JP2016109977A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate ununiformity of a temperature distribution of a fixing member without requiring an additional special configuration.SOLUTION: When determining that a temperature distribution of a fixing member 173 in a rotation shaft direction is a temperature distribution where the temperature on the front side is higher than the temperature on the depth side, a control part 110 controls an air volume distribution changing part that changes a distribution of the volume of a separation air in the rotation shaft direction to change the distribution of the volume of the separation air so that the volume of air on the depth side becomes larger than the volume of air on the front side.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus using toner, a toner image formed by an image forming unit is transferred onto a sheet, and the toner image is melted and fixed on a sheet by heating and pressing with a fixing device including a heater. Yes. The temperature inside the apparatus rises due to heat radiated and diffused from the fixing apparatus. In order to suppress this, a technique is known in which heat radiated from the fixing device is discharged from the exhaust port to the outside of the device together with an air flow generated by a blower fan.

  Since the user performs various operations from the front side of the apparatus main body, it is not preferable to provide the exhaust port on the front side. Further, since a post-processing device that performs various post-processings on the paper on which the image is formed is connected to the side surface of the apparatus main body, it is difficult to provide an exhaust port on the side surface side. Under such circumstances, the exhaust port is generally provided on the back side of the image forming apparatus.

  On the other hand, when an exhaust port is provided on the back side of the apparatus main body, the air flow that cools the periphery of the fixing device flows along the axial direction of the fixing roller. Therefore, the temperature of the air flow far from the exhaust port for taking in outside air is low, but the air flow near the exhaust port is warmed by the heat of the fixing roller. As a result, the surface temperature of the fixing roller has a non-uniform temperature distribution in which the temperature on the back side of the apparatus having the exhaust port relatively high in the axial direction is high and the temperature on the front side is low.

  Since the temperature of the fixing roller affects the image such as the glossiness of the toner image after the fixing, the non-uniform temperature distribution in the axial direction causes a decrease in image quality such as uneven glossiness. To solve such a problem, in the fixing device disclosed in Patent Document 1, in order to eliminate the uneven temperature distribution in the axial direction caused by arranging a cooling fan at the end of the fixing roller, A heater is used in which the light distribution ratio on the side far from the fan is larger than the light distribution ratio on the near side.

JP 2000-089607 A

  However, in Patent Document 1, it is necessary to use a special heater in which the light distribution ratio is adjusted in accordance with cooling by the fan, resulting in an increase in cost.

  The present invention has been made in view of the above circumstances, and provides an image forming apparatus capable of eliminating uneven temperature distribution in the rotation axis direction of a fixing member without requiring a special additional configuration. The purpose is to provide.

  The above object of the present invention is achieved by the following means.

(1) a fixing device that includes a heating unit, forms a fixing nip by a pair of rotating fixing members, and fixes the toner image on the paper to the paper by applying heat to the paper passing through the fixing nip;
A separation blower that includes a blower fan and separates the paper from the fixing member by blowing a separation air blown from the blower fan to the paper that has passed through the fixing nip;
The air flow that is parallel to the rotation axis direction of the fixing member and forms an air flow that flows in a direction from the near side to the back side when viewed from the front of the apparatus, and the temperature is increased by the heat discharged from the fixing member. An exhaust part for discharging the air from the exhaust port to the outside of the machine,
A control unit;
An image forming apparatus comprising:
The separation fan section includes an air volume distribution changing section that changes an air volume distribution of the separated wind in the rotation axis direction,
When the control unit determines that the temperature distribution of the fixing member in the rotation axis direction is a temperature distribution having a higher temperature on the back side than on the near side, the control unit controls the air volume distribution changing unit from the near side. An image forming apparatus that changes the air volume distribution of the separated air so that the air volume on the back side increases.

(2) The sending fan of the separation blowing unit is a plurality of blowing fans arranged along the rotation axis direction,
The image according to (1), wherein the air volume distribution changing unit changes the air volume distribution of the separated air so that the air volume on the back side becomes larger than the near side by changing the air volume from the blower fan. Forming equipment.

  (3) The air volume distribution changing unit changes the air volume distribution of the separated air so that the air volume on the back side becomes larger than the near side by changing the direction of the air flow blown from the blower fan. The image forming apparatus according to (1) above.

(4) The separation blower unit includes a wind direction plate that controls the direction of wind disposed inside a duct that guides air blown from the blower fan to a sheet that passes through the fixing nip,
The image formation according to (3), wherein the air volume distribution changing unit changes the air volume distribution of the separated air so that the air volume on the back side becomes larger than the near side by changing the direction of the wind direction plate. apparatus.

(5) The separation air blower performs air blowing by the air blowing fan after the paper starts to pass through the fixing nip until it finishes passing,
The image forming unit according to any one of (1) to (4), wherein the control unit causes the air volume distribution changing unit to change the air volume distribution at a timing when the sheet starts to pass through the fixing nip. apparatus.

(6) The fixing device includes a plurality of temperature sensors that detect temperatures of the fixing member at different positions in the rotation axis direction.
The control unit controls the air volume distribution changing unit based on a temperature distribution in a rotation axis direction of the fixing member obtained from a detection result of the temperature sensor, and any one of the above (1) to (5) The image forming apparatus according to one.

  (7) The control unit estimates the temperature distribution in the rotation axis direction of the fixing member from the amount of electric power supplied to the heating unit and the amount of exhaust from the exhaust port, and based on the estimated temperature distribution, The image forming apparatus according to any one of (1) to (5), wherein the airflow distribution changing unit is controlled.

  According to the present invention, when it is determined that the temperature distribution in the rotation axis direction of the fixing member is a temperature distribution in which the temperature on the back side is higher than that on the front side, the air volume on the back side becomes larger than the front side. By changing the air volume distribution of the separation air, it is possible to eliminate the uneven temperature distribution of the fixing member without requiring a special additional configuration.

1 is a diagram illustrating a schematic configuration of an image forming apparatus 100 according to a first embodiment. 2 is a block diagram illustrating a hardware configuration of the image forming apparatus 100. FIG. FIG. 2 is a schematic diagram illustrating a configuration around a fixing device 170. FIG. 2 is a schematic diagram illustrating a configuration around a fixing device 170. 3 is a schematic view showing an air flow around the fixing device 170. FIG. 3 is a schematic view showing an air flow around the fixing device 170. FIG. It is a figure which shows the temperature distribution of the axial direction of the heating roller 173. FIG. 3 is a flowchart showing control executed by a control unit 110. It is a figure explaining the effect by control of temperature distribution equalization shown in FIG. 7 is a time chart showing the operation of the separation fan section 180. It is the schematic which shows the structure of the separation ventilation part 180 which concerns on the modification 3. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 100 according to the first embodiment. FIG. 2 is a block diagram illustrating a hardware configuration of the image forming apparatus 100. In FIG. 1 and other drawings to be described later, the X direction indicates the depth direction of the image forming apparatus 100, the upstream side in the X direction is the front side (hereinafter also referred to as “front side”), and the downstream side is the back side (hereinafter referred to as “back”). Also called “side”). The X direction, the Y direction, and the Z direction are orthogonal to each other, the Y direction is a horizontal direction, and the Z direction is a vertical direction. The X direction is parallel to the rotation axis direction described later.

  As shown in FIGS. 1 and 2, the image forming apparatus 100 includes a control unit 110, a memory 120, an operation / display unit 130, an image reading unit 140, a paper feed / conveying unit 150, an image forming unit 160, a fixing device 170, and a separate air blower. Part 180 and exhaust part 190. An image of toner is formed on the paper S by the image forming apparatus 100. The sheet S on which the image is formed is transported to the post-processing device 200, and after various processing such as stapling, folding, and punching is performed as necessary, it is placed on a discharge tray or the like on the downstream side in the transport direction. Be transported.

  The control unit 110 includes a CPU, a RAM, and a ROM, and appropriately reads out various programs stored in the ROM, develops them on the RAM, and implements various functions by executing the programs. The memory 120, which is a large-capacity storage device such as an HDD, stores image data for printing and various setting information.

  The operation / display unit 130 is, for example, a touch sensor superimposed on a display surface of an LCD (liquid crystal display), and accepts various operations by the user. The operation / display unit 130 is provided on the front side of the apparatus.

  The image reading unit 140 includes an optical system including a mirror and a lens and a reading sensor such as a CCD, and reads an original placed on a platen glass or an original conveyed from an ADF (not shown) and outputs an image signal. To do.

  The paper feed conveyance unit 150 includes a plurality of paper feed trays 151, a paper discharge unit 152, a double-sided conveyance path 153, and paper sensors 159a, 159b, and 159c. The sheet feeding / conveying unit 150 includes a plurality of conveyance roller pairs and a conveyance motor (not shown), and conveys sheets fed one by one from one of the sheet feeding trays 151 to a downstream conveyance path. In the double-sided mode, the paper S conveyed from the paper feed tray 151 is image-formed on the front side by the image forming unit 160 and then switched back by the conveyed double-sided conveyance path 153 and turned upside down. The image forming unit 160 again forms an image on the opposite surface (back surface). The sheet S on which the image is formed on one side or both sides is conveyed from the paper discharge unit 152 to the downstream post-processing device 200. The paper sensors 159a, 159b, and 159c detect whether or not the paper is being transported to the detection area by a non-contact sensor such as a contact type or a photoelectric sensor provided with an actuator. The detection area is provided in the paper conveyance path, and is turned on when there is a paper in the detection area. In particular, the sheet sensor 159b is disposed in the conveyance path immediately upstream of the fixing device 170, and the timing at which the sheet S is conveyed to the fixing nip N (see FIG. 3) is determined based on the detection output of the sheet sensor 159b. .

  The image forming unit 160 includes image forming units 161Y, 161M, 161C, 161K that develop toners of Y, M, C, and K, an intermediate transfer belt 162, and a secondary transfer unit 163, respectively. The image forming unit 161 includes a photosensitive drum, a charging device, an exposure device, a cleaning unit, and a developing device. Each toner image developed based on the image signal is superimposed on the intermediate transfer belt 162 and then secondary. The image is transferred onto the paper S by the transfer unit 163. The toner image transferred to the paper S is conveyed to the fixing nip N of the fixing device 170, heated and pressurized, and melted and fixed on the surface of the paper S.

  Next, with reference to FIGS. 3 to 6, configurations of the fixing device 170, the separation air blowing unit 180, and the exhaust unit 190 will be described. 3 to 6 are schematic views showing the configuration around the fixing device 170. FIG. 3 is a view seen from the front side of the apparatus (X direction), FIGS. 4 and 5 are views seen from the left side of the apparatus (Y direction), and FIG. 6 is a view seen from the upper side of the apparatus (Z direction). .

  As shown in FIG. 3, the fixing device 170 includes a fixing housing 171 that covers the entire fixing device, a heater 172, a heating roller 173, a pressure roller 174, and a temperature sensor 175. The heating roller 173 includes, in order from the inside, a cored bar made of a cylindrical metal, an elastic layer made of a material such as silicone rubber or foamed silicone rubber formed on the surface thereof, and a release layer such as a fluororesin. A halogen lamp heater 172 is arranged inside the cored bar. The length of the heating roller 173 in the rotation axis direction (hereinafter, simply referred to as “axial direction”) is long enough to fix the sheet S having the maximum sheet width that can be fed and conveyed. The length of the heater 172 in the axial direction corresponds to the paper S having the maximum paper width. The heater 172 may be composed of a plurality of heaters having different light distribution characteristics corresponding to a plurality of stages of paper widths that can be fed by the apparatus. Further, as the heating unit, instead of a halogen lamp heater, an IH heater or a resistance heating element in which a resistor is embedded in the surface layer of a roller may be applied.

  The pressure roller 174 includes, in order from the inside, a cored bar made of a cylindrical metal, an elastic layer made of a material such as silicone rubber or foamed silicone rubber formed on the surface thereof, and a release layer such as a fluororesin. The outer diameter and axial length of the pressure roller 174 are the same as those of the heating roller 173. A heater may also be arranged inside the core bar of the pressure roller 174.

  The cores of the heating roller 173 and the pressure roller 174 are rotatably supported on the fixing housing 171 by bearings (not shown), and one or both rollers are driven to rotate by a drive motor (not shown). The

  The temperature sensor 175 detects the temperature of the surface of the heating roller 173. As the temperature sensor 175, for example, a thermistor arranged in a non-contact manner is used. In this embodiment, as shown in FIG. 6, the temperature sensors 175 are arranged at three locations along the axial direction of the heating roller 173, the front side (r), the center (c), and the back side (f). The temperature distribution in the axial direction of the heating roller 173 is detected by these temperature outputs.

(Separation fan 180)
The separation blower 180 includes a blower fan 181 and a duct 182 as shown in FIGS. The duct 182 is made of a heat-resistant material such as metal, and the air outlet 182a at the tip thereof is disposed in the vicinity of the fixing nip N. The air outlet 182 a of the duct 182 is a rectangular opening having a uniform width in the Y direction, and the opposite side is connected to a plurality of blower fans 181. The blower fan 181 is a fan that can change the rotation speed (rpm) of the fan in multiple stages. The air volume is changed by changing the rotation speed. In this paper, when the term “air volume” is used, it indicates the volume of gas flowing per unit time (m ³ / sec) unless otherwise specified.

  The air flow blown from the blower fan 181 flows through the inside of the duct 182 and is sent out from the air outlet 182a at the tip. 3 indicates a conveyance path of the sheet S, and the sheet S passing through the fixing nip N is stably separated from the heating roller 173 by the separation air sent from the blowout port 182a (air). Separation).

  As shown in FIG. 4, in this embodiment, the blower fans 181 are arranged side by side along the axial direction of the heating roller 173 at three locations on the front side (r), the center (c), and the back side (f). ing. The air flow blown from each blower fan 181 is rectified in the duct 182, and the blowout port 182a sends out separated air that is perpendicular to the axial direction and has a uniform airflow distribution in the axial direction. Note that the number of the blower fans 181 is not limited to three and may be two or four or more.

(Exhaust part 190)
Hereinafter, the configuration of the exhaust unit 190 and the flow of air around the fixing device 170 will be described with reference to FIGS. 5 and 6, the exhaust unit 190 includes an exhaust fan 191 and an exhaust duct 192. The air inside the apparatus is sucked from the intake port 192b and discharged from the exhaust port 192a to the outside by operating the exhaust fan 191. An intake port 192 b of the exhaust duct 192 is provided in the panel 101 on the back side of the image forming apparatus 100, and an exhaust port 192 a is provided in the exterior 102 on the back side of the image forming apparatus 100.

  As shown in FIGS. 5 and 6, when the exhaust fan 191 of the exhaust unit 190 is activated, an air flow parallel to the axial direction of the heating roller 173 is formed around the fixing device 170 from the front side to the back side of the fixing device 170. Occurs. More specifically, along the axial direction (X direction) inside the fixing casing 171 of the fixing device 170 due to outside air taken in from the gap between the front panel 101 when the exhaust fan 191 operates. Air flow is generated. This air flow enters the inside of the fixing housing 171 through the opening 171a on the near side and exits from the opening 171b on the back side. The air flow along the axial direction inside the fixing housing 171 flows on both sides of the heating roller 173 and the pressure roller 174 in the Y direction. The air flow along the axial direction changes direction after passing by the side of the fixing casing 171 and flows upward along the panel 101 on the back side, and then taken into the exhaust duct 192 and passes through the exhaust port 192a. Discharged outside.

(Temperature distribution of fixing device 170)
The axial temperature distribution of the heating roller 173 of the fixing device 170 will be described with reference to FIG. FIG. 7 is a diagram showing the temperature distribution in the axial direction of the heating roller 173, and plots the detection output (° C.) of the temperature sensor 175. In FIG. The temperature sensor 175 is arranged on the back side, the near side corresponding to both ends of the maximum paper width (for example, 330 mm), and the middle portion in the middle. As shown in the figure, the surface temperature of the heating roller 173 is high on the near side and on the far side, and the temperature difference between them is ΔT (° C.).

  As described with reference to FIGS. 5 and 6, when the exhaust fan 191 of the exhaust unit 190 is operated, an air flow along the axial direction is generated around the fixing device 170. The fixing device 170 is cooled by this air flow. However, since the air taken in from outside the apparatus flows on the upstream side of the air flow, the temperature thereof is close to room temperature. On the other hand, since the air is heated by the heat radiated from the fixing device 170 on the downstream side of the air flow, the temperature of the air flow is higher than the room temperature. For this reason, the front side of the fixing device 170 is cooled by a low-temperature air flow, whereas the back side is cooled by a high-temperature air flow, so that the temperature is hardly lowered. As a result, the surface temperature of the heating roller 173 of the fixing device 170 has a distribution as shown in FIG. The temperature difference ΔT increases as the amount of heat generated by the heater 172 (average supply power W) increases and the amount of exhaust air from the exhaust fan 191 increases. When the temperature difference ΔT exceeds the allowable range, a difference in toner fixability occurs between the near side and the far side, and this can be recognized by a difference in glossiness, which may cause an image defect.

(Control of uniform temperature distribution according to the first embodiment)
In the control of uniform temperature distribution described below, a threshold temperature (hereinafter, “Tα”) smaller than this is set so that the temperature difference ΔT in the axial direction of the heating roller 173 does not exceed the allowable range. When the temperature exceeds the threshold temperature Tα, the distribution of the separated air is controlled so as to reduce the temperature difference ΔT. In the present embodiment, the plurality of blower fans 181 function as an air volume distribution changing unit that changes the air volume distribution of the separated wind in the axial direction.

  FIG. 8 is a flowchart showing the control executed by the control unit 110. The control unit 110 first acquires the temperature of the heating roller 173 from the detection output of the temperature sensor 175 (S101). Then, it is determined whether or not the temperature difference ΔT (see FIG. 7) between the near side and the far side exceeds the threshold temperature Tα (S102). The threshold temperature Tα is 5 ° C., for example.

  When it is determined that the temperature difference ΔT exceeds the threshold temperature Tα (S102: YES), the control unit 110 changes the air volume distribution setting so that the far-side air volume is larger than the near-side air volume. Specifically, among the plurality of blower fans 181 (see FIG. 4) of the separated blower unit 180, the rotational speed setting of the blower fan 181 (r) on the back side is set to the fastest “H”, and the central blower fan 181 ( The rotational speed setting of c) is set to the middle “M”, and the rotational speed of the front blower fan 181 (f) is set to the lowest “L” (S104).

  If it is detected that the leading edge of the paper S has passed through the fixing nip N based on the detection output of the paper sensor 159b, or if it is passing (S104: YES), the rotational speed set in step S103 (or S106) is set. In the setting, each blowing fan 181 is operated (S105).

  On the other hand, if it is determined in step S102 that the temperature difference ΔT does not exceed the threshold temperature Tα (S102: NO), the airflow distribution setting is changed so that the airflow on the back side and the front side is uniform. (Reset to the initial state). Specifically, the rotational speed setting of all the blower fans 181 is set to “L” (or “M”) (S106), and the subsequent operations are executed and the process is terminated.

(effect)
FIG. 9 is a diagram for explaining the effect of the control for uniform temperature distribution shown in FIG. Fig.9 (a) shows the air volume distribution of the separation wind sent out from the blower outlet 182a. In the figure, the dashed white circle is before the change, and the solid black circle indicates the air volume after the change. As shown in the figure, the air flow by the blower fan 181 is changed by switching the rotation speed of the blower fan 181, and the airflow distribution is changed so that the airflow of the separated air on the back side is larger than the airflow of the separated air on the near side. It has changed.

  FIG. 9B shows a change in the temperature distribution of the surface temperature of the heating roller 172 due to the change in the air volume distribution as shown in FIG. 9A. Since the inclination of the air volume distribution in FIG. 9A is set appropriately, it can be seen that the temperature distribution of the heating roller 173 is uniform as shown in FIG. 9B.

  As described above, in the first embodiment, the separate air flow is increased so that the air volume on the back side becomes larger than the front side by the plurality of air blowing fans 181 functioning as the separation air blowing units without requiring any special additional configuration. Change the air volume distribution. This makes it possible to make the temperature distribution in the axial direction of the heating roller 173 uniform, thereby preventing image defects such as uneven glossiness.

(Modification 1)
FIG. 10 is a time chart showing the operation of the separation air blowing unit 180. In the drawing, the timing at which the sheet S passes through the fixing nip N, the operation timing of the blower fan 181 on the rear side and the front side, and the determination result of the temperature difference determination flag are shown in order from the top. The case where the flag is ON is a case where the determination condition of step S102 of FIG. 8 and the temperature difference ΔT> Tα are satisfied.

  As shown in the figure, during the time t1 to t2 from when the first sheet S1 starts to pass through the fixing nip N to when it finishes passing, each of the blower fans 181 on the back side, the center, and the near side has a rotational speed “ L "blows air. The setting of the rotational speed “L” at the time t1 to t2 corresponds to the flag OFF. In this case, the air volume distribution in the axial direction of the separated wind is uniform.

  As the temperature difference determination flag changes to ON at time t4, the rotation speeds of the rear, center, and front fans 181 are changed to “H”, “M”, and “L” settings, respectively. (See S103 in FIG. 8).

  However, in the first modification, the setting change of the rotational speed of each blower fan 181 is not reflected immediately, but is reflected at the timing when the next sheet starts to pass through the fixing nip N. Specifically, as shown in FIG. 10, since the flag has changed from OFF to ON at time t4 while the second sheet S2 is passing through the fixing nip N, time t3 to t5 After t4, each blower fan 181 operates at the rotation speed of “L” set immediately before. The setting change of the fan operation amount is reflected after time t6 when the next sheet S starts to pass through the fixing nip N after time t4 when the flag changes. Since the third and fourth sheets S3 and S4 after the time t6 rotate the blower fans 181 at the rotation speed after the setting change, the air volume distribution of the separated wind is larger in the rear side than in the front side. (Solid black circle in FIG. 9A).

  As described above, the timing of changing the air volume distribution is set to the timing at which the next sheet S starts to pass through the fixing nip N. In addition to the effects of the first embodiment, the separation performance of the sheet S can be further stabilized. .

(Modification 2)
In 1st Embodiment and the modification 1, the example which changes the air volume distribution of a separation wind by changing the rotation speed (rpm) of the ventilation fan 181 was demonstrated. However, the air volume distribution of the separated air may be changed by changing the operating time of the blower fan 181 instead of the rotational speed or together with the rotational speed. In the example of FIG. 10, the operation of the blower fan 181 is stopped and the separation air is not sent out between the sheets S. However, even when the sheet S such as between sheets does not pass through the fixing nip N, By operating only the blower fan 181, the air volume per unit time (several seconds to several tens of seconds) on the back side can be increased. Further, in the example of FIG. 10 and the like, the example in which the rotational speed of the blower fan 181 is changed in three stages is shown. However, a fan that can change the rotational speed in multiple stages may be applied, and less than this You may apply the fan changed in two steps. Further, when a two-stage (high speed and low speed) fan is applied, the sheet 1 is set so that the average air volume sent from the central fan 181 (c) is intermediate between the air volumes sent from the rear and front fans 181. You may control to switch a rotational speed by time division, such as switching a high speed and a low speed alternately according to the passage timing for every sheet.

(Modification 3)
FIG. 11 is a schematic diagram illustrating a configuration of a separation air blowing unit 180 according to the third modification. In the first embodiment, the air volume distribution of the separated air in the axial direction is changed by changing the rotational speeds of the plurality of blower fans 181 to different settings. In the third modification, the air volume distribution of the separated wind in the axial direction is changed by changing the direction of the wind direction plate 184 disposed in the duct of the separated air blowing unit 180. This will be described below.

  As shown in FIG. 11, the separated air blowing unit 180 according to Modification 3 has a plurality of wind direction plates 184 arranged inside a duct 183. In the initial state shown in FIG. 11A, the wind direction plate 184 extends in a direction perpendicular to the axial direction of the heating roller 173 (on the YZ plane), and the direction of the separated wind sent from the outlet 183a of the duct 183 Is a direction perpendicular to the axial direction of the heating roller 173.

  FIG. 11B is a diagram illustrating a state in which the direction of the wind direction plate 184 is inclined to the back side. The wind direction plate 184 is rotatable around a turning axis p provided at the center thereof, and is rotated at an arbitrary angle by the wind direction plate driving unit 185. In the state of FIG. 11 (b), the direction of the air flow inside the duct 183 is directed to the back side, so the air volume distribution in the axial direction of the separated air at the outlet 183a is larger on the back side than on the front side. To be changed. The air volume distribution of the separated wind is the same as that shown in FIG.

  As described above, in the third modification, the wind direction distribution of the separated wind in the axial direction is changed by the wind direction plate 184 and the wind direction plate driving unit 185 that function as the air volume distribution changing unit. Also in the third modification, the temperature distribution in the axial direction of the heating roller 173 can be made uniform as in the first embodiment, thereby preventing image defects such as uneven glossiness.

(Modification 4)
In the first embodiment, the temperature difference ΔT between the near side and the far side of the heating roller 173 is calculated by detecting the temperature of the plurality of temperature sensors 175 arranged along the axial direction. However, the temperature difference ΔT may be estimated from the following equation.

ΔT (° C.) = Γ × x × y
Here, x is an average supply power amount (W · sec / sec or W · hour / hour) supplied to the heater 172 per unit time (for example, 30 sec), and y is an exhaust amount passing through the exhaust port 192a (m ³ / sec), and γ is a constant (° C. · sec / W · m ³ ).

  Thus, the number of temperature sensors 175 can be reduced by estimating and obtaining the temperature difference ΔT.

(Modification 5)
In the third modification, the air volume distribution in the axial direction of the separated wind is changed by changing the direction of the wind direction plate 184. Not limited to this, it is configured to direct the direction of the blower fan 181 directly to the back side, or by operating a partition plate provided in the duct to increase the pressure loss on the front side from the back side, thereby reducing the air volume on the front side. It may be decreased.

(Other variations)
In the fixing device 170 according to the embodiment described with reference to FIG. 3 and the like, an example in which a pair of fixing rollers is used as a rotating fixing member is shown, but the present invention is not limited to this. For example, a fixing device using a fixing belt as one or both of the rotating fixing members may be used. Furthermore, a fixed pad may be used in place of the roller that forms the fixing nip N among the plurality of internal rollers that drive and support the fixing belt.

100 image forming apparatus,
101 panels,
102 exterior,
110 control unit,
120 memory,
130 Operation / display section,
140 image reading unit,
150 paper feeding and conveying section,
151 Paper tray,
152 paper discharge unit,
153 Double-sided conveyance path,
159a, 159b, 159c paper sensor,
160 Image forming unit,
170 fixing device,
171 fixing housing;
172 heater (heating part),
173 Heating roller (fixing member),
174 Pressure roller (fixing member),
175 temperature sensor,
180 separation fan,
181 blower fan,
182, 183 Duct,
182a, 183a outlet,
184 wind direction board,
185 wind direction plate drive unit,
190 exhaust section,
191 Exhaust fan,
192 exhaust duct,
192a exhaust port,
192b Inlet 200 Aftertreatment device.

Claims (7)

A fixing device that includes a heating unit, forms a fixing nip by a pair of rotating fixing members, and fixes the toner image on the paper to the paper by applying heat to the paper passing through the fixing nip;
A separation blower that includes a blower fan and separates the paper from the fixing member by blowing a separation air blown from the blower fan to the paper that has passed through the fixing nip;
The air flow that is parallel to the rotation axis direction of the fixing member and forms an air flow that flows in a direction from the near side to the back side when viewed from the front of the apparatus, and the temperature is increased by the heat discharged from the fixing member. An exhaust part for discharging the air from the exhaust port to the outside of the machine,
A control unit;
An image forming apparatus comprising:
The separation fan section includes an air volume distribution changing section that changes an air volume distribution of the separated wind in the rotation axis direction,
When the control unit determines that the temperature distribution of the fixing member in the rotation axis direction is a temperature distribution having a higher temperature on the back side than on the near side, the control unit controls the air volume distribution changing unit from the near side. An image forming apparatus that changes the air volume distribution of the separated air so that the air volume on the back side increases. The sending fan of the separation blowing unit is a plurality of blowing fans arranged along the rotation axis direction,
The image formation according to claim 1, wherein the air volume distribution changing unit changes the air volume distribution of the separated air so that the air volume on the back side becomes larger than the near side by changing the air volume from the blower fan. apparatus.   The said air volume distribution change part changes the air volume distribution of the said separated wind so that the air volume of the back | inner side may become larger than the near side by changing the direction of the airflow ventilated from the said ventilation fan. The image forming apparatus described in 1. The separation blower unit includes a wind direction plate that controls the direction of wind disposed inside a duct that guides air blown from the blower fan to a sheet that passes through the fixing nip,
The image forming apparatus according to claim 3, wherein the air volume distribution changing unit changes the air volume distribution of the separated air so that the air volume on the back side becomes larger than the near side by changing the direction of the wind direction plate. . The separation air blower blows air from the blower fan after the paper starts to pass through the fixing nip until the paper passes.
5. The image forming apparatus according to claim 1, wherein the control unit causes the air volume distribution changing unit to change the air volume distribution at a timing at which a sheet starts to pass through the fixing nip. The fixing device includes a plurality of temperature sensors that detect the temperature of the fixing member at different positions in the rotation axis direction,
The said control part controls the said air volume distribution change part based on the temperature distribution of the rotating shaft direction of the said fixing member obtained by the detection result of the said temperature sensor, The any one of Claims 1-5. The image forming apparatus described in 1. The control unit estimates the temperature distribution in the rotation axis direction of the fixing member from the amount of electric power supplied to the heating unit and the amount of exhaust from the exhaust port, and changes the air volume distribution based on the estimated temperature distribution The image forming apparatus according to claim 1, wherein the image forming apparatus controls the unit.