JP2006058510A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a monitoring circuit system capable of simultaneously monitoring overheating and disconnection of a heat generation source in a fixing process and to maintain high reliability, without relying on software control for disconnection and high temperature abnormalities. <P>SOLUTION: The voltage across STS 140 is inputted to a comparator 166 for detecting the overheat and a comparator 162 for detecting the overheat, and discrimination of abnormality is performed by the respectively different threshold, in order to simultaneously monitor both of the overheat and disconnection of a fuser lamp 102, without the intervention of a CPU 114 by a hard logic circuit (temperature monitor circuit 142), including a pair of comparators (comparator 166 for detecting the overheat and a comparator 162 for detecting the disconnection); and thus, the simultaneous monitoring of two kinds of the abnormalities is made possible and the monitoring configuration of the high reliability can be built. Also, since the software control by a CPU 114 etc., is not applied at all, high reliability is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine to which an electrophotographic system is applied.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine to which this type of electrophotographic method is applied, the photosensitive drum as an image bearing member is centered and the circumferential surface of the photosensitive drum is opposed. A charging unit, an optical scanning unit, a developing unit, a transfer unit, and the like are arranged as described above.

  That is, the surface of the photosensitive drum is uniformly charged by the charging unit, an electrostatic latent image is formed by the light beam from the light scanning unit, the toner is supplied in the developing unit and developed, and, for example, in the transfer unit After the toner image is transferred to a transfer body or the like, the image is transferred to a recording sheet.

  The recording sheet on which the image has been transferred is subjected to a fixing process in the fixing unit while being conveyed to the discharge port. In this fixing unit, the recording paper is heated and pressurized, and a fuser lamp such as a halogen lamp is applied as a heating source.

  The fuser lamp is on / off controlled based on a signal from a controller that executes image formation processing control by the image forming apparatus, and is maintained at a desired temperature.

  On the other hand, since the fuser lamp is applied as a heating element as described above, it is necessary to sufficiently monitor its temperature control and energization state.

  For this reason, a monitoring function is provided in the vicinity of the fuser lamp that can cut off the energization according to the temperature of a thermostat or the like.

  By the way, there are overheating (excessive temperature rise) and thermistor disconnection (temperature cannot be detected) in monitoring the fuser lamp, but the thermistor detection values that are judged to be abnormal are different. The resistors are switched alternately, each is input to the control circuit, and overheat detection or disconnection detection is performed by software judgment (see Patent Document 1 as an example).

Thereby, overheating detection and disconnection detection are possible by time division, and two different types of detection (overheating detection and disconnection detection) can be performed substantially constantly.
JP-A-11-305594

  However, in the temperature monitoring of the above-described conventional configuration, two thermostats (or one thermostat + temperature fuse) and these are detected in order to reliably and reliably detect overheating and disconnection. A control circuit (software) that discriminates an abnormality based on information is necessary. For example, when there is an abnormality in the control circuit, it depends on only two thermostats. Although energization is not interrupted and the reliability is high at normal times, the response when there is a malfunction in any monitoring circuit system is insufficient.

  In consideration of the above facts, the present invention establishes a monitoring circuit system capable of simultaneously monitoring overheating of the heat source and disconnection in the fixing process, and does not depend on software control for disconnection / high temperature abnormality. It is an object to obtain an image forming apparatus capable of maintaining the property.

  According to a first aspect of the present invention, a predetermined voltage is applied to a charging member adjacent to the surface of the image carrier to uniformly charge the display of the image carrier, and the uniformly charged image An electrostatic latent image is formed by irradiating a carrier with a light beam according to image data, and then developing is performed by supplying toner, and the toner image is transferred to a recording medium, and the transferred toner image is fixed. An image forming apparatus having an image forming engine for forming an image by being applied as a heat source necessary for the fixing and generating heat when energized, and usually based on an instruction signal from a control circuit A power supply line interrupting circuit that is operated and interrupts a power supply line to the heating element; a single temperature detection means that is disposed in the vicinity of the heating element and detects the temperature of the heating element; Detection of temperature detection means A first hard logic circuit that outputs a state information signal of the heating element from each of the comparators; and a pair of comparators that discriminate two different types of abnormalities in the heating element based on the results; And a switching circuit that directly controls the power supply line interruption circuit without going through the control circuit based on the state information signal of the heating element output from the hard logic circuit.

  According to a second aspect of the invention, a predetermined voltage is applied to a charging member adjacent to the surface of the image carrier to uniformly charge the display of the image carrier, and the uniformly charged image An electrostatic latent image is formed by irradiating a carrier with a light beam according to image data, and then developing is performed by supplying toner, and the toner image is transferred to a recording medium, and the transferred toner image is fixed. An image forming apparatus having an image forming engine for forming an image by being applied as a heat source necessary for the fixing and generating heat when energized, and usually based on an instruction signal from a control circuit A power supply line interrupting circuit that is operated and interrupts a power supply line to the heating element; a single temperature detection means that is disposed in the vicinity of the heating element and detects the temperature of the heating element; Detection of temperature detection means A first hard logic circuit that outputs a state information signal of the heating element from each of the comparators; and a pair of comparators that discriminate two different types of abnormalities in the heating element based on the results; Based on the state information signal of the heating element output from the hard logic circuit, a switching circuit that directly controls the power supply line intermittent circuit without passing through the control circuit, and a signal from the temperature detection means as inputs, A temperature management unit that performs temperature management of the heating element in software; and an abnormal content determination unit that determines an abnormal content based on the software temperature management result when the temperature management unit determines that there is an abnormality. .

  In the first and second aspects of the present invention, further comprising a second hard logic circuit that continues the circuit interruption by the power supply line interruption circuit after recovery from the abnormality after the abnormality determination by the comparator. It is a feature.

  In the first and second aspects of the invention, the content of the abnormality is stored in the memory of the main body or the fixing device, and power supply to the fixing device after power on / off is permitted / not permitted by the abnormality content. It is characterized by judging permission.

  Furthermore, the power supply is permitted when the replacement of the fixing device is detected.

  In addition, depending on the content of the abnormality, power supply is not permitted when a fixing device that has once produced an abnormality is mounted.

  Furthermore, in the first invention or the second invention, one of the pair of comparators performs disconnection abnormality detection for determining disconnection of the temperature detecting device of the heating element and its wiring, and the pair of comparators. The other of the above is characterized in that high temperature abnormality detection is performed for determining an overheating state of the heating element.

  According to the first invention, the toner image formed on the recording paper through the image forming process, the developing process, and the transferring process is fixed by the fixing process. In the fixing process, the recording paper is pressurized and heated.

  A heating element for heating (for example, a lamp having a high conversion rate from light energy to thermal energy such as a halogen lamp) is applied, and the temperature of the heating element is closely monitored.

  That is, a single temperature detecting means is provided in the vicinity of the heating element. The result (electrical signal based on temperature) detected by this temperature detection means is input to the input terminals of a pair of comparators that form part of the first hard logic circuit.

  One comparator monitors the overheated state of the heating element and sets a relatively high temperature level as a threshold value. The other comparator monitors the disconnection of the temperature detecting device and sets a relatively high resistance level as a threshold value.

  The output from each comparator (heating element state information signal) controls a relay circuit for connecting / disconnecting the power supply line to the heating element by the switching circuit without going through the soft control circuit.

  As a result, since two different types of abnormalities can be simultaneously monitored by a single temperature detecting means, it is possible to perform highly reliable abnormality monitoring with a simple circuit configuration. In addition, since the software control is not used, the temperature of the heating element can be reliably monitored even if the software control circuit has a malfunction (such as program runaway).

  Furthermore, in the second invention, when the abnormality content determination means determines that an abnormality has occurred, the type of abnormality is determined by performing software temperature detection.

  Furthermore, at the time of abnormality determination, the power supply circuit interrupting means has the second hard logic circuit for continuing to shut off the power supply even after recovery from the abnormality, so that the abnormal state can be maintained when there is an abnormality once. it can. In other words, natural recovery can be avoided.

  Also, when an abnormality is detected, the abnormality content is stored in a memory, and depending on the abnormality content (for example, when a high temperature abnormality occurs), the power supply circuit interruption means continues to be shut off after the power is turned off and on (power supply) Depending on the contents of the abnormality (for example, disconnection of the thermistor applicable to the temperature detection of the heating element), if the power is restored after the power is turned off / on, the power supply is permitted and the power is supplied.

  Further, power supply is permitted when replacement of the fixing device is detected. Further, for example, even if a fixing device that has once caused a high temperature abnormality is attached, power supply is not permitted. Thereby, the recurrence of the abnormality after the return can be prevented.

  As described above, the temperature management of the heating element is ensured, and the reliability can be improved.

  As described above, the present invention establishes a monitoring circuit system capable of simultaneously monitoring overheating of the heat source and disconnection in the fixing process, and does not depend on software control for disconnection / high temperature abnormality, and has high reliability. It has the outstanding effect that it can be maintained.

(Schematic configuration of image forming apparatus)
FIG. 1 shows an outline of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes an engine unit 12, and a paper feeding unit 14 is provided below the engine unit 12.

  The paper feed unit 14 includes a paper tray 22 on which paper is stacked and a paper feed roll 24 that sends out the paper from the paper tray 22. The paper passes through the paper feed path 30 through the paper 26 and 28, and is conveyed to a transfer roll 74 described later.

  After the toner image is transferred onto the paper by the transfer roll 74 and fixed by the fixing roll 32A of the fixing unit 32, the toner image is provided on the upper portion of the engine unit 12 by the discharge roll 36 or the discharge roll 38 depending on the position of the switching claw 34. The discharged first discharge tray 16 or the second discharge tray 18 is discharged.

  Here, in the case of double-sided printing, after the printing of the front surface is completed in the order as described above, before the paper is completely discharged to the first discharge tray 16, the discharge roll 36 is reversed and the paper is reversed. Supplied to the line 40. The paper is then returned to the paper feed path 30 through the transport rolls 42, 44, 46, and 48, and the back side of the paper is printed. In the case of manual printing, by placing paper on the manual feed tray 20, the paper is transported from the manual feed roll 49 to the paper feed path 30 via the transport roll 48 and printed.

  In the fixing unit 32, the fixing roll 32A is heated to a predetermined temperature by lighting a lamp (for example, a halogen lamp), and the toner image is formed on the paper by heating and pressurization by the heated fixing roll 32A. The image is fixed. In other words, since the fixing unit 32 is in a very high temperature environment compared to other parts, temperature control is performed under strict monitoring. The temperature control of the fixing unit 32 will be described later.

  By the way, on the right side of FIG. 1 of the image forming apparatus 10, four developer cartridges 64 filled with a developer for each color (made of toner and magnetic carrier) are arranged. The developer cartridge 64 is connected to developing units 60Y, 60M, 60K, and 60C, which will be described later, arranged in order from the top of FIG. 1 through a developer supply path 65, and the developer in the developer cartridge 64 is stored in the developer cartridge 64. Supplied to developing devices 60Y, 60M, 60K, and 60C.

  An exposure unit 62 is disposed on the left side of the developer cartridge 64 in FIG. 1, and the four laser beams L (Y), L (M), and L (K) corresponding to the image signal are provided from the exposure unit 62. ), L (C) are photosensitive drums 52Y, 52M, 52K, 52C constituting the photosensitive unit 50 arranged on the left side of the exposure unit 62 in FIG. And a latent image is formed on the photosensitive drum 52.

  The photosensitive drum 52 is for yellow (52Y), magenta (52M), black (52K), and cyan (52C) from the top of FIG.

  The exposure unit 62 outputs laser light L (Y), L (M), L (K), and L (C) (hereinafter collectively referred to as laser light L) of each color Y, M, C, and K. The light source unit, a modulation processing unit that modulates and scans the laser light L, an fθ lens that corrects the scanning speed on the exposure surface, a surface tilt correction cylindrical lens that has lens power in the scanning direction, and the like. And an optical system.

  In the exposure unit 62, the laser light L of each color emitted from the light source unit enters the modulation processing unit, is modulated according to the image information for each color, and is scanned by the polygon mirror 67 rotated by the polygon motor 63. (Main scanning). The laser beams L of the respective colors scanned by the polygon mirror 67 are reflected by the mirror group 69 in the arrangement direction of the photosensitive drums 52 corresponding to the respective colors and formed on the respective photosensitive drums 52.

  The photosensitive unit 50 is provided with a charging roll 56 and a refreshing roll 54 corresponding to each photosensitive drum 52, and is provided to rotate in contact with the photosensitive drum 52, respectively. In the charging roll 56, the photosensitive drum 52 is uniformly charged, and toner flying from a magnet roll 80 provided in the developing unit 58 described later is attached to the surface of the photosensitive drum 52. On the other hand, the refresh roll 54 discharges the photosensitive drum 52 to remove residual toner adhering to the surface of the photosensitive drum 52, thereby preventing ghosts and the like caused by the toner remaining on the surface of the photosensitive drum 52.

  Here, the developing unit 58 is arranged on the lower right side of FIG. 1 of each photosensitive unit 50, and four developing units 60Y corresponding to the respective photosensitive drums 52 (52Y, 52M, 52K, 52C). , 60M, 60K, 60C are arranged in the vertical direction.

  On the other hand, an intermediate transfer unit 66 is disposed on the left side of the photoconductor unit 50 in FIG. 1, and three drum-shaped intermediate transfer bodies 68, 70, and 72 are provided. The two first intermediate transfer members 68 and 70 are arranged vertically in the vertical direction, and the upper first intermediate transfer member 68 includes two photosensitive drums 52Y and 52Y arranged at the upper portion of the photosensitive drum 52. The lower first intermediate transfer member 70 rotates in contact with the two photosensitive drums 52K and 52C disposed in the lower portion. Further, the second intermediate transfer member 72 is rotated in contact with both the first intermediate transfer members 68 and 70, and the transfer roll 74 described above is rotated in contact with the second intermediate transfer member 72.

  Accordingly, the toner images are transferred from the photosensitive drums 52Y and 52M to the first intermediate transfer member 68, and the toner images are transferred from the photosensitive drums 52K and 52C to the first intermediate transfer member 70, respectively. The two color toner images transferred to the first intermediate transfer bodies 68 and 70 are transferred to the second intermediate transfer body 72 to form four colors, and the four color toner images are transferred onto the sheet by the transfer roll 74. Will be.

  A cleaning roll 76 and a cleaning brush 78 are disposed in the vicinity of the intermediate transfer members 68, 70, and 72, respectively, and the residual toner on the surface of the intermediate transfer members 68, 70, and 72 is scraped off.

(Schematic configuration of the control system of the entire image forming apparatus)
FIG. 2 is a block diagram of a control system for image formation in the engine unit 12.

  The main power management unit 200 is connected to a commercial power source (not shown), generates LVPS (low voltage power source) and HVPS (high voltage power source), and supplies power to each unit through a power supply line.

  A user interface 204 is connected to the main controller 202, and an instruction relating to image formation or the like is given by a user's operation, and information about the image formation or the like is notified to the user.

  The main controller 202 is connected to a network line with an external host computer (not shown) so that image data is input.

  When the image data is input, the main controller 202 analyzes, for example, the print instruction information included in the image data and the image data, and converts them into a format suitable for the engine unit 12 (for example, bitmap data). The image data is sent to the image formation processing control unit 206 constituting a part of the MCU 100.

  In the image formation processing control unit 206, based on the input image data, together with the image parasitic processing control unit 206, the optical scanning system control unit 208, the drive system control unit 210, the charger control unit 212, and the development that constitute the MCU 100, respectively. Each of the apparatus control unit 214 and the fixing unit control unit 216 is synchronously controlled to execute image formation.

  A unit loading state management unit 218 is connected to the image formation processing control unit 206, and determines the operating state of the engine unit 12 (for example, during processing mode, during sleep mode, during processing during startup from sleep mode, etc.). It is supposed to be. The operating state determined by the unit loading state management unit 218 is sent to the main controller 202.

  The main power management unit 200 is connected to a power-on monitoring sensor 220. The power-on monitoring sensor 220 detects when the power is turned on, and supplies the power-on information via the unit loading state management unit 218. The data is sent to the main controller 202.

  Furthermore, a temperature sensor 221 and a humidity sensor 222 are connected to the main controller 202 as environment detection means. The temperature sensor 221 and the humidity sensor 222 detect the environmental temperature / humidity in the engine unit 1A.

(Schematic configuration of fuser lamp lighting control of the fixing unit 32)
As shown in FIG. 3, a fuser lamp 102 is built in the fixing roll 32A of the fixing unit 32 described above, and the fixing roll 32A is heated by heat generated when the fuser lamp 102 is turned on. ing.

  As shown in FIG. 3, the fuser lamp 102 of the fixing unit (FUSER) 32 includes a fixing unit controller 216 that forms part of the MCU 100 and a low-voltage power source (LVPS) that forms part of the main power management unit 200. 104 to control.

  A signal line 106 connected to one end of the fuser lamp 102 is connected to one end of a switch unit 110 </ b> A of a fuser relay circuit 110 provided in the LVPS 104 via a thermostat 108. The other end of the switch unit 110A is connected to an AC power source (AC Line).

  One end of the coil portion 110B of the fuser relay circuit 110 is connected to 24V INTLK, and the other end is connected to the collector of the main switching transistor 112 (npn type). The emitter of the main switching transistor 112 is grounded, and the base is connected to the CPU 114 of the fixing unit control unit 216.

  Therefore, when a high level signal (H level signal) is output from the CPU 114, the emitter-collector of the main switching transistor 112 is turned on, the coil part 110B is excited, and the switch part 110A is turned on.

  A signal line 116 connected to the other end of the fuser lamp 102 is connected to a switching control unit 118 provided in the LVPS 104.

  The switching control unit 118 includes a primary side and a secondary side, and the signal line 116 is connected to one end of the triac 120 on the primary side. The other end of the triac 120 is connected to an AC power source (AC Nut).

  A capacitor 122 and a resistor 124 are connected in series at both ends of the triac 120.

  Further, both ends of the triac 120 are connected to the primary side (light receiving unit 132A) of the phototriac 132 together with the resistors 126 and 128, the capacitor 130, and the like.

  When predetermined light (light from a secondary light projecting unit 132B described later) is input to the light receiving unit 132A, the signal line 116 is brought into conduction with an AC power source (AC Nut), and the fuser relay circuit 110 is connected. The fuser lamp 102 is lit while the switch section 110A is on.

  One end of the secondary side (light projecting unit 132B) of the phototriac 132 is connected to the collector of a first switching transistor 136 (pnp type) provided in the fixing unit control unit 216 via a resistor 134. The emitter of the first switching transistor 136 is connected to a power supply line (3.3 V) for lighting the light projecting unit 132B of the phototriac 132. The base of the first switching transistor 136 is connected to the CPU 114 of the fixing unit control unit 216 that outputs a control signal. That is, when the L (low level) control signal is output to the base of the first switching transistor 136, the emitter-collector is turned on.

  On the other hand, the other end of the light projecting unit 132B of the phototriac 132 is connected to a collector of a second switching transistor 138 (npn type) provided in the fixing unit control unit 216. The emitter of the second switching transistor 138 is grounded. The base of the second switching transistor 138 is connected to the CPU 114 that outputs a control signal. That is, the emitter-collector is turned on when an H (high level) control signal is output to the base of the second switching transistor 138.

  In the above configuration, as a control signal from the CPU 114, a low level control signal is output to the first switching transistor 136, and at the same time, a high level control signal is output to the second switching transistor 138, whereby the phototriac 132 is output. Can be turned on. As a result, the signal line 116 from the fuser lamp 102 becomes conductive with the AC Nut by the primary side triac 120, and the fuser lamp 102 can be turned on.

  In other words, by simultaneously outputting signals of opposite logic to each other, the light projecting unit 132B of the photo triac 132 is turned on, and when any of the signals causes a malfunction (short circuit or disconnection), This is a problem in the direction of turning off the light projecting unit 132B, and it is possible to avoid the problem of reverse constant lighting.

(Temperature management control of fuser lamp 102)
As shown in FIG. 3, an STS (temperature sensor) 140 is disposed in the vicinity of the fuser lamp 102 as temperature detection means, and its signal line is connected to the CPU 114 of the MCU 100. The CPU 114 always determines whether the temperature of the fuser lamp 102 is normal or abnormal. By the way, the temperature monitoring by the CPU 114 is compared and determined with a temperature threshold value for determining overheating of the fuser lamp 102.

  In this embodiment, the temperature of the fuser lamp 102 is monitored by the temperature monitoring circuit 142 having a hard logic circuit configuration separately from the temperature monitoring by the CPU 114.

  That is, the temperature monitoring circuit 142 is connected to a branch line 144 branched from a signal line connecting the STS 140 and the CPU 114, and a temperature detected by the STS 140 (an electric signal based on the temperature) is input. ing.

  The output signal line 146 of the temperature monitoring circuit 142 is connected to one input terminal of the AND circuit 148. An output signal line 150 from the CPU 114 is connected to the other input terminal of the AND circuit 148, and an output from the AND circuit 148 is determined by a logical product from both output signal lines 146 and 148 (both are high). When level (1), output is high level (1)). Therefore, when the fuser lamp 102 is operating normally, a high level signal is output from both the temperature monitoring circuit 142 and the CPU 114.

  The output signal line 152 of the AND circuit 148 is connected to the base of the main switching transistor 112, and controls energization / non-energization of the coil part 110B of the fuser relay circuit 110.

  The output signal line 152 of the AND circuit 148 is connected to the base of the monitoring switching transistor 154. The monitoring switching transistor 154 has a function of notifying the CPU 114 of the energization state of the fuser relay circuit 110. The collector side is connected to the CPU 114 and the emitter side is grounded.

  As a result, the CPU 114 can confirm the energization state of the fuser relay circuit 110 in the on / off state of the monitoring switching transistor 154.

(Details of temperature monitoring circuit 142)
FIG. 4 shows details of the temperature monitoring circuit 142.

  Both ends of the STS 140 are connected in a loop with a resistor 156 (15 KΩ), a resistor 158 (15 KΩ), and a resistor 160 (2.2 MΩ) connected in series.

  The resistor 158 and the resistor 160 in the loop circuit are connected to the plus-side input terminal of the comparator 162 for detecting disconnection.

  Further, a branch line 164 is connected in a cross shape between one end of the STS 140 and the resistor 156, one of which is connected to the CPU 114 and the other is connected to the negative side input terminal of the comparator 162 for detecting disconnection. It is connected to the plus side input terminal of the comparator 166 for overheat detection (high temperature detection).

  Further, a branch line 168 is connected in a cross shape between the resistor 156 and the resistor 158, one of which is connected to a drive power supply (3.0V), the other is a resistor 170 (15K ohm), and a resistor 172 ( Is connected between the STS 140 and the resistor 160 via 2.4 KΩ. This connection point is grounded.

  A resistor 170 and a resistor 172 in the branch line 168 are connected to the minus side input terminal of the overheat detection comparator 166.

  The output terminals of the disconnection detection comparator 162 and the overheat detection comparator 166 are common, and are connected to the power supply line 176 via a resistor 174. A drive power supply (5 V) is applied to one end of the power supply line 176 via a capacitor 178.

  The power line 176 is connected to one input terminal of the AND circuit 148.

  The other end of the power supply line 176 is connected to the base of the latch transistor 184 that constitutes the latch circuit 182 via the resistor 180. The power source (5 V) is supplied to the emitter of the latch transistor 184 via a resistor 186, and the collector is between the resistor 170 and the resistor 172 of the branch line 168 and the negative side of the overheat detection comparator 166. Connected to the input end. A resistor 188 is interposed between the emitter and base of the latch transistor 184.

  That is, in the latch circuit 182, when an abnormal signal is output from either the disconnection detection comparator 162 or the overheat detection comparator 166, the emitter-collector of the latch transistor 184 is turned on, and the abnormal signal is always output. Is sent to the negative input terminal of the overheat detection comparator 166 (abnormal latch state). When an abnormal latch state is entered by the latch circuit 182, the abnormal latch state is released by the latch release circuit 190.

  The latch release circuit 190 operates in response to a latch release instruction from the reset IC 192 (mounted on the CPU 114).

  When the emitter-collector of the reset IC (transistor structure) is turned on (at the time of reset), the first stage of the two-stage latch release transistors 192 and 194 is turned off, and the second stage is turned on by this off state.

  When the second-stage latch release transistor 194 is turned on (ON between the collector and the emitter), a current flows from the collector of the latch transistor 184 to the second-stage latch release transistor 194, and comparison for overheat detection is performed. The latch signal output to the device 166 is released.

  In the latch release circuit 190, a 3.3V voltage is applied to the collector of the first-stage latch release transistor 192, and a 5V voltage is applied to the collector of the second-stage latch release transistor 194.

  That is, when there is no latch release circuit 190, the latch circuit 182 operates normally when 3.3V rises from 5V as the power supply voltage rise sequence, but when 3V rises first, the latch is not released. For this reason, a latch release circuit 190 is provided, and the latch release of the temperature start circuit 142 is forcibly executed by a reset signal from the CPU 114.

  The operation of this embodiment will be described below.

(Flow of image forming process)
Around each photosensitive drum 52, an image forming (printing) process for each color by a known electrophotographic method is performed as follows.

  First, each photosensitive drum 52 is rotationally driven at a predetermined rotational speed (for example, 95 mm / sec).

  As shown in FIG. 1, the surface of the photosensitive drum 52 is uniformly charged to a predetermined level by applying a DC voltage of a predetermined charging level (for example, about −800 V) to the charging roll 56. . In the present embodiment, only a DC voltage is applied to the charging roll 56, but an AC component may be superimposed on the DC component.

  Next, the surface of each photosensitive drum 52 having a uniform surface potential is irradiated with laser light L corresponding to each color by the exposure unit 62, and an electrostatic latent image corresponding to image information for each color is formed. The Thereby, the surface potential of the exposed portion of the photosensitive drum 52 by the laser light L is neutralized to a predetermined level (for example, about −60 V or less).

  The electrostatic latent image formed on the surface of each photoconductive drum 52 is developed by the corresponding developing unit 58 and visualized on each photoconductive drum 52 as a toner image of each color.

  Next, the toner images of the respective colors formed on the respective photoconductive drums 52 are electrostatically primary-transferred onto the corresponding primary intermediate transfer drums 68 and 70. Here, the Y and M toner images formed on the photosensitive drums 52Y and 52M are on the primary intermediate transfer drum 68, and the K and C toner images formed on the photosensitive drums 52K and 52C are the primary intermediate. Each image is transferred onto the transfer drum 70.

  Thereafter, the toner image formed on the primary intermediate transfer drums 68 and 70 is electrostatically secondary-transferred onto the secondary intermediate transfer drum 72. As a result, on the secondary intermediate transfer drum 72, toner images from a single color image to a quadruple color image of each color of Y, M, K, and C are formed.

  Finally, the toner image formed on the secondary intermediate transfer drum 72 is tertiary-transferred onto the paper passing through the paper conveyance path by the transfer roll 74. After the tertiary transfer, the toner image formed on the paper is heat-fixed by the fixing unit 32, and the image forming process ends.

(Lighting control of fuser lamp 102)
Here, the fixing unit control unit 216 of the MCU 100 performs lighting control of the fuser lamp 102 as a heating source for heating the fixing roll 32A.

  This lighting control is basically executed by a binarized signal from the CPU 114 of the fixing unit control unit 216. First, the CPU 114 sends the power to the fuser lamp 102 to the main switching transistor 112. On the other hand, an H level signal is output.

  As a result, the emitter-collector of the main switching transistor 112 is turned on, and the coil portion 110B of the fuser relay circuit 110 is excited by 24V INTLK. When the coil unit 110B is excited, the switch unit 110A is turned on, and the power supply line is opened.

  In this state, the CPU 114 can turn on and off the fuser lamp 102 by controlling the lighting / extinguishing of the light projecting unit 132A of the phototriac 132 of the switching control unit 118.

  By the way, conventionally, the lighting / extinguishing control of the light projecting unit 132B of the phototriac 132 has transmitted a signal of H level (on) / low level (off) through a single signal line. There are short-circuits (both short-circuited) due to terminal bridges and solder scraps at the output end, disconnection or short-circuiting due to the biting of the harness, etc. When such a failure occurs, the lighting control of the fuser lamp becomes impossible. In the worst case, the fuser lamp There was a possibility that it would be constantly lit (overheated).

  Therefore, in this embodiment, the lighting control of the light projecting unit 132B of the phototriac 132 is executed by two signals having opposite logics, so that at least the worst situation of always lighting even if there is the above problem. To avoid.

  That is, the first switching transistor 136 and the second switching transistor 138 are provided at both ends of the light projecting unit 132B of the phototriac 132, respectively.

  In the first switching transistor 136, a low-level signal is output from the CPU 114, whereby one end of the light projecting unit 132B can be electrically connected to a power supply line of 3.3V that is a power supply voltage (first switching transistor). ON state between the emitter and collector of the jitter 136).

  On the other hand, in the second switching transistor 138, a high level signal is output from the CPU 114, whereby the other end of the light projecting unit 132B can be grounded (the ON-between the emitter and collector of the second switching transistor 138). Status).

  Therefore, even if the terminal bridge or the like occurs in either one, the light projecting unit 132 can be normally controlled by the on / off control of the other, so that one of the signals avoids the worst (always lighting) itself. can do.

(Temperature monitoring control of fuser lamp 102)
In the STS 140, the resistance value changes based on the temperature of the fuser lamp 102, and the voltage input to the CPU 114 changes.

  This voltage value is sent to the CPU 114. In the CPU 114, the temperature of the fuser lamp 102 is controlled by the voltage value (digital value based on the voltage value) from the STS 140.

  Further, the voltage resulting from the voltage division of the resistor 170 (15 KΩ) and the resistor 172 (2.4 KΩ) is input to the minus side input terminal of the overheat detection comparator 166, which serves as a threshold value. Further, the voltage at both ends of the STS 140 is input to the plus side input terminal of the comparator 166 for detecting overheating, and is compared with the threshold value.

  As a result of this comparison, if the voltage between the STSs 140 is below the threshold value, it is determined that the overheat state has occurred, and an abnormal signal is output from the overheat detection comparator 166, and one of the AND circuits 148 shown in FIG. Is input to the input terminal.

  As a result, the output of the AND circuit 148 is switched to a signal for turning off the main switching transistor 112, the energization to the coil part 110B of the fuser relay circuit 110 is cut off, and the switch part 110A of the AC LINE is turned off.

  The output signal of the AND circuit 148 is sent to the base of the monitoring switching transistor 154, and the CPU 114 recognizes that an abnormality has occurred.

  Next, a voltage obtained by dividing the voltage of the resistor 158 (15 KΩ) and the resistor 160 (2.2 MΩ) is input to the plus side input terminal of the comparator 162 for detecting disconnection, and this becomes a threshold value. Further, the voltage at both ends of the STS 140 is input to the negative input terminal of the comparator 162 for detecting disconnection, and is compared with the threshold value.

  As a result of this comparison, if the voltage between the STSs 140 exceeds the threshold value, it is determined that the circuit is disconnected, and an abnormal signal is output from the comparator 162 for detecting disconnection, and one of the AND circuits 148 shown in FIG. Is input to the input terminal.

  As a result, the output of the AND circuit 148 is switched to a signal for turning off the main switching transistor 112, the energization to the coil part 110B of the fuser relay circuit 110 is cut off, and the switch part 110A of the AC LINE is turned off.

  The output signal of the AND circuit 148 is sent to the base of the monitoring switching transistor 154, and the CPU 114 recognizes that an abnormality has occurred.

  In this way, the fuser lamp 102 is overheated without the CPU 114 by the hard logic circuit (temperature monitoring circuit 142) including a pair of comparators (overheat detection comparator 166, disconnection detection comparator 162). In order to monitor both abnormalities and disconnection abnormalities at the same time, the voltage between the STSs 140 is input to the overheat detection comparator 166 and the disconnection detection comparator 162, and the abnormality is determined by different threshold values. Two types of abnormalities can be monitored at the same time, and a highly reliable monitoring configuration can be constructed.

(Return from operation stop due to abnormality)
When an abnormality is detected by any of the above comparators (162 or 166), the abnormality signal is also sent to the latch circuit 182. In this latch circuit 182, the latched transistor 184 turns on the abnormal signal, and even if the abnormal signal is interrupted, a voltage that always gives an abnormality to the negative input terminal of the overheat detection comparator 166 is set to a threshold value. Hold as.

  As a result, if an abnormality occurs even once, even if it recovers, power supply to the fixing unit is avoided from the viewpoint of safety, and an abnormal state (power-off state) can be continued.

  Here, if 3.3V rises from 5V as the order of rise of the power supply voltage, the latch circuit 182 operates normally, but if 3V rises first, the latch is not released. For this reason, a latch release circuit 190 is provided in order to ensure that it is not latched when the power is turned on. The latch release circuit 190 releases the latch using a reset signal from the CPU 114 or the like.

  The latch release circuit 190 can reliably release the latch state of the latch circuit 182 regardless of whether 3.3V rises first or 5V first, and the temperature monitoring circuit can be reset by a reset signal from the CPU 114. 142 can be reliably unlatched.

  By the way, as described above, the CPU 114 monitors overheat abnormality and recognizes the occurrence of abnormality, and as a result, can determine the type of abnormality (overheating abnormality or disconnection abnormality).

  However, if the latch circuit 182 is also powered off, the latch cannot be continued by the hard logic circuit alone, and therefore, one of the AND circuits has a signal that can continue the relay off from the CPU 114. With this signal, it is possible to continue relay-off depending on the type of abnormality even after power-off / on. The relay control at this time has different conditions depending on the type of abnormality.

  That is, when the operation is stopped due to an overheat abnormality, there is some abnormality in the fuser lamp 102, and replacement is essential. For this reason, relay-on is permitted on condition that this exchange work is completed.

  On the other hand, when the operation is stopped due to disconnection, the fuser lamp 102 itself has few problems and mainly has problems with the signal lines 106 and 116. Therefore, in this embodiment, the reset signal output is permitted without any particular condition. To do.

  As described above, since the condition is changed depending on the type of abnormality and the permission / non-permission of the output of the reset signal is determined, early recurrence of the same abnormality can be prevented.

  In the present embodiment, the condition of replacing the fuser lamp 102 is set only when the overheat is abnormal, and the condition is not set when the disconnection is abnormal. However, the presence or absence of the condition is not a problem, and the condition depends on the type of abnormality. If they are different, conditions such as the replacement of the signal lines 106 and 116 or the completion of the continuity test may be set even when the disconnection is abnormal.

  Further, in the present embodiment, the fuser lamp 102 that generates heat by lighting as typified by a halogen lamp is applied as a heating element. However, lighting is not essential if it generates heat when energized, and a high resistance conductive wire ( Heating wire).

1 is a side view showing an image forming apparatus according to the present embodiment. It is a control block diagram of an engine part. It is a circuit block diagram for fuser lamp lighting control of the fixing unit. It is a detailed block diagram of the temperature monitoring circuit provided in the fuser lamp lighting control circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Engine part 32 Fixing part 52 Photosensitive drum 60 Developing device 62 Exposure unit 32A Fixing roll 102 Fuser lamp (heating element)
100 MCU
104 LVPS
110 Fuser Relay Circuit (Relay Circuit)
112 Main switching transistor (switching circuit)
114 CPU (control circuit, abnormality type discrimination means, return form change means)
142 Temperature monitoring circuit (hard logic circuit)
140 STS (temperature detection means)
148 AND circuit (switching circuit)
162 Comparator for disconnection detection 166 Comparator for overheat detection 184 Latch transistor 190 Latch release circuit 192 Reset IC
192, 194 Latch release transistor 200 Main power management unit 216 Fixing unit control unit

Claims (7)

By applying a predetermined voltage to a charging member close to the surface of the image carrier, the display of the image carrier is uniformly charged, and image data is transferred to the uniformly charged image carrier. In response, an electrostatic latent image is formed by irradiating a light beam, and then developing is performed by supplying toner, and the toner image is transferred to a recording medium, and the transferred toner image is fixed to form an image. An image forming apparatus having an image forming engine
A heating element that is applied as a heat source necessary for fixing and generates heat when energized;
Normally operated based on an instruction signal from the control circuit, a power supply line intermittent circuit for interrupting the power supply line to the heating element,
A single temperature detecting means disposed in the vicinity of the heating element for detecting the temperature of the heating element;
A first hard logic circuit comprising a pair of comparators for discriminating two different types of abnormalities in the heating element based on the detection result of the temperature detection means, and outputting a status information signal of the heating element from each comparator When,
A switching circuit that directly controls the power supply line intermittent circuit without going through the control circuit based on the state information signal of the heating element output from the first hard logic circuit;
An image forming apparatus. By applying a predetermined voltage to a charging member close to the surface of the image carrier, the display of the image carrier is uniformly charged, and image data is transferred to the uniformly charged image carrier. In response, an electrostatic latent image is formed by irradiating a light beam, and then developing is performed by supplying toner, and the toner image is transferred to a recording medium, and the transferred toner image is fixed to form an image. An image forming apparatus having an image forming engine
A heating element that is applied as a heat source necessary for fixing and generates heat when energized;
Normally operated based on an instruction signal from the control circuit, a power supply line intermittent circuit for interrupting the power supply line to the heating element,
A single temperature detecting means disposed in the vicinity of the heating element for detecting the temperature of the heating element;
A first hard logic circuit comprising a pair of comparators for discriminating two different types of abnormalities in the heating element based on the detection result of the temperature detection means, and outputting a status information signal of the heating element from each comparator When,
A switching circuit that directly controls the power supply line intermittent circuit without going through the control circuit based on the state information signal of the heating element output from the first hard logic circuit;
With the signal from the temperature detection means as an input, temperature management means for performing temperature management of the heating element in software,
Abnormal content determination means for determining abnormal content from the software temperature management result when it is determined abnormal by the temperature management means;
An image forming apparatus.   3. The second hard logic circuit according to claim 1, further comprising a second hard logic circuit that continues the circuit interruption by the power supply line interruption circuit after the abnormality is determined by the comparator and after the recovery from the abnormality. Image forming apparatus.   The contents of the abnormality are stored in a memory of the main body or the fixing device, and whether to supply power to the fixing device after power on / off is determined based on the abnormality content. The image forming apparatus according to claim 3.   The image forming apparatus according to claim 4, wherein when the replacement of the fixing device is detected, the power supply is permitted.   5. The image forming apparatus according to claim 4, wherein, depending on the content of the abnormality, the power supply is not permitted when the fixing device that has once produced an abnormality is attached.   One of the pair of comparators performs disconnection abnormality detection for determining disconnection of the temperature detection device of the heating element and its wiring, and the other of the pair of comparators is a high temperature for determining the overheating state of the heating element. The image forming apparatus according to claim 1, wherein abnormality detection is performed.

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