JP6123439B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method for thermally fixing a toner image formed on a sheet.

An image forming apparatus such as a printer normally forms a toner image on a sheet for each sheet, heats the formed toner image to a sheet by heat of a fixing device, and then discharges the sheet. In this configuration, the paper is loaded and stored on the discharge tray.
In this way, when a plurality of sheets after heat fixing are stacked and accommodated on the discharge tray, the sheets that are still at a high temperature after heat fixing are stuck with the toner softened by the heat. Tacking is likely to occur.

In order to prevent the occurrence of tacking, the heat-fixed sheet may be cooled by blowing air from the fan, but electric power for driving the fan is required separately.
Patent Document 1 discloses a configuration in which a thermoelectric conversion element that generates electricity by heat of a sheet after heat fixing is provided on a discharge tray, and a fan is driven using electric power generated by the thermoelectric conversion element.

JP 2010-49005 A

The technique of Patent Document 1 is intended to prevent the occurrence of tacking by the electric power generated by the thermoelectric conversion element. However, the tacking is likely to occur depending on the image forming conditions, for example, the density of the formed image. , It may become difficult to occur.
That is, an image portion having a high density existing on a sheet has a large amount of toner per unit area, and the amount of toner that is attracted by contact with other sheets increases accordingly, so that the probability of occurrence of tacking increases. On the other hand, when most of the image portion having a low density or an area where no image exists occupies one sheet, the amount of toner that comes into contact with other sheets is smaller than that of the high density. The probability is low.

Therefore, simply supplying the electric power generated by the thermoelectric conversion element to the fan causes insufficient cooling of the seat when tacking is likely to occur, or the electric power generated by the thermoelectric conversion element when tacking is difficult to occur. It will be consumed in vain.
The present invention has been made in view of the above-described problems, and is an image forming apparatus capable of preventing the occurrence of tacking of a sheet after heat fixing and increasing the efficiency of power use by a thermoelectric conversion element. An object is to provide an image forming method.

  In order to achieve the above object, an image forming apparatus according to the present invention forms a toner image on each of a plurality of continuously conveyed sheets, and the respective sheets are formed on the sheets when passing through a fixing unit. An image forming apparatus that heat-fixes the toner image that has been fixed and then discharges and stacks and accommodates the toner image on a discharge tray. The image forming apparatus is disposed downstream of the fixing unit in the sheet conveyance direction and is not thermally supplied. The electric energy generated by the thermoelectric conversion element is converted into electric energy to generate electric power, and when electric power is supplied, the electric energy generated by the thermoelectric conversion element is converted into electric energy to cool the sheet after heat fixing. A first mode in which power is not supplied to the thermoelectric conversion element and a second mode in which power is supplied to the thermoelectric conversion element based on the supplied power supply unit and the image forming execution condition. Characterized in that it comprises control means for controlling switching between de, a.

The power supply unit is a chargeable / dischargeable power storage unit, and in the first mode, the control unit supplies power generated by the thermoelectric conversion element to the power storage unit to charge the power storage unit. In the second mode, the power storage unit may be discharged and the power of the power storage unit may be supplied to the thermoelectric conversion element.
Here, provided with a detection means for detecting the storage voltage of the power storage unit, the control means, in the second mode, when the storage voltage detected by the detection means is lower than a threshold value, Instead of discharging, power from an external power source may be supplied to the thermoelectric conversion element.

The thermoelectric conversion element may be disposed at a position along a sheet conveyance path between the fixing unit and the sheet discharge port.
Here, a roller disposed at the discharge port, the thermoelectric conversion element is disposed opposite to the roller, and absorbs heat energy of the sheet after heat fixing at each of the power generation and the cooling. The sheet after heat fixing may be conveyed between the roller and the heat absorption surface of the thermoelectric conversion element.

Here, the thermoelectric conversion element is fixedly disposed in the apparatus housing, or is formed in a flexible sheet shape, and another roller disposed opposite to the roller with a sheet conveyance path interposed therebetween. It may be provided.
The control unit includes a determination unit that determines, for each of the plurality of sheets, whether to execute the first mode or the second mode based on an image formation execution condition. For each sheet, while the sheet passes between the roller and the endothermic surface of the thermoelectric conversion element, the mode may be switched to the determined mode and executed.

Further, the control means determines whether to execute the first mode or the second mode based on an image formation execution condition for each job when image formation on the plurality of sheets is a single job. A determination means for determining may be provided, and the determined mode may be continuously executed for each job during execution of the job.
The execution condition of the image formation is any one of a density value of a toner image formed on the sheet, a basis weight of the sheet, and the number of sheets continuously conveyed, and the control unit includes the density value, The second mode may be executed when the basis weight or the number of sheets is equal to or greater than a threshold, and the first mode may be executed when the basis weight or the number of sheets is less than the threshold.

  Further, the image forming mode can be executed by switching between a single-side mode in which an image is formed on only one side of the sheet and a double-side mode in which an image is formed on both sides of the sheet. The control means executes the second mode when the image forming mode is the double-sided mode, and the first mode when the image forming mode is the single-sided mode. May be executed.

  The image forming method according to the present invention forms a toner image on each of a plurality of continuously conveyed sheets, and heat-fixes the toner image formed on the sheet when each sheet passes through a fixing unit. After that, the image forming method is executed in the image forming apparatus that discharges and stacks and accommodates on the discharge tray. The image forming apparatus is disposed downstream of the fixing unit in the sheet conveying direction and is not supplied with power. Sometimes a thermoelectric conversion element that converts heat energy of the sheet after heat fixing into electric energy to generate electric power, converts electric energy into heat energy and cools the sheet after heat fixing when supplied with power, and the thermoelectric conversion element The image forming method supplies power to the thermoelectric conversion element based on image forming execution conditions. And executes a step of including a control step of controlling switching the second mode for supplying a power to the first mode and the thermoelectric conversion elements are.

  According to the above, when the execution condition of image formation is, for example, a condition in which tacking is likely to occur, power is supplied to the thermoelectric conversion element in the second mode, and tacking is performed by cooling the sheet after heat fixing. In the case of a condition in which tacking is unlikely to occur, the power generated by the thermoelectric conversion element in the first mode is supplied to the power-supplied supply unit, thereby using the power generated by the thermoelectric conversion element. Efficiency can be improved.

1 is a diagram illustrating an overall configuration of a printer. It is a schematic perspective view which shows the structure of the discharge part of a printer. It is a block diagram which shows the structure of a control part. It is a figure which shows the structure of a cooling circuit. It is a flowchart which shows the content of the switching control by a cooling control part. It is a flowchart which shows the content of the subroutine of mode determination processing. It is a flowchart which shows the content of the switching control which concerns on a modification.

Hereinafter, embodiments of an image forming apparatus and an image forming method according to the present invention will be described by taking a tandem color printer (hereinafter simply referred to as “printer”) as an example.
(1) Overall Configuration of Printer FIG. 1 is a diagram illustrating the overall configuration of the printer 1.
As shown in the figure, the printer 1 forms an image by a well-known electrophotographic system, and includes an image forming unit 10, a feeding unit 20, a fixing unit 30, a duplex conveying unit 40, and an operation unit. 50, a control unit 60, a discharge unit 70, and the like, connected to a network (for example, a LAN) and receiving an instruction to execute a print (print) job from an external terminal device (not shown), the instruction Based on the above, color image formation of yellow (Y), magenta (M), cyan (C) and black (K) is executed. Further, the printer 1 has a function of switching between a single-side mode in which an image is formed only on one side of one sheet and a double-side mode in which an image is formed on both sides of one sheet as an image forming (printing) mode. Also have.

  The image forming unit 10 includes image forming units 11Y to 11K corresponding to Y to K colors, respectively. When an electrostatic latent image is formed on the charged photosensitive drum 14Y by exposure scanning of the exposure unit 12, the image forming unit 11Y develops the electrostatic latent image with Y-color toner, and develops it. The Y toner image is primarily transferred to the intermediate transfer belt 13. Here, exposure scanning on the photosensitive drum 14Y is performed so that gradation is reproduced by changing the exposure amount in units of one pixel. When the Y toner in the image forming unit 11Y is reduced by the development, the replenishment unit 16Y supplies the replenishment Y color toner.

  The other image forming units 11M, 11C, and 11K also perform the same processes of charging, exposure, development, and primary transfer as the image forming unit 11Y, and intermediate the M color toner image, C color toner image, and K color toner image. Primary transfer is performed on the transfer belt 13. The formation timing of the Y to K color toner images is determined in advance so that the Y to K color toner images are multiplex-transferred on the intermediate transfer belt 13. Further, when the toner in the image forming units 11M to 11K decreases, the replenishing toner is replenished to the corresponding image forming units from the replenishing units 16M, 16C, and 16K.

The Y to K color toner images transferred on the intermediate transfer belt 13 are transferred to the secondary transfer roller 24 disposed opposite to the intermediate transfer belt 13 at the secondary transfer position 241 as the intermediate transfer belt 13 rotates. Are transported.
The feeding unit 20 feeds the sheet P as a recording sheet from the sheet feeding cassette 21 to the sheet conveyance path 25 one by one by the pickup roller 22 and conveys the sheet P to the registration roller pair 23.

The registration roller pair 23 allows the paper P to reach the secondary transfer position 241 when the Y to K color toner images transferred onto the intermediate transfer belt 13 by primary transfer reach the secondary transfer position 241. In addition, the timing for sending the paper P toward the secondary transfer position 241 is taken.
When the paper P conveyed by the registration roller pair 23 passes the secondary transfer position 241, the Y to K color toner images on the intermediate transfer belt 13 are secondarily transferred to the paper P by the secondary transfer roller 24. The The residual toner remaining on the intermediate transfer belt 13 without being secondarily transferred onto the paper P is removed from the intermediate transfer belt 13 by the cleaner 15.

  The fixing unit 30 includes a fixing roller and a pressure roller. The fixing roller is maintained at a fixing temperature necessary for fixing, for example, 180 [° C.], and the sheet P that has passed the secondary transfer position 241 is transferred to the fixing roller. When the toner passes through a nip secured between the pressure roller and the pressure roller, each color toner image is thermally fixed to the paper P by heating and pressure. The paper P after passing through the fixing unit 30 is conveyed to the discharge unit 70.

The discharge unit 70 includes a discharge roller 71, a thermoelectric conversion element 72, and the like that are opposed to each other with the paper transport path 25 for the paper P interposed therebetween.
FIG. 2 is a schematic perspective view showing the configuration of the discharge unit 70, and shows a state where the paper P is conveyed between the discharge roller 71 and the thermoelectric conversion element 72.
As shown in the drawing, the discharge roller 71 is formed by laminating an elastic member such as rubber around the rotation shaft 711, and both ends of the rotation shaft 711 are provided with a compression spring 73 provided between the device housing 75. In response to the force, the thermoelectric conversion element 72 is energized.

  The thermoelectric conversion element 72 converts the heat energy absorbed from the heat absorption surface 721 into electric energy when generating electric power (Seebeck effect), and generates electric energy when receiving electric power. It is an element capable of switching a cooling function (Peltier effect) for converting into heat energy and forcibly reducing the temperature of the heat absorption surface 721. It should be noted that the heat absorption surface 721 remains on the cooling side regardless of power generation by the Seebeck effect or cooling by the Peltier effect, but in order to distinguish this, hereinafter, power generation and cooling will be referred to. The switching control between the power generation and cooling operations by the thermoelectric conversion element 72 will be described later.

The thermoelectric conversion element 72 is formed in a long plate shape along the rotation shaft 711 of the discharge roller 71, and the heat absorption surface 721 faces the discharge roller 71 side (in other words, the heat dissipation surface faces the opposite side). Posture), and is disposed to face the discharge roller 71.
The thermoelectric conversion element 72 is fixedly disposed on the apparatus housing 75, and the discharge roller 71 is pressed against the heat absorption surface 721 of the thermoelectric conversion element 72 by the urging force of the compression spring 73.

When the paper P passes between the peripheral surface of the discharge roller 71 and the heat absorption surface 721 of the thermoelectric conversion element 72, the rotational driving force of the discharge roller 71 is transmitted to the paper P as a transport force, and the paper P is transported in the paper transport direction. During the conveyance, the heat of the sheet P is absorbed from the heat absorbing surface 721 of the thermoelectric conversion element 72 when the heat-fixed sheet P contacts the heat absorbing surface 721 of the thermoelectric conversion element 72.
In the above description, the discharge roller 71 is biased toward the thermoelectric conversion element 72. However, the configuration is not limited thereto. For example, it can also be set as the structure which urges | biases one or both of the discharge roller 71 and the thermoelectric conversion element 72 in the direction which approaches relatively. Any structure may be used as long as the sheet P after heat fixing can be conveyed by the rotational force of the discharge roller 71 and the heat of the sheet P can be absorbed from the heat absorption surface 721 of the thermoelectric conversion element 72.

Returning to FIG. 1, in the single-sided mode, the discharge roller 71 rotates in the direction of the arrow indicated by the solid line, conveys the paper P after heat fixing, and the paper P that has passed through the discharge roller 71 passes through the discharge port 78. It is discharged outside and accommodated on a discharge tray 79.
In the double-side mode, the paper P after thermal fixing (the paper on which image formation has been performed on the first surface (front surface)) is switched back by the discharge unit 70, and the rear end in the transport direction of the paper P is first. In this state, the paper is fed into the double-sided conveyance unit 40. The switchback of the paper P is performed when the discharge roller 71 reverses from the rotation direction indicated by the solid line to the rotation direction indicated by the broken line. The reverse rotation of the discharge roller 71 is performed by reversely driving a motor (not shown) in the discharge unit 70 that rotationally drives the discharge roller 71.

The paper P sent to the double-sided conveyance unit 40 is conveyed toward the registration roller pair 23 along the double-sided conveyance path 41 by the double-sided conveyance roller pairs 4a, 4b, 4c, and 4d. In parallel with the conveyance of the paper P by the double-sided conveyance unit 40, the image forming unit 10 starts a toner image forming operation to be formed on the second surface (back surface) of the paper P.
The sheet P is transferred from the double-sided conveyance unit 40 via the registration roller pair 23 so that the respective color toner images multiplex-transferred onto the intermediate transfer belt 13 in the image forming unit 10 reach the secondary transfer position 241. It is conveyed toward the transfer position 241.

When the paper P passes through the secondary transfer position 241, each color toner image on the intermediate transfer belt 13 is secondarily transferred to the back surface of the paper P, and when the paper P after the secondary transfer passes through the fixing unit 30. Each color toner image secondarily transferred to the back surface of the paper P is thermally fixed.
The paper P (after double-sided printing) that has passed through the fixing unit 30 is discharged from the discharge port 78 to the outside by the discharge unit 70 and is stored on the discharge tray 79.

In the single-sided mode and the double-sided mode, when a plurality of sheets P are continuously passed one by one at intervals, after the images are sequentially formed on the respective sheets P, the plurality of sheets P are It is loaded and accommodated on the discharge tray 79.
The operation unit 50 is arranged on the front side of the apparatus at a position where the user can easily operate. The operation unit 50 includes keys for accepting an operation input from the user, for example, a selection key for selecting a single-sided or double-sided printing mode, and a sheet set in the paper cassette 21. There are provided setting keys for setting paper information such as the size (A4, B4, etc.) and type (plain paper, thick paper, thin paper, etc.) of P, and the basis weight of paper P. The user can select a mode, input a paper size, and the like by operating each key. Information input by the user is sent from the operation unit 50 to the control unit 60.

If the print job data from the external terminal device includes information indicating whether the job should be executed in one-sided or double-sided mode, the configuration is such that the mode to be executed is switched according to the information. Very good.
A paper detection sensor 32 for detecting the paper P to be transported is disposed at a position along the paper transport path 25 between the fixing unit 30 and the discharge unit 70. The paper detection sensor 32 can be, for example, a reflective optical sensor, but is not limited to this, and other methods such as a transmissive optical sensor may be used. By detecting the leading and trailing ends of the transported sheet P in the transport direction, the sheet detection sensor 32 detects the transport position on the sheet transport path 25 of the sheet P transported downstream of the fixing unit 30 in the sheet transport direction. Can be detected. A detection signal from the paper detection sensor 32 is sent to the control unit 60.

(2) Configuration of Control Unit FIG. 3 is a block diagram illustrating a configuration of the control unit 60.
As shown in the figure, the control unit 60 includes a communication interface (I / F) unit 61, a CPU 62, a ROM 63, a RAM 64, an image memory 65, a cooling control unit 66, and the like as main components. Each unit can exchange signals and data with each other.

  The communication I / F unit 61 is an interface such as a LAN card or a LAN board for connecting to a network, here a LAN, and receives print job data sent from an external terminal via the LAN, and receives an image memory 65 is stored. The print job data includes header information including the number of pages, the number of print copies, the number of sheets, and the like in addition to image data including gradation values for each pixel.

The ROM 63 stores a program for executing a print job.
The CPU 62 reads a necessary program from the ROM 63, controls the image forming unit 10, the feeding unit 20, and the like, and performs print jobs in the single-side mode and double-side mode based on the print job data stored in the image memory 65. Let it run.
The RAM 64 is a work area for the CPU 62.

The cooling control unit 66 switches and controls power generation and cooling by the thermoelectric conversion element 72 via the cooling circuit 80 based on the image forming execution condition. Hereinafter, the configuration of the cooling circuit 80 and the contents of the switching control by the cooling control unit 66 will be described in order.
(3) Configuration of Cooling Circuit FIG. 4 is a diagram showing the configuration of the cooling circuit 80.

As shown in the figure, the cooling circuit 80 includes a charging DC / DC converter 81, a discharging DC / DC converter 82, switching elements 83, 84, 85, 86, 87, a secondary battery 88, and a voltage. A total 89 and diodes 90, 91, and 92 are provided, and are roughly composed of three circuits 801 to 803.
The circuit 801 includes a switch element 83, a charging DC / DC converter 81, a diode 90, a switching element 85, a discharging DC / DC converter 82, and a diode 91 connected in series. The circuit 802 includes switch elements 84 and 86 and a diode 92 connected in series. The circuit 803 includes a switch element 87 and a secondary battery 88 connected in series.

The circuits 801 and 802 are connected in parallel, and a portion between the diode 90 and the switch element 85 in the circuit 801 and a portion between the switch elements 84 and 86 in the circuit 802 are connected via the circuit 803. Yes.
Each of the charging DC / DC converter 81 and the discharging DC / DC converter 82 is a transformer having a boosting circuit that boosts and outputs an input DC voltage to a predetermined value.

The secondary battery 88 is a chargeable / dischargeable power storage unit, for example, a lithium ion battery.
The voltmeter 89 is detection means for detecting the voltage (storage voltage) of the secondary batteries 88 connected in parallel, and sends the detected value to the cooling control unit 66.
The switch elements 83 to 86 are single throw switches and switch between opening and closing of the circuit. The switch element 87 is a double throw switch, and switches between a state where the circuits 801 and 802 are connected via the secondary battery 88 and a state where the circuit 801 and 802 are connected via the external power source 99. The switch elements 83 to 87 are switched to switching instructions from the ports P1 to P5 of the cooling control unit 66.

The external power source 99 is a DC power source obtained by stepping down an AC voltage (100 V or the like) of a commercial power source to a DC voltage (24 V or the like) by a power circuit (not shown) provided in the printer 1, for example.
The circuits 801 and 802 are connected in parallel. One end of the circuit 804 connected in parallel is connected to the external terminal 722 connected to the P-type semiconductor element of the thermoelectric conversion element 72, and the other end of the circuit 804 is connected. Is connected to an external terminal 723 connected to the N-type semiconductor element of the thermoelectric conversion element 72.

  In the thermoelectric conversion element 72, P-type semiconductor elements and N-type semiconductor elements are alternately connected, and when the electric power is not supplied from the outside, the temperature is high on the high temperature side (heat absorption side) and low temperature side (heat dissipation side). When a difference occurs, a voltage is generated so that current flows in a direction in which holes of the P-type semiconductor element and electrons of the N-type semiconductor element move from the high temperature side to the low temperature side due to the Seebeck effect, that is, the endothermic surface. The heat energy absorbed from 721 can be converted into electric energy to generate electricity. The heat absorbing surface 721 is a surface facing the conveyance path 25 side of the paper P after heat fixing as described above. When the paper P after heat fixing passes through the thermoelectric conversion element 72, the heat absorption surface 721 is caused by heat at the time of fixing. The heat of the sheet P that is still at high temperature naturally moves to the heat absorbing surface 721, so that the heat of the sheet P is absorbed and the thermoelectric conversion element 72 generates power.

  On the other hand, when a DC voltage is supplied to the thermoelectric conversion element 72 from the P-type semiconductor element to the N-type semiconductor element so that a current in the same direction as during power generation flows, the Peltier effect causes the heat absorption side and the heat dissipation side to A temperature difference is generated between them, the heat absorption side is cooled, and the heat dissipation side generates heat. That is, the thermoelectric conversion element 72 can convert electric energy into heat energy and forcibly reduce the temperature of the heat absorbing surface 721. Thereby, cooling by the thermoelectric conversion element 72 is performed.

  In such a configuration, when the switch elements 83 and 86 are closed (ON), the switch elements 84 and 85 are opened (OFF), and the switch element 87 is switched to the secondary battery side (the state in the figure), the thermoelectric conversion element 72. To the thermoelectric conversion element 72 through the switching element 83, the charging DC / DC converter 81, the diode 90, the switching element 87, the secondary battery 88, the switching element 86, and the diode 92.

  When this circuit is formed, when the electric power of the secondary battery 88 is not supplied to the thermoelectric conversion element 72 and the thermoelectric conversion element 72 is in the power generation state, the DC power generated by the power generation is supplied to the charging DC via the switch element 83. After being input to the DC / DC converter 81 and boosted to the voltage necessary for charging the secondary battery 88 by the charging DC / DC converter 81, the boosted DC power is supplied to the secondary battery 88. The secondary battery 88 is charged (charging of the secondary battery 88).

On the other hand, when the switch elements 83 and 86 are opened, the switch elements 84 and 85 are switched to close, and the switch element 87 is on the secondary battery side, the secondary battery 88, the switch elements 87 and 85, and the DC / DC for discharging. A circuit that returns to the secondary battery 88 through the converter 82, the diode 91, the thermoelectric conversion element 72, and the switch element 84 is formed.
When this circuit is formed, if the voltage of the secondary battery 88 is equal to or higher than a predetermined value (here, the threshold value Vth), the DC power of the secondary battery 88 is supplied via the switch elements 87 and 85 to the DC / DC for discharging. After being input to the DC converter 82 and boosted by the discharge DC / DC converter 82 to a voltage required for cooling by the thermoelectric conversion element 72, the DC power after the boost is supplied to the thermoelectric conversion element 72 via the diode 91. (Discharge of the secondary battery 88). Thereby, cooling by the thermoelectric conversion element 72 which received the electric power supply of the secondary battery 88 is performed.

Since the cooling by the thermoelectric conversion element 72 is cooling by the Peltier effect, the temperature of the endothermic surface 721 of the thermoelectric conversion element 72 is drastically lowered, and compared with a case where heat is absorbed by natural heat transfer due to the Seebeck effect, after heat fixing. The amount of heat transferred (absorbed) per unit time from the sheet P to the thermoelectric conversion element 72 becomes much larger, and the temperature of the sheet P can be further reduced.
If the voltage of the secondary battery 88 is lower than the threshold value Vth, the switch element 87 is connected to the external power supply side because the voltage required for cooling by the thermoelectric conversion element 72 does not reach even if the voltage is boosted by the discharge DC / DC converter 82. And the discharge of the secondary battery 88 is stopped.

The electric power from the external power source 99 is supplied to the thermoelectric conversion element 72 via the switch elements 87 and 85, the discharging DC / DC converter 82, and the diode 91. Even when the charging capacity of the secondary battery 88 is small, the thermoelectric conversion element 72 can be cooled by the electric power of the external power source 99 to cool the paper P after being thermally fixed during conveyance. Note that the threshold value is determined in advance by experiments or the like.
Thus, by the opening / closing control of the switch elements 83 to 87 constituting the cooling circuit 80, the thermoelectric conversion element 72 generates power (charges the secondary battery 88) and cools (discharges the secondary battery 88 or supplies the external power source 99). Can be switched. Power generation by the thermoelectric conversion element 72 is referred to as a first mode, and cooling by the thermoelectric conversion element 72 is referred to as a second mode. This mode switching is controlled by a cooling control unit 66 based on job execution conditions (toner density of a formed image). Is done.

(4) Switching Control by Cooling Control Unit FIG. 5 is a flowchart showing the contents of switching control by the cooling control unit 66, and the switching control is executed for each job.
First, a mode determination process is executed (step S1).
FIG. 6 is a flowchart showing the contents of the subroutine of the mode determination process.

As shown in the figure, an image density value A is acquired (step S31). This image density value A is a value obtained by integrating the gradation values of all the pixels constituting the formed image area for each sheet of paper P to be printed.
Here, the gradation value is, for example, 256 gradations per pixel, and the value becomes higher as the density becomes higher. Therefore, the higher the image density value A, the higher the density image exists. become. The image density value A is acquired as follows.

(A) Of the image data stored in the image memory 65, the gradation value of each pixel of the image data used for printing the job is acquired in units of one page. Here, it is assumed that an image of the page is formed on one sheet of paper P for each page.
(B) For each page, the sum of the gradation values of each pixel of the formed image is used as the image density value A for the page. For example, the image density value A of the image to be formed is acquired for each page, that is, for each sheet of paper, such that the image density value A is A1 for the first page and A2 for the first page.

If it is determined that there is at least one sheet whose image density value A is greater than or equal to the threshold value A0 among the two or more sheets P to be printed ("YES" in step S32), the mode to be executed is the second mode. The mode is determined (step S40), and the process returns. This is done for the following reason.
That is, as the image density value A increases, the density of high-density image areas increases. As the density of high-density image areas increases, the probability that tacking will occur when the heat-fixed sheets P are stacked and accommodated on the discharge tray 79. Becomes higher.

  Therefore, in the present embodiment, based on the relationship between the image density value A and the occurrence of tacking, an experiment is performed in advance with the magnitude of the image density value A that is assumed to cause tacking when the image density value A is greater than a certain value as a threshold value A0. If the image density value A is greater than or equal to the threshold value A0 among a plurality of sheets P that are continuously passed in the job, the second mode is determined to prevent tacking. To do.

If it is determined that the image density value A is smaller than the threshold value A0 (“NO” in step S32), the number of sheets B of the job is acquired (step S33).
The number of sheets B is acquired from the header information among the job data stored in the image memory 65. When the number of sheets B is not included in the header information, the number of sheets B may be a value obtained by multiplying the number of pages by the number of copies.

If it is determined that the number of sheets B is equal to or greater than the threshold B0 (“YES” in step S34), the mode to be executed is determined to be the second mode (step S40), and the process returns. This is due to the following reason.
That is, as the number of sheets B increases, the thickness of the sheet bundle when the sheet P after heat fixing is stacked and accommodated on the discharge tray 79 becomes thicker, and the heat of each sheet P is more likely to be trapped in the sheet bundle. Even if the image density value is small, the probability that tacking will occur increases.

Accordingly, as in the case of the image density value A described above, the second mode is obtained when the number of sheets B on which the occurrence of tacking is assumed is determined as a threshold value B0 from an experiment in advance and the number of sheets B in the job is equal to or greater than the threshold value B0. This is because it is possible to prevent the occurrence of tacking.
If it is determined that the number of sheets B is less than the threshold B0 (“NO” in step S34), the basis weight C of the sheet P used in the job is acquired (step S35).

Acquisition of the basis weight C of the sheet P is performed by acquiring the basis weight information of the sheet P stored in the sheet feeding cassette 21 set and input from the operation unit 50 by the user.
If it is determined that the basis weight C is equal to or greater than the threshold C0 (“YES” in step S36), the mode to be executed is determined to be the second mode (step S40), and the process returns. This is due to the following reason.

That is, as the basis weight C of the paper P increases, the heat capacity of the paper P increases, and the amount of heat of the paper bundle of the paper P after heat fixing that is stacked and accommodated on the discharge tray 79 increases. Even when the number of sheets is small or the number of sheets is small, the probability of occurrence of tacking is increased.
Accordingly, as in the case of the image density value A, when the basis weight C of the paper P to be used is equal to or greater than the threshold value C0, the basis weight C that is assumed to cause tacking is determined as a threshold value C0 in advance through experiments. This is because it is possible to prevent the occurrence of tacking if the second mode is determined.

If it is determined that the basis weight C is smaller than the threshold value C0 (“NO” in step S36), the print mode executed in the job is acquired (step S37).
If it is determined that the print mode is the duplex mode (“YES” in step S38), the mode to be executed is determined to be the second mode (step S40), and the process returns. This is due to the following reason.

  That is, in the single-sided mode, the paper P passes through the fixing unit 30 only once to form an image on only one side of the paper P. However, in the double-sided mode, one paper P is used to form an image on both sides of the paper P. Passes through the fixing unit 30 twice, and the amount of heat supplied to the paper P becomes larger than that in the single-sided mode. In addition to this, when images are formed on both sides of the paper P, the toner formed on the lower surface of the upper paper P of the two papers P that overlap vertically when stacked on the discharge tray 79. This is because the image and the toner image formed on the upper surface of the lower paper P often come into contact with each other, so that the probability of occurrence of tacking increases accordingly.

If it is determined that the mode is the single-sided mode (“NO” in step S38), the mode to be executed is determined to be the first mode (step S39), and the process returns. From this, the mode to be executed is determined to be the first mode when the image density value A <A0, the number of sheets B <B0, the basis weight C <C0, and the single-sided mode. It is determined that the mode is two.
Returning to FIG. 5, in step S <b> 2, it is determined whether or not the leading edge of the first sheet P in the transport direction has been detected by the sheet detection sensor 32.

When the detection of the first sheet P is determined (“YES” in step S2), it is determined whether or not the mode determined in the mode determination process is the first mode (step S3).
When it is determined that the mode is the first mode (“YES” in step S3), switch control for generating a charging circuit for the secondary battery 88 is executed (step S4). The charging circuit for the secondary battery 88 is generated by switching the switch elements 83 and 86 of the cooling circuit 80 ON (closed), switching the switch elements 84 and 85 OFF (open), and switching the switch element 87 to the secondary battery side. .

Thereby, in a state where the electric power of the secondary battery 88 is not supplied to the thermoelectric conversion element 72, each sheet P after the heat fixing in the first sheet and after passes between the discharge roller 71 and the heat absorbing surface 721 of the thermoelectric conversion element 72. Each time the heat of the paper P is absorbed from the heat absorbing surface 721, power is generated by the thermoelectric conversion element 72, and the secondary battery 88 is charged with the generated power.
Then, it is determined whether or not the last sheet P by the job has passed the thermoelectric conversion element 72 (step S5). This determination is made after a predetermined time has elapsed since the image formation on all the sheets P indicated by the number of sheets B has been completed and the trailing edge of the last fed sheet P is detected by the sheet detection sensor 32. It is done depending on whether or not. The predetermined time corresponds to a time obtained by dividing the distance from the position detected by the paper detection sensor 32 on the paper transport path 25 to the downstream end of the thermoelectric conversion element 72 in the paper transport direction by the transport speed.

  When it is determined that the last sheet P has passed through the thermoelectric conversion element 72 (“YES” in step S5), all the switch elements 83 to 86 of the cooling circuit 80 are turned OFF (open) (step S6), and the process is performed. finish. As a result, regardless of whether or not each sheet P is passing through the thermoelectric conversion element 72, the first mode is continuously executed as it is without being switched to the second mode during job execution. .

On the other hand, when it is determined that the mode is not the first mode but the second mode (“NO” in step S3), the current voltage Vb of the secondary battery 88 is detected (step S7). This detection is performed by a voltmeter 89.
It is determined whether or not the detected voltage Vb of the secondary battery 88 is equal to or higher than the threshold value Vth (step S8). The threshold value Vth is a value that is determined in advance by experiments or the like as a minimum voltage value required for cooling by the thermoelectric conversion element 72.

  When it is determined that voltage Vb ≧ threshold value Vth (“YES” in step S8), switch control for generating a discharge circuit of the secondary battery 88 is executed (step S9), and the process proceeds to step S5. The discharge circuit of the secondary battery 88 is generated by switching the switch elements 83 and 86 of the cooling circuit 80 to OFF (open), switching elements 84 and 85 to ON (closed), and switching the switch element 87 to the secondary battery side. .

Thereby, the electric power of the secondary battery 88 is supplied to the thermoelectric conversion element 72, and cooling by the thermoelectric conversion element 72 that receives the electric power supply is started.
With the start of cooling by the thermoelectric conversion element 72, the temperature of the heat absorbing surface 721 is drastically decreased, and each sheet P after heat fixing on the first and subsequent sheets passes between the discharge roller 71 and the heat absorbing surface 721 of the thermoelectric conversion element 72. While passing, more heat is accumulated in each paper P than during power generation due to the Seebeck effect, and each paper P is sufficiently cooled to a temperature at which tacking does not occur and then discharged, It is accommodated on the discharge tray 79.

Since each of the plurality of continuously conveyed sheets P is cooled by the Peltier effect of the thermoelectric conversion element 72 that is supplied with power immediately before being discharged to the discharge tray 79, image formation can be performed under conditions where tacking is likely to occur. Even when executed, it is possible to prevent the occurrence of tacking in a plurality of sheets P stacked and accommodated on the discharge tray 79.
When it is determined that voltage Vb <threshold value Vth (“NO” in step S8), switch control for generating a supply circuit for the external power source 99 is executed (step S10), and the process proceeds to step S5. The supply circuit of the external power supply 99 is generated by turning off the switch elements 83 and 86 of the cooling circuit 80 (open), turning on the switch elements 84 and 85 (closed), and switching the switch element 87 to the external power supply side. By the processing after step S5, the second mode is continuously executed as it is without being switched to the first mode during job execution.

Thereby, since the electric power of the external power source 99 is supplied to the thermoelectric conversion element 72 instead of the secondary battery 88, cooling by the thermoelectric conversion element 72 is executed even if the secondary battery 88 is insufficiently charged. And the occurrence of tacking can be prevented.
As described above, in the present embodiment, power generation by the thermoelectric conversion element 72 (first mode in which no power is supplied to the thermoelectric conversion element 72) and cooling (power is supplied to the thermoelectric conversion element 72) based on the execution conditions for image formation. Switching to the second mode), in the case where it is difficult to generate tacking, the secondary battery 88 is charged by the power generation of the thermoelectric conversion element 72 and the power is reused separately to improve efficiency. In the case where the conditions are such that tacking is likely to occur, the sheet P can be forcibly cooled by applying power to the thermoelectric conversion element 72 to prevent the occurrence of tacking.

  In the above description, the configuration example in which the image density value A, the number of sheets B, the sheet basis weight C, and the print mode (single-sided or double-sided mode) are used as the image forming execution conditions has been described. Absent. Any one or a plurality of them can be used depending on the cause of the occurrence of tacking. For example, when the probability of tacking does not change due to a slight difference in the number of sheets or basis weight, the mode may be switched using only the image density value A.

Further, although the image density value A is the sum of the gradation values (integrated value), the present invention is not limited to this, and it can also be regarded as the maximum density value of the portion where the density is maximum in the toner image existing on the sheet.
Furthermore, the execution condition may be the size of the image area on one sheet P, for example. The larger the image area, that is, the toner image formation area, the more the area where the sheets that overlap vertically when stacked on the discharge tray 79 are in contact with the widened toner image may become more likely to be caught. It is. Furthermore, other execution conditions that may cause the occurrence of tacking may be used.

  The present invention is not limited to an image forming apparatus, and may be an image forming method that performs the switching control described above. The method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.
(1) In the above embodiment, power generation and cooling by the thermoelectric conversion element 72 are controlled to be switched based on the image formation execution condition for each job. However, the present invention is not limited to this. For example, two or more sheets that are continuously passed are used. It is also possible to adopt a configuration in which switching control is performed for S in units of one sheet.

FIG. 7 is a flowchart showing the contents of the switching control according to this modification.
As shown in the figure, first, a variable n is set to 1 (step S51). This variable n indicates the number of sheets P.
The mode determination process is performed on the nth sheet, here the first sheet P (step S52).
This mode determination process is basically the same as the mode determination process (step S1) of FIG. 5 described above, but differs in that the mode determination is performed for only one sheet P. For example, if the image density value is A, the image density value A of the image to be formed on the first sheet P is acquired, and if the basis weight is C, the basis weight of the first sheet P is acquired. The As the thresholds A0 and C0, values suitable for one sheet P are determined in advance. Note that the determination process of the number of sheets B (steps S33 and S34) is deleted.

  When the leading edge of the first sheet P in the transport direction is detected (“YES” in step S53), if the determined mode is the first mode (“YES” in step S54), the secondary battery 88 is charged. Switch control for generating a circuit is executed (step S55). As a result, while the first sheet P passes through the thermoelectric conversion element 72, the secondary battery 88 is charged by executing power generation by the thermoelectric conversion element 72.

It is determined whether or not the rear end in the transport direction of the first sheet P has passed through the thermoelectric conversion element 72 (step S56). This determination is performed by the same method as the determination by the process of step S5.
If it is determined that the first sheet P has passed through the thermoelectric conversion element 72 (“YES” in step S56), if it is not the last sheet (“NO” in step S57), the current variable n is “1”. Is incremented, here n = “2” (step S58), and the process returns to step S52.

In step S52, mode determination processing for the second sheet P is performed.
If the second sheet P is detected (“YES” in step S53) and the first mode is determined for the second sheet P (“YES” in step S54), the same steps as above are performed. The process after S55 is executed. In addition, when the charging circuit of the secondary battery 88 is produced | generated at this time, the charging circuit is continued.

  On the other hand, when the second mode is determined (“NO” in step S54), the current voltage Vb of the secondary battery 88 is detected (step S60), and if Vb ≧ Vth (“ YES ”), switch control for generating a discharge circuit for the secondary battery 88 is executed (step S62). If Vb <Vth (“ NO ”in step S61), switch control for generating a supply circuit for the external power source 99 is performed. Is executed (step S65).

As a result, the second sheet P is switched to the second mode, and while the second sheet P passes through the thermoelectric conversion element 72, the power of the secondary battery 88 or the external power source 99 is changed to the thermoelectric power. By being supplied to the conversion element 72, cooling by the thermoelectric conversion element 72 is executed.
If it is determined that the rear end in the transport direction of the second sheet P has passed through the thermoelectric conversion element 72 (“YES” in step S63), all the switch elements 83 to 86 are turned off (step S64), and the process proceeds to step S57. Move. If it is determined in step S57 that it is not the last, “1” is incremented to the current variable n (= 2), here n = “3” (step S58), and the process returns to step S52.

The processes in and after step S52 are repeatedly executed for each sheet of n (= 3) and subsequent sheets, and when the end is determined (“YES” in step S57), all the switch elements 83 to 86 are turned off (steps). S59), the process ends.
As described above, if the configuration is such that the first mode and the second mode are switched and controlled for each sheet during job execution, power generation and cooling by the thermoelectric conversion element 72 is performed for each sheet based on the image forming execution conditions. Can be switched. Thereby, power is supplied to the thermoelectric conversion element 72 only for the paper P that needs to be cooled by, for example, the thermoelectric conversion element 72 among the plurality of sheets P, and the thermoelectric conversion element 72 is supplied to the other paper P. Can generate electricity.

Electric power is supplied from the secondary battery 88 to the thermoelectric conversion element 72 only when necessary to prevent the occurrence of tacking, and at other times, the secondary battery 88 can be charged with the electric power generated by the thermoelectric conversion element 72. . It is possible to increase the charging opportunities of the secondary battery 88 while preventing the occurrence of tacking, and to more effectively use the electric power generated by the thermoelectric conversion element 72.
In the above description, when the nth sheet P for which the second mode is determined passes through the thermoelectric conversion element 72 (“YES” in step S63), the switch elements 83 to 86 are turned off (step S64). However, it is not limited to this.

For example, even if the nth sheet P passes through the thermoelectric conversion element 72, the discharge circuit of the secondary battery 88 or the supply circuit of the external power source 99 is continued as it is, and the (n + 1) th and subsequent sheets conveyed continuously. When the first mode is first determined for the sheet P (“YES” in step S54), the charging circuit of the secondary battery 88 can be switched (step S55).
When the second mode is determined for both the n-th sheet and the (n + 1) -th sheet P, the (n + 1) -th sheet after the n-th sheet P passes through the thermoelectric conversion element 72. There is no need to turn off the switch elements 83 to 86 until the eye paper P is detected, and the processing load on the CPU provided in the cooling control unit 66 is reduced.

(2) In the above-described embodiment, the configuration example in which the external power source 99 is provided separately from the secondary battery 88 as the power supply source to the thermoelectric conversion element 72 has been described, but is not limited thereto. For example, if only the secondary battery 88 is sufficient, and the occurrence of tacking can be prevented without providing the external power source 99, a configuration without the external power source 99 may be employed.
(3) Moreover, although the structural example which uses the electrical component (power-receiving part) to which the electric power generated by the thermoelectric conversion element 72 is supplied as the secondary battery 88 has been described, it is not limited thereto.

For example, when a dehumidifying heater (not shown) for dehumidifying the paper P in the paper feed cassette 21 is provided, the dehumidifying heater and the secondary battery 88 can be used as a power supply unit. Power saving can be achieved as compared with a configuration in which commercial power is supplied to the dehumidifying heater.
Moreover, the structure which does not provide the secondary battery 88 can also be taken. In this configuration, when power is generated by the thermoelectric conversion element 72, the generated power is supplied to the power supply unit such as the dehumidifying heater and used. When cooling by the thermoelectric conversion element 72 is performed, external power is supplied. A configuration in which the power of the power source 99 is supplied to the thermoelectric conversion element 72 can be employed. If the electric power generated by the thermoelectric conversion element 72 is used effectively and the execution condition of image formation is a condition with a high probability of occurrence of tacking, the electric power is supplied to the thermoelectric conversion element 72 even if some power is consumed. Accordingly, it is possible to prevent the occurrence of tacking of the paper P after heat fixing.

(4) In the above-described embodiment, the configuration example in which the plate-like thermoelectric conversion element 72 is fixedly arranged in the apparatus housing 75 has been described. However, the shape and arrangement method of the thermoelectric conversion element 72 are not limited to this, and after heat fixing Any shape and arrangement method that can absorb heat from the other paper P may be used.
For example, when the image forming surface of the paper P in the single-side mode is the front surface and the opposite surface is the back surface, the discharge roller 71 is placed on the back surface side of the paper P and the thermoelectric conversion element 72 is sandwiched with the paper transport path 25 interposed therebetween. The arrangement is arranged on the front side of the paper P, but this can be reversed, that is, the discharge roller 71 can be arranged on the front side of the paper P, and the thermoelectric conversion element 72 can be arranged on the back side of the paper P. .

In addition, a configuration in which the thermoelectric conversion element 72 is replaced by a sheet-like one, specifically a discharge roller 71, and another opposing roller disposed opposite to the paper conveyance path 25 is provided. The thermoelectric conversion element 72 formed in a flexible sheet shape may be provided on the facing roller by sticking or the like.
In this configuration, the opposing roller and the sheet-like thermoelectric conversion element 72 attached thereto rotate as a unit. In this case, a ring-shaped first electrode connected to the external terminal 722 of the thermoelectric conversion element 72 and a ring-shaped second electrode connected to the external terminal 723 of the thermoelectric conversion element 72 are formed on the peripheral surface of the opposing roller, respectively. In addition, by providing a first brush that is rubbed against the first electrode and a second brush that is rubbed against the second electrode, the thermoelectric conversion element 72 and the cooling circuit 80 are interposed via the first brush and the second brush. Can be electrically connected.

(5) In the above embodiment, the configuration example in which the thermoelectric conversion element 72 is provided in the discharge port 78 of the paper P in the printer 1 has been described, but the arrangement position of the thermoelectric conversion element 72 is not limited to this. Any position that is downstream of the fixing unit 30 in the sheet conveyance direction and can absorb heat from the sheet P after heat fixing is acceptable.
For example, the structure arrange | positioned by sticking etc. on the surface (upper surface) or bottom face of the discharge tray 79 can also be taken. By absorbing the heat from the paper P loaded and accommodated on the discharge tray 79, the power generation and cooling by the thermoelectric conversion element 72 can be switched and controlled.

(6) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a tandem type color printer has been described. However, the present invention is not limited to this. It may be an apparatus capable of executing color image formation or an apparatus capable of executing only monochrome image formation.
Any image forming apparatus that forms a toner image on each of a plurality of continuously conveyed sheets and thermally fixes the toner image on each sheet to the sheet when each sheet passes through the fixing unit. The present invention can be applied to a copying machine, a facsimile machine, an MFP (Multiple Function Peripheral), and the like. Further, the cooling circuit 80 is not limited to the above circuit configuration as long as the circuits for charging and discharging the secondary battery 88 and supplying the external power source 99 can be switched.

  The contents of the above embodiment and the above modification may be combined.

  The present invention can be widely applied to an image forming apparatus that thermally fixes a toner image on a sheet.

DESCRIPTION OF SYMBOLS 1 Printer 25 Paper conveyance path 30 Fixing part 50 Operation part 66 Cooling control part 71 Discharge roller 72 Thermoelectric conversion element 75 Apparatus housing 78 Discharge outlet 79 Discharge tray 80 Cooling circuit 88 Secondary battery 89 Voltmeter 99 External power supply 721 Endothermic surface

Claims (11)

A toner image is formed on each of a plurality of sheets that are continuously conveyed, and when each sheet passes through the fixing unit, the toner image formed on the sheet is thermally fixed, and then discharged and discharged to a discharge tray. An image forming apparatus loaded and accommodated on
The sheet is disposed downstream of the fixing unit in the sheet conveyance direction, and when power is not supplied, the thermal energy of the sheet after heat fixing is converted into electric energy to generate electric power, and when supplied with electric power, the electric energy is converted into heat energy to generate heat. A thermoelectric conversion element for cooling the sheet after fixing;
An electric power supply unit to which electric power generated by the thermoelectric conversion element is supplied;
Control means for switching and controlling between a first mode in which power is not supplied to the thermoelectric conversion element and a second mode in which power is supplied to the thermoelectric conversion element, based on execution conditions of image formation;
An image forming apparatus comprising: The power receiving unit is a chargeable / dischargeable power storage unit,
The control means includes
In the first mode,
Supplying electric power generated by the thermoelectric conversion element to the power storage unit to charge the power storage unit;
In the second mode,
The image forming apparatus according to claim 1, wherein the power storage unit is discharged to supply electric power of the power storage unit to the thermoelectric conversion element. A detecting means for detecting a storage voltage of the power storage unit;
The control means includes
In the second mode, when the storage voltage detected by the detection unit is lower than a threshold value, power from an external power source is supplied to the thermoelectric conversion element instead of discharging the storage unit. Item 3. The image forming apparatus according to Item 2. The thermoelectric conversion element is
The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed at a position along a sheet conveyance path between the fixing unit and the sheet discharge port. A roller disposed at the outlet,
The thermoelectric conversion element is
It is disposed opposite to the roller, and has an endothermic surface that absorbs heat energy of the sheet after heat fixing at the time of power generation and cooling,
The sheet after the heat fixing is
The image forming apparatus according to claim 4, wherein the image forming apparatus is conveyed between the roller and a heat absorbing surface of the thermoelectric conversion element. The thermoelectric conversion element is
It is fixedly arranged in the apparatus housing, or is formed in a flexible sheet, and is provided on another roller that is disposed opposite to the roller with a sheet conveyance path interposed therebetween. The image forming apparatus according to claim 5. The control means includes
A determination unit configured to determine which of the first mode and the second mode is to be executed for each of the plurality of sheets based on an image forming execution condition;
7. For each sheet, while the sheet passes between the roller and the endothermic surface of the thermoelectric conversion element, the mode is switched to the determined mode and executed. The image forming apparatus described in 1. The control means includes
A determination unit configured to determine whether to execute the first mode or the second mode based on an image formation execution condition for each job when image formation on the plurality of sheets is a single job;
The image forming apparatus according to claim 5, wherein the determined mode is continuously executed for each job during execution of the job. The execution conditions for the image formation are as follows:
The density value of the toner image formed on the sheet, the basis weight of the sheet, or the number of sheets continuously conveyed,
The control means includes
The said 2nd mode is performed when the said density | concentration value, basic weight, or a number of sheets is more than a threshold value, The said 1st mode is performed when it is less than a threshold value, The any one of Claims 1-8 characterized by the above-mentioned. The image forming apparatus described in 1. It can be executed by switching between a single-sided mode for forming an image only on one side of the sheet and a double-sided mode for forming an image on both sides of the sheet,
The execution conditions for the image formation are as follows:
Whether the image forming mode to be executed is the single-sided mode or the double-sided mode,
The control means includes
9. The method according to claim 1, wherein the second mode is executed when the image forming mode is a double-sided mode, and the first mode is executed when the image forming mode is a single-sided mode. Image forming apparatus. A toner image is formed on each of a plurality of sheets that are continuously conveyed, and when each sheet passes through the fixing unit, the toner image formed on the sheet is thermally fixed, and then discharged and discharged to a discharge tray. An image forming method executed in an image forming apparatus loaded and accommodated on the image forming apparatus,
The image forming apparatus includes:
The sheet is disposed downstream of the fixing unit in the sheet conveyance direction, and when power is not supplied, the thermal energy of the sheet after heat fixing is converted into electric energy to generate electric power, and when supplied with electric power, the electric energy is converted into heat energy to generate heat. A thermoelectric conversion element for cooling the sheet after fixing;
An electric power supply unit to which electric power generated by the thermoelectric conversion element is supplied,
The image forming method includes:
And executing a step including a control step of switching and controlling between a first mode in which power is not supplied to the thermoelectric conversion element and a second mode in which power is supplied to the thermoelectric conversion element, based on execution conditions for image formation. An image forming method.

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