JPH09114204A - Line width detection method, line width control method, line width detection device, dot diameter detection device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a line width control method enabling good reproducibility of dot and linear image. SOLUTION: By using a line width detection sensor which is constituted by combining a pair of light emission element PS1 and light receiving element PS2 and provided with a condensing lens PS4 on the element PS1 side and a pin hole between the element PS1 and the lens PS4 and whose spot diameter is smaller than the width of a line on an image carrier, the oblique lines having included angle θ in a sub-scanning direction on the image carrier are formed. By scanning the oblique lines, the change of the width of the line in a main scanning direction and in the sub-scanning direction is detected. Besides, an exposure condition is controlled based on data obtained by averaging the changing quantity of the line width in the main scanning direction and in the sub- scanning direction from an initial time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line width detecting method, a line width detecting apparatus and a dot diameter detecting apparatus for detecting a change in the line width of a line formed in an image forming apparatus for forming a digital image by an electrophotographic method. And a line width control method for controlling the line width based on the detected line width, and an image forming apparatus for performing line width detection and line width control.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, in order to correct a change in the density of a copy image caused by a change in the toner density of a developer and other changes in conditions, it is necessary to correct the change in the density of a copy image.
Development in which a plurality of test pattern latent images are formed on the image carrier with a constant exposure intensity, and the rotational speed of the developer carrier is changed for each latent image (that is, the linear velocity of the developer carrier is changed). To develop a test pattern image group, detect the image density of the test pattern image group, and fix the linear velocity of the developer carrier of the developing means to a value at which a sufficient maximum density can be obtained by its output. To do. However, the developer of the developing device is provided with a magnetic permeability sensor at the bottom or the like to monitor the toner concentration of the developer, and when the toner concentration becomes lower than the specified toner concentration, the toner is replenished and the toner concentration of the developer is maintained at a constant value.

Thereafter, a plurality of test pattern latent images are formed with different exposure intensities, the test pattern latent images are developed by a developer carrier having a constant linear velocity, and the image density of the developed test pattern image group is detected. There is known an image forming apparatus which is detected by a means and controls to create a gradation correction curve based on a series of detected density data.

In this image forming method, the image density may be lowered and the gradation may be deteriorated due to the deterioration of the developing performance while continuing the image formation or the abnormal potential of the photosensitive layer of the image carrier. It is necessary to perform maximum density correction and gradation correction of the image for each constant.

In the conventional image forming method, the image density of the test pattern image group is detected by the density detecting means, the data is logarithmically converted, and the image density of the toner image on the image carrier and this toner image are recorded on the recording paper. In order to correct the difference from the image density when the image is transferred and fixed, an inverse function is created from the data of the value obtained by adding the logarithmically converted value of the recording paper to obtain a correction curve.

[0006]

The maximum density control is performed by determining the linear velocity of the developer carrying member, and the γ correction control is performed so that the gradation is γ = 1.0. Good reproduction can be performed. However, the above control does not control the characteristics such as the thickness of the thin line for the halftone dot and line image. Therefore, reproducibility of halftone dot and line images is not good due to changes in the number of copies and environmental conditions.

The present invention has developed a line width detection method and apparatus for halftone dots and line images, provides a line width control method for measuring the line width and feeding back the variation, and provides a line width control method and a difference between environments. It is an object of the present invention to reduce the influence of a change with time due to an increase in the number of printed sheets and the number of printed sheets so that good halftone dot and line images can be reproduced.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to form a line with an included angle θ with respect to main scanning or sub-scanning on an image carrier, and perform scanning across the line to determine the main scanning direction and the sub-scanning direction. A line width detecting method (claim 1) characterized by detecting a change in the line width of a line in the scanning direction, and a line having a sandwiching angle θ for main scanning or sub scanning on an image carrier, The change in the line width of the line in the main scanning direction and the sub-scanning direction is detected by scanning across the line, and the exposure condition is based on the data obtained by averaging the change in the line width in the main scanning direction and the sub-scanning direction from the initial stage. And a line width control method (claim 2) for controlling main scanning or sub-scanning on an image carrier, by forming a line with an included angle θ and performing scanning across the line. How to scan And image formation characterized by detecting a change in the line width of the line in the sub-scanning direction and controlling exposure conditions by data obtained by averaging the change in the line width in the main-scanning direction and the sub-scanning direction from the beginning. Device (Claim 4)
And a line width detecting device comprising a pair of a light emitting element and a light receiving element for detecting a line width, wherein a photodiode is used for the light receiving element (claim 5), and light emission. A line width detecting device for detecting a line width, which comprises a pair of an element and a light receiving element, wherein a lens is installed on the light emitting element side (claim 6), and a light emitting element. And a line width detecting device for detecting the line width, which comprises a combination of a light receiving element and a light receiving element, wherein the spot diameter of the light from the light emitting element on the object to be measured is smaller than the line width of the line on the object to be measured. In a dot width detection device for detecting a dot diameter, which comprises a line width detection device (claim 11) and a pair of a light emitting element and a light receiving element, a lens is installed on the light emitting element side. An image forming apparatus having a dot diameter detecting device (claim 12) and an image signal generating means, an image forming means, and a line width detecting means, wherein the image signal generating means and the image forming means are used. The fine line pattern is detected by the line width detecting means, and the parameter of the image forming means is changed according to the data, which is achieved by an image forming apparatus (claim 17).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a line width detecting method according to the present invention will be described with reference to the drawings.

The line width is detected by forming a latent image of a line with an exposure amount for writing a halftone dot or a line image on the image carrier, reversal developing it into a line of a toner image, and then forming the line width of this line. Is read by a detection means that is a combination of a light emitting element and a light receiving element. The line width is detected because a change in the line width is detected and fed back to form an image on an appropriate line. The line width of a line is generally different between a vertical line (sub scanning direction line) and a horizontal line (main scanning direction line). The horizontal line on the image carrier is rubbed by the developing magnetic brush adhering to the developing sleeve, the toner is scraped off, and the line tends to be thin.

Therefore, if the line width of the horizontal line is detected and the line width is controlled, the vertical line unaffected by the scraping of the developing magnetic brush becomes thick. Further, if the line width is controlled only by the vertical line, the vertical line may be broken (a part of the line is broken). Therefore, it is necessary to detect the line widths of both the vertical lines and the horizontal lines and to control the line widths accordingly.

When measuring the line width of the horizontal line on the image carrier, the line moving direction is perpendicular to the sensor positioned as shown in FIG. 3 (a). It is easy to detect. However, it is not easy to measure the line width of the vertical line on the image carrier, and it is not possible to obtain the sensor output by moving the sensor in the horizontal direction and crossing the vertical line as shown in FIG. Although it is possible, the sensor output is related to the moving speed of the sensor, and the detection accuracy is deteriorated.

According to the present invention, in order to detect a change in line width of a vertical line, an oblique line is drawn with a sandwiching angle θ with respect to main scanning or sub-scanning on an image carrier as shown in FIG. 4 (a). A change in the line width of the diagonal line in the sub-scanning direction is detected. Then, this change is decomposed into a vertical component and a horizontal component so that a change in the line width of the vertical line and the horizontal line can be detected. FIG. 4 (b) is an explanatory view of this figure. If an oblique line having a line width of F in the sub-scanning direction is ΔF thin, the vertical line is thin ΔD (vertical) = ΔF · tan θ The horizontal line is thin ΔD ( Lateral) = ΔF.

By providing the diagonal line and the sensor crossing in this way, it is possible to detect the change in the line width of the vertical line and the horizontal line at the same time, and the feedback considering the respective influences is used for the image formation. Can be applied to laser power.

Next, the line width measuring sensor according to the present invention will be described. 5A is a cross-sectional configuration diagram, and FIG. 5B is a circuit diagram. The light emitted from the light emitting element PS1 is focused on an object SB to be measured such as an image carrier or a transfer paper, and the reflected light is received by the light receiving element PS2 to measure the line width of the line. A pinhole PS3 and a lens PS4 are provided between the object to be measured SB and the light emitting element PS1 side. A light emitting diode (LED) or a laser is used for the light emitting element PS1. A photo transistor or a photo diode is used for the light receiving element PS2.

As the lens PS4, a plano-convex or convex-convex condenser lens is used. The pinhole PS3 is provided so as to use the central portion of the light intensity having a Gaussian distribution of a light emitting diode or a laser, and the hole diameter of the pinhole is appropriately selected according to the light intensity distribution. The pinhole PS3 is omitted when the characteristics including the aberration of the lens PS4 are excellent and a spot having a small diameter of 30 μm or less, which will be described later, is formed on the object SB to be measured and flare does not occur on the periphery of the spot. can do. According to the experiments conducted by the present inventors, when the lens PS4 is a single lens, the pinhole PS3 is required except for the aspherical precision lens.

The line width measuring sensor shown in FIG.
The light emitting element P is arranged in a direction perpendicular to the line of the object to be measured SB.
A small spot is formed by S1, and the light receiving element PS2 receives light at an angle of about 45 °. FIG. 6A shows two sets of light emitting elements PS1 with respect to the SB line of the DUT.
(A), PS1 (b) irradiates light from two directions,
Since the light is received by the light receiving element PS2 in the vertical direction, the influence of the shadow due to the swelling of the toner forming the line is offset, and the measurement accuracy is improved. However, it is necessary to superimpose and match the focal points of the two optical systems on the object to be measured SB, and a high degree of assembly / adjustment accuracy is required.

If the surface of the object SB to be measured is mirror-like, the sensor output shown in FIG. 5A and FIG. 6A receives the scattered component of the reflected light, and therefore the sensor output. However, there is a problem in that the light receiving element needs to be highly sensitive. FIG. 6 (b) shows the correspondence to this, in which the light axes of the light emitting element PS1 and the light receiving element PS2 are aligned and the direct component of the reflected light is received.

FIG. 7 shows the relationship between the thickness of the line on the object SB to be measured and the spot diameter of the light emitting element PS1 and the sensor output thereof. In FIG. 7A, the spot diameter is larger than the line width of the line. In this case, (b) shows the case where the spot diameter is equal to the line width of the line, and (c) shows the case where the spot diameter is smaller than the line width of the line. As is clear from this figure, the minimum value of the line width of the line that can be determined by the line width measurement sensor is the same as the spot diameter of the focus on the object to be measured (FIG. 7B). If the line width of the line is narrower than the spot diameter, the sensor cannot detect the line width of the line (FIG. 7A).

When the sensor detects a line width of a line width larger than the spot diameter (FIG. 7C), the line width L of the line is the line output of the sensor at a certain threshold voltage V _S. It is a product of the part Δt sandwiched when cut and the relative linear velocity X of the line and spot at the time of scanning, and is expressed by L = X · Δt.

The threshold voltage V _S is 50% to 50% of the output V _M of the portion other than the line of the transfer paper or the image carrier.
It is appropriate to set it at the place where it is lowered by 60%. When the calculated value L does not match the actually optically measured line width, it may be corrected by multiplying L by a function or a numerical value.
Further, by normalizing the line output and cutting the line output at the set threshold, it is possible to measure the line width with higher accuracy.

The light receiving element P for detecting the line width of the line
Although a photo transistor or a photo diode can be used for S2, it is necessary to use a photo diode as a light receiving element for an image forming apparatus that performs high-speed processing in a copying machine or a printer. In a high-speed machine, the relative speed between the line width detection device and the line on the image carrier or transfer paper that tries to detect the line width becomes large, and in the case of a phototransistor, it cannot follow. The sensor output is inaccurate for line width measurement. On the other hand, the photodiode has a response speed of about 10 ³ times that of the phototransistor, so that the photodiode can sufficiently respond to a high-speed machine and a correct line width value can be measured. However, the photo diode needs to be a circuit that does not generate noise more than when using the photo transistor.

FIG. 8 shows the output state when the line width of the same line is measured by installing the photo diode and the photo transistor in the same high-speed printer in exchange. Photodiode, (b) shows the sensor output when a phototransistor is used, and shows that the photodiode is necessary for a high speed machine. Note that sb on the output curve
The portion indicated by means the output on the surface of the DUT other than the line.

Further, the spatial frequency (MTF) can be used to detect the change in the line width of the line. FIG. 9 is an explanatory diagram related to this. A plurality of lines are provided as a test pattern on the object to be measured at equal intervals (see FIG. 9).
(A)). The spot diameter formed by the light emitting element is set to be approximately the same as the line width of the line to be measured, and the test pattern is formed so as to have the same spacing as the spot diameter (FIG. 9B). When the sensor is scanned across the test pattern, a sensor output as shown in FIG. 9C is obtained. As a result, MTF = (Vmax-Vmin) / (Vmax-Vmi
n) is required. If the line width of the test pattern changes, V
Since max and Vmin change and MTF changes, the change in line width can be detected from this.

In FIG. 10, a toner image is formed on the image bearing member,
The installation position of the line width detection device in the image forming apparatus of the type that transfers and fixes this toner image on the transfer paper is shown. When detecting the line width of the line formed on the image carrier, transfer from the developing section to the transfer / separation section (a), transfer from the transfer / separation section to the cleaning section (b), or transfer onto the transfer paper. When detecting the line width of the
The sensor is installed so that the line on the object to be measured can be read by the sensor from the separation section to the fixing section (c) or at the position discharged from the fixing section (d). Incidentally, in an image forming apparatus of a system in which a toner image is once transferred to a transfer drum or a transfer belt and then transferred to a transfer paper, by arranging a sensor in a direction in which a line on the transfer drum or the transfer belt can be read,
The line width of a line can be detected.

In the image forming apparatus, the line width control is performed by providing a sensor at the above-mentioned set position, detecting a change in the line width of the line, and applying feedback. In measuring the line width, accuracy can be improved by forming a plurality of lines having the same line width in parallel and averaging the detected measurement values. As feedback, exposure conditions are generally controlled by pulse width modulation or the like. FIG. 11 shows the relationship between the laser power output and the line width of a line obtained by actual measurement. The line width changes proportionally by changing the laser power output. In addition to detecting the change in the line width and applying the feedback, the feedback can be applied to the charging condition, the developing condition, the transfer condition, the fixing condition, etc. in addition to the laser power.

By applying the line width control method of the present invention to an image forming apparatus, it is possible to excellently reproduce a halftone dot or line image. However, the line width control of this line and a gradation image such as a photographic image are possible. FIG. 12 shows a flow of an algorithm that achieves both maximum density control and gradation correction for improving the reproducibility. Further, FIG. 13 shows a block diagram of a device that executes this algorithm.

In the above description, the line width detection method and the line width control method for detecting and controlling the change of the line width of the line have been described as a means for favorably reproducing the halftone dot and line images. Instead of detecting and controlling the change in the line width, the dot diameter formed by the digital image exposure means is measured, and the dot diameter control is performed by feeding back the changed amount to obtain a good halftone dot and line image. Can be reproduced.

The dot diameter detecting device is shown in FIG.
A measuring sensor having exactly the same configuration as the line width detecting device of FIG. 6 is used. That is, it is composed of a pair of a light emitting element and a light receiving element. A plano-convex or convex-convex condenser lens is provided on the light emitting element side, and a pinhole is provided between the light emitting element and the condenser lens. A light emitting diode or a laser is used for the light emitting element, and a photo transistor or a photo diode is used for the light receiving element. The light from the light emitting element forms a minute spot on the object to be measured, but the spot diameter of the minute spot needs to be the same as or smaller than the dot diameter to be measured. Then, when the line width of the line is detected, the change in the dot diameter is obtained in the same manner, and the dot diameter is controlled.However, regarding the dot diameter detection, the dot center and the spot center that relatively move during measurement are momentarily It needs to be measured in an overlapping manner. On the other hand, a large number of dots with the same diameter are formed by a preset pattern on the object to be measured, and this is scanned in the sub-scanning direction by the dot diameter detection device, and from the detected values of the large number of dots, It is also possible to estimate the dot diameter using a statistical method (for example, MTF), which is excellent in practicality.

Next, the structure and operation of the image forming apparatus to which the present invention is applied will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a block diagram showing a control system of the apparatus of FIG.

First, a normal copy operation of this image forming apparatus will be described. The image forming apparatus includes an image reading unit 10, a writing unit 20 which is a digital writing system, an image forming unit 30, a paper feeding unit 40, a document placing unit 50, and the like.

On the upper part of the image forming apparatus, a document placing portion 5 including a document table 51 made of a transparent glass plate and a document cover 52 for covering a document D placed on the document table 51.
0, which is below the document table 51, and in the main body of the apparatus, an image reading unit 10 including a first mirror unit 12, a second mirror unit 13, an imaging lens 14, an imaging element 15 such as a CCD array, and the like is provided. Has been.

The image of the document D on the document table 51 is displayed by the illumination lamp 12A of the image reading unit 10 and the first mirror 12B.
The parallel movement of the first mirror unit 12 including the above from the solid line to the position indicated by the broken line, and the first mirror unit 12 of the second mirror unit 13 integrally including the second mirror 13A and the third mirror 13B facing each other. The entire surface is illuminated and scanned by the follow-up movement of 1/2 speed with respect to the first mirror 12B and the second mirror 1 by the imaging lens 14.
An image is formed on the image sensor 15 via the third mirror 3A and the third mirror 13B. When scanning is completed, the first mirror unit 12 and the second mirror unit 13 return to their original positions, and stand by until the next image formation.

The image data obtained by photoelectric conversion by the image pickup device 15 is converted into a digital signal,
The image signal processing unit 60 performs processing such as MTF correction and γ correction, and temporarily stores it as an image signal in the memory.
Next, the image signal is read from the memory under the control of the CPU 90, pulse width modulated, and then input to the writing unit 20.

Under the control of the CPU 90, the image forming section 30 outputs a writing unit 20 in which the image signal is composed of a drive motor 21, a polygon mirror 22, an fθ lens 23, mirrors 24, 25 and 26, a semiconductor laser (not shown), a correction lens and the like. When it is input to, the image recording operation is started.
That is, the photoconductor drum 31, which is an image carrier, rotates clockwise as shown by the arrow, and is discharged by the static eliminator 36 which performs pre-exposure before charging to eliminate static electricity, and then is charged by the charger 32. Therefore, an electrostatic latent image corresponding to the image of the document D is formed on the photosensitive drum 31 by the laser beam L from the writing unit 20. After that, the electrostatic latent image on the photosensitive drum 31 is a developing sleeve 33 which is a developer bearing member to which a bias voltage of the developing device 33 is applied.
Reversal development is performed by the developer carried on A to form a visible toner image.

On the other hand, from the paper feed cassette 41A or 41B loaded in the paper feed section 40, one transfer paper P of a specified size is transferred.
The carry-out roller 42A carries out the paper one by one, and the carry-out roller 4
The sheet is fed toward the image transfer portion through the sheet 3 and the guide member 42. The fed transfer sheet P is sent onto the photosensitive drum 31 by the registration roller 44 which operates in synchronization with the toner image on the photosensitive drum 31. The toner image on the photoconductor drum 31 is transferred to the transfer paper P by the action of the transfer device 34, separated from the photoconductor drum 31 by the charge removal action of the separator 35, and then fixed via the conveyor belt 45. After being sent to the container 37 and fused and fixed by the heating roller 37A and the pressure roller 37B, the discharge roller 3
It is discharged to the tray 54 outside the apparatus by 8, 46. 53
Is a paper feed table for manual feeding.

The photoconductor drum 31 continues to rotate, and the toner remaining on the surface of the photoconductor drum 31 without being transferred is removed and cleaned by the cleaning blade 39A that is in pressure contact with the cleaning device 39, and the charge is removed again by the charge remover 36 and then charged. The electric charge is uniformly applied by the device 32, and the process for image formation for the next time starts.

Incidentally, the stirring screw 33C of the developing device 33
The magnetic permeability sensor TS provided at the bottom of the CPU monitors the toner concentration of the developer in the developing unit 33 by utilizing the fact that the magnetic permeability changes when the toner concentration of the developer changes, and the CPU 90 causes the toner concentration of the developer to be detected. It is a sensor that sends out information. CP
The U90 sends a toner replenishment instruction to the toner replenishing unit 33T to replenish the toner when the toner concentration decreases below a certain value according to the information of the magnetic permeability sensor TS, so that the toner concentration of the developer can be always kept constant. it can.

In this embodiment, a two-component developer composed of a polyester-based toner having a weight average particle diameter of 8.5 μm and a carrier having a resin coating on ferrite and a weight average particle diameter of 60 μm is used, and the toner concentration is 6 to 6. Although 9% was used, the toner concentration fluctuation can be kept within ± 0.3% by the above toner concentration control.

In the image forming apparatus described above, the photosensitive drum 31 is a drum coated with an OPC photosensitive member that is negatively charged, and has a writing density of 400 dpi (Dot per in).
ch)), the standard image forming conditions are shown in Table 1 below.
It is as follows.

[0042]

[Table 1]

An encoder (not shown) is provided on the rotary shaft of the photosensitive drum 31. The phase signal from this encoder is sent to the CPU 90 and used for process control that requires accurate knowledge of the image position.

The image forming apparatus of the present embodiment performs the maximum density correction and the gradation correction together with the line width detection. The line width detection sensor WS, the maximum density correction density detection sensor DS ₁ , The density detection sensor DS ₂ for correcting the gradation is opposed to the peripheral surface of the photosensitive drum 31, and is connected to the developing device 33 to the transfer device 34.
And between the separator 35 and the cleaning device 39.

The sensor WS for detecting the line width has already been described (see FIG. 5).

In this embodiment, LN is used as the light emitting element PS1.
66 (manufactured by Kagoshima Matsushita Co., Ltd.) was used. Emission wavelength is 9
The wavelength is 50 nm and does not affect the photosensitive characteristics of the image carrier. The phototransistor PN10 is used as the light receiving element.
7 (manufactured by Kagoshima Matsushita Co., Ltd.) was used. Condensing lens PS
Aspherical resin lens T170 (made by Konica Corp.) and pinhole PS3 were φ0.5 mm. The light receiving element PS2 receives light at a sandwiching angle of 40 ° with respect to the light emitting element PS1 that projects light perpendicularly to the image carrier.

In this embodiment, the linear velocity of the image carrier is 280 mm.
Since / s, a phototransistor is used. The line width of the line and the measured value of the sensor have a linear relationship as shown in FIG. 14A, and both the phototransistor and the photodiode can be accurately measured. For a high-speed machine of 620 mm / s, it is impossible to measure with a phototransistor as shown in FIG. 14 (b). It can be measured well.

Density detection sensor DS ₁ and density detection sensor D
Since S ₂ is an approximate configuration, it will be described together. The concentration detection sensors DS ₁ and DS ₂ are, for example, as shown in FIG. 15A, light emitting elements that irradiate infrared light with an incident angle of about 40 ° installed in two mounting holes formed in the casing CK. The light emitting diode LED, the phototransistor PT which is a light receiving element for receiving light at a reflection angle of about 40 °, and the dustproof member BG such as glass for preventing contamination by toner or the like. The infrared rays have no sensitivity to the photosensitive layer of the image carrier, for example, have a wavelength of 900 to 9
Infrared light of 80 nm is used. A photodiode can be used instead of the phototransistor PT. LN66 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used for the light emitting diode LED, and PN101 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used for the phototransistor PT.

The density detection sensors DS ₁ and DS ₂ are shown in FIG.
5 (b) is combined with the electric circuit shown in FIG. 5 (b) to form a concentration detecting device. A variable DC power supply Ve having a maximum output of 10 V is connected to the anode terminal of the light emitting diode LED, which is a light emitting element, so that the amount of light emitted from the light emitting diode LED can be changed. The light emitting diode LED is a resistor R for controlling the current.
Connected in series with ₈ and semi-fixed resistor VR ₁ from the DC power supply 1
A voltage of 0V is applied, and the semi-fixed resistor VR ₁ can adjust the variation of the resistance value of the light emitting diode LED and then fix it. Light emitting diode LED
Is lit when terminal Te is connected to ground.

Phototransistor PT which is a light receiving element
Is connected in series with the load resistance R ₇ and is
Power is applied. The output current of the phototransistor PT that receives the reflected light from the toner image illuminated by the light of the light emitting diode LED changes according to the intensity of the reflected light,
A voltage proportional to the output current of the phototransistor PT is generated across the load resistor R ₇ . This voltage is input to the (+) input terminal of IC1 which is an operational amplifier and amplified.
As a result, when the resistance connected between the output terminal and the (−) input terminal is R _5, and the resistance connected between the (−) input terminal and the ground is R ₆ , the resistance R ₅ is Vout = R ₅ / R ₆ × Vi between the output terminals Oa and Ob connected to both ends
The voltage of n is output. Where Vin is (+) of IC1
With the voltage applied to the input terminal, the voltage gain (voltage gain) Vout / Vin of the amplifier circuit in this case becomes R ₅ / R ₆ .
C1 is a capacitor for bypassing surge voltage and other noises.

The line width detection sensor WS of the present invention is combined with the density detection sensor DS ₁ for maximum density correction and the density detection sensor DS ₂ for gradation correction, and the algorithm shown in FIG. 12 is executed. It is possible to control both the gradation and the line width in a compatible manner, and to control the photographic image and the halftone dot / line image in a compatible manner against changes due to the number of copies, the number of prints, the environment, etc. The line width control will be described step by step.

Rotational speed of developing sleeve 254.1 rp
m (sleeve / image carrier linear velocity ratio of 1.90), laser power of 0.420 mW, and toner density of 6% in the developing device to perform maximum density control and gradation control. In this situation, RO
According to the program recorded in M95, a diagonal line having a width of 200 μm (θ = 4 in FIG. 4A) is formed on the image carrier.
5 °), and this is read by the line width detection sensor WS and stored in the memory 91. Also, a gradation image sample at this time is collected. This situation is called the initial stage.

Rotation speed of developing sleeve is 375.0 rp
m (sleeve / image carrier linear velocity ratio of 2.81) and the toner density in the developing device to 9% to perform maximum density control and gradation correction control, and draw a diagonal line with a width of 200 μm. An oblique line is drawn on the image carrier under the same exposure conditions as when the line width is detected, and this is read by the line width detection sensor WS. In addition, a gradation image sample at this time is collected. This situation is referred to as excessive development.

In the above-mentioned excessive development, the change in the line width of the oblique line on the image carrier with respect to the above-mentioned initial stage is obtained, and the change is decomposed into a horizontal component and a vertical component (see FIG. 4).
(B)), the change in the line width of the vertical line and the horizontal line due to the excessive development is obtained from each of them.

From the changes in the line widths of the vertical lines and the horizontal lines obtained above, the results are summed up and averaged, and the laser power conversion table of FIG. 16 recorded in the RAM 96 is used from the changes in the average line widths. The line width control of the diagonal line is performed using the algorithm of FIG. That is, the shift amount of the laser power is determined by using the table of FIG. 16 according to the change in the average line width of the vertical line and the horizontal line, and the laser power is shifted, and the maximum density control and the gradation correction control are performed. Here, draw an oblique line again to find the change in the line width from the initial vertical and horizontal lines. If the change is outside the allowable range (10 μm or more), finely adjust the laser power to return to the initial state, Control and gradation correction control.

Gradation image samples are similarly taken in this situation. This situation is defined as after line width control.

The relationship between the change in the line width and the correction value of the laser power shown in the laser power conversion table of FIG. 16 is effective in the developability under the above condition where the toner concentration is increased, and the developability is changed. Or, another conversion table is needed when the environment changes. Therefore, it is advisable to prepare a table in advance under typical conditions such as the number of copies and the environment, select the table closest to the situation when executing line width control, and use this to perform control.

In the above embodiment, the change in the line width of the vertical component and the horizontal component is obtained by using the oblique line. However, the horizontal line and the oblique line are drawn, and the change in the line width in the sub-scanning direction is detected by the horizontal line. However, it is also possible to adopt a method in which a change in the line width in the main scanning direction is then detected by an oblique line and feedback is applied according to each change.

(Results) At the time of initial setting, the overdeveloped state, the respective gradation characteristics after line width control, and the line width will be compared. FIG. 17 shows gradation at the initial stage, after overdevelopment, and after line width control. In all cases, γ = 1.0 with almost the same slope.
It is. Therefore, the gradation is controlled in the initial stage, after excessive development, and after the line width control.

The change in line width at the time of initial setting of vertical lines and horizontal lines and in the state of excessive development was 50 μm and 40 μm, respectively, as measured by the line width detection sensor WS (FIG. 1).
8). Therefore, the average line width change of vertical and horizontal lines is 45μ
Using m as a conversion table of laser power with respect to changes in line width in FIG. 16, line width control was performed to weaken the output of 0.07 mW laser power. The line width of the diagonal line drawn on the image carrier at this time (after line width control) is measured by precise measurement, and the line width for the initial vertical and horizontal lines after line width control is adjusted by the vertical and horizontal components. Then, it was confirmed that the vertical line and the horizontal line were controlled up to the initial line width as shown in FIG.

Therefore, from the change in the line width of the oblique line drawn on the image carrier, the change in the line width of the vertical line and the horizontal line can be detected, and the line width can be controlled based on the change. confirmed. It was also confirmed that this line width control does not affect the gradation.

As described above, the line width control is performed by detecting the change of the line width of the line. However, the change of the dot diameter is detected by a method similar to this, and the dot diameter control is performed based on this. It can be carried out.

Under the initial conditions, a dot group having a diameter of 200 μm is written on the image carrier, and this is read by the dot diameter control sensor and stored in the memory.

Under the condition of excessive development, the dot group is written on the image carrier under the same exposure condition as the case where the dot group having the diameter of 200 μm is formed, and the dot diameter control sensor reads the dot group.

In the above situation, the laser power conversion table shown in FIG. 19 is used, and the dot diameter control is performed using the same algorithm as that shown in FIG. 12 used at the time of line width control. The difference from the dot diameter read in step S1 is taken, the laser power conversion table for dot diameter control in FIG. 19 is used to determine the amount of laser power shift, the laser power is shifted to control the dot diameter, and maximum density control and gradation are performed. Correction control is performed. Here, the dot group is written again, the dot diameter is measured, the laser power is finely adjusted if necessary, and maximum density control and gradation correction control are performed.

(Results) FIG. 20 shows the initial, overdeveloped, and dot diameter after dot diameter control measured by actual measurement. A dot 50 μm thicker than the initial dot diameter due to excessive development shows the laser power in FIG. The dot diameter was controlled to the initial value of 200 μm by weakening it by about 0.07 mW by the laser power conversion table of No. 2. In addition, the gradation is γ =
It was controlled to the almost same state of 1.0.

[0067]

By using the line width detecting device or the dot diameter detecting device according to the present invention, the line width or dot diameter of a line can be accurately measured. Therefore, the existing maximum density sensor and gradation correction sensor can be used. By using the line width control method according to the present invention in combination with the line width control, it becomes possible to make the control of the line width compatible with the control of the gradation, and for both the photographic image and the halftone dot / line image, the copy number and print It is now possible to obtain images that are stable and have good reproducibility with respect to changes in number or environment.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus of the present invention.

FIG. 2 is a block diagram showing a control system of the image forming apparatus of the present invention.

FIG. 3 is an explanatory diagram related to line line width detection.

FIG. 4 is an explanatory diagram of line width detection of a diagonal line.

5A and 5B are a cross-sectional configuration diagram and a circuit diagram of a line width measuring sensor.

FIG. 6 is a cross-sectional configuration diagram of a line width measuring sensor according to another embodiment.

FIG. 7 is an explanatory diagram showing a relationship between a line width of a line and a spot diameter.

FIG. 8 is an explanatory diagram showing output states of a photo diode and a photo transistor.

FIG. 9 is an explanatory diagram of a line width measuring method using spatial frequency.

FIG. 10 is an explanatory diagram showing set positions of the line width detection device.

FIG. 11 is a graph showing the relationship between line width and laser power.

FIG. 12 is a flow for performing an algorithm for line width control of the present invention.

FIG. 13 is a block diagram showing an algorithm of line width control according to the present invention.

FIG. 14 is a graph showing a relationship diagram between a line width and a sensor measurement value for a photo diode and a photo transistor.

FIG. 15 is a cross-sectional configuration diagram and circuit diagram of a concentration detection sensor.

FIG. 16 is a laser power conversion table during line width control.

FIG. 17 is a graph showing gradation at the time of initial setting, excessive development, and line width control.

FIG. 18 is a graph showing changes in line width after vertical line and horizontal line initial settings, excessive development, and line width control.

FIG. 19 is a laser power conversion table when controlling the dot diameter.

FIG. 20 is a graph showing changes in dot diameter after initial dot setting, excessive development, and dot diameter control.

[Explanation of symbols]

10 image reading unit 20 writing system unit 30 image forming unit 31 photoconductor drum (image carrier) 32 charger 33 developing unit 60 image signal processing unit 90 CPU 91 memory 95 ROM 96 RAM DS ₁ , DS ₂ density detection sensor WS line Width detection device (sensor) PS1 Light emitting element PS2 Light receiving element PS3 Pinhole PS4 (Condensing) lens

Claims (18)

[Claims] 1. A main scanning or a sub scanning on an image carrier is made into a line with an included angle θ, and scanning is performed across the line to change the line width of the line in the main scanning direction and the sub scanning direction. A line width detecting method characterized by detecting. 2. A line is formed at an included angle θ with respect to main scanning or sub-scanning on an image carrier, and scanning is performed across the line to change the line width of the line in the main-scanning direction and the sub-scanning direction. A line width control method, which comprises detecting and controlling exposure conditions based on data obtained by averaging changes in line widths in the main scanning direction and the sub scanning direction from the initial stage. 3. The line width control method according to claim 2, wherein the initial line width is created by a sequence other than the normal sequence. 4. A line width is changed in the main scanning direction and the sub scanning direction by forming a line with an included angle θ with respect to the main scanning or the sub scanning on the image carrier and performing scanning across the line. An image forming apparatus, which detects and controls exposure conditions based on data obtained by averaging changes in line widths in the main scanning direction and the sub scanning direction from the initial stage. 5. A line width detecting device comprising a pair of a light emitting element and a light receiving element for detecting a line width, wherein a photodiode is used for the light receiving element. 6. A line width detecting device comprising a pair of a light emitting element and a light receiving element for detecting a line width, wherein a lens is installed on the light emitting element side. 7. The line width detecting device according to claim 6, wherein the lens is a plano-convex or convex-convex condenser lens. 8. The line width detecting device according to claim 6, wherein a pinhole is provided between the light emitting element and the lens. 9. The line width detection device according to claim 6, wherein an LED or a laser is used as the light emitting element. 10. The line width detecting device according to claim 6, wherein a phototransistor or a photodiode is used for the light receiving element. 11. A line width detecting device for detecting a line width, which comprises a pair of a light emitting element and a light receiving element, wherein a spot diameter of light from the light emitting element on a measured object is a line on the measured object. A line width detection device characterized by being smaller than the line width. 12. A dot diameter detecting device comprising a pair of a light emitting element and a light receiving element for detecting a dot diameter, wherein a lens is installed on the light emitting element side. 13. The dot diameter detecting device according to claim 12, wherein the lens is a plano-convex or convex-convex condenser lens. 14. A pinhole is provided between the light emitting element and the lens.
The dot diameter detection device described. 15. The dot diameter detecting device according to claim 12, wherein an LED or a laser is used as the light emitting element. 16. The dot diameter detecting device according to claim 12, wherein a phototransistor or a photodiode is used for the light receiving element. 17. An image forming apparatus having an image signal generating means, an image forming means, and a line width detecting means, wherein the thin line pattern created by the image signal generating means and the image forming means is detected by the line width detecting means. An image forming apparatus, wherein a parameter of the image forming unit is changed according to the data. 18. The parameter to be changed is an exposure light amount and / or a developing condition.
The image forming apparatus as described in the above.