JPH08160813A - Detection of life of contact electrostatic charging member - Google Patents

Abstract

PURPOSE: To provide a method for detecting the life of a contact electrostatic charging member capable of preventing the occurrence of leakage by detecting the life of the electrostatic charging member with higher accuracy. CONSTITUTION: This image forming device has at least a photosensitive drum (image carrying member) 1, an electrostatic charging roller (contact electrostatic charging member) 2 which comes into contact with the surface of the photosensitive drum 1 and a high-voltage power source 3 which uniformly electrostatically charges the surface of the photosensitive drum 1 by impressing a bias to the electrostatic charging roller 2. The surface of the electrostatic charging roller 2 is provided with plural current detecting members 4a, 4b, 4c which are divided in the longitudinal direction of the roller and come into contact with its surface. Judgment is made that the life of the electrostatic charging roller 2 runs out when the max. current value Imax among the current values detected by these current detecting members 4a, 4b, 4c attains the predetermined upper limit value of the prescribed current or above. The film thickness of the surface layer is detected by the current values at the plural points in the longitudinal direction of the electrostatic charging roller 2. The current value (max. current value Imax) of the part where the thickness is smallest and the predetermined upper limit value of the current are compared, by which the life of the electrostatic charging roller 2 is detected with the high accuracy and the occurrence of the leakage is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the life of a contact charging member used in an image forming apparatus.

[0002]

2. Description of the Related Art FIG. 15 shows an example of a conventional image forming apparatus. In FIG.
Reference numeral 1 denotes a cylindrical photosensitive drum which is an image carrier, and the photosensitive drum 111 rotates in one direction around its axis. The contact charging member 103 is in contact with the photosensitive drum 111, and the high voltage power supply 108 is applied to the contact charging member 103.
The surface of the photosensitive drum 111 is uniformly charged to a predetermined potential by applying a predetermined high voltage bias supplied from the exposure device 102, and a latent image is formed on the photosensitive drum 111 by the exposure device 102.

Further, 104 is a developing device, which is provided with a hopper 104 for storing and storing the developer 109, a developing sleeve 105 as a developer carrying member, and a developing blade 107 as a developer regulating member. , Photosensitive drum 11
The developer 109 is supplied to the latent image formed on 1 to visualize it as a developer image. A high-voltage power source (not shown) is connected between the photosensitive drum 111 and the developing sleeve 105, and an appropriate developing bias is applied between them.

On the other hand, the transfer material 114 accommodated in the paper feed cassette 117 is fed by a paper feed roller 116, and is synchronized with the developer image on the photosensitive drum 111 by a registration roller (not shown) to transfer the transfer device 110. Transferred to the transfer material 1
14, the developer image on the photosensitive drum 111 is transferred to the transfer device 110.
Transcribed by Then, the developer image transferred to the transfer material 114 is conveyed to the fixing device 115 together with the transfer material 114 and is fixed by heat or pressure to form a recorded image. The developer remaining on the photosensitive drum 111 without being transferred after the transfer is removed by the cleaning device 112 having the blade 113. Then, the surface of the photosensitive drum 111 is charged again by the contact charging member 103, and the above steps are repeated.

By the way, as for the form of an image forming apparatus, there are a great number of models used by exchanging necessary parts or replenishing consumables according to the life setting of each of the apparatuses forming the image forming apparatus. . In these models, generally, the timing of replenishment of consumables (for example, toner) is judged by the remaining amount detection mechanism, and a warning is given to the user.
Also, regarding the replacement timing of each part, the service person or the device itself judges the nominal life (specified by the number of used sheets) of each part based on, for example, a print number counter (not shown) provided in the main body of the image forming apparatus and replaces it. Methods have been used to perform work or alert the user.

Incidentally, in the image forming apparatus shown in FIG. 15, the photosensitive drum 111, the developing device 104, the cleaning device 104, and the contact charging member 103 are the independent parts of the image forming portion as the exchange part. There is.

[0007]

However, in the setting of the nominal life depending on the number of used sheets as in the above-described conventional example, the life of each part is actually determined because the manufacturer assumes the general use state. Depending on the usage status of each user, there may be cases where the nominal life of each part is inconsistent.

Particularly, in an image forming apparatus using a contact charging member and in which the contact charging member and the photosensitive drum can be replaced separately, the lifespan of the contact charging member and the photosensitive drum is likely to be inconsistent. The reason is as follows.

That is, FIG. 16 shows an example of the charging roller 103, which is a contact charging member, and the photosensitive drum 111.

The thickness of the charging roller 103 is reduced as the number of printed sheets increases, and the thickness of the antifouling layer 103d on the surface layer decreases due to frictional wear with the photosensitive drum 111 and deterioration of the resin due to discharge during the charging operation to reach the nominal life. The life is often longer than that of the photosensitive drum 111. This is because there is no contact with a very stressful member such as a cleaning blade.

However, the surface layer 1 of the charging roller 103
The thickness of 03d is very thin, around 10 μm, and it is difficult to obtain uniform thickness over the lengthwise direction of the charging roller 103. Therefore, the life depending on the thickness of the surface layer 103d also varies greatly, and the number of printed sheets varies from the charging roller. It was difficult to estimate the life of 103.

When such a charging roller 103 is used, the photosensitive drum 111 is often replaced at the same time as the charging roller 103 before the nominal life of the photosensitive drum 111 depending on the situation described below.

Even when the photosensitive drum 111 is within the nominal life, when the charging roller 103 is used beyond the nominal life, the charging roller 103 whose pressure resistance has dropped has its conductive elastic layer 103b and the photosensitive drum core 111a. A leak occurs between the charging roller 103 and the charging roller 103 and damages the photosensitive drum 111 in a sound state.

Once a leak occurs, a large amount of current flows out from the leak, so that local charging cannot be performed.
If a black spot-like abnormal image is generated on the image or becomes worse, it becomes impossible to uniformly charge the photosensitive drum 111 in the longitudinal direction, and a horizontal black streak appears on the image.
Then, if the photosensitive drum 111 and the charging roller 103 are further used as they are, the respective leak points serve as cores to increase the number of leak points, resulting in an increase in defective images. In this way, the charging roller 1
03 is used over its life, the photosensitive drum 1
This is because there is a problem that even if 11 is still within the life range, both of them cannot be used at the same time due to the occurrence of leak.

As described above, in the image forming apparatus in which the contact charging member is used and the contact charging member and the photosensitive drum are separately replaceable, the life of the charging roller is reduced in order to prevent damage due to leakage. There was a need for a way to guess.

In the above method, for example, the amount of wear of the surface layer is detected by bringing a conductive detection member into contact with the charging roller, which is a contact charging member, in the longitudinal direction thereof and detecting a change in the resistance value of the charging roller itself. It was thought to be possible to estimate the life of the charging roller based on this assumption.

However, in general, the wear portion of the charging roller immediately before the leak occurs is very small, and it is difficult to detect the decrease in the resistance value by the batch resistance measurement in the longitudinal direction of the charging roller. Realization was difficult. Therefore, there is still no effective means for estimating the life of the charging roller, and a detection method therefor has been desired.

The present invention has been made in view of the above circumstances. The object of the present invention is to provide a contact charging member capable of detecting the life of the contact charging member with higher accuracy and preventing the occurrence of leaks. It is to provide a life detection method.

[0019]

To achieve the above object, the invention according to claim 1 provides at least an image bearing member, a contact charging member that contacts the surface of the image bearing member, and a bias to the contact charging member. In an image forming apparatus provided with a high-voltage power supply for uniformly charging the surface of the image carrier by applying, a plurality of current detection members are provided that are in contact with each other in the longitudinal direction of the surface of the contact charging member. When the maximum current value Imax among the current values detected by the current detection member exceeds a predetermined predetermined current upper limit value, it is determined that the contact charging member has reached the end of its life. To do.

According to a second aspect of the present invention, at least the image bearing member, the contact charging member that contacts the surface of the image bearing member, and the surface of the image bearing member are removed by applying a bias to the contact charging member. In the image forming apparatus provided with a high voltage power source for charging like above, a plurality of current detecting members which are divided in the longitudinal direction of the surface of the contact charging member and contact each other are provided, and among the current values detected by the current detecting member, Maximum current value I
max and the leakage limit current value Ileak of the contact charging member
And the coefficient α determined by the individual difference in leak performance of the contact charging member satisfies Imax ≧ α × Ileak, it is determined that the contact charging member has reached the end of its life.

According to a third aspect of the present invention, at least the image carrier, the contact charging member that comes into contact with the surface of the image carrier, and the surface of the image carrier by applying a bias to the contact charging member are provided. In the image forming apparatus provided with a high voltage power source for charging like above, a plurality of current detecting members which are divided in the longitudinal direction of the surface of the contact charging member and contact each other are provided, and among the current values detected by the current detecting member, Maximum current value I
max and the leakage limit current value Ileak of the contact charging member
And the coefficient α determined by the individual difference in the leak performance of the contact charging member satisfies Imax ≧ α × Ileak, or the total average current value Iave of the current values detected by the current detecting member. The contact charging member reaches the end of its life when the relationship between the maximum current value Imax and the coefficient β determined from the leakage performance of the contact charging member in the longitudinal direction of the contact charging member satisfies Imax ≧ β × Iave. It is characterized by judging that it is a thing.

A fourth aspect of the present invention is characterized in that, in the first, second or third aspect of the invention, the current detecting member is configured to be separable from and contact with the contact charging member.

According to a fifth aspect of the present invention, in the first, second or third aspect of the invention, the current detecting member is formed by arranging conductive sponge elastic bodies and insulating sponge elastic bodies alternately in the longitudinal direction. It is characterized by having done.

[0024]

According to the invention described in claim 1, the surface layer film thickness is detected by a current value at a plurality of points in the longitudinal direction of the contact charging member, and the current value of the thinnest portion (maximum current value Ima) is detected.
By comparing x) with the predetermined upper limit value of the predetermined current, it is possible to accurately detect the life of the contact charging member and prevent the occurrence of leakage.

According to the second aspect of the invention, the surface layer film thickness is detected by the current value at a plurality of locations along the longitudinal direction of the contact charging member, and the current value of the thinnest portion (the maximum current value I
By comparing (max) with a predetermined upper limit value (α × Ileak), it becomes possible to detect the life of the contact charging member with high accuracy and prevent leakage from occurring.

According to the third aspect of the present invention, based on the criterion of the second aspect of the invention, the maximum current value Imax and the total average current value Iave are related to the leakage performance against the deviation of the current value in the longitudinal direction of the contact charging member. It is possible to further improve the accuracy of detecting the life of the contact charging member by adding a criterion for comparison with a value obtained by multiplying the determined coefficient β.

According to the fourth aspect of the present invention, by contacting the current detection member only during detection, it is possible to eliminate unnecessary rubbing against the contact charging member and extend the life of the contact charging member. .

According to the fifth aspect of the present invention, the current detecting member also has the ability of the cleaning member, so that it is possible to prevent the image defect due to the dirt of the contact charging member.

[0029]

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

<First Embodiment> FIG. 1 is a block diagram of the main part of an image forming apparatus to which the life detecting method according to the first embodiment of the present invention is applied. FIG. 2 is a sectional view of the entire image forming apparatus. 3 is a sectional view of the charging roller, and in FIG. 2, the same elements as those shown in FIG. 15 are designated by the same reference numerals.

In FIG. 1, a photosensitive drum 1 which is an image carrier is constituted by forming an organic photosensitive layer 1b having a predetermined thickness on a conductive Al core bar 1a, and the core bar 1a is a contact (not shown). Connected to earth via.

The charging roller 2 which is a contact charging member,
For example, as shown in FIG. 3, a conductive elastic layer 2b, a high resistance layer 2c and a stain prevention layer 2d are formed on a conductive cored bar 2a to form a multilayer structure. The photosensitive drum 1 and the charging roller 2 are in contact with each other with a predetermined contact pressure, the photosensitive drum 1 rotates in the direction of the arrow in FIG. 2, and the charging roller 2 is driven to rotate.

Thus, a predetermined high voltage is applied to the charging roller 2 from the cored bar 2a via a sliding contact (not shown). In this embodiment, it is assumed that a high voltage in which a direct current component controlled to a constant voltage and an alternating current component controlled to a constant current are superposed is applied to the charging roller 2 from the charging power source 3 shown in FIG. As shown in FIG. 1, a ground switch 10 for electrically turning on / off is provided between the charging power source 3 and the ground.

On the other hand, with respect to the charging roller 2, the conductive detecting members 4a, 4b, which are divided into a plurality in the longitudinal direction,
4c are in contact with each other, and these detection members 4a, 4b, 4c
Are switch parts 5a, 5b, which electrically turn on / off,
Via each of 5c, it is connected to a current detecting section 6a, 6b, 6c for detecting a direct current. The detection member 4
Although the detection accuracy of a, 4b, and 4c increases as the coverage rate in the longitudinal direction by them increases and the number of divisions increases, the case of three divisions will be described for simplification of description.

A resistor having a value corresponding to the DC electric resistance of the photosensitive drum 1 viewed from the charging roller 2 is used for the resistor 9 connected to the ends of the current detectors 6a, 6b, 6c. This prevents the charging roller 2 from being damaged by an excessive current flowing at the time of detection.

Thus, in the present embodiment, the current detector 6a,
Based on the values obtained by 6b and 6c, the calculation unit 7 determines the change in the current value (that is, the change in the resistance value) of each part of the charging roller 2, and when it is determined that the charging roller 2 is about to reach the end of its life. , The display unit 8 allows the user to charge the charging roller 2
A warning prompting you to replace the.

The principle of detecting the life of the charging roller 2 according to this embodiment will be described below with reference to an actual example.

First, the setting conditions of the actual machine will be shown.

Process speed: 80 mm / sec Photosensitive drum 1: Outer diameter = φ30 mm, A1 core metal 1a thickness = 1
mm, organic photoreceptor layer 1b thickness = 30 μm Charging roller 2: outer diameter = φ15 mm, core metal 2a = SUS made φ8 mm Conductive elastic layer 2b = carbon dispersion in isoprene rubber, volume resistance value = about 10 ³ Ωcm, thickness = 3 .2 mm High-resistance layer 2c = Carbon dispersion in urethane rubber, volume resistance = about 10 ⁵ Ωcm, thickness = 280 μm Stain prevention layer 2d = Carbon dispersion in resin, volume resistance = about 10 ⁶ Ωcm, thickness = 10 μm Charging power source 3: AC constant current value = 800 μA, DC constant voltage value = −600 V Detection members 4a to 4c: 1 cm wide metal brush Resistance part 9: Resistance value = 50 MΩ In FIG. Show the situation.

The surface layer (fouling prevention layer) 2d of the charging roller 2 is very thin, around 10 μm, so that the film thickness is several μm.
The rate of change with respect to the whole is likely to be very large even if it is shaken by m. In FIG. 4, a, b, and c indicate the state of the film thickness of the charging roller 2 at three locations. When the charging roller 2 in such a state is used, the dirt prevention layer 2d, which is the surface layer, is scraped as shown in FIG. 4 due to friction with the photosensitive drum 1 as the number of durable sheets increases. Then, when the thinnest portion c of the charging roller 2 reached about 3 μm, a leak occurred with the photosensitive drum 1. Therefore, it can be determined that the life of the charging roller 2 of this configuration is when the film thickness of the surface layer 2d reaches the lower limit film thickness of 3 μm.

FIG. 5 shows the relationship between the film thickness of the surface layer 2d of the charging roller 2 used in this embodiment and the resistance and current values.

In the present embodiment, when the charging roller 2 reaches the end of its life, the film thickness of the surface layer 2d is detected by utilizing the relationship shown in FIG. 5, and DC flowing through the detection members 4a, 4b, 4c.
It can be estimated by the current value. When the film thickness of the surface layer 2d at the end of its life shown in FIG. 4 is about 3 μm, according to FIG. 5, the resistance value of that portion of the charging roller 2 is about 2.1 × 10 ⁵ Ω, and the leakage is caused. It can be seen that the immediately preceding detected current value (leakage limit current Ileak) was about 8.5 μA.

Therefore, in this embodiment, the current value (α × Ileak) in consideration of the margin (α) before the leakage is set as the upper limit current value, and the detection members 4a, 4 are divided into a plurality of parts.
It is sufficient to determine that the charging roller 2 has reached the end of life when the detected current value at any one of b and 4c exceeds the upper limit current value (α × Ileak).

By the way, this upper limit current value (α × Ileak)
Regarding the method of determining, especially, the surface layer 2d of the charging roller 2
It is necessary to consider the variation in the material composition (voltage resistance) of the above as a margin (α). Here, a specific method of obtaining the margin (α) will be described below.

When the variation in the charging roller 2 of the present embodiment configuration is examined using the above-mentioned main body configuration, n = 3
The leakage current limit current value at 0 is an average value of 8.5 μ.
A, σ = 0.25 μA. Considering the margin of 3σ, 3σ = 0.75 μA, which corresponds to 8.7% of the average value (0.75 / 8.5 = 0.088).

Therefore, in this embodiment, it is sufficient to allow a variation of about 10%. Therefore, in this embodiment, α = 90% = 0.9 may be set. Then, the upper limit current value (α × Ileak) is 8.5 × 0.9 =
It can be determined that 7.65≈7.7 μA.

Next, the sequence of this embodiment will be described with reference to the timing chart of FIG. 6 and the flowchart of FIG.

Here, the case where the life of the charging roller 2 is detected during the pre-rotation before the image forming operation is shown. Hereinafter, the description will be given mainly with reference to FIG. 6, and is indicated by the symbols of the processing steps F1 to F9 shown in FIG.

When the image forming operation is started, the charging power source 3 is soon turned on (F1). Then, the detection switch 5
a, 5b, 5c are turned on, and these are the current detectors 6a, 6
Ground switch 10 is turned off at the same time as it is connected to b and 6c.
Then, the connection with the ground is lost, and the photosensitive drum 1 is floated (F2). As a result, all of the DC current from the charging power source 3 flows through the current detectors 6a, 6b, 6c, and the change in current value due to the state of the photosensitive drum 1 can be prevented.

Detecting members 4a, 4b, 4c and current detecting section 6
After a, 6b, and 6c are connected, current value detection is performed in each part (F3). The detection switches 5a, 5b, and 5c are turned off when the detection of all the parts is completed (detection time t).
Then, the earth switch 10 is turned on, and the state returns to the image forming state.

Next, the maximum current value among the current values detected at a plurality of points is examined, and it is temporarily set as Imax (F
5). Then, the preset current upper limit value (α ×
Ileak) and Imax are compared (F6), and if Imax is smaller, the image forming operation is continued as it is (F9). If Imax is larger, the image forming operation is stopped (F7) and the charging roller replacement display is performed. Warn the user (F8).
Regarding the detection timing, the same effect can be obtained when the rotation is performed before the image forming apparatus is started up or after the image formation is performed.

Thus, according to the present embodiment, in the image forming apparatus which could not conventionally determine the life of the charging roller until a leak occurs, it is determined that the life of the charging roller reaches the end just before the leak occurs. As a result, the charging roller and the photosensitive drum can be used to their full lives without damaging the photosensitive drum.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS.

FIG. 8 is a block diagram of an essential part of an image forming apparatus to which the life detecting method according to the second embodiment is applied, FIG. 9 is an enlarged detailed view of a driving means of the apparatus, and FIG. 10 is a cam portion of the driving means. 9 is an enlarged detailed view of FIG. 8, in which the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The feature of the present embodiment is that the detecting members 4a, 4b, 4c used in the first embodiment are constructed so that they can be brought into and out of contact with the photosensitive drum 1 by using the driving means 11, and these are detected as current. The point is that it comes into contact with the photosensitive drum 1 only when. This prevents the detection members 4a, 4b, 4c from always slidingly contacting the charging roller 2.
The life of can be extended.

Here, the operation principle of the drive means 11 for the detection members 4a, 4b, 4c will be described.

As shown in FIG. 9, the detection member 4 (4a, 4a
b, 4c), an electrically conductive support rod 11e is fixed, and the support rod 11e is supported by being passed through a support member 11f having a hole having the same diameter as the support rod 11e formed in the center thereof. Has been done. A spring member 11d is installed between the support member 11f and the detection member 4 so as to surround the support rod 11e, and the detection member 4 is always biased upward in FIG. 9 by the spring member 11d.

A cam member 11c for pushing down the detection member 4 is provided near each detection member 4 (4a, 4b, 4c).
It is rotationally driven by the drive shaft 1b from a. Incidentally, FIG.
FIG. 10 is a diagram of the cam member 11c shown in FIG.

By the way, the sequence of the present embodiment is shown in the flow chart of FIG.
This is almost the same as that of the embodiment, and the ON / OFF of the detection switch (see FIG. 7) in the first embodiment is set to 0 of the driving means.
I just replaced it with N / OFF.

An endurance test was conducted to compare the second embodiment with the first embodiment. The experimental conditions (image forming apparatus configuration) were the same as those in the first embodiment except for the detecting member 4. The one was used as it was.

As a result, the detection member 4 (4a, 4b, 4
In the case of the first embodiment in which c) is constantly in contact with the charging roller 2, it was determined that the charging roller 2 has reached the end of its life when the number of printed sheets is about 20K. On the other hand, in the case of this embodiment,
When the number of printed sheets was about 26K, it was determined that the charging roller 2 was at the end of its life, and it was confirmed that the life of the charging roller 2 was longer than that of the first embodiment. Further, when the contact surface of the detection member 4 was observed, it was confirmed that the contact surface of the first embodiment was rougher.

Needless to say, the means for enabling the detection member 4 to be brought into and out of contact is not limited to the configuration described in this embodiment.

As described above, the life of the charging roller 2 can be extended by arranging the detection member 4 to contact only during the detection.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS. Note that FIG. 12 is a diagram showing a change in durability of the surface layer thickness when the thickness variation of the charging roller is large, and FIG. 13 is a flowchart showing the sequence of the third embodiment.

The feature of this embodiment is that the maximum current value Ima described in the first and second embodiments is used as the criterion for determining the life of the charging roller.
In addition to comparing x with the current upper limit value (α × Ileak), the maximum current value Imax and the total average current value Iave are also compared to further improve the estimation accuracy of the charging roller life. Is.

The configuration of the image forming apparatus used in this embodiment is the same as that described in the first and second embodiments, and the only difference is the above-mentioned criterion.

FIG. 12 shows an example in which the life detection accuracy can be improved by using this embodiment, which is particularly effective when the film thickness variation of the surface layer of the charging roller during molding is large. This figure is a diagram showing the state of abrasion of the surface layer of the charging roller due to durability, and a, b, and c represent different locations.

The table below shows the film thickness of the charging roller.

[0069]

[Table 1] Table 1 shows the difference in film thickness variation before and after the durability test. In the normal roller (FIG. 4), the average film thickness at the time of molding was 9.7 μm, and the ratio of the lower limit film thickness c to the average film thickness was about 83%.

However, in the roller having a large variation in the film thickness (FIG. 12), the average value of the film thickness at the time of molding is 11 μm, whereas the ratio of the lower limit film thickness c to the average film thickness is 73%.
If it becomes small, there is a possibility that a leak may occur before the life is judged based on only the judgment criteria (maximum current value management) of the first or second embodiment. The reason is as follows.

That is, the direct current flowing through each of the detection members 4 (4a, 4b, 4c) flows in at a ratio inversely proportional to the ratio of the resistance value at each detection location. That is, a large amount of liquid flows into a place having a small resistance value (a place having a small film thickness). Generally, in the charging roller having the structure shown in this embodiment, the variation in the film thickness at the time of molding is up to about 30%, so the variation in the resistance value and the variation in the ratio of the current flow are up to about 30%. is there. Within such a normal variation range, it is guaranteed that the charging roller has almost no change in leakage performance from the entire roller.

However, if the variation exceeds the normal range, the surface layer cannot withstand the magnitude of the current deviation,
The possibility of leaks increases. Moreover, this means that as the durability progresses and the total surface layer film thickness decreases, and the ratio of the lower limit film thickness c to the average value of the total film thickness becomes smaller,
It becomes more prominent. In fact, as shown in FIG. 4, in the case of an ordinary roller in which the ratio of the initial film thickness c at which the leakage occurs at the lower limit film thickness is about 83%, the ratio of the film thickness c at the time of leakage is reduced by 6%.
Although about 4% is sufficient, the durability of the charging roller having the film thickness variation as shown in FIG. 12 is the thinnest when the ratio of the film thickness c is about 73% at the initial stage. Leakage occurred before the layer reached the lower limit film thickness, and the ratio of the film thickness c at that time was reduced to about 57%.

From these facts, in order to detect the life even more reliably in the charging roller having a large variation in the surface layer film thickness, in addition to the control method for the lower limit film thickness described in the previous embodiment, one It is necessary to examine the ratio of the thinnest film thickness to the overall average film thickness and determine that the life is reached when the value becomes equal to or less than a predetermined value (that is, when the deviation becomes large). For that purpose, the total average film thickness is represented by the total average current value Iave of the current values obtained from the plurality of current detection members, and the thinnest film thickness is the largest among the current values obtained from the plurality of detection members. When the maximum current value Imax is expressed and the coefficient determined from the leak performance against the deviation of the current value in the longitudinal direction of the charging roller is expressed by β, the following equation;

[0074]

## EQU1 ## It may be determined that the charging roller has reached the end of its life when Imax ≧ β × Iave is satisfied.

By the way, the coefficient β determined from the leakage performance with respect to the deviation of the current value in the longitudinal direction of the charging roller used in this embodiment is, for example, according to the example shown in FIG. If the life is determined to be determined when the ratio is about 60%, it is possible to warn the user of the life before a leak occurs. In other words, 60% of this film thickness ratio
Is converted to the ratio in current, β is obtained, and β = 1 /
0.6≈1.7. Therefore, in this embodiment,

[0076]

## EQU2 ## When Imax ≧ 1.7 × Iave is satisfied, it can be determined that the charging roller has reached the end of its life.

When the above judgment conditions are also taken into consideration, the life detection sequence in this embodiment is as shown in the flow chart of FIG.

That is, the operation up to the current detection operation (F4) of each part is the same as in the previous embodiment. After the detection, the maximum current value Imax is found, and at the same time, the total average current value Iave is calculated (F
5). Next, if Imax ≧ 1.7 × Iave, it is determined that the charging roller has reached the end of its life (F6), the image forming operation is stopped (F8), and the user is warned (F).
9). If Imax <1.7 × Iave, then Imax is compared with 0.9 × Ileak (current upper limit value) as in the previous embodiment to determine whether the charging roller has reached the end of its life.

Using the present embodiment as described above, the first embodiment is carried out by using two charging rollers having a large variation in film thickness as shown in FIG. 12 (having a thinnest layer thickness ratio of about 70%). We compared with the case of the example. As a result, in the case of the first embodiment, a leak occurred before the detection of the life at the time when the number of durable sheets was about 21K. However, in this embodiment, it can be determined that the charging roller has reached the end of its service life when the number of durable sheets is about 20K, and at that time before the occurrence of leakage, the effect of this embodiment can be confirmed.

As described above, according to this embodiment, the criterion for determining the life of the charging roller is based on the comparison between the maximum current value Imax and the current upper limit value Iuplim (= 0.9 × Ileak) described in the previous embodiment. In addition, by comparing the maximum current value Imax with the total average current value Iave, the estimation accuracy of the charging roller life can be further improved.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 14 is a block diagram of an apparatus for carrying out the life detecting method according to the present embodiment. In this figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The feature of this embodiment is that the current detecting member also functions as a cleaning member for the charging roller 2.

In an image forming apparatus using a charging roller, toner is gradually deposited on the surface of the charging roller, especially in a low humidity environment, and the resistance value with respect to the photosensitive drum may change, resulting in image deterioration due to defective charging. . Further, if the surface of the charging roller becomes dirty, it may affect the accuracy of detecting the surface layer film thickness in the present invention.

Therefore, for the purpose of solving the above-mentioned problems, the present embodiment is provided with the cleaning function in the detecting member. In this embodiment, reference numeral 12 shown in FIG. 14 is a current detecting member / cleaning member, and the other structures are the same as those described in the first embodiment. Further, the life judgment of the charging roller 2 can be performed by any of the methods of the first and third embodiments.

The current detecting member / cleaning member 12
Is a conductive sponge part 1 around the insulating core shaft 12f.
2a, 12b, 12c and insulating sponge portion 12d, 1
2e are alternately arranged in the longitudinal direction, and the conductive sponge portions 12a, 12b, 12c serve as a current detection portion of the charging roller 2. The reason why the sponge portions 12a to 12e are used for the current detection member / cleaning member 12 is as follows.
This is to improve the cleaning performance. This sponge part 1
Materials of 2a to 12e include urethane rubber and EPD
M, polystyrene, polyolefin, polyester, polyamide, etc. are used, and if conductivity is required, carbon, metal oxide, etc. may be added in appropriate amounts. still,
Conductive sponge parts 12a to 12c constituting the current detection part
Volume resistance is 10 ¹ Ωcm to 10 ⁴ Ω
A range of cm is suitable.

The current detecting member / cleaning member 12 having the above-described structure is brought into contact with the charging roller 2 by a spring member (not shown) and is driven to rotate. Further, sliding contacts (not shown) are in contact with the conductive sponge portions 12a, 12b, 12c, and the sponge portions 12a to 12c contact the detection switch 5 through the contact points.
a, 5b, 5c are electrically connected respectively.

The results of comparative experiments between this embodiment and the first embodiment are shown below. The configuration of this embodiment is as follows. The components not shown are the same as those described in the first embodiment.

Cleaning member 12 also serving as a detecting member: outer diameter φ
15 mm, core shaft diameter = φ6 mm, core shaft material = polyacetal Conductive sponge = EPDM + carbon (volume resistance 10 ³
Ωcm) Insulating sponge = EPDM Durability test with the above structure at a temperature of 15 ° C and humidity of 10%
As a result of carrying out in the environment of 1, the charging roller 2 was certainly judged to have reached the end of its service life at the time of 23K sheets before the leak occurred in the first embodiment. Some images were seen.

On the other hand, also in this embodiment, it is surely determined that the charging roller 2 has reached the end of its life at the time of 22K sheets before the leak occurs, and no image defect due to stain is observed. The effect of the example was confirmed.

As described above, according to the present embodiment, the current detecting member also functions as the charging roller cleaning member, so that the charging roller can be used for its entire life and is affected by toner stains. A stable image can be obtained.

[0091]

As is apparent from the above description, claim 1
According to the invention described above, the surface layer film thickness is detected by a current at a portion extending in the longitudinal direction of the contact charging member, and the current value of the thinnest portion (maximum current value Imax) and a predetermined current determined in advance. By comparing with the upper limit value, it is possible to accurately detect the life of the contact charging member and prevent leakage from occurring.

According to the second aspect of the invention, the surface layer film thickness is detected by the current at a portion extending in the longitudinal direction of the contact charging member, and the current value of the thinnest portion (maximum current value Imax) is obtained.
By comparing with the upper limit value (α × Ileak) determined in advance, it is possible to detect the life of the contact charging member with high accuracy and prevent the occurrence of leaks.

According to the third aspect of the invention, the maximum current value Imax and the total average current value I are based on the criteria of the second aspect of the invention.
An effect that the accuracy of detecting the life of the contact charging member can be further improved by adding a criterion to compare ave with a value obtained by multiplying the coefficient β determined from the leak performance against the bias in the longitudinal direction of the contact charging member Is obtained.

According to the invention described in claim 4, by bringing the current detecting member into contact only during the detection, it is possible to eliminate unnecessary rubbing against the contact charging member and prolong the life of the contact charging member. Is obtained.

According to the fifth aspect of the invention, since the current detecting member also has the function of the cleaning member, it is possible to prevent the image defect due to the contamination of the contact charging member.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an image forming apparatus to which a life detection method according to a first embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view of the entire image forming apparatus to which the life detecting method according to the first embodiment of the present invention is applied.

FIG. 3 is a sectional view of a charging roller of the image forming apparatus according to the first exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a change in durability of a surface layer thickness of a charging roller.

FIG. 5 is a diagram showing the relationship between the surface layer thickness of the charging roller, the resistance, and the DC current.

FIG. 6 is a timing chart of the sequence of the life detecting method according to the first embodiment of the present invention.

FIG. 7 is a flowchart of a sequence of a life detecting method according to the first embodiment of the present invention.

FIG. 8 is a configuration diagram of a main part of an image forming apparatus to which a life detecting method according to a second embodiment of the present invention is applied.

FIG. 9 is an enlarged detailed view of the drive means for the detection member.

FIG. 10 is an enlarged detailed view of a cam portion of the driving means.

FIG. 11 is a flowchart of a sequence of a life detecting method according to a second embodiment of the present invention.

FIG. 12 is a diagram showing a change in durability of the surface layer film thickness when the film thickness variation of the charging roller is large.

FIG. 13 is a flowchart of a sequence of a life detecting method according to a third embodiment of the present invention.

FIG. 14 is a configuration diagram of a main part of an image forming apparatus to which a life detecting method according to a fourth embodiment of the present invention is applied.

FIG. 15 is a sectional view of a conventional image forming apparatus.

FIG. 16 is a partial cross-sectional view of a charging roller and a photosensitive drum showing a situation of occurrence of leakage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image bearing member) 2 Charging roller (contact charging member) 3 High voltage power source for charging 4a to 4c Current detection member 5a to 5c Detection switch 6a to 6c Current detection unit 7 Calculation unit 8 Display unit 11c Cam member 12 Current detection Member and cleaning member 12a to 12c Conductive sponge part (conductive sponge elastic body) 12d, 12e Insulating sponge part (insulating sponge elastic body)

Claims (5)

[Claims] 1. A high voltage power source for charging at least an image carrier, a contact charging member in contact with the surface of the image carrier, and a bias applied to the contact charging member to uniformly charge the surface of the image carrier. And a plurality of current detecting members which are divided in the longitudinal direction of the surface of the contact charging member and contact each other, and the maximum current value Imax among the current values detected by the current detecting members is set in advance. The method for detecting the life of a contact charging member is characterized by determining that the contact charging member has reached the end of its life when the current exceeds the predetermined upper limit value. 2. At least an image carrier, a contact charging member that contacts the surface of the image carrier, and a high-voltage power supply that uniformly charges the surface of the image carrier by applying a bias to the contact charging member. And a maximum current value Imax among the current values detected by the current detection member, wherein a plurality of current detection members are provided that are in contact with each other in the longitudinal direction of the surface of the contact charging member. When the relationship between the leakage limit current value Ileak of the contact charging member and the coefficient α determined by the individual difference in the leak performance of the contact charging member satisfies Imax ≧ α × Ileak, the contact charging member reaches the end of its life. A method for detecting the life of a contact charging member, which is characterized by determining that it is a thing. 3. A high voltage power source for charging at least an image bearing member, a contact charging member contacting the surface of the image bearing member, and a bias applied to the contact charging member to uniformly charge the surface of the image bearing member. And a maximum current value Imax among the current values detected by the current detection member, wherein a plurality of current detection members are provided that are in contact with each other in the longitudinal direction of the surface of the contact charging member. The relationship between the leak limit current value Ileak of the contact charging member and the coefficient α determined by the individual difference in the leak performance of the contact charging member satisfies Imax ≧ α × Ileak, or is detected by the current detecting member. The relation between the total average current value Iave of the current values, the coefficient β determined from the leakage performance with respect to the current value deviation in the longitudinal direction of the contact charging member, and the maximum current value Imax satisfies Imax ≧ β × Iave And when, life detection method of the contact charging member to which the contact charging member, characterized in that determined to have reached the end of its life. 4. The current detecting member is configured to be detachable from and contact with the contact charging member.
2. A method for detecting the life of a contact charging member according to 2 or 3. 5. The contact charging according to claim 1, wherein the current detecting member is configured by arranging conductive sponge elastic bodies and insulating sponge elastic bodies alternately in the longitudinal direction. How to detect the life of a member.