JP3618992B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer.
[0002]
[Prior art]
In an electrophotographic color image forming apparatus (for example, a copying machine or a laser beam printer), an image is formed as follows. First, the photosensitive drum is uniformly charged by a charging device, and an electrostatic latent image is formed by laser or LED exposure. Next, toner is attached to the electrostatic latent image to develop it as a toner image, and this toner image is transferred onto a recording material such as paper. This is performed for each color of magenta, cyan, yellow, and black to form a color image by superimposing four color toner images on the recording material. The color image is fixed on the recording material by heat to complete the image formation. At the time of transferring the toner image, a small amount of toner remains on the surface of the photosensitive drum without being transferred onto the recording material. The transfer residual toner is scraped off and removed by a cleaning device arranged around the photosensitive drum.
[0003]
In recent years, there has been a demand for cost reduction and size reduction of image forming apparatuses, and so-called cleanerless image forming apparatuses that do not have a dedicated cleaning device around the photosensitive drum have been proposed.
[0004]
In such a cleanerless image forming apparatus, as a method for removing the transfer residual toner on the photosensitive drum, for example, the transfer residual toner is once taken into a contact-type charging device disposed around the photosensitive drum to statically remove the toner. A method is known in which the electrical characteristics are changed and returned to the photosensitive member again, and then this toner is recovered by the developing device and reused. By this method, control is performed such that the transfer residual toner on the surface of the photosensitive drum is collected for a certain time between recording materials in the print job or by post-rotation at the end of the print job.
[0005]
[Problems to be solved by the invention]
However, during continuous printing of high-density images, the amount of transfer residual toner increases, so that the process of returning the toner once taken onto the photosensitive drum cannot catch up with the process of taking the transfer residual toner into the charging device. In this case, the toner and the ferrite carrier forming the dielectric brush are mixed in the charging device, and the amount of toner increases. When the amount of toner increases, there is a problem that the surface of the photosensitive drum cannot be uniformly charged to a predetermined potential, and a toner image obtained by subsequent exposure and development does not reach a target image density. .
[0006]
As a method for solving this first problem, in order to cope with continuous printing of high-density images (continuous image formation), the transfer residual toner removal operation time (collection time) at the time of post-rotation is set sufficiently long. However, the following two problems occur when setting in this way. One problem is that when the amount of toner remaining after transfer is small, useless removal operation time is prolonged, and the user cannot immediately start the next printing (the waiting time is long). Another problem is that deterioration of the surface of the photosensitive drum is promoted by prolonging the removal operation time. This is because, in a contact-type charging device, the charging member is in contact with the surface of the photosensitive drum, and therefore, as the removal operation time increases and the rotation of the photosensitive drum increases, the wear of the photosensitive drum surface proceeds. is there.
[0007]
Therefore, the present invention minimizes the toner removal operation time at the time of post-rotation, thereby reliably removing the transfer residual toner even during continuous printing of high-density images, and having a low waiting time. An object of the present invention is to provide an image forming apparatus in which deterioration of the surface of an image carrier (photosensitive drum) is reduced.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a charging member that contacts the image carrier and charges the image carrier, a detection unit that detects a video count value per unit area from an image information signal, and the number of images formed in a job And a counting means for counting the toner image, and without a dedicated cleaning means for removing the transfer residual toner remaining on the image carrier without being transferred to the transferred member after the transfer of the toner image, In the image forming apparatus in which the charging member removes the transfer residual toner on the image carrier, the operation time for discharging the toner attached to the charging member when the image carrier is rotated after the image formation of one job is The video count value per unit area is longer as the number of image formations on which image formation is higher than a predetermined value is increased.
[0009]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the charging member is a charging member having magnetic particles in contact with the image carrier .
[0010]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, when a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging member during image formation, the discharge operation time is increased. Is characterized in that a DC voltage is applied.
[0011]
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the detection means is detected using the number of LED light emitting elements .
[0018]
[Action]
The main action based on the above configuration (the action corresponding to claim 1) is as follows. The dual-purpose device performs the toner removal operation during post-rotation based on the image density detected by the density detection unit and the number of image formations counted by the count unit, thereby reducing the amount of residual toner adhered to the image carrier. The required minimum toner removal operation can be performed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
<Embodiment 1>
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a four-color full-color copying machine including a color reader unit I and a printer unit II, and includes four image forming units, that is, yellow (Y), magenta (M), Image forming units for forming toner images of four colors of cyan (C) and black (K) are individually provided.
[0021]
The color reader unit I has a platen glass 11 on the upper part thereof, and a document feeder 12 for automatically feeding a document to the platen glass 11 is disposed above the platen glass 11. Instead of the document feeder 12, a specular pressure plate that presses the document against the platen glass 11 from the back side may be mounted.
[0022]
A first carriage 13 is disposed below the platen glass 11. Within the first carriage 13, light sources (halogen lamps) 14 and 15, reflectors 16 and 17 for condensing the light from these light sources 14 and 15 on the document, and a mirror 18 for reflecting the reflected light or projection light from the document. Is installed. Further, mirrors 20 and 21 are mounted on the second carriage 19, and the reflected light from the mirror 18 is condensed on the CCD 24 on the substrate 23 via the lens 22. The first carriage 13 described above is mechanically moved by the driving device 25 at a speed V and the second carriage 19 at a speed V / 2 in a direction perpendicular to the electrical scanning (main scanning) direction of the CCD 24. Thus, the entire surface of the original on the platen glass 11 is scanned (sub-scanning).
[0023]
Further, the image processing unit 26 connected to the CCD 24 is included. As shown in the block diagram of FIG. & S / H & A / D section 26a, shading section 26b, stitching & MTF correction & document detection section 26c, input masking section 26d, selector 26e, color space compression & background removal & LOG conversion section 26f, delay 26g, moire removal section 26h, scaling A processing unit 26i, a UCR & masking & black character reflection unit 26j, a γ correction unit 26k, a filter unit 26l, an external I / F unit 26m, a background removal unit 26n, and a black character determination unit 26o are provided.
[0024]
The document on the platen glass 11 reflects the light from the light sources 14 and 15, and the reflected light is guided to the CCD 24 and converted into an electrical signal. Note that in the case of a color sensor, the CCD 24 is an RGB color filter mounted inline in the order of RGB on a one-line CCD, or a three-line CCD, with an R filter, a G filter, and a B filter, respectively. It may be arranged for each CCD. Further, the filter may be on-chip, or the filter may be configured separately from the CCD.
[0025]
The electrical signal (analog image signal) from the CCD 24 is input to the image processing unit 26. As shown in FIG. 2, the electrical signal is firstly clamped & Amp. & S / H & A / D unit 26a samples and holds (S / H), clamps the dark level of the analog image signal to the reference potential, and amplifies it to a predetermined amount (the above-mentioned processing order is not necessarily in the notation order). For example, RGB signals are converted into 8-bit digital signals. Note that the above processing order is not limited to the above.
The RGB signal is subjected to shading correction and black correction by the shading unit 26b, and then, when the CCD 24 is a three-line CCD in the stitching & MTF correction & document detection unit 26c, the stitching processing differs in the reading position between the lines. Therefore, the delay amount for each line is adjusted in accordance with the reading speed, the signal timing is corrected so that the reading positions of the three lines are the same, and the MTF for reading changes according to the reading speed and the variable magnification. The change is corrected, and the document detection recognizes the document size on the platen glass 11.
[0026]
The digital signal whose reading timing is corrected corrects the spectral characteristics of the CCD 24 and the spectral characteristics of the light sources 14 and 15 and the reflectors 16 and 17 by the input masking unit 26d. The output of the input masking unit 26d is input to a selector 26e that can be switched with a signal from the external I / F unit 26m.
[0027]
One of the signals output from the selector 26e is input to the color space compression & background removal & LOG conversion unit 26f and the background removal unit 26n. The signal input to the background removal unit 26n is subjected to background removal, and then input to the black character determination unit 26o for determining whether the document is a black character in the document, thereby generating a black character signal from the document. The other output signal from the selector 26e is input to the input color space compression & background removal & LOG conversion unit 26f to determine whether the read image signal is within a range that can be reproduced by the printer. If not, the image signal is corrected so that it can be reproduced by the printer. Then, background removal processing is performed, and RGB signals are converted to CMY signals by LOG conversion.
[0028]
This is to correct the timing of the signal from the color space compression & background removal & LOG conversion unit 26f with the signal generated by the black character determination unit 26o. The timing is adjusted by the delay 26g. These two kinds of signals are subjected to moiré removal by the moire removal unit 26h, and then subjected to scaling processing in the main scanning direction by the scaling processing unit 26i.
[0029]
The signal processed by the scaling processing unit 26i is generated by the UCR & masking & black character reflecting unit 26j from the CMY signal by the UCR process to generate a CMYK signal. The determination signal generated by the determination unit 26o is fed back to the CMYK signal.
[0030]
The signal processed by the UCR & masking & black character reflection unit 26j is subjected to density adjustment by the γ correction unit 26k and then smoothed or edge processed by the filter unit 26l.
[0031]
The signal processed as described above is converted from an 8-bit multilevel signal to a binary signal by the binary conversion unit 27a shown in FIG. This conversion method may be any of a dither method, an error diffusion method, an improved error diffusion method, and the like.
[0032]
The signal from the image processing unit 26 is binarized by the binary conversion unit 27a and sent to the video signal counting unit 27b. The video signal counting unit 27b can count the total number of LED light emitting elements for each color image. Thereafter, the binarized image signal is delayed in accordance with the distance between the leading edge sensor 51 (described later) that detects the leading edge of the recording material P in the delay section 27c and each image forming position, and is sent to the LED drive 27d. . The LED drive 27 d generates a signal for driving the LED unit 33.
[0033]
Next, returning to FIG. 1, the printer unit II will be described.
[0034]
In the figure, a Y image forming unit 30Y, an M image forming unit 30M, a C image forming unit 30C, and a K image forming unit 30K are a photosensitive drum 31, a charger 32, an LED unit 33, a developing unit 34, and an auxiliary charger, respectively. 35. Further, the charger 32 includes a charging sleeve (sleeve) 36, and the developing device 34 includes a developing sleeve 37.
[0035]
Since the respective configurations are the same, the Y image forming unit 30Y will be described in detail, and description of the other image forming units will be omitted.
[0036]
The Y image forming unit 30Y is provided with a photosensitive drum 31, around which a charger 32, an LED unit 33, a developing unit 34, an auxiliary charger 35, and the like are arranged.
[0037]
In these operations, first, the photosensitive drum 31 is charged by the auxiliary charger 35 and the charger 32. As shown in FIG. 4, the charger 32 rotates a charging sleeve 36 containing a magnet 36a as a magnetic field generating means in a direction away from the photosensitive drum 31 (therefore, the surfaces of the charging sleeves 36 are opposite to each other at the opposite portions). In other words, a dielectric brush (magnetic brush) is formed by the low-resistance ferrite carrier 38 to uniformly charge the surface of the photosensitive drum 31 to prepare for latent image formation.
[0038]
Next, returning to FIG. 1, an electrostatic latent image is formed on the surface of the photosensitive drum by the light from the LED unit 33, and the toner is attached by the developing device 34 to be developed as a toner image. The developing device 34 includes a developing sleeve 37 for developing by applying a developing bias.
[0039]
A transfer charger 39 is arranged below the developing unit 34 with the transfer belt 40 interposed therebetween, and the toner image on the photosensitive drum 31 is carried on the transfer belt 40 by discharging from the back surface of the transfer belt 40. Transfer is performed on the surface of a recording material P such as paper as a member to be transferred.
[0040]
After the transfer of the toner image, the transfer residual toner 41 (see FIG. 4) remaining on the surface of the photosensitive drum 31 without being transferred to the transfer material P is once taken into the charger 32, the electrostatic characteristics are changed, and the photosensitive drum is again exposed. It is returned to the drum 31 and collected by the developing unit 34 and reused.
[0041]
Next, a procedure for forming an image on the recording material P will be described. The recording materials P stored in the cassettes 42 and 43 on the right side in FIG. 1 are fed one by one by the pickup rollers 44 and 45 and conveyed to the feeding rollers 46 and 47 on the rotating transfer belt 40. To be supplied. The transfer belt 40 is disposed below the Y image forming unit 30Y, the M image forming unit 30M, the C image forming unit 30C, and the K image forming unit 30K, and is driven by a transfer belt roller 48.
[0042]
The leading edge of the recording material P supplied to the transfer belt 40 is detected by a paper leading edge sensor 51. The detection signal of the paper leading edge sensor 51 is sent from the printer unit II to the color reader unit I, and is used as a sub-scanning synchronization signal when a video signal is sent from the color reader unit I to the printer unit II.
[0043]
Thereafter, the recording material P is conveyed while being supported on the surface of the transfer belt 40, and toner images are transferred to the surface in the order of YMCK in the image forming units 30Y, 30M, 30C, and 30K.
[0044]
The recording material P that has passed through the K image forming unit 30K is separated from the transfer belt 40 after being neutralized by the neutralization charger 52 in order to facilitate separation from the transfer belt 40. A peeling charger 53 is provided adjacent to the charge eliminating charger 52, and the peeling charger 53 prevents image disturbance due to peeling discharge when the recording material P is separated from the transfer belt 40.
[0045]
The separated recording material P is charged by the pre-fixing chargers 54 and 55 and then the toner image is thermally fixed by the fixing device 56 in order to compensate for the toner adsorption force and prevent image distortion. The paper is discharged onto the paper tray 57. The transfer belt 40 is neutralized by the internal and external neutralizers 58 and 59.
[0046]
Next, LED image recording will be described with reference to FIG. In the figure, the signal from the image processing unit is binarized by the binary conversion unit 27a and sent to the video signal counting unit 27b. The video signal counting unit 27b can count the total number of LED light emitting elements for each color image.
[0047]
Thereafter, the binarized image signal is delayed in the delay unit 27c according to the distance between the paper leading edge sensor 51 and each image forming position, and sent to the LED drive 27d. The LED drive 27d generates a signal for driving the LED unit 33.
[0048]
Next, a method for removing the transfer residual toner on the photosensitive drum in the post-rotation at the end of the print job according to the image density in the print job, which is a characteristic part of the present invention, will be described in detail.
[0049]
First, the image density is detected in each print (image formation) in the print job. Here, as the image density, a value obtained by dividing the total number of LED light emitting elements counted by the video signal counting unit (density detecting means) 27b of FIG.
[0050]
FIG. 5 shows details of the video signal count unit 27b. The other video signal count unit 27b has the same configuration.
[0051]
Reference numeral 60 denotes an image signal sent from the binary conversion unit 27a. The image signal for one image is counted in parallel every 8 bits by 29-bit counters 61 to 68, and these results are added by a 32-bit adder 69. The total number of LED light emitting elements is obtained as 32-bit data.
[0052]
This process is performed for each image formation to obtain the total number of LED light emitting elements, and the value divided by the area of the recording material P at that time is used as the image density, and the number of sheets in which this image density exceeds a predetermined value during the print job is determined. The number is counted by a counting means for counting the number of printed sheets (number of formed images), and the number is set as N _over .
[0053]
Then, _Nover / _Ntotal is obtained with the total number of images formed in the print job as _Ntotal .
[0054]
Next, a control method of the toner removal operation for removing the transfer residual toner performed in the post-rotation will be described with reference to FIG.
[0055]
At the start of post-rotation, the above-mentioned N _over / N _total value is obtained (S 1). If this value is equal to or smaller than a predetermined threshold value (S 2), the toner taken in the charger 32 is sufficiently discharged and the developer 34. A normal cleaning operation is carried out (S3). In this operation, with respect to the rotating photosensitive drum 31, the sleeve is driven by applying -700V DC and 1.1kV _PP , 1kHz, 50% duty rectangular wave AC bias to the charger 32, and the developing device 34. The sleeve is driven by applying a DC bias of −550 V and an AC bias of 1 kV _PP , 2.2 kHz, 50% duty square wave. As a result, the charger 32 takes in the toner on the photosensitive drum to change the electrostatic characteristics, returns it to the photosensitive drum again, and then the developing unit 34 collects the toner.
[0056]
Next, when the above-mentioned N _over / N _total value is equal to or greater than a predetermined threshold value, that is, when most of the image formation during the print job is performed at a high image density, the toner taken into the charger 32 is removed. In addition to the normal cleaning operation (S4), in addition to the normal cleaning operation (S4), only the AC bias of the charger 32 is turned off and the toner taken into the charger is discharged (S5).
[0057]
Since the toner removal operation is controlled as described above, the toner removal time can be minimized, and the toner and the low-resistance carrier (ferrite carrier) 38 forming the dielectric brush are mixed in the charger 32. Therefore, the charging performance of the charger 32 can be maintained, and unnecessary toner removal operation is not performed. Therefore, the photosensitive drum 31 is rubbed with the photosensitive drum 31 due to friction between the photosensitive drum 31 and the charger 32. Deterioration can be suppressed. Furthermore, since the toner removal time is the minimum necessary, the waiting time can be shortened and the user can start the next printing immediately.
[0058]
<Embodiment 2>
In the first embodiment described above, a process for discharging toner from the charger 32 is added when N _over / N _total is equal to or greater than the threshold value during post-rotation. However, the operation time for discharging toner according to the value of N _over / N _total Can also be changed.
[0059]
In the first embodiment described above, the AC bias of the charger 32 is turned off in the toner discharging operation in the case where N _over / N _total is equal to or greater than the threshold value during post-rotation, but by outputting another value. Further, the efficiency of discharging the toner can be increased (the same applies to other high pressure values).
[0060]
In the first embodiment described above, the image density is obtained using the total number of LED light emitting elements. However, the same control can be performed using a video count in an image forming apparatus that forms an electrostatic latent image with a laser.
[0061]
Further, as a method for obtaining the image density, a potential sensor can be provided around the photosensitive drum and the potential of the photosensitive drum 31 can be measured.
[0062]
【The invention's effect】
As described above, according to the present invention, the post-rotation control according to the image density in the print job, that is, the toner removal, is performed in the image forming apparatus in which the charger is also used as the cleaning device without using a dedicated cleaning device. By performing the control that minimizes the time, it is possible to prevent the toner in the charger from being mixed with the low-resistance carrier that forms the dielectric brush, so that the charging performance of the charger can be maintained. In addition, since unnecessary toner removal operation is not performed, deterioration of the image carrier due to sliding friction between the image carrier and the charger can be suppressed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view illustrating a configuration of a color image forming apparatus according to a first embodiment.
FIG. 2 is a block diagram illustrating a configuration of a digital image processing unit according to the first embodiment.
FIG. 3 is a block diagram illustrating a configuration of an LED driving unit according to the first embodiment.
FIG. 4 is a longitudinal sectional view showing a schematic configuration of a charger of the image forming apparatus.
FIG. 5 is a block diagram showing a configuration of a video signal count unit.
FIG. 6 is a flowchart illustrating post-rotation control.
[Explanation of symbols]
27b Concentration detection means (video signal count unit)
31 Image carrier (photosensitive drum)
32 Combined device (charger, conductive brush)
36 Sleeve (Charging sleeve)
36a Magnetic field generating means (magnet)
38 Low resistance carrier (ferrite carrier)
P Transfer member (recording material)

Claims (4)

A charging member that contacts the image carrier and charges the image carrier; a detection unit that detects a video count value per unit area from an image information signal; and a count unit that counts the number of images formed in a job. The charging member does not have a dedicated cleaning means for removing the transfer residual toner remaining on the image carrier without being transferred to the transfer member after the toner image is transferred. In the image forming apparatus for removing the transfer residual toner,
The operation time for discharging the toner attached to the charging member during the post-rotation of the image carrier after the image formation of one job is completed is an image formation in which the video count value per unit area is higher than a predetermined value. The longer the number, the longer
An image forming apparatus. The charging member is a charging member having magnetic particles in contact with the image carrier.
The image forming apparatus according to claim 1. A voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging member at the time of image formation, and a DC voltage is applied to extend the discharge operation time .
The image forming apparatus according to claim 2. The detection means is detected using the number of LED light emitting elements.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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