JP6808342B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus, and more particularly to a detection control of an abnormally low temperature state of a fixing temperature due to a drop in an input voltage in a double-sided printing mode.

As a conventional image forming apparatus of this kind, for example, the one described in Patent Document 1 is known. That is, a fixing device (fixing means) having a heating body and a pressurizing member that press-contacts the heating body to form a nip portion, a temperature detecting means for detecting the temperature of the heating body, and electric power supplied to the heating body. It is provided with a control means for controlling the temperature. The control means is adapted to control the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature.
In areas with poor power supply conditions, the AC input voltage may be lower than the rated voltage, and if the input voltage drops below the rated voltage, the input power required by the fuser will decrease, resulting in poor fixing. Become. In particular, when the heating body is pressed against the pressure member via a film that is in sliding contact with the heating body, the toner on the transfer material is deposited on the film, and the transfer material is wrapped around due to the viscosity of the toner. It ends up. In such a state, it is necessary to replace the units or parts that make up the fuser. Therefore, when the detection temperature of the heating body falls below a predetermined temperature (hereinafter, abnormal low temperature threshold value), the image formation operation is performed. It was controlled to stop.

Japanese Unexamined Patent Publication No. 2006-119527

On the other hand, as the first print time, which is the discharge time of the first image forming apparatus, is shortened, the resistance value of the heater used in the fuser is being lowered so that the electric power can be turned on instantly. .. As a result, even in a low voltage state where the input voltage is lower than the rated voltage, the temperature drop of the heating body is smaller than in the conventional case.
Under such circumstances, when the method for detecting an abnormally low temperature state based on the abnormally low temperature threshold value as in Patent Document 1 is applied to the double-sided print mode, the abnormally low temperature state may not be detected appropriately.
Hereinafter, detection of an abnormally low temperature state in the double-sided print mode will be described with reference to FIG.
FIG. 10A shows an example of the target temperature Ta and the detection temperature TH of the heating body in the double-sided print mode in a state where the input voltage is lowered by about 40% of the rated voltage in the conventional fuser configuration. In this figure, the heating body is not reduced in resistance.
In the double-sided print mode, the target temperature of the heating body is set to the first target temperature Ta1 when the first surface image is formed, and the target temperature is set to the second target temperature Ta2 lower than the first target temperature Ta1 when the second surface image is formed. Is set to. The abnormal low temperature threshold value A is set lower than the second target temperature Ta2. In the figure, when the resistance of the heating body is high and the input voltage is lowered, the first detection temperature TH1 and the second detection temperature TH2 are significantly lower than the abnormal low temperature threshold value A, so that the abnormal low temperature state can be detected without any problem. it can.

On the other hand, when the resistance of the heated body is lowered, as shown in FIG. 10B, the detection temperature does not decrease much, and the first detection temperature TH1 and the second detection temperature TH2 rise to the vicinity of the abnormal low temperature threshold A. However, unless the input voltage drops significantly, the abnormally low temperature state cannot be detected properly.
As a result, the image forming operation is continued in a state where the input voltage is significantly lower than the rated voltage, the heat generated by the semiconductor element of the power supply board becomes large, and in the worst case, the power supply board may be damaged. Therefore, it is conceivable to cool the power supply board, but as the image forming apparatus is miniaturized, the power supply board is also required to be miniaturized, and it is difficult to expand the heat sink for cooling the components of the power supply board or add a cooling fan. In the situation.
It is also conceivable to provide a circuit for directly detecting the voltage and current of the input power supply or a circuit for detecting abnormal heat generation of the semiconductor element in the power supply board, but adding these circuits is the size of the board. It will expand and increase costs.

An object of the present invention is to provide an image forming apparatus capable of appropriately detecting a state in which an input voltage is lowered from the detection temperature of a heating body in a double-sided printing mode.

In order to achieve the above object, the first invention
A heating body that generates heat when energized, a pressure member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and a temperature detecting means that detects the temperature of the heating body. And the fixing means having
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
When the detection temperature becomes equal to or lower than the abnormal low temperature threshold value, the control means stops the power supply to the heating body to stop the image forming operation, and the second abnormal low temperature threshold value on the second side of the double-sided printing mode is the double-sided printing. It is set lower than the first abnormal low temperature threshold on the first side of the mode .
The first abnormal low temperature threshold value is a value obtained by multiplying the first target temperature by the first ratio, and the second abnormal low temperature threshold value is set to the second target temperature higher than the first ratio. It is characterized in that it is a value multiplied by a second ratio .

The second invention comprises a heating body that generates heat when energized, a pressure member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and the heating body. A fixing means having a temperature detecting means for detecting the temperature,
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
The control means comprises a first detection temperature detected by the temperature detecting means during the image formation of the first surface and a second detection temperature detected by the temperature detecting means during the image formation of the second surface. When the difference value is within a preset value, the power supply to the heating body is stopped to stop the image forming operation.

Further, the third invention comprises a heating body that generates heat by energization, a pressurizing member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and the heating body. A fixing means having a temperature detecting means for detecting the temperature,
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
The control means calculates a first difference value between the first target temperature and the detection temperature on the first surface and a second difference value between the second target temperature and the detection temperature on the second surface, and calculates the first difference value and the first difference value in advance. The set first
It is characterized in that the abnormal low temperature state due to a decrease in the input voltage is discriminated from the abnormal low temperature threshold value and the comparison result between the second difference value and the second abnormal low temperature threshold value set in advance.

According to the present invention, in the double-sided print mode, a state in which the input voltage is lowered can be appropriately detected from the detection temperature of the heating body.

The schematic cross-sectional view which shows an example of the image forming apparatus to which this invention is applied. FIG. 3 is a schematic cross-sectional view showing an example of the fixing device of FIG. The figure which shows an example of the power supply circuit of the fuser of FIG. The relationship diagram of the target temperature, the detection temperature and the abnormal low temperature threshold of the heater in Example 1. FIG. The flowchart in Example 1. The relationship diagram of the target temperature, the detection temperature and the difference value of the heater in Example 2. FIG. The flowchart in Example 2. The relationship diagram of the target temperature, the detection temperature and the difference value of the heater in Example 3. FIG. The flowchart in Example 3. The relationship diagram of the target temperature, the detection temperature and the abnormal low temperature threshold of the conventional heating body.

The present invention will be described in detail below with reference to the illustrated examples.
[Example 1]
(Rough configuration of image forming apparatus)
FIG. 1 is a cross-sectional view of an image forming apparatus to which the present invention is applied. The illustrated example shows a laser printer using an electrophotographic method as an example of an image forming apparatus.
In the figure, the image forming apparatus 101 includes a process cartridge 108 as an image forming portion for forming a toner image on the photoconductor drum 8 which is an image carrier. The process cartridge 108 is provided with a charging roller 81 and a developing roller 82 as a developing agent carrier around the photoconductor drum 8. Then, a beam corresponding to the image signal is exposed by the scanning optical device 100 on the surface of the photoconductor drum 8 uniformly charged by the charging roller 81 to form an electrostatic latent image, which is developed as a toner image by the developing roller 82. Will be done. The scanning optical device 100 is installed on an optical table 103 composed of a part of the housing of the image forming device 101.
The image forming apparatus 101 also includes a paper feed unit 104 on which the transfer material P as a recording material is placed, a paper feed roller 105, a transfer roller 106 as a transfer means arranged to face the photoconductor drum 8, and an image. A fixing device 107 as a heating device and a double-sided transport path 121 are provided.
When printing is started, the transfer material P is fed from the paper feed unit 104 by the paper feed roller 105, and the toner image formed on the photoconductor drum 8 is transferred by the transfer roller 106. After that, in the fixing device 107, the toner image as the developer image on the transfer material P is fixed to the transfer material P by heat and pressure. The transfer material P to which the toner is fixed is discharged to the paper ejection tray 120 by the paper ejection roller 110, and the image formation is completed.
On the other hand, when the image is formed on the transfer material P on both sides (when the double-sided print mode is specified), the rear end of the image-formed transfer material P on the first side sent out from the fixing device 107 is the paper ejection roller 110. The paper ejection roller 110 is rotated in the reverse direction at the timing when it reaches. As a result, the transfer material P is switched back into the image forming apparatus from the output tray 120 side (the transport direction is switched in the opposite direction). The transfer material P that has been switchback-conveyed by the reverse rotation of the paper ejection roller 110 is introduced into the double-sided transport path 121. Then, the transfer material P is conveyed in the double-sided transfer path 121 by the double-sided transfer rollers 122, 123, and 124, and is again conveyed to the transfer roller 106 at a predetermined timing in the front-back inverted state. As a result, the transfer material P transfers the toner image to the second surface (back surface), the toner image is fixed by the fixing device 107, and the transfer material P is discharged to the paper ejection tray 120 by the paper ejection roller 110.

(Structure of fuser)
Next, the fuser 107 will be described with reference to FIG.
The fuser 107 has a heater 201 (heater) that generates heat when energized, and a fixing nip NI (nip portion) that is pressed against the heater 201 to heat a toner image formed on the transfer material P on the recording material. It includes a pressurizing roller 203 (pressurizing member) to be formed. The heater 201 is pressed against the pressure roller 203 via a tubular and heat-resistant film 202, and the inner peripheral surface of the film 202 is in sliding contact with the heater 201 at the fixing nip NI. The film 202 has a configuration in which the film 202 is guided by a holding member 204 that holds the heater 201 and rotates, and the stay 205 holds the pressure contact force with the pressure roller 203.
The heater 201 is a ceramic heater, and a thermistor 207 as a temperature detecting means for detecting the temperature of the heater 201 is provided on the surface of the heater 201 opposite to the fixing nip NI. Reference numeral 206 denotes a circuit for supplying electric power to the heater 201.

Next, the power feeding circuit 206 will be described with reference to FIG.
Here, 301 indicates a commercial AC power source, and 302 is a triac that controls the power supply to the heater 201. Reference numeral 303 denotes a switching element that operates by the driving DRV signal of the triac 302 generated from the control unit 308, and this embodiment is a transistor. With the continuity of the transistor 303, the gate current of the thyrac 302 is supplied via the photo thyrac coupler 304, and the thyrac 302 is controlled. Further, 305 and 306 are resistors for current limiting, respectively, and 307 is a relay.
The control unit 308 as a control means controls the electric power supplied to the heater 201 according to the detection temperature TH of the thermistor 207 and the target temperature. That is, in order to control the heater 201 to the target temperature required for image formation, the electric power to the heater 201 is controlled from the value of the detected temperature TH by the driving DRV signal.
The control unit 308 is composed of a one-chip microcomputer, and although not shown in particular, it has a CPU and a storage device that perform arithmetic processing, and depending on the programs of various control modes written in the storage device, The power supply to the heater 201 is controlled. The control mode has a double-sided print mode.
FIG. 4 shows the relationship between the target temperature Ta, the detected temperature TH, and the abnormal low temperature threshold Tb in the double-sided print mode.
The double-sided print mode is a mode in which the image formation of the first side and the second side is continuous through the paper. The control unit 308 sets the target temperature to the first target temperature Ta1 when forming the image of the first surface in the double-sided print mode, and sets the target temperature to the second target temperature Ta1 lower than the first target temperature Ta1 when forming the image of the second surface. The power to the heater 201 is controlled by setting it to Ta2. Since the transfer material P is warmed by adjusting the temperature of the first surface on the second surface of the double-sided print mode, the second target temperature Ta2 is set to a target temperature lower than the first target temperature Ta1. Then, when the detection temperature TH becomes equal to or lower than the abnormal low temperature threshold value through the first surface and the second surface, the power supply to the heater 201 is stopped and the image forming operation is stopped.
In the first embodiment, the heater 201 has a low resistance structure, and even when the input voltage drops below the rated voltage, the drop in the detection temperature of the heater 201 is small. In the figure, the second detection temperature TH2 on the second surface is lower than the second target temperature Ta2, but is maintained at a temperature higher than the level of the target temperature Ta3 between the papers. The first detection temperature TH1 on the first surface is lowered to the same level as the second detection temperature TH2 on the second surface.
Even in such a case, the abnormal low temperature thresholds of the first surface and the second surface are made different so that the drop in the input voltage can be detected from the detection temperature, and the second abnormal low temperature threshold Tb2 of the second surface is the first abnormal low temperature threshold of the first surface. It is set lower than Tb1. Information regarding the first abnormal low temperature threshold value Tb1 and the second abnormal low temperature threshold value Tb2 is stored in a storage device (not shown) of the control unit 308.

In the first embodiment, the first abnormal low temperature threshold Tb1 is a value obtained by multiplying the first target temperature Ta1 by the first ratio C (Tb1 = Ta1 * C), and the second abnormal low temperature threshold Tb2 is the second. It is a value obtained by multiplying the target temperature Ta2 by the second ratio D (Tb2 = Ta2 * D). The second ratio D is set higher than the first ratio C.
The reason for setting such a ratio is that the first abnormal low temperature threshold value Tb1 on the first surface needs to be set with a certain difference from the first target temperature Ta1 assuming that the transfer material P has a low temperature. Because. On the other hand, the second abnormal low temperature threshold Tb2 on the second surface is different from the target temperature than the first surface because the transfer material P is warmed and the second target temperature Ta2 is lower than the first surface. Must be set small.

The detection control of the abnormally low temperature state due to the decrease in the input voltage needs to prevent erroneous detection due to fluctuation of the detection temperature depending on the type of transfer material P and the printing mode, and erroneous detection due to the momentary decrease in the input voltage. Therefore, in the first embodiment, the image forming operation is controlled to stop when the detection temperature TH is equal to or lower than the abnormal low temperature threshold value Tb to some extent through the first surface and the second surface.
In order to determine the continuation of this abnormality detection, the control unit 308 acquires the detection temperature at regular intervals through the first and second surfaces of the double-sided print mode. Then, the counter CN counts the number of times that the first detection temperature TH1 on the first surface becomes equal to or lower than the first abnormal low temperature threshold value and the number of times that the second detection temperature TH2 on the second surface becomes equal to or lower than the second abnormal low temperature threshold value. When the count number N becomes equal to or higher than the preset value α (N ≧ α), the power supply to the heater 201 is stopped to stop the image forming operation. The α that is the threshold value of the count number N is arbitrary, but for example, N ≧ 256 is set.
Further, when the first detection temperature TH1 and the second detection temperature TH2 are higher than the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2, they may be subtracted.

(Control flow at abnormally low temperature)
FIG. 5 shows a specific detection control flow of an abnormally low temperature state due to a drop in the input voltage in the double-sided print mode.
First, at the start of image formation, the counter CN that counts the abnormally low temperature state is initialized, and the count number is set to N = 0 (step S101).
Next, the power of the first surface is controlled according to the first detection temperature TH1 and the first target temperature Ta1 (step S102). That is, in order to control the first target temperature Ta1 on the first surface during double-sided printing, power control is performed based on the first detection temperature TH1 detected by the thermistor 207.
Next, after the tip of the transfer material P rushes into the fixing nip NI, the comparison between the first detection temperature TH1 and the first abnormal low temperature threshold Tb1 is started (step S103). As described above, the first abnormal low temperature threshold value Tb1 is Ta1 * C, where the first detection temperature TH1 is a temperature lowered to the ratio of C with respect to the first target temperature Ta1. Therefore, when the tip of the transfer material P rushes into the fixing nip NI, the control unit 308 starts a comparison calculation to determine whether the first detection temperature TH1 is Ta1 * C or less.
As a result of the comparison operation, if TH1> Ta1 * C is not satisfied, the counter CN is set to +1 (step S105). Then, it is determined whether or not the count number N accumulated in the counter CN is smaller than the preset threshold value α (N <α), and if it is smaller than the threshold value α, the image forming operation is continued and the process proceeds to step S108. If the count number N is equal to or greater than the threshold value α, an abnormal low temperature error is notified and the image forming operation is stopped (step S118).
On the other hand, in step S105, if the first detection temperature TH1 is TH1> Ta1 * C, the counter CN is subtracted by -1 (step S107), and the process proceeds to step S108. Then, in step S108, the transfer material on the first surface is used. It is determined whether or not the rear end of P has passed through the fixing nip NI, and if not, the process returns to step S104, and the control of steps S104 to S107 is repeated until N ≧ α.
Then, when N ≧ α and the rear end of the transfer material P passes through the fixing nip N1, the process proceeds to step S109, which is the start of the control flow for image formation on the second surface.

In step S109, the power of the second surface is controlled according to the second detection temperature TH2 and the second target temperature Ta2. That is, in order to control the second target temperature Ta2 on the second surface, power control is performed based on the second detection temperature TH2 detected by the thermistor 207.
Next, after the tip of the transfer material P rushes into the fixing nip NI, the comparison between the second detection temperature TH2 and the second abnormal low temperature threshold Tb2 is started (step S110). As described above, the second abnormal low temperature threshold value Tb2 on the second surface is Ta2 * D at a temperature at which the second detection temperature TH2 is lowered to a ratio of D with respect to the second target temperature Ta2. Therefore, when the tip of the transfer material P rushes into the fixing nip NI, it is compared whether the second detection temperature TH2 is Ta2 * D or less.
As a result of the comparison operation, if TH2> Ta2 * D is not satisfied, the counter CN is set to +1 (step S112). Then, it is determined whether or not the count number N of the counter CN is smaller than the threshold value α, and if it is smaller than the threshold value α, the image forming operation is continued and the process proceeds to step S113. If the count number N is equal to or greater than the threshold value α, an abnormal low temperature error is notified and the image forming operation is stopped (step S118).
On the other hand, in step S112, if the second detection temperature TH2 is TH2> Ta2 * D, the counter CN is subtracted by -1 (step S114), and the process proceeds to step S115.
Then, in step S115, it is determined whether or not the rear end of the transfer material P on the second surface has passed through the fixing nip N1, and if not, the process returns to step S111, and from step S111 until N ≧ α. The control in step S114 is repeated.
Then, when N ≧ α and the rear end of the transfer material P passes through the fixing nip N1, the process proceeds to step S116, and it is determined whether or not the print job is completed. If the print job is completed, the image forming operation is ended, and if the print job is continued, control is repeated from step S102 for image formation on the next transfer material (step S116).

In the above description, a method of setting the calculated values obtained by multiplying the first target temperature Ta1 and the second target temperature Ta2 by the ratios C and D, respectively, as the first abnormal low temperature threshold value Tb1 and the second abnormal low temperature threshold value Tb2 has been described. .. However, the present invention is not limited to this, and a value obtained by multiplying the first target temperature Ta1 and the second target temperature Ta2 by C and D may be set as a fixed value in advance.
Further, the same effect can be obtained by setting the calculated value and the fixed value in combination on the first surface and the second surface. That is, the first surface is a fixed value, the second surface is a calculated value, the first surface is a calculated value, and the second surface is a fixed value.
In the first embodiment, the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2 are set by multiplying the first target temperature Ta1 and the second target temperature Ta2 by different ratios C and D, respectively. However, the second abnormal low temperature threshold value Tb2 may be set lower than the first abnormal low temperature threshold value Tb1, and C = D may be set, or C> D may be set in some cases.
As described above, according to the first embodiment, even in the configuration in which the fuser using the heater 201 with reduced resistance is adopted, the AC input voltage is rated by setting the abnormal low temperature threshold value according to each target temperature. It becomes possible to detect a state lower than the voltage.

[Example 2]
Next, Example 2 of the present invention will be described with reference to FIGS. 6 and 7. In the following description, items that are different from those of the first embodiment will be mainly described, and description of overlapping items will be omitted.
FIG. 6 shows the relationship between the target temperature Ta, the detection temperature TH, and the difference value ΔTH in the double-sided print mode when the AC input voltage is lower than the rated voltage in the fuser configuration in which the heater 201 has a low resistance. ing.
In the figure, although the first target temperature Ta1 on the first surface is higher than the second target temperature Ta2 on the second surface, the input power is insufficient, and there is a difference between the first detection temperature TH1 and the second detection temperature TH2. It indicates a state in which it cannot be used. The decrease in the input voltage is smaller than that of the first embodiment, and the first detection temperature TH1 and the second detection temperature TH2 are relatively higher than those of the first embodiment.
In the second embodiment, the difference value ΔTH between the first detection temperature TH1 during image formation on the first surface having a high target temperature and the second detection temperature TH2 during image formation on the second surface with a low target temperature is calculated (ΔTH). = TH1-TH2), it is detected that the AC input voltage has dropped. In the illustrated example, the difference value ΔTH is the difference between the maximum value of the first detection temperature TH1 and the maximum value of the second detection temperature TH2.
Then, a threshold value α2 is set in advance from the resistance value of the heater 201 used for the fuser and the electric power obtained by the AC input voltage, and when the difference value ΔTH is within the preset threshold value (ΔTH ≦ α2), the heater 201 is reached. The power supply is stopped and the image forming operation is stopped.

FIG. 7 shows a specific control flow for detecting an abnormally low temperature state due to a drop in the input voltage in the double-sided print mode in the second embodiment.
When the image forming operation starts, first, the power of the first surface is controlled according to the first detection temperature TH1 and the first target temperature Ta1 (step S201). That is, in order to control the temperature of the heater 201 to the first target temperature Ta1 on the first surface, power control is performed based on the first detection temperature TH1 detected by the thermistor 207.
Next, when the tip of the transfer material P rushes into the fixing nip NI, the first detection temperature TH1 is stored in the storage device of the control unit 308 (step S202), and whether the rear end of the transfer material P has passed through the fixing nip NI. It is determined whether or not (step S203).
If the rear end of the transfer material P has not passed through the fixing nip N1, the process returns to step S202, and the procedure of storing the first detection temperature TH1 in the storage device is repeated. This procedure is performed at predetermined intervals while the transfer material P passes through the fixing nip N1, and the stored first detection temperature TH1 is updated to, for example, a maximum value.
Then, when the rear end of the transfer material P has passed through the fixing nip N1, the process proceeds to step S204, and the power of the second surface is controlled according to the second detection temperature TH2 and the second target temperature Ta2. That is, in order to control the second target temperature Ta2 on the second surface, power control is performed based on the second detection temperature TH2 detected by the thermistor 207.
Next, when the tip of the transfer material P rushes into the fixing nip NI, the second detection temperature TH2 is stored in the storage device of the control unit 308 (step S205). Next, the difference value ΔTH between the first detection temperature TH1 and the second detection temperature TH2 stored in the storage device of the control unit 308 is calculated, and the difference value ΔTH and the threshold value α2 are compared (step S206).
As a result of comparison, if TH1-TH2> α2, it is determined whether or not the rear end of the transfer material P has passed through the fixing nip NI (step S207), and the rear end of the transfer material P has passed through the fixing nip N1. If not, the process returns to step S205, and the second detection temperature TH2 is read again. Then, the difference value ΔTH between the first detection temperature TH1 and the second detection temperature TH2 is calculated, and the difference value ΔTH and the threshold value α2 are compared and calculated again. As a result of the calculation, if TH1-TH2> α2, the process proceeds to step S207, it is determined whether or not the rear end of the transfer material P has passed through the fixing nip NI, and until the rear end of the transfer material P has passed through the fixing nip N1. , Step S205 to step S207 are repeated. This procedure is performed at predetermined intervals while the second surface of the transfer material P passes through the fixing nip N1, and the second detection temperature TH2 for calculating the difference value ΔTH is a sequentially read value.
On the other hand, while repeating this procedure, if TH1-TH2> α2 does not exist in step S206, that is, if the difference value ΔTH is within the threshold value α2 (TH1-TH2 ≦ α2), an abnormal low temperature error is notified. , The image forming operation is stopped (step S209).
Then, the case where TH1-TH2> α2 does not continue continues, and when the rear end of the transfer material P passes through the fixing nip N1, the process proceeds to step S208, it is determined whether or not the print job is completed, and if there is a print job, the next The control of the image fixing of the transfer material P is repeated from step S201 (step S208).
As described above, in the second embodiment, the decrease in the AC input voltage is accurately detected by calculating the difference value ΔH between the first detection temperature TH1 and the second detection temperature TH2 on the first and second surfaces in the double-sided print mode. It is possible to prevent the power supply from being damaged.

[Example 3]
Next, Example 3 of the present invention will be described with reference to FIGS. 8 and 9. Regarding the third embodiment as well, the description of the items overlapping with the first embodiment will be omitted, and the same components will be designated by the same reference numerals and the description thereof will be omitted.
FIG. 8 shows the target temperature Ta, the detected temperature TH, and the difference value ΔHa between the target temperature Ta and the detected temperature TH in the double-sided print mode when the input voltage is lowered in the fuser configuration in which the heater 201 has a low resistance. Shows the relationship.
When the difference value ΔHa between the target temperature Ta and the detection temperature TH is larger, it indicates that the input voltage is lowered and the input power is insufficient. Using this correspondence, in the third embodiment, the control unit 308 calculates the difference value ΔHa between the target temperature Ta and the detection temperature TH, and the comparison result between this difference value ΔHa and the preset abnormal low temperature threshold value Tc. To determine the abnormally low temperature state due to the decrease in input voltage. That is, the first difference value ΔHa1 (ΔHa1 = Ta1-TH1) between the first target temperature Ta1 and the first detection temperature TH1 on the first surface, and the second difference value between the second target temperature Ta2 and the second detection temperature Ta2 on the second surface. Calculate ΔHa2 (ΔHa2 = Ta2-TH2). Then, from the comparison result between the first difference value ΔHa1 and the preset first abnormal low temperature threshold Tc1 and the second difference value ΔHa2 and the preset second abnormal low temperature threshold Tc2, the abnormal low temperature state due to the decrease in the input voltage is obtained. Is designed to be determined.

In particular, in the third embodiment, the detection temperature is acquired at regular intervals through the first and second surfaces of the double-sided print mode. Then, the number of times that the first difference value ΔHa1 between the first target temperature Ta1 and the first detection temperature TH1 on the first surface becomes equal to or higher than the first abnormal low temperature threshold value, and the second target temperature Ta2 and the second detection temperature on the second surface. The counter CN counts the number of times that the second difference value ΔHa2 from TH2 becomes equal to or higher than the second abnormal low temperature threshold value. When the count number N of the counter CN becomes equal to or higher than a preset value (N ≧ α3), it is controlled to stop the power supply to the heater 201 and stop the image forming operation in an abnormally low temperature state. To.
The first abnormal low temperature threshold Tc1 on the first surface and the second abnormal low temperature threshold Tc2 on the second surface are at least two values that gradually increase. In this example, the first abnormal low temperature threshold Tc1 is E and F. Two values, F and G, are set as the threshold value and the second abnormal low temperature threshold value Tc2.
Therefore, when E <Ta1-TH1 <F, the decrease in the input voltage is small, so the addition value of the counter CN is set to +1. When Ta1-TH1> F, the input voltage is significantly reduced, and the counter CN is added. The value is twice that +2.
Similarly for the two surfaces, the second thresholds G and H have a relationship of G <H. Further, since the second target temperature Ta2 on the second surface is lower than that on the first surface, the second threshold values G and H are also set to values smaller than the first threshold values E and F. When G <Ta2-TH2 <H, the decrease in the input voltage is small, so the addition value of the abnormal low temperature counter CN is +1. When Ta2-TH2> H, the input voltage is significantly reduced. The added value is +2.
In this way, the added value counted by the counter CN is set to a larger value when it reaches a larger threshold value out of each of the two threshold values of the first abnormal low temperature threshold Tc1 and the second abnormal low temperature threshold Tc2. ..

FIG. 9 shows a specific control flow for detecting an abnormally low temperature state due to a drop in the input voltage in the double-sided print mode of the third embodiment.
First, at the start of image formation, the counter CN that counts the abnormally low temperature state is initialized, and the count number N is set to N = 0 (step S301).
Next, the power of the first surface is controlled according to the first detection temperature TH1 and the first target temperature Ta1 (step S302). That is, in order to control the first target temperature Ta1 on the first surface during double-sided printing, power control is performed based on the first detection temperature TH1 detected by the thermistor 207.
Next, after the tip of the transfer material P has entered the fixing nip NI, the control unit 308 starts a comparison calculation between the first detection temperature TH1 and the first target temperature Ta1 (step S303).
In the control unit 308, the first difference value ΔH between the first target temperature Ta1 and the first detection temperature TH1.
a is calculated (ΔHa = Ta1-TH1) and compared with the value E of the first abnormal low temperature threshold Tc1 (step S304). As described above, the first abnormal low temperature threshold value Tc1 on the first surface has two values E and F and is set to E <F.
Then, if Ta1-TH1 <E, that is, if the first difference value ΔHa1 is E or more, the process proceeds to step S305.
In step S305, when the first difference value ΔHa1 is larger than E and smaller than F, that is, when the condition of E <Ta1-TH1 <F is satisfied, the counter CN is added by a predetermined addition value + 1. (Step S306).
In step S305, if the condition of E <Ta1-TH1 <F is not satisfied, that is, if the first difference value ΔHa1 is F or more, the counter CN is added by a predetermined addition value +2 (step S307). This added value +2 is twice the added value +1 corresponding to the smaller first threshold value E.
After counting up the counter CN in steps S306 and S307, it is determined whether or not the count number N is smaller than the threshold value α3 (step S308). Then, when N <α3, the image forming operation is continued, and when N is α3 or more (N ≧ α3), an abnormal low temperature error is notified and the image forming operation is stopped (step S321).
On the other hand, if Ta1-TH1 <E in step S304, that is, when the first difference value ΔHa1 is smaller than E, the temperature drop is small, so the counter CN is subtracted by a predetermined subtraction value -1 (step S309). ..
Next, it is determined whether or not the rear end of the transfer material P on the first surface has passed through the fixing nip NI (step S310). If the rear end of the transfer material P has not passed through the fixing nip N1, the process returns to step S304, and the control of steps S304 to S309 is repeated until N ≧ α3.
Then, when the count number N does not reach α3 and it is determined in step S310 that the rear end of the transfer material P has passed through the fixing nip N1, the process proceeds to step S311 which is the start of the control flow for image formation on the second surface. ..

In step S311, the power of the second surface is controlled according to the second detection temperature TH2 and the second target temperature Ta2. That is, the target temperature is set to the second target temperature Ta2, and the power of the heater 201 is controlled based on the second detected temperature TH2 detected by the thermistor 207.
Next, after the tip of the transfer material P rushes into the fixing nip NI, the control unit 308 starts a comparison calculation between the second detection temperature TH2 and the second target temperature Ta2 (step S312).
The control unit 308 calculates the second difference value ΔHa2 between the second target temperature Ta2 and the second detection temperature TH2 (ΔHa2 = Ta2-TH2) and compares it with the value G of the second abnormal low temperature threshold Tc2 (step S313). .. As described above, the second abnormal low temperature threshold value Tc2 on the second surface has two values G and H and is set to G <H.
Then, if Ta2-TH2 <G, that is, if the second difference value Δa2 is G or more, the process proceeds to step S314.
In step S314, when the second difference value ΔHa2 is larger than G and smaller than H, that is, when the condition of G <Ta2-TH2 <H is satisfied, the counter CN is added by a predetermined addition value + 1. (Step S315).
In step S314, if the condition of G <Ta2-TH2 <H is not satisfied, that is, if the second difference value ΔHa2 is H or more, the counter CN is added by a predetermined addition value +2 (step S316). This added value +2 is twice the added value +1 corresponding to the smaller value G of the second abnormal low temperature threshold Tc2.
After counting up the counter CN in steps S306 and S307, it is determined whether or not the count number N is smaller than the threshold value α3 (step S308).
After counting up the counter CN in steps S315 and S316, it is determined whether or not the count number N is smaller than the threshold value α3 (step S317).
Then, when N <α3, the image forming operation is continued, and when N is α3 or more (N ≧ α3).
, Notifies an abnormal low temperature error and stops the image forming operation (step S321).
On the other hand, in step S313, when Ta2-TH2 <G, that is, when the second difference value ΔHa2 is smaller than G, the temperature drop is small, so the counter CN is subtracted by a predetermined subtraction value -1 (step S318). ..
Next, it is determined whether or not the rear end of the transfer material P on the second surface has passed through the fixing nip NI (step S319). If the rear end of the transfer material P has not passed through the fixing nip N1, the process returns to step S313, and the control of steps S313 to S318 is repeated until N ≧ α3.
Then, when N ≧ α3 and the rear end of the transfer material P passes through the fixing nip N1, the process proceeds to step S320, and it is determined whether or not the print job is completed. When the print job is completed, the image forming operation is ended, and if the print job is continued, the control is repeated for the next transfer material after returning to step S302 for the image formation on the next transfer material.

As described above, in the third embodiment, the first difference value ΔHa1 between the first target temperature Ta1 and the first detection temperature TH1 on the first surface, and the second target temperature Ta2 and the second detection temperature TH2 on the second surface. 2 It has a first abnormal low temperature threshold Tc1 and a second abnormal low temperature threshold Tc2 according to the difference value ΔHa2. As a result, when the input voltage drops below the rated voltage, the first detection temperature TH1 on the first surface is slightly lower than the second target temperature Ta2 on the second surface, and the input voltage state is reached. It becomes possible to detect.
Furthermore, by changing the added value of the counter according to the magnitude of the difference between the target temperature and the detection temperature, it is possible to detect the decrease in the input voltage quickly and accurately, stop the image formation operation, and form the image. It is possible to prevent damage to the device. The abnormal low temperature threshold value may be finely set in three or more steps.

In the first embodiment, the number of times that the first detection temperature TH1 and the second detection temperature TH2 acquired at regular intervals becomes equal to or higher than the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2 is counted. The invention is not limited to such a method.
For example, the average value, the maximum value, the minimum value, or only one point of the first detection temperature TH1 and the second detection temperature TH2 acquired at regular intervals may be used as representative values. In this case, when the first detection temperature TH1 and the second detection temperature TH2 become equal to or higher than the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2 without using the counter, the energization of the heater 201 is stopped and the image It is controlled to stop the forming operation.
Further, in the second embodiment, while the second surface is passing through the fixing nip N1, the difference value ΔTH from the first detection temperature TH1 is obtained for each data of the second detection temperature TH2 acquired at regular intervals, and a predetermined threshold value is obtained. Although the comparison calculation is performed with α2, the present invention is not limited to the method of successive comparison calculation. For example, the average value, the maximum value, the minimum value, or only one point of the second detection temperature TH2 acquired at regular intervals is used as a representative value, the difference value from the first detection temperature TH1 is calculated, and the comparison calculation is performed with the threshold value α2. You may do so.
Further, in the third embodiment, the first detection temperature TH1 and the second detection temperature TH2 are acquired at regular intervals, and the first difference value ΔHa1 and the second difference value ΔHa2 from the first target temperature Ta1 and the second target temperature Ta2 are obtained. Is sequentially calculated, but the control method is not limited to this. For example, the average value, the maximum value, the minimum value, or only one point of the first detection temperature TH1 and the second detection temperature TH2 are used as representative values, and the first difference value between the first target temperature Ta1 and the second target temperature Ta2. ΔHa1 and the second difference value ΔHa2 may be obtained. In this case, the first difference value ΔHa1 and the second difference value ΔHa2 are compared with the first abnormal low temperature threshold Tc1 and the second abnormal low temperature threshold Tc2, and it is determined from the comparison result whether or not the state is an abnormal low temperature due to a decrease in the input voltage. To. For example, when the first abnormal low temperature threshold Tc1 and the second abnormal low temperature threshold Tc2 are one each, and the first difference value ΔHa1 or the second difference value ΔHa2 becomes the first abnormal low temperature threshold Tc1 or the second abnormal low temperature threshold Tc2 or more, It may be determined that it is in an abnormally low temperature state. In this case, the energization of the heater 201 is stopped, and the image forming operation is controlled to be stopped.

101 Image forming device 107 Fixer (fixing means)
201 heater (heater)
202 Film 203 Pressurized roller (pressurized member)
207 Thermistor (Temperature detection means)
NI fixing nip (nip part)
P transfer material (transfer material)
308 Control unit (power control means)
CN counter, N count number Ta target temperature, Ta1 1st target temperature, Ta2 2nd target temperature Tb abnormal low temperature threshold, Tb1 1st abnormal low temperature threshold, Tb2 2nd abnormal low temperature threshold Tc abnormal low temperature threshold, Tc1 1st abnormal low temperature threshold , Tc2 2nd abnormal low temperature threshold E, F 1st abnormal low temperature threshold value, G, H 2nd abnormal low temperature threshold value TH detection temperature, TH1 1st detection temperature, TH2 2nd detection temperature ΔTH difference value (TH1-TH2) )
ΔHa difference value (Ta-TH)
ΔHa1 first difference value (Ta1-TH1), ΔHa2 second difference value (Ta2-TH2), α, α2, α3 threshold value

Claims (8)

A heating body that generates heat when energized, a pressure member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and a temperature detecting means that detects the temperature of the heating body. And the fixing means having
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
When the detection temperature becomes equal to or lower than the abnormal low temperature threshold value, the control means stops the power supply to the heating body to stop the image forming operation, and the second abnormal low temperature threshold value on the second side of the double-sided printing mode is the double-sided printing. It is set lower than the first abnormal low temperature threshold on the first side of the mode .
The first abnormal low temperature threshold value is a value obtained by multiplying the first target temperature by the first ratio, and the second abnormal low temperature threshold value is set to the second target temperature higher than the first ratio. An image forming apparatus characterized by being a value multiplied by a second ratio . The control means acquires the detected temperature at regular intervals through the first and second surfaces of the double-sided print mode, the number of times the first detected temperature of the first surface becomes equal to or lower than the first abnormal low temperature threshold value, and the second surface. The number of times the second detection temperature of the above is equal to or less than the second abnormal low temperature threshold is counted by a counter, and when the count number becomes equal to or more than a preset value, the power supply to the heating body is stopped to form an image. The image forming apparatus according to claim 1, wherein the operation is stopped. The image forming apparatus according to claim 2 , wherein when the first detection temperature and the second detection temperature are larger than the first abnormal low temperature threshold value and the second abnormal low temperature threshold value, they are subtracted from the counter. A heating body that generates heat when energized, a pressure member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and a temperature detecting means that detects the temperature of the heating body. And the fixing means having
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
The control means comprises a first detection temperature detected by the temperature detecting means during the image formation of the first surface and a second detection temperature detected by the temperature detecting means during the image formation of the second surface. An image forming apparatus, characterized in that, when the difference value is within a preset value, the power supply to the heating body is stopped to stop the image forming operation. A heating body that generates heat when energized, a pressure member that forms a nip portion that presses against the heating body to heat a developer image formed on a recording material, and a temperature detecting means that detects the temperature of the heating body. And the fixing means having
A control means for controlling the electric power supplied to the heating body according to the temperature detected by the temperature detecting means and the target temperature is provided.
The control means sets the target temperature to the first target temperature when forming an image on the first surface in the double-sided print mode, and sets the target temperature to a second target temperature lower than the first target temperature when forming an image on the second surface. In the image forming apparatus set to the temperature,
The control means calculates a first difference value between the first target temperature and the detection temperature on the first surface and a second difference value between the second target temperature and the detection temperature on the second surface, and calculates the first difference value and the first difference value in advance. An image forming apparatus characterized in that an abnormal low temperature state due to a decrease in input voltage is discriminated from a set first abnormal low temperature threshold and a comparison result between the second difference value and a preset second abnormal low temperature threshold. .. The control means acquires the detected temperature at regular intervals through the first and second surfaces of the double-sided print mode, and the difference value between the first target temperature of the first surface and the first detected temperature of the first surface is the first abnormality. The number of times the temperature exceeds the low temperature threshold value and the number of times the difference between the second target temperature on the second surface and the second detection temperature on the second surface exceeds the second abnormal low temperature threshold value are counted by a counter, and the count number is counted. The image forming apparatus according to claim 5 , wherein when the temperature exceeds a preset value, the power supply to the heating body is stopped to stop the image forming operation. The first abnormal low temperature threshold value and the second abnormal low temperature threshold value each have at least two threshold values that gradually increase, and the addition value counted by the counter is the larger of the at least two threshold values. , The image forming apparatus according to claim 6 , which is set to a larger value. The heating body is configured to be in pressure contact with the pressurizing member via a tubular and heat-resistant film, and the inner peripheral surface of the film is in sliding contact with the heating body at a nip portion, according to any one of claims 1 to 7 . The image forming apparatus according to item 1.