JPH05216316A - Image forming device - Google Patents

Abstract

PURPOSE:To uniformize an image by reducing the difference of the glossiness between the front side and back side and the density of the fixed image by controlling the electrostatic charge quantity or the exposure of the surface of a latent image carrier when a latent image is formed on the latent image carrier. CONSTITUTION:A VD curve is plotted on the front surface of a recording material. Then, the output density DAO obtained on the back surface of the recording material when measured potential is VAO is the potential obtained also on the front surface of the recording material when the measured potential is Va. Besides, the output density DFF on the back surface of the recording material when the measured potential is VFF is a value obtained on the front surface of the recording material when the measured potential is Vb. Therefore, when the measured potential is corrected to Va and Vb in the case that the measured potential should be set to VAO and VFF at the image forming time of the front surface of the recording material, the difference of the density of the image between the front side and back side is eliminated. Since inputted density data (e) giving the measured potential VAO and VFF at the image forming time of the back surface of the recording material is (eAO) and (eFF), a look-up table is corrected so as to obtain the measured potential Va and Vb at the image forming time of the front surface of the recording material when the inputted density data is (eAO) and (eFF).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a developer image on both sides of a recording material, and more particularly to an apparatus for controlling a latent image forming portion thereof.

[0002]

2. Description of the Related Art A conventional fixing device in an image forming apparatus is, as shown in FIG. 5, a fixing roller 401 rotatable in a direction of an arrow b and a driven roller rotating in the direction of an arrow b ', which is disposed so as to face the fixing roller 401. And a heater is provided inside each of the rollers. In addition, the fixing roller 401 has an oil applying unit 4
03 is arranged so as to abut, and the fixing roller 4
The surface of 01 is coated with silicone oil as a release agent. Further, the fixing roller 401 and the pressure roller 402 have cleaning means 404a, 4
04b are arranged so as to contact each other, and each roller is cleaned.

In such a fixing device, as shown in FIG. 5, a recording material P carrying an unfixed developer image (hereinafter, a developer is a toner and a developer image is a toner image) T is carried. When the recording material P is conveyed in the direction of arrow a, the fixing roller 401 and the pressure roller 402 contact the recording material P at their pressure contact portions.
The toner image T on the recording material P.
Is melted by heat and pressure and fixed on the recording material P.

As described above, in order to obtain a good image on the recording material P, it is necessary to sufficiently melt the toner. In particular, when forming a full-color image, the toner image T in which various toners of yellow, magenta, cyan, and black are laminated is fixed on the recording material P. Therefore, in order to reproduce a color close to the original document, the toners of the plural layers are formed. It is necessary to heat and melt the image T to mix the colors, and for that purpose, it is necessary to use a toner having a low softening point, that is, a low melting point and a sharp melt, and to supply sufficient heat energy.

However, during the formation of the full-color image, the sharp-melt toner is melted to an extremely low viscosity as described above, and the toner layers of a plurality of colors are laminated to thicken the toner layer. Offset tended to occur easily. Further, each fixing temperature range (a temperature range in which proper fixing can be performed) is different due to the difference in the melting property caused by the difference in the pigment contained in each color toner, and the common fixing temperature range is narrower than that of monochromatic fixing. This is also a cause of easy offset.

Therefore, in order to prevent this offset, it is indispensable to apply a release agent made of heat resistant oil such as silicone oil, and at the same time, in order to supply sufficient thermal energy to the toner, it is necessary to use a fixing roller. It was necessary to increase the nip amount of the pressure roller. Therefore, it is difficult to use a fluororesin-based hard roller such as Teflon (trade name) generally used in a black-and-white image fixing device as the surface material of the fixing roller and the pressure roller in the color image forming device. A rubber elastic material typified by silicone rubber is used which has high heat resistance and good wettability with silicone oil as a release agent.

On the other hand, the image forming apparatus includes an apparatus for forming a double-sided image in addition to the apparatus for forming a single-sided image as described above. In such an apparatus, the recording material P that has undergone the above-described fixing process on one side of the recording material P is conveyed to the toner image forming step start position on the conveying path, and the toner image of the recording material P is already formed. The toner image is formed again on the back surface (the surface on which the toner image is not formed; hereinafter, the surface B) of the formed surface (hereinafter referred to as the surface A), and the recording is performed by performing the fixing process described above again. The image formation on both sides of the material P is completed. Hereinafter, such a process is referred to as double-sided image formation.

Also in the image forming apparatus for performing such double-sided image formation, the above-mentioned rubber elastic material is used as the surface material of the fixing roller and the pressure roller to prevent the offset.

[0009]

However, according to the above-mentioned conventional example, although the offset at the time of double-sided image formation can be prevented to some extent, there is a problem that a difference in glossiness of the toner image occurs between the front and back sides of the recording material. Has occurred.

This is because the pressure roller 402 is in a heated state sufficient to melt the toner during the fixing process on the B side.
Comes in contact with the toner image on the side A that is fixed first,
This occurs because the toner layer on the side A is again converted from the solid phase to the liquid phase. Examples of such difference in glossiness between the front and back of the recording material are shown in FIGS. 6 to 8.

FIG. 6 to FIG. 8 show the relationship between the gray scale on the horizontal axis and the glossiness on the vertical axis. This gradation is V of a general VD curve, which corresponds to the latent image potential of the photoconductor by laser exposure, and almost corresponds to the amount of toner on the recording material P. On the other hand, the above-mentioned glossiness is measured by a gloss checker IG-320 manufactured by Horiba Ltd.

In FIG. 6, R-1 represents the glossiness of the B side which is the last image formed in a red double-sided image, and R-2 represents the glossiness of the A side which is the first image formed. Y in FIGS. 7 and 8
The same applies to (yellow) and M (magenta), and R
(Red) is when a toner in which Y and M toners are laminated is fixed. Here, R is larger in gloss (glossiness) and the difference in gloss between the front side and the back side at the time of double-sided image is larger than that of a single color such as Y and M. This is due to the thicker toner layer This is because the surface shape becomes difficult to spread and the surface of the toner layer is made smoother.

As described above, the difference in the glossiness of the image on the front and back of the recording material is caused by the phase conversion of the toner layer, and becomes more remarkable as the toner layer thickness increases, but similarly, the difference in gloss on the front and back of the recording material occurs. The larger the image density difference, the larger the difference in glossiness. The image density difference between the front and back of the recording material will be described below with reference to FIGS. 9 to 11.

FIGS. 9 to 11 show the image densities measured by Macbeth RD 914 for the densities of the sample images used to measure the glossiness shown in FIGS. It shows the relationship when is taken.

As can be seen from these figures, when double-sided image formation is carried out, the image density of the first formed A side becomes higher than that of the B side. This is because the surface B that is finally fixed has undergone only one fixing step, but the surface A that is first fixed has undergone the fixing step twice, so that the heat supplied to the toner layer on the recording material is This is because the energy is almost doubled (substantially, it cannot be doubled because it is cooled in the conveyance process toward the second fixing process), and the fixing roller 401 and the pressure roller made of a rubber elastic body are used. It is considered that the contact state of the toner 402 with the toner becomes denser than that of the hard roller for forming a black-and-white image, and the smoothness of the toner image surface is increased.

As a countermeasure against this, a method of lowering the surface temperature on the pressure roller side during double-sided image than that on the fixing roller side to reduce the difference in image density and the difference in glossiness between the front and back sides can be considered. It takes some time for heating and cooling to detect the surface temperature of the roller and then control the temperature, which is not practical.

A method of reducing the heat energy supply amount to the toner of the A side by making the image fixing time of the A side shorter than the fixing time of the B side can be considered, but the effect is small.

The present invention solves the above problems and provides a fixing roller and a pressure roller whose surfaces are made of a rubber elastic body.
An object of the present invention is to provide an image forming apparatus capable of reducing the difference between the glossiness and the image density of a toner image formed on a recording material at the time of double-sided image formation (image homogenization) without changing the configuration of the image fixing device. There is.

[0019]

According to the present invention, the above object is to provide a latent image carrier whose surface is endlessly movable.
Charging means for uniformly charging the surface of the latent image carrier,
Exposure means for exposing the charged surface, developing means for developing the exposed surface with a developer, transfer means for transferring the unfixed image formed on the surface onto a recording material, and the unfixed image A fixing device that heats and pressurizes the recording material to fix the recording material on the recording material, and the recording material after fixing again on the latent image carrier to form a new image on the back surface of the surface of the recording material on which the image is fixed. In an image forming apparatus that is provided with a conveying means for conveying and forms an image on both sides of a recording material, the image is formed on the surface of the latent image carrier at the time of image formation on the front surface of the recording material where fixing is performed first. The surface of the latent image bearing member is charged so that the amount of developer of the unfixed image is less than the amount of developer given to the original image of the same density during image formation on the back surface of the recording material. Amount or exposure to the surface It is accomplished by having a means for controlling.

[0020]

According to the present invention, when an image is formed on both sides of a recording material, first, in order to form an image on the front surface of the recording material,
The surface of the latent image carrier is uniformly charged by the charging means,
Further, the surface is exposed by exposure means. And
The developing unit gives a developer in an amount corresponding to the charge amount or the exposure amount, and an unfixed image is formed on the surface of the latent image carrier. The exposure amount or the charge amount during image formation on the front surface of the recording material is the developer amount given according to these, and the developer amount given during the image formation on the back surface of the recording material with respect to the original image of the same density. Is controlled to be less than. The unfixed image thus formed is transferred onto the front surface of the recording material by the transfer means and is heated and pressed by the fixing device to be fixed on the front surface. Further, the recording material is conveyed again to the periphery of the latent image carrier by the conveying means, and the unfixed image is transferred to the back surface of the recording material through the same steps as above. However, the amount of developer applied during the image formation on the back side is controlled to be a normal amount. Then, the unfixed image transferred to the back surface of the recording material is heated and pressed by the fixing unit to be fixed, and at this time, the image on the front surface of the recording material which is previously fixed is also heated and pressed again.
Pressurized. As described above, the image on the front surface of the recording material receives more thermal energy and pressure than the image on the front surface of the recording material, but as described above, the developer amount of the image formed on the front surface of the recording material is the same. Since the density of the original image is smaller than that formed on the back surface, the difference in image density and the difference in glossiness between the front and back of the recording material of the final fixed image are eliminated.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing an embodiment of an electrophotographic image forming apparatus capable of forming a color image on both sides of a recording material according to the present invention.

As shown in FIG. 1, the apparatus of this embodiment comprises a printer unit 1 and a reader 2. The reader 2 is a contact type CC which applies light emitted from a halogen lamp 202 to an original O.
The image is read by the D line sensor 201, and the image forming signal is converted into an electric signal and output to the printer unit 1.

The printer unit 1 includes a recording material conveying system I formed on the lower side of the apparatus from the right side to the central portion, a latent image forming section II formed above the recording material conveying system I, and A rotary developing device II, which is a developing means disposed on the left side of the latent image forming portion II.
Basically, I, a fixing device 40 and a double-sided conveyance system V, which are arranged on the upper right side of the recording material conveyance system I, are provided.

First, the recording material conveying system I includes recording material supply cassettes 101 and 102 which are detachable from an opening formed on the right side of the printer unit 1 and recording material feeding cassettes 101 and 102. Paper feed roller 1 arranged almost directly above
03 and 104, so that the recording material can be supplied at any time. Further, the paper feeding rollers 103, 1
The paper feed roller 10 is provided at both ends in the front of the recording material transporting direction 04.
Paper feed guides 107 and 108 including 5 and 106 are provided to guide the supplied recording material to a transfer drum 110 as a transfer unit. The transfer drum 11
Reference numeral 0 is arranged rotatably in the arrow direction in front of the recording material conveying direction of the paper feed guide 108, and grips, transfers and separates the conveyed recording material. Therefore, the recording material contact roller 109, the gripper 111, the recording material separating charger 114 and the separating claw 115 are sequentially provided around the periphery thereof from the upstream side to the downstream side in the rotation direction, and further, inside the transfer drum 110. Is a transfer charger 112
And a recording material separating charger 113. Further, a conveying belt means 116 is provided above the paper feed guides 107 and 108 so that one end of the conveyor belt means 116 is close to the separating claw 115 and the other end is close to the fixing device 40. The recording material after transfer is fixed to the fixing device 40. It is designed to be transported to. The above is the schematic configuration of the recording material conveyance system I.

Next, the fixing device 40 is provided at a position where the recording material conveyed by the conveyor belt means 116 is sandwiched and conveyed on the extension of the end portion of the conveying belt means 116 in the recording material conveyance direction. The configuration is similar to that of the conventional example shown in FIG.

Further, the double-sided conveyance system V includes the fixing device 40.
Has a double-sided paper feed roller 42 and a discharge tray 41 at the front of the recording material conveying direction, and conveys the recording material discharged from the fixing device 40 after the image forming process is completed at the time of double-sided image formation. It is designed to be sent to system I. Therefore, the discharge tray 41 is movably arranged at the double-sided conveyance position shown by the solid line and the single-sided discharge position shown by the broken line, and the double-sided paper feed roller 42 is also at the standby position shown by the solid line and the double-sided supply position shown by the broken line. It is rotatable to the paper position.

On the other hand, the latent image forming section II is the transfer drum 1
A photosensitive drum 20 serving as a latent image bearing member is provided at a substantially upper end of 10 so as to come into contact with the transfer drum 110, and the photosensitive drum 20 is rotatable in an arrow direction. Further, around the photosensitive drum 20, a cleaning unit 22, a primary charger 21, and a potential sensor 23 are sequentially arranged from the upstream side to the downstream side in the rotation direction of the photosensitive drum 20. Further, on the upper right portion of the photoconductor drum 20, an image exposure means 24 for irradiating a laser beam E for forming an electrostatic latent image on the outer peripheral surface of the photoconductor drum 20, and a child image exposure reflection of a polygon mirror. And means 25.

On the other hand, the rotary developing device III is provided with a rotating body 3 composed of a rotatable casing at a position close to the left side of the photosensitive drum 20. The rotating body 3 is equipped with a yellow developing device 3Y, a magenta developing device 3M, a cyan developing device 3C and a black developing device 3BK, and each developing device is electrostatically charged at a position facing the outer peripheral surface of the photosensitive drum 20. It is configured to visualize or develop the latent image.

The apparatus of this embodiment as described above has a latent image forming section.
The color unfixed toner image formed by the rotary developing device III and the developing device III is carried on the front surface of the recording material conveyed by the recording material conveying system I, and the front surface of the recording material is fixed by the fixing device 40. An apparatus capable of forming a color image on the back surface of the recording material by a similar process after fixing the recording material on the surface as a permanent color image and then returning the recording material to the recording material carrying system I again by the double-sided carrying system V. Is.

Conventionally, a color image is formed on both sides of the recording material by such a process, but as described in the conventional example, the recording material is first fixed on the front surface and then fixed on the recording material. There is a problem that a difference in glossiness and a difference in image density occur between the back surface and the back surface.

Therefore, in the present invention, the toner amount of the image formed on the front surface of the recording material is smaller than the toner amount of the image formed on the back surface for the original image having the same density. This problem is solved by controlling the amount of light emitted from the laser at the stage of forming a latent image on the photoconductor drum 20.

That is, the amount of laser light emitted to the photosensitive drum 20 at the time of image formation on the front surface of the recording material is applied to the original image of the same density at the time of image formation on the back surface of the recording material. It is controlled so that it is less than one. Hereinafter, the control method in this embodiment will be described, and the mechanism from the reading of the original to the irradiation of the laser will be described.

As described above, the image of the original O is input to the CCD line sensor 201 as reflected light of the light emitted to the original O from the halogen lamp 202 provided in the reader 2 and converted into an electrical image signal. To be converted.

The image signal output from the CCD line sensor 201 is input to the analog processing section and separated into each color. That is, since the signal of the CCD line sensor 201 has a configuration in which cyan (C), green (G), and yellow (Y) signals are sequentially output for each pixel,
In the analog processing section, first, the C, G, and Y colors are separated. Next, the developing units 3Y, 3M, 3 of the printer unit 1
Since the toner in C corresponds to yellow (Y), magenta (M), and cyan (C), the image signal is converted into red (R), green (G), and blue (B) signals. This is performed by arithmetic processing according to the equations C−G = B and Y−G = R.

Further, since the output voltage of these signals separated into R, G, and B changes linearly with respect to the concentration, 00H to FFH (H indicates a hexadecimal number) by the A / D converter. The same applies to the following.), Which is converted to 8-bit density data e.

The density data e for each color digitized in this manner is input into the gradation control circuit of the printer unit 1 through various processes. The density data e corresponds to the color reproduction density of the printer unit 1 in the gradation control circuit, and a look-up table RAM (hereinafter referred to as LUTRAM).
Address, and the gradation control circuit outputs converted data E corresponding to this address.

The converted data E is converted into an analog signal, pulse-width modulated by a binarization circuit and output as an image signal to a laser driver. The laser driver drives the laser to form a latent image on the photosensitive drum 20. Is done.

The relationship between the output pulse width and the laser emission light quantity is as shown in FIG. Therefore, in order to use the linear portion of this characteristic curve as wide as possible for the range 00H to FFH of the conversion data E, the minimum value 00H of the conversion data E should correspond to the pulse width when the curve starts to become linear. The maximum value FFH of the converted data E is adjusted so as to correspond to the pulse width immediately before the curve deviates from the linear region.

As described above, the laser emission light amount is determined by the level of the conversion data E corresponding to the density data e of the image. That is, even for the same density data e, if the value of the look-up table in the LUTRAM referred to by the gradation control circuit is different, the conversion data E, that is, the light emission amount of the laser is different.

However, conventionally, since the same look-up table is used when forming the image on the front surface and the image on the rear surface of the recording material, the amount of laser emission light at the time of forming the front and back images for the original image having the same density is reduced. The amount of toner forming an image was also equal. As a result, there is a problem that the image density on the front surface of the recording material on which the fixing is performed first becomes high. For example, as shown in the red gradation-density characteristics (hereinafter referred to as VD curve) in FIG. 9, the density of the front surface of the recording material is about 0.1 when the gradation is A0H and FFH. Is higher than.

Therefore, in this embodiment, this is prevented by reducing the amount of toner of the image formed on the front surface of the recording material in advance to that of the image formed on the back surface. At the time of image formation, a look-up table modified to reduce the laser emission light amount is used.

That is, in the case of the red color shown in FIG. 9, the gradation is FFH and A0H when the image is formed on the front surface of the recording material.
When both sides are to be corrected to V _b and V _a respectively, the same density as the back side can be obtained on the front side of the recording material at the end of double-sided image formation. Thus, in order to reduce the gradation (latent image potential of the photoconductor drum) to V _b and V _a , it is sufficient to reduce the light emission amount of the laser.
The conversion data that determines the amount of emitted light is changed by modifying the lookup table.

The VD curve is shown in FIGS.
As shown in FIG. 1, the toner color varies depending on the toner color, and further varies depending on the environmental characteristics of the developer, the laser power, and the clock of the binarization circuit. Was changed to measure a plurality of VD curves on both sides of the recording material, and lookup tables for both sides of the recording material were created based on the VD curves. Then, after setting the plurality of look-up tables in the LUTRAM in advance, the look-up table is appropriately selected according to the color of the toner or the surface of the recording material on which the image is formed.

Next, the process of creating the lookup table will be described with reference to FIG. FIG. 3 shows the relationship between the input image signal (digitized density data e) and the output image density (the density of the image fixed on the recording material measured by Macbeth RD914 is expressed by the following equation). In the figure, the first quadrant is the output density D (FIGS. 9 to 11) with respect to the input density data e expressed in the range of 00H to FFH.
(Corresponding to the "density" in the above), the second quadrant is the relationship (lookup table) of the converted data E with respect to the input density data e, and the third quadrant is the measured potential V (Fig. 9 to Fig. 9) for the converted data E by the potential sensor. 11 (corresponding to the “tone”) (EV curve), and the fourth quadrant is the relationship of the output density D to the measured potential V (VD curve. FIGS. 9 to 11).
Of the measured potential V here.
And the output density D are expressed by the following equations.

V = {(measured value by potential sensor-V _FF )
/ (V ₀₀ −V _FF )} × FFH D = (density / maximum density) × FFH V ₀₀ ; a value measured by a potential sensor of the laser output when the conversion data E is 00H V _FF ; conversion data E is FFH The value of the laser output measured at this time by the potential sensor

The lookup table is created based on the VD curve drawn in the fourth quadrant of FIG. First, since it is ideal that the output density D has a linear characteristic that is equal to the input density data e, a straight line with a slope of 1 is drawn in the first quadrant as shown in FIG. Next, the EV curve in the third quadrant also has a linear characteristic in which the displacement of the converted data E and the displacement of the measured potential V are equal, and a straight line with a slope of 1 is drawn as shown in FIG. Then, from these linear relationships, the x-axis input density level e in the first and second quadrants can be replaced with the y-axis output density D in the first and fourth quadrants, and the second quadrant can be replaced. And the converted data E on the y-axis in the third quadrant can be replaced with the measured potential V on the x-axis in the third and fourth quadrants. Therefore, as long as the EV curve in the third quadrant has the linear characteristic as described above, the lookup table in the second quadrant is the VD curve itself in the fourth quadrant.
The solid line look-up table shown in the second quadrant of FIG. 3 thus represents the input density data e on the y-axis of the fourth quadrant.
Further, the VD curve in which the x-axis of the fourth quadrant is replaced with the converted data E is drawn with the input density data e as the x-axis of the second quadrant and the converted data E as the y-axis of the second quadrant. ..

However, since the EV curve in the third quadrant does not actually have the linear characteristic as described above, the potential is measured as follows. First, a predetermined pattern (a value in the range of 00H to FFH) corresponding to the input density data e is output from the pattern generator according to a predetermined sequence (hereinafter, referred to as PG output), and the data is looked up in the second quadrant. The converted data is converted into the converted data E based on the above, and the laser is output as described above. For example, if the PG output is e _i1 in FIG. 3, the converted data is E _i , and the laser output corresponding to this value is performed.

After that, the actual surface potential of the photosensitive drum 20 due to the laser output is read by the potential sensor 23 arranged near the photosensitive drum 20, and the actual potential is measured. In FIG. 3, the measured potential is V _i for the converted data E _i .

When the potential thus measured is plotted, the EV curve is as shown in FIG. 3 and it can be seen that it is not a linear characteristic. Therefore, if the lookup table is equal to the VD curve as described above, the characteristic of the output density D with respect to the input density data e is not linear,
For example, in FIG. 3, the output density D is the input density data e
D values to be obtained with respect to _{i1 i1} (= e _i1) instead D
_i2 .

Therefore, the input density data e is e _i2 (=
The output density D when D _i2) to modify the look-up table so as to D _i2. That is, when the input density data e is e _i2 , the look-up table is rewritten so that the conversion data E becomes E _i .

Thereafter, the correction is repeated in the same manner as this to create a new lookup table. In this embodiment, PG
Since the output is performed in 16 steps, 16 LUT data are created, and the lookup table is completed from 00H to FFH by line approximation from this data. With the look-up table created in this way, the relationship between the input density data e and the output density D can be approximated to an ideal linear characteristic.

Next, a method of correcting the look-up table created as described above for the front surface of the recording material will be described with reference to FIG. VD shown by the solid line in the fourth quadrant of FIG.
The curve is, for example, the VD curve of the back surface of the recording material represented by R-1 in FIG. 9, and the lookup table shown by the solid line in the second quadrant is the lookup table for the back surface of the recording material created by the above method. is there.

In the fourth quadrant of FIG. 4, for example, R in FIG.
The VD curve of the front surface of the recording material represented by -2 is drawn by a dashed line. Then, the output density D _A0 obtained at the measurement potential V _A0 on the back surface of the recording material is the value obtained at the measurement potential V _{a on} the front surface of the recording material. The output density D _FF at the measured potential V _FF on the back surface of the recording material is a value obtained at the measured potential V _{b on} the front surface of the recording material. Therefore, at the time of forming an image on the front surface of the recording material, if the measured potentials should be V _A0 and V _FF , respectively, if the measured potentials are corrected to V _a and V _b , respectively, linearity of the input density data e and the output density D in the first quadrant can be obtained. This relationship is maintained, and the difference between the front and back of the image density is eliminated.

Therefore, since the input density data e giving the measured potentials V _A0 and V _FF at the time of image formation on the back surface of the recording material are e _A0 and e _FF , respectively, these input densities at the time of image formation on the front surface of the recording material. The look-up table is modified so that the measured potentials V _a and V _b can be obtained when the data e _A0 and e _FF are obtained. As a result, when the input density data are e _A0 and e _FF , the conversion data E are E _a and E _b , respectively, and the measured potentials are V _a and V _b .

Thereafter, the look-up table for the front surface of the recording material can be created by making the same corrections.

Next, the sequence of the entire image forming apparatus having the above configuration will be briefly described by taking as an example the case where images are formed on both sides of the recording material in the full color mode.

First, when the photosensitive drum 20 rotates in the direction of the arrow shown in FIG. 1 and the photosensitive layer on the photosensitive drum 20 is uniformly charged by the primary charger 21, it is modulated by the yellow image signal of the original O. Image exposure is performed by the laser beam E thus generated according to the look-up table corrected as described above, and an electrostatic latent image of a yellow image is formed on the photoconductor drum 20. The electrostatic latent image of the yellow image is developed by the yellow developing device 3Y which is fixed at the developing position in advance by the rotation of the rotating body 3 of the developing device III.

On the other hand, the paper feed guide 107 and the paper feed roller 10
6. The recording material (not shown) conveyed through the paper feed guide 108 is electrostatically held by the contact roller 109 and the electrode facing the contact roller 109 which is held by the gripper 111 at a predetermined timing. It is wound around the transfer drum 110. The transfer drum 110 is rotating in the direction of the arrow shown in FIG.
The visible image developed with Y is transferred to the transfer charger 11 at a portion where the outer peripheral surface of the photosensitive drum 20 and the transfer drum 110 are in contact with each other.
2 is transferred. The transfer drum 110 continues to rotate and prepares for transfer of the next color (magenta in FIG. 1).

On the other hand, the photosensitive drum 20 is cleaned by the cleaning means 22 and then charged again by the primary charging device 21, and the same look for the front surface of the recording material is corrected by the next magenta image signal. Receive image exposure according to the up table. The developing device III rotates while the electrostatic latent image is formed on the photoconductor drum 20 by the above-mentioned image exposure by the image forming signal of magenta, so that the magenta developing device 3M is fixed at the developing position and the predetermined magenta is generated. Develop. Subsequently, the above-described process is performed for cyan and black, respectively, and when the transfer of the four colors is completed, the recording material on which the visible images of the four colors are formed is discharged by the chargers 113 and 114. To be done. And
The gripping of the recording material by the gripper 111 is released, and the recording material is separated from the transfer drum 110 by the separation claw 115, and the image fixing device 40 is conveyed by the conveyor belt means 116.
Sent to. The fixing device 40 mixes and fixes the visible image of the four colors by applying heat and pressure to the recording material and the visible image of the four colors on the recording material, and ejects the recording material onto the ejection tray 41. .. As a result, the sequence of full-color printing on one side of the recording material is completed, and a desired full-color print image is formed.

Thereafter, as a double-sided image forming sequence,
The discharge tray 41 on which the discharged recording material is placed descends to the position shown by the solid line in FIG.
Also rotates to the broken line position. Then, the double-sided paper feeding roller 42
Contacts the recording material and conveys the recording material again to the paper feed roller 105, and starts the above-described full-color printing sequence on the back surface of the recording material. However, since the lookup table used in this case is a normal one that has not been modified, the toner amount of the image formed on the back surface of the recording material is a normal amount larger than that on the front surface.
Therefore, an image with good density reproducibility is formed on this back surface. On the other hand, the amount of toner in the image on the front surface of the recording material is smaller than that on the back surface,
Appropriate density and gloss are obtained by applying pressure.
Thus, at the end of fixing, good images can be obtained on both sides of the recording material, and there is no difference between image density and glossiness between the front and back.

The present invention not only controls the amount of laser light emitted by the output pulse width as shown in FIG. 2 (controls the light emission time by pulse width modulation), but also changes the image signal from the reader to the laser drive current. It is also effective in a light intensity modulation method in which the emission intensity of a laser is controlled according to the above, and a method using a combination thereof.

Further, the latent image forming means is not limited to a laser, and an image signal can be generated without using a digital latent image forming means such as an LED, a liquid crystal or ionography and an image reading means such as the reader 2. It is also effective in so-called analog latent image forming means in which light is directly formed on the photoconductor. In such an analog latent image formation, since there is no control means such as a look-up table, it is possible to control the recording material by controlling the illumination system of the original document or the charge amount (latent image potential) of the photosensitive drum. The amount of toner formed on the front and back sides is changed to reduce the density difference between the front and back sides. In the case of such a means, it is difficult to align the high density portion and the low density portion of the image on the front and back like a look-up table, but as shown in FIGS. 6 to 11, the difference in glossiness and the difference in image density are remarkable. Sufficient effects can be obtained by controlling mainly the high-concentration areas that are seen. Therefore, even when a look-up table is used, a curve mainly composed of a high density portion may be selected.

In the above embodiment, the case where the look-up table is set in the RAM has been described.
A plurality of data groups may be written in the ROM in advance and appropriate data may be selected from the data stored in this ROM.

Further, the fixing device according to the present invention is particularly effective for double-sided fixing of a full-color image forming device which mixes toner at the time of fixing, but is also effective for double-sided fixing of a monochrome image fixing device, such as a fixing roller and a fixing roller. The material of the pressure roller is not limited to silicone rubber, but may be a heat-resistant, high-release rubber material such as fluororubber or fluorosilicone rubber.

[0065]

As described above, according to the present invention,
The amount of developer of the image on the front surface of the recording material to be fixed first is less than the amount of developer of the image formed on the original image of the same density on the back surface of the recording material to be fixed thereafter. As described above, the charge amount or exposure amount of the latent image carrier surface is controlled at the stage of forming the latent image on the latent image carrier, so that the difference between the glossiness and the density of the fixed image can be reduced. Image uniformity can be achieved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a laser light amount and a pulse width in the apparatus shown in FIG.

FIG. 3 is a diagram illustrating a method of creating a lookup table according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining a look-up table correction method according to an embodiment of the present invention.

FIG. 5 is a sectional view showing a schematic configuration of a conventional device.

FIG. 6 is a diagram showing a gloss difference between a front surface and a back surface of a recording material for a red toner in a conventional example.

FIG. 7 is a diagram showing a gloss difference between a front surface and a back surface of a recording material for yellow toner in a conventional example.

FIG. 8 is a diagram showing a gloss difference between a front surface and a back surface of a recording material for a magenta toner in a conventional example.

FIG. 9 is a diagram showing the difference in density between the front and the back of a recording material for red toner in a conventional example.

FIG. 10 is a diagram showing a difference in density between the front and back of a recording material for yellow toner in a conventional example.

FIG. 11 is a diagram showing a difference in density between the front and the back of a recording material for a magenta toner in a conventional example.

[Explanation of symbols]

 20 Photoreceptor Drum (Latent Image Bearing) 21 Primary Charger (Charging Means) 24 Image Exposure Means (Exposure Means) 40 Fixing Device 110 Transfer Drum (Transfer Means) III Rotary Developing Device (Developing Means) V Double-sided Conveying System ( (Transportation means)

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Claims (1)

[Claims] 1. A latent image carrier whose surface is endlessly movable, charging means for uniformly charging the surface of the latent image carrier, exposure means for exposing the charged surface, and exposure. Developing means for developing the surface thus formed with a developer, transfer means for transferring the unfixed image formed on the surface onto a recording material, and heating and pressurizing the unfixed image to fix it on the recording material. Both sides of the recording material are provided with a fixing device and a conveying means for conveying the recording material after fixing again around the latent image carrier to form a new image on the back surface of the surface of the recording material on which the image is fixed. In the image forming apparatus for forming an image on the surface of the recording material, the amount of the developer of the unfixed image formed on the surface of the latent image carrier is the same when the image is formed on the front surface of the recording material which is first fixed. The back of the recording material for the original image with the density of Image forming means comprising means for controlling the amount of charge on the surface of the latent image bearing member or the amount of exposure to the surface so that the amount of developer applied to the surface is less than the amount of developer applied. apparatus.