JP2021117403A - Fixing device and image forming device - Google Patents

Abstract

[Problem] To make it possible to appropriately control a sub-heater arranged outside a fixing unit. [Solution] A fixing device includes a fixing belt 131 having an outer circumferential surface facing a medium to which a developer image has been transferred, and a planar heater 134 provided inside the fixing belt 131. The planar heater 134 includes a main heater 134a for heating a first region that is a part of the fixing belt 131 in the main scanning direction, and sub-heaters 134b and 134c for heating a second region that is a part of the fixing belt 131 other than the first region in the main scanning direction, and when images are continuously formed on the medium, the heat generation amount of the sub-heaters 134b and 134c relative to the heat generation amount of the main heater 134a changes depending on the number of completed image formations on the medium. [Selected Figure] Figure 4

Description

The present invention relates to a fixing device and an image forming device.

The electrophotographic image forming apparatus fixes the toner image transferred to the paper as a medium by heating and pressurizing the toner image with a fixing device.
Here, conventionally, a technique has been known in which a plurality of heaters are provided in a fuser and a heater for heating is selected from among the plurality of heaters according to the width of the paper to be fixed to save power. ing.
In such a case, for example, as described in Patent Document 1, a technique of providing a temperature sensor at the center in the paper transport direction and controlling the temperature of the fuser by the temperature measured by the temperature sensor. There is.

JP-A-2019-113785

However, with the conventional technique, it has been difficult to appropriately control the sub-heater arranged in the fuser.

Therefore, one or a plurality of aspects of the present invention make it possible to appropriately control the sub-heater arranged in the fuser.

The fixing device according to one aspect of the present invention includes a rotating body having an outer peripheral surface facing the medium on which the developer image is transferred, and a heat generating portion provided inside the rotating body. A main heater that heats a first region that is a part of the rotating body in the main scanning direction and a second region that is a part of the rotating body other than the first region in the main scanning direction are heated. When an image is continuously formed on the medium, the amount of heat generated by the sub-heater relative to the amount of heat generated by the main heater depends on the number of times the formation of the image on the medium is completed. It is characterized by changing.

Further, the image forming apparatus according to one aspect of the present invention is characterized by including the fixing apparatus.

According to one or more aspects of the present invention, the sub-heater arranged in the fuser can be appropriately controlled.

It is sectional drawing of the image forming apparatus. It is a block diagram which shows the structure of the print control part. (A) and (B) are block diagrams showing a hardware configuration example. It is a front view which shows the structure of the fuser schematicly. It is a side view which shows the structure of the fuser schematicly. It is a block diagram which shows the structure of the fixing temperature control part. It is the schematic of the heater ON pattern table which shows the ON pattern of a planar heater. (A) and (B) are tables and graphs showing correction values when the medium has a standard size. It is a flowchart which shows an example which controls so that the temperature detected by the 2nd thermistor and the 3rd thermistor does not fall below 100 degreeC. It is a time chart which shows the temperature detected when the B5 vertical size medium is continuously printed, and the operation example of the 1st subheater and the 2nd subheater. It is the schematic which shows the 1st distribution of the temperature of the fixing belt in the longitudinal direction when printing is performed on the B5 vertical size medium. It is a graph for demonstrating the correction value. It is a time chart of the correction value and the final DUTY ratio correction value when 100 pages of B5 vertical size medium are printed continuously. It is the schematic which shows the 2nd distribution of the temperature of the fixing belt in the longitudinal direction at the time of printing on the B5 vertical size medium.

FIG. 1 is a cross-sectional view of the image forming apparatus 100 according to the present embodiment.
The image forming apparatus 100 includes a paper feed cassette 101, a hopping roller 102, resist rollers 103 and 104, a conveying belt 105, a driving roller 106, a driven roller 107, and an ID (Image Drum) unit as an image forming unit. It includes 120K, 120Y, 120M, 120C, transfer rollers 108K, 108Y, 108M, 108C, a fixing device 130 as a fixing device, and discharge rollers 109, 110.
In the following description, it is assumed that the symbol K added to the end of the symbol indicates black, the symbol Y indicates yellow, the symbol M indicates magenta, and the symbol C indicates cyan. The symbols K, Y, M and C shall be omitted as appropriate.

The paper cassette 101 holds the medium PA.
The hopping roller 102 feeds out the medium PA held in the paper feed cassette 101.
The resist rollers 103 and 104 correct the skew of the delivered medium PA and send the medium PA to the transport belt 105 at a predetermined timing.
The transport belt 105 transports the medium PA. Specifically, the transport belt 105 is hung on the drive roller 106 and the driven roller 107, and transports the sent medium PA to the ID unit 120 and the fuser 130.
The drive roller 106 is a roller that drives the transport belt 105.
The driven roller 107 is a roller that rotates according to the drive of the drive roller 106.

Each of the ID units 120K, 120Y, 120M, and 120C forms a toner image as a developer image.
Since each of the ID units 120K, 120Y, 120M, and 120C has the same configuration, the ID unit 120K will be described here.

The ID unit 120K includes a photoconductor drum 121K as an image carrier and an LED (Light Emitting Diode) head 122K as an exposure apparatus.
An electrostatic latent image is formed on the charged photoconductor drum 121K by the LED head 122K, and a toner as a developer is adhered to the formed electrostatic latent image to form a toner image as a developer image. Is formed.

Each of the transfer rollers 108K, 108Y, 108M, and 108C is a transfer unit that transfers the toner image formed by each of the photoconductor drums 121K, 121Y, 121M, and 121C to the medium PA conveyed by the transfer belt 105. .. Then, the transfer rollers 108K, 108Y, 108M, 108C convey the medium PA on which the toner image is transferred to the fuser 130.

The fuser 130 heats and melts the toner image and pressurizes the toner image to fix it on the medium PA.
The discharge rollers 109 and 110 discharge the medium PA on which the toner image is fixed to the outside of the image forming apparatus 100.

FIG. 2 is a block diagram showing a print control unit 111 as an image formation control unit that controls image formation (printing) in the image forming apparatus 100.
The print control unit 111 is connected to the fixing control unit 112. Then, the print control unit 111 commands the fixing control unit 112 to set the target temperature according to the print conditions as the image formation conditions such as the thickness or width of the medium PA. Then, when the fixing control unit 112 determines that the warm-up of the fixing device 130 is completed, the printing control unit 111 causes the fixing device 130 to perform fixing.

Further, the print control unit 111 is connected to the paper feed motor 113. The paper feed motor 113 is a stepping motor for feeding and transporting the print medium.
The print control unit 111 is connected to the belt motor 114. The belt motor 114 is a stepping motor for driving the transport belt 105.
The print control unit 111 is connected to the ID motor 115. The ID motor 115 is a brushless DC (Direct Current) motor for driving the ID unit 120.
The print control unit 111 is connected to the fixing motor 116. The fixing motor 116 is a brushless DC motor for driving the fixing device 130, the discharge rollers 109, and 110.

The print control unit 111 is connected to the LED heads 122K, 122Y, 122M, and 122C. Each of the LED heads 122K, 122Y, 122M, 122C exposes the surface of each of the charged photoconductor drums 121K, 121Y, 121M, 121C.
The print control unit 111 is connected to the high voltage circuit 117. The high-voltage circuit 117 is a circuit that generates a high voltage for charging, developing, and transferring in the ID unit 120 and the transfer roller 108.

A part or all of the print control unit 111 and the fixing control unit 112 described above execute the memory 10 and the program stored in the memory 10 as shown in FIG. 3A, for example. It can be configured by a processor 11 such as a CPU (Central Processing Unit). Such a program may be provided through a network, or may be recorded and provided on a recording medium. That is, such a program may be provided as, for example, a program product.

Further, a part or all of the print control unit 111 and the fixing control unit 112 may be, for example, a single circuit, a composite circuit, a programmed processor, or a parallel programmed processor, as shown in FIG. 3 (B). , ASIC (Application Specific Integrated Circuits) or FPGA (Field Programmable Gate Array) or the like.
As described above, the print control unit 111 and the fixing control unit 112 can be realized by the processing network.

FIG. 4 is a front view schematically showing the configuration of the fuser 130.
FIG. 5 is a side view schematically showing the configuration of the fuser 130.
In the fuser 130, the fixing belt 131 and the backup roller 132 are arranged to face each other so as to sandwich the medium PA conveyed from the conveying belt 105, and the nip portion as a fixing portion for fixing the toner image on the medium PA. To form. In FIG. 4, the medium PA is assumed to be transported from the front to the back of FIG. The direction A, which is the direction intersecting the transport direction of the medium PA (here, the vertical direction), is the main scanning direction. Then, the toner image transferred to the medium PA and adhered only by a weak electrostatic force is melted by the heat of the fixing belt 131 and fixed to the medium PA by the pressing force of the backup roller 132. The backup roller 132 functions as a pressurizing unit that pressurizes the medium PA in the direction of the fixing belt 131.

The fixing belt 131 is a cylindrical film, and has an elastic layer made of silicone rubber, a metal such as PI (PolyImide) or SUS (Steel Use Stainless: stainless steel) as a base material, and a PTFE (PolyTetraFluoroEthilen), PFA. It has a multi-layered structure in which a fluororesin coating typified by (PerFluorokoxy Alkane) or a surface layer made of a tube formed by processing them is superposed. The fixing belt 131 is a heating target of the planar heater 134 described later, and is used to melt the toner image. The fixing belt 131 functions as a rotating body that rotates in the transport direction of the medium PA as the backup roller 132 rotates. The outer peripheral surface 131a of the fixing belt 131 faces the medium PA. The rotating body is not limited to the fixing belt 131, and may be, for example, a roller-shaped fixing roller. In other words, in this embodiment, a fixing roller may be used instead of the fixing belt 131.

A heat diffusion member 133 and a planar heater 134 are provided inside the fixing belt 131. The heat diffusion member 133 and the planar heater 134 are urged in the direction of the backup roller 132 by an urging member such as a spring (not shown). Sliding grease (not shown) is applied to the surface of the heat diffusing member 133 to improve the slidability with the fixing belt 131.

The heat diffusion member 133 is a member that conducts the heat of the planar heater 134 to the fixing belt 131, and is made of, for example, a metal having high thermal conductivity such as stainless steel. As shown in FIG. 5, one surface 133a of the heat diffusion member 133 is in contact with the planar heater 134, the other surface 133b is in contact with the fixing belt 131, and a part thereof is in contact with the fixing belt 131. The heat generated by the planar heater 134 is conducted to the fixing belt 131 while reducing unevenness in the longitudinal direction. For the sake of simplicity, the description of the heat diffusion member 133 will be omitted below.

The planar heater 134 is a planar heating unit extending in a direction perpendicular to the circumferential direction of the fixing belt 131, in other words, in a direction parallel to the axis of the planar heater 134. For example, the planar heater 134 is configured by laminating an electrical insulating layer, a resistance heating element, and a protective layer in this order on a SUS substrate, and connecting electrodes to the resistance heating element. By supplying electric power to the planar heater 134, the planar heater 134 can be heated.

The planar heater 134 is divided into five in the direction in which the planar heater 134 extends. Specifically, the planar heater 134 includes a main heater 134a, which is a first heating element located at the center, and a first subheater 134b, which is a second heating element arranged at both ends of the main heater 134a. And a second subheater 134c, which is a third heating element arranged at both ends of the first subheater 134b.

The first sub-heater 134b is divided into both ends of the main heater 134a, but is electrically connected and is heated at the same time by energizing. Similarly, the second sub-heater 134c is heated at the same time by energizing.

The main heater 134a heats the first region of the fixing belt 131. Further, the first sub-heater 134b and the second sub-heater 134c function as sub-heaters for heating a second region that is a part of the fixing belt 131 other than the first region in the main scanning direction A. Here, the main heater 134a heats the central region, which is the central region of the fixing belt 131. Further, the first sub-heater 134b and the second sub-heater 134c function as sub-heaters for heating the outer region, which is the outer region of the central region heated by the main heater 134a, in the main scanning direction A of the medium PA. The main heater 134a heats one end side of the fixing belt 131 in the main scanning direction A, and the first subheater 134b and the second subheater 134c heat the other end side of the fixing belt 131 in the main scanning direction A. It may be.

As will be described later, the calorific value of the sub-heater with respect to the calorific value of the main heater 134a changes according to the number of printed pages, which is the number of completed formation of the image on the medium PA. For example, the calorific value of the sub-heater relative to the calorific value of the main heater 134a decreases as the number of printed pages increases. Here, the reduction in the calorific value of the sub-heater with respect to the calorific value of the main heater 134a may be performed when the width of the medium PA in the main scanning direction A is within a predetermined range.
In the following, the width of the medium PA in the main scanning direction A may be simply referred to as a width.

The main heater 134a has a length of a portion that generates heat of 138 mm, and corresponds to a medium PA having a width of B6 vertical size (128 mm).
The first sub-heater 134b, together with the main heater 134a, has a length of a portion that generates heat of 230 mm, and corresponds to a medium PA having a width of Letter vertical size (215.9 mm).
The second sub-heater 134c, together with the main heater 134a and the first sub-heater 134b, has a length of a portion that generates heat of 306 mm and corresponds to a medium PA having a width of A4 width (297 mm).

By adjusting the energization of the first sub-heater 134b and the second sub-heater 134c according to the size of the medium PA and the direction in which the medium PA is conveyed by the transfer belt 105, the fixing belt 131 in the region where the medium PA does not pass is adjusted. It is possible to suppress the temperature rise of.

As shown in FIG. 4, the fuser 130 detects the temperatures of the first thermistor 135a, which is the main heater temperature detection unit for detecting the temperature of the main heater 134a, and the temperature of the first subheater 134b. A second thermistor 135b, which is a first sub-heater temperature detection unit for the purpose, and a third thermistor 135c, which is a second sub-heater temperature detection unit for detecting the temperature of the second sub-heater 134c, are provided. ..

Further, outside the fixing belt 131, an infrared temperature sensor 136, which is a surface temperature detecting unit for detecting the surface temperature of the fixing belt 131, is provided. The infrared temperature sensor 136 functions as a main temperature detection unit that detects the temperature in the central region heated by the main heater 134a.
As shown in FIG. 5, the infrared temperature sensor 136 is installed so as to face the side surface of the fixing belt 131 on the entrance side in the direction D in which the medium PA is conveyed, and the infrared rays emitted from the surface of the fixing belt 131. It is a non-contact temperature sensor that receives infrared rays and converts them into temperature. The infrared temperature sensor 136 is arranged in the central portion heated by the main heater 134a in the direction perpendicular to the circumferential direction of the fixing belt 131, and is preferably arranged at the same position as the first thermistor 135a.

Further, the fuser 130 is provided with BU thermistors 137a, 137b, and 137c, which are backup temperature sensors, in order to detect the temperature of the surface of the backup roller 132. The BU thermistors 137a, 137b and 137c indirectly detect the temperature of the surface of the fixing belt 131. This is good, especially when the narrow medium PA is continuously printed, it is possible to monitor the temperature rise of the portion where the medium PA does not pass on the surface of the fixing belt 131.

The second thermistor 135b and the third thermistor 135c can also be used to monitor the temperature rise of the portion through which the medium PA does not pass. However, when the second thermistor 135b or the third thermistor 135c is used, the surface temperature of the same fixing belt 131 can be various depending on the thickness of the passing medium PA and the like. Therefore, the first thermistor 135a It is desirable to monitor the temperature difference between the second thermistor 135b and the third thermistor 135c. For example, if the temperature difference between the temperature detected by the second thermistor 135b or the third thermistor 135c and the temperature detected by the first thermistor 135a is large, the temperature of the region where the medium PA does not pass through the fixing belt 131 will be the temperature in the region where the medium PA does not pass. It can be judged that the temperature is high.

The fixing belt 131, the heat diffusion member 133, and the planar heater 134 described above constitute a heating unit 138 for heating the medium PA.

FIG. 6 is a block diagram showing a configuration of a fixing temperature control unit 140 that controls the fixing temperature in the fixing device 130.
The fixing temperature control unit 140 includes a fixing control unit 112, a first triac 141a, a second triac 141b, a third triac 141c, and a triac drive circuit 142.
A commercial power supply 119, which is a power source for applying a voltage to the planar heater 134, is connected to an electrode on one side of the planar heater 134.
Further, the commercial power supply 119 is connected to the first triac 141a, the second triac 141b, and the third triac 141c.

The fixing control unit 112 calculates the calorific value of the first sub-heater 134b and the second sub-heater 134c from the calorific value of the main heater 134a, and uses the main heater 134a and the first sub-heater 134b and the second sub-heater 134c. Control.
For example, in the case of continuous printing, when the fixing control unit 112 calculates the calorific value of the first subheater 134b and the second subheater 134c, the first subheater 134b and the first subheater 134b and the second subheater 134b are calculated according to the number of printed pages. The calorific value of the sub-heater 134c of 2 is changed.

Here, the fixing control unit 112 controls the amount of heat generated from the commercial power supply 119 by the duty ratio of the voltage applied to the main heater 134a and the first subheater 134b and the second subheater 134c.
For example, the fixing control unit 112 sets the duty ratio of the voltage applied from the commercial power supply 119 to the main heater 134a, the first coefficient (correction value α described later) determined according to the width of the medium PA, and the number of printed pages. By multiplying the second coefficient (correction value β described later) that changes accordingly, the duty ratio of the voltage applied from the commercial power supply 119 to the first subheater 134b and the second subheater 134c is calculated.

The fixing control unit 112 controls the amount of heat generated by the main heater 134a based on the temperature detected by the infrared temperature sensor 136.
Hereinafter, the control by the fixing control unit 112 will be specifically described.

The fixing control unit 112 receives signals from the first thermistor 135a, the second thermistor 135b, the third thermistor 135c, the infrared temperature sensor 136 and the BU thermistor 137a, 137b, and 137c, and the temperature detected by these. To get.

The fixing control unit 112 performs PID (Proportional Integral Differential) control based on the difference between the temperature detected by the infrared temperature sensor 136 and the target temperature determined by the printing conditions (image forming conditions), and heats the triac drive circuit 142. The ON signal SG1 is output. As a result, the portion of the fixing belt 131 near the main heater 134a is heated so as to reach the target temperature.
Further, the fixing control unit 112 performs PID control based on the heater ON signal to the main heater 134a, and outputs the heater ON signal SG2 to the triac drive circuit 142. As a result, the portion of the fixing belt 131 near the first sub-heater 134b is heated.
Further, the fixing control unit 112 performs PID control based on the heater ON signal to the main heater 134a, and outputs the heater ON signal SG3 to the triac drive circuit 142. As a result, the portion of the fixing belt 131 near the second sub-heater 134c is heated.

The first triac 141a is a semiconductor switch that is connected to the main heater 134a and functions as a first switching unit that switches between supplying and disconnecting power from the commercial power supply 119 to the main heater 134a.
The second triac 141b is a semiconductor switch that is connected to the first subheater 134b and functions as a second switching unit that switches between supplying and disconnecting power from the commercial power supply 119 to the first subheater 134b.
The third triac 141c is a semiconductor switch that is connected to the second subheater 134c and functions as a third switching unit that switches between supplying and disconnecting power from the commercial power supply 119 to the second subheater 134c.
The gate terminals of the first triac 141a, the second triac 141b, and the third triac 141c are connected to the triac drive circuit 142.

The triac drive circuit 142 controls the drive of the first triac 141a, the second triac 141b, and the third triac 141c. For example, the triac drive circuit 142 is configured to use a photo triac to insulate the primary side from the secondary side. As a result, the triac drive circuit 142 conducts the first triac 141a, the second triac 141b, or the third triac 141c according to the pulse widths (DUTY ratio) of the input heater ON signals SG1, SG2, and SG3. The power supply to the planar heater 134 is adjusted by changing the operation time.

In the fixing control unit 112, when the temperature difference between the temperature detected by the second thermistor 135b or the third thermistor 135c and the temperature detected by the first thermistor 135a is larger than a predetermined threshold value. In the fixing belt 131, it may be determined that the non-passing region temperature, which is the temperature of the region through which the medium PA does not pass, is high, and the heating of the second thermistor 135b and the third thermistor 135c may be stopped. ..

Further, the fixing control unit 112 stops heating by the planar heater 134 when the temperature detected by at least one of the thermistas 135a, 135b and 135c reaches a predetermined upper limit temperature. This makes it possible to prevent the planar heater 134 from becoming abnormally high in temperature. Here, the upper limit temperature may be predetermined so as to be able to detect an abnormality in the planar heater 134.

Next, the fixing control by the fixing temperature control unit 140 will be described.
Here, first, normal fixing control will be described.
FIG. 7 is a schematic view of a heater ON pattern table 143 showing an ON pattern of the planar heater 134.
It is assumed that the heater ON pattern table 143 is stored in advance in the memory 112a of the fixing control unit 112.

The heater ON pattern table 143 includes a No row 143a, a PID calculation result row 143b, and an ONOFF pattern row 143c.
Column No. 143a is an identification number which is identification information for identifying an ONOFF pattern which is a pattern for turning the heater ON or OFF.
The PID calculation result column 143b shows the range of the duty ratio calculated by the fixing control unit 112. Here, an ONOFF pattern is defined for each range of 10%.
The ONOFF pattern sequence 143c shows an ONOFF pattern which is an ON / OFF pattern every 100 ms which is a predetermined cycle. Here, a pattern for turning on or off the first triac 141a connected to the main heater 134a is defined every 10 ms.

Then, during the printing operation (during the image forming operation), the fixing control unit 112 performs PID calculation based on the difference between the detected temperature detected by the infrared temperature sensor 136 and the target temperature determined by the printing conditions in the temperature control cycle. It is performed every 100 ms to obtain the DUTY ratio of the heater ON signal.

The calculation formula of the first duty ratio, which is the duty ratio for the main heater 134a in the nth cycle (n is an integer of 1 or more), is shown by the following formula (1).
First DUTY ratio _{(n) = K p × ε} + K i × Σε + K d × dε / dt
+ 1st DutyMod (n-1) (1)
Here, ε is a temperature deviation and is calculated by subtracting the detection temperature of the infrared temperature sensor 136 from the target temperature. K _p is a proportional gain, _Ki is an integral gain, and K _d is a differential gain, which are predetermined.
The first duty mod (n-1) is the remainder in the first duty ratio (n-1) calculated in the n-1th cycle. In other words, the first duty mod (n-1) is the remainder of the first duty ratio that was not consumed in the previous control cycle. The first DutyMod (n-1) may not be used.

As shown in the equation (1), the first duty ratio is a function with respect to the deviation ε between the target temperature and the current temperature detected by the infrared temperature sensor 136.
As shown in FIG. 7, the duty ratio is a value in increments of 10%, the range of the value is 0 to 100%, and the remainder is carried over to the next control cycle.
For example, if the duty ratio of the previous control cycle is 98%, 90% is consumed and 8% is used as a remainder for PID calculation in the next cycle.

The fixing control unit 112 sends the heater ON signals SG1 and SG2 to the triac drive circuit 142 according to the ONOFF pattern shown in the heater ON pattern table 143 shown in FIG. 7, according to the calculation result of the first duty ratio. , SG3 is output.

For example, when the first duty ratio is 100% in the PID calculation result, the fixing control unit 112 outputs the heater ON signal SG1 at a high level continuously for 100 ms.
When the first duty ratio is 25%, the fixing control unit 112 sets the heater ON signal SG1 to High for 0 ms to 10 ms, sets the heater ON signal SG1 to Low for 10 ms to 40 ms, and sets the heater ON signal SG1 to Low for 40 ms to 50 ms. , The heater ON signal SG1 is set to High, and the heater ON signal SG1 is set to Low during 50 ms to 90 ms.

The fixing control unit 112 corrects and outputs the DUTY ratios of the heater ON signals SG2 and SG3 to the first subheater 134b and the second subheater 134c according to the width of the medium PA during the printing operation. "I do.

The formula for calculating the second duty ratio, which is the duty ratio of the first subheater 134b in the nth cycle, is the following formula (2).
Second DUTY ratio (n) = {first DUTY ratio (n) -first DutyMod (n-1)} x α1 + second DutyMod (n-1) (2)
In the equation (2), the correction value α1 is used, and the second duty ratio is obtained every 100 ms of the control cycle. The second DutyMod (n-1) may not be used.

The calculation formula for the third duty ratio, which is the duty ratio of the second subheater 134c in the nth cycle, is the following formula (3).
Third DUTY ratio (n) = {(first DUTY ratio (n) -first DutyMod (n-1))} × α2 + third DutyMod (n-1) (3)
In the equation (2), the correction value α2 is used, and the third duty ratio is obtained every 100 ms of the control cycle. The third DutyMod (n-1) may not be used.

The correction value α1 is calculated by a cubic function with respect to the width L [mm] of the medium PA as shown in the following equation (4).
α1 = a1 × L ³ + b1 × L ² + c1 × L + d1 (4)
Here, it is assumed that the coefficient a1, the coefficient b1, the coefficient c1 and the coefficient d1 are predetermined.

Further, the correction value α2 is calculated by a cubic function with respect to the width L of the medium PA as shown in the following equation (5).
α2 = a2 × L ³ + b2 × L ² + c2 × L + d2 (5)
Here, it is assumed that the coefficient a2, the coefficient b2, the coefficient c2 and the coefficient d2 are predetermined.

8 (A) and 8 (B) are tables and graphs showing a correction value α1 and a correction value α2 when the medium PA has a standard size. For example, in the case of A4 width, α1 = 100% and α2 = 95% are controlled.
In the following, when it is not necessary to distinguish between the correction value α1 and the correction value α2, each of the correction value α1 and the correction value α2 is referred to as a correction value α. The correction value α is the above-mentioned first coefficient.

The width L of the medium PA may be set by the user, or a sensor for detecting the width of the medium PA may be provided on the transport path of the medium PA of the image forming apparatus 100 and measured by the sensor. The sensor for detecting the width of the medium PA may be, for example, a line sensor provided in the medium transport path, or a sensor for detecting the medium guide width of the paper cassette 101.

The purpose of performing the duty ratio correction control is to simplify the control. The main heater 134a, the first subheater 134b, and the second subheater 134c are provided with the first thermistor 135a, the second thermistor 135b, and the third thermistor 135c, respectively. Each of the main heater 134a, the first subheater 134b and the second subheater 134c can be controlled independently.
However, in the actual use of the image forming apparatus 100, the appropriate temperature to be detected by the first thermistor 135a, the second thermistor 135b, and the third thermistor 135c changes depending on the size or thickness of the medium PA.

For example, the fixing control unit 112 sets the main heater 134a, so that the temperature detected by the first thermistor 135a and the temperature detected by the second thermistor 135b or the third thermistor 135c become substantially the same temperature. Even if the first sub-heater 134b and the second sub-heater 134c are controlled, fixing failure may occur due to insufficient temperature at the end of the surface of the fixing belt 131. Further, under another condition, on the contrary, the end temperature may rise too much and a hot offset may occur.
As described above, it is not realistic to find the optimum independent control method (for example, target temperature) under all conditions in each of the main heater 134a, the first subheater 134b, and the second subheater 134c.

Since the planar heater 134 is divided in the longitudinal direction thereof, from the viewpoint of fixing the toner, for example, when printing a B5 vertical size (width L = 182 mm), the duty ratio of the second subheater 134c is 0%. It doesn't matter.
However, in general, when the surface temperature of the fixing belt 131 is low, the driving torque of the fixing device 130 increases due to the increase in the viscosity of the sliding grease (not shown) adhering to the inner surface of the fixing belt 131. Problems such as abnormal noise, motor lock error due to the fixing motor 116 losing the load and unable to maintain the predetermined rotation speed, and damage to the drive gear of the fixing device 130 occur. There is a risk of

In order to prevent the above-mentioned problems, when it is determined that the first subheater 134b and the second subheater 134c are not necessary for fixing the toner, in other words, the duty ratio correction control brings the duty ratio to nearly 0%. Even when calculated, the temperature detected by the second thermistor 135b and the third thermistor 135c is controlled so as not to fall below 100 ° C.

FIG. 9 is a flowchart showing an example of controlling the temperature detected by the second thermistor 135b and the third thermistor 135c so as not to fall below 100 ° C.
The fixing control unit 112 determines whether or not the control of the planar heater 134 is completed (S10). For example, the fixing control unit 112 determines that the control of the planar heater 134 is completed when the printing (image forming) by all the printing jobs (image forming jobs) of the image forming apparatus 100 is completed. If the control of the planar heater 134 is not completed (Yes in S10), the process proceeds to step S11.

In step S11, the fixing control unit 112 determines whether or not the temperature detected by the second thermistor 135b or the third thermistor 135c is less than 100 ° C. If the temperature detected by the second thermistor 135b or the third thermistor 135c is less than 100 ° C. (Yes in S11), the process proceeds to step S12 of the second thermistor 135b and the third thermistor 135c. When the temperature detected in both is 100 ° C. or higher (No in S11), the process proceeds to step S13.

In step S12, the fixing control unit 112 controls at least one of the first subheater 134b and the second subheater 134c in which a temperature of less than 100 ° C. is detected to be turned on. For example, the fixing control unit 112 drives the sub-heater at a duty ratio = 20% (fixed value) for one control cycle = 100 ms.

On the other hand, in step S13, the fixing control unit 112 performs the duty ratio correction control described above.

FIG. 10 is a time chart showing the temperature detected when the medium PA of the B5 vertical size (width 182 mm) is continuously printed and the operation example of the first subheater 134b and the second subheater 134c.
Here, TE1 in FIG. 10 is the temperature detected by the first thermistor 135a, TE2 is the temperature detected by the second thermistor 135b, and TE3 is detected by the third thermistor 135c. It is the temperature, and TE4 is the temperature detected by the infrared temperature sensor 136.

First, the fixing control unit 112 starts warming up at time T01. In the warm-up state, the fixing control unit 112 can shorten the warm-up time by setting the correction values α1 and α2 of both the first subheater 134b and the second subheater 134c to 100%.

When the warm-up is completed at the time T02, the fixing control unit 112 is subjected to the first correction value α1 = 94% and the correction value α2 = 0% calculated by using the above equations (3) and (4). Controls the sub-heater 134b and the second sub-heater 134c.

Then, at time T03, when the temperature TE3 detected by the third thermistor 135c becomes less than 100 ° C., the fixing control unit 112 sets the second subheater 134c to the second subheater 134c for one control cycle = 100 ms and the duty ratio = 20% (). It is driven by a fixed value). When the temperature TE3 becomes 100 ° C. or higher, the fixing control unit 112 returns the correction value α2 = 0%.

As a result of the above, as shown in FIG. 10, the temperature TE3 changes at around 100 ° C. The same effect can be obtained even if the fixing control unit 112 controls the correction value α2 of the second subheater 134c as a target of 100 ° C. by PID control instead of setting the correction value α2 to a fixed value (here, 20%).

By performing the above control, the medium PA having a width corresponding to the width of any one of the main heater 134a, the first subheater 134b, and the second subheater 134c, for example, the B6 vertical corresponding to the width of the main heater 134a. Size (128 mm), Letter vertical size (216 mm) corresponding to the combined width of the first sub-heater 134b and main heater 134a, corresponding to the combined width of the main heater 134a, the first sub-heater 134b and the second sub-heater 134c Even for a medium PA other than the A4 horizontal size (297 mm), control can be performed at an appropriate temperature within the region through which the medium PA passes.

However, in the method using only the correction values α1 and α2 described above, the temperature of the non-passing region through which the medium PA does not pass in the heating region of the first subheater 134b or the second subheater 134c rises significantly. In some cases.

FIG. 11 is a schematic view showing the temperature distribution of the fixing belt 131 in the longitudinal direction when printing is performed on the medium PA having a B5 vertical size (width 182 mm).
When printing in B5 vertical size, the correction value α1 = 94% and the correction value α2 = 0% according to the above equations (3) and (4).

When the print job is received and the warm-up is started, the fixing control unit 112 first heats the correction values α1 and α2 to 100%, and then the correction value for printing determined by the above equations (3) and (4). Switch to α1 and α2. After the switching, the print control unit 111 starts conveying the medium PA.

The broken line L1 in FIG. 11 shows the temperature distribution of the fixing belt 131 when printing of about 5 pages is performed after switching to the correction values α1 and α2 for printing.
As shown by the broken line in FIG. 11, in the region RE1 where the main heater 134a is heated, the temperature of the fixing belt 131 is targeted based on the temperature detected by the infrared temperature sensor 136 which detects the temperature of the central portion thereof. The temperature is controlled to be, for example, 160 ° C. As shown by the broken line in FIG. 11, this region RE1 has a uniform temperature distribution.

Of the regions RE2a and RE2b heated by the first sub-heater 134b, the regions RE2a1 and RE2b1 corresponding to the portion through which the medium PA passes have a lower temperature than the region RE1 because the DUTY of the heater ON is lower than that of the region RE1. Become.
On the other hand, the regions RE2a2 and RE2b2 through which the medium PA does not pass have no heat transferred to the medium PA and are heated in the same manner as the regions RE2a1 and RE2b1 through which the medium PA passes, so that the temperature rises.

The solid line L2 in FIG. 11 shows the temperature distribution of the fixing belt 131 after printing is continued and about 100 pages are printed.

Of the regions RE2a and RE2b heated by the first subheater 134b, the temperature of the regions RE2a2 and RE2b2 through which the medium PA does not pass rises significantly as compared with the initial stage of printing (about 5 pages) to about 200 ° C.
On the other hand, among the regions RE2a and RE2b heated by the first subheater 134b, the temperature of the regions RE2a1 and RE2b1 through which the medium PA passes is the same as the heating amount of the first subheater 134b in the region RE1 at the initial stage of printing. Although it is lower than the initial value, it is higher than the initial value due to the influence of an increase in heat transfer in the width direction from the regions RE2a2 and RE2b2 where the temperature has been greatly increased.

As described above, in the regions RE1, RE2a1 and RE2b1 through which the medium PA passes, the temperature of the fixing belt 131 becomes substantially uniform, but the temperature of the regions RE2a2 and RE2b2 through which the medium PA does not pass rises. When printing a medium PA with a width wider than the B5 vertical size, for example, an A4 vertical size (width 210 mm), the temperature of the fixing belt 131 is locally high in the range outside 182 mm. Therefore, hot offset may occur.

In order to avoid the occurrence of hot offset, when switching from the narrow medium PA to the wide medium PA, the temperature of the fixing belt 131 may be leveled and then printing may be performed. While the leveling control is being performed, the user waits.

Therefore, in order to suppress the occurrence of hot offset or to shorten the time required for controlling the temperature leveling, it is necessary to suppress the excessive temperature rise in the region where the medium PA does not pass.
Therefore, in the present embodiment, when the width of the region where the medium PA does not pass is equal to or larger than a predetermined threshold value in the heating region of the first subheater 134b or the second subheater 134c. The fixing control unit 112 lowers the heating amount of at least one of the first subheater 134b and the second subheater 134c as printing continues.

In the present embodiment, the fixing control unit 112 uses the following equations (6) and (7) instead of the above equations (2) and (3), and the first equation in the nth cycle. The second duty ratio, which is the duty ratio of the sub-heater 134b, and the third duty ratio, which is the duty ratio of the second sub-heater 134c in the nth cycle, are calculated.
Second Duty Ratio (n) = {First Duty Ratio (n) -First DutyMod (n-1)} x α1 x β1 + Second DutyMod (n-1) (6)
Third DUTY ratio (n) = {(first DUTY ratio (n) -first DutyMod (n-1))} × α2 × β2 + third DutyMod (n-1) (7)

In equation (6), the correction is performed using the correction value β1. Further, in the equation (7), the correction is performed using the correction value β2. The first DutyMod (n-1), the second DutyMod (n-1), or the third DutyMod (n-1) may not be used.
FIG. 12 is a graph for explaining the correction values β1 and β2.
In the following, when it is not necessary to distinguish each of the correction values β1 and β2, each of the correction values β1 and β2 is referred to as a correction value β. The correction value β is the second coefficient described above.

In the present embodiment, the correction value β is a correction value that varies depending on the number of printed pages (the number of image-formed pages) when continuous printing is performed.
Here, continuous printing corresponds to a case where one print job prints on a plurality of medium PAs, and a case where a plurality of print jobs are processed continuously, or a case where a plurality of print jobs are processed in a predetermined period. May include cases where it is done within.

The correction value β is used for the purpose of suppressing a temperature rise in a region where the medium PA does not pass in the heating region of the first subheater 134b or the second subheater 134c. Therefore, it is not necessary when there is no non-passing region in the heating region, which is a region through which the medium PA does not pass, or when the non-passing region is narrow.

For example, when the width of the medium PA is larger than 210 mm, the region of the portion where the medium PA does not pass is sufficiently narrow or eliminated in the heating region of the first subheater 134b, so that the first subheater 134b By setting the correction value β1 corresponding to the above to 100% as shown in FIG. 12, the control is the same as the control in the above equation (2).

Further, when the width of the medium PA is larger than 280 mm, the region of the portion where the medium PA does not pass is sufficiently narrow or eliminated in the heating region of the second subheater 134c, so that the second subheater 134c By setting the correction value β2 corresponding to the above to 100% as shown in FIG. 12, the control is the same as the control in the above equation (3) without multiplying the correction value β2.

On the contrary, when the width of the medium PA is 210 mm or less and wider than 138 mm, the correction value β1 is changed from 100% to a predetermined value (for example, 90%) depending on the number of printed pages. It is gradually reduced so that it becomes. The predetermined value here is also referred to as a first value. In other words, when the correction value β1 is continuously printed (image formation) and the width of the medium PA is within a predetermined range (first range), the number of printed pages increases as the number of printed pages increases. It is a value that reduces the duty ratio of the first sub-heater 134b.

When the width of the medium PA is 280 mm or less and wider than 230 mm, the correction value β2 is set to a predetermined value (for example, 90%; first) from 100% depending on the number of printed pages. It is gradually reduced so that it becomes (value of). In other words, when the correction value β2 is continuously printed, if the width of the medium PA is within a predetermined range (second range), the second subheater increases as the number of printed pages increases. It is a value that reduces the DUTY ratio of 134c.

Specifically, as shown in FIG. 11, at the initial stage of printing, the temperature rise in the non-passing region is small, and the temperature in the passing region, which is the region through which the medium PA passes, is also low. Therefore, the fixing control unit 112 Sets the correction value β to 100%. After that, by the time printing of a predetermined number of pages (for example, 20 pages) is completed, the temperature of the non-passing region rises significantly and the temperature of the passing region also begins to stabilize. The correction value β starts to decrease. The predetermined number of pages here is also referred to as the first number of pages.

After that, by the time printing of a predetermined number of pages (for example, 70 pages) is completed, the temperature of the passing region has risen from the initial stage of printing, and even if the correction value β is 90%, the passing region The temperature can be secured. The predetermined number of pages here is also referred to as a second number of pages. By this time, the temperature rise in the passing region and the non-passing region is approximately saturated, and the fluctuation thereafter is minor. Therefore, the fixing control unit 112 subsequently fixes the correction value to 90%.

From page 20 to page 70, the correction value is complemented so as to be approximately a straight line. For example, every time printing of a predetermined number of pages (for example, 5 pages) is completed, the fixing control unit 112 , The correction value β is reduced by a predetermined value (for example, 1%). The predetermined number of pages here is also referred to as a third page number, and the predetermined value here is a second value.

The method for deriving the correction value β as described above may be stored in advance in the memory 112a of the fixing control unit 112. For example, a correction value table, which is a table in which the number of printed pages and the correction value β are associated with each other, may be stored, and the function between the number of printed pages and the correction value β is stored in the form of a mathematical formula. It may have been done.

FIG. 13 is a time chart of correction values α, correction values β, and final duty ratio correction values α × β when 100 pages of B5 vertical size (width 182 mm) medium PA are printed continuously. Here, the duty ratio correction value α × β is also referred to as a third coefficient.
First, the image forming apparatus 100 is in a standby state until the image forming apparatus 100 receives the print job. At this time, since the main heater 134a, the first subheater 134b, and the second subheater 134c are not controlled, the main heater 134a is in the OFF state, and the correction values α and the second subheater 134b of the first subheater 134b are in the OFF state. The correction value β of the sub-heater 134c is also set to 0.

When the image forming apparatus 100 receives the print job at the time T11, the image forming apparatus 100 transitions to the warm-up state. The fixing control unit 112 performs PID control based on the temperature detected by the infrared temperature sensor 136 so that the main heater 134a reaches the target temperature. In the warm-up state, the fixing control unit 112 sets the correction value α and the correction value β to 100% in order to shorten the time, as in the normal fixing control.

At time T12, when the temperature detected by the infrared temperature sensor 136 reaches the target temperature, the warm-up is completed and the image forming apparatus 100 transitions to the printing state. Here, the fixing control unit 112 sets the correction value α and the correction value β to the values for printing. Here, the fixing control unit 112 sets the correction value α1 = 94% and the correction value α2 = 0% from the width of the medium PA. Further, since the number of printed pages is 0 immediately after the start of printing, the fixing control unit 112 sets the correction value β1 = 100% and the correction value β2 = 100%. At this time, the duty ratio correction value α1 × β1 = 94% × 100% = 94% and the duty ratio correction value α2 × β2 = 0% × 100% = 0%.

When printing is continued and the number of printed pages reaches 20 at time T13, the correction value β starts to decrease.
Then, at time T14, when the number of printed pages reaches 70, the correction value β becomes 90%, and thereafter, the correction value β = 90% is fixed until the printing of 100 pages is completed. At this time, the duty ratio correction value α1 × β1 = 94% × 90% ≈85%, and the duty ratio correction value α2 × β2 = 0% × 90% = 0%.

When the printing of 100 pages is completed, the image forming apparatus 100 transitions to the standby state, the main heater 134a is turned off as in the case before receiving the print job, and the first subheater 134b and the second subheater 134c The correction value α and the correction value β also return to 0.

FIG. 14 is a schematic view showing the temperature distribution of the fixing belt 131 in the longitudinal direction when printing is performed on the medium PA of the B5 vertical size (width 182 mm) under the control shown in FIG.
The broken line L3 in FIG. 14 shows the temperature distribution of the fixing belt 131 when printing of about 5 pages is performed after switching to the correction values α1 and α2 for printing.
In the initial stage of printing, the operation is equivalent to the fixing control that does not use the correction value β, so that the temperature distribution shown by the broken line L3 is the same as that of the broken line L1 in FIG.

On the other hand, in the temperature distribution after printing on page 100 shown by the solid line L4 in FIG. 14, since the duty ratio of the first subheater 134b is lowered by the correction value β, it is possible to suppress the temperature rise in the non-passing region. can.
The temperature of the passing region is also lower than that of the solid line L2 in FIG. 11, but since the duty ratio is lowered after the fuser 130 is heated, it is higher than the state at the initial stage of printing. Since the high temperature can be maintained, it is possible to prevent the deterioration of toner fixing.

By performing the above operation, it is possible to prevent an excessive temperature rise in the non-passing region without causing deterioration of toner fixation due to a temperature drop in the passing region of the medium PA. Therefore, even if the medium PA having a narrow width is used for printing, the occurrence of hot offset can be suppressed. Therefore, it is possible to prevent an increase in the waiting time of the user.

In the embodiment described above, the correction value β is reduced by 1% every 5 pages, but the embodiment is not limited to such an example. For example, the correction value β may be reduced by 10% only once after printing the 50th page. Further, the correction value β may be lowered every time one page is printed.

Further, the standard for reducing the correction value β is not limited to the number of printed pages, but may be a standard that can be inferred that the temperature of the non-passing region rises due to continuous printing. .. For example, the image forming apparatus 100 may include a timer as a time measuring unit, and the correction value β may become smaller as the elapsed time from the start of printing, which is measured by the timer, becomes longer.

Further, even if the number of printed pages is the same, in the transport direction of the medium PA, the temperature rise in the non-passing region of the long medium PA and the short medium PA is larger in the long medium PA, so that the medium PA The correction value β may be reduced as the product of the length in the transport direction and the number of printed pages increases.

Further, in the above embodiment, the calorific value of the first subheater 134b or the second subheater 134c is changed by the DUTY ratio of the heater, but the embodiment is not limited to such an example. For example, the calorific value of the first subheater 134b or the second subheater 134c may be changed by changing the voltage applied to the first subheater 134b or the second subheater 134c or the current flowing through the second subheater 134c.

The image forming apparatus 100 described above may be an electrophotographic printer, a copier, a facsimile apparatus, or a multifunction printer having a plurality of these functions.

100 image forming apparatus, 101 paper feed cassette, 102 hopping roller, 103, 104 resist roller, 105 transport belt, 106 drive roller, 107 driven roller, 108K, 108Y, 108M, 108C transfer roller, 109, 110 discharge roller, 112 fixing Control unit, 120K, 120Y, 120M, 120CID, 130 fuser, 131 fixing belt, 131a outer peripheral surface, 132 backup roller, 133 heat diffusion member, 134 planar heater, 134a main heater, 134b first sub-heater, 134c first 2 sub-heaters, 135a 1st thermistor, 135b 2nd thermistor, 135c 3rd thermistor, 136 infrared temperature sensor, 137a, 137b, 137c BU thermistor, 138 heating unit, 141a 1st triac, 141b 2nd triac , 141c Third triac, 142 triac drive circuit.

Claims (8)

A rotating body having an outer peripheral surface facing the medium on which the developer image is transferred, and
A heat generating portion provided inside the rotating body is provided.
The heat generating part is
A main heater that heats a first region that is a part of the rotating body in the main scanning direction, and
A sub-heater for heating a second region that is a part of the rotating body other than the first region in the main scanning direction is provided.
When images are continuously formed on the medium, the calorific value of the sub-heater with respect to the calorific value of the main heater changes according to the number of images completed on the medium. Fixing device. Claim 1 is characterized in that, when the width of the medium in the main scanning direction is within a predetermined range, the calorific value of the sub-heater with respect to the calorific value of the main heater changes according to the number. The fixing device according to. The fixing device according to claim 1 or 2, wherein the calorific value of the sub-heater with respect to the calorific value of the main heater decreases as the number increases. A fixing control unit that calculates the calorific value of the sub-heater from the calorific value of the main heater and controls the calorific value of the main heater and the sub-heater is further provided.
Any of claims 1 to 3, wherein the fixing control unit changes the calorific value of the sub-heater with respect to the calorific value of the main heater according to the number when calculating the calorific value of the sub-heater. The fixing device according to one item. Further provided with a power source for applying a voltage to the main heater and the sub heater,
The fourth aspect of claim 4, wherein the fixing control unit controls the amount of heat generated by the main heater and the amount of heat generated by the subheater according to the duty ratio of the voltage applied from the power source to the main heater and the subheater. Fixing device. The fixing control unit has a duty ratio of a voltage applied from the power source to the main heater, a first coefficient determined according to the width of the medium in the main scanning direction, and a second coefficient that changes according to the number. The fixing device according to claim 5, wherein the duty ratio of the voltage applied from the power source to the sub-heater is calculated by multiplying the coefficient by. A main temperature detection unit for detecting the temperature of the first region of the rotating body is further provided.
The fixing device according to any one of claims 4 to 6, wherein the fixing control unit controls a calorific value of the main heater according to a temperature detected by the main temperature detecting unit. A transport belt for transporting the medium and
An image forming unit that forms the developer image and
A transfer unit that transfers the developer image to the medium, and
An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 7.

Images