JP2001180036A - Method of adjusting image and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of adjusting an image and an image forming apparatus capable of stabilizing a binary image and a multi-value image for a long time while using the apparatus. SOLUTION: In this image adjusting method, an optical quantity of a laser light emitted from a laser optical system in the image forming apparatus is controlled and a latent image is formed on an image carrier body by the laser light by controlling the pulse width of the laser light and to be developed. The density adjustment of the binary image is executed by controlling the light quantity of the laser light and the gradation adjustment of the multi-value image is executed by controlling the pulse width of the laser light selected by the density adjustment of the binary image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to an image forming apparatus such as a copying machine, a printer or a facsimile by an electrophotographic system, and an image adjusting method for stabilizing an image, and an image forming method to which the method is applied. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic copying machine, a printer, or the like, when writing image information to a laser beam on an image carrier such as a photosensitive drum or a photosensitive belt, the amount of laser light is determined on a prospective basis. For example, it has been difficult to stabilize an image due to contamination of a writing optical system, deterioration of a photosensitive drum, and the like. In particular, in a binary image, since the image depends on the laser power, a problem may occur in the image stability, and particularly, a large fluctuation occurs in the toner consumption.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides an image forming apparatus capable of stabilizing a binary image and a multi-valued image for a long period of time while using the apparatus. A method and an image forming apparatus to which the method is applied are provided.

[0004]

In order to achieve the above object, the present invention provides a method for controlling the amount of laser light output from a laser optical system and controlling the pulse width of the laser light while controlling the pulse width of the laser light. An image adjustment method for an image forming apparatus for forming a latent image on an image carrier and visualizing the image, wherein the density of a binary image is adjusted by adjusting the light amount of the laser light, and the multi-valued image is adjusted. The gradation adjustment is performed by adjusting the pulse width of the laser beam selected by the density adjustment of the binary image.

According to this image adjustment method, the density of a binary image is adjusted by adjusting the amount of laser light, and the pulse width of a laser beam selected by adjusting the density of the binary image is adjusted. For example, even if the laser optical system becomes dirty or the image carrier deteriorates, the binary image and the multi-valued image can be corrected in accordance with the gradation adjustment. Can be stabilized.

In this case, the density of the binary image is adjusted by sampling a plurality of test patterns composed of isolated dots visualized on the image carrier by changing the light amount of the laser beam using an optical sensor. , By selecting the amount of laser light.

The gradation of the multivalued image can be adjusted by gradation control for normalizing printer characteristics from a plurality of test patterns visualized on an image carrier by changing a pulse width. .

Further, the density of the binary image is adjusted by changing the laser light amount, sampling a plurality of test patterns consisting of isolated dots visualized on the image carrier with an optical sensor, and then selecting the laser light amount. By doing
The gradation adjustment of the multi-valued image can be performed by gradation control for normalizing printer characteristics from a plurality of test patterns visualized on the image carrier by changing a pulse width.

Further, the adjustment of the binary image and the adjustment of the multi-valued image can be performed using the same optical sensor.

Further, the adjustment of the binary image and the adjustment of the multi-valued image can be performed using an optical sensor utilizing diffused light.

A test pattern used for adjusting the binary image can be created by an error diffusion method.

It is preferable that the density of the test pattern used for adjusting the binary image is 0.7 or less in absolute density.

Further, by performing the image adjustment for each fixed copy, the image can be appropriately corrected, which is preferable.

Further, the image forming apparatus of the present invention detects the amount of adhered toner having a substantially maximum image density visualized on an image carrier using an optical sensor in order to control the maximum image density. In an image forming apparatus that controls the number of rotations of the developer conveyance body to perform image density adjustment so that the number of rotations of the developer conveyance body has a predetermined reference value,
The adjustment of the light amount of the laser light for adjusting the density of the binary image is performed when the rotation speed of the developer transport body is at the predetermined reference value, and the gradation control of the multi-valued image is performed by the selected laser light. Is performed.

According to this image forming apparatus, the binary image adjusts the amount of laser light based on a predetermined reference value of the number of rotations of the developer conveying member, and the multi-valued image is processed by the selected laser light. Since the tone control is performed, for example, even if the laser optical system is stained or the image carrier is deteriorated, the binary image and the multi-valued image can be corrected in accordance therewith. Can be stabilized.

Further, by performing the image density adjustment for each fixed copy, the image can be appropriately corrected, which is preferable.

Further, according to the present invention, in order to control the maximum image density, an optical sensor is used to detect the amount of adhered toner having a substantially maximum image density visualized on the image bearing member so that the image density becomes constant. In an image forming apparatus configured to control the number of rotations of a developer transporter to perform image density adjustment, the number of rotations of the developer transporter has a predetermined reference value, and a plurality of rotations of the developer are visualized on an image carrier. The tone control for normalizing the printer characteristics from the test pattern is performed immediately after the image density adjustment and after the rotation speed reaches a reference value.

In this case, it is preferable that the gradation control performed after the rotation speed reaches the reference value is performed immediately after the completion of image formation.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of a main portion of an electrophotographic image forming apparatus showing an embodiment of the present invention.

As shown in FIG. 1, the image forming apparatus includes a photosensitive drum 1 serving as an image bearing member which rotates in a rotation direction R and has a photosensitive layer on its surface. , Separation unit 2b, optical density sensor 9, cleaner 4
0, a band electrode 5, a temperature and humidity detection sensor 10, and a developing unit 6 are arranged. The photosensitive layer of the photosensitive drum 1 can be made of OPC, amorphous silicon, selenium, or the like.

Further, an exposure section 8 for exposing the photosensitive drum 1 based on image information to form a latent image is provided.
The exposure unit 8 includes a semiconductor laser and a laser optical system, and writes image information on the photosensitive drum 1 while scanning laser light emitted from the semiconductor laser.

The band electrode 5 uniformly charges the surface of the photosensitive drum 1 to a predetermined voltage prior to the latent image forming process. Also,
The laser optical system 7 forms a latent image on the photosensitive drum 1 by exposing a laser beam modulated based on a predetermined image signal while scanning the photosensitive drum on the photosensitive drum.

The developing device 6 stirs the toner developer by rotating the stirring screws 6b, 6c and 6d, and forms a magnetic brush on the outer periphery of a rotating sleeve 6a having a magnet roller therein, and a developing sleeve. By applying a predetermined bias voltage to 6a, the latent image on the photosensitive drum 1 is visualized as a toner image. The developing sleeve 6a is driven to rotate by the developing sleeve driving unit 7.

The transfer section 2a superimposes the transfer paper P on the toner image electrostatically carried on the photosensitive drum 1, discharges the charge on the transfer paper P, and transfers the toner image on the photosensitive drum 1 to the transfer paper P. Transfer to The transfer paper P on which the transfer has been completed is de-electrified by the separation unit 2b and separated from the photosensitive drum 1. Thereafter, the transfer paper P is transported in the transport direction F, undergoes a fixing process, and is discharged outside the apparatus.

The cleaner 40 contacts the surface of the photosensitive drum 1 with the blade 4 so that the photosensitive drum 1
The toner and dust adhering to the surface are scraped off and collected in the cleaner box 40a. A recycled toner path 41 is formed from inside the cleaner box 40a to inside the developing device 6, and the cleaner box 40a
The toner collected inside is returned to the developing device 6 and reused.

The optical density sensor 9 is a sensor that uses diffused light, emits light from a light emitting diode (LED) to the surface of the photosensitive drum 1, and condenses the reflected light with a phototransistor according to the light intensity. By converting the voltage to a voltage, the density can be detected, and the toner adhesion amount of the toner image on the photosensitive drum 1 can be obtained. Thereby, the photosensitive drum 1
The density of the test pattern formed and visualized thereon can be detected. Note that a sensor using reflected light may be used as the optical density sensor.

The temperature and humidity sensor 10 is arranged to measure the temperature and humidity near the photosensitive drum 1.

Signals output from the optical density sensor 9 and the temperature / humidity sensor 10 are input to the control unit 30. The control unit 30 controls the exposure unit 8 based on these input signals, and controls the amount of laser light output from the exposure unit 8 and the width of the laser light. Further, the control unit 30 controls the developing sleeve driving unit 7 to adjust the image density by controlling the rotation speed of the developing sleeve 6a. In this case, the developing sleeve 6a is controlled to rotate at a predetermined reference rotation speed. For example, when the maximum density cannot be obtained, the rotation speed increases to obtain a predetermined density.

After the control unit 30 controls the exposure unit 8 to form a plurality of test patterns composed of isolated dots on the photosensitive drum 1 and visualize them, the optical density sensor 8 detects the density of the test patterns. The light amount of the laser beam can be corrected based on the detected density of the test pattern.

Next, a method for adjusting the amount of laser light will be described with reference to FIGS. This adjustment method is for selecting an optimal light amount of laser light and optimally adjusting the density of a binary image.

First, a test pattern is created based on an error diffusion (ED) method with a target of a constant density (for example, 0.4). As shown in FIG. 2, under the control of the control unit 30, the amount of laser light emitted from the exposure unit 8 to the photosensitive drum 1 is changed from small to large to form a plurality of latent images and visualize them. As a result, a plurality of test patterns (a) to (f) (toner images) composed of isolated dots having different densities are formed on the photosensitive drum 1.

Next, the density of each test pattern is detected by the optical density sensor 9 shown in FIG. 1, and as shown in FIG. 3, the light amount P (horizontal axis) of the laser beam and each test pattern when each test pattern is formed. By linearly approximating the relationship with the detected density D by the least square method, the light amount P1 of the laser light corresponding to the preset density threshold D1 is selected as the optimum light amount. The optimal light amount P1 thus selected
Is irradiated from the exposure unit 8 during image formation. Further, the density adjustment of such a binary image is performed by the developing sleeve 6.
This can be performed when a rotates at a predetermined number of rotations.

Next, gradation control for adjusting the density of a multi-valued image by controlling the width of the laser beam selected as described above will be described with reference to FIGS. That is, multi-value gradation is performed by gradation control for normalizing printer characteristics from a plurality of test patterns visualized on the image carrier by pulse width modulation (PWM). Here, pulse width modulation (PW
M) refers to changing the maximum emission time of the semiconductor laser stepwise and changing its pulse width.

First, as described above, on the photosensitive drum 1,
By changing the PWM level of the laser light emitted from the exposure unit 8, a plurality of test patterns as density strips that change stepwise from 0 to 255 levels are formed and visualized. FIG. 4 shows the relationship between the image density detected by the optical density sensor 9 and the PWM level used in the density adjustment of the binary image from each test pattern.
Indicates printer characteristics. As can be seen from FIG. 4, the printer characteristics do not change with a constant density gradient according to the PWM level.

FIG. 5 is a diagram showing printer characteristics as a relationship between the PWM level and the image density. FIGS. 4 and 5 are data in which data are exchanged with each other. By multiplying the γ characteristic shown in FIG. 4 by the γ characteristic shown in FIG. 5, the printer characteristic can be normalized as shown in FIG. In FIG. 6, the vertical axis indicates the image density level.
The scale is given at 55 levels, and the horizontal axis indicates the density signal level obtained in the image forming apparatus.

As described above, the normalization of the printer characteristics is achieved by converting the characteristic curve of the image density obtained from the test pattern by the output signal of the optical density sensor into a straight line using a curve having an inverse shape (a curve having an inverse function). As a result, as shown in FIG. 6, the characteristic curve indicating the printer characteristic is corrected to a straight line, and furthermore, has a 45 ° slope that matches the gradation level of the input / output signal. . Tone control can be performed by converting to a PWM level that changes stepwise with a constant density gradient based on the highest image density obtained by the immediately preceding printer characteristic and normalizing the printer characteristic.

As described above, when obtaining the printer characteristics from a plurality of test patterns, if the maximum image density as a control target cannot be obtained, the control unit 30 of FIG. By performing the control, the rotation speed of the developing sleeve 6a can be increased so as to obtain the maximum image density as a control target.

The tone control for normalizing the printer characteristics from the plurality of test patterns is preferably performed immediately after the image density adjustment and after the rotation speed of the developing sleeve 6a reaches the reference value.

[0039]

Next, Comparative Examples 1 to 3 are described in Examples 1 to 3 below.
4 will be described more specifically.

In this embodiment, a modified Konica 7050 machine employing a toner recycling system was used. The specific conditions are as follows. 1. Photosensitive drum: Organic (OPC) with a thickness of 15 to 35 μm
Φ80 drum with photoreceptor layer formed. 2. 2. Photoconductor linear velocity: 270 mm / sec 3. Developer: 8 μm toner + 60 μm carrier (two-component developer) Development conditions: Vbias 600 V, VH 750 V Linear velocity of developing sleeve: Can be arbitrarily changed, and is changed according to image density.

<Example 1>

As shown in FIG. 3, the light amount of the laser beam was adjusted, and the density of the binary image was adjusted with the optimum light amount. The toner consumption (corresponding to a 6% original) when an optimal binary image was selected in each environment and the reproducibility of a dot having a diameter of 100 μm were confirmed. This control was performed every 50 kc. The results are shown in Table 1 below.

Table 1

Laser power Toner consumption Dot diameter Start (HH) 330 μW 26 mg / copy 105 μm 100 kc (HH) 375 μW 25 mg / copy 100 μm After 200 kc (HH) 420 μW 26 mg / copy 105 μm Start (L.H.) L.) 355 μW 24 mg / copy 95 μm 100 kc (LL) 400 μW 26 mg / copy 105 μm After 200 kc (LL) 450 μW 25 mg / copy 100 μm (HH: high temperature and high humidity, LL: low temperature and low humidity)

As can be seen from Table 1, in each environment (high temperature, high humidity, low temperature, low humidity), stable toner consumption and dot diameter are maintained. Further, when the density adjustment of the multi-valued gradation was executed by gradation control for normalizing the printer characteristics from a plurality of test patterns visualized on the photosensitive drum by changing the pulse width, a low temperature and low humidity environment and a high temperature and high humidity In both environments, good linearity was maintained from the start to 200 kc.

<Comparative Example 1>

As Comparative Example 1, image formation was performed with the amount of laser light fixed from the start. Toner consumption when a binary image is selected (equivalent to 6% original) and diameter 10
When the dot reproducibility of 0 μm was confirmed, the results shown in the following Table 2 were obtained.

Table 2

Laser power Toner consumption Dot diameter Start 480 μW 32 mg / copy 110 μm After 200 kc 370 μW 22 mg / copy 70 μm (Environment: normal temperature and normal humidity)

As can be seen from Table 2, if the light amount of the laser beam is not adjusted, the contamination of the laser optical system and the photosensitive drum
The toner consumption and the dot diameter vary due to the deterioration of the developer and the like. Further, the density adjustment of the multi-value gradation is performed by performing gradation control for normalizing printer characteristics from a plurality of test patterns visualized on the photosensitive drum by changing the pulse width. The tonality lacked linearity at the start at 200 kc.

<Comparative Example 2>

While correcting the amount of laser light by the number of copies, the amount of toner consumed (corresponding to a 6% original) and the reproducibility of a dot having a diameter of 100 μm when a binary image was selected in each environment were checked. Correction of the amount of laser light
The laser power was increased by 25 μW to 50 kc sheets by prospective control. The results are shown in Table 3 below.

Table 3

Laser power Toner consumption Dot diameter Start (HH) 350 μW 28 mg / copy 110 μm After 200 kc (HH) 450 μW 32 mg / copy 120 μm Start (LL) 350 μW 24 mg / copy 90 μm After 200 kc ( LL) 450 μW 25 mg / copy 100 μm (HH: high temperature and high humidity, LL: low temperature and low humidity)

As can be seen from Table 3, it can be seen that contamination correction of the laser optical system and deterioration of the photoreceptor / developer are compensated for by the prospect correction, but it is not possible to correct environmental variations. Further, the density adjustment of the multi-value gradation was executed by gradation control for normalizing printer characteristics from a plurality of test patterns visualized on the photosensitive drum by changing the pulse width. 20 from the start in low-temperature, low-humidity environments
Although good linearity was maintained up to 0 kc, the linearity of the multi-valued image in a high-temperature and high-humidity environment lacked linearity at the start of 200 kc.

<Example 2>

In the second embodiment, an optical density sensor is used to control the maximum image density to detect the amount of toner adhering to a substantially maximum image density visualized on the photosensitive drum, and develop the image to a constant image density. The image density is adjusted by controlling the number of rotations of the sleeve, and the amount of laser light for adjusting the density of the binary image is adjusted after the developing sleeve reaches a predetermined number of rotations. When gradation control of the multi-valued image was performed, the dot diameter was controlled to an appropriate size (105 μm), and the toner consumption was maintained at an appropriate value of 26 mg.

<Comparative Example 3>

Comparative Example 3 is the same as Example 2, but before the developing sleeve reaches a predetermined number of revolutions, the light amount of the laser light for adjusting the density of the binary image is adjusted. When the gradation control of the multi-valued image was performed with the light amount of, the dot diameter after the developing sleeve reached the predetermined number of rotations became large (120 μm). In addition, the toner consumption increased to 33 mg.

<Embodiment 3>

In a third embodiment, an optical density sensor is used to control the maximum image density, and the amount of adhered toner having a substantially maximum image density visualized on the photosensitive drum is detected and developed to a constant image density. Immediately after performing image density adjustment to control the number of rotations of the sleeve and after the number of rotations of the developing sleeve reaches the reference value, gradation control for normalizing printer characteristics from a plurality of test patterns visualized on the photosensitive drum is performed. As a result, it was found that the gradation linearity was always maintained in all environments.

<Comparative Example 4>

As Comparative Example 4, tone control for normalizing the same printer characteristics as in Example 3 was performed only immediately after the image density adjustment described above. After 10kc, it got worse.

[0064]

According to the present invention, it is possible to provide an image adjusting method and an image forming apparatus capable of stabilizing a binary image and a multi-valued image for a long period of time while using the apparatus.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing test patterns (af) for adjusting the density of a binary image according to the embodiment.

FIG. 3 is a diagram for explaining a method of selecting an optimal light amount of laser light for adjusting the density of a binary image in the present embodiment.

FIG. 4 is a diagram illustrating a relationship between an image density detected by an optical density sensor from each test pattern and a PWM level for gradation adjustment of a multi-valued image in the present embodiment.

FIG. 5 is a diagram illustrating printer characteristics as a relationship between a PWM level and an image density in the present embodiment.

FIG. 6 is a diagram showing printer characteristics normalized from FIGS. 4 and 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 7 Developing sleeve drive part 8 Exposure part 9 Optical density sensor 30 Control part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA53 AA54 AA65 AA66 CA05 CA09 CA10 CA11 CB73 CB80 2H027 DA09 EA02 EA20 EB01 EC03 EC06 ED06 HB02 HB04 2H076 AB05 AB34 DA07 DA08 DA17 DA19 DA21 DA22

Claims (13)

[Claims] An image forming a latent image on an image carrier by the laser light while controlling a light amount of the laser light output from the laser optical system and controlling a pulse width of the laser light. An image adjustment method for a forming apparatus, wherein a density adjustment of a binary image is performed by adjusting a light amount of the laser beam, and a gradation adjustment of a multi-value image is selected by the density adjustment of the binary image. An image adjustment method which is performed by adjusting a pulse width of light. 2. The density adjustment of the binary image is performed by sampling a plurality of test patterns composed of isolated dots visualized on the image carrier by changing a light amount of the laser light using an optical sensor. 2. The image adjustment method according to claim 1, wherein the method is performed by selecting a light amount of the laser light. 3. The gradation adjustment of the multi-valued image is performed by gradation control for normalizing printer characteristics from a plurality of test patterns visualized on an image carrier by changing a pulse width. Image adjustment method described in 1. 4. The density adjustment of the binary image is performed by changing a laser light amount, sampling a plurality of test patterns composed of isolated dots visualized on an image carrier by an optical sensor, and selecting a laser light amount. The tone adjustment of the multi-valued image is performed by tone control for normalizing printer characteristics from a plurality of test patterns visualized on an image carrier by changing a pulse width.
Image adjustment method described in 1. 5. The image adjustment method according to claim 1, wherein the adjustment of the binary image and the adjustment of the multi-valued image are performed using the same optical sensor. 6. The adjustment of the binary image and the adjustment of the multi-valued image are performed using an optical sensor using diffused light.
The image adjustment method according to any one of claims 1 to 5. 7. The image adjustment method according to claim 1, wherein the test pattern used for adjusting the binary image is created by an error diffusion method. 8. The test pattern used for adjusting the binary image has a density of 0.7 or less in absolute density.
The image adjustment method according to any one of the above. 9. The image adjustment method according to claim 1, wherein the image adjustment is performed for each fixed copy. 10. A developer transporter for detecting the amount of adhered toner having a substantially maximum image density visualized on an image carrier using an optical sensor in order to control the maximum image density so that a constant image density is obtained. In the image forming apparatus, the number of rotations of the developer is controlled to adjust the image density. The number of rotations of the developer conveyance body has a predetermined reference value, and the amount of laser light for adjusting the density of the binary image. The image forming apparatus is characterized in that the adjustment is performed when the number of rotations of the developer conveying body is at the predetermined reference value, and the gradation control of the multi-valued image is performed by the selected laser light. 11. The image forming apparatus according to claim 10, wherein the image density adjustment is performed for each fixed copy. 12. A developer transporter for detecting the amount of adhered toner having a substantially maximum image density visualized on an image carrier using an optical sensor to control the maximum image density so as to maintain a constant image density. In the image forming apparatus wherein the image density is adjusted by controlling the number of rotations of the developer, the number of rotations of the developer conveyance body has a predetermined reference value, and the number of test patterns visualized on the image carrier is determined from the plurality of test patterns. An image forming apparatus, wherein tone control for normalizing printer characteristics is performed immediately after the image density adjustment and after the rotation speed reaches a reference value. 13. The image forming apparatus according to claim 12, wherein the gradation control performed after the rotation speed reaches a reference value is performed immediately after the completion of image formation.