JPH0792749A - Device and method for forming image - Google Patents

Abstract

PURPOSE:To provide a device and a method for forming images, in which laser resolution is varied according to the image formation mode selected, so that good images can be obtained in all of the modes. CONSTITUTION:When laser resolution is changed to 400 or 300 dpi by the control of a copy-mode designating key or a print-mode designating key which are mode selection means, the laser power of a semiconductor laser generator 42, the surface potential (V0) of a photoconductor drum 50, and the developing bias (VB) of the developing roller 54a of a developing unit 54 are changed to respective appropriate values by a CPU serving as variation means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method capable of selecting a copy mode which is a first image forming mode and a printer mode which is a second image forming mode.

[0002]

2. Description of the Related Art Conventionally, in a digital image forming apparatus capable of selecting a copy mode and a printer mode, there is a method in which the laser resolution of an exposure device is switched to 400 dpi in the copy mode and 300 dpi in the printer mode according to the needs of the user.

However, in the prior art, even if the resolution of the laser is changed according to the image forming mode, the laser power of the exposure device, the surface potential (V _O ) of the photoconductor as the image carrier, and the developing bias of the developing device. Image formation is performed without changing (V _B ).

[0004]

As described above, in the conventional digital image forming apparatus capable of changing the laser resolution, even if the laser resolution is changed according to the image forming mode, the laser power and the surface of the photosensitive member are changed. Image formation was carried out without changing the potential (V _O ) and the developing bias (V _B ) of the developing device.

However, the proper values of the laser power, the photosensitive member surface potential, and the developing bias of the developing device for obtaining a good image differ depending on the resolution of each laser.
well known.

Therefore, the conventional method has a problem in that a good image cannot be obtained at all laser resolutions. The present invention has been made based on the above circumstances, and an object thereof is to change the laser resolution according to the selection of the image forming mode,
An image forming apparatus and an image forming method capable of obtaining a good image in each mode.

[0007]

As a first image forming apparatus capable of solving the problems, the present invention controls the number of revolutions of the light deflecting means without changing the laser beam diameter and the peripheral speed of the image carrier. In the image forming apparatus including the exposure unit that changes the laser resolution to the first resolution and the second resolution, the first image can be selected from the first image forming mode and the second image forming mode. Mode selecting means for selecting a forming mode and a second image forming mode, and resolution switching means for switching the laser resolution of the exposing means to the first resolution or the second resolution according to the mode selection by the mode selecting means, The laser power, the surface potential of the image bearing member, and the developing bias are changed to appropriate values according to the resolutions switched by the resolution switching unit. It is obtained by the configuration that.

Further, as the second image forming apparatus, a charging means for charging the surface of the image carrier and an electrostatic latent image by irradiating the surface of the image carrier charged by the charging means with a laser beam are formed. Exposure means for forming, developing means for developing the electrostatic latent image on the image carrier formed by the exposure means, mode selecting means for selecting the first image forming mode and the second image forming mode In the image forming apparatus including the above, the resolution switching means for switching the laser resolution of the exposure means to the first resolution or the second resolution according to the mode selection by the mode selection means, and the resolution switching means for switching the resolution. The laser power of the exposing unit, the surface potential of the image carrier by the charging unit, and the developing bias of the developing unit are changed to appropriate values according to the resolutions Is obtained by a provided to become a configuration and changing means that.

Further, as an image forming method, in the image forming method capable of selecting the first image forming mode and the second image forming mode, a mode for selecting the first image forming mode and the second image forming mode. The selection step, the resolution switching step of switching the laser resolution of the exposure means to the first resolution or the second resolution according to the mode selection in the mode selection step, and the laser according to the resolution switched by the resolution switching step. And a switching step for changing the power, the surface potential of the image carrier, and the developing bias to appropriate values.

[0010]

According to the above-mentioned image forming apparatus and image forming method, when the laser resolution is changed according to the image forming mode, the laser power, the surface potential of the photosensitive member, and the developing bias of the developing device are adjusted to appropriate values. Since it is changed, it is possible to obtain a good image in each mode.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a digital image forming apparatus 2. The image forming apparatus 2 includes an apparatus body 3
The image reading unit 4 and the image forming unit 6 are integrally provided therein.

The image reading section 4 is a document table 10 on which an object to be read, that is, a document D is placed, a size plate 10a arranged at one end of the document table 10 and indicating a position where the document D should be placed, and The original document holder 12 is formed so as to be openable and closable with respect to the original document table 10 and allows the original document D placed on the original document table 10 to come into close contact with the original document table 10.

Inside the document table 10 (below), an illumination lamp 22 for illuminating the document D placed on the document table 10 and an illumination lamp
A reflector 24 that collects the illumination light generated from 22 onto the document D,
Further, the first carriage 20 that reflects the reflected light from the document D toward the second carriage 30 is arranged.

The first carriage 20 incorporates a first mirror 26 that bends the reflected light from the document D. The first carriage 20 is arranged so as to be movable in parallel with the document table 10,
It is moved in parallel along the document table 10 by a pulse motor (not shown) via a toothed belt (not shown).

The second carriage 30 includes the first carriage 20.
The second mirror 32 and the third mirror 34, which sequentially bend the reflected light from the document D that is bent via the first mirror 26, are arranged at right angles to each other. The second carriage 30 is driven by the first carriage 20 by a toothed belt (not shown) that drives the first carriage 20, and moves to the document table 10 at a speed half that of the first carriage 20. Moved in parallel along.

Below the first carriage 20, in the plane including the optical axis of the light reflected by the second carriage 30, it is movably formed by a driving mechanism (not shown).
While focusing the reflected light from the second carriage 30, the moving lens itself causes the reflected light to form an image at a desired magnification, and the reflected light focused through the lens 36. It has a CCD sensor 38 that performs photoelectric conversion and outputs an electric signal (the image of the document D is converted) to an image memory 78 described later.

The image forming section 6 includes a light source, that is, a semiconductor laser oscillator 42, and changes the intensity of the light from the semiconductor laser oscillator 42 in accordance with the image information of the document D read through the image reading section 4. It has an exposure device 40 that is directed toward a photosensitive drum 50 as an image carrier described later.

The exposure device 40 gives a focusing property to the laser beam LB generated from the semiconductor laser oscillator 42 and converts it into a laser beam LB having a substantially circular cross-sectional shape via a first lens and a first lens (not shown). A polygon mirror 44 as a light deflecting means for deflecting the light converted into the laser beam LB having a circular cross-sectional shape along the axial direction of the photosensitive drum 50 described later, and the deflected laser beam LB the photosensitive drum described later. In order to sequentially form images at desired positions on the photosensitive drum 50, the deflection angle of the laser beam LB and the photosensitive drum 50
The second lens 46 for matching the distance from the optical axis to the position where the beam is to be imaged, and the laser beam L
It includes a mirror 48 that folds B towards the photosensitive drum 50.

Further, a photosensitive drum 50 as an image carrier having a conductive support, a photoconductive layer and an insulating layer as a basic structure is arranged substantially at the center of the image forming section 6. Around the photosensitive drum 50, a pre-exposure device 51 as a residual charge removing unit for irradiating the photosensitive drum 50 with light along the rotation direction (direction of arrow A) to remove residual charges, and the photosensitive drum.
Charging device 5 as a charging means for uniformly charging the surface of 50
2. Development as a developing means for developing the electrostatic latent image formed on the surface of the photosensitive drum 50 by irradiating the laser beam LB from the exposure device 40 with a two-component developer composed of toner and carrier A device 54, a transfer device 56 as a transfer unit for transferring the toner image formed on the photosensitive drum 50 onto a sheet (copy sheet, OHP sheet, etc.) P as a transfer-target material fed from a sheet cassette 55, A peeling device 57 as a peeling unit for peeling the paper P on which the toner image is transferred from the photosensitive drum 50, and a cleaner device 58 as a cleaning unit for scraping off the toner remaining on the photosensitive drum 50 are sequentially arranged. .

A paper cassette 55 is provided in the main body 3 of the apparatus.
The paper P fed from the paper feed roller 59 or the paper P fed from the manual feed tray 60 via the paper feed roller 61 is fed between the photosensitive drum 50 and the transfer device 56. A sheet conveyance path 64 is formed on the left side surface of the apparatus main body 3 to lead to a sheet discharge tray 63 through an image transfer section 62 formed therebetween.

On the upstream side of the image transfer portion 62 of the paper transport path 64, the front end of the paper P is aligned and the photosensitive drum is
An aligning roller pair 65 for feeding the paper P to the image transfer section 62 in time with the image forming timing of 50 and an aligning roller pre-switch provided near the upstream position of the aligning roller pair 65 for detecting the fed paper P 66 is provided.

Further, on the downstream side of the image transfer portion 62 of the paper transport path 64, a transport device 67 for transporting the paper P separated from the photoconductor drum 50 by the separation device 57, and an electrostatic charge transferred to the paper P. The fixing device 68 that melts the toner image in a state of being adhered by heating and fixes it on the paper P, and the pair of discharge rollers 69 that discharges the paper P on which the toner image is fixed onto the paper discharge tray 63. Is provided.

As shown in FIGS. 2 and 3, various data (and control signals) for copying operation and reading or outputting image data can be input to the front portion of the upper surface of the apparatus main body 3. An operation panel 18 is provided.

On the operation panel 18, a start key 18a for outputting a copy or print start signal in response to an input from the user, "0" used for the number of copies, copy magnification, etc.
~ Numerical key for outputting numerical signal corresponding to "9"
18b, the data at the input stage can be returned to "0", and the stop key 18c that can interrupt the already started copy operation or print operation, interrupt all operations and initialize the operation of the image forming apparatus 2 (initial) An all clear key 18d for returning to the state, a display section 18e for displaying the set number of copies, a copy magnification, etc., a copy mode designating key 18f for selecting a copy mode which is the first image forming mode, A display unit that lights up to indicate which one of the print mode designating key 18g, the copy mode designating key 18f and the print mode designating key 18g, which is a mode selecting means for selecting the printer mode which is the second image forming mode, is pressed. 18h, 18j, etc. are arranged.

FIG. 4 shows a control system of the image forming apparatus 2. The main control section 70 for controlling the image reading section 4 and the image forming section 6 includes a CPU 72 as a main control apparatus which is a control means.
A ROM 74 connected to the CPU 72 and storing rules for operating the image forming apparatus 2, numerical data input from the operation panel 18, for example, numerical data such as the number of copies and copying magnification, and the numeric key 18b are pressed. The RAM 76 that stores the number of times, that is, the number of numerical data, and the image memory 78 that temporarily stores the image signal output from the CCD sensor 38 and converted into a digital signal through an A / D conversion circuit 92a described later. Etc. are included.

The image data stored in the image memory 78 is
It is converted into binary data via a signal conversion unit 92 described later. Further, the CPU 72 includes a high voltage transformer (not shown) for supplying a desired voltage to the charging device 52 and the transfer device 56, a switch group and a solenoid for detecting the position of the paper P or the remaining amount in the cassette. A motor driver for urging a driving unit 80 for urging the mechanism unit, a motor for urging the first and second carriages 20 and 30, the photoconductor drum 50, the developing device 54, the conveying device 67, and the like. 82,
A lamp control unit 84 for turning on the illumination lamp 22, the heater lamp 68a of the fixing device 68, and the like are connected.

The CPU 72 is further provided with an internal interface 90 for causing the CPU 72 to read numerical data input from the operation panel 18, and binary data capable of outputting the image data stored in the image memory 78 by the image forming section 6. An image signal different from the image signal from the signal converting unit 92 and the image reading unit 4 for converting into data, for example, from an external device for using the image forming unit 6 as a printer device, that is, a host computer or a word processor not shown. An external interface 94 for inputting the image signal of, and a timer 98 for counting a time limit defined according to various inputs, such as an input waiting time in a plurality of operation modes, are connected.

The signal converter 92 converts the analog image signal output from the CCD sensor 38 into a digital signal A.
A / D conversion circuit 92a, a resolution conversion circuit 92b for matching image data output to the CCD sensor 38 with a resolution unique to the CCD sensor 38, and an A / D conversion circuit 92.
The signal converted into a digital signal through a is C caused by the individual error of the CCD sensor 38 and the ambient temperature change.
Shading correction circuit 92 for correcting the fluctuation of the threshold level with respect to the output signal from the CD sensor 38.
c, the image data passing through the shading correction circuit 92c is separated into, for example, a luminance signal and a color difference signal, and then subjected to filtering, trimming, masking, edge enhancement or character identification, and an image quality improving circuit 92d and an image quality improving circuit. The document D includes a binarization circuit 92e that binarizes the light from the laser beam LB of the exposure device 40 based on the image data output from the document 92d.
Image is converted into a binary print signal.

The CPU 72 includes an exposure device 40 and a charging device.
As shown in FIG. 2, the CPU 72, which is connected to the developing device 54 and the developing device 54, will be described later according to the copy mode selection which is the first image forming mode by the copy mode designation key 18f which is the mode selecting means. Then, the laser resolution of the exposure device 40 is switched to the first resolution (400 dpi), and as will be described later in accordance with the printer mode selection which is the second image forming mode by the print mode designation key 18g as shown in FIG. The resolution switching means 100 for switching the laser resolution of the exposure device 40 to the second resolution (300 dpi) is also used.

The laser resolution is switched by controlling the rotation speed of the polygon mirror 44, which is the light deflecting means, without changing the diameter of the laser beam LB and the peripheral speed of the photosensitive drum 50. The first resolution (400
It can be changed to dpi) and the second resolution (300dpi).

Further, the CPU 72 controls the resolution switching means 100.
Operation panel according to the resolution switched by
When the copy mode designation key 18f or the print mode designation key 18g of 18 is operated, the laser power of the semiconductor laser oscillator 42 of the exposure device 40, the surface potential of the photoconductor drum 50 by the charging device 52, and the Changing means for changing the developing bias of the developing device 54 to an appropriate value
It is designed to double as 110.

Next, the operation of the image forming apparatus 2 will be described with reference to FIG. First, the operation of the charging device 52 causes the photosensitive drum
The surface potential of 50 is uniformly charged. After that, the semiconductor laser oscillator 42 of the exposure device 40 oscillates based on the image information, is modulated according to an input signal to a modulator (not shown), and is scanned by a polygon mirror 44 to form an imaging lens.
The laser beam LB is applied to the surface of the photosensitive drum 50 via 36. As a result, the surface potential of the photoconductor drum 50 irradiated with the laser beam LB is optically attenuated and an electrostatic latent image is formed.

On the other hand, a constant bias voltage is applied to the developing roller 54a in the developing device 54, and when the photosensitive drum 50 carrying an electrostatic latent image comes into contact with the developing roller 54a, the photosensitive drum 50a. Due to the potential difference between the developing roller 54a and the developing roller 54a, the toner magnetically adhered to the developing roller 54a adheres to the laser-irradiated portion on the surface of the photosensitive drum 50.

As a result, the electrostatic latent image on the surface of the photosensitive drum 50 is visualized. After that, the toner image on the photosensitive drum 50 is transferred onto the paper P sent to the image transfer portion 62 by the transfer device 56.
Is transferred electrostatically.

The sheet P having the toner image transferred thereto is sent to a fixing device 68 and subjected to a toner image fixing process. The apparatus applied to the present invention has a laser resolution of 30 as described above.
It can be switched between 0dpi and 400dpi.

Switching between 300 dpi and 400 dpi is performed by changing the diameter of the laser beam LB (main scanning 70 μm, sub-operation 70 μm),
Pulses can be obtained by changing the rotation speed of the polygon motor 44A, which is the driving source of the polygon mirror 44, to 18897,637 rpm at 300 dpi and 250196,850 rpm at 400 dpi without changing the peripheral speed (160.8 mm / sec) of the photosensitive drum. It is controlled by changing the width.

FIG. 5 shows a diagram of 1 dot in the above control. In FIG. 5, (a) shows the case of 400 dpi, 6
It is settled within the area of 3.5 μm × 63.5 μm. (B) shows the case at 300 dpi, 84.6 μm x 8
It is settled within the area of 4.6 μm.

FIG. 6 shows laser resolutions of 300 dpi and 400.
The changes in resolution and fine line reproducibility of vertical and horizontal 1 dot pair lines in dpi are shown with laser power. It can be seen that the laser power (appropriate value) for obtaining a good image is different between the laser resolutions of 300 dpi and 400 dpi.

The appropriate value for each is 400 dpi.
About 5-6 nJ / mm ² , sometimes about 300 dpi, about 6.
It is 5 to 8.5 nJ / mm ² . FIG. 7 shows the relationship between laser power and image density at a laser resolution of 400 dpi, and FIG. 8 shows the relationship between laser power and image density at a laser resolution of 300 dpi.

At room temperature and humidity, the laser resolution is 300 dp.
The image density is the maximum for both i and 400 dpi. At low temperature and low humidity, the image density is extremely low due to development characteristics and the like, so both 300 dpi and 400 dpi are low.

At this low temperature and low humidity, the image density at 300 dpi is 400 dpi even if 400 dpi is within the allowable range.
Much lower than that (indicated by the solid line position). And it will be in the allowable range. This is because the spot diameter of the 1-dot laser beam LB is the same at 300 dpi and 400 dpi, but the size of 1 dot changes (see FIG. 5), and a gap is formed, which is a decrease.

FIG. 9 shows the image density (MA) when the developing bias (V _B ) is increased at a low temperature and low humidity of 300 dpi.
X time) is shown. As you can see from this figure, 300dpi
It can be seen that even when the temperature is low and the humidity is low, the image density becomes equivalent to 400 dpi which is within the allowable range by changing the developing bias (V _B ).

Therefore, the developing bias (V _B ) is changed so that the image density becomes high. At this time, because of the relationship with fog,
To the photosensitive member surface potential and (V _O) the difference between the developing bias (V _B) constant, raising the surface potential of the photosensitive member at the same value as the developing bias _{(V B) (V O)} | V O -V B | Was constant.

At 400 dpi, V _O : -650 V, V _B :
-450V, but at 300dpi, V _O : -700
V, V _B : 400dpi by changing to -500V
It was almost the same as (at low temperature and low humidity). From the above results (shown by the broken line position in FIG. 8), appropriate values of the laser power, the developing bias (V _B ) and the photoconductor surface potential (V _O ) are different at different laser resolutions. I can't get a good image.

Therefore, in the apparatus of the present invention, when changing the laser resolution, the laser power, the developing bias (V _B ), and the photoconductor surface potential (V _O ) are set to appropriate values at the respective laser resolutions. It is supposed to be changed to.

Next, referring to FIG. 10, one sheet of paper P
Power and development bias (V
_B ) and the method of setting the photosensitive member surface potential (V _O ). However, there are two types of laser resolution, 300dpi and 400dpi.

In step 1 (S ₁ ), the laser power, developing bias (V _B ) and photoconductor surface potential (V _O ) are set for 300 dpi, and the polygon motor 44A is also set to 300.
Rotate for dpi.

Step 2 (S ₂ ) is a standby state. In step 3 (S ₃ ), the laser resolution is set to 30.
0dpi or set to 400dpi polygon motor speed, laser power, the developing bias (V _B), and photosensitive member surface potential (V _O) is set to the appropriate value of the set resolution, in step 4 (S ₄₎ Printing is performed. The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0049]

As described above, according to the image forming apparatus and the image forming method of the present invention, when the laser resolution is changed according to the image forming mode such as the copy mode and the printer mode, the laser power, Since the surface potential of the photoconductor and the developing bias of the developing device are changed to appropriate values, it is possible to obtain an excellent image in each mode.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an image forming apparatus according to an embodiment of the present invention.

2 is a schematic partial plan view of an operation panel provided in the image forming apparatus shown in FIG.

FIG. 3 is a schematic partial plan view of an operation panel provided in the image forming apparatus shown in FIG.

4 is a block diagram schematically showing a control system incorporated in the copying machine shown in FIG.

FIG. 5 is an explanatory diagram showing the size of 1 dot of 400 dpi and 300 dpi.

[Figure 6] Vertical at laser resolution of 300dpi and 400dpi,
Explanatory drawing which shows the change with the laser power about the resolution of a 1 dot horizontal line, and the fine line reproducibility.

FIG. 7 is an explanatory diagram showing the relationship between laser power and image density at a laser resolution of 400 dpi.

FIG. 8 is an explanatory diagram showing the relationship between laser power and image density at a laser resolution of 300 dpi.

FIG. 9 is an explanatory diagram showing the image density when the developing bias is increased at a low temperature and low humidity of 300 dpi.

FIG. 10: Laser power until printing on one sheet of paper,
6 is a flowchart showing a method for setting a developing bias and a photosensitive member surface potential.

[Explanation of symbols]

2 ... Image forming device, 3 ... Device body, 4 ... Image reading unit, 6
... image forming unit, 10 ... document placing table, 18 ... operation panel, 18a
… Print (start) key, 18b… Numeric key, 18c…
Stop key, 18d ... All clear key, 18e ... Display section, 18f ... Copy mode designation key (mode selection means), 18
g… Print mode designation key (mode selection means), 40…
Exposure device (exposure means), 42 ... Semiconductor laser oscillator (light source), 44 ... Polygon mirror (light deflection means), 44A ... Polygon motor, 50 ... Photosensitive drum (image carrier), 52 ... Charging device (charging means) , 54 ... Developing device (developing means), 54a ...
Developing roller, 56 ... Transfer device (transfer means), 57 ... Peeling device (peeling means), 58 ... Cleaner device (cleaning means), 62 ... Image transfer section, 64 ... Paper transport path, 65 ... Aligning roller pair, 66 … Aligning roller front switch, 68
... fixing device, 70 ... main control unit, 72 ... CPU (control means),
74 ... ROM, 76 ... RAM, 78 ... Image memory, 90 ... Internal interface, 92b ... Resolution conversion circuit, 94 ... External interface, 100 ... Resolution switching means, 110 ... Changing means, P ... Paper (transferred material).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03G 15/06 21/00 384 2107-2H

Claims (3)

[Claims] 1. An exposure unit for changing a laser resolution between a first resolution and a second resolution by controlling the number of revolutions of a light deflecting unit without changing a laser beam diameter and a peripheral speed of an image carrier. An image forming apparatus having the first image forming mode and the second image forming mode, the mode selecting unit selecting the first image forming mode and the second image forming mode, and the mode selecting unit. Resolution switching means for switching the laser resolution of the exposing means to the first resolution or the second resolution according to the mode selection by the means, and the laser power and the surface of the image carrier depending on the resolution respectively switched by the resolution switching means. An image forming apparatus comprising: an electric potential and a changing unit that changes the developing bias to an appropriate value. 2. A charging means for charging the surface of the image carrier, an exposing means for forming an electrostatic latent image by irradiating the surface of the image carrier charged by the charging means with a laser beam, and the exposing means. An image forming device comprising: a developing device for developing the electrostatic latent image formed on the image carrier by the developing device; and a mode selecting device for selecting the first image forming mode and the second image forming mode. In the apparatus, resolution switching means for switching the laser resolution of the exposure means to a first resolution or a second resolution according to the mode selection by the mode selection means, and the exposure according to the resolution switched by the resolution switching means. The laser power of the developing means, the surface potential of the image carrier by the charging means, and the changing means for changing the developing bias of the developing means to an appropriate value. Image forming apparatus characterized by. 3. An image forming method capable of selecting a first image forming mode and a second image forming mode, a mode selecting step of selecting the first image forming mode and the second image forming mode, A resolution switching step of switching the laser resolution of the exposure means to the first resolution or the second resolution in accordance with the mode selection in the mode selection step, and a laser power and an image carrier of the image carrier which are switched in the resolution switching step. An image forming method comprising: a switching step of changing the surface potential and the developing bias to appropriate values.