JP2017187645A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of detecting a state where an input voltage is decreased from a detection temperature, in a both-side print mode, regardless of the resistance value of a heating body.SOLUTION: The image forming apparatus includes fixing means which includes the heating body, a pressure member which comes into press- contact with the heating body, to form a nip part, and temperature detection means for detecting the temperature of the heating body and control means for controlling electric power supplied to the heating body according to the detection temperature by the temperature detection means and a target temperature and sets the target temperature to a first target temperature, when an image is formed on a first surface in the both-side print mode and sets the target temperature to a second target temperature lower than the first target temperature, when the image is formed on a second surface. When the detection temperature becomes an abnormal low temperature threshold or less, the control means stops the supply of the electric power to the heating body, to stop an image forming operation. The second abnormal low temperature threshold of the second surface in the both-side print mode is set lower than the first abnormal low temperature threshold of the first surface in the both-side print mode.SELECTED DRAWING: Figure 4

Description

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

As a conventional image forming apparatus of this type, for example, the one described in Patent Document 1 is known. That is, a fixing device (fixing means) having a heating body and a pressure member that presses against the heating body to form a nip portion, a temperature detection means for detecting the temperature of the heating body, and power supplied to the heating body And a control means for controlling. The control means controls the power supplied to the heating body according to the temperature detected by the temperature detection means and the target temperature.
In areas where power supply conditions are poor, there is a possibility that the AC input voltage will be lower than the rated voltage.If the input voltage drops below the rated voltage, the input power required by the fixing unit will be reduced, resulting in poor fixing. Become. In particular, when the heating body is pressed against the pressure member through a film that is in sliding contact with the heating body, the toner on the transfer material accumulates on the film, and the transfer material is wrapped around by the viscosity of the toner. End up. In such a state, it is necessary to replace a unit or a part constituting the fixing device. Therefore, when the detected temperature of the heating body becomes a predetermined temperature (hereinafter referred to as an abnormal low temperature threshold) or less, the image forming operation is performed. It was controlled to stop.

JP 2006-119527 A

On the other hand, the resistance value of the heating element used in the fixing device has been lowered so that power can be instantaneously supplied with the shortening of the first print time which is the discharge time of the first sheet of the image forming apparatus. . 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 element is reduced compared to the conventional case.
Under such circumstances, when the method for detecting an abnormally low temperature state using the abnormally low temperature threshold as in Patent Document 1 is applied to the double-sided print mode, the abnormally low temperature state may not be appropriately detected.
Hereinafter, detection of an abnormally low temperature state in the duplex printing 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 element in the double-sided print mode in a state where the input voltage is reduced by about 40% of the rated voltage in the conventional fixing device configuration. In this figure, the heating element is not reduced in resistance.
In the double-sided printing mode, the target temperature of the heating element is set to the first target temperature Ta1 when the first image is formed, and the second target temperature Ta2 is lower than the first target temperature Ta1 when the second image is formed. Is set. The abnormal low temperature threshold A is set lower than the second target temperature Ta2. In the figure, when the resistance of the heating element 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 A, so that the abnormal low temperature state is detected without any problem. it can.

On the other hand, when the resistance of the heating element is lowered, as shown in FIG. 10B, the decrease in the detected temperature is small, and the first detected temperature TH1 and the second detected temperature TH2 rise to near the abnormal low temperature threshold A. If the input voltage does not drop significantly, an 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 generation of the semiconductor element of the power supply board is increased, and the power supply board may be damaged in the worst case. Therefore, it is conceivable to cool the power supply board. However, as the image forming apparatus is downsized, the power supply board is also required to be downsized. Is in the situation.
In addition, it is 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 elements in the power supply board. Expansion and cost increase.

  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 in a double-sided printing mode from a detection temperature of a heating body.

In order to achieve the above object, the first invention provides:
A heating body that generates heat when energized, a pressure member that forms a nip portion that heats the developer image formed on the recording material in pressure contact with the heating body, and a temperature detection unit that detects the temperature of the heating body. Fixing means having
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means stops the image forming operation by stopping the power supply to the heating body when the detected temperature becomes equal to or lower than the abnormal low temperature threshold, and the second abnormal low temperature threshold of the second side in the double-sided printing mode is set to the double-sided printing. It is characterized by being set lower than the first abnormal low temperature threshold on the first surface of the mode.

According to a second aspect of the present invention, there is provided a heating body that generates heat when energized, a pressure member that presses against the heating body and forms a nip portion for heating a developer image formed on a recording material, A temperature detecting means for detecting the temperature, and a fixing means,
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means includes a first detection temperature detected by the temperature detection means during image formation on the first surface and a second detection temperature detected by the temperature detection means during image formation on the second surface. When the difference value is within a preset value, the power supply to the heating body is stopped and the image forming operation is stopped.

Further, the third invention is a heating body that generates heat when energized, a pressure member that presses against the heating body and forms a nip portion for heating a developer image formed on a recording material, A temperature detecting means for detecting the temperature, and a fixing means,
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means calculates a first difference value between the first target temperature and the detected temperature on the first surface and a second difference value between the second target temperature and the detected temperature on the second surface, and the first difference value and Set first
An abnormal low temperature state due to a decrease in input voltage is determined from an abnormal low temperature threshold and a comparison result between the second difference value and a preset second abnormal low temperature threshold.

  According to the present invention, in the double-sided printing mode, it is possible to appropriately detect the state where the input voltage is lowered from the detection temperature of the heating body.

1 is a schematic sectional view showing an example of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device in FIG. 1. The figure which shows an example of the circuit for electric power feeding of the fixing device of FIG. FIG. 3 is a relationship diagram of a target temperature of a heater, a detected temperature, and an abnormally low temperature threshold in the first embodiment. 2 is a flowchart in the first embodiment. FIG. 10 is a relationship diagram of a target temperature, a detected temperature, and a difference value of a heater in the second embodiment. 10 is a flowchart according to the second embodiment. FIG. 10 is a relationship diagram of a target temperature, a detected temperature, and a difference value of a heater in the third embodiment. 10 is a flowchart according to the third embodiment. The related figure of the target temperature of the conventional heating body, detection temperature, and abnormally low temperature threshold value.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.
[Example 1]
(Schematic 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 system as an example of an image forming apparatus.
In the figure, an image forming apparatus 101 includes a process cartridge 108 as an image forming unit that forms a toner image on a photosensitive drum 8 that is an image carrier. The process cartridge 108 is provided with a charging roller 81 and a developing roller 82 as a developer carrier around the photosensitive drum 8. The surface of the photosensitive drum 8 uniformly charged by the charging roller 81 is exposed to a beam corresponding to the image signal by the scanning optical device 100 to form an electrostatic latent image, and developed as a toner image by the developing roller 82. Is done. The scanning optical device 100 is installed on an optical bench 103 constituted by a part of the casing of the image forming apparatus 101.
In addition, the image forming apparatus 101 further includes a paper feed unit 104 on which a transfer material P as a recording material is placed, a paper feed roller 105, a transfer roller 106 as a transfer unit disposed opposite to the photosensitive drum 8, and an image A fixing device 107 as a heating device and a double-sided conveyance 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 photosensitive drum 8 is transferred by the transfer roller 106. Thereafter, 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 on which the toner is fixed is discharged to the paper discharge tray 120 by the paper discharge roller 110, and the image formation is completed.
On the other hand, when the image formation on the transfer material P is double-sided (when the double-sided print mode is designated), the rear end of the image-formed transfer material P sent from the fixing unit 107 is the discharge roller 110. The paper discharge roller 110 is reversely rotated at the timing of reaching. As a result, the transfer material P is switched back into the image forming apparatus from the discharge tray 120 side (the transport direction is switched to the reverse direction). The transfer material P that has been transported back by the reverse rotation of the paper discharge roller 110 is introduced into the double-sided transport path 121. Then, the transfer material P is transported through the double-sided transport path 121 by the double-sided transport rollers 122, 123, and 124, and is transported again to the transfer roller 106 again at a predetermined timing in the front-back state. As a result, the toner image is transferred onto the second surface (back surface) of the transfer material P, the toner image is fixed by the fixing device 107, and discharged to the discharge tray 120 by the discharge roller 110.

(Fixer configuration)
Next, the fixing device 107 will be described with reference to FIG.
The fixing device 107 includes a heater 201 (heating member) that generates heat when energized, and a fixing nip NI (nip portion) that is pressed against the heater 201 and heats a toner image formed on a transfer material P that is a recording material. And a pressure roller 203 (pressure member) to be formed. The heater 201 is pressed against the pressure roller 203 via a cylindrical 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 is configured to rotate while being guided by a holding member 204 that holds the heater 201, and holds the pressure contact force with the pressure roller 203 by a stay 205.
The heater 201 is a ceramic heater, and a thermistor 207 as 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 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 power supply to the heater 201. Reference numeral 303 denotes a switching element that operates according to the driving DRV signal of the triac 302 generated from the control unit 308. In this embodiment, a transistor is used. Along with the conduction of the transistor 303, the gate current of the triac 302 is supplied via the phototriac coupler 304, and the triac 302 is controlled. 305 and 306 are current limiting resistors, and 307 is a relay.
A control unit 308 serving as a control unit controls the power supplied to the heater 201 in accordance with the detected temperature TH of the thermistor 207 and the target temperature. That is, in order to control the heater 201 to the target temperature necessary for image formation, power control to the heater 201 is performed 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 particularly shown, has a CPU and a storage device that perform arithmetic processing, and according to various control mode programs written in the storage device, Power supply to the heater 201 is controlled. As a control mode, a double-sided print mode is provided.
FIG. 4 shows the relationship between the target temperature Ta, the detected temperature TH, and the abnormal low temperature threshold value Tb in the double-sided printing mode.
The double-sided printing mode is a mode in which image formation on the first side and the second side is continued through a sheet. The control unit 308 sets the target temperature to the first target temperature Ta1 when the first side image is formed in the double-sided print mode, and the second target temperature lower than the first target temperature Ta1 when the second side image is formed. The power control to the heater 201 is performed by setting Ta2. In the double-sided printing mode, the second target temperature Ta2 is set to a target temperature lower than the first target temperature Ta1 because the transfer material P is heated by the temperature control of the first side. Then, through the first and second surfaces, when the detected temperature TH becomes equal to or lower than the abnormal low temperature threshold value, 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 reduced resistance, and even when the input voltage is lower than the rated voltage, the decrease in the detected 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 sheets. 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 threshold value for the first surface and the second surface is made different so that the decrease in the input voltage can be detected from the detected temperature, and the second abnormal low temperature threshold value Tb2 for the second surface is the first abnormal low temperature threshold value for 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 abnormal low temperature threshold Tb2. This 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 this ratio is that the first abnormal low temperature threshold value Tb1 on the first surface needs to be set with some difference from the first target temperature Ta1 assuming that the transfer material P is low temperature. Because. On the other hand, the second abnormal low temperature threshold value 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 smaller.

Detection control of an abnormally low temperature state due to a decrease in input voltage needs to prevent erroneous detection due to fluctuations in detection temperature depending on the type of transfer material P and the printing mode, and erroneous detection due to a momentary decrease in input voltage. For this reason, in the first embodiment, control is performed so that the image forming operation is stopped when the state where the detected temperature TH is equal to or lower than the abnormal low temperature threshold Tb is continued to some extent through the first and second surfaces.
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 in the duplex printing mode. Then, the counter CN counts the number of times the first detection temperature TH1 on the first surface is equal to or lower than the first abnormal low temperature threshold and the number of times the second detection temperature TH2 on the second surface is equal to or lower than the second abnormal low temperature threshold. When the count number N is equal to or greater than a preset value α (N ≧ α), control is performed so that the power supply to the heater 201 is stopped and the image forming operation is stopped. The threshold α for the count number N is arbitrary, but for example, N ≧ 256.
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, respectively, subtraction may be performed.

(Control flow at abnormally low temperature)
FIG. 5 shows a specific detection control flow in an abnormally low temperature state due to a decrease in input voltage in the duplex printing mode.
First, at the start of image formation, a counter CN that counts an abnormally low temperature state is initialized, and the count number is set to N = 0 (step S101).
Next, power control is performed on the first surface in accordance with the first detected temperature TH1 and the first target temperature Ta1 (step S102). That is, power control is performed based on the first detected temperature TH1 detected by the thermistor 207 in order to control to the first target temperature Ta1 of the first surface during duplex printing.
Next, after the leading edge of the transfer material P enters the fixing nip NI, the comparison between the first detected 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, which is the temperature at which the first detected temperature TH1 is reduced to the ratio C with respect to the first target temperature Ta1. Therefore, when the leading edge of the transfer material P enters the fixing nip NI, the control unit 308 starts a comparison operation to determine whether the first detected temperature TH1 is equal to or lower than Ta1 * C.
If TH1> Ta1 * C is not the result of the comparison operation, the counter CN is incremented by 1 (step S105). Then, it is determined whether or not the count number N accumulated in the counter CN is smaller than a preset threshold value α (N <α). If 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, if the first detected temperature TH1 is TH1> Ta1 * C in step S105, the counter CN is decremented by -1 (step S107), and the process proceeds to step S108. It is determined whether or not the rear end of P has passed through the fixing nip NI. If not, the process returns to step S104, and the control from step S104 to step S107 is repeated until N ≧ α.
If N ≧ α is not satisfied and the trailing edge 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, power control of the second surface is performed according to the second detected temperature TH2 and the second target temperature Ta2. That is, in order to control to the second target temperature Ta2 on the second surface, power control is performed based on the second detected temperature TH2 detected by the thermistor 207.
Next, after the leading edge of the transfer material P enters the fixing nip NI, the comparison between the second detected temperature TH2 and the second abnormal low temperature threshold value Tb2 is started (step S110). As described above, the second abnormal low temperature threshold Tb2 on the second surface is Ta2 * D, which is the temperature at which the second detected temperature TH2 is reduced to the ratio D with respect to the second target temperature Ta2. Therefore, when the leading edge of the transfer material P enters the fixing nip NI, it is compared whether the second detection temperature TH2 is equal to or lower than Ta2 * D.
If TH2> Ta2 * D is not the result of the comparison calculation, the counter CN is incremented by +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. 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, if the second detected temperature TH2 is TH2> Ta2 * D in step S112, the counter CN is decremented by -1 (step S114), and the process proceeds to step S115.
In step S115, it is determined whether or not the trailing edge of the transfer material P on the second side 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.
If N ≧ α is not satisfied and the trailing edge of the transfer material P has passed through the fixing nip N1, the process proceeds to step S116 to determine whether the print job is finished. If the print job is finished, the image forming operation is finished. If the print job is continued, the control is repeated from step S102 on the image formation on the next transfer material (step S116).

In the above description, a method has been described in which calculated values obtained by multiplying the first target temperature Ta1 and the second target temperature Ta2 by the ratios C and D, respectively, are used as the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2. . 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 in advance as a fixed value.
Also, the same effect can be obtained by setting the calculated value and the fixed value in combination on the first and second surfaces. That is, the first surface can be combined with the fixed value, the second surface can be combined with the calculated value, the first surface can be combined with the calculated value, and the second surface can be combined with the fixed value.
In the first embodiment, the settings of the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2 are multiplied by different ratios C and D, respectively, with respect to the first target temperature Ta1 and the second target temperature Ta2. However, it is only necessary that the second abnormal low temperature threshold value Tb2 is set lower than the first abnormal low temperature threshold value Tb1, and C = D or, in some cases, C> D.
As described above, according to the first embodiment, the AC input voltage is rated by setting the abnormal low temperature threshold corresponding to each target temperature even in the configuration in which the fixing device using the heater 201 with reduced resistance is employed. It becomes possible to detect a state lower than the voltage.

[Example 2]
Next, Embodiment 2 of the present invention will be described with reference to FIGS. 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 a relationship among the target temperature Ta, the detected temperature TH, and the difference value ΔTH in the duplex printing 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, the first target temperature Ta1 on the first surface is insufficient for the input power despite the higher target temperature than the second target temperature Ta2 on the second surface, and there is a difference between the first detection temperature TH1 and the second detection temperature TH2. It shows a state where it can no longer be used. The decrease in the input voltage is smaller than that in the first embodiment, and the first detection temperature TH1 and the second detection temperature TH2 are relatively higher than those in the first embodiment.
In the second embodiment, a difference value ΔTH between the first detection temperature TH1 during the image formation on the first surface having a high target temperature and the second detection temperature TH2 during the image formation on the second surface having 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 a 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 fixing device and the electric power obtained from the AC input voltage, and when the difference value ΔTH is within the preset threshold value (ΔTH ≦ α2), the heater 201 is input. 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 decrease in input voltage in the duplex printing mode in the second embodiment.
When the image forming operation starts, first, power control of the first surface is performed 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 detected temperature TH1 detected by the thermistor 207.
Next, when the leading edge of the transfer material P enters the fixing nip NI, the first detection temperature TH1 is stored in the storage device of the control unit 308 (step S202), and 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 for storing the first detected 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 a maximum value, for example.
When the trailing edge of the transfer material P has passed through the fixing nip N1, the process proceeds to step S204, and the power control of the second surface is performed according to the second detected temperature TH2 and the second target temperature Ta2. That is, in order to control to the second target temperature Ta2 on the second surface, power control is performed based on the second detected temperature TH2 detected by the thermistor 207.
Next, when the leading edge of the transfer material P enters the fixing nip NI, the second detected 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 is compared with the threshold value α2 (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 detected 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 is compared with the threshold value α2 again. If TH1-TH2> α2 as a result of the calculation, the process proceeds to step S207, where 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. The procedure from step S205 to step S207 is repeated. This procedure is performed at a predetermined interval while the second surface of the transfer material P passes through the fixing nip N1, and the second detected temperature TH2 for calculating the difference value ΔTH is a value read sequentially.
On the other hand, if TH1-TH2> α2 is not satisfied in step S206 while this procedure is repeated, that is, if the difference value ΔTH is within the threshold value α2 (TH1-TH2 ≦ α2), an abnormal low temperature error is notified. Then, the image forming operation is stopped (step S209).
If TH1-TH2> α2 continues, and the trailing edge of the transfer material P passes through the fixing nip N1, the process proceeds to step S208, where it is determined whether the print job is completed. For image fixing of the transfer material P, control is repeated from step S201 (step S208).
As described above, in the second embodiment, in the double-sided printing mode, by calculating the difference value ΔH between the first detection temperature TH1 and the second detection temperature TH2 on the first side and the second side, a decrease in the AC input voltage can be accurately detected. It is possible to prevent the power supply from being damaged.

[Example 3]
Next, Embodiment 3 of the present invention will be described with reference to FIGS. Also in the third embodiment, the description of the same items as those in the first embodiment is omitted, and the same components are denoted by the same reference numerals and the description thereof is 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 fixing device configuration in which the heater 201 has a low resistance. Shows the relationship.
If the difference value ΔHa between the target temperature Ta and the detected temperature TH is larger, this indicates a state where the input voltage is lowered and the input power is insufficient. Using this correspondence relationship, in the third embodiment, the control unit 308 calculates a difference value ΔHa between the target temperature Ta and the detected temperature TH, and compares the difference value ΔHa with a preset abnormal low temperature threshold Tc. From the above, an abnormally low temperature state due to a decrease in input voltage is determined. 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. ΔHa2 is calculated (ΔHa2 = Ta2-TH2). Then, from the comparison result between the first difference value ΔHa1 and the first abnormal low temperature threshold value Tc1 set in advance and the second difference value ΔHa2 and the second abnormal low temperature threshold value Tc2 set in advance, the abnormal low temperature state due to the decrease of the input voltage Is to be determined.

In particular, in the third embodiment, the detected temperature is acquired at regular intervals through the first and second surfaces in the duplex printing mode. The number of times the first difference value ΔHa1 between the first target temperature Ta1 on the first surface and the first detection temperature TH1 is equal to or greater than the first abnormal low temperature threshold, and the second target temperature Ta2 and the second detection temperature on the second surface. The counter CN counts the number of times the second difference value ΔHa2 from TH2 is equal to or greater than the second abnormal low temperature threshold. When the count number N of the counter CN becomes equal to or greater than a preset value (N ≧ α3), control is performed to stop the image forming operation by stopping the power supply to the heater 201 as an abnormally low temperature state. The
The first abnormal low temperature threshold value Tc1 on the first surface and the second abnormal low temperature threshold value Tc2 on the second surface are at least two values that increase stepwise. In this example, two of E and F are used as the first abnormal low temperature threshold value Tc1. Two values of F and G are set as the threshold and the second abnormal low temperature threshold Tc2.
Therefore, since the decrease of the input voltage is small when E <Ta1-TH1 <F, the addition value of the counter CN is set to +1, and when Ta1-TH1> F, the input voltage is greatly decreased, and the addition of the counter CN The value is doubled to +2.
Similarly, the second threshold values G and H on the two surfaces have a relationship of G <H. Furthermore, since the second target temperature Ta2 of the second surface is lower than that of the first surface, the second threshold values G and H are also set to values smaller than the first threshold values E and F. Since the decrease in the input voltage is small when G <Ta2-TH2 <H, the added value of the abnormal low temperature counter CN is +1, and when Ta2-TH2> H, the input voltage is greatly decreased, and the counter CN The added value is +2.
Thus, the added value counted by the counter CN is set to a larger value when the larger threshold value is reached among the two threshold values of the first abnormal low temperature threshold value Tc1 and the second abnormal low temperature threshold value Tc2. .

FIG. 9 shows a specific control flow for detecting an abnormally low temperature state due to a decrease in input voltage in the duplex printing mode of the third embodiment.
First, at the start of image formation, a counter CN that counts an abnormally low temperature state is initialized, and the count number N is set to N = 0 (step S301).
Next, power control of the first surface is performed according to the first detected temperature TH1 and the first target temperature Ta1 (step S302). That is, power control is performed based on the first detected temperature TH1 detected by the thermistor 207 in order to control to the first target temperature Ta1 of the first surface during duplex printing.
Next, after the leading edge of the transfer material P enters the fixing nip NI, the control unit 308 starts a comparison operation between the first detected 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.
If Ta1−TH1 <E, that is, if the first difference value ΔHa1 is equal to or greater than E, 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 incremented by a predetermined addition value + 1. (Step S306).
In step S305, if the condition E <Ta1-TH1 <F is not satisfied, that is, if the first difference value ΔHa1 is greater than or equal to F, the counter CN is incremented 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.
In step S306 and step S307, after counting up the counter CN, it is determined whether or not the count number N is smaller than the threshold value α3 (step S308). If N <α3, the image forming operation is continued. If 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, if the first difference value ΔHa1 is smaller than E, the temperature decrease 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 trailing edge of the transfer material P does not pass through the fixing nip N1, the process returns to step S304, and the control from step S304 to step S309 is repeated until N ≧ α3.
If the count number N does not reach α3 and it is determined in step S310 that the trailing edge 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 side. .

In step S311, power control on the second surface is performed according to the second detected temperature TH2 and the second target temperature Ta2. That is, the power of the heater 201 is controlled based on the second detected temperature TH2 detected by the thermistor 207 with the target temperature as the second target temperature Ta2.
Next, after the leading edge of the transfer material P enters the fixing nip NI, the control unit 308 starts a comparison operation between the second detected temperature TH2 and the second target temperature Ta2 (step S312).
In the control unit 308, a second difference value ΔHa2 between the second target temperature Ta2 and the second detected temperature TH2 is calculated (ΔHa2 = Ta2-TH2) and compared with the value G of the second abnormal low temperature threshold Tc2 (step S313). . As described above, the second abnormal low temperature threshold Tc2 on the second surface has two values G and H, and is set to G <H.
If Ta2−TH2 <G is not satisfied, that is, if the second difference value Δa2 is equal to or greater than G, 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 incremented 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 equal to or greater than H, the counter CN is incremented 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.
In step S306 and step S307, after counting up the counter CN, 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).
If N <α3, the image forming operation is continued. If N is α3 or more (N ≧ α3).
Then, an abnormal low temperature error is notified, and the image forming operation is stopped (step S321).
On the other hand, if Ta2-TH2 <G in step S313, that is, if 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 trailing edge of the transfer material P does not pass through the fixing nip N1, the process returns to step S313, and the control from step S313 to step S318 is repeated until N ≧ α3.
If N ≧ α3 is not satisfied and the rear end of the transfer material P has passed through the fixing nip N1, the process proceeds to step S320, and it is determined whether or not the print job is finished. If the print job is finished, the image forming operation is finished. If the print job is continued, the process returns to step S302 for the image formation on the next transfer material, and the control is repeated for the next transfer material.

Thus, in the third embodiment, the first difference value ΔHa1 between the first target temperature Ta1 on the first surface and the first detection temperature TH1, and the second difference between the second target temperature Ta2 and the second detection temperature TH2 on the second surface. The first abnormal low temperature threshold value Tc1 and the second abnormal low temperature threshold value Tc2 are provided according to the two difference values ΔHa2. As a result, when the input voltage is lower than 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, even in the input voltage condition where the input power is in an abnormally low temperature. It becomes possible to detect.
Furthermore, by changing the added value of the counter according to the difference value between the target temperature and the detected temperature, it is possible to detect a drop in the input voltage quickly and accurately, stopping the image forming operation and forming an image. Damage to the device can be prevented. The abnormal low temperature threshold may be set finely in three or more stages.

In the first embodiment, the number of times that the first detection temperature TH1 and the second detection temperature TH2 acquired at regular intervals are 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, each average value, maximum value, 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 the representative value. In this case, when the first detection temperature TH1 and the second detection temperature TH2 are equal to or higher than the first abnormal low temperature threshold Tb1 and the second abnormal low temperature threshold Tb2 without using a counter, the energization to the heater 201 is stopped, and the image Control is performed to stop the forming operation.
In the second embodiment, a difference value ΔTH from the first detection temperature TH1 is obtained for each data of the second detection temperature TH2 acquired at regular intervals while the second surface passes through the fixing nip N1, and a predetermined threshold value is obtained. Although the comparison operation is performed with α2, the present invention is not limited to the method of performing the successive comparison operation. 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, and the difference value with respect to the first detection temperature TH1 is calculated and compared with the threshold value α2. You may do it.
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 between the first target temperature Ta1 and the second target temperature Ta2. However, the present invention is not limited to such a control method. For example, each average value, maximum value, minimum value, or only one point of the first detection temperature TH1 and the second detection temperature TH2 is used as a representative value, and the first difference value between the first target temperature Ta1 and the second target temperature Ta2 is used. You may obtain | require (DELTA) Ha1 and 2nd difference value (DELTA) Ha2. In this case, the first difference value ΔHa1 and the second difference value ΔHa2 are compared with the first abnormal low temperature threshold value Tc1 and the second abnormal low temperature threshold value Tc2, and it is determined from the comparison result whether or not the abnormal low temperature state is caused by a decrease in the input voltage. The For example, when each of the first abnormal low temperature threshold Tc1 and the second abnormal low temperature threshold Tc2 is one, when the first difference value ΔHa1 or the second difference value ΔHa2 is equal to or more than the first abnormal low temperature threshold Tc1 or the second abnormal low temperature threshold Tc2, You may make it discriminate | determine from an abnormally low temperature state. In this case, control is performed to stop energization of the heater 201 and stop the image forming operation.

101 Image forming apparatus 107 Fixing device (fixing means)
201 Heater (Heating body)
202 Film 203 Pressure roller (Pressure member)
207 Thermistor (temperature detection means)
NI fixing nip (nip)
P Transfer material (transfer material)
308 Control unit (power control means)
CN counter, N count number Ta target temperature, Ta1 first target temperature, Ta2 second target temperature Tb abnormal low temperature threshold, Tb1 first abnormal low temperature threshold, Tb2 second abnormal low temperature threshold Tc abnormal low temperature threshold, Tc1 first abnormal low temperature threshold , Tc2 Second abnormal low temperature threshold value E, F First abnormal low temperature threshold value, G, H Second abnormal low temperature threshold value TH detection temperature, TH1 first detection temperature, TH2 second 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 values

Claims (10)

A heating body that generates heat when energized, a pressure member that forms a nip portion that heats the developer image formed on the recording material in pressure contact with the heating body, and a temperature detection unit that detects the temperature of the heating body. Fixing means having
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means stops the image forming operation by stopping the power supply to the heating body when the detected temperature becomes equal to or lower than the abnormal low temperature threshold, and the second abnormal low temperature threshold of the second side in the double-sided printing mode is set to the double-sided printing. An image forming apparatus, wherein the image forming apparatus is set lower than a first abnormal low temperature threshold value on a first surface of a mode.   The first abnormal low temperature threshold is a value obtained by multiplying the first target temperature by a first ratio, and the second abnormal low temperature threshold is a value obtained by multiplying the second target temperature by a second ratio. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 2, wherein the second ratio is set higher than the first ratio.   The control means acquires the detected temperature at regular intervals through the first and second sides of the double-sided printing mode, and the number of times that the first detected temperature on the first side is equal to or lower than the first abnormal low temperature threshold, and the second side. The number of times that the second detected temperature of the second detection temperature becomes equal to or lower than the second abnormally low temperature threshold is counted by a counter. The image forming apparatus according to claim 1, wherein the operation is stopped.   The image forming apparatus according to claim 4, wherein the first detection temperature and the second detection temperature are subtracted from a counter when the first detection temperature and the second detection temperature are larger than the first abnormal low temperature threshold and the second abnormal low temperature threshold, respectively. A heating body that generates heat when energized, a pressure member that forms a nip portion that heats the developer image formed on the recording material in pressure contact with the heating body, and a temperature detection unit that detects the temperature of the heating body. Fixing means having
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means includes a first detection temperature detected by the temperature detection means during image formation on the first surface and a second detection temperature detected by the temperature detection means during image formation on the second surface. An image forming apparatus, wherein 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 heats the developer image formed on the recording material in pressure contact with the heating body, and a temperature detection unit that detects the temperature of the heating body. Fixing means having
Control means for controlling the power supplied to the heating body in accordance with the temperature detected by the temperature detection means and the target temperature,
The control means sets the target temperature to the first target temperature when the first side image is formed in the duplex printing mode, and sets the target temperature lower than the first target temperature when the second side image is formed. In the image forming apparatus that sets the temperature,
The control means calculates a first difference value between the first target temperature and the detected temperature on the first surface and a second difference value between the second target temperature and the detected temperature on the second surface, and the first difference value and An image forming apparatus, wherein an abnormal low temperature state due to a decrease in input voltage is determined from a comparison result between a set first abnormal low temperature threshold value and the second difference value and a preset second abnormal low temperature threshold value. .   The control means acquires the detected temperature at regular intervals through the first and second sides of the duplex printing mode, and the difference value between the first target temperature on the first side and the first detected temperature on the first side is a first abnormality. The counter counts the number of times that the temperature is equal to or higher than the low temperature threshold, and the number of times that the difference value between the second target temperature on the second surface and the second detected temperature on the second surface is equal to or higher than the second abnormal low temperature threshold. The image forming apparatus according to claim 7, wherein when the value becomes equal to or greater than a preset value, the power supply to the heating body is stopped to stop the image forming operation.   Each of the first abnormal low temperature threshold and the second abnormal low temperature threshold has at least two thresholds that increase stepwise, and the added value counted by the counter is the larger of the at least two thresholds. The image forming apparatus according to claim 8, wherein the image forming apparatus is set to a larger value. The heating body is configured to be in pressure contact with the pressing member via a cylindrical heat-resistant film, and an inner peripheral surface of the film is in sliding contact with the heating body at a nip portion. The image forming apparatus according to claim 1.