JPH10198196A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of dispensing with a preceding exposure device. SOLUTION: The image forming device uniformly electrifies a surface of a photosensitive drum 1 by applying a voltage including AC component on a transferring roller 4 in a prepare processing stage of the image forming. A controlling device 9 applies the specified voltage on an electrifying roller 2. Then, on detecting the DC component in the current flowing to the photosensitive drum 1, and based on the detection result, the exposure quantity by the exposure device 6 is decided. The exposure device 6 performs the exposure by the exposure quantity decided by the controlling device 9. Since potential on the surface of the photosensitive drum 1 is made uniform by the electrifying roller 4, the DC component detection by controlling means 9 becomes correct. By means of applying the voltage including the DC component on the transferring roller 4, an effect of cleaning on the transferring roller 4 is raised.

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 by an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic process, means for charging a surface to be charged such as a photoreceptor as an image carrier, and a developer (toner) on the image carrier. As a means for transferring a visualized image onto a transfer paper, a method using corona discharge is widely used.

However, these methods utilizing corona discharge, which is an air discharge, have disadvantages such as requiring a high-voltage power supply and generating a large amount of ozone during discharge.

[0004] For this reason, in recent years, contact charging and contact transfer have been increasingly used as methods capable of lowering the voltage of a power supply and generating less ozone. In these methods, charging or transfer is performed by directly contacting a charging member to which a voltage is applied or a transfer member with a photoconductor as an image carrier. For example, a roller composed of a cored bar and a conductive rubber around the core is brought into contact with the photoconductor,
In a configuration in which the photosensitive member is driven to rotate together with the rotation of the photosensitive member, charging or transfer is performed on the photosensitive member by supplying a voltage to the core of the roller.

Hereinafter, the contact charging and the contact transfer will be described in more detail with reference to FIG.

In FIG. 5, reference numeral "1" denotes a photosensitive drum. Similarly, reference numeral "2" denotes a charging roller, "3" denotes a power source, "4" denotes a transfer roller, "5" denotes a power source, "6" denotes an exposure device, "7" denotes a cleaner, "8" denotes a developing machine, and "8". 9 '"is a control device.

First, contact charging by the charging roller 2 will be described.

[0008] The charging roller 2 is a roller-type contact charging member, and includes a central metal core and conductive rubber on the outer periphery thereof. The charging roller 2 is rotatably supported at both ends of a metal core by a bearing member (not shown), and is disposed parallel to the photosensitive drum 1. The photosensitive drum 1 is pressed against the surface of the photosensitive drum 1 with a constant pressing force by a pressing member (not shown), and is rotated by the photosensitive drum 1. It is also possible to attach a gear or the like, transmit the driving force, and rotate the photosensitive drum 1 in the forward or reverse direction. From the power supply 3 to the charging roller 2,
By applying a predetermined voltage, the surface of the rotating photosensitive drum is charged to a predetermined polarity and potential.

In such contact charging, a method in which only a DC voltage is applied to a charging member (hereinafter referred to as a "DC method") and a method in which a DC voltage is superimposed on an AC voltage and applied (hereinafter referred to as "quadrature superposition"). Method).

The orthogonal superposition method is widely used because it has better charging uniformity than a DC method and can provide a beautiful image. However, the orthogonal superposition method has a problem that the film thickness of the drum becomes thinner as the use of the apparatus progresses, because the surface of the photosensitive drum is cut off about five times as much as the DC method. When the film thickness of the photosensitive drum is reduced, the photosensitive sensitivity is reduced accordingly, so that the surface potential does not drop sufficiently and the potential contrast between the dark portion potential and the bright portion potential is narrowed. Then, in the normal development system, when trying to obtain a sufficient development contrast at the time of development, a sufficient reverse contrast is not obtained with respect to the bright portion potential, and the development in which the bright portion potential portion is thinly developed to produce a "fog" image is performed. Become noticeable. On the other hand, in the reversal development system, since the development contrast cannot be sufficiently obtained, the image density becomes low. Therefore, the orthogonal superposition method has the drawbacks that the above-mentioned "fog" and "image density lightness" occur earlier and the durability life is very short (about 1/5 of the DC method).

In order to remedy such a drawback, in an image forming apparatus employing the orthogonal superposition method, as the thickness of the photoreceptor is reduced, the image exposure amount is increased in order to compensate for the decrease in photosensitivity. Control method is used.
Such a method of controlling the amount of image exposure utilizes the fact that when a certain voltage is applied to the charging member, the current flowing from the charging member to the photoconductor increases as the thickness of the photoconductor decreases. . That is, the current flowing through the photoconductor when a certain voltage is applied to the charging member is detected, and the image exposure amount is determined according to the detected current value.

In order to perform this control system well and stably, it is necessary to detect the detection current stably and accurately.
The current flowing from the charging member to the photoreceptor depends on the potential of the photoreceptor surface that enters the charged portion of the charging member. Therefore, when detecting the current flowing from the charging member to the photoconductor, it is necessary to keep the potential of the surface of the photoconductor entering the charged portion constant and uniform. Conventionally, a pre-exposure device such as a fuse lamp is provided on the upstream side of a charged portion, and the surface of the photoreceptor upstream of the charged portion is discharged by exposure of the pre-exposure device to reduce the potential of the photoreceptor surface which enters the charged portion. It is always constant and uniform (in this case, near 0 v). By controlling the amount of image exposure in accordance with the thickness of the photoreceptor, the life of the apparatus is more than doubled.

Next, contact transfer by the transfer roller 4 will be described.

The transfer roller 4 is a roller-type contact transfer member, like the charging roller 2, is composed of a cored bar and conductive rubber, and is rotatably supported. The photosensitive drum 1 is driven and rotated with a constant pressing force. Then, by applying a predetermined voltage from the power supply 5 to the transfer roller 4, the toner image on the photosensitive drum is transferred to the transfer paper.

The voltage applied to the transfer roller 4 in the contact transfer is generally a DC voltage. This is because there is no difference in the effect as in the case of the charging roller 2 between the DC current alone and the voltage obtained by superimposing the DC current on the AC current, since the transfer is performed via the paper.

[0016] Such contact transfer has a disadvantage of "back stain". "Back contamination" is a phenomenon in which toner adhered to a non-image area on a drum adheres to a transfer roller due to an electric field at the time of transfer, and adheres to a surface of the next transfer paper in contact with the transfer roller. . This “back stain” is remarkable when the transfer paper size is smaller than the toner image size on the photosensitive drum, and when the transfer width of the image is narrower in the longitudinal direction of the transfer roller.

Conventionally, in an image forming apparatus employing a contact transfer method, a bias having a polarity opposite to that of the transfer roller for at least one rotation of the transfer roller is applied to the transfer roller before or after the transfer in order to prevent the back stain. A cleaning step of returning the toner adhering to the transfer roller to the drum by applying the toner is provided.

[0018]

When the contact charging method is employed, the following problems are caused because the charged surface is neutralized by a pre-exposure device such as a fuse lamp. -The toner may deteriorate due to heat generated by the pre-exposure device.・ The equipment becomes larger. -The cost of the pre-exposure device is high.

On the other hand, even in the contact transfer system, even if the above-described cleaning step is provided, the back stain cannot be completely eliminated. Therefore, a more effective cleaning method of the transfer roller has been desired.

In the present invention, while employing the contact transfer method,
It is an object of the present invention to provide an image forming apparatus which is small in size, simple and inexpensive, and can form high-quality images for a long period of time.

In the present invention, while employing the contact transfer method,
An object of the present invention is to provide an image forming apparatus in which back dirt is less likely to occur.

[0022]

Means for Solving the Problems In order to achieve the above object, the present inventor has studied and conducted experiments on contact charging and contact transfer from various angles. As a result, for contact charging, if the photoconductor is uniformly charged using the transfer member,
It was concluded that the detection current could be accurately detected without a pre-exposure device. In the contact transfer, in the cleaning step in which the transfer member is in direct contact with the charged surface of the image carrier, it is more effective to apply a voltage including an AC voltage than to apply only a DC voltage, rather than to apply only a DC voltage. Was found to be high. The invention of the present application has been made based on such examination results and findings.

According to a first aspect of the present invention, an image carrier having a charged surface made of a photoreceptor and a predetermined voltage separately set are applied to the charged surface to apply a predetermined voltage to the charged surface. Charging means for charging, exposure means for forming a latent image on the charged surface by irradiating light to the charged surface charged by the charging means, and development for visualizing the latent image with a developer A transfer unit for transferring the visualized image to the sheet by pressing a separately supplied sheet against the charged surface by the transfer member, and a measuring end. A characteristic measuring means for measuring a current-voltage characteristic between the measuring end and the charged surface by applying a predetermined voltage to the measuring end in a state where the end is in contact with the charged surface, According to the measurement result of the measuring means, Control means for setting the amount of exposure of the charged surface by light means, wherein the transfer means applies a predetermined voltage to the transfer member prior to measurement by the characteristic measuring means. Is directly contacted with the charged surface to charge the charged surface, and the characteristic measuring unit sets the current-
An image forming apparatus for measuring a voltage characteristic is provided.

It is preferable that the voltage applied by the transfer means to the transfer member includes an AC component.

The charging means includes a charging member configured to apply a desired voltage, and the charged surface is charged by bringing the charging member into contact with the charged surface. The member may double as the measuring end.

According to a second aspect of the present invention, there is provided an image carrier having a surface to be charged, and a charging means for charging the surface to be charged by applying a predetermined voltage separately set to the surface to be charged. An exposure unit that forms a latent image on the surface to be charged by irradiating light to the surface to be charged in a state charged by the charging unit, and a developing unit that visualizes the latent image with a developer. A transfer unit that includes a transfer member and performs a transfer process of transferring an image visualized by the developing unit to the sheet by pressing a separately prepared sheet material against the surface to be charged by the transfer member. The transfer unit cleans the transfer member by contacting the transfer member with the charged surface while applying a voltage including an AC component to the transfer member before or after the transfer process. Also It is preferable that.

The operation will be described.

The transfer means applies a predetermined voltage including an AC component to the transfer member. Then, by bringing the transfer member in that state into contact with the surface to be charged, the surface to be charged is uniformly charged. The characteristic measuring means contacts the measurement end with the uniformly charged surface to be charged, and measures the current-voltage characteristics between the measurement end and the surface to be charged. In this case, the measurement is accurate because the charged surface to be measured is uniformly charged in advance. It is not always necessary to provide a dedicated member for the measuring end, and the measuring end may also be used as a charging member.

The current-voltage characteristic measured by the characteristic measuring means reflects the thickness of the photosensitive member constituting the charged surface.
Therefore, the control unit sets the exposure amount of the charged surface by the exposure unit according to the measurement result of the characteristic measurement unit.

Thereafter, the charging means charges the surface to be charged by bringing the charging member to which a predetermined voltage is applied into contact with the surface to be charged. Subsequently, the exposure unit forms a latent image on the charged surface by irradiating the charged surface with light with light. The exposure amount is set by the control means as described above, and is optimal according to the thickness of the photoconductor at that time.

Thereafter, the developing means visualizes the latent image with a developer. Further, the transfer unit presses the supplied sheet against the surface to be charged by the transfer member, thereby transferring the visualized image to the sheet.

The transfer means is provided before (or after) the transfer.
Then, the transfer section is cleaned by directly contacting the transfer member with the surface to be charged while a predetermined voltage including an AC component is applied to the transfer member. Since a voltage including an AC component is applied, the cleaning effect is high.

The application of a voltage for this cleaning and
Prior to the measurement by the characteristic measuring means, the application of the voltage for uniformly charging the charged surface may be performed collectively.

[0034]

Embodiments of the present invention will be described below with reference to the drawings.

The present embodiment is an electrophotographic image forming apparatus. First, an outline of the image forming apparatus will be described with reference to FIG. Note that portions having the same functions as those of the related art are denoted by the same reference numerals and description thereof may be omitted.

The photosensitive drum 1 is an image carrier, and has a diameter of 30 mm in this embodiment. The photosensitive drum 1 is driven to rotate by a motor (not shown) in a direction indicated by an arrow in the figure. Photosensitive drum 1
Around the photosensitive drum 1 in order along the rotation direction.
A charging roller 2 having a diameter of 12 mm, which is a contact charging member for uniformly charging the surface of the photosensitive drum to a predetermined potential; an exposure device 6 for forming an electrostatic latent image on the photosensitive drum 1 in accordance with image information separately input; A developing device 8 (in this embodiment, a reversal developing system using a negative toner is used) for attaching toner to an electro-latent image to form a toner image, and a toner image on the photosensitive drum 1 is transferred to transfer paper. A transfer roller 4 having a diameter of 12 mm and a cleaner 7 for removing and collecting residual toner adhering to the surface of the photosensitive drum 1 after the transfer of the toner image are disposed.

A predetermined voltage is applied to the charging roller 2 and the exposure device 6 from the power supply 3 at a predetermined timing. The power supply 3 detects a DC component of a current flowing from the charging roller 2 to the photosensitive drum 1,
A function of outputting the detection result to the control device 9 is provided. Further, a predetermined voltage is applied to the transfer roller 4 by a power supply 5 at a predetermined timing. The application of the voltage by the power supply 3 and the power supply 5 is controlled by the control device 9. This embodiment is most characterized by control of voltage application to the charging roller 2 and the transfer roller 4. This feature will be described later in FIG.
This will be described in detail with reference to FIG.

The control device 9 controls the entire image forming apparatus. The control device 9 has, for example, a function of detecting a DC component of a current flowing from the charging roller 2 to the photosensitive drum 1 and controlling a light amount of the exposure device 6 according to the detected current. Further, the charging roller 2 and the transfer roller 4
It also controls the voltage applied to the device. In addition, it has a function of controlling the rotation of a motor (not shown) that drives the photosensitive drum 1. The control device 9 is specifically composed of a memory storing various data and programs, a CPU for executing the programs, and the like.

In addition, the image forming apparatus includes a mechanism for supplying and conveying a sheet material on which an image is formed. These are also controlled by the control device 9.

Next, an outline of the image forming operation will be described.

The photosensitive drum 1 rotates at a predetermined peripheral speed in the direction of the arrow based on a signal from the control device 9.

First, the control device 9 determines the exposure amount by the exposure device 6. The determination of the exposure amount is performed based on a current applied to the photosensitive drum 1 when a predetermined voltage is applied to the charging roller 2. Details will be described later.

Thereafter, a predetermined voltage is applied to the charging roller 2 by the power supply 3. Thereby, the photosensitive drum 1
Is uniformly charged to a potential of -650 V. afterwards,
The charged surface of the photosensitive drum 1 is exposed to target image information by an exposure device 6 controlled to a desired light amount by a control device 9. As a result, the surface potential of the region where the image information is present (the exposed region) becomes -150V. That is, an electrostatic latent image is formed. Next, a toner image is formed by the developing device 8. Thereafter, a DC current of +6 KV is applied from the power supply 5 to the transfer roller 4, and the toner image on the photosensitive drum 1 is fixed on the sheet material. On the other hand, the photosensitive drum 1 after the transfer is cleaned by a cleaner 7 to remove residual toner adhering to its surface, and is ready for the next image formation. The transfer roller 4 is also cleaned after applying a predetermined cleaning bias.

Next, the control operation of the charging roller 2 and the transfer roller 4, which is the most characteristic part of the present embodiment, in particular, the control of the applied voltage will be described with reference to FIG.

FIG. 2 shows an operation sequence of the charging roller 2 and the transfer roller 4. The horizontal axis indicates time, and indicates the range in which two-sheet continuous image formation is performed. The vertical axis indicates the magnitude of the voltage. In the figure, only a DC voltage is shown as a voltage applied to the charging roller 2 for convenience.

In the present embodiment, the amount of exposure by the exposure device 6 is controlled in accordance with the magnitude of the DC component of the current (detection current) flowing from the charging roller 2 to the photosensitive drum 1, so that the photosensitive member on the photosensitive drum 1 is controlled. A constant image quality is always obtained regardless of the thickness of the image. In this case, in order to accurately detect the detection current, the surface of the photosensitive drum 1 needs to be uniformly charged in advance at the time of detection. The present embodiment is characterized in that the operation of uniformly charging the surface of the photosensitive drum 1 before the detection is performed by the transfer roller 4. Further, it is characterized in that the transfer roller 4 is effectively cleaned by including an AC component in the voltage applied to the transfer roller 4.

In this embodiment, the voltages applied by the transfer roller 4 and the charging roller 2 will be summarized. Note that the resistance of the charging roller 2 and the transfer roller 4 in the present embodiment at the time of driving is 10 ⁶ Ω,
⁹ Ω. (1) Applied voltage to transfer roller 4 First applied voltage (hereinafter referred to as “transfer first applied voltage”) The first applied transfer voltage is applied from charging roller 2 to photosensitive drum 1
This is a voltage applied to uniformly charge the surface of the photosensitive drum 1 to a predetermined potential (−1000 V in this embodiment) in preparation for detection of a current flowing to the photosensitive drum 1. In the present embodiment, current detection for determining the light amount of the exposure device 6 is performed for each image formation start signal. Therefore, the charging process by applying the first transfer voltage is performed for one round of the surface of the photosensitive drum 1 in the preparation stage of the image formation. The period b shown in FIG.
It is the time required for the photosensitive drum to make one revolution at the peripheral speed of.

In this embodiment, the surface of the transfer drum 4 is also cleaned during the preparation stage for printing. The transfer first applied voltage also serves as a cleaning bias at this time.

The specific transfer first applied voltage in this embodiment is an AC voltage (constant voltage 1 KV, frequency 800H
Z) is a voltage obtained by superimposing a DC voltage (constant voltage −5 KV) on Z). Second applied voltage (hereinafter referred to as “transfer second applied voltage”) The transfer second applied voltage is applied at the time of transfer. The specific transfer second applied voltage in the present embodiment is:
DC voltage (constant voltage +6 KV). Third applied voltage (hereinafter referred to as “transfer third applied voltage”) In the present embodiment, the cleaning of the transfer roller 4 is performed before the first transfer and after each transfer. The transfer third applied voltage is a voltage applied when the transfer roller 4 is cleaned after each transfer. A specific transfer third applied voltage in the present embodiment is a DC voltage (constant voltage-1 KV). In this embodiment, the cleaning is performed for two rotations of the transfer roller. Period c in FIG.
Is the time required for the transfer roller 4 to make two rotations. The cleaning bias applied before the transfer of the first sheet also serves as the transfer first applied voltage as described above. (2) Applied Voltage to Charging Roller 2 First Applied Voltage (hereinafter referred to as “charging first applied voltage”) The first applied charging voltage is applied to determine the amount of light of the exposure device 6. The specific first charging voltage in the present embodiment is a voltage obtained by superimposing a DC current (constant current -200 V) on an AC current (constant current 800 μA, frequency 820 HZ). The detection of the current for determining the light amount of the exposure device 6 is performed for each image formation start signal, so that the first charging applied voltage is applied in a preparation stage of the image formation start. The second applied voltage (hereinafter, referred to as a “second charged voltage”) is applied to the surface of the photosensitive drum 1 at a uniform potential (−650 V in the present embodiment) before forming a latent image. To be charged It is intended to be applied. In this embodiment, the specific second charging voltage is an AC voltage (constant current 8
DC current (constant current -6)
50V).

Next, a control operation for applying a voltage to the transfer roller 4 during the image forming operation will be described with reference to FIG. The voltage application to the transfer roller 4 described below is all performed by the power supply 5 in accordance with an instruction from the control device 9.

Based on the image formation start signal, the rotation drive of the photosensitive drum 1 which has been in the standby state until then is started.
Then, first, the control device 9 applies the first transfer voltage to the transfer roller 4 from the power supply 5 to uniformly charge the surface of the photosensitive drum 1 to −1000V. This charging process is performed for one rotation of the surface of the photosensitive drum 1 (period b in FIG. 2 is the time required for the photosensitive drum to make one rotation at the peripheral speed of the photosensitive drum 1). At this time, the toner attached to the surface of the transfer roller 4 is attached to the photosensitive drum 1 by the electric field of the transfer first applied voltage, and then removed by the cleaning device 7.

Thereafter, the controller 9 applies the second transfer voltage to the transfer roller 4 at the timing when the leading end of the toner image on the photosensitive drum reaches the transfer position. Then, the first toner image on the photosensitive drum 1 is transferred.

After the end of the transfer, the control device 9 cleans the transfer roller 4 by applying the transfer third applied voltage for a period (period b) for two rotations of the transfer roller 4.

Thereafter, the transfer of the second sheet is performed, the cleaning after the transfer is performed again, and the process is completed.

Next, a control operation of applying a voltage to the charging roller 2 during the image forming operation will be described. The voltage application to the charging roller 2 described below is all performed by the power supply 3 in accordance with an instruction from the control device 9.

Based on the image formation start signal, the rotation drive of the photosensitive drum 1 which has been in the standby state is started.

Then, first, the transfer roller 4 sets -10
At the timing when the area charged to 00V (that is, the area to which the transfer first applied voltage is applied) reaches the position of the charging roller 2, the control device 9 applies the charging first applied voltage to the charging roller 2. Note that the period a shown in FIG.
Is the time required for the photosensitive drum 1 to reach the charging roller 2 from the transfer roller 4 at the peripheral speed.

At the same time, the controller 9 starts detecting the DC component of the current flowing from the charging roller 2 to the photosensitive drum 1. This current detection is performed by the transfer roller 4 at -10
This is performed a plurality of times in the region charged to 00V. The control device 9 calculates an average value of the plurality of detected DC current values, and determines an appropriate exposure amount by the exposure device 6 according to the calculation result. The determination of the appropriate exposure amount can be performed by referring to data provided in the control device 9 in advance, or
This is performed by performing a substitution operation on a previously provided operation expression.

After the end of the current detection, the control means 9 applies the second charging voltage to the charging roller 2 by the power supply 3 so as to uniformly charge the surface of the photosensitive drum 1 to -650 V.

Thereafter, the first image is formed by the exposure device 6, and the exposure amount at this time is the appropriate exposure amount determined previously.

When an image was formed by the image forming apparatus of the present embodiment, it was possible to control the amount of image exposure according to the film thickness of the photosensitive drum 1 irrespective of the absence of the pre-exposure device. Even during long-term use, the potential contrast between the dark portion potential and the bright portion potential could be normally maintained, and sufficient image density and image quality could be obtained.

According to the embodiment described above, the state of the photosensitive drum can be accurately measured without using a pre-exposure device. Therefore, it is possible to extend the life of the device while reducing the size and cost of the device. Also, the transfer roller 4
Cleaning can be performed more reliably.

In this embodiment, the charging process for detecting the current from the charging roller 2 to the photosensitive drum 1 is performed for one rotation of the photosensitive drum 1. However, the range in which the charging process is performed is not limited to this, and any range may be used as long as the range is sufficient to detect the current. In the present embodiment, the timing of the current detection is also performed for each image formation start signal, but may be performed at the time of post-rotation of the photosensitive drum 1 after the end of the image forming process. In this way, the first print time is not delayed. Alternatively, the number of image formations may be detected and the image formation may be performed for each fixed number of sheets. In this way, the voltage application time to the photosensitive drum 1 can be reduced as much as possible to extend the durability life of the photosensitive drum (generally, the longer the voltage application time to the photosensitive drum, the less the film thickness of the photosensitive drum is reduced. The amount will increase). In this embodiment, the current flowing from the charging roller 2 to the photosensitive drum 1 is detected. However, the charging roller 2
The DC voltage applied to the charging roller 2 when the DC current flowing from the photosensitive drum 1 to the photosensitive drum 1 is controlled at a constant current,
It is also possible to determine the image exposure amount based on the detected voltage.

In the present embodiment, in order to obtain a sufficient cleaning effect, the cleaning of the transfer roller 4 is performed for two rotations of the transfer roller. However, the amount of cleaning is not less than one rotation of the transfer roller and is not limited as long as a sufficient cleaning effect can be obtained. Generally, the effect of cleaning the transfer roller is proportional to the magnitude of the cleaning bias, and thus may be arbitrarily determined according to the cleaning bias.

Since the transfer roller of this embodiment had relatively high resistance, a high voltage was required to uniformly charge the photosensitive drum. However, by lowering the resistance of the transfer roller, it is possible to reduce the required applied voltage and reduce the scraping of the photosensitive drum. In the present embodiment, the first applied charging voltage and the second applied charging voltage are different. However, they may be the same.

The voltages applied to the charging roller 2 and the transfer roller are not limited to those of the present embodiment. The following conditions 1
Any voltage that satisfies condition 5 may be used.

Condition 1. The first charging voltage, the second charging voltage, and the first transfer voltage can uniformly process the surface of the photosensitive drum 1 to a predetermined potential.

Condition 2. The surface potential of the photosensitive drum 1 due to the application of the first charging voltage is different from the surface potential of the photosensitive drum 1 due to the first transfer voltage. This is because the greater the absolute value of the difference between the two surface potentials, the higher the current detection accuracy.

Condition 3. The surface potential of the photosensitive drum 1 by the applied second charging voltage is suitable for image formation.

Condition 4. The third transfer voltage is suitable for cleaning the transfer roller 4.

Condition 5. The transfer second applied voltage is suitable for transferring a toner image on the photosensitive drum 1.

FIGS. 3 and 4 show modified examples 1 and 2, respectively, in which the applied voltage is changed within the range satisfying the conditions 1 to 5.

The first modification shown in FIG. 3 is an example in which the same voltage as the first transfer voltage in the above-described embodiment (FIG. 2) is applied as the third transfer voltage. Even in this case, the same effect as in the above-described embodiment (FIG. 2) can be obtained. Further, in the transfer third applied voltage (the same voltage as the transfer first applied voltage in the above-described embodiment) in the first modification, the DC voltage is large and the AC voltage is included, so that the cleaning effect is obtained. Is improved.
Therefore, each cleaning time can be reduced to the length of one round of the transfer roller (indicated by reference numeral d in the figure).

In the modification 2 shown in FIG. 4, an AC voltage (constant voltage 1 KV, frequency 800H
This is an example in which a voltage obtained by superimposing a DC voltage (constant voltage −1 KV) on Z) is adopted. This is because the transfer third applied voltage (constant voltage -1 KV) in the above-described embodiment is replaced by the AC component of the transfer first applied voltage (constant voltage 1 KV,
This is equivalent to applying only a frequency of 800 Hz.
Even in this case, the above-described embodiment (FIG. 2) and Modification 1
The same effect as that of FIG. 3 can be obtained. Further, the DC voltage applied when the transfer roller 4 is cleaned
Since it is 1/5 of (FIG. 3), the load on the photosensitive drum can be reduced by that much as compared with the first modification.

The “charging means” in the claims corresponds to the charging roller 2, the power supply 3, and the control device 9 in the above-described embodiment (FIG. 1). “Charging member” corresponds to the charging roller 2. “Image carrier” corresponds to the photosensitive drum 1. "Charged surface"
Is equivalent to a region on the outer periphery of the photosensitive drum 1 where a latent image is to be formed. “Exposure means” corresponds to the exposure device 6. “Developing means” corresponds to the developing device 8. "Transfer means" corresponds to the transfer roller 4, the power supply 5, and the control device 9. The “transfer section” corresponds to the transfer roller 2. In the present embodiment, the “characteristic measuring unit” also serves as the charging roller 2, the power supply 3, and the control device 9. The “measurement end” also serves as the charging roller 2. “Control means” corresponds to the control device 9. "Current-potential characteristics"
This corresponds to the relationship between the current (detection current) flowing from the charging roller 2 to the photosensitive drum 1 and the voltage applied by the charging roller 2. However, in the above embodiment, since a known constant voltage is applied to the charging roller 2, the actual control device 9 detects only the current value. In the above embodiment, the charging member (charging roller 2) also serves as the measurement end, but both may be provided separately. Further, the transfer first applied voltage has both the voltage application for cleaning and the voltage application for uniformly charging the surface of the photosensitive drum 1. However, both may be separately applied at different timings.

[0076]

As described above, according to the present invention,
Without using a pre-exposure device, it is possible to control the amount of image exposure satisfactorily in accordance with the thickness of the member to be charged. Therefore,
The potential contrast between the dark part potential and the light part potential can be always maintained normally even for long-term use, and sufficient image density and image quality can always be obtained. Further, since a pre-exposure device is not required, problems such as toner deterioration and change in resistance of a charging member due to heat generation of the pre-exposure device can be avoided, and cost reduction and
The device can be simplified and space can be reduced. Further, the effect of cleaning the surface of the transfer member is high.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a sequence diagram according to the embodiment of the present invention.

FIG. 3 is a sequence diagram showing a first modification.

FIG. 4 is a sequence diagram showing a second modification.

FIG. 5 is a diagram illustrating a configuration of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Power supply 4 Transfer roller 5 Power supply 6 Exposure device 7 Cleaning device 8 Developing device 9 Control device

Claims (4)

[Claims] An image bearing member having a charged surface made of a photoreceptor; a charging unit for charging the charged surface by applying a predetermined voltage separately set to the charged surface; Exposure means for forming a latent image on the charged surface by irradiating light to the charged surface in a state charged by means, developing means for visualizing the latent image with a developer, and a transfer member, A transfer unit for transferring the visualized image to the sheet by pressing a separately supplied sheet onto the surface to be charged by the transfer member; and a measuring end, wherein the measuring end contacts the surface to be charged. By applying a predetermined voltage to the measurement end in a state where the measurement is performed, a characteristic measurement unit for measuring a current-voltage characteristic between the measurement end and the surface to be charged, and according to a measurement result of the measurement unit The charged object by the exposure means. Control means for setting an exposure amount of a surface, wherein the transfer means directly transfers the transfer member to the charged surface in a state where a predetermined voltage is applied to the transfer member prior to measurement by the characteristic measuring means. The characteristic measuring unit measures the current-voltage characteristic with the charged surface charged by the transfer unit as a measurement target. An image forming apparatus, characterized in that: 2. The image forming apparatus according to claim 1, wherein the voltage applied by the transfer unit to the transfer member includes an AC component. 3. The charging means includes a charging member configured to apply a desired voltage, and the charged surface is charged by bringing the charging member into contact with the charged surface. The image forming apparatus according to claim 1, wherein the charging member doubles as the measurement end. 4. An image carrier having a surface to be charged, charging means for charging the surface to be charged by applying a predetermined voltage separately set to the surface to be charged, and charged by the charging means. An exposure unit that forms a latent image on the surface to be charged by irradiating light to the surface to be charged in a charged state, a developing unit that visualizes the latent image with a developer, and a transfer member. Transfer means for performing a transfer process of transferring an image visualized by the developing means to the sheet by pressing the sheet material pressed against the charged surface by the transfer member. Before or after the transfer processing, the transfer unit is cleaned by contacting the transfer member with the charged surface while applying a voltage including an AC component to the transfer member. Feature Image forming device.