JPH1039588A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the heating time of a fixing roller and to make heating efficiency excellent by inhibiting the image forming action of both surfaces and enabling the image forming action of one surface to be executed when the temperature of a fixing member faced to the front surface of a transfer paper is proper and the temperature of a fixing member faced to the back surface of the transfer paper is lowered. SOLUTION: A fixing unit 17 is constituted so that the surface temperature of an upper roller 17a is detected by an upper thermistor 173 and the surface temperature of a lower roller 17b is detected by a lower thermistor 174. By a heater control means 21, an upper and a lower heaters 171 and 172 are controlled to be turned on or off according to the respective temperature detected by the thermistors 173 and 174. When a continuous copying action is executed in a one-surface copying mode, the heater 172 is turned off. When a both-surface copying mode is inputted from a control panel 22 in such a state, the copying action is inhibited until the temperature of the upper roller becomes >= the threshold temperature thereof and the temperature of the lower roller becomes >=the threshold temperature thereof. Then, when the condition is satisfied, the both-surface copying action can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus for performing one-sided or two-sided copying on transfer paper.

[0002]

2. Description of the Related Art Conventionally, a toner image formed on an image forming body is transferred to the front surface of a transfer paper, and the toner image formed on the image forming body is once transferred to a toner image receiving body, and then the back surface of the transfer paper is transferred. There is an image forming apparatus capable of performing double-sided copying by re-transferring the toner image onto a transfer sheet and fixing the toner image collectively by a first fixing unit and a second fixing unit. For example, in the above-described apparatus, a technique is disclosed in which the first fixing means and the second fixing means are independently set at respective temperatures and heated (see JP-A-3-171390).

[0003]

However, the temperature of the fixing rollers of the first fixing means and the fixing roller of the second fixing means described in the prior art are independently set and heated independently. For example, after heating the fixing roller on the opposite side of the visible image of the one-sided copy in one-sided copying, when using both fixing rollers in the two-sided copy, since the heating of the fixing roller is performed independently, Poor heating efficiency,
There is a problem that the heating time is slow.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing roller having a short heating time, good heating efficiency, and a shortest fixing in each of a one-side copy mode and a two-side copy mode. An object of the present invention is to provide an image forming apparatus in which the idling time is set or the idling time relating to the fixing in the two-sided copy mode and the one-sided copy mode is unified.

[0005]

The above object is achieved by the following means. That is, (1) first image forming means for transferring the toner image formed on the image forming body to the surface of the transfer paper, and once transferring the toner image formed on the image forming body to the toner image receiving body, Second retransfer to the back side of transfer paper
In an image forming apparatus comprising: an image forming unit, and a fixing unit for fixing a toner image transferred onto a transfer sheet, the temperature of a fixing member facing the surface of the transfer sheet is appropriate for a set temperature, and An image forming apparatus, wherein when the temperature of the fixing member facing the rear surface of the fixing member is lower than the set temperature, image formation on both sides is prohibited, and image formation on one side is enabled. 2) First image forming means for transferring the toner image formed on the image forming body to the surface of the transfer paper, and once transferring the toner image formed on the image forming body to the toner image receiving body, In an image forming apparatus including a second image forming unit that retransfers to the back surface and a fixing unit that fixes the toner image transferred onto the transfer paper, the temperature of the fixing member facing the front surface of the transfer paper is higher than a set temperature. Suitable for transfer paper When the temperature of the fixing member opposed to the surface is lowered with respect to the set temperature, an image forming apparatus characterized by a prohibiting both sides and one side of the image forming.

Here, that the temperature of the fixing member is appropriate for the set temperature means that the temperature of the fixing member is equal to or higher than the set temperature.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 An image forming apparatus according to an embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a configuration of an image forming apparatus according to the first embodiment, FIG. 2 is a cross-sectional view of a main part of the image forming apparatus of the first embodiment, and FIG. FIG. 4 is an explanatory diagram of the operation of the apparatus.

Referring to FIG. 1, the overall structure of the image forming apparatus will be described. The photosensitive drum 10 is an image carrier, for example, a cylindrical base formed of a transparent member is provided inside, and a transparent conductive layer a- A photosensitive layer such as a Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated in the direction of the arrow. Also, a scorotron charger 11 as a charging means
Is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and is opposed to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10. Attach it. The scorotron charger 11 includes a control grid maintained at a predetermined potential with respect to the organic photoconductor layer of the photoconductor drum 10, and the discharge electrode 1
As 1a, a charging action is performed by corona discharge having the same polarity as the toner, and a uniform potential is applied to the photosensitive drum 10.

The exposure unit 12 for each color is provided with an exposure position on the photosensitive drum 10 between the scorotron charger 11 and the developing unit 13 on the upstream side in the rotation direction of the photosensitive drum with respect to the developing sleeve 131. It is arranged in a state. Also,
The exposure unit 12 includes an exposure element 12a in which a plurality of LEDs (light emitting diodes) and the like arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10 are arranged in an array, and a selfoc lens 12b as an equal magnification imaging element. Are configured as an exposure unit attached to the holding member 12e. The holding member 12e includes an exposure unit 12 for each color, a uniform exposure device 12
c and a transfer simultaneous exposure unit 12 d are mounted and housed inside the base body of the photosensitive drum 10.

The developing unit 13 has yellow (Y) and magenta (M) developing units on the left side of the photosensitive drum 10 with respect to the rotation direction of the photosensitive drum 10, and cyan (C) and black (K) developing units. The developing device is arranged on the right side of the photosensitive drum 10. Y and M scorotron chargers 11 are provided below the developing casing 138 of the Y and M developing units 13, and C and K are also provided.
The C and K scorotron chargers 11 are disposed above the developing casing 138 of the developing device 13. The developing units 13 for the respective colors contain one-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K), respectively. And a developing sleeve 131 formed of an aluminum material that rotates in the same direction as the rotation direction of the photosensitive drum 10 at the developing position while maintaining a predetermined gap. Further, the developing device 13
Is maintained at a predetermined value from the photosensitive drum 10 by an abutting roller (not shown). When a developing operation is performed by the developing device 13 for each color, a developing bias obtained by applying a DC voltage or an AC voltage AC to the developing sleeve 131 is applied. Applied,
Jumping development is performed by a one-component or two-component developer accommodated in the developing device, and a DC bias having the same polarity as that of the toner is applied to the negatively charged photosensitive drum 10 that grounds the transparent conductive layer, thereby exposing the light. Attach toner to the section.

The developing device 13 for each color described above converts the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12 into a non-conductive image by applying a developing bias voltage. In a state of contact, reversal development is performed with toner having the same polarity as the charged polarity. As an original image, an original image read by an image sensor of an image reading device separate from this apparatus or an image edited by a computer is temporarily stored in a memory as image data of each color of Y, M, C and K. Stored and stored. At the start of image recording, a photoconductor drive motor (not shown) is started, and at the same time, a yellow (Y) developing device 13 is located on the left side of the photoconductor drum 10.
The application of a potential to the photosensitive drum 10 is started by the charging action of the Y scorotron charger 11 disposed below the developing casing 138 of FIG. After a potential is applied to the photosensitive drum 10, exposure by an electric signal corresponding to the Y image data is started in the Y exposure unit 12, and the rotation of the drum scans the photosensitive layer on the surface to form the Y image of the original image. A corresponding electrostatic latent image is formed.

The electrostatic latent image is reversal-developed by the Y developing device 13 in a state where the developer on the developing sleeve is not in contact with the developer, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10. . Next, the photosensitive drum 10 is placed on the magenta (M) developing device 13 on the yellow (Y) toner image.
Is applied by the charging action of the magenta (M) scorotron charger 11 disposed below the developing casing 138, and exposure is performed by an electric signal corresponding to the M image data of the M exposure unit 12, and Developing unit 13
Yellow (Y) by non-contact reversal development
A magenta (M) toner image is sequentially superimposed on the toner image.

By the same process, a developing casing 13 of a developing unit 13 for cyan (C) is provided on the right side of the photosensitive drum 10.
The cyan (C) toner image and the photosensitive drum 10 are further provided by a cyan (C) scorotron charger 11, a cyan (C) exposure unit 12 and a cyan (C) developing device 13 disposed above the photosensitive drum 10. , The black (K) scorotron charger 1 disposed above the developing casing 138 of the black (K) developing device 13 below the cyan (C).
1. A black (K) toner image is sequentially superimposed by the exposure unit 12 and the developing device 13 so that the photosensitive drum 10
A color toner image of a back side image is formed thereon, and the superimposed color toner image is stretched between a driving roller 14d and a driven roller 14e in a transfer area 14b by a transfer unit 14c to which a voltage having a polarity opposite to that of the toner is applied. Then, the toner image is collectively transferred onto a toner image receiving member 14a provided in proximity to or in contact with the photosensitive drum 10. At this time, uniform exposure is performed by the simultaneous transfer exposure device 12d using, for example, a light-emitting diode so that good transfer is performed (second image forming unit).

Next, a superposed color toner image of yellow (Y), magenta (M), cyan (C) and black (K) of the surface image is formed in the same manner as in the above-described color image forming process. (First image forming unit).

Here, the recording paper P is sent out from the paper feed cassette 15 by a feed-out roller 15a, and is conveyed to a timing roller 15b. The recording paper P is driven by the timing roller 15b, and the color toner image of the surface image carried on the photosensitive drum 10 and the toner image receiver 14a.
The sheet is fed to the transfer area 14b in synchronization with the color toner image of the back side image carried on the sheet. At this time, the support shaft 15
2 can be brought into contact with and released from the toner image receiving member 14a using the rotation fulcrum 2 as a rotating fulcrum, and the leading end brought into contact with the recording paper P has the same polarity as the toner by the brush-shaped paper charger 150. The paper is charged, adsorbed on the toner image receiving body 14a, and fed to the transfer area 14b. By charging the paper with the same polarity as the toner, the toner is prevented from being attracted to the toner image on the toner image receiving body or the toner image on the image carrier, thereby preventing the toner image from being disturbed. Simultaneously with the passage of the recording paper P, the paper charger 150 is separated from the toner image receiving body 14a, and the contact is released.

The surface image on the peripheral surface of the photosensitive drum 10 is collectively transferred to the upper surface side (front surface side) of the recording paper P by the transfer device 14c to which a voltage having a polarity opposite to that of the toner is applied. At this time, the back surface image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a. Next, the back surface image on the peripheral surface of the toner image receiver 14a is collectively transferred to the lower surface side (back surface side) of the recording paper P by the back surface transfer device 14g to which a voltage having a polarity opposite to that of the toner is applied.

The recording paper P on which the color toner images are formed on both sides is discharged by an AC discharger 14h for separating the transfer paper, is separated from the toner image receiving body 14a, and is fixed to the fixing unit 1.
7. Here, the upper roller 1 as a fixing member
By applying heat and pressure between the lower roller 7a and the lower roller 17b, which is a fixing member, the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P is sent by the paper discharge roller 18 and the outside of the apparatus. Is discharged to the tray. The fixing device 17
Will be described in detail with reference to FIG.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is brought into contact with the toner image receiver 14a using the support shaft 142 as a rotation fulcrum and the toner image receiver cleaning blade 141 capable of releasing the contact. Cleaning. The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is scraped off by the cleaning blade 19a of the cleaning device 19. Cleaning device 19
The photosensitive drum 10 from which the residual toner has been removed is uniformly charged by the Y scorotron charger 11 and enters the next image forming cycle.

In FIG. 2, a fixing unit 17 as a fixing unit applies heat and pressure to the front and back surfaces of the recording paper P having the adhered toner to fix the recording paper. The fixing device 17 has an upper roller 17a.
And the lower roller 17b. The rotation of the motor 178 causes the upper roller 17a to rotate, and the rotation of the upper roller 17a causes the lower roller 17b to rotate. Further, an upper thermistor 173 is provided on the surface of the upper roller 17a to detect the temperature of the upper roller 17a. Similarly, the lower roller 17b facing the back surface of the transfer paper is attached to a rotatable lever 175 with a 176 support shaft, and is rotated by being pressed against the upper roller 17a by a spring 177. A lower heater 172 is provided inside the lower roller 17b to heat the lower roller 17b. Further, a lower thermistor 174 is provided on the surface of the lower roller 17b to detect the temperature of the lower roller 17b.

When there is a temperature difference between the upper roller and the lower roller, the fixing device 17 is configured to transfer heat while rotating both rollers. For example, when the lower roller temperature is lower than a predetermined temperature range, the lower roller is heated by the lower heater 172 of the lower roller itself, and further heated by heat conduction by rotation of the upper roller.
Further, the heating time can be shortened.

The heater control means 21 is means for controlling the fixing device 17, and includes an upper thermistor 173 and a lower thermistor 174.
Of the upper heater 171 as a heating means and the lower heater 172 as a heating means,
OFF control is performed, and the drive of the motor 17 is controlled.

The operation panel 22 includes operation buttons for operating the apparatus, a display, and the like. As the mode selection 23, a two-sided copy mode key 231 and a one-sided copy mode key 23
The two-sided copy mode key 231 selects the two-sided copy mode, and the one-sided copy mode key 232 selects the one-sided copy mode. The copy button 25 is a button for performing copying. In addition, the display 26 displays the completion of the warm-up in the double-sided copy mode or the single-sided copy mode. The CPU 20 is a computer that controls the apparatus sequentially and controls each driving unit.

Next, a method of judging whether copying is possible according to the embodiment will be described with reference to FIG. When the one-sided copy mode is selected in the copy mode selection (F11), the determination of whether or not one-sided copy is possible starts, and it is checked whether the upper roller temperature T _U ≧ the upper roller threshold temperature T _UL (F12). The heating of the upper roller is continued, and if YES, a one-sided copy enable signal is issued (F13). The upper roller threshold temperature refers to a lower limit temperature of a set temperature range of the upper roller.

Next, when the duplex copy mode is selected (F
21) and upper roller temperature T _U ≧ upper roller threshold temperature T _UL
It is checked whether or not (F23), if NO, the heating of the upper roller is continued while rotating, and if YES, the next check is started (F23). Also, it is checked whether the lower roller temperature T _D ≧ the lower roller threshold temperature T _DL (F22),
If NO, continue heating the lower roller while rotating.
If S, the next check is entered. Upper roller temperature T _U ≧
Upper roller threshold temperature T _UL and lower roller temperature T _D
≥Check if lower roller threshold temperature T _DL (F2
4) If YES, a double-sided copy enable signal is output (F
25). The lower roller threshold temperature refers to the lower limit temperature of the set temperature range of the lower roller.

(Explanation of Operation Example) Here, an example of a copy operation of the image forming apparatus according to the embodiment will be described with reference to FIGS. FIG. 4 shows the state of (a) upper roller temperature T _U , (b) lower roller temperature T _D , (c) upper roller temperature T _U ≧ upper roller threshold temperature T _UL , and (d) lower roller temperature T _D ≧ The relationship between the state of the lower roller threshold temperature _TDL and (e) the double-sided copyable range is shown with respect to time.

First, a main switch (not shown) of the apparatus is turned on, and as shown in FIG. 2, both the upper heater 171 and the lower heater 172 are turned on. Subsequently, continuous copying is performed in the one-sided copy mode. At this time, since the unfixed image is only on the upper roller 17a side, the lower heater 17
2 is OFF. Therefore, as time elapses, the temperature of the lower roller 17b decreases, and at the end of copying,
The temperature is lower than the set temperature (see FIG. 4B).

In this state, as shown in FIG. 2, a double-sided copy mode key 231 on the operation panel 22 is keyed. In the case of double-sided copying in which an unfixed image is present on both sides of the transfer paper, if the temperature of the lower roller 17b is low, the fixability of the back side image is reduced. Therefore, when the double-sided copy mode is input, copying is prohibited until the upper roller temperature T _U ≧ the upper roller threshold temperature T _UL and the lower roller temperature T _D ≧ the lower roller threshold temperature T _DL. When the formula is satisfied, the warm-up is completed, and a double-sided copy is enabled (see FIG. 4E). Here, the copy button 25 is pressed to perform duplex copying.

In order to obtain the same fixability on the front and back surfaces of the transfer paper, it is preferable that the upper roller temperature T _U and the lower roller temperature T _D satisfy T _U −T _D ≦ 15 ° C.

(Embodiment 2) Next, an image forming apparatus according to an embodiment will be described with reference to the drawings. FIG. 5 is a cross-sectional view of a main part of the image forming apparatus according to the second embodiment. FIG. 6 is a flowchart for determining whether or not copying is possible according to the second embodiment, and FIG. Note that the overall configuration of the image forming apparatus according to the present embodiment is not described because it is not mechanically different from FIG. 1 described in the first embodiment.

Referring to FIG. 5, mainly the parts different from those of FIG. 2 will be described. The operation panel 22 includes operation buttons and a display for operating the apparatus. The power button 24 is a key for starting warm-up, and the copy button 25 is a button for starting copying. The display 26 displays the completion of the warm-up. The CPU 20 is a computer that controls the apparatus sequentially and controls each driving unit.

Referring to FIG. 6, a description will be given of a method of judging whether or not copying is possible in the apparatus of the embodiment. When the power button 24 is pressed (F31), determination of whether copying is possible or not is started, and it is checked whether or not upper roller temperature T _U ≧ upper roller threshold temperature T _UL . If NO, heating of the upper roller is continued while rotating. ,
If YES, the next check is entered (F32). Also, it is checked whether or not lower roller temperature T _D ≧ lower roller threshold temperature T _DL . If NO, heating of the lower roller is continued while rotating, and if YES, the next check is performed (F
33). Here, it is checked whether the upper roller temperature T _U ≧ the upper roller threshold temperature T _UL and the lower roller temperature T _D ≧ the lower roller threshold temperature T _DL (F34). Is issued (F35). When single-sided and double-sided copying become possible, copy each.

(Explanation of Operation Example) Here, an example of a copy operation of the image forming apparatus according to the embodiment will be described with reference to FIGS. In FIG. 7, (a) upper roller temperature T _U , (b) lower roller temperature T _D , (c) upper roller temperature T _U ≧ upper roller threshold temperature T _UL , (d) lower roller temperature T _D ≧ Lower roller threshold temperature _TDL and (e) the double-sided and single-sided copyable ranges with time are shown.

First, the upper heater 171 and the lower heater 17
2 are both turned on. The temperature of the upper roller and the lower roller is set to an upper roller temperature T _U ≧ upper roller threshold temperature T _UL , and a lower roller temperature T _D ≧ lower roller threshold temperature T so that both one-sided copy and two-sided copy can be fixed. Control to _DL . Subsequently, when continuous copying is performed in the one-sided copy mode, since the unfixed image is only on the upper roller 17a side, the lower heater 172 is turned off during copying. Therefore, as time passes, the temperature of the lower roller 17b decreases, and at the end of copying, the temperature is lower than the temperature of the upper roller 17a (see FIG. 7B).

As shown in FIG. 5, when the power button 24 of the operation panel 22 is pressed, the upper roller temperature T _U ≧ the upper roller threshold temperature T _UL , and the lower roller temperature T _D ≧ the lower roller threshold temperature T _DL. When the condition is satisfied, warm-up is completed,
A single-sided and double-sided copy are enabled. Copy button 25
Press to make one-sided or two-sided copies.

In this state, if single-sided copying is performed again,
Fixing is possible as long as the temperature of the upper roller 17a is appropriate, but in a two-sided copy mode in which an unfixed image is provided on both sides of the transfer paper, if the temperature of the lower roller 17b is low, the fixability of the back surface image is reduced. In this case, it is conceivable that double-sided copy is prohibited and single-sided copy is possible. However, if the single-sided copy and double-sided copy are prohibited and the waiting time for warm-up is set, the operation is simplified.

In the first and second embodiments, the upper roller 17a is used for fixing one-sided copy, but the lower roller 17b may be used depending on the structure of the image forming apparatus.

[0037]

As described above, the following effects can be obtained. According to the first aspect, an image forming apparatus having a short heating time of the fixing roller and good heating efficiency is provided. Also,
Further, the image forming apparatus is configured such that the idling time relating to the shortest fixing in each of the one-sided copy mode and the two-sided copy mode is obtained. According to the second aspect, the image forming apparatus has good heating efficiency of the fixing roller. Further, the image forming apparatus has a uniform idling time for fixing in the double-sided copy mode and the single-sided copy mode.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a cross-sectional view illustrating a configuration of a main part of the image forming apparatus according to the first exemplary embodiment.

FIG. 3 is a flowchart for judging whether copying is possible according to the first embodiment.

FIG. 4 is an operation explanatory diagram of the first embodiment.

FIG. 5 is a sectional view of a main part of an image forming apparatus according to a second embodiment.

FIG. 6 is a flowchart for judging whether or not copying is possible according to a second embodiment.

FIG. 7 is an operation explanatory diagram of the second embodiment.

[Explanation of symbols]

Reference Signs List 10 photoconductor drum (image carrier) 12 exposure unit 13 developing device 140 toner image receiver cleaning device 14a toner image receiver 14b transfer area 14g back surface transfer device 15 paper cassette 150 paper charger 17 fixing device (fixing means) 17a Upper roller (first fixing roller) 17b Lower roller (second fixing roller) 171 Upper heater (heating means) 172 Lower heater (heating means) 173 Upper thermistor 174 Lower thermistor 175 Lever 18 Paper discharge roller 19 Cleaning device 21 Heater control means 22 operation panel 23 mode selection 231 duplex copy mode key 232 side copy mode key 24 power button 25 copy button P recording paper (transfer sheet) on T _U on roller temperature T _D under roller temperature T _UL roller threshold temperature T _DL under Roller threshold temperature

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Matsubara Konica Corporation, 2970 Ishikawacho, Hachioji-shi, Tokyo (72) Inventor Tadayoshi Ikeda 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Invention Person Masakazu Fukuchi 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation

Claims (4)

[Claims] A first image forming means for transferring a toner image formed on the image forming body to a surface of a transfer sheet; and a method for temporarily transferring the toner image formed on the image forming body to a toner image receiving body.
In an image forming apparatus including a second image forming unit that retransfers to the back surface of a transfer sheet and a fixing unit that fixes a toner image transferred onto the transfer sheet, the temperature of a fixing member facing the front surface of the transfer sheet is set. When the temperature of the fixing member facing the back surface of the transfer sheet is lower than the set temperature, the image forming apparatus is configured to prohibit image forming on both sides and enable image forming on one side. Characteristic image forming apparatus. 2. The fixing device according to claim 1, wherein the fixing member is a pair of fixing rollers each having a heating unit therein, and when a double-sided copy mode is designated, the surface temperature of the first fixing roller facing the surface of the transfer paper is set to a set temperature. When the surface temperature of the second fixing roller facing the back surface of the transfer paper is lower than the set temperature, the first fixing roller and the second fixing roller are A heater control means for rotating in a state of being pressed and simultaneously heating the roller by at least a heating means inside the second fixing roller and controlling the surface temperature of the second fixing roller to be appropriate with respect to a set temperature; The image forming apparatus according to claim 1, wherein: 3. A first image forming means for transferring a toner image formed on an image forming body to the surface of a transfer paper, and after a toner image formed on the image forming body is once transferred to a toner image receiving body,
In an image forming apparatus including a second image forming unit that retransfers to the back surface of a transfer sheet and a fixing unit that fixes a toner image transferred onto the transfer sheet, the temperature of a fixing member facing the front surface of the transfer sheet is set. An image forming apparatus, which is suitable for the temperature, and inhibits image formation on both sides and one side when the temperature of a fixing member facing the back surface of a transfer sheet is lower than a set temperature. 4. The fixing member is a pair of fixing rollers each having a heating means therein, and when a double-sided copy mode is designated, the surface temperature of the first fixing roller facing the surface of the transfer paper is set to a set temperature. When the surface temperature of the second fixing roller facing the rear surface of the transfer sheet is lower than the set temperature, the first fixing roller and the second fixing roller are rotated while being pressed against each other, 4. A heater control means for simultaneously heating the roller by at least a heating means inside the second fixing roller and controlling the surface temperature of the second fixing roller to be appropriate with respect to a set temperature. An image forming apparatus according to claim 1.