JP3310128B2 - Image forming device - Google Patents

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,
More specifically, the present invention relates to an image forming apparatus using a contact charging device.

[0002]

2. Description of the Related Art In general, an electrophotographic method is known as one of image forming methods. In this method, an electrostatic latent image corresponding to a document image is formed on a photosensitive member as a latent image carrier by exposure. The electrostatic latent image, which has been subjected to visible image processing by a developer, is transferred to a transfer paper to obtain a copy. Such an electrophotographic system is frequently used in a copying machine, a printer, a facsimile, and the like. In the electrophotographic method, a charging step of uniformly charging a photoconductor is performed before a step of exposing a document image. Conventionally,
As a charging method used in the charging step, there has been a non-contact method using corona discharge.

[0003] This method has been required to be replaced because of the large amount of power consumed and the harmfulness of ozone generated by discharge.

In recent years, instead of the non-contact charging method, a conductive member such as a rubber roller mixed with a conductive material such as carbon has been brought into contact with a photoreceptor, and a DC voltage or a superimposed voltage of DC and AC has been recently developed. Has been proposed and implemented.

[0005] The contact charging system has advantages such as lower power consumption and less generation of ozone than the non-contact charging system.

In the contact charging system, it is important to make uniform contact between the photoreceptor and the charging roller in contact with the photoreceptor in order to prevent uneven charging.

One of the causes of the uneven charging is the adhesion of impurities to the surface of the charging member used in the contact charging system. As the impurities, extraneous substances such as surplus toner and paper powder remaining on the photoreceptor are applicable.

Heretofore, as a method of removing such impurities from the photosensitive member, there is a method of cleaning the photosensitive member after image transfer using a scraping member such as a cleaning blade. As a method of removing the impurities, there is a method using a cleaning blade as in the case of the photoreceptor.

However, in the method using a cleaning blade, the same surface of the cleaning blade always contacts the surface of the photoreceptor as an impurity blocking surface in the moving direction of the photoreceptor. When the amount of P is large, some of the impurities blocked by the cleaning blade may be rubbed by the movement of the photosensitive member and may escape from the impurity blocking surface of the cleaning blade.

Therefore, when the photosensitive member faces the charging roller, the impurities adhere to the charging roller. As a result, uniform contact of the charging roller with the photoconductor is hindered, and uneven charging occurs. When the charging unevenness occurs, a part of an image formed on the photoconductor is lost.

Conventionally, in order to solve such a problem, after the image forming process is completed, the photosensitive member is moved in a direction opposite to the direction during the image forming process to deposit on the damming surface of the cleaning blade. It has been proposed to eliminate the impurities present (for example, JP-A-5-341624).

[0012]

However, the method described in the above publication has the following problems.

In general, in a cleaning unit having a cleaning blade, a part of the photosensitive member enters the unit to scrape impurities, and the scraped impurities leak out of the unit. Not to be. For this reason, an opening is formed in the cleaning unit to allow a part of the photoconductor to enter.

However, when the photoconductor is moved in the opposite direction, the scraped-off impurities may drop from a gap existing between the vicinity of the lower edge of the opening and the photoconductor.

For example, if a transfer path for a transfer sheet is provided below the cleaning unit, the dropped impurities accumulate on the transfer path and contaminate the transfer sheet.

If the amount of movement of the photosensitive member in the reverse direction is large, the amount of movement in the reverse direction is large because the charging member is also driven in contact with the photosensitive member. Therefore, the cleaning on the charging member side
The number of times the impurities deposited on the blade reach the contact position with the photoreceptor also increases, and the amount of impurities deposited at the contact position with the photoreceptor increases. Moreover, if the movement is completed when the impurities reach the contact position, the impurities are solidified at the contact position, and charging and image formation cannot be performed on this portion, so that a part of the image is lost. Will be lost.

In the case where the photoreceptor is repeatedly rotated in the reverse direction as in the configuration described in the above publication, there is a possibility that the amount of the reverse rotation becomes unstable as the reverse rotation is repeated. This is because, as shown by the solid line in FIG. 5, the transmission amount changes from the initial set amount due to the life, the aging, or the increase of the frictional engagement force with respect to the connection relationship between the mechanisms when the drive mechanisms are used. In particular, it is to decrease.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transfer method using impurities removed from a latent image carrier in view of the above-described conventional image forming apparatus, particularly, a problem in removing impurities by a cleaning blade when a contact-type charging device is used. An object of the present invention is to provide an image forming apparatus capable of preventing paper from being soiled.

Another object of the present invention is to provide an image forming apparatus capable of preventing the amount of reversal from changing over time.

Still another object of the present invention is to provide an image forming apparatus which can completely prevent the adhesion of impurities to the charging device due to the reversal of the latent image carrier, and can eliminate the influence of the impurities even if they do. Is to provide.

[0021]

To achieve this object, the invention according to claim 1 has a photoconductive layer on the surface,
A latent image carrier capable of rotating forward and reverse, a contact charging device for uniformly charging the photoconductive layer by contacting the latent image carrier, and an electrostatic latent image formed on the latent image carrier is visible. A cleaning device having a blade in contact with the surface of the latent image carrier for cleaning the surface of the latent image carrier after transferring the image-processed image. Is moved in the forward direction at the time of image formation, and is moved in the reverse direction at the end of image formation. An angle (α) corresponding to the amount of rotation in the reverse direction is formed in the cleaning device, and the tip of the cleaning blade is moved. An angle smaller than the angle around the center of the latent image carrier corresponding to the width of the opening having the upper edge located and the lower edge having a gap abutting or equivalent to the surface of the latent image carrier, and Formed on the cleaning device A transfer path for a transfer sheet on which the visible image carried on the latent image carrier is transferred is formed below the opening, and impurities such as excess developer and paper dust adhered to itself are removed. A part of the extended portion of the transfer belt with which the cleaning blade is in contact,
Is characterized in that the amount of rotation in the reverse direction is variable .

According to a second aspect of the present invention, in addition to the first aspect of the invention, the amount of rotation of the latent image carrier in the reverse direction is an initial amount.
Adjusted to the time when different conditions occur
It is characterized by that.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

According to the first aspect of the present invention, since the amount of reverse rotation of the latent image carrier is set to be equal to or less than the opening width, the impurities blocked by the cleaning blade pass through the lower edge of the opening and move downward. It does not fall. Moreover, if the impurities dropped from the lower edge of the opening are received on the transfer belt, they are removed by the cleaning blade in contact with the transfer belt. In addition, the amount of reverse rotation of the latent image carrier is variable
Therefore, the speed reduction mechanism and transfer belt are loose.
Or the initial state due to an increase in sliding resistance at the sliding part.
The amount of rotation is not obtained and the removal of impurities becomes inconsistent
Can be prevented.

According to the second aspect of the present invention, the reverse of the latent image carrier
The amount of rotation in the direction may differ from the initial condition.
The latent image carrier over time.
Adjust the amount of reversal according to the
It can be maintained at a predetermined amount.

[0030]

[0031]

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is a schematic diagram for explaining the main configuration of a copying machine (one of image forming apparatuses) showing an embodiment of the present invention.

In FIG. 1, the copying machine 10 includes a photosensitive drum 11 as a latent image carrier.

The photoreceptor drum 11 has a photoconductive layer made of an organic material such as OPC on its surface. As shown in FIG. Each can be rotated.

Around the photosensitive drum 11, a charging device 12 for executing an image forming process along the forward direction,
An exposure device 13, a developing device 14, a transfer device 15, and a cleaning device 16 are arranged.

At the time of rotation in the forward direction, an image forming process including a process of transferring a visible image by the transfer device 15 of the above-described devices is performed. The removal of the impurities deposited on the cleaning blade is performed.

In the figure, reference numeral 17 denotes an exposure lamp before transfer,
8 denotes a quenching lamp for static elimination and 19 denotes an eraser. A registration roller 20 for feeding the transfer paper S toward a nip portion between the photosensitive drum 11 and the transfer device 15 is provided near the photosensitive drum 11.
Is provided.

The charging device 12 is composed of a conductive roller that can rotate while being in contact with the photoconductive layer of the photoreceptor drum 11, and is connected to a high voltage power supply 12A to supply a DC voltage or a DC and AC voltage. A superimposed voltage is applied to uniformly charge the photoconductive layer.

The charging device 12 can be brought into and out of contact with the photosensitive drum 11 by a contacting / separating mechanism (not shown). Contacting the surface of the photosensitive drum 11 until the development process and the transfer process are completed;
After the transfer step is completed, the photosensitive drum 11 can be separated from the photosensitive drum 11. Note that the separation time may be from when the charging step is completed to before the next charging step is performed.

A cleaning member 12B is disposed at a position separated from the charging device 12, and can clean the surface of the rotating charging device 12 at this position.

The exposure device 13 has a plurality of mirrors and an image forming lens (not shown) for forming an optical path for forming an image on the photoconductive layer of reflected light from a document on a document table (not shown). Thus, an electrostatic latent image corresponding to the original image is formed on the photoconductive layer. In the present embodiment, the negative charge disappears in the photoconductive layer due to the intensity of the reflected light, and the portion where the charge remains remains is formed as an electrostatic latent image.

As the developing device 14, a magnetic brush developing device having a well-known structure is used, and the magnetic developer carried and transported by the developing sleeve 14A comes into contact with the electrostatic latent image on the conductive layer to form the electrostatic latent image. Visible image processing is performed.

The pre-transfer exposure lamp 18 is used for lowering the charging potential of the toner attached to the electrostatic latent image so as not to lower the transfer efficiency even when there is an environmental change such as temperature and humidity.

The transfer device 15 includes a transfer belt 15A wound around a pair of rollers and a transfer bias roller 15B.
, A transfer belt 15A contact / separation mechanism 15C, and a cleaning blade 15D.

In the transfer device 15, the registration timing is set by the registration roller 20, and
The transfer paper S fed from the transfer roller 1 is conveyed while being pinched by a nip formed between the transfer paper S and the surface of the photoconductive layer of the photosensitive drum 11, and the bias voltage from the transfer bias roller 15B via the high-voltage power supply 15B1. By applying the visible light, the visible image carried on the photoconductive layer is transferred to the transfer paper S.

The transfer belt 15A is separated from the photoconductive layer of the photosensitive drum 11 at the time of non-transfer.
The contact / separation mechanism 15C is displaced toward the photosensitive drum 11 by a solenoid 15C2 whose operation is controlled by a control plate 15C1. Impurities such as surplus toner, transfer paper fibers, and paper dust attached to the transfer belt 15A are removed by a cleaning blade 15D provided in contact with the transfer belt 15A. The electrode plate denoted by reference numeral 15E is provided to stabilize the current flowing from the transfer bias roller 15B to the photoconductor side and stabilize the transfer performance.

The transfer paper S to which the visible image on the photoconductive layer has been transferred by the transfer device 15 is conveyed by the transfer belt 15A, brought to the fixing roller 22, and discharged to a discharge tray (not shown).

The cleaning device 16 includes the photosensitive drum 1
Cleaning blade 16A contacting one photoconductive layer
And a transport screw 16B for collecting excess toner on the photoconductive layer scraped off by the cleaning blade 16A toward the developing device 14.

As shown in FIG. 2, the cleaning device 16 has an opening 16 C at a position facing the photosensitive drum 11.

The opening 16C is provided at the tip of the cleaning blade 16A in the direction of rotation of the photosensitive drum 11 and at the lower edge 1 which faces the surface of the photosensitive drum 11 opposite thereto.
6D. The opening lower edge 16D
Is not limited to the case where the photosensitive drum 11 is brought into contact with the photosensitive drum 11 as described above. For example, the photosensitive drum 11 may be arranged close to the photosensitive drum 11 with a gap equal to or less than the size of a developer used for visible image processing. It is possible.

Transfer belt 15A in transfer device 15
The length of the cleaning blade 16A in the width direction corresponding to the direction perpendicular to the moving direction is made longer than that of the cleaning blade 16A, and as shown in FIG.
A part of the extending portion is positioned below the opening 16C of the opening. Accordingly, even if there is an impurity dropped from the position of the opening 16C, it can be received, and the received impurity can be scraped off by the cleaning blade 15D which is in contact with itself. .

The photosensitive drum 11 is denoted by a symbol P in FIG.
Are set in the following relationship.

Now, in FIG. 2, when the angle corresponding to the amount of rotation of the photosensitive drum 11 in the reverse direction is (α),
The following relationship is established.

In FIG . 2, the angle indicated by the symbol .theta.
16C, that is, the cleaning blade 1
6A, the lower edge of the opening 16C,
The cleaning device 16 contacts the surface of the latent image carrier.
Or an opening 16 having an equivalent gap.
When the angle is about the center of the latent image carrier corresponding to the width of C
In addition, the amount of reverse rotation is specified at an angle smaller than the angle θ.
I have.

In this embodiment, when the outer diameter of the photosensitive drum 11 is 60 mm, the amount of rotation in the opposite direction is set to 1 to 5 mm, and the angle (α) corresponding to this amount of rotation is:
1.9 to 9.55 °, which is smaller than the value of the right term in the above equation. In this case, the opening width is set to a size such that impurities do not drop from the lower edge of the opening toward the transfer belt 15A.

The amount of reverse rotation (α) in the reverse direction does not exceed an angle (θ) corresponding to the opening width, thereby preventing a situation where impurities pass through the lower edge 16D of the opening. .

The photosensitive drum 11 can change the amount of reverse rotation.

The photosensitive drum 11 is driven by a stepping motor that is also used for the transfer belt 15A and various rollers, and the position and the rotation amount are controlled by the number of steps output to the stepping motor. Is being done. The photoreceptor drum 11 is configured to transmit a driving force to the rotating shaft via a speed reduction mechanism (not shown) connected to a stepping motor. Due to an increase in sliding resistance or the like in the moving part, the same amount of rotation as in the initial state may not be obtained with the number of steps in the initial condition. Therefore, the control unit (not shown) of the stepping motor adjusts the pulse width modulation (P) as shown in FIG.
WM) to adjust the amount of rotation. Thereby, as shown by the two-dot chain line in FIG. 5, the state in which the amount of rotation in the reverse direction decreases with time (the state shown by the solid line) is prevented. The adjustment of the amount of rotation in the reverse direction is performed not only based on the timing at which a state different from the preset initial condition occurs in the control unit of the stepping motor, but also, for example, of the copying machine 10. A switch capable of selecting an adjustment mode may be arranged in an operation unit (not shown), and the pulse width may be changed according to the number of times the switch is turned on.

The forward / reverse rotation timing of the photosensitive drum 11 is shown in FIG.
Is shown in

In the figure, when rotating in the forward direction, a normal image forming process is executed. In this case, a pulse signal for causing the stepping motor to rotate in the normal rotation direction is output.

The image forming process is executed by the rotation in the normal rotation direction, and when the process is completed, the output of the pulse signal to the stepping motor is stopped, and then the pulse signal for performing the rotation in the reverse direction is output. Is done.

Since the present embodiment has the above configuration,
When the image forming process is performed, the photosensitive drum 11 is rotated in the forward direction. When the image forming process is executed, the electrostatic latent image is transferred to the developing device 1 on the photosensitive drum 11.
4, the visible image is processed, and the visible image is transferred to the transfer paper S fed from the paper feeding device 22. After the transfer step, the photoreceptor drum 11 is scraped by a cleaning blade 16A of the cleaning device 16 to remove impurities such as excess toner and paper powder remaining on the surface. In this case, the cleaning blade 16 </ b> A removes impurities from the photosensitive drum 11 with a part of the surface of the photosensitive drum 11 entering the opening 16 </ b> C formed in the cleaning device 16. Since the lower edge 16D of the opening 16C is in contact with the surface of the photoconductor drum 11,
It is prevented from falling down and collected in the cleaning device 16.

Assume that the surface of the photosensitive drum 11 and the opening 16
C, there is a slight gap, and the impurities that have fallen downward from this gap are placed on the transfer belt 15A and the cleaning blade 15 that is in contact with the transfer belt 15A.
D scraped. Thereby, the transfer belt 15
Even if there is an impurity that has fallen on A, the impurity is entirely removed from the transfer belt 15A, so that there is no occurrence of back contamination of the transfer paper S that is conveyed next.

When the image forming process is completed, the charging device 12 is separated from the surface of the photosensitive drum 11 and the photosensitive drum 11 stops.

The surface of the charging device 12 is cleaned by a cleaning member 12 B provided at a position separated from the photosensitive drum 11, and attached impurities are removed. The photosensitive drum 11 starts to rotate in the opposite direction due to the inversion of the output form of the pulse signal to the stepping motor.

The amount of reverse rotation at this time is based on the above-mentioned relational expression. Therefore, the pulse signal corresponding to the amount of reverse rotation is also input to the stepping motor.

When the photosensitive drum 11 rotates in the opposite direction,
The impurities deposited on the damping surface of the cleaning blade 16A for scraping off the impurities are dragged and discharged in accordance with the rotation of the photosensitive drum 11, and fall into the cleaning device 16. However, as shown in FIG. 2, when a part of the impurities falls downward from a gap existing between the surface of the photosensitive drum 11 and the lower edge 16D of the opening 16C of the cleaning device 16, the above-described transfer is performed. It is eliminated by cleaning on the belt 15A side.

The dropping of impurities is a phenomenon in which foreign matter accumulated on the upstream side of the opening lower edge 16D in contact with the photosensitive drum 11 drops due to an impact when the photosensitive drum 11 reversely rotates. Even in such a case, the transfer paper S located below the opening is completely cleaned in the transport path, so that the transfer paper S is not stained. Moreover, the length of the transfer belt 15A in the width direction is the cleaning blade 1
6A, the impurities that have fallen from the lower edge 16D of the opening can be almost completely dropped onto the transfer belt 15A, so that they may fall to a position other than the transfer belt 15A and contaminate the periphery. Can be prevented.

According to the above-described embodiment, the amount of reverse rotation of the photosensitive drum 11 in the reverse direction is also reduced in accordance with the outer diameter of the photosensitive drum 11, particularly when the diameter is reduced. It has to be correspondingly much less,
Although it is difficult to control the driving system, it is possible to prevent the transfer paper S from being contaminated on the transport path even if the amount of reverse rotation cannot be minimized by allowing the transfer belt 15A to collect the falling impurities. Becomes possible.

[0071]

According to the first aspect of the present invention, the contact between the latent image carrier and the latent image carrier is reversed until the image is reversed.
By defining the amount of reversal of the latent image carrier, impurities deposited on the cleaning blade can be removed from the cleaning device so as not to be inadvertently dropped, thereby preventing adhesion of impurities to the contact charging device beforehand. ,
Even if impurities fall from the cleaning device,
By receiving the impurities by the transfer belt and removing the impurities, it is possible to collect the impurities and prevent the transfer paper from being stained by the collected impurities. Moreover, the latent image
Since the amount of reverse rotation of the holding body is variable,
Looseness of the photo belt or increase of sliding resistance at the sliding part
The same amount of rotation as in the initial state,
It is possible to prevent the departure from becoming unstable.

According to the second aspect of the present invention, the latent image carrier
The amount of rotation in the opposite direction may differ from the initial condition.
The latent image carrier over time.
The amount of reversal is adjusted according to the
Keep the amount at the specified level and scrape with the cleaning blade.
The impurities removed from the lower edge of the opening of the cleaning device
Completely prevent falling out and falling
It becomes possible.

[0073]

[0074]

[Brief description of the drawings]

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

FIG. 2 is a local layout diagram for explaining a relationship between a photosensitive drum constituting a latent image carrier and a cleaning device in the copying machine shown in FIG. 1;

FIG. 3 is a diagram for explaining the contents of drive control for a photosensitive drum serving as a latent image carrier.

FIG. 4 is a timing chart for explaining a state of drive control of a photosensitive drum serving as a latent image carrier.

FIG. 5 is a diagram for explaining a state of a temporal change with respect to a rotation amount of a photosensitive drum constituting a latent image carrier and a means for correcting the rotation amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Copier as one of image forming apparatuses 11 Photoconductor drum forming a latent image carrier 12 Charging roller forming a contact-type charging device 12B Cleaning member 15 Transfer device 15A Transfer belt 15D Cleaning blade 16 Cleaning device 16A Cleaning blade 16C Opening 16D Opening lower edge α Rotation amount of photoconductor drum in the reverse direction θ Opening width along the rotation direction of photoconductor drum D Outer diameter of photoconductor drum

Continuation of the front page (56) References JP-A-3-243977 (JP, A) JP-A-5-53413 (JP, A) JP-A-6-161336 (JP, A) JP-A-2-129968 (JP, A) JP-A-5-341624 (JP, A) JP-A-3-130787 (JP, A) JP-A-5-249774 (JP, A) JP-A-3-20368 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 21/10 G03G 21/00 370-540 G03G 21/14

Claims (2)

(57) [Claims] A latent image carrier having a photoconductive layer on its surface and capable of rotating forward and reverse; a contact charging device for uniformly charging the photoconductive layer by contacting the latent image carrier; After transferring an image obtained by subjecting the electrostatic latent image formed on the latent image carrier to a visible image processing, cleaning is performed by disposing a blade in contact with the surface of the latent image carrier to clean the latent image carrier. The latent image carrier is moved in the forward direction at the time of image formation, and is moved in the reverse direction at the end of image formation, and an angle (α) corresponding to the amount of rotation in the reverse direction is provided. ) Is formed in the cleaning device, and a latent image corresponding to the width of an opening having an upper edge where the tip of the cleaning blade is located and a lower edge having a gap abutting or equivalent to the surface of the latent image carrier. Set the angle smaller than the angle around the center of the carrier. ,
Further, below the opening formed in the cleaning device, a conveying path of a transfer paper on which the visible image carried on the latent image carrier is transferred, and excess developer adhered to itself. The latent image carrier is variable in the amount of rotation in the opposite direction by positioning a part of the extended portion of the transfer belt in contact with a cleaning blade for removing impurities such as paper and paper dust.
An image forming apparatus, comprising: 2. The image forming apparatus according to claim 1 , wherein the amount of rotation of the latent image carrier in the opposite direction is different from the initial condition.
The image forming apparatus is adjusted in accordance with a time when a state occurs .