JP2001154426A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device of high image quality which obviates the occurrence of a photo-fatigue memory to an image plane by a light source of a density detecting sensor for regulating an image density and the image unevenness by the same. SOLUTION: The image forming device has an amorphous silicon photoreceptor, an electrostatic charging means for electrostatically charging the amorphous silicon photoreceptor, an image exposure means for subjecting the amorphous silicon photoreceptor to image exposure in accordance with image information, an erasing exposure means for erasing the electrostatic charging potential of the amorphous silicon photoreceptor surface, a density detecting sensor for detecting the image density of the prescribed toner image formed on the amorphous silicon photoreceptor to control image density and a control means for controlling the image density in accordance with the density information detected by this density sensor. The peak wavelength of the light source of the density detecting sensor described above is shorter than the peak wavelength of the erasing exposure means described above.

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 capable of preventing light fatigue memory of an amorphous silicon photoreceptor and preventing density unevenness caused by the light fatigue memory.

[0002]

2. Description of the Related Art In an image forming apparatus, erasing exposure means (hereinafter simply referred to as P
CL), and light irradiation from a light source such as an image exposure unit or a density detection sensor is performed on the photoconductor.
When the peak wavelength of each light source such as the light source of the density detection sensor is increased, electric charges of the surface potential are trapped as carriers in a deep portion of the photosensitive layer formed of amorphous silicon, and the erasing by the erasing exposure unit is insufficient. When the next charge is carried out as it is, new charges are difficult to be deposited on the trapped portion, the surface of the photoreceptor is not uniformly charged, and the previous history remains in the photo-fatigue memory, thereby causing density unevenness. May occur, which means that it is not preferable to use a concentration detection sensor having a light source having a long peak wavelength. In particular, as image formation speeds up, the time from erasing exposure to the next charge becomes shorter, and the recovery time of light fatigue is shortened, so that light fatigue memory is more likely to occur and the normal state is restored. The next image is formed without performing the above operation, and the location where the light fatigue memory is generated causes a phenomenon of density unevenness, and the image quality is remarkably deteriorated.

Conventionally, the peak wavelength of a PCL light source has been set to 600 to
What is specified as 700 nm is disclosed in
No. 7, and the peak wavelength of the PCL light source is 6
JP-A-61-183681 discloses that the peak wavelength of the image exposure means is set to be 700 nm or more, and that the light source is used to prevent the occurrence of light fatigue memory by the density detection sensor. Nothing mentions the effect of the wavelength.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and examines the relationship between the peak wavelengths between light sources that do not generate light fatigue memory, and finds conditions that do not cause light fatigue memory. Accordingly, an object of the present invention is to provide an image forming apparatus which does not cause density unevenness in an image to be formed.

[0005]

This object is achieved by any of the following technical means (1) to (11).

(1) Amorphous silicon photoreceptor, charging means for charging the amorphous silicon photoreceptor, image exposure means for exposing the amorphous silicon photoreceptor to image based on image information, and erasing the charged potential on the surface of the amorphous silicon photoreceptor Erasing exposure means, a density detection sensor for detecting the image density of a predetermined toner image created on the amorphous silicon photoreceptor to control the image density,
In an image forming apparatus having control means for controlling image density based on density information detected by the density detection sensor,
An image forming apparatus, wherein a peak wavelength of a light source of the density detection sensor is shorter than a peak wavelength of the erasing exposure unit.

(2) Amorphous silicon photoreceptor, charging means for charging the amorphous silicon photoreceptor, image exposure means for exposing the amorphous silicon photoreceptor to image based on image information, and erasing the charged potential on the surface of the amorphous silicon photoreceptor Erasing exposure means, a density detection sensor for detecting the image density of a predetermined toner image created on the amorphous silicon photoreceptor to control the image density,
In an image forming apparatus having control means for controlling image density based on density information detected by the density detection sensor,
The control unit controls turning on and off of a light source of the density detection sensor, and forms the predetermined toner image on the amorphous silicon photoconductor when detecting the image density of the predetermined toner image by the density detection sensor. An image forming apparatus for controlling lighting and extinguishing so as to detect an image density by turning on a light source of the density detection sensor only in a selected area.

(3) The control means controls the timing of turning on and off the light so that the spot of the light source of the density detection sensor enters the area of the predetermined toner image. The image forming apparatus as described in the above.

(4) Lighting and extinguishing are controlled so that the center of the spot of the light source of the density detecting sensor is located at a position inside a half of the spot diameter from an end of the predetermined toner image. The image forming apparatus according to (3), wherein a density of the predetermined toner image is detected.

(5) The light source according to any one of (2) to (4), wherein a peak wavelength of the light source of the density detection sensor is longer than a peak wavelength of the erasing exposure unit. Image forming device.

(6) Amorphous silicon photoreceptor, charging means for charging the amorphous silicon photoreceptor, image exposure means for exposing the amorphous silicon photoreceptor to image based on image information, and erasing the charged potential on the surface of the amorphous silicon photoreceptor Erasing exposure means, a density detection sensor for detecting the image density of a predetermined toner image created on the amorphous silicon photoreceptor to control the image density,
In an image forming apparatus having control means for controlling image density based on density information detected by the density detection sensor,
The image forming apparatus according to claim 1, wherein the predetermined toner image is a predetermined toner image formed in an axial direction of the amorphous silicon photoconductor and outside an image forming area.

(7) The image forming apparatus according to (6), wherein a peak wavelength of a light source of the density detecting sensor is longer than a peak wavelength of the erasing exposure unit.

(8) The image forming apparatus according to any one of (1) to (7), wherein the light source of the density detection sensor is a light emitting diode.

(9) The image forming apparatus according to any one of (1) to (8), wherein a peak wavelength of a light source of the density detection sensor is 700 nm or less.

(10) The image forming apparatus according to any one of (1) to (9), wherein the light source of the erasing exposure unit is a light emitting diode.

(11) The image forming apparatus according to any one of (1) to (10), wherein a peak wavelength of a light source of the erasing exposure unit is 700 nm or less.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of an image forming apparatus according to the present invention will be described first with reference to a schematic configuration diagram of the image forming apparatus shown in FIG. 1 and a schematic diagram showing each process arrangement around a photoreceptor in FIG. Give an explanation.

The image forming apparatus shown in FIG. 1 is a digital type image forming apparatus, and includes an image reading section A, an image processing section B (not shown), an image forming section C, and transfer paper transport as transfer paper transport means. It is composed of a section D.

An automatic document feeder for automatically transporting a document is provided above the image reading section A.
The original placed on the original 1 is moved by the original transport roller 12 to the original
The sheets are separated and conveyed, and the image is read at the reading position 13a. The document for which the reading of the document has been completed is discharged onto the document discharge tray 14 by the document conveying roller 12.

On the other hand, the image of the original when placed on the platen glass 13 is read out at a speed v of a first mirror unit 15 comprising an illumination lamp and a first mirror constituting a scanning optical system, and a V-shaped image is formed. Reading is performed by moving the second mirror unit 16 including the second mirror and the third mirror located at the speed v / 2 in the same direction.

The read image is formed on a light receiving surface of an image sensor CCD, which is a line sensor, through a projection lens 17. The line-shaped optical image formed on the image sensor CCD is sequentially photoelectrically converted into an electric signal (brightness signal), and then A
After performing / D conversion and performing processing such as density conversion and filter processing in the image processing unit B, the image data is temporarily stored in the memory.

In the image forming section C, an amorphous silicon photosensitive member 21 as an image forming unit,
Charger 22 as charging means, developing device 2 as developing means
3. Transfer unit 24 as a transfer unit, separator 25 as a separation unit, density detection sensor 28 for detecting the image density of a predetermined toner image (also referred to as a patch) 21A, cleaning unit 26, and PCL (precharge lamp) 27 Are arranged in the order of operation. Amorphous silicon photoreceptor 21
The photoreceptor (hereinafter sometimes simply referred to as a photoreceptor) is a photoreceptor formed by applying a photoconductive layer mainly composed of, for example, a silicon hydride compound as a photoconductive compound on a drum base, and is driven and rotated clockwise in the drawing. You.

After the rotating photoconductor 21 is uniformly charged by the charger 22, image exposure based on the recorded image signal called from the memory of the image processing unit B is performed by the image exposure unit 30. Will be The image exposing means 30, which is a writing means, uses a laser (not shown) as a light emitting light source. The optical path is bent by a reflecting mirror 32 through a rotating polygon mirror 31, an fθ lens (no sign), and a cylindrical lens (no sign), and main scanning is performed. The photoreceptor 21
Is subjected to image exposure at the position of Ao,
A latent image is formed by one rotation (sub-scan).

The latent image on the photosensitive member 21 is reversely developed by the developing device 23, and a visible toner image is formed on the surface of the photosensitive member 21. In the transfer paper transport section D, paper feed units 41 (A) and 41 (B) as transfer paper storage means in which transfer papers P of different sizes are stored below the image forming unit.
41 (C) is provided, and a manual paper feed unit 42 for performing manual paper feed is provided on the side, and the transfer paper P selected from any of them is guided along the transport path 40 by the guide roller 43. The transfer sheet P is temporarily stopped by a pair of registration rollers 44 that corrects the inclination and the deviation of the transfer sheet to be fed.
The toner image on the photoreceptor 21 is transferred to the transfer sheet P by the transfer unit 24 at the transfer position Bo, guided by the pre-transfer roller 43a and the transfer entry guide plate 46, and then discharged by the separator 25, and the transfer sheet P is exposed to light. The sheet is separated from the surface of the body 21 and transported to the fixing device 50 by the transport device 45.

The fixing device 50 has a fixing roller 51 and a pressure roller 52. By passing the transfer paper P between the fixing roller 51 and the pressure roller 52, the transfer paper P is heated and pressed to remove toner. Weld. The transfer paper P on which the toner image has been fixed is discharged onto the discharge tray 64.

Hereinafter, prevention of the density unevenness caused by the light fatigue memory caused by the density detection sensor 28 for detecting the image density which is a special feature of the present invention will be described in detail.

As described above, the case where the image density of the predetermined toner image (patch) 21A on the amorphous silicon photoreceptor 21 is detected by using the density detection sensor 28 to control the image density and the image density is controlled. In this case, a phenomenon called a light fatigue memory due to the light source of the concentration detection sensor 28 occurs. This is likely to occur due to long-wavelength light. Charges as carriers remain trapped deep in the photosensitive layer on the surface of the photoreceptor made of amorphous silicon, and the charges as carriers cannot be sufficiently erased as they are. It turned out to be a phenomenon. For example, if the peak wavelength is 550, 600, 7
When an experiment was performed using each of the LEDs of 00 and 800 nm, 5
At 50 nm, the occurrence of light fatigue memory is almost completely absent.
It has been experimentally confirmed that the occurrence of the photo-fatigue memory becomes increasingly significant as the thickness becomes 00, 700 and 800 nm.

Therefore, the present invention has made the following improvements as a countermeasure. First, the peak wavelength when a light emitting diode (hereinafter simply referred to as an LED) is used as the light source of the density detection sensor 28 is shorter than the peak wavelength when an LED is used as the light source of the PCL 27. I do. By doing so, the charge as a carrier partially trapped by the light source light of the density detection sensor 28 in the deep portion of the photosensitive layer is converted into the PCL 27 which is an erasing exposure unit which is a uniform exposure light having a longer wavelength. By giving uniform light fatigue to the whole, the apparent light fatigue memory can be erased, and density unevenness can be suppressed. That is, when a long wavelength light source irradiates a partial region of the surface of the photosensitive layer made of amorphous silicon, electric charge as a carrier from the surface potential remains trapped in a deep portion of the photosensitive layer. When charging for the next cycle is performed, the surface of the photoreceptor is not uniformly charged, and the surface potential of the portion where the charge as a carrier is trapped is reduced, so that a light fatigue memory appears. As a means for solving this, uniform trapping is performed including other portions other than the trapped portion. For this purpose, uniform exposure is performed using a PCL having a long wavelength peak wavelength, and the following process is performed. This is to lead to uniform charging of the cycle.

Second, as shown in the schematic diagram of FIG. 3, the lighting area of the LED as the light source of the density detection sensor 28 indicates the lighting position and the light-off position with respect to the patch 21A.
Only within the area of 1A. By doing so, it is possible to suppress the generation of carriers that cause light fatigue due to light absorption by the toner layer, and it is possible to suppress density unevenness without generating light fatigue memory. Density detection sensor 28
When the light emitting diode (LED) is used as the light source of the LED and the peak wavelength of the LED is longer than the peak wavelength of the LED when the light emitting diode (LED) is used as the light source of the PCL 27. Is desirable.

Third, as shown by E in the developed view of the photoconductor surface in FIG. 4, the lighting area of the LED as the light source of the patch 21A and the density detection sensor 28 is set at a position outside the image forming area in the axial direction of the photoconductor. Moved to By doing so, it is possible to suppress the generation of carriers that cause light fatigue in the image forming area, and it is possible to suppress density unevenness without generating light fatigue memory in the image forming area. LE when an LED is used as a light source of the density detection sensor 28
It is desirable to apply this method when the peak wavelength of D is longer than the peak wavelength of the LED when the LED is used as the light source of the PCL 27.

As described above, according to the present invention, since the density detection sensor 28 does not cause the photo fatigue memory to cause the density unevenness, it is possible to provide an image forming apparatus which can always hold a high quality image. .

[0032]

EXAMPLES The following experiments were conducted as examples based on the above-described embodiment, and the results are shown below. First, the configuration conditions common to the experiments of each embodiment at that time will be described.

The amorphous silicon photoreceptor 21 has a drum shape and has hydrogenated amorphous silicon in a photosensitive layer, has a total thickness of 20 to 100 μm, and has a surface layer provided with a layer made of amorphous silicon carbide. The outer diameter was 80 mm.

As the density detecting sensor 28, a type which obtains the image density of the toner image on the photoreceptor 21 by condensing the reflected light of the light irradiated by the LED with a phototransistor and converting the voltage into a voltage is used.

The PCL 27 is used as an erasing light for erasing the surface potential of the surface of the drum-shaped photosensitive member.
A laser or the like can be used, and it is preferable to use an LED from the viewpoint of power saving and the like. In this embodiment, the LED is used.

In the present embodiment, a modified Konica 7050 machine employing a toner recycling system was used as an experimental machine.

In conducting the experiment, the common conditions of this machine are as follows. Photoconductor: amorphous silicon photoconductor (φ80) Photoconductor linear velocity: 270 mm / sec Developer: two-component developer using 8 μm toner and 60 μm carrier Developing conditions: Vbias 600 V, VH 750 V Light source of image exposure means: peak wavelength Laser light of 650 nm Example 1 Peak wavelength of PCL27 and LED of concentration detection sensor
An experiment was conducted by combining the peak wavelengths of the above.
Table 1 shows the results.

In the experiment, when five continuous copies of a halftone image having an image density of 0.7 were made, the L of the density detection sensor was measured.
Whether or not the light fatigue memory caused by the ED occurs was determined based on the following criteria (the light fatigue memory has a higher density than other parts).

：: Light fatigue memory is not generated. Δ: Light fatigue memory is slightly present. X: Light fatigue memory is significantly generated.

[0040]

[Table 1]

From this result, it can be seen that when the peak wavelength of the PCL 27 is shorter than the peak wavelength of the LED of the density detection sensor, the photo fatigue memory is generated, and when it is longer, the photo fatigue memory is not generated.

Embodiment 2 The L of the density detection sensor is determined from the peak wavelength of the light source of the PCL 27.
When the peak wavelength of the light source of the ED was set to a long wavelength, an experiment was performed under the conditions using this peak wavelength. The peak wavelength of the PCL used in the experiment was 660 nm, and the peak wavelength of the LED was 950 nm.

The spot diameter of the LED used to irradiate the photosensitive drum surface is 7 mm, and as shown in FIG. 3, the on / off position of the patch (size m = 30 mm, n = 20 mm) is (1). ) To (10). In the experiment, when five halftone images with an image density of 0.7 were successively copied, L
The judgment was made based on whether or not a light fatigue memory caused by the ED occurred. The evaluation criterion for the resulting density unevenness is the same as in the first embodiment. Table 2 shows the results.

：: Light fatigue memory is not generated. Δ: Light fatigue memory is slightly present. X: Light fatigue memory is significantly generated.

[0045]

[Table 2]

From these results, it can be seen that 1/1 of the spot diameter of the LED is
It was found that light fatigue memory occurs when the LED is turned on at a timing faster than 3.5 mm, or turned off at a later timing.

As a result, if the lighting of the LED is limited to the area of the predetermined toner image (patch), the light source light is blocked by the toner particles forming the predetermined toner image, and
It can be seen that the photosensitive layer does not reach the photosensitive layer and no light fatigue memory occurs.

Example 3 As shown in FIG. 4, an experiment was conducted with the position of the density detection sensor 28 and the patch 21A set at the position E outside the image forming area of the photosensitive member 21 in the drum axis direction. PC used for the experiment
The peak wavelength of L is 660 nm, and the peak wavelength of LED is 9
It was 50 nm.

As in the first and second embodiments, an experiment was conducted to determine whether or not light fatigue memory caused by the LED of the density detection sensor occurs when five halftone images having an image density of 0.7 were successively copied five times. Judgment was made, but no light fatigue memory was found in the image forming area.

[0050]

According to the present invention, an image forming apparatus has been completed which eliminates the occurrence of light fatigue memory on the surface of the amorphous silicon photoreceptor due to the light source of the density detecting sensor for adjusting the image density, thereby obtaining a high quality image without density unevenness. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram showing an arrangement of each process around a photoconductor in the present invention.

FIG. 3 is a schematic diagram showing each position when an LED lighting position and a light-off position of a density detection sensor are experimentally changed with respect to an image density adjusting patch.

FIG. 4 is a development view of the photoconductor surface showing an image area and a patch area of a drum-shaped photoconductor in an axial direction and a rotation direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Amorphous silicon photoreceptor 21A Predetermined toner image (patch) 22 Charger 23 Developing device 24 Transfer device 25 Separator 26 Cleaning means 27 PCL 28 Density detection sensor 30 Image exposure means

Claims (11)

[Claims] 1. An amorphous silicon photoreceptor, charging means for charging the amorphous silicon photoreceptor, image exposure means for exposing the amorphous silicon photoreceptor to an image based on image information, and erasing a charged potential on the surface of the amorphous silicon photoreceptor An erasing exposure unit, a density detection sensor for detecting an image density of a predetermined toner image formed on the amorphous silicon photoconductor for controlling the image density, and an image density based on density information detected by the density detection sensor. An image forming apparatus having a control unit for controlling, wherein a peak wavelength of a light source of the density detecting sensor is shorter than a peak wavelength of the erasing exposure unit. 2. An amorphous silicon photoreceptor, a charging unit for charging the amorphous silicon photoreceptor, an image exposing unit for exposing the amorphous silicon photoreceptor to an image based on image information, and erasing a charged potential on the surface of the amorphous silicon photoreceptor. An erasing exposure unit, a density detection sensor for detecting an image density of a predetermined toner image formed on the amorphous silicon photoconductor for controlling the image density, and an image density based on density information detected by the density detection sensor. In the image forming apparatus having control means for controlling, the control means controls lighting and extinguishing of a light source of the density detection sensor, and when the density detection sensor detects an image density of a predetermined toner image, the amorphous silicon The density detection sensor is provided only in the area where the predetermined toner image is formed on the photosensitive member. Image forming apparatus and controls the on and off so as to detect the image density of the light source on. 3. The control device according to claim 2, wherein the control unit controls the timing of turning on and off the light so that the spot of the light source of the density detection sensor enters the area of the predetermined toner image. Image forming device. 4. The method according to claim 1, wherein the center of the spot of the light source of the density detecting sensor is one spot diameter from the end of the predetermined toner image.
4. The image forming apparatus according to claim 3, wherein the on / off control is performed such that the predetermined toner image density is detected at a position inside the position of / 2. 5. 5. The image forming apparatus according to claim 2, wherein a peak wavelength of a light source of the density detection sensor is longer than a peak wavelength of the erasing exposure unit. 6. An amorphous silicon photoreceptor, charging means for charging the amorphous silicon photoreceptor, image exposing means for exposing the amorphous silicon photoreceptor to image based on image information, and erasing a charged potential on the surface of the amorphous silicon photoreceptor. An erasing exposure unit, a density detection sensor for detecting an image density of a predetermined toner image formed on the amorphous silicon photoconductor for controlling the image density, and an image density based on density information detected by the density detection sensor. In the image forming apparatus having control means for controlling, the predetermined toner image is a predetermined toner image formed in an axial direction of the amorphous silicon photoconductor and outside an image forming area. . 7. The image forming apparatus according to claim 6, wherein a peak wavelength of a light source of the density detection sensor is longer than a peak wavelength of the erasing exposure unit. 8. The light source according to claim 1, wherein the light source of the density detection sensor is a light emitting diode.
Item 10. The image forming apparatus according to item 1. 9. The light source according to claim 1, wherein a peak wavelength of the light source of the density detection sensor is 700 nm or less.
9. The image forming apparatus according to any one of 8. 10. A light source according to claim 1, wherein a light source of said erasing exposure means is a light emitting diode.
Item 10. The image forming apparatus according to item 1. 11. The apparatus according to claim 1, wherein a peak wavelength of a light source of said erasing exposure means is 700 nm or less.
The image forming apparatus according to claim 10.