JP3319881B2 - 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 electrophotographic image forming apparatus using a contact charging system.

[0002]

2. Description of the Related Art A conventional electrophotographic image forming apparatus represented by the Carlson process employs a non-contact charging method using corona discharge, which is a non-contact charging method, in order to uniformly charge a photosensitive member at a predetermined charging voltage. Although this method has been used, a large amount of ozone is generated because the discharge space is ionized to charge the photoconductor.

In recent years, a negatively charged organic photoreceptor has been used as a photoreceptor. However, a negative discharge for charging the photoreceptor generates a larger amount of ozone than a positive discharge. This has become a serious problem along with the stricter environmental standards.

[0004] In contrast to a non-contact charging method such as corona discharge, a contact charging method in which a charging member is brought into contact with a photoreceptor to perform charging is applied to a charging member in order to obtain the same charging voltage of the photoreceptor. Is lower than the discharge voltage, and the generation of ozone is very small. For this reason, an image forming apparatus using a roller or a brush-shaped contact charging member has been commercially available.

On the other hand, if the photoreceptor is used even after its life has expired, the correction based on the exposure amount and the like cannot be covered due to wear of the photoreceptor and the resulting sensitivity deterioration, and the image becomes dark. Alternatively, the thickness of the photoconductor becomes too thin, causing problems such as white spots on the image and leakage of the photoconductor due to a decrease in withstand voltage. In addition, since the image quality decreases extremely gradually, it is very difficult to notice the change. Therefore, it is very important to determine the life or conversion time of the photoconductor.

[0006] Therefore, as is generally known, a method of determining the service life based on the number of times of driving of a specific member or device, or the cumulative operation time, for example, is disclosed in Japanese Patent Application Laid-Open No. 60-173.
No. 571, a method based on the total number of copies, a method based on the total number of rotations of the photosensitive member as disclosed in JP-A-61-138267, or a method based on the total number of rotations of the photosensitive member.
As disclosed in Japanese Patent No. 1269, there has been proposed a method based on a cumulative time of passage of sheets.

[0007] Alternatively, a method for more directly detecting the wear of the photoreceptor and the state of deterioration associated therewith, for example, the method disclosed in
As described in JP-A-93964 and JP-A-62-75664, the photoreceptor is irradiated with light, the amount of reflected light is detected, and the reflectance is obtained to determine the life or replacement time of the photoreceptor. Methods have been proposed.

[0008]

However, the life determining method based on the total number of driving times and operating times of a specific member or apparatus is an indirect method that does not directly detect a decrease in the thickness of the photosensitive member. Therefore, for example, when the toner consumption changes due to the density of the screen, various factors such as a difference in the abrasion amount of the photoconductor in the cleaning unit overlap, and the variation in the life determined with respect to the actual life of the photoconductor is reduced. It was big.

On the other hand, the method of directly detecting the abrasion or the deterioration state of the photoreceptor should have less variation in principle, but the optical method using the reflectance of the photoreceptor requires cost and cost. Since the light source and the sensor must be installed in a place where they do not affect the image, there are severe restrictions, and if the light source and the sensor are soiled by toner or the like, there is a problem that correct detection cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to prevent deterioration of image quality due to abrasion of a photoreceptor with time and performance deterioration accompanying the same, and to always obtain high-quality images. I do.

[0011]

According to the present invention, there is provided an electrophotographic image forming apparatus for charging a photosensitive member by applying a voltage to the charging member in contact with the photosensitive member. The maximum applied voltage in a state where no charging current flows is defined as a charging start voltage, and the charging start voltage when the photoconductor is new is defined as an initial charging start voltage, as follows .

That is, the life of the photosensitive member is determined in advance.
The belt corresponding to the thickness of the photoconductor at the time of replacement
Above a threshold voltage set to electric starting voltage applied to the charging member
A determination means is provided for detecting whether or not the charging current flows, and determining that the life of the photosensitive member or the time for replacement has come when the charging current flows.

[0013]

[0014]

[0015]

[0016]

In the image forming apparatus constructed as described above, the determination means determines in advance that the photosensitive member has reached the end of its life or replacement time.
The charging current flows by applying a threshold voltage set to the charging start voltage corresponding to the film thickness of the photoreceptor to the charging member.
If the charging current does not flow, the photosensitive member can still be used, and if the charging current flows, it is determined that the life or the replacement time has come. Therefore, the life and replacement time can be determined very easily and surely, so that the image quality can be prevented from deteriorating and a high-quality image can always be obtained.

[0017]

[0018]

[0019]

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 3 is a schematic configuration diagram showing a configuration of a main part of a copying machine which is an embodiment of an electrophotographic image forming apparatus according to the present invention.

The copying machine shown in FIG. 3 has a photosensitive drum 1 made of a metal, for example, aluminum, the surface of which is covered with a photosensitive member 2 made of a thin film of an organic photoconductor. A charging roller 3, a developing unit 4, a transfer roller 5, a cleaning unit 6, and a charge removing lamp 7, which are charging members disposed, and a fixing unit 8 disposed on a conveyance path of the transfer paper 10 away from the photosensitive drum 1 It is configured.

A photosensitive drum 2 rotating clockwise as shown by an arrow together with a photosensitive drum 1 whose central axis is connected to the ground.
First, the surface thereof is charged by a charging roller 3 to which a predetermined voltage is applied while being driven to rotate while being in contact with the photosensitive drum 1. Next, the document illuminated by a light source such as a halogen lamp (not shown) is exposed by an image formed on the photoreceptor 2 by a copying lens, and the exposed portion is discharged to form an electrostatic latent image. You.

The formed electrostatic latent image on the photoreceptor 2 is developed by a developing roller 4 a to which a bias voltage of the developing unit 4 is applied.
Is converted into a visible toner image by the toner supplied from the printer, and the toner image is transferred by the transfer roller 5 to which a bias voltage is similarly applied, in synchronization with the peripheral speed of the photosensitive drum 1. 10 is transferred.

The toner remaining on the photoreceptor 2 after the transfer is removed by the edge 6a of the cleaning unit 6 and collected in the cleaning unit 6, and the electric charge remaining on the photoreceptor 2 is removed by a discharging lamp. The discharge of 7 completely discharges and eliminates electricity, thereby completing one cycle of image formation.

On the other hand, the toner image transferred onto the transfer paper 10 is sandwiched between a heating roller 8a and a pressure roller 8b constituting the fixing unit 8, and is fixed on the transfer paper 10 by the heat and pressure. After that, the sheet is discharged outside the copying machine by a discharge roller (not shown).

FIG. 4 is a circuit diagram showing an example of a control system of the copying machine shown in FIG. The control system shown in FIG.
An electric system including an applied voltage control circuit 21, a charging current detection circuit 22, a light quantity control circuit 23, a static elimination lamp power supply 24, and a display device 25 centered on 0, and a light quantity adjustment member 12 for adjusting an exposure amount to the photoreceptor 2. It is composed of

The CPU 10 controls the sequence of controlling the timing of turning on / off the lamp, turning on / off the voltage / current or rotating / stopping the drum / roller, and controlling the light quantity, voltage, current and the like to optimal values. Process control and
Information processing such as data calculation and storage is performed using peripheral components such as a memory.

The applied voltage control circuit 21 controls the applied voltage applied to the charging roller 3 in accordance with a command from the CPU 20. The charging current detection circuit 22 controls the applied voltage control circuit 21.
The charging current flowing through the charging roller 3 is detected according to the applied voltage.

The light amount control circuit 23 controls the light amount adjusting member 12 in accordance with a command from the CPU 20, and adjusts the amount of exposure to the photosensitive member 2 to an optimum value.

The static elimination lamp power supply 24 blinks the static elimination lamp 7 by turning on / off the supply current in response to a command from the CPU 20. The display device 25 displays the state and setting conditions of the copying machine, instructions to the operator, alarm signals, warning messages, and the like.

[0031]

[Table 1]

Table 1 shows definitions of symbols used for items such as various voltages, currents, film thicknesses and the like used below, and Table 2 shows an example of conditions in the embodiment described below. When an organic photoconductor is used as the photoconductor as shown in Table 2, both the voltage and the current take a negative value, but all of them will be described below as positive values (absolute values).

[0033]

[Table 2]

FIG. 5 is a diagram showing an example of the relationship between the applied voltage Vt (horizontal axis) and the charging voltage Vc (vertical axis) under the conditions shown in Table 2. The solid line indicates the initial state of the photosensitive member. (D
(0 = 27 μm), the hatched lines shown by broken lines show the respective characteristics when the photosensitive member reaches the limit (dsh = 18 μm).

The oblique line indicating the characteristic, that is, the characteristic straight line, moves parallel to the left as the photoconductor thickness d decreases, but the applied voltage Vt at the intersection of the characteristic straight line and the horizontal axis changes the charge in that state. Start voltage Vcs and applied voltage Vt
> In the range of charging start voltage Vcs or charging voltage Vc> 0,
The applied voltage Vt is the sum of the charging start voltage Vcs and the charging voltage Vc as shown in Expression 1, and the charging voltage Vc = 0 when the applied voltage Vt ≦ the charging start voltage Vcs.

[0036]

(Equation 1)

The charging start voltage Vcs is determined by the relative dielectric constant k of the photosensitive member.
And the film thickness d, and in the case of the contact charging system, a relational expression (experimental expression) as shown in Expression 2 is known. However, the thickness d of the photoconductor and the charging start voltage Vcs
Are μm and V, respectively.

[0038]

(Equation 2)

FIG. 6 shows the photoconductor thickness d calculated by substituting the relative dielectric constant of the photoconductor k = 3 (Table 2) into the relational expression shown in Expression 2.
FIG. 4 is a graph showing the relationship between the charging start voltage Vcs (vertical axis) and the horizontal axis (vertical axis). When the initial film thickness d0 = 27 μm, Vcs = 63.
It is 2 V, and it can be seen that when the film thickness reaches the limit dsh = 18 μm, it changes to Vcs = 565 V. According to the value of Vcs when the film thickness is at the limit value, the threshold value of the discharge starting voltage Vsh = 56
5V.

Accordingly, the photosensitive drum 1 (FIG. 3) is rotated at a peripheral speed of 120 μm / sec shown in Table 2 to turn on the neutralizing lamp 7 (exposure is performed by applying toner to the photosensitive drum in accordance with the applied voltage and each polarity of the toner). In a state where it is determined whether or not to perform exposure so as not to adhere to the drum 1, the applied voltage control circuit 21
When the threshold voltage Vsh is applied to the charging roller 3 according to FIG. 4, the charging start voltage Vcs is higher than the threshold Vsh as long as the photoconductor film thickness d does not reach the limit value. Does not flow.

As the photosensitive member wears and the film thickness d decreases, the charging start voltage Vcs decreases as shown in FIG.
When the film thickness d becomes less than the limit value dsh, it becomes less than the threshold value Vsh,
As shown in FIG. 5, the charging is started, and the charging current Ic flows even a little.

In the first embodiment of the present invention, the charging current I
The charging current detection circuit 22 detects whether or not c flows, and determines whether or not the film thickness d has reached the limit value dsh, that is, whether or not the service life has expired and the replacement time has come. FIG. 7 shows a flowchart of a routine of the first embodiment.

When the routine shown in FIG. 1 starts,
In step 1, a threshold voltage Vsh is applied to the charging roller 3 by the applied voltage control circuit 21. In step 2, the charging current detection circuit 22 detects whether or not the charging current Ic is 0 (does not flow). If it is determined that the photoconductor is still usable, the process jumps to the end.

If the result in step 2 is negative, that is, if the charging current Ic flows even slightly, it is determined that the photosensitive member has reached the end of its life.
In step 3, the display device 25 indicates that the photosensitive member has reached the end of its life or it is time to replace it, and the process ends. If there is no display device, an alarm may be emitted or the copy speed may be reduced to notify the operator that the life has expired.

In the first embodiment, a predetermined threshold voltage Vsh is applied to the charging roller 3, and the life is determined based on whether or not the charging current Ic flows. In the past, in the case of a contact charging type copying machine, the applied voltage control circuit 21 was indispensable to perform stable charging. Further, the charging current detection circuit 22 detects whether or not a current flows, and it is not necessary to detect the current value. Therefore, the cost increase is small.

In addition, since the life is determined based on the limit value of the charging start voltage Vcs where the change in the film thickness d directly affects the performance, the life or replacement time can be more reliably determined than by detecting the film thickness of the photoconductor itself. You can decide. Further, unlike an apparatus that detects a film thickness by a change in reflectance, there is no influence of contamination such as toner.

In FIG. 5, the initial value Vcs of the charging start voltage is shown.
If 0 = 630 V, the charging voltage Vc on the photoreceptor surface is 8
In order to obtain 00V (Table 2), the initial value of the applied voltage must be Vt0 = 1430V from Equation 1. Similarly, when the photoconductor thickness d reaches the limit value dsh = 18 μm (lifetime limit or replacement time), the charging start voltage Vcs becomes the threshold value Vsh = 565 V, so the appropriate applied voltage is Vt =
It becomes 1365V.

However, if the applied voltage Vt is not changed from the initial value Vt0 even if the film thickness d decreases, the charging voltage Vc becomes 1430V-565V = 865V (Equation 1) at the limit, so that the charging voltage Vc becomes The voltage exceeds 65 V, the density of the image changes, and the image quality is reduced. Charging voltage Vc
In order to keep the constant, the charging start voltage Vcs is detected and
As shown in Equation 3, it is necessary to apply a voltage obtained by subtracting the absolute value of the difference between the detected charging start voltage Vcs and its initial value Vcs0 from the initial value Vt0 of the applied voltage.

[0049]

(Equation 3)

If the exposure amount E (lux-sec) is defined as the exposure amount required to reduce the charging voltage Vc of the charged photoreceptor surface to 1/10, the exposure amount E is also equal to that of the photoreceptor. The relationship changes according to the film thickness d, and in this embodiment, the relationship becomes the relationship shown in Expression 4. The sensitivity of the photoreceptor is proportional to the reciprocal of the exposure amount.

[0051]

(Equation 4)

FIG. 7 is a diagram showing the relationship between the photosensitive member film thickness d (horizontal axis) and the exposure amount E (vertical axis) calculated by the relational expression shown in Expression 4, and the initial film thickness d0 = At 27 μm, E =
0.76 lux = sec, E = 1.01 l at the limit film thickness dsh
It can be seen that it changes to ux-sec. Limit value dsh of film thickness d =
The value of 18 μm is set by back-calculating the exposure amount E from Expression 3 because it is difficult to increase the exposure amount E to 1 lux-sec or more in a normal copying machine.

Therefore, if the exposure amount E is not changed from the initial value even when the film thickness d becomes thin due to abrasion, when the film thickness d reaches the limit value, the underexposure is 25% of the proper exposure amount. , The image density changes and the image quality deteriorates. Therefore, not only the applied voltage Vt but also the exposure amount E should be adjusted so that high quality image quality can be obtained even when the film thickness d changes.

To detect the charging start voltage Vcs, as in the first embodiment, the photosensitive drum 1 is rotated at the set peripheral speed, the discharge lamp 7 is turned on, and the exposure is performed so that the toner does not adhere. In the state where it is determined whether or not to perform the charging, the initial charging start voltage Vcs0 is applied by the applied voltage control circuit 21, for example.
The charging current Ic is detected by the charging current detection circuit 22 while gradually lowering the applied voltage Vt from the above, and the applied voltage Vt when the charging voltage Ic becomes 0 is changed to the charging start voltage Vcs.
And Conversely, the charging current Ic is increased while increasing the applied voltage Vt.
May be detected at the point where the flow starts.

As soon as the charging start voltage Vcs is detected, an appropriate applied voltage Vt can be obtained by the equation (1). FIG.
As is clear from the above, since the thickness d can be considered to be practically linear in the range of d = 27 to 18 μm, the thickness d can be easily obtained from the charging start voltage Vcs, and the obtained film is obtained. From the thickness d, an appropriate exposure amount E can be calculated by Expression 4. Furthermore, by comparing the charging start voltage Vcs with the threshold voltage Vsh, it is possible to determine whether the life has been reached.

In the reference example relating to the present invention, first, the charging start voltage Vcs is detected, and then it is determined whether or not the life has expired based on the charging start voltage Vcs. Next, if not, the applied voltage Vt and the exposure amount E are adjusted to appropriate values. FIG. 2 shows a flowchart of a routine of the reference example .

When the routine shown in FIG. 2 starts,
In step 10, the applied voltage control circuit 21 first tests the test voltage V starting from the initial value Vcs0 of the charging start voltage.
Is applied to the charging roller 3, and in step 11, the charging current detection circuit 22 detects whether or not the charging current Ic flows. If the charging current Ic flows, the process returns to step 10, and in each case, the test voltage V dropped by 5V is applied. The application is repeated up to 20 times.

In the meantime, if it is detected in step 11 that the charging current Ic stops flowing, the process proceeds to step 12 and the test voltage V at that time is set as the charging start voltage Vcs. When the test is repeated up to 20 times, the test voltage V drops to 100 V from the initial value Vcs0 to 532 V, and the charging current Ic
Means that the film thickness d is less than 15 μm. Therefore, as a practical matter, the charging current Ic stops flowing before reaching 20 times.

Subsequently, in step 13, it is determined whether or not the detected charging start voltage Vcs has become equal to or lower than the threshold voltage Vsh (565V). If it is equal to or lower than 565V, it is determined that the photosensitive member has reached the end of its life. Proceeding to 14, the display device 25 indicates that the photosensitive member has reached the end of its life or it is time to replace it, and goes to the end.

No at step 13, that is, the charging start voltage V
If cs exceeds 565 V, it is determined that the photoreceptor is still usable, and the process proceeds to step 15, where the applied voltage Vt is determined from the charging start voltage Vcs according to Expression 3, and the applied voltage Vt is determined.
t is applied to the charging roller 3 by the applied voltage control circuit 21. Incidentally, the applied voltage Vt can also be obtained by Equation 1.

Further, proceeding to step 16, solving Equation 2 as a quadratic equation of the square root of d from the charging start voltage Vcs,
The film thickness d is obtained by considering the curve shown in FIG. 6 as a straight line and solving a first-order approximation formula, and an appropriate exposure amount E is calculated from the obtained film thickness d by Expression 4.

The light amount control circuit 23 controls the light amount adjusting member 12 so that the exposure amount is adjusted to E, and the operation ends. The light amount adjusting member 12 may be, for example, a member for increasing the lighting voltage of a halogen lamp for illuminating a document (not shown) or a member for increasing the width of a slit provided in the exposure optical path.

Although this reference example appears to be more complicated than the first embodiment, it is almost the same as the first embodiment in terms of hardware, except that the number of processing steps is increased. Also, in the adjustment of the exposure amount E, for example, the control for stabilizing or varying the light amount of the halogen lamp, that is, the illuminance of the original, is also performed in the conventional copying machine, so that the increase in the cost is slight. .

Further, in addition to the effects of the first embodiment, the life is determined by detecting the charging start voltage Vcs, the control of the applied voltage Vt for keeping the charging voltage Vc constant, and the photoconductor film thickness Since the adjustment of the exposure amount E according to the change of d can be easily performed at the same time, the effect of maintaining high-quality image quality over the life of the photoconductor is extremely large.

While the copier of the contact charging type based on the electrophotographic method using a visible light source has been described above, the present invention can also be applied to an image forming apparatus such as an electronic printer using an infrared light source or a near infrared light source. Needless to say.

[0066]

As described above, the image forming apparatus according to the present invention can prevent the deterioration of the image quality due to the wear of the photosensitive member over time and the deterioration of the performance due to the wear, and can always obtain a high quality image. I can do it.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a routine according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a routine according to a reference example of the present invention.

FIG. 3 is a schematic configuration diagram showing a configuration of a main part of a copying machine according to an embodiment of the present invention;

4 is a circuit diagram showing an example of a control system of the copying machine shown in FIG.

FIG. 5 is a diagram showing an example of a relationship between an applied voltage and a charging voltage in the copying machine shown in FIG. 3;

FIG. 6 is a diagram showing an example of a relationship between a photoconductor thickness and a charging start voltage in the copying machine shown in FIG. 3;

FIG. 7 is a diagram illustrating an example of a relationship between a photoconductor thickness and an exposure amount in the copying machine illustrated in FIG. 3;

[Explanation of symbols]

1: photoconductor drum 2: photoconductor 3: charging roller (charging member) 7: static elimination lamp 20: CPU (means for determining life, charging start voltage detection means) 21: applied voltage control circuit (applied voltage control means) 22: Charge current detecting circuit 23: Light amount control circuit (exposure amount control means) Vc: Charging voltage Ic: Charging current Vt: Applied voltage Vt0: Initial applied voltage Vcs: Charging start voltage Vcs0: Initial charging start voltage Vsh: Threshold voltage E : Exposure

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Claims (1)

(57) [Claims] 1. An electrophotographic image forming apparatus in which a voltage is applied to a charging member in contact with a photoreceptor to charge the photoreceptor, wherein charging is started at a maximum applied voltage in a state where no charging current flows through the charging member. voltage advance said photosensitive member to said charging start voltage when the photoreceptor is new as the initial charge starting voltage
Thickness of the photoreceptor at the time when
Detecting whether or not the charging current flows by applying a threshold voltage set to the charging start voltage corresponding to
And, an image forming apparatus, characterized in that the charging current is provided determining means and become life or replacement timing of the photosensitive body When flow.