line 110 to the ground GND by outputting a high level signal from each of the switching terminals SI1 and SI2.

[0110] (4) The printer 1 also includes four signal line ground switching circuits 111 corresponding to the four toner cartridges 60. This allows surge protection to be implemented for the signal lines 105Y, 105M, 105C, and 105K connected to the four toner cartridges 60. Furthermore, by not connecting surge protection components such as capacitors to all of the four signal lines 105, it is possible to prevent the signals input to the ASIC 81 via each signal line 105 from becoming dull.

[0111] (5) The switching terminal SI1 is connected to four signal line ground switching circuits 111. According to this, the ASIC 81 can collectively turn on the transistors TR_Y etc. of the four signal line ground switching circuits 111 by outputting a high-level signal from the switching terminal SI1. The four signal lines 105 can be collectively connected to the ground GND. The four signal lines 105 can be collectively switched.

[0112] (6) Each of the four cartridge ICs 64 also has an open-collector circuit. The printer 1 further includes a pull-up voltage switching circuit 113. The pull-up voltage switching circuit 113 switches between applying a pull-up voltage from the pull-up power supply Vcc1 to each of the four pull-up resistors RY2, RM2, RC2, and RK2 based on a signal from the ASIC 81. When the ASIC 81 outputs a high-level signal from the switching terminal SI1, the pull-up voltage switching circuit 113 turns off the transistor TR1 and does not apply a pull-up voltage to the four pull-up resistors RY2, etc. When the ASIC 81 outputs a low-level signal (an example of the second signal of the present application) from the switching terminal SI1, the pull-up voltage switching circuit 113 turns on the transistor TR1 and applies a pull-up voltage to the four pull-up resistors RY2, etc. The four signal line ground switching circuits 111 also turn off the transistors TR_Y, etc., and disconnect the four signal lines 105 from the ground section GND.

[0113] This allows the ASIC 81 to use the same signal to control the pull-up voltage switching circuit 113 and the four signal line ground switching circuits 111. When not communicating with the cartridge IC 64, the ASIC 81 outputs a high-level signal from the switching terminal SI1 to turn off the pull-up voltage switching circuit 113 and not apply a pull-up voltage, and to turn on the four signal line ground switching circuits 111, thereby connecting the four signal lines 105 to the ground section GND. Furthermore, when communicating with the cartridge IC 64, the ASIC 81 outputs a low-level signal from the switching terminal SI1 to turn on the pull-up voltage switching circuit 113, apply a pull-up voltage to the four pull-up resistors RY2, etc., and turn off the four signal line ground switching circuits 111 to disconnect the four signal lines 105 from the ground section GND. This allows the pull-up voltage switching circuit 113 and the signal line ground switching circuit 111 to be controlled in synchronization using the same signal.

[0114] (7) The printer 1 may also include a cover sensor 121 in the device main body 10. In this case, when the ASIC 81 detects that the front cover 13 is open based on a signal from the cover sensor 121, it may control the signal line ground switching circuit 111 to connect the signal line 105 to the ground GND. According to this, when there is a possibility that the front cover 13 is opened and the drum unit 11 is removed, the signal line 105 can be connected to the ground GND to protect the ASIC 81 from surges.

[0115] (8) Furthermore, when the temperature inside the device main body 10 cannot be detected based on the signal from the internal temperature sensor 98, the ASIC 81 controls the sensor signal line ground switching circuit 115 to connect the sensor signal line 110 to the ground GND. With this, when the drum unit 11 is removed and the main body electrode 87 connected to the internal temperature sensor 98 is open, the sensor signal line ground switching circuit 115 is turned on to connect the sensor signal line 110 to the ground GND. This protects the ASIC 81 from surges input to the main body electrode 87 for the internal temperature sensor 98.

[0116] (9) Furthermore, when the temperature inside the device main body 10 cannot be detected based on the signal from the internal temperature sensor 98, the ASIC 81 controls the four signal line ground switching circuits 111 in addition to the sensor signal line ground switching circuit 115 to connect the four signal lines 105 to the ground section GND. According to this, when it is detected that a 1.8V input voltage Vin is input to the temperature sensor terminal ThM and there is a possibility that the drum unit 11 having the internal temperature sensor 98 has been removed, all four signal lines 105 are connected to the ground GND in addition to the sensor signal line 110. This allows the ASIC 81 to be more reliably protected from surges.

[0117] (10) The emitter of the transistor TR_Y, which is an NPN transistor, is connected to the ground GND, the base is connected to the switching terminal SI1 of the ASIC 81 via a resistor RY1, and the collector is connected to the signal line 105Y. According to this, the ASIC 81 can switch the transistor TR_Y on and off by changing the signal level of the signal output to the base of the transistor TR_Y, and can switch the connection between the signal line 105Y and the ground section GND.

[0118] (11) The cartridge IC 64 also has a memory (an example of the cartridge memory of the present application) that stores information related to the toner cartridge 60. The ASIC 81 controls the signal line ground switching circuit 111 to receive information from the memory via the signal line 105 while the signal line 105 is disconnected from the ground GND. This allows the signal line 105 to be disconnected from the ground GND when reading information from the memory. By disconnecting the signal line 105 from the ground GND, the digital signal (data) from the memory can be detected with high accuracy.

[0119] (12) The printer 1 also includes a fixing fan 31, a low-pressure fan 32, and a charging fan 33. With the sensor signal line ground switching circuit 115 turned off and the sensor signal line 110 disconnected from the ground GND, the ASIC 81 detects the temperature inside the device main body 10 based on the input voltage Vin from the internal temperature sensor 98, and controls the fixing fan 31 and other fans based on the detected temperature. This allows the sensor signal line 110 to be disconnected from the ground GND when detecting the temperature based on the input voltage Vin from the internal temperature sensor 98. By disconnecting the sensor signal line 110 from the ground GND, the voltage value of the input voltage Vin from the internal temperature sensor 98 can be detected with high accuracy. This allows the fixing fan 31 and other components to be controlled with high accuracy based on the temperature.

[0120] (Second embodiment) Next, a second embodiment of the present invention will be described. While the main board 26 of the first embodiment described above includes the signal line ground switching circuit 111, the pull-up voltage switching circuit 113, and the sensor signal line ground switching circuit 115, the configuration of the main board of the present invention is not limited to this. A main board 26A provided in a printer of the second embodiment differs from the main board 26 of the first embodiment in that it does not include the pull-up voltage switching circuit 113. FIG. 13 shows the connection configuration of the main board 26A according to the second embodiment. In the following description of the second to fourth embodiments, components similar to those of the first embodiment described above will be designated by the same reference numerals, and their description will be omitted where appropriate.

[0121] As shown in FIG. 13, the main board 26A does not include a pull-up voltage switching circuit 113. The pull-up resistors RY2 and RM2 connected to each of the four signal lines 105 are directly connected to a pull-up power supply Vcc1. Note that FIG. 13 only illustrates the pull-up resistors RY2 and RM2. The pull-up power supply Vcc1 connected to the four pull-up resistors RY2 and RM2 may be a single power supply such as the power supply terminal V_SUPPLY (see FIG. 6) or separate power supplies. The ASIC 81 on the main board 26A has four switching terminals SI1_Y, SI1_M, SI1_C, and SI1_K as switching terminals for controlling the four signal line ground switching circuits 111 (only SI1_Y and SI1_M are shown in FIG. 13). The four switching terminals SI1_Y and SI1_M are connected to the bases of the transistors (TR_Y, etc.) of the four signal line ground switching circuits 111, respectively.

[0122] In this configuration, the four signal line ground switching circuits 111 can be turned on or off, i.e., the connection states of the four signal lines 105 to the ground GND can be individually switched by signals output from the four switching terminals SI1_Y, SI1_M, SI1_C, and SI1_K. For example, in a configuration in which the toner cartridges 60 can be individually replaced while the drum unit 11 is attached to the device main body 10, only the signal line 105 that was connected to the removed toner cartridge 60 can be connected to the ground GND.

[0123] (Third embodiment) Next, a third embodiment of the present invention will be described. The ASIC 81 of the main board 26 of the first embodiment described above was provided with a separate switching terminal SI1 for switching the signal line ground switching circuit 111 and a switching terminal SI2 for switching the sensor signal line ground switching circuit 115, but this is not limited to this. The main board 26B provided in the printer of the third embodiment differs from the main board 26 of the first embodiment in that it is provided with a single switching terminal for switching between the signal line ground switching circuit 111 and the sensor signal line ground switching circuit 115. Note that, as an example, the main board 26B of the third embodiment does not include the sensor signal line ground switching circuit 115, similar to the main board 26A of the second embodiment.

[0124] 14 and 15 show a connection configuration of a main board 26B according to the third embodiment. As shown in Fig. 14 and 15, a switching terminal SI1 of an ASIC 81 on the main board 26B is connected to the sensor signal line ground switching circuit 115 in addition to the four signal line ground switching circuits 111. The switching terminal SI1 is connected to the base of a transistor TR_S via a resistor RS1.

[0125] Therefore, when a low-level signal is output from the switching terminal SI1, not only the four signal lines 105 but also the sensor signal line 110 are disconnected from the ground GND. Also, when a high-level signal is output from the switching terminal SI1, not only the four signal lines 105 but also the sensor signal line 110 are connected to the ground GND. In this configuration, the single switching terminal SI1 can control not only the signal line ground switching circuit 111 but also the sensor signal line ground switching circuit 115. This reduces the number of terminals required for the ASIC 81.

[0126] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described. A main board 26C included in a printer of the fourth embodiment differs from the main board 26 of the first embodiment in that it does not include a sensor signal line ground switching circuit 115. Note that, as an example, the main board 26C of the fourth embodiment does not include a sensor signal line ground switching circuit 115, similar to the main board 26A of the second embodiment. Also, as an example, the ASIC 81 of the main board 26C includes four switching terminals SI1_Y, SI1_M, SI1_C, and SI1_K, similar to the main board 26A of the second embodiment.

[0127] As shown in FIG. 16 , the main board 26C of the fourth embodiment does not include a sensor signal line ground switching circuit 115. Furthermore, the ASIC 81 does not include a switching terminal SI2 that controls the sensor signal line ground switching circuit 115. With this configuration, only the signal line 105 connected to the cartridge IC 64 can be switched between ground and GND. This protects the ASIC 81 from surges input from the main body electrode 87 connected to the cartridge IC 64. In the configuration of the fourth embodiment, the internal temperature sensor 98 may be located in a location other than the drum unit 11. For example, the internal temperature sensor 98 may be attached to the case of the device main body 10, and the internal temperature sensor 98 may be constantly connected to the ASIC 81 regardless of whether the drum unit 11 is attached or detached.

[0128] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, the configuration of the printer 1 in each of the above-described embodiments is merely an example and can be modified as appropriate. Similar to the signal line ground switching circuit 111, the main board 26 may also include a signal line ground switching circuit that switches the connection between the signal lines 108A, 108B connected to the EEPROM 97 provided on the drum unit relay board 92 and the ground GND. The printer 1 may also be configured to include either the signal line ground switching circuit 111 or the sensor signal line ground switching circuit 115. Therefore, the main board 26 may be configured to include only the sensor signal line ground switching circuit 115. The ASIC 81 may also be configured not to include the switching terminal SI1. Furthermore, a circuit similar to the pull-up voltage switching circuit 113 may be connected to the sensor signal line 110. For example, a pull-up voltage switching circuit that switches the connection between the sensor signal line 110 and the pull-up power supply Vcc2 based on a signal from a switching terminal SI2 may be provided in the path connecting the sensor signal line 110 and the pull-up power supply Vcc2. In addition, in the above-described embodiments, the image forming unit 22 that performs color printing is used as the image forming unit of the present invention, but this is not limited to this. For example, the image forming unit may be a printing unit that can accommodate only one toner cartridge 60 and perform monochrome printing. Therefore, the main board 26 may be configured to include only one signal line ground switching circuit 111. Furthermore, the image forming unit of the present application is not limited to a printing unit that performs printing, but may also be an image forming unit that forms other images, such as fax data, on sheets. Therefore, the image forming apparatus of the present application is not limited to a printer, but may also be a fax machine. Furthermore, the image forming apparatus of the present application may also be a multifunction peripheral that has multiple functions, such as a printing function, a copying function, a fax function, and a scanning function. Therefore, the configuration of the image forming unit is appropriately changed depending on the functions of the image forming apparatus. Furthermore, the printer 1 may not be provided with a fan such as the fixing fan 31. Furthermore, the printer 1 may not be provided with sensors such as the internal temperature sensor 98. Furthermore, the printer 1 may not be provided with the cover sensor 121. [Explanation of symbols]

[0129] 1 color laser printer (image forming apparatus), 10 device body, 10A removal port, 13 front cover (cover), 31 fixing fan (fan), 32 low-pressure fan (fan), 33 charging fan (fan), 50 drum unit, 55, 55Y, 55M, 55C, 55K photosensitive drum (1st to 4th photosensitive drum), 61 developing roller (1st to 4th developing roller), 60, 60Y, 60M, 60C, 60K toner cartridge (1st to 4th toner cartridge), 64, 64Y, 64M, 64C, 64K cartridge IC (1st to 4th cartridge control circuit), 81 ASIC (control unit), 85 main body electrode board, 87 main body electrode (1st to 4th main body electrode, main body electrode for sensor), 92 drum unit relay board (relay board), 93 drum unit contact board, 95 Contact terminals (first to fourth contact terminals, sensor contact terminal), 98 internal temperature sensor (sensor, temperature detection sensor), 105, 105Y, 105M, 105C, 105K signal line (first to fourth signal lines), 110 sensor signal line, 111, 111Y, 111M, 111C, 111K signal line ground switching circuit (first to fourth signal line ground switching circuit), 113 pull-up voltage switching circuit, 115 sensor signal line ground switching circuit, 121 cover sensor, GND ground section, RY2, RM2, RC2, RK2 pull-up resistors (first to fourth pull-up resistors), SI1, SI2 switching terminals, TR_Y, TR_M, TR_C, TR_K transistors (first semiconductor transistors), RY1, RM1, RC1, RK1 resistors (first resistors), Vcc1 pull-up power supply, Vin input voltage (signal).

Claims

1. A device body, a drum unit that is attachable to the device main body, the drum unit having a first toner cartridge that has a first photosensitive drum, a first developing roller that carries a first toner and supplies the first toner to the first photosensitive drum, and a first cartridge control circuit, and a drum unit contact board that has a first contact terminal that is electrically connected to the first cartridge control circuit; a main electrode substrate having a first main electrode, the first contact terminal and the first main electrode being in contact with each other when the drum unit is attached to the apparatus main body; a control unit electrically connected to the first main body electrode by a first signal line, the control unit transmitting and receiving signals to and from the first cartridge control circuit via the first signal line when the drum unit is attached to the apparatus main body; an electrically grounded ground portion; a first signal line ground switching circuit that switches whether or not the first signal line and the ground unit are connected based on control by the control unit; An image forming apparatus comprising:

2. A device body, a drum unit that is attachable to the device main body, the drum unit having a first toner cartridge that has a first photosensitive drum and a first developing roller that carries a first toner and supplies the first toner to the first photosensitive drum, a relay board on which a sensor is disposed, and a drum unit contact board that has a sensor contact terminal that is electrically connected to the sensor; a main electrode substrate having a main electrode for a sensor, the main electrode substrate having a sensor contact terminal and the main electrode for a sensor in contact with each other when the drum unit is attached to the apparatus main body; a control unit electrically connected to the sensor main body electrode by a sensor signal line, the control unit receiving a signal from the sensor via the sensor signal line when the drum unit is attached to the apparatus main body; an electrically grounded ground portion; a sensor signal line ground switching circuit that switches whether the sensor signal line and the ground unit are connected or not based on control by the control unit; An image forming apparatus comprising:

3. The drum unit is a relay board electrically connecting the first contact terminal and the first cartridge control circuit, the relay board having a sensor disposed thereon, The drum unit contact board is Further, a sensor contact terminal electrically connected to the sensor, The main electrode substrate is The drum unit further includes a sensor main body electrode, and when the drum unit is attached to the apparatus main body, the sensor contact terminal and the sensor main body electrode come into contact with each other. The control unit Furthermore, the sensor main body electrode is electrically connected to the sensor signal line, and when the drum unit is attached to the device main body, the sensor receives the detection result from the sensor via the sensor signal line. a sensor signal line ground switching circuit that switches whether the sensor signal line and the ground unit are connected or not based on control by the control unit; Equipped with 2. The image forming apparatus according to claim 1.

4. The control unit It has a switching terminal, The switching terminal is electrically connected to the first signal line ground switching circuit and the sensor signal line ground switching circuit, The first signal line ground switching circuit connecting the first signal line to the ground portion in response to a first signal input from the switching terminal; The sensor signal line ground switching circuit connecting the sensor signal line and the ground part in response to a first signal input from the switching terminal; 4. The image forming apparatus according to claim 3.

5. The drum unit is Furthermore, a second toner cartridge including a second photosensitive drum, a second developing roller for carrying a second toner and supplying the second toner to the second photosensitive drum, and a second cartridge control circuit; a third toner cartridge including a third photosensitive drum, a third developing roller for carrying a third toner and supplying the third toner to the third photosensitive drum, and a third cartridge control circuit; a fourth toner cartridge including a fourth photosensitive drum, a fourth developing roller for carrying a fourth toner and supplying the fourth toner to the fourth photosensitive drum, and a fourth cartridge control circuit; and The drum unit contact board is Furthermore, a second contact terminal electrically connected to the second cartridge control circuit; a third contact terminal electrically connected to the third cartridge control circuit; a fourth contact terminal electrically connected to the fourth cartridge control circuit; and The main electrode substrate is Further, the device has a second body electrode, a third body electrode, and a fourth body electrode, When the drum unit is attached to the apparatus main body, the second contact terminal and the second main body electrode are in contact with each other, the third contact terminal and the third main body electrode are in contact with each other, and the fourth contact terminal and the fourth main body electrode are in contact with each other, The control unit Furthermore, the second body electrode and the second signal line, the third body electrode and the third signal line, and the fourth body electrode and the fourth signal line are electrically connected to each other, When the drum unit is attached to the apparatus main body, signals are transmitted and received to and from the second cartridge control circuit, the third cartridge control circuit, and the fourth cartridge control circuit via the second signal line, the third signal line, and the fourth signal line, respectively; a second signal line ground switching circuit that switches whether or not the second signal line and the ground section are connected based on control by the control section; a third signal line ground switching circuit that switches whether or not the third signal line and the ground unit are connected based on control by the control unit; a fourth signal line ground switching circuit that switches whether or not the fourth signal line and the ground unit are connected based on control by the control unit; Equipped with 4. The image forming apparatus according to claim 3.

6. The control unit a switching terminal electrically connected to the first signal line ground switching circuit, the second signal line ground switching circuit, the third signal line ground switching circuit, and the fourth signal line ground switching circuit, The first signal line ground switching circuit connecting the first signal line to the ground portion in response to a first signal input from the switching terminal; The second signal line ground switching circuit connecting the second signal line and the ground portion in response to a first signal input from the switching terminal; The third signal line ground switching circuit connecting the third signal line and the ground portion in response to a first signal input from the switching terminal; The fourth signal line ground switching circuit connecting the fourth signal line and the ground portion in response to a first signal input from the switching terminal; 6. The image forming apparatus according to claim 5.

7. the first cartridge control circuit, the second cartridge control circuit, the third cartridge control circuit, and the fourth cartridge control circuit each have an open collector circuit, Furthermore, a first pull-up resistor connected to the first signal line; a second pull-up resistor connected to the second signal line; a third pull-up resistor connected to the third signal line; a fourth pull-up resistor connected to the fourth signal line; A pull-up power supply; a pull-up voltage switching circuit that switches whether or not a pull-up voltage is applied from the pull-up power supply to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor in response to a signal from the control unit; Equipped with When the control unit outputs a first signal from the switching terminal, the pull-up voltage switching circuit does not apply a pull-up voltage to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor, the first signal line ground switching circuit connects the first signal line to the ground section, the second signal line ground switching circuit connects the second signal line to the ground section, the third signal line ground switching circuit connects the third signal line to the ground section, and the fourth signal line ground switching circuit connects the fourth signal line to the ground section; When the control unit outputs a second signal different from the first signal from the switching terminal, the pull-up voltage switching circuit applies a pull-up voltage to each of the first pull-up resistor, the second pull-up resistor, the third pull-up resistor, and the fourth pull-up resistor; the first signal line ground switching circuit disconnects the first signal line from the ground section; the second signal line ground switching circuit disconnects the second signal line from the ground section; the third signal line ground switching circuit disconnects the third signal line from the ground section; and the fourth signal line ground switching circuit disconnects the fourth signal line from the ground section.

7. The image forming apparatus according to claim 6.

8. The device body includes: The drum unit further includes a removal opening for removing the drum unit, a cover for opening and closing the removal opening, and a cover sensor for detecting whether the cover is open or closed, The control unit When it is detected that the cover is open based on a signal from the cover sensor, the first signal line ground switching circuit is controlled to connect the first signal line to the ground portion.

2. The image forming apparatus according to claim 1.

9. The sensor a temperature detection sensor that outputs a signal corresponding to the temperature inside the image forming apparatus; The control unit When the temperature cannot be detected based on the signal from the temperature detection sensor, the sensor signal line ground switching circuit is controlled to connect the sensor signal line to the ground portion.

3. The image forming apparatus according to claim 2.

10. The sensor a temperature detection sensor that outputs a signal corresponding to the temperature inside the image forming apparatus; The control unit When the temperature cannot be detected based on the signal from the temperature detection sensor, the first signal line ground switching circuit is controlled to connect the first signal line to the ground portion, and the sensor signal line ground switching circuit is controlled to connect the sensor signal line to the ground portion.

4. The image forming apparatus according to claim 3.

11. The first signal line ground switching circuit a first semiconductor transistor and a first resistor, an output terminal of the first semiconductor transistor being connected to the ground section, a control terminal of the first semiconductor transistor being connected to the control section via the first resistor, and an input terminal of the first semiconductor transistor being connected to the first signal line; 2. The image forming apparatus according to claim 1.

12. The first cartridge control circuit a cartridge memory for storing information relating to the first toner cartridge; The control unit controlling the first signal line ground switching circuit to disconnect the first signal line from the ground portion, and receiving information related to the first toner cartridge from the cartridge memory via the first signal line; 2. The image forming apparatus according to claim 1.

13. Furthermore, it is equipped with a fan, The control unit a temperature detecting circuit for detecting a temperature inside the image forming apparatus based on a signal from the temperature detecting sensor while the sensor signal line is disconnected from the ground portion by controlling the sensor signal line ground switching circuit, and controlling the fan based on the detected temperature; 10. The image forming apparatus according to claim 9.

Images