JPH10207149A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with an overhead transparent sheet (OHT) a cardboard or the like and to perform both-sided image formation satisfactorily in image formation conditions such as a transfer rate and a toner sticking amount by altering the image formation conditions according to a first image formation mode or a second image formation mode. SOLUTION: In an image formation process by a both-sided image formation program P1 in the first image formation mode, an image formation process by all of image formation process member is performed at a normal speed which is higher than that used in an image formation process in the second image formation mode using a second speed. On the hand, in the case one-sided image formation on only a surface is selected by a control parts as the selection of an image formation method and, further, such a king of transfer material as OHT or a cardboard is selected as a transfer material, one-sided image formation program P3, on only a surface, in a third image formation mode using a second sped stored in a ROM is read into a RAM via a control part, and an image formation process only on the surface is performed by the control part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for forming an image by transferring and fixing a toner image formed on an image carrier onto a transfer material in a copying machine, a printer, a facsimile or the like. In particular, an image is formed on both the front and back surfaces of the transfer material by transferring the toner image on the image carrier to the front surface of the transfer material or transferring the toner image once onto the toner image receiver and then to the back surface of the transfer material. The present invention relates to an image forming apparatus capable of performing such operations.

[0002]

2. Description of the Related Art Conventionally, in double-sided copying, an image on one side formed on an image carrier is transferred and fixed on a transfer material, and this is temporarily stored in a two-sided reversing paper feeder, and the image bearing is again performed. A method has been adopted in which a transfer material is fed from a double-sided reversing sheet feeder in synchronization with an image formed on the body, and an image on the other surface is transferred and fixed onto the transfer material.

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 reliability of transfer of the transfer material is low. And so on. In contrast, JP-B-49-37538 and JP-B-54-28740.
And JP-A-1-44457 and JP-A-4-21
Japanese Patent Application Laid-Open No. 4-44576, Japanese Patent Application Laid-Open No. 4-214576, and the like propose a method in which a toner image is formed on both surfaces of a transfer material and then fixed once. A method has been proposed in which a plurality of sets of image forming means including a body, a charging means, an image exposing means, a developing means and the like are arranged in parallel on a toner image receiving body to form a double-sided copy of a color image.

[0004]

However, Japanese Patent Application Laid-Open Nos. Hei 1-44457 and Hei 4-214576 mentioned above.
In the double-sided color image formation proposed in Japanese Patent Application Laid-Open Publication No. H08-27, the transferability of the transfer material is improved, but the color toner images are superimposed one by one on the toner image receiver, so that color misregistration, toner scattering and rubbing, etc. Image degradation easily occurs.

On the other hand, the present inventors once transfer the toner image formed on the image carrier (first image carrier) to a toner image receiver (second image carrier) at one time, Although a toner image is formed on the image carrier again, and a toner image on the toner image receiving body and a toner image formed on the image carrier again are transferred to both surfaces of the transfer material, a double-sided image forming method is being studied. ,
Compared to front-side image formation, which requires only one transfer from the image carrier to the transfer material, back-side image formation is performed from the image carrier to the toner image receiver,
Since the transfer is performed twice from the toner image receiver to the transfer material,
The image density of the back side image decreases. This occurs because the transfer rate is about 90% at the time of transfer and the toner adhesion amount is reduced by about 10%. Further, the toner image is scattered (the halftone dot is widened and γ is generally increased) by the two transfer of the toner image, and the gradation is changed. In addition, a color image has a new color tone problem as compared with a monochrome image. FIG. 16 shows the problem of forming a two-sided color toner image. As shown in FIG. 16, the order of superposition of the color toners is reversed between the front and back sides of the transfer material. Color is emphasized, or the color tone is changed due to a decrease in the amount of adhesion due to retransfer, which causes a problem that good color image formation is not performed. That is, there is a problem that image forming conditions such as a transfer rate and a toner adhesion amount are changed.

In particular, when an image is formed using an OHT (overhead transparency) or thick paper as a transfer material, it is necessary to lower the fixing speed, and if the image is formed in accordance with the fixing speed, the image forming conditions change. And
In addition to the further reduction in the transfer rate of the toner image to the transfer material and the amount of toner attached to the transfer material in the back side image by the toner image receiving body as described above, the transfer rate of the front image to the transfer material and the amount of toner attached also decrease. As a result, there is a problem that good color image formation is not performed. Naturally, there is also a problem that a good color image cannot be formed due to a decrease in image density and gradation due to the double transfer of the back side image and a change in color tone and the like in the color image.

The present invention solves the above-mentioned problems, and provides an image forming apparatus capable of forming a double-sided image which is compatible with OHT, thick paper, and the like, and has image transfer conditions such as a transfer rate and a toner adhesion amount. The purpose is to:

[0008]

An object of the present invention is to provide a first image carrying means for carrying a toner image formed by a toner image forming means, and a transfer of the toner image carried by the first image carrying means. A second image holding means for holding the transferred toner image on the surface, a first transfer means for transferring the toner image carried on the first image holding means to a surface of a transfer material, An image forming apparatus comprising: a second transfer unit configured to transfer a toner image carried by a second image carrying unit to a back surface of the transfer material; and a fixing unit configured to fix the toner images transferred to both surfaces of the transfer material. A first image forming mode in which double-sided image formation is performed at a first speed in the apparatus, and a second image forming mode which is slower than the first speed when thick paper is used as the transfer material.
A second image forming mode in which double-sided image formation is performed at a speed of 2. The image forming condition is changed according to the first image forming mode or the second image forming mode. This is achieved by a device (first invention).

The above object is also achieved by a first image holding means for holding a toner image formed by a toner image forming means,
A second image carrier for transferring the toner image carried on the first image carrier, and carrying the transferred toner image on the surface; and a toner image carried on the first image carrier. Transfer means for transferring a toner image carried by the second image carrying means to the back surface of the transfer material, and first and second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material. An image forming apparatus having a fixing unit for fixing a toner image transferred to a first image forming mode in which double-sided image formation is performed at a first speed, and when OHT or cardboard is used as the transfer material, A third image forming mode for forming a single-sided image only on the front surface at a second speed lower than the first speed, wherein an image is formed according to the first image forming mode or the third image forming mode. Characterized by changing the formation conditions It is achieved by an image forming apparatus (second invention).

The above object is also achieved by a first image carrying means for carrying a toner image formed by a toner image forming means,
A second image carrier for transferring the toner image carried on the first image carrier, and carrying the transferred toner image on the surface; and a toner image carried on the first image carrier. Transfer means for transferring a toner image carried by the second image carrying means to the back surface of the transfer material, and first and second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material. An image forming apparatus having a fixing unit for fixing a toner image transferred to a first image forming mode in which double-sided image formation is performed at a first speed, and when OHT or cardboard is used as the transfer material, A fourth image forming mode for performing single-sided image formation only on the back surface at a second speed lower than the first speed, and an image is formed according to the first image forming mode or the fourth image forming mode. Characterized by changing the formation conditions It is achieved by an image forming apparatus (third invention).

[0011]

Embodiments of the present invention will be described below. The description of the present embodiment does not limit the technical scope of the claims and the meaning of terms. Also,
The assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, when a color toner image is transferred to a transfer material, the transfer is performed on the surface of the transfer material facing the first image carrying means in the transfer area (referred to as the surface of the transfer material). The image to be transferred is referred to as a front image, and the image transferred to the other surface of the transfer material (referred to as the back surface of the transfer material) is referred to as a back image.

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 sectional view of a color printer as a color image forming apparatus showing an embodiment of the image forming apparatus of the present invention. FIG. 2 is a side sectional view of the image carrier of FIG. FIG. 4 is a diagram showing a state where toner images are formed on both sides, FIG. 4 is a diagram showing an enlarged view of a main part of FIG. 1 and showing a state at the time of measuring potential, and FIG. 5 is a control block diagram of the image forming apparatus. FIG. 6 shows an example of a digital image processing system for color reproduction.

A double-sided image formation is selected as an image forming method selection shown in FIG. 5 by an operation unit (not shown).
An OHT or 6 as a transfer material shown in FIG.
No transfer material type such as thick paper exceeding 0 kg / m ² has been selected, and the transfer material is in an image forming state of 45-60 kg / m ² plain paper recording paper.
The transfer material is 45 to 6 by the transfer material type detecting means described below.
When it is determined that the recording paper is 0 kg / m ² plain paper, FIG.
The double-sided image forming program P1 in the first image forming mode at the first speed stored in the ROM is read into the RAM through the control unit, and the control unit controls the double-sided image forming program in the first image forming mode. P1 is executed, and the image forming process described below is performed.

The image forming process by the double-sided image forming program P1 in the first image forming mode is performed at a normal speed higher than the image forming process by the second image forming mode at a second speed which will be described later. An image forming process of the member is performed. The driving speed of the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like is a normal speed, and the charging unit, the first transfer unit, and the second transfer unit The current or voltage of the transfer material charging means and the transfer material separating means is controlled at a current value or a voltage value corresponding to a normal speed.

In the case where the transfer material type detecting means is used, prior to the start of the image forming process described below, first, a feed roller 15a is fed from the paper feed cassette 15.
As a result, the recording paper P as the transfer material is sent out to the timing roller 15c via the detection roller 15A and the feed roller 15b, and the type of the transfer material is determined by the detection roller 15A. The detection roller 15A, which is grounded, is made of a conductive member. A low DC voltage is applied to the detection roller 15A, and the type of the transfer material is determined based on the value of the conduction current. The value of the conduction current is high for plain paper of 45 to 60 kg / m ^2, the conduction current is low for OHT or thick paper, and the conduction current hardly flows for OHT.

A photosensitive drum (also referred to as an image bearing member) 10 as a first image bearing member is provided with a cylindrical base formed of a transparent member of, for example, optical glass or transparent acrylic resin, and is provided with a transparent substrate. A photosensitive layer such as a 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.

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10b at both ends for engaging and fixing the photosensitive drum.
Are supported by the bearings B1 and B2 fitted in the flange members 10a and 10b at both ends on the drum shaft 30 erected and fixed to the apparatus main body, and are rotatably supported.
The gear G integrated with the flange member 10b is rotated at a constant speed in a predetermined direction by being driven by meshing with a drive gear (not shown) on the apparatus main body side.

In the present embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount capable of giving an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photoreceptor drum in the present embodiment does not need to be 100%, and may be such that a certain amount of light is absorbed when the exposure beam is transmitted. As the material of the translucent substrate, an acrylic resin, particularly one polymerized using methyl methacrylate monomer, has transparency, strength, accuracy,
Acrylic, fluorine used for other general optical members, etc.
Various translucent resins such as polyester, polycarbonate, and polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. The light-transmitting conductive layer is made of indium-tin-oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, or a light-transparent metal thin film made of Au, Ag, Ni, Al, or the like. As a film forming method, a vacuum evaporation method, an active reaction evaporation method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

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 carrier. It is installed facing the body drum 10,
The control action of the control grid 115, which is maintained at a predetermined potential with respect to the above-described organic photoconductor layer of the photoconductor drum 10, and the corona discharge electrode 111, for example, using a sawtooth-shaped electrode, and a corona discharge having the same polarity as that of the toner. In the embodiment, negative charging is performed to apply a uniform potential to the photosensitive drum 10. As the corona discharge electrode 111, a wire electrode or a needle electrode may be used.

As shown in FIG. 4, the scorotron charger 11 has a support member 112 on which a U-shaped side plate 113 as a shield member and a corona discharge electrode 111 having a saw-tooth electrode are attached. Further, the support member 11
2, a control grid 115 is attached to the corona discharge electrode 111 to constitute a scorotron charger 11.

An exposure unit 12 serving as an image exposure means for each color moves an exposure position on the photosensitive drum 10 between a corona discharge electrode 111 of the scorotron charger 11 and a development position of the developing device 13 by a developing sleeve. It is arranged in a state provided on the upstream side in the rotation direction of the photosensitive drum with respect to 131.

The exposure unit 12 is a linear exposure device in which a plurality of LEDs (light emitting diodes) 121 as light emitting elements of image exposure light arranged in the main scanning direction in parallel with the axis of the photosensitive drum 10 are arranged in an array. Element 12a and light converging light transmitter (trade name, Selfoc lens) 1 as an imaging element
2b is configured as an exposure unit attached to a holder (not shown). The exposure unit 12 for each color is attached to the holding member 20. In addition to the exposure unit 12 for each color, the uniform exposure unit 12c and the simultaneous transfer exposure unit 12d are attached to the holding member 20 to form the base of the photosensitive drum 10. Housed inside. 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 exposure element, an element in which a plurality of light-emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The light emission wavelength of the light emitting element used in this embodiment is usually in the range of 780 to 900 nm, which is high in transmittance of the Y, M, and C toners when performing image exposure from the outside. Since the exposure method is used, a shorter wavelength of 400 to 780 nm, which does not sufficiently transmit light to the color toner, may be used.

The developing device 1 provided in accordance with the color sequence in which the image is formed and the rotating photosensitive drum 10 in accordance with the color sequence
3, in the present 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 on the photosensitive drum 10 indicated by arrows 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 developing casing 1 of the C and K developing units 13 is disposed on the right side of the body drum 10.
The C and K scorotron chargers 11 are arranged above 38.

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. A non-magnetic cylindrical member having a thickness of, for example, 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 the body drum 10 Developing sleeve 131 made of stainless steel or aluminum material.

As shown in FIG. 4, the fixed magnet 132 is included in the developing sleeve 131, N and S magnetic poles are alternately arranged, and is fixed concentrically with the developing sleeve 131.
A magnetic force acts on the peripheral surface of the non-magnetic sleeve. The thin layer forming rod 133 as a thin layer forming member is a member that regulates the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 131,
It is made of a magnetic material having a circular cross section and has a diameter of 3 to 10 mm, and is uniformly pressed against the peripheral surface of the developing sleeve 131 with a predetermined load. A scraper 134 serving as a removing means for removing the two-component developer from the developing sleeve 131
Is made of a plate-like elastic member, such as SUS or urethane rubber, provided by pressing one end of a long side of the belt in parallel with the developing sleeve 131. Stirring screws 136 and 13
7 rotates at a constant speed in opposite directions to each other, and
The toner and the carrier inside are stirred and mixed to form a two-component developer containing a predetermined toner component evenly. Further, the two-component developer is supplied to the stirring section by the supply roller 135, or is transported and supplied to the developing sleeve 131 from the stirring section. 13a is a developing casing.

The developing device 13 is moved by a not-shown abutting roller between the photosensitive drum 10 and a predetermined gap, for example, 100 to 5 mm.
The developing unit 13 is kept in a non-contact state with an interval of
Is applied to the developing sleeve 131, a developing bias in which a DC voltage and an AC voltage are superimposed is applied, and non-contact development is performed by a one-component or two-component developer accommodated in the developing device, thereby forming a transparent conductive layer. A non-contact reversal development is performed in which a DC bias having the same polarity as the toner (in this embodiment, a negative polarity) is applied to the negatively charged photosensitive drum 10 that grounds the toner, and 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.

The developing unit 13 for each color described above converts the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image writing by the exposure unit 12 into a DC voltage and an AC voltage. In a non-contact state by a non-contact developing method by applying a developing bias in which the developing roller is superimposed, reverse development is performed 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).

As shown in FIG. 4, the sensor unit 100 includes a potential sensor 101 mounted on a sensor mounting member 104 rotatable about a support shaft 105 and reflection using infrared light for Y, M, and C. A density sensor 102 and a reflection density sensor 103 for K, and as shown in FIG. 1, a developing unit 13 for Y, M, C, and K as a plurality of developing units arranged in the order of toner image formation. Is disposed downstream of the K developing unit 13 at the most downstream position in the rotation direction of the photosensitive drum 10. Further, a reflection density sensor 102a is disposed on the outer side of the toner image receiver 14a in the rotation direction upstream of the toner image receiver 14a of the toner image receiver cleaning device 140 so as to face the toner image receiver 14a.

The reason why infrared light is used is that the Y, M, and C toners have a high spectral reflectance in the infrared region and can be used in common by the reflection density sensor 102. When a carbon-based coloring material is used for the K toner, the K toner has a low reflectance in the infrared region, and therefore the K reflection density sensor 103 is not shared. Of course, if a K toner is made of a coloring material having a high spectral reflectance in the infrared,
The reflection density sensor 102 for M and C and the reflection density sensor 103 for K can be shared.

In the sensor unit 100, the potential sensor 101 and the reflection density sensors 102 for Y, M, and C and the reflection density sensor 103 for K do not face the surface of the photosensitive drum 10 during the color image formation. , Are placed in a retracted state.

As a document image, an image read by an image pickup device of an image reading apparatus separate from the apparatus or an image edited by a computer is temporarily stored as image data for each of Y, M, C, and K colors. And stored.

The photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 by starting a photosensitive member driving motor (not shown) at the start of image recording, and at the same time, developing yellow (Y) on the left side of the photosensitive drum 10. Developing casing 1 of container 13
The application of a potential to the photoconductor drum 10 is started by the charging action of the Y scorotron charger 11 arranged below 38.

After the photosensitive drum 10 is applied with a potential, the Y exposure unit 12 starts exposure scanning with an electric signal corresponding to the first color signal, that is, the Y image data. An electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface.

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 in accordance with the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is placed on the yellow (Y) toner image, and further on the left side of the photosensitive drum 10 and above the yellow (Y), a magenta (M) developing device 1 is formed.
An electric signal corresponding to the second color signal of the M exposure unit 12, that is, the 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 sequentially superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13.

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

These Y, M, C and K exposure units 1
2 is performed on the photosensitive layer of the photosensitive drum 10 through the above-described transparent substrate from inside the drum. Therefore, the writing 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. Can be formed.

By the above-described image forming process, a superimposed color toner image serving as a back surface image is formed on the photosensitive drum 10 as the first image carrying means.
0 is the transfer area 1
At 4b, the transfer device 14c to which a DC voltage having the opposite polarity (positive polarity in this embodiment) to the toner is applied is stretched between the driving roller 14d and the driven roller 14e, and comes close to or contacts the photosensitive drum 10. Is collectively transferred onto a toner image receiving member 14a as a second image carrying means provided. 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.

[0040] In an endless rubber belt toner image receiving body 14a as a second image bearing means, for example a thickness of 0.5 to 2.0 mm, 10 ⁸ ~ of silicone rubber or urethane rubber
A semiconductive substrate having a resistance value of 10 ¹² Ω · cm, and a toner filming prevention layer having a thickness of 5
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, semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate or the like having a thickness of 0.1 to 0.5 mm can be used.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the photoconductive drum AC static eliminator 16, and then enters a cleaning device 19 as a cleaning means for the photoconductive drum 10. The photosensitive drum is cleaned by a cleaning blade 19a made of a rubber material in contact with the drum 10. Further, in order to eliminate the history of the photoconductor in the previous image formation, for example, the light is exposed by a uniform exposure device 12c before charging using a light emitting diode. The peripheral surface of the photoconductor is neutralized, and the next image is formed.

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

The recording paper P, which is a transfer material, is fed from a paper feed cassette 15 serving as a transfer material storage means by a detection roller 15A and a feed roller 15a, and is conveyed to a timing roller 15b serving as a transfer material feed means. The photosensitive drum 10 is driven by the driving of the timing roller 15b.
The color toner image of the front surface image carried thereon and the color toner image of the rear surface image carried on the toner image receiver 14a are synchronized and fed to the transfer area 14b. At this time, the toner image receiving body 14a is
And a brush-shaped paper charger 150 as a transfer material charging means to which a direct current voltage having the same polarity as that of the toner is applied, which can be brought into contact with and released from the recording paper P.
The recording paper P as a transfer material is charged with the same polarity as the toner, 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 member 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. Simultaneously with the passage of the recording paper P, the paper charger 150 is separated from the toner image receiving body 14a, and the contact is released.

The paper charger 150 is released from the toner image receiving member 14a immediately before or simultaneously with the passage of the rear end of the recording paper P and is separated from the recording paper P. Further, the voltage is applied to the paper charger 150 only when the recording paper P is being fed, and the voltage applied to the paper charger 150 is cut off simultaneously with the separation from the recording paper P.

Further, as the transfer material charging means, it is also possible to use a conductive roller capable of contacting and releasing contact with the toner image receiving member 14a and applying a DC voltage having the same polarity as the toner.

A surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on a recording paper by a transfer unit 14c as a first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. It is transferred to the upper surface side (front side) of P. 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 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. At the time of transfer by the transfer device 14c, uniform exposure is performed by a simultaneous transfer exposure device 12d using, for example, a light emitting diode, provided inside the photosensitive drum 10 so as to perform good transfer so as to face the transfer device 14c. May be performed.

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

The reversal development is repeated on the photoreceptor drum 10, 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 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.

As described above, in the color image formation, the first transfer means is operated to form a color toner image on the surface of the transfer material by using the above-described image forming method for the front surface and the back surface. 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 means is preferably employed.

The recording paper P on which the color toner images are formed on both sides is transferred to a paper separating AC neutralizer 14h as a transfer material separating means.
, And is separated from the toner image receiver 14a.
The conveyance unit 150 provided with a spur 152 for preventing the rear surface toner image from being disturbed during conveyance of the recording paper P conveyed from the toner image receiver 14a to the fixing device 17 and conveying the recording paper P to the fixing unit. Then, the sheet is conveyed to a fixing device 17 as a fixing unit including two rollers having heaters inside both rollers. By applying heat and pressure between the fixing roller 17a provided in the fixing device 17 and the pressure roller 17b, the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P on which the double-sided image recording has been performed. Are sent with the front and back images reversed, and are discharged to a tray outside the apparatus by the discharge rollers 18.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is provided to a toner image receiver cleaning device 140 as a toner image receiver cleaning means. Image receiver 14a
The cleaning is performed by a toner image receiving body cleaning blade 141 that can be brought into contact with and released from the contact.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16 in the same manner as in the case of double-sided image formation. The toner is scraped into the cleaning device 19 by a cleaning blade 19a made of a rubber material, which is in contact with the photoconductor drum 10, and is collected by a screw 19b into 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.

Since the superimposed color toner images are collectively transferred by using the above-described method, the color image on the toner image receiving member 14a is hardly discolored, the toner is scattered or rubbed, and the image deterioration is small. A double-sided color image is formed.

A single-sided image formation of only the front side or the back side is selected by an operation unit (not shown), and the image forming process of the first image forming mode at the normal speed is performed by the color image forming apparatus described above. It is a matter of course that an image is formed only on one side by the photosensitive drum 10 or the toner image receiving body 14a as an image forming body using the image forming apparatus.

As shown in FIG. 6, the control of the image forming conditions at the time of forming a color image in the color printer described above is performed by controlling the image data processing conditions of the digital image processing unit in S1 to S8 and the printer unit. The control is performed by controlling image forming process conditions such as a charging unit, an image exposing unit, a developing unit, and a front and back transfer unit in PR.

When the back side image is transferred from the image bearing member to the toner image receiving member and when the toner image receiving member is transferred from the toner image receiving member to the recording paper P, the amount of adhered toner decreases by about 10%. Compared with the front side image which is only transferred to the paper P, the back side image has a lower image density or the toner image is scattered by two transfers (the halftone dot is widened and γ is generally high), so that the gradation is changed. Further, in a color image, the color tone changes because the overlapping order of the toner images is inverted on the recording paper P. For this reason, in order to increase the amount of adhesion of the backside image during image formation and to adjust the color tone, it is necessary to change the charging potential by measurement with a potential sensor according to the time of formation of the frontside image and the backside image, image exposure light, development conditions, The printer unit responds by changing the process conditions described above and the process conditions that are the transfer conditions for transferring the backside image from the image carrier to the toner image receiver. Further, the change can be made in the image processing unit, and the setting can be performed by the parameter setting for color correction shown in the masking processing unit S6 or the γ conversion shown in S7.

In one embodiment described below,
The potential sensor sequentially measures a plurality of potential patterns produced by a plurality of charging means of Y, M, C and K and corresponding image exposure means at one place, and determines a charging potential of Y, M, C and K. The reflection density sensor controls the charging potential of the Y, M, C, and K charging means and the light quantity of the image exposure light from the image exposure means.
With respect to the adjusted Y, M, C, and K potential patterns, the corresponding Y, M, C, and K developing means are operated to form Y, M, C, and K toner image patterns, and one reflection is performed. Using a density sensor, the reflection densities of the Y, M, C, and K toner image patterns are sequentially measured to create a gamma correction table for each color, and an image for each color is generated using the gamma correction table for each color. The gamma correction of the data is performed, and the reflection densities of the Y, M, and C toner image patterns are sequentially measured to set parameters for color correction for each color.

First, correction of process conditions corresponding to the surface image will be described.

First, correction of the charged potential and the amount of image exposure light by the potential sensor will be described with reference to FIGS. 7, 8 and 4. FIG. FIG. 7 is a diagram showing a potential pattern, and FIG.
FIG. 4 is a diagram showing correction of a potential pattern.

As described in the above image forming process, uniform charging is performed by the scorotron charger 11. Subsequently, the LED 121 as a light emitting element of the exposure unit 12 provided inside the photosensitive drum 10
Based on the test pattern stored in the memory of the control unit (not shown), the output of the LED 121 is set to 0 by pulse width modulation.
% To 100% (the maximum output of the LED) is, for example, 1
The operation is performed stepwise and continuously in steps of 0%, and a stepwise and continuous potential pattern EP is formed on the photosensitive drum 10 as shown in FIG. Scorotron charger 11 for each color
And the exposure unit 12, a potential pattern EP for each color of Y, M, C and K (not shown) is formed on the photosensitive drum 10.

At this time, the scorotron charger 11 from the next step after the formation of the potential pattern is not operated. That is,
When a potential pattern of M color is formed, the scorotron charger 11 to be operated is for the Y and M colors, and the one for C and K colors is not operated. Otherwise, the formed potential pattern is erased.

At this time, the developing units 13 of Y, M, C and K, which are a plurality of developing units arranged in the order of toner image formation,
K developing device 1 at the most downstream position in the rotation direction of photosensitive drum 10
The potential sensor 101 provided on the sensor mounting member 104 of the sensor unit 100 disposed downstream of
5 is rotated to a position facing the surface of the photosensitive drum 10.

The Y, M, and M formed on the photosensitive drum 10
The charged potential of the stepwise potential pattern EP for each color of C and K is sequentially measured by the potential sensor 101. When the potential pattern EP is formed and when the potential sensor 101 measures the charged potential of the potential pattern EP, the developing device 13 for each color is used.
Is stopped.

As shown in FIG. 8, the maximum charging potential VS of the stepwise charging potential measured by the potential sensor 101 is
The grid voltage applied to the control grid 115 is adjusted, for example, to -900 V, and the minimum charging potential VL determined by the maximum exposure amount E1 of the LED 121 is set to the LED.
By adjusting the current value of 121 and setting it to, for example, -200 V, the potential decay characteristic of the photosensitive drum 10 is adjusted.

LED 121 for setting minimum charging potential VL
The maximum exposure amount E1 is adjusted to a value such as 80% or 60% of the maximum output of the LED 121. The setting of the potential decay characteristic by the grid voltage adjustment by the control grid 115 and the current value adjustment of the LED 121 is performed for each color.

In the above description, it is also possible to adjust the developing bias applied to the developing device 13 or the rotational speed of the developing sleeve, instead of the adjustment based on the charging potential and the exposure amount.

Next, the creation of a gamma correction table used when outputting image data will be described with reference to FIGS. 9 is an enlarged view of a main part of FIG. 1 showing a state at the time of measuring the reflection density, FIG. 10 is a view showing a toner image pattern, and FIG. 11 is a view explaining γ correction.

By adjusting the charging potential, the LED 121
, The maximum exposure amount E set to, for example, 80%
For example, using a pulse width modulation output obtained by dividing 1 into 10
A stepwise and continuously corrected potential pattern (gray scale pattern) is formed on the photosensitive drum 10 uniformly charged by the scorotron charger 11. Subsequently, the developing unit 13 is set in an operating state, and the gray scale pattern is developed to produce a toner image pattern DP. The toner image pattern DP of each color of Y, M, C and K (not shown) shown in FIG. 10 is formed on the photosensitive drum 10 by the scorotron charger 11, the exposure unit 12, and the developing device 13 for each color. You. This toner image pattern forming process is the same as a normal color image forming process except that the latent image forming pattern is changed.

At this time, the developing units 13 of Y, M, C and K, which are a plurality of developing units arranged in the order of toner image formation,
K developing device 1 at the most downstream position in the rotation direction of photosensitive drum 10
The reflection density sensor 102 provided on the sensor mounting member 104 of the sensor unit 100 disposed downstream of the sensor unit 3 is rotated around the support shaft 105 to a position facing the surface of the photosensitive drum 10. By doing so, the potential sensor 101
Can be prevented from being stained by the toner.

The Y, M, and M formed on the photosensitive drum 10
The density data of the stepwise toner image pattern DP for each color of C and K is sequentially measured by the reflection density sensor 102. The relationship between the density (exposure amount) of the gray scale pattern by the 10-part pulse width modulated exposure light and the density data obtained by the reflection density sensor is shown by a black circle in FIG. 11, and a curve a shown by a dotted line connecting the black circles Indicates the γ characteristic of the density data of the toner image pattern. a straight line c whose γ characteristic is indicated by a dashed line;
That is, a correction value for the curve a so that γ = 1 (circled)
Is a γ correction curve indicated by a curve b. Based on the γ correction curve, for example, the values of the density (exposure amount) and the density data of the gray scale pattern at a plurality of points indicated by circles are stored in a memory of a control unit (not shown) as a γ correction table. Γ for each color of Y, M, C and K
A correction table is created and stored in the memory. In reality, γ is set slightly higher than 1 (harder as an image).

Using the reflection density sensor 103 and setting the reflection density sensor 103 to the operating state facing the photosensitive drum 10, only the black (K) toner density pattern is individually measured, and a K γ correction table is created. Is also good.

As described with reference to FIG. 1, the image read by the image pickup device of the image reading apparatus separate from the color image forming apparatus or the image edited by the computer is
Image data for each color of Y, M, C and K is temporarily stored and stored in a memory.
At the time of image recording, according to the density data values of the image data for each of Y, M, C, and K, the γ of the corresponding Y, M, C, and K are used.
An exposure amount (density of a gray scale pattern) corresponding to the density data is set by the correction table, and the LEDs 121 arranged in an array as an exposure element are set at the exposure amount.
Lighting is individually performed by pulse width modulation output.

The correction of the surface image has been described above.
For the back side image, the process conditions (charge potential and exposure amount) and image data are corrected in the same manner as the adjustment for the front side image. As a correction method, adjustment for the back side image is individually performed in the same manner as the front side image adjustment. The correction at this time is performed with high accuracy by detecting and correcting the toner image formed on the toner image receiver 14a by the reflection density sensor 102a provided facing the toner image receiver 14a. be able to. Alternatively, as another correction method, the process conditions (charging potential and exposure amount) of the back surface image are estimated from process data (charge potential and exposure amount) and image data correction conditions estimated from experimental data obtained in advance. And a method of determining correction of image data. For example, the maximum charging potential VS can be increased by 10% when forming a backside image, as opposed to forming a front side image,
Adjustment conditions such as increasing the maximum exposure amount E1 by 10% or using a distorted γ correction curve are determined in advance, and adjustments such as changing the conditions of the back image based on the conditions of the front image are performed.

In the setting of the image forming process conditions of the color image forming apparatus, the setting of the transfer characteristics of the first transfer means when transferring the back side image from the first image bearing means to the second image bearing means. This will be described with reference to FIGS. 12, 13 and FIGS. FIG. 12 is a diagram illustrating an example of a transfer toner image pattern, and FIG. 13 is a diagram illustrating optimal transfer conditions.

At the time of adjusting the image forming conditions for setting the image forming conditions (in this example, setting the transfer characteristics of the first transfer means at the time of transferring the back side image from the first image carrying means to the second image carrying means) ), The conveyance of the recording paper P as the transfer material to the transfer section is prohibited, a toner image is formed on the photosensitive drum 10, and the toner image formed on the photosensitive drum 10 is transferred to the transfer device 14c.
The toner image (transferred toner pattern DP2) for transfer characteristic setting formed on the toner image receiver 14a is read by the reflection density sensor 102a. The amount of untransferred toner adhering to the peripheral surface is read by the reflection density sensor 102, and the toner density of the transfer toner density pattern DP2 for setting transfer characteristics for each color formed on the peripheral surface of the toner image receiver 14a, and the photoreceptor The transfer rate is calculated by comparing the toner density of the untransferred toner amount adhering to the peripheral surface of the drum 10 with the toner density of the corresponding portion, and Y, M, C, and K are calculated.
The optimum value V1 of the transfer voltage applied to the transfer roller 14c as the transfer device is set. After the detection, the toner image on the toner image receiver 14a is cleaned by the toner image receiver cleaning device 140.

When setting the transfer conditions, a plurality of solid transfer toner image patterns for each color are formed on the photosensitive drum 10 by the scorotron charger 11, the exposure unit 12, and the developing device 13, and the transfer toner image is formed. The pattern is transferred to the toner image receiver 14a while changing the transfer voltage of the transfer device 14c.
And a transfer toner image pattern DP2 of each color is formed on the toner image receiver 14a, and the toner density of the transfer toner image pattern DP2 is detected by a reflection density sensor 102a provided opposite to the toner image receiver 14a. The transfer characteristic is set by detecting the toner concentration of the transfer residual toner of the transfer toner image pattern DP2 on the photosensitive drum 10 by the reflection density sensor 102.

FIG. 12 shows a transfer toner image pattern D for each color.
P2, an exposure unit 12 for each color is placed on a photosensitive drum 10 charged by a Y scorotron charger 11.
8, the entire surface is exposed at the maximum exposure amount E1 set to, for example, 80% of the maximum output of the LED as the exposure element 12a described with reference to FIG. A plurality of solid color toner patterns are formed on the toner image receiving member 14a while changing the transfer voltage of the transfer device 14c, thereby forming a transfer toner image pattern for setting transfer characteristics. DP2.

The toner density and the transfer residual toner density of the transfer toner image pattern DP2 for setting the transfer characteristics for each color are read by the reflection density sensors 102a and 102 corresponding to the respective colors, and the transfer voltage and transfer are performed. FIG. 13 shows an example of a graph obtained by interpolating the rate and the data. The area where the transfer rate is the maximum is defined as the optimum condition range, and the optimum value of the transfer voltage V1 common to each color is determined from the optimum condition range.

The optimum value of the transfer voltage is calculated from the transfer rate determined by the detection of the reflection density sensor 102a and the reflection density sensor 102, recorded in the RAM, and the transfer voltage V1 determined at the time of image formation by the image forming apparatus. Transfer device 14c
Output to

As described above, the process conditions for proper transfer characteristics when the back side image is transferred from the first image bearing means to the second image bearing means by the first transfer means are set.

Further, in addition to the correction of each density data, it is necessary to change the setting of the masking parameter for color correction shown in S6 of FIG. 6 as the image data processing condition in the case of a color image. That is, FIG. 14 shows a superimposed color toner image formed by the color image forming apparatus described with reference to FIG. 1, and FIG. 14A shows a color toner image formed on the surface of the transfer material. And FIG.
FIG. 4B is a diagram illustrating a color toner image formed on the back surface of the transfer material.
When the color toner images are formed in the order of M, C, and K, the front surface image is sequentially superimposed on C, M, and Y with black (K) down on the recording paper P as shown in FIG. Therefore, it is necessary to attach a large amount of the toner of the lowermost layer K to the recording paper P. In addition, as shown in FIG. M, C,
K is superimposed sequentially, K is the top layer, black (K)
Is excessively emphasized, so that the amount of K toner
Need to be attached to The same applies to other Y, M, and C.

FIG. 15 is a diagram showing the UCR.
When the UCR amount is 100% or less than the mixing ratio of the M and C colors, reproduction is performed with four colors of three-color toner and black toner. This UCR is also changed between the front side image and the back side image as described above.
In addition, since the toner image is formed on the back surface image by two transfer operations, the color tone is different due to a decrease in the amount of adhesion.
In consideration of this point, it is necessary to perform color correction different from the surface for adjusting the color tone.

The masking section for performing the above-described color correction includes color processing such as masking / inking and UCR.
As the masking, generally used linear masking or, when performing advanced color correction, non-linear masking or masking using a look-up table is used.

As described above, when a monochrome or color image is formed by the color image forming apparatus, the image is formed using the image forming conditions such as the process conditions and the image data processing conditions set above. A double-sided image having the adjusted image density and color tone is formed.

Further, as a modification, the back side image may be formed by changing only one condition. In particular, in the case of a monochrome image, color correction is unnecessary, and if the maximum density of black is a saturated image density, an image of a sufficient level can be reproduced even with gradation correction.

A double-sided image formation is selected as an image forming method selection shown in FIG. 5 by an operation unit (not shown), and a transfer material of 60 kg / m ² shown in FIG.
When the transfer material type of thick paper exceeding 60 kg / m ² is selected, or when the transfer material is determined to be a thick recording paper exceeding 60 kg / m ² by the transfer material type detecting means, the ^second paper stored in the ROM shown in FIG. The double-sided image forming program P2 in the second image forming mode at the speed is read into the RAM through the control unit, and the control unit executes the double-sided image forming program P2 in the second image forming mode to execute the image forming process. Will be

In the case where the transfer material type detecting means is used, before the start of the image forming process, the feeding roller 15a
As a result, the recording paper P as the transfer material is sent out to the timing roller 15c as the transfer material feeding means via the detection roller 15A and the feed roller 15b, and the detection roller 15A
Is used to determine the type of transfer material. The detection roller 15A, which is grounded, is made of a conductive member. A low DC voltage is applied to the detection roller 15A, and the type of the transfer material is determined based on the value of the conduction current. For thick paper exceeding 60 kg / m ² low conduction current, the higher value of the conduction current in the plain paper 45~60kg / m ^2. In the case of OHT, almost no conduction current flows.

The image forming process in the second image forming mode is performed in the same manner as the image forming process in the first image forming mode described with reference to FIGS. The image forming process by the double-sided image forming program P2 is the image forming process of all the image forming process members at the second speed which is lower than the normal speed of the image forming process in the first image forming mode at the first speed. The process takes place. The driving speeds of the fixing unit, the first image carrying unit, the second image carrying unit, the transfer material feeding unit, the developing unit, and the like are performed at a low speed (second speed). Therefore, current or voltage control of the charging unit, the first transfer unit, the second transfer unit, the transfer material charging unit, the transfer material separation unit, and the like is performed at a normal speed, and the current value corresponding to the first image forming mode is controlled. Alternatively, it is performed at a current value or a voltage value lower than the voltage value.

That is, as the speed of the fixing unit is reduced, charging of the first image bearing unit by the charging unit, formation of a latent image by image exposure of the image exposing unit, and development of the latent image by the developing unit are performed. Forming a toner image of the back side image (toner image forming means), transferring the toner image of the back side image carried by the first image carrying means to the second image carrying means by the first transfer means;
Forming a toner image of a surface image on a first image carrier by a charging unit, an image exposing unit, and a developing unit; transferring a surface image to a transfer material by a first transfer unit; Since the image forming process such as the transfer of the toner image of the back side image to the transfer material, the separation of the transfer material by the transfer material separating means, and the fixing of the front and back toner images on the transfer material by the fixing means, are performed at a low speed. The process conditions for the front and back images at the speed of 2 are set.

That is, as the setting of the process conditions, the charging potential and the image exposure amount by the potential sensor similar to that described with reference to FIGS. 7 and 8 are set at the second speed according to the second image forming mode. Is corrected to be set lower as the setting of the front and back images. In addition, the rotation speed of the developing means may be reduced,
Since the maximum exposure amount is set low, the front and back images are set at the second speed according to the second image forming mode of the γ correction table in the same manner as described with reference to FIGS. Further, in the same manner as described with reference to FIGS. 12 and 13, the first transfer unit adjusts the first speed in accordance with the second speed.
The transfer characteristic is corrected so that the transfer voltage at the time of transferring the back side image from the image carrying means to the second image carrying means is set low. Further, in the same manner as described with reference to FIGS. 14 and 15, the front and back images are corrected at the second speed in accordance with the second image forming mode of the image data processing condition. In addition to correcting image forming conditions such as process conditions and image data processing conditions according to the second image forming mode, the process conditions and image data processing conditions for front and back image formation described in the first image forming mode are described. Are corrected.

As described above, even in the case of double-sided image formation of a transfer material using thick paper at the second speed lower than the first speed, the transfer material using plain paper at the normal speed at the first speed is also used. Also in the case of double-sided image formation, a double-sided image is formed under image forming conditions such as a transfer rate and a toner adhesion amount, and a good surface image such as image density and color tone is formed. Further, appropriate image forming conditions are set for each of the time of forming the front surface image and the time of forming the back surface image on the transfer material, and satisfactory image formation is performed. Further, all the driving speeds of the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like are lower than the normal speed as the first speed and the first speed. It is only necessary to switch to the second speed. For example, the driving speed of a main motor (not shown) that drives the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like is changed. Since only switching is required, switching control is facilitated.

An operation unit (not shown) selects single-sided image formation of only the front side as an image forming method selection shown in FIG. 5, and an operation unit (not shown) uses OH shown in FIG. 5 as a transfer material.
If the transfer material type of T or thick paper is selected, or if the transfer material is determined to be OHT or thick paper by the transfer material type detecting means, the third image at the second speed stored in the ROM shown in FIG. The single-sided single-sided image forming program P3 in the forming mode is read into the RAM through the control unit, and the single-sided single-sided image forming program P3 in the third image forming mode is executed by the control unit to perform the image forming process. .

In the case where the transfer material type detecting means is used, first, before the image forming process is started, the feeding roller 15a
As a result, the recording paper P as the transfer material is sent out to the timing roller 15c as the transfer material feeding means via the detection roller 15A and the feed roller 15b, and the detection roller 15A
Is used to determine the type of transfer material. The detection roller 15A, which is grounded, is made of a conductive member. A low DC voltage is applied to the detection roller 15A, and the type of the transfer material is determined based on the value of the conduction current. For OHT not flow conduction current is almost in the case of thick paper exceeding 60 kg / m ² low conduction current, the higher value of the conduction current in the plain paper 45~60kg / m ^2.

The image forming process in the third image forming mode is the same as the image forming process described with reference to FIGS. 1 to 5, and is a single-sided image forming process of only the surface image by the first image carrier. Done. The image forming process according to the single-sided image forming program P3 for only the front surface in the third image forming mode is a low-speed second speed lower than the normal speed of the image forming process in the first image forming mode at the first speed. Then, the image forming process of all the image forming process members is performed. The driving speeds of the fixing unit, the first image carrying unit, the second image carrying unit, the transfer material feeding unit, the developing unit, and the like are performed at a low speed (second speed). Therefore, when the toner image of the surface image from the charging unit and the first image bearing unit is transferred to the OHT or the thick paper as the transfer material, the current of the first transfer unit, the transfer material charging unit and the transfer material separating unit, or the like. The voltage control is performed at a current value or a voltage value lower than the current value or the voltage value corresponding to the first image forming mode performed at the normal speed.

As the speed of the fixing means is reduced,
The first image carrier is charged by the charging device, the latent image is formed by the image exposure of the image exposure device, the toner image of the surface image is formed by the development of the latent image by the developing device, and the first transfer is performed by the first transfer device. Second image of the toner image of the surface image carried by the image carrying means
Transfer to OHT or cardboard as a transfer material conveyed by the image carrying means, transfer of the transfer material by the second image carrying means, separation of the transfer material by the transfer material separating means, surface image on the transfer material by the fixing means Since the image forming process such as fixing of the toner image is performed at a low speed, the first image forming process at the second speed is performed.
The process conditions for the surface image in the image carrying means are set.

That is, as the setting of the process conditions, the charging potential by the potential sensor and the image exposure amount similar to those described with reference to FIGS. 7 and 8 are set at the second speed according to the third image forming mode. Is corrected so as to be set low as the setting of the surface image in the first image holding means. Further, since the rotation speed of the developing unit is reduced and the maximum exposure amount is set low, the second correction according to the third image forming mode of the γ correction table is performed in the same manner as described with reference to FIGS. Set the surface image at the speed of. Further, the surface image is corrected at the second speed according to the third image forming mode of the image data processing condition in the same manner as described with reference to FIGS. In addition to correcting image forming conditions such as process conditions and image data processing conditions according to the third image forming mode, the process conditions and image data processing conditions for the front and back image formation described in the first image forming mode. Are corrected.

As described above, even in the case of single-sided image formation of only the surface image of the transfer material using the OHT or the thick paper at the second speed lower than the first speed, the normal speed at the normal speed at the first speed is used. Even in the case of forming a double-sided image of a transfer material using paper, a double-sided image is formed with image forming conditions such as a transfer rate and a toner adhesion amount being adjusted, and a good surface image such as image density and color tone is formed. Will be Further, all the driving speeds of the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like are lower than the normal speed as the first speed and the first speed. It is only necessary to switch to the second speed. For example, the driving speed of a main motor (not shown) that drives the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like is changed. Since only switching is required, switching control is facilitated.

As described above, in the case where OHT or cardboard is used as the transfer material, the single-sided image formation process using only the front side image using the first image carrying means is preferably used. The second to explain
It is also possible to use a single-sided image forming process using only the back side image by the image carrying means.

That is, a single-sided image formation on only the back side is selected as an image forming method selection shown in FIG. 5 by an operation unit (not shown), and an OHT or a thick paper shown in FIG. 5 is transferred as a transfer material by an operation unit (not shown). When the material type is selected or when the transfer material type is determined to be OHT or thick paper by the transfer material type detection means, the back surface in the fourth image forming mode at the second speed stored in the ROM shown in FIG. Only the single-sided image forming program P4 is read into the RAM through the control unit, and the control unit executes the single-sided image forming program P4 for only the back surface in the fourth image forming mode to perform the image forming process.

In the case where the transfer material type detecting means is used, before the start of the image forming process, the feeding roller 15a
As a result, the recording paper P as the transfer material is sent out to the timing roller 15c as the transfer material feeding means via the detection roller 15A and the feed roller 15b, and the detection roller 15A
Is used to determine the type of transfer material. The detection roller 15A, which is grounded, is made of a conductive member. A low DC voltage is applied to the detection roller 15A, and the type of the transfer material is determined based on the value of the conduction current. For OHT not flow conduction current is almost in the case of thick paper exceeding 60 kg / m ² low conduction current, the higher value of the conduction current in the plain paper 45~60kg / m ^2.

The image forming process in the fourth image forming mode is the same as the image forming process described with reference to FIGS. 1 to 5, and is a single-sided image forming process of only the back side image by the second image carrying means. Done. The image forming process according to the single-sided image forming program P4 for only the back surface in the fourth image forming mode is the second speed, which is lower than the normal speed of the image forming process in the first image forming mode at the first speed. Then, the image forming process of all the image forming process members is performed. The driving speeds of the fixing unit, the first image carrying unit, the second image carrying unit, the transfer material feeding unit, the developing unit, and the like are performed at a low speed (second speed). Therefore, when the toner image of the back side image from the charging unit and the first image holding unit is transferred to the second image holding unit, the toner image of the back side image from the first transfer unit and the second image holding unit is transferred. The current or voltage control of the second transfer means, the transfer material charging means, the transfer material separation means, etc., at the time of transfer to OHT or thick paper as a transfer material is performed at a normal speed. The current corresponding to the first image forming mode is used. This is performed at a current value or a voltage value lower than the value or the voltage value.

As the speed of the fixing means is reduced,
Charging of the first image carrying means by the charging means, formation of a latent image by image exposure of the image exposing means, formation of a toner image of the back side image by developing the latent image by the developing means (toner image forming means), The transfer of the toner image of the back side image carried on the first image carrying unit to the second image carrying unit by the transfer unit, and the transfer of the toner image of the back side image by the second transfer unit by the second image carrying unit. Image transfer processes such as transfer to OHT or cardboard as a transfer material, separation of the transfer material by a transfer material separating unit, and fixing of the front and back toner images on the transfer material by the fixing unit are performed at a low speed. At the speed of 2, the process conditions for the back side image are set by the second image carrier.

That is, as the setting of the process conditions, the charging potential by the potential sensor and the image exposure amount similar to those described with reference to FIGS. 7 and 8 are set at the second speed according to the fourth image forming mode. Is corrected so as to be set lower as the setting of the back side image in the second image carrier. Further, since the rotation speed of the developing unit is reduced and the maximum exposure amount is set low, the second correction according to the fourth image forming mode of the γ correction table is performed in the same manner as described with reference to FIGS. Set the surface image at the speed of. Also, in the same manner as described with reference to FIGS. 12 and 13, the transfer of the back side image from the first image bearing unit to the second image bearing unit by the first transfer unit is performed in accordance with the second speed. The transfer characteristic is corrected such that the transfer voltage of the transfer is set low. Further, the surface image is corrected at the second speed according to the third image forming mode of the image data processing condition in the same manner as described with reference to FIGS.
In addition to correcting image forming conditions such as process conditions and image data processing conditions in accordance with the fourth image forming mode, the process conditions and image data processing conditions for front and back image formation described in the first image forming mode. Are corrected.

As described above, in the single-sided image formation, the first
In the case of single-sided image formation of only the back surface image of the transfer material using the OHT or the thick paper at the second speed lower than the speed of the first speed, both sides of the transfer material using the normal paper at the normal speed at the first speed Even in the case of image formation, a double-sided image is formed under image forming conditions such as a transfer rate and a toner adhesion amount, and a good surface image such as image density and color tone is formed. Further, all the driving speeds of the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like are lower than the normal speed as the first speed and the first speed. It is only necessary to switch to the second speed. For example, the driving speed of a main motor (not shown) that drives the fixing unit, the first image holding unit, the second image holding unit, the transfer material feeding unit, the developing unit, and the like is changed. Since only switching is required, switching control is facilitated.

[0105]

According to the first or second aspect, even in the case of forming a double-sided image of a transfer material at a normal speed at a first speed, the method of forming a double-sided image of a transfer material using thick paper at a second speed is also used. Also in this case, a double-sided image is formed with image forming conditions such as a transfer rate and a toner adhesion amount being adjusted, and a double-sided image with good image density and color tone is formed.

According to the present invention, appropriate image forming conditions are set for each of the time of forming a front surface image and the time of forming a rear surface image on a transfer material, and good image formation is performed.

According to claims 4 to 7, even in the case of forming a double-sided image of a transfer material at the normal speed at the first speed, the method of forming a single-sided image of the transfer material using the OHT or cardboard at the second speed is also used. Also in this case, image formation is performed with image formation conditions such as the transfer rate and the amount of toner adhered, and good image formation such as image density and color tone is performed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color printer as a color image forming apparatus showing an embodiment of the image forming apparatus of the present invention.

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

FIG. 3 is a diagram illustrating a state where toner images are formed on both surfaces.

FIG. 4 is an enlarged view of a main part of FIG. 1, showing a state at the time of measuring potential;

FIG. 5 is a control block diagram of the image forming apparatus.

FIG. 6 is a diagram illustrating an example of a digital image processing system for color reproduction.

FIG. 7 is a diagram showing a potential pattern.

FIG. 8 is a diagram showing correction of a potential pattern.

FIG. 9 is an enlarged view of a main part of FIG. 1, showing a state at the time of measuring a reflection density.

FIG. 10 is a diagram illustrating a toner image pattern.

FIG. 11 is a diagram illustrating γ correction.

FIG. 12 is a diagram illustrating an example of a transfer toner image pattern.

FIG. 13 is a diagram showing optimum transfer conditions.

FIG. 14 is a diagram illustrating a superimposed color toner image.

FIG. 15 is a diagram showing a UCR.

FIG. 16 is a diagram illustrating a problem in forming a two-sided color toner image.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure unit 13 developing device 14a toner image receiver 14c transfer device 14g backside transfer device 15A detection roller 17 fixing device 100 sensor unit 101 potential sensor 102, 102a, 103 reflection density sensor P recording paper

Claims (7)

[Claims] A first image carrying means for carrying the toner image formed by the toner image forming means; and a toner image carried by the first image carrying means is transferred. A second image carrying means carried on the surface; a first transferring means for transferring the toner image carried on the first image carrying means onto a surface of the transfer material; and a carrying means carried on the second image carrying means. An image forming apparatus comprising: a second transfer unit configured to transfer the toner image transferred to the back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. There is a first image forming mode for performing double-sided image formation, and a second image forming mode for performing double-sided image formation at a second speed lower than the first speed when thick paper is used as the transfer material. And the first image forming mode or before Image forming apparatus characterized by changing an image forming condition in accordance with the second image forming mode. 2. An image forming condition such as a toner adhesion amount and a γ correction of an image formed on the first image carrier is changed between the first image forming mode and the second image forming mode. The image forming apparatus according to claim 1, wherein: 3. An image forming condition such as a toner adhesion amount and a γ correction of a toner image to be formed on the first image holding means is changed between when a front image is formed on the transfer material and when a back image is formed on the transfer material. The image forming apparatus according to claim 1, wherein: 4. A first image carrying means for carrying a toner image formed by a toner image forming means, and a toner image carried by the first image carrying means is transferred. A second image carrying means carried on the surface; a first transferring means for transferring the toner image carried on the first image carrying means onto a surface of the transfer material; and a carrying means carried on the second image carrying means. An image forming apparatus comprising: a second transfer unit configured to transfer the toner image transferred to the back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. A first image forming mode in which double-sided image formation is performed, and a third image in which single-sided image formation of only the front surface is performed at a second speed lower than the first speed when OHT or thick paper is used as the transfer material And a forming mode, wherein the first Image forming apparatus characterized by changing the image forming condition in accordance with the image forming mode or the third image forming mode. 5. An image forming condition such as a toner adhesion amount and γ correction of an image to be formed on the first image carrier is changed between the first image forming mode and the third image forming mode. The image forming apparatus according to claim 4, wherein: 6. A first image carrying means for carrying a toner image formed by a toner image forming means, and a toner image carried by the first image carrying means is transferred, and the transferred toner image is A second image carrying means carried on the surface; a first transferring means for transferring the toner image carried on the first image carrying means onto a surface of the transfer material; and a carrying means carried on the second image carrying means. An image forming apparatus comprising: a second transfer unit configured to transfer the toner image transferred to the back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. A first image forming mode for performing double-sided image formation, and a fourth image for performing single-sided image formation on only the back surface at a second speed lower than the first speed when OHT or thick paper is used as the transfer material. And a forming mode, wherein the first Image forming apparatus characterized by changing the image forming condition in accordance with the image forming mode or the fourth image forming mode. 7. An image forming condition such as a toner adhesion amount and γ correction of an image to be formed on the second image carrier is changed between the first image forming mode and the fourth image forming mode. The image forming apparatus according to claim 6, wherein: