JP2001194845A - Image forming device and its controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of an image so as to eliminate variation between devices by an easy controlling method and to make the line width of respective line images extended in main and sub-scanning directions uniform in the image forming device of an electrophotograhic system. SOLUTION: The surface of a photoreceptor 1 is uniformly electrified by a primary electrifying device 2, and an electrostatic latent image is formed by a semiconductor laser 31, and it is developed by sticking toner by a developing device 4. Then, a toner image is transferred to a sheet material by a transferring/separating device 5, and is fixed by a fixing device 8, and it is ejected. Also, a patch latent image consisting of plural linear images extended in the scanning direction of a laser beam and the patch latent image consisting of the plural line images extended in the sub scanning direction perpendicular to it are formed, and the density of the patch latent images is detected by a reflected light quantity sensor 10, and the laser driving current amount of the semiconductor laser 31 or the like is controlled in accordance with the level of detected density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electrophotographic image forming apparatus having respective steps of charging, latent image and development, and a control method thereof.

[0002]

2. Description of the Related Art In a digital image forming apparatus using an electrophotographic technique such as a copying machine or a printer, an original image is formed on a photosensitive layer on the surface of a photoreceptor uniformly charged by a charging device utilizing corona discharge or the like. Is irradiated by a light source such as a laser to form an electrostatic latent image. Recently, semiconductor lasers have been increasingly used as light sources.

In the latent image process, laser light is first collimated by a lens, and the collimated laser light is irradiated on a rotating polygon mirror (hereinafter, referred to as a polygon mirror). Light scans the photoreceptor surface in the axial direction of the photoreceptor.

Then, toner is adhered to the electrostatic latent image formed as described above by a developing device, so that the latent image on the photoreceptor is visualized, and the toner image is transferred to a sheet material by a transfer device. Transcribed. The toner image transferred to the sheet material is heated and pressed by a fixing device. In addition, after the toner that has not been transferred to the sheet material is removed by the cleaning device, the photoreceptor that has passed through the transfer device is irradiated with light by the pre-exposure device to remove the electrostatic latent image on the surface. .

In a digital image forming apparatus using such a laser beam, a line width of a thin line extending in a laser scanning direction (referred to as a main scanning direction) and a direction perpendicular to the laser scanning (sub scanning direction). The optical system is designed so as to optimize the spot shape of the laser beam formed on the surface of the photoconductor so that the line widths of the thin lines extending to the same length are equalized. Further, the developing sleeve and the developing bias are optimized so that the line width does not largely differ between the main and sub-scanning directions during the development.

Further, the process speed of the apparatus itself has been increased by increasing the speed of rotation of the polygon mirror and adopting a multi-beam laser in recent years. Such an increase in the process speed naturally requires an increase in the rising speed (switching response speed) of the laser. If the rising speed of the laser is not sufficient, there occurs a problem that a line extending in the sub-scanning direction is not reproduced firmly. To solve such a problem,
In some lasers, a certain amount of direct current, for example, a current that does not cause laser resonance light emission, is always applied from a laser drive circuit to the laser to improve the rise at the time of light emission (at the time of laser ON).

[0007]

However, the conventional image forming apparatus as described above has the following problems.

[0008] Even if the laser spot diameter is optimized,
The developing characteristics of the developing device easily change greatly depending on, for example, environmental conditions and the like, and parts such as a photoreceptor deteriorate with long-term use. In addition, variations in individual parts such as a developing sleeve cause a difference in developing characteristics between machines. Further, the scattering of the toner line image generated when the toner image on the photosensitive member is transferred to the transfer material is also easily influenced by environmental conditions.

[0009] Further, there is variation in the laser drive circuit that controls the laser characteristics and the current supplied to the laser, and therefore, the rising speed of the laser also varies. These may eventually cause variations in printer characteristics. However, measuring all the characteristics of each laser and variations in the laser drive circuit to adjust the current value leads to an increase in cost and an increase in manufacturing time.

Therefore, in the above conventional example, even in a system in which a gradation patch is printed on a photoreceptor, the density thereof is detected, and feedback control is performed to the main body, a line image extending in the main and sub scanning directions is obtained. Each line width is different,
As a result, the quality of a thin line image such as a character image or a design drawing may deteriorate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a simple control method in an electrophotographic image forming apparatus that performs a latent image by using a laser beam. Therefore, the line width of each line image extending in the main and sub-scanning directions is uniform, and the quality of a fine line image such as a character image or a design drawing is improved.

[0012]

An image forming apparatus and a control method therefor according to the present invention are configured as follows.

(1) A photoconductor, an exposure unit for scanning the photoconductor with light to form a latent image, and a developing unit for visualizing the latent image, wherein the scanning of the exposure unit with light is performed. A patch latent image composed of a plurality of line images extending in the direction and a patch latent image composed of a plurality of line images extending in a direction perpendicular to the scanning direction are formed on the photosensitive member.

(2) In the configuration of the above (1), there is provided a density detecting means for detecting the density of the patch latent image, and at least a charging means for the photosensitive member in accordance with the detection result of the density of the two types of patch latent images; Either the exposure means or the development means is controlled.

(3) In the above configuration (1) or (2), the exposure means is a laser.

(4) In the configuration of (3), a laser drive circuit for controlling the amount of laser drive current in the non-image area is provided.

(5) A method for controlling an image forming apparatus having a photoreceptor, an exposing unit and a developing unit, comprising: a patch latent image composed of a plurality of line images extending in a scanning direction of light of the exposing unit; Forming a patch latent image composed of a plurality of line images extending in a direction perpendicular to the direction on the photoconductor, detecting the density of the patch latent image, and at least charging means and exposure means for the photoconductor in accordance with the detection result , One of the developing means is controlled.

(6) In the configuration of the above (5), the exposure means is a laser, and the amount of laser drive current in the non-image portion is controlled in accordance with the detected densities of the two types of patch latent images.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention forms patch latent images in the scanning and sub-scanning directions, detects the density of those patch latent images, obtains the line width ratio between the vertical line and the horizontal line, and determines the line width based on the magnitude result. Process control is performed so as to be equally optimized.

(First Embodiment) FIG. 1 is a sectional view showing the structure of a main part of an image forming apparatus according to a first embodiment of the present invention. In the figure, 1 is 300 clockwise for 1 second in the drawing.
A photosensitive member 2 mainly made of drum-shaped amorphous silicon which is driven to rotate at a peripheral speed of mm is a primary charging device (charging means) for charging the surface of the photosensitive member.

Reference numeral 3 denotes a laser driving circuit which drives a semiconductor laser (exposure means) 31 to emit light corresponding to an image binarized at a resolution of 600 DPI by an error diffusion process in an image processing device (not shown). The light emitted from the semiconductor laser 31 is collimated by a collimator lens (not shown), and the surface of the photoconductor is scanned in the axial direction of the photoconductor 1 by a polygon mirror (not shown).

The size of a spot of light emitted from the semiconductor laser 31 on the surface of the photoreceptor 1 (portion of 1 / e 分布 2 or more of the peak size in the light intensity distribution) is 45 μm in the main scanning direction. , In a sub-scanning direction of 50 μm.

The developing device (developing means) 4 attaches a positively charged toner to the portion exposed by the semiconductor laser 31, so that the latent image on the surface of the photoconductor is visualized (reversal phenomenon) and transferred. The toner image is transferred to the sheet material by the separating device 5. The toner image transferred to the sheet material is heated and pressed and fixed by the fixing device 8.

Reference numeral 6 denotes a cleaning device for collecting untransferred toner on the photoconductor, and the remaining electrostatic latent image on the photoconductor is
It is removed by irradiating light with the pre-exposure device 7. Reference numeral 9 denotes a surface potential sensor for detecting the surface potential of the photoconductor in the vicinity of the developing device. Numerical values of the surface potential described below are all values detected by the surface potential sensor 9.

A reflected light amount sensor (density detecting means) 10 detects the density of the patch image developed on the photosensitive member.
And an LED and a light receiving device. The photoconductor surface potential in the vicinity of the developing device when not exposed at all by the semiconductor laser 31 is Vd, and the photoconductor surface potential corresponding to a solid black portion (image area), that is, the semiconductor laser 3
The potential when 1 is completely emitted is V1 and the current value at this time is I1. The photoconductor surface potential corresponding to the solid white portion (non-image area), that is, the potential when a current much lower than the solid black portion exposure is supplied to the semiconductor laser 31 is Vw, and the current value at this time is Id. And

In the image forming apparatus of this embodiment, Vw
Is set to 400V, and the target value of V1 is set to 50V. The developing bias applied to the developing roller of the developing device 4 has a DC component of 280 V, and the AC component has a rectangular wave of 1000 V.

In general, the current-light intensity characteristic of a semiconductor laser sharply changes from a threshold value Ith of a certain drive current as shown in FIG. That is, the laser resonates in response to an increase in the current value at Ith or more, and a laser beam is emitted. However, the laser does not resonate at a current amount less than Ith, and emits light only by coupling of excited electrons. .

FIG. 3 shows that the semiconductor laser is driven for about 15 ns for one pixel.
FIG. 3 is a diagram schematically showing a rise time response characteristic of light intensity when a current is applied only for a period of time, that is, when a current is applied only for Ic in FIG. 2 from time t0 to time t1. The solid line in FIG. 7 shows the rising characteristic from the current Id = I0 = 0 when the current Id is Id in FIG. 2, and the laser emission is obtained by setting Id to Ib close to Ith. Indicates that the rising response of the signal becomes faster.

When the rising response of the laser emission is slow, the line width of the line extending in the sub-scanning direction becomes narrow, and when the response is fast, the line width of the line extending in the sub-scanning direction becomes large. That is, the line width in the sub-scanning direction can be controlled by changing the magnitude of Id. If this Id value is uniquely set to an optimum value, the line widths in the main and sub-scanning directions can be kept equal.
The ratio of the line width in the main / sub-scanning direction changes depending on the difference between the airframes and environmental conditions.

Adjusting the current value by measuring all the rising characteristics of each laser while observing the waveform with an oscilloscope or the like leads to an increase in cost and an increase in manufacturing time. Therefore, it is desirable to control the line width by a simple method with as little frequency as possible for each aircraft.

This embodiment solves this problem. Next, a line width control method according to the embodiment shown in the flowchart of FIG. 4 will be described. The control process shown in this flowchart is executed according to a program stored in advance by a CPU (not shown) of the control unit of the apparatus in FIG. 1. First, a predetermined initial current value Id = Ido The potential control of Vw and VL is performed (S1). This Ido
The value is lower than the typical value of Ith (about 35 mA) of the laser used. In addition, the Ido is set to 20 mA. In the apparatus used in the present embodiment, the line width of one dot line extending in the main scanning direction and the sub-scanning direction in the initial state of the apparatus at room temperature of 22 ° C. and 55% of humidity are used. This is the condition when the line widths of the one-dot lines extending to the same length are substantially equal.

Naturally, such numerical values may be determined according to the type of laser used, the type of laser driver (drive circuit), the performance of the developing device, and the like. Generally, Vw is controlled by controlling a current flowing through the primary charging device 2 or a voltage applied to the grid, and VL is controlled by controlling a laser supply current amount (Ic in FIG. 2) during laser emission. However, details are omitted here.

Next, as shown in FIG. 5A, a latent image patch a which is repeated at intervals of one dot line and three dot lines extending in the main scanning direction is formed, and this is (S2). The size of the patch a may be any size as long as the reflected light amount can be read by the reflected light amount sensor 10 with necessary accuracy. In this embodiment, the size is 3 cm × 3 cm.
And

Then, the density of the patch a is read by the reflected light amount sensor 10 (S3). The reflected light quantity is log-converted to obtain the density, and the density does not need to be corrected for control. However, the density is described here for the sake of simplicity.

Next, the density (Da) of the patch a is 0.28
It is determined whether it is within the range of ~ 0.32 (S
4) If it does not seem to be contained, the developing bias DC component is increased from 280 V to (0.3-density of patch a) × 250.
Increase by (v) (S5). Then, the patch output, the density measurement, and the developing bias adjustment are repeated until the density of the patch a falls within the range of 0.28 to 0.32.

When the density of the patch a falls within the range of 0.28 to 0.32, one dot line extending in the sub-scanning direction as shown in FIG. Is repeated to form a latent image patch b, and the latent image patch b is sequentially developed by the developing device 4 (S6). Then, the density of the patch b is read by the reflected light amount sensor 10 (S
7) It is determined whether or not the density (Db) of the patch b is within the range of 0.28 to 0.32 (S8). If it does not, the Id is increased from 20 mA to (0.3-D
b) Increase by × 100 mA (S9). Then, the patch output, the density measurement, and the Id adjustment are repeated until the density of the patch b falls within the range of 0.28 to 0.32.

In this manner, the line widths of the line images extending in the main and sub scanning directions are equal by a simple control method without variation between apparatuses, and the quality of a fine line image such as a character image or a design drawing can be reduced. Can be improved. In this embodiment, both the density of the patch a and the density of the patch b are in the range of 0.28 to 0.
Although it is assumed that the density falls within the range of 32, this density range may be determined according to the characteristics of the toner and the characteristics of the machine.

(Second Embodiment) In the above-described first embodiment, the embodiment in which the density of the patch on the photoreceptor is detected by the reflection light amount sensor 10 has been described. Often do not have 10. Therefore, in a second embodiment, an example of an apparatus in which a user outputs a test patch and manual line width adjustment is performed by the user will be described. The configuration of the device is basically the same as that shown in FIG. 1 of the first embodiment, and the only difference is that in this embodiment, the reflected light amount sensor 10 is not provided. Is omitted.

Next, a line width control method according to this embodiment will be described. FIG. 6 is a diagram illustrating a test pattern for setting a developing bias according to the present embodiment, and FIG. 7 is a diagram illustrating a test pattern for equalizing line widths in the main scanning and sub scanning directions.

First, potential control of Vw and VL is performed by setting a predetermined initial current value to Id = Ido. Here, the Ido is set to 20 mA, which is the line width of one dot line extending in the main scanning direction and the sub-scanning in the initial state of the apparatus, the room temperature of 22 ° C. and the humidity of 55% in the apparatus used in this embodiment. This is the condition when the line width of one dot line extending in the direction becomes substantially equal. In general, Vw is controlled by controlling a current flowing through the primary charging device 2 or a voltage applied to the grid, and VL is controlled by controlling a laser supply current amount (Ic in FIG. 2) during laser emission. However, details are omitted here.

Next, a test pattern A as shown in FIG. 6A is output. The test pattern A includes A1
6B is developed with a developing bias Vdc component of 280 V, and the portions A2 to A4 are developed with a pattern as shown in FIG.
The c component is developed at 270, 280, and 290 V, respectively.

Then, the user selects which patch is closest to the density of A1, and inputs the result from an operation unit (not shown) or the like. Thereafter, the developing bias is set to the bias when developing the patch selected by the user.

Next, a test pattern B as shown in FIG. 7A is output. The test pattern B includes B1
6B, the pattern shown in FIG. 6C is printed on the left half, and the pattern shown in FIG. 7B is printed on the right half at Id = 10 mA, 20 mA, and 30 mA, respectively. .

The user selects which patch pair has the closest density of the left and right patches, and inputs the result from an operation unit (not shown) or the like. Then, Id is set to Id when the patch pair selected by the user is printed.

As described above, even in this embodiment, the line width of each line image extending in the main and sub-scanning directions is equal by a simple control method without variation between devices, and a thin line such as a character image or a design drawing is obtained. The image quality can be improved.

Although the first and second embodiments assume a printer, any digital copying machine having an original reading means and having the function of replacing the original reflected light with an image signal can be used. Alternatively, the density of the patch output may be detected by the document reading means, and the line width control as described in the first and second embodiments may be performed.

[0047]

As described above, according to the present invention,
With a simple control method, there is no variation between apparatuses, the line widths of the line images extending in the main and sub scanning directions are equal, and the quality of thin line images such as character images and design drawings can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing typical characteristics of current and light intensity in a semiconductor laser.

FIG. 3 is a diagram showing a time response characteristic when a semiconductor laser emits light for one pixel;

FIG. 4 is a flowchart illustrating a line width control operation according to the first embodiment;

FIG. 5 is a diagram showing a patch pattern according to the first embodiment;

FIG. 6 is a diagram showing a test pattern for setting a developing bias according to a second embodiment.

FIG. 7 is a diagram showing a test pattern for equalizing line widths in the main scanning and sub scanning directions according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Primary charging device 3 Laser drive circuit 4 Developing device 5 Transfer / separation device 6 Cleaning device 7 Pre-exposure device 8 Fixing device 9 Surface potential sensor 10 Reflected light amount sensor (density detection means) 31 Semiconductor laser (exposure means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H003 BB11 CC01 DD03 DD08 DD14 2H027 DA02 DA10 DB01 DE02 DE07 EA01 EA02 EA05 EC03 EC06 EC07 EC10 ED02 ED07 2H076 AB02 AB09 AB12 AB16 DA07 DA14 2H077 AD36 DA04 DA08 DA47 DA63 DB08 GA17

Claims (6)

[Claims] An image forming apparatus comprising: a photosensitive member; an exposure unit configured to scan the photosensitive member with light to form a latent image; and a developing unit configured to visualize the latent image. An image forming apparatus for forming, on a photoreceptor, a patch latent image composed of a plurality of linearly extending line images and a patch latent image composed of a plurality of linearly extending line images in the scanning direction. And a density detecting unit for detecting the density of the patch latent image, wherein at least one of the charging unit, the exposing unit, and the developing unit of the photoconductor is determined according to the detection result of the density of the two types of patch latent images. The image forming apparatus according to claim 1, wherein the control is performed. 3. An image forming apparatus according to claim 1, wherein said exposure means is a laser. 4. The image forming apparatus according to claim 3, further comprising a laser drive circuit for controlling a laser drive current amount in the non-image portion. 5. A method for controlling an image forming apparatus having a photoreceptor, an exposure unit, and a development unit, comprising: a patch latent image including a plurality of line images extending in a scanning direction of light of the exposure unit;
A patch latent image composed of a plurality of line images extending in a direction perpendicular to the scanning direction is formed on the photoconductor, the density of the patch latent image is detected, and at least a charging unit of the photoconductor is detected according to the detection result. A control method for an image forming apparatus, wherein one of an exposure unit and a development unit is controlled. 6. An apparatus according to claim 5, wherein said exposure means is a laser, and controls an amount of laser drive current in a non-image portion in accordance with the detected densities of the two types of patch latent images.
The control method of the image forming apparatus described in the above.