JP2942019B2 - 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 that forms a full-color or multi-color image by an electrophotographic method, most developing devices use a two-component developer from the viewpoint of the tint 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. 7 shows an overall configuration example of an image forming apparatus having a conventional developer concentration control means, in this example, an electrophotographic digital copying machine. 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 one 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 description, in the case of a color copier, 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 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.

[0006]

In a digital electrophotographic laser beam printer, for example, the method of forming pixels is based on a so-called "solid image" such as a photograph or a picture and a so-called "line" such as a character or a line. "Image". As an example, as shown in FIG. 4, a method of forming one pixel at 400 dpi (dot / inch) in both the laser scanning direction and the rotation direction of the photoconductor drum, and a method of forming a photoconductor at 200 dpi in the laser scanning direction. There is a method of forming one pixel at 400 dpi in the rotation direction of the drum. In the present specification, the former method (400 × 400) is used.
dpi) is called the 400-line image method, and the latter (200 × 4
00 dpi) will be referred to as the 200-line image method. An image for which the expression of details such as characters and lines is required is formed by a 400-line image method with high resolution.
In many cases, switching means is provided so as to form the image by the 00-line image method. In such a case, as shown in FIG. 5, the results obtained by performing pixel formation by a laser beam on a photoreceptor drum of, for example, a fluorocyanine-based OPC (organic semiconductor) are shown in FIG. , The amount of toner consumed for the same video count is different,
When an image is formed by the 200-line image method, the amount of consumed toner is larger. Therefore, if the video count number obtained by integrating the output level of the digital image signal for each pixel is uniquely converted to the toner supply time and the toner is predicted and supplied as in the above-described conventional example, a supply error occurs, and a stable density is obtained. There is a disadvantage that a high quality image cannot be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to convert the density information of an image of an image information signal into a toner replenishment amount by changing the toner replenishment amount in accordance with a difference in a pixel forming method, thereby suppressing an error generated during toner replenishment. An object of the present invention is to provide an image forming apparatus provided with a developer concentration control means.

[0008]

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, toner replenishing means for replenishing toner to the developing means, developer concentration controlling means for operating the toner replenishing means based on image density information of the image information signal to replenish toner, and And a pixel density switching unit for switching a pixel density when forming an image, wherein the developer density control unit is operated by the developer density control unit according to the pixel density switched by the pixel density switching unit. An image forming apparatus is characterized in that the operation time of the toner supply unit is corrected to supply the toner.

In one embodiment of the present invention, second developer concentration control means for detecting the toner concentration of the two-component developer is provided, and the second developer control means is operated at a predetermined timing. An error in toner supply by the developer density control means is corrected by an output signal corresponding to the toner density from the second developer density control means.

In another embodiment of the present invention, there is provided a conversion table for converting image density information of an image information signal into operation time of the toner replenishing means in accordance with the pixel density switched by the pixel density switching means. change.

[0011]

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, for example, 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 method, an electrostatic recording method, or the like, and forms the latent image with A visible image (toner image) is formed by developing with a developing device using a two-component developer mainly composed of particles and carrier particles, and the visible image is transferred to a transfer material such as paper, and is permanently fixed by a fixing unit. What is necessary is just the thing of the structure which makes an 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 the image of the document 31 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 light 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 light 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, etc. 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.

In this embodiment, a pixel density changeover switch 77 is provided, and the pulse width modulation circuit 35 is controlled by a pixel density changeover signal from the pixel density changeover switch 77, and the pixel width is changed according to the difference in the 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, a 400-line image and 2
Since the image is a 00-line image, the pulse width modulation circuit 35 outputs a signal 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 a 200-line image recording.
A pulse having a width twice the pulse width for recording a line image is output.

For simplicity of explanation, only one 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 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, and on the photosensitive drum of each image forming station. An electrostatic latent image of each color obtained by color-separating the image of the document is sequentially formed, developed by a developing device having a corresponding color toner, and sequentially transferred to a transfer material 48 held and transported by a transfer material carrying belt 47. Will be done.

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

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.

Developer stirring screws 58 and 59 are disposed 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 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 device 44 due to the development of the electrostatic latent image, that is, to control the amount of toner supplied to the developing device 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 (A4 maximum video count is 3707 × 10 ⁶ ). Thus, the pulse integrated signal C ₁ for each image from the counter 66.
(Video count number) is obtained by dividing the toner image of the original 31 by 1
This corresponds to the amount of toner consumed from the developing device 44 to form the image.

Therefore, this video count is stored in the CPU 6
7 and stored in the RAM 68. CPU67
Has a conversion table showing the correspondence between the video count number and the toner replenishment time. Based on the input video count number, toner replenishment is carried out with toner 63 in an amount corresponding to the toner amount consumed from the developing device 44. The rotation driving time of the transport screw 62 required to supply the toner from the tank 60 to the developing device (that is, the toner supply time) is calculated, and the motor driving circuit 69 is controlled to drive the motor 70 for the calculated time. Thus, in general, if the video count is large, the driving time of the motor 70 is longer, and if the video count 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 through 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.

However, as described above, the toner consumption is different even for the same video count number due to the difference in the pixel forming method (400-line image and 200-line image). And an image having a stable density 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 based on the contents of the original to be copied.
It instructs the pixel density changeover switch 77. Thereby, the pixel density changeover switch 77 is connected to the pulse width modulation circuit 3.
5 and a modulation pulse width of 20 is sent.
Switching is performed for the 0-line image or the 400-line image. Further, the CPU 67 has two conversion tables indicating the correspondence between the video count numbers of the 400-line image and the 200-line image and the toner supply time (replenishment amount) as shown in FIG. When it is determined that one pixel is to be formed, the video count number accumulated by the counter 66 is converted into a toner supply time using a conversion table corresponding to the pixel. The conversion table converts the video count number into a toner supply time to supply the toner.

Further, as described above, the image of the original to be copied is photoelectrically converted, the output level of each pixel of the pixel image signal obtained by signal processing is integrated, converted into a video count number, and converted to a video count number. Replenishing toner to the developing device 44 by converting it into a replenishing amount and estimating the consumption amount is different from directly detecting the actual toner concentration of the developer and replenishing the toner based on the detected toner concentration. Because of the replenishment, if the amount of toner replenished from the toner replenishing tank 60 to the developing unit 44 or the expected amount of toner consumed from the developing unit 44 changes, the fluctuation of the consumption system and the replenishment system causes , Developing unit 44
The toner concentration of the developer 43, that is, the mixture ratio of the toner particles and the carrier particles gradually deviates from the initial set value (specified value). If this deviation is not corrected, the toner density greatly deviates from the allowable range of the initial set value, and the toner density becomes unstable.

For this reason, in the present embodiment, the second developer concentration control means is provided, and the second developer concentration control means is provided at a predetermined timing, for example, each time toner is supplied, or The photosensitive drum 40 is operated at a timing such as each time one copy operation is completed, each time the number of copies reaches a predetermined number, or each time the video count reaches a predetermined value. A reference image is formed thereon.

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 this generating circuit 72 is applied 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 may be 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 so as to correct the next toner supply operation in consideration of the remaining amount of toner. For example, when the actual toner density of the developer 43 detected by the photoelectric conversion element 74 is smaller than a specified value, that is, when the toner is insufficiently replenished, the CPU 67 develops the insufficient toner. The screw 62 is operated to supply the container 44. That is, based on the output signal from the comparator 75, the screw rotation time required to supply the insufficient toner to the developing device 44 is calculated, and the motor driving circuit 69 is controlled to rotate the motor 70 for that time. The shortage of toner is supplied to the developing device 44. Also, the photoelectric conversion element 74
When the actual toner density of the developer 43 detected by the CPU 67 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 excess toner amount in the medium is calculated. Then, in the subsequent image formation using the original, the toner is replenished so as to eliminate the excessive toner amount, or the image is formed without replenishing the toner until the excessive toner amount is consumed, that is, the toner is not supplied. An image is formed by replenishment, the excess toner amount is consumed, and control is performed such that the toner replenishment operation is performed as described above when the excess toner amount is consumed.

As described above, by providing the second developer density control means and forming the reference image on the photosensitive drum 40 at a predetermined timing, the error of the replenishment toner amount by the first developer density control means can be obtained. Can be corrected, and the toner density can be constantly maintained within the allowable range of the initial set 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 an original, block S1 is pressed.
The original is read at 01, and a photoelectric conversion signal corresponding to the density of each pixel of the original image is generated. Next, based on the content of the original, the CPU 67 determines in step S102 that 1
As a method of forming a pixel, a 400-line image or 200
It is determined whether or not to perform a line image, 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 of the photoelectric conversion signal is counted and integrated to calculate a video count number.
Send to The CPU 67 determines 2 in the above-described determination block S102.
If the 00-line image method is selected (YES), a conversion table for a 200-line image is selected in block S104, and the video count number is calculated using the selected conversion table in block S105. And 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, a copying operation is started in block S106, and the above-described image forming operations such as latent image formation, development, and transfer are performed. When one toner image is formed, before forming the next toner image in block S107, the screw 62 is rotated by the number of revolutions determined in block S105 to supply toner. Next, in block S108, the second developer concentration control means is operated,
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 conversion table of the 200-line image is correct, and if there is an error in the replenishment amount, the error is corrected. Take appropriate measures. Next, it is determined in a decision block S109 whether or not the copy operation has been completed.
S) Return to the start as it is, and if the copy operation is not completed (NO), return 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.
In step S0, a conversion table for a 400-line image is selected. In block S111, the video count is converted into a toner supply time using the selected conversion table, and one sheet corresponding to the input video count is converted. The toner supply time per image, that is, the rotation speed of the screw 62 is determined. Thereafter, the process is the same as the case of the 200-line image, and the copying operation is started in block S106, and the above-described image forming operations such as latent image formation, development, and transfer are executed. When one toner image is formed, before forming the next toner image in block S107, the screw 62 is rotated by the rotation speed determined in block S111 to supply toner. Next, in block S108, the second developer concentration control unit is operated to form a reference image on the photosensitive drum 40 and perform the above-described operation. 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, the error is corrected. Take appropriate measures. Next, it is determined in a decision block S109 whether or not the copy operation has been completed, and if completed (YES), the process returns to the start, and
If the copy operation has not been completed (NO), block S
Returning to 106, the copying 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, the toner can be supplied stably with high accuracy 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 a stable density can be obtained.

In the above embodiment, the whole original is formed by the 200-line image method according to the contents of the original.
It was determined whether the image was formed by the line image method, and the video count was converted into the toner supply time using a conversion table corresponding to the line image method. When the original is read, the “solid image” and the “line image” are separated, that is, the image area is separated, and the video count of the 200-line image and the 400-line image are mixed. The video count numbers may be calculated, the video count numbers may be converted into the toner replenishment time using a corresponding conversion table, and the toner replenishment time may be added to perform the toner replenishment. In this case, there is an advantage that a finer image can be formed.

In the above-described embodiment, the toner is supplied every time one toner image is formed. However, each time the number of copies reaches a predetermined number regardless of whether the image is a 200-line image or a 400-line image,
Alternatively, the toner may be supplied collectively each time the video count reaches a predetermined value. As described above, when the toner is replenished in a lump, for example, when a replenishment system that replenishes the toner by rotating the transport screw from the toner replenishing tank as shown in FIG. Since an error is likely to occur, there is an advantage that there is less room for the error to enter and the replenishment accuracy is further improved.

Further, in the above-described embodiment, the second developer density control means is operated every time one toner image is formed, and a replenishment error caused by the first developer density control means is corrected. After it is determined that the operation has been completed, the second developer concentration control means may be operated to correct the replenishment error. Alternatively, the replenishment error may be corrected by operating the second developer concentration control means each time the number of copies reaches a predetermined number or whenever the video count reaches a predetermined value. As described above, when the number of operations of the second developer concentration control unit is reduced, it is possible to suppress in-machine contamination and toner consumption.

In the above embodiment, the actual toner density of the developer in the developing unit was measured by forming a patch image on the photosensitive drum and measuring the density of the image. An inductance detecting type developer concentration control unit that detects an apparent magnetic permeability based on a mixing ratio of the carrier and the toner and detects and corrects an actual toner concentration based on a change in the output is used as a second developer concentration control unit. 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 not much difference in the spectral reflectance between the toner and the carrier, so that the detection accuracy of the toner concentration is deteriorated by this method,
Not preferred.

In the above embodiment, the case where the present invention is applied to an electrophotographic digital copying machine has been described. The present invention is equally applicable to an image forming apparatus such as a printer. For example, the present invention can be applied to an image forming apparatus that performs shading expression of an image by a dither method, or 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 configuration of the image forming apparatus and the control system as needed.

[0043]

As described above, the image forming apparatus according to the present invention comprises a latent image forming means for forming an electrostatic latent image corresponding to an image information signal on an image carrier, and a static image formed on the image carrier. Developing means for developing the electrostatic latent image using a two-component developer, toner replenishing means for replenishing toner to the developing means, and replenishing toner by operating toner replenishing means based on image density information of the image information signal In the image forming apparatus, comprising: a developer density control unit for causing the pixel density to be switched when the image is formed; and a pixel density switching unit for switching the pixel density when the image is formed. The operation time of the toner supply means operated by the means is corrected to supply the toner, so that
Highly accurate toner replenishment according to the amount of toner consumed
The toner concentration of the developer can always be reliably kept within the allowable range of the initial set value. Therefore, there is a remarkable effect that a high quality image with a stable high density can be always obtained.

[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 schematic diagram illustrating a difference in a method of forming one pixel.

FIG. 5 is a characteristic diagram illustrating a relationship between a video count number and a consumed toner amount that differ depending on a pixel forming method.

FIG. 6 is a flowchart for explaining a basic operation of one embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating 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 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 77 pixel density changeover switch

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 (3)

(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. Developing means, toner replenishing means for replenishing toner to the developing means, developer concentration control means for operating the toner replenishing means based on image density information of the image information signal to replenish toner, and An image forming apparatus comprising: a pixel density switching unit for switching a pixel density when forming; wherein the toner replenishment actuated by the developer density control unit in accordance with the pixel density switched by the pixel density switching unit. An image forming apparatus which corrects the operation time of the means and supplies toner. 2. A second developer concentration control means for detecting a toner concentration of the two-component developer is provided, and the second developer control means is operated at a predetermined timing so as to operate the second developer concentration. 2. The image forming apparatus according to claim 1, wherein an error in toner supply by said developer density control means is corrected by an output signal corresponding to the toner density from said control means. 3. A conversion table for converting image density information of an image information signal into an operation time of the toner replenishing means according to the pixel density switched by the pixel density switching means. Item 1. The image forming apparatus according to Item 1.