JP3172170B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus, and more particularly, to a developing bias control mechanism used in, for example, a color copying machine.

(Prior Art) As is well known, in an image forming apparatus, in order to prevent a decrease in image quality, for example, a decrease in image quality due to background dirt, a predetermined visible image pattern formed on a photoconductor is subjected to a photo sensor. And a structure for correcting a charging potential, a developing bias or an exposure amount at the time of forming an image on the photoconductor in accordance with the density detection level of the photosensor.

In the above-described image forming apparatus, when a visible pattern is formed with the developing bias kept constant, not only does the consumption of toner increase due to an increase in the residual potential of the photoconductor, but also the residual potential of the photoconductor becomes a constant value. In the above case, the density of the visualized pattern reaches the saturation amount, so that it may not be possible to accurately detect the residual potential based on the density detection level.

For this reason, for example, it has been proposed to improve the detection accuracy with respect to the residual potential of the photoconductor by forming a visible image pattern with a developing bias corrected based on the immediately preceding density detection level (for example, 63-1423
No. 70).

(Problems to be Solved by the Invention) However, in the above-described method, for example, when applied to a full-color copying machine, the toner charge amount of the developer (particularly, cyan and yellow) is particularly high under a low-temperature and low-humidity environment. Therefore, in order to accurately obtain the image density, the toner concentration must be increased. For this reason, when a two-component developer having toner adhered to the carrier is used, the toner holding power of the carrier decreases, So-called sleeve contamination is likely to occur, and the electric charge of the toner deposited on the sleeve causes a shift in the effective developing bias, thereby causing the entire background to be contaminated, deteriorating the image quality, and reducing the toner density on the actual photosensitive member. When the correction is required, there is a problem that the correction cannot be performed in time and the image density may vary.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of promptly correcting the toner density without causing background contamination and preventing image quality from being impaired.

(Means for Solving the Problems) In order to achieve this object, a predetermined visual pattern is formed on a latent image carrier, and the visual pattern is read by an optical sensor. In an image forming apparatus configured to change a developing bias based on a detection signal, a plurality of times at a constant value, a plurality of developing biases that are changed stepwise, the developed image pattern detected by the reflected light detection signal is detected. Average toner density,
It is characterized in that the developing bias is variably controlled according to the gradient of the change in the toner density.

(Operation) According to the present invention, when the reflection density of the visualized pattern does not correspond to the target density, a constant value is used a plurality of times.
The shift amount of the developing bias is calculated based on the average value of the density detection outputs from the plurality of visualized patterns changed stepwise and the inclination of the detection output, and the developing bias is corrected.

(Embodiment) FIG. 2 shows an overall configuration of a color copying machine which is one of the image forming apparatuses according to the present embodiment. This color copying machine is roughly classified into a scanner unit 1 for reading a document. An image processing unit 2 for electrically processing an image signal output from the scanner unit 1 as a digital signal;
And a printer unit 3 for forming an image on a transfer sheet based on the image recording information for each color processed by the printer.

The above-described scanner unit 1 has a lamp, for example, a fluorescent lamp 5 for exposing and scanning an original on the original mounting table 4. Fluorescent light 5
The reflected light from the document that has been exposed and illuminated by
The light is reflected by 8 and enters the imaging lens 9. Thereafter, an image is formed on the dichroic prism 10 by the imaging lens 9, and the light is split into, for example, three kinds of wavelength light of red R, green G, and blue B. The split light for each wavelength is incident on individual light receivers, for example, CCDs 11R, 11G, and 11B. These CCDs 11R, 11G, and 11B convert incident light into digital signals and output the digital signals. The output is subjected to necessary processing in an image processing unit 2, and recording color information of each color, for example, black BK, yellow Y, magenta The signals are converted into recording formation signals of each color of M and cyan C.

Although the present embodiment shows an example in which four colors of BK, Y, M, and C are formed, a color image can be formed using only three colors. In this case, the number of recording devices in the figure may be reduced by one.

The signal from the image processing unit 2 is input to the printer unit 3 and sent to the laser light emitting devices 12BK, 12c, 12M, and 12Y of the respective colors.

In the illustrated example, four sets of recording devices 13BK, 13
c, 13M, 13Y are also provided. Each recording device 13 is composed of the same components, and for simplicity of description, here, for example, a recording device for cyan C will be described, and other colors will be omitted. Note that, for each color, the same parts are given the same reference numerals, and the subscripts BK, M, and Y are used to distinguish each color.

The recording device 13c has, for example, a drum-shaped photoconductor 14c in addition to the writing laser light emitting device 12c. As is well known, a charging charger 15c, an exposure position by a laser beam emitting device 12c, a developing device 16c, a charging charger 17c, and the like are provided in this order around the photoconductor 14c. On the photoconductor 14c uniformly charged by the charging charger 15c, a latent image of a cyan light image is formed by exposure by the laser beam emitting device 12c, and a visible image is formed by development by the developing device 16c. The transfer paper fed from the paper feed unit 19, for example, one of the two paper feed cassettes by the paper feed roller 18, has its leading ends aligned by registration rollers 20, and is sent to the transfer belt 21 at the same time. The transfer paper conveyed by the transfer belt 21 is sequentially sent to the photoconductors 14BK, 14C, 14M, and 14Y on which the visualized images are formed, and the visualized images are transferred by the operation of the transfer charger 17.
The transfer paper on which the developed image has been transferred is fixed by the fixing roller 22, and then discharged by the discharge roller. In such an operation, the transfer paper is electrostatically attracted to the transfer belt 21 and is conveyed with high accuracy according to the belt.

For each of the photoconductors 14BK, 14C, 14M, and 14Y, a reflection type photosensor (hereinafter, referred to as a P sensor) 24BK, 24C, 24M is used as an optical sensor for optically detecting the amount of toner adhered to a toner image pattern described later. , 24Y.

The image processing unit 2 controls the operation of each unit of the printer unit 3 according to a predetermined program stored in the internal memory, and writes the amount of light (laser power) in the writing laser light emitting devices 12BK, 12C, 12M, and 12Y. While changing the gradation from 1 to 7 values, it is possible to output a signal for forming a visualized pattern by the writing laser emitting device,
The laser power at the time of writing the visualized pattern is set to, for example, gradation 4.

Further, each of the developing sleeves (e.g., a developing sleeve 25C for cyan as a representative) are by the image processing unit 2, which is a developing bias V _B to be variably controlled.

In such a configuration, an image signal is output as a digital signal from the scanner unit 1, and when this signal is electrically processed by the image processing unit 2, based on image recording information of each color from the image processing unit 2, The printer unit 3 forms an image on transfer paper.

As in the case of such normal image formation, the image processing unit 2 includes, for example, in the case of cyan, a writing laser emitting device 12C, a charging charger 17C, and a developing device.
A visible pattern is formed by the sensor pattern forming means consisting of 16C, and this pattern is read by the photosensor 24C. Then, based on the detection information of the visualized pattern, at least one of the developing bias of the developing device 16C, the charged potential of the photoconductor 24C, or the writing light amount in the writing laser emitting device 12C is appropriately controlled.

On the other hand, the image processing unit 2 is a control unit 100, and the control unit 100 is configured by a microcomputer that performs arithmetic control processing on the main body 100A. A ROM 100B storing basic programs and basic data for these processes and a RAM 100C for loading various data are connected.

The main unit 100A has an I / O interface 100
An external device is connected via D, and on the input side of the I / O interface 100D, a photo sensor 101 (combined with a light emitting element and a light receiving element attached to each developing device (see FIG. 2)) Each sensor 24 _BK , 24 _C , 2 shown in FIG.
4 _M , 24 _Y ) are connected.
Is designed to detect the amount of toner adhering to the visualized pattern formed on the photoreceptor, that is, the toner concentration (TC) of the visualized image.

Further, on the output side of the I / O interface 100D, a developing bias control unit 102, a charging control unit 103, a clutch driving unit 104 of a toner supply unit, a bias potential control unit 105 of a toner supply unit, and an exposure lamp control unit 1
06 are connected.

In the external device described above, the I / O interface 100
The developing bias unit 102 connected to the output side of D is a driving unit for setting a bias potential for the toner on the developing sleeve, and the charging control unit 103 is for setting the charging potential for the background portion of the photoconductor. Of the driving unit.

Further, the clutch driving unit 104 of the toner replenishing unit is for rotating the discharge blade located in the replenishing unit when replenishing the toner, and the bias potential control unit 105 is configured to control the bias to the replenishing unit. The application is performed.

The control unit 100 controls the developing bias of the developing device after or before the image forming operation.

That is, by supplying a toner developing on the photosensitive drum by the developing bias V _B having a small potential difference in the direction of reversing the magnitude relation in the image formed for the background potential V ₀ photosensitive drum, for the toner image by output V _K of the photo sensor is shifted development bias V _B to be constant,
Developing bias V _B can be kept constant with respect to the background potential V ₀ photosensitive drum, thus improving the image quality deviation of the effective developing bias is prevented.

Specifically, in FIG. 4, the magnitude relationship during normal image formation with respect to the background potential V ₀ of the photosensitive drum (shown by a solid line in the drawing)
(V _B is larger than the negative potential V ₀ ) in a direction in which the developing bias V _B having a small potential difference ΔV _OB of, for example, about 1/5 or less of the image forming potential is applied to the developing sleeve. The toner is adhered on the photosensitive drum.

Then, during this drawing the developing bias V _B so that the output V _K of the photo sensor for reading the density of the toner image (detection potential at small potential) is constant, is shifted in the direction indicated by the arrow S _1, S _2. In this method, the shift amount (V _BS ) is considered as a deviation between the effective developing bias and the output developing bias, and this is added to the developing bias at the time of image formation.

That is, the shift amount of the effective bias is determined based on the background potential V ₀ of the photosensitive drum as a sum of the value V _BS for canceling the shift amount between the developing bias V _B (target value) and the effective developing bias. And V _B = V _B (target value) + V _BS (1) V _B (target value) = V ₀ + V _BK (2) V _B = V ₀ + V _BK + V _BS (3) V ₀ : background potential of the photosensitive drum V _BK : V _K imaging potential (for example, 24 V) As the output V _K of the photo sensor at this time, V is set so that the output V _{K of the} photo sensor becomes the target value V _{K0. When B} is shifted, the shift amount of the effective developing bias, in other words, the optimum shift amount can be determined.

In this embodiment, as shown in FIG. 3, as an initial condition, the developing bias (V _B1 ) is set to V _B1 = V ₀ −V _ST (4). A visual pattern is formed on the photoreceptor with a minute potential difference (for example, ΔV = 8 V) (V _Bn = V _B1 + (n−1) · ΔV), and a density change of the pattern is detected. The state of background contamination of the photoreceptor is determined based on the change.

The shift of the developing bias by small potential difference as described above, in FIG. 3, as indicated by reference numeral Arufa～ipushiron, background potential when background smear on the photoconductor does not occur (V _SG) is, for example,
When the peak having 4V decreases in the non-image portion where no toner is attached, the average value of five density detection outputs and the slope of this detection output are calculated as follows. GRD = 1/10 ｛2 · V _S (1) + V _S (2) −V _S (4) −2 · V _S (5)｝ (6)

When the density detection value from the photo sensor is the above average value, the developing bias (V _B ) is set to V _B (AVE)
And the developing bias at the detection output V _S (5) is V _B
(END), V _B (AVE) = V _B (END) −4 × 8 V / 2 = V _B (END) −16 V (7), and the detection output from the photo sensor is as described above. If V _B at V _K0 is V _B (V _K0 ), V _B (V _K0 ) −V _B (AVE) = (AVE−V _K0 ) / GRD × 8
(8).

Therefore, the shift amount of the developing bias is obtained from this equation as follows.

V _BS = V _B (V _K0 ) − (V ₀ +48) = V _B (END) −16+ (AVE−V _K0 ) / GRD × 8 (9) The shift amount of the developing bias thus obtained , The developing bias is corrected in the same manner as in the equation (3) to obtain the target bias value.

Since the present embodiment has the above configuration, the operation will be described below with reference to the flowchart of FIG. 4 for explaining the operation of the control unit.

That is, FIG. 4 is a flowchart showing the processing of the developing bias correction control. As an initial condition, the developing bias (V _B ) is set to a value obtained by subtracting a predetermined value from the background potential. The concentration detection potential between the time of the image (V _S (1)) ~
(V _S (5)) is set to the ground potential of the photoconductor when the development sleeve is stopped and the photoconductor is operating.

Then, “8”
V), the developing bias is shifted, and the density detection potential of the visual pattern is detected.
Concentration detection potential of the visible image pattern when the background potential is lowered to (V _S (1)) and the detected value, to the memory detection output value of the last five times.

The shift of the developing bias in the above-described steps affects the change in the background potential as shown in FIG. 3, and specifically, the developing bias is set so that the amount of toner adhered to the photoreceptor increases. It can be determined whether this setting corresponds to the control of the amount of toner adhesion.

The third detection potential V _S (3) corresponding to the center of the five detection output values is the target value of the detection output.
It is determined whether it is smaller than V _K0 , and if it is larger, it is determined whether the detection has been performed a predetermined number of times, and the processing based on the result is executed.If it is smaller, it is determined that correction of the developing bias is necessary. The processing for that is performed.

That is, the average of the detected output values and the slope of the detected output value are obtained from the above equations (5) and (6), and if there is a slope, the shift amount of the developing bias is calculated by the above equations (7) to (9). After the calculation, the developing bias is corrected by the equation (3).

In such control, the background potential of the photosensitive drum is
Supplies toner onto the photosensitive drum by the developing bias V _B having a predetermined potential difference in a direction reverse the magnitude relation in the image forming developed against V _0, the output V _K of the photosensor for the toner image is fixed by being shifted development bias V _B while tracking so that, the developing bias V _B is maintained constant at all times with respect to the background potential V ₀ photosensitive drum, and,
The deviation of the effective developing bias is corrected in a state where the correction is performed at a constant speed by setting the potential difference, thereby improving the image quality.

(Effects of the Invention) As described above, according to the present invention, when the developing bias is changed with a predetermined potential difference and the developing bias is corrected by the density change due to the change in the developing bias, the toner density on the photosensitive member is always changed. Tracking is detected and the appropriate bias value is obtained by comparing the reflection density from the visualized pattern with the target density.If the effective development bias with respect to the charging potential of the photoconductor is kept constant, the effective development The bias can be set immediately when the toner density changes, and the image quality can be always maintained satisfactorily by preventing background contamination.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining a control unit which is a main part of the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a layout diagram for explaining the overall configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram for explaining the development density characteristics obtained by the operation of the control unit shown in FIG. 1, and FIG. 4 is a flowchart for explaining the operation of the control unit shown in FIG. . DESCRIPTION OF SYMBOLS 1 ... Scanner part, 2 ... Image processing part, 3 ... Printer part, 100 ... Control part, 100A ... Control part main body, 101 ... Photosensor, 102 ... Developing bias control unit, 103 ...
Charging control unit, 104: clutch driving unit of toner supply unit, 106: exposure lamp control unit.

Continuation of the front page (56) References JP-A-59-174862 (JP, A) JP-A-63-276070 (JP, A) JP-A-60-260066 (JP, A) JP-A-60-49365 (JP JP-A-60-80871 (JP, A) JP-A-60-217376 (JP, A) JP-A-1-288869 (JP, A) JP-A-60-19176 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/00 G03G 21/00

Claims (1)

(57) [Claims] 1. A method for forming a predetermined visual pattern on a latent image carrier, reading the visual pattern by an optical sensor, and changing a developing bias based on a reflected light detection signal from the optical sensor. In the image forming apparatus described above, the average value of the toner density of the visible image pattern detected by the reflected light detection signal and the plurality of An image forming apparatus that variably controls a developing bias according to a change gradient.