JPH096191A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of forming an image of more preferable quality. CONSTITUTION: The image forming device for executing an image forming operation, so that a photoreceptor electrified to a fixed potential by an electrifying means is exposed by an exposure means, based on image data and toner is stuck to an electrostatic latent image on the photoreceptor formed by the exposure means by a developing means, is provided with a sensor for detecting the quantity of the toner stuck to a reference pattern formed in a process similar to the image forming operation, before it and a detecting means for detecting the toner distribution state of the reference pattern, from the results of the detection for a specified time by the sensor.

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 for forming an image based on the state of a toner image formed on a reference pattern on a photosensitive member.

[0002]

2. Description of the Related Art In an image forming apparatus, the density of an image reproduced on a sheet changes due to changes in temperature and humidity inside the image forming apparatus. Therefore, in order to detect the image density predicted to be reproduced on the paper in advance, before the image forming operation, a part of the photosensitive member is rotated in the rotational direction of the photosensitive member by the same process as the normal image forming operation. The reference pattern formed along is well known. An AIDC sensor that optically detects the amount of toner attached to the reference pattern has been conventionally known. The AIDC sensor will be briefly described. In the ADIC sensor, light is incident on a reference pattern and the intensity of reflected light from the reference pattern is detected. Here, since there is a characteristic as shown in FIG. 1 between the reflected light intensity (detection output detected by the AIDC sensor) and the toner adhesion amount, the reflected light intensity is detected based on this characteristic. The amount of toner adhered to the reference pattern can be detected. Therefore, conventionally, the image density is automatically controlled by detecting the toner adhesion amount with respect to the entire reference pattern and automatically changing the image forming conditions such as the charging voltage based on the detected amount.

[0003]

[Problems to be Solved by the Invention] However, the above A
Although the image density is automatically controlled by the IDC sensor, there are cases in which a desired image cannot be reproduced on the sheet due to various conditions. Hereinafter, this case will be described. Here, a digital copying machine will be described as an example of the image forming apparatus. (A) Case of Change in Environment FIG. 2A shows an ideal attenuation state of the surface potential V ₀ of the photoconductor caused by the irradiation of the laser beam based on the image data such as characters and line drawings having edge portions. It is a figure.
The toner image formed on the paper in this case is as shown in FIG.
As shown in, the image becomes sharp with sharp edges. However, since the intensity of the laser beam actually has a Gaussian distribution, the attenuation state of the surface potential V ₀ of the photoconductor is as shown in FIG. Then, as shown in FIG. 3B, the toner adheres in a bowl shape on the actual paper. Especially in digital color copiers that require strict laser beam mounting accuracy, the distance from the laser optical system to the photoconductor is subtle due to subtle expansion and contraction of parts due to environmental changes such as temperature and humidity inside the copier. Changes to. In this case, the focus of the laser beam is deviated, and the spot diameter of the laser on the surface of the photoconductor becomes large.
As shown in (a), the range of attenuation of the surface potential V ₀ of the photoconductor is widened, while the maximum amount of attenuation is reduced. FIG.
Compared with the case of (a), since the exposure amount on the surface of the photoconductor is the same, the total amount of toner adhering to the paper is the same, but the range in which the surface potential V ₀ is attenuated is widened, and therefore, FIG.
As shown in (b), the toner adhering to the paper diffuses. In such a state, there arises a problem that it is not possible to obtain a sharp reproduced image of a character image or a line drawing. (B) Due to Deterioration of Developer When a two-component developer composed of toner and carrier is used, when the humidity inside the copying machine is high, or when the developer deteriorates with time, they are conveyed by the same carrier. The amount of toner that is used is reduced. In particular, when the developer deteriorates with time, the amount of toner actually attached to the paper is as shown in FIG.
As shown in (b) and (b), there is a problem that unevenness occurs. (C) Case of Development Characteristics Normally, when a two-component developer consisting of toner and carrier is used, in order to prevent fogging occurring on a reproduced image,
150 to 2 between the surface potential V ₀ and the developing bias voltage V _B
An appropriate potential difference of about 00V is set. For example, FIG.
As shown in (a), the developing bias voltage V _{B is set} to −400.
V and surface potential V ₀ are set to −600V. in this case,
An electric field indicated by a solid line is generated between the latent image portion formed by the laser beam irradiation and the developing bias portion. If the developing process of the toner is executed only in the parallel electric field portion in the latent image portion and the developing bias portion, no problem will occur, but the electric field formed between the surface potential V ₀ and the decay potential V _I is the toner. Affect the development process. The surface potential V ₀ and the decay potential V _I
Due to the electric field formed between them, as shown in FIG. 6B, a problem arises in that toner is excessively attached to the end portion α and a so-called leading edge is formed. This phenomenon tends to strongly appear in proportion to the expansion of the potential difference between the surface potential V ₀ and the developing bias voltage V _B.

An object of the present invention is to provide an image forming apparatus which forms an image having more preferable image quality.

[0005]

In the image forming apparatus of the present invention, the photosensitive member charged to a predetermined potential by the charging unit is
In the image forming apparatus, an image forming operation is performed in which an exposing unit exposes an image based on image data, and a developing unit attaches toner to an electrostatic latent image formed on the photosensitive member by the developing unit. Previously, a sensor that detects the toner adhesion amount of the reference pattern formed in the same process as the image forming operation, and a detection unit that detects the toner distribution state of the reference pattern from the detection result of the sensor for a predetermined time. Equipped with. Here, when the toner distribution state detected by the detection unit has a variation of a predetermined amount or more, it is preferable to include a warning unit that prompts the operator to replace the toner in the developing unit. Further, it is preferable to include a control unit that changes the image forming condition of the image forming operation according to the toner distribution state detected by the detecting unit. Further, in an image forming apparatus different from the above, the photoconductor charged to a predetermined potential by the charging unit is exposed by the exposure unit based on the image data, and the electrostatic image on the photoconductor formed by the exposure unit is exposed. In an image forming apparatus for performing an image forming operation in which toner is attached to a latent image by a developing unit, a reference pattern formed in the same process as the image forming operation along the rotation direction of the photoconductor before the image forming operation. A sensor for detecting the toner adhesion amount of the toner according to the rotation of the photoconductor, and a change in the detection value detected at regular intervals for a predetermined time from the start of the detection of the toner adhesion amount by the sensor, A detection unit that detects whether the amount of change is less than or equal to a predetermined value, and a control unit that executes edge enhancement processing on the image data when the detection amount is detected to be less than or equal to a predetermined value. Prepare . In still another image forming apparatus, a photosensitive member charged to a predetermined potential by a charging unit is exposed by an exposing unit based on image data, and an electrostatic latent image on the photosensitive member formed by the exposing unit is exposed. In an image forming apparatus that performs an image forming operation in which toner is adhered to the toner by a developing unit, the toner of the reference pattern formed in the same process as the image forming operation along the rotation direction of the photoconductor before the image forming operation. A sensor for detecting the adhered amount according to the rotation of the photoconductor, a detection unit for detecting the maximum value of the detection value by the sensor, and a detection value of the detection value for a predetermined time after the detection of the maximum value by the detection unit. A controller is provided for detecting the variation and for reducing the absolute value of the difference between the charging voltage for charging the photoconductor and the voltage applied to the developing means when the detected variation is not less than a predetermined value.

[0006]

In the image forming apparatus of the present invention, the result of detection of the toner adhesion amount of the reference pattern by the sensor for a predetermined time
The toner distribution state of the reference pattern is detected. Here, if the toner distribution has a predetermined variation or more,
To indicate that the toner in the developing means has deteriorated over time, the operator is warned to prompt replacement of the toner in the developing means. Further, the image forming condition of the image forming operation is changed according to the toner distribution state. Further, after detecting the maximum value of the toner adhesion amount of the reference pattern by the sensor, a change in the detection value during a predetermined time is detected, and when the change amount is detected to be less than or equal to the predetermined value, the edge of the image data is detected. Performs emphasis processing.
Further, after the maximum value of the toner adhesion amount of the reference pattern is detected by the sensor, a variation in the detected value during a certain time is detected, and when the variation is equal to or more than a predetermined value, the charging voltage for charging the photoconductor and the developing unit are set. Reduce the absolute value of the applied voltage difference.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present embodiment, the following description will be given taking a digital color copying machine which is an example of an image forming apparatus as an example. FIG. 7 is a diagram showing the overall configuration of a digital color copying machine. The digital color copying machine is roughly divided into an image reading unit 100 that reads a document image and a copying unit 200 that reproduces the image data read by the image reading unit 100. In the image reading unit 100, the scanner 10 includes an exposure lamp 12 that irradiates a document, a rod lens array 13 that collects reflected light from the document, and a contact-type CCD color that converts the collected light into an electric signal. The image sensor 14 is provided. When reading a document image, the scanner 10 is driven by the scan motor 11 and moves in the direction of the arrow (sub-scanning direction) to scan the document placed on the document table 15. The reflected light from the original document irradiated by the exposure lamp 12 is converted by the image sensor 14 into multi-valued electric signals of three colors of red, green and blue (hereinafter, R, G, B). The multi-valued electric signal output from the image sensor 14 is converted into 8-bit gradation data of any one of cyan (C), magenta (M), yellow (Y), and black (BK) in the image signal processing unit 20. After the conversion, it is stored in the synchronization buffer memory 30. In the copying unit 200, the printer head unit 31 performs tone correction (γ correction) on the input tone data according to the tone characteristics of the photoconductor, and then D / A the corrected image data. The laser diode drive signal is converted to generate a laser diode drive signal, and the semiconductor laser is caused to emit light by this drive signal. The laser beam generated from the printer head unit 31 corresponding to the gradation data is reflected by the reflecting mirror 3.
The photosensitive drum 41 which is rotationally driven via 7 is exposed. The photosensitive drum 41 is irradiated by the eraser lamp 42 before being exposed for each copy, and is uniformly charged by the charging charger 43. When exposure is performed in this state, an electrostatic latent image of the document is formed on the photosensitive drum 41. Only one of the cyan (C), magenta (M), yellow (Y), and black (BK) toner developing units 45a to 45d is selected to develop the electrostatic latent image on the photosensitive drum 41. I do. The developed toner image is transferred by a transfer charger 46 onto a copy paper wound around a transfer drum 51. Photoconductor drum 41 and transfer drum 5
1, the drum diameter is configured to have an integer ratio and is driven in a linked manner, and the photosensitive drum 41 and the transfer drum 51 are always in contact with each other at the same position. This eliminates the deviation when the toners are superposed. The printing process is repeated for four colors of cyan (C), magenta (M), yellow (Y), and black (BK). At this time, the scanner 10 repeats the scanning operation in synchronization with the operations of the photosensitive drum 41 and the transfer drum 51. Thereafter, the copy paper is separated from the transfer drum 51 by operating the separation claw 47, and is fixed through the fixing device 48.
The paper is discharged to the paper discharge tray 49. The copy paper is fed from the paper cassette 50, and the chucking mechanism 52 on the transfer drum 51 chucks the front end of the copy paper to prevent misalignment during transfer. Also, AID
The C sensor 211 is set near the photosensitive drum 41. Further, when the amount of adhered toner is detected, the pre-transfer eraser 55 is turned off in order to prevent the light of the pre-transfer eraser 55 from entering the light receiving portion of the AIDC sensor 211.

FIG. 8 shows the entire block portion of the printer control system of the copying section of the digital color copying machine. In the copy section,
A printer control unit 201 that controls general copying operation is provided. A printer control unit 201 including a CPU is connected to a control ROM 202 that stores a control program and a data ROM 203 that stores various data such as a γ correction table for γ correction. Printer control unit 201
Controls the printing operation according to each of the ROM data. The printer control unit 201 includes a potential sensor 210 that detects the surface potential V ₀ of the photosensitive drum 41, an AIDC sensor 211 that optically detects the toner adhesion amount of the reference toner image that adheres to the surface of the photosensitive drum 41, and a temperature. Analog signals from various sensors such as the sensor 212 and the humidity sensor 213 are input. Further, the main eraser 17 is connected to the parallel I / O sensor 215 and the drive I / O 216.
Drive the pre-transfer eraser 55 in parallel I / O
It drives via 217 and drive I / O218. In addition, the charging charger 4 is connected via the V _G generation unit 241.
3 is supplied with the charging potential V _G and the V _B generation unit 2
A developing bias voltage V _B is supplied to the developing device 45 via 42. The image signal processing unit 20 supplies an image signal to the printer control unit 201. In addition, various data are displayed on the operation panel
It is input to the printer control unit 201 via the parallel I / O 221 by the key input of 20. Further, the editor 230 uses the I / O 231 to execute the printer control unit 201.
Send a signal to

FIG. 9 is a block diagram of the image signal processing section 20. The R, G, B multi-valued electrical signals read by the CCD color image sensor 14 are converted into an A / D conversion unit 25.
After the analog / digital conversion is performed at 0, the reading error of the sensor is corrected at the shading correction circuit 251. The log conversion circuit 252 executes conversion processing from reflectance data to density data. Undercolor removal / black printing processing circuit (UCR / BP processing circuit) 253
Removes unnecessary black coloring and forms true black (BK) data based on the R, G, and B image data converted into the density data. log conversion circuit 25
The density data output from 2 is the black character determination circuit 254.
Is also entered. The black character discrimination circuit 254 detects the black character area of the document. The detection of the black character area is performed, for example, by detecting a location where the density data of the black pixel changes abruptly. Information on whether it is a black character area is
It is input to the masking processing circuit 255, the density correction circuit 256, and the spatial frequency correction circuit 257, and is used as one of the processing parameters in each circuit. The masking processing circuit 255 converts the input density data into cyan (C),
It is converted into data of three colors of magenta (M) and yellow (Y). The density correction circuit 256 executes edge enhancement processing of the input image data. Spatial frequency correction circuit 257
Then, the γ correction is executed using the γ correction table.

FIG. 10 shows a flowchart of this embodiment. First, in step S100, a toner image is formed on the reference pattern of the photosensitive drum 41 in the same process as a normal image forming operation. Then, step S10
In step 1, the AIDC sensor 211 reads the toner image of the reference pattern. Then, in step S102, 0.5 seconds after the start of image density detection of the reference pattern, that is,
AIDC sensor 211 for the edge of the reference pattern
Change in output value (change in density) is detected. The reference pattern is provided along the rotation direction of the photosensitive drum 41. The AIDC sensor 211 of this embodiment can detect the toner image density every 0.01 seconds as the photosensitive drum 41 rotates. That is, it is possible to detect an output value of 50 points for the edge portion of the reference pattern. The determination in step S102 corresponds to detection of the rising edge of the edge portion of the image.
When the change in the output value of the IDC sensor 211 is 3.0 V or more, it is determined that the image has sufficiently sharp edges as shown in FIG. 3B. On the other hand, AIDC
When the change in the output value of the sensor 211 is less than 3.0 V, it is determined that the rising edge portion of the image is gentle, as shown in FIG. When it is determined in step S102 that the rising of the edge portion is gentle, the process proceeds to step S103, and the density correction circuit 256 of the image signal processing unit 20 applies, for example, a primary differential filter or 2 to the image data. An edge enhancement process is executed by applying a second derivative filter. As one example of one of these differential filters, FIG. 11 shows a primary differential filter in the main scanning direction consisting of a 3 × 3 matrix, FIG. 12 shows a primary differential filter in the sub scanning direction consisting of a 3 × 3 matrix, and FIG. Shows a second-order differential filter composed of a 5 × 5 matrix. After the edge enhancement processing is executed, step S
Proceeding to 104, the γ correction table number is determined from the table of “Table 1” shown below based on the detected toner adhesion amount, and the grid voltage V _G and the developing bias voltage V _B are determined.
Change and set.

[Table 1] Next, in step S105, variations in the density of the reference pattern are detected. Here, for the detection of this variation, the AIDC sensor 211 takes 1.5 seconds from the detection start of the image density of the reference pattern to the detection end, that is, 1
The output value of 50 points is detected. This step S10
The determination of 5 corresponds to detection of unevenness in image output due to deterioration of the developer over time. For example, when the variation of the output value of 150 points is 1.0 V or more,
As shown in (b), it is determined that unevenness occurs during image output, and in step S106, a message requesting replacement of the developer is displayed on the operation panel 220 to prompt the operator to replace the developer. On the other hand, the variation of the output value is 1.0
If it is less than V, it is determined to be normal. Next, in step S107, the presence or absence of a rising protrusion at the edge of the reference pattern is detected. In detecting the presence or absence of a rising protrusion at the edge portion, the AIDC sensor 21
In No. 1, after detecting the image density of the reference pattern, the output value of 20 points is detected for 0.2 seconds from the time when the maximum output is detected. The difference between the absolute values of the maximum value and the minimum value of the output value during this period is 0.5 V or more, and the variation between them is 1 V.
If it is less than the above, it is determined that there is a protrusion at the tip of the edge. If it is determined that there is a protrusion at the tip of the edge, the process proceeds to step S108, and control is performed to reduce the absolute value of the difference between the grid voltage V _G and the developing bias voltage V _B. On the other hand, when it is determined that there is no protrusion at the tip of the edge, the grid voltage V _G and the developing bias voltage V _B are not changed. Then, the rise of the edge portion of the reference pattern described above is detected (step S102), the variation in the density of the reference pattern is detected (step S105), and the presence or absence of a protrusion at the tip of the reference pattern edge is detected (step S).
After the step 107) is completed, step S1 is performed based on the set creation conditions such as the grid voltage V _G and the developing bias voltage V _B.
At 09, an image forming operation is executed. In this embodiment, detection of rising edges of the reference pattern (step S102), detection of variation in density of the reference pattern (step S105), and detection of presence / absence of protrusion at the tip of the reference pattern (step S107). However, any one of them may be appropriately detected.

As described above, the printer controller 2
Reference numeral 01 indicates a change in the environment inside the copying machine, for example, an increase in humidity, deterioration of the two-component developer over time, or a grid voltage V _G , based on the distribution of adhesion of toner formed on the surface of the photosensitive drum 41.
And the developing bias voltage V _B are not properly set, and the grid voltage V _G and the developing bias voltage V _B are set according to these conditions to set the edge emphasis processing and the developer replacement request. Display the screen. If the grid voltage V _G and the developing bias voltage V _B are not properly set, the settings are reset. By executing the above-described image stabilization processing, it is possible to form an image of stable density and image quality on a paper sheet in response to changes in the environment inside the copying machine. Although the present embodiment describes a digital color copying machine,
It goes without saying that the configuration of the present invention can be applied to an image forming apparatus such as an analog copying machine or a micro reader printer.

[0012]

With the above arrangement, the toner distribution state of the reference pattern can be accurately detected. Moreover, it is possible to detect the deterioration of the toner in the developing unit with time from the detection result of the toner distribution state. Further, the image forming condition of the image forming operation can be optimally changed according to the toner distribution state. In addition, a sharp image can be formed by performing the edge enhancement processing based on the toner distribution state. Further, by reducing the absolute value of the difference between the charging voltage for charging the photoconductor and the voltage applied to the developing unit based on the toner distribution state, the generation of the leading edge that occurs at the rising edge of the image edge is suppressed. You can also

[Brief description of drawings]

FIG. 1 shows the amount of toner adhering to a reference pattern and AI.
7 is a graph showing a relationship with a detection value by the DC sensor 211.

FIG. 2A is a diagram showing an ideal attenuation state of the surface potential V ₀ of the photosensitive member due to laser beam irradiation,
(B) shows the distribution state of the toner adhering to the paper in this case.

FIG. 3A is a diagram showing a decay state of the surface potential V ₀ of the photoconductor that actually occurs due to laser beam irradiation,
(B) shows the distribution state of the toner adhering to the paper in this case.

FIG. 4A is a diagram showing a state of attenuation of the surface potential V ₀ when the distance from the laser optical system to the surface of the photoconductor is changed, and FIG. 4B is attached to the paper in this case. The toner distribution state is shown.

5A is a toner adhesion distribution state when the developer is deteriorated, and FIG. 5B is a sectional view thereof.

FIG. 6A shows an ideal electric field formed between the surface potential V ₀ and the attenuation potential V _I, and FIG. 6B shows an actually formed electric field.

FIG. 7 is a diagram showing an overall configuration of a digital color copying machine.

FIG. 8 shows an overall block diagram of a control system of the copying machine.

9 is a block diagram of the image signal processing unit 20. FIG.

FIG. 10 shows a flowchart of this embodiment.

FIG. 11 shows an example of a primary differential filter in the main scanning direction.

FIG. 12 shows an example of a primary differential filter in the sub-scanning direction.

FIG. 13 shows an example of a second derivative filter.

[Explanation of symbols]

 20 ... Image signal processing unit 41 ... Photosensitive drum 43 ... Charging charger 45 ... Developing device 201 ... Printer control unit 202 ... Control ROM 203 ... Data ROM 211 ... AIDC sensor 220 ... Operation panel

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Claims (5)

[Claims] 1. A photosensitive member charged to a predetermined potential by a charging unit is exposed by an exposing unit based on image data, and an electrostatic latent image on the photosensitive member formed by the exposing unit is developed by a developing unit. In an image forming apparatus that performs an image forming operation for adhering toner by means of a sensor for detecting the toner adhesion amount of a reference pattern formed in the same step as the image forming operation before the image forming operation, and a predetermined amount by the sensor. An image forming apparatus comprising: a detection unit that detects a toner distribution state of the reference pattern based on a time detection result. 2. A warning means for urging an operator to replace the toner in the developing means when the toner distribution detected by the detecting means has a variation more than a predetermined value.
An image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, further comprising a control unit that changes an image forming condition of the image forming operation according to a toner distribution state detected by the detecting unit. 4. A photosensitive member charged to a predetermined potential by a charging unit is exposed by an exposing unit based on image data, and a voltage is applied to an electrostatic latent image on the photosensitive member formed by the exposing unit. In an image forming apparatus for performing an image forming operation of adhering toner by a developing unit to which is applied, a reference pattern formed in the same process as the image forming operation along the rotation direction of the photoconductor before the image forming operation. A toner adhesion amount of a sensor for detecting the toner adhesion amount according to the rotation of the photoconductor, and a predetermined time from the start of detection of the toner adhesion amount by the sensor, for detecting a change in the detection value detected at regular intervals,
Detection means for detecting whether the amount of change is less than or equal to a predetermined value, and control means for executing edge enhancement processing on image data when the detection amount is detected by the detection means as less than or equal to a predetermined value. An image forming apparatus comprising: 5. A photosensitive member charged to a predetermined potential by the charging unit is exposed by the exposing unit based on image data, and a voltage is applied to the electrostatic latent image on the photosensitive member formed by the exposing unit. In an image forming apparatus for performing an image forming operation of adhering toner by a developing unit to which is applied, a reference pattern formed in the same process as the image forming operation along the rotation direction of the photoconductor before the image forming operation. A sensor for detecting the toner adhesion amount of the photosensitive member according to the rotation of the photoconductor, a detection unit for detecting the maximum value detected by the sensor, and a predetermined time period after the detection of the maximum value by the detection unit. A variation in the value is detected, and when the detected variation is equal to or more than a predetermined value, a control means for reducing the absolute value of the difference between the charging voltage for charging the photoconductor and the voltage applied to the developing means is provided. Image forming apparatus.