JP2001125324A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can attain reduction of running cost and toner consumption by saving excessive toner sticking to the latent image on a photoreceptor which satisfying the image quality request by a user. SOLUTION: Since the reflection density of the output image is saturated at a point that the development contrast is high, the image density appears identical to a user, regardless of the toner quantity on the image beyond that, and the toner is wasted. In this image forming device, patches are formed on a photosensitive drum with the density from A0H to FFH, measured by a sensor, and a part where the density difference of two adjoining patches becomes below 0.05 is defined as the development contrast. Since the developing bias is constant in this case, the development contrast is controlled by the potential of the maximum image part in the case of forming an electrostatic latent image on the photosensitive drum. This means the development contrast is controlled by the maximum light quantity of a laser. In the case the density difference becomes 0.06 by B0H and 0.00 by C0H, the C0H is made to be the maximum light quantity as the laser power.

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 such as a copying machine, a laser beam printer, a facsimile, and a printing apparatus using an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art In recent years, the demand for copying machines and laser beam printers has increased, and the amount of developer (toner) consumed has also increased. On the other hand, due to problems such as resource depletion and waste disposal, there is a strong demand for energy saving and waste reduction. Under these circumstances, reducing the consumption of developer has become an important issue in electrophotographic and electrostatic recording type copiers, laser beam printers, facsimile machines, etc. There is a demand for a reduction in running costs.

Generally, an electrophotographic image forming apparatus forms an electrostatic latent image on an image carrier by uniformly charging the surface of the image carrier and performing analog exposure or image exposure using a semiconductor laser or LED. It is known that the toner image is developed by a developing device, visualized as a toner image, the toner image is transferred to a transfer material, the transfer material is separated from an image carrier, and the image is output after being fixed by a fixing device. I have.

The image forming process will be described with reference to FIG. The image forming apparatus has, for example, a drum-shaped photoconductor, that is, a photoconductor drum 1 as an image carrier, and the photoconductor drum 1 includes a photoconductive layer of OPC, a-Si, or the like on a surface thereof,
It is rotated in the direction of arrow A. The surface of the photosensitive drum 1 is uniformly charged to, for example, -700 V by the primary charger 3, and then image exposure 12 is performed by a signal of image information to attenuate the surface potential of the exposed portion on the photosensitive drum 1 to, for example, -200V. Then, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1. For the image exposure 12, for example, a semiconductor laser or an LED array is used.

Next, the electrostatic latent image is developed by the developing device 2 and visualized as a toner image. The developing method of the developing device 2 includes two-component development using toner and carrier, and jumping development using only toner (magnetic one-component developer). At the time of development, a DC bias of, for example, about -500 V is applied as a development bias to the developer carrying member of the developing device 2 to perform reversal development (or regular development) of the latent image.

Thereafter, if necessary, the post-charging device 10
The toner image is subjected to a pre-transfer process (usually by applying a corona by DC or AC or a combination of light elimination, etc.), and is transferred by the transfer charger 4 onto the transfer material supplied to the photosensitive drum 1. Next, the transfer material is separated from the photosensitive drum 1 by the separating and removing unit 5 and sent to the fixing unit 7, where the toner image is fixed to obtain a final print.
On the other hand, the cleaning device 6 removes the transfer residual toner remaining on the surface of the photosensitive drum 1 to prepare for the next image formation.

Techniques for reducing the amount of toner consumption include:
A method is known in which a toner save mode is provided in an image forming apparatus, and a user who actually uses the mode selects the mode, thereby lowering the toner density.
348094, JP-A-7-160150).

[0008]

However, conventionally,
The toner save mode is effective for printing a test copy or for the purpose of recognizing characters only, because the line density of the image is low, but it is not very effective for ordinary commercial distribution documents that print a large amount. Did not. Further, fine adjustment of the image density in the toner save mode has to be performed by the user at each time, which is difficult to use.

SUMMARY OF THE INVENTION An object of the present invention is to satisfy the user's requirement for image quality and to save unnecessary toner adhering to a latent image on a photoreceptor, thereby minimizing toner consumption. Therefore, it is an object of the present invention to provide an image forming apparatus which has a low running cost and is highly environmentally friendly.

[0010]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image forming apparatus that develops and visualizes an electrostatic latent image formed on an image bearing member using a developer by a developing unit, wherein a generating unit that generates a plurality of density gradation patterns on the image bearing unit; Reflection density detection means for detecting reflection density information of a density gradation pattern developed by the development means, and the developing means based on a density gradient of the gradation pattern detected by the reflection density detection means. An image forming apparatus for controlling a developing contrast potential determined by a difference between a developing bias potential of the developing device and a potential of an image carrier that gives a maximum image.

According to the present invention, when the density difference between a plurality of continuous density gradation patterns becomes a certain value or less, the developing contrast potential control is performed for the density gradation pattern given the certain value or less. This is performed by a method in which the difference between the potential and the DC component of the developing bias is defined as the developing contrast.
Further, gradation correction of the output image is performed according to the development contrast potential control. The development contrast potential control is performed for each fixed number of image formations or when the power of the image forming apparatus main body is turned on. The transfer residual developer remaining on the image carrier after the transfer is collected by a cleaning unit, and the collected developer is returned to the developing unit and reused.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

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

The present image forming apparatus is a black and white digital copying machine having a process speed of 350 milliseconds and forming 65 images per minute. The image forming apparatus includes a photosensitive drum (drum-shaped electrophotographic photosensitive member) 1 made of a-Si as an image carrier. The photosensitive drum 1 has an outer diameter of 108 mm and is rotated at a process speed in the direction of arrow A. a-
Si is more durable than an organic photoreceptor (OPC), has a service life of 3 million images, and is suitable for high-speed machines.

The surface of the photosensitive drum 1 is uniformly charged to, for example, +400 V by the charger 3 and then subjected to image exposure 12 at 600 dpi. The image exposure 12 is performed using a semiconductor laser as a light source, and forms an electrostatic latent image on the surface of the photosensitive drum 1 by attenuating the surface potential of the exposed portion to, for example, +50 V. The wavelength of the laser light of the semiconductor laser is 680 nm.

Although a scanner section for reading the document and an image processor section for creating image data are not shown, the reflected light from the document imaged on the CCD of the scanner is A
600 dpi, 8 bits (256 gradations) after / D conversion
And then sent to the image processor. The image processor performs a well-known luminance-density conversion (Log conversion), converts the image signal into a density signal, and then performs edge enhancement, smoothing,
After passing through filter processing such as removal of high-frequency components, and then applying density correction processing (so-called γ processing), binary processing is performed through, for example, binarization processing such as an error diffusion method or screen processing using a dot concentration type dither matrix. Be transformed into Of course, the latent image may be formed by driving the semiconductor laser by a well-known PWM (pulse width modulation) method or the like with 8 bits as it is. However, in the present invention, a binary value is used from the viewpoint of easy handling of image data. Adopted.

Thereafter, the image signal is sent to the laser driver, and drives the laser according to the signal. The laser light is applied to the photosensitive drum 1 via a collimator lens, a polygon scanner, an fθ lens, a folding mirror, dustproof glass, and the like. Laser light is 600 dpi 1
An image is formed on the photosensitive drum with a spot diameter of about 55 μm, which is slightly larger than the pixel = 42.3 μm, and as described above, the exposed portion is discharged to about +50 V to form an electrostatic image.

The electrostatic latent image formed on the photosensitive drum 1 is
Developed by the developing device 2 and visualized as a toner image. Then, the post-charging device 10 provided a total current of +100 μA (AC + D
C) to charge the toner image, and then transfer the toner image to a transfer material (paper) P traveling in the direction of the arrow by the transfer charger 4, and separate the transfer material P from the photosensitive drum 1 by the separation and neutralization device 5 to fix the toner image. 7, where the toner image is fixed to obtain a final print.

In the present embodiment, the developing device 2 employs a jumping development system using a black magnetic toner (magnetic one-component developer), which is a development system that is simple and requires no maintenance until the life of the development sleeve. The developing device 2 used in this embodiment will be described in detail.

The developing device 2 has a developing sleeve 20 rotatably provided in an opening facing the photosensitive drum 1, and a roller-shaped magnet 21 is provided in the developing sleeve 20 in a non-rotating manner as shown in FIG. Are located. The magnetic toner contained in the developing device 2 is conveyed to the developing sleeve 20 by two toner conveying members 23, and the rotating developing sleeve 2
The magnetic blade 22 is supported on the surface of the developing sleeve 20 by the magnetic force of the magnet 21 and is spaced apart from the developing sleeve 20 by a predetermined distance.
After the thickness of the photosensitive drum 1 is regulated, the sheet is conveyed to a developing area facing the photosensitive drum 1. Then, the toner flies and adheres to the electrostatic latent image on the photosensitive drum 1 by the developing bias applied to the developing sleeve 20, and the latent image is visualized as a toner image.

A toner supply hopper 2 is provided above the developing device 2.
When the magnetic toner near the toner conveying member 23 on the side close to the developing sleeve 20 runs out, the control signal CP is detected by the detection signal of the piezoelectric element 25 installed there.
U27 outputs a signal for rotating the magnet roller 26 in the lower portion of the hopper 24 to a motor (not shown), whereby the magnet roller 26 rotates to cut out magnetic toner from the hopper 24 and supply it to the developing device 2.

The magnetic pole pattern of the magnet 21 is formed, for example, as shown in FIG.

[0023]

[Table 1] In this embodiment, the developing sleeve 20 rotates at a peripheral speed of 150% with respect to the photosensitive drum 1. The interval (SB gap) between the developing sleeve 20 and the magnetic blade 22 is set to 250 μ
m, the distance between the developing sleeve 20 and the photosensitive drum 1 (S-D
Gap) was 250 μm. The developing bias applied to the developing sleeve 20 is a rectangular wave AC voltage having a peak-to-peak voltage of 1.5 kV, a frequency of 2.7 kHz, and a duty (Duty) of 50% as shown in FIG.
Was superimposed and used. Therefore, the development contrast is 230 V in the flight direction to the photosensitive drum 1 and the fog removal (toner pullback) contrast is 120 V.

In the present embodiment, a positive toner having a particle diameter of 8.0 μm, in which magnetic particles are dispersed in a styrene acrylic resin, was used as the magnetic toner. This toner was used with 1.0% by weight of SiO ₂ added externally.

Next, wasteful consumption of toner in the conventional image forming apparatus will be described. FIG. 5 shows the relationship between the development contrast and the image reflection density (VD curve), and FIG. 6 shows the relationship between the development contrast and the image transmission density. These two densities include the density of paper as a transfer material. Thus, FIG. 7 shows the result obtained by subtracting the density of the paper. This is a value obtained by subtracting 0.08 for the reflection density and 0.5 for the transmission density as paper densities.

From these figures, the reflection density shows a saturation characteristic at a high development contrast. The fact that this saturation characteristic is shown means that the image density looks almost the same for the user. On the other hand, the transmission density increases with the development contrast. This means that the toner amount increases with the development contrast. Therefore, in a region where the reflection density is saturated, any further toner is wasted.

A feature of the present invention is to reduce useless toner that is not reflected as reflection density to a user. This is shown in FIG. 8, in which the toner T constituting the toner image is stacked on the paper P, and the toner T 'in the upper portion of the toner image represents waste toner that is not reflected on the reflection density. ing. Therefore, in the present invention, the development contrast is controlled so as to minimize such useless toner.

A method for controlling the development contrast in this embodiment will be described.

As shown in FIG. 1, a reflection density sensor 40 is provided at a position downstream of the developing device 4 with respect to the photosensitive drum 1. Then, as shown in FIG. 9, a patch pattern (abbreviated as patch) 302 of a predetermined density formed on the photosensitive drum 1
Is irradiated with light from the light emitting unit 303 of the sensor 40, and the reflected light from the patch 302 is received by the light receiving unit 304.
The density (reflection density) of the patch is measured, and the development contrast is controlled based on the gradient of the measured density data.

FIG. 10 shows an example of a patch used in this embodiment. For convenience of explanation, it is assumed that the patch is a seven-step gradation pattern. As shown in FIG. 10, the patch density is expressed in hexadecimal notation from 0 to 255 levels, and A0
H, B0H, C0H, D0H, E0H, F0H, FFH
In the above seven patterns, the full power of the laser at the time of FFH is set to 5 mW. In this method, the potentials of the photosensitive drums do not become equal at intervals because the light amount of the laser is changed. However, in this embodiment, the potential is about 20 V at 10 H in this embodiment.

FIG. 11 shows density data obtained by measuring a patch on the photosensitive drum with a density sensor. The horizontal axis in FIG. 11 shows a video signal of the patch. Here, for simplicity, 0
An example in which patches from 0H to FFH are formed is shown. What is actually used is from A0H to FFH. The reflection density here is obtained by subtracting the reflection density of only the photosensitive drum when no patch is formed on the photosensitive drum.
FIG. 12 shows the density difference between two adjacent patches, such as the difference between A0H and B0H and the difference between B0H and C0H.

In this embodiment, since the developing contrast value is set at a position where the reflection density is substantially saturated, the portion where the density difference becomes 0.05 or less is defined as the developing contrast. In the case of this embodiment, the DC component of the developing bias is 280.
Since the system has a constant V, the developing contrast is controlled by the maximum image portion potential V1 when forming an electrostatic latent image on the photosensitive drum, that is, by the maximum amount of laser light. By adjusting the laser emission amount so that the first development contrast at which the reflection density becomes a saturation value becomes the maximum image portion potential, the development contrast can be reduced as much as possible, and as a result, the toner that does not contribute much to the reflection density Can be reduced. According to FIG. 12, 0.06 for B0H and 0.0 for C0H.
03, C0H is set as the maximum light amount as the laser power.

In an ordinary image forming apparatus, since the development contrast is not controlled by the maximum light amount of the laser as described above, the development contrast is set to be considerably large in consideration of the environment, durability, and differences in the machine body. However, in the present invention, the above control guarantees the maximum density as the reflection density,
It is possible to automatically suppress further unnecessary toner adhesion. When the development contrast is changed, tone correction is newly set for the image signal read from the reader in accordance with the change.

Next, the details of the image signal control section for controlling the laser for performing the above-described image exposure 12 will be described with reference to FIG.

As shown in FIG. 13, the image signal control unit
Image processing section 201, γ correction section 202, binary section 203, L
UT calculation unit 205, pattern generator 206, RO
M207, CPU 208 and RAM 209 are provided. The CPU 208 comprehensively controls each component of the image signal control unit according to a control program or the like stored in the ROM 209, and the RAM 209 is used as a work area of the CPU 209.

The image processing unit 201 performs image processing desired by the operator such as resolution conversion on the input image signal, and the γ correction unit 202 performs LUT processing on the image signal from the image processing unit 201. The gamma correction is performed with reference to the lookup table (LUT) from the calculation unit 205. Binary part 20
3 generates a laser drive signal based on the image signal after the γ correction, drives the laser unit 204 based on the drive signal, and performs image exposure 12 corresponding to the image unit. LU
The T calculation unit 205 determines the development contrast according to the density measurement value of the patch pattern obtained by the density sensor 40, and at the same time, compares the LUT in the γ correction unit 202 with the newly set development contrast. Newly calculated and updated as appropriate in the operating environment.
The pattern generator 206 holds image data of a sample patch pattern in advance.

In this embodiment, as described above, in addition to an appropriate development contrast, an appropriate gradation correction (for example, γ correction) is performed. Then, the LUT calculation unit 205 sets the γ correction unit 202 so that the obtained gradation characteristic becomes an ideal density reproduction curve (TRC: Tone Reproduction Curve).
LUT is updated. The TRC is stored, for example, in the ROM 207.

Next, Table 2 shows a case where the toner consumption is improved when the control of the present embodiment is performed, and a case in which the conventional case is not improved. The toner consumption is the amount of toner consumed per sheet when 10,000 sheets of a standard chart having an image ratio of 6% are output.

[0039]

[Table 2] As shown in Table 2, when the control of this embodiment was performed, the toner consumption was able to be reduced by about 19.6% compared to the conventional case where this control was not performed.

In the above, the development contrast control is performed when the power of the image forming apparatus is turned on and every 2,000 sheets of image formation because the potential of the photosensitive drum, the charged state of the toner, and the like often differ between morning and evening. . By doing so, the image quality,
After satisfying the density, the toner can be saved stably.

As described above, according to the present embodiment,
After satisfying the user's image quality requirements, it is possible to reduce unnecessary toner adhering to the electrostatic latent image on the photosensitive drum, minimize toner consumption, and reduce running costs. In addition, an image forming apparatus having high environmental measures can be realized.

Embodiment 2 Another embodiment of the present invention will be described. In this embodiment,
A significant feature is that the method of forming patches (patch patterns) has been improved in order to more precisely control the development contrast control. This method is particularly effective when one round of the image carrier such as a belt-shaped photoconductor is relatively long.

LED or laser power fully-lit FF
A patch is formed on the photoconductor with H to change the DC component of the developing bias. This is because, in the case of a video signal using LED light (or laser light), particularly when controlling every 10H, the potential slightly changes depending on the sensitivity of the photoconductor, the lot of the LED, the optical system, and the like, so that the potential is relatively stable during patch formation. It is more advantageous to change the developing bias by, for example, 20 V at a full lighting potential to control the developing contrast more finely. However, when the developing bias is changed, the response of the high voltage to the control signal is relatively slow as compared with the light (laser light), so that the length of the patch becomes somewhat longer. It is preferably applied to an image forming apparatus using a belt-shaped photoconductor.

The image forming apparatus of this embodiment will be described with reference to FIG. As shown in FIG. 14, the present image forming apparatus includes a belt-shaped photosensitive member, that is, a photosensitive belt 101 as an image carrier, and this photosensitive belt 101 is made of an OPC photosensitive member and rotates in the direction of arrow A in the figure. . The photosensitive belt 101 is, for example, −600 by a primary charger 102.
After being uniformly charged to V (dark portion potential), image exposure 103 corresponding to the image signal is performed to form an electrostatic latent image.

The image exposure 103 is performed by a LED of 600 dpi, and its wavelength is 680 nm. The image signal control unit for controlling the LEDs was the same as in the first embodiment. After the light emitted by the LED passes through the coupling lens,
The photosensitive belt 101 is irradiated, the surface potential of the exposed portion is attenuated according to the image signal level, and a latent image is formed. At this time, the surface potential of the photosensitive belt is, for example, -100 V at the maximum density portion. As the exposure device, not only the LED but also a semiconductor laser or the like can be used.

The latent image is developed by a developing device 121 using a two-component developer composed of negatively charged black toner and magnetic particles such as ferrite, and is visualized as a toner image.
In the developing device 121, a developing bias is applied to the developing sleeve 120 by an AC voltage of 200 Hz and 1500 Vpp by −5.
A voltage on which a direct current voltage (Vdc) of 00 V is superimposed is applied, and the latent image is reversely developed.

The toner image formed on the photosensitive belt 101 is applied with a voltage obtained by superimposing an AC voltage on a DC voltage by a post-charging device (not shown) to optimize the charge amount.
The image is transferred by a transfer charger 150 to a transfer material P such as recording paper sent to the photosensitive belt 101. Next, the transfer material P is separated from the photosensitive belt 101 by the charge removal by the separation charge remover 151 and the curvature of the photosensitive belt 101. Then, the sheet is sent to the fixing device 160, where it is fixed, and then discharged outside the image forming apparatus. On the other hand, the photosensitive belt 101 is subjected to the pre-exposure 180 after the residual toner is removed by the cleaning device 170, and is electrically initialized, and then subjected to the next image forming process.

The development contrast control in this embodiment will be described. As shown in FIG.
1 and the reflection density sensor 14 on the downstream side of the developing device 121.
0, the density of the patch (patch pattern) formed on the photosensitive belt 101 is measured by the density sensor 140 as in the first embodiment, and the development contrast is controlled based on the gradient of the obtained density data. .

As in the case of the first embodiment, the patches to be formed are gradation patterns of seven steps. In this embodiment, however, as described above, in order to control the development contrast more accurately and stably, numerically, the patches are formed. The formation method was improved. That is, L
An electrostatic latent image of a patch was formed on the photosensitive belt by FFH with ED power full lighting, and developed by changing the DC component of the developing bias in seven steps to obtain a seven-step pattern.

This is LED light (or laser light)
In particular, when the video signal is controlled every 10H, the video signal slightly changes depending on the sensitivity of the photoreceptor and the like, and it is difficult to grasp the value of the development contrast unless a potential sensor or the like is used. Therefore, when forming a patch, it is better to set the full lighting potential at which the potential is relatively stable and to change the developing bias by, for example, 20 V at a time when there is no potential sensor.
This is more advantageous when performing numerical control management of the development contrast.

The normal setting is charging by the primary charger 102, the potential of the photosensitive belt 101 is set to -600V, the DC component of the developing bias is set to -500V, and the full lighting potential of the LED is set to -100V. On the other hand, in the present embodiment, the developing bias is changed by 20 V in increments of -500 V,
-480V, -440V, -420V, -400V,-
380V and 7 levels are changed.

FIG. 15 shows a change in density of the patch on the photosensitive belt in this embodiment. When the patch is formed by changing the density by the developing bias, the high-voltage output response of the developing bias is slightly slower than when the patch is formed by changing the density by the light amount. The overall length increases.

Also in the present embodiment, since the development contrast value is set at a point where the reflection density is substantially saturated, the density difference is set to 0.
A value of 05 or less was defined as the development contrast (reflection density is subtracted from the reflection density of only the photosensitive belt in which no patches are formed on the photosensitive belt).

In particular, since the developing property is low in a high humidity environment, the developing contrast is initially set to 400 V and the fogging contrast (| primary charging potential-developing bias DC component |) is set to 100 V for a developing bias of -500 V. I have. On the other hand, when the environment is low humidity, the developability is enhanced. When the gradient of the reflection density is obtained under the above conditions, the difference between the patch density at the development bias of −400 V and the patch density of −420 V becomes 0.04, which is 0.05 or less. Therefore, in order to set −420 V as the DC component value of the developing bias and further set the fog removal contrast to 100 V, the primary charging potential is set to −60 V.
Change from 0V to -500V. At this time, if the primary charging potential, which is the dark portion potential, changes, the potential decreases even when the photosensitive belt 101 is irradiated with light of the same FFH. Therefore, a patch is formed again to control the development contrast. .

In the ordinary image forming apparatus, since the development contrast control as in this embodiment is not performed, the development contrast must be set to be considerably large in view of the environment, durability, and the difference in the machine main body. However, according to the control of this embodiment, the maximum density is guaranteed as the reflection density, and further unnecessary toner adhesion can be suppressed.

When the development contrast is changed, tone correction is newly set for the image signal read from the reader in accordance with the change.

As described above, according to this embodiment, the development contrast can be controlled more accurately, stably, and quantitatively as a numerical value, and accordingly, the accuracy of gradation correction can be improved. Stability of image quality and gradation can be improved.

When the control of this embodiment is performed (after improvement)
Is shown in Table 2 in comparison with the conventional case (before improvement). Similarly, this is the amount of toner consumed per sheet when 10,000 sheets of the standard chart having an image ratio of 6% are output.

As shown in Table 2, when the control of this embodiment was performed, the toner consumption could be suppressed by about 20.6% as compared with the conventional case where this control was not performed.

The timing for controlling the development contrast is set when the power of the image forming apparatus is turned on and every 2,000 sheets of image formation since the potential of the photosensitive belt, the charged state of the toner, and the like often differ between morning and evening. By doing so, it is possible to stably save the toner while further satisfying the image quality and density for the user.

As described above, according to this embodiment as well, while satisfying the user's image quality requirements, unnecessary toner adhering to the electrostatic latent image on the photosensitive drum can be saved.
The toner consumption can be controlled to a minimum, the running cost can be reduced, and an image forming apparatus with high environmental measures can be realized.

Embodiment 3 FIG. 16 is a sectional view showing still another embodiment of the image forming apparatus of the present invention. This image forming apparatus is a digital copying machine using an a-Si drum as an image carrier, and has a process speed of 120 mm at 560 mm / sec.
Sheets / minute.

Photosensitive drum 201 composed of a-Si drum
Is uniformly charged to +500 V by the primary charger 203, and then charged using a semiconductor laser having a wavelength of 680 nm.
An exposure 212 by PWM is performed at 00 dpi to form an electrostatic latent image on the photosensitive drum 201. Next, the developing device 20
2, the latent image is regularly developed and visualized as a toner image.

The developing method of the developing device 202 is a jumping development using a negative magnetic one-component toner as a developer, and the particle diameter of the magnetic toner is 6.0 μm. In two-component development, the serviceman must replace the carrier every 100,000 sheets, and maintenance is free. Therefore, the advantage of reuse is not so much taken advantage of. However, the jumping development using magnetic one-component toner has the durability. It is infinite, maintenance-free and maximizes the benefits of reuse. The developing sleeve 202a is S
It is made of US and has an outer diameter of 32 mm. The developing bias applied to the developing sleeve 202a is 2000 Hz, 1
+20 to 500Vpp, 50% duty AC voltage
A voltage obtained by superimposing a DC voltage of 0 V was used. The SB gap was 250 μm, and the SD gap was 250 μm.

After that, the post-charger 210 makes the total current −2
After the toner image is charged by flowing 00 μA, the toner image is transferred to the transfer material P that moves in the direction of the arrow by the transfer charger 204, and then the transfer material P is sent to the fixing device 207 to fix the toner image.
The transfer residual toner on the surface of the photosensitive drum 201 having been transferred is collected by the cleaning device 206 to prepare for the next image formation.

The toner collected by the cleaning device 206 is stored in the hopper 209B of the developing device 202 through the transport pipe 208. The transport pipe 208 has a screw-shaped transport member installed therein, and transports the collected toner to the developing hopper 209B by rotating the transport member. Hopper 2 containing new toner separately in developing unit 202
09A is installed.

The new toner in the hopper 209A and the collected toner in the hopper 209B are supplied to the developing device 202 by rotating the mag rollers 209A1 and 209B1 at the lower part of the hopper, respectively. Are mixed. Usually, 20% of the collected toner is mixed with 80% of the new toner. The mixing of these two toners may be performed in the lower part of the hoppers 209A and 209B. The mixed toner is sent to the developing sleeve 202a again and used for developing the photosensitive drum 201.

Developing unit 202 of reuse type image forming apparatus
Contains the toner collected from the photosensitive drum 201 remaining without being transferred. This collected toner has a very small charge amount of the toner due to deterioration as compared with the new toner, and the developing property deteriorates. As shown in FIG. 17, as compared with a non-reusable developing device using only toner,
Large concentration fluctuation. V-D
It can be seen that the variation of the curve is large even in the same environment, the density is lower than in the case of only the new toner, the development contrast is further required, and the difference is large. In this embodiment,
This was implemented to deal with this. This means that in the case of using only the new toner, the setting is made to consume extra toner that is not much reflected on the reflection density.

Therefore, it is more effective to apply the developing contrast control of the present invention to the developing device of such a reuse type image forming apparatus. Therefore, also in this embodiment, the development controller control is performed. The control method and control timing of the developing controller performed in the present embodiment are the same as those in the first embodiment.

When the control of this embodiment is performed (after improvement)
Is shown in Table 2 in comparison with the conventional case (before improvement). 100 standard charts with 6% image ratio
This is the amount of toner consumed per sheet when 0 sheets are output.

As shown in Table 2, when the control of this embodiment is performed, the toner consumption can be reduced by about 32.8% as compared with the conventional case where this control is not performed. It was possible to suppress the concentration fluctuation which is easily caused.

As described above, according to the present embodiment,
In a reusable image forming apparatus, after satisfying the user's image quality requirements, control the amount of toner consumption to a minimum by saving more toner than necessary to adhere to the electrostatic latent image on the photosensitive drum. Can reduce running costs,
In addition, an image forming apparatus having high environmental measures can be realized.

[0073]

As described above, according to the image forming apparatus of the present invention, the density gradation pattern obtained by developing the electrostatic latent image of the density gradation pattern formed on the image carrier is developed. The reflection density of the visible image is detected by reflection density detection means, and the development contrast potential is set based on the detected density gradation pattern of the density gradation pattern when the density difference between a plurality of successive density gradation patterns is equal to or less than a certain value. When the reflection density of the output image is equal to or higher than a predetermined development contrast, such as determining the difference between the potential of the density gradation pattern given a certain value or less and the DC component of the development bias as the development contrast. Since the control is performed using the saturation characteristics, it is possible to satisfy the user's image quality requirements and save unnecessary toner adhering to the latent image on the photosensitive drum, minimizing toner consumption. By suppressing the, reduces running costs, it can have high image forming apparatus in environmental resistance.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a developing device installed in the image forming apparatus of FIG.

FIG. 3 is an explanatory diagram showing a developing sleeve and a magnet of the developing device of FIG. 2;

FIG. 4 is a waveform chart showing a developing bias used in the embodiment of FIG.

FIG. 5 is a graph showing the relationship between development contrast and image reflection density.

FIG. 6 is a graph showing a relationship between development contrast and image transmission density.

FIG. 7 is a graph showing the relationship between the image reflection density and the image transmission density obtained by subtracting the density of the paper from the development contrast.

FIG. 8 is an explanatory diagram showing that toner constituting a toner image on paper has waste.

FIG. 9 is an explanatory diagram showing that a patch pattern is formed on a photosensitive drum and the density is measured by a reflection density sensor in the embodiment of FIG. 1;

FIG. 10 is an explanatory diagram showing a patch pattern formed in the embodiment of FIG. 1;

11 is an explanatory diagram showing video signals and measured densities of patches formed on the photosensitive drum in the embodiment of FIG. 1;

12 is an explanatory diagram showing a relationship between a video signal of the patch of FIG. 11 and a density difference between two adjacent patches.

FIG. 13 is a block diagram illustrating an image processing unit in the embodiment of FIG. 1;

FIG. 14 is a sectional view showing another embodiment of the image forming apparatus of the present invention.

FIG. 15 is an explanatory diagram showing a patch pattern formed in the embodiment of FIG.

FIG. 16 is a sectional view showing still another embodiment of the image forming apparatus of the present invention.

17 is an explanatory diagram showing development characteristics in the reuse type image forming apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Primary charging device 2 Developing device 12 Image exposure 20 Developing sleeve 40 Reflection density sensor 302 Patch

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA02 DA04 DA41 DD02 DE02 DE04 DE10 EA05 EA06 EB01 EC03 EC10 ED09 EF02 HB02 2H034 CB01 2H073 AA02 BA04 BA09 BA13 BA23 BA28 BA36 CA02 CA14 2H077 AA11 AD12 AD02 AD02 DA04 DA16 DA42 DA63 DA75 DA80 DA82 DB01 EA13 EA16 GA04

Claims (6)

[Claims] 1. An image forming apparatus for developing an electrostatic latent image formed on an image bearing member using a developer by a developing unit and visualizing the electrostatic latent image, wherein a plurality of density gradation patterns are formed on the image bearing member. Generating means, and reflection density detecting means for detecting reflection density information of the density gradation pattern developed by the developing means, based on a density gradient of the gradation pattern detected by the reflection density detecting means. An image forming apparatus for controlling a developing contrast potential determined by a difference between a developing bias potential of the developing unit and an image carrier potential for providing a maximum image. 2. The development contrast potential control according to claim 1, wherein, when a density difference between a plurality of successive density gradation patterns becomes a certain value or less, the potential of the density gradation pattern given the certain value or less and a developing bias. 2. The image forming apparatus according to claim 1, wherein the difference from the DC component is determined as a development contrast. 3. The image forming apparatus according to claim 1, wherein a tone correction of the output image is performed in accordance with the control of the development contrast potential. 4. The image forming apparatus according to claim 1, wherein the control of the developing contrast potential is performed for each fixed number of image formations. 5. The image forming apparatus according to claim 1, wherein the developing contrast potential control is performed when a power supply of the image forming apparatus main body is turned on. 6. The image forming apparatus according to claim 1, wherein the transfer residual developer remaining on the image carrier after the transfer is collected by a cleaning unit, and the collected developer is returned to the developing unit and reused. An image forming apparatus according to any one of the above items.