JP3595894B2 - Control method of image forming apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that forms an image by an electrophotographic method, and a method of controlling the image forming apparatus. Particularly, a toner image is formed on both surfaces of a transfer material, and the toner image is collectively heated and fixed to form a double-sided image. The present invention relates to an image forming apparatus that performs formation, and a method for controlling the image forming apparatus.
[0002]
[Prior art]
Conventionally, in double-sided copying, an image on one side formed on an image carrier is transferred and fixed on a transfer material, which is temporarily stored in a two-sided reversing sheet feeding device, and formed again on the image carrier. In this method, a transfer material is fed from a two-sided reversing paper feeder in synchronization with the image, and the image on the other surface is transferred and fixed onto the transfer material.
[0003]
As described above, this double-sided copying apparatus transports a transfer material such as feeding to a two-sided reversing paper feeder or passing through a fixing device twice, so that the transfer distance of the transfer material is long, so that many copies are required. The processing time is long, the reliability of transfer of the transfer material is low, and this causes a jam or the like. On the other hand, once a toner image is formed on both surfaces of a transfer material according to JP-B-49-37538, JP-B-54-28740, JP-A-1-44457 and JP-A-4-214576, once It is proposed that the fixing is performed by using the following method.
[0004]
[Problems to be solved by the invention]
It is not easy to fix a transfer material having toner images on both sides at once. As will be described later, in the process of transferring the toner image formed on the image carrier to both sides of the transfer material, the charge of the toner on one side is minus and the charge of the toner on the other side is plus.
[0005]
On the other hand, as a surface material of the fixing roller for fixing, a fluorine-based resin or a silicon-based resin is often used, and as a friction charging series, the negative charging property is strong. It is negatively charged. Accordingly, when the positively charged toner adhering to the transfer material surface comes into contact with the negatively charged roller, the toner is strongly adhered to the roller due to the Coulomb force therebetween. Normally, when the toner is heated by the fixing roller to be in a molten state, the so-called offset phenomenon that adheres to the fixing roller due to an increase in physical adhesive force occurs, thereby contaminating the image. The increase in the resilience further enhances the adhesion to the roller, and as a method of reducing the adhesion between the roller and the toner that is usually applied, the release property is imparted by applying silicone oil to the roller, It is no longer possible to eliminate the adhesion of the toner to the roller and the offset can no longer be eliminated only by selecting a good roller surface material and improving the toner by providing a releasability by increasing the melt elasticity of the toner.
[0006]
In order to eliminate the above-mentioned offset, the present inventors applied a charge of the same polarity to the positively charged toner on the surface of the transfer material having electrical adhesion to the roller to increase the electrical repulsion, thereby increasing the offset. As a result, when the transfer material having a toner image on only one side is fixed, the offset can be eliminated, and good results can be obtained. However, in the case of a transfer material having toner images on both sides, although it was effective for eliminating the offset on the front surface of the transfer material, on the other hand, a more significant offset was generated on the back surface.
[0007]
This is because when the upper roller is positively charged, the lower roller is pressed against the upper roller and rotates, so the positive charge applied to the upper roller is transferred to the lower roller and the lower roller is also positively charged. This causes electrical adhesion to be generated between the negatively charged toner on the back surface of the transfer material and the lower roller, causing the same problem as that occurring in the upper roller. it is conceivable that.
[0008]
The present invention has been made in view of the above considerations, and (1) an image forming apparatus in which no offset occurs on both the front and back surfaces even when a transfer material holding a toner image on both surfaces is collectively transferred by image formation. And (2) It is an object of the present invention to provide a control method of an image forming apparatus capable of forming an image on one side or both sides without causing an offset.
[0009]
[Means for Solving the Problems]
[0011]
UpOfMy goal is,
A first image forming step of directly transferring a toner image formed on an image carrier to a surface of a transfer material, and a toner image formed on the image carrier via an intermediate transfer body capable of holding the toner image A second image forming step of transferring to the transfer material,Toner images on both sides of transfer materialToFormationAfterFixing means for heating and fixing all at onceAnd a control unit for controlling image formation and fixingImage forming apparatus provided withIn the control method of,The fixing unit includes an upper fixing roller and a lower fixing roller, and a first electric field forming unit and a second electric field forming an electric field between the upper fixing roller and the lower fixing roller, respectively. Forming means are provided;Form toner image on one side of transfer materialThen fix1st mode to form toner images on both sides of transfer materialThen fixA first mode and a second mode.To specify the mode frommeansThe control unit, when the first mode is designated by the designation unit, fixing the first electric field forming unit provided in the fixing unit is operated, without operating the second electric field forming unit, When the second mode is specified by the specifying unit, the first electric field forming unit and the second electric field forming unit provided in the fixing unit are operated to perform fixing.Image formationControlFor controlling an image forming apparatus characterized by performingLaw
ToMore achieved.
[0012]
In the above invention,The electric field forming means includes an upper fixing roller and a lower fixing roller.It is a preferred embodiment that the charging member is a biasing means for applying a voltage to the fixing member, or a charging member for applying a charge to the surface of the fixing member.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Prior to the description of the present invention, an embodiment of an image forming apparatus in which a toner image is formed on both surfaces to which the present invention is applied and fixed collectively 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. Further, in the following description of the embodiment, when transferring a color toner image to a transfer material, an image to be transferred to a surface of the transfer material facing the image carrier in the transfer area is a surface image, the other of the transfer material. The image transferred to the surface on the side of is referred to as the back surface image. Each of the embodiments described below is an example of a color image forming apparatus for forming a color image, but the present invention is also applied to a monochrome image forming apparatus.
[0014]
An image forming process and each mechanism of the embodiment of the color 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 carrier of FIG. 1, and FIG. It is a figure showing a formation state.
[0015]
The photosensitive drum 10 serving as an image carrier has, for example, a cylindrical base formed of a transparent member of optical glass or transparent acrylic resin provided inside, and a transparent conductive layer, 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. 1 in a grounded state.
[0016]
As shown in FIG. 2, the photoreceptor drum 10 has flange members 10a and 10b at both ends for engaging and fixing the same. The gears G integrally formed with the flange member 10b are rotatably supported by bearings 110a and 110b, and are rotated in a predetermined direction at a constant speed by being driven by meshing with a driving gear on the apparatus main body side. .
[0017]
A scorotron charger 11 as a charging unit is used in image forming processes of yellow (Y), magenta (M), cyan (C), and black (K), and moves in a direction in which a photosensitive drum 10 as an image carrier is moved. A control grid attached to the photosensitive drum 10 in a direction orthogonal to the photosensitive drum 10 and maintained at a predetermined potential with respect to the above-described organic photosensitive layer of the photosensitive drum 10, and a sawtooth-shaped discharge electrode 11a, for example. The charging action (minus charging in the present embodiment) is performed by corona discharge having the same polarity as the toner using the electrodes, and a uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.
[0018]
The exposure unit 12 as an image exposure unit 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 with respect to the development sleeve 131. It is arranged in a state provided on the upstream side in the rotation direction of the photosensitive drum.
[0019]
The exposure unit 12 includes a linear exposure element 12a in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10 are arranged in an array. The selfoc lens 12b as a double imaging element is configured as an exposure unit attached to a holder (not shown). 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 substrate 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.
[0020]
As the exposure element, an element in which a plurality of light emitting elements such as FL (phosphor emission), EL (electroluminescence), PL (plasma discharge), and LED (light emitting diode) 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 the transmittance of the Y, M, and C toners. A shorter wavelength which does not have sufficient transparency may be used.
[0021]
In the present embodiment, the developing unit 13 provided in accordance with the color order in which the image is formed and the rotating photoconductor drum is arranged in the rotation direction of the photoconductor drum 10 indicated by an arrow in FIG. The Y and M developing units 13 are arranged on the left side of the photosensitive drum 10, and the C and K developing units 13 are arranged on the right side of the photosensitive drum 10, and below the developing casing 138 of the Y and M developing units 13. The Y and M scorotron chargers 11 and the C and K scorotron chargers 11 are arranged above the developing casing 138 of the C and K developing units 13.
[0022]
A developing device 13 as a developing means for each color contains a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K), respectively. For example, a cylindrical non-magnetic stainless steel having a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm rotating in the same direction as the rotation direction of the photosensitive drum 10 at the developing position while maintaining a predetermined gap with respect to the peripheral surface of A developing sleeve 131 made of an aluminum material is provided.
[0023]
The developing device 13 is kept out of contact with the photosensitive drum 10 by a contact roller (not shown) with a gap of a predetermined value, for example, 100 to 1000 μm, and when the developing device 13 for each color performs a developing operation, the developing sleeve 131 is used. A developing bias to which a DC voltage or an AC voltage AC is further applied is applied to the photosensitive drum, a jumping development is performed by a one-component or two-component developer accommodated in the developing device, and the transparent conductive layer is grounded. A DC bias having the same polarity as the toner (minus polarity in the present embodiment) is applied to the drum 10 to perform non-contact reversal development in which the toner adheres to the exposed portion. At this time, the accuracy of the development interval needs to be about 20 μm or less in order to prevent image unevenness.
[0024]
The developing unit 13 for each of the above-mentioned colors is configured to contact 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 manner by applying a developing bias voltage. In a non-contact state by the developing method, the toner image is reversely developed with a toner having the same polarity as the charged polarity (in the present embodiment, the photosensitive drum is negatively charged and has a negative polarity).
[0025]
An image read by an image sensor of an image reading apparatus separate from the apparatus or an image edited by a computer as an original image is temporarily stored in a memory as image data for each of Y, M, C and K colors. Is stored.
[0026]
A gear 10G provided on a rear flange 10b of the photosensitive drum 10 is rotated through a driving gear G1 by the start of a photosensitive member drive motor (not shown) at the start of image recording, and the photosensitive drum 10 is indicated by an arrow in FIG. It rotates clockwise, and at the same time, the potential of the photosensitive drum 10 is changed by the charging action of the Y scorotron charger 11 disposed below the developing casing 138 of the yellow (Y) developing device 13 to the left of the photosensitive drum 10. The grant is started.
[0027]
After the photosensitive drum 10 is applied with a potential, the exposure is started by a first color signal, that is, an electric signal corresponding to the Y image data in the Y exposure unit 12, and the original is formed on the photosensitive layer on the surface by the rotation scanning of the drum. An electrostatic latent image corresponding to the Y image is formed.
[0028]
The latent image is reversal-developed by the Y developing device 13 in a state where the developer on the developing sleeve is not in contact with the developer, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.
[0029]
Next, the photosensitive drum 10 is disposed on the yellow (Y) toner image, further to the left of the photosensitive drum 10, above the yellow (Y), and below the developing casing 138 of the magenta (M) developing unit 13. An electric potential is applied by the charging action of the scorotron charger 11 of magenta (M), and exposure is performed by the second color signal of the M exposure unit 12, that is, an electric signal corresponding to M image data, and development of M is performed. The magenta (M) toner image is sequentially superimposed on the yellow (Y) toner image by the non-contact reversal development by the container 13.
[0030]
In the same process, a cyan (C) scorotron charger 11, a C exposure unit 12, and a C developing unit disposed on the right side of the photosensitive drum 10 above the developing casing 138 of the cyan (C) developing unit 13. 13 further arranges a cyan (C) toner image corresponding to the third color signal on the right side of the photosensitive drum 10, below the C and above the developing casing 138 of the black (K) developing unit 13. A black (K) toner image corresponding to the fourth color signal is sequentially superimposed by the black (K) scorotron charger 11, the exposure unit 12, and the developing unit 13 within one rotation of the photosensitive drum 10. Then, a color toner image is formed on the peripheral surface.
[0031]
The exposure of the organic photosensitive layer of the photosensitive drum 10 by the Y, M, C and K exposure units 12 is performed from the inside of the drum through the above-mentioned transparent substrate. 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 the same exposure as the image corresponding to the first color signal is performed. An electrostatic latent image can be formed.
[0032]
Through the above-described image forming process, a superimposed color toner image serving as a back image is formed on the photosensitive drum 10 (first image carrying means) as an image carrier, and the superimposed color of the back image on the photosensitive drum 10 is formed. In the transfer area 14b, the toner image is stretched between the drive roller 14d and the driven roller 14e by the transfer unit 14c to which a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. Is transferred collectively onto a toner image receiving member 14a (intermediate transfer member) provided close to or in contact with the toner image receiving member. 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.
[0033]
The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the image carrier AC static eliminator 16, and then enters a cleaning device 19 or a cleaning blade made of a rubber material abutted on the photosensitive drum 10. In order to eliminate the history of the photoreceptor up to the previous print, the photoreceptor peripheral surface is discharged by, for example, exposure by the uniform exposure unit 12c before charging using a light emitting diode, and the photoreceptor is removed by the previous print. After the charge is removed, a color image of the next surface image is formed.
[0034]
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 placed on the photosensitive drum 10 in the same manner as the above-described color image forming process. It is formed. It is necessary to change the image data so that the front side image formed at this time is a mirror image of the back side image formation on the image carrier.
[0035]
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.
[0036]
The recording paper P is synchronized with the color toner image of the front surface image carried on the photosensitive drum 10 and the color toner image of the back surface image carried on the toner image receiver 14a by driving the timing roller 15c. Then, it is fed to the transfer area 14b. 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 unit, 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, the toner is prevented from being attracted to the toner image on the toner image receiving body or the toner image on the image carrier, and the disturbance of the toner image is prevented. Further, as the transfer material charging means, a conductive roller or a brush charger capable of contacting and releasing contact with the toner image receiver can be used.
[0037]
The surface image on the peripheral surface of the photosensitive drum 10 is collectively collected by the 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. Side (front side). At this time, the back surface image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a. Next, a backside image on the peripheral surface of the toner image receiver 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 this embodiment) is applied. The image is transferred to the lower surface (back surface) of the paper P. At the time of transfer by the transfer unit 14c, uniform exposure is performed by a simultaneous transfer exposure unit 12d using, for example, a light-emitting diode, provided inside the photosensitive drum 10 so as to perform excellent transfer so as to face the transfer unit 14c. Is performed.
[0038]
Since the toner images of the respective colors overlap with each other, it is preferable that 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 a double-sided image formation in which the polarity of a color toner image formed on the toner image receiving body 14a is inverted by corona charging or the polarity of a color toner image formed on an image carrier is inverted by corona charging, the lower layer is formed. The toner is not sufficiently charged to the same polarity, so that the transfer becomes unfavorable.
[0039]
The reversal development is repeated on the image carrier, and the color toner images of the same polarity formed by superimposition are collectively transferred to the toner image receiver 14a without changing the polarity, and then collectively transferred onto the recording paper P without changing the polarity. Transferring is preferable because it contributes to the improvement of the transferability of backside image formation. For the surface image formation, reversal development is repeatedly performed on the image carrier, and the color toner images of the same polarity formed by superimposition are collectively transferred to the recording paper P without changing the polarity. It is preferable because it contributes to improvement of the properties.
[0040]
From the above, in the color image formation, the first transfer unit is operated to form a color toner image on the surface of the transfer material using the above-described front and back surface image forming method, and then the second A double-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the transfer means is preferably employed.
[0041]
The toner image receiver 14a is an endless rubber belt having a thickness of 0.5 to 2.0 mm, and is made of silicone rubber or urethane rubber.⁸-10¹²It has a two-layer structure in which a semiconductive substrate having a resistance value of Ω · cm and a fluorine coating having a thickness of 5 to 50 μm as a toner filming preventing layer are formed on the outside of a rubber substrate. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like having a thickness of 0.1 to 0.5 mm can also be used.
[0042]
The recording paper P on which the color toner images are formed on both sides is discharged by a paper separation AC discharger 14h for transfer material separation, separated from the toner image receiving body 14a, and heated inside both upper and lower rollers described later. Is transported to a fixing device 30 as a fixing unit composed of two rollers having The recording paper P is applied heat and pressure between the upper fixing roller 310 and the lower fixing roller 320 so that the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P on which double-sided image recording is performed. Is sent by a paper discharge roller 18 and discharged to a tray outside the apparatus.
[0043]
The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer can be brought into contact with and released from the toner image receiver 14a provided in a toner image receiver cleaning device 14i as cleaning means for the toner image receiver. Is cleaned by a suitable blade. The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the image carrier AC static eliminator 16 and then enters the cleaning device 19 or is made of a rubber material that is in contact with the photoconductor drum 10. The toner is scraped 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 uniformly charged by the Y scorotron charger 11, and enters the next image forming cycle.
[0044]
Here, the potential of the toner adhering to the transfer material will be considered. Here, the photosensitive drum 10 serving as an image carrier is negatively charged, and the latent image on the photosensitive drum 10 is subjected to reversal development with toner having negative charge, so that the toner image having negative charge is exposed. The case in which it is formed on the body drum 10 will be described.
[0045]
In the first image forming step of directly transferring the toner image of the surface image formed on the photosensitive drum 10 onto the recording paper P, the potential of the toner on the recording paper P when entering the fixing device 30 is: As shown in the explanatory diagram of FIG. That is, the toner image of the negative polarity surface image formed on the photosensitive drum 10 is transferred to the positive polarity voltage by the transfer unit 14c via the recording paper P and the toner image receiving body 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 separated from the toner image receiving body 14a by the paper separation AC neutralizer 14h, and enters the fixing device 30 (FIG. 4B).
[0046]
A first image forming step of directly transferring the toner image of the front surface image formed on the photoconductor drum 10 onto the recording paper P, and the toner image of the rear surface image formed on the photoconductor drum 10 via an intermediate transfer member The potential of the toner on the recording paper P when entering the fixing device 30 with the toner images adhered to both surfaces of the recording paper P in the second image forming step of transferring the recording paper P onto the recording paper P is shown in FIG. As shown in FIG. In other words, the toner image of the negative polarity rear surface image formed on the photosensitive drum 10 is transferred to the toner image receiving member 14a by applying a positive polarity voltage from behind the toner image receiving member 14a by the transfer device 14c. (FIG. 5A). Subsequently, a toner image of a negative polarity surface image is formed on the photosensitive drum 10. The toner image of the front surface image is transferred to the upper surface of the recording paper P by applying a positive polarity voltage by the transfer device 14c via the recording paper P and the toner image receiving body 14a holding the toner image of the rear surface image behind the recording paper P. (FIG. 5B). Next, the toner image of the back side image adhered on the toner image receiver 14a is transferred to the lower side of the recording sheet P by applying a positive polarity voltage from the upper side of the recording sheet P by the back side transfer unit 14g. 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). The recording paper P is separated from the toner image receiver 14a by the paper separation AC neutralizer 14h in a state where the toner image of the positive polarity front image is held on the upper surface of the recording paper P and the toner of the negative polarity back image is held on the lower surface. Then, it enters the fixing device 30 (FIG. 5D).
[0047]
6 to 8 are cross-sectional views showing the configuration of the embodiment of the fixing device 30. Members having the same function are denoted by the same reference numerals, and description thereof is omitted.
[0048]
Each of the upper fixing roller 310 and the lower fixing roller 320 is provided with a heater 311, 321 made of a halogen lamp or the like on an inner core portion, and is a fixing rotating body having substantially the same structure. The roller portions of the fixing rollers 310 and 320 are provided with intermediate layers 310b and 320b made of a silicone rubber layer having a thickness of 0.8 to 2.2 mm on the upper side of metal cores 310a and 320a made of a metal pipe. A PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) layer having a thickness of 0.05 to 0.25 mm is provided. As the surface layers 310c and 320c, other than PFA, a heat-resistant high release layer such as a fluororesin such as PET (polyethylene terephthalate) or PTFE (polytetrafluoroethylene) or a silicon resin is used.
[0049]
The surface of the fixing rollers 310 and 320 is configured to lightly contact web cleaning devices 312 and 322 made of, for example, a nonwoven fabric in order to clean toner, paper powder, and the like attached to the surfaces.
[0050]
In order to enhance the releasability of the fixing rollers 310 and 320, oil applying rollers 313 and 323 impregnated with a sponge-like oil for applying a releasing agent such as dimethyl silicone oil or modified silicone oil to the roller surface are provided. I have.
[0051]
Further, temperature sensors 314 and 324 composed of a thermistor or the like are provided at positions in contact with or in close proximity to each of the upper fixing roller 310 and the lower fixing roller 320, and the ambient temperature of the rollers is detected. Blinking control of the heaters 311 and 321 is performed based on the temperature, and the temperature is kept within a predetermined temperature range.
[0052]
The upper fixing roller 310 and the lower fixing roller 320 are pressed against each other at a linear pressure of 0.8 to 1.8 kg / cm by a biasing member such as a spring (not shown). The length varies depending on the linear pressure and the hardness of the roller surface, but is about 2 to 7 mm. The upper fixing roller 310 and the lower fixing roller 320 are driven by the same driving source so as not to cause a slip at the nip portion, rotate at the same linear speed (160 mm / sec in this embodiment), and perform double-sided fixing at the nip portion. Done.
[0053]
(Embodiment 1)
In the image forming apparatus of the present invention (claim 1), the fixing device 30 as a fixing unit is provided between each of the upper and lower fixing rollers 310 and 320 as a fixing member and the recording paper P nipped and conveyed therebetween. FIG. 6 is a cross-sectional view showing the configuration of the first embodiment. In the figure, reference numeral 316 denotes a corona charger provided as an electric field forming means, which is provided to face the upper fixing roller 310, and applies a positive charge having the same polarity as the toner charge of the toner image on the upper surface of the recording paper P to the surface of the insulating roller. It is a corona charger provided as a charging means for applying. Reference numeral 326 denotes a corona charger provided to face the lower fixing roller 320, and a negative charge having the same polarity as the toner charge of the toner image on the lower surface of the recording paper P is applied to the surface of the insulating roller. As described above, the corona charger is used as the electric field forming means, the upper fixing roller 310 is charged with the same polarity as the toner charge of the upper toner image, and the lower fixing roller 320 is charged with the same polarity as the toner charge of the lower toner image. In the image forming apparatus for fixing the two-sided toner image at a time by increasing the electric repulsion between the toner and the roller by charging the toner, the electric electrostatic offset can be completely eliminated. Was.
[0054]
FIG. 7 is a sectional view showing the configuration of the second embodiment. In the figure, reference numerals 317 and 327 denote roller chargers which are conductive and can be sponge-like driven to rotate. The roller charger 317 to which a voltage of +200 V is applied is rotated in contact with the insulating roller surface of the upper fixing roller 310, and the insulating roller surface of the lower fixing roller 320 is rotated. The roller charger 327 to which a voltage of -200 V is applied is rotated in contact with the roller so that the surface of the roller has the same polarity as the toner, and the occurrence of the electrostatic offset at the time of fixing is eliminated as in the first embodiment.
[0055]
FIG. 8 shows a third embodiment. In this embodiment, the rollers are made of a conductive material in which the surface layers 310c and 320c of the upper and lower fixing rollers 310 and 320 and the intermediate layers 310b and 320b contain, for example, carbon black or titanium oxide and have conductivity. By connecting the bias power supplies 318 and 328 to the roller cores 310a and 320a via safety resistors, a bias voltage of +200 V is applied to the upper fixing roller 310 and -200 V is applied to the lower fixing roller 320. When a large number of recording papers P having a double-sided image were fixed at the same time in such a configuration, no electrical electrostatic offset was observed on any of the front and back surfaces. In the above embodiment, a bias voltage having the same polarity as the toner and having an absolute value of 200 V is applied, but the effect can be obtained by applying a voltage having an absolute value of 50 to 300 V.
[0056]
In still another embodiment, the lower fixing roller is electrically connected to the ground and the upper fixing roller is insulative so that the roller surface is positively charged by a corona charger or a roller charger. When the transfer material having the toner images on both sides was collectively fixed in such a configuration, no electrical electrostatic offset was observed on either the front surface or the back surface of the transfer material. This is because the lower fixing roller, which is in pressure contact with the upper fixing roller, is grounded, so that even if positive charges transfer from the upper fixing roller to the lower side, it flows to the ground and the lower fixing roller is discharged. it is conceivable that.
[0057]
In another embodiment, the lower fixing roller is conductive and is grounded to the ground, and the upper fixing roller is conductive and a bias of +200 V is applied from a bias power supply via a safety resistor. Neither was observed on the front surface or the back surface of the transfer material. This is because the bias voltage applied to the upper fixing roller leaks when the upper fixing roller and the lower fixing roller are pressed against and rotated, but when the transfer material enters between the rollers, the upper fixing roller is fixed. It is considered that a positive bias voltage is applied to the portion of the roller through which the transfer material passes, due to the insulating property of the transfer material, thereby preventing electrostatic offset.
[0058]
As described above, the embodiment in which the electrostatic offset is eliminated by providing the electric field forming means for forming the electric field between the fixing roller and the transfer material has been described. However, the present invention uses a belt other than the fixing roller as the fixing member. Similar effects can be obtained for the fixing device.
[0059]
(Embodiment 2)
The image forming apparatus of the present invention includes a first mode in which a toner image is formed on one surface (front surface) of a transfer material and fixing is performed, and a second mode in which a toner image is formed on both surfaces of the transfer material and collectively fixed. When the mode is designated by the designation unit, excellent control is performed on image formation and fixing, and excellent image recording is performed. Hereinafter, this control method will be described.
[0060]
FIG. 9 is a block diagram showing the control of the present invention. A mode selection button is provided on the operation panel of the image forming apparatus main body, and the user selects the first mode or the second mode. In addition, a third mode for automatic selection is provided. 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 of the document is detected. When an image is detected, the second mode is automatically selected to perform image formation and fixing.
[0061]
When the first mode is selected, the control unit calls up the image information of the front surface from the memory or the document reading device to form a toner image of the front surface image on the photosensitive drum 10, and The toner image of the image is transferred onto the recording paper P fed in synchronization with the transfer device 14c (first image forming step). The fixing device 30 holds the toner image on the upper surface and forms electric field forming means (a corona charger 316 and a roller) so as to form a negative electric field with respect to the upper fixing roller 310 on the recording paper P conveyed to the fixing device 30. The charger 317 and the bias power supply 318) are operated. On the other hand, the electric field forming means (corona charger 326, roller charger 327, bias power supply 328) is not operated for the lower 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.
[0062]
When the second mode is selected, the control unit first calls the back side image information from the memory or the document reading device to form a back side image toner image on the photosensitive drum 10, and then transfers the back side toner image to the intermediate transfer. The transfer is performed on the toner image receiving body 14a. Next, a toner image of a surface image is formed on the photosensitive drum 10 after the transfer and cleaning. Then, the toner image of the front surface image is transferred onto the upper surface of the recording paper P fed in synchronization by the transfer device 14c (first image forming step), and the toner image of the rear surface image on the toner image receiver 14a is The transfer is performed on the lower surface of the recording paper P by the back transfer device 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 (corona charger 316, The roller charger 317 and the bias power supply 318) are operated. On the other hand, the electric field forming means (corona charger 326, roller charger 327, bias power supply 328) is operated so as to form a negative electric field with respect to the lower fixing roller 320. The lower 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 to a tray outside the apparatus by the discharge roller 18.
[0063]
【The invention's effect】
[0064]
According to the present inventionIs a conventional image forming apparatus that forms toner images on both sides of a transfer material and performs batch fixingControl methodThenElectrical electrostatic offset is completely eliminated, and good image recording is performed for a long time,For single-sided images, improved image quality tended to be inferior to that of general image forming devices, and by switching modes for single-sided and double-sided image recording, electrical electrostatic offset was eliminated. However, control of image formation is performed so that good image recording is performed over a long period of time.
[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 carrier of FIG. 1;
FIG. 3 is an explanatory diagram illustrating a state where toner images are formed on both surfaces.
FIG. 4 is an explanatory diagram illustrating a state of toner charge when an image is formed on one surface of a transfer material.
FIG. 5 is an explanatory diagram illustrating a state of toner charge during image formation on both surfaces of a transfer material.
FIG. 6 is a cross-sectional view illustrating a configuration of a fixing device (first embodiment).
FIG. 7 is a cross-sectional view illustrating a configuration of a fixing device (second embodiment).
FIG. 8 is a cross-sectional view illustrating a configuration of a fixing device (third embodiment).
FIG. 9 is a block diagram showing control for switching between one side and both sides.
[Explanation of symbols]
10 Photoconductor drum
11 Scorotron charger
12 Exposure unit
13 Developing device
14a Toner image receiver (intermediate transfer member)
14c transfer unit
14g back transfer unit
14h Paper separation AC neutralizer
30 Fixing device
310 Upper fixing roller
320 Lower fixing roller
310a, 320a cored bar
310b, 320b Intermediate layer
310c, 320c Surface layer
311,321 Heater
312,322 Web cleaning device
313,323 Oil application roller
314,324 temperature sensor
316,326 Corona charger
317,327 Roller charger
318,328 bias power supply

Claims (3)

A first image forming step of directly transferring the toner image formed on the image carrier to the surface of the transfer material, and a toner image formed on the image carrier via an intermediate transfer body capable of holding the toner image An image provided with a fixing unit for forming a toner image on both sides of the transfer material and then heating and fixing the toner image collectively by the second image forming step of transferring to the transfer material, and a control unit for controlling image formation and fixing In the method for controlling a forming apparatus,
The fixing unit includes an upper fixing roller and a lower fixing roller, and a first electric field forming unit and a second electric field, respectively, for forming an electric field between the upper fixing roller and the lower fixing roller with a transfer material. A first mode in which a toner image is formed and fixed on one side of the transfer material; and a second mode in which a toner image is formed and fixed on both sides of the transfer material. And designating means for designating a mode from the second mode,
When the first mode is designated by the designation unit, the control unit activates the first electric field forming unit provided in the fixing unit and performs fixing without activating the second electric field forming unit. When the second mode is designated by (1), the first electric field forming means and the second electric field forming means provided in the fixing means are operated to control image formation for fixing. Control method. 2. The method according to claim 1, wherein the electric field forming unit is a charging member that applies a charge to the surface of the fixing member . 2. The control method according to claim 1, wherein the electric field forming unit is a bias applying unit that applies a voltage to the fixing member .

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