JP2001249548A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which transfer material is always stably separated from an image carrier without causing an image defect or wire breakage because of voltage attack to the image carrier. SOLUTION: When the leak of a current is detected in the case of the operation of a copying machine (image forming device) 50, a control circuit 40 reduces separation voltage being the AC component of a separation difference current. A control map for deciding the separation difference current is switched corresponding to the reduction of the separation voltage. By switching the control map, the difference current under an equal humidity condition is set to be about 30 μA lower when the separation voltage is reduced than when the separation voltage is applied ordinarily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image, and more particularly to an image forming apparatus which forms an image on an image carrier by an electrophotographic method and transfers the image onto a transfer material to obtain an image. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art Conventionally, this type of image forming apparatus visualizes an electrostatic latent image formed on a surface of an image carrier such as a photosensitive drum with toner, and transfers the developed image to a recording paper or the like. It is well known as an apparatus for transferring to a material.

FIG. 19 schematically shows an example of such a conventional image forming apparatus.

In the image forming apparatus 1000 shown in FIG. 1, a member 1001 is an image carrier (photosensitive drum) for forming an electrostatic latent image, 1002 is a primary charger for charging the surface of the photosensitive drum 1001, and 1004 is a developing sleeve 1004a.
A developing device 1010 that applies a voltage between the photosensitive drum 1001 and develops an electrostatic latent image to form a toner image on the photosensitive drum 1001 makes the charge amount of the toner image formed on the photosensitive drum 100 uniform. A pre-transfer charger 1007 removes unnecessary potential on the photosensitive drum 1001 and removes the transfer material P
Is a pre-transfer exposure unit that facilitates separation from the photosensitive drum 1001, and 1008 is a transfer charger 1005, 10 that transfers the toner image formed on the photosensitive drum 1001 to the transfer material P.
Reference numeral 06 denotes a separation first charger and a separation second charger 1011 for separating the transfer material P from the photosensitive drum 1001, and toner remaining on the photosensitive drum 1001 without being transferred to the transfer material P (transfer residual toner). A cleaning device 1012 for irradiating L modulated by an image signal; The laser beam L is applied to the rotating polygon mirror 1
The light is reflected by 014 and raster-scans the photosensitive drum 1001 via the imaging lens 1016. The member 1017 is a reflecting mirror.

The image forming apparatus 10 having such a configuration
At 00, a toner image is formed on the photosensitive drum 1001 through an image forming process of charging, light image exposure, and development,
This toner image is transferred to the transfer material P. And transfer material P
The final image-formed product is obtained by fixing the toner image transferred to the toner image.

In the image forming apparatus as described above, the separation chargers 1005 and 1006 apply a DC superimposed voltage to a high-voltage AC having a polarity opposite to that of the transfer to the conductive wire extended into the low-potential metal shield case, The biased bipolar ions are supplied to the back surface of the transfer material P with respect to the photosensitive drum 1001. By supplying such bipolar ions, the transfer electric field is almost neutralized and reduced. That is, the electrostatically attracted charge is removed from the transfer material P electrostatically attracted to the curvature surface of the photosensitive drum 1001. Then, the transfer material P is separated from the curvature surface of the photosensitive drum 1001 by the mass and rigidity of the transfer material P itself.

In the image forming apparatus 1000 employing the above-described separation method for separating the transfer material P and the photosensitive drum 1001, a series of operations such as transfer of a toner image to the transfer material P, separation from the photosensitive drum 1001, and conveyance are performed. The operation stability and reliability greatly depend on the voltage applied to the transfer charger 1008 and the separation chargers 1005 and 1006.

First, with regard to the transfer, generally, when a large amount of current is passed, the toner image on the photosensitive drum 1001 can be efficiently transferred onto the transfer material P.

Next, regarding the separation, generally, the AC component of the applied voltage has a large voltage, and the separation is performed efficiently on the high frequency side. On the other hand, with respect to the DC component, the electric charge on the transfer material P at the time of transfer tends to be eliminated by largely biasing the polarity opposite to that of the transfer, so that the transfer can be more efficiently separated.

However, in practice, the above-described conditions of both transfer and separation affect each other. Therefore, the optimum separation and transfer conditions cannot be obtained simply by separately considering each condition.

For example, if the voltage applied to the transfer charger 1008 is unnecessarily high, the amount of charge on the transfer material P increases, and the charge removal effect in the separation chargers 1005 and 1006 decreases. As a result, the separation efficiency decreases. This may cause poor separation and the like.

On the other hand, if the DC bias current applied to the separation chargers 1005 and 1006 is unnecessarily large and the charge removing effect of the transfer material P is too strong, the toner image once transferred to the transfer material P Then, a so-called retransfer phenomenon occurs, in which the transfer material P returns to the photosensitive drum 1001 again.

As described above, the voltage applied to the transfer charger 1008 and the voltage applied to the separation chargers 1005 and 1006 need to be set within appropriate ranges.

Further, the optimum value of the applied voltage varies depending on environmental conditions such as humidity and the thickness and type of the transfer material P.

In order to stabilize the separation performance, it has been considered to appropriately adjust the separation difference current (voltage) applied to the separation charger in accordance with the total image amount.

As an extreme example, when a plain white image (image amount is almost 0), there is no toner particle interposed between the photosensitive drum and the transfer material, so that the electrostatic attraction of the transfer material to the photosensitive drum is very low. Therefore, a strong separation effect is required, and a large separation difference current is required. On the other hand, in the case of a black-and-white image (maximum image amount), if the transfer material is excessively discharged, toner once transferred onto the transfer material is reversely transferred onto the photosensitive drum (so-called retransfer phenomenon). Therefore, it is necessary to set the separation difference current to a value not too large.

Therefore, it is beneficial to adjust the separation difference current based on the total image amount.
As in the method described in Japanese Patent Application Laid-Open No. H10-105, the separation difference current is controlled according to the image density of the original to be read.
As in the method described in Japanese Patent No. 78705, there has been proposed a method of calculating the image ratio of the entire document and controlling the separation difference current accordingly.

Further, as in the method described in Japanese Patent Application Laid-Open No. 52-67643, it has been proposed to appropriately adjust the separation difference current applied to the separation charger according to the amount of moisture in the air. When the humidity environment is high, the volume resistance of the transfer material is reduced, and the charge cannot be effectively removed by the separation charger. Therefore, it is necessary to increase the separation difference current. In a low-humidity environment, the volume resistance of the transfer material increases, and there is a tendency for the charge to be removed excessively by the separation charger. Conversely, it is necessary to reduce the separation difference current. May be required, and this is not always the case. However, in any case, it is effective to change the separation difference current depending on the amount of moisture in the air, and it is a method widely used by those skilled in the art.

[0019]

However, in particular, in a network printer or the like, which has been increasing in speed in recent years, high-speed printout has been required since data is successively input. For speeding up printout, transfer material transfer performance related to transfer material separation performance has also become important. In particular, the transfer material must be always separated at a fixed position relative to the photosensitive drum. Therefore, the faster the operation speed of the image forming apparatus, the shorter the separation.

For such a short separation, the rigidity of the transfer material and its own weight tend to be insufficient, and the higher the operation speed of the image forming apparatus, the shorter the discharge current becomes. There is a problem of becoming stable.

To solve such a problem, the potential of the photosensitive drum is reduced as an absolute value using a pre-transfer exposure device,
By lowering the adsorbing force between the transfer material and the photosensitive drum, or using regular development in which the potential of the white photosensitive drum is small as an absolute value,
It is effective to make the separation easy by reducing the attraction force between the photosensitive drum and the transfer material in the white portion where separation is particularly severe.

On the other hand, the separation performance may be improved by increasing the total amount of current for separation by increasing the applied voltage or the like.

However, if the applied voltage is excessive, current leakage easily occurs at the shield portion of the separation charger. In particular, when the device has been used for a long period of time, paper dust and scattered toner on the transfer paper accumulate as dirt on the shield part of the separation charger, and discharge to the low potential shield part as a discharge counter electrode. Unevenness occurs as an impedance, and charges flow intensively in a low impedance portion, so that leakage occurs extremely frequently.

In a high-humidity environment, a substance contaminating the shield absorbs moisture, and particularly easily leaks due to moisture absorption of long fibrous paper dust.

As a problem caused by the leak, a voltage attack at the time of the leak on the photosensitive drum may cause a hole to be formed, resulting in a defective image or a disconnection of the discharge wire of the separation charger.

The present invention has been made in view of such circumstances, and it is an object of the present invention to transfer an image from an image carrier without causing a defective image or a broken wire due to a voltage attack on the image carrier. An object of the present invention is to provide an image forming apparatus that always stably separates materials.

[0027]

In order to achieve the above object, the present invention develops an electrostatic latent image formed on an image carrier as a toner image and transfers the toner image to a transfer material. In an image forming apparatus that forms an image, a transfer material separating unit that separates the transfer material from the image carrier by applying a voltage obtained by superimposing a DC current on an AC voltage to a transfer material onto which a toner image has been transferred. An AC voltage changing unit that changes the AC voltage; a DC current changing unit that changes the DC current in accordance with the change in the AC voltage; and a DC current changing unit that changes the DC voltage in accordance with the change in the AC voltage. The present invention further comprises a separation performance changing means for changing the separation performance between the transferred transfer materials.

According to the above configuration, even if the voltage applied to separate the transfer material from the image carrier, that is, the so-called separation voltage, is reduced under a condition in which a current leak occurs or in a low-pressure environment, While sufficiently suppressing instability of the aspect,
The reliability of the separation can also be suitably maintained.

By the way, the image bearing member having the above-mentioned structure includes:
For example, it is preferable to use a photosensitive member such as a photosensitive drum. As the transfer material, any medium having a transfer surface for transferring a toner image can be used. For example, a sheet material such as a recording paper or a heat-resistant plastic sheet may be used.

Further, it is preferable that the separation performance changing means increases the separation performance by lowering the potential of the image carrier on which the toner image has been developed.

The separation performance changing means may irradiate at least the image carrier on which the toner image has been developed to change the separation performance between the image carrier and the transfer material on which the toner image has been transferred. It may be. Such a change in separation performance is preferably performed, for example, through an exposure device that irradiates light.

The separation performance changing means changes the separation performance between the image carrier and the transfer material onto which the toner image has been transferred by changing at least the amount of charge required for transferring the toner image to the transfer material. It may be that.
Such a change in separation performance is preferably performed, for example, through a transfer charger for transferring a toner image to an image carrier.

Further, the separation performance changing means changes the separation performance between the image carrier and the transfer material onto which the toner image has been transferred by making at least the charge amount of the toner image developed on the image carrier uniform. It may be that. Such a change in the separation performance is preferably performed, for example, through a pre-transfer charger for making the charge amount of the toner image uniform prior to the transfer.

Further, the separation performance changing means may change the separation performance between the image carrier and the transfer material onto which the toner image has been transferred by adjusting at least the curl amount of the transfer material. Such a change in separation performance is preferably performed, for example, through a curling roller that controls the curl amount of the transfer material.

Further, a leak amount detecting means for detecting a leak amount of the applied current by the transfer material separating means, and an AC voltage applied to the transfer material by the transfer material separating means based on the detected leak amount of the applied current. May be provided.

In addition, the apparatus further comprises an atmospheric pressure detecting means for detecting the atmospheric pressure, and an AC voltage and atmospheric pressure correcting means for correcting the AC voltage applied to the transfer material by the transfer material separating means according to the detected atmospheric pressure. Is also good.

An image density detecting means for detecting an image density of the toner image; and a direct current image density for correcting a direct current applied to the transfer material by the transfer material separating means in accordance with the detected image density. Correction means may be further provided.

Further, a water amount detecting means for detecting a water amount in the atmosphere, and a DC current water amount correcting means for correcting a DC current applied to the transfer material by the transfer material separating means according to the detected water amount. May be further provided.

The DC current changing means changes the DC current according to at least an AC voltage applied to the transfer material and a separating performance between the image carrier and the transfer material on which the toner image is formed. It may be that.

The DC current changing means may decrease the DC current as the AC voltage decreases, and increase the DC current as the AC voltage increases.

Further, the separation performance changing means may increase the separation performance as the AC voltage decreases, and decrease the separation performance as the AC voltage increases.

Further, a toner image may be developed with a toner having a polarity opposite to that of the electrostatic latent image formed on the image carrier.

The above configurations can be combined as much as possible.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the image forming apparatus of the present invention is applied to a copying machine will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a schematic configuration of a copying machine according to the present embodiment.

In FIG. 1, a member 1 includes a photosensitive drum (image carrier) for forming an electrostatic latent image on its photosensitive surface (image bearing surface),
2 is a primary charger for charging the photosensitive surface of the image photosensitive drum 1,
Reference numeral 4 denotes a developing device that applies a voltage between the developing sleeve 4a and the photosensitive drum 1 to develop an electrostatic latent image to form a toner image on the photosensitive drum 1, and 7 eliminates unnecessary potential on the photosensitive drum 1. A pre-transfer exposing device 10 for easily separating the transfer material P from the photosensitive drum 1, a pre-transfer charger 10 for uniforming the charge amount of the toner image formed on the photosensitive drum 1, and 8 being formed on the photosensitive drum 1. Transfer chargers 5 and 6 for transferring the transferred toner image to the transfer material P, a separation first charger and a separation second charger for separating the transfer material P from the photosensitive drum 1, and 11 a transfer material P
A cleaning device for removing toner (transfer residual toner) remaining on the photosensitive drum 1 without being transferred to the photosensitive drum 1; and 12, a semiconductor laser for emitting a laser beam L modulated by an image signal. This laser beam L is applied to the rotating polygon mirror 1
The raster scanning is performed on a predetermined photosensitive surface on the photosensitive drum 1 through the imaging lens 16 after being reflected by the imaging lens 16. The member 17 is a reflecting mirror. The humidity sensor S1 calculates the amount of moisture (humidity) in the atmosphere.
Is a well-known detector for detecting. The density sensor S2 is a known detector that detects the density (image amount) of the toner transferred onto the transfer material P in the transfer operation. Control circuit 4
0 inputs the detection signals from the detectors S1 and S2, and receives the photosensitive drum 1, the primary charger 2, the laser beam L, the developing device 4, the pre-transfer exposure device 7, the pre-transfer charger 10,
It controls the driving of various members such as the transfer charger 8, the separation chargers 5 and 6, and the cleaning device 11.

The copier 50 performs a charging operation for uniformly charging the surface of the photosensitive drum 1 by the primary charger 2, an exposure operation for forming an electrostatic latent image on the photosensitive drum 1 by irradiating a laser beam L, and a developing device. 4, a developing operation of attaching toner and developing as a toner image, a transfer operation of transferring the toner image to an electrostatic latent image on a transfer material P by a transfer charger 8;
An image is formed on the transfer material P by a series of operations such as a separation operation of separating the transfer material P from the photosensitive drum 1 and a fixing operation of fixing toner on the transfer material P.

In this embodiment, each of the chargers 2 for charging the photosensitive drum 1 (the photosensitive surface of the photosensitive drum)
It is assumed that a well-known corona charging method is adopted for 5, 6, 8, and 10.

Hereinafter, of the operations included in such a series of image forming operations, particularly the operations characteristic of the present embodiment will be described in detail.

First, FIGS. 2A to 2F show the copying machine 50.
5 schematically shows the transition of the surface potential on the photosensitive drum 1 or the transfer material P in the charging to separating operation of FIG.

As shown in FIG. 2A, in the charging operation,
First, the photosensitive drum 1 is set at a predetermined potential Vd by the primary charger 2.
(+400 V).

Next, as shown in FIG. 2B, an electrostatic latent image of a predetermined potential Vl (+50 V) is formed by irradiation with the laser beam L. Here, the potential Vd corresponds to the potential when charged by the primary charger 2, and the potential Vl corresponds to the potential when attenuated by the irradiation of the laser beam L.

The DC voltage Vs is applied to the developing sleeve 4a.
Is applied, the electrostatic latent image is reversely developed with the positively charged toner, and a toner image is formed on the photosensitive drum 1 as shown in FIG. Then, the pre-transfer charger 10 makes the charge amount of the toner substantially uniform.

Next, as shown in FIG. 2D, the potential Vd is attenuated by the pre-transfer exposure device 7 to weaken the attraction force between the transfer material P and the photosensitive drum 1 (particularly, Vd).

Then, as shown in FIG. 2E, one charge is applied to the back surface of the transfer material P by the transfer charger 8, the back surface potential of the transfer material P is set to -450 V, and the toner image is transferred to the transfer material P. Is transferred to

Then, as shown in FIG. 2F, unnecessary positive charges applied to the back surface of the transfer material P are removed by the separation chargers 5 and 6, and the potential of the transfer material P becomes about 0V. . That is, the attraction force between the transfer material P and the photosensitive drum 1 is weakened, the transfer material P is separated from the photosensitive drum 1 satisfactorily, and a desired image can be obtained on the transfer material P.

In the charging operation, the pre-transfer charger 10
Applies a voltage obtained by superimposing a direct current on an alternating current. This alternating current is a rectangular wave having an amplitude Vpp (peak to peak; hereinafter, referred to as a separation voltage) of 9 kV and a frequency of 700 Hz, and is a constant voltage. On the other hand, DC is a constant current (hereinafter, a DC component of a voltage obtained by superimposing DC on AC is called a difference current).
00 μA, but 0 μA (not applied) to +300 μA
And is appropriately adjusted by the control circuit 40.

A direct current is applied to the transfer charger 8, which is normally -400 μA, but 0 μA (not applied).
It is variable up to -650 μA, and is appropriately adjusted by the control circuit 40. A voltage obtained by superimposing a direct current on an alternating current is applied to the separation chargers 5 and 6.
A constant voltage of a 00 Hz rectangular wave, and a separation voltage Vp
Although p is usually 10.5 kV, as will be described later, it is appropriately adjusted by the control circuit 40 at the time of leak detection or low pressure (high altitude). The difference current (separation difference current) is a constant current variable from 0 (no output) to +500 μA.

As described in the prior art, it is desirable that the output of the separation difference current is controlled so as to be appropriately changed according to the image density and the absolute humidity.

FIG. 3 shows experimental data confirmed by the inventor regarding the settable range of the separation difference current when the amount of water and the amount of image are changed.

The data shown in FIG. 9 shows that the transfer material P is thin, and its paper weight is short, its own weight is small because of short paper fibers, and it has no rigidity (low rigidity).
^This is the case where the recycled paper of No. ² is used.

As shown in the drawing, separation is performed well and retransfer does not occur within the range of the arrow, but either separation failure or retransfer occurs outside the range of the arrow. Confirmed by the inventor.

Next, FIG. 5 is a control table for the control circuit 40 to determine the separation difference current based on the atmospheric humidity, which is created based on the experimental data of FIG.

As shown in the control table of FIG. 5, the separation difference current is controlled to be a minimum value at an absolute humidity of 11 g / kg. That is, the difference current is increased as the absolute humidity becomes higher or lower than 11 g / kg.

On the other hand, with regard to the image density, a known detector reads the total amount of the image from the leading end of the transfer material P to 5 cm, and the control circuit 40 determines that the image amount is within the range of 00H (minimum recognition value) to 28H. In some cases, it is recognized that the image amount is small, and a relatively large difference current is applied.
When it is in the range of H to FFH (maximum recognition value), it is recognized that the image amount is large, and a relatively small difference current is applied.
In the intermediate range 29H to 87H, a difference current corresponding to the intermediate value is applied.

Next, in the copying machine 50 of the present embodiment,
A description will be given of what value the control circuit 40 changes the voltage applied to the separation chargers 5 and 6 when a current leak is detected.

During operation of the copying machine 50, when a current leak is detected, the control circuit 40 reduces the separation voltage Vpp which is an AC component of the separation difference current.

Further, in response to the reduction of the separation voltage Vpp, the control map for determining the separation difference current is also switched.

That is, FIG. 4 shows experimental data confirmed by the inventor regarding the settable range of the separation difference current when the amount of water and the amount of image are changed, similarly to FIG. 3 described above. In particular, the results under the condition where a current leak has occurred and the separation voltage Vpp has been reduced are shown.

FIG. 6 shows a control table for the control circuit 40 to determine the separation difference current based on the humidity of the atmosphere, similarly to FIG. 5 described above, and is particularly based on the experimental data of FIG. Indicates what has been set.

As shown in FIG. 6, when the separation voltage Vpp is reduced, in other words, even when a current leaks, the correspondence between the atmospheric humidity (absolute humidity) and the separation difference current is shown in FIG. The result shows a tendency similar to that of the fifth example. However, when the separation voltage Vpp is reduced (FIG. 6), the difference current under the same humidity condition is set to be smaller by about 30 μA than when the normal separation voltage Vpp is applied (FIG. 5).

This is apparent from the comparison between FIGS. 3 and 4 that the settable range of the separation difference current is equal to the separation voltage V.
This is due to the fact that the pp reduction is biased toward the lower current side.

That is, when the separation voltage Vpp is reduced,
As for the charge removal of the transfer material P having the transfer charge in the separation chargers 5 and 6, the effect of the soft charge removal which is a feature of the AC charge removal is weakened. Then, a strong separation difference current partially flows into the back surface of the transfer material P, and a retransfer phenomenon occurs in that portion. Therefore, when the separation voltage Vpp is reduced, it is necessary to reduce the separation difference current and prevent retransfer.

As described above, according to the present embodiment, the separation of the transfer material P from the photosensitive drum 1 becomes slightly unstable due to such control for reducing the difference current at the time of leakage, Only with the decrease in stability, it is possible to easily and suitably suppress the leak in the separation charging shield, and to prevent an image defect due to a broken charging wire or a hole in the photosensitive layer of the drum.

In this embodiment, the normal voltage is set to 10.
5 kVpp, but 9.2 kVp at the time of reduction application
p. This voltage is set to an appropriate voltage according to the shape of the separation charger, the printing speed of the image forming apparatus, and the like, and is not limited to the numerical value in the present embodiment. In addition, the adjustment may be performed steplessly according to the magnitude of the current leak amount.

In the present embodiment, the amount of decrease in the difference current is 30 μA, but is not limited to this value. It is more preferable to change the amount of reduction between the first side and the second side.

If the separation voltage Vpp can be switched a plurality or steplessly, it is more preferable to have the amount of reduction of the difference current for each of the switched separation voltages Vpp.

Further, in this embodiment, the amount of change in the separation difference current is constant irrespective of the amount of water and the amount of image, but it may be changed as needed.

Next, the leak detecting method used in the present embodiment will be described.

When a current of a predetermined value or more flows through the corona wire for 5 milliseconds (ms) or more, it is temporarily estimated that a leak has occurred (leak detection).

However, in consideration of the possibility of erroneous detection, if it is tentatively estimated that the leak is detected, the voltage input is once turned off (OFF) and then immediately turned on (ON) again. Leak detection is performed four times until the work is completed by pressing the copy button or until the work is completed after the work operation start command signal is output from an external control device such as a personal computer. In this case, it is assumed that the leak is constantly occurring, and the AC voltage (isolation voltage) Vpp10.5 kV is reduced to 9.2 kV in order to prevent the leakage failure.

By configuring the apparatus as described above, the separation voltage Vpp for the separation operation of the transfer material P is normally set to a relatively high value to ensure stable separation. Reduces the separation voltage Vpp.

That is, according to the present embodiment, it is possible to suppress a voltage attack on the photosensitive drum 1, which is a failure induced by a leak, and to prevent the occurrence of a defective image or a broken wire.

By appropriately changing the separation difference current according to the degree of reduction of the separation voltage Vpp, the separation voltage Vpp
Instability in the separation operation of the transfer material P due to the reduction of
By minimizing it, a stable separation operation can always be ensured.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The second embodiment will be described focusing on the differences from the first embodiment.

In the first embodiment, as an example of a high-speed image forming apparatus in which the present invention has a particularly advantageous effect, an apparatus having a pre-transfer exposure device has been described.

This embodiment is an example of a high-speed image forming apparatus in which the present invention has a particularly advantageous effect, and is applied to a copying machine (image forming apparatus) employing a regular development system.

FIG. 7 is a schematic diagram showing a schematic configuration of a copying machine according to the present embodiment.

In the copying machine 250 shown in the figure, the photosensitive drum 201, the primary charger 202, the developing device 204, the pre-transfer charger 210, the transfer charger 208, the separated first charger 2
05, separation second charger 206, cleaning device 21
1. Rotating polygon mirror 214, imaging lens 216, reflecting mirror 21
7, a control circuit 240 and the like.

The copying machine 250 of the present embodiment
It does not have a pre-transfer exposure device that removes unnecessary potential on the photosensitive drum and facilitates separation of the transfer material P from the photosensitive drum. The configuration is different from the first embodiment.

That is, the copying machine 2 in the present embodiment
Reference numeral 50 denotes a photosensitive drum 201 particularly in the charging operation.
The apparatus has an apparatus configuration to apply a so-called regular development method, such as forming a toner image on the photosensitive drum 201 by using a toner having a charge of a polarity opposite to that of the electrostatic latent image formed thereon.

However, the basic structure and function of the other various constituent members are almost the same as those in the first embodiment, and the detailed description of these members will be omitted.

FIGS. 8A to 8E schematically show changes in the surface potential on the photosensitive drum 201 or on the transfer material P during the charging and separating operations of the copying machine 250. FIG.

In the copying machine 250 of this embodiment, the transfer paper 2
When the image is formed on the photosensitive drum 1 at +400 V by the primary charger 202 as shown in FIG.
(Potential Vd), and as shown in FIG. 8B, +50 V (potential Vl) by the irradiation of the laser beam L.
Is formed. Here, the potential Vd is a potential when charged by the primary charger 202, and Vl is a potential when attenuated by irradiation of the laser beam L.
Then, by applying the DC voltage Vs to the developing sleeve 204a, the electrostatic latent image is regularly developed with the negatively charged toner to form a toner image as shown in FIG. 8C. Furthermore, the pre-transfer charger 210 makes the charge amount of the toner substantially uniform. Then, the transfer charger 20
8, a positive charge is applied to the back surface of the transfer material P, and the back surface potential of the transfer material P is set to +700 V as shown in FIG.
And the toner image is transferred to the transfer material P. And
Unnecessary positive charges applied to the back surface of the transfer material P are removed by the separation chargers 205 and 206, and the potential of the transfer material P becomes about 0 V as shown in FIG. That is,
The attraction force between the transfer material P and the photosensitive drum 201 is weakened, and the transfer material P is favorably separated from the photosensitive drum 201, so that a desired image can be obtained on the transfer material P.

As in the first embodiment, a voltage obtained by superimposing a direct current on an alternating current is applied to the separation chargers 205 and 206. The alternating current is a rectangular wave having a frequency of 700 Hz and a constant voltage. And Vpp is usually 10.5 kV. The difference current is a constant current that can be varied from 0 (no output) to +500 μA, and is appropriately output depending on the image density and the absolute humidity.

FIG. 9 is a control table for the control circuit 240 to determine the separation difference current based on the atmospheric humidity in the present embodiment, which is applied in a normal time when no current leak is detected. (Normal separation voltage Vp
p), that is, it corresponds to the control table of FIG. 5 in the first embodiment.

FIG. 10 is a similar control table which is applied when a current leak is detected (when the separation voltage Vpp is reduced), that is, the control table of FIG. 6 in the first embodiment. It corresponds to a control table.

As shown in FIGS. 9 and 10, in the present embodiment employing the regular development method, the correspondence between the separation difference current and the humidity (absolute humidity) of the atmosphere is different from that of the first embodiment. Different (see also FIGS. 5 and 6). However, as is apparent from comparison between FIGS. 9 and 10, in the control mode of the present embodiment, the relative correspondence between the absolute humidity and the separation difference current is not changed by changing the separation voltage Vpp. When the voltage Vpp is reduced (FIG. 10), the difference current is set to be smaller by about 30 μA under the same humidity condition than when the normal separation voltage Vpp is applied (FIG. 9). It is common to the control mode of the form.

In this embodiment, the same leak detection method as in the first embodiment is used.

By adopting the above configuration, as in the first embodiment, stable separation can be ensured by increasing the separation voltage Vpp normally, and if a leak occurs, In addition, the reduction in Vpp suppresses a voltage attack on the photosensitive drum 201, which is a leakage-induced failure, and can prevent image defects and wire breakage.

By appropriately changing the separation difference current according to the degree of reduction of the separation voltage Vpp, the separation voltage Vpp
By appropriately changing the separation difference current in accordance with the reduction of the distance, the separation difference current can be minimized, and a stable separation operation can always be ensured.

(Third Embodiment) Next, a third embodiment in which the image forming apparatus of the present invention is applied to a copying machine will be described.
The following description focuses on the differences from the first embodiment.

FIG. 11 is a schematic diagram showing a schematic configuration of a copying machine according to the present embodiment.

In the copying machine 350 shown in the figure, the photosensitive drum 301, the primary charger 302, the developing device 304, the pre-transfer charger 310, the pre-transfer exposure device 307, and the transfer charger 30
8, a separation first charger 305, a separation second charger 306, a cleaning device 311, a rotating polygon mirror 314, an imaging lens 316, a reflection mirror 317, a control circuit 340, and the like. The basic configurations and functions of these various components are substantially the same as those in the first embodiment, and a detailed description thereof will be omitted.

The copying machine 350 of this embodiment includes an atmospheric pressure sensor S3 for detecting the atmospheric pressure and outputting a detection signal to the control circuit 340, which is different from the first embodiment. The configuration is different.

It is known that the current leak of corona discharge depends on the atmospheric pressure. Specifically, when the atmospheric pressure decreases, the discharge starting voltage decreases. That is, when the pressures are compared at the same voltage, the lower the pressure is, the more the leak is likely to occur. For this reason, in an image forming apparatus using corona discharge, a current sensor can be suitably suppressed by providing an air pressure sensor and changing the voltage applied to the corona charger accordingly.

Particularly, copying machine 350 of the present embodiment
Control is performed so that the separation voltage Vpp is changed according to the change in the atmospheric pressure, and the separation difference current is also changed according to the separation voltage Vpp.

FIG. 12 is a diagram showing the correspondence between the change in the atmospheric pressure and the separation voltage Vpp showing how the separation voltage Vpp is changed according to the change in the air pressure in the copying machine 350 of the present embodiment.

FIG. 13 is a correspondence diagram between the separation voltage Vpp and the separation difference current showing how the separation difference current is changed according to the change of the separation voltage Vpp.

The control of the separation difference current based on the correspondence between the parameters in both figures, in other words,
By changing the separation voltage Vpp according to the change in the atmospheric pressure, and further changing the separation difference current according to the changed separation voltage Vpp, even if the air pressure changes, the maximum separation voltage within a range that does not cause a leak. It has been confirmed by the inventor that the separation operation can be ensured and the stability of the separation operation can be suitably maintained.

That is, according to the above configuration, the separation voltage Vpp is set as high as possible within a range in which current leakage does not occur in accordance with atmospheric pressure fluctuations, so that the stability of the separation operation is as high as possible. And Vpp
By properly changing the separation difference current according to the reduction,
It is possible to minimize the instability of separation due to the reduction of the separation voltage Vpp.

Accordingly, the operation of separating the transfer material P from the photosensitive drum 301 is always performed in a stable operation mode.

In the present embodiment, in the event of a leak occurring, in the case of FIG.
Also, if the control based on the control table of FIG. 6 is executed, the separation voltage Vpp is further reduced, and the separation difference current is changed in accordance with the reduction of the separation voltage Vpp, the suppression of the voltage attack, the image failure, the disconnection of the wire, The effect of prevention is also achieved.

(Fourth Embodiment) Next, a fourth embodiment in which the image forming apparatus of the present invention is applied to a copying machine will be described.
The following description focuses on the differences from the first embodiment.

FIG. 14 is a schematic diagram showing a schematic configuration of the copying machine according to the present embodiment.

In the copying machine 450 shown in the figure, the photosensitive drum 401, the primary charger 402, the developing device 404, the pre-transfer charger 410, the pre-transfer exposure device 407, and the transfer charger 40
8, separation first charger 405, separation second charger 406, cleaning device 411, rotating polygon mirror 414, imaging lens 416, reflection mirror 417, control circuit 440, humidity sensor S
1, a density sensor S2 and the like. The basic configuration and functions of these various components are described in the first section.
This is almost the same as that in the embodiment, and the detailed description here is omitted.

The laser printer 450 according to the present embodiment detects the voltage applied to the separation chargers 405 and 406, that is, the amplitude of the alternating current (separation voltage) when detecting the leak of the separation first charger 405 and the separation second charger 406. The reduction of Vpp is common to the above embodiments.

However, this embodiment differs from the above embodiments in that the light amount of the pre-transfer exposure device 407 is changed according to the degree of reduction of the separation voltage Vpp.

More specifically, when a current leak is detected during the operation of the copying machine 450, the control circuit 440 reduces the voltage applied to the separation chargers 405 and 406, and controls the light amount of the pre-transfer exposure unit 407. And further alter the separation difference current.

When a current leak occurs in the separation charger, the settable range of the separation difference current when the moisture amount (humidity) and the image amount are the same is narrowed, as described in the first embodiment. (FIGS. 3 and 4)
See also).

When such a current leak occurs, the settable range of the separation difference current can be expanded by increasing the amount of light of the pre-transfer exposure device 407, and the separation operation can be stabilized. It has been confirmed by the inventor that the property is increased and the so-called separation performance is improved.

However, although the settable range of the separation difference current is expanded due to the increase in the amount of light of the pre-transfer exposure device 407, it does not reach completely the same condition as that in which no leakage occurs. That is, there is a shift in the mutual settable range.

When the light amount of the pre-transfer exposure device 407 is increased, the potential V of the non-image portion on the photosensitive drum 401 is increased.
d decreases, and the attraction force between the transfer material P and the photosensitive drum 401 decreases.

Therefore, in the present embodiment, when a leak is detected, an increase in the amount of light of the pre-transfer exposure device 407 and the separation voltage Vpp
And the change of the separation difference current in accordance with the reduction of the separation voltage Vpp.

Next, in the copying machine 450 of the present embodiment, when a current leak is detected in the separated first charger 405 or the separated second charger 406 during the operation, the control circuit 440 determines The specific processing procedure will be described with reference to the flowchart in FIG.

The routine shown in FIG.
At the time of the image forming operation (printing operation) of 50, the operation is repeatedly executed through the control circuit 450 during the period from the start to the end of the operation.

When the printing operation is started and the process proceeds to this routine, the control device 450 firstly executes step S1.
At 01, it is determined whether or not the occurrence of current leakage in the separation chargers 405 and 406 has been detected.

Here, as a method of detecting the occurrence of a leak, the same method as in the first embodiment is employed.

That is, during the printing operation of the copying machine 450, a current of a predetermined value or more is applied to the corona wire for 5 milliseconds (m
s) If it flows more than this, it is temporarily estimated that a leak has occurred (leak detection).

However, in consideration of the possibility of erroneous detection, if it is supposed that the leak is detected, the voltage input is once turned off (OFF) and then immediately turned on (ON) again. Leak detection is performed four times until the work is completed by pressing the copy button or until the work is completed after the work operation start command signal is output from an external control device such as a personal computer. When a leak occurs, it is assumed that the leak is occurring in a steady state, and the occurrence of the leak is determined.

That is, in step S101, the control circuit 450 determines whether the tentative estimation of the leak occurrence has reached four times, and if the determination is affirmative, the processing proceeds to step 102.
Move to Incidentally, if the determination in step S101 is negative, the control circuit 450 once ends the processing.

In step S102, an alternating voltage (isolation voltage) Vpp1
Reduce 0.5 kV to 9.2 kV.

In the following step S103, the light quantity of the pre-transfer exposure unit 407 is increased from, for example, the normal set value of 0.14 lux / sec to 0.21 lux / sec.

In step S104, the separation difference current is changed based on the separation difference current control table shown in FIG. As will be described in detail later, the current value determined based on the separation difference current control table of FIG. 17 is about 50 μA lower than the normal value determined based on the separation difference current control table of FIG. . After changing the separation difference current, control circuit 440 proceeds to step 105.

In step 105, whether or not a leak has occurred is determined again based on the same criterion as in step S101.

If the determination in step 105 is affirmative, the control circuit 440 shifts the processing to step 106 to display an error or the like and temporarily suspends the copying operation.

On the other hand, if the determination in step S105 is negative, control circuit 440 ends the processing once.

Based on such a procedure, when a current leak is detected in the first separation charger 405 or the second separation charger 406 during the operation of the copying machine 450, the separation voltage Vpp and the transfer exposure unit 407 are detected. The change and adjustment of the light amount and the separation difference current are executed.

Next, the characteristics of the separation difference current control tables shown in FIGS. 16 and 17 will be described in detail.

FIGS. 16 and 17 are control tables for the control circuit 440 to determine the separation difference current based on the atmospheric humidity in the present embodiment.

In particular, the control table shown in FIG.
This is applied when pp is set to the normal value (10.5 kV), and is applied when the control table in FIG. 17 is set to a relatively small value (9.2 kV). It is.

The correspondence relationship between the atmospheric humidity (absolute humidity) and the separation difference current shown in both control tables shows a tendency similar to each other in FIGS. However, when the separation voltage Vpp is lowered (FIG. 17), compared with the normal time (FIG. 16),
The separation difference current under the same humidity condition is set to be smaller by about 50 μA.

The reason for this is basically the same as the reason explained in the first embodiment regarding the relationship between the change in the separation voltage Vpp and the separation difference current to be made to correspond to this change (see FIGS. 3 and 4). Is the same. That is, when the separation voltage Vpp is reduced, the separation charger 40 of the transfer material P bearing the transfer charge is reduced.
Regarding the static elimination in 5, 406, the effect of soft static elimination, which is a feature of AC static elimination, is weakened. Then, a strong separation difference current partially flows into the back surface of the transfer material P, and a retransfer phenomenon occurs in that portion. Therefore, when the separation voltage Vpp is reduced, it is necessary to reduce the separation difference current and prevent retransfer.

In addition, in this embodiment, the pre-transfer exposure device 4
Since the change of the light amount of 07 is also performed, the change of the light amount (increase of the light amount) causes a decrease in the potential Vd of the non-image portion on the photosensitive drum 401 and a decrease in the attraction force between the transfer material P and the photosensitive drum 401. In consideration of the above, the reduction amount of the separation difference current is further increased.

In this embodiment, the normal voltage is set to 10.
5 kVpp, but 9.2 kVp at the time of reduction application
p. This voltage is set to an appropriate voltage according to the shape of the separation charger, the printing speed of the image forming apparatus, and the like, and is not limited to the numerical value in the present embodiment. In addition, the adjustment may be performed steplessly according to the magnitude of the current leak amount.

In the present embodiment, the amount of decrease in the difference current is 50 μA. However, the present invention is not limited to this value. It is more preferable to change the amount of reduction between the first side and the second side.

Further, if the configuration is such that the separation voltage Vpp can be switched a plurality or steplessly, it is more preferable that the difference current is reduced for each switching-changed separation voltage Vpp.

Further, in the present embodiment, the amount of change in the separation difference current is constant irrespective of the amount of water or the amount of image, but it may be changed as needed.

Next, the setting of the amount of increase in the amount of light of the pre-transfer exposure unit 407 will be described in detail.

When the light amount of the pre-transfer exposure device 407 is increased, a very small amount of toner scatters in the vicinity of the actual image.
The so-called scattering phenomenon, which lowers the sharpness of an image, is exacerbated.

Since the difference between the non-image portion potential Vd and the image portion potential Vl is reduced by the pre-transfer exposure device 407, the force for binding the toner to the image portion potential Vl is weakened, and the toner is transferred to the non-image portion. This is because it is easy to go and splattering easily occurs.

Note that scattering occurs very remarkably when the toner layer potential Vt is higher than the non-image portion potential Vd.

Further, when the contact between the transfer material P and the image carrier 401 is unstable, the scattering is remarkable, and by bringing the transfer material P into stable contact with the image carrier 401,
It is known that this can be avoided by increasing the nip area between the transfer material 1 and the transfer material P.

However, the transfer material P having high rigidity is formed by an image carrier.
The nip area tended to be small because it was difficult to follow 1 and it was easy to splatter.

Therefore, the amount of increase in the optical power of the pre-transfer exposure device 7 depends on the separation property of the transfer material P having low rigidity and the transfer material P having high rigidity.
I decided on the balance of the splatters. Table 1 shows the relationship between the light amount of the post-exposure unit 407 and scattering and separation failure. The experiment was performed at a temperature of 20 ° C. and a humidity of 50 × RH. The voltage was applied to the separation chargers 405 and 406.

The difference current was measured for each separation voltage Vpp under optimum conditions for separation.

[0157]

[Table 1] The exposure amount by the pre-transfer exposure device 7 in Table 1 is a value measured at the surface position of the image carrier 1 at a portion facing the pre-transfer exposure device 7.
Also, the rigidity value of the transfer material is JISP8143-1967.
The measurement was performed in accordance with the test method described above, and the value of a generally used transfer material was used.

The evaluation was performed according to the following criteria.

(Scattering) A: Slightly splattering around characters is observed at a microscope observation level, but hardly noticeable. ：: Cannot be determined by visual observation. Δ: Visual observation discrimination is possible, but characters are not bleeding. ×: Characters can be easily distinguished by visual observation, and characters can be seen.

(Defective separation) A: Very good without any flapping or floating. ：: Floating can be confirmed very rarely. Δ: Floating or fluttering, but the apparatus does not stop due to paper jam. ×: The apparatus stops due to a paper jam.

As shown in Table 1, the separation voltages Vpp10.
At 5 kV, the light amount of the pre-transfer exposure device 407 is optimally 0.14 lux / sec in consideration of the balance between the scattering and the separation failure. However, when the separation voltage Vpp is reduced to 9.2 kV, the separation failure becomes worse.

For this reason, it can be seen that 0.21 lux / sec is desirable from the viewpoint of the balance between poor separation and scattering, although scattering is slightly deteriorated. Therefore, in this embodiment, the light amount of the pre-transfer exposure device 7 was set to 0.14 lux / sec when the separation voltage Vpp was 10.5 kV, and was set to 0.21 lux / sec when the separation voltage Vpp was 9.2 kV.

According to the above configuration, stable isolation can be ensured by increasing the isolation voltage Vpp normally. Even if a leak occurs, the Vpp is reduced by reducing the Vpp. Thus, a voltage attack on the photosensitive drum 201, which is a derivative trouble of the above, can be suppressed, and an image defect and a broken wire can be prevented.

By appropriately changing the separation difference current according to the degree of reduction of the separation voltage Vpp, the separation voltage Vpp
As a result, the instability of the separation mode due to the reduction of the amount is minimized, and a stable separation operation can always be ensured.

In the present embodiment, the pre-transfer exposure device 7 may not be operated normally for giving priority to scattering but may be operated only when the separation voltage Vpp is reduced.

Further, since the rigidity of the transfer material P changes according to the absolute humidity, the pre-transfer exposure device 40 depends on the absolute humidity.
7 may be changed so as to be changed in accordance with the reduction of the separation voltage Vpp.

(Fifth Embodiment) Next, a fifth embodiment in which the image forming apparatus of the present invention is applied to a copying machine will be described.
The following description focuses on the differences from the first embodiment.

FIG. 18 is a schematic diagram showing a schematic configuration of the copying machine according to the present embodiment.

In the copying machine 550 shown in the figure, the photosensitive drum 501, the primary charger 502, the developing device 504, the pre-transfer charger 510, the pre-transfer exposure device 507, and the transfer charger 50
8, separation first charger 505, separation second charger 506, cleaning device 511, rotating polygon mirror 514, imaging lens 516, reflection mirror 517, control circuit 540, humidity sensor S
1, a density sensor S2 and the like. The basic configuration and functions of these various components are described in the first section.
This is almost the same as that in the embodiment, and the detailed description here is omitted.

In the copying machine 550 of this embodiment, the voltage applied to the separation chargers 505 and 506, that is, the amplitude of the alternating current (separation voltage) is also detected when the leakage of the separation first charger 505 and the separation second charger 506 is detected. ) VPP is reduced in common with the above embodiments.

However, the present embodiment differs from the above embodiments in that the current applied to the transfer charger 508 is changed according to the degree of reduction of the separation voltage Vpp.

More specifically, when a leak of current is detected during the operation of the copying machine 550, the control circuit 540 reduces the voltage applied to the separation chargers 505 and 506 and applies the voltage to the transfer charger 508. Current value to be reduced, and further, the separation difference current is changed.

As described in the prior art, the larger the transfer current is, the better the transfer property is, while the lower the transfer current is, the worse the transfer property is.
Separability tends to be better.

In the fourth embodiment, the light amount of the pre-transfer exposure device is determined so as to suppress both scattering and separation failure.

In the present embodiment, instead of such a configuration, the current applied to the transfer charger 508 is reduced, so that the adverse effect when the transfer current is reduced, especially the transfer failure in a high-temperature and high-humidity environment. It is necessary to determine the amount of decrease in the transfer current based on the balance between the separation and the separation failure.

Table 2 shows the relationship between the transfer current and transfer failure and separation failure.

[0177]

[Table 2] Separation of the experimental temperature 20 ° C., carried out under the conditions of humidity 50XRH, as the transfer material, the stiffness is used as stringent isolation of 25 cm ^3/100.

The difference current applied to the separation chargers 505 and 506 was determined for each separation voltage Vpp under the optimum conditions for separation.

The evaluation was performed according to the following criteria.

(Defective transfer) A: Transfer efficiency is 90X or more. (No problem as an image) ：: Transfer efficiency is 85X or more and less than 90X. (Slightly thin, not noticeable by visual inspection) ○ △: Transfer efficiency is 80X or more and less than 85X. Δ: Transfer efficiency is 70 × or more and less than 80 ×. (It can be seen that the characters are thin, but characters are not difficult to read.) ×: Transfer efficiency is less than 70 ×. (It is very thin and it is difficult to read letters etc.)

(Defective separation) A: Very good without fluttering or floating. ：: Floating can be confirmed very rarely. Δ: Floating or fluttering, but the apparatus does not stop due to paper jam. ×: The apparatus stops due to a paper jam.

As shown in Table 2, the separation voltages Vpp10.
At 5 kV, the transfer current is optimally −400 μA in consideration of the balance between the transfer failure and the separation failure. However, when the separation voltage Vpp is reduced to 9.2 kV, the separation failure becomes worse.
For this reason, it can be seen that −250 μA is desirable from the balance between the separation failure and the transfer failure, although the transfer failure is slightly aggravated. Therefore, in the present embodiment, when the separation voltage Vpp is 10.5 kV, the transfer current is −400 μm.
A, at 9.2 kV, the voltage was -250 μA.

That is, even if the copying machine 550 is configured as described above, the same effects as those of the fourth embodiment can be obtained.

Modifications and the like: In the fourth and fifth embodiments, when a leak is detected from the separation charger of the laser printer (image forming apparatus), the voltage applied to the separation charger, that is, While reducing the AC amplitude (separation voltage) Vpp and changing the light amount of the transfer exposure device (4th
Embodiment 5) or the apparatus is configured to change the current value applied to the transfer charger (Fifth Embodiment).

The change (increase) in the amount of light of the transfer exposure device and the change (increase) in the current value applied to the transfer charger in response to such a change (decrease) in the separation voltage Vpp are both performed. This is nothing but an operation mode of changing (enhancing) the performance of separation from the object.

Therefore, as a modification of the fourth or fifth embodiment, the apparatus may be configured as follows.

First, although not particularly shown, in an image forming apparatus such as a normal copying machine, an increase in the amount of light of the pre-transfer exposure device and a reduction in the transfer current are performed through a curling roller provided for controlling the curl amount of the transfer material. The apparatus may be configured to perform an operation of changing the separation performance of the transfer material (hereinafter, a separation function changing operation). That is, control may be performed to increase the pressure of the curling roller or to reduce the difference current of the pre-transfer charger. Further, any one of the operation modes of the separation performance change operation may be applied in combination with another separation performance change operation.

Here, the operation of increasing the pressure of the curling roller is performed within a range where the nip between the photosensitive drum and the transfer material is reduced due to the increase in the curl of the transfer material and the “scatter” does not increase. The same or similar effects to the fourth or fifth embodiment can be obtained.

The operation of changing the difference current of the pre-transfer charger is performed within a range in which the charge amount of the toner on the photosensitive drum becomes nonuniform and transfer failure does not occur. An effect equivalent to or equivalent to that of the fifth embodiment can be obtained.

In any case, when the leakage of the current is detected, the separation voltage Vpp is changed, the separation performance is appropriately variably controlled within a range where no problem occurs, and the separation voltage Vpp and the degree of change in the separation performance are further changed. The separation difference current may be changed in accordance with

With such a configuration, it is possible to suppress a voltage attack on the photosensitive drum which is a leak-induced failure, to prevent a defective image or a broken wire, and to always ensure a stable separation operation.

The image bearing member is not limited to the photosensitive drum applied in each of the above embodiments, but may be constituted by applying another image bearing member having a curved surface having photosensitivity or a flat surface.

Further, in each of the above embodiments, the image forming apparatus of the present invention is applied to a copying machine. However, other electrophotographic image forming apparatuses such as a laser beam printer and a facsimile apparatus may be used. The present invention can be applied to other devices using a separation charger for separating a transfer material from an image carrier such as a photosensitive drum.

Further, in this case, the number of mounted separation chargers is also
It is not limited to two as in the above embodiments,
One or three or more separate chargers may be provided.

Further, instead of the humidity sensor S1, density sensor S2, or pressure sensor S3 applied in each of the above embodiments, the humidity, image density,
The device may be configured to detect and recognize atmospheric pressure.

In place of the control circuit applied in each of the above embodiments, control is performed using any other means such as a computer which is provided outside the image forming apparatus and outputs a control signal through a cable or the like. No problem.

The separation charger, pre-transfer exposure unit, transfer charger, and pre-transfer charger used in each of the above embodiments may be replaced with a corona charging type charger, such as a contact roller type charging device. Any charging means may be employed.

[0198]

As described above, according to the present invention,
Voltage attack on the image carrier, which is a leak-induced obstacle, can be suppressed, and image defects and broken wires can be prevented, and a stable separation operation can always be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a schematic configuration of a copying machine according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a transition of a surface potential of a photosensitive drum or a transfer material in the embodiment.

FIG. 3 is a diagram showing a settable range of a separation difference current when the amount of water or the amount of image is changed in the embodiment.

FIG. 4 is a diagram showing a settable range of a separation difference current when a leak occurs.

FIG. 5 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 10.5 kV is set in the embodiment.

FIG. 6 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 9.2 kV is set in the embodiment.

FIG. 7 is a schematic diagram illustrating a schematic configuration of a copying machine according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram showing a transition of a surface potential of a photosensitive drum or a transfer material in the embodiment.

FIG. 9 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 10.5 kV is set.

FIG. 10 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 9.2 kV is set.

FIG. 11 is a schematic diagram illustrating a schematic configuration of a copying machine according to a third embodiment of the present invention.

FIG. 12 is a diagram showing a correspondence relationship between a pressure change and a separation voltage in the embodiment.

FIG. 13 is a diagram showing a correspondence relationship between a separation voltage and a separation difference current in the embodiment.

FIG. 14 is a schematic diagram illustrating a schematic configuration of a copying machine according to a fourth embodiment of the present invention.

FIG. 15 is a flowchart showing a processing procedure related to a change of the separation difference current and the like in the embodiment.

FIG. 16 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 10.5 kV is set in the embodiment.

FIG. 17 is a control table for determining a separation difference current based on atmospheric humidity when a separation voltage of 9.2 kV is set in the embodiment.

FIG. 18 is a schematic diagram illustrating a schematic configuration of a copying machine according to a fifth embodiment of the present invention.

FIG. 19 is a schematic diagram illustrating a schematic configuration of a conventional image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 4 developing device 4a developing sleeve 5 separation first charger (separation charger) 6 separation second charger (separation charger) 7 pre-transfer exposure device 8 transfer charger 10 pre-transfer charger 11 cleaning device 12 semiconductor Laser 14 rotating polygon mirror 16 imaging lens 17 reflecting mirror 40 control circuit 50 copying machine (image forming apparatus)

Claims (13)

[Claims] 1. An image forming apparatus for developing an electrostatic latent image formed on an image carrier as a toner image and transferring the toner image to a transfer material to form an image, wherein the toner image is transferred. A transfer material separating unit that separates the transfer material from the image carrier by applying a voltage obtained by superimposing a DC current on an AC voltage, an AC voltage changing unit that changes the AC voltage, DC current changing means for changing the DC current according to the change, and separation performance changing means for changing the separation performance between the image carrier and the transfer material on which the toner image has been transferred, according to the change in the AC voltage. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the separation performance changing unit irradiates at least the image carrier on which the toner image has been developed to transfer the image carrier and the toner image. An image forming apparatus, wherein the separation performance between transfer materials is changed. 3. The image forming apparatus according to claim 1, wherein the separation performance changing unit changes the amount of charge required for transferring the toner image to a transfer material at least by changing the amount of charge applied to the image carrier and the toner image. An image forming apparatus that changes the separation performance between transferred transfer materials. 4. The image forming apparatus according to claim 1, wherein the separation performance changing unit uniforms at least a charge amount of the toner image developed on the image carrier, and performs the separation. An image forming apparatus characterized by changing the separation performance between an image carrier and a transfer material onto which a toner image has been transferred. 5. The image forming apparatus according to claim 1, wherein the separation performance changing unit adjusts at least a curl amount of the transfer material to form the image carrier and the toner image. An image forming apparatus that changes the separation performance between transfer materials onto which the image has been transferred. 6. The image forming apparatus according to claim 1, wherein: a leakage amount detecting unit that detects a leakage amount of an applied current by the transfer material separating unit; and the detected applied current. An image forming apparatus, further comprising: an AC voltage leakage correction unit configured to change an AC voltage applied to the transfer material by the transfer material separation unit based on a leakage amount of the transfer material. 7. An image forming apparatus according to claim 1, wherein said transfer material separating means comprises a transfer material separating means for detecting an air pressure, and wherein said transfer material separating means is responsive to said detected pressure. And an AC voltage / pressure correcting unit for correcting an AC voltage applied to the image forming apparatus. 8. The image forming apparatus according to claim 1, wherein: an image density detecting unit configured to detect an image density of the toner image; An image forming apparatus further comprising a DC current image density correction unit for correcting a DC current applied to the transfer material by the transfer material separation unit. 9. An image forming apparatus according to claim 1, wherein said transferring means is configured to detect an amount of moisture in the atmosphere, and the transfer is performed in accordance with the detected amount of moisture. An image forming apparatus further comprising a DC current moisture amount correction unit for correcting a DC current applied to the transfer material by the material separation unit. 10. The image forming apparatus according to claim 1, wherein the DC current changing unit includes at least an AC voltage applied to the transfer material, and an image carrier and a toner image. An image forming apparatus, wherein the DC current is changed in accordance with the separation performance between the formed transfer materials. 11. The image forming apparatus according to claim 1, wherein the DC current changing unit decreases the DC current with a decrease in the AC voltage, and reduces the DC current. An image forming apparatus, wherein the DC current is increased with an increase. 12. The image forming apparatus according to claim 1, wherein the separation performance changing unit increases the separation performance in accordance with a decrease in the AC voltage, and increases the separation performance. An image forming apparatus characterized in that the separation performance is reduced with an increase. 13. An image forming apparatus according to claim 1, wherein the toner image is developed with a toner having a polarity opposite to that of the electrostatic latent image formed on the image carrier. An image forming apparatus comprising: