JP3050400B2 - Electrophotographic image forming apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus using a dry two-component magnetic brush in a reversal developing system, and for example, an electrophotographic image forming apparatus used in a copying machine or a printer. The present invention relates to an image forming apparatus.

[Conventional technology]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, high image quality, that is, stabilization of image density, prevention of background smear, high contrast image, and the like have been demanded. Deterioration of image quality is likely to occur due to factors.

The first factor is considered to be deterioration of image quality due to a change in the potential of the electrostatic latent image due to environmental changes, replacement of parts for maintenance or replacement of parts for maintenance, and the like. As an electrophotographic image forming apparatus for preventing image quality deterioration due to such factors, a potential detecting means for detecting a potential of a photoconductor is provided, and a latent image reference pattern having a saturated exposure potential is formed outside an image area of the photoconductor. There has been proposed a device that adjusts various latent image forming conditions based on the detection result of the pattern. In particular, when reversal development is employed, it is conceivable to maintain a constant image quality by controlling the development bias according to the potential of the reference pattern.

As the second factor, when the developer is a two-component developer composed of a toner and a carrier, a change in image quality due to a change in the toner concentration of the developer can be considered. As an electrophotographic image forming apparatus for preventing image quality deterioration due to such factors, a reference image is formed outside an image area of a photoreceptor, an optical reflection density of the reference image is detected, and the reflection density becomes a constant value. In order to control the amount of toner supplied to the developer, there has been proposed a method in which the amount of toner supplied to the developer is adjusted. When a reference image for adjusting the toner density is formed, in order to obtain a halftone potential difference, the potential of the exposed portion is made closer to the developing bias than the saturation potential to obtain a low contrast potential.

Specific examples for improving the image quality as described above include, for example, those described in JP-A-60-254061, JP-A-56-5562, and JP-A-60-66272. Documents described in the first publication detect potentials of an electrostatic latent image formed on a charge carrier, an optical density of a developed image obtained by developing the latent image, an image density on a recording paper, and the like, and each process is different. By controlling the elements, even if a characteristic change of each process element occurs, it is easily compensated for, and a stable recording density is maintained. In the method disclosed in the following publication, in a method for controlling the concentration of toner on a photosensitive drum, a correction is made for a variation factor in an exposure process and a development process so that the toner concentration is accurately controlled. In the last publication, the amount of light emission is adjusted based on the measured surface potential of the photoreceptor, thereby stabilizing the density of a printed image in response to a change in image forming conditions.

[Problems to be solved by the invention]

However, in such a conventional electrophotographic image forming apparatus, the latent image contrast in the image area and the toner density in the developing device cannot be balanced for the following reasons, and the image quality is improved. There was a problem that it became difficult to do.

That is, as shown in FIG. 7, since the light attenuation curve of the photoconductor is not linear, the halftone is obtained by the same variation as the exposure variation A required to change the potential near the saturation exposure potential by, for example, 40 V. When the exposure potential is changed, the potential changes by 100V. Therefore, when the exposure amount is controlled based on the potential of the latent image reference pattern having the saturated exposure potential and the toner supply amount is adjusted based on the reflection density of the halftone reference image, the latent image contrast set at the initial stage is controlled. Disappears. For example, when the potential of the saturated exposure section increases, the exposure amount is controlled according to the electrometer detection. When the exposure duty is changed in accordance with the change in the potential of the image portion, the latent image condition is maintained in a desired range, but the amount of change in the potential of the toner density control pattern increases, and the amount of toner adhered to the photoconductor increases. Therefore, it is determined that the toner density in the developer is high, the toner supply amount is small, and the toner density is too low with respect to the image portion latent image contrast. Conversely, when the potential of the saturated exposure portion decreases, the toner density increases. Further, as shown in FIG. 8, the amount of change in the potential of the photoreceptor when the same amount of light is applied becomes different due to fatigue during use and deterioration due to the environment.
In order to solve this problem, there is a method of repeating detection and control until the potential falls within a desired range. However, a new problem such as a longer waiting time for the user occurs. The above three publications cannot solve these problems.

[Object of the invention]

Accordingly, the present invention provides a method in which the amount of change in the amount of exposure by the control unit is different for each reference image latent image having a different amount of exposure,
The control means controls the latent image forming means based on the integrated light amount exposing the photoconductor or the integrated number of images formed by the photoconductor, so that the latent image contrast in the image area and the toner concentration of the developer can be easily balanced. Enable
It is intended to improve image quality without performing control operations many times.

[Configuration of the invention]

In order to achieve the above object, an electrophotographic image forming apparatus according to the present invention forms a reference image latent image by exposing a charged image carrier and a predetermined area on the surface of the charged image carrier. Latent image forming means, potential detecting means for detecting the surface potential of the image carrier in the region carrying the reference image latent image, and the potential of the image carrier in the region carrying the reference image latent image becomes a predetermined control potential As described above, based on the detection result of the potential detection means, control means for controlling the latent image forming means to change the exposure amount,
A plurality of the reference image latent images are formed such that the exposure amounts are different from each other, and the control potential is set for each reference image latent image. The control unit controls the latent image forming unit so that the amount of change in the exposure amount is different for each reference image latent image, and the control unit controls the exposure of the image carrier from the start of use of the image carrier. The control potential of each reference image latent image is changed based on the integrated light amount obtained by integrating the light amounts of the reference images.

Further, the electrophotographic image forming apparatus according to the present invention, when charged, forms an image carrier and a latent image forming means for exposing a predetermined area on the surface of the charged image carrier to form a reference image latent image. And a potential detecting means for detecting a surface potential of the image carrier in a region where the reference image latent image is carried, and a potential detecting device so that the potential of the image carrier in the region carrying the reference image latent image becomes a predetermined control potential. Control means for controlling the latent image forming means to change the exposure amount based on the detection result of the means, wherein the reference image latent images have different exposure amounts from each other. The control potential is set for each reference image latent image, and the control means controls the latent image forming means such that the amount of change in the exposure amount by the control means differs for each reference image latent image. The control means uses the image carrier. The control potential of each reference image latent image to be changed is integrated based on the integrated light amount obtained by integrating the light amount of light exposing the image carrier from the start, and the image forming integration by integrating the number of image formations from the start of use of the image carrier. The control potential of each reference image latent image is changed based on the number of sheets.

 Hereinafter, the present invention will be specifically described based on examples.

FIGS. 1 to 6 show an embodiment of an electrophotographic image forming apparatus according to the present invention, in which a black portion is exposed using a negatively charged organic photoreceptor, and a negative toner is developed with a two-component developer. This is an example applied to a development type device.

 First, the configuration will be described.

In FIG. 1, reference numeral 1 denotes a photoconductor as an image carrier, and the photoconductor 1 is formed of a negatively charged organic photoconductor. Reference numeral 2 denotes a scorotron charger. A voltage is applied to the grid of the scorotron charger 2 so that the surface potential of the photoconductor 1 can be controlled. That is, a voltage is supplied to the scorotron charger 2 from the high voltage power supplies 3 and 4. Reference numeral 5 denotes a laser light source, and 6 denotes a polygon mirror. The laser light source 5 and the polygon mirror 6 expose a predetermined area on the surface of the charged photosensitive member 1 to form a latent image forming a reference image latent image described later. Configure means. Reference numeral 7 denotes an electrometer, and the electrometer 7 constitutes a potential detecting unit that detects a surface potential of the photoconductor 1 in an area that carries the reference image latent image. Reference numeral 8 denotes a CPU including a microcomputer and the like.
Control means for controlling the laser light source 5 based on the detection result of the electrometer so as to change the exposure amount so that the potential of the photoreceptor 1 in the region carrying the reference image latent image becomes a predetermined control potential described later. I do.

The reference image latent image is, for example, as shown at P1 and P2 in FIG. 2. In FIG. 2, T is an unexposed charged area charged by the scorotron charger 2, and the reference image latent image P1 corresponds to an intermediate exposure portion charged to a half tone by the laser light source 5, and the reference image latent image P2 corresponds to a black portion exposure portion which has been saturatedly exposed. In this embodiment, the pattern of the reference image latent image is formed using pulse width modulation. At the time of the first pattern formation, the reference image latent image P1 is written with a pulse width of 50% duty, and the reference image latent image P2 is formed with the pulse width. Write at 100% duty. Therefore, a plurality of reference image latent images are formed so that the exposure amounts are different from each other, a control potential is set for each of the reference image latent images P1 and P2, and the amount of change in the exposure amount by the CPU 8 is changed for each reference image. The CPU 8 controls the laser light source 5 so as to be different for each of the latent images P1 and P2.

On the other hand, when the reference image latent image P1 is developed by the developing unit 9, the reference image latent image P1 becomes a toner density detection reference image for detecting toner density. The developing unit 9 stores a two-component developer including a toner and a carrier in a developer chamber 9a, and the toner is supplied to the developer chamber 9a by driving a toner supply roller 9b. The amount of toner attached to the toner density detection reference image is detected by the toner density detection sensor 10. The detection result of the toner concentration detection sensor 10 is input to the CPU 8, and the CPU 8 controls the driving of the toner supply roller 9a and adjusts the toner supply amount based on the detection result.

Here, another configuration and an image forming operation of the present embodiment will be briefly described.

11 is a transfer charger, 12 is a separation charger, 13 is a cleaning unit, 14 is a quenching lamp, and 15 is a transfer paper.

When an image is formed, first, the photoconductor 1 rotates in the direction of the arrow in FIG. 1, and the photoconductor 1 is charged by the scorotron charger 2. Next, laser light having image information is emitted from the laser light source 5, and the photosensitive member 1 is irradiated and exposed through the polygon mirror 6, and a latent image is formed in an image forming area on the surface of the photosensitive member 1. Next, the latent image is developed by the developing unit 9 to be visualized, and a toner image is formed. Next, the toner image is transferred to the transfer paper by the transfer charger 11.
The transfer paper 15 is separated from the photoconductor 1 by the separation charger 12. Next, the visible image transferred to the transfer paper 15 is fixed by a fixing unit (not shown). On the other hand, the toner remaining on the photoconductor 1 after the transfer is removed by the cleaning unit 13, and the toner remaining on the photoconductor 1 is removed by the quenching lamp 14.

Next, the operation will be described with reference to the flowchart of FIG.

First, in S1, the reference image latent images P1 and P2 are formed on the surface of the photoconductor 1 outside the image forming area.
The potentials V _LM and _{VL of} P 1 and P 2 are detected by the electrometer 7. That is, the detection data is transmitted from the electrometer 7 to the CPU 8, and the data is sampled. In this embodiment, as shown in FIG. 3, the first threshold value is -500 V and the second threshold value is -30.
As 0V, data it obtains the 8 bytes of the mean value of the head of the data of 12 bytes before the time of falling below the first threshold and V _D, after the time when the drops below the first threshold value of four consecutive data discarding, then we obtain an average value of 8 bytes of data and V _LM, four successive data after the time when the drops below the second threshold discarding,
After that, the average value of the 8-byte data is obtained and set to _VL . In addition, the first control potential of each of _VL and _VLM is set to V
_L0 = 100V, _VLM0 = 400V. In S3, | V _L −V _L0 | <20,
If | V _LM −V _LM0 | <20, the routine ends; otherwise, the process proceeds to S4. At S4, the control potentials V _L0 , V _L0 , V
_LM0 is set, and in S5, the reference image latent image P is set based on the magnitude of | V _L −V _L0 | and | V _LM −V _LM0 | and the control target values V _L0 and V _LM0.
The amount of change in the exposure for each of P1 and P2 is calculated separately. Specifically, for example, in the photoreceptor 1 in the early stage of use, V _L
0.1m but 30 V, if V _LM is displaced 25V, and 0.6mW up the exposure amount to control the V _L, the exposure amount to control the V _LM
W may be increased, but when the photoconductor 1 is used to some extent and the integrated light amount increases, if there is the same shift amount,
Was 1.0mW up the exposure amount to control the V _L, will 0.2mW up the exposure amount to control the V _LM. In S6, the pulse width duty of the reference image latent images P1, P2 to be formed next is changed so that the exposure amount changes by the calculated change amount, and the process returns to S1. If one of the two conditions is not satisfied in S3, the process returns from S6 to S1 to form only the reference image latent image that does not satisfy the above conditions in forming the reference image latent image. You may make it.

In S3 described above, | V _L −V _L0 | <20 and | V _LM −V _LM0 | <20
The latent image P1 is developed by the developing unit 9 to form a reference image for toner density detection.
An output Vsp corresponding to the toner adhesion amount of the toner density detection reference image is output from the toner density detection sensor 10 to the CPU 8. Next, the developing roller of the developing unit 9 is
The driving of 9b is based on the output Vsp. Specifically, the output of the toner concentration detection sensor 10 when toner is not attached is Vs
Assuming g, 1/13 <V s based on 1/11,
Control is performed within the range of p / V sg <1/11. When V sp / V sg ≦ 1/13, the toner concentration is determined to be low, and toner is supplied to the developing chamber 9a. That is, the toner supply amount is set to about 0.45 mg / cm ² , and the reference is based on the case where the sensor output Vsp = 0.36 V at that time, as is clear from the characteristic curve shown in FIG.

As described above, in this embodiment, a plurality of reference image latent images (P1 and P2
And control potentials V _L0 and V _LM0 are set as control targets for each of the reference image latent images P1 and P2, and the amount of change in the exposure amount by the CPU 8 is set for each of the reference image latent images P1 and P2. Since the CPU 8 controls the laser light source 5 differently, each of the saturation exposure potential and the halftone potential can be controlled to the optimum potential corresponding to the light attenuation curve of the photoconductor 1. Therefore, a desired latent image contrast can be easily obtained. On the other hand, since the halftone potential is optimally controlled, the reference image latent image having the optimally controlled potential is controlled.
By detecting the toner density of the developer from the toner adhesion amount of the toner density detection reference image formed by developing P1, the toner density can be easily controlled to the target value. Therefore, the contrast of the latent image in the image area and the toner density in the developing device can be easily balanced, and the image quality can be improved.

Also, the target control potentials V _L0 , V _{L0 of} each reference image latent image
_{Since LM0} is changed based on the integrated light amount of the light that has exposed the photoconductor 1, the control can be performed accurately without repeating the detection control many times.

Further, since the reference image latent image P1 and the latent image of the toner density detection reference image are also used, the laser light source 5
Can be easily controlled. Needless to say, they may be formed separately without being shared as described above.

On the other hand, here, instead of the flowchart of FIG.
The potential control may be performed according to the flowchart in the figure. The difference between FIG. 4 and FIG. 6 is that, instead of the accumulated light amount in S4 in FIG. 4, in S14 in FIG. 6, the number of copies from the start of use of the photoconductor 1, that is, the accumulated number of image formation sheets In that the control potentials V _L0 and V _LM0 are changed based on the Even in this case, the same effects as those described above can be obtained.

〔effect〕

According to the present invention, a plurality of reference image latent images are formed such that the exposure amounts are different from each other, and a control potential is set for each reference image latent image. Since the control unit controls the latent image forming unit so as to be different for each reference image latent image, the latent image contrast in the image area and the toner concentration of the developer can be easily balanced, and the image quality can be improved. Since the control potential can be changed according to the integrated light amount, the control can be performed accurately without repeating the detection control many times. In addition, since the control potential can be changed according to the number of integrated images, the control can be accurately performed without repeating the detection control many times.

[Brief description of the drawings]

1 to 6 are views showing an embodiment of an electrophotographic image forming apparatus according to the present invention. FIG. 1 is a schematic overall view thereof, and FIG.
FIG. 3 is a diagram showing a pattern of the reference image latent image, FIG. 3 is a diagram for explaining a sampling operation of the potential data,
FIG. 4 is a flowchart of a potential control program for the photoconductor, FIG. 5 is a graph showing the relationship between the reflected output voltage and the amount of toner adhered, FIG. 6 is a flowchart of another potential control program for the photoconductor, and FIG. And FIG. 8 are graphs for explaining the prior art. Reference Signs List 1 photoreceptor (image carrier), 5 laser light source (latent image forming means), 6 polygon mirror (latent image forming means), 7 electrometer (potential detecting means), 8 CPU (Control means), P1, P2 ... Reference image latent image.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/04-15/04 120 G03G 15/00 303 G03G 21/00 370-500 G03G 21/14

Claims (2)

(57) [Claims] An image bearing member that is exposed to light, exposes a predetermined area on the surface of the charged image bearing member to form a reference image latent image, and carries a reference image latent image. Potential detecting means for detecting the surface potential of the image carrier in the selected area, and a potential detecting means based on the detection result of the potential detecting means so that the potential of the image carrier in the area carrying the reference image latent image becomes a predetermined control potential. Control means for controlling the image forming means to change the exposure amount, in the electrophotographic image forming apparatus, wherein the reference image latent image is formed in a plurality, so that the exposure amount is different from each other, each The control potential is set for each reference image latent image, and the control means controls the latent image forming means so that the amount of change in the exposure amount by the control means differs for each reference image latent image. The light that exposed the image carrier from the start of use of the image carrier An electrophotographic image forming apparatus characterized in that the control potential of each reference image latent image is changed based on the integrated light amount obtained by integrating the light amounts of the reference images. And a latent image forming means for exposing a predetermined area on the surface of the charged image carrier to form a reference image latent image, and carrying the reference image latent image. Potential detecting means for detecting the surface potential of the image carrier in the selected area, and a potential detecting means based on the detection result of the potential detecting means so that the potential of the image carrier in the area carrying the reference image latent image becomes a predetermined control potential. Control means for controlling the image forming means to change the exposure amount, in the electrophotographic image forming apparatus, wherein the reference image latent image is formed in a plurality, so that the exposure amount is different from each other, each The control potential is set for each reference image latent image, and the control means controls the latent image forming means so that the amount of change in the exposure amount by the control means differs for each reference image latent image. , The number of images formed since the start of use of the image carrier An electrophotographic image forming apparatus, wherein the control potential of each reference image latent image is changed based on the accumulated number of image formation.