JPH10171215A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of obtaining an excellent image over a long period by reducing the shaving quantity of a body to be electrified, so as to maintain excellent electrostatic chargeability over the long period, in an image forming device using a contact electrifier for electrifying a photoreceptor surface, in such a manner that an electrifying member to which a voltage is applied is brought into contact with a photoreceptor, as an electrification processing means for the photoreceptor. SOLUTION: In the image forming device, an image is formed by an image forming means including the body to be electrified 1 and electrifying means 2 and 3 for executing the uniform electrification processing of the surface 1a of the body to be electrified and it is repeatedly used for forming the image. In such a case, the electrifying means 2 and 3 are of a contact type so as to electrify the surface 1a of the body to be electrified, in such a manner that the electrifying member 2 to which an electrifying bias is applied is brought into contact with the body to be electrified and a detecting means 17 for detecting a deterioration in the body to be electrified 1 is provided. Then, the electrifying bias applied to the electrifying member 2 is controlled according to the degree of the deterioration of the body to be electrified 1 by the detecting means 17.

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 such as a copying machine and a laser beam printer, and more particularly to an image forming apparatus having a contact charging means.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus (copier, optical printer, etc.) and an electrostatic recording apparatus, as a means for charging a surface of an image carrier as a member to be charged such as a photoconductor or a dielectric, Contact-type charging devices that contact a charging member to which a voltage is applied with the surface of an object to be charged have the following advantages: ・ Lower power supply voltage ・ Lower ozone generation, etc. Means.

In a contact type charging device, a charging member is
A “DC charging method” in which only a DC voltage Vdc is applied as a charging bias to charge an object to be charged, and an oscillating voltage (a voltage whose voltage value changes periodically with time) is applied to charge an object to be charged. There is an “AC charging method”.

An oscillating voltage is an oscillating voltage component or a superimposed voltage of the oscillating voltage component and a DC voltage component (a voltage corresponding to a target charging potential). The oscillating voltage component has a waveform such as a sine wave, a rectangular wave, or a triangular wave. It is appropriate. Alternatively, a rectangular wave voltage formed by periodically turning on / off a DC power supply may be used.

In any case, the surface to be charged is charged to a predetermined polarity and potential by the contact charging member to which the bias voltage is applied.

In the AC charging system, the charging member includes a contact area where the charging member contacts the object to be charged, and a separation area where the distance from the surface of the object to be charged becomes larger downstream of the contact area in the moving direction of the object to be charged. A DC voltage component, and a peak-to-peak voltage component (Vp) that is twice or more the applied voltage value of the charging member when the DC voltage is applied to the charging member to start charging the member to be charged.
p) by applying a voltage having the following relationship between the member to be charged and the charging member to form an oscillating electric field between the surface of the member to be charged and the separation surface region of the charging member. In the method or the apparatus, since the AC component smoothes out the unevenness of the charging, and converges to a predetermined potential by the DC component, it is possible to obtain a function and effect that uniform and stable charging can be achieved without causing charging unevenness. In recent years, it has been widely used.

[0007]

In an image forming apparatus, a member to be charged (hereinafter, referred to as a photoreceptor) has its outer peripheral surface scraped by a cleaning blade and a developer as the number of image formations increases. As a result, the thickness of the photosensitive layer (the thickness of the photosensitive member) decreases. On the other hand, it is known that there is a strong correlation between the amount of current flowing through the photoconductor and the shaving amount of the photoconductor, and the shaving amount increases as the current amount increases. In the above-described AC charging method, since a large current ranging from several hundred μA to several mA flows, the shaving amount is much larger than in the DC charging method. Therefore, the film thickness of the photoreceptor rapidly decreases as the number of image formations increases, and the surface potential of the photoreceptor changes. In addition, when the thickness of the photoconductor is reduced, leakage from the charging member to the photoconductor substrate is likely to occur.
As the process proceeds further, the photoconductor itself disappears, and image formation becomes impossible. Further, when the amount of current flowing through the photoconductor in the AC charging system is lower than a certain value, a white and black dot-shaped poorly-charged image, that is, a so-called “sand background” is easily generated.

On the other hand, the DC charging method has an advantage that the shaving amount of the photosensitive member is small. However, when the durability is advanced and the photoreceptor is deteriorated, there is a disadvantage that charging unevenness is likely to occur as a result, and remarkable density unevenness is likely to occur.

Therefore, an object of the invention according to the present application is to use a contact-type charging device for charging a member to be charged by bringing a charging member to which a voltage is applied into contact with the member to be charged as a means for charging the member to be charged. It is an object of the present invention to provide an image forming apparatus capable of maintaining good chargeability over a long period of time by reducing the shaving amount of a member to be charged and obtaining a good image over a long period of time.

[0010]

[Means for Solving the Problems]

(1) In an image forming apparatus for performing image formation by an image forming unit including a charging target and a charging unit for uniformly charging the surface of the charging target, and repeatedly subjecting the charging target to image formation, The charging means is of a contact type in which a charging member to which a charging bias is applied is brought into contact with a member to be charged to charge the surface of the member to be charged, and includes a detecting unit for detecting deterioration of the member to be charged,
An image forming apparatus, wherein the charging bias applied to the charging member is controlled in accordance with the degree of deterioration of the member to be charged detected by the detecting means.

(2) When the degree of deterioration of the charged body detected by the detecting means is smaller than a predetermined amount, a charging bias of only a DC voltage is applied to the charging member, and the charged body detected by the detecting means is detected. The image forming apparatus according to (1), wherein an oscillating voltage is applied to the charging member when the degree of deterioration of the charged body has advanced by a predetermined amount.

(3) An image forming apparatus in which an image is formed by an image forming means including a charged body and a charging means for uniformly charging the surface of the charged body, and the charged body is repeatedly subjected to image formation. In the above, the charging means is a contact type in which a charging member to which a charging bias is applied is brought into contact with a charging target to charge a surface of the charging target, and a detecting means for detecting deterioration of the charging target is provided. When the degree of deterioration of the member to be charged detected by the means is smaller than a predetermined amount, a charging bias of only a DC voltage is applied to the charging member, and the degree of deterioration of the member to be charged detected by the detecting means is equal to the predetermined amount. Image forming characterized by applying a bias in which an alternating voltage and a DC voltage are superimposed on the charging member while changing the alternating voltage value or the current value in accordance with the detection result of the detecting means, in a state advanced from the amount of apparatus.

(4) The detecting means for detecting the deterioration of the member to be charged is a means for counting the number of sheets of transfer material which have been introduced into the apparatus and on which the image forming means forms an image. The image forming apparatus according to any one of (1) to (3).

(5) The detecting means for detecting the deterioration of the member to be charged is a means for counting the number of rotations when the member to be charged is repeatedly subjected to image formation by rotational driving. The image forming apparatus according to any one of (1) to (3).

(6) The detecting means for detecting the deterioration of the charged member applies a predetermined detection voltage to the charging member when the charged member corresponds to the non-image area of the charged member. A means for measuring the amount of current flowing from the charging member to the member to be charged at this time to detect the thickness of the photosensitive layer of the member to be charged. The image forming apparatus according to any one of the above.

<Action> By controlling the charging bias applied to the charging member in accordance with the degree of deterioration of the member to be charged detected by the detecting means, the amount of scraping of the member to be charged can be reduced and good chargeability can be maintained for a long time. To be able to maintain over.

In particular, when the degree of deterioration of the member to be charged detected by the detecting means is smaller than a predetermined amount, a charging bias of only a DC voltage is applied to the charging member, and the charged member detected by the detecting means is charged. By applying an oscillating voltage to the charging member when the state of deterioration of the body has advanced more than a predetermined amount, a DC charging method is used in an initial stage in which the degree of deterioration is small, and in the initial stage where shaving is small, deterioration of the charged band is reduced. When the advance was detected, the system was switched to the AC charging system, the charging performance was maintained in a good state, and the image formation for a long period of time was made possible while reducing the shaving amount of the photoconductor.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> (1) Example of Image Forming Apparatus FIG. 1 is a schematic diagram of an image forming apparatus of the present embodiment. The image forming apparatus of this embodiment is a transfer type laser beam printer or copying machine utilizing an electrophotographic process.

Reference numeral 1 denotes a drum-type electrophotographic photoreceptor (hereinafter, referred to as a photoreceptor) as an image carrier, and a conductive substrate 1b such as aluminum and a photoconductive layer 1a formed on the outer periphery thereof.
, And is rotationally driven at a predetermined process speed in a clockwise direction indicated by an arrow in the figure. The photosensitive member 1 is uniformly charged to a predetermined polarity and potential by the primary charging device 2 during the rotation process. In this example, the photosensitive member 1 is subjected to a negative charging process.

The primary charging device 2 of the present embodiment is a contact charging roller, and is driven to rotate as the photosensitive member 1 rotates.

Then, by applying a predetermined bias voltage from the power supply 3, the peripheral surface of the rotary photosensitive member 1 is charged to a predetermined polarity and potential by a contact charging method.

Next, the charged surface is subjected to image exposure processing of target image information by image exposure means 10 such as laser scanning, so that an electrostatic latent image of the target image information is formed on the surface of the photoconductor 1. .

The electrostatic latent image is developed by a thin layer of toner carried on the developing sleeve 6a of the developing device 6 to become a visible image (toner image). The developing sleeve is controlled by a clutch (not shown) and rotates in an image area.
Then, a predetermined bias voltage (DC voltage, vibration voltage, hereinafter referred to as a developing bias) is applied from a power supply (not shown), so that the toner is supplied to the photoconductor.

In this embodiment, reversal development is performed using negatively charged toner (negative toner).

In the transfer section, which is a contact nip section between the photoreceptor 1 and the transfer member 12 brought into contact with the photoreceptor 1, the transfer of the toner image to the transfer section from the paper supply section at a predetermined timing. It is sequentially transferred to the material P.

The transfer member 12 of this embodiment is a contact charging transfer roller, which is pressed against the photosensitive member 1 and rotates following the rotation of the photosensitive member 1.

The transfer material P is fed to the transfer section.
When the leading end of the transfer material P enters the transfer portion, the transfer roller 1
2, a predetermined transfer bias is applied from a power supply 13, and the back surface of the transfer material with which the transfer roller 12 is in contact is charged by a contact charging method with a polarity opposite to that of the toner, so that the toner image on the photoconductor 1 is transferred to the front surface of the transfer material Is transferred to

The transfer material P to which the toner image has been transferred through the transfer portion is separated from the surface of the photoreceptor 1 and sent to an image fixing means (not shown), and the transferred toner image is permanently fixed on the transfer material P. The image is fixed as an image, and is discharged outside the machine as a print or a copy.

On the other hand, the surface of the photoreceptor 1 after passing through the transfer section is cleaned by removing the residual toner and other attached matter by the cleaner section 14, and further, a static eliminator (static elimination lamp)
The static electricity is initialized by the static electricity 15 and repeatedly provided for image formation.

The contact charging type charging roller and the transfer roller may be provided with gears and the like, and may be forcibly driven by a driving means such as a motor.

(2) Change of charging condition In this example, the photosensitive member is charged to -730V. The voltage required for this is DC voltage -1400 V in the case of the DC charging method, and DC voltage -7 in the case of the AC charging method.
50 V + AC voltage 1500 Vpp (peak-to-peak voltage). In the case of the AC charging method, the potential of the photoreceptor substantially converges to the value of the applied DC voltage due to the influence of the AC voltage. Therefore, it is not necessary to apply a high DC voltage as in the DC charging method.

As shown in FIGS. 2 and 3, when the DC charging system is used, the damage (scraping) to the photoreceptor can be reduced, but there is a disadvantage that the level of charging uniformity deteriorates as durability increases.

On the other hand, when the AC charging method is used, the level of charging uniformity is good, but the current flowing into the photoreceptor increases.
There is a disadvantage that the photoconductor is easily shaved.

Therefore, in the present embodiment, the above-described image forming means 1, 2, (3), 6, 12, 1
The number of passing sheets of the transfer material P on which an image (toner image) is formed by 4, 15, and 16 is detected and counted by a detecting unit 17 provided in the conveyance path, and the number of passing sheets is initially used by using a DC charging method. That is, when the durable number reaches a predetermined value, the system is switched to the AC charging system.

For example, as shown in FIG. 2, according to the DC charging system, the charging uniformity becomes an unacceptable level after about 20,000 endurable sheets. Therefore, by switching to AC charging when the number of durable sheets reaches 20,000, the charging uniformity is maintained at a good level. As described above, when the charging method is switched at the time of 20,000 sheets, the total shaving amount of the photoconductor can be reduced as compared with the case where only the AC charging method is used, as shown by the line α in FIG.

As described above, in this embodiment, since the DC charging system and the AC charging system are switched in accordance with the deterioration of the photoconductor, a good image without uneven charging can be obtained, and the shaving amount of the photoconductor is further improved. Can be reduced.

In this embodiment, the detecting means 17
A dedicated device for detecting the number of sheets of the transfer paper P passing therethrough may be provided, or a sensor (top sensor) for detecting the leading end of the transfer paper P introduced into the transfer unit, a paper feed sensor, a paper discharge sensor, and the like. It may be used also as a detecting means.

Second Embodiment Next, a second embodiment of the present invention will be described.

The present embodiment is different from the first embodiment in that the minimum necessary AC current Iac is changed according to the number of endurable sheets, and other configurations are substantially the same.

(1) AC Charging Method According to the AC charging method, when the surface potential of the photosensitive member 1 exceeds a certain value Ith of a current flowing into the photosensitive member 1, a DC voltage value applied regardless of the environment. Converges to a value close to.

In FIG. 4, line A is an AC charging voltage V
It shows a relationship between pp and a DC voltage (Vdc) for obtaining a constant surface potential. On the other hand, the line B has the AC charging voltage Vp
2 shows a relationship between p and an alternating current Iac flowing through the photoconductor 1.

The inflection point in the line A indicates a switching point from the state where DC charging is substantially performed without reverse charging to the state where AC charging is performed.
Assuming that the AC charging voltage Vpp at this time is a voltage value Va,
As shown on the line B, the minimum AC current Iac required for AC charging is the current value Ith.

Here, when the AC charging voltage Vpp is in the range from the voltage value Va to the voltage value Vb in the figure, that is, when the current value Ipp
When the current value is in the range from a to the current value Ib, the effect of leveling unevenness of charging is not sufficient. As a result, a so-called “sand” phenomenon (white and black dot-shaped poorly charged images) occurs. Generally, in the AC charging system, constant current control is performed at a minimum current value Iac within a range in which the sand phenomenon does not occur.

(2) Control method However, as shown in the line D in FIG. 5, the value of Ith gradually decreases as the durability progresses. It becomes lower as it progresses. Therefore, if the constant current control is performed with the initially set current value, the control with an unnecessarily high current value will be performed at the end of the endurance.

Therefore, in the present embodiment, the DC charging method is performed at the initial stage, and thereafter the mode is switched to the AC charging method, and then the AC current value is changed according to the deterioration of the photoconductor.

As a specific value, when the process speed is 105 mm / sec, the frequency of the AC component is 919 Hz, and the initial minimum current value at which no sand occurs is Ib, Ib = 1100 μA. When durability is attained until the life of the photoconductor is reached, the value of Ib drops to about 950 μA. Therefore, as shown in line C of FIG. 5, when the number of durable sheets reaches a predetermined value, the AC current value is changed stepwise. According to this method, a DC charging system is used initially, and A
Even after switching to the C charging method, in order to always keep the current value to the minimum necessary, as shown in line β in FIG. 3, it is necessary to obtain a good image without charging unevenness and further reduce the shaving amount of the photoconductor. It is possible.

In this embodiment, the description has been given of the AC constant current control. However, the same concept can be applied to the case of the constant voltage control.

<Embodiment 3> This embodiment is different from Embodiments 1 and 2 described above in the structure of the means for detecting the deterioration of the photosensitive band 1, and the other structures are substantially the same.

In the first and second embodiments, the method of counting the number of durable sheets has been described as a means for detecting the deterioration of the photosensitive member 1. However, strictly speaking, the transfer material P
The deterioration of the photoreceptor 1 may be different even for the same durable number of sheets due to the influence of the difference in the size of the photoconductor 1 and the like.

Therefore, in the present embodiment, the photosensitive member 1
As a means for more accurately detecting deterioration of the photoconductor 1, a method of counting the number of rotations of the photoconductor 1 is used. That is, the number of rotations of the photoconductor 1 is counted, and when the number of rotations reaches a predetermined number, the DC charging system is switched to the AC charging system.

The detection of the number of rotations is performed by providing a detecting means 17 such as a photo sensor near the photosensitive member.

FIG. 6 shows the charging uniformity level by the DC charging method with respect to the number of rotations of the photosensitive member 1. In this example, since the charging uniformity due to DC charging is at an unacceptable level when the number of rotations reaches about 270,000 times, it is sufficient to switch to the AC charging method here.

<Embodiment 4> This embodiment differs from Embodiments 1 and 2 in the structure of the means for detecting the deterioration of the photosensitive belt 1 as shown in FIG. Are approximately the same.

In the present embodiment, a method for detecting the amount of scraping of the photoconductor 1 will be described as a means for detecting the deterioration of the photoconductor 1 more accurately.

As means for detecting the amount of scraping of the photoconductor 1 between the conductive base 1b of the photoconductor 1 and the ground,
Detecting means 1 having a resistance R for measuring the current flowing through
7 are provided. When a predetermined AC or DC detection voltage is applied to the charging roller 2, the thickness of the photosensitive layer of the photosensitive member 1 is detected by measuring the voltage between the terminals of the resistor R.

FIG. 8 shows the amount of DC current measured when an AC voltage of 1.5 kVpp is superimposed on a DC voltage of 750 V and applied to the charging roller.

As can be seen from this, as the thickness (film thickness) of the photosensitive layer 1a decreases, the amount of current flowing through the photosensitive member 1 increases.

According to this method, the photosensitive layer 1a of the photosensitive member 1
Since the film thickness can be accurately detected, it is particularly effective when the charging condition is changed stepwise as described in the second embodiment.

In this embodiment, the case where the detecting means 17 is provided between the conductive base 1b of the photoreceptor 1 and the ground has been described. However, the present invention is not limited to this. The above-described detection means may be provided between the high-voltage power supply 3 and the ground.

[0060]

As described above, according to the present invention,
Depending on the degree of deterioration of the charged band, the DC charging method is used initially, and when it is detected that the deterioration of the charged band has advanced, A
By switching to the C charging method, it is possible to reduce the shaving amount of the member to be charged, maintain good charging properties for a long period of time, and provide a good image for a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing the relationship between the number of endurance sheets and the level of charge uniformity.

FIG. 3 is a diagram showing the relationship between the number of durable sheets and the shaving amount of a photoconductor.

FIG. 4 is a diagram illustrating characteristics of AC charging.

FIG. 5 is an explanatory diagram showing a current value control method according to a second embodiment.

FIG. 6 is a diagram showing the relationship between the rotation speed of the photoconductor and the level of uniformity of charging.

FIG. 7 is a schematic configuration diagram of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a characteristic diagram relating to detection of the thickness of the photosensitive layer.

[Description of Signs] 1 Photoconductor drum 2 Charging roller as a contact charging member 3 Charging bias application power source 6 Developing unit 10 Image exposure unit 12 Transfer unit (transfer roller) 14 Cleaner unit 17 Detecting unit P Transfer material

Claims (6)

[Claims] 1. An image forming apparatus for forming an image by an image forming means including a member to be charged and a charging unit for uniformly charging the surface of the member to be charged, and repeatedly subjecting the member to be used for image formation. The charging means is a contact type in which a charging member to which a charging bias is applied is brought into contact with the charged body to charge the surface of the charged body, and includes a detecting means for detecting deterioration of the charged body. An image forming apparatus configured to control a charging bias applied to the charging member in accordance with a degree of deterioration of a member to be charged due to the charging bias. 2. When the degree of deterioration of the member to be charged detected by said detecting means is smaller than a predetermined amount, a charging bias of only a DC voltage is applied to said charging member, and said charged member detected by said detecting means is charged. 2. The image forming apparatus according to claim 1, wherein an oscillating voltage is applied to the charging member when the state of deterioration of the body is more than a predetermined amount. 3. An image forming apparatus for performing image formation by an image forming means including a charged body and a charging means for uniformly charging the surface of the charged body, and repeatedly subjecting the charged body to image formation. The charging means is a contact type in which a charging member to which a charging bias is applied is brought into contact with the charged body to charge the surface of the charged body, and includes a detecting means for detecting deterioration of the charged body. When the degree of deterioration of the member to be detected detected in the step (c) is smaller than a predetermined amount, a charging bias of only a DC voltage is applied to the charging member, and the degree of deterioration of the member to be charged detected by the detecting means is the predetermined amount. An image forming apparatus, wherein, when the charging member is in a state advanced from the amount, a bias obtained by superimposing an alternating voltage and a DC voltage on the charging member is applied while changing the alternating voltage value or the current value according to the detection result of the detection means. . 4. The apparatus according to claim 1, wherein the detecting means for detecting the deterioration of the member to be charged is a means for counting the number of sheets of the transfer material which is introduced into the apparatus and on which the image forming means forms an image. Item 4. The image forming apparatus according to any one of Items 1 to 3. 5. The apparatus according to claim 1, wherein the detecting means for detecting the deterioration of the member to be charged is means for counting the number of rotations when the member to be charged is repeatedly used for image formation by rotational driving. Item 4. The image forming apparatus according to any one of Items 1 to 3. 6. A detecting means for detecting deterioration of the member to be charged applies a predetermined detection voltage to the charging member when the member corresponds to a non-image area of the member to be charged. 4. The method according to claim 1, wherein the detecting means detects a deterioration of the charged body by measuring an amount of current flowing from the charging member to the charged body. Image forming device.