JP2014185992A - Temperature detecting device, image forming apparatus, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature detecting device which is capable of temperature detection, disconnection detection, and overheating abnormality detection, with a simple configuration using one temperature detecting element, and to provide an image forming apparatus and a program.SOLUTION: The temperature detecting device includes a variable resistance part which is connected to between a voltage generation source generating a reference voltage and the temperature detecting element and whose resistance value can be switched between a first value and a second value larger than the first value, temperature detecting means for detecting the temperature of a heating element, on the basis of a potential between the variable resistance part and the temperature detecting element, and overheating detecting means for detecting the overheating of the heating element, on the basis of the potential between the variable resistance part and the temperature detecting element and a predetermined reference potential. When the temperature of the heating element detected by the temperature detecting means is less than a predetermined temperature, the variable resistance part is controlled so that the resistance value of the variable resistance part is alternately switched to the first value and the second value. When the temperature of the heating element detected by the temperature detecting means is the predetermined temperature or more, the variable resistance part is controlled so as to obtain the first value.

Description

  The present invention relates to a temperature detection apparatus, an image forming apparatus, and a program.

In Patent Document 1, a thermistor having a negative temperature coefficient whose one end is connected to one pole of a DC power source, and connected between the other one pole of the DC power source and the other end of the thermistor,
A reference resistor whose resistance value can be switched between a first resistance value and a second resistance value greater than the first resistance value, and a voltage across the thermistor are sampled at a predetermined timing, and the next sample Sample / hold means for holding until time, comparison means for comparing the thermistor voltage with a predetermined threshold voltage, latch means for latching the output of the comparison means at a predetermined timing, and resistance value of the reference resistor Is a first resistance value, a switching command for switching between a temperature measurement mode and a disconnection detection mode which is a second resistance value, a sample command to the sample / hold means during the temperature measurement mode, and a disconnection There is disclosed a temperature detection circuit comprising command generation means for outputting a latch command to the latch means during a detection mode period.

JP-A-11-281499

  An object of the present invention is to provide a temperature detection device, an image forming apparatus, and a program capable of detecting temperature, detecting disconnection, and detecting overheating with a simple configuration using one temperature detection element.

  In order to achieve the above object, a temperature detection device according to claim 1 includes a temperature detection element whose resistance value changes according to a temperature change of a heating element to be detected, a voltage generation source that generates a reference voltage, A variable resistance portion connected between the temperature detection element and having a resistance value switchable between a first value and a second value greater than the first value; the variable resistance portion; and the temperature detection Based on the temperature detection means for detecting the temperature of the heating element based on the potential between the element, the potential between the variable resistance portion and the temperature detection element and a predetermined reference potential, When the temperature of the heat generating element detected by the temperature detecting means is less than a predetermined temperature, the resistance value of the variable resistance portion is the first value. And the variable so as to switch alternately to the second value A control for controlling the variable resistance unit so as to be the first value when the temperature of the heating element detected by the temperature detecting means is equal to or higher than the predetermined temperature. Means.

  According to a second aspect of the present invention, in the first aspect of the present invention, the disconnection detecting means for detecting a disconnection of the temperature detection element based on a potential between the variable resistance portion and the temperature detection element. In addition, when the temperature of the heating element detected by the temperature detection means is lower than the predetermined temperature, the temperature detection means in a period during which the resistance value of the variable resistance portion becomes the first value. When the temperature is detected and the disconnection detecting means detects the disconnection during the period of the second value, the temperature of the heating element detected by the temperature detecting means is equal to or higher than the predetermined temperature. The temperature detecting means detects the temperature.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the variable resistance portion includes a second resistor having a second resistance value, the second resistance value, Whether to enable parallel connection of the first resistor to which the combined resistance value when connected in parallel to the resistor is the first value, and the first resistor to the second resistor Switching means for switching whether to invalidate is provided.

The invention according to claim 4 further includes a second switching means for causing a current to flow intermittently through the temperature detection element in the invention according to any one of claims 1 to 3. ,
The control means further controls the second switching means to flow an electric current intermittently to the temperature detecting element when the temperature of the heating element is equal to or higher than a predetermined temperature.

  Furthermore, in order to achieve the above object, an image forming apparatus according to claim 5 includes the temperature detection device according to any one of claims 1 to 4, wherein the heating element is a fixing device. .

On the other hand, in order to achieve the above object, a program according to claim 6
It is for making it function as the said control means in the image forming apparatus of Claim 5.

  According to the first, fifth, and sixth aspects of the invention, compared with the case where the present invention is not applied, the temperature detection, the disconnection detection, and the overheating can be performed with a simple configuration using one temperature detection element. The effect that abnormality detection becomes possible can be acquired.

  In addition, according to the invention described in claim 2, it is possible to obtain an effect that temperature detection, disconnection detection, and overheat abnormality detection can be performed with simpler processing than in the case where the present invention is not applied. it can.

  Further, according to the invention described in claim 3, it is possible to obtain an effect that temperature detection, disconnection detection, and overheat abnormality detection can be performed more reliably than in the case where the present invention is not applied.

  Furthermore, according to the invention described in claim 4, the temperature increase of the temperature detecting element is suppressed and the accuracy of the detected temperature is improved as compared with the case where the second switching unit of the present invention is not provided. Can be obtained.

1 is a side cross-sectional view illustrating an example of a configuration of an image forming apparatus according to an embodiment. 2 is a block diagram illustrating an example of a configuration for temperature monitoring control of a fixing roller according to an embodiment. FIG. 6 is a graph illustrating an example of a relationship between a temperature of a fixing roller and a temperature signal according to the embodiment. FIG. 3 is a circuit diagram illustrating an example of a circuit configuration for temperature monitoring control of the fixing roller according to the first embodiment. 6 is a time chart for explaining an operation example of temperature monitoring control of the fixing roller according to the first embodiment. It is a flowchart which shows the flow of a process of the temperature monitoring control program which concerns on 1st Embodiment. FIG. 10 is a circuit diagram illustrating an example of a circuit configuration for temperature monitoring control of a fixing roller according to a second embodiment. 10 is a time chart for explaining an operation example of temperature monitoring control of the fixing roller according to the second embodiment. It is a flowchart which shows the flow of a process of the temperature monitoring control program which concerns on 2nd Embodiment. FIG. 6 is a circuit diagram illustrating a circuit configuration for temperature monitoring control of a fixing roller according to a conventional technique. 6 is a time chart for explaining an operation of temperature monitoring control of a fixing roller according to a conventional technique.

  Hereinafter, the image forming apparatus 1 according to the present embodiment will be described in detail with reference to the drawings.

[First Embodiment]

FIG. 1 is a side sectional view showing an internal configuration of an image forming apparatus 1 according to the present embodiment.
The overall configuration and operation of the image forming apparatus 1 will be described below with reference to FIG.
The image forming apparatus 1 includes a control device 10, a paper feeding device 20, a photosensitive unit 30, a developing device 40, a transfer device 50, and a fixing device 60. On the upper surface of the image forming apparatus 1, a discharge unit 1 a for discharging and storing a sheet on which an image is formed is provided.

  The control device 10 includes a controller 11 that controls the operation of the image forming apparatus 1, an image processing unit 12 that is controlled by the controller 11, and a power supply device 13. The power supply device 13 applies a voltage to a charging roller 32, a developing roller 42, a primary transfer roller 52, a secondary transfer roller 53, and the like which will be described later.

  The image processing unit 12 converts print information acquired from an external information processing apparatus (for example, a personal computer or the like, not shown) into image information for forming a latent image, and corresponds to the image information at a preset timing. A drive signal is output to the exposure apparatus LH. As an example, exposure apparatus LH of the present embodiment is configured to include an LED head in which LEDs (Light Emitting Diodes) are linearly arranged.

  A paper feeding device 20 is provided at the bottom of the image forming apparatus 1. The sheet feeding device 20 includes a sheet stacking plate 21, and a large number of sheets P are stacked on the upper surface of the sheet stacking plate 21. The sheets P loaded on the sheet stacking plate 21 and positioned in the width direction by a regulating plate (not shown) are pulled out one by one from the upper side by the sheet drawer 22 (leftward in FIG. 1). Thereafter, the sheet is conveyed to the nip portion of the registration roller pair 23.

  Four photoconductor units 30 are provided in parallel above the sheet feeding device 20 and each include a photoconductor 31 that is rotationally driven. A charging roller 32, an exposure device LH, a developing device 40, a primary transfer roller 52, and a cleaning blade 34 are arranged along the rotation direction of the photoconductor 31 (the direction represented by A in FIG. 1). A cleaning roller 33 for cleaning the surface of the charging roller 32 is disposed opposite to and in contact with the charging roller 32.

The developing device 40 includes a developing housing 41 in which a developer is accommodated. In the developing housing 41, a developing roller 42 disposed to face the photoreceptor 31, and a developer disposed obliquely below the back side of the developing roller 42 (rightward in FIG. 1) are developed roller 42. A pair of supply parts 44 and 45 for stirring and transporting to the side are provided. A layer regulating member 46 that regulates the layer thickness of the developer is disposed adjacent to the developing roller 42.
Each of the developing devices 40 is configured in the same manner except for the developer accommodated in the developing housing 41, and each of them develops yellow (Y), magenta (M), cyan (C), and black (K) toner images. Form.

  The surface of the rotating photoreceptor 31 is charged by the charging roller 32, and an electrostatic latent image is formed on the charged surface by the latent image forming light emitted from the exposure device LH. The electrostatic latent image formed on the photoreceptor 31 is developed as a toner image by the developing roller 42.

The transfer device 50 includes an intermediate transfer belt 51 on which the toner images of the respective colors formed on the photoconductors 31 of the photoconductor units 30 are transferred, and an intermediate image of each color formed on the photoconductor units 30. A primary transfer roller 52 that sequentially transfers (primary transfer) to the transfer belt 51 is provided.
Further, the transfer device 50 includes a secondary transfer roller 53 that collectively transfers (secondary transfer) toner images of each color transferred onto the intermediate transfer belt 51 onto the paper P.

  Each color toner image formed on the photoreceptor 31 of each photoreceptor unit 30 is transferred onto the intermediate transfer belt 51 by a primary transfer roller 52 to which a predetermined transfer voltage is applied from a power supply device 13 or the like controlled by the controller 11. Then, electrostatic transfer (primary transfer) is sequentially performed to form a superimposed toner image in which toner images of respective colors are superimposed.

  The superimposed toner image on the intermediate transfer belt 51 is conveyed to a region (secondary transfer portion T) where the secondary transfer roller 53 is disposed as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer unit T, the paper P is supplied from the paper feeding device 20 to the secondary transfer unit T in accordance with the timing. Then, a predetermined transfer voltage is applied to the secondary transfer roller 53 from the power supply device 13 or the like controlled by the controller 11, and the intermediate transfer is performed on the paper P that is fed from the registration roller pair 23 and guided by the conveyance guide. Multiple toner images on the belt 51 are collectively transferred.

  Residual toner on the surface of the photoconductor 31 is removed by the cleaning blade 34 and collected in a waste developer container (not shown). Thereafter, the surface of the photoreceptor 31 is recharged by the charging roller 32. Residue that cannot be completely removed by the cleaning blade 34 and adheres to the charging roller 32 is captured and accumulated on the surface of the cleaning roller 33 that rotates in contact with the charging roller 32.

The sheet P on which the toner image is transferred in the transfer device 50 is conveyed to the fixing device 60 via the conveyance guide in a state where the toner image is not fixed.
The fixing device 60 includes a fixing roller 61 and a pressure roller 62, and a nip portion N (fixing region) is formed by a pressure contact region between the fixing roller 61 and the pressure roller 62. The fixing roller 61 includes a fixing lamp 63, and the fixing roller 61 is heated by the fixing lamp 63.

  When the paper P is conveyed to the fixing device 60, the toner image on the paper P is fixed by the action of pressure bonding and heating by the fixing roller 61 and the pressure roller 62. The sheet P on which the fixed toner image is formed is guided by the conveyance guides 65 a and 65 b and is discharged from the discharge roller pair 69 to the discharge unit 1 a on the upper surface of the image forming apparatus 1.

Next, temperature monitoring control of the fixing roller 61 of the fixing device 60 in the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating an example of a configuration for temperature monitoring control of the fixing roller 61 of the image forming apparatus 1.
The temperature monitoring control target may be either the fixing roller 61 or the fixing lamp 63.
In the present embodiment, an example in which the temperature monitoring control of the fixing roller 61 is executed will be described.

  As described above, the fixing roller 61 of the fixing device 60 includes the fixing lamp 63 as an example of the heating element, and the fixing roller 61 is heated by the heat generated when the fixing lamp 63 is turned on. A fixing lamp 63 of the fixing device 60 includes a controller 11 connected to a thermistor 110 as an example of a temperature detecting element via an AD converter (analog / digital converter) 159 and a low voltage that constitutes a part of the power supply device 13. It is controlled by the power supply 130. The controller 11 includes a CPU (Central Processing Unit) 11a, a ROM 11b, a RAM 11c, and a storage unit 11d.

The thermistor 110 detects the temperature of the fixing roller 61 and outputs it as a temperature signal Vs. Then, temperature data indicating the temperature detected by the temperature signal Vs is output to the CPU 11 a of the controller 11 via the AD converter 159.
The CPU 11a controls the operation of the entire image forming apparatus 1. The ROM 11b functions as a storage unit that stores in advance a control program for controlling the operation of the image forming apparatus 1, a temperature monitoring control program to be described later, various parameters, and the like. The RAM 11c is used as a work area when various programs are executed. The storage unit 11d is for storing image information of an image read by a scanner unit (not shown) provided in the image forming apparatus 1 or an average value of the temperature signal Vs.

  On the other hand, a circuit including the AC power source 14, the switch element 112, and the fixing relay 111 is connected to the fixing lamp 63.

The fixing relay 111 as an example of means for interrupting the power supply path is a switch element that operates by being supplied with a driving voltage from the low voltage power supply 130, and energizes or interrupts the power supplied from the AC power supply 14 to the fixing lamp 63. To do.
The fixing relay 111 may be, for example, a solid state relay, a triac, or other switch element.

  Based on the temperature data corresponding to the temperature signal Vs input from the thermistor 110 via the AD converter 159, the CPU 11 a turns on or off the fixing lamp 63 via the switch element 112, and the surface temperature of the fixing roller 61. Is controlled to a temperature suitable for fixing.

  Next, the temperature monitoring control of the fixing roller 61 will be described more specifically with reference to FIG. FIG. 3 is a graph showing an example of the relationship between the temperature signal Vs obtained by the thermistor 110 and the temperature of the fixing roller 61.

As shown in FIG. 3, the temperature signal Vs monotonously decreases as the temperature of the fixing roller 61 increases.
As temperature drops, it increases monotonously. When the temperature signal Vs is larger than the preset threshold value Vl (the temperature is smaller than the target temperature Tl), the fixing roller 61 is heated (the fixing lamp 63 is energized) and the temperature rises. Get smaller.
On the contrary, when the temperature signal Vs is smaller than the preset threshold value Vu (the temperature is larger than the target temperature Tu), the energization to the fixing lamp 63 is cut off, and the temperature of the fixing roller 61 is lowered and the temperature signal is decreased. Vs increases.

  That is, when the temperature indicated by the temperature signal Vs is equal to or lower than the preset target temperature Tl, the CPU 11a closes the switch element 112 and supplies power from the AC power supply 14 to the fixing lamp 63 to When the temperature indicated by the signal Vs exceeds the preset target temperature Tu, the switch element 112 is opened and the energization to the fixing lamp 63 is interrupted.

Further, the CPU 11a always determines whether the temperature of the fixing roller 61 is normal or abnormal during temperature monitoring control. Specifically, the above determination is performed by comparing with a temperature threshold value for determining overheating of the fixing roller 61.
For example, when the temperature signal Vs becomes smaller than a threshold value (reference voltage) Vref of a comparator 154 (see also FIG. 4), that is, when the temperature of the fixing roller 61 exceeds the threshold temperature Th, The energization of the fixing lamp 63 is interrupted by the fixing relay 111.

Further, when the thermistor 110 is disconnected, the temperature signal Vs exceeds the threshold value for determining the disconnection, for example, the voltage of the reference power supply (3.3 volts in the present embodiment, expressed as Vc in FIG. 3). Indicates. In this state, in order to prevent the fixing lamp 63 from being turned on and overheating, the energization to the fixing lamp 63 is interrupted by the fixing relay 111.
Note that the threshold for determining disconnection is set, for example, in the CPU 11a. Further, Tm and Vm shown in FIG. 3 will be described later.

By the way, even if the thermistor 110 is normally connected, the resistance of the thermistor 110 increases at a low temperature, for example, near 0 ° C., and approaches the voltage Vc of the reference power supply, for example. There is.
As a conventional technique for avoiding this erroneous detection, there is a method of shifting the offset of the temperature signal Vs of the thermistor 110 between the case of detecting the temperature and the case of detecting the disconnection.

  FIG. 10 shows a circuit configuration diagram for temperature monitoring control of the fixing roller 61 of the fixing device 60 according to the prior art employing this method. As shown in the figure, the fixing roller temperature monitoring control circuit 150 includes a disconnection detection circuit and a high temperature detection circuit.

  The disconnection detection circuit is connected in series to the thermistor 110 that detects the temperature of the fixing roller 61, and a pull-up resistor 151 (resistor having a resistance value of 1 MΩ as an example in the present embodiment) that divides the voltage Vc of the reference power supply. A transistor 152 (a PNP transistor as an example in the present embodiment) and a resistor 153 (as an example in this embodiment) having a resistance value of 1.6 kΩ connected in parallel to the pull-up resistor 151 and detecting disconnection of the thermistor 110 ). The transistor 152 is controlled by a signal from the disconnection detection port DP of the CPU 11a. Note that a node S in FIG. 10 indicates a location where the temperature signal Vs is generated (a location where the above partial pressure is applied).

  The high temperature detection circuit includes a comparator 154 as an example of a comparator that operates when the temperature signal Vs that is divided and input falls below a predetermined threshold value (Vref), and the output voltage from the comparator 154 A delay circuit 155 for delaying the rise, a discharge circuit 156 for rapidly discharging the output voltage, a latch circuit 157 for sending a latch signal holding the abnormal signal when an abnormal signal is output from the comparator 154, and an inverter 174 And 176.

When an abnormality is latched by the latch circuit 157, the latch state is released by a latch release circuit 158 (indicated as “reset IC” in FIG. 7).
The threshold value (Vref) set in the comparator 154 is determined in advance according to the temperature characteristics of the thermistor 110 used.

An input portion of an AD converter 159 as an example of a conversion unit that converts the divided temperature signal Vs into an AD (Analog Digital) and notifies the CPU 11a of the thermistor 110 when the disconnection detection port DP is set to a high level (H). The disconnection detection value is input from, and the temperature detection value is input when the level is low (L).
Note that a filter 164 and a buffer 162 are connected to the input unit of the AD converter 159, but these may be provided as necessary and are not essential.

  An output signal from the latch circuit 157 of the high temperature detection circuit is input to one input terminal of the 2-input NAND circuit 160. The output signal from the CPU 11a is input to the other input terminal of the NAND circuit 160, and the output of the NAND circuit 160 is determined by the logical product of both input signals. As a result, the fixing relay 111 is fixed from the AC power supply 14. The power supplied to the lamp 63 is energized or cut off.

In FIG. 10, the output of the NAND circuit 160 directly drives the fixing relay 111. However, the present invention is not limited to this, and a switch is provided between the low voltage power supply 130 and the fixing relay 111 to output the NAND circuit 160. The switch may be opened and closed.
Further, when the high temperature detection is only the detection by hardware, the level of the signal input from the CPU 11a to the NAND circuit 160 may be set to a high level (H).

  FIG. 11 is a time chart for explaining an operation example of temperature monitoring control of the fixing roller of the fixing device 60 according to the conventional technique.

  FIG. 11 shows a signal for each state of the disconnection detection circuit of the temperature signal Vs output from the thermistor 110 and input to the fixing roller temperature monitoring control circuit 150 (FIG. 11A), and an output signal of the comparator 154 in the high temperature detection circuit. (Node A) (FIG. (B)), an output signal from the delay circuit 155 (node B) (FIG. (C)), and an abnormal signal (node C) input to the latch circuit 157 (FIG. (D) )) Is schematically shown over time.

  In the fixing roller temperature monitoring control circuit 150, the time constant CR of the delay circuit 155 connected to the output of the comparator 154 of the high temperature detection circuit is set so as not to affect the temperature control of the fixing device 60. Specifically, it is determined in consideration of self-heating due to current supply to the thermistor 110 in the low resistance region, smokeless limit time of the fixing device 60 when the program executed by the CPU 11a runs out of control, false detection, etc. As an example, it is set to 100 ms to 500 ms. In this prior art, the time constant CR of the delay circuit 155 is 100 ms.

  As shown in FIG. 11A, in the low temperature state, the CPU 11a switches the offset value of the temperature signal Vs every 50 ms, for example, so that the temperature signal Vs is alternately used as a disconnection detection voltage value or a temperature detection voltage value. take in. Therefore, normal operation is possible in the low temperature region without erroneously detecting the low temperature as a disconnection.

On the other hand, when the fixing lamp 63 is turned on and the temperature of the fixing roller 61 gradually increases, both the disconnection detection voltage value and the temperature detection voltage value gradually decrease. Then, as shown in FIG. 11B, the voltage on the disconnection detection side reaches a preset threshold value (Vref) of the comparator 154 and the output signal (node A) of the comparator 154 is inverted once, but 50 ms Since the voltage is switched to the temperature detection voltage value at this time, it deviates from the threshold value (Vref), and the output signal (node A) of the comparator 154 is inverted again and returned to its original state.
At this time, as shown in FIG. 11C, since the transmission of the output of the latch circuit to the fixing relay 111 is blocked by the time constant CR of the delay circuit 155 connected to the output section of the comparator 154, the high temperature detection circuit Does not work. (Range of time ta to tb in FIG. 11)

  Then, as shown in FIG. 11C, when both the disconnection detection voltage value and the temperature detection voltage value decrease and reach the voltage value that should actually be detected at a high temperature, the disconnection detection voltage value and the temperature detection are detected in 50 ms. When the voltage value is switched, the threshold value (Vref) of the comparator 154 is reached at any voltage, so that the latch is performed after the time constant CR (100 ms in this embodiment) set by the delay circuit 155 has elapsed. The circuit operates. Then, as shown in FIG. 11D, the fixing relay 111 is forcibly opened at this timing. (The portion at time tc in FIG. 11)

  In this prior art, the threshold value (Vref) of the comparator 154 is set to a value of the temperature signal Vs corresponding to the temperature when the target temperature Tu of the fixing roller 61 is 250 ° C., for example, 0.7 volts. Is set.

  If the fixing roller temperature monitoring control circuit 150 according to the conventional technique is used, the disconnection detection and the high temperature detection are discriminated without the control by the CPU 11a, and the fixing relay 111 operates. For this reason, even when a program executed by the CPU 11a runs away, overheating of the fixing roller 61 is surely prevented.

  Further, since the delay circuit 155 is connected to the output section of the comparator 154, the voltage on the disconnection detection side reaches a threshold value (Vref) set in advance in the comparator 154, and the output signal (node A) of the comparator 154 Is inverted, the time constant CR of the delay circuit 155 prevents the output signal of the latch circuit 157 from being transmitted to the fixing relay 111, and the high temperature detection circuit does not operate.

  Further, when both the disconnection detection voltage value and the temperature detection voltage value decrease and reach the voltage value that should actually be detected at a high temperature, the time constant CR (100 ms in this embodiment) set by the delay circuit 155 is reached. The latch circuit 157 operates after a lapse of time.

  However, in the fixing roller temperature monitoring control circuit 150 according to the prior art, it is necessary to provide the delay circuit 155 and the discharge circuit 156, so that the circuit becomes complicated and the cost is high.

  Therefore, in the fixing roller temperature monitoring control circuit 170 of the image forming apparatus 1 according to the present embodiment, the delay circuit 155 and the discharge circuit 156 are deleted, and erroneous detection of high temperature detection at a high temperature caused by the deletion is performed. This is avoided by the control of the CPU 11a.

FIG. 4 shows a circuit configuration of the fixing roller temperature monitoring control circuit 170 according to this embodiment. A fixing roller temperature monitoring control circuit 170 shown in FIG. 4 is obtained by removing the delay circuit 155 and the discharging circuit 156 from the fixing roller temperature monitoring control circuit 150 according to the prior art shown in FIG.
Other circuits are the same as those in FIG. Therefore, the same reference numerals are assigned to the same components, and the description thereof is omitted.

In FIG. 4, since the delay circuit 155 is not connected to the output section of the comparator 154, the temperature of the fixing roller 61 rises and the disconnection detection period occurs when the avoidance measure according to the present embodiment is not applied. When the temperature signal Vs falls below the threshold value (Vref) of the comparator 154, the output of the comparator 154 is inverted although there is no actual overheating abnormality.
Then, the latch circuit 157 operates, the fixing relay 111 is opened, and erroneous detection of high temperature detection occurs due to the supply of power from the AC power supply 14 to the fixing lamp 63 being cut off.

In the fixing roller temperature monitoring control circuit 170 according to the present embodiment, in order to avoid the erroneous detection, when the temperature of the fixing roller 61 is equal to or higher than a predetermined temperature, the disconnection detection voltage value and the temperature detection voltage are detected. A mode for switching between values (hereinafter, this mode may be referred to as “switching mode”) and only a temperature detection voltage value (hereinafter, this mode may be referred to as “temperature detection mode”). .) Hereinafter, the predetermined temperature is referred to as “mode switching temperature Tm”, and the value of the temperature signal Vs at the mode switching temperature Tm is referred to as “mode switching voltage Vm” (see FIG. 3).
In addition, the value of the mode switching voltage Vm is set to, for example, 2.5 V, and the value of the mode switching temperature Tm is set to, for example, 50 ° C.

  With this avoidance measure, when the temperature signal Vs is equal to or lower than the mode switching voltage Vm (the temperature of the fixing roller 61 is equal to or higher than the mode switching temperature Tm), the disconnection detection is not performed and only the temperature detection is performed. The When the temperature signal Vs is higher than the mode switching voltage Vm (when the temperature of the fixing roller 61 is lower than the mode switching temperature Tm), the disconnection detection voltage value and the temperature detection voltage value are switched (switching mode) as in the prior art described above. ) To perform disconnection detection and temperature detection, so that erroneous detection of a low temperature as disconnection when the temperature of the fixing roller 61 is reduced is also avoided.

In this case, there is no problem because the disconnection detection is performed as follows when the temperature signal Vs is equal to or lower than the mode switching voltage Vm (the temperature of the fixing roller 61 is equal to or higher than the mode switching temperature Tm).
That is, when the thermistor 110 is disconnected, as is apparent from the circuit diagram of FIG.
Since the voltage at the node S becomes the voltage Vc of the reference power supply (3.3 V in this embodiment), the CPU 11a that has input the voltage at the node S via the AD converter 159 determines that the temperature of the fixing roller 61 has decreased. To do. Then, since it transfers to the switching mode which controls a disconnection detection circuit and switches a disconnection detection voltage value and a temperature detection voltage value, a disconnection detection becomes possible again.

  FIG. 5 shows a time chart for explaining an operation example of the fixing roller temperature monitoring control circuit 170 according to the present embodiment. 5A shows a change in the temperature signal Vs over time, FIG. 5B shows a change in the output of the comparator 154 (node D) over time, and FIG. 5C shows over time. The change in the sampling signal of the CPU 11a, FIG. 5 (d) shows the output (node E) of the NAND circuit 160 over time.

  As shown in FIG. 5A, the time region in which the temperature of the fixing roller 61 is a relatively low value (in FIG. 5A, the value of the temperature signal Vs decreases until it matches the mode switching voltage Vm. In the region (2), the value of the temperature signal Vs is alternately repeated in the cycle of the disconnection detection voltage value and the temperature detection voltage value of 50 ms (switching mode). For example, this state is immediately after the image forming apparatus 1 is turned on. Hereinafter, the time width indicating the disconnection detection voltage value may be referred to as “disconnection detection section”, and the time width indicating the temperature detection voltage value may be referred to as “temperature detection section”.

  In this region, the CPU 11a captures the value of the temperature signal Vs as a value for detecting disconnection via the AD converter 159 in the disconnection detection section, and the value of the temperature signal Vs via the AD converter 159 in the temperature detection section. As a value for detecting.

  FIG. 5C shows a sampling signal indicating the timing at which the CPU 11a captures these signals. That is, the CPU 11a takes in the temperature signal Vs as a signal for detecting the temperature of the fixing roller 61 by the sampling signal at time t0, and takes in the temperature signal Vs as a signal for detecting disconnection of the thermistor 110 by the sampling signal at time t1. Hereinafter, the same applies until time t5.

  In the figure, the sampling signal is generated in synchronization with the rise or fall of the disconnection detection interval and the temperature detection interval. However, the present invention is not limited to this, and the generation timing of the sampling signal is not limited to the disconnection detection interval or the temperature. Any timing in the detection section may be used.

In FIG. 5A, the disconnection detection voltage value and the temperature detection voltage value gradually decrease with the passage of time to energize the fixing lamp 63, and the temperature signal Vs reaches the mode switching voltage Vm at time t6 (fixing). The temperature of the roller 61 has reached the mode switching temperature Tm).
Then, as shown in FIGS. 5A and 5C, the CPU 11a detects that the temperature signal Vs is equal to or lower than the mode switching voltage Vm based on the sampling signal at time t7.

When detecting that the temperature signal Vs is equal to or lower than the mode switching voltage Vm, the CPU 11a controls the disconnection detection circuit to stop the switching mode and shift to the temperature detection mode.
As shown in FIG. 5A, when the mode is shifted to the temperature detection mode, the CPU 11a stops the switching of the transistor 152 and continues the ON state, and fixes the voltage at the node S to the temperature detection voltage value. Further, as shown in FIG. 5C, the CPU 11a switches the period of the sampling signal from the previous period (50 ms) to a longer period (100 ms in the present embodiment).

FIG. 5A shows how the value of the temperature signal Vs gradually decreases after the temperature signal Vs reaches the mode switching voltage Vm. In the sampling signal at time t8,
The CPU 11a detects the temperature of the fixing roller 61 that is decreasing by the temperature signal Vs.

  Since the temperature signal Vs reaches the threshold value (Vref) of the comparator 154 at time t9, the output D of the comparator 154 is inverted as shown in FIG. 5B, and high temperature detection (overheat abnormality detection) is performed. As shown in FIG. 5D, the fixing relay 111 is forcibly turned off.

As described above in detail, when the temperature signal Vs is larger than the mode switching voltage Vm, the CPU 11a detects the temperature of the fixing roller 61 in the switching mode and also detects the disconnection of the thermistor 110 and monitors the occurrence of the disconnection. ing.
On the other hand, when the temperature signal Vs becomes equal to or lower than the mode switching voltage Vm, the CPU 11a shifts to the temperature detection mode and executes only temperature detection at a constant cycle. If the temperature signal Vs falls below the threshold value (Vref) of the comparator 154 during this period, the comparator 154 detects an overheating abnormality of the fixing roller 61 by hardware.

  If disconnection occurs in the region where the temperature signal Vs is equal to or lower than the mode switching voltage Vm, the voltage at the node S is fixed to the voltage Vc of the reference power supply, so that the CPU 11a shifts to the switching mode again to detect disconnection. State.

  Next, the operation of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  FIG. 6 is a flowchart showing a processing flow of the temperature monitoring control program for the fixing roller 61 according to the present embodiment. As described above, in the present embodiment, the temperature monitoring control process is realized by a software configuration using a computer by executing a program, but is not limited thereto. For example, you may implement | achieve by the hardware structure which employ | adopted ASIC (Application Specific Integrated Circuit), or the combination of a hardware structure and a software structure.

  Hereinafter, a case will be described in which the image forming apparatus 1 according to the present embodiment executes the temperature monitoring control of the fixing roller 61 by executing the program. In this case, the program is installed in advance in the ROM 11b or the storage unit 11d, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. A form or the like may be applied.

In FIG. 6, first, in step S500, the level of the disconnection detection port DP is set to L level, the transistor 152 is turned on, and the disconnection detection circuit is set to the temperature detection side.
In the next step S502, the temperature signal Vs is taken in as a temperature detection signal, and the temperature of the fixing roller 61 is detected.

  In the next step S504, it is determined whether or not the temperature signal Vs is greater than the mode switching voltage Vm. If the determination is affirmative, the process proceeds to step S508. If the determination is negative, the process proceeds to step S506. After maintaining the current state for a predetermined period (100 ms in this embodiment) (after waiting), the process returns to step S502.

Here, the loop formed in steps S502, S504, and S506 corresponds to the temperature detection mode, and the 100 ms wait time corresponds to the 100 ms sampling period shown in FIG.
When the disconnection occurs in the temperature detection mode, the voltage at the node S in FIG. 4 becomes the voltage Vc (3.3 V) of the reference power supply, so an affirmative determination is made in step S504 and the transition to the switching mode occurs again. The disconnection is detected.

In step S508, a predetermined period (in this embodiment, 50 ms) is waited. In the next step S510, the level of the disconnection detection port DP is set to H level, the transistor 152 is turned off, and the disconnection detection circuit is connected to the disconnection detection side. To.
In the next step S512, the temperature signal Vs is captured as a disconnection detection signal for detecting whether or not the thermistor 110 is disconnected.

  In the next step S514, it is determined whether or not the temperature signal Vs is greater than the disconnection threshold voltage Vd. If the determination is negative, the process returns to step S500 after waiting for 50 ms in step S516, If YES, step 518 follows.

Here, the disconnection threshold voltage Vd is a threshold voltage for determining whether or not the thermistor 110 is disconnected. Specifically, the reference threshold voltage Vc (3 in the present embodiment) is used. .3V) with a margin, for example, 3.0V. The threshold voltage Vd is set in the CPU 11a, for example.
The loop formed in steps S500 to S516 corresponds to the switching mode, and the 50 ms wait time in steps S508 and S516 corresponds to the 50 ms sampling period shown in FIG. 5C.

In the next step S518, after executing the disconnection process, the temperature monitoring control program is terminated.
Here, the disconnection processing according to the present embodiment means that, for example, the operation of the image forming apparatus 1 is stopped and the disconnection of the thermistor 110 is detected on a display device such as a UI (user interface) panel (not shown). A process for displaying and generating a warning.

  As described above in detail, according to the image forming apparatus 1 according to the present embodiment, temperature detection, disconnection detection, and overheat abnormality detection are performed with a simple configuration using one temperature detection element.

  In this embodiment, the temperature signal Vs is read in step S502 to obtain the temperature of the fixing roller 61 at that time, but the present invention is not limited to this. For example, when the temperature signal Vs is read in step S502 and the temperature of the fixing roller 61 is detected, an average value with the previous detected temperature value may be taken and the average value may be used as the temperature of the fixing roller 61. In this case, the average value of the temperature of the fixing roller 61 may be stored in the storage unit 11d, for example.

  In the present embodiment, the disconnection detection section and the temperature detection section in the switching mode are set to 50 ms, and the sampling period of the CPU 11a in the temperature detection mode is set to 100 ms. However, the present invention is limited to this. Rather, these values may be variously changed in specific implementation.

[Second Embodiment]
In the present embodiment, a protection circuit for preventing overheating of the thermistor 110 in the temperature detection mode is added to the first embodiment.

  Here, as described in the first embodiment, when the mode is shifted to the temperature detection mode, the CPU 11a turns on the transistor 152 shown in FIG. At this time, the thermistor 110 self-heats due to the current, whereby the temperature of the thermistor 110 rises, and an error may occur in the temperature indicated by the temperature signal Vs of the thermistor 110. In the present embodiment, the self-heating of the thermistor 110 is suppressed, and the occurrence of an error in the temperature indicated by the temperature signal Vs is suppressed.

  FIG. 7 shows a circuit diagram of the fixing roller temperature monitoring control circuit 180 according to this embodiment. Compared with the fixing roller temperature monitoring control circuit 170 shown in FIG. 4, the fixing roller temperature monitoring control circuit 180 is different in that a protection transistor 172 is added in series with the thermistor 110. The protection transistor 172 is connected to the CPU 11a and is controlled by the CPU 11a.

  More specifically, in the present embodiment, when the temperature signal Vs is equal to or lower than the mode switching voltage Vm and the mode is shifted to the temperature detection mode, the protection transistor 172 is turned off at a timing other than the temperature detection timing. The control which provides the time which does not flow is performed. For example, if the time for turning on / off the protection transistor 172 is 1: 1, the average current flowing through the thermistor 110 is halved, and the temperature rise of the thermistor 110 is suppressed accordingly.

  FIG. 8 is a time chart for explaining an operation example of the fixing roller temperature monitoring control circuit 180 according to this embodiment. 8A shows a change in the temperature signal Vs over time, FIG. 8B shows a change in the sampling signal of the CPU 11a over time, and FIG. 8C flows through the thermistor 110 over time. It shows the change in current. In FIG. 8, the operation in the region until the temperature signal Vs reaches the mode switching voltage Vm is the same as the operation in the same region in FIG.

  In FIG. 8A, as described in FIG. 5, the switching mode is set until the temperature signal Vs reaches the mode switching voltage Vm at time t6. Accordingly, the current of the thermistor 110 shown in FIG. 8C is also the resistance value of the pull-up resistor 151 or the parallel combined resistance value of the pull-up resistor 151 and the resistor 153 (in the example of FIG. 7, the resistance value of the pull-up resistor 151 is the resistance 153 Since the resistance value is negligibly large, the current corresponding to the resistance value of the resistor 153 is actually flowing alternately.

When the temperature signal Vs reaches the mode switching voltage Vm at the time t6, the CPU 11a switches to the temperature detection mode at the time t7 and switches the protection transistor 172 on and off alternately to intermittently pass the current flowing through the thermistor 110. It shall be
Therefore, after time t7 in FIG. 8C, the current value flowing through the thermistor 110 is
The current value corresponding to the resistor 153 is intermittent between the current value corresponding to 0 or a current value close to 0.

Next, the operation of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.
FIG. 9 is a flowchart showing a flow of processing of the temperature monitoring control program for the fixing roller 61 according to the present embodiment, and the program is installed in advance in, for example, the ROM 11b or the storage unit 11d.

First, in step S600, the protection transistor 172 is turned on.
The next steps S602 to S606 are the same as steps S500 to S504 in FIG. 6, the temperature is switched to the temperature detection side in step S602, the temperature signal Vs is read as a temperature detection signal in step S604, and the temperature of the fixing roller 61 is detected. In S606, it is determined whether or not the temperature signal Vs is larger than the mode switching voltage Vm.

  If a negative determination is made in step S606, the process proceeds to step S608, which will be described later, to switch the temperature detection mode. If an affirmative determination is made, the process proceeds to step S616, in order to continue the switching mode. In this embodiment, steps S616 to S626 indicating the switching mode are the same as steps S508 to S518 in FIG.

  In step S608, the process waits for 50 ms, and in the next step 610, the protection transistor 172 is turned off. In the next step S612, after waiting for 50 ms again, in the next step S614, the protection transistor is turned on again, and the process returns to step S604.

Here, the wait time of 50 ms in step S608 and step S612 is:
This corresponds to the period of 100 ms of intermittent current flowing through the thermistor 110 after time t7 shown in FIG.

  As described above, according to the image forming apparatus 1 according to the present embodiment, the temperature rise of the temperature detecting element is suppressed, and the accuracy of the detected temperature is improved.

In each of the above embodiments, a configuration using a heating type fixing device using a fixing lamp typified by a halogen lamp as a heating element has been described as an example, but the present invention is not limited thereto,
For example, the present invention is also applied to an electromagnetic induction heating type fixing device.

  Further, the processing flow of the temperature monitoring control program described in each of the above embodiments (see FIGS. 6 and 9) is an example, and unnecessary steps may be deleted or newly added within the scope not departing from the gist of the present invention. Various steps may be added or the processing order may be changed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1a Discharge part 10 Control apparatus 11 Controller 11a CPU
11b ROM
11c RAM
11d Storage unit 12 Image processing unit 13 Power supply unit 14 AC power supply 20 Paper supply unit 21 Paper stacking plate 22 Paper drawer unit 23 Registration roller pair 30 Photoreceptor unit 31 Photoreceptor 32 Charging roller 33 Cleaning roller 34 Cleaning blade 40 Development device 41 Development Housing 42 Developing rollers 44 and 45 Supply unit 46 Layer regulating member 50 Transfer device 51 Intermediate transfer belt 52 Primary transfer roller 53 Secondary transfer roller 60 Fixing device 61 Fixing roller 62 Pressure roller 63 Fixing lamps 65a and 65b Conveying guide 69 Discharging roller Pair 110 Thermistor 111 Fixing relay 112 Switch element 130 Low voltage power supply 150, 170, 180 Fixing roller temperature monitoring control circuit 151 Pull-up resistor 152 Transistor 153 Resistor 154 Comparator 155 Delay circuit 156 Discharging Path 157 latch circuit 158 latch release circuit 159 AD converter 160 NAND circuit 162 buffer 164 filter 172 protection transistor 174, 176 inverter DP disconnection detection port LH exposure device N nip P paper T secondary transfer section Tm mode switching temperature Vm mode switching voltage Vs Temperature signal

Claims (6)

A temperature detecting element whose resistance value changes in accordance with a temperature change of a heating element to be detected;
A variable resistance unit that is connected between a voltage generation source that generates a reference voltage and the temperature detection element, and that can be switched between a first value and a second value that is greater than the first value; ,
Temperature detecting means for detecting the temperature of the heating element based on a potential between the variable resistance portion and the temperature detecting element;
Overheat detecting means for detecting overheating of the heating element based on a potential between the variable resistance portion and the temperature detecting element and a predetermined reference potential;
When the temperature of the heating element detected by the temperature detection unit is lower than a predetermined temperature, the resistance value of the variable resistance unit is alternately switched between the first value and the second value. The variable resistance unit is controlled so as to have the first value when the temperature of the heating element detected by the temperature detecting means is equal to or higher than the predetermined temperature. Control means for controlling;
Including temperature detection device. Further comprising a disconnection detecting means for detecting disconnection of the temperature detection element based on a potential between the variable resistance portion and the temperature detection element;
When the temperature of the heating element detected by the temperature detection means is lower than the predetermined temperature, the temperature detection means controls the temperature during a period in which the resistance value of the variable resistance portion is the first value. Detecting the disconnection detection means in a period of detecting the second value,
The temperature detection device according to claim 1, wherein the temperature detection means detects the temperature when the temperature of the heating element detected by the temperature detection means is equal to or higher than the predetermined temperature. The variable resistance unit includes a second resistor having a resistance value of the second value, and a combined resistance value when the resistance value is connected in parallel to the second resistor becomes the first value. The temperature detection device according to claim 1, further comprising a switching unit that switches between enabling and disabling the resistor and the parallel connection of the first resistor to the second resistor. . A second switching means for causing a current to flow intermittently to the temperature detection element;
The control means further controls the second switching means to flow an electric current intermittently to the temperature detecting element when the temperature of the heating element is equal to or higher than a predetermined temperature. The temperature detection apparatus of any one of Claim 3. The image forming apparatus including the temperature detection device according to claim 1, wherein the heating element is a fixing device. A program for causing a computer to function as the control unit in the image forming apparatus according to claim 5.

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