JP2004029209A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an excellent image continuously by keeping the state of an image carrier excellent. <P>SOLUTION: The image forming apparatus, having an image carrier, a developing means of visualizing an electrostatic latent image on the image carrier, a transfer means of transferring the developer image on the image carrier to a recording material, a cleaning means of collecting sticking matter left on the image carrier, and a control means of controlling the respective means, is characterized in that it has an image density detecting means for detecting the amount of the toner of the developer image; and the control means forms the developer image in an image non-formation area according to the time when the developing means is in operation except in an image formation area and the detection result of the image density detecting means. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrostatic copying machine and a printer for forming an image based on digital signal image information.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus including a developing unit that develops an electrostatic latent image formed on a surface of a photoreceptor, which is an image carrier, with a toner in a powder developer has been widely used. As an example, as shown in FIG. 5, there is a full-color electrophotographic image forming apparatus having four photosensitive drums and using an intermediate transfer member. Around the photoreceptor drum, four process units as image forming means including charging means, exposure means, developing means, cleaner and the like are provided. In each process unit, yellow, magenta, cyan and black are provided. The image on the photosensitive drum on which the image of each color is formed is primary-transferred sequentially at the primary transfer portion N1 onto the intermediate transfer member moving and passing adjacent to the photosensitive drum, and the image transferred on the intermediate transfer member is Further, in the secondary transfer portion N2, secondary transfer is performed to a recording material such as paper. Since each process unit has the same configuration, the process unit Pd will be exemplified in the drawings and the description will be omitted with the reference numeral d omitted.
[0003]
After the transfer of the toner image, the cleaner 160 removes extraneous matter such as residual toner from the photosensitive drum 101. The cleaner 160 includes a cleaning blade 161 and a transport screw 162. The cleaning blade 161 is in contact with the photosensitive drum 101 at a predetermined angle and pressure by a pressing unit (not shown). Collect the toner remaining on the surface. The photosensitive drum from which the residual toner has been removed by the cleaner 160 returns to the charging step again, and the above-described series of image forming operations is repeated.
[0004]
In the above-described conventional example, the cleaning blade 161 cleans the surface of the photoconductor by rubbing the surface of the photoconductor, but the toner and external additives remaining on the surface of the photoconductor after the transfer process are removed by the blade and the surface of the photoconductor. It has an important role in improving the lubricating properties between the layers and in polishing the photoreceptor to a suitable amount. For example, an external additive having an effect of increasing lubricity, such as titanium oxide or alumina fine powder, or an effect of increasing abrasiveness, such as strontium titanate powder, cerium oxide powder, and calcium titanate powder. In the case where an external additive having a characteristic is used, the effect of the external additive is large. That is, these external additives have the effect of increasing the lubricity of the surface of the photoreceptor and polishing the photoreceptor to an appropriate amount, and the components in the toner and the discharge products of the charger adhere to the surface of the photoreceptor. This has the effect of preventing the image from becoming defective and the friction coefficient of the surface of the photoreceptor being increased, whereby the cleaning blade is prevented from slipping.
[0005]
[Problems to be solved by the invention]
However, some of these external additives have a weak adhesive force to the toner, and others are charged to a polarity opposite to the triboelectric charging polarity of the toner. Even if an electric field is formed between the developer carrier and the photoconductor so that the toner flies away from the toner on the developer carrier in the developing means or the toner does not adhere to the photoconductor, an external additive charged to the opposite polarity is provided. The agent may separate from the toner and adhere to the photoreceptor. Therefore, if the developing means is continuously operated except during image formation, the amount of the external additive in the developer decreases. Unless the toner in the developer is consumed, new toner is not replenished, so that the amount of the external additive is decreasing.
[0006]
When the amount of the external additive present in the developer in the developing unit decreases, the amount of the external additive adhered to the photosensitive member together with the toner also decreases in the image forming portion, and the amount of the external additive which is transferred to the cleaner as transfer residue is reduced. Less additives. Therefore, the effect of increasing the lubricity between the photoreceptor surfaces and reducing the effect of polishing and appropriately shaving the photoreceptor is reduced, so that components in the toner and discharge products of the charging means adhere to the photoreceptor surface, resulting in image defects. In addition, the friction coefficient of the surface of the photoconductor increases, and the sliding of the cleaning blade becomes poor. This causes a problem that the cleaning blade 161 is chattered or turned up. Such a problem occurs when the developing unit is operated for a long time during non-image formation, but becomes longer in the following cases.
[0007]
For example, in a so-called tandem type color image forming apparatus in which four color image forming units (process units) are arranged in series, the pre-rotation step and the post-rotation step are often long. This causes a time lag in image formation from the upstream process unit to the downstream process unit. However, if the start / stop operation of the developing unit or the ON / OFF operation of the developing bias is performed in the process unit during non-image formation, the image is not changed. This is because it is necessary to operate the developing unit even during non-image formation in order to prevent image density unevenness from occurring due to mechanical shock or electrical noise generated in the process unit during formation. Further, when performing various adjustment modes during the pre-rotation, the pre-rotation may be long.
[0008]
In addition, when performing continuous image formation on thick paper, the interval between image forming areas (so-called paper interval) is often lengthened. This is because, if the fixing process is continuously performed on a recording material having a large basis weight, the temperature of the fixing unit is greatly reduced, so that a fixing defect is likely to occur. Therefore, many apparatuses change the sheet interval depending on the recording material used for image formation. Generally, when a recording material having a large basis weight is used, the sheet interval is increased.
[0009]
Such a sheet interval does not have enough time to start / stop the developing means. In particular, in the case of a tandem type color image forming apparatus, there is a time lag between image formation from an upstream process unit to a downstream process unit. However, in consideration of the shock as described above, it is difficult to temporarily stop the operation of the developing unit even if there is a considerably long sheet interval.
[0010]
In addition, although there are various cases depending on the image forming apparatus, if the time during which the non-image forming area is formed by operating the developing means is long as described above, the above-described problem, that is, the cleaning blade is chattered. And the problem of turning over is likely to occur.
[0011]
Accordingly, an object of the present invention is to maintain a good state of the image carrier and continuously form a good image.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a representative configuration of the present invention is an image carrier, a developing unit that visualizes an electrostatic latent image on the image carrier, and a developer image on the image carrier. In the image forming apparatus, comprising: a transfer unit that transfers the toner image onto a recording material; a cleaning unit that collects the deposits remaining on the image carrier; and a control unit that controls each unit. The control unit controls the time during which the developing unit is operating in a region other than the image forming area, and the non-image forming unit based on the detection result of the image density detecting unit. It is characterized in that a developer image is formed in an area.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
Hereinafter, embodiments of the image forming apparatus of the present invention will be described in detail with reference to the drawings. The operation of the image forming apparatus according to the first embodiment of the present invention will be described using the image forming apparatus of FIG. The feature of this embodiment is that toner (developer) is consumed separately from image formation by forming a toner image (developer image) in a non-image forming area, that is, a position not corresponding to a recording material. .
[0014]
The image forming apparatus is a full-color electrophotographic image forming apparatus having four photosensitive drums and using an intermediate transfer member. In each process unit P (Pa, Pb, Pc, Pd) for forming an image of each color of yellow, magenta, cyan, and black, a photosensitive drum 1 (1a, 1b, 1c, 1d) is disposed, respectively. Each photosensitive drum is rotatable in the direction of the arrow. Further, a charging roller 2 (2a, 2b, 2c, 2d) as a primary charging unit and an exposure unit 3 (3a, 3b, 3c, 3d) are provided around each photosensitive drum 1 (1a, 1b, 1c, 1d). ), Developing means 4 (4a, 4b, 4c, 4d) and a cleaner 6 (6a, 6b, 6c, 6d) are sequentially arranged along the rotation direction of the photosensitive drum. Hereinafter, the process units will be described in detail with reference to FIG. 2, but the four process units have the same configuration. Here, description will be made while omitting the symbols of a, b, c, and d. Incidentally, each processing means acting on the photosensitive drum 1 in image formation is controlled by a control means (not shown).
[0015]
As shown in FIG. 2, the process unit P includes a photosensitive drum 1 as an image carrier rotatably supported. The photoreceptor drum 1 is a cylindrical electrophotographic photoreceptor having, as a basic configuration, a conductive base 11 such as aluminum and a photoconductive layer 12 formed on the outer periphery thereof. At the center thereof, a support shaft 13 is provided, and the drive shaft (not shown) is driven to rotate around the support shaft 13 in the direction of arrow R1.
[0016]
A charging roller 2 is disposed above the photosensitive drum 1. The charging roller 2 contacts the surface of the photosensitive drum 1 and uniformly charges the surface to a predetermined polarity and potential. The charging roller 2 has a roller shape. A negative bias voltage is applied to the charging roller 2 by a power supply 24, whereby the surface of the photosensitive drum 1 is charged uniformly and in contact. An exposure unit 3 is provided downstream of the charging roller 2 in the rotation direction of the photosensitive drum 1. The exposing unit 3 scans the laser beam corresponding to the image data while turning it off / on to form an electrostatic latent image.
[0017]
The developing means 4 disposed downstream of the exposing means 3 has a developing container 41 containing two-component toner, and a developing sleeve 42 is rotatably installed in an opening of the container 41 facing the photosensitive drum 1. In the developing sleeve 42, a magnet roller 43 for carrying toner on the developing sleeve 42 is fixedly arranged so as not to rotate with respect to the rotation of the developing sleeve 42. At a position above the developing sleeve 42 of the developing container 41, a regulating blade 44 for regulating the toner carried on the developing sleeve 42 to form a thin toner layer is provided. An ATR sensor (developer concentration detecting means) 49 for detecting the concentration is provided. Further, a partitioned developing chamber 45 and a stirring chamber 46 are provided in the developing container 41, and a replenishing chamber 47 containing replenishing toner is provided above the partitioned developing chamber 45 and a stirring chamber 46.
[0018]
When the toner formed on the thin toner layer is conveyed to the developing area facing the photoreceptor drum 1, the toner rises due to the magnetic force of the developing main pole located in the developing area of the magnet roller 43, and the toner A magnetic brush is formed. By rubbing the surface of the photosensitive drum 1 with the magnetic brush and applying a developing bias voltage to the developing sleeve 42 by the power supply 48, the toner adhering to the carrier constituting the ears of the magnetic brush is electrostatically charged. The latent image adheres to the exposed portion and is developed, and a toner image is formed on the photosensitive drum 1. As described above, the toner in the toner is consumed in the developing process. When the toner is consumed, a change in the toner density detected by the optical ATR sensor 49 or the like causes a change in the amount of new toner consumed from the replenishing chamber 47. Replenished. In this way, the image density is kept constant.
[0019]
A transfer roller 53 is provided below the photosensitive drum 1 downstream of the developing unit 4. The transfer roller 53 is pressed against the surface of the photosensitive drum 1 via the intermediate transfer belt 51 with a predetermined pressing force, and a primary transfer portion N1 is formed between the photosensitive drum 1 and the transfer roller 53. An intermediate transfer belt 51 is sandwiched in the transfer nip portion, and the negatively charged toner is transferred from the surface of the photosensitive drum 1 to the surface of the intermediate transfer belt 51 by the potential difference between the surface of the photosensitive drum and the transfer roller 53. You.
[0020]
After the transfer of the toner image, the cleaner 6 removes attached matter such as residual toner from the photosensitive drum 1. The cleaner 6 includes a cleaning blade 61 and a transport screw 62. The cleaning blade 61 is in contact with the photosensitive drum 1 at a predetermined angle and pressure by a pressing unit (not shown). Collect the toner remaining on the surface. The photosensitive member from which the residual toner has been removed by the cleaner 6 returns to the charging step again, and the above-described series of image forming operations is repeated.
[0021]
An intermediate transfer unit 5 is provided below each photosensitive drum 1. The intermediate transfer unit 5 includes an intermediate transfer belt 51, transfer rollers 53 (53a, 53b, 53c, 53d), secondary transfer rollers 56, 57, and an intermediate transfer belt cleaner 55.
[0022]
The toner images of respective colors formed on the photosensitive drums 1 (1a, 1b, 1c, 1d) are sequentially transferred onto the intermediate transfer belt 51 as described above, and then conveyed to the secondary transfer portion N2 with the rotation of the belt. Is done. On the other hand, the recording material S taken out of the feeding cassette 8 up to this time is supplied to the conveying roller 82 via the pickup roller 81, and further conveyed to the left in FIG. The above-described toner image is transferred onto the recording material S by the secondary transfer bias applied between the rollers 56 and 57. The transfer residual toner and the like on the intermediate transfer belt 51 are removed and collected by the intermediate transfer belt cleaner 55. When the recording material is conveyed, the fixing unit 7 is pressurized and heated at a pressure and temperature to melt and fix the unfixed toner image on the recording material surface, and a full-color image is formed on the recording material S. It is formed.
[0023]
The toner used in the present embodiment is obtained by adding strontium titanate powder having an average particle size of 1 μm to color toner particles having an average particle size of 8 μm, which is formed from a polyester resin as the toner, and a length average particle size. An externally added 0.1 μm hydrophobic alumina fine powder is used. A ferrite carrier having an average particle size of 50 μm is used as the carrier. A video counter is used as the image density detecting means. When the laser beam is turned on / off based on the image information and the photosensitive drum 1 is exposed by the exposing means 3, the video counter ( (Not shown), the number of image data (the number of videos) of the latent image formed by the exposure is counted, and the integrated value is measured.
[0024]
Here, a description will be given of a process in which a band-shaped patch (toner band image) is developed with toner between recording materials (between papers) which are non-image forming portions and toner is forcibly consumed. In this embodiment, each time one image is formed, the integrated value of the number of videos per image in each process unit P is detected by the video counter as the image density detecting means. Since the integrated value and the toner consumption amount are substantially proportional, the predicted toner consumption amount is calculated from the video integrated value in the CPU of the control means (not shown). For example, it is determined whether the estimated toner consumption is 40 mg / sheet or less per A4 size recording material, and further, 20 mg / sheet or more.
[0025]
On the other hand, the size of the recording material is detected, such as whether the image forming mode at that time is for plain paper or thick paper. In the apparatus of the present embodiment, the time interval (inter-paper time) of the image forming process is changed according to the image forming mode. For example, the inter-paper time when performing continuous image formation on plain paper A4 size is 0.3 seconds, and the inter-paper time when performing continuous image formation on thick paper A4 size is 2.0 seconds. The paper interval time at the time of image formation can be known from the type of recording material used, the toner consumption can be estimated from the number of videos, and the non-image forming area (area not corresponding to the recording material S) can be formed from the time interval and the number of videos The amount of toner to be consumed is determined, and a toner image corresponding to this amount is developed on the photosensitive drum 1 during the next sheet interval. The reflection density of a toner image formed between sheets is about 0.8, and a belt-like halftone image extending in the longitudinal direction is formed. Further, the width of the belt-shaped toner image in the sub-scanning direction is changed so as to obtain the optimum toner consumption based on the inter-sheet time and the number of videos.
[0026]
For reference, FIG. 3 shows an example of the width under each condition in the present embodiment. These optimum toner band widths are values determined from the results obtained by experimenting with the inventors on the amount of reduction in the inter-sheet time and the amount of the external additive in the toner. The CPU in the image forming apparatus stores the width of the toner band corresponding to all types of recording materials to be used as a table, and controls the band width. FIG. 4 is a development view of a toner band image formed on the photosensitive drum. Here, a case where the recording material is plain paper and a case where the recording material is thick paper are exemplified. It should be noted that the toner band image formed between the sheets during non-image formation passes through the transfer section without receiving a transfer bias, is carried to the cleaner 6, and is scraped by the cleaning blade 61.
[0027]
As in the present embodiment, by changing the width of the toner band image formed between sheets according to the number of videos in the non-image forming area and the time between sheets, the developing unit can be operated under any image forming conditions. The amount of the external additive present in the toner does not become insufficient. Therefore, the components in the toner and the discharge products of the charger adhere to the surface of the photoreceptor, resulting in an image failure or an increase in the friction coefficient of the surface of the photoreceptor, causing the cleaning blade to slip and causing the blade to chatter. Or turning over can be prevented.
[0028]
As described above, the present invention focuses on the fact that the external additive decreases when the developing means 4 operates in the non-image forming area. It consumes toner. Since the toner is detected by the toner concentration sensor in the developing unit and the toner concentration is lower than the reference amount, the developing unit 4 is supplied with the toner based on the detected toner concentration. , New toner is supplied to the developing means 4. A predetermined amount of an external additive is externally added to the new toner. That is, a predetermined amount of toner is forcibly adhered to the non-image forming area on the surface of the photosensitive drum 1 and consumed. Thus, the toner always enters and exits the developing unit 4. Therefore, the toner supplied with the external additive at a predetermined ratio is always supplied to the cleaner 6. Thereby, the state of the photosensitive drum 1 can be maintained in a good condition for a longer period, and a good image can be continuously formed.
[0029]
(2nd Embodiment)
A second embodiment of the present invention will be described. In the first embodiment, a belt-shaped toner image without transfer is formed between papers. In the present embodiment, a belt-shaped toner image formed on the photosensitive drum 1 between papers is formed in the same manner as a normal image. Then, a positive charge having a polarity opposite to that of the toner is applied to the transfer roller 53 to transfer the toner to the intermediate transfer belt 51.
[0030]
The toner used in the present embodiment also employs the same negatively charged toner as the previous embodiment, but with strontium titanate powder and hydrophobic alumina fine powder externally added. The toner powder has a property of being positively triboelectrically charged, which is opposite to the toner. Therefore, when a transfer bias is applied to transfer the belt-shaped toner image formed on the drum between the sheets to the intermediate transfer belt, most of the toner is transferred to the intermediate transfer belt, but most of the strontium titanate powder is The toner remains on the photosensitive drum 1 and is sent to the cleaning blade 61. The toner is transferred, and the strontium titanate is separated from the toner and remains on the photoreceptor, so that the ratio of the strontium titanate is larger than that of the toner. When the ratio of strontium titanate is high, the effect of scraping the photosensitive drum 1 by the cleaning blade 61 is further improved.
[0031]
Therefore, compared to the first embodiment, components in the toner and the discharge products of the charger adhere to the surface of the photoconductor, resulting in an image failure, and the friction coefficient of the surface of the photoconductor increases, so that the cleaning blade slips. It is possible to prevent inconveniences such as the occurrence of chattering and turning of the blade.
[0032]
Also, as in the first embodiment, the toner is forcibly consumed by changing the band width between the papers based on the inter-paper time and the integrated value of the video counter in the non-image forming area, so that the toner is not excessively consumed. Since the external additive does not become insufficient in the developing unit, the external additive (strontium titanate) does not decrease in the toner in any image forming mode. The toner band image transferred to the intermediate transfer belt 51 passes through the secondary transfer portion N2 in which the transfer bias is turned off at a timing when there is no recording material, and is collected by the intermediate transfer belt cleaner 55.
[0033]
As described above, when this method is used in an apparatus using fine particles charged to the opposite polarity to the toner as the external additive, the toner is transferred to the transfer belt or the intermediate transfer belt 51, and the external additive of the opposite polarity is Since the toner remains on the surface of the photosensitive drum 1 and is supplied to the cleaner 6, the toner having a higher external additive ratio is supplied. Can be polished and moderately ground. The point of the second embodiment is that attention is paid to the fact that the external additive that decreases in the toner has a polarity opposite to that of the toner. By applying a transfer bias, the toner supplied to the cleaner 6 is reduced in the external additive ratio. And the effect is greater than in the first embodiment. In this way, the state of the photosensitive drum 1 can be kept good for a long period of time, so that a good image can be continuously formed.
[0034]
(Other embodiments)
In the above-described embodiment, a printer has been described as an example of an image forming apparatus. However, the present invention is not limited to this, and may be applied to a copying machine or a facsimile machine.
[0035]
Further, in the above-described embodiment, an example in which the image is transferred to the recording material via the intermediate transfer body after the image is formed is described. However, the present invention is not limited to this, and the recording material is directly conveyed to the image forming unit. The present invention is also effective in an image forming apparatus having a conveyer body that performs the operation.
[0036]
【The invention's effect】
As described above, in the present invention, the image carrier, the developing means for visualizing the electrostatic latent image on the image carrier, and the transfer for transferring the developer image on the image carrier to a recording material An image density for estimating a toner amount of the developer image in an image forming apparatus including: a cleaning unit that collects deposits remaining on the image carrier; and a control unit that controls each unit. A control unit configured to form a developer image in a non-image forming area based on a time during which the developing unit is operating in an area other than an image forming area and a detection result obtained by the image density detecting unit; Therefore, the state of the image carrier can be kept good, and a good image can be continuously formed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus.
FIG. 2 is a configuration diagram around a process unit.
FIG. 3 is a table illustrating an example of a type of a recording material and a toner consumption amount.
FIG. 4 is a development view of a toner band image formed on a photosensitive drum.
FIG. 5 is a configuration diagram of a conventional image forming apparatus.
[Explanation of symbols]
N1 Primary transfer unit N2 Secondary transfer unit P Process unit S Recording material 1 Photoconductor drum 2 Charge roller 3 Exposure unit 4 Developing unit 5 Intermediate transfer unit 6 Cleaner 7 Fixing unit 8 Feeding cassette 11 ... Conductive substrate 12 ... Photoconductive layer 13 ... Support shaft 24 ... Power supply 41 ... Developing container 42 ... Developing sleeve 43 ... Magnet roller 44 ... Regulator blade 45 ... Developing chamber 46 ... Stirring chamber 47 ... Supply chamber 48 ... Power supply 49 ATR sensor 51 Intermediate transfer belt 53 Transfer roller 55 Intermediate transfer belt cleaner 56 Secondary transfer roller 57 Secondary transfer roller 61 Cleaning blade 62 Transport screw 81 Pickup roller 82 Transport roller

Claims (4)

An image carrier; developing means for visualizing an electrostatic latent image on the image carrier; transfer means for transferring a developer image on the image carrier to a recording material; Cleaning means for collecting the adhered matter, and control means for controlling each means,
Having an image density detection unit for estimating the toner amount of the developer image,
The control unit forms a developer image in a non-image forming region based on a time during which the developing unit is operating outside the image forming region and a detection result of the image density detecting unit. Image forming apparatus. The image forming apparatus according to claim 1,
Image density detecting means for detecting the density of a predetermined image formed by development, or developer density detecting means for detecting the density of the developer in the developing container,
The image forming apparatus according to claim 1, wherein the control unit determines a supply amount of the developer to the developing unit based on a detection result of the image density detecting unit or the developer density detecting unit. The image forming apparatus according to claim 1, wherein:
An intermediate transfer member that transfers an image formed on the image carrier to the recording material by carrying a conveying member that conveys a recording material to the image carrier,
The image forming apparatus according to claim 1, wherein the control unit transfers the developer image to a non-image forming area of the conveyance pair or the intermediate transfer body where an image is not transferred to a recording material. The image forming apparatus according to claim 2 or 3, wherein
The image forming apparatus according to claim 1, wherein the developer has externally added fine particles that are triboelectrically charged in a polarity opposite to that of the developer.

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