JP4006236B2 - Image forming apparatus and gradation control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and a gradation control method thereof, and more particularly to an image forming apparatus such as a laser beam printer and an electrostatic recording apparatus and a gradation control method thereof.
[0002]
[Prior art]
FIG. 1 is a schematic configuration diagram of a general color image forming apparatus conventionally used.
[0003]
The conventional color image forming apparatus has a digital color image reader unit in the upper part and a digital color image printer unit in the lower part.
[0004]
In the reader section, the original 30 is placed on the original table glass 31, and the reflected light image from the original 30 exposed and scanned by the exposure lamp 32 is condensed and photoelectrically converted by the lens 33 onto the full-color sensor 34 to obtain a color separation image. Get a signal. The color-separated image signal is processed by a video processing unit (not shown) through an amplifier circuit (not shown) and sent to a printer unit.
[0005]
In the printer unit, a photosensitive drum 1 as an image carrier is rotatably supported in a clockwise direction, and a pre-exposure lamp 11, a corona charger 2, a laser beam exposure optical system 3, a potential sensor 12, Four developing devices 4y, 4c, 4m, 4bk, a transfer device 5, and a cleaning device 6 are arranged.
[0006]
The laser beam exposure optical system 3 receives an image signal from the reader unit and converts it into an optical signal by a laser output unit (not shown), then reflects the laser beam by the polygon mirror 3a, and the lens 3b and the mirror 3c. Then, the surface of the photosensitive drum 1 is converted into an optical image E that is scanned linearly (raster scan).
[0007]
At the time of image formation by the printer unit, first, the photosensitive drum 1 is rotated clockwise, discharged by the pre-exposure lamp 11, and then uniformly charged by the corona charger 2, and an optical image E is generated for each separated color. Irradiate to form an electrostatic latent image.
[0008]
Next, a predetermined developing device is operated for each separation color to develop the electrostatic latent image on the photosensitive drum 1, and an image is formed on the photosensitive drum 1 with toner using a resin as a base. The developing devices 4y, 4c, 4m, and 4bk alternatively approach the photosensitive drum 1 according to the respective separation colors by the operations of the eccentric cams 24y, 24c, 24m, and 24bk.
[0009]
Further, the toner image on the photosensitive drum 1 is transferred from the recording material cassette 7 to the recording material supplied to the position facing the photosensitive drum 1 via the transport system and the transfer device 5. In this conventional example, the transfer device 5 includes a transfer drum 5f, a transfer charger 5b, an adsorption charger 5c for electrostatically adsorbing a recording material, an adsorption roller 5g opposed thereto, an inner charger 5d, and an outer charger 5e. A recording material carrying sheet (not shown) made of a dielectric material is integrally stretched in a cylindrical shape in the opening area of the peripheral surface of the transfer drum 5f that is rotatably supported. A dielectric sheet such as a polycarbonate film is used for the recording material carrying sheet.
[0010]
As the transfer drum 5f is rotated, the toner image on the photosensitive drum 1 is transferred onto the recording material carried on the recording material carrying sheet by the transfer charger 5b.
[0011]
In this way, a desired number of color images are transferred to the recording material sucked and conveyed by the recording material carrying sheet, thereby forming a full-color image.
[0012]
In the four-color mode, when the transfer of the four-color toner images is completed in this manner, the recording material is separated from the transfer drum 5f by the action of the separation claw 8a, separation push-up roller 8b, and separation charger 5h, and the heat roller fixing device. The sheet is discharged to the tray 10 via 9.
[0013]
On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.
[0014]
When images are to be formed on both sides of the recording material, after the heat roller fixing device 9 is discharged, the conveyance path switching guide 19 is driven immediately, and after passing through the discharge vertical path 20 to the reverse path 21a, the recording is performed. The material is temporarily stopped, and by reverse rotation of the reversing roller 21b, the recording material is turned over and stocked on the intermediate tray 22 with the trailing edge at the time of feeding turned back in the direction opposite to the feeding direction. Thereafter, an image is formed on the other surface again by the above-described electrophotographic image forming process.
[0015]
Further, the toner adheres to the recording material carrying sheet on the transfer drum 5f when the photosensitive drum 1, the developing device 4, the cleaning device 6 and the like are scattered and the recording material is jammed (paper jam). In addition, the oil on the recording material may adhere when the double-sided image is formed, and the like. However, the backup brush 15 that opposes the fur brush 14 with the fur brush 14 and the recording material carrying sheet interposed therebetween, and the oil removal roller After being cleaned by the action of a backup brush 17 facing the oil removal roller 16 via 16 and a recording material carrying sheet, it is again subjected to the image forming process. Such cleaning is performed at the time of pre-rotation and post-rotation, and at any time when a jam occurs.
[0016]
In this conventional example, the transfer drum eccentric cam 25 is operated, and the cam follower 5i integrated with the transfer drum 5f is operated, whereby the gap between the recording material carrying sheet and the photosensitive drum 1 is set at a predetermined interval. The configuration can be set to. For example, during standby or when the power is off, the distance between the transfer drum 5f and the photosensitive drum 1 can be increased so that the rotation of the transfer drum 5f can be made independent of the rotational driving of the photosensitive drum 1.
[0017]
Each of the developing devices 4y, 4c, 4m, and 4bk includes first and second agitating / conveying means (not shown), both of which are configured to convey the developer in opposite directions. Yes. A developing sleeve (not shown) is disposed above the first stirring / conveying means.
[0018]
In the series of image forming operations described above, the developing device 4 operates as follows. When the electrostatic latent image reaches the development position, a development bias in which an AC voltage and a DC voltage are superimposed is applied to the development sleeve from a development bias power source (not shown), and development is performed by a development sleeve driving device (not shown). The sleeve rotates in a predetermined direction, and the developing device 4 is pressurized toward the photosensitive drum 1 by the developing pressure cam 24 to visualize the electrostatic latent image.
[0019]
2 is a transfer drum on which a visualized toner image is placed using a near-infrared light LED as a light emitting element and a photodiode (PD) as a light receiving element. The density is detected based on regular reflection light and irregular reflection light from 5f. The method will be described below.
[0020]
Reference numerals 13e, 13f, and 13g denote photodiodes, and 13h and 13i denote prisms. The light emitted from the LED 13c is separated by the prism 13h into a component (s-wave light) that vibrates in a direction perpendicular to the incident surface and a component (p-wave light) that vibrates in a direction parallel to the incident surface. The s-wave light is applied to the photodiode 13e, and the p-wave light is applied to the toner surface.
[0021]
The p-wave light incident on the surface serving as a base for density detection, such as a photoconductor or an intermediate transfer member, is substantially specularly reflected and passes through the prism 13i as a p-wave and enters the photodiode 13f. The p-wave light applied to the toner surface is irregularly reflected to become s-wave and p-wave, passes through the prism 13i, the p-wave is incident on the photodiode 13f and is specularly reflected, and the s-wave is incident on the photodiode 13g. , Irregularly reflected light is detected.
[0022]
FIG. 3 shows the outputs of the photodiodes 13f and 13g with respect to the toner density. According to this, it is considered that the irregular reflection component is actually incident on the photodiode 13f. Therefore, subtracting the output of the photodiode 13f multiplied by the correction coefficient k in the output of the photodiode 13g, that is,
Correction output = (p wave output) −k × (s wave output)
Thus, a true regular reflection output as shown in FIG. 4 is obtained.
[0023]
The following control is performed in order to maintain the gradation from the toner image density thus detected.
[0024]
8 bits, that is, 0, 32, 64, 96, 128, 160, 192, 224, 255 level toner patches are formed among the input signals of quantized values of levels 0 to 255, and read by the density detection sensor 13, Interpolation, inverse transformation, etc. are performed to create a γLUT (γ look-up table).
[0025]
[Problems to be solved by the invention]
In the above conventional γLUT creation method, if the number of levels of the input signal is too large, the control accuracy is improved, but the control time is increased and the amount of toner consumed by the control is increased. On the other hand, if the number of levels of the input signal is too small, there is a problem that the control accuracy is lowered.
[0026]
An object of the present invention is to provide an image forming apparatus and a gradation control method thereof that can solve the above-described problems.
[0027]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an image carrier on which a latent image corresponding to an image signal is formed, an image transfer body to which a visible image based on the latent image is transferred, and an image formed on the image transfer body. Detection means for detecting the density of a visual image, conversion means for reading a plurality of patch patterns formed by signals of different density levels by the detection means to create a γ conversion table, and γ conversion created by the conversion means An image forming apparatus comprising a control means for controlling the gradation of an output image using a table, prior to the formation of the plurality of patch patterns, a reference patch pattern having a predetermined density level as a reference is formed on the image transfer body. A reference density creating means formed on the image forming apparatus, a comparing means for comparing a density of the reference patch pattern read by the detecting means with a reference density, and a density read from the reference patch pattern When the density is higher than the quasi-density, the number of patch patterns having a density lower than the predetermined density level among the plurality of patch patterns is larger than the number of patch patterns having a higher density than the predetermined density level. And determining a density level of the plurality of patch patterns, and when the density read from the reference patch pattern is lower than the reference density, a patch pattern having a density lower than the predetermined density level among the plurality of patch patterns Level determination means for determining density levels of the plurality of patch patterns to be formed so that the number of patch patterns is less than the number of patch patterns having a higher density than the predetermined density level.
[0028]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in the image forming apparatus according to the first aspect, the reference density is one, which is substantially an intermediate density in the entire density region.
[0030]
According to a third aspect of the present invention, there is provided an image carrier on which a latent image corresponding to an image signal is formed, an image transfer body to which a visible image based on the latent image is transferred, and an image formed on the image transfer body. Detection means for detecting the density of a visual image, conversion means for reading a plurality of patch patterns formed by signals of different density levels by the detection means to create a γ conversion table, and γ conversion created by the conversion means In a gradation control method for an image forming apparatus comprising a control means for controlling the gradation of an output image using a table, a reference patch pattern having a predetermined density level as a reference is created prior to the creation of the plurality of patch patterns. A reference density creation step formed on the image transfer member, a comparison step of comparing the density of the reference patch pattern read using the detection means with a reference density, and the reference patch pattern read When the captured density is higher than the reference density, the number of patch patterns having a lower density than the predetermined density level among the plurality of patch patterns is greater than the number of patch patterns having a higher density than the predetermined density level. When the density of the plurality of patch patterns to be formed is determined and the density read from the reference patch pattern is lower than the reference density, the density level of the plurality of patch patterns is lower than the predetermined density level. And a level determining step for determining density levels of the plurality of patch patterns to be formed so that the number of low density patch patterns is smaller than the number of patch patterns having a higher density than the predetermined density level.
[0031]
According to a fourth aspect of the present invention, in the gradation control method according to the third aspect, in the comparison step, a substantially intermediate density of all density areas is used as a reference density.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image forming apparatus and a gradation control method thereof according to the present invention will be described in more detail with reference to the drawings. In the following description of the embodiments, the present invention is embodied in the above-described image forming apparatus and its gradation control method, and therefore detailed description of the overall configuration and functions of the image forming apparatus is omitted. The features of the present invention will be described.
[0037]
(First embodiment)
A first embodiment of the present invention will be described.
[0038]
In the gradation control process in the present embodiment, first, a toner patch of level 128 out of levels 0 to 255 is formed as a toner patch having a reference density level. The patch is read by the density detection sensor 13. When the read density is higher than a predetermined density, a toner patch is formed by setting the toner patch pattern group signals of a plurality of density signals as 0, 16, 32, 48, 64, 128, 192, 255. ΓLUT is created by interpolation, inverse transformation, and the like. Conversely, when the toner patch of the reference density level of level 128 is lower than the predetermined density, the toner patch pattern group signal of the plurality of density signals is set to 0, 64, 128, 192, 208, 224, 240, 255 and the toner. A patch is formed, and a γLUT is created by interpolation, inverse transformation, or the like.
[0039]
This is based on the following concept.
[0040]
In a system that exhibits the γ characteristic as shown in FIG. 5 in a certain reference state, when the gradation characteristic changes to a higher density side than the reference state, for example, FIG. At this time, if the signal level of the toner patch group used for gradation control is a fixed value as in the conventional example, information on a portion with little gradation change is detected in the high density portion, which is not very effective. It is more effective to use that amount for detecting a low density portion where the gradation changes greatly. Further, when the gradation characteristic is changed to a lower density side than the reference state, for example, as shown in FIG. At this time, if the signal level of the toner patch group used for gradation control is a fixed value as in the conventional example, information on a portion with little gradation change is detected in the low density portion, which is not very effective. It is more effective to use that amount for detecting a high density portion where the gradation changes greatly.
[0041]
Based on the above concept, in the present embodiment, when the reference density level is higher than a predetermined density, the toner patch pattern group signals of a plurality of density signals are set to 0, 16, 32, 48, 64, 128. , 192, 255 and emphasizing the low density, the toner patch is formed. Conversely, when the toner patch of the reference density level is lower than the predetermined density, the signal of the toner patch pattern group of the density signal of the plurality of levels is set to 0, 64, 128, 192, 208, 224, 240, and 255, toner patches are formed with an emphasis on high density, and a γLUT is created by interpolation, inverse transformation, or the like.
[0042]
As described above, the image forming apparatus according to this embodiment includes an image carrier on which a latent image corresponding to an image signal is formed, and an image transfer body on which a visible image based on the latent image is transferred through exposure and development. And a color image forming apparatus for forming a γ table by forming a toner patch pattern group of density signals of a plurality of levels, reading with the optical sensor, and a photosensor for detecting a visualized toner image density Thus, the signal level of the toner patch pattern group of the plurality of density signals is made to differ in two ways according to the comparison result between the read signal of the reference level toner patch and one reference density (predetermined density). As a result, it was possible to perform highly accurate gradation control without increasing the control time.
[0043]
(Second Embodiment)
This embodiment is an example in which the first embodiment is more finely controlled. The same parts as in the first embodiment will be omitted and described.
[0044]
In the gradation control process in the present embodiment, first, a toner patch of level 128 out of levels 0 to 255 is formed as a toner patch having a reference density level. The patch is read by the density detection sensor 13. When the read density is higher than a predetermined density 1, a toner patch is formed with the toner patch pattern group signals of a plurality of density signals as 0, 8, 16, 24, 82, 140, 198, 255. If the predetermined density 1 is lower than the predetermined density 1 and higher than the predetermined density 2 (<predetermined density 1), the toner patch pattern group signals of a plurality of levels are set to 0, 16, 32, 48, 64, When toner patches are formed as 128, 192, and 255 and are lower than a predetermined density 2 and higher than a predetermined density 3 (<predetermined density 2), the toner patch pattern group signal of a plurality of density signals is output. When toner patches are formed as 0, 58, 116, 174, 232, 240, 248, and 255 and the density is lower than a predetermined density 3, a plurality of levels are used. The toner patch pattern group of signal No. toner patch formed as 0,64,128,192,208,224,240,255, interpolation, to create a γLUT by inverse transformation like.
[0045]
As described above, the image forming apparatus according to this embodiment includes an image carrier on which a latent image corresponding to an image signal is formed, and an image transfer body on which a visible image based on the latent image is transferred through exposure and development. And a color image forming apparatus for forming a γ table by forming a toner patch pattern group of density signals of a plurality of levels, reading with the optical sensor, and a photosensor for detecting a visualized toner image density According to the comparison result between the read signal of the reference level toner patch and a plurality of reference densities having different densities (predetermined densities 1, 2, and 3), the signal of the toner patch pattern group of the multiple levels of density signals By configuring so that the levels are varied in four ways, it is possible to perform gradation control with higher accuracy than in the first embodiment without increasing the control time.
[0046]
(Third embodiment)
This embodiment is an example in which the present invention is applied to cluster printing in which a plurality of printers are centrally managed and output is controlled. The configuration and functions of the printer are the same as those in the first and second embodiments, and description of these similar parts will be omitted and only this embodiment will be described.
[0047]
This embodiment is a cluster printing system including one server, two RIPs, and two printers as shown in the schematic configuration diagram of FIG.
[0048]
In the cluster printing system, there is a usage example in which an output file consisting of 100 pages, for example, is output 50 pages by the printer 1 and 50 pages by the printer 2 in order to improve the total productivity. If the colors between the two printers differ at that time, it cannot be said that the system is of high quality.
[0049]
Therefore, in this embodiment, the present invention is applied, each device is equipped with a density detection sensor, and the high-accuracy gradation control process described in the first embodiment is provided, so that the density between two different units can be accurately adjusted. We were able to provide a high-quality cluster printing system.
[0050]
【The invention's effect】
As described above, according to the image forming apparatus and the gradation control method thereof according to the present invention, an image carrier on which a latent image corresponding to an image signal is formed, and a visible image based on the latent image through exposure and development. In a color image forming apparatus including an image transfer body to which an image is transferred and a photosensor for detecting the density of a visualized toner image, a toner patch pattern group of a plurality of levels of density signals is formed to form an optical sensor. In the image forming apparatus that creates a γ table, the control time is lengthened by changing the signal level of the toner patch pattern group of the multi-level density signal according to the read signal of the reference level toner patch. In addition, there is an effect that gradation control with high accuracy can be performed.
[0051]
In addition, when the reading density of the reference level toner patch is high, the number of low density signal portions of the plurality of patch patterns is made larger than that of the high density signal portion, and when the read density is lower than the reference density, By creating the γ conversion table so that the low density signal portion of the patch pattern is less than the high density signal portion, there is an effect that high-precision gradation control can be performed without lengthening the control time.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an image forming apparatus shown in each embodiment and a conventional example according to the present invention.
2 is a configuration diagram of the density detection sensor in FIG. 1. FIG. 3 is a characteristic diagram showing sensor output with respect to density in the density detection sensor shown in the conventional example.
FIG. 4 is a characteristic diagram showing a correction sensor output with respect to density in the density detection sensor shown in the conventional example.
FIG. 5 is a characteristic diagram showing a γ characteristic in a reference state according to the first embodiment of the present invention.
FIG. 6 is a characteristic diagram showing a γ characteristic in a high concentration state of the first embodiment according to the present invention.
FIG. 7 is a characteristic diagram showing a γ characteristic in a low concentration state of the first embodiment according to the present invention.
FIG. 8 is a schematic diagram showing a cluster printing system according to a third embodiment of the present invention.
[Explanation of symbols]
1 Photosensitive drum (photoconductor)
2 Corona charger 3 Laser beam exposure optical system 3a Polygon mirror 3b Lens 3c Mirror 4, 4y, 4c, 4m, 4bk Developing device 5 Transfer device 5b Transfer charger 5c Adsorption charger 5d Inner charger 5e Outer charger 5f Transfer drum 5g Adsorption roller 5h Separation charger 5i Cam follower 6 Cleaning device 7 Recording material cassette 8a Separation claw 8b Roller 9 Heat roller fixing device 10 Tray 11 Pre-exposure lamp 12 Potential sensor 13 Concentration detection sensor 13c LED
13e, 13f, 13g Photodiode 13h, 13i Prism 14 Fur brush 15, 17 Backup brush 16 Oil removal roller 19 Transport path switching guide 20 Discharge vertical path 21a Reverse path 21b Reverse roller 22 Intermediate tray 24 Developing pressure cams 24y, 24c , 24 m, 24 bk Eccentric cam 25 Transfer drum eccentric cam 30 Original 31 Original plate glass 32 Exposure lamp 33 Lens 34 Full color sensor

Claims (4)

An image carrier on which a latent image corresponding to an image signal is formed, an image transfer body to which a visible image based on the latent image is transferred, and a density of the visible image formed on the image transfer body are detected. A detection unit; a conversion unit that reads a plurality of patch patterns formed by signals of different density levels by the detection unit to create a γ conversion table; and a γ conversion table created by the conversion unit, In an image forming apparatus comprising a control means for controlling gradation,
Prior to the formation of the plurality of patch patterns, a reference density creating means for forming a reference patch pattern of a predetermined density level serving as a reference on the image transfer member;
Comparison means for comparing the density of the reference patch pattern read by the detection means with a reference density;
If the density read from the reference patch pattern is higher than the reference density, the number of patch patterns whose density is lower than the predetermined density level among the plurality of patch patterns is higher than the predetermined density level. The density levels of the plurality of patch patterns to be formed are determined so as to be larger than the number of patterns, and when the density read from the reference patch pattern is lower than the reference density, the patch pattern among the plurality of patch patterns Level determining means for determining the density levels of the plurality of patch patterns to be formed so that the number of patch patterns having a lower density than the predetermined density level is less than the number of patch patterns having a higher density than the predetermined density level;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the reference density is one and is a substantially intermediate density of all density regions. An image carrier on which a latent image corresponding to an image signal is formed, an image transfer body to which a visible image based on the latent image is transferred, and a density of the visible image formed on the image transfer body are detected. A detection unit; a conversion unit that reads a plurality of patch patterns formed by signals of different density levels by the detection unit to create a γ conversion table; and a γ conversion table created by the conversion unit, In a gradation control method for an image forming apparatus comprising a control means for controlling gradation,
Prior to the creation of the plurality of patch patterns, a reference density creation step of forming a reference patch pattern of a predetermined density level as a reference on the image transfer body;
A comparison step of comparing the density of the reference patch pattern read using the detection means with a reference density;
If the density read from the reference patch pattern is higher than the reference density, the number of patch patterns whose density is lower than the predetermined density level among the plurality of patch patterns is higher than the predetermined density level. The density levels of the plurality of patch patterns to be formed are determined so as to be larger than the number of patterns, and when the density read from the reference patch pattern is lower than the reference density, the patch pattern among the plurality of patch patterns A level determining step for determining density levels of the plurality of patch patterns to be formed so that the number of patch patterns having a lower density than a predetermined density level is less than the number of patch patterns having a higher density than the predetermined density level;
A gradation control method comprising: The gradation control method according to claim 3,
A gradation control method characterized in that, in the comparison step, a substantially intermediate density of all density areas is used as a reference density.

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