JP2004138639A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shut off the feeding of power in times of abnormality, to prevent receiving any damage due to smoking or heat when the fixing device is actually in an excessively heated state and to realize space saving in a control substrate and bringing down of the cost by improving the precision in detection time in an output shorted-circuited state of a triac controlling a heating means in a fixing device. <P>SOLUTION: The feeding and shutting off of power to the heat fixing roller 21 is changed over by the triac 173, the temperature is detected by a thermistor 32 and the temperature of a fixing roller 21 is controlled to a specified temperature by a controller 100. Then, in a safety circuit 200, the edge interval of the state detecting signal of power feeding to the fixing roller 21 is measured when the control signal to the triac 173 is in a power shut off state. An abnormal signal is outputted when judgement is made that the measured edge interval is longer than a first set time. Furthermore, continuous output of the abnormal signal for more than a second set time is measured and the control signal to the triac 173 is set from these results. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, and more particularly, to an image forming apparatus having a fixing device incorporating a heating unit.
[0002]
[Prior art]
2. Description of the Related Art As an image forming apparatus of this type, an electrophotographic copying machine that performs heat fixing has been known. In the fixing device provided in this copying machine, a heating means such as a halogen heater is incorporated in the fixing roller, the surface temperature of the fixing roller is detected by a temperature detecting element such as a thermistor, and a triac or the like connected to the heating means is used. By controlling (ON) / OFF (OFF) the switch elements, the surface temperature of the fixing roller is controlled to be a predetermined temperature.
[0003]
Further, a temperature fuse, a thermoswitch, and the like are arranged on the surface of the fixing roller and connected to the heating means, so that when the temperature of the fixing roller is excessively increased due to an abnormality in the heating control, power is supplied to the heating means. And take safety measures such as fire prevention.
[0004]
In addition, state detecting means such as SSR for detecting whether power to a heating means such as a halogen heater is in a supply state or in a cutoff state is provided, and a switch element such as a triac is turned off. Nevertheless, safety measures have been taken to detect a short-circuit in the output section of a switch element such as a triac by detecting a state in which electric power is supplied to heating means such as a halogen heater. This is because switch elements such as triacs do not have mechanical contacts, so they are much more durable than relays in terms of ON / OFF times. However, because they are made of semiconductors, lightning strikes and excessive This is because a failure of an output short circuit may occur when an instantaneous large stress due to an inrush current or noise is applied.
[0005]
[Problems to be solved by the invention]
By the way, in the case of a triac, for example, the switch element has two states of output short-circuit failure. This is a fault state in which one of the two thyristors constituting the triac is short-circuited, and a fault state in which one of the thyristors is short-circuited.
[0006]
For example, when both sides of the triac are in a failure state, a high-level or low-level fixed signal indicating the power supply state is always output from the state detection element such as the SSR.
[0007]
On the other hand, when one side of the triac is in a failure state, two different logic signals indicating the power supply state and the power cutoff state are switched in a pulse-like state that is switched in a half cycle of the power supply to the heater. Output as a signal.
[0008]
For this reason, conventionally, an integrator for smoothing the pulse signal at the time of the one-side fault is provided, and the short-circuit fault is detected by comparing the smoothed signal with a predetermined reference value by comparing means. ing.
[0009]
However, the above-mentioned integrator is mainly composed of electric components such as a capacitor and a resistor, and the time constant determined by these electric components greatly varies depending on component tolerances and temperature characteristics. Further, in order to use components with small characteristic variations, the cost has to be increased, and a space for mounting these components is also required.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and in view of the above points, a switch element such as a triac for controlling a heating unit such as a halogen heater in a fixing device of an image forming apparatus. It is an object of the present invention to provide a detecting means capable of improving the detection time accuracy of an abnormal state such as an output short state. Another object of the present invention is to make the detection means a digital circuit and incorporate it into an internal circuit such as a system IC, so that the space and cost of the control board can be reduced.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is directed to an image forming apparatus including a fixing device having a heating unit, wherein a temperature detection unit for detecting a temperature of the fixing unit, and supply and cutoff of power to the heating unit are provided. Switch means for switching, control means for controlling the switch means based on a detection signal from the temperature detection means to control the temperature of the fixing device to a predetermined temperature, and power supply to the heating means or a cutoff state State detecting means for detecting whether or not the state is present, and a first measurement for measuring an edge interval of the state detecting signal when a switch control signal for controlling the switch means is in a power cutoff state. Means for determining whether an edge interval measured by the first measuring means is equal to or longer than a first set time, outputting an abnormal signal; And a second measuring means for measuring that the signal has been output continuously for a second set time or more, wherein the switch means is provided with an electric power based on an output signal of the second measuring means or an output signal of the control means. It is configured to be set in the cutoff state.
[0012]
Further, the first measuring means is a counting means for counting an interval between a rising edge and a falling edge of the state detection signal by a counter.
[0013]
It is preferable that the first set time in the determination means be shorter than half the time of the power supply cycle supplied to the image forming apparatus main body.
[0014]
In addition, when the switch control signal is in a power cutoff state, the switch control signal has a third measurement unit that measures that the state detection signal is continuously output for a third set time or more, and the switch unit includes: It is preferable that the power cutoff state is set by an output signal of the second measuring means, an output signal of the third measuring means, or an output signal of the control means.
[0015]
Further, a second switch for switching between supply and cutoff of power to an image forming apparatus main body including the fixing device is provided at a stage preceding the switch for switching supply and cutoff of electric power to the heating unit, The second switch means is preferably set to a power cutoff state by an output signal of the second measurement means, an output signal of the third measurement means, or an output signal of the control means.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a sectional view showing an example of the configuration of an image forming apparatus to which the present invention is applied, and shows a schematic configuration of an electrophotographic color copying machine.
[0018]
In FIG. 1, reference numeral 40 denotes a copying machine main body (image forming apparatus main body), and an automatic document feeder 41 for automatically feeding originals 44 separated one by one on the upper part of the copying machine main body 40; A document reading device 42 that reads an image of a document 44 transported by the automatic document transport device 41 is provided.
[0019]
A document reading device 42 illuminates a document 44 placed on a platen glass 43 with a light source 45, and converts a reflected light image from the document 44 into a reduction optical system including optical mirrors 46, 47, 48 and an imaging lens 49. A scanning exposure is performed on an image reading element 50 such as a CCD through a system, and the color reading light image of the original 44 is read at a predetermined dot density by the image reading element 50.
[0020]
The color material reflected light image of the document 44 read by the document reading device 42 is sent to the image processing device 51 as data of three colors of R (red), G (green), and B (blue). The image processing device 51 performs image processing such as shading correction, gamma (γ) correction, and color space processing on the R, G, and B data of the document 44.
[0021]
The image data subjected to predetermined image processing by the image processing device 51 is sent to the exposure device 5 as Y (yellow), M (magenta), C (cyan), and K (black) image data. At 5, image exposure with laser light is performed according to the image data.
[0022]
Exposure of an image by the exposure device 5 is performed on the photosensitive drum 1, and the photosensitive drum 1 is provided so as to be rotatable in the direction of arrow A in the figure by a motor (not shown). Around the photosensitive drum 1, a primary charger 4, an exposure device 5, a color developing unit 7, a black and white developing unit 8, a transfer charger 9, and a cleaner device 6 are arranged.
[0023]
In forming an image, first, a voltage is applied to the primary charger 4 and the surface of the photosensitive drum 1 is uniformly negatively charged at a predetermined charging portion potential. Subsequently, exposure is performed by an exposure device 5 including a laser scanner based on the image data so that the charged image portion on the photosensitive drum 1 has a predetermined exposure portion potential. A latent image is formed thereon. At this time, the exposure device 5 forms a latent image corresponding to the image by turning on / off based on the image data.
[0024]
The color developing unit 7 has three color developing devices 7Y, 7M, and 7C for performing full-color development. The color developing devices 7Y, 7M, 7C and the black-and-white developing device 8 develop the latent image on the photosensitive drum 1 with Y, M, C, and K toners to visualize the latent image. At this time, when developing the toner of each color, the color developing unit 7 is rotated by a motor (not shown) in the direction of arrow R in the figure, and the developing device of the color is aligned so as to contact the photosensitive drum 1.
[0025]
The developed toner images of the respective colors on the photosensitive drum 1 are sequentially transferred to the transfer belt 2 as an intermediate transfer body by the transfer charger 9, whereby the four color toner images are superimposed. A belt cleaner 14 is provided at a position facing the transfer belt driving roller 10 with the transfer belt 2 interposed therebetween, and residual toner on the transfer belt 2 is scraped off by a blade.
[0026]
The toner image transferred to the transfer belt 2 is further transferred to a sheet by a transfer roller 15 as a secondary transfer device. During full-color printing, four color toners are superimposed on a belt and then transferred to recording paper. The recording paper is drawn out of the recording paper cassette 16 into a transport path by a pickup roller 17 and is fed by a pair of transport rollers 18 and 19 to a nip portion, that is, a contact portion between the transfer roller 15 and the transfer belt 2.
[0027]
Further, the toner remaining on the photosensitive drum 1 is set in a state where the toner is easily cleaned by the preliminary cleaning device, and is removed and collected by the cleaner device 6. Finally, the photosensitive drum 1 is uniformly discharged to near 0 volts by a not-shown discharging device to prepare for the next image forming cycle.
[0028]
The sheet on which the toner image has been transferred is then fed to the fixing device 3. Further, the toner image on the recording paper is heat-fixed by the fixing device 3 and discharged out of the apparatus main body.
[0029]
Here, the image forming timing of the color copying machine is controlled based on a predetermined position on the transfer belt 2. The transfer belt 2 is stretched around the rollers 10, 11, 12, and 13. Of these, the transfer belt driving roller 10 is coupled to a driving source (not shown) and functions as a driving roller for driving the transfer belt 2, and the transfer belt tension rollers 11 and 12 are tension rollers for adjusting the tension of the transfer belt 2. The transfer belt backup roller 13 functions as a backup roller for the transfer roller 15 as a secondary transfer device.
[0030]
A reflection type sensor 20 for detecting a reference position is arranged near the tension roller 12. The reflective sensor 20 detects a marking on a reflective tape or the like provided at an end of the outer peripheral surface of the transfer belt 2 and outputs an I-top signal.
[0031]
Further, the outer peripheral length of the photosensitive drum 1 and the peripheral length of the transfer belt 2 have an integer ratio represented by 1: n (n is an integer). With this setting, the photosensitive drum 1 rotates an integer while the transfer belt 2 makes one revolution, and returns to the same state as before the one revolution of the belt, so that when the four colors are superimposed on the transfer belt 2, (The transfer belt 2 makes four revolutions), it is possible to avoid color shift due to uneven rotation of the photosensitive drum 1.
[0032]
In the image forming apparatus of the intermediate transfer system as described above, after detecting the I-top signal from the reflection type sensor 20, the exposure is started by the exposure device 5 including a laser scanner after a predetermined time has elapsed. Further, as described above, the photosensitive drum 1 rotates an integer while the transfer belt 2 makes one revolution, and returns to the same state as before the one revolution of the belt, so that the toner image of each color is always at the same position on the transfer belt 2. Is formed. Further, the toner image size changes depending on the paper size, but there is a range on the transfer belt 2 where the toner image never falls.
[0033]
The fixing device 3 includes a fixing roller 21 serving as a fixing member having a halogen heater 22 therein as a heating unit (heating unit), and a pressure roller 23 serving as a fixing member also having a halogen heater 24 therein as a heating unit. The fixing members are configured to be rotatable while being pressed against each other by a pressing mechanism (not shown).
[0034]
The fixing roller 21 has an HTV (high-temperature vulcanization type) silicone rubber layer provided on the outer periphery of a core made of aluminum, and further has an RTV (room temperature vulcanization type) silicone rubber layer as a heat-resistant elastic layer on the outer periphery of the HTV silicone rubber layer. Is formed, and the thickness is 3 [mm] and the diameter is 40 [mm].
[0035]
The pressure roller 23 is provided with an HTV silicone rubber layer having a thickness of 1 [mm] on the outer periphery of a core made of aluminum, and further provided with a fluororesin layer on the outer periphery of the HTV silicone rubber layer to have a diameter of 40 [mm]. Is formed.
[0036]
By combining the fixing roller 21 and the pressure roller 23 having the above-described configuration, the releasability from the toner is further improved.
[0037]
An external heating roller 29 serving as an external heating member is provided on the outer peripheral surface of the fixing roller 21 so as to be able to contact / retreat. That is, the external heating roller 29 is moved by an abutting / retracting mechanism (not shown) and abuts / retreats on the outer peripheral surface of the fixing roller 21. At this time, the fixing roller 21 is pressed by a spring (not shown) and rotates following the fixing roller 21.
[0038]
For example, the external heating roller 29 is supported by a support rod such as a heat insulating bush. Then, the support rod is moved to press and attach / detach the fixing roller 21. This attachment / detachment is achieved by using a well-known technique such as a spring clutch and a solenoid.
[0039]
Further, the external heating roller 29 has a halogen heater 30 built therein, and a metal such as aluminum, iron, stainless steel or the like having a high thermal conductivity, a rubber or a resin having a high mold release property is provided on the outer periphery thereof. On a metal surface. The external heating roller 29 is held at both ends by a heat-insulating bush having high heat resistance.
[0040]
Although not shown, a thermistor is disposed in contact with the fixing roller 21, the pressure roller 23, and the external heating roller 29, and the thermistor detects the surface temperature of each of the rollers 21, 23, 29, The control device controls the halogen heaters 22, 24, 30 based on the temperature information, and thereby controls the temperatures of the rollers 21, 23, 29.
[0041]
As an example of the temperature adjustment, the temperature of the external heating roller 29 as the external heating member is set to be higher than the temperature of the fixing roller 21 and the pressure roller 23 as the fixing member pair. , The fixing roller 21 and the pressure roller 23 are set at 180 ° C.
[0042]
In this way, the unfixed image formed of the developer such as toner transferred onto the sheet passes through the nip between the fixing roller 21 and the pressure roller 23 controlled at a predetermined temperature, and is heated and heated. By being pressed, it is fixed on the recording paper and discharged.
[0043]
Although not shown, the above-described color copier includes a sheet processing apparatus, a sheet processing apparatus input unit, a sheet processing apparatus path, a sheet processing apparatus path switching conveyance path, a processing tray, a stapler, a processing tray unloading unit, and a lower part. A stack tray, an upper stack tray, a sheet processing apparatus path switching unit, a package binding apparatus, a package binding sheet insertion unit, and the like are provided.
[0044]
FIG. 2 is a block diagram showing a configuration of a control system of the image forming apparatus according to the embodiment of the present invention.
[0045]
In FIG. 2, reference numeral 100 denotes a controller (control means) constituting the above-described control device, which has a CPU 100a, a ROM 100b, a RAM 100c, and the like, and controls the entire copy sequence based on a program stored in the ROM 100b.
[0046]
An operation unit 112 includes setting keys for a copy mode (single-sided copy, double-sided copy, multiple copy, copy magnification, cassette selection, etc.), numeric keys for setting the number of copies, a start key for instructing a start of a copy operation, and an instruction for a stop of a copy operation. A key input unit such as a stop key for resetting the operation mode, a reset key for returning the operation mode to a standard state, and a display unit such as an LED and a liquid crystal for displaying a setting state of the operation mode are arranged.
[0047]
The thermistors 32, 34, and 36 are thermistors as temperature detecting means disposed on the fixing roller 21, the pressure roller 23, and the external heating roller 29, and detect the respective surface temperatures. The A / D converted (digital-analog converted) value is input to the controller 100. The controller 100 controls the surface temperatures of the fixing roller 21, the pressure roller 23, and the external heating roller 29 to be a predetermined value based on the detection values of the thermistors 32, 34, and 36.
[0048]
The high-voltage controller 103 controls a high-voltage unit 104 that applies a predetermined potential to charging systems such as the primary charger 4, the transfer charger 9, and the color developing unit 7.
[0049]
The motor control unit 105 controls driving of a motor 106 such as various stepping motors and a main drive motor.
[0050]
The DC load control unit 107 controls driving of a solenoid, a clutch, a fan, and the like.
[0051]
The sensors 108 are various sensors for detecting a paper jam of transfer paper (recording paper), and their outputs are input to the controller 100.
[0052]
The AC driver 109 controls an AC load 110 such as a light source (document illumination lamp) 45 and the like, and supplies AC power to the fixing roller 21, the pressure roller 23, and the external heating roller 29. Further, an abnormality of the fixing roller 21, the pressure roller 23, the external heating roller 29, and the like is detected, and the fixing relay 130 is turned off.
[0053]
The DC power supply 113 supplies DC power to the controller 100 and the like. The AC power input from the power plug 116 is input to the DC power supply 313 via the door switch (DSW) 115 and the main switch (MSW) 114.
[0054]
The paper deck 151 is a paper feeding device for increasing the number of transfer papers to be stacked, and is optionally connected.
[0055]
The editor 152 is for inputting position information such as trimming and masking processing, and is optionally connected.
[0056]
The feeder 153 is for automatically setting a plurality of originals, and is optionally connected.
[0057]
The sorter 154 sorts the transfer paper to be discharged, and is optionally connected.
[0058]
Next, the fixing heater control will be described with reference to FIGS. Although the apparatus of the present embodiment has three rollers of the fixing roller 21, the pressure roller 23, and the external heating roller 29, an embodiment when the present invention is applied to any of the rollers, Since the same effect is obtained, only the fixing roller 21 will be described here, and the other two rollers will not be described.
[0059]
FIG. 3 is a circuit diagram showing a configuration of a general fixing heater control unit. The fixing heater control unit includes an overheating detection circuit for the fixing roller 21 and an abnormality detection circuit for detecting output short-circuit of the switch element.
[0060]
In the configuration shown in FIG. 3, AC power is supplied to the halogen heater 22 of the fixing roller 21 via the door switch 115 and the fixing relay 130, and the halogen heater 22 is turned on when the triac 173, which is a switch for switching between power supply and cutoff, is turned on. The heater 22 is energized to heat the fixing roller 21.
[0061]
The triac 173 is controlled in a power supply state or a power cutoff state by a switch control signal from the controller 100. When the controller 100 outputs a High signal to the base of the transistor Tr104, the transistor Tr104 is turned on, and the transistor Tr104 is turned on. Turning on also turns on the transistor Tr103. As a result, a current flows from the emitter of the transistor TR103 to the collector, and the triac 173 is turned on. Further, when a Low signal is output from the controller 100, the transistors TR104 and Tr103 are turned off, so that the triac 173 is also turned off.
[0062]
The thermistor 32 detects the surface temperature of the fixing roller 21, and the resistance of the thermistor 32 changes according to the surface temperature of the fixing roller 21 (the higher the temperature, the lower the resistance). This resistance value is detected as a voltage divided by the resistor R101 and the thermistor 32 (the divided voltage decreases as the temperature increases), and the voltage is A / D converted by the A / D converter 101. Are detected by the controller 100. In the controller 100, correspondence data between the surface temperature and the A / D conversion value according to the characteristics of the thermistor 32 is set in advance, and based on the correspondence data, the fixing roller 21 is set to a predetermined temperature. It controls the triac 173.
[0063]
When the controller 100 detects that the surface temperature of the fixing roller 21 has exceeded a specified value based on the A / D conversion value from the thermistor 32, the controller 100 outputs a High signal to the base of the transistor Tr101 as an abnormal state, and performs fixing. By turning off the relay 130, the AC power supply to the halogen heater 22 is cut off. Further, even when an abnormal signal of a triac 173 described later is detected, an operation of outputting a High signal to the transistor Tr101 to turn off the fixing relay 130 is performed.
[0064]
The excessive temperature rise detection circuit includes comparators 171 and 172, and the temperature detection signal from the thermistor 32 is input to the negative input terminal of the comparator 171. Further, a specified value (a value corresponding to the detected overheating temperature) set by the resistors R102 and R103 is input to the positive input terminal of the comparator 171 as a reference value.
[0065]
The output signal of the comparator 171 is input to the positive input terminal of the comparator 172, and the reference value set by the resistors R107 and R108 is input to the negative input terminal.
[0066]
When the temperature detected by the thermistor 32 is lower than the specified temperature (when the detected voltage is high), the value of the negative input terminal of the comparator 171 becomes larger than the value of the positive input terminal, and the output of the comparator 171 becomes a low signal. And the value of the positive input terminal of the comparator 172 becomes lower than the value of the negative input terminal, so that the output signal of the comparator 172 becomes a low signal.
[0067]
On the other hand, when the temperature detected by the thermistor 32 becomes higher than the specified temperature (the detected voltage becomes lower), the value of the negative input terminal becomes lower than the value of the positive input terminal. The value of the positive input terminal increases in voltage according to a time constant determined by the resistor R105 and the capacitor C101 (the resistor R104 has a value sufficiently smaller than the resistor R105).
[0068]
When the value of the positive input terminal of the comparator 172 exceeds the reference value of the negative input terminal, the output of the comparator 172 enters a high impedance state. At this time, by turning on the transistor Tr101 via the diode D101, the fixing relay 130 is turned off. Then, the AC power supplied to the fixing roller 21 is cut off.
[0069]
In the present embodiment, a time constant of about 3 seconds is provided by the resistor R105 and the capacitor C101 in order to prevent a malfunction due to noise or the like, but the time constant is not provided as necessary. Is also good.
[0070]
The triac abnormality detection circuit is a circuit that detects an output short-circuit state in which the triac 173 is in an on state, although the controller 100 outputs an off signal to the triac 173. The state detection signal indicating the state of the triac 173 is generated by a state detection unit including the diode bridge 174 and the photocoupler 175.
[0071]
When the triac 173 is normal, a voltage is generated at both ends of the triac 173 when the triac 173 is off, a current flows to the input side of the photocoupler 175 via the diode bridge 174, and the photocoupler 175 is turned on. State. At this time, the current flowing to the diode bridge 174 has a value at which the fixing roller 21 does not generate heat.
[0072]
When the photocoupler 175 turns on, the voltage at the positive input terminal of the comparator 176 becomes lower than the voltage at the negative input terminal to which the reference value set by the resistors R116 and R117 is input. Is a Low output. At this time, the transistor Tr105 is off because the Low signal is output from the controller 100 to the base.
[0073]
On the other hand, when the triac 173 is in an on state despite the controller 100 outputting an off signal to the triac 173, both ends of the triac 173 are at the same potential and the photocoupler 175 is turned off. Since it is turned off, the voltage at the positive input terminal of the comparator 176 rises according to the time constant of the integrator constituted by the resistors R121 and R122 and the capacitor C103.
[0074]
When the voltage of the positive input terminal of the comparator 176 exceeds the reference value of the negative input terminal, the output goes to a high state. The controller 100 receives this signal, determines that the triac 173 is in an abnormal state, and turns off the triac 173. At the same time, the fixing relay 130 is turned off, and the AC power supplied to the fixing heater 21 is cut off.
[0075]
When the fixing roller 21 is controlled to be on, the voltage of the positive input terminal of the comparator 176 is always at the Low level by turning on the transistor Tr105 by the controller 100, and the short-circuit failure of the triac 173 is not detected.
[0076]
Here, in the above-described circuit, the abnormality detection time when the two thyristors 173a and 173b constituting the triac 173 short-circuit the output on both sides is determined by using the resistors R121 and R122 and the capacitor to prevent malfunction due to noise or the like. It is about 5 seconds by an integrator by C103. Further, the abnormality detection time when either one of the thyristors 173a and 173b is short-circuited is such that the photocoupler 175 turns on when the AC current flows to the normal thyristor side and the AC coupler flows when the AC current flows to the faulty thyristor side. Since ON / OFF such as turning off the photocoupler 175 is switched and repeated in a half cycle of the power supply, the detection time is approximately doubled to about 10 seconds.
[0077]
FIG. 4 is a circuit diagram showing a configuration of a fixing heater control unit according to the embodiment of the present invention. Circuits other than the output short detection portion of the triac 173 are the same as those described with reference to FIG.
[0078]
In the circuit shown in FIG. 3, the time constant of the triac output short-circuit determined by the integrators of the resistors R121 and R122 and the capacitor C103 greatly varies depending on the tolerance of components and the temperature characteristics. In addition, in order to use a component having a small characteristic variation, the cost of the component has to be increased, and a space for mounting an integrator by these components has been required. On the other hand, in the circuit of FIG. 4, the safety circuit 200 is digitized to improve the accuracy of the output short detection time of the triac 173. Further, the safety circuit 200 is incorporated into the controller 100 of the system, so that the advantages of space saving of a board and cost reduction can be obtained at the same time.
[0079]
FIG. 5 is a block diagram showing the internal configuration of the safety circuit 200.
[0080]
The fixing heater control signal (HEAT_ON) from the controller 100 is in the ON control state at High and is input to the AND gates 201 and 210. Further, the control signal (HEAT_ON_OUT) supplied to the triac 173 for driving the fixing roller 21 is in a high-on control state, and is output from the AND gate 210. A triac error signal (triac ERR) is input to the other input terminal of the AND gate 210, and is in an abnormal state at low. Therefore, when the triac error signal is in an abnormal state (when the triac ERR = L), the HEAT_ON_OUT signal is fixed to the low output, and the fixing roller 21 is not driven.
[0081]
Similarly, the drive signal (RELAY_ON_OUT) for driving the fixing relay 130 is input to the input terminal of the AND gate 209 together with the control signal and the triac error signal from the controller 100, and when the triac error signal is in an abnormal state (triac ERR) = L), the RELAY_ON_OUT signal is fixed at the Low output, and the fixing relay 130 is not driven.
[0082]
The triac error signal (abnormal signal) is generated by a circuit of the counters 202 and 203, the comparator 204, and the counters 205 and 206, or a circuit of the counter 207. The circuits of the counters 202 and 203, the comparator 204, and the counters 205 and 206 detect a one-sided short-circuit failure of the triac 173, and the circuit of the counter 207 detects a short-circuited output of the triac 173 on both sides.
[0083]
First, a one-side short detection circuit will be described.
[0084]
The AND gate 201 has a state detection signal SSR (High when the power is supplied) indicating whether the power to the fixing roller 21 is supplied or cut off, and a fixing heater control signal ( High) is input during the power supply state. Therefore, the AND gate 201 outputs an SSR signal that goes high when the fixing roller 21 is on, despite the fact that the fixing roller 21 is off-controlled.
[0085]
The counter 202 and the counter 203 constitute a first measuring means for measuring the edge interval between the rising edge and the falling edge of the SSR signal output from the AND gate 201. The first measuring means is a counting means using a counter.
[0086]
The counter 202 clears the count value once at the timing of the rising edge of the SSR signal, and then proceeds with the count operation. Further, the SSR signal operates only during a High period, and when the SSR signal becomes Low, the counting is stopped and the count value is held. Then, when the SSR signal changes to High again, the count value is cleared to zero again, and then the counting operation is started.
[0087]
The counter 203 always receives the count value from the counter 202, and latches the current count value at the timing when the SSR signal falls. At this time, the latched count value is output to the next-stage comparator 204. That is, the counter 203 outputs the previously latched value to the next-stage comparator 204 while the SSR signal is High, and updates the output value to the currently latched value at the timing when the SSR signal falls.
[0088]
The comparator 204 is a judging means for judging whether or not the edge interval of the SSR signal detected by the counter 202 and the counter 203 is normal by comparing with a predetermined value. That is, one of the two input terminals of the comparator 204 receives the above-described count value, and the other has a reference value (first set time) appropriate for determining the edge interval of the SSR. ing.
[0089]
The reference value in this embodiment has a width shorter than a half cycle of the power supply cycle. This is because when one side of the triac 173 is in a failure state, two different logic signals indicating the power supply state and the power cutoff state are switched at a half cycle of the power supplied to the fixing roller 21. (The high period of the SSR signal does not have a width of more than a half cycle of the power supply at the time of one-side short-circuit failure.) If the reference value in the comparator 204 is set longer than a half cycle of the power supply cycle This is because one-sided short circuit cannot be detected.
[0090]
On the other hand, if the setting value of the comparator 204 is extremely shortened, strictly speaking, the SSR signal instantaneously becomes High at the zero-cross point even when the fixing roller 21 is normally turned off. An error is recognized by mistake at the timing. Therefore, it is desirable to set this set value to about one quarter of the power supply cycle.
[0091]
Further, the comparator 204 outputs a one-side short ERR1 signal (abnormal state at High) when the edge interval of the SSR signal exceeds the reference value. This one-side short-circuit ERR1 signal is input to the next-stage counter 206 via the counter 205 including a D flip-flop.
[0092]
The counter 206 is a second measuring means (counting means) for detecting that the one-side short ERR1 signal has been continuously output for a set reference time (second set time) or more, and when it is detected, Outputs a one-sided short ERR2 signal (abnormal state at Low). This is provided to prevent erroneous recognition of a failure when the one-side short ERR1 signal becomes High due to suddenly generated noise or the like, and is set in the counter 206 in this embodiment. The reference time is 1 second. This reference value can be shorter or longer as needed.
[0093]
When the one-side short ERR2 signal is output from the counter 206, this signal is notified to the CPU 100a in the controller 100 via the NOR gate 210 and is input to the AND gates 209 and 210. As a result, the ON signal of the fixing roller 21 and the ON signal of the fixing relay 130 are forcibly fixed to Low and turned off by the output signals of the AND gates 209 and 210. In addition, the controller 100 turns off the control signal of each heater and displays an error on the display unit to stop the operation of the apparatus.
[0094]
Next, a circuit for detecting a double-sided short-circuit fault will be described.
[0095]
When the output parts on both sides of the triac 173 have a short-circuit fault at the same time, the SSR signal is always a signal of Hgih (power supply state). The counter 207 monitors the duration of the high state of the SSR signal. Here, when the high state of the SSR signal continues for 1 second or more, it is determined that a double-sided failure has occurred. This detection time may be shorter or longer as necessary. However, when the detection time is shortened, error recognition is not performed due to sudden noise or the like. However, it is necessary to set it in consideration of failure due to excessive temperature rise.
[0096]
When the counter 207 detects a short circuit on both sides of the triac 173, the counter 207 outputs a short circuit on both sides ERR signal (abnormal state at High), and this signal is input to the NOR gate 208.
[0097]
Then, a triac ERR signal is output from the NOR gate 208, and this signal is input to the AND gates 209 and 210 to perform various safety functions in the same manner as in the case of the one-side short circuit, and is notified to the CPU 100a in the controller 100. The operation of the device stops.
[0098]
That is, when the control signal to the triac 173 is in the power cutoff state, the counter 207 measures the continuous output of the SSR signal (state detection signal) for the third set time or more. (Counting means). The triac 173 is set to a power cutoff state in response to an output signal from the counter 206, an output signal from the counter 207, or an output signal from the controller 100.
[0099]
The AND gates 209 and 210 constitute second switch means for switching between supply and cutoff of electric power to the entire copying machine body 40 at a stage (upstream side) before the triac 173, and this second switch means , In response to an output signal from the counter 206 or an output signal from the controller 100, the power cutoff state is set.
[0100]
FIG. 6 is a flowchart showing a control procedure of the fixing heater of the above-described embodiment. The control processing shown in this flowchart is executed by the CPU 100a in the controller 100 in accordance with a program stored in the ROM 100b in advance.
[0101]
6, S1, S2, and S3 indicate the surface temperatures of the external heating roller 29, the fixing roller 21, and the pressing roller 23, respectively, and H1, H2, and H3 indicate the halogen heaters 30 for the external heating roller, respectively. The halogen heater 22 for the fixing roller and the halogen heater 24 for the pressure roller are shown.
[0102]
First, it is checked whether or not the surface temperature of the external heating roller 29 has reached the control temperature of 200 ° C. (step S101). If not, the halogen heater 30 for the external heating roller is turned on (step S104). If so, the halogen heater 30 for the external heating roller is turned off (step S102).
[0103]
When the halogen heater 30 for the external heating roller is turned off, a short circuit detection of the triac for driving the external heating heater is performed in the safety circuit 200 (S103). If it is determined that the triac is normal, the process proceeds to step S105, and the next normal operation is performed. Move on to the sequence. If the safety circuit 200 determines that an abnormality has occurred, the safety circuit 200 forcibly fixes the drive signals of various heaters and the fixing relay to the off side, and the controller 100 controls the halogen heater 30 for the external heating roller. After the control signals for all the heaters of the fixing roller halogen heater 22 and the pressure roller halogen heater 24 and the fixing relay are turned off (step S113), the operation of the color copying machine is stopped with an error (step S114).
[0104]
After checking the surface temperature of the external heating roller 29, it is checked whether the surface temperature of the fixing roller 21 has reached the control temperature of 180 ° C. (step S105).
[0105]
If the temperature of the fixing roller 21 has not reached the control temperature in step S105, the fixing roller halogen heater 22 is turned on (step S108), and if it has reached, the fixing roller halogen heater 22 is turned off (step S108). S106).
[0106]
When the fixing roller halogen heater 22 is turned off, a short circuit detection of the fixing heater driving triac is performed in the safety circuit 200 (S107). If it is determined that the triac is normal, the process proceeds to step S109, and the next normal sequence is performed. Move on. If the safety circuit 200 determines that an error has occurred, the color copying machine is stopped in an error in the same sequence as described above (steps S113 and S114).
[0107]
After checking the surface temperature of the fixing roller 21, it is checked whether the surface temperature of the pressure roller 23 has reached the control temperature of 160 ° C. (step S109).
[0108]
If the temperature of the pressure roller 23 has not reached the control temperature in step S109, the halogen heater 24 for the pressure roller is turned on (step S112), and if it has, the halogen heater 24 for the pressure roller is turned off. (Step S110).
[0109]
When the halogen heater 24 for the pressure roller is turned off, the safety circuit 200 detects a short circuit of the triac for driving the pressure roller (S111). Move on. If the safety circuit 200 determines that an error has occurred, the color copying machine is stopped in an error in the same sequence as described above (steps S113 and S114).
[0110]
The embodiments of the present invention have been described above. In the present invention, as described above, in an image forming apparatus including a fixing device having a heating unit (heating unit), a temperature detecting unit for detecting a temperature of the fixing unit is provided. Switch means for switching between supply and cutoff of electric power to the heating means, control means for controlling the switch means based on a detection signal from the temperature detection means to control the temperature of the fixing device to a predetermined temperature, State detecting means for detecting whether power is supplied to the heating means or in a cut-off state and outputting a state detection signal; and the state when a switch control signal for controlling the switch means is in a power cut-off state. A first measuring means for measuring an edge interval of the detection signal; and outputting an abnormal signal when the edge interval measured by the first measuring means is determined to be longer than a first set time. And a second measuring means for measuring that an abnormal signal is continuously output from the determining means for a second set time or more, and wherein the switch means outputs the output of the second measuring means. The power cutoff state is set by a signal or an output signal of the control means.
[0111]
For this reason, it is possible to improve the detection time accuracy of an output short-circuit state such as a triac that controls a heating unit such as a halogen heater in the fixing device. Therefore, it is possible to prevent the fixing device from actually being overheated and damaged by smoke and heat, thereby improving safety and reliability. In addition, since the detection means can be constituted by a digital circuit, the space can be saved and the cost of the control board can be reduced by incorporating it into an internal circuit such as a system IC.
[0112]
Further, the present invention can have the following embodiments based on the above configuration (1).
[0113]
(2) In the image forming apparatus having the configuration of (1), the first measuring unit is a counting unit that counts an interval between a rising edge and a falling edge of the state detection signal using a counter.
[0114]
(3) In the image forming apparatus having the configuration of (1) or (2), the first set time in the determination unit is set to be shorter than a half of a power supply cycle supplied to the image forming apparatus main body.
[0115]
(4) In the image forming apparatus having the configuration of (3), when the switch control signal is in the power cutoff state, a third measurement for measuring that the state detection signal is continuously output for a third set time or more. Measuring means, wherein the switch means is set to a power cutoff state by an output signal of the second measuring means, an output signal of the third measuring means, or an output signal of the control means. I do.
[0116]
(5) In the image forming apparatus having the configuration of (4), before and after the switch unit that switches between supply and cutoff of power to the heating unit, supply and cutoff of power to the image forming apparatus main body including the fixing unit. And a second switch means for switching power by an output signal of the second measurement means, an output signal of the third measurement means, or an output signal of the control means. Be set to the cutoff state.
[0117]
【The invention's effect】
As described above, according to the present invention, the detection time accuracy of an abnormal state such as an output short-circuit state of a switch element such as a triac that controls a heating unit such as a halogen heater in a fixing device can be improved. Since the power supply to the image forming apparatus main body can be cut off, it is possible to prevent the fixing unit from actually being overheated and being damaged by smoke or heat, thereby improving safety and reliability. be able to. In addition, since the detection means can be constituted by a digital circuit, the space can be saved and the cost can be reduced by taking in the internal circuit such as the system IC.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus to which the present invention is applied.
FIG. 2 is a block diagram showing a configuration of a control system according to the embodiment of the present invention.
FIG. 3 is a circuit diagram showing a configuration of a general fixing heater control unit.
FIG. 4 is a circuit diagram illustrating a configuration of a fixing heater control unit according to the embodiment.
FIG. 5 is a block diagram showing a configuration of a safety circuit according to the embodiment.
FIG. 6 is a flowchart illustrating a control procedure of a fixing heater according to the embodiment.
[Explanation of symbols]
1 Photoconductor drum
2 Transfer belt
3 Fixing device
4 Primary charger
5 Exposure equipment
6 cleaner device
7 Color development unit
8 Black and white developing device
9 Transfer charger
10 Transfer belt drive roller
11 Transfer belt tension roller
12 Transfer belt tension roller
13 Transfer belt backup roller
14 Belt cleaner
15 Transfer roller
16 Recording paper cassette
17 pickup roller,
18 Transport rollers
19 Transport roller
20 Reflection type sensor
21 Fixing roller
22 Halogen heater (heating means)
23 Pressure roller
24 Halogen heater (heating means)
29 External heating roller
30 Halogen heater (heating means)
31 External heater
32 Thermistor (Temperature detecting means)
40 Copy machine body (image forming apparatus body)
41 Automatic Document Feeder
42 document reading device,
43 Platen glass
44 manuscript
45 light source
46 Optical mirror
47 Optical mirror
48 Optical mirror
49 Imaging lens
50 Image reading element
51 Image processing device
100 controller (control means)
100a CPU
100b ROM
100c RAM
101 A / D converter
114 Main switch
115 Door switch
130 fusing relay
171 Comparator
172 Comparator
173 Triac (switch means)
174 diode bridge (state detection means)
175 Photocoupler (state detection means)
176 counter
200 Safety Circuit
201 AND gate
202 counter (first measuring means)
203 counter (first measuring means)
204 Comparator (judgment means)
205 D flip-flop
206 counter (second measuring means)
207 counter (third measuring means)
208 NOR gate
209 AND gate (second switch means)
210 AND gate (second switch means)

Claims (1)

In an image forming apparatus including a fixing device having a heating unit,
Temperature detection means for detecting the temperature of the fixing device;
Switch means for switching between supply and cutoff of power to the heating means,
Control means for controlling the switch means based on a detection signal from the temperature detection means to control the temperature of the fixing device to a predetermined temperature;
State detection means for detecting whether power is supplied to the heating means or in a cutoff state and outputs a state detection signal;
First measurement means for measuring an edge interval of the state detection signal when a switch control signal for controlling the switch means is in a power cutoff state;
Determining means for outputting an abnormal signal when determining that the edge interval measured by the first measuring means is equal to or longer than a first set time;
A second measuring means for measuring that the abnormal signal is continuously output for a second set time or more from the determining means,
The image forming apparatus according to claim 1, wherein the switch unit is set to a power cutoff state by an output signal of the second measuring unit or an output signal of the control unit.

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