JPH06250504A - Image forming device - Google Patents

Abstract

PURPOSE:To use an electrifying member as long period of time as possible while stabilizing an image by arranging a stain detecting means to detect that the electrifying member is stained, and cleaning the electrifying member sufficiently without degrading it by cleaning the electrifying member more than necessary. CONSTITUTION:An ammeter 9 as a stain detecting means is connected between a high voltage electric power supply 4 and an electrifying roller 3. A degree of a stain of the electrifying roller 3 is judged from change in impedance by using a phenomenon that the impedance of a system containing a photosensitive drum 2 upon which high pressure voltage is impressed or the electrifying roller 3 or an electric circuit changes when a stain is stuck on the electrifying roller 3, and a cleaning member 1 is operated. Since the high voltage electric power supply 4 supplies constant voltage as the method to measure a change in the impedance in a voltage system, when a value of an electric current flowing in the ammeter 9 connected in series to the high voltage system is measured, the impedance is determined.

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 printer using electrophotography, and more particularly to an image forming apparatus having a charging member which contacts an image carrier to charge the image carrier.

[0002]

2. Description of the Related Art Conventionally, a charging device using a corona discharge has been widely used as a charging device used in an electrophotographic image forming apparatus such as a copying machine. Recently, however, it is possible to prevent adverse effects of ozone generation due to high-voltage discharge. For this purpose, a contact charging method has also been used in which a charging member such as a conductive rubber roller or a rubber blade is brought into direct contact with the photoconductor to give a potential to the photoconductor.

For example, a charging roller in which a conductive rubber is arranged around a core is brought into contact with the photosensitive drum at a predetermined pressure, and a fixed voltage is applied to the core of the charging roller while being rotated by the rotation of the photosensitive drum. Then, the photosensitive drum is uniformly charged.

In such a contact charging system, scattered toner, scraped photoconductor powder, dirt such as dust and the like are likely to adhere to the charging roller, and in such a case, there are adverse effects such as uneven charging and insufficient charging. .

As a first conventional example, there is one in which a cleaning member for rubbing the surface of the charging roller to scrape off dirt is added.

In this case, if the cleaning member continues to rub against the charging roller for a long period of time, the charging member may be damaged or worn, which may cause charging failure. However, the device has been devised to bring the cleaning member into contact with the charging roller only for the minimum time required for cleaning.

For example, cleaning is performed once a day under normal use conditions by a sequence in which the cleaning member is brought into contact with the charging roller only for a certain time each time the power switch of the main body is turned on.

Alternatively, in a machine having a large average number of copies per day, for example, a cleaning sequence in which the cleaning member is brought into contact with the charging roller for 1 second for every 50 copies is adopted. is there.

As a second conventional example, when a charging roller which is very weak against rubbing due to process conditions is used, or a blade-shaped charging member is used, the charging member and the photosensitive member can be easily exposed. When the cleaning mechanism cannot be arranged at the contact portion of the drum, the cleaning member is not provided, and the conductive member is regularly replaced, or a serviceman inspects it and replaces it if it is dirty.

Further, as a third conventional example, in a low-priced copying machine, instead of applying a cleaning member with a low contact pressure, a mechanism for contacting and separating the cleaning member is not provided, and the cleaning member is always contacted with the charging roller. Even at this time, the periodical replacement time was set, and replacement and cleaning were performed by inspection.

[0011]

However, the above-mentioned first problem
In the conventional example, the following drawbacks remained.

That is, the degree of dirt adhering to the charging member may change due to various factors such as variations in the material of the charging member, image density, copy intervals, installation state of the machine body, temperature and humidity. Therefore, when the cleaning interval of the charging member is determined based on the average condition, uneven charging occurs when the condition is such that dirt easily attaches.

On the contrary, if the cleaning interval is shortened on the assumption that dirt is most likely to adhere to the cleaning member, the cleaning member rubs the charging member for a long time even under the condition that the dirt hardly adheres. The charging member was damaged or worn, and the life was shortened unnecessarily.

Further, in the second and third conventional examples, the charging member is regularly replaced or cleaned regardless of variations in the speed at which the charging member is soiled. Therefore, it may be costly or may not be exchanged even though it is already soiled. .

Further, since the service person took an image sample in order to check the dirt of the charging member and overhauled it, the downtime of the copying machine was long and the cost was high.

As a further problem, even if dirt is attached to the charging member, even if a constant voltage is applied to the charging member, the potential applied to the photosensitive drum changes, so that there is no unevenness. As a result, the image density became lighter or darker overall.

The first object of the present invention is to clean the charging member more than necessary by the cleaning means to prevent deterioration of the charging member and to perform sufficient cleaning to stabilize the image and keep the charging member as long as possible. It can be used.

A second object of the present invention is to detect stains on the charging member by the image forming apparatus itself and to judge whether or not the charging member is replaced or manually cleaned at an optimum time to stabilize quality and reduce cost. At the same time, it saves the trouble of checking the charging member.

A third object of the present invention is to maintain a constant electric potential applied to the image carrier even if the charging member is contaminated to obtain a good image.

[0020]

In order to achieve the first object, the present invention provides an image forming apparatus having a charging member for contacting an image carrier to charge the image carrier. It is characterized in that a dirt detecting unit is provided for detecting that the charging member is dirty.

Further, it has a cleaning means for cleaning the charging member, and controls the cleaning means based on the detection result of the stain detecting means.

Further, in order to achieve the second object, the present invention has a display section for displaying that the charging member is dirty, and controls the display section based on the detection result of the dirt detection means. To do.

Further, the main body internal memory for storing the detection result of the dirt detecting means may be provided.

Further, a communication line for transmitting the detection result of the dirt detection means to a device outside the main body may be provided.

In order to achieve the third object, according to the present invention, the voltage applied to the charging member is controlled based on the detection result of the dirt detecting means.

The dirt of the charging member may be detected by the change in impedance of the charging path including the charging member.

It is also possible to have a potential detecting means for detecting the potential of the image carrier and detect the dirt on the charging member based on the detection result of the potential detecting means.

It is also possible to have an image density detecting means for detecting the image density formed on the image carrier, and to detect the dirt on the charging member based on the detection result of the image density detecting means.

It is also possible to have a reflectance detecting means for detecting the surface reflectance of the charging member and detect the dirt on the charging member based on the detection result of the reflectance detecting means.

Further, the cleaning method of the cleaning means may be controlled based on the detection result of the dirt detection means.

Further, the cleaning means is provided with a cleaning member which can be brought into contact with and separated from the charging member, and the contact pressure or the contact time when the cleaning member is brought into contact with the charging member for cleaning is determined by the contamination detecting means. You may make it control based on a detection result.

Further, at least 2 in the longitudinal direction of the charging member.
It is preferable to dispose the dirt detection means in different places, such as at least one place.

Further, it is desirable to detect the change in impedance of the charging path excluding the change in impedance of the charging member which is not caused by the contamination of the charging member.

[0034]

According to the present invention having the above-described structure, since the dirt detecting means is provided, it can be detected that the charging member is dirty.

Since the cleaning of the charging member is contacted with the charging member for cleaning when the charging member is contaminated, the charging member can be sufficiently cleaned while the deterioration of the charging member is minimized. Can be cleaned.

When the charging member is detected to be dirty,
The information is displayed, stored in the internal memory, or transmitted to the outside, so that replacement or cleaning can be performed only when necessary.

When the charging member is detected to be dirty,
Since the voltage applied to the charging member is adjusted to the optimum value, it is possible to prevent image defects due to stains on the charging member.

[0038]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of an electrophotographic copying apparatus as an image forming apparatus according to the first embodiment of the present invention.

A charging roller 3 as a charging member is arranged in contact with the photosensitive drum 2 as an image carrier. The charging roller 3 is a conductive rubber roller having a conductive metal cored bar, and a voltage is applied to the cored bar portion from a high voltage power source 4 through a contact (not shown). 13 is an image exposure according to the image information of the original, 5 is a developing device, 6 is a transfer device, 7 is a cleaning device, and 8 is a fixing device. A transfer sheet 14 is fed from a sheet feeding device (not shown) and conveyed to the fixing device 8. A cleaning member 1 can be brought into contact with and separated from the charging roller 3.

FIG. 2 shows a perspective view of the cleaning member 1 as the cleaning means. The cleaning member 1 has a fine fiber member 1b attached to a cleaning member body 1a having one end in the longitudinal direction formed into a lever shape. The cleaning member 1 is a solenoid 10 whose hole 1d is centered on the integrally formed metal swing shaft 1c and whose hole 1d is shown in FIG.
Can be swung by pulling. Solenoid 1
0 is driven by the power supply 12. Further, an ammeter 9 as a dirt detecting means is connected between the high voltage power source 4 and the charging roller 3 to monitor the current flowing through the charging roller 3 and the value thereof is sent to the central controller 11. The central controller 11 controls the sequence of the entire copying machine including the driving of the solenoid 10.

Next, the operation of the electrophotographic copying machine to which the present invention is applied will be described. When the start button is pressed, the main motor (not shown) rotates, and the photosensitive drum 2 that is being connected and driven rotates. At this time, the charging roller 3 pressed against the photosensitive drum 2 is driven to rotate with respect to the photosensitive drum.

First, in order to charge the surface of the photosensitive drum 2 to a uniform potential, the charging roller 3 is supplied with −150 from the high voltage power source 4.
A constant voltage of 0V is applied. At this time, the photosensitive drum 2 is about -7
It is uniformly charged to 50V.

Next, the charged photosensitive drum 2 is imagewise exposed to form an electrostatic latent image and then developed by the developing device 5 to form a toner image. Further, this toner image is transferred onto the transfer paper 14 by the transfer device 6. The transfer paper 14 is conveyed to the fixing device 8 and the toner image is fixed by heat and pressure. On the other hand, the untransferred residual toner remaining on the photosensitive drum 2 is removed by the cleaning device 7.

In the image forming process, the cleaning member 1 is normally biased by the compression spring 20 to the position indicated by the chain double-dashed line in FIG. 1 and separated from the charging roller 3.

In this embodiment, when dirt is attached to the charging roller 3, the impedance of the system including the photosensitive drum 2 to which a high voltage is applied, the charging roller 3 and the electric circuit is changed, The cleaning member 1 is operated by determining the degree of contamination of the charging roller 3 from the impedance change. As a method for measuring the change in impedance of the high-voltage system, the high-voltage power supply 4 supplies a constant voltage, so that an ammeter 9 connected in series to the high-voltage system.
If the value of the current flowing through is measured, the impedance is determined by the well-known physical law.

The control of the charging roller 3 in this embodiment will be described in more detail below. As described above, the charging roller 3 is applied with a voltage of -1500V. At this time, the current flowing through the charging roller 3 was usually about 30 μA. That is, the impedance of the system including the charging roller 3, the photosensitive drum 2, the electric contacts (not shown), and the power supply circuit is about 5
It is 0 MΩ. As a result of the experiment, in the present embodiment, when the toner powder or the scraped powder of the photoconductor adheres to the charging roller 3 and becomes dirty, the electric resistance value of the surface of the charging roller 3 increases, and when the system impedance becomes about 60 MΩ or more. It was found that the uneven charging due to the dirt exceeded the allowable level. Since the current flowing to the charging roller 3 when the impedance is 60 MΩ is 25 μA, in this embodiment, when the charging current detected by the ammeter 9 becomes 25 μA or less, the central controller 11 issues a command to the power source 12 to drive the solenoid 10. Was set to clean the charging roller 3.

In this embodiment, if the cleaning member 1 is brought into contact with the photosensitive drum 2 while the charging roller 3 is charging for image formation, the image may be uneven.
A single cleaning time was set so that the cleaning member 1 was in contact with the charging roller 3 for three rotations after the voltage application by the charging roller 3 was completed.

According to the experiments, in almost all cases, the entire impedance was immediately recovered to about 50 MΩ immediately after the cleaning member 1 was contacted and cleaned as described above.

However, on rare occasions when the dirt adheres strongly or when the charging roller is used for a long period of time, the dirt cannot be sufficiently removed in the above-mentioned normal cleaning mode.
Sometimes the impedance did not go down. In order to deal with such a case, in the present embodiment, when the impedance does not drop below 60Ω even if the cleaning is performed once (the ammeter 9
In the case where the detected current in (1) does not exceed 25 μA), the central control unit 11 continuously drives the solenoid with respect to the power source 12 for 10 rotations of the charging roller 3 to bring the cleaning member 1 into contact with the charging roller 3.

In addition to the method used in this embodiment, when the central control unit 11 determines that dirt cannot be easily removed: The cleaning member 1 is changed by changing the voltage applied to the solenoid 10.
To increase the contact pressure of the cleaning device.-The solenoid 10 is turned on and off many times in a short period of time to clean the charging roller 3 with the cleaning member 1.-The hardness of the material of the fine fiber member 1b of the cleaning member 1 Another pair of auxiliary cleaning members having different surface roughnesses and their driving devices are provided, and the auxiliary cleaning members are brought into contact with each other. As such, it can be cleaned in a more effective manner.

In this embodiment, the cleaning time is lengthened when the cleaning effect is not obtained as described above, but if the impedance still does not fall below 60 MΩ, the following measures are taken. In this case, charging roller 3
It is judged that the dirt adhered to the cleaning member 1 cannot be completely removed by the cleaning member 1, and the cleaning member 1 is charged to the charging roller 3 only once for every three rotations of the charging roller 3 every time 50 sheets are copied as in the conventional example. Contact 3 By doing so, it is possible to prevent the cleaning member 1 from remaining in contact with the charging roller and rapidly damaging the charging roller. Further, although there is some image unevenness due to uneven charging, it is possible to prevent the charging roller from being further soiled.

Further, in this embodiment, the following method is adopted in order to detect the dirt of the charging roller 3 due to the impedance change more accurately.

According to the experiment, the dominant factor that changes the impedance of the system including everything from the high-voltage power supply 4 to the charging roller 3 and the photosensitive drum 2 is the dirt adhering to the charging roller 3, but to some extent the photosensitive drum 2 It was also found that it also depends on the change in the film thickness of the photoconductor layer coated on the surface of. In this embodiment, the thickness of the photoconductor layer is 30 μm in the initial stage.
However, when copying 60,000 sheets, which is equivalent to the service life of the photosensitive drum 2, the photoconductor layer is thinned to about 20 μm, and as a result, the impedance of the entire high-voltage system rises from 50 MΩ to 56 MΩ. I understood it. Therefore, in this embodiment, in order to cancel the influence of the change in the thickness of the photoconductor layer, the impedance setting value of 60 MΩ for the cleaning operation is set to 1 based on the copy number information stored in the storage device 21. The correction is performed such that it is increased by 1 MΩ for every 10,000 copies. Therefore, when replacing the photosensitive drum, a serviceman resets the number information of the storage device.

In this embodiment, there was little effect, but depending on the material of the charging roller 3 and the characteristics of the photosensitive drum 2, for example, the resistance value of the conductive rubber of the charging roller 3 changes with time,
It is also possible that the impedance of the high-voltage system changes due to changes in temperature and humidity. In such a case, information on the number of copies after replacement of the charging roller, information on the elapsed time obtained by the time measuring device after replacement of the charging roller, or a temperature sensor,
Impedance changes due to effects other than dirt on the charging roller can be canceled based on the temperature and humidity information from the humidity sensor.

As described above, according to this embodiment, the charging roller is cleaned as necessary and sufficient, so that the life of the charging roller becomes long and the image quality becomes good.

Further, even if strong dirt is attached, the cleaning time of the charging roller is lengthened to effectively clean it.

Further, when uncleanable dirt adheres, cleaning is performed every certain number of sheets to prevent further dirt from adhering and to prevent the charging roller from being extremely damaged.

Further, by canceling the impedance change due to the decrease in the film thickness of the photosensitive drum, the dirt on the charging roller is detected more accurately.

(Second Embodiment) FIG. 3 shows a second embodiment in which the present invention is applied to a copying machine. The same parts as those in the first embodiment are given the same numbers. Above the charging roller 3, there is provided a reflectance sensor 15 as a reflectance detecting means having a red LED light projection port and a light receiving sensor, and an output signal is sent to the central control unit 11. Reference numeral 16 is an operation panel provided on the upper part of the main body and has a display unit 17. The cleaning member 3 is not provided in this embodiment.

In the above structure, the reflectance sensor 15 can detect the surface reflectance of the charging roller 3. Since the charging roller 3 used in this embodiment is made of conductive rubber containing carbon, the initial reflectance is low, but the reflectance increases as dirt is attached. Therefore, the upper limit value of the reflectance of the charging roller 3 at which uneven charging starts to occur is determined. When a signal above the upper limit value continues for a certain period of time or more, the central control unit 11 instructs the display section 17 to contact the service person. I will send out a message. The user is allowed to continue copying even during this display, but there is no problem because the effect of dirt on the charging roller 3 is slight at this point. The charge roller is replaced by the service person who received the notification, and the image quality is restored.

As described above, according to the present embodiment, the charging roller can be saved more than a simple periodical replacement. In addition, even if the charging roller 3 gets dirty very quickly due to a sudden accident or variation in products, the service person can quickly deal with it.

After the central controller determines that the dirt on the charging roller 3 has reached the allowable limit, the following measures may be taken in addition to the above method.

The charging roller 3 is constructed so that it can be easily removed, and the user cleans it. On the display unit 17, "Clean the charging roller" is displayed. Alternatively, a cleaning member for manually cleaning the charging roller 3 inside the main body may be provided to be operated by the user. By doing this, there is no need for service personnel to come.

In a copying machine having a short regular inspection period, the information about the dirt of the charging roller 3 is stored in the internal memory of the main body of the central control unit 11 without displaying it on the display unit 17, so that the service person can carry out the regular inspection. Be prepared to check during inspection. This can shorten the inspection time of the service person.

-Automatically notify the service person through the communication line. This allows the service person to know the time for maintenance without the user getting confused.

Furthermore, in the first embodiment, it is effective to provide a display prompting replacement or inspection on the main body display unit 17 even when the charging roller 3 is not cleaned even if the cleaning time is lengthened.

In the second embodiment, the reflectance sensor 15
Although the example in which the dirt of the charging roller 3 is detected is shown by the above, the gist of the present invention is not impaired even if the following means are taken.

As shown in FIG. 4, the dirt of the charging roller 3 may be detected by the surface potential of the photosensitive drum 2 by the potential sensor 18 as the potential detecting means. In this case, the influence of abrasion and deterioration of the photosensitive layer of the photosensitive drum 2 is included, but this embodiment has no practical problem. When this configuration is adopted under process conditions that have a large influence, it is sufficient to correct the surface potential according to the number of copies and the elapsed time since the photosensitive drum was replaced.

As shown in FIG. 5, the density sensor 19 serving as an image density detecting means, which is a reflectance sensor for measuring the reflectance of the reference density toner image formed on the surface of the photosensitive drum 2, indirectly controls the charging roller 3. You may detect dirt. In this case, the reference density toner image is obtained by exposing the reference density surface provided outside the original image area on the back surface of the original table glass with a predetermined amount of light. This is an effective means when the reflectance sensor 15 for the charging roller 3 and the surface electrometer 1 cannot be provided due to space limitations.

In any of FIGS. 3, 4 and 5, the position where the dirt of the charging roller 3 is detected may be a plurality of positions in the longitudinal direction of the charging roller 3. By thus comparing the outputs from the respective sensors, it is possible to detect partial charging unevenness.

(Third Embodiment) FIG. 6 shows a third embodiment of the present invention. Only the points different from the second embodiment will be described.

High-voltage power supply 4 for applying voltage to the charging roller 3
Was a constant voltage power supply in both the conventional example and the first and second embodiments. In these examples, the voltage applied to the charging roller 3 is −
1500V, and as a result, the photosensitive drum 2 has -750.
A uniform potential of V was applied.

However, when dirt adheres to the charging roller 3, even if a potential of -1500V is applied, the potential applied to the photosensitive drum 2 does not reach the predetermined value of -750V, resulting in a decrease in image density. It was A predetermined potential can be obtained by applying a voltage to the charging roller 3 by correcting such a change in the applied potential due to the dirt on the charging roller 3 so as to cancel it.

In FIG. 6, the storage device 21 stores a correspondence map of the surface reflectance and the correction voltage corresponding to the dirt on the charging roller 3.

Based on the information on the contamination of the charging roller 3 obtained by the reflectance sensor 15, the central control unit 11 issues a command to the high temperature power source 4 to apply an optimum voltage according to the map in the storage unit 21. I did it.

As a result, it was possible to almost eliminate the influence of stains attached to the entire charging roller 3 other than local stains.

The means for detecting the dirt adhering to the charging roller 3 may be any means such as impedance and the surface potential of the photosensitive drum, regardless of the above construction.

[0079]

As described above, according to the present invention,
Since the dirt detecting unit is provided, it can be detected that the charging member is dirty.

Since the cleaning of the charging member is detected by contacting the cleaning member of the charging member with the cleaning of the charging member, the deterioration of the charging member is minimized and the charging member is sufficiently cleaned. Can be cleaned.

Further, by detecting that the charging member is dirty,
The information is displayed, stored in the internal memory, or transmitted to the outside, so that replacement or cleaning can be performed only when necessary.

Further, by detecting that the charging member is dirty,
Since the voltage applied to the charging member is adjusted to the optimum value, it is possible to prevent image defects due to stains on the charging member.

[Brief description of 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 perspective view of a cleaning member of the apparatus.

FIG. 3 is a schematic configuration diagram of an image forming apparatus using a reflectance sensor in the second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of an image forming apparatus using a potential sensor in the example.

FIG. 5 is a schematic configuration diagram of an image forming apparatus using a density sensor in the example.

FIG. 6 is a schematic configuration diagram of an image forming apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cleaning member (cleaning means) 2 Photosensitive drum (image carrier) 3 Charging roller (charging member) 9 Ammeter (dirt detection means) 15 Reflectance sensor (reflectance detection means) 17 Display section 18 Potential sensor (potential detection means) ) 19 Density sensor (image density detection means)

Claims (14)

[Claims] 1. An image forming apparatus having a charging member for charging an image bearing member by contacting the image bearing member, the image forming apparatus comprising a stain detecting unit for detecting that the charging member is soiled. Forming equipment. 2. The image forming apparatus according to claim 1, further comprising cleaning means for cleaning the charging member, wherein the cleaning means is controlled based on a detection result of the stain detecting means. 3. The image forming apparatus according to claim 1, further comprising a display unit for displaying that the charging member is soiled, and controlling the display unit based on the detection result of the soiling detection unit. 4. The image forming apparatus according to claim 1, further comprising a main body internal memory that stores a detection result of the dirt detection unit. 5. The image forming apparatus according to claim 1, further comprising a communication line for transmitting the detection result of the dirt detection unit to a device outside the main body. 6. The image forming apparatus according to claim 1, wherein the voltage applied to the charging member is controlled based on the detection result of the dirt detection unit. 7. The image forming apparatus according to claim 1, wherein contamination of the charging member is detected by a change in impedance of a charging path including the charging member. 8. The image forming apparatus according to claim 1, further comprising a potential detecting unit that detects a potential of the image carrier, and detects a stain on the charging member based on a detection result of the potential detecting unit. 9. The image forming apparatus according to claim 1, further comprising image density detecting means for detecting an image density formed on the image bearing member, and detecting a stain on the charging member based on a detection result of the image density detecting means. . 10. The image forming apparatus according to claim 1, further comprising reflectance detecting means for detecting a surface reflectance of the charging member, and detecting dirt on the charging member based on a detection result of the reflectance detecting means. 11. Based on the detection result of the dirt detection means,
The image forming apparatus according to claim 2, wherein a cleaning method of the cleaning unit is controlled. 12. The cleaning means comprises a cleaning member that can be brought into contact with and separated from the charging member, and the contact pressure or the contact time when the cleaning member is brought into contact with the charging member for cleaning is determined by the contamination detecting means. The image forming apparatus according to claim 11, which is controlled based on a detection result. 13. The dirt detecting means is arranged at at least two different locations in the longitudinal direction of the charging member.
The image forming apparatus described. 14. The image forming apparatus according to claim 7, wherein the change in the impedance of the charging path is detected by excluding those which are not caused by dirt on the charging member.