JP2942018B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or electrostatic recording system for forming a visible image by attaching a developer to a latent image formed on an image carrier. The present invention relates to an apparatus, and more particularly, to an image forming apparatus having a developer concentration control unit for appropriately controlling the toner concentration of a two-component developer.

[0002]

2. Description of the Related Art Generally, a two-component developer mainly composed of toner particles and carrier particles is used in a developing device provided in an electrophotographic or electrostatic recording type image forming apparatus. In particular, in a color image forming apparatus for forming a full-color or multi-color image by an electrophotographic method, most developing devices use a two-component developer from the viewpoint of the color of the image. As is well known, the toner concentration (that is, the ratio of the weight of the toner particles to the total weight of the carrier particles and the toner particles) of the two-component developer is a very important factor in stabilizing the image quality. The toner particles of the developer are consumed during development, and the toner concentration changes. For this reason, the toner concentration of the developer is accurately detected in a timely manner by using the developer concentration control means (ATR), the toner is replenished in accordance with the change, the toner concentration is constantly controlled to be constant, and the image quality is improved. Need to be retained.

FIG. 5 shows an overall configuration example of a conventional image forming apparatus provided with a developer concentration control means, in this example, a digital copying machine of an electrophotographic system. First, if the image of the original 21 is CC
An analog image signal read and obtained by D1 is amplified to a predetermined level by an amplifier 2, and is converted into a digital image signal of, for example, 8 bits (0 to 255 gradations) by an analog-digital converter (A / D converter) 3. Is converted to Next, the digital image signal is supplied to a γ converter (a converter constituted by a 256-byte RAM in this example and performing a density conversion by a look-up table method) 5 to be γ-converted.
After being corrected, it is input to a digital-analog converter (D / A converter) 9. Here, the digital image signal is converted into an analog image signal again and supplied to one input of the comparator 11. The other input of the comparator 11 is supplied with a triangular wave signal of a predetermined period generated from the triangular wave generating circuit 10. The analog image signal supplied to one input of the comparator 11 is compared with the triangular wave signal and pulsed. It is width modulated. The pulse width modulated binarized image signal is input to the laser drive circuit 12 as it is, and is used as an on / off control signal for light emission of the laser diode 13. The laser beam emitted from the laser diode 13 is scanned in the main scanning direction by a well-known polygon mirror 14, passes through an f / θ lens 15 and a reflection mirror 16, and rotates in the direction indicated by an arrow in FIG. Illuminated above to form an electrostatic latent image.

On the other hand, the photosensitive drum 17 is uniformly discharged by the exposure device 18 and is uniformly charged, for example, negatively by the primary charger 19. Thereafter, an electrostatic latent image corresponding to the image signal is formed by receiving the above-described laser light irradiation. This electrostatic latent image is developed into a visible image (toner image) by the developing device 20. This toner image is stretched between two rollers 25 and 26 and is transferred to a transfer material 23 held on a transfer material carrying belt 27 which is driven endlessly in the direction of the arrow in FIG.
Is transcribed by the action of The residual toner remaining on the photosensitive drum 17 is scraped off by the cleaner 24 thereafter. Although only a single image forming station (including a photosensitive drum 17, an exposing unit 18, a primary charging unit 19, a developing unit 20, and the like) is shown for simplicity of explanation, the case of a color image forming apparatus will be described. For example, the image forming stations for the respective colors of cyan, magenta, yellow, and black are sequentially arranged on the transfer material carrying belt 27 along the moving direction.

Further, in order to correct the changed toner density in the developing device 20 due to the development of the latent image, a video count type developer density control means is provided, and the output level of the digital image signal for each pixel is adjusted. Accumulation is performed and toner is replenished in a predictable manner. That is, the analog-digital converter 3
The output level of the image signal converted into a digital signal is integrated for each pixel, and this is converted into a video count number by the video counter 4 and sent to the CPU 6. The CPU 6 converts the video count into a replenishment amount and sends it to the motor drive circuit 7 as a toner replenishment signal. The motor drive circuit 7 drives the motor 28 for a time corresponding to the toner replenishment signal, and rotates and drives the toner conveying screw 30 in the toner replenishment tank 8 containing the toner 29 for the above-mentioned predetermined time. An appropriate amount of toner is replenished in the developing device 20 so that the toner concentration in the developing device 20 is kept constant.

As described above, the conventional developer concentration control means converts the video count number of the original image into the replenishment amount and predicts the consumption amount to perform the replenishment of the toner. It is inevitable that a minute error occurs, and a minute error due to fluctuations in the consumption system and the supply system may also occur.
Due to these minute errors, the toner concentration, that is, the mixing ratio between the toner particles and the carrier particles is gradually shifted from the initial set value (specified value). Since the above-mentioned conventional developer concentration control means does not have a means for correcting this deviation, there is a serious disadvantage that the toner concentration greatly deviates from the allowable range of the initial set value.

For this purpose, a second developer concentration control means is provided, and the second developer concentration control means is operated at a predetermined timing. At this time, a patch-like reference image formed on the photosensitive drum 17 is formed. To determine whether the toner is excessively replenished or insufficiently replenished. Based on this determination, the next video count from the video counter 4 is corrected, and the toner replenishment from the CPU 6 is performed. A developer concentration control method for correcting the signal, that is, the second developer concentration control means for correcting the deviation of the toner concentration from the initial set value to the first developer concentration control means of the video counter system. Has been proposed.

[0008]

However, in the above-mentioned conventional developer concentration control system, the second developer concentration control means is operated every time the copy operation reaches a certain number of copies (that is, at intervals of a certain number of copies). An error in the replenishment toner amount is detected and corrected. If the second developer density control means is operated at regular intervals as described above, the amount of toner consumed in the copy operation for each sheet varies depending on the original image. Naturally, there is a difference in the amount of replenished toner supplied by the first developer concentration control means during the operation of. For example, there is a large difference in the amount of consumed toner between the case where a fixed number of copies of a document image having a relatively high image density are copied and the case where a fixed number of copies are made of a document image having a relatively low image density. Different. As described above, the replenishment of the toner by the first developer concentration control means is a predicted replenishment, and an error is likely to occur. Also, a small error due to fluctuations in the consumption system and the supply system may occur. Therefore, when a large amount of toner is supplied, a replenishment error becomes large, and there is a disadvantage that the image density is largely different between the first copy image and the last copy image. In particular, when a large number of copies of the same document are made, such unevenness in image density is a fatal defect.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress the fluctuation range of an error occurring during toner replenishment and to maintain the toner concentration of a two-component developer within an allowable range of an initial set value at all times. An object of the present invention is to provide an image forming apparatus provided with a control unit.

[0010]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention uses a latent image forming means for forming an electrostatic latent image corresponding to an image information signal on an image carrier, and a two-component developer for forming the electrostatic latent image formed on the image carrier using a two-component developer. Developing means for developing the developing means, a toner replenishing means for replenishing toner to the developing means, and operating the toner replenishing means based on image density information of the image information signal to replenish toner every time an image is formed. First developer concentration control means, second developer concentration control means for detecting the toner concentration of the two-component developer, and actuating the toner replenishing means based on the detection result to replenish the toner; The image forming apparatus includes an integrating means for integrating the image density information of the image information signal, and the second developer density controlling means is activated every time the integrated value becomes equal to or more than a predetermined value. Image characterized by It is formed apparatus.

In one embodiment of the present invention, the integrating means converts the output level of each pixel of the read original image into a pulse number, and sequentially adds the pulse numbers to integrate the image density information. I do.

[0012]

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

An image forming apparatus to which the present invention can be applied forms a latent image corresponding to an image information signal on an image carrier such as a photosensitive member or a dielectric by an electrophotographic system, an electrostatic recording system, or the like. The image is developed by a developing device using a two-component developer containing toner particles and carrier particles as main components to form a visible image (toner image), and the visible image is transferred to a transfer material such as paper. Any configuration may be used as long as the image is a permanent image.

First, an overall configuration of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to an electrophotographic digital copying machine. However, it goes without saying that the present invention can be equally applied to various other image forming apparatuses of an electrophotographic type and an electrostatic recording type.

In FIG. 1, an image of a document 31 to be copied is projected by a lens 32 onto an image pickup device 33 such as a CCD. The image sensor 33 decomposes an original image into a number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The analog image signal output from the image sensor 33 is sent to an image signal processing circuit 34, where the image signal is converted into a pixel image signal having an output level corresponding to the density of the pixel. Sent.

The pulse width modulation circuit 35 forms and outputs a laser drive pulse having a width (time length) corresponding to the level of each input pixel image signal. That is, as shown in FIG. 3A, a wider drive pulse W is applied to a high-density pixel image signal, and a narrower drive pulse S is applied to a low-density pixel image signal. , A drive pulse I having an intermediate width is formed for a medium-density pixel image signal.

The laser drive pulse output from the pulse width modulation circuit 35 is supplied to the semiconductor laser 36, and causes the semiconductor laser 36 to emit light for a time corresponding to the pulse width. Therefore, the semiconductor laser 36 is driven for a longer period of time for the high-density pixels, and is driven for a shorter period of time for the low-density pixels. Therefore, the photosensitive drum 40
By using the optical system described below, a longer range is exposed in the main scanning direction for high density pixels, and a shorter range is exposed in the main scanning direction for low density pixels. That is, the dot size of the electrostatic latent image differs according to the density of the pixel.
Therefore, it goes without saying that the toner consumption for the high density pixels is larger than that for the low density pixels. In FIG. 3D, the electrostatic latent images of the low, medium and high density pixels are indicated by L, M and H, respectively.

The laser beam 36a emitted from the semiconductor laser 36 is swept by a rotating polygon mirror 37, and a lens 38 such as an f / θ lens and a fixed mirror 39 for directing the laser beam 36a toward a photosensitive drum 40 as an image carrier. As a result, a spot image is formed on the photosensitive drum 40. Thus, the laser light 36a scans the photosensitive drum 40 in a direction (main scanning direction) substantially parallel to the rotation axis of the drum 40,
An electrostatic latent image will be formed.

The photosensitive drum 40 is an electrophotographic photosensitive drum having amorphous silicon, selenium, OPC or the like on its surface and rotating in the direction of the arrow. Is charged uniformly. Thereafter, exposure scanning is performed with a laser beam modulated in accordance with the image information signal described above, whereby an electrostatic latent image corresponding to the image information signal is formed. This electrostatic latent image is reversely developed by a developing device 44 using a two-component developer 43 in which toner particles and carrier particles are mixed, and a visible image (toner image) is formed. Here, the reversal development is a development method in which a toner charged to the same polarity as the latent image is attached to a region of the photoconductor exposed to light, and the toner is visualized.
This toner image is stretched between two rollers 45 and 46,
The image is transferred onto a transfer material 48 held on a transfer material carrying belt 47 driven endlessly in the direction of the arrow by the action of a transfer charger 49.

The transfer material 48 onto which the toner image has been transferred is separated from the transfer material carrying belt 47, is conveyed to a fixing device (not shown), and is fixed to a permanent image. Further, the residual toner remaining on the photosensitive drum 40 after the transfer is removed by the cleaner 50 thereafter.

Although only a single image forming station (including a photosensitive drum 40, an exposing unit 41, a primary charging unit 42, a developing unit 44, etc.) is shown in FIG. In the case of (1), for example, image forming stations for each color of cyan, magenta, yellow, and black are sequentially arranged on the transfer material carrying belt 47 along the moving direction, and a document is placed on the photosensitive drum of each image forming station. Are sequentially formed, developed by a developing device having a corresponding color toner, and sequentially transferred to a transfer material 48 held and conveyed by a transfer material carrying belt 47. Will be.

FIG. 2 shows an example of the developing device 44. As shown in the drawing, the developing device 44 is disposed so as to face the photosensitive drum 40, and the inside thereof has a partition wall 5 extending in the vertical direction.
1, a first chamber (developing chamber) 52 and a second chamber (stirring chamber) 5
It is divided into three. A non-magnetic developing sleeve 54 that rotates in the direction of the arrow is disposed in the first chamber 52, and a magnet 55 is fixedly disposed in the developing sleeve 54. The developing sleeve 54 carries and transports a layer of a two-component developer (including a magnetic carrier and a non-magnetic toner) whose thickness is regulated by a blade 56, and transfers the developer in a developing area opposed to the photosensitive drum 40. To develop the electrostatic latent image. In order to improve the development efficiency, that is, the rate at which toner is applied to the latent image, a development bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the development sleeve 54 from a power supply 57.

The first chamber 52 and the second chamber 53 are provided with developer stirring screws 58 and 59, respectively. The screw 58 stirs and conveys the developer in the first chamber 52, and the screw 59 communicates with the toner 63 supplied by the rotation of the conveying screw 62 from a toner discharge port 61 of a toner replenishing tank 60 which will be described later. Developer 43
Are agitated and conveyed to make the toner concentration uniform. The partition 51 has a first chamber 52 at the front and rear ends in FIG.
A developer passage (not shown) is formed to allow the first chamber and the second chamber 53 to communicate with each other. The toner is consumed by the development due to the conveying force of the screws 58 and 59, and the toner concentration is reduced. The developer in the second chamber 53 moves into the second chamber 53 from one passage, and the developer whose toner concentration has been recovered in the second chamber 53 moves into the first chamber 52 from the other passage. I have.

The image signal processing circuit 34 is used to correct the changed developer concentration in the developing unit 44 due to the development of the electrostatic latent image, that is, to control the amount of toner supplied to the developing unit 44. Is counted for each pixel. This counting is performed as follows in the embodiment of FIG.

First, the output signal of the pulse width modulation circuit 35 is supplied to one input of an AND gate 64.
A clock pulse oscillator 65 is connected to the other input of the ND gate.
(Pulse shown in FIG. 3 (b)). Therefore, as shown in FIG. 3C, the AND gate 64 outputs a number of clock pulses corresponding to the respective pulse widths of the laser driving pulses S, I and W, that is, a number of clock pulses corresponding to the density of each pixel. A pulse is output.
The number of clock pulses is integrated by the counter 66 for each image, and the video count is calculated. The pulse integration signal C ₁ (video count number) for each image from the counter 66 corresponds to the amount of toner consumed from the developing device 44 to form one toner image on the document 31. I have.

Therefore, the pulse integration signal C ₁ is sent to the CPU
The data is supplied to the RAM 67 and stored in the RAM 68. CPU6
Reference numeral 7 denotes a rotation driving time of the transport screw 62 required to supply the toner 63 in an amount corresponding to the toner amount consumed from the developing device 44 from the toner replenishing tank 60 to the developing device based on the pulse integration signal C _1. After the calculation, the motor driving circuit 69 is controlled to drive the motor 70 only during the calculated time. Thus, in general, if the pulse integration value is large, the driving time of the motor 70 is longer, and if the pulse integration value is small, the driving time of the motor 70 is shorter.

The driving force of the motor 70 is transmitted to the conveying screw 62 via a gear train 71,
Reference numeral 2 conveys the toner 63 in the toner replenishing tank 60 to replenish the developing device 44 with a predetermined amount of toner. This toner supply is performed each time the development of one image is completed.

By the way, the toner is supplied to the developing device based on the density information obtained by photoelectrically converting the image of the document to be copied as described above, because the actual toner density of the developer is detected and based on the detected toner density. This is not a replenishment of toner, but a kind of speculative replenishment. Therefore, as described above, the amount of toner replenishment from the toner replenishment tank 60 to the developing device 44 and the
When the toner consumption amount changes from the expected value, the toner concentration of the developer 43 in the developing device 44 gradually deviates from the initial set value due to fluctuations in the consumption system and the supply system. If this deviation is not corrected, the toner density will deviate significantly from the allowable range of the initial set value.

Therefore, in this embodiment, when the integrated value of the number of pulses supplied from the counter 66 to the CPU 67 reaches a certain number, that is, the pulse integrated signal C ₁ (video count number) for each image from the counter 66. ) Are sequentially added, when the total count reaches a certain value, before the image formation for the next original is started, the second developer density control unit is operated to activate the photosensitive drum 40. To form a reference image.

More specifically, a reference image signal generation circuit 72 for generating a reference image signal having a signal level corresponding to a predetermined density is provided, and the reference image signal from this generation circuit 72 is transmitted to the pulse width modulation circuit 35. To generate a laser drive pulse having a pulse width corresponding to the predetermined density. The laser drive pulse is supplied to the semiconductor laser 36, the laser 36 emits light for a time corresponding to the pulse width, and the photosensitive drum 40 is scanned. (At this time, the counter 66 is not operated.) Thereby, a reference electrostatic latent image corresponding to the predetermined density is formed on the photosensitive drum 40, and this reference electrostatic latent image is developed by the developing device 44. I do. The patch-like reference toner image thus obtained is irradiated with light from a light source 73 such as an LED, and the reflected light is received by a photoelectric conversion element 74. Since the output signal of the photoelectric conversion element 74 corresponds to the density of the reference toner image, the output signal eventually corresponds to the actual toner density of the two-component developer in the developing device 44.

The output signal of the photoelectric conversion element 74 is supplied to one input of a comparator 75. A reference signal corresponding to a specified toner density of the developer 43 (toner density at an initial set value) is input from the reference voltage signal source 76 to the other input of the comparator 75. Accordingly, since the comparator 75 compares the specified toner density with the actual toner density in the developing device, as a result of comparing the two input signals, the comparator 75 determines the actual toner density of the developer 43 in the developing device 44. An output signal indicating that the toner density is higher than the specified value or an output signal indicating that the toner density is lower than the specified value is generated. When there is no difference between the two input signals, an output signal indicating the difference is generated.

The output signal of the comparator 75 is supplied to the CPU 67. In this embodiment, the CPU 67 controls the next toner supply operation based on the output signal from the comparator 75 as follows.

First, when the actual toner density detected by the photoelectric conversion element 74 is the same as the specified toner density, the CPU 67 executes the immediately preceding second developer density control means stored in the RAM 68. After the operation of, the total integrated value obtained by sequentially adding the number of pulses supplied from the counter 66 is canceled, and the toner replenishing operation accompanying the next image forming operation is performed as described above.

Next, when the actual toner density of the developer 43 detected by the photoelectric conversion element 74 is lower than the specified value, that is, when the toner is insufficiently replenished, the CPU 67 determines the shortage. The screw 62 is operated so as to supply the toner to the developing device 44. That is, the comparator 7
5, a screw rotation time required to supply the insufficient toner to the developing device 44 is calculated,
By controlling the motor drive circuit 69, the motor 70
Is rotated to supply the insufficient toner to the developing device 44. When an image is formed from the next original, the toner supply operation is performed as described above. Of course, the second
The total integrated value obtained by sequentially adding the number of pulses supplied from the counter 66 after the operation of the developer concentration control means is canceled.

Further, when the actual toner concentration of the developer 43 detected by the photoelectric conversion element 74 is higher than a specified value, that is, when the toner is excessively replenished, the CPU 67 sets the comparator 75 The amount of excess toner in the developer is calculated based on the output signal from. Then, when an image is formed from a document, toner is supplied so as to eliminate the excess toner amount. For example, a toner replenishment amount per image is calculated so as to offset the excess toner amount, and the toner is replenished, or an image is formed without replenishing the toner until the excessive toner amount is consumed. Form an image without replenishment, consume excess toner,
When the excess toner amount is consumed, control is performed such that the toner supply operation is performed as described above. Also in this case, the total integrated value obtained by sequentially adding the number of pulses supplied from the counter 66 after the operation of the second developer concentration control unit immediately before is canceled.

The above control operation will be further described with reference to the flowchart of FIG.

First, when the start button is pressed to copy a document, the document is read as described above in block S101, and a photoelectric conversion signal corresponding to the density of each pixel of the document image is generated. Next, in block S102, the output level of each pixel is counted and integrated to calculate a video count. This pulse integrated value is sent to the memory by the blotter S103, added to the currently stored pulse integrated value, and stored as a total integrated value. If there is no stored pulse integrated value, such as the case of the first pulse integrated value, this pulse integrated value is stored. Next, in block S104, the amount of toner replenishment per image, that is, the number of rotations of the screw 62, is determined from the pulse integrated value. Is performed. When one toner image is formed, before the formation of the next toner image in block S106, the screws 62 are rotated by the rotation speed determined as described above.
Is rotated to supply toner. Next, decision block S
The total integrated value stored in the memory at 107 is a predetermined video count number K ₀ (constant value) stored in the memory in advance.
Is determined, and if it has been reached (YES), the second developer concentration control means is operated in block S108,
A reference image is formed and the above-described operation is performed. Then, it is determined in a decision block S109 whether or not the copy operation has been completed. If the copy operation has been completed (YES), the process returns to the start, and if not, the process returns to the block S105 to continue the copy operation. Also, the decision block S10
When the total integrated value has not reached the predetermined video count number K ₀ in 7 (NO), decision block S110
To determine whether or not the copy operation has been completed. If the copy operation has been completed (YES), the process returns to the start.
O) Return to block S105 and continue the copy operation.
Hereinafter, the total integrated value of the memory is equal to a predetermined video count number K.
Each time it reaches ₀ , the same operation is repeated by operating the second developer concentration control means.

As described above, in this embodiment, the integrated value (video count number) obtained by counting the output level of each pixel of the read original image is sequentially added, and this total integrated value is set to a predetermined constant value. Since the second developer concentration control means is activated when it reaches, the second developer concentration control means is activated every time substantially the same amount of toner is consumed by the development of the latent image. Will be. That is, the second developer concentration control means is activated each time substantially the same amount of toner is replenished. Accordingly, there is almost no difference in the amount of toner replenished by the first developer density control means while the second developer density control means is operating, so that the change width of the image density can be suppressed and the toner density can be initialized. It can always be maintained within the allowable range of values.

[0039]

Further, in a full-color copying machine or the like, the amount of toner replenishment differs for each color even if toner is replenished for a certain period of time due to differences in physical properties of toners of different colors. In this case, a correspondence table between the toner replenishment time and the toner replenishment amount is provided for each toner of each color, and the time for replenishing the toner of each color is determined with reference to this table, and the toner is replenished. In this case, the replenishment accuracy is improved.

Further, in the above embodiment, the actual toner density of the developer in the developing device was measured by forming a patch image on the photosensitive drum and measuring the density of this image. The actual toner concentration of the developer can also be measured by directly irradiating the developer on the developing sleeve or the like with light and measuring the reflected light. However, if the toner is colored black with carbon black, there is no significant difference in the spectral reflectance between the toner and the carrier.
In this method, the detection accuracy of the toner density is poor. Therefore, when such a toner is used, the toner density can be measured with higher accuracy by using the above-described method based on the patch image.

Note that the present invention can be applied to an image forming apparatus which performs shading of an image by a dither method. The present invention is also applicable to an image forming apparatus that forms a toner image based on an image information signal output from a computer or the like instead of copying a document. Of course, as described above, the present invention can be applied to a color image forming apparatus. In this case, the above-described image forming unit may be provided for each color along the traveling direction of the transfer material carrying belt 47. However, the image of the document may be color-separated to form an image information signal for each color, and toner supply may be controlled for each color in the same manner as described above. The present invention is also applicable to a color image forming apparatus having a configuration in which a plurality of developing units are arranged around a photosensitive drum. Further, it goes without saying that various modifications and changes can be made as necessary.

[0043]

As described above, according to the image forming apparatus of the present invention, the latent image forming means for forming an electrostatic latent image corresponding to the image information signal on the image carrier, and the latent image forming means formed on the image carrier. Developing means for developing the electrostatic latent image using a two-component developer,
A toner replenishing unit for replenishing toner to the developing unit, a first developer concentration control unit for operating the toner replenishing unit based on image density information of an image information signal to replenish toner every time image formation is performed, A second developer concentration control unit that detects the toner concentration of the two-component developer and operates the toner supply unit based on the detection result to supply the toner;
The image forming apparatus has an integrating means for integrating the image density information of the image information signal, and the second developer density controlling means is activated every time the integrated value becomes equal to or more than a certain value. With this configuration, the second developer concentration control means operates each time substantially the same amount of toner is replenished. Accordingly, there is almost no difference in the amount of toner supplied by the first developer density control means while the second developer density control means is operating, so that the change width of the image density can be suppressed, and the toner density is always set to the initial value. There is a remarkable effect that the set value can be maintained within the allowable range. Thus,
Even if a minute error occurs due to the predicted replenishment of the toner by the first developer concentration control unit, or a minute error occurs due to fluctuations in the consumption system and the supply system, the second developer concentration control unit operates. There is no disadvantage that the image density of the first copy image differs greatly from that of the last copy image.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view illustrating a schematic configuration of a developing device included in the image forming apparatus of FIG.

3 is a waveform diagram illustrating a method of counting density information of an image information signal in the image forming apparatus of FIG.

FIG. 4 is a flowchart for explaining a basic operation of one embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating an overall configuration of an example of a conventional image forming apparatus.

[Explanation of symbols]

 Reference Signs List 40 photosensitive drum 43 two-component developer 44 developing device 60 toner supply tank 63 toner 65 clock pulse oscillator 66 counter 67 CPU 68 RAM 69 motor drive circuit 70 motor 72 reference image signal generation circuit 73 light source 74 photoelectric conversion element 75 comparator 76 Reference voltage signal source

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/00 303 G03G 15/08-15/08 115 G03G 21/00 370-520 H04N 1/29

Claims (2)

(57) [Claims] 1. A latent image forming means for forming an electrostatic latent image corresponding to an image information signal on an image carrier, and developing the electrostatic latent image formed on the image carrier using a two-component developer. A developing unit, a toner replenishing unit that replenishes the developing unit with toner, and a first replenishing unit that operates the toner replenishing unit based on image density information of the image information signal to replenish toner every time image formation is performed. Developer concentration control means, and second developer concentration control means for detecting the toner concentration of the two-component developer and actuating the toner supply means based on the detection result to replenish the toner. The image forming apparatus according to claim 1, further comprising: integrating means for integrating the image density information of the image information signal, wherein the second developer density controlling means is operated each time the integrated value becomes equal to or more than a predetermined value. Image forming apparatus characterized by the following 2. The image processing apparatus according to claim 1, wherein the integration unit converts an output level of each pixel of the read original image into a pulse number and sequentially adds the pulse numbers to integrate the image density information. Item 1. The image forming apparatus according to Item 1.