JP6417307B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine, which includes a fixing unit that performs thermal fixing.

  The conventional image forming apparatus cools the center part and the end part in the width direction of the fixing device (see, for example, Patent Document 1).

JP 2007-122044 (paragraphs 0048-0062, FIG. 7-9)

  However, the above-described conventional technique has a problem that depending on the medium width of the medium used for printing, the temperature difference between the passing area and the non-passing area of the medium becomes large, and thus good fixing may not be performed.

In order to solve the above problems, the present invention provides an image forming apparatus in which an image forming unit that forms a developer image on a print medium, a fixing member that heats the developer image on the print medium, and the fixing a pressure member for pressurizing member, the downstream side of the pre-Symbol print medium of the pressing member, wherein are arranged so as to blow air from the pressure member side to the fixing member side across the printing medium, wherein A blowing unit that blows air toward an area of the fixing member that exceeds the minimum width of the print medium and less than the maximum width, and a first temperature detection unit that detects a surface temperature of the fixing member through the print medium. A second temperature detection means for detecting a surface temperature of a non-passage area of the print medium of the fixing member , a medium information acquisition unit for acquiring medium information that is information about the print medium , The surface temperature of the non-passing area of the print medium The so as to keep below a predetermined temperature, and a control unit for controlling the air volume of the blower means, as the air volume of the blower means, a first flow rate to reduce the surface temperature of the non-passing area of the fixing member And a second air volume that gently increases the surface temperature of the non-passage area of the fixing member, and the temperature difference is determined from the detected temperature of the second temperature detecting means by the first temperature detecting means. As a value obtained by subtracting the detected temperature, a first temperature difference and a second temperature difference smaller than the first temperature difference are set, and the control unit adds the medium information acquired by the medium information acquisition unit to the medium information. A printing speed is determined based on the determined printing speed, and the second temperature difference is set based on the determined printing speed. When the temperature difference is equal to or greater than the first temperature difference, the air volume of the blowing unit is set. Switching to the first air volume, the temperature difference is the second temperature. And it switches to the second air volume when it is the following.

  As a result, the present invention can appropriately control the temperature of the medium passing region of the fixing member, and the effect that satisfactory fixing can be performed is obtained.

Explanatory drawing which shows the printer of an Example Explanatory drawing which shows the process unit of an Example Explanatory drawing which shows the paper conveyance path of the supply cassette of an Example. Explanatory drawing which shows the fixing unit of the embodiment Explanatory drawing which shows the temperature detection area | region of the fixing belt of an Example. Block diagram showing the control system of the printer of the embodiment Explanatory drawing which shows the air volume switching process of the fixing unit of an Example Flowchart showing image forming process of printer of embodiment Explanatory drawing which shows temperature distribution at the time of printing of the fixing belt of an Example Explanatory diagram showing temperature distribution depending on the presence or absence of air blowing during printing on the fixing belt Explanatory drawing which shows the effect | action of the ventilation means of an Example. Explanatory drawing which shows the effect | action of the ventilation means of an Example.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

Hereinafter, the printer of this embodiment will be described with reference to FIGS.
A printer 1 as an image forming apparatus according to the present embodiment is an electrophotographic color printer that prints a color image. As shown in FIG. 1, a sheet as a printing medium is provided on one side of the apparatus main body 1a. A supply cassette 1b for storing P is disposed, and a storage cassette 1c for storing printed paper P is disposed on the other side.
The paper P of the present embodiment is a roll paper on which a belt-like paper P as a continuous paper is wound. The paper P is set in a setting unit in the supply cassette 1b, printed in the apparatus main body 1a, and then stored in the storage cassette 1c. Is wound into a roll shape and stored.

  In the apparatus main body 1a, an image forming unit 4 having a process unit 3 for forming a toner image as a developer image of each color is disposed at the upper part thereof, and a toner image formed by the image forming unit 4 at a lower part thereof. A transfer unit 6 as a transfer means for transferring the toner image onto the paper P, and a fixing unit 8 as a fixing means for fixing the toner image transferred onto the paper P by the transfer unit 6 onto the paper P by pressure and heating. Etc. are arranged.

  In the image forming unit 4 of this embodiment, the set colors set to each, that is, special colors (S: white in this embodiment), cyan (C), magenta (M), yellow (Y), black ( K) Five independent process units 3s, 3c, 3m, 3y, and 3k containing toner as a developer are arranged in the order in which toner images are formed, and these five process units 3 have the same structure. Therefore, one process unit 3 will be described below.

As shown in FIG. 2, the process unit 3 includes a photosensitive drum 11 as an image carrier on which an electrostatic latent image is formed, a charging roller 12 that uniformly charges the photosensitive drum 11, and the photosensitive drum 11. A developing roller 13 as a developer carrying member for developing the toner by attaching the toner to the electrostatic latent image, a supply roller 14 for supplying toner to the developing roller 13, a developing blade 15 for thinning the toner on the developing roller, and a set color Toner cartridge 16 containing the toner.
Further, an exposure head 18 as an exposure unit is disposed above each photoconductive drum 11 of each process unit 3 so as to face each other.

The exposure head 18 includes a light emitter composed of an LED (Light Emitting Diode) array. The LED array emits light in accordance with an image data signal, irradiates light on the surface of the photosensitive drum 11, and An electrostatic latent image is formed on the surface.
In the supply cassette 1b, a delivery roller 21, a paper width sensor 22, a paper thickness sensor 23, a cutter unit 24 for cutting the belt-like paper P, and the like are provided.
The feed roller 21 is composed of two rollers arranged opposite to each other so that one roller presses the other roller, and the roll-shaped paper P set in the set portion in the supply cassette 1b is indicated by a broken line in FIG. The paper is sent out from the delivery outlet in the direction of the storage cassette 1c along the paper conveyance path 25.

As shown in FIG. 3, the paper width sensor 22 has a paper guide 27 disposed facing the reference surface 26 in the paper P transport direction (a direction from the supply cassette 1 b toward the storage cassette 1 c, referred to as a paper transport direction). The amount of movement of the rod 22a accompanying the movement in the width direction that is the orthogonal direction is detected, and the sheet width that is the length in the width direction of the sheet P is detected.
The paper guide 27 is a guide member that guides the paper P that is conveyed while being in contact with the other end of the paper P used for printing, with one end being in contact with the reference surface 26, in the width direction of the paper conveyance path 25. It is configured to be movable along the formed guide groove 27a.
FIG. 3 is an arrow view seen from the direction of arrow A in FIG.

The paper thickness sensor 23 is a transmissive optical sensor in which a light emitting portion and a light receiving portion are arranged to face each other with a light transmitting hole 23a provided in the paper conveyance path 25 interposed therebetween, and the paper handled by the printer 1 of this embodiment. P is disposed within the passage area of the minimum width paper P, and the light transmission from the light emitting part that has passed through the paper P is received by the light receiving part, and the paper thickness is detected according to the transmission quantity. Output a signal.
In the following description, among the papers P handled by the printer 1, the passing area of the paper P having the minimum width is the minimum paper passing area, the passing area of the paper P having the maximum width is the maximum paper passing area, and the paper used for printing. The passing area of P is called a paper passing area.

  As shown in FIG. 1, the transfer unit 6 presses a transfer belt 31 as an intermediate transfer body onto which a toner image is transferred and the photosensitive drum 11 of each process unit 3 with a predetermined pressing force with the transfer belt 31 in between. The secondary transfer roller 33a that presses the secondary transfer roller 33b with a predetermined pressing force across the primary transfer roller 32, the transfer belt 31 and the paper P (hereinafter referred to as the secondary transfer roller 33 if it is not necessary to distinguish between them). The transfer belt 31 is stretched between the transfer belt drive roller 31a, the driven roller 31b, and the secondary transfer roller 33a.

The transfer belt 31 is rotationally driven in the belt driving direction (clockwise in FIG. 1) by the transfer belt driving roller 31a, and the toner images formed on the photosensitive drums 11 of the process units 3 by the primary transfer rollers 32 are sequentially formed. Transcribed.
When the toner image transferred to the transfer belt 31 passes through the secondary transfer nip formed by the secondary transfer roller 33a and the secondary transfer roller 33b, the paper P transported by the paper transport path 25 passes through the secondary transfer nip portion. Then, it is transferred onto the paper P by the secondary transfer roller 33.

  The sheet conveyance path 25 of this embodiment includes a plurality of conveyance rollers 35, a plurality of passage detection sensors 36, an entry detection sensor 37a and a discharge detection sensor 37b that detect the entry and exit of the sheet P into and from the fixing unit 8, and a storage cassette. A discharge roller 38 and the like disposed in 1c are provided, and the belt-like sheet P set in the supply cassette 1b and sent out from the delivery port by the delivery roller 21 passes through the secondary transfer nip portion, the fixing unit 8 and the like. And it conveys to the winding-up part of the storage cassette 1c.

Each of the transport rollers 35 and the discharge rollers 38 is composed of two rollers disposed so as to face each other so that one roller presses the other roller.
Each passage detection sensor 36, the entry detection sensor 37a, and the discharge detection sensor 37b are cantilever mechanical sensors, respectively, and detect the passage of the paper P by detecting that the tip of the lever has been pressed on the back surface of the paper P. To do.
The transport roller 35a is disposed in the immediate vicinity of the delivery outlet of the supply cassette 1b on the downstream side in the paper transport direction, and sandwiches the paper P sent out from the feed outlet by the delivery roller 21 and transports it downstream.

The passage detection sensor 36a is arranged in the immediate vicinity of the conveyance roller 35a on the downstream side in the sheet conveyance direction, and detects that the leading edge of the sheet P is held between the conveyance rollers 35a.
The conveyance roller 35b is disposed on the downstream side of the conveyance roller 35a in the sheet conveyance direction, sandwiches the sheet P conveyed from the conveyance roller 35a, and conveys the sheet P to the downstream side.
The passage detection sensor 36b is disposed in the immediate vicinity of the conveyance roller 35b on the downstream side in the sheet conveyance direction, and detects that the leading edge of the sheet P is held between the conveyance rollers 35b.

The conveyance roller 35c is disposed downstream of the conveyance roller 35b in the sheet conveyance direction and upstream of the secondary transfer roller 33. The conveyance roller 35c sandwiches the sheet P conveyed from the conveyance roller 35b and conveys the sheet P to the downstream side.
The passage detection sensor 36c is disposed in the immediate vicinity of the conveyance roller 35c on the downstream side in the sheet conveyance direction, and detects that the leading edge of the sheet P is held between the conveyance rollers 35c.

The transport roller 35d is disposed downstream of the fixing unit 8 in the paper transport direction and upstream of the intake port of the storage cassette 1c. The transport roller 35d receives the printed paper P that has been fixed by the fixing unit 8 from the fixing unit 8. Then, it is conveyed in the direction of the intake port of the storage cassette 1c.
The discharge roller 38 is disposed immediately downstream of the take-in port of the storage cassette 1c in the paper conveyance direction, and is conveyed downstream from the carry roller 35d and sandwiches the printed paper P that has entered from the take-in port to the downstream side. While being transported to the take-up unit, the front end of the unprinted paper P that has entered from the take-in port during the initial setting of the belt-like paper P is put on standby.

As shown in FIG. 4, the fixing unit 8 includes a fixing belt 41 as a fixing member, a pressure belt 42 as a pressure member, a driving roller 43, a pressure roller 44, a support roller 45, a heater 46, a reflection plate 47, An infrared sensor 48 as a first temperature detecting means, a temperature sensor 49 as a second temperature detecting means, and the like are provided.
Further, the fixing unit 8 is provided with a blower unit 53 including a blower 51 and a blower duct 52.

The fixing belt 41 is an endless metal belt made of a thin plate such as a stainless steel plate, and a driving roller 43, a support roller 45a, and the like are disposed inside the fixing belt 41.
The pressure belt 42 is an endless metal belt made of a thin plate such as a stainless steel plate, and a pressure roller 44 and a support roller 45b are disposed inside the pressure belt 42.

The driving roller 43 and the pressure roller 44 are pressed against each other with a predetermined pressing force across the fixing belt 41 and the pressure belt 42, and the support roller 45a and the support roller 45b sandwich the fixing belt 41 and the pressure belt 42. It is pressed with a predetermined pressing force.
As a result, a nip portion is formed by the fixing belt 41 and the pressure belt 42 between the drive roller 43 and the pressure roller 44 and the support roller 45a and the support roller 45b.

Heaters 46a and 46b as heat sources such as halogen heaters and a reflector 47a are arranged inside the fixing belt 41 of this embodiment, and heaters 46c as heat sources such as halogen heaters are arranged inside the pressure belt 42. A reflector 47b is arranged.
The reflection plate 47 is a plate-like member having a reflection surface formed by mirror-treating the surface of a base material such as aluminum. The reflection plate 47a includes heaters 46a and 46b, a drive roller 43, and a support roller 45a. A reflective surface is disposed between the heaters 46a and 46b, and heat rays from the heaters 46a and 46b are reflected on the inner surface of the fixing belt 41 to concentrate heat, and the drive roller 43 and the support roller 45a are not heated. It is configured.

The reflection plate 47b is disposed between the heater 46c, the pressure roller 44, and the support roller 45b with a reflection surface facing the heater 46c, and heat is reflected by reflecting the heat rays from the heater 46c to the inner surface of the pressure belt 42. The pressure roller 44 and the support roller 45b are configured not to be heated while being concentrated.
The infrared sensor 48 is a temperature detection element that detects the surface temperature of the fixing belt 41 in a non-contact manner. In this embodiment, the infrared sensor 48 measures the amount of infrared rays emitted from the measurement object by the thermopile, and A thermopile that detects temperature is used.

The temperature sensor 49 is a temperature detection element that detects the surface temperature of the fixing belt 41 by contact. In the present embodiment, a thermistor is used.
The belt-like paper P of the present embodiment is transported along one end of the paper edge reference regardless of the paper width (referred to as a one-sided transport).
Therefore, as shown in FIG. 5, the infrared sensor 48 is installed in the minimum sheet passing area so as to always measure the surface temperature of the sheet P passing area.

Further, the temperature sensor 49 is installed in the non-sheet passing area outside the maximum sheet passing area (on the side opposite to the sheet edge reference) so as to always measure the surface temperature of the non-passing area of the sheet P.
FIG. 5 shows temperature detection regions of the infrared sensor 48 and the temperature sensor 49 when the fixing unit 8 is viewed from the downstream side in the paper transport direction.
The blowing unit 53 is installed on the downstream side of the fixing unit 8 in the sheet conveyance direction (see FIG. 1).
The blower 51 is an axial fan that linearly blows air from the air inlet toward the blow duct 52.

The blower duct 52 is a duct member that guides the air blown from the blower 51 toward the fixing belt 41, and the blowout port 52 a has a back surface across the sheet P to be conveyed on the pressure belt 42 side. It arrange | positions at the side and it installs so that it may blow toward the fixing belt 41 (refer FIG. 4).
Further, as shown in FIG. 5, the air outlet 52 a of the air duct 52 has an area of the fixing belt 41 (the air blowing area) that exceeds the minimum paper passing area and is less than the maximum paper passing area from the paper edge reference during the one-sided conveyance. (Ie, not facing the minimum sheet passing area on the paper end reference side of the fixing belt 41), but facing the area of the fixing belt 41 within the maximum sheet passing area excluding the minimum sheet passing area. To be installed.

The control system of the printer 1 of this embodiment has the configuration shown in FIG.
The control unit 61 controls each unit of the printer 1 by a command / image processing unit 62, an input / display control unit 63, a sheet information acquisition unit 64, a sheet conveyance control unit 65, an image formation control unit 66, a fixing temperature control unit 67, and the like. To do.
The command / image processing unit 62 is a processing unit that interprets commands and image data received by the communication unit 68 and develops them into bitmap data based on them, and includes a microprocessor, RAM, and hardware for development. Wear.

The communication unit 68 is connected to a host device 70 such as a personal computer or a server via a communication network 69 such as a wired LAN, wireless LAN, USB, or Centronics interface, and a control unit receives a print instruction received from the host device 70. The information from the control unit 61 is transmitted to the host device 70.
The input / display control unit 63 sends the input information from the operation display unit 71 operated by the user to the control unit 61, and also generates display information such as character information for the user to operate based on the input information. Is displayed on the display screen of the operation display unit 71.

The operation display unit 71 is provided on the front surface of the printer 1 and includes a display screen such as an LCD and an input means such as a touch panel. The user setting input screen and the input / display control unit 63 are generated on the display screen. Display information and the like are displayed, and input from the user is received by the input means.
The paper information acquisition unit 64 uses information on the paper P (referred to as paper information) based on user settings such as paper width (media size), paper thickness (media weight), and paper type (media type) based on the operation information of the operation display unit 71. ) And sheet information including the sheet width and sheet thickness detected by the sheet width sensor 22 and the sheet thickness sensor 23, and the sheet information is sent to the control unit 61.

The paper transport control unit 65 controls the transport of the paper P by driving the paper transport mechanism 72 of the paper transport path 25 based on a transport command from the control unit 61 and sends a drive signal to the fixing unit drive control unit 73. Then, the fixing unit driving control unit 73 drives the fixing unit driving mechanism 74 to control the rotation of the fixing belt 41 and the pressure belt 42 related to paper conveyance.
In addition, the paper conveyance control unit 65 outputs a drive signal to the transfer belt drive control unit 75, and the transfer belt drive control unit 75 drives the transfer belt rotation mechanism 76 to control the rotation of the transfer belt 31 related to the paper conveyance. .

The sheet transport mechanism 72, the fixing unit driving mechanism 74, and the transfer belt driving mechanism 76 are configured by an electric motor such as a DC motor or a stepping motor, and a belt and / or a gear train that is rotationally driven by the electric motor.
Further, the control unit 61 controls the paper conveyance control unit 65 so that the paper conveyance control unit 65 conveys the paper P at the corresponding printing speed based on the printing speed read from the printing speed management table 83 described later. .

Based on the image formation command from the control unit 61, the image formation control unit 66 is applied from the high voltage power supply unit 77 to the rollers of each process unit 3 in order to form an image by the electrophotographic process using each process unit 3. To control the voltage.
Based on the surface temperature of the fixing belt 41 detected by the infrared sensor 48, the fixing temperature control unit 67 determines the surface temperature of the sheet passing area of the fixing belt 41 from the control target temperature Tg stored in the storage unit 81 described later. Then, a heater control signal is output to the heater power supply unit 78.

The heater power supply unit 78 supplies electric power supplied from a commercial AC power supply to each heater 46 based on the heater control signal output from the fixing temperature control unit 67.
The air blowing control unit 79 determines whether or not air blowing by the air blowing unit 53 is necessary based on the paper width obtained by the paper information obtaining unit 64, and the fixing detected by the infrared sensor 48 obtained by the fixing temperature control unit 67. Based on the surface temperature of the sheet passing area of the belt 41 and the surface temperature of the non-sheet passing area of the fixing belt 41 detected by the temperature sensor 49, the air volume is switched by the blowing means 53.

The cover opening / closing detection sensor 80 is a mechanical or optical sensor, and detects opening / closing of the cover of the supply cassette 1b that is opened and closed when the user sets the roll-shaped paper P in the supply cassette 1b.
The storage unit 81 stores an image forming processing program executed by the control unit 61, various data used therefor, processing results by the control unit 61, and the like.

  The storage unit 81 also has a control target temperature Tg (180 ° C. in this embodiment) that is a target temperature for controlling the surface temperature of the sheet passing area of the fixing belt 41 and an allowable temperature range (± in this embodiment). 5 ° C.), a large air flow rate difference X as a first temperature difference, which is a temperature difference between the temperature sensor 49 and the temperature detected by the infrared sensor 48 when controlling the surface temperature of the non-sheet passing region of the fixing belt 41. It is preset and stored.

  Further, the storage unit 81 stores a printing speed management table 83 that stores printing speeds set by experiments or the like in association with combinations of paper widths and paper thicknesses. A small air flow rate difference table 84 storing a small air flow rate temperature difference Y as a second temperature difference, which is a temperature difference between the temperature sensor 49 and the infrared sensor 48 when controlling the surface temperature of the sheet passing area. Are stored in advance.

  In the fixing belt 41 of this embodiment, a margin is set so that the temperature of the fixing belt 41 does not exceed the heat-resistant temperature when the device stops urgently due to a device abnormality such as a jam occurring in the printer 1. An upper limit temperature is set as a predetermined temperature. That is, the upper limit temperature is a temperature at which the fixing belt 41 can be prevented from being overheated and damaged if the surface temperature of the fixing belt 41 is kept below the temperature. Set to

The large air flow blast temperature difference X is set from the temperature difference between the upper limit temperature of the fixing belt 41 and the control target temperature Tg. In this embodiment, the heat resistance temperature of the fixing belt 41 is 250 ° C. Since the control target temperature Tg is set to 20 ° C. and the control target temperature Tg is 180 ° C., the upper limit temperature of the fixing belt 41 is set to 230 ° C., and the large air flow rate difference X is set to 50 ° C. (= 230 ° C.−180 ° C.).
In addition, the small air flow blast temperature difference Y is intended to suppress the temperature distribution of the surface temperature of the fixing belt 41 in the sheet passing area, and the temperature of the sheet passing area in the blowing area is the lower limit of the fixing temperature during printing. A temperature difference obtained in advance by experiments or the like so as not to fall below the temperature (= control target temperature Tg−allowable temperature range / 2), and is set for each printing speed.

Below, the printing process by the printer 1 of the present embodiment will be described.
Upon receiving a print instruction from the host device 70 via the communication unit 68, the control unit 61 of the printer 1 sends the image data to the command / image processing unit 62, and the command / image processing unit 62 develops the image data. Processing is performed, and the bitmap data of the image that has undergone the expansion process is sent to the control unit 61, and the control unit 61 temporarily stores the bitmap data in the storage unit 81.

In addition, the control unit 61 starts the warm-up of the fixing unit 8 by the fixing temperature control unit 67 and simultaneously drives the transfer belt drive mechanism 76 by the transfer belt drive control unit 75 to rotate the transfer belt 31.
When the fixing unit 8 has finished warming up, the control unit 61 sends an application command to the image formation control unit 66 in order to perform a printing operation. A high-voltage bias set in advance is supplied to each roller of each process unit 3, and a paper conveyance command with a printing speed is sent to the paper conveyance control unit 65 to start conveyance of the paper P.

In the following description, since the processing operation of the toner image forming process by each process unit 3 is the same, the processing operation of the toner image forming process in the black process unit 3k will be described.
When each high-voltage bias is supplied by the image forming control unit 66, a charging voltage of, for example, -1100V is supplied to the charging roller 12, and the surface of the photosensitive drum 11 is charged to, for example, -600V.

The developing roller 13 is supplied with a developing voltage of −200 V, for example, and the supply roller 14 is supplied with a supply voltage of −250 V, for example. The developing roller 13 is supplied from the developing roller 13 to the supplying roller 14 in the vicinity of the nip region between the developing roller 13 and the supplying roller 14. An electric field is formed in the direction of heading.
The process unit 3k contains black toner, and the supplied toner is strongly rubbed against the developing roller 13 and the supply roller 14 to be frictionally charged.

In this embodiment, the toner is frictionally charged to a negative polarity due to the characteristics of the developing roller 13 and the supply roller 14.
The toner frictionally charged to the negative polarity adheres on the developing roller 13 by the Coulomb force received from the electric field directed from the developing roller 13 toward the supply roller 14.
The adhered toner is carried to the contact portion between the developing roller 13 and the developing blade 15 as the developing roller 13 rotates, and a thin toner layer having a uniform thickness is formed by the developing blade 15.

When the developing roller 13 further rotates, the thinned toner layer is carried to the nip portion between the developing roller 13 and the photosensitive drum 11.
On the other hand, the control unit 61 reads one piece of bitmap data from the bitmap data stored in the storage unit 81, and sends the read bitmap data to the image formation control unit 66.
The image formation control unit 66 blinks the LED of the exposure head 18 corresponding to the received bitmap data, exposes the photosensitive drum 11 charged to −600 V, discharges it to −50 V, and removes the surface of the photosensitive drum 11. An electrostatic latent image is formed thereon.

  When the electrostatic latent image formed on the surface of the photosensitive drum 11 reaches the nip portion with the developing roller 13 as the photosensitive drum 11 rotates, the gap between the developing roller 13 and the photosensitive drum 11 is reached. Since an electric field in the direction from the photosensitive drum 11 toward the developing roller 13 is formed in the exposed portion that has been discharged to −50V, a reverse electric field is formed in the non-exposed portion that has not been discharged at −600V. The toner selectively adheres only to the exposed portion from the negatively charged toner layer on the roller 13, and the electrostatic latent image is developed as a toner image.

  On the other hand, the transfer belt 31 is pressed against the photoconductive drum 11 by the primary transfer roller 32, and the transfer belt 31 and the photoconductive drum 11 come into contact with each other to form a primary transfer nip portion, which is formed on the photoconductive drum 11. When the image formation control unit 66 outputs a primary transfer voltage generation signal to the high-voltage power supply unit 77 in synchronization with the timing at which the toner image reaches the primary transfer nip portion, the high-voltage power supply unit 77 supplies, for example, to the primary transfer roller 32. A primary transfer voltage of +3000 V is supplied.

At this time, an electric field in a direction from the transfer belt 31 toward the photosensitive drum 11 is formed in the primary transfer nip portion, and a negative polarity toner image formed on the photosensitive drum 11 is primarily transferred onto the transfer belt 31. .
In this way, the toner image forming process by the process unit 3 is performed, and a primary transferred color image including the toner images of the respective colors formed by the respective process units 3 is formed on the transfer belt 31.

Then, the controller 61 drives the paper transport mechanism 72 by the paper transport controller 65 before the toner image primarily transferred onto the transfer belt 31 reaches the secondary transfer nip portion by the secondary transfer roller 33, The unprinted portion of the paper P is conveyed in the direction of the secondary transfer nip portion by the conveyance roller 35c, and the image formation control unit 66 increases the pressure in accordance with the timing at which the toner image on the transfer belt 31 reaches the secondary transfer nip portion. A secondary transfer voltage generation signal is output to the power supply unit 77, and the high voltage power supply unit 77 supplies a secondary transfer voltage of, for example, +2500 V to the secondary transfer roller 33.
At this time, an electric field in the direction from the secondary transfer roller 33a to the secondary transfer roller 33b is formed in the secondary transfer nip portion, and the negative polarity toner image primarily transferred onto the transfer belt 31 is transferred onto the sheet P. Next transferred.

When the second-transferred paper P reaches the fixing unit 8, the toner on the paper P is heated and melted by the fixing belt 41 that has already reached the printable temperature due to warming up and the pressure belt 42 that presses the fixing belt 41. The second-transferred toner image is fixed on the paper P.
The control unit 61 takes in the paper P after fixing into the storage cassette 1c by the transport roller 35d and the discharge roller 38, and winds and stores the printed paper P by the winding unit.
When printing a plurality of sheets, the above printing operation is repeated.
In this way, the printing process by the printer 1 of this embodiment is executed.

Hereinafter, temperature control of the fixing temperature in the fixing unit 8 of the present embodiment will be described.
The temperature control process of the fixing temperature of the present embodiment is executed when printing on the paper P narrower than the maximum paper width. When printing on the paper P having the maximum paper width that can be passed, the fixing temperature control unit 67 After the warm-up process described below, based on the temperature detected by the infrared sensor 48 (referred to as infrared sensor temperature), the temperature of the fixing belt 41 is controlled only by controlling the power supply to each heater 46.

The temperature control process for the fixing temperature is executed by the fixing temperature control unit 67 that has received a temperature control command from the control unit 61 at the start of the printing operation.
When printing on a sheet P having a sheet width less than the maximum sheet width that can be passed, the fixing temperature control unit 67 drives the blowing unit 53 by the blowing control unit 79 after the warm-up process.
The fixing temperature control unit 67 monitors the temperature of the infrared sensor and the temperature detected by the temperature sensor 49 (referred to as temperature sensor temperature) while the printing process is being executed, and the temperature difference between them (= temperature sensor temperature). -The air volume of the blowing means 53 is repeatedly switched based on the infrared sensor temperature), and the temperature control process of the fixing temperature is continued until the printing operation is completed.

Hereinafter, the warm-up process and the air volume switching process of the blowing unit 53 in the fixing temperature control of the fixing unit 8 will be described.
When the fixing temperature control is started, the fixing temperature control unit 67 starts a warm-up process of the fixing belt 41 while monitoring the infrared sensor temperature while rotating the fixing belt 41 and the pressure belt 42 by the fixing unit driving mechanism 74. However, as shown in FIG. 7, the surface temperature of the fixing belt 41 detected by the infrared sensor 48 is the lower limit temperature of the fixing belt 41 (= allowable temperature of the control target temperature Tg). When reaching the lower limit value of the range, the warm-up process is terminated, and when printing on the paper P narrower than the maximum paper width, the air volume switching process of the air blowing means 53 is started.

During the warm-up process, the air blowing by the air blowing means 53 is stopped in order to shorten the warm-up time.
When the air volume switching process is started, the fixing temperature control unit 67 controls the temperature of the fixing belt 41 by supplying electric power to each heater 46 while the air blowing control unit 79 causes the air blowing means 53 to reduce the air volume as the second air volume. Drive with air volume.

  When air is blown with a small amount of air, the temperature detected by the temperature sensor 49 indicated by a solid line in FIG. 7 has a slower rising speed than that during warm-up, and is measured by a thermometer specially provided for the experiment. The sheet passing area temperature in the area (see the fine broken line shown in FIG. 7) and the sheet passing area temperature outside the air blowing area detected by the infrared sensor 48 (see the rough broken line shown in FIG. 7) once overshoot, but control It decreases toward the control target temperature Tg without exceeding the upper limit of the allowable temperature range (also referred to as printable temperature) of the target temperature Tg.

When the temperature difference between the infrared sensor temperature and the temperature sensor temperature is equal to or larger than the large air flow rate difference X described above, the fixing temperature control unit 67 uses the air flow control unit 79 to change the air flow of the air blowing means 53 to the first air flow rate. Switch to a large air volume as the air volume.
When the air flow with a large air volume is started, the temperature sensor temperature starts to decrease, and when the temperature difference between the infrared sensor temperature and the temperature sensor temperature becomes equal to or less than the above-described small air volume air temperature difference Y, the fixing temperature control unit 67 The air volume of the air blowing means 53 is switched to a small air volume by the air blowing control unit 79.

As described above, in the air volume switching process of the air blowing means 53 of the present embodiment, the air flow of the air blowing means 53 is switched to the small air volume or the large air volume based on the temperature difference between the infrared sensor temperature and the temperature sensor temperature. The temperature of the non-sheet passing area 41 is controlled so as not to exceed the upper limit temperature of the fixing belt 41, and the temperature of the sheet passing area including the sheet passing area in the blowing area of the fixing belt 41 is always the printable temperature. Control to be
As a result, in the fixing unit 8 of this embodiment, the non-sheet passing area can be prevented from being overheated and the fixing unit 8 can be prevented from being broken, and the temperature in the sheet passing area can be kept within an appropriate temperature range. Good fixing can be performed.

  The large air volume (first air volume) in the air volume switching process is the rated air volume of the blower 51 and decreases the surface temperature of the non-sheet passing area of the fixing belt 41 detected by the temperature sensor 49, that is, positively. The air volume to be cooled is referred to as a small air volume (second air volume), which is an air volume that is smaller than a large air volume that is about half of the rated air volume and that gradually increases the surface temperature of the non-sheet passing region of the fixing belt 41 I mean.

Hereinafter, the image forming process by the printer 1 of the present embodiment will be described according to the step indicated by S in FIG.
S1: When the user turns on the printer 1, the image forming processing program stored in the storage unit 81 of the printer 1 is automatically activated.

S2: When the image forming processing program is started, the control unit 61 confirms the outputs from the paper thickness sensor 23 and the discharge detection sensor 37b, the paper thickness sensor 23 detects the thickness of the paper P, and discharge detection. If the sensor 37b detects the presence of the paper P, it is determined that the belt-like paper P has been set, and the process proceeds to step S5.
If any one of the sheet thickness sensor 23 and the discharge detection sensor 37b has not detected the sheet P, it is determined that the sheet P is not set, and the process proceeds to step S3.

S3: The control unit 61 that has determined that the paper P is not set has no paper on which the wording that the paper P is not set is displayed on the display screen of the operation display unit 71 by the input / display control unit 63 A notification screen is displayed to notify the user that the paper P is not set, and the process proceeds to step S4.
In this case, when the paper thickness sensor 23 detects the presence of the paper P and the discharge detection sensor 37b does not detect the presence of the paper P, the control unit 61 starts the paper setting by the operation display unit 71. Informs the user that the operation is urged.

Further, when the sheet thickness sensor 23 does not detect the presence of the sheet P and the discharge detection sensor 37b detects the presence of the sheet P, it indicates that the sheet P remains on the sheet conveyance path 25. Inform the wording together.
When the user newly sets the roll-shaped paper P in the supply cassette 1b, the user sets the roll-shaped paper P in the setting portion of the supply cassette 1b and sends one end in the width direction along the reference surface 26. The sheet 21 is inserted between the rollers 21, the sheet guide 27 is brought into contact with the other end of the sheet P, and a sheet setting start operation is performed by the operation display unit 71.

In this case, if the remaining of the paper P is notified, the setting operation is performed after the residual paper is removed.
When the user confirms the inside of the supply cassette 1b and the leading edge of the paper P to be printed is already held by the feed roller 21, the operation display unit 71 performs a paper setting start operation.

  The control unit 61 that has recognized the start operation of the paper setting by the input / display control unit 63 sends a paper setting command to the paper conveyance control unit 65, and the paper conveyance control unit 65 drives the paper conveyance mechanism 72 to convey the paper. Each transfer roller 35 in the path 25 is rotated in the transfer direction, the transfer belt drive control unit 75 drives the transfer belt drive mechanism 76 to rotate the transfer belt 31 in the transfer direction, and the fixing unit drive control unit 73 fixes the fixing unit. The driving mechanism 74 is driven to rotate the fixing belt 41 and the pressure belt 42 in the transport direction.

  The paper conveyance control unit 65 conveys the paper P while monitoring the paper jam in the fixing unit 8 and the winding around the fixing belt 41 by the discharge detection sensor 37b, and the discharge detection sensor 37b detects the presence of the paper P. After a predetermined time has elapsed, the paper transport operation related to the paper set is stopped, the leading edge of the paper P is held between the discharge rollers 38, and the input / display control unit 63 displays the display screen of the operation display unit 71. Then, a word to the effect that the leading edge of the paper P is to be wound around the winding portion of the storage cassette 1c is displayed, and the process proceeds to step S4.

S4: The control unit 61 waits for the user to wind the leading end of the paper P around the take-up unit of the storage cassette 1c, and to perform a paper setting end operation by the operation display unit 71. Is recognized, it is determined that the paper P has been set, and the process proceeds to step S5. If the user's end operation is not recognized, the standby is continued.
S5: The control unit 61 that has determined that the paper P has been set displays a paper information input screen such as paper width and paper thickness on the display screen of the operation display unit 71. When the user inputs the paper information, the input is performed. The paper information set by the user is acquired by the display control unit 63 and the paper information acquisition unit 64.

S6: The control unit 61 that has acquired the sheet information set by the user sets the sheet information of the set sheet including the sheet width detected by the sheet width sensor 22 and the sheet thickness detected by the sheet thickness sensor 23 by the sheet information acquisition unit 64. Acquire and move to step S7.
S7: The control unit 61 that has acquired the paper information set by the user and the paper information of the set paper compares the two pieces of paper information. If the two pieces of paper information are different, the process proceeds to step S8. If both are the same, the process proceeds to step S9.

  S8: The control unit 61 that has determined that the sheet information set by the user and the sheet information of the set sheet are different from each other is displayed on the display screen of the operation display unit 71 and the input sheet information including sheet width, sheet thickness, and the like is supplied. A message indicating that the paper P set in the cassette 1b does not match is displayed to prompt the user to confirm or change the user setting, and the process returns to step S4 to wait for the user to finish the paper setting. .

  S9: The control unit 61 that has determined that the sheet information set by the user matches the sheet information of the set sheet, based on the sheet width and sheet thickness acquired by the sheet information acquisition unit 64, the printing speed management table of the storage unit 81. From 83, the printing speed corresponding to the combination is read, and the process proceeds to step S10.

S10: The controller 61 monitors the output signal from the cover open / close detection sensor 80 of the supply cassette 1b. When the cover close signal is output from the cover open / close detection sensor 80, the process proceeds to step S11.
When a cover open signal is output from the cover open / close detection sensor 80, the process returns to step S4 and waits for the user to finish the paper setting operation.

S11: The control unit 61 waits for the communication unit 68 to receive a print instruction from the higher-level device 70 via the communication network 69. When receiving a print instruction from the higher-level device 70, the control unit 61 proceeds to step S12. To do.
If the print instruction from the host apparatus 70 has not been received, the process returns to step S10, the output signal from the cover open / close detection sensor 80 is monitored in step S10, and the print instruction from the host apparatus 70 in step S11 is waiting to be received. Continue waiting.

S12: The control unit 61 that has received the print instruction from the upper apparatus 70 performs the image data expansion process of the print instruction in the same manner as described in the print process by the printer 1, and the bit after the expansion process is completed. Map data is temporarily stored in the storage unit 81.
Further, the control unit 61 starts the fixing temperature control of the fixing unit 8 by the fixing temperature control unit 67, and rotates the transfer belt 31 by the transfer belt drive control unit 75, and proceeds to Step S13.

S13: The control unit 61 that has started the fixing temperature control warms up the fixing unit in the same manner as described in the warm-up process in the fixing temperature control of the fixing unit 8, and the fixing temperature control unit 67 causes the infrared sensor to It waits for the surface temperature of the fixing belt 41 detected by 48 to reach the printable temperature, and when the surface temperature of the fixing belt 41 reaches the printable temperature, it is determined that printing is possible and the process proceeds to step S14. .
When the surface temperature of the fixing belt 41 does not reach the printable temperature, the standby is continued.

  S14: The control unit 61 that has determined that printing is possible when the surface temperature of the fixing belt 41 has reached the printable temperature supplies a high-voltage bias that is set in advance to each roller of each process unit 3 by the image formation control unit 66. At the same time, a paper conveyance command with the printing speed read in step S9 is sent to the paper conveyance control unit 65 to start the printing operation.

S15: The control unit 61 that has started the printing operation determines whether or not the blowing means 53 needs to blow air based on the paper width detected by the paper width sensor 22 acquired in step S6, and the acquired paper width can be passed. If it is less than the maximum sheet width, it is determined that the air blowing means 53 needs to blow, and the process proceeds to step S17.
If the acquired sheet width is the maximum sheet width, it is determined that the blowing by the blowing unit 53 is unnecessary, and the process proceeds to step S16.

  S16: The control unit 61 that has determined that the blowing by the blowing unit 53 is unnecessary is in the same manner as described in the printing process by the printer 1 while waiting for the end of the printing operation while waiting for the printing operation to be performed. When the printing operation of all the image data (including repeated printing of the designated identical image data) is completed, the process proceeds to step S22.

S17: On the other hand, the control unit 61 that has determined that the blowing by the blowing unit 53 is necessary reads the large air flow rate temperature difference X from the storage unit 81, and based on the printing speed read in step S9, the low air flow rate temperature difference The corresponding small air volume blowing temperature difference Y is read from the table 84, and the large air volume read out to the fixing temperature control section 67 in the same manner as described in the air volume switching process of the blowing means 53 in the fixing temperature control of the fixing unit 8. A temperature control command with the air temperature difference X and the small air volume air temperature difference Y is sent, and air blowing with the small air volume is started, and the process proceeds to step S18.
Note that the details of the air volume switching processing of the air blowing means 53 of the present embodiment have been described in the fixing temperature control of the fixing unit 8, so only the main points will be described in the following description.

  S18: The fixing temperature control unit 67 monitors the infrared sensor temperature and the temperature sensor temperature, and their temperature difference (= temperature sensor temperature−infrared sensor temperature) is greater than or equal to the large air flow rate difference X or the small air flow rate. The process waits for the difference Y or less to be satisfied, and when any one of the conditions is satisfied, it is determined that the air volume switching control is necessary, and the process proceeds to step S19. If neither condition is satisfied, the process proceeds to step S20.

  S19: Fixing that the air volume switching control is determined to be necessary when the temperature difference between the infrared sensor temperature and the temperature sensor temperature satisfies one of the conditions of the large air volume air temperature difference X or more or the small air volume air temperature difference Y or less. When the temperature difference is greater than or equal to the large air flow blast temperature difference X, the temperature control unit 67 switches the small air flow during blowing to a large air flow, and the temperature difference is less than or equal to the small air flow blast temperature difference Y. In that case, the large air volume during blowing is switched to the small air volume, and the process proceeds to step S20.

S20: The control unit 61 waits for the end of the printing operation in the same manner as in step S16 while performing the air volume switching process in the fixing temperature control by the fixing temperature control unit 67, and prints all image data of the print instruction. When the operation is finished, the process proceeds to step S21.
If the printing operation has not been completed, the process returns to step S18 to continue determining whether or not the air volume switching is necessary in S18 and waiting in the waiting state for completion of the printing operation in step S20.
S21: The control unit 61 that has finished the printing operation while performing the air volume switching process stops the blowing by the blowing unit 53 by the fixing temperature control unit 67, and proceeds to step S22.

S22: The controller 61 that has finished the printing operation stops the supply of power to each heater 46 by the fixing temperature controller 67, and proceeds to step S23.
S23: The control unit 61 that has stopped heating by the heater 46 cuts the strip-shaped paper P by the cutter unit 24 of the supply cassette 1b, winds the cut paper P by the winding unit of the storage cassette 1c, and stores it in the storage cassette 1c. Store in. At this time, the cut end of the unprinted paper P in the supply cassette 1 b is stopped while being sandwiched between the rollers of the delivery roller 21.

S24: The control unit 61 that has cut the paper P terminates the current image forming process when the printer 1 is powered off. If the power is not shut off, the process returns to step S10, and the output signal from the cover opening / closing detection sensor 80 is monitored in step S10, and the standby in the waiting state for receiving the print instruction from the host device 70 in step S11 is continued.
In this way, the image forming process by the printer 1 of this embodiment is executed.

  In step S7, when the paper information set by the user is different from the paper information of the set paper, it has been described that the fact is notified. However, the paper width and the paper input from the operation display unit 71 are described. The user setting of the thickness may be automatically changed to a value detected by the paper width sensor 22 and the paper thickness sensor 23.

  As described above, in this embodiment, when printing on the paper P having the maximum paper width, the temperature of the fixing belt 41 is controlled by the heaters 46 while the air blowing by the air blowing unit 53 is stopped. Since the fixing belt 41 is cooled as the sheet P passes, temperature control is performed without exceeding the upper limit temperature of the fixing belt 41 in the entire area in the width direction of the fixing belt 41 as shown in FIG. This can prevent damage to the fixing belt 41 due to overheating.

Further, as shown in FIG. 9, the temperature distribution in the width direction of the surface temperature of the fixing belt 41 in the maximum sheet passing area can be controlled within the allowable temperature range of the control target temperature Tg, and the temperature in the sheet passing area can be controlled. Good fixing can be performed while maintaining an appropriate temperature range.
When printing on a paper P having a width less than the maximum paper width, as shown in FIG. 10, unless air is blown by the air blowing means 53, the paper passing area side is brought to an appropriate temperature range by cooling accompanying the passage of the paper P. Although the non-sheet passing area is not cooled by the passage of the sheet P, the non-sheet passing area is overheated and exceeds the upper limit temperature of the fixing belt 41 (see the temperature distribution indicated by a solid line in FIG. 10). Inadequate fixing or damage to the fixing unit 8 will occur.

  Further, when the air blowing by the air blowing means 53 is performed with a large air volume, as shown in FIG. 11, when the paper P having a relatively narrow paper width is used, the cooling region indicated by hatching in FIG. 11 is wide. Thus, since the area (non-sheet passing area) of the fixing belt 41 corresponding to the cooling area is excessively cooled, the surface temperature of the fixing belt 41 in the sheet passing area is set like the temperature distribution indicated by the broken line in FIG. It becomes difficult to keep within the allowable temperature range of the control target temperature Tg.

  For this reason, in this embodiment, when printing on the paper P having a width less than the maximum paper width, the temperature of the fixing belt 41 is controlled by each heater 46, and the air flow is determined based on the temperature difference between the infrared sensor temperature and the temperature sensor temperature. The air volume of the means 53 is switched to a small air volume or a large air volume to control the temperature of the non-sheet passing area of the fixing belt 41 to be equal to or lower than the upper limit temperature of the fixing belt 41, and the sheet passing area of the fixing belt 41 in the air blowing area The temperature of the paper passing area including the paper is always controlled to a printable temperature.

Further, as shown in FIG. 4, the air outlet 52 a of the air duct 52 is disposed downstream of the pressure belt 42 in the paper conveyance direction and on the back surface side of the paper P to be conveyed, and blows toward the fixing belt 41. Therefore, as shown in FIG. 12, when printing on the paper P having a width less than the maximum paper width, the paper P can function as a wind shield in the paper passing area in the air blowing area, and the fixing belt in the paper passing area can be used. It is possible to suppress the cooling of 41 and cool only the non-ventilated area of the blowing area.
Thereby, the fixing belt 41 of this embodiment can automatically change the cooling region according to the sheet width.

As described above, in this embodiment, the air blowing unit 53 is arranged on the downstream side of the fixing unit 8 in the paper conveyance direction, and the outlet 52a of the air duct 52 is arranged on the back side of the paper P to be conveyed. When the sheet width acquired by the sheet width sensor 22 is less than the maximum sheet width that can be passed, the air volume by the blower 53 is switched based on the temperature difference between the sheet passing area temperature and the non-sheet passing area temperature. The fixing belt 41 in the non-sheet passing area can be prevented from being overheated, and the temperature in the sheet passing area can be appropriately controlled to perform good fixing.
In the above embodiment, the special color accommodated in the process unit 3s has been described as white, but the special color may be clear.

In the above embodiment, the fixing belt 41 and the pressure belt 42 of the fixing unit 8 have been described as endless metal belts, but are endless rubber belts made of heat-resistant synthetic rubber or the like. Also good.
Furthermore, in the above-described embodiment, the temperature sensor 49 is described as a contact-type temperature detection element, but may be a non-contact-type temperature detection element.

Furthermore, in the above-described embodiment, the print medium is described as a roll-like continuous paper. However, the print medium may be a bellows-like continuous paper folded at a perforation or the like, and has a predetermined size such as A4. A single paper such as paper P may be used.
Further, in each of the above embodiments, the image forming apparatus is described as an electrophotographic color printer. However, the image forming apparatus is not limited to the above, and heat fixing such as an MFP apparatus, a facsimile apparatus, or a copying apparatus is performed. Any device can be used, and the same effect as described above can be obtained by applying the present invention to any device.

DESCRIPTION OF SYMBOLS 1 Printer 1a Apparatus main body 1b Supply cassette 1c Storage cassette 3, 3s, 3c, 3m, 3y, 3k Process unit 4 Image formation part 6 Transfer unit 8 Fixing unit 11 Photosensitive drum 12 Charging roller 13 Developing roller 14 Supplying roller 15 Developing blade 16 toner cartridge 18 exposure head 21 delivery roller 22 paper width sensor 22a rod 23 paper thickness sensor 23a light transmitting hole 25 paper transport path 26 reference surface 27 paper guide 27a guide groove 31 transfer belt 31a transfer belt drive roller 31b driven roller 32 primary transfer Roller 33, 33a, 33b Secondary transfer roller 35, 35a, 35b, 35c, 35d Conveyance roller 36, 36a, 36b, 36c Passage detection sensor 37a Ingress detection sensor 37b Ejection detection sensor 38 Ejection low La 41 Fixing belt 42 Pressure belt 43 Driving roller 44 Pressure roller 45a, 45b Support roller 46, 46a, 46b, 46c Heater 47, 47a, 47b Reflector plate 48 Infrared sensor 49 Temperature sensor 51 Blower 52 Blower duct 52a Outlet 53 Blowing means 61 Control unit 62 Command / image processing unit 63 Input / display control unit 64 Paper information acquisition unit 65 Paper conveyance control unit 66 Image formation control unit 67 Fixing temperature control unit 68 Communication unit 69 Communication network 70 Host device 71 Operation display unit 72 Paper transport mechanism 73 Fixing unit drive control unit 74 Fixing unit drive mechanism 75 Transfer belt drive control unit 76 Transfer belt drive mechanism 77 High voltage power supply unit 78 Heater power supply unit 79 Blower control unit 80 Cover open / close detection sensor 81 Storage unit 83 Printing speed management Table Le 84 small air flow temperature difference table

Claims (2)

An image forming unit for forming a developer image on a print medium;
A fixing member for heating the developer image on the print medium;
A pressure member that pressurizes the fixing member;
At the conveying direction downstream side of the pre-Symbol print medium of the pressing member, wherein is from across the print medium the pressure member side is disposed so as to blow air into the fixing member side, of the fixing member, the top of the print medium Blowing means for blowing air toward a region exceeding the minimum width and less than the maximum width
First temperature detecting means for detecting a surface temperature of a passage region of the print medium of the fixing member;
Second temperature detecting means for detecting a surface temperature of a non-passage area of the print medium of the fixing member;
A medium information acquisition unit that acquires medium information that is information about the print medium;
Wherein the fixing member, the surface temperature of the non-passing area of the print medium so as to keep below a predetermined temperature, and a control unit for controlling the air volume of the blower unit,
As the air volume of the blowing means, a first air volume that decreases the surface temperature of the non-passing area of the fixing member and a second air volume that gently increases the surface temperature of the non-passing area of the fixing member are set. And
The temperature difference is a value obtained by subtracting the detected temperature of the first temperature detecting means from the detected temperature of the second temperature detecting means, and the first temperature difference and the second temperature smaller than the first temperature difference. Set the difference and
The controller is
A printing speed is determined based on the medium information acquired by the medium information acquisition unit,
Based on the determined printing speed, the second temperature difference is set,
The air volume of the blowing means is switched to the first air volume when the temperature difference becomes greater than or equal to the first temperature difference, and the air volume when the temperature difference becomes less than or equal to the second temperature difference. 2. An image forming apparatus , wherein the air volume is switched to 2 . The image forming apparatus according to claim 1 .
The image forming apparatus according to claim 1, wherein the control unit performs blowing by the blowing unit when the print medium is less than a maximum width that allows the sheet to pass.

Images