JPH1152633A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which favorable fixing can be provided by small power consumption even when transfer material holding toner images on both surface is fixed in a lamp. SOLUTION: In an image forming device comprising a photosensitive drum, a means to form a toner image on the photosensitive drum, a first transferrer to transfer a toner image on the photosensitive drum onto a surface of a toner image receiving body or a recording paper P, a second transferrer to retransfer the toner image transferred to the toner image receiving body to a back surface of the recording paper P, and a fixing device 30 to fix the toner image transferred on the recording paper P, the fixing device 30 comprises at least a first fixing roller 310 to face the surface of the recording paper P, a first heater 311 to heat the first fixing roller 310, a second fixing roller 320 to face the back surface of the recording paper P, and a second heater 321 to heat the second fixing rollers 320, where the maximum power consumption of the first heater 311 is set to be smaller than the maximum power consumption of the second heater 321.

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 for forming an image by an electrophotographic method, and more particularly, to forming a toner image on both sides of a transfer material and heating and fixing the toner images collectively to form a double-sided image. The present invention relates to an image forming apparatus that performs the following.

[0002]

2. Description of the Related Art Conventionally, in a two-sided copy in which a toner image is formed on both sides of a transfer material, an image on one side formed on an image forming body is transferred and fixed on the transfer material, and this is once inverted on both sides. A method in which a transfer material is fed from a double-sided reversing paper feeder in a timely manner with the image formed on the image forming body, and the image on the other surface is transferred and fixed on the transfer material. Has been taken.

In this double-sided copying apparatus, as described above, the transfer of the transfer material such as feeding to the two-sided reversing paper feeder and passing through the fixing device twice is performed, so that the transfer distance of the transfer material becomes longer, so that copying is performed. This requires a lot of processing time, and once again the transfer material, which has been easily curled through the fixing device, is fed again, so that the reliability of the transfer of the transfer material is low, causing a jam or the like.

On the other hand, JP-B-49-37538, JP-B-54-28740, and JP-A-1-444.
No. 57, Japanese Patent Application Laid-Open No. 4-214576, and the like have proposed a device in which a toner image is formed on both surfaces of a transfer material and then fixed once.

[0005]

However, it is not easy to fix a transfer material having toner images on both sides at once. To fix a transfer material having a toner image on both sides in a batch, it is necessary to have heating means on both sides of the transfer material, and since power is supplied to both of the heating means, power consumption by the fixing means is required. Is inevitably large. Also in this method,
Since the interval at which the transfer material is conveyed to the fixing device is different between one-sided continuous copying and two-sided continuous copying, the fixing device of the conventional system causes defective fixing or wastes power.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. Even if a transfer material holding a toner image on both sides is collectively fixed, good fixing can be performed with low power consumption, and transfer with a toner image held on one side can be performed. It is another object of the present invention to provide an image forming apparatus capable of performing good fixing with low power consumption for a material.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming body, means for forming a toner image on the image forming body, an intermediate transfer body, and a method for transferring the toner image on the image forming body to the intermediate transfer body. Or a first transfer unit for transferring the toner image transferred on the intermediate transfer body, a second transfer unit for re-transferring the toner image transferred on the intermediate transfer body to the back surface of the transfer material, and a toner transferred on the transfer material. In an image forming apparatus having a fixing unit for fixing an image, the fixing unit includes at least a first fixing roller facing a front surface of the transfer material, a second fixing roller facing a back surface of the transfer material, A first heating unit for heating the first fixing roller, and a second heating unit for heating the second fixing roller, the maximum power consumption of the first heating unit,
This is achieved by the image forming apparatus (first invention of claim 1), wherein the power consumption is smaller than the maximum power consumption of the second heating means.

In the above invention, the second fixing roller is a roller having an elastic layer, and the first fixing roller is a metal roller having no elastic layer or an elastic layer of the second fixing roller. An image forming apparatus, wherein the heat capacity of the first fixing roller is larger than the heat capacity of the second fixing roller. The device is a preferred embodiment.

Further, the object is to provide an image forming body, means for forming a toner image on the image forming body, an intermediate transfer body, and a method for transferring the toner image on the image forming body to the intermediate transfer body or the transfer material. A first transfer unit that transfers the toner image onto the front surface, a second transfer unit that re-transfers the toner image transferred onto the intermediate transfer member to the back surface of the transfer material, and fixes the toner image transferred onto the transfer material. An image forming apparatus having a fixing unit, wherein the fixing unit includes at least a first member facing a surface of the transfer material.
A fixing roller, a second fixing roller facing the back surface of the transfer material, a first heating unit for heating the first fixing roller, and a second heating unit for heating the second fixing roller. The power supplied to the first heating means and the second heating means is made variable, the power supplied to the first heating means in the one-side copy mode is P _K1 , and the power supplied to the second heating means in the one-side copy mode is and P _K2, when the power supplied to the first heating means in the duplex copy mode P _R1, the electric power supplied to the second heating means in the duplex copy mode and P _R2, P _R1 ≦ P _R2 and P _K1 ≧ said first heating means so as to satisfy the relationship of P _K2 and the second
This is achieved by an image forming apparatus (second aspect of the present invention) that controls the power supplied to the heating means.

In the above invention, the supply power is controlled by variably controlling an effective voltage value or an effective current value supplied to the first heating means and the second heating means in accordance with a copy mode. Or at least one of the first heating unit and the second heating unit includes a plurality of heating units, and controls the supply power by switching a combination of output and non-output to each heating unit. An image forming apparatus characterized in that the operation is performed is a preferred embodiment.

Still another object of the present invention is to provide an image forming body, means for forming a toner image on the image forming body, an intermediate transfer body,
A first transfer unit that transfers the toner image on the image forming body to the surface of the intermediate transfer body or the transfer material; and a second transfer unit that retransfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material. (2) an image forming apparatus comprising: a transfer unit; and a fixing unit configured to fix the toner image transferred onto the transfer material.
The fixing unit includes at least a first fixing roller facing a front surface of the transfer material, a second fixing roller facing a back surface of the transfer material, a first heating unit that heats the first fixing roller, A second heating means for heating the second fixing roller; a sum of a maximum power consumption of the first heating means and a maximum power consumption of the second heating means; and a maximum consumption of the first heating means. The sum of the power and the maximum power consumption of the second b heating unit is set to be equal to or less than the maximum power consumption allowed by the fixing unit, and
This is achieved by an image forming apparatus (third invention of claim 7), wherein simultaneous energization of the a heating means and the second b heating means is prohibited.

In the above-mentioned invention, in a one-sided copy mode in which a toner image is formed only on the surface of the transfer material, the first heating means and the second a heating means are energized so that toner images are formed on both surfaces of the transfer material. In a preferred embodiment, the first heating means and the second b heating means are energized in the double-sided copy mode for forming the image.

Further, the object is to provide an image forming body, means for forming a toner image on the image forming body, an intermediate transfer body,
A first transfer unit that transfers the toner image on the image forming body to the surface of the intermediate transfer body or the transfer material; and a second transfer unit that retransfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material. In an image forming apparatus having a transfer unit and a fixing unit for fixing a toner image transferred onto the transfer material, the fixing unit includes at least a first fixing roller facing a surface of the transfer material; A second fixing roller opposed to the back surface of the material, a first heating unit for heating the first fixing roller, a second heating unit for heating the second fixing roller, and a second heating unit for heating the second fixing roller; In a one-sided copy mode in which a toner image is formed only on the surface of the transfer material, the first heating unit and the second a heating unit are energized, and in a two-sided copy mode in which a toner image is formed on both surfaces of the transfer material, the first Thermal means, is achieved by an image forming apparatus characterized by energizing the 2a heating means and the 2b heating means (4th invention of claim 9).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of each invention, an embodiment common to an image forming apparatus in which toner images are formed on both surfaces to which each invention is applied and fixed at once will be described. The present invention is not limited to the embodiments described below. The description in this section does not limit the technical scope of the claims and the meaning of terms. Also,
In the following description of the embodiment, when a color toner image is transferred to a transfer material, an image to be transferred to a surface of the transfer material on the side facing the image forming body in the transfer area is a surface image, the other side of the transfer material. The image transferred to the surface is referred to as a back surface image. Each of the embodiments described below is an example of an image forming apparatus for forming a color image, but the present invention is also applied to a monochrome image forming apparatus.

An image forming process and each mechanism of the embodiment of the image forming apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a color image forming apparatus according to an embodiment of the present invention, FIG. 2 is a side cross-sectional view of the image forming body of FIG. 1, and FIG. It is a figure showing a state.

The photosensitive drum 10 serving as an image forming body is provided with a cylindrical base formed of a transparent member of, for example, optical glass or transparent acrylic resin, and has a transparent conductive layer,
A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated clockwise as indicated by an arrow in FIG.

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10a at both ends for engaging and fixing it.
b is rotatably supported by bearings 110a and 110b fitted into flange members 10a and 10b at both ends with respect to a drum shaft 110 erected and fixed to the apparatus main body, and is rotatably supported. Is driven at a constant speed in a predetermined direction by being driven by meshing with a drive gear on the apparatus body side.

Scorotron charger 11 as charging means
Is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and is exposed in a direction orthogonal to a moving direction of the photosensitive drum 10 as an image forming body. A control grid fixed to a predetermined potential with respect to the above-described photosensitive layer of the photosensitive drum 10 and a discharge electrode 11a formed of, for example, a saw-tooth electrode, and having the same polarity as the toner. The charging action (minus charging in the present embodiment) is performed by the corona discharge to give a uniform potential to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

The exposure unit 12 as an image exposure means for each color moves the exposure position on the photosensitive drum 10 between the discharge electrode 11a of the scorotron charger 11 and the development position of the development device 13 by a developing sleeve 131. Is provided on the upstream side in the rotation direction of the photosensitive drum.

The exposure unit 12 includes light emitting elements L arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10.
It comprises a linear light-emitting element 12a in which a plurality of EDs (light-emitting diodes) are arranged in an array, and a holder (not shown) to which a selfoc lens 12b as an equal-magnification imaging element is attached. The exposure unit 12, the uniform exposure unit 12c, and the simultaneous transfer exposure unit 12d for each color are attached to the holding member 20, and are accommodated inside the base of the photosensitive drum 10.
Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal.

As the light emitting device, a device in which a plurality of light emitting devices such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The emission wavelength of the light-emitting element used in this embodiment is preferably in the range of 680 to 900 nm, which is generally high in transmittance for the Y, M, and C toners. The wavelength may be shorter than this, since the color toner does not have sufficient transparency since the image exposure is carried out in the step (1).

The developing device 13 provided along the peripheral surface of the photosensitive drum rotated according to the color order in which an image is formed,
In this embodiment, the Y and M developing units 13 are on the left side of the photosensitive drum 10 and the C and K developing units 13 are photosensitive units in the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG. The Y and M scorotron chargers 11 are disposed below the developing casing 138 of the Y and M developing units 13, and the C and K developing units are disposed above the developing casing 138 of the C and K developing units 13. , K are arranged.

The developing device 13 as a developing means for each color includes
One-component or two-component developers of yellow (Y), magenta (M), cyan (C), and black (K) are accommodated, respectively, while maintaining a predetermined gap with respect to the peripheral surface of the photosensitive drum 10. A developing sleeve 131 made of non-magnetic stainless steel or aluminum and having a thickness of, for example, 0.5 to 1 mm and an outer diameter of 15 to 25 mm is provided. The developing sleeve 131 rotates in a forward direction with respect to the rotation direction of the photosensitive drum 10 at the developing position. I have.

The developing sleeve 131 is urged by an abutting roller (not shown) to a predetermined gap, for example, 1
In the developing operation of the developing unit 13 for each color, a developing voltage is applied to the developing sleeve 131 by applying a DC voltage or further an AC voltage. Jumping development is performed with a one-component or two-component developer contained in the photosensitive drum 10 and a direct current of the same polarity as the toner (in this embodiment, a negative polarity) is applied to the negatively charged photosensitive drum 10 that grounds the transparent conductive layer. By applying a bias, non-contact reversal development is performed in which toner is attached to an exposed portion. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

The developing device 13 for each color described above applies the developing latent voltage to 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. In a non-contact state by a non-contact developing method by application, reversal development is performed with toner having the same polarity as the charged polarity (in the present embodiment, the photosensitive drum is negatively charged and has negative polarity).

In an image reading apparatus separate from the present apparatus, image data of a document image read by an image pickup device or image data of an image edited by a computer is Y (yellow), M (magenta), (Cyan) and K (black) are temporarily stored and stored in the memory as image signals for respective colors.

When image recording is started, a gear G provided on the back side flange 10b of the photosensitive drum 10 is rotated through a driving gear (not shown) by starting a photosensitive member driving motor (not shown). Is rotated in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, by the charging action of the Y scorotron charger 11 disposed below the developing casing 138 of the yellow (Y) developing device 13 on the left side of the photosensitive drum 10. The application of a potential to the photosensitive drum 10 is started.

After the photosensitive drum 10 is applied with a potential, a first color signal, that is, Y
Exposure by an electric signal corresponding to the image data is started, and an electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface of the photosensitive drum 10 by rotational scanning.

The latent image is reversal-developed by the Y developing device 13 in a non-contact state, and a yellow (Y) toner image is formed in accordance with the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is placed on the yellow (Y) toner image, and further on the left side of the photosensitive drum 10 and above the yellow (Y), the magenta (M) developing device 1.
An electric signal corresponding to a second color signal of the M exposure unit 12, that is, an M image data, is applied by the charging action of the magenta (M) scorotron charger 11 disposed below the third developing casing 138. Is performed, and a magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the M developing device 13.

By the same process, the developing casing 13 of the developing unit 13 for cyan (C) is located on the right side of the photosensitive drum 10.
The cyan (C) toner image corresponding to the third color signal is further provided by a cyan (C) scorotron charger 11, an exposure unit 12 of C, and a developing unit 13 of C, which are disposed above the photoconductor 8 A black (K) scorotron charger 11, an exposure unit 12, and a developing unit 13 are disposed on the right side of the drum 10 and below the developing casing 138 of the black (K) developing unit 13 at the lower part of the fourth unit C. Black (K) toner images corresponding to the signals are sequentially superimposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10.

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.

By the above-described image forming process, a superimposed color toner image as a backside image is formed on the photosensitive drum 10 as an image forming body, and the superimposed color toner image of the backside image on the photosensitive drum 10 is transferred. Area 14b
, A first transfer unit 14c to which a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied, is stretched between the driving roller 14d and the driven roller 14e, and comes close to or in contact with the photosensitive drum 10. The image is collectively transferred onto a toner image receiving member 14a which is an intermediate transfer member provided as described above. At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using a light emitting diode so that good transfer is performed.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the image forming body AC static eliminator 16, and then reaches the cleaning device 19, where the toner is removed from the rubber material in contact with the photoconductive drum 10. In order to eliminate the history of the photoconductor up to the previous print, the peripheral surface of the photoconductor is neutralized by exposure by a uniform exposure device 12c before charging using, for example, a light emitting diode. After the charge during printing is removed, the next color image is formed.

The back side image formed on the toner image receiver 14a is synchronized with the transfer area 14b, and the surface image of the superimposed color toner image is transferred to the photosensitive drum in the same manner as in the above-described color image forming process. 10 is formed. FIG. 3 shows the toner image formation state of the surface image formed on the toner image receiver 14a and the surface image formed on the photosensitive drum 10 at this time. It is necessary to change the image data so that the front surface image formed at this time is a mirror image of the back surface image formation on the photosensitive drum 10.

The recording paper P, which is a transfer material, is sent out by a feed roller 15a from a paper feed cassette 15, which is a transfer material storage means, is fed by a feed roller 15b, and is conveyed to a timing roller 15c.

The recording paper P is driven by a timing roller 15c to form a color toner image of a front image carried on the photosensitive drum 10 and a color toner image of a back image carried on the toner image receiver 14a. The paper is fed to the transfer area 14b in synchronization. At this time, the recording paper P is charged to the same polarity as the toner by a paper charger 14f as a transfer material charging means, is attracted to the toner image receiver 14a, and is fed to the transfer area 14b. By charging the paper with the same polarity as the toner, it is possible to prevent the toner from being attracted to the toner image on the toner image receiving member 14a or the toner image on the photosensitive drum 10,
Prevents toner image disturbance. Further, as the transfer material charging unit, a conductive roller, a brush charger, or the like, which can be brought into contact with and released from the toner image receiving member 14a, can be used.

A surface image on the peripheral surface of the photosensitive drum 10 is collectively collected by a first transfer unit 14c as a first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. The image is transferred onto the upper surface side (front surface side) of the recording paper P. At this time, the back side image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P, and the toner image receiver 14a
Exists. Next, a backside image on the peripheral surface of the toner image receiving body 14a is collectively recorded by a backside transfer unit 14g as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. The image is transferred to the lower surface (back surface) of the paper P.

Since the toner images of the respective colors overlap each other, it is preferable that the toners in the upper layer and the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. Accordingly, in the double-sided image formation in which the polarity of the color toner image formed on the toner image receiving body 14a is inverted by corona charging or the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, Since the toner of the lower layer is not sufficiently charged to the same polarity, the transfer becomes unfavorable.

The reversal development is repeated on the photosensitive drum 10, and the color toner images of the same polarity formed by superimposition are collectively transferred to the toner image receiving member 14a without changing the polarity, and then recorded without changing the polarity. Batch transfer to paper P is preferable because it contributes to improving the transferability of backside image formation. Also for the surface image formation, reversal development is repeatedly performed on the photosensitive drum 10 to collectively transfer color toner images of the same polarity formed by superimposition onto the recording paper P without changing the polarity.
It is preferable because it contributes to improvement of the transferability of surface image formation.

From the above, in color image formation, the first transfer means and the second transfer means are separately provided, and the first transfer means is operated to form a color toner image on the surface of the transfer material. Next, a two-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the second transfer unit is preferably adopted.

The toner image receiver 14a has a thickness of 0.1-2.
An endless rubber belt having a thickness of 0 mm, a semiconductive substrate having a resistance value of 10 ⁸ to 10 ¹⁴ Ω · cm such as silicon rubber or urethane rubber, and a thickness of 5 to 5 mm as a toner filming prevention layer outside the rubber substrate. It has a two-layer structure with a 50 μm fluorine coating. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, the thickness is 0.1 to 0.1.
A 5 mm semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like can also be used.

The recording paper P, which is a transfer material having a color toner image formed on both sides, is neutralized by a paper separating AC static eliminator 14h for separating the transfer material, and is separated from the toner image receiver 14a. The sheet is conveyed to a fixing device 30 as a fixing unit including two fixing rollers having a heating unit (heater) inside both rollers. By applying heat and pressure to the recording paper P between the first fixing roller 310 on the upper side and the second fixing roller 320 on the lower side, the toner adhered to the front and back of the recording paper P is fixed, and the two-sided image recording is performed. The discharged recording paper P is fed by a paper discharge roller 18 and discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer contacts and contacts the toner image receiver 14a provided in a toner image receiver cleaning device 14i which is a cleaning means of the toner image receiver. It is cleaned by a blade that can be released. Further, the toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the image forming body AC static eliminator 16, reaches the cleaning device 19, and is made of a rubber material that has contacted the photoconductor drum 10. The toner is scraped off into the cleaning device 19 by the cleaning blade 19a, and is collected by a screw 19b in a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is subjected to uniform charge removal by the Y scorotron charger 11 after the peripheral surface of the photosensitive member is neutralized by exposure by the uniform exposure device 12c, and the next image is formed. Enter the formation cycle.

Next, the state of the toner image from when the toner image formed on the photosensitive drum 10 is transferred to both sides or one side of the recording paper P and enters the fixing device will be described with reference to FIGS. explain. Here, the photosensitive drum 10 serving as an image forming body is negatively charged, and the latent image on the photosensitive drum 10 is subjected to reversal development by a toner having a negative charge, so that a toner image having a negative charge is exposed. The case in which it is formed on the body drum 10 will be described.

FIG. 4 shows a state in which the toner image of the surface image formed on the photosensitive drum 10 is directly transferred onto the recording paper P by the first image forming step, and the toner image is adhered to only the surface of the recording paper P. FIG. 4 is an explanatory diagram when the vehicle enters the fixing device 30. The toner image of the negative polarity surface image formed on the photoconductor drum 10 is applied with a positive polarity voltage by the first transfer unit 14c via the recording paper P and the toner image receiver 14a which is an intermediate transfer body behind the recording paper P. Is applied, and transfer is performed on the recording paper P (FIG. 4A). The recording paper P holding the toner image of the negative polarity surface image on the upper surface is discharged by the paper separation AC discharger 14h and separated from the toner image receiver 14a, and the first fixing roller 310 and the second fixing roller 320 (FIG. 4B).

FIG. 5 shows a first example in which the toner image of the surface image formed on the photosensitive drum 10 is directly transferred onto the recording paper P.
And a second image forming step in which the toner image of the back side image formed on the photosensitive drum 10 is transferred onto the recording paper P via the intermediate transfer member, toner images are formed on both sides of the recording paper P. FIG. 4 is an explanatory diagram when the toner enters the fixing device 30 in a state of being attached. The toner image of the negative polarity rear surface image formed on the photoconductor drum 10 is a toner image receiver 1
A positive polarity voltage is applied by the first transfer unit 14c from the rear of the toner image transfer member 4a, and the toner image is transferred onto the toner image receiver 14a (FIG. 5A). Subsequently, a toner image having a negative polarity surface image is formed on the photosensitive drum 10. The first transfer unit 14c applies a positive polarity voltage to the toner image of the front surface image via the recording paper P and a toner image receiving body 14a holding the toner image of the back surface image behind the recording paper P, and the upper surface of the recording paper P (FIG. 5B). Next, the toner image of the back surface image adhered to the toner image receiver 14a is applied to the lower surface of the recording paper P by applying a positive polarity voltage from the upper side of the recording paper P by a back transfer device 14g as a second transfer unit. The transfer is made. At this time, the potential of the toner image of the front surface image on the upper surface of the recording paper P is changed from a negative polarity to a positive polarity by applying a positive voltage from directly above by the back transfer unit 14g (FIG. 5C). In a state where the toner image of the front surface image of the positive polarity is held on the upper surface of the recording paper P and the toner image of the rear surface image of the negative polarity is held on the lower surface, the recording paper P is discharged by the paper separating AC neutralizer 14h. It is separated from the image receiver 14a and enters the fixing device 30 (FIG. 5D).

Next, the fixing device according to the present invention will be described. 6 and 7 are cross-sectional views showing the configuration of an embodiment of the fixing devices 30 and 30a. Members having the same function are denoted by the same reference numerals, and description thereof is omitted.

Each of the first fixing roller 310 and the second fixing roller 320 is provided with a first heater 311 as a first heating means and a second heater 321 as a second heating means comprising a halogen lamp or the like on an inner core. The fixing rotator has substantially the same structure. First and second fixing rollers 310 and 320
Roller parts are metal cores 310a, 32 made of metal pipes.
On the upper side of the first fixing roller 310 and the second fixing roller 320, elastic layers 310b and 32 made of an elastic material such as silicon rubber having a thickness of 0.8 to 2.2 mm and different thicknesses.
0b and a thickness of 0.0 as the surface layers 310c and 320c.
A PFA (perfluoroalkyl vinyl ether) layer of 5 to 0.25 mm is provided. The surface layers 310c and 32
As 0c, a heat-resistant high release layer such as a fluororesin such as PTFE (polytetrafluoroethylene) or a silicon resin is used in addition to PFA.

The elastic layer 31 of the first fixing roller 310
0b is the thickness of the elastic layer 310 of the second fixing roller 320.
The layer thickness may be smaller than the layer thickness a or the layer thickness may be set to 0 to form a so-called hard roller, and the second fixing roller 320 may be a soft roller. Further, the heat capacity of the first fixing roller 310 is made larger than the heat capacity of the second fixing roller 320 by increasing the thickness of the core metal 310 a of the first fixing roller 310.

The surface of the first and second fixing rollers 310 and 320 is lightly contacted with web cleaning devices 312 and 322 made of, for example, a non-woven fabric in order to clean toner, paper powder and the like adhering to the surfaces. Have been.

The first and second fixing rollers 310 and 320
In order to enhance the releasability of the oil, a sponge-shaped oil-impregnated oil application roller 313 for applying a release agent such as dimethyl silicone oil or modified silicone oil to the roller surface is used.
323 are provided.

Further, a first temperature sensor 314, which is a first and a second temperature detecting means comprising a thermistor or the like, is provided at a position in contact with or very close to each of the first fixing roller 310 and the second fixing roller 320, and a second temperature sensor 314. A temperature sensor 324 is provided to detect the surface temperature of the roller, and based on this detection signal, energization control of the first heater 311 and the second heater 321 is performed as described later, and the temperature is maintained within a predetermined temperature range. Is done.

First fixing roller 310 and second fixing roller 3
20 is pressed by a biasing member such as a spring (not shown) at a linear pressure of 0.8 to 1.8 kg / cm, and the length of the nip portion at this time depends on the linear pressure and the roller. Although the length differs depending on the hardness, the length of the nip portion is approximately 2 to 7 mm by using the second fixing roller 320 as a soft roller. First fixing roller 310 and second fixing roller 32
0 is driven by the same drive source so that no slip occurs in the nip portion, and has the same linear velocity (16 in this embodiment).
(0 mm / sec), and double-sided fixing is performed at the nip portion.

In this image forming apparatus, the fixing device 30, which is a fixing means, forms an electric field between each of the first and second fixing rollers 310 and 320 and the recording paper P sandwiched and conveyed therebetween. An electric field forming means such as a corona charger shown in the drawing or a roller charger which is capable of driven and driven by a sponge is provided, or the first and second fixing rollers 31 are provided.
0, 320 surface layers 310c, 320c and elastic layer 3
For example, a bias power source (not shown) and roller cores 310a and 3b are made of a conductive material in which carbon black or titanium oxide is added to 10b and 320b.
20a are connected to each other via a safety resistor, and the first fixing roller 310 is driven by an electric field forming means such as applying a bias voltage of + 200V to the first fixing roller 310 and -200V to the second fixing roller 320. 310 is charged with the same polarity as the toner charge of the upper toner image.
In the image forming apparatus, the fixing roller 320 is charged with the same polarity as the toner charge of the lower toner image to increase the electric repulsion between the toner and the roller, thereby fixing the double-sided toner image collectively. In this case, the electric electrostatic offset is completely eliminated.

The fixing device 30a shown in FIG. 7 and the fixing device 3 shown in FIG.
What is different from 0 is that the second fixing roller 320 is provided with a second (a) second heating means, ie, a second (a) heating means.
a heater 321a and a second b heater 321b as a second b heating means.

In the above image forming apparatus, one side (front side) of the transfer material is used.
A single-sided copy mode in which a toner image is formed and fixed only on a single-sided copy mode, and a double-sided copy mode in which a toner image is formed on both surfaces of a transfer material and fixed at once, and when the mode is designated by a designation unit, Excellent control is performed on image formation and fixing, and good image recording is performed. Hereinafter, this control method will be described.

FIG. 8 is a block diagram showing the control of the present invention. The operation panel of the main body of the image forming apparatus is provided with a copy mode selection button as a single-sided or double-sided copy mode selection means, and the user selects a single-sided copy mode or a double-sided copy mode. In addition to this, an automatic copy mode for performing automatic selection is provided, and when an image of a document is read by a document reading device (not shown), the presence or absence of an image on the back side of the document is detected. If a back side image is detected, the mode is automatically selected for duplex copy mode,
Image formation and fixing are also performed.

When the one-sided copy mode is selected, the control unit 50 calls up the image information on the front side from the memory or from the document reading apparatus, forms a toner image of the front side image on the photosensitive drum 10, and The first transfer unit 14c transfers the toner image of the front surface image on the recording paper P synchronously fed by the first transfer unit 14c (first image forming step). The toner image is held on the upper surface, and the fixing device 30 operates the electric field forming means (not shown) so as to form a negative electric field with respect to the first fixing roller 310 with respect to the recording paper P conveyed to the fixing device 30. Let it. On the other hand, the electric field forming means (not shown) is not operated for the second fixing roller 320. By such control, the surface image is fixed, and the recording paper P on which the fixing is completed is sent by the paper discharge roller 18 and discharged to a tray outside the apparatus.

When the two-sided copy mode is selected, the control unit 50 first retrieves the image information of the back side from the memory or from the document reading device, forms a toner image of the back side image on the photosensitive drum 10, and The toner image receiving member 14a, which is an intermediate transfer member, is used to transfer the back toner image by one transfer device 14c.
Transfer on top. Next, a toner image of a surface image is formed on the photosensitive drum 10 after the transfer and cleaning. Then, a toner image of a front surface image is transferred onto the upper surface (front surface) of the recording paper P fed in synchronization by the first transfer device 14c (first image forming step), and the lower surface transfer device is transferred onto the lower surface of the recording paper P. The toner image of the back surface image on the toner image receiver 14a is transferred by 14g (second image forming step). The fixing device 30 holds the toner image on both sides of the recording paper P conveyed to the fixing device 30, and the electric field forming means (not shown) forms a positive electric field with respect to the first fixing roller 310. (Charger, roller charger, bias power supply) are operated. On the other hand, an unillustrated electric field forming means (corona charger, roller charger, bias power supply) is operated so as to form a negative electric field with respect to the second fixing roller 320. Note that the second fixing roller 320 may be controlled so that the roller is grounded as a conductive roller. By such control, the double-sided image is fixed, and the recording paper P after the fixing is discharged by a discharge roller 18 to a tray outside the apparatus.

(Embodiment 1) In the image forming apparatus of the first invention (the invention of claim 1), the maximum power consumption of the first heater 311 as the first heating means in the fixing device 30 of the image forming apparatus is as follows. , A second heater 321 as a second heating means
Is set so as to be smaller than the maximum power consumption.

In the case of the one-sided copy mode, the toner image is formed only on the surface of the recording paper P.
Only the heating is required. On the other hand, in the duplex copy mode, the first fixing roller 31 is used to fix both sides of the recording paper P.
It is necessary to heat both the 0 and the second fixing roller 320. However, in the double-sided copy mode, the interval at which the recording paper P to be fixed is conveyed to the fixing device 30 is equal to the interval between the photosensitive drums 1.
The toner image formed on the toner image receiving member 14a is transferred to the toner image receiving member 14a, which is an intermediate transfer member, and then is re-transferred to the recording paper P. Then, the toner image reaches the fixing device 30. Intermittent transport takes time. As described above, the heat capacity of the first fixing roller 310 is
Since it is larger than the fixing roller 320 and has a configuration close to the hard roller or the hard roller, the thermal conductivity is good, the surface temperature is quickly restored, and the amount of power supplied to the first heater 311 is the amount of power supplied to the second heater 321. It may be smaller than the amount.

Therefore, good fixing can be performed in both the one-sided copy mode and the two-sided copy mode with low power consumption.

In the above-described invention, when the double-sided copy mode is selected, the control unit 50 controls the second temperature sensor 32
4, the second fixing roller 3 facing the back surface of the recording paper P
When the surface temperature of the recording paper P is detected to be lower than the set temperature, the first fixing roller 310 and the second fixing roller 320 are rotated while being pressed against each other before the recording paper P enters the fixing device 30. At the same time, the second fixing roller 320 is heated by at least the second heater 321 inside the second fixing roller 320, so that the surface temperature of the second fixing roller is controlled to be appropriate for the set temperature. With such a configuration, it is possible to save the amount of power supplied to the fixing device 30 and to quickly cope with the fixing possible state at the time of mode switching.

(Embodiment 2) In the image forming apparatus of the second invention (the invention of claim 4), in the fixing device 30 of the image forming apparatus, the first heater 31 as the first heating means is provided.
The power supplied to the second heater 321 as the first and second heating means is made variable, the power supplied to the first heater 311 in the one-sided copy mode is supplied to P _K1 , and the power supplied to the second heater 321 in the one-sided copy mode is supplied. The power is P _K2 , and the power supplied to the first heater 311 in the duplex copy mode is P _K2 .
_R1, when the supply power to the second heater 321 in the duplex copy mode and P _R2, P _K1 ≧ P _K2 and P in the control unit 50 so as to satisfy the relationship of P _R1 ≦ P _{R2 K1,}
P _K2 , P _R1 , and P _R2 are controlled.

FIG. 9 shows an example of this relationship. By performing such control, unnecessary power is not supplied excessively, the amount of power supplied to the fixing device 30 in both the one-sided copy mode and the two-sided copy mode is saved, and satisfactory fixing is realized. be able to.

In the above invention, the supply power is controlled according to a single-sided or double-sided copy mode according to the case where the power supply for supplying power to the first heater 311 and the second heater 321 uses a DC power supply. 10 (a), it is preferable to control by pulse width control (PWM), and in the case of an AC power supply, it is preferable to control the effective voltage value or the effective current value by phase control as shown in FIG. 10 (b). (A portion to which power is applied).

Alternatively, at least one of the first heater 311 and the second heater 321 is, for example, a combination of two heaters, and the supply power is controlled by turning off both of the heaters.
Or by switching a combination of output and non-output, such as turning one ON, turning the other OFF, or turning both ON.

(Embodiment 3) An image forming apparatus according to a third invention (an invention of claim 7) includes a fixing device 30a shown in FIG. 7, in which the maximum power consumption of the first heater 311 and the fixing device 30a are shown. The sum of the maximum power consumption of the second heater 321a, the maximum power consumption of the first heater 311 and the sum of the maximum power consumption of the second heater 321b are respectively set to be equal to or less than the maximum power consumption allowed by the fixing unit. 2
It is prohibited to energize the heater 321a and the second heater 321b at the same time. In this image forming apparatus, in addition to the one-sided copy mode (one-sided copy mode for only the front side) and the two-sided copy mode, the recording paper P
A backside copy mode in which a toner image is formed only on the backside of the printer is also enabled.

In this fixing device 30a, the first fixing roller 310 has a large heat capacity and good heat conduction, so that the temperature of the first fixing roller is slightly reduced even in continuous copying in the one-sided copy mode. Therefore, when the fixing is performed satisfactorily and the mode is switched from the one-sided copy mode to the two-sided copy mode, the surface temperature can reach the fixable range in a short time by heating the first fixing roller 310.

For example, in FIG. 7, the fixing device 30a
When the allowable power of the first heater 311
Power consumption of the second heater 321a is 300W, and power consumption of the second heater 321b is 50W.
Set to 0W. By setting the power consumption of each heater in this manner, as shown in FIG. 11, in the case of the one-sided copy mode (one-sided copy mode of only the front side), the first heater 311 and the second heater 321a are energized to perform the two-sided copy mode. In the case (1), the first heater 311 and the second b heater 321b are energized, so that the power consumption does not exceed the allowable power (1000 W) in any case. In the one-sided copy mode, the recording paper P is continuously fixed at short time intervals.
a, the maximum power is supplied to the first fixing roller 310, so that the temperature of the first fixing roller 310 does not decrease and the fixing is performed without any trouble.

According to this configuration, it is possible to cope with a single-sided copy mode in which an image is formed only on the back surface of the recording paper P. In the recording paper P fixed in the single-sided copy mode on the back side, the toner image formed on the photosensitive drum 10 is temporarily transferred to the toner image receiving body 14a which is an intermediate transfer body.
Thereafter, the toner image reaches the fixing device 30a through a process of being re-transferred to the recording paper P, so that intermittent conveyance is performed with a relatively long time interval. Therefore, there is enough time for the lowered temperature to return to the predetermined temperature, and the power consumption of the internal heater of the second fixing roller 320 can be small.

In the above-mentioned invention, in the one-sided copy mode in which a toner image is formed only on the surface of the recording paper P, the first heater 311 and the second heater 321a are energized, and the toner is applied to both sides of the recording paper P. When the toner image is formed on one side of only the back side in the double-sided copy mode for forming an image, the first heater 311 and the second b heater 321b are energized.

The fixing device 30a includes a first temperature sensor 314 for detecting the surface temperature of the first fixing roller 311;
And a second temperature sensor 324 for detecting the surface temperature of the second fixing roller 321. The control unit 50 controls the first temperature based on temperature information detected and output by the first temperature sensor 314.
The power supply to the heater 311 is controlled, and the second temperature sensor 324 is controlled.
2a heater 3 based on the temperature information detected and output by
The power supply to the heaters 21a and 321b is controlled independently of each other, and the surface temperatures of the first fixing roller 310 and the second fixing roller 320 are maintained at appropriate temperatures.

A specific example of the above control will be described.

The first heater 311 and the second heater 321a
And the second b heater 321b are controlled independently.

(A) Single-sided copy mode (single-sided copy of front side only): first heater 311 and second heater 3a
The following control is performed by using the 21a. When the temperature detected by the first temperature sensor 314 becomes 170 ° C. or lower, the first heater 311 is turned on.

When the temperature detected by the first temperature sensor 314 exceeds 180 ° C., the first heater 311 is turned off.

When the temperature detected by the second temperature sensor 324 falls below 165 ° C., the second heater 321a is turned on.

When the temperature detected by the second temperature sensor 324 exceeds 175 ° C., the second heater 321a is turned off.

(A) In the case of the double-sided copy mode, the following control is performed using the first heater 311 and the second heater 321b. When the temperature detected by the first temperature sensor 314 becomes 170 ° C. or less, the first heater 311 is turned on. Turn ON.

When the temperature detected by the first temperature sensor 314 exceeds 175 ° C., the first heater 311 is turned off.

When the temperature detected by the second temperature sensor 324 drops below 170 ° C., the second heater 321b is turned on.

When the temperature detected by the second temperature sensor 324 exceeds 175 ° C., the second heater 321b is turned off.

(C) In the case of the back side copy mode (one side copy of only the back side): the first heater 311 and the second b heater 32
The following control is performed using 1b. When the temperature detected by the first temperature sensor 314 becomes 150 ° C. or lower, the first heater 311 is turned on.

When the temperature detected by the first temperature sensor 314 exceeds 160 ° C., the first heater 311 is turned off.

When the temperature detected by the second temperature sensor 324 drops below 170 ° C., the second heater 321b is turned on.

When the temperature detected by the second temperature sensor 324 exceeds 180 ° C., the second heater 321b is turned off.

In the back side copy mode, the first fixing roller 31
Although it is not necessary to manage the temperature of 0, the temperature of the first fixing roller 310 is set to a temperature that can be used immediately when the first copy mode or the second copy mode is selected after the back side copy mode. Electric power is supplied not only to the second heater 321b but also to the first heater 311. Even in this case, the probability of selecting the back side copy mode is very low, so that power consumption is small.

The fixing device 30a in this case is preferably controlled as follows.

The first heater 311 and the second b heater 321b are continuously energized during warm-up. The first heater 31 during idling (copy standby state).
Turn ON / OFF the first and second heaters 321a. When the mode is switched from the one-sided copy mode to the two-sided copy mode or the backside copy mode, the toner image receiver 14a
It is not necessary to rotate and operate the fixing device 30a while the toner image is being transferred thereon (at the time of backside image formation), but also during this period, the fixing device 30a is rotated and operated (preliminary rotation) to perform the first fixing. Heat is supplied from the roller 310 to the second fixing roller 320 to shorten the time required for raising the temperature of the second fixing roller 320 to a use state and to make the surface temperature uniform. ・ The second heater 321a and the second heater 321b are used. The heating range is made different in the axial direction, and the end portion (recording paper P
(A portion through which no air passes) prevents the maximum power consumption of the first heater 311 from being reduced by the second heater 32.
The power consumption is set to be larger than the maximum power consumption of the 1a or 2b heater 321b (as described above, since the heating of the second fixing roller 320 may be intermittent, the 2a heaters 321a and 2b
The power consumption of the heater 321b may be reduced, so that the overall power consumption can be reduced. During the copy standby, the pulse width control (PWM),
Alternatively, it is preferable to control an effective voltage value or an effective current value by phase control to save power consumption.

(Embodiment 4) An image forming apparatus according to a fourth invention (an invention of claim 9) includes a fixing device 30a shown in FIG. 7, in which the maximum power consumption of the first heater 311 and the fixing device 30a are shown. The sum of the maximum power consumption of the second heater 321a and the second b heater 321b is set to be equal to or less than the maximum power consumption allowed by the fixing unit, and the first heater is used in a one-sided copy mode in which a toner image is formed only on the front surface. The heater 311 and the second heater 321a are energized, and in the double-side copy mode, the first heater 311 and the second heater 321a and the second heater 321b are simultaneously energized. In this image forming apparatus, a backside copy mode in which a toner image is formed only on the backside of the recording paper P is also possible in addition to the one-sided copy mode (one-sided copy mode for only the front side) and the two-sided copy mode.

In this fixing device 30a, since the first fixing roller 310 has a large heat capacity and good heat conduction, the temperature of the first fixing roller is slightly reduced even in continuous copying in the one-sided copy mode. Therefore, when the fixing is performed satisfactorily and the mode is switched from the one-sided copy mode to the two-sided copy mode, the surface temperature can reach the fixable range in a short time by heating the first fixing roller 310.

For example, in FIG. 7, the fixing device 30a
12, the power consumption of the first heater 311 is 400 W, the power consumption of the second heater 321 a is 200 W, and the second heater 32 b is, as shown in FIG.
The power consumption of 1b is set to 400W. In this way, the power consumption of each heater is set, and the first heater 311 and the second heater 321a are energized in the one-sided copy mode (one-sided copy mode of the front side only), and the first heater 311 in the two-sided copy mode. And the second heater 321a and the second heater 321a
By supplying electricity to the heater 321b, the power consumption does not exceed the allowable power (1000 W) in any case. In the one-sided copy mode, the recording paper P continuously passes through the fixing device 30a at short time intervals, but since the first fixing roller 310 has a large heat capacity and a good thermal conductivity as described above, the first fixing roller 310 The fixing is performed without any trouble without lowering the temperature.

According to this configuration, it is possible to cope with a single-sided copy mode in which an image is formed only on the back surface of the recording paper P. In the single-sided copy mode on the back side, the recording paper P to be fixed is intermittently conveyed with a relatively long time interval as described above. Therefore, there is enough time for the lowered temperature to return to the predetermined temperature, and the second fixing roller 320
In this case, the power consumption of the second heaters 321a and 321b can be small. Further, it is preferable to save power consumption by controlling the effective voltage value or the effective current value by the pulse width control (PWM) or the phase control during copy standby.

In the above invention, the fixing device 30a
Has a first temperature sensor 314 for detecting the surface temperature of the first fixing roller 311 and a second temperature sensor 324 for detecting the surface temperature of the second fixing roller 321. The control unit 50 The power supply to the first heater 311 is controlled based on the temperature information detected and output by the temperature sensor 314, and the second heater 321a and the second b heater 321b are controlled based on the temperature information detected and output by the second temperature sensor 324. The surface temperatures of the first fixing roller 310 and the second fixing roller 320 are maintained at appropriate temperatures by controlling the energization of the first fixing roller 310 and the second fixing roller 320 independently or in conjunction with each other.

The conventional fixing device includes a first fixing roller 310
The structure of the second fixing roller 320 is the same as that of the first fixing roller 31.
0 and the heater as the heating means of the second fixing roller 320 is 1
The power consumption of the first heater 311 is 6
In general, the power consumption of the second heater 321 is set to 400W.

In the one-sided copy mode (single-sided copy of the front side only), only the first heater 311 is used (at this time, the maximum power consumption is 600 W). In the two-sided copy mode, the first heater 311 and the second heater 321 are used. (The maximum power consumption at this time was 1000 W), and the backside single-sided copy was the same as in the double-sided copy mode.

In such an example, the first fixing roller 310
In view of the configuration of FIG.
Since the temperature is as low as 0 W, when the environmental temperature is low or when thick paper is used as the recording paper P, the continuous fixing may lower the fixing roller temperature and cause insufficient fixing. In contrast, the apparatus of the present invention supplies sufficient power to each heater within the maximum power consumption in any copy mode,
The temperature of each fixing roller can be maintained within an appropriate range.

Although the embodiment of the image forming apparatus capable of minimizing the power consumption and obtaining a stable and good image has been described, the present invention is not limited to a fixing apparatus using a fixing roller. Similar effects can be obtained for an image forming apparatus provided with a fixing device using a fixing belt.

[0101]

According to the first invention (claims 1, 2 and 3), in an image forming apparatus for forming a toner image on both surfaces of a transfer material and fixing the toner images collectively, the first fixing roller of the fixing means is fixed. By making the heat capacity and the heat conductivity larger and better than the heat capacity and the heat conductivity of the second fixing roller, it is possible to save the amount of power supplied to the heating means of the fixing means, and to efficiently use the small power consumption. An image having good fixation can be obtained.

According to the second invention (claims 4, 5, and 6), in the image forming apparatus, by appropriately allocating the amount of power supplied to each heating unit, an image having a good fixation with low power consumption can be obtained. Can be obtained.

According to the third invention (claims 7 and 8), in the image forming apparatus, the heat capacity and the heat conductivity of the first fixing roller of the fixing means are larger than the heat capacity and the heat conductivity of the second fixing roller. In addition, by providing a plurality of heating means for the second fixing roller, the amount of power supplied to the heating means can be saved, and an image with good fixing can be obtained with low power consumption.

According to the fourth invention (claim 9), in the image forming apparatus, even if the transfer material holding the toner image on both sides is collectively fixed, good fixing can be performed with low power consumption, and one side can be formed. When the mode is switched from the copy mode (one side only on the front side) to the two-sided copy mode, the heat conduction from the first fixing roller to the second fixing roller increases, and the surface temperature of the second fixing roller 320 falls within a feasible range in a short time. Can be reached.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating an example of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side sectional view of the image forming body of FIG. 1;

FIG. 3 is an explanatory diagram illustrating a state where toner images are formed on both sides.

FIG. 4 is an explanatory diagram illustrating a state of a toner image when an image is formed on one surface of a transfer material.

FIG. 5 is an explanatory diagram illustrating a state of a toner image when images are formed on both surfaces of a transfer material.

FIG. 6 is a cross-sectional view illustrating a configuration of an example of a fixing device.

FIG. 7 is a cross-sectional view illustrating a configuration of another example of the fixing device.

FIG. 8 is a block diagram showing control for switching between one side and both sides.

FIG. 9 is a bar graph showing an example of power consumption of each heater.

FIG. 10 is a diagram illustrating an example of controlling the electric energy.

FIG. 11 is a diagram illustrating power consumption and a control example of a fixing device according to a third invention.

FIG. 12 is a diagram illustrating power consumption and a control example of a fixing device according to a fourth invention.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum (image forming body) 11 scorotron charger 12 exposure unit 13 developing unit 14a toner image receiving body (intermediate transfer body) 14c first transfer unit (first transfer unit) 14g back surface transfer unit (second transfer unit) 14h Paper separation AC neutralizer 30, 30a Fixing device (fixing unit) 310 First fixing roller 320 Second fixing roller 310a, 320a Core bar 310b, 320b Elastic layer 310c, 320c Surface layer 311 First heater (first heating unit) 321 second heater (second heating means) 321a second a heater (second a heating means) 321b second b heater (second b heating means) 314 first temperature sensor (first temperature detecting means) 324 second temperature sensor (second Temperature detection means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Haneda Konica Corporation 2970 Ishikawacho, Hachioji-shi, Tokyo

Claims (9)

[Claims] 1. An image forming member, means for forming a toner image on the image forming member, an intermediate transfer member, and a toner image on the image forming member is transferred to a surface of the intermediate transfer member or a transfer material. First
An image including a transfer unit, a second transfer unit that re-transfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material, and a fixing unit that fixes the toner image transferred on the transfer material In the forming apparatus, the fixing unit includes at least a first fixing roller facing a front surface of the transfer material; a second fixing roller facing a back surface of the transfer material;
A first heating unit for heating the fixing roller; and a second heating unit for heating the second fixing roller, wherein the maximum power consumption of the first heating unit is smaller than the maximum power consumption of the second heating unit. An image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the second fixing roller is a roller having an elastic layer, and the first fixing roller is a metal roller having no elastic layer or a layer thicker than the elastic layer of the second fixing roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is a roller having an elastic layer having a small size. 3. The heat capacity of the first fixing roller is changed to the second fixing roller.
2. The image forming apparatus according to claim 1, wherein the heat capacity is larger than a heat capacity of the fixing roller. 4. An image forming member, means for forming a toner image on the image forming member, an intermediate transfer member, and transferring the toner image on the image forming member to a surface of the intermediate transfer member or a transfer material. First
An image including a transfer unit, a second transfer unit that re-transfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material, and a fixing unit that fixes the toner image transferred on the transfer material In the forming apparatus, the fixing unit includes at least a first fixing roller facing a front surface of the transfer material; a second fixing roller facing a back surface of the transfer material;
A first heating unit that heats the fixing roller; and a second heating unit that heats the second fixing roller. The power supplied to the first heating unit and the second heating unit is variable, and one-sided copying is performed. In the mode, the power supplied to the first heating means is P _K1 , and the power supplied to the second heating means is P _K2.
In a copy mode in which a toner image is formed on both surfaces of the transfer material, when the supply power to the first heating unit is P _R1 and the supply power to the second heating unit is P _R2 , P _R1 ≦ P _R2 And an image forming apparatus that performs control so as to satisfy a relationship of P _K1 ≧ P _K2 . 5. The image forming apparatus according to claim 3, wherein the control of the supplied power variably controls an effective voltage value or a current value supplied to the first and second means according to a copy mode. . 6. A method in which at least one of the first heating means and the second heating means comprises a plurality of heating means, and controls the supply power by switching a combination of output and non-output to each heating means. Claim 4
An image forming apparatus according to claim 1. 7. An image forming body, means for forming a toner image on the image forming body, an intermediate transfer body, and transferring the toner image on the image forming body to a surface of the intermediate transfer body or a transfer material. First
An image including a transfer unit, a second transfer unit that re-transfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material, and a fixing unit that fixes the toner image transferred on the transfer material In the forming apparatus, the fixing unit includes at least a first fixing roller facing a front surface of the transfer material; a second fixing roller facing a back surface of the transfer material;
A first heating means for heating the fixing roller; a second heating means for heating the second fixing roller; and a second heating means for heating the second fixing roller.
The sum of the maximum power consumption of the heating means and the sum of the maximum power consumption of the first heating means and the maximum power consumption of the second b heating means are respectively set to be equal to or less than the maximum power consumption allowed for the fixing means. 2a heating means and the second
b. An image forming apparatus wherein simultaneous application of power to the heating means is prohibited. 8. A single-sided copy mode in which a toner image is formed only on the surface of the transfer material, the first heating unit and the second heating unit are energized to form a toner image on both surfaces of the transfer material. The image forming apparatus according to claim 7, wherein in the copy mode, the first heating unit and the second b heating unit are energized. 9. An image forming body, means for forming a toner image on the image forming body, an intermediate transfer body, and transferring the toner image on the image forming body to a surface of the intermediate transfer body or a transfer material. First
An image including a transfer unit, a second transfer unit that re-transfers the toner image transferred on the intermediate transfer body to the back surface of the transfer material, and a fixing unit that fixes the toner image transferred on the transfer material In the forming apparatus, the fixing unit includes at least a first fixing roller facing a front surface of the transfer material; a second fixing roller facing a back surface of the transfer material;
The first heating unit for heating the fixing roller, the second heating unit for heating the second fixing roller and the second heating unit for heating, when in a one-sided copy mode for forming a toner image only on the surface of the transfer material, In the double-sided copy mode in which the first heating unit and the second heating unit are energized to form toner images on both surfaces of the transfer material, the first heating unit, the second heating unit and the second heating unit are energized. An image forming apparatus.