JP2004347751A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable image forming apparatus not using a heating means (heater) for an image carrier such as a photoreceptor drum, maintaining uniformity in image density and furthermore without any image defect such as image deletion. <P>SOLUTION: Electrifying bias is changed over between DC and AC + DC or its size is controlled according to environmental condition such as temperature or humidity in interior of a device or in the vicinity. When on the high humidity side, it is turned to DC with less likely occurrence of image deletion and the AC current is reduced even in AC electrification. Furthermore, the size and changing over condition can be changed according to a mode (such as copy, facsimile and print), an image mode (such as characters and photographs) or resolution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control method for an electrophotographic image forming apparatus having a contact-type charging unit. More specifically, image formation is performed by applying an image forming process including a step of charging the surface of the image carrier to an image carrier such as an electrophotographic photosensitive member and an electrostatic recording dielectric, which is a member to be charged. The charging means for the image bearing member relates to a control method for an image forming apparatus, which is a contact-type charging means for charging a surface by bringing a charging member into contact with the image bearing member.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus, a corona discharge device has been widely used as a device for charging a surface of a photosensitive drum serving as an image carrier. This is because the corona discharger is arranged in a non-contact manner with its discharge opening facing the photosensitive drum, which is the member to be charged, and by exposing the surface of the photosensitive drum to a corona current from the discharge opening, it has a predetermined polarity and potential. It is to be charged. However, there are problems such as requiring a high-voltage power supply and generating a large amount of ozone.
[0003]
On the other hand, a contact-type charging method in which a charging member to which a voltage is applied is brought into contact with a photosensitive drum to perform a charging process has advantages such as a lower voltage of a power supply and a smaller amount of ozone generated. And are being used. A conventional image forming apparatus using a charging roller as a contact type charging member will be described with reference to FIG.
[0004]
FIG. 9 is a cross-sectional view of a main part of a conventional image forming apparatus. In FIG. 9, reference numeral 1 denotes a photosensitive drum as an image bearing member. Then, the primary charging roller 2 charges the battery to a uniform potential (for example, -700 V). Then, an image exposure 3 is irradiated onto the photosensitive drum 1 from an image exposure means (not shown) corresponding to the original, thereby forming an electrostatic latent image on the photosensitive drum 1. The electrostatic latent image is formed by the developing device 4. It is developed and visualized as a toner image.
[0005]
On the other hand, the transfer material P is fed at a predetermined timing, and the toner image on the photosensitive drum 1 is carried on a transfer belt 21 as a transfer material carrier by an electrostatic force generated by a bias applied to a bias roller (transfer roller) 12. Is transferred to the transferred transfer material P. Then, the transfer material P to which the toner image has been transferred is carried and conveyed by the transfer belt 21, and is heated and pressed by passing through the fixing roller pair 14 so that the toner image is fixed.
[0006]
The toner remaining on the photosensitive drum 1 after the transfer is removed by the drum cleaning device 5, and the residual potential of the photosensitive drum 1 is removed again by light irradiation by the pre-exposure lamp 15, and the photosensitive drum 1 is used for the next image formation.
[0007]
Further, the toner scattered mainly during the operation of the developing device 4 in the image forming apparatus or at the time of transfer or fog toner before and after image formation adheres to the transfer belt 21 or is directly transferred due to jam during transfer material transfer. The cleaning device 16 for removing the attached toner may be disposed in contact with the transfer belt 21.
[0008]
The charging roller 2 may have various prescriptions and layer configurations. For example, the charging roller 2 includes a central core, a conductive layer formed on the outer periphery, and a resistance layer and a protective layer formed on the outer periphery.
[0009]
The charging roller 2 has both ends of a core metal rotatably supported by bearing members (not shown), and is arranged in parallel with the drum-type photoconductor 1. The photosensitive member 1 is pressed and pressed by the pressing force, and is rotated by the rotation of the photosensitive member 1.
[0010]
[Patent Document 1]
JP 2001-109332 A
[Patent Document 2]
JP-A-11-194579
[Patent Document 3]
JP-A-11-174785
[0011]
[Problems to be solved by the invention]
However, in the above-described conventional example, it is known that if the image forming operation of the image forming apparatus is continued, a problem such as blurring of an image, that is, a so-called image deletion occurs particularly in a high humidity environment. This phenomenon is caused by discharge products generated during charging adhere to the surface of the photosensitive drum, and the moisture contained in the air is adsorbed to lower the surface resistance of the photosensitive drum, causing a lateral flow of charges and causing latent image contrast. Is reduced.
[0012]
In addition to the discharge products, toner adhering to the surface of the photosensitive drum includes toner as a developer and additives contained therein.
[0013]
In terms of structure, this can occur particularly remarkably in an image forming apparatus that does not have a blade-shaped cleaning member for removing a developer or an additive such as toner remaining on the surface of an image carrier such as a photosensitive drum.
[0014]
Conventionally, this problem has been solved by installing a heating means (heater) for heating and drying the surface of the photosensitive drum inside or near the photosensitive drum. Even if a discharge product or the like adheres to the surface of the photosensitive drum, the surface resistance does not decrease, so that the occurrence of image deletion is prevented.
[0015]
However, in recent years, awareness of environmental problems has increased, and there has been a demand for a reduction in energy consumption, particularly during standby, making it difficult to use heating means (heaters).
[0016]
Although the details will be described in the embodiment, the charging system is roughly classified into two types depending on the type of the applied bias. This is so-called DC charging in which the bias applied to the contact-type charging member is DC, and so-called AC charging in which AC is superimposed on DC. As described above, the amount of the discharge products and the like generated at the time of charging adhere to the surface of the photosensitive drum is larger in the case of AC charging, and the level of image deletion is also deteriorated. Also, the deterioration of the photosensitive drum surface due to the repetition of the image forming operation is relatively large.
[0017]
On the other hand, AC charging is superior to charging uniformity and image density uniformity.
[0018]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to use a heating means (heater) for an image carrier such as a photosensitive drum, to maintain image density uniformity, and to further reduce image flow. It is an object of the present invention to provide a highly reliable image forming apparatus free from image defects at low cost.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided an image carrier, a contact-type charging member that contacts the image carrier and charges a surface thereof, and applies a charging bias to the contact-type charging member. And an image forming apparatus that does not have a blade-shaped cleaning member for removing a developer or an additive such as toner remaining on the image carrier. And the bias applied to the contact-type charging member is switched between DC and AC + DC in accordance with the result.
[0020]
In the invention according to claim 2, the environmental condition is defined as data such as temperature and humidity inside or near the apparatus at the time of starting image formation, moisture content in air, or a time that is a predetermined time after the start of image formation. The data is a plurality or continuous data until the image formation is restarted.
[0021]
According to a third aspect of the present invention, there is provided a so-called DC charging in which the bias applied to the contact-type charging member is DC when the environmental condition is on the high humidity side, and a so-called AC charging in which AC is superimposed on DC in the low humidity side. Switching is performed so that
[0022]
According to the above configuration, the amount of discharge products generated can be suppressed particularly in a high-humidity environment in which image deletion is likely to occur, thereby enabling prevention of image deletion or improvement of the level. In addition, by making environmental data such as temperature and humidity and the amount of water in the air into plural or continuous data from the time when a predetermined time has elapsed from the start of image formation to the time of resuming image formation, the output value of the environmental sensor However, even if there is a mismatch between the actual photosensitive drum surface state and the actual state, the problem can be solved. This is because even when the sensor determines that the humidity is low at the start of image formation, for example, when the environmental condition changes suddenly, for example, immediately after the air conditioner starts operating in the room where the image forming apparatus is installed, This is effective in a state where moisture is adsorbed on the surface.
[0023]
The invention according to claim 4 is characterized in that, when so-called DC charging in which the bias applied to the contact-type charging member is DC is selected, or when so-called AC charging in which AC is superimposed on DC is selected, Further, the magnitude of the DC bias value or the AC bias value is controlled according to the environmental condition.
[0024]
According to the above-described configuration, it is possible to appropriately balance, for example, by changing the magnitude of the AC bias value, depending on the required level of charging uniformity and the easiness of image deletion, which differ depending on environmental conditions.
[0025]
According to a fifth aspect of the present invention, the image forming apparatus is of a digital type and is of a multi-function type having a plurality of image forming modes such as copying, facsimile, and printer, or has a plurality of image modes (character mode, photograph mode, Mode) or a resolution switching unit, environmental conditions for switching between DC charging and AC charging are controlled so as to be different depending on conditions such as the image forming mode, the image mode, and the resolution. When the charging is selected or the AC charging is selected, the magnitude of the DC bias value or the AC bias value is controlled in each case even under the same environmental condition.
[0026]
With the above-described configuration, a facsimile mode having many character images, a character mode, and the like, when it is determined that the influence on the image density is small even if there is actually some charging unevenness, even under the same environmental conditions, The charging bias can be controlled so that the adhesion of discharge products to the photosensitive drum is small. Conversely, when high charge / density uniformity is required, such as in a high resolution mode or photo mode, control can be performed to increase the charge uniformity even if the deposition of discharge products is temporarily sacrificed somewhat. It is.
[0027]
Therefore, it is possible to control the image flow prevention due to the adhesion of the discharge product to the photosensitive drum and control the uniformity of the charge and the density to an optimum state according to the environmental conditions and the image mode.
[0028]
The invention according to claim 6 is characterized in that the contact-type charging member is formed of a roller, a blade, a sheet, or a brush.
[0029]
In the above configuration, in the present invention, since the image forming apparatus does not have a blade-shaped cleaning member for removing the developer and the additive such as the toner remaining on the image carrier, the developer and the additive are particularly preferable. It is possible to further increase the above-described effect with respect to a charging member that has a small effect of removing the toner.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0031]
<Example 1>
FIG. 1 is a cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention, in which the same elements as those shown in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted. I do.
[0032]
In FIG. 1, a temperature / humidity sensor 23 is disposed near the charging roller 2, and its output is sent to a charging roller bias control circuit 22 to control the bias applied to the charging roller 2.
[0033]
Here, the difference in the charging status depending on the charging method will be described below with reference to the drawings.
[0034]
FIG. 2 shows the relationship between the primary DC bias Vdc when only the DC bias is applied and the surface potential Vs of the photosensitive drum as the image carrier. As shown in FIG. 2, Vs increases linearly from the point where the DC bias Vdc exceeds a certain threshold value Vth. Also, its features are:
(1) The amount of ozone and discharge products generated in the minute nip between the charging roller and the photosensitive drum is smaller than that of AC charging.
(2) The amount of shaving of the film thickness on the photosensitive drum surface due to durability is relatively small with respect to AC charging.
(3) A phenomenon such as filming and fusing, in which no vibration occurs between the charging member typified by the primary charging roller and the photosensitive drum at the time of charging and the toner as a developer is thinly coated on the surface of the photosensitive drum. It is hard to get up.
On the other hand, the convergence of the charged potential is poor, but the following disadvantages are obtained.
(4) The charging potential varies due to partial resistance unevenness of the charging member and surface contamination.
(5) When the surface of the photosensitive drum is scraped due to durability and the thickness of the dielectric layer is reduced, the charging potential changes. In order to maintain a constant potential, it is necessary to control a DC bias value.
[0035]
Further, the film is not uniformly cut, and the film thickness unevenness becomes remarkable depending on the position in one photosensitive drum, so that the charging potential also changes. Therefore, density unevenness is likely to occur in a portion in the image.
[0036]
On the other hand, in the AC charging method, as shown in JP-A-3-52058 as an example, the charging member has a region where the distance to the surface of the member to be charged is increased on the downstream side in the moving direction of the member to be charged, By applying a voltage component and a voltage having a peak-to-peak voltage value that is twice or more the charging start voltage value for the charged body between the charged body and the charging member, the surface of the charged body and the region of the charging member are By forming an oscillating electric field between them, the object to be charged can be uniformly charged without charging unevenness.
[0037]
As the charging characteristics, the alternating current component smoothes out the unevenness of the charging, and converges to a predetermined potential by the direct current component. Therefore, as shown in FIG. 3, the charging is performed so as to be substantially close to the direct current bias Vdc.
[0038]
As a feature of the AC charging method, contrary to the DC charging,
(1) The amount of ozone and discharge products generated in the minute nip between the charging roller and the photosensitive drum is larger than in DC charging. Therefore, the level of image deletion is worse than DC charging when compared under the same temperature and humidity conditions.
(2) The film thickness of the photosensitive drum surface due to the endurance is relatively large compared to DC charging. The ratio varies depending on the type of developer used, the prescription of the photosensitive drum, the configuration / presence of the cleaning means for the photosensitive drum surface, the rotation speed, and the like. However, as shown in FIG. There is. Therefore, the life of the photosensitive drum is shortened accordingly.
[0039]
Further, when the peak voltage of the AC component is further increased, the convergence of the potential is enhanced, but the shaving amount is further increased.
[0040]
In the present invention, since there is no blade-shaped cleaning member for removing a developer or an additive such as toner remaining on the image carrier, the amount of shaving is relatively small as a whole. The size changes depending on the type of charging means and the type of charging means and the state of pressure contact with the photosensitive drum. Further, shaving unevenness is likely to occur due to partial contact unevenness.
(3) Vibration is generated between the charging member and the photosensitive drum during charging, so that problems such as vibration noise, filming, and fusion are relatively likely to occur. However, it can be prevented by optimizing various settings such as the setting of the AC current value, the developer, the material and prescription of the surface of the photosensitive drum, the cleaning means of the photosensitive drum, and the filling of the inside of the photosensitive drum.
Although there are disadvantages such as the above, there are the following advantages due to the good convergence of the charged potential.
(4) Variations in the charging potential due to the influence of the charging member itself, such as partial resistance unevenness of the charging roller, and its surface deposits are small.
(5) Even if the thickness of the dielectric layer on the surface of the photosensitive drum becomes thinner as a result of use, or if the thickness of the dielectric layer becomes uneven, relatively uniform charging is possible. Therefore, a change in charging potential and an increase in charging unevenness due to durability are small, and relatively uniform and stable charging can be performed. That is, the image density becomes relatively uniform.
[0041]
FIG. 4 shows how the film thickness of the photosensitive drum changes with the use of the AC charging system and the DC charging system (increase in the number of endurable sheets used). Although the value varies depending on the prescription of the photosensitive drum to be used, the configuration of the cleaning device, and the conditions such as bias, the amount of scraping is usually 1.5 to 2.5 times larger in the AC charging system. Further, as described above, when the peak voltage of the AC component is further increased (AC reinforcement in FIG. 4), the convergence of the potential is increased, but the shaving amount and the generation amount of ozone / discharge products are further increased.
[0042]
Here, the discharge attack on the surface of the photosensitive drum and the discharge product will be compared and described in more detail.
[0043]
In the contact charging method, the charging member is brought into direct contact with and close to the image carrier to charge the image carrier. For example, a bias voltage is applied to the charging roller, and the charging roller and the image carrier utilize a discharge that occurs in a minute gap just before they rotate and come into contact with each other. This discharge is a discharge having a smaller gap than that of the scorotron or corotron method. It is said that a discharge having a small gap has a higher moving speed of ions and electrons than a discharge having a large gap. For this reason, it is considered that the contact charging method is such that ions or electrons having high energy collide with the surface of the image carrier as compared with the corotron method or the scorotron method. In general, when an ion or an electron collides with a polymer, the bonding state of the surface molecule changes, and the polymer may be activated to increase the surface energy.
[0044]
When an organic photosensitive drum having a surface layer formed of a polymer material such as polycarbonate is used as an image carrier and charged by a contact charging method, the surface energy of the photosensitive drum increases as compared with a corotron method or a scorotron method. Sometimes. The increase in surface energy may promote molecules in the air to be adsorbed on the surface of the image bearing member, or may cause an increase in the adhesion of toner or external additives as a developer to the surface of the photosensitive drum.
[0045]
In addition, the contact charging method generates a small amount of discharge products, and generally does not require an ozone filter or the like even when air is discharged from the inside of the device to the outside. However, the discharge is directly generated in the minute gap, and is generated in the very vicinity of the photosensitive drum surface. Therefore, the influence on the image carrier is greater than that of a charger such as a scorotron, and ozone / discharge products are more likely to adhere. In addition, the surface of the image carrier is greatly deteriorated by the discharge energy, and foreign matter is easily attached due to an increase in adhesion of toner and the like.
[0046]
Further, since the discharge current is increased in the AC charging method, a large amount of such discharge-producing substances is generated, which has a greater effect than DC charging. In addition, the number of times of discharging is increased as compared with the DC charging, and thus the stress is applied to the image carrier, which promotes an increase in the adhesive force of the toner and the like, and in addition, the surface state of the image carrier may greatly change.
[0047]
When an amorphous silicon photoreceptor is used, although the amount of shaving on the surface of the photosensitive drum is extremely small, it is difficult to remove toner, external additives, discharge products, and the like once adhered, and the same problem occurs.
[0048]
Now, in the above-described image forming apparatus, after 100 images are continuously formed under various temperature and humidity conditions, the image forming apparatus is left as it is for 12 hours, and then 100 continuous images are formed again. FIG. 5 shows the state of occurrence of image deletion for the last 100 sheets.
[0049]
As can be seen from the figure, especially when the humidity is high and the amount of water contained in the air is large, the occurrence of image deletion is remarkable. However, the level of the image deletion can be greatly improved by DC charging. I understand.
[0050]
Therefore, as a control method, the absolute moisture content is calculated from the measured temperature and humidity data, and when the value is 10 or more, the bias applied to the primary charging roller may be DC only. Here, the image density unevenness in the case where there is unevenness in the resistance of the charging roller and unevenness in the surface layer is also shown in FIG. In the case of AC charging, since the convergence of charging is good, the potential becomes relatively uniform even if there is resistance unevenness or stain unevenness, and as a result, density unevenness becomes small. In the case of DC charging, on the contrary, the charging uniformity is poor, so that the density unevenness becomes relatively large. However, in either case, in the high humidity area, the influence of the resistance unevenness and the stain unevenness on the image is reduced, so that the bias dependency is small. Therefore, even when the primary charging bias is switched to DC in a high humidity region, the level of image density unevenness does not decrease so much.
[0051]
As described above, the absolute moisture content is calculated from the measured temperature and humidity data, and when the value is in a high humidity region of 10 or more, the bias applied to the primary charging roller is set to DC, and In the case of a low humidity region, control is performed so as to be AC + DC bias. As a result, it is possible to prevent or suppress image deletion without significantly deteriorating image density unevenness.
[0052]
Note that the switching condition between the DC bias and the AC + DC bias is set to 10 in the above example, but this can be changed as appropriate depending on the configuration, material, and the like of the apparatus.
[0053]
<Example 2>
In the first embodiment, the absolute water content is calculated from the measured temperature and humidity data, and the bias applied to the primary charging roller is set to DC (DC charging) or AC + DC (AC charging) according to the calculation result. Controlled to switch.
[0054]
The present embodiment is an example in which the bias condition is further changed depending on the condition among the respective bias systems.
[0055]
On the low humidity side, an AC + DC bias is applied, but as shown in FIG. 6, when the absolute water content is less than 3, the AC current is increased to 1150 μA. When the value is 3 or more and less than 9, 1000 μA, and when the value is 10 or more, DC bias is applied as in the first embodiment. By controlling in this way, it is possible to prevent image deletion on the high humidity side in the same manner as in Example 1, and to improve the charging uniformity on the low humidity side to prevent and suppress image unevenness. If it is less than 3 where image deletion does not occur in each region, the charging uniformity is improved and the image density unevenness can be eliminated.
[0056]
As described above, in the present embodiment, among the respective bias methods, the AC current value is further increased in the lower humidity side area where image deletion does not occur even when the number of sheets increases, thereby improving charging uniformity. Therefore, the level of image density unevenness due to resistance unevenness and stain unevenness of the charging roller can be improved.
[0057]
<Example 3>
In the second embodiment, the low humidity side area is further divided into two areas, and even in a large number of sheets, the AC current value is further increased in the low humidity side area where image deletion does not occur, so that the charging uniformity is improved. Control was performed so as to increase the level of image density unevenness due to resistance unevenness and stain unevenness of the charging roller.
[0058]
In this embodiment, on the contrary, the high humidity side region is further divided into two regions to control the bias.
[0059]
The amount of charge of a toner used as a developer used in an image forming apparatus changes depending on the environment (temperature and humidity), and the amount of charge usually decreases on the high humidity side. Therefore, the development contrast required at the time of development may be small. Since the charging potential may be reduced by that amount, as shown in FIG. 7, when the absolute water content is 20 or more, the primary DC bias is reduced by 100 V to -1150 V.
[0060]
Although this control is generally performed, in the present invention, the primary charging bias can be simultaneously performed while switching and controlling the primary charging bias between DC and AC + DC under environmental conditions such as temperature and humidity. If necessary, the DC bias of AC + DC can be changed as shown in FIG.
[0061]
As described above, the optimum image density can always be obtained by simultaneously changing the DC bias value in each control in order to obtain the necessary development contrast.
[0062]
In this embodiment, the switching of the bias is described as two types for both the DC charging and the AC charging. However, it goes without saying that the control may be performed by setting the switching more finely.
[0063]
<Example 4>
The embodiment of the present invention can also be embodied in the image forming apparatus shown in FIG. 1 and differs from Embodiments 1 to 3 in that the control method is changed depending on the image forming mode and the difference in resolution.
[0064]
Specifically, the image forming apparatus is of a digital type and a multi-function type having a plurality of image forming modes such as copying, facsimile, and printer, or a plurality of image modes (character mode, photograph mode, etc.) and resolution. In the case of having the switching means, for example, depending on the conditions such as the image forming mode, the image mode, and the resolution, the environmental conditions for switching between DC charging and AC charging are controlled to be different, or DC charging is selected. When AC charging is selected, the magnitude of the DC bias value or the AC bias value is controlled under the same environmental conditions in each case.
[0065]
FIG. 8 shows an example of the control of this embodiment.
[0066]
In the present embodiment, in the facsimile mode having many character images, the character mode, etc., even if there is actually some charging unevenness, the effect on the image density is small, or even if there is some density unevenness, there is a practical problem. When it is determined that there is no discharge bias, even under the same environmental conditions, the charging bias can be controlled so that the adhesion of the discharge product to the photosensitive drum is small. In this embodiment of FIG. 8, DC bias is always applied regardless of environmental conditions.
[0067]
Conversely, in the case of the photograph / high-resolution mode in which high image quality is required, in a low humidity environment where image deletion is unlikely to occur, an AC + DC bias is applied to avoid the occurrence of charging unevenness and image density unevenness, and the high humidity environment side In, control is performed so as to switch to DC bias in order to prevent / suppress image flow. As described above, on the high humidity side, the resistance unevenness and the stain unevenness of the charging roller hardly affect the image. Further, the resistance unevenness itself usually becomes smaller in a high humidity environment.
[0068]
As described above, the environmental conditions for switching between DC charging and AC charging are controlled to be different or the magnitude of the bias value is controlled to be different depending on the image forming mode and the resolution. With this control, if it is determined that the influence on the image density is small even if there is actually some charging unevenness, such as a facsimile mode with many character images and a character mode, even under the same environmental conditions, The charging bias can be controlled so that the adhesion of discharge products to the photosensitive drum is small. Conversely, when high charge / density uniformity is required, such as in a high resolution mode or photo mode, control can be performed to increase the charge uniformity even if the deposition of discharge products is temporarily sacrificed somewhat. It is.
[0069]
Therefore, it is possible to control the image flow prevention due to the adhesion of the discharge product to the photosensitive drum and control the uniformity of the charge and the density to an optimum state according to the environmental conditions and the image mode.
[0070]
As described above, the charging roller has mainly been described as the contact charging member, but the contact charging member is not limited to the charging roller, and may be a blade, a sheet, or a brush.
[0071]
In the present invention, since the image forming apparatus does not have a blade-shaped cleaning member for removing a developer or an additive such as a toner remaining on the image carrier, the developer particularly adheres to the surface of the photosensitive drum. The above effect is greater for a charging member having less effect of removing the toner and additives.
[0072]
Further, the present invention is not limited to the configuration of the image forming apparatus, and can be applied to various image forming apparatuses such as a monochrome / color copying machine, a printer, and a facsimile.
[0073]
【The invention's effect】
As described above, according to the first aspect of the present invention, an image carrier, a contact-type charging member that contacts the image carrier and charges the surface thereof, and applies a charging bias to the contact-type charging member. And an image forming apparatus having no blade-like cleaning member for removing a developer or an additive such as toner remaining on the image carrier. It is characterized in that the environmental conditions are detected and the bias applied to the contact-type charging member is switched between DC and AC + DC according to the result.
[0074]
In the invention according to claim 2, the environmental condition is defined as data such as temperature and humidity inside or near the apparatus at the time of starting image formation, moisture content in air, or a time that is a predetermined time after the start of image formation. The data is a plurality or continuous data until the image formation is restarted.
[0075]
According to a third aspect of the present invention, there is provided a so-called DC charging in which the bias applied to the contact-type charging member is DC when the environmental condition is on the high humidity side, and a so-called AC charging in which AC is superimposed on DC in the low humidity side. Switching is performed so that
[0076]
According to the above configuration, the amount of discharge products generated can be suppressed particularly in a high-humidity environment in which image deletion is likely to occur, thereby enabling prevention of image deletion or improvement of the level. In addition, by making environmental data such as temperature and humidity and the amount of water in the air into plural or continuous data from the time when a predetermined time has elapsed from the start of image formation to the time of resuming image formation, the output value of the environmental sensor However, even if there is a mismatch between the actual photosensitive drum surface state and the actual state, the problem can be solved. This is because even when the sensor determines that the humidity is low at the start of image formation, for example, when the environmental condition changes suddenly, for example, immediately after the air conditioner starts operating in the room where the image forming apparatus is installed, This is effective in a state where moisture is adsorbed on the surface.
[0077]
The invention according to claim 4 is characterized in that, when so-called DC charging in which the bias applied to the contact-type charging member is DC is selected, or when so-called AC charging in which AC is superimposed on DC is selected, Further, the magnitude of the DC bias value or the AC bias value is controlled according to the environmental condition.
[0078]
According to the above-described configuration, it is possible to appropriately balance, for example, by changing the magnitude of the AC bias value, depending on the required level of charging uniformity and the easiness of image deletion, which differ depending on environmental conditions.
[0079]
According to a fifth aspect of the present invention, the image forming apparatus is of a digital type and is of a multi-function type having a plurality of image forming modes such as copying, facsimile, and printer, or has a plurality of image modes (character mode, photograph mode, Mode) or a resolution switching unit, environmental conditions for switching between DC charging and AC charging are controlled so as to be different depending on conditions such as the image forming mode, the image mode, and the resolution. When the charging is selected or the AC charging is selected, the magnitude of the DC bias value or the AC bias value is controlled in each case even under the same environmental condition.
[0080]
With the above-described configuration, a facsimile mode having many character images, a character mode, and the like, when it is determined that the influence on the image density is small even if there is actually some charging unevenness, even under the same environmental conditions, The charging bias can be controlled so that the adhesion of discharge products to the photosensitive drum is small. Conversely, when high charge / density uniformity is required, such as in a high resolution mode or photo mode, control can be performed to increase the charge uniformity even if the deposition of discharge products is temporarily sacrificed somewhat. It is.
[0081]
Therefore, it is possible to control the image flow prevention due to the adhesion of the discharge product to the photosensitive drum and control the uniformity of the charge and the density to an optimum state according to the environmental conditions and the image mode.
[0082]
The invention according to claim 6 is characterized in that the contact-type charging member is formed of a roller, a blade, a sheet, or a brush.
[0083]
In the above configuration, in the present invention, since the image forming apparatus does not have a blade-shaped cleaning member for removing the developer and the additive such as the toner remaining on the image carrier, the developer and the additive are particularly preferable. It is possible to further increase the above-described effect with respect to a charging member that has a small effect of removing the toner.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an image forming apparatus using a transfer belt and a charging roller according to an embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between a DC bias by a DC charging bias and a photosensitive drum surface potential.
FIG. 3 is a diagram illustrating a relationship between a DC component bias due to an AC + DC charging bias and a photosensitive drum surface potential.
FIG. 4 is a diagram showing the amount of shaving of the photosensitive drum surface by DC charging and AC + DC charging bias.
FIG. 5 shows an example of bias control based on the amount of water in Example 1 of the present invention, and the occurrence of image deletion and image density unevenness in each environment of AC charging and DC charging.
FIG. 6 shows an example of bias control based on the amount of water in Example 2 of the present invention, and the occurrence of image deletion and image density unevenness under each environment of AC charging.
FIG. 7 is an example of bias control based on the amount of water in Embodiment 3 of the present invention.
FIG. 8 is an example of bias control based on the amount of water in Embodiment 4 of the present invention.
FIG. 9 is a schematic sectional view of an image forming apparatus using a conventional transfer belt.
[Explanation of symbols]
1 Photosensitive drum
2 Primary charging roller
3 Image exposure (laser etc.)
4 Developing device
5 Cleaner
12 Transfer member (bias roller)
15 Pre-exposure
20 Transfer bias power supply
21 Primary charging bias power supply
22 Primary charging bias control circuit
23 Environment sensor (temperature and humidity sensor)

Claims (6)

An image carrier, a contact-type charging member that contacts the image carrier and charges the surface thereof, and a unit that applies a charging bias to the contact-type charging member, such as toner remaining on the image carrier. In an image forming apparatus that does not have a blade-shaped cleaning member for removing the developer and additives,
An image forming apparatus which detects environmental conditions such as temperature and humidity inside or near the image forming apparatus and switches a bias applied to a contact-type charging member between DC and AC + DC according to the result. The above environmental conditions are data such as temperature and humidity inside or near the apparatus at the start of image formation, moisture content in the air, or a plurality of or continuous data from a predetermined time from the start of image formation to the time of resuming image formation. The image forming apparatus according to claim 1, wherein the data is data. When the environmental condition is on the high humidity side, the bias is applied to the contact-type charging member so that the bias is applied to DC. The image forming apparatus according to claim 1. When the so-called DC charging in which the bias applied to the contact-type charging member is DC is selected, or when the so-called AC charging in which AC is superimposed on DC is selected, in each case, the DC bias value or The image forming apparatus according to claim 1, wherein the magnitude of the AC bias value is controlled. When the image forming apparatus is of a digital type and is a multi-function type having a plurality of image forming modes such as copy, facsimile, and printer, or has a plurality of image modes (character mode, photograph mode, etc.) and resolution switching means. In
Controlling the environmental conditions for switching between DC charging and AC charging to be different according to the conditions such as the image forming mode, the image mode, and the resolution;
Alternatively, when DC charging or AC charging is selected, the magnitude of the DC bias value or AC bias value is controlled even in the same environmental condition in each case. Item 5. The image forming apparatus according to any one of Items 1 to 4. The image forming apparatus according to claim 1, wherein the contact-type charging member is formed of a roller, a blade, a sheet, or a brush.

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