JP2003195582A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of realizing image stabilization by performing more accurate image stabilization control. <P>SOLUTION: This image forming apparatus is provided with a photoreceptor drum (image carrier) 4, an image forming means for forming an image on the drum 4, an optical detection means for detecting image information of the image on the drum 4, and an adjusting means for adjusting an image forming condition. In the apparatus, a plurality of optical density sensors 40a and 40b are arranged in the same thrust direction as the optical detection means and are respectively used for the control of the different image forming conditions. The regular reflection type optical density sensor 40b used for control whose response speed is high is arranged on a more upstream side in a developer feeding direction than the scattering type optical density sensor 40a. <P>COPYRIGHT: (C)2003,JPO

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 copying machine or a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, the following method is known as a method for stabilizing the image density of an image forming apparatus such as a copying machine or a printer.

First, as a method of adjusting image processing characteristics (image control method), a specific pattern (patch image) is applied to a photosensitive drum or the like after the image forming apparatus is started and its warm-up operation is completed or during output operation. Formed on the image carrier,
There is a method of stabilizing the quality of an image to be formed by reading the density of the formed pattern and changing the operation of a circuit that determines an image forming condition such as a γ correction circuit based on the read density value. .

Further, when the image forming apparatus is used for a long period of time, the density of the pattern read on the image carrier and the density of the actually printed image may not match. Therefore, a method is known in which a specific pattern is formed on a recording material and the image forming condition is corrected by the density value thereof.

As a method for adjusting the toner density in the developing device, toner is supplied by a method of detecting and controlling the amount of reflected light from the developer (developer reflection ATR). At that time, on the image carrier. From the output signal of the density difference of the specific pattern (patch image), the toner excess / deficiency required to restore the patch image density to the initial density is calculated, and the toner replenishment amount is added / subtracted to / from the target value set in the developer reflection ATR. And correct it,
A method of stabilizing the image density by performing the toner replenishment control by the developer reflection ATR method with the corrected toner replenishment amount is also known.

[0006]

However, in the above-mentioned conventional example, it is necessary to read the patch image during both the normal image forming operation by the correction of the image processing characteristic and the correction of the toner density control in the developing device. Further, in order to perform each control with higher accuracy, a sensor suitable for each control is required, and thus two sensors are required. Since the control accuracy varies depending on the position of the sensor in the thrust direction, it should be placed at the optimum position, but in many cases, due to space and sequence restrictions, two sensors will be placed in the same thrust direction. It was difficult to improve control accuracy.

The present invention has been made in view of the above problems, and its object is to achieve the effect of each control by arranging the most suitable sensor when two sensors are arranged in the same thrust direction. An object of the present invention is to provide an image forming apparatus capable of stabilizing an image by increasing the image stabilization control with higher precision.

[0008]

In order to achieve the above object, the invention according to claim 1 provides an image carrier, an image forming means for forming an image on the image carrier, and an image forming means on the image carrier. It has an optical detecting means for detecting the image information of the image and an adjusting means for adjusting the image forming conditions. As the optical detecting means, a plurality of optical density sensors are arranged in the same thrust direction. In an image forming apparatus used for controlling different image forming conditions, a sensor used for fast response control is arranged on the upstream side in the developer feeding direction.

According to a second aspect of the invention, in the first aspect of the invention, a scattering type optical density sensor and a specular reflection type optical density sensor are used as the plurality of optical density sensors.

According to a third aspect of the present invention, in the first or second aspect of the invention, the toner density control in the developing device and the γLUT correction are used as the control of the different image forming conditions.

According to a fourth aspect of the present invention, in the second or third aspect of the invention, the toner concentration in the developing device is controlled by the scattering type optical density sensor, and the γLUT correction is performed by the specular reflection type optical density sensor. It is characterized by performing.

According to a fifth aspect of the invention, in the invention according to any one of the first to fourth aspects, the image signal formed by the image forming means is an image signal converted according to the correction information. Is characterized by.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the image forming means are arranged substantially parallel to each other in the vicinity of the developer carrying member, and the developer is supplied to the image forming means. A developing means provided with a conveying and supplying member in the longitudinal direction,
The developer feeding direction is a developer feeding direction along the longitudinal direction of the supply member.

A seventh aspect of the invention is characterized in that, in the invention according to any one of the first to sixth aspects, the image carrier has a photosensitive layer on a surface thereof.

An eighth aspect of the invention is characterized in that, in the invention according to any one of the first to sixth aspects, the image carrier is composed of a transfer body on which a toner image is transferred from a photosensitive body. To do.

According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the toner image on the transfer member is transferred to a recording material.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 shows the basic arrangement of an image forming apparatus according to the present invention.

A full-color image forming method will be described below with reference to FIG.

A document 10 placed on the platen glass 102
1 is irradiated by the light source 103, and the original image is formed on the CCD sensor 105 via the optical system 104. CC
The D sensor 105 has three rows of red, green,
The blue CCD line sensor group generates red, green, and blue color component signals for each line sensor.
These reading optical system units convert the image of the original 101 into an electric signal data sequence for each line by scanning in the direction of the arrow in the figure.

The image signal obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108, then sent to the printer unit B, and subjected to image processing by the printer control unit 109.

Next, the image processing unit 108 will be described.

FIG. 2 is a block diagram showing the flow of image signals in the image processing section 108 of the reader section A. As shown in the figure, the image signal output from the CCD sensor 105 is input to the analog signal processing unit 201, where gain adjustment and offset adjustment are performed, and then the A / D converter 2
02, an 8-bit digital image signal R1 for each color signal
Converted to G1 and B1. After that, the digital image signal R
1, G1 and B1 are input to the shading correction unit 203, and publicly known shading correction using the read signal of the reference white plate is performed for each color.

The clock generator 211 generates a clock for each pixel. Further, the main scanning address counter 212
Then, counting the clocks from the clock generator 211,
Generate a pixel address output for one line. Then, the decoder 213 decodes the main scanning address from the main scanning address counter 212, and the CCD drive signal for each line such as a shift pulse or a reset pulse or the CCD sensor 1 is detected.
V representing the effective area in the 1-line read signal from 05
The E signal and the line synchronization signal HSYNC are generated.

Each line sensor of the CCD sensor 105 is
Since they are arranged at a predetermined distance from each other, the line delay circuit 204 shown in FIG. 2 corrects the spatial shift in the sub-scanning direction. Specifically, the R and G signals are line-delayed in the sub-scanning direction in the sub-scanning direction with respect to the B signal to be matched with the B signal.

The input masking section 205 is a section for converting the read color space determined by the spectral characteristics of the R, G, and B filters of the CCD sensor into the NTSC standard color space, and performs the matrix calculation as shown in the following equation.

Light quantity / density converter (LOG converter) 206
Is a lookup table ROM, and R
The luminance signals of 4, G4 and B4 are converted into density signals of C0, M0 and Y0. The line delay memory 207 is a black character determination unit (not shown) and delays the image signals C0, M0, and Y0 by the line delay from the R4, G4, and B4 signals to the determination signals such as UCR, FILTER, and SEN. Let

The masking and UCR circuit 208 receives the black signal (B) from the input three primary color signals of Y1, M1 and C1.
k) is extracted, and the calculation for correcting the color turbidity of the recording color material in the printer unit B is performed, and the signals of Y2, M2, C2, and Bk2 are sequentially read for each reading operation to a predetermined bit width (8
output).

The γ correction circuit 209 performs density correction in the reader unit A so as to match the ideal gradation characteristics of the printer unit B. Further, the spatial filter processing unit (output filter) 210 performs edge enhancement or smoothing processing.

M4, C4, Y4 thus treated
The Bk4 frame-sequential image signal is sent to the printer control unit 109, and the printer unit B performs density recording by PWM.

Reference numeral 214 denotes C for controlling the reader unit A.
PU, 215 is RAM, and 216 is ROM. Again 2
Reference numeral 17 denotes an operation unit, which has a display 218.

Next, the printer section B will be described.

In FIG. 1, the photosensitive drum 4 is uniformly charged by the primary charger 8. The image data is converted into laser light through a laser driver and a laser light source 110 included in the printer control unit 109, and the laser light is reflected by the polygon mirror 1 and the mirror 2.
It is irradiated onto the uniformly charged photosensitive drum 4, and a latent image is formed on the photosensitive drum 4.

The photosensitive drum 4 on which a latent image has been formed by scanning with laser light rotates in the direction of the arrow shown. Then, the developing device 3 sequentially develops each color.

In the present embodiment, a two-component system is used as the developing system, and around the photosensitive drum 4, the developing devices 3 for the respective colors are arranged from upstream to black (Bk), yellow (Y), and cyan (C). , Magenta (M) are arranged in this order, and the developing device 3 corresponding to the image signal performs the developing operation at the timing of developing the latent image area formed on the photosensitive drum 4.

On the other hand, the transfer paper 6 is wound around the transfer drum 5 and rotated once in the order of M, C, Y and Bk, for a total of 4
The toner images of the respective colors are rotated and transferred in multiple layers onto the transfer paper 6.

When the transfer of the toner image onto the transfer paper 6 is completed, the transfer paper 6 is separated from the transfer drum 5 and the toner image is fixed onto the transfer paper 6 by the fixing roller pair 7, whereby a full-color image print is completed. .

A surface potential sensor 12 and a cleaner 9 for cleaning the transfer residual toner on the photosensitive drum 4 are arranged upstream of the developing device 3 of the photosensitive drum 4. In this embodiment, the photosensitive drum 4 is used as the image carrier, but a photosensitive belt on a belt having a photosensitive layer on the surface can be used as the image carrier.

Further, as shown in FIG. 3, an optical density sensor using LED light sources 10a and 10b and photodiodes 11a and 11b for detecting the amount of reflected light of a toner patch pattern, which will be described later, formed on the photosensitive drum 4. Two are provided in the same thrust direction. One is a scattering type optical density sensor 40a used for controlling the toner density in the developing device 3, and the other is a specular reflection type optical density sensor 40b used for γLUT correction.

The scattering type optical density sensor 40a is a type of sensor which detects the patch density by increasing or decreasing the light quantity of the scattered light from the toner and the image carrier, and in the present embodiment, the reflectance with respect to the projected light is colored. Toner / photosensitive drum 4
Since the black toner is higher in order, the sensor output increases when the amount of color toner on the photosensitive drum 4 increases, and the sensor output decreases when the amount of black toner increases, thereby detecting the density.
As long as it is a sensor that determines the density by increasing / decreasing the scattered light, the sensor is a scattering type optical density sensor even if specularly reflected light enters the sensor light receiving portion.

The specular reflection type optical density sensor 40b is a sensor of the type that detects the patch density by increasing or decreasing the light quantity of the specular reflection light from the image carrier, and in the present embodiment, it projects onto the photosensitive drum 4 on the mirror surface. When the toner that scatters the light is placed, the sensor output is lowered and the patch density is detected as described later. As long as the sensor determines the density by increasing / decreasing the specular reflection light, the specular reflection type optical density sensor is used even if the scattered light enters the sensor light receiving portion.

Here, a γLUT having a fast control response
The feature of the present embodiment is that the specular reflection type optical density sensor 40b used for correction is arranged on the upstream side in the developer feeding direction. Further, the control with fast response is a control in which the time from when the control is activated until the effect appears in the output image is short, and in the present embodiment, the γLUT correction is performed from the next output image when the γLUT is changed. In contrast to the effect of the γLUT correction, it takes time to control the toner concentration because the toner concentration in the developing device 3 is passed through the stirring / conveying path before the toner concentration on the developing sleeve 54 actually increases. , After control, no effect appears in the next output image.

An example of the developing device 3 is shown in FIG.

As shown in FIG. 4, the developing device 3 is disposed so as to face the photosensitive drum 4, and the interior thereof is divided into a first chamber (developing chamber) 52 and a second chamber by a partition wall 51 extending in the vertical direction. (Stirring chamber) 53. A non-magnetic developing sleeve 54 that rotates in the arrow direction is arranged in the first chamber 52, and a magnet 55 is fixedly arranged in the developing sleeve 54.

On the upper part of the developing device 3, as shown in FIG.
A toner replenishing tank 60 containing replenishment toner 63 is attached, and a toner conveying screw 62 is installed in the lower portion of the toner replenishing tank 60. The toner carrying screw 6 is driven by the motor 70 connected through the gear train 71.
The toner 6 in the replenishing tank 60 is driven by rotating 2
3 is conveyed and supplied into the developing device 3. The toner supply by the carrying screw 62 is controlled by the CPU 28 controlling the rotation of the motor 70 via the motor drive circuit 69. RAM68 connected to CPU28
The control data and the like to be supplied to the motor drive circuit 69 are stored in.

Developer stirring screws 58 and 59 are arranged in the first chamber 52 and the second chamber 53, respectively. The developer stirring screw 58 is arranged along the longitudinal direction of the developing sleeve, and stirs and conveys the developer in the first chamber 52. The developer stirring screw 59 conveys the developer from the toner replenishing tank 60 shown in FIG. The toner 63 supplied by the rotation of the screw 62 and the developer already in the developing device 3 are agitated and conveyed to make the toner concentration of the developer uniform. Partition wall 5
1, the first end at the front end and the rear end in FIG.
A developer passage (not shown) that connects the chamber 52 and the second chamber 53 to each other is formed. Toner replenishment from the toner replenishing tank 60 is performed on the front side, and the developer in the first chamber 52 in which the toner concentration has decreased due to the toner consumption by the development due to the conveying force of the developer stirring screws 58 and 59 is in front. Of the developer whose toner concentration has recovered in the second chamber 53 from the inner passage to the first chamber 5.
2 is configured to move into. Here, the developer feeding direction in the present embodiment is the developer feeding direction of the screw 58 adjacent to the developing sleeve 54.

The two-component developer in the developing device 3 is carried on the developing sleeve 54 by the magnetic force of the magnet 55, and then the layer thickness is regulated by the blade 56, and the developing sleeve 5
Along with the rotation of the photosensitive drum 4, the toner is conveyed to the developing area facing the photosensitive drum 4. Then, in the developing area, the developer is used for developing the latent image on the photosensitive drum 4. In order to improve the developing efficiency (that is, the toner application rate to the latent image), a developing bias voltage in which a DC voltage is superimposed on an AC voltage is applied from a power source 57 to the developing sleeve 54.

By the way, by developing the electrostatic latent image, the developing device 3
Since the toner concentration of the developer in the developing device 3 decreases, the toner concentration of the developer in the developing device 3 is controlled to be constant by performing the replenishment control for replenishing the toner 63 from the toner replenishing tank 60 to the developing device 3 by the toner concentration control. Alternatively, the image density is controlled to be constant.

The image forming apparatus according to the present invention, as a density control device, forms a patch image on the photosensitive drum 4 for reference, and the image density of the patch image is opposed to the photosensitive drum 4. The light emitting portion 10a and the light receiving portion 11a. Method for detecting and controlling by a scattering type optical density sensor 40a having a light emitting diode (patch detection ATR)
And a light emitting part 77a and a light receiving part 77 installed in the developing device 3.
A method of detecting and controlling the toner density of the developer in the developing device 3 by the density sensor 77 having the value b (developer reflection AT
R).

Thus, in the present invention, the output signal of the toner replenishment control by the patch detection ATR which is the first density control device is corrected by the toner replenishment control by the developer reflection ATR which is the second density control device. To use.

FIG. 6 is a block diagram showing the arrangement of the image forming apparatus according to the present invention.

As shown in FIG. 6, the printer controller 109
Is composed of a CPU 28, a ROM 30, a RAM 32, a test pattern storage unit 31, a density conversion circuit 42, and an LUT 25, and the reader unit A and the printer engine unit 100.
You can communicate with.

In the printer engine section 100, the LED light sources 10a arranged around the photosensitive drum 4,
A scattering type optical density sensor 40a as two optical reading devices consisting of 10b and photodiodes 11a and 11b.
The specular reflection type optical density sensor 40b, the primary charging device 8, the laser 101, the surface potential sensor 12, and the developing device 3 are controlled.

Further, the image forming apparatus is provided with an environment sensor 213 for measuring the amount of water in the air inside the machine. The surface potential sensor 12 is provided on the upstream side of the developing device 3, and the grid potential of the primary charger 8 and the developing bias of the developing device 3 are controlled by the CPU 28 as described later.

FIG. 7 is a block diagram showing the arrangement of an image signal processing circuit for obtaining a gradation image.

The luminance signal of the image is obtained by the CCD 105,
The reader image processing unit 108 converts the image signal into a frame-sequential image signal. This image signal is the γ of the printer at the initial setting.
The LUT 25 (γ is set so that the density of the original image represented by the input image signal and the density of the output image match.
The density characteristics are converted by the LUT).

FIG. 8 is a 4-limit chart showing how the gradation is reproduced.

The first quadrant shows the reading characteristics of the reader unit A for converting the original density into the density signal, the second quadrant shows the conversion characteristics of the LUT 25 for converting the density signal into the laser output signal, and the third quadrant shows the conversion characteristics. The recording characteristics of the printer section B for converting the laser output signal into the output density are shown, and the quadrant IV shows the total gradation reproduction characteristics of the image forming apparatus showing the relationship between the original density and the output density. Since the number of gradations is processed by a digital signal of 8 bits, there are 256 gradations.

In this image forming apparatus, in order to make the gradation characteristic of the fourth quadrant linear, the non-linear printer characteristic of the third quadrant is corrected by the LUT 25 of the fourth quadrant. The LUT 25 is generated by the calculation result described later.

After density conversion by the LUT 25, the signal is converted into a signal corresponding to the dot width by the pulse width modulation (PWM) circuit 26 and sent to the laser driver 27 which controls ON / OFF of the laser 110.

In this embodiment, the gradation reproduction method by the pulse width modulation processing is used for all the colors of Y, M, C and Bk.
The latent image having a predetermined gradation characteristic is formed on the photosensitive drum 4 by the scanning of the laser 110 due to the change of the dot area, and the gradation image is reproduced through a series of processes of development, transfer and fixing.

In this embodiment, when the optical density sensors used in the two independent control systems are arranged in the same thrust direction, the specular reflection type optical density sensor 40b used for the quick response control is provided on the upstream side in the developer feeding direction. It is characterized in that it is arranged in (see FIG. 3). A control system for performing optimum control using the scattered light type optical density sensor 40a and the specular reflection type optical density sensor 40b, which are two sensors arranged in the same thrust direction, will be described below.

(First Control System: γLUT Correction) γLUT correction control relating to stabilization of image reproduction characteristics of a system including both the reader unit A and the printer unit B will be described.

First, the calibration of the printer unit B using the reader unit A will be described with reference to the flowchart of FIG. In addition, this flow chart shown in FIG.
It is executed by the CPU 214 that controls the reader unit A and the CPU 28 that controls the printer unit B.

This control is started by pressing a mode setting button called automatic gradation correction provided on the operation unit 217.

In S51, the print start button 81 of the test print 1 appears on the display 218 (see FIG.
0 (a)), and by pressing it, the image of the test print 1 shown in FIG. 11 is printed out by the printer unit B.

As the print paper used in this control, generally-used large size paper is used in order to avoid an error due to an error in vertical placement and horizontal placement during a subsequent reading operation. That is, B4, A3, 11 × 17, and LGR are set to be used.

The pattern 62 is a maximum density patch of each color of Y, M, C and Bk, and a density signal value of 255 levels is used.

In S52, the image of the test print 1 is placed on the original platen glass 102 as shown in FIG.
The reading start button 91 shown in FIG. 13A is pressed to start reading. The following formula (2) is used to convert the optical density from the obtained RGB values. The correction coefficient (k) is adjusted to obtain the same value as a commercially available densitometer. Alternatively, the luminance information of RGB may be converted into density information of M, C, Y, and Bk by using a LUT separately.

M = -km * log10 (G / 255) C = -kc * log10 (R / 255) (2) Y = -ky * log10 (B / 255) Bk = -kbk * log10 (G / 255) Next, a method of correcting the maximum density from the obtained density information will be described.

FIG. 14 shows the relationship between the relative drum surface potential and the image density obtained by the above calculation.

The contrast potential used at that time, that is, the difference between the developing bias potential and the surface potential of the photosensitive drum when the maximum level is hit with laser light after being primary charged is obtained by setting A. In the case of the maximum density DA obtained, the image density mostly corresponds to the relative drum surface potential linearly as shown by the solid line L in the maximum density range. However, in the two-component developing system, when the toner density in the developing device fluctuates and drops, the non-linear characteristic may occur in the density range of maximum density as indicated by the broken line N. Therefore, although the final target value of the maximum density is set to 1.6 here, the control amount is determined by setting 1.7 as the target value of the control for matching the maximum density in consideration of the margin of 0.1. .

The contrast potential B here is obtained using the following equation (3).

B = (A + Ka) × 1.7 / DA (3) Here, Ka is a correction coefficient, and it is preferable to optimize the value according to the type of developing system. In practice, the setting of the contrast potential A in the electrophotographic system must be changed in accordance with the environment so that the image density does not match, and the output of the environment sensor 33 for monitoring the amount of water in the machine described above is shown in FIG. To change the settings.

Next, a method for obtaining the grid potential and the developing bias potential from the contrast potential will be briefly described.

FIG. 16 shows the relationship between the grid potential and the surface potential of the photosensitive drum.

Set the grid potential to -200V,
The surface potential sensor 12 measures the surface potential VL when scanning is performed with the laser light level set to the minimum. Similarly, VL and VH are measured when the grid potential is set to -400V. Interpolate -200V data and -400V data,
By extrapolation, the relationship between the grid potential and the surface potential can be obtained. The control for obtaining this potential data is called potential measurement control.

The developing bias VDC is set by providing a difference of Vbg (here, set to 100 V) set so that the fog toner does not adhere to the image from VL. The contrast potential Vcont is a differential voltage between the developing biases VDC and VH, and as described above, the larger the Vcont, the larger the maximum density can be.

From the relationship shown in FIG. 16, it is possible to calculate how many grid potentials and how many developing bias potentials are necessary to obtain the calculated contrast potential B.

In order to obtain this contrast potential,
The CPU 28 sets the grid potential and the developing bias potential. When the calculated contrast potential is abnormal, the limiter value is multiplied by a limiter for correction control (S
55), control is continued.

As described above, the CPU 28 sets the grid potential and the developing bias potential so that the contrast potential obtained in S53 is obtained.

FIG. 17 shows a density conversion characteristic diagram.

By the maximum density control in which the maximum density is set higher than the final target value in the present embodiment, the printer characteristic diagram of the third quadrant becomes a solid line J. If such control is not performed, the printer characteristic may not reach 1.6 as shown by the broken line H. In the case of the characteristic of the broken line H, no matter how the LUT 25 is set, the LUT 25 does not have the ability to increase the maximum density.
Concentrations between H and 1.6 are not reproducible.

If the setting is set to slightly exceed the maximum density as indicated by the solid line J, the density reproduction range can be surely guaranteed with the total gradation characteristics of the fourth quadrant.

Next, as shown in FIG. 18A, a print start button 150 for the image of the test print 2 appears on the operation panel, and when the button is pressed, the image of the test print 2 shown in FIG. 19 is printed out. (S5
6). During printing, the display is as shown in FIG.

As shown in FIG. 19, the test print 2 has a total of 64 colors of Y, M, C, Bk, 4 columns and 16 rows.
It consists of a gradation patch group of gradations, where 64 gradations are assigned laser output levels with emphasis on a low density area out of a total of 256 gradations, and a high density area is laser output. The levels have been thinned out. By doing so, it is possible to satisfactorily adjust the gradation characteristics especially in the highlight portion.

In FIG. 19, 71 is a resolution of 200 lp
i (lines / inch) patch, 72 is 400 lpi (li
nes / inch) patch. In order to form an image of each resolution, the pulse width modulation circuit 26 can be realized by preparing a plurality of cycles of a triangular wave used for comparison with image data to be processed.

In this image forming apparatus, the gradation image is 200
A line image such as characters is created at a resolution of 400 lpi with a resolution of 1 lpi. Although the patterns of the same gradation level are output with these two types of resolutions, if the gradation characteristics greatly differ due to the difference in resolution, it is more preferable to set the previous gradation level according to the resolution. . Further, the test print 2 is generated from the pattern generator 29 without the LUT 25 acting.

FIG. 20 is a schematic view seen from above when the output of the test print 2 is placed on the platen glass 102, and the upper left wedge-shaped mark T is a mark for abutting the document on the platen. A message was displayed on the operation panel so that the pattern of Bk came to the abutment mark T side and that the front and back sides were not mistaken (Fig. 18 (c)).

As the reading points per patch (73 in FIG. 19), as shown in FIG. 21, reading points (x) of 16 points are taken inside the patch, and the obtained signals are averaged.

The RGB signal obtained by averaging the values of 16 points for each patch was converted into a density value by the above-described conversion method to optical density, and the laser output level was plotted on the horizontal axis using this as the output density. FIG. 22.

Further, as shown on the right vertical axis, the base density of paper (0.08 in this example) is set to 0 level, and 1.60 set as the maximum density of this image forming apparatus is set to 255 level. It is normalized.

When the obtained data has a specific high density such as the point C or a low density such as the point D, there is a stain on the platen glass 102 or a defect on the test pattern. Since there are cases where there are cases, the slope is corrected by a limiter so that continuity is preserved in the data string.

As described above, the content of the LUT 25 is such that the density level of FIG. 22 is the input level (density signal axis of FIG. 8).
In addition, the laser output level can be easily created simply by replacing the coordinates with the output level (laser output signal axis in FIG. 8). For density levels that do not correspond to patches, values are obtained by interpolation calculation. At this time, a limiting condition is provided so that the output level becomes 0 level with respect to the input level 0 level. Then, in S58, the conversion contents created as described above are set in the LUT 25.

This completes the contrast potential control using the reading device and the preparation of the γ conversion table. During the above process, the display as shown in FIG. 18D is made, and when it is completed, the display as shown in FIG. 18E is made.

By this control, the image forming apparatus is constructed so as to have a linear characteristic with respect to the density signal, and as a result, it is possible to suppress the variation in the density gradation characteristics among the machines and to set the standard state. It became so.

Further, by releasing this control to the general user, when it is judged that the gradation characteristic of the image forming apparatus is deteriorated, the control is performed as necessary, so that the floor of the system including both the reader / printer is controlled. It becomes possible to easily execute the correction of the tonality characteristic.

Next, the control relating to the stabilization of the image reproduction characteristic of the printer section B alone after the control of the gradation characteristic of the system including both the reader / printer will be described.

In this control, the patch pattern density on the photosensitive drum 4 is detected, and the LUT 25 is corrected to achieve image stabilization. As the patch pattern, 200 lpi used for the gradation image is used.

FIG. 23 shows a processing circuit for processing a signal from the specular reflection type optical density sensor 40b composed of the LED light source 10b and the photodiode 11b facing the photosensitive drum 4. Regular reflection optical density sensor 40b used in this control
Of the two optical density sensors arranged at the same thrust direction position facing the photosensitive drum in the present embodiment, is arranged on the upstream side in the developer feeding direction, and only specular reflection light from the photosensitive drum 4 is detected. Is configured to detect. Since this control corrects γLUT, the effect clearly appears at the time of the next image formation after the patch formation. Therefore, the accuracy of control can be improved by forming the patch using the developer that is easy to reflect the state of the next image on the upstream side in the developer feeding direction.

On the other hand, since the patch detection ATR, which will be described later, is a feedback to the toner replenishment, the effect gradually appears with a time lag, so the influence of the thrust position is relatively small. Therefore, in this control, the specular reflection type optical density sensor 40b used for γLUT correction is provided on the upstream side in the developer feeding direction.
Was placed.

The near infrared light from the photosensitive drum 4 incident on the specular reflection type optical density sensor 40b is converted into an electric signal by the specular reflection type optical density sensor 40b, and the electric signal is A
The output voltage of 0 to 5 V is set to 0 to 25 by the / D conversion circuit 41.
The signal is converted into a 5-level digital signal and the density conversion circuit 42
Is converted to concentration by.

The toners used in the present embodiment are yellow, magenta, and cyan color toners, and these are composed of styrene copolymer resin as a binder and the colorants of respective colors dispersed therein.

The photosensitive drum 4 is an OPC drum,
The reflectance (960 nm) of near-infrared light is about 40%, and if the reflectance is about the same, an amorphous silicon drum or the like may be used.

FIG. 24 shows the relationship between the output of the specular reflection type optical density sensor 40b and the output image density when the density on the photosensitive drum 4 is changed stepwise by the area gradation of each color.

The output of the specular reflection type optical density sensor 40b when the toner is not attached to the photosensitive drum 4 is 5V.
(Ie, 255 level).

As can be seen from FIG. 24, as the area coverage of each toner increases and the image density increases, the specular reflection type optical density sensor 40b from the photosensitive drum 4 alone.
Output becomes smaller. Based on these characteristics, the density signal can be accurately read for each color by having the table 42a for converting the sensor output signal dedicated to each color into the density signal.

Since the purpose of this control system is to maintain stable color reproducibility achieved by the control system including the reader / printer, the state immediately after the control by the control system including the reader / printer is set as the target value. . The flow of setting the target value is shown in FIG. When the control of the system including both the reader / printer is completed, a patch pattern for each color of Y, M, C, Bk is formed on the photosensitive drum 4 and detected by the specular reflection type optical density sensor 40b.

Here, the laser output of the patch uses 128 levels in the density signal (density signal axis of FIG. 8) for each color. At this time, the contents of the LUT 25 and the setting of the contrast potential are those obtained by the control system including the reader / printer.

The sequence of forming the patch on the photosensitive drum 4 was performed as shown in FIG.

In the present embodiment, since the large-diameter photosensitive drum 4 is used, in order to obtain density data accurately and efficiently in a short time, the eccentricity of the photosensitive drum 4 is taken into consideration.
A patch of the same color is formed at a position opposed to the photosensitive drum 4 by 180 °, measurement is performed, and a plurality of samplings are performed to obtain an average.

By forming patches of different colors so as to sandwich the patch, data for two colors was obtained in one round. In this way, data for 4 colors can be obtained in 2 rounds,
A density value is obtained using the density conversion table 42a shown in FIG. The density value D128 at this time is set as a target value for this control and is backed up. The target value is updated every time the control by the control system including the reader / printer is performed.

In this control, the patch density formed in the non-image area during normal image formation is detected, and the LUT 25 (γLUT) obtained by the control of the system including both the reader / printer is corrected as needed. In the present embodiment, since the position on the photosensitive drum 4 corresponding to the joint portion of the transfer sheet on the transfer drum 5 is the non-image area, the patch is formed on that portion. The sequence for forming the patch on the non-image area on the photosensitive drum 4 during the normal image formation was performed as shown in FIG. 27 in the case of continuous full-color output of A4 paper.

It is important that the laser output of the patch is the same as when the target value is set, and 128 levels are used for the density signal (density signal axis in FIG. 8) for each color. At this time, LUT
The contents of 25 and the setting of the contrast potential are the same as in the normal image formation at that time. That is, what is obtained by the control of the system including both the reader / printer and corrected by the gradation control of the printer unit B up to the previous time is used.

The density signal 128 is controlled so that the patch output density becomes D128 on the density scale obtained by normalizing 1.6 to 255, but the image characteristics of the printer are unstable and can always change. Since it has the property, the measured result may not be D128 but may be deviated by ΔD. Based on this ΔD, the reader /
LUT25 (γLU created by the control system including the printer
Correct T).

FIG. 28 shows the density signal 128 in the case of this embodiment.
Corresponding to the change of the output density in the general density signals 0 to 255 when the output density is deviated by ΔDx
9 shows an LUT correction table. This is held in advance, the γ correction table is standardized so that the value of the density signal 128 of the γLUT correction table becomes ΔD during control, and the LUT 25 is corrected by adding the LUT formed so as to cancel this to the LUT 25. The timing of rewriting the LUT 25 is different for each color, and is performed by the TOP signal while the laser writing of the color is not performed when the rewriting is ready.

In the present embodiment, this control is activated when a non-image area can be developed during normal image formation. That is, when A4 size is continuously output in full color, each color is output once every two sheets are output, and in the case of intermittent one sheet, the γLUT correction is performed by the main gradation control for each color.
However, when it coincides with the patch formation timing of the patch detection ATR described later, the patch formation of this control is not performed.

Since the control system including the reader / printer is accompanied by human work, it is difficult to assume that it will be performed frequently. Therefore,
A serviceman controls the system including both the reader / printer for the installation work of the image forming apparatus, and if there is no problem with the image, the printer unit controls the characteristics automatically for a short period of time. For those that change gradually over a long period of time, the role of performing calibration by controlling the system including both the reader / printer can be shared, and as a result, the gradation characteristics can be maintained until the life of the image forming apparatus. Like

(Second Control System: Toner Density Control) First,
The patch detection ATR is operated at a predetermined timing to form a patch image on the photosensitive drum 4 as a reference image for density detection. The patch formation sequence is the same as in the gradation control of the printer alone, and a non-image area is formed during normal image formation. The activation frequency is the non-image area developable timing after outputting 25 sheets regardless of the paper size since the last patch formation.

When the non-image area is developable in the first control system, patch images are all formed, so that the patch formation timings always overlap with each other, and the first patch detection ATR is performed.
It was decided not to form a patch in the control system. The patch forming conditions are optimized in each control, and in many cases, both cannot be formed simultaneously due to the configuration. LU is the patch image
T25 (γLUT) is not passed, but is formed through a dedicated environment LUT. The resolution is 400 lpi.

That is, as shown in FIG. 6, a pattern generator 29 for generating a patch image signal having a signal level corresponding to a predetermined density is provided, and the patch image signal from the pattern generator 29 is supplied to the pulse width modulation circuit. To generate a laser drive pulse having a pulse width corresponding to the above-mentioned predetermined density. This laser drive pulse is supplied to the semiconductor laser 110,
The laser 110 is caused to emit light for a time corresponding to the pulse width, and the photosensitive drum 4 is scanned. As a result, a patch electrostatic latent image corresponding to the predetermined density is formed on the photosensitive drum 4, and the patch electrostatic latent image is developed by the developing device 3.
To develop.

Next, the patch image (toner image) thus obtained is irradiated with light from the LED light source 10a of the scattering type optical density sensor 40a for patch detection ATR, and the reflected light is reflected by a photoelectric conversion element or the like. Light is received by the photodiode 11a, and the actual patch density of the patch image is detected. The detected patch density corresponds to the actual density of the developer in the developing device 3. Since the output of the scattering type optical density sensor 40a detects scattered light from the toner, the output increases when the amount of toner on the photosensitive drum 4 increases, contrary to the case of the specular reflection type optical density sensor 40b. However, since the black toner absorbs the irradiation light, the scattered light from the photosensitive drum 4 is detected as a sensor output, and the output decreases as the toner amount increases.

The output signal from the photodiode 11a, which detects the actual patch density, is supplied to one input of the comparator. A reference signal corresponding to the specified density (initial density) of the patch image is input to the other input of the comparator. The comparator compares the actual density of the patch image with the initial density to find the density difference, and outputs the density difference output signal as C
Supply to the PU 28. The output signal of this density difference is used for toner replenishment control to the developer in the developing device 3 by the developer reflection ATR.

Since the yellow, magenta, and cyan color developers can detect the change in tint by the amount of reflected light, the developing device 3 is used.
It is possible to maintain the toner density at a certain level by using the developer reflection ATR by the density sensor 77 installed inside. However, if there is a change in the toner triboelectric charge amount due to a change in environmental humidity, it is not possible to follow the image density change due to the change in toner charge amount.

Therefore, for the color developer, the developer reflection AT
The toner replenishment control by R is performed, but at that time, the CPU 28
, The toner excess / deficiency amount (toner supply amount) of the color developer required to restore the patch image density to the initial density is calculated from the output signal of the density difference of the patch image (yellow, magenta, cyan), and the toner The replenishment amount is used as a toner correction amount and converted into a signal level corresponding to the toner correction amount, and each developing device
Give feedback to. Then, the signal of the toner correction amount is added to or subtracted from the signal level of the toner replenishment amount with respect to the target density set in the developer reflection ATR to correct it, and the developer reflection AT
The toner replenishment control by the R method is performed with the corrected toner replenishment amount.

For black developer, developer reflection AT
Since R cannot be applied, in the present invention, the toner excess / deficiency amount (toner replenishment) of the black developer necessary for returning the patch image density to the initial density is output from the output signal of the density difference of the patch image (black). Amount) is calculated and toner is replenished.
Therefore, the frequency of the black patch detection ATR is alternately formed with the patches of the first control system every time the non-image area can be developed during the normal image formation.

In the present invention, when the toner replenishment control of the two-component developer of yellow, magenta, cyan, and black is performed, the toner replenishment amount in the toner replenishment control by each patch detection ATR is obtained, and yellow, magenta,
For the cyan color developer, the toner replenishment amount is used as a correction toner amount to correct the toner replenishment control by the developer reflection ATR, and for the black developer, the toner replenishment amount is used to replenish the environment. The toner density of the developer can be controlled to a density that can obtain an appropriate image density for the toner image by coping with the fluctuation of the developing property of the toner due to the fluctuation and the fluctuation of the toner consumption amount of the toner consuming system. It is possible to form a high-quality color image in which the image density of the image is properly controlled.

As described above, when the optical density sensors used in the two independent control systems are arranged in the same thrust direction,
By arranging the sensor used for the quick response control on the upstream side in the developer feeding direction, optimum image stabilization control can be performed, and thus image stabilization can be achieved.

In this embodiment, since the patch forming sequence is the same in the two independent control systems as described above, the two sensors are arranged in the same thrust direction, but they may not be exactly the same. For example, if two sensors are juxtaposed in the thrust direction on the same stay in the thrust direction and there is a deviation of about the width of the light emitting / receiving section due to the shape of the sensors, a method of extending the length of the patch image in the drum circumferential direction or the like is used. The same effect can be obtained by performing the same control as in the present embodiment by using the same patch forming sequence in the above. Also, the patch forming sequences may be provided independently.

<Second Embodiment> Next, a second embodiment of the present invention will be described.

The present embodiment is a mode in which the density signal of the patch is set to a low density region in the control system of the printer alone in the first embodiment. The same parts as those in the first embodiment will be omitted, and only different parts will be described.

The object of the present invention is to stabilize the tint, and it is generally said that the lower the density, the greater the color difference due to the density fluctuation. Therefore, the patch density used for the control is set to the low density range, and the control in the low density range is performed. By increasing the precision,
In the present embodiment, image control is performed to further suppress the color variation.

FIG. 29 shows the relationship between the density difference and the color difference in the copying machine used in this embodiment.

From the sensor sensitivities shown in FIGS. 29 and 24 and the sensitivity to fluctuations that can be read from FIG. 28, the laser output of the patch in this embodiment is the same as the density signal for each color when the target value is set and when the normal image is formed. 64 levels (concentration around 0.4) were used (concentration signal axis in FIG. 8).

When a low density patch is detected by the density sensor, it is strongly influenced by the condition of the surface of the underlying photosensitive drum. Therefore, in the present embodiment, before the patch is formed, the surface of the photosensitive drum at the position where the patch is to be formed is formed. The upper part is measured by a density sensor, and the sensor output during patch measurement is corrected based on the measured value.

The sequence of setting the target value is the same as that of the first embodiment, and the measurement of the background is performed.
It just increases the number of laps. The sequence for forming a patch on the non-image area on the photosensitive drum 4 during normal image formation is the same as that in the first embodiment, but the base is measured at the time of pre-rotation at the start of each JOB.

Thus, in the present embodiment, sufficient stabilization is achieved in the vicinity of the density level where the patch is formed, so that the fluctuation in the low density region is suppressed, and the control for suppressing the tint fluctuation is performed. I was able to.

[0138]

As is apparent from the above description, according to the present invention, an image carrier, image forming means for forming an image on the image carrier, and image information of the image on the image carrier. Has a plurality of optical density sensors arranged in the same thrust direction as the optical detection means, and these optical density sensors have different image forming conditions. In the image forming apparatus used for the control, since the sensor used for the quick response control is arranged on the upstream side in the developer feeding direction, it is possible to achieve the image stabilization by performing the image stabilization control with higher accuracy. can get.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration of a reader image processing unit of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a layout diagram of an optical density detection sensor in the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a developing device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of a toner supply device of the image forming apparatus according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a control system of the image forming apparatus according to the first embodiment of the present invention.

FIG. 7 is a block diagram showing configurations of a reader unit and a printer unit of the image forming apparatus according to the first embodiment of the present invention.

FIG. 8 is a fourth limit chart showing gradation reproduction characteristics.

FIG. 9 is a flowchart of control of a system including both a reader / printer.

FIG. 10 is a diagram showing display contents of a display device.

FIG. 11 is a diagram illustrating an example of a test print.

FIG. 12 is a diagram showing how to place the test print 1 on the document table.

FIG. 13 is a diagram showing display contents of a display device.

FIG. 14 is a diagram showing a relationship between relative drum surface potential and image density.

FIG. 15 is a diagram showing the relationship between the absolute water content and the contrast potential.

FIG. 16 is a diagram showing a relationship between a grid potential and a surface potential.

FIG. 17 is a diagram showing density conversion characteristics.

FIG. 18 is a diagram showing a display content of a display device.

FIG. 19 is a diagram showing an example of a test print 2.

FIG. 20 is a diagram showing how to place the test print 2 on the document table.

FIG. 21 is a diagram showing reading points of a patch pattern.

FIG. 22 is a diagram showing an example of reading the test print 2.

FIG. 23 is a flow chart from photosensor to density conversion.

FIG. 24 is a diagram showing the relationship between photosensor output and image density.

FIG. 25 is a flowchart for setting a target value.

FIG. 26 is a diagram showing an example of detection by gradation control of the printer alone.

FIG. 27 is a sequence diagram of forming a patch in a non-image area.

FIG. 28 is a diagram showing a γLUT correction table.

FIG. 29 is a diagram showing a relationship between a density difference and a color difference.

[Explanation of symbols]

3 Developing Device 4 Photosensitive Drum (Image Carrier) 5 Transfer Drum (Intermediate Transfer Body) 6 Transfer Paper (Recording Material) 7 Fixing Roller Pair 8 Primary Chargers 10a, 10b LED Light Sources 11a, 11b Photodiode 12 Surface Potential Sensor 25 γLUT 29 Pattern generator 33 Environment sensor 40a Scattered light type optical density sensor (optical detection means) 40b Specular reflection light type optical density sensor (optical detection means) 100 Printer engine 105 CCD sensor 108 Reader image processor 109 Printer controller 110 Semiconductor laser

Continued front page    F term (reference) 2H027 DA02 DA10 DE02 DE07 DE09                       EA01 EA02 EA05 EA06 EC03                       EC06 EC09 ED03 ED06 ED09                       ED10                 2H077 AB15 AB18 AC02 AD02 AD06                       BA08                 2H200 GA23 GA44 HB12 JA01 JB02                       JB10 JC02

Claims (9)

[Claims] 1. An image carrier, image forming means for forming an image on the image carrier, optical detecting means for detecting image information of an image on the image carrier, and adjustment for adjusting image forming conditions. And a plurality of optical density sensors are arranged in the same thrust direction as the optical detecting means, and these optical density sensors are used for controlling different image forming conditions, and are used for fast response control. An image forming apparatus in which a sensor is arranged on the upstream side in the developer feeding direction. 2. The image forming apparatus according to claim 1, wherein a scattering type optical density sensor and a specular reflection type optical density sensor are used as the plurality of optical density sensors. 3. As control of the different image forming conditions,
The image forming apparatus according to claim 1, wherein the toner density control in the developing device and the γLUT correction are used. 4. The scattering optical density sensor controls the toner density in the developing device, and the specular reflection optical density sensor performs γLUT correction.
The image forming apparatus described. 5. The image forming apparatus according to claim 1, wherein the image signal formed by the image forming unit is an image signal converted according to the correction information. 6. The image forming means has a developing means which is disposed substantially parallel to the vicinity of a developer carrying member and which is provided with a conveying and supplying member in a longitudinal direction while supplying the developer to the developer carrying body. The image forming apparatus according to any one of claims 1 to 5, wherein the developer transport direction is along the longitudinal direction of the supply member. 7. The image forming apparatus according to claim 1, wherein the image carrier has a photosensitive layer on its surface. 8. The image forming apparatus according to claim 1, wherein the image carrier is a transfer body on which a toner image is transferred from a photoconductor. 9. The image forming apparatus according to claim 1, wherein the toner image on the transfer body is transferred onto a recording material.