JP2020095169A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent a failure in fixing at the ends of a sheet.SOLUTION: A control unit 100 of an image forming apparatus can execute first heating control of energizing a heater 83 such that the temperature of a heating unit 81 becomes a fixing temperature based on the temperature of a center part of the heating unit 81 (first detection temperature), and second heating control of energizing the heater 83 such that the temperature of the heating unit 81 becomes the fixing temperature based on the first detection temperature, the control of increasing a lower limit of the amount of energization of the heater 83 per unit time compared with that in the first heating control. At a timing after the first heating control is started and before a sheet S reaches a fuser 8, the control unit 100 determines whether the temperature of the ends of the heating unit 81 (second detection temperature) is equal to or lower than a first temperature that is lower than the fixing temperature, when the second detection temperature is higher than the first temperature, continues the first heating control, and when the second detection temperature is equal to or lower than the first temperature, switches from the first heating control to the second heating control before the sheet S reaches the fuser 8.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus including a fixing device that fixes a developer image on a sheet.

Conventionally, a fixing device that has a heating roller, a pressure roller, and a heater that heats the heating roller, fixes a developer image on a sheet, a center thermistor that detects the temperature of the central portion of the heating roller, and an end portion of the heating roller. An image forming apparatus including a side thermistor that detects the temperature of the above is known (for example, Patent Document 1). In this technique, the electric power supplied to the heater is controlled based on the output signal of the center thermistor so that the temperature of the heating roller reaches the fixing temperature, and the temperature of the end portion of the heating roller is controlled based on the output signal of the side thermistor. When the upper limit temperature is exceeded, power supply to the heater is stopped.

JP, 2008-063395, A

By the way, in a heating unit such as a heating roller, the temperature rise at the end may be slower than that at the center due to factors such as the environment in which the image forming apparatus is installed. Then, when fixing the developer image on the sheet with the fixing device, even if the temperature of the central portion of the heating portion is suitable for fixing, the temperature of the end portion of the heating portion does not reach the temperature suitable for fixing. In some cases, there is a concern that defective fixing may occur at the edge of the sheet.

Therefore, it is an object of the present invention to provide an image forming apparatus capable of suppressing the fixing failure at the end portion of the sheet.

In order to achieve the above-mentioned object, an image forming apparatus of the present invention includes a developer image forming section for forming a developer image on a sheet, a conveying section for conveying the sheet toward the developer image forming section, and a sheet contacting the sheet. And a heating unit that heats the heating unit, and a pressing unit that sandwiches the sheet between the heating unit and the heating unit, and a fixing unit that fixes the developer image on the sheet; A first temperature detecting section that detects a first detected temperature that is a temperature of a central portion of the sheet, a second temperature detecting section that detects a second detected temperature that is a temperature of an end portion of the heating section in the width direction of the sheet, and a control And a section.
The control unit energizes the heater so that the temperature of the heating unit becomes the fixing temperature for fixing the developer image on the sheet based on the first detected temperature, and the heating unit of the heating unit based on the first detected temperature. Second heating control for energizing the heater so that the temperature becomes the fixing temperature, in which the lower limit value of the amount of electricity energized to the heater per unit time is made larger than the first heating control It is possible.
The control unit determines whether or not the second detected temperature is equal to or lower than the first temperature lower than the fixing temperature at a predetermined timing after the first heating control is started and before the sheet reaches the fixing device, When the second detected temperature is higher than the first temperature, the first heating control is continued, and when the second detected temperature is equal to or lower than the first temperature, the first heating control is performed before the sheet reaches the fixing device. To the second heating control.

With such a configuration, when the temperature rise at the end of the heating unit is slow, the second heating control for increasing the amount of electricity to the heater per unit time is executed, so that the sheet reaches the fixing device. Before the heating, the end of the heating unit can be heated to a temperature range in which fixing can be performed. As a result, it is possible to suppress the fixing failure at the end portion of the sheet.

In the above-described image forming apparatus, the control unit does not rotate the fixing device when the first detected temperature is lower than the second temperature lower than the fixing temperature, and when the first detected temperature is equal to or higher than the second temperature. The rotation control for rotationally driving the fixing device can be performed, and the predetermined timing can be a timing before the sheet reaches the fixing device after the rotational driving of the fixing device is started.

When the fixing device is rotationally driven, heat is taken by the pressurizing unit and the temperature of the end portion of the heating unit hardly rises. Therefore, after the fixing device is rotationally driven, the first heating control is switched to the second heating control. It is possible to heat the end portion of the heating portion to a temperature range in which fixing can be effectively performed. As a result, it is possible to effectively suppress the fixing failure at the end portion of the sheet.

In the above-described image forming apparatus, the control unit can execute the conveyance control for conveying the sheet toward the developer image forming unit when the first detected temperature is equal to or higher than the third temperature lower than the fixing temperature. The predetermined timing may be a timing before the sheet reaches the fixing device after the sheet is started to be conveyed.

In the above-described image forming apparatus, the control unit may be configured to continue the second heating control while the sheet is between the heating unit and the pressing unit when the second heating control is being executed. ..

According to this, heat is absorbed by the sheet while the sheet is between the heating unit and the pressurizing unit. Therefore, during this period, by continuing the second heating control in which the energization amount per unit time to the heater is large. It is possible to prevent the temperature of the heating section from decreasing. As a result, fixing failure can be suppressed.

In the above-described image forming apparatus, the control unit may change the second heating control to a second sheet when the fixing of a predetermined number of sheets is completed in the case of continuously forming images on a plurality of sheets. The heating control may be switched to the first heating control.

According to this, when images are continuously formed on a plurality of sheets, the end portion of the heating unit is maintained in a temperature range in which fixing can be performed in the middle, so that the second heating control is performed to the heater. By switching to the first heating control in which the lower limit value of the energization amount per unit time is small, it is possible to prevent the heating unit from being heated more than necessary.

In the above-described image forming apparatus, the control unit controls the temperature of the heating unit at the duty ratio according to the difference obtained by subtracting the first detected temperature from the fixing temperature in the first heating control and the second heating control, and the duty ratio The lower limit value of the duty ratio is set to 0% in the first heating control, and the lower limit value of the duty ratio is set to be larger than 0% in the second heating control.

In the above-described image forming apparatus, the control unit sets the duty ratio to 0% when the first detection temperature is higher than the fixing temperature in the first heating control, and sets the duty ratio to be higher than the fixing temperature in the second heating control. When the detected temperature is high, the duty ratio can be set to be larger than 0%.

In the above-described image forming apparatus, the heater may be configured to heat the entire region of the heating unit that is in contact with the sheet in the width direction of the sheet.

In the above-described image forming apparatus, the second temperature detection unit may be arranged outside the region of the heating unit in contact with the sheet in the width direction of the sheet.

In the above-described image forming apparatus, the control unit may be configured to execute the second heating control on condition that the image is present at the end portion in the width direction of the sheet.

According to this, the second heating control can be executed when there is a possibility that defective fixing may occur at the edge portion of the sheet, so that defective fixing at the edge portion of the sheet can be effectively suppressed.

In the above-described image forming apparatus, the control unit may be configured such that, in the second heating control, the lower limit value of the energization amount per unit time to the heater is increased as the second detected temperature is lower.

According to this, the slower the temperature rise at the end of the heating unit is, the larger the amount of electricity supplied to the heater per unit time can be, so that the end of the heating unit can be heated to a temperature range in which fixing can be performed. It is possible to further suppress the fixing failure at the edge portion of the sheet.

According to the present invention, it is possible to suppress the fixing failure at the end portion of the sheet.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment. It is a figure which shows the structure for controlling a heater. FIG. 3 is a diagram of the fixing device, the first temperature detecting unit, and the second temperature detecting unit as viewed from a direction orthogonal to the sheet conveying direction and the width direction. A table (a) for setting a duty ratio in the first heating control and a table (b) for setting a duty ratio in the second heating control. It is a flow chart which shows operation of a control part. 6 is a time chart showing the operation of the control unit. It is a table which sets the duty ratio according to the 2nd detected temperature in the 2nd heating control concerning a modification.

Next, an embodiment of the invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main body housing 2, a sheet supply unit 3, an exposure device 4, a developer image forming unit 5, a fixing device 8, and a fixing device 8. The first temperature detection unit 9C, the second temperature detection unit 9S (see FIG. 3), the first sheet detection unit 11, the second sheet detection unit 12, and the control unit 100 are provided.

The sheet supply unit 3 is provided in the lower portion of the main body housing 2, and has a sheet tray 31 in which a sheet S such as paper is stored, a pressure plate 32, and a conveyance that conveys the sheet S toward the developer image forming unit 5. And part 33. The transport unit 33 includes a pickup roller 33A, a separation pad 33B, a first transport roller 33C, a registration roller 33R, and the like. The sheet supply unit 3 draws the sheets S in the sheet tray 31 to the pickup roller 33A by the pressure plate 32, separates them one by one by the pickup roller 33A and the separation pad 33B, and sends them out, and by the first conveyance roller 33C and the registration roller 33R. The image is conveyed toward the developer image forming unit 5.

The exposure device 4 is arranged in the upper portion of the main body housing 2 and includes a light source device (not shown), a polygon mirror, a lens, a reflecting mirror, etc., which are not shown. The exposure device 4 exposes the surface of the photoconductor 61 by scanning the surface of the photoconductor 61 at high speed with a light beam (see the alternate long and short dash line) based on the image data emitted from the light source device.

The developer image forming unit 5 is a device that forms a developer image on the sheet S, and is arranged below the exposure device 4. The developer image forming unit 5 is detachably attached as a process cartridge to the main body housing 2 through an opening formed when the front cover 21 provided at the front portion of the main body housing 2 is opened. The developer image forming section 5 includes a photoconductor cartridge 6 and a developing cartridge 7.

The photoconductor cartridge 6 includes a photoconductor 61 that is a cylindrical photoconductor drum, a charger 62 that is a corona charger, and a transfer roller 63. The developing cartridge 7 is attachable to and detachable from the photoconductor cartridge 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, an accommodating portion 74 for accommodating a developer made of dry toner, and an agitator 75. It has and.

The developer image forming section 5 uniformly charges the surface of the photoconductor 61 by the charger 62. Then, the surface of the photoconductor 61 is exposed by the light beam emitted from the exposure device 4, so that an electrostatic latent image based on image data is formed on the photoconductor 61. Further, the developer in the container 74 is supplied to the supply roller 72 while being stirred by the agitator 75, and then supplied from the supply roller 72 to the developing roller 71. Then, as the developing roller 71 rotates, the developer enters between the developing roller 71 and the layer thickness regulating blade 73 and is carried on the developing roller 71 as a thin layer having a constant thickness.

The developer image forming unit 5 supplies the developer carried on the developing roller 71 to the electrostatic latent image formed on the photoconductor 61 from the developing roller 71. As a result, the electrostatic latent image is made visible and a developer image is formed on the photoconductor 61. After that, the sheet S passes between the photoconductor 61 and the transfer roller 63, so that the developer image on the photoconductor 61 is transferred onto the sheet S.

The fixing device 8 is a device that fixes the developer image on the sheet S, and is arranged behind the developer image forming unit 5. The fixing device 8 includes a heating unit 81, a pressure unit 82, and a heater 83.
The heating unit 81 is a cylindrical heating roller made of metal. The heating unit 81 is configured to contact the sheet S conveyed between the heating unit 81 and the pressure unit 82 to heat the sheet S.

The pressure unit 82 is a pressure roller having an elastic layer around the cored bar. The pressurizing unit 82 is arranged in a state of being pressed by being in contact with the heating unit 81, and sandwiches the sheet S with the heating unit 81.
The heater 83 is a heat source that heats the heating unit 81. The heater 83 is configured as a halogen heater having a filament 83A (see FIG. 2), and heats the heating unit 81 with radiant heat. The heater 83 is arranged inside the heating unit 81.

The fixing device 8 is rotationally driven by driving a motor M provided inside the main body housing 2. As an example, in the fixing device 8, when the driving force is input from the motor M, the heating unit 81 is rotationally driven, and the pressurizing unit 82 is driven to rotate in accordance with the rotational driving of the heating unit 81.

The fixing device 8 fixes the developer image transferred on the sheet S to the sheet S by passing the sheet S between the heating unit 81 and the pressure unit 82. The sheet S having the developer image fixed thereon is discharged onto the discharge tray 22 by the second transport roller 23 and the discharge roller 24.

The control unit 100 is a device that controls each unit of the laser printer 1, such as the fixing device 8 and the motor M, and is configured by a single or a plurality of electric circuits. The control unit 100 outputs a control signal or a drive voltage to each unit of the laser printer 1 to control each unit. As shown in FIG. 2, the control unit 100 includes a CPU 110, a ROM 120, a RAM 130, a heater controller 140, a switching circuit 150, and the like.

The CPU 110 performs a process of instructing the operation timing of each part of the laser printer 1 and sending a command value as the target temperature of the fixing device 8 to the heater controller 140.
The ROM 120 stores data such as programs for controlling each unit of the laser printer 1 and various setting information.
The RAM 130 is used as a work area when the CPU 110 executes various programs and a temporary storage area for data.

The heater controller 140 sets the duty ratio of the switching circuit 150 based on the target temperature of the fixing device 8 and the temperature detected by the first temperature detector 9C. In this embodiment, the CPU 110 and the heater controller 140 are integrated as a single semiconductor element.
The switching circuit 150 energizes the heater 83 by switching the AC voltage at the set duty ratio.

As shown in FIG. 3, the first temperature detection unit 9C is a sensor that detects the first detection temperature Tc, which is the temperature of the central portion of the heating unit 81 in the width direction of the sheet S. The width direction of the sheet S is a direction orthogonal to the conveyance direction of the sheet S in the laser printer 1. Hereinafter, the width direction of the sheet S is simply referred to as “width direction”.

9 C of 1st temperature detection parts are arrange|positioned in the area|region (henceforth a "sheet contact area") CA which contacts the sheet|seat S of the heating part 81 in the width direction, and near the center of the sheet contact area CA in the width direction. ing. Further, when the laser printer 1 is capable of transporting a plurality of types of sheets S having different widths, the first temperature detection unit 9</b>C is located within a region where the sheet S having the smallest width capable of being transported by the laser printer 1 is in contact with the heating unit 81. It is located in. In addition, the first temperature detection unit 9C is arranged to face the surface of the heating unit 81 in a non-contact state with a predetermined distance from the surface of the heating unit 81. 9 C of 1st temperature detection parts output the signal according to the surface temperature of the heating part 81 to the control part 100.

The first detected temperature Tc that the control unit 100 acquires based on the output signal from the first temperature detection unit 9C does not linearly correspond to the output signal from the first temperature detection unit 9C, and the heating unit 81. It may be a temperature corrected to correspond to the actual surface temperature of. For example, the first detected temperature Tc may be a temperature obtained by correcting the output of the first temperature detection unit 9C according to the elapsed time from the start of heating of the heating unit 81.

As an example, the control unit 100 can acquire the first detected temperature Tc (correction value) by the following equation.
Tc=a(t)×TcS+b(t)
Here, TcS is a temperature detected by the first temperature detection unit 9C, specifically, an output signal of the first temperature detection unit 9C. Further, a(t) is a correction coefficient, and b(t) is a correction term. The correction coefficient a(t) and the correction term b(t) are functions of the time t from the start of heating of the heating unit 81, respectively.

The second temperature detection unit 9S is a sensor that detects the second detection temperature Ts that is the temperature of the end portion of the heating unit 81 in the width direction. The second temperature detection unit 9S is arranged outside the sheet contact area CA of the heating unit 81 in the width direction. In addition, the second temperature detection unit 9S is arranged to face the surface of one end of the heating unit 81 in the width direction while being in contact with the surface of the heating unit 81. The second temperature detector 9S outputs a signal according to the second detected temperature Ts to the controller 100. The second detected temperature Ts acquired by the control unit 100 based on the output signal from the second temperature detection unit 9S may also be the corrected temperature, like the first detected temperature Tc.

As the first temperature detection unit 9C and the second temperature detection unit 9S, for example, a thermistor whose electric resistance changes according to temperature can be used.

One heater 83 is arranged inside the heating portion 81, and is provided so as to heat the entire sheet contact area CA of the heating portion 81 in the width direction. Specifically, the heater 83 has a plurality of heat generating portions 83B in which the filaments 83A are densely wound and arranged in the width direction, and a heat generating area 83C including the plurality of heat generating portions 83B is a sheet of the heating portion 81 in the width direction. It is provided over the entire contact area CA.

The pressurizing portion 82 is larger than the sheet contact area CA of the heating portion 81 and the heat generating area 83C of the heater 83 in the width direction. As a result, at the end portion of the sheet contact area CA, the heat of the heating portion 81 heated by the heater 83 is taken by the pressurizing portion 82, so that the temperature rise may be slower than at the center of the sheet contact area CA. . The second temperature detection unit 9S is arranged outside the sheet contact area CA of the heating unit 81 and inside the end of the pressing unit 82 in the width direction. The second detected temperature Ts is a temperature related to the temperature of the end of the sheet contact area CA of the heating unit 81 and the temperature of the end of the pressing unit 82.

As shown in FIG. 1, the first sheet detection unit 11 is a sensor that detects the sheet S conveyed from the registration roller 33R toward the space between the photoconductor 61 and the transfer roller 63. The first sheet detection unit 11 is disposed downstream of the registration roller 33R and upstream of the photoconductor 61 in the sheet S transport direction. The first sheet detection unit 11 is arranged closer to the registration roller 33R than the photoconductor 61.

The second sheet detection unit 12 is a sensor that detects the sheet S conveyed between the heating unit 81 and the pressure unit 82 toward the second conveyance roller 23. The second sheet detection unit 12 is disposed downstream of the heating unit 81 and upstream of the second transport roller 23 in the transport direction of the sheet S. Further, the second sheet detection unit 12 is arranged closer to the heating unit 81 than the second transport roller 23.

The first sheet detection unit 11 and the second sheet detection unit 12 include, for example, a swing lever that is swung by being pushed by the conveyed sheet S and an optical sensor that detects the swing of the swing lever. Has been done. In the present embodiment, the first sheet detecting unit 11 and the second sheet detecting unit 12 output an ON signal to the control unit 100 when the swing lever is tilted by the sheet S, and the swing lever is not tilted. Sometimes, the OFF signal is output to the control unit 100 (specifically, the ON signal is not output).

The control unit 100 can execute first heating control, second heating control, rotation control, and conveyance control.
The first heating control and the second heating control are controls for energizing the heater 83 so that the temperature of the heating unit 81 becomes the fixing temperature Tf based on the first detection temperature Tc acquired from the first temperature detection unit 9C.

The fixing temperature Tf is a target temperature for temperature control of the heating unit 81 for fixing the developer image on the sheet S. The fixing device 8 can fix the developer image on the sheet S if the temperature of the heating unit 81 is within a predetermined temperature range including the fixing temperature Tf. As an example, the fixing temperature Tf is 200°C. Note that the specific numerical values shown in this specification are examples.

In the first heating control and the second heating control, the control unit 100 energizes the heater 83 with a duty ratio according to the difference ΔT obtained by subtracting the first detection temperature Tc from the fixing temperature Tf, and the temperature of the heating unit 81. To control. In the first heating control and the second heating control, the control unit 100 increases the duty ratio as the difference ΔT increases.

In the second heating control, the control unit 100 makes the lower limit value of the amount of electricity supplied to the heater 83 per unit time larger than that in the first heating control. Specifically, in the second heating control, the control unit 100 makes the lower limit value of the duty ratio larger than that in the first heating control.

As an example, the control unit 100 sets the duty ratio based on a table as shown in FIG. 4A when executing the first heating control, and when performing the second heating control, The duty ratio is set based on the table shown in FIG.

For example, in the first heating control, the control unit 100 sets the duty ratio to 30% when the difference ΔT is 0° C. or more and less than 2° C. or more based on the table shown in FIG. When the temperature is 10° C. or higher and lower than 12° C., the duty ratio is set to 60%. Further, in the second heating control, the control unit 100 sets the duty ratio to 40% when the difference ΔT is 0° C. or more and less than 2° C. or more based on the table shown in FIG. When the temperature is 10° C. or higher and lower than 12° C., the duty ratio is set to 60%.

As shown in FIG. 4A, the control unit 100 sets the lower limit value of the duty ratio to 0% in the first heating control. Specifically, in the first heating control, the control unit 100, based on the table shown in FIG. 4A, when the difference ΔT is less than 0° C., that is, when the first detection temperature Tc is higher than the fixing temperature Tf. Sets the duty ratio to 0% of the lower limit value.

On the other hand, as shown in FIG. 4B, the control unit 100 makes the lower limit value of the duty ratio larger than 0% in the second heating control. Specifically, the control unit 100 sets the lower limit value of the duty ratio to 40% in the second heating control. Specifically, in the second heating control, the control unit 100 sets the duty ratio to 40% of the lower limit value when the difference ΔT is less than 4° C. based on the table shown in FIG. Further, in the second heating control, the control unit 100 sets the duty ratio to be larger than 0% when the first detection temperature Tc is higher than the fixing temperature Tf, specifically 40%. ..

In the second heating control, the control unit 100 prevents the heating unit 81 from being excessively heated when the first detection temperature Tc is higher than the fixing temperature Tf by a predetermined temperature or more. The power supply to the heater 83 is stopped.

In the rotation control, after the first heating control is started, if the first detection temperature Tc is lower than the second temperature Tth2, the fixing device 8 is not rotationally driven, and the first detection temperature Tc is equal to or higher than the second temperature Tth2. In this case, the fixing device 8 is rotated. Specifically, after starting the first heating control, the control unit 100 does not rotate and drive the heating unit 81 and the pressurizing unit 82 until the first detected temperature Tc reaches the second temperature Tth2. After heating 81 and the first detected temperature Tc reaches the second temperature Tth2, the heating unit 81 is heated while driving the motor M to rotate the heating unit 81 and the pressurizing unit 82. The second temperature Tth2 is lower than the fixing temperature Tf and is set in advance. As an example, the second temperature Tth2 is 100°C.

The conveyance control is control for conveying the sheet S toward the developer image forming unit 5 when the first detected temperature Tc becomes equal to or higher than the third temperature Tth3 after the first heating control is started. Specifically, when the first detection temperature Tc becomes equal to or higher than the third temperature Tth3 after the first heating control is started, the control unit 100 causes the driving force from the motor M to be applied to the pickup roller 33A by the clutch mechanism (not shown). The sheet S is sent toward the developer image forming unit 5 by rotating the pickup roller 33A to the developer image forming unit 5, and is conveyed toward the developer image forming unit 5 by the registration roller 33R or the like. The third temperature Tth3 is higher than the second temperature Tth2 and lower than the fixing temperature Tf, and is preset. As an example, the third temperature Tth3 is 150°C.

When a print job including a print instruction or image data to be printed is input to the laser printer 1, the control unit 100 starts the first heating control. Then, the control unit 100 determines at a predetermined timing whether the second detected temperature Ts acquired from the second temperature detection unit 9S is equal to or lower than the first temperature Tth1.

The predetermined timing is the timing before the sheet S reaches the fixing device 8 after the first heating control is started. Specifically, the predetermined timing is a timing before the sheet S reaches the fixing device 8 after the rotational driving of the fixing device 8 is started in the rotation control. More specifically, the predetermined timing is a timing after the conveyance of the sheet S is started in the conveyance control and before the sheet S reaches the fixing device 8.

In the present embodiment, the control unit 100 starts the conveyance control and sends the sheet S toward the developer image forming unit 5 by the pickup roller 33A, and then the first sheet detection unit 11 causes the registration roller 33R to move the photosensitive member. The second detection temperature Ts is detected at the timing when the sheet S conveyed toward the space between the transfer roller 63 and the transfer roller 63 is detected, specifically, at the timing when the first sheet detection unit 11 outputs an ON signal to the control unit 100. It is determined whether the temperature is equal to or lower than the first temperature Tth1.

The controller 100 continues the first heating control when the second detected temperature Ts is higher than the first temperature Tth1. Moreover, the control part 100 switches from 1st heating control to 2nd heating control, when the 2nd detected temperature Ts is below the 1st temperature Tth1. Specifically, the control unit 100 switches from the first heating control to the second heating control when the second detected temperature Ts becomes equal to or lower than the first temperature Tth1. Therefore, when the second detected temperature Ts is equal to or lower than the first temperature Tth1, the control unit 100 switches from the first heating control to the second heating control before the sheet S reaches the fixing device 8.

The first temperature Tth1 is lower than the fixing temperature Tf and is set in advance. As an example, the first temperature Tth1 is 120°C.

In the case of continuously forming images on a plurality of sheets S, the control unit 100 switches from the first heating control to the second heating control and then when the fixing of a predetermined number of sheets S is completed, Switch from 2 heating control to 1st heating control. Specifically, the control unit 100 performs the second heating control when the fixing of the first sheet S is completed after switching to the second heating control when performing continuous printing on the plurality of sheets S. To the first heating control.

More specifically, the control unit 100 causes the first sheet S discharged from between the heating unit 81 and the pressurizing unit 82 to tilt the swing lever of the second sheet detection unit 12 to move the second sheet. The detection unit 12 outputs an ON signal to the control unit 100, and thereafter, the first sheet S is conveyed toward the discharge tray 22 to release the swing of the swing lever of the second sheet detection unit 12. Then, when the second sheet detection unit 12 outputs an OFF signal to the control unit 100, the second heating control is switched to the first heating control.

The controller 100 switches from the first heating control to the second heating control before the sheet S reaches the fixing device 8, and switches from the second heating control to the first heating control after the sheet S passes through the fixing device 8. .. Therefore, when the second heating control is being executed, the control unit 100 continues the second heating control while the sheet S is between the heating unit 81 and the pressing unit 82.

In the present embodiment, the control unit 100 executes the second heating control on condition that the first detected temperature Tc0 when the first heating control is started is equal to or lower than the predetermined temperature threshold Tth0. That is, the control unit 100 does not execute the second heating control when the first detected temperature Tc0 when the first heating control is started is higher than the temperature threshold Tth0. The temperature threshold Tth0 is a temperature lower than the second temperature Tth2 and is set in advance. As an example, the temperature threshold Tth0 is 50°C.

Further, in the present embodiment, as shown in FIG. 3, the control unit 100 executes the second heating control on condition that there is an image to be formed on the end portion SE in the width direction of the sheet S. That is, the control unit 100 does not execute the second heating control when there is no image to be formed on the edge portion SE of the sheet S. As an example, the edge portion SE is a portion 20 mm from the edge of the sheet S in the width direction. The control unit 100 acquires information on whether or not there is an image to be formed on the edge portion SE of the sheet S from the image data included in the print job.

Next, the operation of the control unit 100 will be described with reference to the flowchart.
As shown in FIG. 5, when a print job is input (START), the control unit 100 acquires the first detected temperature Tc0 at the start of printing (S101) and starts the first heating control (S102). .

Next, the control unit 100 determines whether the first detected temperature Tc is equal to or higher than the second temperature Tth2 (S103). When the first detected temperature Tc is equal to or higher than the second temperature Tth2 (S103, Yes), the control unit 100 drives the motor M to rotate the fixing device 8 (S104).

Next, the control unit 100 determines whether the first detected temperature Tc has become equal to or higher than the third temperature Tth3 (S105). Then, when the first detected temperature Tc becomes equal to or higher than the third temperature Tth3 (S105, Yes), the control unit 100 drives the pressure plate 32 and the transport unit 33 to move the sheet S toward the developer image forming unit 5. The conveyance is started (S106).

Next, the control unit 100 determines whether or not the first sheet detection unit 11 has detected the sheet S (S107). When the first sheet detection unit 11 detects the sheet S (S107, Yes), the control unit 100 determines whether the first detection temperature Tc0 at the start of printing is equal to or lower than the temperature threshold Tth0 (S108). ).

When the first detection temperature Tc0 at the start of printing is equal to or lower than the temperature threshold value Tth0 (S108, Yes), the control unit 100 determines whether or not there is an image to be formed at the end SE of the sheet S (S109). .. Then, when there is an image on the edge portion SE of the sheet S (S109, Yes), the control unit 100 determines whether the second detected temperature Ts is equal to or lower than the first temperature Tth1 (S110). When the second detected temperature Ts is equal to or lower than the first temperature Tth1 (S110, Yes), the control unit 100 switches from the first heating control to the second heating control (S111).

If the first detected temperature Tc0 at the start of printing is higher than the temperature threshold value Tth0 in step S108 (No), if there is no image on the edge SE of the sheet S in step S109 (No), or in step S110 the second temperature is detected. When the detected temperature Ts is higher than the first temperature Tth1 (No), the controller 100 fixes the sheet S by the first heating control, and proceeds to step S115.

After switching from the first heating control to the second heating control in step S111, the control unit 100 determines whether to perform continuous printing (S112). Then, when performing continuous printing (S112, Yes), the control unit 100 determines whether the fixing of the first sheet S is completed (S113). Then, when the fixing of the first sheet S is completed (S113, Yes), the control unit 100 switches from the second heating control to the first heating control (S114), and the first heating control is performed for the second and subsequent sheets. The sheet S is fixed.

When the continuous printing is not performed in step S112 (No), the control unit 100 fixes the sheet S by the second heating control.

Then, when the printing is completed in step S115 (Yes), the control unit 100 ends the process (END).

Next, the operation of the control unit 100 will be described with reference to a time chart.
As shown in FIG. 6, when a print job is input at time t0, the control unit 100 starts the first heating control. As a result, the temperature of the heating unit 81 (first detected temperature Tc and second detected temperature Ts) rises.

After that, at time t1, when the first detected temperature Tc reaches the second temperature Tth2, the control unit 100 rotationally drives the fixing device 8. By rotating the fixing device 8, the heat of the heating part 81 is easily transferred to the pressurizing part 82, so that the gradient of the temperature rise of the heating part 81 is slightly reduced.

After that, at time t2, when the first detected temperature Tc reaches the third temperature Tth3, the control unit 100 starts the conveyance of the sheet S toward the developer image forming unit 5.

Then, at time t3, when the sheet S conveyed toward the developer image forming unit 5 tilts the swing lever of the first sheet detecting unit 11, the first sheet detecting unit 11 outputs an ON signal. At this time, since the first detection temperature Tc0 at the start of printing (time t0) is the temperature threshold Tth0 or less and the second detection temperature Ts is the first temperature Tth1 or less, the control unit 100 starts the first heating control. Switch to the second heating control. When the second heating control is executed, the lower limit value of the duty ratio is set to 40%.

After that, at time t4, the fixing of the first sheet S is completed, the first sheet S passes through the second sheet detection unit 12, and the swing lever of the second sheet detection unit 12 is released from swinging. Then, when the second sheet detection unit 12 outputs the OFF signal, the control unit 100 switches from the second heating control to the first heating control. After that, the control unit 100 fixes the second and subsequent sheets S by the first heating control.

Here, if the first heating control is executed at times t3 to t4, the duty ratio becomes smaller than 40% as shown by the chain double-dashed line, so that the heating portion 81 is sufficiently heated by the heater 83. Therefore, there is a possibility that the temperature of the end portion of the heating portion 81 does not rise sufficiently as indicated by the chain double-dashed line. In the present embodiment, by performing the second heating control from the time t3 to t4, the duty ratio is maintained at 40% at the minimum, so that the heater 83 can sufficiently heat the heating portion 81 and the heating. The temperature at the end of the portion 81 can be increased.

According to the present embodiment described above, when the second detected temperature Ts is equal to or lower than the first temperature Tth1 and the temperature rise at the end of the heating unit 81 is slow, the second heating control for increasing the duty ratio is executed. Therefore, before the sheet S reaches the fixing device 8, the end portion of the heating unit 81 can be heated to a temperature range in which fixing can be performed. As a result, it is possible to suppress defective fixing of the end portion SE of the sheet S.

Further, when the fixing device 8 is rotationally driven, heat is taken by the pressurizing portion 82 and the temperature of the end portion of the heating portion 81 is hard to rise, but after the fixing device 8 is rotationally driven, the second heating control is performed. By switching to the heating control, the end portion of the heating unit 81 can be heated to a temperature range in which fixing can be effectively performed. As a result, defective fixing of the end portion SE of the sheet S can be effectively suppressed.

Further, heat is taken by the sheet S while the sheet S is between the heating unit 81 and the pressurizing unit 82. Therefore, by continuing the second heating control with a large duty ratio, the temperature of the heating unit 81 is increased. Can be suppressed. As a result, fixing failure can be suppressed.

Further, when performing continuous printing, the end of the heating unit 81 is maintained in the temperature range in which fixing can be performed in the middle, so that after the fixing of the first sheet S is completed, the second heating control is performed. By switching to the first heating control in which the lower limit of the duty ratio is small, it is possible to prevent the heating unit 81 from being heated more than necessary during printing.

Further, the second heating control is executed under the condition that an image is present at the edge SE of the sheet S, so that the second heating control is performed when the fixing failure may occur at the edge SE of the sheet S. be able to. As a result, defective fixing of the end portion SE of the sheet S can be effectively suppressed.

Although the embodiment has been described above, the present invention is not limited to the embodiment. The specific configuration can be changed as appropriate without departing from the spirit of the invention.
For example, the control unit 100 may be configured such that, in the second heating control, the lower limit value of the energization amount per unit time to the heater 83 is increased as the second detection temperature Ts is lower.

As an example, as shown in FIG. 7, when the control unit 100 makes a determination for switching from the first heating control to the second heating control, if the second detected temperature Ts is 100° C. or higher, the duty ratio When the second detection temperature Ts is 80° C. or higher and lower than 100° C., the lower limit value of the duty ratio is set to 50%, and the second detection temperature Ts is lower than 80° C. In this case, the lower limit of the duty ratio may be set to 55%.

With such a configuration, as the temperature rise at the end of the heating unit 81 is slower, the duty ratio can be increased to heat the end of the heating unit 81 to a temperature range in which fixing can be performed. It is possible to further suppress the improper fixing of the end portion SE.

Further, in the above-described embodiment, the second heating control is executed on the condition that there is an image on the end portion SE of the sheet S, but the second heating control may be executed regardless of the presence or absence of the image of the end portion of the sheet. You can

Moreover, in the said embodiment, although the 2nd temperature detection part 9S was arrange|positioned outside the sheet|seat contact area|region CA of the heating part 81, the 2nd temperature detection part has a width in the sheet|seat contact area|region of a heating part, for example. It may be arranged at the end in the direction.

Further, in the above-described embodiment, the duty ratio according to the difference ΔT is set based on the table as shown in FIG. 4, but for example, PI control or PID control is performed based on the deviation between the fixing temperature and the first detection temperature. The duty ratio (heater operation amount) may be set using a method.

Further, in the above-described embodiment, in the case of performing continuous printing, the first sheet is exemplified as the predetermined number of sheets for switching from the second heating control to the first heating control when fixing is completed. It may be a sheet after the eyes.

Further, in the above-described embodiment, the timing for determining whether or not the second detected temperature Ts is lower than or equal to the first temperature Tth1 is the timing at which the first sheet detection unit 11 detects the sheet S as shown in FIG. It was (time t3), but the invention is not limited to this. For example, it may be the timing (time t2) when the conveyance of the sheet S is started, or the timing (time t1) when the rotational driving of the fixing device 8 is started. Further, it may be any timing between times t2 and t3, or any timing between times t1 and t2. Further, the timing may be between the times t0 and t1 and after a predetermined time has elapsed after the first heating control is started (after the second detected temperature rises to some extent).

Further, in the above-described embodiment, the third temperature Tth3 for starting the conveyance of the sheet S is higher than the second temperature Tth2 for starting the rotational driving of the fixing device 8, but the third temperature Tth3 is the second temperature. The temperature may be the same as Tth2 or may be lower than the second temperature Tth2. That is, the laser printer 1 may start the rotational driving of the fixing device 8 at the same time when the transportation of the sheet S is started, or may start the rotational driving of the fixing device 8 after the transportation of the sheet S is started. Good.

Further, in the above embodiment, in the rotation control, the fixing device 8 is rotationally driven by driving the motor M. However, in the rotation control, for example, the driving force from the motor is transmitted to the fixing device 8 by the clutch mechanism. The fixing device 8 may be driven to rotate.

Moreover, in the said embodiment, although the 1st temperature detection part 9C and the 2nd temperature detection part 9S were provided so that the temperature of the heating part 81 might be detected, a 1st temperature detection part and a 2nd temperature detection part are provided. For example, it may be provided so as to detect the temperature of the pressurizing unit or the heater. Further, contrary to the above embodiment, the first temperature detection unit may be a contact type thermistor and the second temperature detection unit may be a non-contact type thermistor. Further, the first temperature detecting unit and the second temperature detecting unit may be temperature sensors other than the thermistor.

Further, although the heating roller is exemplified as the heating unit 81 in the above-described embodiment, the heating unit may be, for example, a heating unit having an endless heating belt. Further, in the above-described embodiment, the pressure roller is illustrated as the pressure unit 82, but the pressure unit may be, for example, a pressure unit including an endless pressure belt.

Further, in the above-described embodiment, the halogen heater that uses radiant heat is illustrated as the heater 83, but the heater may be, for example, a ceramic heater or a carbon heater that uses heat generated by a resistor. Further, the heater may be arranged outside the heating unit instead of inside the heating unit.

Further, in the above-described embodiment, the laser printer 1 that forms a monochrome image on the sheet S is exemplified as the image forming apparatus, but the image forming apparatus is, for example, a printer configured to form a color image on the sheet. It may be. Further, the image forming apparatus is not limited to the printer, and may be, for example, a copying machine or a multi-function machine including a document reading device such as a flatbed scanner.

Further, in the above-described embodiment, the process cartridge is illustrated as the developer image forming unit 5, but the developer image forming unit 5 is not limited to this. For example, an image forming apparatus is capable of forming a color image on a sheet and has a process unit having a plurality of photoconductors arranged, and a transfer unit for transferring the developer image formed on the photoconductors to the sheet. In the case of including a transfer unit having a belt or the like, the developer image forming unit can be configured to include a process unit and a transfer unit.

In addition, the respective elements described in the above-described embodiment and modification can be implemented in an appropriate combination.

1 Laser Printer 5 Developer Image Forming Section 8 Fixing Device 9C First Temperature Detection Section 9S Second Temperature Detection Section 33 Transport Section 81 Heating Section 82 Pressurizing Section 83 Heater 100 Control Section CA Sheet Contact Area S Sheet

Claims (11)

A developer image forming portion for forming a developer image on the sheet;
A transport unit that transports the sheet toward the developer image forming unit;
A heating unit that heats in contact with the sheet, a heater that heats the heating unit, and a pressure unit that sandwiches the sheet between the heating unit and the fixing unit that fixes the developer image on the sheet,
A first temperature detecting unit for detecting a first detected temperature which is a temperature of a central portion of the heating unit in the width direction of the sheet;
A second temperature detecting section for detecting a second detected temperature which is a temperature of an end portion of the heating section in the width direction of the sheet;
And a control unit,
The control unit is
First heating control for energizing the heater so that the temperature of the heating unit becomes the fixing temperature for fixing the developer image on the sheet based on the first detected temperature;
A second heating control for energizing the heater so that the temperature of the heating unit becomes the fixing temperature based on the first detected temperature, wherein a lower limit value of the energization amount per unit time to the heater is And a second heating control that is larger than the first heating control,
At a predetermined timing after the first heating control is started and before the sheet reaches the fixing device, it is determined whether or not the second detected temperature is equal to or lower than a first temperature lower than the fixing temperature, When the second detected temperature is higher than the first temperature, the first heating control is continued, and when the second detected temperature is equal to or lower than the first temperature, the sheet reaches the fixing device. An image forming apparatus, characterized in that the first heating control is switched to the second heating control before. When the first detected temperature is lower than the second temperature lower than the fixing temperature, the controller does not rotate the fixing device, and when the first detected temperature is equal to or higher than the second temperature. It is possible to execute rotation control for rotating the fixing device,
The image forming apparatus according to claim 1, wherein the predetermined timing is a timing before the sheet reaches the fixing device after the rotational driving of the fixing device is started. The control unit is capable of performing a transport control for transporting a sheet toward the developer image forming unit when the first detected temperature is equal to or higher than a third temperature lower than the fixing temperature,
The image forming apparatus according to claim 1, wherein the predetermined timing is a timing before the sheet reaches the fixing device after the sheet is started to be conveyed. The control unit, when executing the second heating control, continues the second heating control while the sheet is between the heating unit and the pressing unit. The image forming apparatus according to claim 3. In the case where images are continuously formed on a plurality of sheets, the control unit switches from the second heating control, and after fixing a predetermined number of sheets, completes the second heating control. The image forming apparatus according to claim 1, wherein the image forming apparatus is switched to the first heating control. The control unit is
In the first heating control and the second heating control, the temperature of the heating unit is controlled with a duty ratio according to a difference obtained by subtracting the first detected temperature from the fixing temperature, and the duty ratio is large. So big,
In the first heating control, the lower limit of the duty ratio is 0%,
The image forming apparatus according to claim 1, wherein a lower limit value of the duty ratio is set to be larger than 0% in the second heating control. The control unit is
In the first heating control, when the first detected temperature is higher than the fixing temperature, the duty ratio is set to 0%,
The image forming apparatus according to claim 6, wherein, in the second heating control, the duty ratio is set to be larger than 0% when the first detected temperature is higher than the fixing temperature. The image forming apparatus according to claim 1, wherein the heater heats an entire region of the heating unit that is in contact with the sheet in the width direction of the sheet. The image forming apparatus according to claim 1, wherein the second temperature detection unit is arranged outside a region of the heating unit in contact with the sheet in the width direction of the sheet. apparatus. The image according to any one of claims 1 to 9, wherein the control unit executes the second heating control on condition that there is an image at an end portion in the width direction of the sheet. Forming equipment. The control unit, in the second heating control, increases the lower limit value of the energization amount to the heater per unit time as the second detected temperature is lower. The image forming apparatus according to any one of items.

Images