JPH06202413A - Image forming device - Google Patents

Abstract

PURPOSE:To enhance the positional accuracy of an image forming device with respect to a transfer material. CONSTITUTION:A transfer drum 2 is made abut on a photosensitive drum 1, and both of them are respectively rotatably disposed in the direction shown by an arrow. An irradiated position P for forming an electrostatic latent image is set on the photosensitive drum 1, and a leading edge detection position R for detecting the leading edge of the carried transfer material S is set on the transfer drum 2; furthermore, the transfer position Q for transferring a toner image on the photosensitive drum 1 to the transfer material S on the transfer drum 2 is set on both drums 1 and 2. Providing that a distance between P and Q in the peripheral direction is L1, the distance between Q and R in the peripheral direction is L2; and exposing (electrostatic latent image formation) is started at the position P when the transfer drum 2 is rotated by (L2-L1) after a photointerrupter 36 detects the leading edge of the transfer material S at the position R. Thus, the positional accuracy of the toner imaged formed on the transfer material S with respect to the transfer material S is kept well.

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 such as a color copying machine or a laser beam printer.

[0002]

[Prior art]

<Prior Art 1> Conventionally, in an image forming apparatus, a method of transferring a toner image formed on a photosensitive drum (image carrier) to a transfer material carried on a transfer drum (transfer material carrier) is known. Has been. As an example of such an image forming apparatus, FIG. 5 schematically shows a four-color full-color copying machine. This one forms toner images of magenta, cyan, yellow, and black colors one by one on the photosensitive drum 1 in order,
These toner images are transferred one by one onto the transfer material on the transfer drum 2 one by one, and the four color toner images are superposed on each other to finally obtain a full color image of four colors.

An example of forming an image on both sides of a transfer material will be described below.

The transfer material S such as copy sheets stacked in the transfer material stacking cassette 3 set at the bottom of the main body of the image forming apparatus passes through the paper feed roller 5, the transport rollers 6, 7, 9 and the registration roller 10. After being conveyed, it is attracted to the transfer sheet 2a of the photosensitive drum 2 by the attraction roller 11 and is rotated by the rotation of the transfer drum 2.

During this period, a latent image is formed on the photosensitive drum 1 by image information sent from an output device (not shown) such as a document reading device or a computer, and this latent image is magenta forming the developing device 12. , Cyan, yellow, black developing devices 12M, 12C, 12Y, 12B
Are developed one after another. The toner image is transferred to the transfer material S on the transfer drum 2 each time development of each color is performed.
And a full-color image is formed on the transfer material S. Subsequently, the transfer material S is separated from the transfer drum 2 by the separation claw 13, conveyed on the conveyance unit 15 and sent to the fixing roller pairs 16 and 17, and a full color image is fixed on the transfer material S at this nip portion. Then, the sheet is discharged by the sheet discharge roller 18 to the outside of the machine.

On the other hand, when performing a so-called double-sided copy after the first side of the transfer material S is copied, the flapper 19 is urged to the position shown in FIG. Transfer material S on which a full-color image is fixed
Is sent to the reversing roller 22 via the transport rollers 20 and 21. In the reversing roller 22, the transfer material S is sent to the reversing path 23 leaving only its rear end portion, and then is rotated in the reverse direction to be conveyed in the reverse direction. At this time, the flapper 25 is biased in the direction of arrow R25, and the transfer material S
Is conveyed in the direction of the guide 26 and is fed to the refeed cassette 27.
Loaded on top. The loaded transfer material S is reversed in its front and back from that when it was first loaded in the paper feed cassette 3, so that the same copying operation feeds the transfer material S to the transfer drum 2 again. When copying is performed, a full-color image is formed on the back surface of the transfer material S, and double-sided copying is completed.

Further, in the above-mentioned image forming apparatus,
In order to increase the copy productivity, when the transfer material S is of a small size such as A4 or LTR, two transfer materials S are adsorbed onto the transfer drum 2 at one time to perform transfer. Further, in the case of a single-color copy, the transfer is continuously performed by adsorbing only about half the circumference from the suction roller 11 to the separation claw 13.

In the operation sequence of such an image forming apparatus, conventionally, various operation sequence timings are set based on the detection signal of the rotation angle of the transfer drum 2 detected.

That is, as shown in FIGS. 6 and 7, inside the transfer drum 2, infrared light shielding flags (hereinafter simply referred to as "flags") 31a, 31b, which rotate integrally with the transfer sheet 2a, are provided. An angle detection sensor 30 including a photo interrupter 32a and a photo interrupter 32b fixed at an arbitrary position is provided. Where the flag 31
When a and 31c simultaneously shield the photo interrupters 32a and 32b, respectively, the rotation angle of the transfer sheet 2a indicates that the leading end when the transfer material S1 is adsorbed is the position A shown in FIG. As shown in FIG. 7, when the transfer drum 2 rotates about 180 ° and only the flag 31b shields the photo interrupter 32a from light, the transfer sheet 2a
The rotation angle of indicates that the tip portion when the transfer material S2 is adsorbed is at the position A in the figure. Therefore, in synchronization with the signals from the photo interrupters 32a and 32b, a latent image is formed on the photosensitive drum 1, and
By synchronizing the operation of an electromagnetic clutch or the like for controlling the timing of feeding / conveying and adsorbing the transfer material S with this signal, at a predetermined position on the transfer sheet 2a,
An image can be formed on the transfer material S. <Prior Art 2> Conventionally, in an image forming apparatus such as a copying machine or a laser beam printer, a toner image is transferred onto a transfer material, the toner image is fixed by a fixing device, and then the same transfer material is re-used. It is known that a toner image is repeatedly transferred and fixed.

Such an image forming apparatus is roughly classified into two types: "double-sided" and "multiplexed". Here, the both sides mean that the toner image is transferred and fixed on the first surface (hereinafter referred to as “first surface”) of the transfer material, and then on the surface opposite to the first surface (hereinafter referred to as “second surface”). Similarly, the toner image is transferred and fixed to form an image on both sides of the transfer material. On the other hand, the term "multiplexing" generally means that an image is formed by transferring and fixing a toner image of a different color to the first surface on which the toner image is first transferred and fixed.

FIG. 19 shows an outline of a conventional copying machine as an example of an image forming apparatus capable of forming an image as described above. The copying machine includes a photosensitive drum 51 as an image carrier that rotates in the direction of arrow R1. Photosensitive drum 51
After the surface is uniformly charged by the primary charger 52, an electrostatic latent image is written through the mirror groups 55, 56, 57 when the scanner 53 reads an original document placed on the original document table. . A developing unit 59 develops the above-mentioned electrostatic latent image with toner by a predetermined method. The developed toner image (developed image) is transferred by a transfer charger 61 onto a transfer material such as copy paper. The transfer material onto which the toner image has been transferred is subsequently conveyed to the fixing unit, and is heated and pressed by the fixing roller groups 62 and 63 to be fixed, and then multiple or double-sided image formation is performed. 6
The toner image, which is visualized by the developing device 60 this time, is transferred to the transfer unit again via 5, 66, and 67, and is fixed again by the fixing rollers 62 and 63. It is discharged to 69. Further, the toner remaining on the photosensitive drum 51 without being transferred to the transfer material is removed by the cleaning blade 70 a of the cleaning device 70.

[0012]

[Problems to be Solved by the Invention]

<Problem of the first invention> However, in the above-mentioned conventional technique 1, the suction position on the transfer sheet 2a may be deviated from the target position depending on the environment change or the paper type of the transfer material S. In some cases, the relative position between the front end of the transfer material S and the front end of the image is not always constant. In particular, during double-sided copying, an image has already been formed on the first side and the surface condition of the transfer material S has changed, so that the transfer roller S is affected by slippage of the registration roller 10 and the like, so that the first side and the second side are transferred. There is a possibility that the suction position on the sheet 2a is different. Therefore, there is a problem that the leading edge of the image formed in synchronization with the signal from the angle detection sensor 30 of the transfer drum 2 is different on the transfer material S between the first surface and the second surface.

Therefore, according to the first aspect of the present invention, the leading edge of the transfer material carried by the transfer material carrying member is detected, and the leading end position of the latent image on the image carrying member is adjusted based on the detection result. It is an object of the present invention to provide an image forming apparatus in which the transfer position accuracy of a toner image on a transfer material is improved. <Problem of the Second Invention> However, according to the conventional technique 2, the following problems in image quality occur when double-sided color copying or multiple color copying is performed.

In both cases of double-sided and multiplex, the transfer material is 2
It will pass through the fixing section over and over. That is,
The toner image which has been heated and pressed by the first passage of the fixing unit after the first image forming operation is finished is again heated and pressurized when passing through the fixing unit again in the second image forming operation. As a result, the gloss increases. For this reason,
The image of the first time has higher gloss than the image of the second time, and as a result, the phenomenon that the density looks high occurs.

In view of this, the present invention provides an image forming apparatus in which the image forming conditions of the first and second image forming processes are changed on the basis of the output of the density detecting means to suppress the density difference between the two. It is intended to be provided.

[0016]

The present invention (first invention and second invention) has been made in view of the above circumstances, and has the following configurations, respectively. <Means of the First Invention> A first invention is a latent image forming means for forming a latent image on an image carrier, a developing means for adhering toner to the latent image to form a toner image, and a transfer material. And a transfer material carrier for supporting the transfer material carrier on a predetermined position, wherein the toner image formed on the image carrier is transferred to the transfer material carried by the transfer material carrier. A latent image forming means for detecting a carrying position of the leading edge of the transfer material with respect to the body; Is adjusted.

Further, a latent image forming means for forming a latent image on the image carrier, a developing means for adhering toner to the latent image to form a toner image, and a transfer material carrying means for carrying a transfer material at a predetermined position. An image forming apparatus including a body and a double-sided image forming mechanism, which transfers a toner image formed on the image carrier to a transfer material carried by the transfer material carrier, and forms an image on the first surface of the transfer material. Image information detecting means for detecting the image information at the time, and the latent image forming means forms a latent image corresponding to the second surface of the transfer material formed on the image carrier based on the output of the image information detecting means. It is characterized in that the tip position is adjusted. <Means of the Second Invention> The second invention is a series of methods for transferring a toner image formed on an image carrier onto a transfer material, and heating and pressing the toner image to fix the toner image on the transfer material. In an image forming apparatus in which the image forming process is performed at least twice successively for one transfer material, pattern forming means for forming a predetermined pattern on an image carrier with a color material used for image formation, and the pattern forming means. A density detecting means for detecting the density of the pattern formed by the means, and based on the output of the density detecting means, the image forming conditions in the first image forming process and the second image forming process. It is characterized by being changed.

The image forming condition is the primary charge amount, the developing bias, the light amount of the reader light source, the light amount of the exposure device, the light emission time of the exposure device, or the LUT, and at least one of these image forming conditions should be changed. You can

[0019]

[Action]

<Operation of the First Invention> With the above configuration, according to the first invention, the transfer material detection unit is a transfer target of the toner image.
Since the position of the transfer material carried on the transfer material carrier is detected, if the toner image on the image carrier is transferred to the transfer material based on this detection output, the transfer position of the toner image on the transfer material will be accurate. Can be <Operation of Second Invention> Further, according to the second invention, the toner image conventionally formed by the first image forming process is heated and pressed again in the fixing unit during the second image forming process. When the toner image formed in the second image forming process is darker and the density difference between the two toner images tends to occur, the image forming conditions of the first and second images are changed to change the density of the two images. The difference in density can be eliminated.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1 of the First Invention> FIG. 1 schematically shows a transfer material detecting means of an image forming apparatus according to the present invention. The overall image forming apparatus is almost the same as the conventional image forming apparatus shown in FIG.

A laser beam (shown by a dotted line) emitted according to image information sent from an original reading device or an output device such as a computer is passed through a polygon mirror 33 and a folding mirror 35 which form a part of the exposing means 34. Then, the photosensitive drum 1 as an image carrier is irradiated.
If the distance along the surface of the photosensitive drum 1 from the irradiation position P where the laser light is irradiated to the transfer position Q is L1, the transfer material detecting unit 36 is L1 along the surface of the transfer drum 2.
The tip detection position R is installed on the upstream side of Q by a longer distance L2 (L2> L1).

With the start of the copying operation, the transfer material S is fed in accordance with the signal from the angle detection sensor provided inside the transfer drum 2 in the same manner as the operation described in the prior art 1 described above. Further, it is adsorbed at a predetermined position on the transfer sheet 2a. At this time, the latent image by the laser light is not yet formed on the photosensitive drum 1, and the transfer drum 2 is
Perform idle rotation once.

When the tip of the transfer material S adsorbed on the transfer sheet 2a is rotated to reach the position R,
The transfer material detecting unit 36 detects the leading edge of the transfer material S, irradiates laser light in accordance with the detection signal, and forms a latent image on the photosensitive drum 1. That is, after the transfer material detection unit 36 detects the leading edge of the transfer material S (L2-L
When the transfer drum 2 is rotated by the distance 1), the suction position of the transfer material S is slightly displaced on the transfer sheet 2a by controlling the number of clocks so that the image front end of the latent image is formed at the position P. Even if the error occurs, the positional relationship between the front end of the transfer material S and the front end of the image can always be made constant.

Next, a specific structure of the transfer material detecting means 36 will be described with reference to FIG. In FIG. 2A, the transfer material detecting means 3
Reference numeral 6 denotes a reflection-type photointerplater in which a light source that emits infrared light and a light receiving portion (light receiving element) that receives the reflected light are integrally formed, and the light source and the light receiving portion face the transfer sheet 2a. In addition, it is provided close to the transfer sheet 2a so that the reflected light can be sufficiently detected. The transfer sheet 2a is made of a transparent material such as EPDM,
Normally, the infrared light emitted from the photo interrupter is transmitted through the transfer sheet 2a and diffused far, so that the reflected light is not detected by the light receiving portion. However, when the transfer material S is adsorbed on the transfer sheet 2a,
The infrared light is reflected by the transfer material S and detected by the light receiving section. That is, the moment when the light receiving element detects the reflected light can be detected as the front end of the transfer material S.

On the other hand, FIG. 2B shows a transmissive photo interrupter in which the light source 36a is provided inside the transfer sheet 2a and the light receiving portion 6b is provided outside the transfer sheet 2a so as to face each other. When there is no transfer material S, the light source 36
The infrared light emitted from a passes through the transfer sheet 2a and is detected by the light receiving section 36b. On the other hand, when the transfer material S adsorbed on the transfer sheet 2a reaches the position where the light source 36a and the light receiving portion 36b face each other, the infrared light is blocked and the light receiving portion 36b does not detect the infrared light. . This moment can be detected as the front end of the transfer material S.

The transfer material detecting means 36 according to this embodiment is
Either a reflection type or a transmission type photo interrupter may be used.

As described above, the transfer material detecting means 36
The latent image formed in synchronism with the leading end position of the transfer material S detected by is visualized by, for example, a magenta developing device 12M of the developing device 12, and is transferred onto the transfer material S at the Q position. . Subsequently, for each of the other colors, the image synchronized with the leading end position of the transfer material S is transferred in the same manner. Thereafter, the transfer material S is separated from the transfer sheet 2a by the separation claw 13 and the image is fixed by the pair of fixing rollers 16 and 17.

Further, when performing double-sided copying, the sheet is re-fed after being reversed by the same operation as in the conventional example.
It is loaded on 7. Next, in the copy of the second side, the transfer material S is fed / adsorbed to the transfer drum 2 in accordance with the signal from the angle detection sensor of the transfer drum 2 as in the case of the first side. Further, the transfer drum 2 idles once and the leading edge of the transfer material S is rounded.
When the transfer material detecting means 36 detects the leading edge position of the transfer material, the image is formed in synchronization with this signal. Therefore, even if the suction position of the second surface of the transfer material with respect to the transfer sheet 2a and the suction position of the first surface are different, the image is formed with the leading edge of the transfer material S as the reference as in the case of the first surface. The image positions of the first surface and the second surface can be matched with high accuracy.

In particular, it is very effective when a part of the created image is cut out from the transfer material S and used, for example, when a card having images on both front and back surfaces is created.

Only when it is desired to match the image positions of the first side and the second side with high accuracy, it is possible to use the tip position detecting means and the image leading edge determining means of the transfer material according to the present invention.
If it is set to be selectable, in normal double-sided copying, the image is formed only by detecting the rotation angle of the transfer drum, and the idle rotation for detecting the leading edge of the transfer material is not performed. Thus, the copy speed can be improved. <Second Embodiment of First Invention> Next, a second embodiment will be described.

In this embodiment, the position of the leading edge of the image on the second side during duplex copying is determined by detecting the image information on the first side.

Now, consider a case where an image F is to be formed on both front and back surfaces of the transfer material S as shown in FIG. The image on the first side may be formed in the same manner as in the previous embodiment. At this time, if the position of the image F on the transfer material S is required with high accuracy, the leading edge of the transfer material S may be detected to determine the leading edge of the image on the first side.
Unless specifically requested, the leading edge of the image on the first surface may be determined by detecting the angle of the transfer drum 2. The transfer material S on which the image formation on the first side is completed is re-fed after the image is fixed. The transfer material S is adsorbed in synchronism with the signal from the angle detection sensor of the transfer drum 2, and further rotates idle to reach the position R of the transfer material S. Here, the transfer material detection means 36 is a reflection type photo interrupter, and detects the image information of the first surface by this. That is, since the image on the first side is adsorbed on the inner side, as shown in FIG. 4A, the reflected light is detected by the light receiving portion of the photo interrupter as the transfer material S passes through. , And transfer drum 2
Rotates, and when the leading edge of the image F on the transfer material S passes,
The amount of reflected light is reduced due to absorption of infrared light, which can be detected as the leading edge of the image. Therefore, in synchronization with the signal that detects the leading edge of the image on the first side,
If the image of the second side is created, the image positions of the first side and the second side can be matched with higher accuracy. That is, if the latent image of the image front end of the second surface is formed at the position P when the transfer drum 2 is rotated by the distance L2-L1 after detecting the image front end of the first surface, the control is performed by the number of clocks. Good.

As described above, in the second embodiment, the transfer material detecting means 36 functions as the image information detecting means.

The image F on the first side is a light color,
When the density difference between the transfer material S and white is small, there is no significant difference in the amount of reflected light from the photo interrupter, and it may be difficult to detect the leading edge of the image. In such a case, as shown in FIG. 3, a black marker M may be created in a portion other than the required image area on the first surface. Then, when the image of the second surface is created, as shown in FIG. 4B, a change in the amount of reflected light at the marker M may be detected, and the leading edge of the image of the second surface may be determined based on this signal. <Embodiment 1 of the Second Invention> FIG. 8 schematically shows an image forming apparatus according to the second invention. In the following,
Description will be made focusing on the parts different from the conventional image forming apparatus shown in FIG. Therefore, substantially the same configurations and operations are denoted by the same reference numerals, and the description thereof will be omitted.

A little downstream of the transfer portion of the photosensitive drum 51,
A density detection sensor (hereinafter referred to as “patch sensor”) 71 is arranged on the upstream side of the cleaning device 70 so as to face the surface of the photosensitive drum 51. Patch sensor 71
Is composed of a combination of an LED 72 that illuminates the surface of the photosensitive drum 51 and a photodiode 73 that receives the reflection of the LED 72.

A reference density plate 76 whose density is controlled is attached to the non-image forming portion on the lower surface of the document table 75 above the photosensitive drum 51.

Next, a control flow will be described with reference to FIG.

In this image forming apparatus, after the power is turned on and after the warm-up is completed, the reference density plate 76 attached to the non-image forming portion of the document table 75 is moved by the light source 53 set to a predetermined voltage. Irradiation is performed to form an electrostatic latent image on the photosensitive drum 51, and this is developed to form a reference patch pattern toner image (hereinafter referred to as “patch”).

The patch sensor 71 measures the reflected light amount output of the patch formed on the photosensitive drum 3. The gain of the patch sensor 71 is adjusted in advance so that the set density can be reproduced when the output is 3.0V.

FIG. 10 shows the relationship between the patch sensor output and the voltage difference ΔV of the light source 53. The light source voltage difference ΔV is set according to the obtained patch sensor output. However, for an image (toner image) that is heated and pressed twice by passing through the fixing unit twice, A in FIG. The line B sets the light source voltage, while the line B sets the light source voltage for an image that passes through the fixing unit only once, including normal single-sided copying.

By carrying out the above control, the difference between the image density of the first time and the image density of the second time can be reduced. <Embodiment 2 of the Second Invention> In Embodiment 2, a full-color digital image forming apparatus will be described. In FIG. 11, a document D placed on a document table glass 75.
Is imaged on the CCD 79 by the light source 76 and the optical lens 77 and converted into an image signal according to the amount of received light.

The image signal is converted into a digital value by the A / D conversion 90, and the image is processed by the CPU 91, and then the laser light source 92 is driven.

The emitted laser light is reflected by the polygon mirror 9
3 and the mirror 95, and irradiates the photosensitive drum 51.

The photosensitive drum 51 is preliminarily cleaned by the cleaning device 70 so as not to have toner on it, and then uniformly charged by the charger 52.

First, the photosensitive drum 51 is rotationally driven in the direction of arrow R1 by a driving means (not shown), and first, by scanning with laser light based on a Y (yellow) image signal,
An electrostatic latent image is formed on the surface. Then, the electrostatic latent image
The developing device 59Y attaches yellow toner to form a toner image.

Further, the photosensitive drum 51 is rotated to attract the transfer material S to the transfer drum 96, and the toner image formed on the photosensitive drum 51 is transferred onto the transfer material S by the transfer charger 97.

Next, after the latent image is formed and developed with the image signal of M (magenta), the yellow toner image on the transfer material S is magenta toner on the transfer material S under the positional condition where the registration of the image is adjusted. Multiple transfer of images. Similarly, for C (cyan) and BK (black), image formation and multiple transfer are performed, and four color toner images are multiple transferred onto the transfer material S,
The transfer material S is separated from the transfer drum 96, and these toner images are fixed by a pair of fixing rollers 62 and 63 to complete a color image print.

Further, a patch sensor 71 is provided between the developing device 59BK on the most downstream side and the transfer nip N, where the LED 72 applies light to the toner image developed by the photosensitive drum 51 and the photodiode 73 receives the returned light. Placed in.

In this embodiment, the LED 72 has a wavelength of 950 nm.
Near infrared light was used. The target color toner has a property of reflecting all colors in this wavelength range, while the photosensitive drum 1 has a property of moderately reflecting.

FIG. 12 shows a graph for converting the output of the patch sensor into the image density signal.

Similar to the first embodiment, after the power is turned on and the warm-up is completed, a patch pattern serving as a reference for each color is created on the photosensitive drum 51, and the reflected light amount output thereof is measured by the patch sensor.

The color contrast potentials (V _cont Y, V _cont M, V _cont C, V _cont BK) are determined from the table of the difference between the patch sensor output and the set contrast potential shown in FIG. By the way, the contrast potential here is
Photosensitive drum 5 when exposed to obtain maximum density
It is the potential difference obtained by subtracting the developing bias potential from the surface potential of 1.

At the time of the first image formation in the case of multiplex or double-sided image formation, the image formation with a lower density difference is performed in anticipation of the density increase by passing the contrast potential of each color twice through the fixing section. Therefore, it is set in advance by the following formula.

V _cont Y1 = V _cont Y -ΔY V _cont M1 = V _cont M -ΔM V _cont C1 = V _cont C -ΔC V _cont BK1 = V _cont BK-ΔBK where ΔY, ΔM, ΔC and ΔBK are It is desirable to set the difference voltage for correcting the density difference in advance according to the characteristics of the front surface and the back surface of the image forming apparatus.

By carrying out such control, the image densities of the front and back sides are matched in the case of both sides, and the image densities of all the areas are matched in the case of multiplex for a long period of time, and a preferable image quality is obtained. It was <Third Embodiment of the Second Invention> FIG. 14 is a block diagram of an image signal processing for obtaining a gradation image according to this embodiment.

The luminance signal of the image is obtained by the CCD 79, and the luminance signal is converted into a digital luminance signal by the A / D conversion circuit 90.

The obtained luminance signal has the sensitivity variation of each CCD element corrected by the shading circuit 100, and the corrected luminance signal is converted into a density signal by the LOG conversion circuit 101.

Further, the γ characteristic of the printer at the time of initial setting is converted by the LUT (look-up table) 102 so that the image density and the output image match, and then the pulse width modulation circuit 103 makes the proportional to the density signal. The laser emission time is modulated. Next, the gradation image is formed by being sent to the laser driver circuit 105 and expressing the density gradation by area gradation.

FIG. 15 is a 4-limit chart showing how the gradation is reproduced.

The quadrant I shows the reader characteristic for converting the document density into the density signal, the quadrant II shows the LUT for converting the density signal into the laser output signal, and the quadrant III is the output density from the laser output signal. Shows the printer characteristics to be converted into, and the fourth quadrant shows the total gradation characteristics of this image forming apparatus showing the relationship between the document density and the output density.

Since the number of gradations is processed by an 8-bit digital signal, there are 256 gradations.

It is known that printer characteristics in the third quadrant have various shapes depending on conditions such as photoreceptor characteristics, laser spot diameter and developing characteristics.

Here, the case of the printer characteristic having the S-shaped characteristic will be described.

In order to faithfully reproduce a full-color image, it is important to linearize the total gradation characteristic which shows the relationship between the original density and the output density in the fourth quadrant. It is necessary to bend the LUT of S into an S shape as shown in FIG.

In the case of the electrophotographic system, the printer characteristics may fluctuate due to changes in characteristics due to environmental changes in temperature and humidity, and changes in characteristics of the photoreceptor due to fatigue of the photoreceptor due to endurance and abrasion of the photoreceptor.

Conventionally, as shown in FIG. 18, the photosensitive drum 5
1. A multi-tone patch pattern A is formed on 1, the patch pattern A is measured by a reflected light amount sensor for the amount of reflected light corresponding to the gradation patch, and the reflected light amount is converted into image density. Obtain the printer characteristics, find the LUT in the second quadrant as shown in FIG. 15 from the characteristic data, and control the total gradation characteristics in the fourth quadrant so that they are constant even if the above characteristics are varied. It has been known.

FIG. 16 shows a gradation characteristic diagram. C indicates a normal gradation characteristic of only one side, and a gradation characteristic of a double-sided and multiplex second image. D is a double-sided, multiplex first image, 2
The gradation characteristics that have passed the second fixing are shown.

As described above, the density increase is large in the high density area where the toner amount is large, and the density does not necessarily increase in proportion to the document density.

FIG. 17 shows the LUT. When the LUT characteristic of E is set in order to obtain the characteristic of C, the characteristic of C is obtained when the first image of both sides and multiplex passes through the fixing section twice. In order to obtain, it is preferable to set an LUT such as F.

Therefore, in this embodiment, the difference between E and F is registered in advance, and the LU is created by gradation control.
For T, the image formation is performed by a LUT that subtracts the difference when a double-sided, multiplex first image passes through the fixing unit twice, and if it is a double-sided image, the gradation of front and back images If the values are matched and multiplex, the tonality of the image in all the areas is matched for a long period of time, and a preferable image quality is obtained.

[0071]

As described above, according to the present invention,
It has the following effects. <Effect of the first invention> According to the first invention, the latent image formed on the image carrier is detected by the output of the transfer material detecting unit that detects the carrying position of the transfer material carried on the transfer material carrier. By determining the position, an image can be formed on the transfer material with high positional accuracy. This allows
For example, when images are formed on both sides of a transfer material, the image positions of the first side and the second side in double-sided copying should be matched with high accuracy even if the transfer material carrying position on the transfer material carrying body is slightly displaced in the circumferential direction. You can <Effect of the Second Invention> According to the second invention, the first image forming process and the second image are generated based on the output of the density detecting unit that detects the density of the pattern formed on the image carrier. By changing the image forming conditions with the forming process, even when double-sided, multiplex, etc. transfer material is passed through the fixing section multiple times, the density and gradation of the final image formed on the transfer material. It is possible to effectively prevent variation in sex.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an operation of a transfer material detecting unit according to a first embodiment of the first invention.

FIG. 2A is an explanatory diagram of the operation of a reflective photo interrupter. FIG. 7B is an operation explanatory view of the transmissive photo interrupter.

FIG. 3 is a plan view of a transfer material which is a detection target according to the second embodiment of the first invention.

FIG. 4A is a diagram showing the relationship between the rotational displacement of the transfer drum and the amount of reflected light in the reflective photointerrupter.
FIG. 6B is a diagram showing the relationship between the rotational displacement of the transfer drum in the reflective photointerrupter and the amount of reflected light when a marker is attached to the transfer material.

FIG. 5 is a schematic view of a four-color full-color image forming apparatus having a double-sided image forming mechanism.

FIG. 6 is an operation explanatory diagram of an angle detection sensor.

FIG. 7 is an operation explanatory view of the angle detection sensor.

FIG. 8 is a schematic diagram of an image forming apparatus according to a first embodiment of the second invention.

FIG. 9 is a flowchart of the first embodiment.

FIG. 10 is a diagram showing the relationship between the patch sensor output and the light source voltage difference of the first embodiment.

FIG. 11 is a schematic diagram of an image forming apparatus according to a second embodiment of the second invention.

FIG. 12 is a diagram showing a relationship between a patch sensor output and an image density level according to the second embodiment.

FIG. 13 is a diagram showing a relationship between the output of the patch sensor and the contrast potential difference of the second embodiment.

FIG. 14 is a block diagram of image signal processing according to the second embodiment.

FIG. 15 is a four-limit chart showing gradation characteristic conversion of the second embodiment.

FIG. 16 is a gradation characteristic diagram of the third embodiment.

FIG. 17 is a diagram showing a relationship between LUT input and output.

FIG. 18 is a perspective view showing a conventional operation of measuring a reflected light amount of a patch pattern on a photosensitive drum.

FIG. 19 is a schematic view of a conventional image forming apparatus.

[Explanation of symbols]

1 image carrier (photosensitive drum) 2 transfer material carrier (transfer drum) 12 developing means (developing device) 34 latent image forming means (exposure means) 36 transfer material detecting means (image information detecting means, photo interrupter) 51 image carrying Body (photosensitive drum) 71 Concentration detection means (patch sensor)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G03G 15/02 102

Claims (4)

[Claims] 1. A latent image forming means for forming a latent image on an image carrier, a developing means for adhering toner to the latent image to form a toner image, and a transfer material carrying means for carrying a transfer material at a predetermined position. An image forming apparatus comprising a body and a toner image formed on the image carrier and transferred to a transfer material carried by the transfer material carrier, wherein a carrying position of the tip of the transfer material with respect to the transfer material carrier A transfer material detection unit for detecting the
An image forming apparatus, characterized in that the tip position of the latent image formed on the image carrier is adjusted based on the output of the transfer material detecting means. 2. A latent image forming means for forming a latent image on an image carrier, a developing means for adhering toner to the latent image to form a toner image, and a transfer material carrying means for carrying a transfer material at a predetermined position. In an image forming apparatus including a body and a double-sided image forming mechanism, the toner image formed on the image carrier is transferred to a transfer material carried by the transfer material carrier. Image information detecting means for detecting the image information at the time, and the latent image forming means forms a latent image corresponding to the second surface of the transfer material formed on the image carrier based on the output of the image information detecting means. An image forming apparatus characterized in that the tip position is adjusted. 3. A series of image forming processes in which a toner image formed on an image carrier is transferred onto a transfer material, and the toner image is heated and pressed to be fixed on the transfer material. On the other hand, in an image forming apparatus which is successively performed at least twice, pattern forming means for forming a predetermined pattern on an image carrier by a color material used for image formation, and density of the pattern formed by the pattern forming means are detected. An image having a density detecting unit, wherein image forming conditions in the first image forming process and the second image forming process are changed based on an output of the density detecting unit. Forming equipment. 4. The image forming condition is a primary charge amount, a developing bias, a light amount of a reader light source, a light amount of an exposing device, a light emitting time of an exposing device, or an LUT, and at least one of these image forming conditions is changed. The image forming apparatus according to claim 3, wherein the image forming apparatus comprises: