JP2000122354A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the toner supply amount by executing ADC control by forming reference pattern every time when a toner electrostatic charge quantity decreases by making it possible to normally decrease the formation frequencies of the reference patterns to the irreducible minimum and to reduce the consumption of toners to the irreducible minimum and continuously outputting high-density images. SOLUTION: If the number of sheets of the output images Print# from the reference pattern formation of the previous time is below a reference value (20 sheets), the reference patterns are not formed (S1). If the integrated value of the pixel value of the output images from the reference pattern formation of the previous time Pix Count Buff is above the regulated value, the reference patterns are formed (S2). The density of the reference patterns is measured after the reference pattern formation and the toner supply rate is corrected by comparing the measured value with a target value (S4). Further, the output images are formed after Print# and Pix CountBuff are set at zero. The toners are then supplied to a developing device (S6). Print# is thereafter increment by one (one sheet) and the integrated value of the pixel value of the output images Pix Count for one sheet is read. The toner supply amount is computed and Pix Count Buff is updated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an electrophotographic image forming apparatus for controlling a toner supply amount so that an image density becomes a target value.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, it is very common to control a toner supply amount in order to maintain an optimum image quality, especially an image density.

[0003] In the conventional toner supply control, a reference density patch is formed and its density is measured to monitor the density reproducibility state, to obtain an error from a target density, and to determine an error from the target density. The most common method is to variably control the amount of toner supplied to the developing device. This is called ADC (Au
This method is called a “Density Control” method, and a typical prior art is disclosed in JP-A-63-1423.
79 and JP-A-63-296071.

However, this ADC method has a drawback that a response delay occurs because the toner supply amount is determined so as to compensate for the change after the image density changes.

Further, there is a disadvantage that a reference density patch is required, and the toner is consumed by the reference density patch.

[0006] With respect to the response delay of the ADC system, the amount of toner consumed by the output image is grasped by integrating the pixel values of the output image, and the toner corresponding to the consumed amount is supplied, thereby responding. There are ways to reduce the delay. This is called pixel count method or ICDC
(Image Count Density Cont
rol) method, and as a typical conventional technology,
There are those disclosed in JP-A-1-108070 and JP-A-1-314268.

However, since the ICDC method is a feedforward control, even a small error accumulates in a long term, and the toner amount in the developing device is not in a preferable state. Therefore, usually, the ICDC method and the ADC
Often, the disadvantages are compensated for by using a combination of methods. JP-A-3-44669 and JP-A-5-4040
No. 8 discloses such a method.

Further, with respect to toner consumption due to creation of a reference density patch, ADC control is performed by forming a reference density patch once for every fixed number of output images, for example, once 20 images are output. In general, this is dealt with by forming a reference density patch with the minimum necessary frequency.

[0009]

In a developing device used in an electrophotographic image forming apparatus, a sufficient amount of toner is agitated by stirring the developer in order to perform sufficient triboelectric charging of the supplied toner. And the toner must be rubbed.

However, in the case of continuously outputting a high-density image which consumes a large amount of toner, the newly supplied toner is subjected to development before it is not sufficiently rubbed with the carrier. As a result, the toner charge amount decreases, the toner amount developed with the same electrostatic latent image increases, and the image density becomes too high.

In the ICDC method, the toner supply amount is determined according to the integrated value of the pixel value of the image. Therefore, even when the image density becomes too high, the toner amount is continuously supplied according to the integrated value of the pixel value. Will be.

The ADC system corrects the toner supply amount by such an ICDC system. However, as described above, since the reference density patch is not created every time, the next time the reference density patch is created. Cannot be fixed. To work around this in the traditional way,
Even when it is not necessary to correct the toner supply amount by the ICDC method, a reference density patch must always be formed, and the toner is wasted. Also, usually
After the developed reference density patch is measured by an optical sensor or the like, it is cleaned by a cleaner, so that the cleaner is immediately filled with waste toner and the frequency of replacement is greatly increased.

Therefore, according to the present invention, normally, the frequency of creating the reference density patch can be minimized, the consumption of toner can be minimized, and a high-density image can be continuously output. In this case, when the toner charge amount is reduced by performing the above operation, the toner supply amount can be optimized by forming a reference density patch and performing ADC control each time.

[0014]

According to the present invention, in an electrophotographic image forming apparatus for controlling a toner supply amount so that an image density becomes a target value, a pixel value integrating means for integrating pixel values of an output image is provided. A toner supply amount determining unit for determining a toner amount to be supplied to the developing device according to the integrated pixel value; a developing toner amount measuring unit for measuring a developed toner amount; and the measured developing toner. Toner supply amount correction means for correcting the toner supply amount determined by the toner supply amount determination means based on the amount, and integrated pixel value comparison means for comparing the pixel value integrated by the pixel value integration means with a specified value The developing toner amount measuring unit measures the developing toner amount when the pixel value integrated by the pixel value integrating unit exceeds the specified value, and when the pixel value does not exceed the specified value. , And measures the amount of the developing toner for each constant number of output images.

In this case, the developing toner amount measuring means can measure the developing toner amount by measuring the reference density patch formed under the standard image forming condition. Further, in this case, the developing toner amount measuring means can measure the developing toner amount by measuring a transferred image or a fixed image of the reference density patch.

[0016]

In the image forming apparatus according to the present invention having the above-described configuration, if the pixel value integrated by the pixel value integrating means does not exceed the specified value, the amount of the developed toner is changed every fixed number of image output sheets. The amount of developing toner is measured by the measuring means, and unless the number of output images reaches a certain number, the amount of developing toner is not measured by the developing toner amount measuring means.
Therefore, the frequency of creating the reference density patch for measuring the amount of the developed toner can be minimized, and the consumption of toner can be minimized.

On the other hand, when the pixel value integrated by the pixel value integrating means exceeds the specified value, the developing toner amount is measured by the developing toner amount measuring means for each image output. Therefore, in the case where the toner charge amount is reduced by continuously outputting high-density images, the toner supply amount should be optimized by forming a reference density patch and performing ADC control each time. Can be.

[0018]

FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus of this example includes an image output unit 1
0, an image processing unit 20, an image input unit 30, a reference pattern generator 40, and a control unit 50 for controlling toner supply.

In the image input section 30, an image on a document is read by a scanner to obtain input image data, or image data generated on an external computer is taken into the apparatus as input image data. Image processing unit 2
In the case of 0, image processing such as color conversion and gradation conversion is performed on the input image data from the image input unit 30, and output image data to be output by the image output unit 10 is obtained.

The image output unit 10 is of an electrophotographic type, and output image data obtained from the image processing unit 20 is output from a screen generator (not shown in the drawing of the image output unit 10) in accordance with pixel values (image data values). Is converted into a binary image signal for laser on / off pulse width modulated by
By the binary image signal, a laser diode not shown in the drawing of the laser output unit 1 constituting the exposure device unit is driven, and the laser beam R for exposure modulated by the binary image signal is output from the laser output unit 1. can get.

The output image data is 8 bits, 25 bits.
It has six gradations and can take a value from 0 to 255 as a pixel value. Therefore, the pulse width of the binary image signal from the screen generator and the laser light R from the laser output unit 1 can be changed to 256 levels within one pixel period.

Laser light R modulated by an image signal
Irradiates the surface of the photoconductor 2 with a raster. The photoreceptor 2 is uniformly charged by the scorotron charger 3, and the laser light R
Is applied, an electrostatic latent image corresponding to the image signal is formed on the surface.

The electrostatic latent image formed on the photoreceptor 2 is developed into a toner image by a developing device 4 loaded with a developer. The developing device 4 is provided with a toner supply unit that supplies toner inside. As shown in FIG. 2, the toner supply unit includes a dispense motor 6a for controlling toner supply.
Is rotated, the auger 6b rotates, and the toner 5a in the toner cartridge 5 is supplied into the developing device 4.

The toner image is transferred onto a sheet 9 conveyed from the sheet tray 8 onto the photoreceptor 2 by the transfer device 7, and the toner image on the sheet 9 is fixed by the fixing device 11. Thereafter, the photoreceptor 2 is cleaned by the cleaner 12, and the charge is removed by the charge remover 13, thereby completing one image forming operation.

The reference pattern generator 40 generates a reference pattern signal for controlling toner supply. In this example, the reference pattern is formed as a development patch on a so-called empty area 2b outside the image area 2a of the photoconductor 2 as shown in FIG. Further, a development density sensor 19 for detecting the density of the development patch formed on the empty area 2b is provided so as to face the photoconductor 2.

The development patch is for monitoring the output image density. In this example, as shown in FIG. 4, as a development patch, a mid (half-dot coverage 50%) density patch PA1 having a size of 2 cm square is used. Is formed.

As described above, this mid-density patch P
A1 is formed on the free area 2b of the photoconductor 2. That is, after the electrostatic latent image is formed on the image area 2a,
A mid-density patch PA1 is formed on the empty area 2b. Therefore, after the density is detected by the developing density sensor 19, the mid-density patch PA1 is erased when it passes through the cleaner 12 without being transferred to the paper 9.

As shown in FIG. 5, a developing density sensor 19 irradiates the surface of the photoreceptor 2 with light.
And a light receiving element 19b that receives specularly reflected light or diffused light from the surface of the photoreceptor 2. A line L1 shown in FIG. 4 is a detection line of the development density sensor 19. That is, the mid density patch PA1 is formed on the detection line L1 of the development density sensor 19 and passes near the development density sensor 19.

FIG. 6 shows an example of an output signal of the developing density sensor 19. As shown in the drawing, as the output signal of the development density sensor 19, first, a density detection signal DI corresponding to the image of the document is obtained, and then the density detection signal DPA1 of the mid density patch PA1 is obtained.

In this example, the development patch is used as a reference pattern and its density is detected because the development patch has a high correlation with the density of a fixed image (final image) obtained by a user and has a cleaner. 12 is possible.

However, when the development patch is formed at a timing other than the time of image output, it may be formed in the image area 2a. Further, another halftone dot coverage may be formed.

As shown in FIG. 1, the measurement output of the development density sensor 19 is taken into the control unit 50. Further, in this example, the image data obtained from the image processing unit 20 is taken into the control unit 50 for integration of the pixel values of the output image.

The controller 50 controls the toner supply to the developing device 4 by a toner supply control routine as shown in FIG.

That is, the toner supply control routine is started when the apparatus is turned on, when the user instructs the apparatus to be set up, or when a normal image output instruction is issued. First, step S
In 1, the control unit 50 determines whether to create a reference pattern.

When the power is turned on to the apparatus, after setting up the initial settings, it is determined that a reference pattern should be created. It is also determined that a reference pattern should be created when a user gives an instruction to set up the apparatus.

When a normal image output instruction is given,
Whether to create a reference pattern is determined by the following two items of judgment. The first item is Pr, which is the number of output images (number of pages) since the previous generation of the reference pattern.
The value of int # is compared with the reference value (20 sheets),
If t # is less than the reference value, no reference pattern is created,
If it is equal to or more than the reference value, it is determined that a reference pattern is created.

The second item is PixCo which is the integrated value of the pixel values of the output image from the previous generation of the reference pattern.
Set the value of untBuff to a specified value (234 as described later).
Compared with 0), if PixCountBuff is less than the specified value, the reference pattern is not created.

Then, when a reference pattern is to be created, the control section 50 proceeds from step S1 to step S2 to form a reference pattern on the photoreceptor 2, that is, a mid-density patch PA1 in the above example, Step S3
The development pattern sensor 19 reads the reference pattern, that is, the mid-density patch PA1 in the above example, and takes the measured density value into the control unit 50.

Next, the control unit 50 proceeds to step S4, compares the measured density value Pm of the reference pattern by the developing density sensor 19 with the target density value Pt, and calculates the following equation (1), Td = (Pm −Pt) × k1 (1) The toner supply amount Td is corrected. Where k1
Is a conversion coefficient for converting the difference between the measured density value Pm and the target density value Pt into the toner supply amount Td. The value of the conversion coefficient k1 is obtained in advance.

After correcting the toner supply amount Td in step S4, the control unit 50 proceeds to step S5 to execute the above P
After resetting the values of print # and PixCountBuff to zero, the process proceeds to step S6.

When it is determined in step S1 that the reference pattern is not to be created, the creation of the reference pattern, the measurement of the density of the reference pattern, the correction of the toner supply amount Td, Print # and PixCountB are performed in steps S2 to S5.
The process proceeds from step S1 to step S6 without resetting uff.

In step S6, the control unit 50 forms an output image and drives the dispense motor 6a for a time corresponding to the toner supply amount Td to supply the toner 5a into the developing device 4.

When the output of one image (one page) is completed, the control unit 50 proceeds to step S7, where
The value of nt # is incremented by 1 (one sheet), and the process proceeds to step S8 to read the value of PixCount, which is the integrated value of the pixel values of the output image of one sheet (one page).

As described above, the pixel value (image data value) of the output image is from 0 to 2 for each pixel.
There are 256 gradations up to 55. In the image forming apparatus of this example, the maximum size of the output image is A4 size and the resolution is 400 dpi. Therefore, the maximum value of PixCount, which is the total pixel value of the output image for one sheet (one page), is 255 × 4678 × 3300 = 3936537000 = EAA2C9A8h (2). The value actually used is the upper 8 bits of these, and EAh = 234.

In step S1, Pi which is an integrated value of the pixel values of the output image from the previous generation of the reference pattern is used.
In this example, the specified value of xCountBuff is 234 × 10 = 2340 (= 924h) as an integrated value when ten solid (dot area ratio 100%) images are output over the entire A4 size. And

The specified value is determined based on the capacity of the developing unit 4 and the maximum toner supply amount when one sheet (one page) of image is output. 4 is set smaller than a value at which the charge amount of the supplied toner starts to decrease.

Next, the control section 50 proceeds to step S9 to calculate the toner supply amount. That is, the toner supply amount according to the above PixCount is added to the toner supply amount Td obtained by the previous calculation or corrected in step S4, and the toner supply amount corresponding to the toner supply in step S6 is further reduced. By doing. In the expression, Td = Td + PixCount × k2-Tm (4) Here, k2 is a conversion coefficient for converting the value of PixCount into a toner supply amount, and Tm is a value of step S6.
Is the toner supply amount corresponding to the toner supply.

Next, the control unit 50 proceeds to step S10, where PixCoP, which is an integrated value of PixCount, is
The value of unBuff is added to the value of Pi read in step S8.
Add the value of xCount to PixCountBuf
Update the value of f.

Next, the control unit 50 proceeds to step S11 to determine whether or not the image output has been completed. If not, the control unit 50 returns to step S1 to perform a series of toner supply control and image forming processing. When the image output is repeated, the toner supply control routine is also terminated.

(Other Embodiments) The above example is for a single-color image forming apparatus. However, the present invention can be similarly applied to a color image forming apparatus, and the same effects can be obtained. it can.

The reference pattern for monitoring the output image density is not limited to the development density patch on the photoreceptor, but may be a patch transferred onto paper or a patch fixed on paper. .

The reference pattern measuring means is not limited to the development density sensor, but may be any type such as a CCD sensor as long as it can correctly measure the density of the reference pattern.

The integration of the pixel values of the output image can be performed not by using the image data but also by, for example, providing a laser light measuring means in the laser exposure device and integrating the emission time of the laser light.

[0054]

As described above, according to the present invention, normally, the frequency of producing the reference density patch can be minimized, the consumption of toner can be minimized, and the high density can be obtained. When the toner charge amount is reduced by continuously outputting the images of
The toner supply amount can be optimized by forming a reference density patch and performing ADC control. That is,
When necessary, it is possible to reduce the toner consumption due to the creation of the reference density patch while creating the reference density patch.

When a high-density image is continuously output and the toner charge amount decreases, a reference density patch is always formed, so that the developing state can be grasped with high accuracy. By controlling the supply amount, a decrease in the toner charge amount can be prevented, and a constant image density can be always maintained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating an example of a developing device and a toner supply unit.

FIG. 3 is a diagram illustrating an example of a creation position of a reference pattern.

FIG. 4 is a diagram illustrating an example of a reference pattern.

FIG. 5 is a diagram illustrating an example of a developing toner amount measuring unit.

FIG. 6 is a diagram illustrating an example of an output of a developing toner amount measuring unit.

7 is a diagram illustrating an example of a toner supply control routine performed by a control unit of the apparatus in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image output part 1 ... Laser output part 2 ... Photoconductor 4 ... Developer 5 ... Toner cartridge 5a ... Toner 6a ... Dispense motor 6b ... Auger 19 ... Development density sensor 20 ... Image processing part 30 ... Image input part 40 ... Reference Pattern generator 50: Control unit PA1: Mid density patch (reference pattern)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA09 DA10 DA45 DB01 DE07 EA06 EC03 EF01 2H077 DA04 DA08 DA22 DA47 DA49 DA63 DB03 9A001 KK42 KZ37 LL09

Claims (3)

[Claims] An image forming apparatus of an electrophotographic type for controlling a toner supply amount so that an image density becomes a target value, a pixel value integrating means for integrating pixel values of an output image, and a pixel value integrated by the integrated pixel value A toner supply amount determining means for determining an amount of toner to be supplied to the developing device, a developing toner amount measuring means for measuring a developed toner amount, and the toner supply amount based on the measured developed toner amount. A toner supply amount correction unit that corrects the toner supply amount determined by the amount determination unit; and an integrated pixel value comparison unit that compares the pixel value integrated by the pixel value integration unit with a specified value. The amount measuring means, when the pixel value integrated by the pixel value integrating means exceeds the specified value,
An image forming apparatus which measures a developing toner amount and, when the amount does not exceed the developing toner amount, measures the developing toner amount for each fixed number of image outputs. 2. The image forming apparatus according to claim 1, wherein said developing toner amount measuring means measures the developing toner amount by measuring a reference density patch formed under a standard image forming condition. Image forming device. 3. An image forming apparatus according to claim 2, wherein said developing toner amount measuring means measures a developing toner amount by measuring a transferred image or a fixed image of said reference density patch. apparatus.