JPH0527598A - Image forming device - Google Patents

Abstract

PURPOSE:To suppress an error in a toner replenishing caused by the difference of an image forming method. CONSTITUTION:A CPU 67 determines whether the formation of one picture element from the contents of an original is executed in a method for the image of 400-lines, or in a method for the image of 200-lines, instructs a picture element density changing over switch 77 to change over the modulated pulse width of a pulse width modulating circuit 35, for the image of 200-lines or 400-lines. The CPU 67 has two conversion tables for showing the correspondence relation of the number of video counts and a toner replenishing time (a replenishing quantity) in the images of 400-lines and 200-lines, and when one picture element is formed by the image of 200-lines, the number of the video counts integrated on a counter 66 is converted into the toner replenishing time through the use of the conversion table corresponding to the image of 200-lines. On the other hand, when one picture element is formed by the image of 400-lines, the number of the video counts is converted into the toner replenishing time through the use of the conversion table corresponding to the image of 400-lines, to replenish the toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming for a copying machine, a printer, etc., such as an electrophotographic system or an electrostatic recording system in which a developer is attached to a latent image formed on an image carrier to make it a visible image. More specifically, the present invention relates to an image forming apparatus including a developer concentration control device that appropriately controls the toner concentration of a two-component developer.

[0002]

2. Description of the Related Art Generally, a two-component developer containing toner particles and carrier particles as a main component is used in a developing device provided in an electrophotographic or electrostatic recording type image forming apparatus. Particularly, in a color image forming apparatus that forms a full-color image or a multi-color image by an electrophotographic method, most developing apparatuses use a two-component developer from the viewpoint of image tint and the like. As is well known, the toner concentration (that is, the ratio of the weight of toner particles to the total weight of carrier particles and toner particles) of this 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. Therefore, the developer concentration control device (ATR) is used to accurately detect the toner concentration of the developer at appropriate times, toner is replenished according to the change, and the toner concentration is constantly controlled to maintain the image quality. Need to hold.

FIG. 7 shows an example of the overall configuration of an image forming apparatus equipped with a conventional developer concentration control apparatus, in this example, an electrophotographic digital copying machine. First, the image of the document 21 is CC
An analog image signal read and obtained by D1 is amplified to a predetermined level by an amplifier 2 and is, for example, an 8-bit (0 to 255 gradation) digital image signal by an analog-digital converter (A / D converter) 3. Is converted to. Next, this digital image signal is supplied to a γ converter (a converter which is composed of a 256-byte RAM in this example, and which performs density conversion by a look-up table method) 5 and outputs γ.
After being corrected, the digital-analog converter (D / A converter) 9 is input. Here, the digital image signal is converted again into an analog image signal 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 cycle generated from the triangular wave generating circuit 10, and the analog image signal supplied to one input of the comparator 11 is compared with this triangular wave signal and pulsed. It is width modulated. This pulse-width-modulated binary image signal is directly input to the laser drive circuit 12 and used as an ON / OFF control signal for emission of the laser diode 13. The laser light emitted from the laser diode 13 is scanned in the main scanning direction by a well-known polygon mirror 14, passes through the f / θ lens 15 and the reflection mirror 16, and is rotated in the arrow direction. It will be illuminated above and will form an electrostatic latent image.

On the other hand, the photosensitive drum 17 is uniformly discharged by the exposing device 18, and is uniformly charged by the primary charging device 19, for example, to be negative. Then, upon receiving the above-mentioned laser light irradiation, an electrostatic latent image corresponding to the image signal is formed. This electrostatic latent image is developed into a visible image (toner image) by the developing device 20. This toner image is stretched between the two rollers 25 and 26, and is transferred to the transfer material 23 held on the transfer material carrying belt 27 which is endlessly driven in the direction of the arrow in the figure, and the transfer charger 22
Is transcribed by the action of. The residual toner remaining on the photosensitive drum 17 is then scraped off by the cleaner 24. Note that only one image forming station (including the photoconductor drum 17, the exposure device 18, the primary charging device 19, the developing device 20 and the like) is shown for simplification of description, but in the case of a color copying machine, For example, four image forming stations having the same configuration for each color of cyan, magenta, yellow, and black are sequentially arranged on the transfer material carrying belt 27 along its moving direction.

Further, in order to correct the toner density which has changed in the developing device 20 due to the development of the latent image, a video count type developer density control device is provided to control the output level of the digital image signal for each pixel. The toner has been added up and the toner is being predicted to be replenished. That is, the analog-digital converter 3
The output level of the image signal converted into a digital signal by each pixel is integrated, 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 number 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 only for the time corresponding to the toner replenishment signal, and rotationally drives the toner conveying screw 30 in the toner replenishment tank 8 containing the toner 29 for the above predetermined time, and the toner replenishment tank 8 develops the toner. An appropriate amount of toner is replenished in the developing device 20 to keep the toner density in the developing device 20 constant.

[0006]

By the way, for example, in a digital electrophotographic laser beam printer or the like, a method of forming pixels includes a so-called "solid image" such as a photograph and a picture and a so-called "line" such as characters and lines. "Image" may be changed. As an example, as shown in FIG. 4, a method of forming one pixel at 400 dpi (dots / inch) in both the laser scanning direction and the photoconductor drum rotation direction, and 200 dpi in the laser scanning direction and the photoconductor There is a method of forming one pixel at 400 dpi in the rotating direction of the drum. In the present specification, the former (400 × 400
dpi) is called a 400-line image method, and the latter (200 × 4)
00 dpi) will be referred to as a 200-line image method. An image for which details such as characters and lines are required is formed by a 400-line image method with high resolution, and an image for which gradation is desired, such as photographs and pictures, can be dot-modulated.
Switching means is often provided so as to form the 00-line image method. In such a case, according to the 200-line image method and the 400-line image method, for example, as shown in FIG. 5, results obtained when pixels are formed by a laser beam on a photoconductor drum of OPC (organic semiconductor) of a Florocyanine system. , The toner consumption for the same video count is different,
The amount of consumed toner is larger when the image is formed by the 200-line image method. Therefore, as in the above-mentioned conventional example, if the video count number obtained by integrating the output level of the digital image signal for each pixel is uniquely converted into the toner replenishment time and the toner is replenished with a predictive replenishment error, a replenishment error occurs and a stable density is obtained. There is a drawback that a high quality image cannot be obtained.

Therefore, an object of the present invention is to change the toner replenishment amount in accordance with the difference in pixel forming method when converting the density information of the image of the image information signal into the toner replenishment amount, and suppress the error that occurs during toner replenishment. An image forming apparatus including the developer concentration control device is provided.

[0008]

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention forms an electrostatic latent image corresponding to an image information signal on an image carrier, develops the electrostatic latent image with a two-component developer to form a visible image, and In an image forming apparatus for transferring an image to a transfer material, a toner replenishing means for replenishing the toner of the two-component developer and a toner replenishing means for operating the toner replenishing means according to the image density information of the image information signal to replenish the toner. An operation time of the toner replenishing means, which is equipped with a first developer concentration control device and is operated by the first developer concentration control device in accordance with a difference in a pixel forming method for forming the electrostatic latent image. The image forming apparatus is characterized in that the toner is corrected and toner is replenished.

In one embodiment of the present invention, a second developer concentration control device for detecting the toner concentration of the two-component developer is provided, and the second developer concentration control device is operated at a predetermined timing. The toner replenishment error by the first developer concentration control device is corrected by the output signal from the lever of the second developer concentration control device according to the toner concentration.

In another embodiment of the present invention, the video count number obtained from the density information of the image of the image information signal is supplied to the toner replenishing means in accordance with the difference in the pixel forming method for forming the electrostatic latent image. The conversion table for converting the operating time is changed and toner is replenished.

[0011]

Embodiments of the present invention will be described in detail below 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 photoconductor or a dielectric by an electrophotographic system, an electrostatic recording system, or the like, and the latent image is formed by a toner. Particles and carrier particles are used as the main components to develop with a developing device that uses a two-component developer to form a visible image (toner image). These visible images are transferred to a transfer material such as paper and permanently fixed by a fixing unit. It may be of any structure.

First, the overall construction of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. Although the present embodiment shows the case where the present invention is applied to an electrophotographic digital copying machine, it goes without saying that the present invention is equally applicable to other various image forming apparatuses such as an electrophotographic type and an electrostatic recording type.

In FIG. 1, an image of an original 31 to be copied is projected by a lens 32 onto an image pickup device 33 such as a CCD. The image pickup device 33 decomposes the image of the original 31 into a large number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The analog image signal output from the image pickup device 33 is sent to the image signal processing circuit 34, where it is converted into a pixel image signal having an output level corresponding to the density of the pixel for each pixel, and the pixel image signal is supplied to the pulse width modulation circuit 35. 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 provided for a high-density pixel image signal, and a narrower drive pulse S is provided for a low-density pixel image signal. , A drive pulse I having an intermediate width is formed for the 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 the semiconductor laser 36 is caused to emit light for a time corresponding to the pulse width. Therefore, the semiconductor laser 36 is driven for a longer period of time with respect to the high-concentration pixels, and is driven for a shorter period of time with respect to the low-concentration pixels. Therefore, the photosensitive drum 40
The optical system described below exposes a high density pixel in a longer range in the main scanning direction and a low density pixel in a shorter range in the main scanning direction. That is, the dot size of the electrostatic latent image differs depending on the density of the pixel.
Therefore, of course, the toner consumption amount for the high density pixels is larger than that for the low density pixels. In FIG. 3D, the electrostatic latent images of low, medium and high density pixels are shown by L, M and H, respectively.

A laser beam 36a emitted from the semiconductor laser 36 is swept by a rotary 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 which is an image carrier. Thus, a spot image is formed on the photosensitive drum 40. Thus, the laser beam 36a scans the drum 40 in a direction (main scanning direction) substantially parallel to the rotation axis of the photosensitive drum 40,
An electrostatic latent image will be formed.

The photosensitive drum 40 is an electrophotographic photosensitive drum that has amorphous silicon, selenium, OPC, etc. on its surface and rotates in the direction of the arrow. After being uniformly discharged by the exposure device 41, the primary charging device 42 is used. Are uniformly charged by. After that, the laser light modulated corresponding to the above-mentioned image information signal is exposed and scanned, whereby an electrostatic latent image corresponding to the image information signal is formed. This electrostatic latent image is reverse-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 toner charged with the same polarity as the latent image is attached to a region of the photoconductor exposed to light to visualize the toner.
This toner image is stretched between two rollers 45 and 46,
It is transferred to the transfer material 48 held on the transfer material carrying belt 47 which is endlessly driven in the direction of the arrow in the figure by the action of the transfer charger 49.

In this embodiment, a pixel density changeover switch 77 is provided, and the pulse density modulation circuit 35 is controlled by a pixel density changeover signal from the pixel density changeover switch 77, depending on the difference in pixel forming method. The pulse width of the pulse signal output from the pulse width modulation circuit 35 is changed. That is, in this embodiment, 400 line images and 2
Since it is a 00 line image, the pulse width modulation circuit 35, when the pixel density switching signal indicates a 200 line image,
For a pixel image signal of the same density level from the image signal processing circuit 34, 400 for recording a 200-line image.
A pulse having a width twice the pulse width for recording a line image is output.

Although only one image forming station (including the photosensitive drum 40, the exposure device 41, the primary charging device 42, the developing device 44, etc.) is shown in the figure for the sake of simplicity, the color image forming apparatus is not shown. In this case, for example, four 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 thereof, and on the photoconductor drum of each image forming station. An electrostatic latent image for each color obtained by color-separating the image of the original is sequentially formed, developed by a developing device having corresponding color toner, and sequentially transferred to a transfer material 48 which is held and conveyed by a transfer material carrying belt 47. Will be done.

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

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

Developer stirring screws 58 and 59 are arranged in the first chamber 52 and the second chamber 53, respectively. The screw 58 stirs and conveys the developer in the first chamber 52, and the screw 59 and the toner 63 supplied by the rotation of the conveying screw 62 from the toner discharge port 61 of the toner replenishing tank 60, which will be described later, and the inside of the developing device. Developer 43 in
And are conveyed by stirring to make the toner concentration uniform. The partition wall 51 has a first chamber 52 at the front and rear end portions in FIG.
And a second chamber 53 are connected to each other through a developer passage (not shown), and the first chamber in which the toner concentration is lowered due to the consumption of toner by the development due to the conveying force of the screws 58 and 59. The developer in 52 moves from one passage into the second chamber 53, and the developer whose toner concentration has recovered in the second chamber 53 moves from the other passage into the first chamber 52. There is.

Now, in order to correct the changed developer density in the developing device 44 due to the development of the electrostatic latent image, that is, to control the amount of toner replenished to the developing device 44, the image signal processing circuit 34 is used. The level of the output signal of 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 the AND gate 64, and this A
The clock pulse oscillator 65 is connected to the other input of the ND gate.
The clock pulse (the pulse shown in FIG. 3 (b)) is supplied. Therefore, from the AND gate 64, as shown in FIG. 3C, the number of clock pulses corresponding to the pulse width of each of the laser driving pulses S, I, and W, that is, the number of clock pulses corresponding to the density of each pixel. A pulse is output.
This clock pulse number is integrated by the counter 66 for each image, and the video count number is calculated (A4 maximum video count number is 3707 × 10 ⁶ ). Then, the pulse integration signal C ₁ from the counter 66 for each image is obtained.
(Video count number) is the toner image of the original 31 is 1
This corresponds to the amount of toner consumed from the developing device 44 to form one toner.

Therefore, this video count number is calculated by the CPU 6
7 and store it in the RAM 68. CPU67
Has a conversion table showing the correspondence relationship between the video count number and the toner replenishment time. Based on the input video count number, toner 63 is replenished with an amount of toner 63 commensurate with the toner amount consumed from the developing device 44. The rotation driving time (that is, toner replenishment time) of the conveying screw 62 required to supply the toner from the tank 60 to the developing device is calculated, and the motor drive circuit 69 is controlled to drive the motor 70 only during the calculated time. Thus, in general, the higher the video count number, the longer the drive time of the motor 70, and the lower the video count number, the shorter the drive time of the motor 70.

The driving force of the motor 70 is transmitted to the carrying screw 62 through the gear train 71, and the carrying screw 6
2 conveys the toner 63 in the toner replenishing tank 60 to replenish the developing device 44 with a predetermined amount of toner. The toner is replenished every time the development of one image is completed.

However, as described above, the toner consumption amount is different due to the difference in pixel forming method (400 line image and 200 line image) even with the same video count number. Occurs and a stable density image cannot be obtained.

Therefore, in this embodiment, the CPU 67 determines whether to form one pixel by the 400-line image method or the 200-line image method from the content of the original to be copied.
The pixel density changeover switch 77 is instructed. As a result, the pixel density changeover switch 77 is operated by the pulse width modulation circuit 3
The pixel density switching signal is sent to 5, and the modulation pulse width is set to 20.
It is switched to 0 line image or 400 line image. Further, the CPU 67 has two conversion tables showing the correspondence relationship between the video count numbers of 400-line images and 200-line images and the toner replenishment time (replenishment amount) as shown in FIG. When it is determined that one pixel is formed, the video count number accumulated by the counter 66 is converted into the toner replenishment time by using a conversion table corresponding thereto, and when it is determined that one pixel is formed by the 400-line image method, it is correspondingly The video count number is converted into the toner replenishment time using a conversion table for replenishing the toner.

Further, as described above, the image of the original to be copied is photoelectrically converted, and the output level of each pixel of the pixel image signal obtained by signal processing is integrated and converted into a video count number. Converting to the replenishment amount, predicting the consumption amount and replenishing the toner to the developing device 44 is different from directly detecting the actual toner concentration of the developer and replenishing the toner based on the actual toner concentration. Since it is replenishment, if the amount of toner replenished from the toner replenishment tank 60 to the developing device 44 or the expected amount of toner consumption from the developing device 44 changes, the consumption system and the replenishment system also change. , Developing unit 44
The toner concentration of the developer 43 inside, that is, the mixing ratio of the toner particles and the carrier particles gradually deviates from the initial setting value (specified value). If this deviation is not corrected, the toner density deviates largely from the allowable range of the initial setting value, and the toner density is not stable.

Therefore, in the present embodiment, a second developer concentration control device is provided, and the second developer concentration control device is provided at a predetermined timing, for example, every time toner is replenished, or. The photoconductor drum 40 is activated at a timing such as after each copy operation is completed, or when the number of copies reaches a predetermined number, or when the number of video counts reaches a predetermined value, or the like. Form a reference image on top.

More specifically, a reference image signal generating 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 the generating circuit 72 is supplied to the pulse width modulation circuit 35. To generate a laser drive pulse having a pulse width corresponding to the predetermined density. The laser driving pulse is supplied to the semiconductor laser 36, the laser 36 is caused to emit 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, the reference electrostatic latent image corresponding to the predetermined density is formed on the photosensitive drum 40, and the reference electrostatic latent image is developed by the developing device 44. To 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, this 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 the comparator 75. A reference signal corresponding to the specified toner concentration of the developer 43 (toner concentration at the initial setting value) is input from the reference voltage signal source 76 to the other input of the comparator 75. Therefore, the comparator 75 compares the specified toner density with the actual toner density in the developing unit, and as a result of the comparison between the two input signals, the comparator 75 determines the actual amount of the developer 43 in the developing unit 44. An output signal indicating that the toner density is higher than a specified value or an output signal that indicates that the toner density is lower than the specified value is generated. If there is no difference between the two input signals, an output signal indicating that may be generated.

The output signal of the comparator 75 is supplied to the CPU 67. In this embodiment, the CPU 67 controls so as to correct the next toner replenishing operation in consideration of the remaining toner amount based on the output signal from the comparator 75. For example, when the actual toner concentration of the developer 43 detected by the photoelectric conversion element 74 is lower than the specified value, that is, when the toner is insufficiently supplied, the CPU 67 develops the insufficient toner. The screw 62 is operated to replenish the container 44. That is, the screw rotation time required to replenish the developing device 44 with the insufficient toner is calculated based on the output signal from the comparator 75, and the motor drive circuit 69 is controlled to rotationally drive the motor 70 for that time. , Shortage toner is supplied to the developing device 44. In addition, the photoelectric conversion element 74
When the actual toner density of the developer 43 detected by the developer is higher than the specified value, that is, when the toner is excessively replenished, the CPU 67 determines the developer based on the output signal from the comparator 75. The amount of excess toner inside is calculated. Then, in the subsequent image formation by the original, the toner is replenished so as to eliminate the excess toner amount, or the image is formed without replenishing the toner until the excess toner amount is consumed, that is, there is no toner. Replenishment forms an image to consume the excess toner amount, and when the excess toner amount is consumed, the toner replenishing operation is performed as described above.

As described above, by providing the second developer concentration control device and forming the reference image on the photoconductor drum 40 at a predetermined timing, the error of the amount of replenishment toner by the first developer concentration control device is increased. Can be corrected, and the toner density can always be maintained within the allowable range of the initial setting value.

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, block S1
At 01, the original is read and a photoelectric conversion signal corresponding to the density of each pixel of the original image is generated. Next, based on the contents of the document, the CPU 67 sets 1 in decision block S102.
As a pixel forming method, a 400 line image or 200
It is determined whether or not the line image is used, and this is instructed to the pixel density changeover switch 77. Whether the 200-line image method is determined (YES) or the 400-line image method is determined (N
O), in block S103, the output level of each pixel of the pixel image signal obtained by signal processing the photoelectric conversion signal is counted and integrated to calculate the video count number.
Send to. The CPU 67 executes 2 in the above decision block S102.
If the 00-line image method is determined (YES), the conversion table for 200-line images is selected in block S104, and the video count number is set to the toner replenishment time using the selected conversion table in block S105. The toner supply time per image corresponding to the input video count number, that is, the rotation number of the screw 62 is determined. Then, in block S106, the copy operation is started, and the above-described image forming operations such as latent image formation, development, and transfer are executed. When one toner image is formed, before the next toner image is formed in block S107, the screw 62 is rotated by the number of rotations determined in block S105 to replenish the toner. Next, in block S108, the second developer concentration control device is activated,
A reference image is formed on the photosensitive drum 40 and the above-described operation is performed. That is, it is checked whether or not the predicted replenishment amount obtained by converting the video count number into the toner replenishment time using the 200-line image conversion table is correct, and if there is an error in the replenishment amount, it is corrected as described above. Take appropriate measures. Next, in a decision block S109, it is determined whether or not the copy operation is completed, and if it is completed (YE
S) The process directly returns to the start. If the copy operation is not completed (NO), the process returns to block S106 to continue the copy operation.

On the other hand, if the 400-line image method is determined in the decision block S102 (NO), the block S11 is executed.
0, a conversion table for 400-line images is selected, and the video count number is converted into toner replenishment time using this selected conversion table in block S111, and one sheet corresponding to the input video count number is selected. The toner supply time per image, that is, the rotation speed of the screw 62 is determined. After that, as in the case of the 200-line image, the copy operation is started in block S106, and the above-mentioned image forming operations such as latent image formation, development, and transfer are executed. When one toner image is formed, before the next toner image is formed in block S107, the screw 62 is rotated by the number of rotations determined in block S111 to replenish the toner. Next, in block S108, the second developer concentration control device is operated to form a reference image on the photosensitive drum 40, and the above-described operation is performed. That is, it is checked whether or not the predicted replenishment amount obtained by converting the video count number into the toner replenishment time using the 400-line image conversion table is correct, and if there is an error in the replenishment amount, correct it. Take appropriate measures. Next, in a decision block S109, it is determined whether or not the copy operation is finished. If it is finished (YES), the process directly returns to the start, and
If the copy operation is not completed (NO), block S
Returning to 106, the copy operation is continued. Hereinafter, the same operation is repeated for each copy operation.

As described above, in this embodiment, when the CPU 67 converts the toner supply time from the video count number,
Select an appropriate conversion table according to the pixel formation method,
Since the toner replenishment time is determined, highly accurate and stable toner replenishment can be performed regardless of the selected pixel forming method, and the toner concentration of the developer can be kept substantially constant. Therefore, there is an advantage that a high-quality image with stable density can be obtained.

In the above embodiment, whether the entire one original is formed by the 200-line image method according to the contents of one original is 400
It was decided whether to form by the line image method, and the video count number was converted to the toner replenishment time using the conversion table corresponding to it. However, different types of images (solid image) such as characters and photographs in one original And the line image) are mixed, after the original is read, the “solid image” and the “line image” are separated, that is, image area separation is performed, and the video count number of the 200-line image and the 400-line image are separated. It is also possible to calculate each video count number, convert each of these video count numbers into a toner replenishment time using a corresponding conversion table, and add both toner replenishment times to replenish toner. In this case, there is an advantage that a finer image can be formed.

Further, in the above embodiment, the toner is replenished every time one toner image is formed, but when the number of copies reaches a predetermined number regardless of 200 line image and 400 line image,
Alternatively, toner may be replenished collectively when the video count reaches a predetermined value. Thus, when toner is replenished collectively, when a small amount of toner is replenished when a replenishment system for replenishing toner from the toner replenishing tank as shown in FIG. Since an error is likely to occur, there is little room for the error to be introduced, and there is an advantage that the replenishment accuracy is further improved.

Further, in the above-described embodiment, the second developer concentration control device is operated every time one toner image is formed, and the replenishment error by the first developer concentration control device is corrected. After it is determined that the operation is completed, the second developer concentration control device may be operated to correct the replenishment error. Alternatively, the second developer concentration control device may be operated to correct the replenishment error each time the number of copies reaches a predetermined number or when the video count number reaches a predetermined value. By thus reducing the number of times the second developer concentration control device is operated, it is possible to suppress the in-machine contamination and the toner consumption amount.

In the above embodiment, in order to measure the actual toner density of the developer in the developing device, a patch image is formed on the photosensitive drum and the density of this image is measured. Uses an inductance detection type developer concentration control device that detects the apparent magnetic permeability based on the mixture ratio of carrier and toner, and detects and corrects the actual toner concentration based on the change in the output as the second developer concentration control device. You may. Alternatively, the actual toner concentration of the developer can be measured by directly irradiating the developer on the developing sleeve or the like with light and measuring the reflected light. However, when the toner is colored black with carbon black, there is no great difference in the spectral reflectance between the toner and the carrier, so this method deteriorates the toner density detection accuracy,
Not preferable.

In the above embodiment, the present invention is applied to the electrophotographic digital copying machine. However, the present invention is not limited to the embodiment, but various electrophotographic and electrostatic recording type copying machines, It is equally applicable to image forming apparatuses such as printers. For example, the present invention can be applied to an image forming apparatus that performs grayscale representation of an image by a dither method, and also 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. The present invention can also be applied. Further, it goes without saying that various modifications and changes can be made to the configurations of the image forming apparatus and the control system as necessary.

[0043]

As described above, the image forming apparatus according to the present invention selects the conversion table adapted to the pixel forming method, converts the video count number into the toner replenishment time (replenishment amount), and replenishes the toner. Therefore, the toner can be replenished with high accuracy according to the amount of consumed toner, and the toner concentration of the developer can always be reliably kept within the allowable range of the initial setting value. Therefore, there is a remarkable effect that a stable image having high image quality and stable density can be obtained at all times.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view showing 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 schematic diagram illustrating a difference in a method of forming one pixel.

FIG. 5 is a characteristic diagram showing a relationship between a video count number and a toner consumption amount which differ depending on a pixel forming method.

FIG. 6 is a flow chart for explaining the basic operation of the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing an overall configuration of an example of a conventional image forming apparatus.

[Explanation of symbols]

34 Image signal processing circuit 35 Pulse width modulation circuit 40 photoconductor drum 43 Two-component developer 44 Developer 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 77 Pixel density switch

Claims (3)

[Claims] 1. An electrostatic latent image corresponding to an image information signal is formed on an image carrier, the electrostatic latent image is developed with a two-component developer to form a visible image, and the visible image is transferred. In the image forming apparatus for transferring to a material, a toner replenishing means for replenishing the toner of the two-component developer and a first toner replenishing means for activating the toner replenishing means according to the image density information of the image information signal. A developer concentration control device for correcting the operation time of the toner replenishing means operated by the first developer concentration control device in accordance with a difference in pixel forming method for forming the electrostatic latent image. An image forming apparatus that replenishes toner. 2. A second developer concentration control device for detecting a toner concentration of the two-component developer is provided, and the second developer concentration control device is operated at a predetermined timing to obtain the second developer. 2. The image forming apparatus according to claim 1, wherein the toner supply error by the first developer density control device is corrected by an output signal from the density control device according to the toner density. 3. A conversion table for converting the image density information of the image information signal into the operating time of the toner replenishing means is changed according to the difference in the pixel forming method for forming the electrostatic latent image. The image forming apparatus according to claim 1.