JPH1152781A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize excellent fixation with low power consumption even when the fixation of transfer material holding a toner image on both sides or one side is executed without reducing the throughput of the transfer material by changing an image forming interval in accordance with the temperature of a fixing means. SOLUTION: The fixation of the surface toner image is executed in a state where a 1st fixing roller being a hard roller is kept at almost initial regulated temperature t0 at the time of fixation. Meanwhile, in the case of recording paper whose heat capacity is large or recording paper whose size is larger than standard size, the surface temperature at the time of fixation gradually falls on a 2nd fixing roller being a soft roller. The temperature of the 1st fixing roller is apt to somewhat fall because it is influenced by the temperature of the 2nd fixing roller. When the temperature falls to be equal to or under set temperature t1 lower than the regulated temperature t0 at which the fixation can be executed, a control part 50 judges to change an image interval through an image interval change judging circuit 51A and changes the image interval through an image interval control means 52A.

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.

The present invention solves the above-mentioned problems, and achieves good fixing with little power consumption even when a transfer material holding toner images on both sides is collectively fixed without reducing the number of processed transfer materials as much as possible. It is another object of the present invention to provide an image forming apparatus capable of performing good fixing on a transfer material having a toner image on one side with low power consumption.

[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. An image forming apparatus comprising: a fixing unit for fixing an image; and a control unit for changing an interval at which an image is formed according to a temperature of the fixing unit. And an image forming body, means for forming a toner image on the image forming body, an intermediate transfer body, and a first for transferring the toner image on the image forming body to a surface of the intermediate transfer body or a transfer material. Transfer means, and a toner image transferred on the intermediate transfer body. Second to retransfer to the backside of the serial transfer material
In an image forming apparatus including a transfer unit and a fixing unit that fixes a toner image transferred onto the transfer material, a control unit that changes an interval at which an image is formed according to a material of the transfer material is provided. Characteristic image forming apparatus (Claim 4)
And 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 the surface of the intermediate transfer body or the transfer material A first transfer unit that transfers the toner image transferred onto the intermediate transfer body to a back surface of the transfer material;
An image forming apparatus comprising: a fixing unit for fixing a toner image transferred onto the transfer material; and a control unit for changing an image forming interval in accordance with the size of the transfer material. This is achieved by a forming apparatus (the invention according to claim 7).

[0008]

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 an 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, which is an image forming body, has 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 the same.
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 an exposure position on the photosensitive drum 10 between a discharge electrode 11a of the scorotron charger 11 and a development position of the developing 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 is a light emitting element 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).

A developing unit 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, such as 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 unit 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.

The gear G provided on the rear flange 10b of the photosensitive drum 10 is rotated through a driving gear (not shown) by the start of a photosensitive member driving motor (not shown) when image recording is started, and the photosensitive drum 10 is rotated. 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 a potential is applied to the photosensitive drum 10, the 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 reversely developed in a non-contact state by a Y developing unit 13 to form a yellow (Y) toner image 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 to the left of the photosensitive drum 10 and above the yellow (Y), a magenta (M) developing device 1 is provided.
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 device 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 serving as a back image is formed on the photosensitive drum 10 as an image forming body, and the superimposed color toner image of the back 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.

After the transfer, the toner remaining on the peripheral surface of the photosensitive drum 10 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 photosensitive 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 receiving body 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.

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, fed by a feed roller 15b, and conveyed to a timing roller 15c.

The recording paper P is driven by the timing roller 15c to form a color toner image of the front image carried on the photosensitive drum 10 and a color toner image of the 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 the present 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 with each other, it is preferable that the toner in the upper layer and the toner in the lower layer of the toner layer are charged with the same charge amount and the same polarity 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 photoreceptor 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 0.5-2.
An endless rubber belt of 0 mm, a semiconductive substrate such as silicon rubber or urethane rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 to 5 mm outside the rubber substrate as a toner filming prevention layer. 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 is brought into contact with and abuts on the toner image receiver 14a provided in a toner image receiver cleaning device 14i as cleaning means for 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.

In the above-described image forming apparatus, it is a matter of course that only the one-sided copy can be made by the first image bearing means or the second image bearing means. Although copying (single-sided image formation) is often used, as shown in FIG. 4, recording paper P passing through the fixing device 30 when forming only a single-sided image on the front surface by the photosensitive drum 10 is continuously performed. The recording paper P passing through the fixing device 30 at the time of image formation is intermittently formed because the process of once forming the back surface image on the toner image receiver 14a and then forming the front surface image on the photosensitive drum 10 is repeated. Therefore, the printing speed at the time of forming a double-sided image is half that at the time of forming a single-sided image of only the front surface.

The fixing device 30 used in the image forming apparatus of the present invention includes a first fixing roller 31 facing the surface toner image.
0, it is necessary that both the second fixing roller 320 facing the back side toner image have a heating means to heat and fix the recording paper P from both sides, and the first fixing roller 310 and the second fixing roller 320 It is necessary for fixing to form a nip portion of several mm in the recording paper conveyance direction in the contact portion,
In order to form the nip portion, it is necessary to provide one of the rollers with an elastic layer made of an elastic material such as silicon rubber. Since the elastic layer has a lower thermal conductivity than the metal material, the fixing roller provided with the elastic layer loses heat to the recording paper when the recording paper passes, and the lowered roller surface temperature is often large. Time is required. Therefore, the first fixing roller 310, which is responsible for forming a single-sided image only on the surface having a high printing speed, is a hard roller, and the second fixing roller 320
Is a soft roller provided with an elastic layer.

FIG. 5 is a configuration diagram showing an embodiment of a fixing device used in the present image forming apparatus.

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 comprising a halogen lamp or the like and a second heater 321 as a second heating means at 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 second fixing roller 320 is a so-called hard roller having a layer thickness smaller than the layer thickness a or a layer thickness of 0, and the second fixing roller 320 is 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 configured to lightly contact with web cleaning devices 312 and 322 made of, for example, a nonwoven 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 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.

FIG. 13 is a block diagram showing an image forming apparatus provided with such a fixing device 30.
A copy mode selection button is provided as 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. When a back side image is detected, a double-sided copy mode is automatically selected to perform image formation and fixing.

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 device, 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 fixing device 30 holds the toner image on the upper surface, and the fixing device 30 fixes the surface image on the recording paper P conveyed to the fixing device 30.
The recording paper P on which the fixing has been completed is sent by a paper discharge roller 18 and discharged to a tray outside the apparatus.

When the double-sided copy mode is selected, the control unit 50 first calls up 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 fixes the double-sided image on the recording paper P, which holds the toner image on both sides and is conveyed to the fixing device 30, and the fixed recording paper P is discharged to the outside of the device by a discharge roller 18. It is discharged to a tray.

In the image forming apparatus of this embodiment, the first fixing roller 310 is a hard roller, and the second fixing roller is an elastic layer in order to cope with the two-sided copy mode and the one-sided copy mode in which high-speed printing is performed. Soft rollers provided. Therefore, the first fixing roller 310 has good thermal responsiveness, whereas the second fixing roller 320 has poor thermal responsiveness. For this reason, in the double-sided copy mode or the backside copy mode, there is a problem that the roller surface temperature of the second fixing roller 320 decreases when continuous printing is performed.

FIG. 6 is an explanatory view schematically showing this relationship. FIG. 6A shows the surface temperature state (A1) of the first fixing roller 310 in the single-sided print mode. Since the first fixing roller 310 is a hard roller, the first heater 3
The amount of heat emanating from 11 is transmitted within a short time to the roller surface by heat conduction, and since the heat capacity is large, the temperature drop due to the passage of the first recording paper is slight, and the second recording paper Although the time interval i1 until the temperature reaches a small _value , the temperature has sufficiently returned to the initial temperature t ₀ , and good fixing is performed intermittently even with a large number of continuous copies.

FIG. 6B shows the surface temperature state (B1) of the first fixing roller 310 and the surface temperature state (B2) of the second fixing roller 320 in the duplex copy mode. Since the second fixing roller 320 is a soft roller, the amount of heat taken away by the passage of the first recording sheet is not sufficiently replenished by heat conduction, and the second fixing roller after the first recording sheet has passed. The surface temperature of 320 has dropped. The lowered surface temperature of the second fixing roller 320 rises during a relatively long time interval i2 until the second recording sheet arrives,
It will return to the initial temperature t ₀ . Although the heat conduction of the amount of heat generated from the inside of the second heater 321 also contributes to the temperature rise on the surface of the second fixing roller 320 within the time interval i2, the first rotating member mainly rotates in the contact relationship. This is due to heat conduction from the fixing roller 310.

FIG. 7 shows the state of the surface temperature of the second fixing roller 320 in the two-sided copy mode, and shows the state of the surface temperature when plain paper is used as the recording paper to be fixed. The state is shown. (C
2) shows the surface temperature state when a material having a large heat capacity is used as the recording paper. When fixing is performed on a material having a large heat capacity, such as thick paper, as the recording paper, the recording paper absorbs a larger amount of heat than the plain paper at the time of fixing, and the surface temperature of the second fixing roller 320 becomes low. Accordingly, when an image is formed on a recording sheet having a large heat capacity by an image forming apparatus configured for plain paper, the surface temperature of the second fixing roller 320 is reduced when the leading end of the second recording sheet reaches the fixing device 30. Without returning to the initial temperature t ₀ , t ₀ −Δ
It is in a temperature state of t _C. When the second and third sheets are continuously printed as they are, the fixing temperature of the second fixing roller 320 decreases by approximately Δt _C. Initially, there is almost no effect on the fixing, but if the fixing is continued for a large number of sheets continuously, the back side toner image will eventually have a fixing defect.

FIG. 8 also shows the state of the surface temperature of the second fixing roller 320 in the double-sided copy mode in the same manner as in FIG. 7, and (B2) shows ordinary-size plain paper as recording paper for fixing. 2 shows the surface temperature state when using. (D2) shows the surface temperature state when a large-sized plain paper recording paper passes. In the case of a large-size recording paper, heat is absorbed from the rollers to the recording paper for a longer time than in the normal size, and when the first sheet is fixed, the surface temperature of the second fixing roller 320 is reduced. It becomes low temperature. Therefore, when an image is formed on a large-size recording sheet by an image forming apparatus configured for a normal-size recording sheet, when the second large-size recording sheet reaches the fixing device 30, the second fixing roller The surface temperature of 320 does not return to the initial temperature t ₀ , and is in a temperature state of t ₀ −Δt _D. If continuous printing is performed on the second and third sheets and the large-size recording sheet as it is, the fixing temperature of the second fixing roller 320 decreases by approximately Δt _D. Initially, there is almost no effect on the fixing, but if a large number of sheets of several to several tens are continuously fixed, the backside toner image eventually causes a fixing failure.

The image forming apparatus of the present invention performs continuous printing using recording paper having a larger heat capacity than plain paper in the double-sided copy mode or the backside copy mode, or prints recording paper having a large size compared to normal size. Even if continuous printing is performed, control is performed to increase the image interval for forming an image without changing the process speed so that a fixing failure or the like does not occur on the back side toner image. This control is performed not for each sheet but for several to several tens of continuous prints.

(Embodiment 1) The image forming apparatus of this embodiment has a control means for changing the image interval. When the temperature change of the second fixing roller 320 with respect to the specified temperature is larger than an allowable range, the image interval is changed. Is changed to be larger. FIG. 9 is an explanatory diagram of the present embodiment, and FIG. 10 is a block diagram showing the control system of the present embodiment.

FIG. 9 shows the first fixing roller 310 and the second fixing roller 3 when continuous copying is performed in the duplex copy mode.
20 shows a fluctuation state of the surface temperature with 20. The first fixing roller 310 is a hard roller is kept at t ₀ is substantially the initial prescribed temperature fixing surface the toner image is performed at the time of fixing as shown in (A1). On the other hand, if the recording paper is a recording paper having a large heat capacity or a recording paper having a size larger than the standard, the surface temperature at the time of fixing is gradually increased as shown by the second fixing roller 320 (E2) which is a soft roller. Comes down. At this time, the temperature of the first fixing roller 310 tends to decrease slightly due to the temperature of the second fixing roller 320. In the present embodiment, the fixing is enabled, but when the temperature drops to the set temperature t ₁ or lower which is lower than the specified temperature t ₀ , the control unit 50 changes the image interval change determination circuit 51.
It is determined that the image interval is changed by A, and the image interval is changed by the image interval control unit 52A. It is appropriate to change the image interval to 1.5 to 4 times the image interval at the time of the above determination (current). By such a change in the image interval, the surface temperature at the time of fixing by the second fixing roller 320 gradually approaches the fixing temperature t ₀ while continuing the fixing operation as shown in FIG.

Although the image interval is widened by the image interval control means 52A, the temperature detected by the second temperature sensor 324 for a plurality of sheets, for example, five or more sheets, is less than the set temperature t ₁ . When the distance is smaller than that, it is also possible to perform secondary image interval control so as to further increase the image interval.

Further, a counter is provided in the control unit 50, and after the continuous copying is started, the second fixing roller 320 is set at the set temperature t.
_{The number} of copies is weighed until it becomes ₁ or less. For example, when the temperature falls below the set temperature t ₁ within 20 copies, the image interval is controlled to be four times the current value, and the set temperature t ₁ exceeds 20 copies. When the following conditions are satisfied, image formation is performed while minimizing a reduction in the processing speed of image processing by performing a plurality of stages of image interval control, such as controlling the image interval to double the current interval.

(Embodiment 2) The image forming apparatus of this embodiment has a control means for changing the image interval, and the heat capacity of the transfer material is reduced to the heat capacity of plain paper in accordance with the material of the transfer material for performing continuous copying. If it is larger, the image interval is changed to be larger. FIG. 11 is a block diagram showing the control system according to the present embodiment.

For detecting the material of the transfer material, a paper quality detecting means 53B may be provided along the transfer material conveyance path.
It is also possible to detect the paper quality using the paper charger 14f in the image forming apparatus shown in FIG. That is, a voltage having an AC component is temporarily applied to the paper charger 14f while the transfer material is sandwiched between the paper charger 14f, which is a brush charger, and the toner image receiving body 14a, and the paper thickness is determined from the impedance. (Heat capacity)
The image interval change determination circuit 51B compares the impedance of plain paper stored in advance as a memory with the image interval change determination circuit 51B to determine whether to increase the image interval. If it is determined that the cardboard has a larger heat capacity, the image interval is changed to 1.5 to 4 times the current image interval by the image interval controller 52B. It is not necessary to change the image interval from the beginning of the continuous copy.
Control may be performed to increase the image interval after copying.

In the case where the recording paper is thick paper, manual feeding is often performed. Therefore, the manually fed recording paper is unconditionally determined to be thick paper, and control is performed so as to widen the image interval. Is also good.

In the image forming apparatus of the present embodiment, the image interval is controlled so as to be changed in accordance with the material of the recording paper. In the embodiment, the temperature at the time of fixing the second fixing roller 320 described in (Embodiment 1) is used. When the temperature is lowered to a temperature lower than the specified temperature, the control is performed in such a manner that the image interval is widened, whereby an excellent effect that good fixing is performed without unnecessarily lowering the processing speed unnecessarily can be obtained.
For example, at the time of continuous copying in the double-sided copy mode, the paper quality detecting means 53B first detects whether or not the paper is thick paper, and when it is detected that the paper is thick, for example, after 11 copies, the image interval is set to 1.5 to the initial image interval. Change to 3 times. After this change, the second temperature sensor 324 detects the roller surface temperature of the second fixing roller 320 and compares the detected temperature with the set temperature t _1.
When 0 of the roller surface temperature is lower than the set temperature t ₁ changes the image interval 1.5-3 times the image interval at that time, the processing speed of the image formed by such a combination control There is provided an image forming apparatus capable of performing satisfactory double-sided fixing without lowering it.

(Embodiment 3) The image forming apparatus of this embodiment has control means for changing the image interval, and the size in the transport direction of the transfer material for performing continuous copying is a reference size (for example, A4 size). If it is larger, change so as to increase the image interval. FIG. 12 is a block diagram showing the control system of the present embodiment.

The transfer material size is detected by the paper size detecting means 5.
3C. This paper size detection means 53C is performed by detecting the passage time of the transfer material by a photo sensor provided along the transfer material conveyance path, and also changes the size of the recording paper from the size of the paper cassette into which the discharged recording paper is built. Is detected. Image interval change determination circuit 51
In C, a reference size (for example, A4
Size). This comparison may be a comparison of the length of the fed recording paper in the feeding direction, a B4 size,
It may be a comparison of standardized sizes such as A3 size. If it is determined that the recording paper on which continuous copying is to be performed is larger than the reference size, the image interval is changed to 1.5 to 4 times the current image interval by the image interval controller 52C. When the detected recording paper size is B4 size with respect to the reference size A4, the current image interval is doubled, and when the detected paper size is A3 size, it is quadrupled. It is also possible to change the image interval by using a program. It is not necessary to change the image interval from the beginning of the continuous copy. For example, when the detected recording paper size is the B4 size, the current image interval is set to 20 copies, and the image interval is set to 2 after 21 copies. If the detected recording paper size is A3 size, control can be performed such that the current image interval is up to 10 copies and the image interval is quadrupled after 11 copies.

In the image forming apparatus of this embodiment, when the detected recording paper size is larger than the reference size, control is performed so as to change the image interval, but this embodiment has also been described earlier (Embodiment 2). In the same manner as described in the first embodiment, the control is performed by increasing the image interval when the temperature at the time of fixing of the second fixing roller 320 decreases to a temperature lower than the specified temperature as described in (Embodiment 1). There is provided an image forming apparatus capable of performing satisfactory fixing without lowering the speed more than necessary.

The image interval may be changed in several steps in order to change the fixing temperature and the change in the temperature one by one, so that the user is not conscious of the change in the print speed.

[0069]

According to the present invention, even if the transfer material is thick paper or a large-size transfer material, even if continuous copying is performed in the double-sided copy mode, no fixing failure occurs and the operation is stopped. Thus, an image forming apparatus capable of forming a good image at the same process speed without providing the same is provided.

[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 showing a relationship between a copy mode and an image interval.

FIG. 5 is a cross-sectional configuration diagram of a fixing device used in the present invention.

FIG. 6 is an explanatory diagram illustrating a surface temperature state of a first fixing roller in a single-sided and double-sided copy mode.

FIG. 7 is an explanatory diagram illustrating a surface temperature state of a second fixing roller when a material of a transfer material is different.

FIG. 8 is an explanatory diagram illustrating a surface temperature state of a second fixing roller when the paper size is different.

FIG. 9 is an operation explanatory view of the first embodiment.

FIG. 10 is a block diagram of a control system according to the first embodiment.

FIG. 11 is a block diagram of a control system according to the second embodiment.

FIG. 12 is a block diagram of a control system according to a third embodiment.

FIG. 13 is a block diagram of a control system common to the first to third embodiments.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum (image forming body) 11 scorotron charger 12 exposure unit 13 developing unit 14a toner image receiver (intermediate transfer body) 14c first transfer unit (first transfer unit) 14g back surface transfer unit (second transfer unit) 14h Paper separation AC neutralizer 30 Fixing device (fixing unit) 310 First fixing roller 320 Second fixing roller 311 First heater (first heating unit) 321 Second heater (second heating unit) 314 First temperature sensor (first unit) 1 temperature detection means) 324 second temperature sensor (second temperature detection means) 51A, 51B, 51C image interval change determination circuit 52A, 52B, 52C image interval control means 53B paper quality detection means 53C paper size detection means

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 An image forming apparatus, comprising: a control unit for changing an interval at which an image is formed according to a temperature of the fixing unit. 2. The image forming apparatus according to claim 1, wherein an interval at which an image is formed is increased when a temperature change of the fixing unit is larger than an allowable range. 3. The fixing device according to claim 1, wherein the first fixing roller facing the front toner image is a hard roller, and the second fixing roller facing the rear toner image is a soft roller. An image forming apparatus according to claim 1. 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 An image forming apparatus, comprising: a control unit for changing an interval at which an image is formed according to a material of the transfer material. 5. The image forming apparatus according to claim 4, wherein when the heat capacity of the transfer material is larger than a reference value, the interval at which an image is formed is increased. 6. The fixing device according to claim 4, wherein the first fixing roller facing the front toner image is a hard roller, and the second fixing roller facing the rear toner image is a soft roller. 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 An image forming apparatus, comprising: a control unit that changes an interval at which an image is formed according to a size of the transfer material. 8. The image forming apparatus according to claim 7, wherein when the transfer material size is larger than a reference size, an image forming interval is increased. 9. The fixing device according to claim 7, wherein the first fixing roller facing the front toner image is a hard roller, and the second fixing roller facing the back toner image is a soft roller. An image forming apparatus according to claim 1.