JP2000235299A - Charging device and image forming device - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a charging device and an image forming apparatus capable of reliably stabilizing the surface potential of a member to be charged. SOLUTION: A charging roller 21 for charging a photosensitive drum 3 by discharging, a power supply unit 23 for applying a charging voltage to the charging roller 21, a speed detecting unit 29 for detecting a surface speed of the photosensitive drum 3, a speed, The charging device 5 includes a CPU 25 that controls the voltage applied to the charging roller 21 in accordance with the detection signal of the detection unit 29. The CPU 25 includes a CPU 25 that controls the surface potential of the photosensitive drum 3 with respect to the applied voltage corresponding to the speed. The inclination is input in advance, and the CPU 25 applies a constant voltage to the charging roller 21, measures a current flowing thereby, calculates a discharge starting voltage using the current and the constant voltage, and calculates the discharge starting voltage and the discharge starting voltage. The power supply unit 23 applies the applied voltage calculated from the slope of the surface potential according to the detection signal of the speed detection unit 29 to the charging roller 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device and an image forming apparatus such as a printer, a copying machine, a facsimile and the like.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, as a charging means for an image carrier such as a photoconductor or an electrostatic recording dielectric, a charging device (not in contact with a photoconductor as an image carrier) is used. A corona discharger or the like, or a charging device (a charging roller or the like) that comes into contact with the photoconductor is used. Generally, corona dischargers are widely used, but corona dischargers require high voltage application, poor charging efficiency,
There are various problems such as generation of corona discharge products (O ₃ , NOx, etc.), and contamination of the discharge wire.

Accordingly, in recent years, a charging roller having characteristics such as low generation of ozone (ozone-less) and low applied voltage (low power) has been widely used. The charging roller is a device that brings a conductive roller portion into contact with the photoconductor, applies a voltage to the roller portion, causes the photoconductor to discharge, and charges the surface of the photoconductor to a predetermined voltage. .

[0004] The charging of the photoconductor by the charging roller is performed by discharging, but the discharging does not cause the charging of the photoconductor unless a voltage higher than a predetermined threshold is applied. That is, if the discharge start voltage from the charging roller is a voltage Vth (predetermined threshold value) at which the photoconductor starts charging, the photoconductor starts charging, and the surface potential of the photoconductor rises from the voltage Vth. start.

When the relationship between the surface potential of the photosensitive member and the discharge starting voltage (applied voltage) is represented by a graph, the relationship has a slope of 1. The surface potential of the photosensitive member has a slope of 1 with respect to the discharge voltage.
Rise at a rate of Therefore, in order to obtain the required surface potential Vd required for the image forming apparatus, the threshold Vt
A voltage Vc (Vc = Vth + Vd) obtained by adding Vd to h is initially set, and this voltage Vc is applied to the charging roller.

[0006] However, due to scraping due to the durability (aging) of the photoreceptor and the surrounding environment such as temperature and humidity, for example,
When the capacitance or electric resistance of the photoconductor or the charging roller changes, the threshold value V1 may change. In this case, the value of the initially set applied voltage Vc fluctuates (displacement occurs), so that there is a problem that image quality defects (image disturbance) such as background dirt and image density decrease occur. I do.

On the other hand, in Japanese Patent Application Laid-Open No. Hei 6-194933, an approximate value Vth1 of the threshold value Vth is measured by applying a constant current to the charging roller in advance.
Vc1 (Vc1 = Vth1 +
There is disclosed a technique for applying Vd) to a charging roller to prevent image disturbance.

[0008]

However, in an actual image forming apparatus, the surface potential and the discharge starting potential of the photoreceptor are also affected by the peripheral speed (linear velocity) of the photoreceptor and the material of the charging roller. The inclination may not be 1 in some cases. In this case, the threshold value Vth (V
th1) and the required surface potential Vd is added to Vc (Vc
There is a problem that the charge potential of the photoconductor is not reliably stabilized just by obtaining 1). If the charging potential of the photoconductor is not reliably stabilized, this may cause image quality defects.

Accordingly, an object of the present invention is to provide a charging device and an image forming apparatus capable of reliably stabilizing the surface potential of a member to be charged.

[0010]

According to a first aspect of the present invention, there is provided a charging member for charging an object to be charged by discharging, a power supply member for applying a charging voltage to the charging member, and a speed of a surface of the object to be charged. A charging device comprising: a speed detection unit for detecting; and a control unit for controlling an applied voltage to the charging member according to a detection signal of the speed detection unit. The gradient of the surface potential of the body is input in advance, the control unit applies a constant voltage to the charging member, measures the current flowing thereby, calculates the discharge starting voltage using this current and the constant voltage, An application voltage calculated from the discharge start voltage and a slope of the surface potential according to the detection signal of the speed detection unit is applied from the power supply member to the charging member.

According to the first aspect of the present invention, when charging an object to be charged, the control unit first applies a constant voltage to the charging member, measures a current flowing at this time, and determines the current and the constant current. The voltage at which the charging member starts discharging (the voltage at which the member to be charged starts charging) is calculated using the voltage and the voltage. The discharge start voltage changes depending on, for example, deterioration due to the durability (aging) of the member to be charged and environmental conditions (temperature, humidity, etc.). Since the control unit calculates the discharge start voltage, the value of the discharge start voltage is Will be appropriate.

Next, the control unit calculates the applied voltage based on the measured discharge start voltage and the slope of the surface potential according to the detection signal of the speed detection unit. The reason why the applied voltage is calculated in this manner is that the gradient of the surface potential with respect to the applied voltage changes depending on the speed of the surface of the member to be charged. Thereafter, the control unit causes the power supply member to apply the calculated applied voltage to the charging member.

Since an applied voltage corresponding to the deterioration of the member to be charged due to the durability (aging) and the change of the discharge starting voltage due to environmental conditions and the speed corresponding to the speed of the surface of the member to be charged are applied to the charging member, The surface potential of the member to be charged can be reliably stabilized.

According to a second aspect of the present invention, there is provided a charging member for charging an object to be charged by discharging, a power supply member for applying a charging voltage to the charging member, a material detecting unit for detecting a material of the charging member, and a material detecting unit. A control unit that controls an applied voltage to the charging member in accordance with a detection signal of the charging unit, wherein the control unit includes a gradient of a surface potential of the member to be charged with respect to an applied voltage corresponding to a material of the charging member. Is input in advance, the control unit applies a constant voltage to the charging member, measures a current flowing thereby, calculates a discharge starting voltage using the current and the constant voltage, and calculates the discharge starting voltage, An applied voltage calculated from a slope of a surface potential according to a detection signal of the material detection unit is applied from the power supply member to the charging member.

According to the second aspect of the present invention, when charging an object to be charged, the control unit first applies a constant voltage to the charging member, measures a current flowing at this time, and determines the current as a constant. Using the voltage, the discharge starting voltage by the charging member is calculated. The discharge starting voltage changes depending on, for example, deterioration of the member to be charged due to durability (aging) and environmental conditions (temperature, humidity, and the like). Since the control unit calculates the discharge starting voltage,
The value of the discharge starting voltage becomes appropriate.

Next, on the control date, the applied voltage is calculated based on the measured discharge starting voltage and the slope of the surface potential according to the detection signal of the material detecting section. The reason why the applied voltage is calculated in this manner is that the slope of the surface potential with respect to the applied voltage changes depending on the material of the charging member. After that, the control unit
The calculated applied voltage is applied from the power supply member to the charging member.

[0017] Since a charging voltage corresponding to the deterioration of the member to be charged due to durability (aging) and a change in the discharge starting voltage due to environmental conditions is applied to the charging member corresponding to the material of the charging member. The surface potential of the body can be reliably stabilized.

According to a third aspect of the present invention, there is provided a rotating image carrier, a charging member for charging the image carrier by discharging, a power supply member for applying a charging voltage to the charging member, and a speed of a peripheral surface of the image carrier. A charging device having a speed detection unit for detecting a voltage and a control unit for controlling an applied voltage to the charging member in accordance with a detection signal of the speed detection unit. The slope of the surface potential of the image carrier with respect to the corresponding applied voltage is input in advance, and the control unit applies a constant current to the charging member, measures the current flowing thereby, and uses this current and the constant voltage. A discharge start voltage is calculated, and an applied voltage calculated from the discharge start voltage and a gradient of a surface potential according to a detection signal of the speed detection unit is applied from the power supply member to the charging member.

According to the third aspect of the present invention, when charging the image carrier, the control unit first applies a constant voltage to the charging member, measures a current flowing at this time, and determines the current and the constant current. The voltage at which the charging member starts discharging (the voltage at which the image carrier starts charging) is calculated using the voltage. The discharge start voltage varies depending on, for example, deterioration such as abrasion due to the durability (time) of the image carrier and environmental conditions (temperature, humidity, etc.). Since the control unit calculates the discharge start voltage, the discharge start voltage is changed. Is appropriate.

Next, the control unit calculates the applied voltage based on the measured discharge start voltage and the slope of the surface potential corresponding to the detection signal of the speed detection unit. The reason why the applied voltage is calculated in this manner is that the slope of the surface potential with respect to the applied voltage changes depending on the speed of the peripheral surface of the image carrier. Thereafter, the control unit causes the power supply member to apply the calculated applied voltage to the charging member.

Since an applied voltage corresponding to the speed of the peripheral surface of the image bearing member is applied to the charging member in addition to the deterioration of the image bearing member due to durability, such as abrasion due to durability, and the change of the discharge starting voltage due to environmental conditions. In addition, the surface potential of the image carrier can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

According to a fourth aspect of the present invention, there is provided a rotating image carrier, a charging member for charging the image carrier by discharging, a power supply member for applying a charging voltage to the charging member, and a material for detecting the material of the charging member. A charging unit having a detection unit and a control unit that controls a voltage applied to the charging member in accordance with a detection signal of the material detection unit. The gradient of the surface potential of the image carrier with respect to the applied voltage is input in advance, and the control unit applies a constant current to the charging member, measures the current flowing thereby, and discharges using the current and the constant voltage. A starting voltage is calculated, and an applied voltage calculated from the discharge starting voltage and a slope of a surface potential according to a detection signal of the material detection unit is applied from the power supply member to the charging member.

According to the fourth aspect of the invention, when charging the image carrier, the control unit first applies a constant voltage to the charging member, measures a current flowing at this time, and determines the current and the constant current. Using the voltage, the discharge starting voltage by the charging member is calculated. The discharge starting voltage is, for example, the deterioration such as abrasion due to the durability (time) of the image carrier, or environmental conditions (temperature, humidity, etc.)
However, since the control unit calculates the discharge start voltage, the value of the discharge start voltage becomes appropriate.

Next, the control unit calculates an applied voltage based on the measured discharge start voltage and the slope of the surface potential according to the detection signal of the material detection unit. The reason why the applied voltage is calculated in this manner is that the slope of the surface potential with respect to the applied voltage changes depending on the material of the charging member. After that, the control unit
The calculated applied voltage is applied from the power supply member to the charging member.

[0025] Since an applied voltage corresponding to the material of the charging member is applied to the charging member in addition to the deterioration such as collapse due to the durability (aging) of the image carrier and the change of the discharge starting voltage due to environmental conditions, The surface potential of the image carrier can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment will be described in detail with reference to the accompanying drawings. FIG. 1 is a laser beam printer (image forming apparatus) according to a first embodiment.
It is a block diagram which shows schematically. The laser beam printer 1 includes a photosensitive drum (charged body) 3 as an image carrier,
A charging device 5 for charging the photosensitive drum 3; a laser beam scanner 7 for exposing the photosensitive drum 3 to light; a developing device 9 for developing the electrostatic latent image on the photosensitive drum 3 as a toner image; The image forming apparatus includes a transfer roller 11 that presses the toner image onto the transfer material P by pressing the transfer member 3 and a fixing device 12 that fixes the toner image on the transfer material P.

The photosensitive drum 3 has a thickness of 25 mm on the peripheral surface of the cylindrical base 13 made of aluminum material.
A μm charge transport layer (CT layer) 15 is formed. Although not shown, a basic layer and a charge generation layer are formed between the charge transport layer 15 and the base 13. In this embodiment, the photosensitive drum 3 has a diameter of about 30 mm.
Cylindrical OPC photoreceptor, and an arrow X about the central axis
It is rotationally driven at a predetermined process speed (peripheral speed) in the direction.

In the present embodiment, the peripheral speed of the photosensitive drum 3 can be changed under the control of a CPU 29 described later, and the peripheral speed at this time is approximately 180 mm /
sec. Note that the diameter and the peripheral speed of the photosensitive drum 3 are not limited to the above numerical values.

The peripheral surface of the photosensitive drum 3 is uniformly charged (negatively charged in the present embodiment) by a charging device 5 described later, and a laser beam scanner 7
Is irradiated (scanning exposure) with a laser beam L whose image has been modulated. The potential of the exposed portion is attenuated by the laser beam L output from the laser beam scanner 7 to form an electrostatic latent image. In the present embodiment, the required surface potential Vd of the photoconductor drum 3 is approximately 900 V, and the charging device 5 performs charging such that the surface potential Vd of the photoconductor drum 3 becomes approximately 900 V. Will be described later).

When the electrostatic latent image on the photosensitive drum 3 reaches a developing portion of the developing device 9 facing the developing device 17 with the rotation of the photosensitive drum 3, charged toner is supplied from the developing device 17. A toner image is formed by reversal development. In the present embodiment, the developing device 9 employs a two-component developing system, and the electrostatic latent image on the photosensitive drum 3 is subjected to reversal development with non-magnetic toner, and the exposed portion is Visualized as an image.

When the toner image reaches a nip portion (transfer portion) between the photosensitive drum 3 and the transfer roller 11, the guide plate 1 is fed from a sheet feeding device (not shown) at the same time.
The transfer material P fed via the printer 9 is supplied to a transfer portion. Transfer material P is supplied to the transfer site (feeded)
Then, a predetermined voltage (a polarity opposite to that of the toner image) is applied to the transfer roller 11 at a predetermined timing by a power supply unit (HTV) 23 described later, and the toner image is transferred from the surface of the photosensitive drum 3 to the transfer material P. You. Although the voltage applied to the transfer roller 11 is not particularly limited, in the present embodiment, the transfer is performed by applying a voltage of approximately 3 kV to the transfer roller 11.

The transfer material P to which the toner image has been transferred is conveyed to the fixing device 12, where the toner image is fixed by the fixing device 12, and is discharged outside the apparatus. On the other hand, the toner remaining on the peripheral surface of the photosensitive drum 3 without being transferred is scraped off by, for example, a urethane counter blade (cleaning blade) 20, and the toner is scraped off (the surface is cleaned). The body drum 3 prepares for the next image formation.

The charging device 5 includes a charging roller (charging member) 2
1, an HTV (power supply unit) 23 as a power supply member, and a CPU
(Control unit) 25. It should be noted that reference numeral 27 in FIG.
Denotes an ammeter, which measures a current flowing from the power supply unit 23 to the charging roller 21.

The charging roller 21 is in contact with the peripheral surface of the photosensitive drum 3, and rotates in the direction of arrow Y following the rotation of the photosensitive drum 3. The charging roller 21 has a two-layer structure having a high resistance layer on the peripheral surface (surface). For example, when a pinhole is formed in the photosensitive drum 3, the charging voltage is concentrated on this portion, and the charging roller 21 To prevent the surface potential from dropping, resulting in poor charging of the horizontal streaks. Note that the charging roller 21 may not be in contact with the photosensitive drum 3.

The charging roller 21 applies a charging bias (charging voltage), which is a DC voltage, to the photosensitive drum 3 by applying an applied voltage from the power supply unit 23. As a result, the peripheral surface of the photosensitive drum 3 is uniformly charged to a predetermined polarity and potential. The power supply unit 23 applies a predetermined voltage to the transfer roller 11 and the charging roller 21 under the control of the CPU 25.

The CPU 25 controls the linear velocity (peripheral velocity) of the photosensitive drum 3, the applied voltage (DC voltage) of the laser beam scanner 7, and the power supply unit 23. The CPU 25
It has a speed detection unit 29, and this speed detection unit 29
The linear speed switching signal from the CPU 25 is detected.

The CPU 25 calculates the charging start voltage of the photosensitive drum 3 (discharge starting voltage of the charging roller 21) Vth. Calculation of charging start voltage (discharge starting voltage) Vth under control of CPU 25, and charging start voltage Vt
The reason for calculating h will be described below.

FIG. 2 is a graph in which the horizontal axis indicates the voltage value V of the charging start voltage Vth and the vertical axis indicates the current value μA.
FIG. 3 is a graph illustrating the calculation of the charging start voltage Vth by the CPU 25.

When a DC voltage is applied to the charging roller 21, the applied voltage is the charging start voltage Vt of the photosensitive drum 3.
Charging starts when h (threshold) or more. The reason why the charging start voltage Vth is constant is, for example, the deterioration (CT) due to the environment (temperature, humidity, etc.) and the durability (aging) of the photosensitive drum 3.
This is the case where the scraping of the layer 15 is ignored. In this case, the CPU 25 sets the charging start voltage Vth of the photosensitive drum 3 to the surface potential Vd = 9 required by the photosensitive drum 3.
A voltage obtained by adding 00V may be calculated, and this may be used as the applied voltage Vc of the power supply unit 23 (Vc = Vth + Vd).

However, actually, as shown in FIG. 2 and Table 1, when the environment is changed or when the CT of the photosensitive drum 3 is changed.
When the layer 15 is scraped, the charging start voltage Vth changes. In addition, Table 1 shows that the charging start voltage Vth in the initial state of the CT layer 15 and the state after the CT layer 15 has been shaved (after endurance),
And normal temperature and normal humidity indicated by N / N (for example, 23 ° C., 65% R
H) state and low temperature and low humidity indicated by L / L (for example, 15 ° C., 1
This is data obtained by experimentally obtaining the charging start voltage Vth in the state of 0% RH.

[0041]

[Table 1]

As is apparent from Table 1, there is a difference of 160 V between the charging start voltage Vth after endurance in the N / N environment and the initial charging start voltage Vth in the L / L environment. For example, the CPU 25 determines that the charging start voltage V
When th is set to the initial state of the N / N environment (Vth = 640) and constant voltage control is performed, the surface potential Vd of the photosensitive drum 3 becomes significantly high in the L / L environment, and The concentration will be lower.

Therefore, in this embodiment, the CPU 25
Calculates the charging start voltage Vth of the photosensitive drum 3 from the applied voltage applied to the charging roller 21 and the charging current flowing thereby.

More specifically, the CPU 25 first sets the surface potential of the photosensitive drum 3 to zero by exposing the laser beam scanner 7 to an image. This is because the relationship between the charging voltage and the charging current is not clear unless the surface potential of the photosensitive drum 3 is a certain value.

After setting the surface potential of the photosensitive drum 3 to 0,
As shown in FIG. 3, the charge start voltage (discharge start voltage) Vt
The two voltages V1 and V2 of h or more are applied to the charging roller 21, and the currents Ia and Ib flowing through the charging roller 21 are measured. FIG.
In the graph, the point A indicates the discharge starting voltage Vth,
The relationship between the currents Ia and Ib flowing when V1 and V2 are applied is as follows.
It is represented by the following equation.

[0046]

(Equation 1)

That is, in the above equation (1), when I = 0, V is the discharge starting voltage Vth.
The PU 25 calculates a discharge start voltage (charge start voltage) Vth. The CPU 25 measures the voltage applied to the charging roller 21 and the current flowing therethrough to measure the charging start voltage V
Since th is calculated, it is not necessary to provide a surface potential measuring device or the like of the photosensitive drum 3 in the main body of the laser beam printer 1, so that the number of parts can be reduced and the apparatus can be downsized.

On the other hand, as shown in FIG. 4, the inclination α of the surface potential with respect to the applied voltage according to the linear velocity of the photosensitive drum 3 is input to the CPU 25 in advance. CPU25
Calculates the voltage Vc to be applied to the charging roller 21 using the slope α and the above-described discharge start voltage Vth. C
The following describes the calculation of the applied voltage Vc using the gradient α and the discharge start voltage Vth under the control of the PU 25, and the reason for using the gradient α. FIG. 4 is a graph in which the horizontal axis represents the applied voltage V of the power supply unit 23 and the vertical axis represents the surface potential V of the photosensitive drum 3. Represents the relationship.

When a DC voltage is applied to the charging roller 21, similarly to the above case, for example, the deterioration (CT) due to the environment (temperature, humidity, etc.) and the durability (time) of the photosensitive drum 3 (CT)
When the scraping of the layer 15 is neglected, the surface potential of the photosensitive drum 3 is the same as the increase in the applied voltage from the application start voltage Vth (slope T = 1), as shown by the slope T in FIG. ) To increase. In this case, the CPU 25 calculates a voltage obtained by adding the charging start voltage Vth of the photoconductor drum 3 to the surface potential Vd = 900 V required for the photoconductor drum 3, and calculates the applied voltage Vc (Vc = Vc = Vth +
Vd).

However, in practice, the peripheral speed of the photosensitive drum 3, that is, the speed (linear velocity) of the surface of the photosensitive drum 3
As a result, the surface potential of the photosensitive drum 3 with respect to the applied voltage becomes
In some cases, the inclination T does not occur. In this case, even if the charging start voltage Vth is appropriate, the slope of the surface potential Vd is different, and as a result, the value of the applied voltage Vc of the power supply unit 23 becomes higher or lower than a predetermined value. As a result, poor image quality may occur. Therefore, in the present embodiment, the CPU 25 performs the calculation represented by the following equation using the previously input gradient α.

[0051]

(Equation 2)

That is, the CPU 25 calculates the applied voltage Vc of the power supply unit 23 by performing the calculation according to the above equation (2) using the inclination α based on the speed switching signal from the speed detection unit 29.

Next, the operation of the first embodiment based on the above-described configuration will be described. The photosensitive drum 3 is driven to rotate at a linear velocity of about 180 mm / s (inclination α = 0.9 at this time) based on a signal from the speed detection unit 29, and performs image formation in the above-described steps. The environment at this time is N /
N, the photosensitive drum 3 has already passed a large number of transfer materials P, and the CT layer 15 of the photosensitive drum 3
It is shaved to 5 μm.

After completion of the image formation, the CPU 25 performs image exposure with the laser beam scanner 7 on the photosensitive drum 3 whose surface has been cleaned by the cleaning blade 20, and makes its surface potential substantially 0V. Then, CP
U25 is supplied to the power supply unit 23 as approximately 1200 V, V2 as V1.
About 1800 V is applied, and the currents Ia = 30 μA and Ib = 60 μA flowing at these times are measured, respectively. Using these V1, V2, Ia, and Ib, the CPU 25 performs the calculation according to the above equation (1) to calculate the charging start voltage Vth = 600V.

Next, the CPU 25 determines the linear velocity (about 180 mm) of the photosensitive drum 3 based on a signal from the speed detector 29.
/ S), the above-described equation (2) is used to calculate using the previously input slope α = 0.9. That is, a value obtained by multiplying the surface potential Vd = 900 V required for the photosensitive drum 3 by 1 / α, Vd / α = 818 V, and the above-described Vth = 600
By adding V, an applied voltage Vc = 1418 V is calculated.
The inclination α is not limited to this, and the inclination is different depending on the linear velocity of the photosensitive drum 3.
Needless to say, the number has been input to 25. afterwards,
The CPU 25 supplies the applied voltage Vc = 141 to the power supply unit 23.
8 V is applied to the charging roller 21.

When an image was actually formed with the applied voltage Vc = 1418 V, a good image could be obtained.
The surface potential of the photosensitive drum 3 at this time is approximately 890 V, and the surface potential Vd required by the photosensitive drum 3 is 900
A value close to V was obtained.

On the other hand, when the present invention is not used and the calculation is performed with the slope α of the surface potential of the photosensitive drum 3 with respect to the applied voltage as the slope T in FIG. 4, Vth = 60
Vd / α (α = T = 1) = 900 V was added to 0 V to calculate an applied voltage Vc = 1500 V. In this case, the surface potential of the photosensitive drum 3 becomes approximately 980 V,
The potential of the image portion increased, and the image density became low (bright).

As described above, the applied voltage Vc corresponding to the deterioration of the photosensitive drum 3 due to the durability (aging) and the change of the discharge starting voltage Vth due to environmental conditions and the applied voltage Vc corresponding to the speed of the surface of the photosensitive drum 3 are charged. Since the voltage is applied to the roller 21, the surface potential of the photosensitive drum 3 can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

Next, a description will be given of a second embodiment. In the description, portions having the same functions and effects as those described above will be denoted by the same reference numerals and description thereof will be omitted. FIG. 5 is a configuration diagram schematically showing a laser beam printer according to a second embodiment. FIG. 6 is an enlarged perspective view showing the vicinity of a roller shaft of a charging roller.
Is a graph in which the horizontal axis represents the applied voltage V of the power supply unit 23 and the vertical axis represents the surface potential V of the photosensitive drum 3, and shows the relationship between the applied voltage V and the surface potential V obtained experimentally. ing.

In the second embodiment, the CPU 25 determines the applied voltage V of the power supply unit 23 based on the gradient α1 of the surface potential with respect to the applied voltage according to the material of the charging roller 21 (see FIG. 7).
c is calculated.

The charging device 5 has a width detection sensor (material detection unit) 31. The width detection sensor 31 is formed on the roller shaft 21 a of the charging roller 21. ) Is detected. FIG.
As shown in the figure, the width of the roller shaft 21a according to the material of the charging roller 21 is determined in advance, and the inclination α corresponding to this width is determined.
1 is input to the CPU 25.

When a plurality of charging rollers of different materials are used, grooves of different widths are formed on the roller shaft of each charging roller, and the surface potential of the photosensitive drum 3 is determined by the material of the charging roller according to the width. May be input to the CPU.

The CPU 25 calculates the voltage Vc to be applied to the charging roller 21 using the gradient α1 and the above-described discharge start voltage Vth. The inclination α under the control of the CPU 25
Next, the calculation of the applied voltage Vc using 1 and the discharge start voltage Vth, and the reason for using the gradient α1 will be described.

When a DC voltage is applied to the charging roller 21, similarly to the above-described case, for example, the deterioration (CT) due to the environment (temperature, humidity, etc.) and the durability (time) of the photosensitive drum 3 (CT).
When the scraping of the layer 15 is ignored, the surface potential of the photosensitive drum 3 is the same as the increase in the applied voltage from the application start voltage Vth (slope T = 1), as shown by the slope T in FIG. ) To increase. In this case, the CPU 25 calculates a voltage obtained by adding the charging start voltage Vth of the photoconductor drum 3 to the surface potential Vd = 900 V required for the photoconductor drum 3, and calculates the applied voltage Vc (Vc = Vc = Vth +
Vd).

However, actually, the surface potential of the photosensitive drum 3 with respect to the applied voltage depends on the material of the charging roller 21.
In some cases, the inclination T does not occur. In this case, even if the charging start voltage Vth is appropriate, the slope of the surface potential is different, and as a result, the value of the applied voltage Vc of the power supply unit 23 becomes higher or lower than a predetermined value. In some cases, poor image quality may occur. Therefore, in the present embodiment, the CPU 25 calculates the applied voltage Vc of the power supply unit 23 by performing the calculation according to the above equation (2) using the previously input gradient α1.

In the present embodiment, the CT layer 15 is formed under the N / N environment by using the charging roller 21 made of an elastomer resin (the inclination α1 = 0.8 at this time).
The above-described control was performed using the photosensitive drum 3 cut to 5 μm.

After completion of the image formation, the CPU 25 performs image exposure with the laser beam scanner 7 on the photosensitive drum 3 whose surface has been cleaned by the cleaning blade 20 to reduce the surface potential to approximately 0V. Then, CP
U25 is supplied to the power supply unit 23 as approximately 1200 V, V2 as V1.
About 1800 V is applied, and the currents Ia = 30 μA and Ib = 60 μA flowing at these times are measured. Using these V1, V2, Ia, and Ib, the CPU 25 performs the calculation according to the above equation (1) to calculate the charging start voltage Vth = 600V.

Next, the CPU 25 sets the width detection sensor 31
The inclination α1 = 0.8 previously input according to the material (elastomer-based resin) of the charging roller 21 based on the detection signal from
Is used to perform the calculation according to the above equation (2). That is, the surface potential Vd required by the photosensitive drum 3 is set to 900 V,
/ Α1 multiplied by Vd / α1 = 1125V, and the above-mentioned V
th = 600V, and the applied voltage Vc = 1725V
Is calculated. Note that the inclination α1 is not limited to this, and the value varies depending on the material of the charging roller 21, and it is needless to say that this different value is also input to the CPU 25.
Thereafter, the CPU 25 sends the applied voltage V
c = 1725 V is applied to the charging roller 21.

When an image was actually formed with the applied voltage Vc = 1725 V, a good image could be obtained.
At this time, the surface potential of the photosensitive drum 3 was approximately 890 V, and a value close to the voltage Vd required for the photosensitive drum 3 = 900 V was obtained.

On the other hand, without using the present invention, when the inclination α1 of the surface potential of the photosensitive drum 3 with respect to the applied voltage is calculated as the inclination T in FIG. 7, Vth = 6
The applied voltage Vc = 1500 V was calculated by adding Vd / α1 (α1 = T = 1) = 900 V to 00V. In this case, the surface potential of the photosensitive drum 3 became approximately 770 V, the potential of the image portion dropped, and the image density became high (dark).

As described above, the applied voltage Vc corresponding to the deterioration of the photosensitive drum 3 due to the durability (aging) and the change of the discharge starting voltage Vth due to the environmental conditions, and the applied voltage Vc corresponding to the material of the charging roller 21 are applied to the charging roller 21. Since the voltage is applied, the surface potential of the photosensitive drum 3 can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, as the image carrier, the photosensitive drum 3
However, the present invention is not limited to this, and may be an intermediate transfer member, a photosensitive belt, or the like. In addition, the photoreceptor drum 3 which is an image carrier is used as a member to be charged.
It is not limited to this.

Further, in the first embodiment, the linear velocity of the photosensitive drum 3 is detected by a signal from the speed detecting unit 29. For example, the photosensitive drum 3 may be detected by using an encoder provided separately from the CPU 25. The linear velocity of the drum 3 may be detected.

In the second embodiment, what is formed on the roller shaft 21a of the charging roller 21 is not limited to a groove, but may be any shape such as a triangle, a square, a circle, and the like. What is necessary is just to detect 31. Further, the material detecting unit is not limited to the above-described width detecting sensor, but may be any sensor that can detect the material of the charging roller 31.

Although the present invention has been applied to the laser beam printer 1, the present invention is not limited to this.
The same operation and effect can be obtained even when applied to a facsimile or the like.

[0076]

According to the first aspect of the present invention, the applied voltage corresponding to the deterioration of the member to be charged due to durability (aging), the change of the discharge starting voltage due to environmental conditions, and the speed of the surface of the member to be charged. Is applied to the charging member, so that the surface potential of the member to be charged can be reliably stabilized.

According to the second aspect of the present invention, it is possible to cope with deterioration due to durability (aging) of the member to be charged and a change in the discharge starting voltage due to environmental conditions, and to apply an applied voltage corresponding to the material of the charging member to the charging member. Since the voltage is applied, the surface potential of the member to be charged can be reliably stabilized.

According to the third aspect of the present invention, the applied voltage corresponding to the speed of the peripheral surface of the image bearing member can be controlled in response to the deterioration such as abrasion due to the durability of the image bearing member, the change in the discharge starting voltage due to environmental conditions, and the like. Since the voltage is applied to the charging member, the surface potential of the image carrier can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

According to the fourth aspect of the present invention, the applied voltage corresponding to the material of the charging member can be reduced while responding to the deterioration such as collapse due to the durability (aging) of the image carrier and the change of the discharge starting voltage due to environmental conditions. Since the voltage is applied to the charging member, the surface potential of the image carrier can be reliably stabilized. Therefore, the occurrence of image quality defects can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a laser beam printer according to a first embodiment.

FIG. 2 is a graph showing a relationship between an applied voltage and current according to changes in temperature and humidity.

FIG. 3 is a graph showing a relationship between an applied voltage and a current.

FIG. 4 is a graph illustrating a relationship between a surface potential of the photosensitive drum and an applied voltage according to a speed of the surface of the photosensitive drum.

FIG. 5 is a configuration diagram schematically showing a laser beam printer according to a second embodiment.

FIG. 6 is an enlarged perspective view showing the vicinity of a shaft of a charging roller.

FIG. 7 is a graph showing a relationship between a surface potential of a photosensitive drum and an applied voltage according to a material of a charging roller.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser beam printer (image forming apparatus) 3 photoconductor drum (image carrier, charged object) 5 charging device 21 charging roller (charging member) 23 HTV (power supply member) 25 CPU (control unit) 29 speed detection unit 31 width Detection sensor (material detection part)

Claims (4)

[Claims] 1. A charging member for charging a member to be charged by discharging, a power member for applying a charging voltage to the charging member, a speed detector for detecting a speed of a surface of the member to be charged, and a detection signal of the speed detector. A control unit for controlling an applied voltage to the charging member according to the control unit, wherein a gradient of the surface potential of the member to be charged with respect to the applied voltage according to the speed is input in advance, The control unit applies a constant voltage to the charging member, measures a current flowing thereby, calculates a discharge start voltage using the current and the constant voltage, and outputs the discharge start voltage and a detection signal of the speed detection unit. A charging device characterized in that an applied voltage calculated based on a slope of a corresponding surface potential is applied from a power supply member to a charging member. 2. A charging member for charging an object to be charged by discharging, a power supply member for applying a charging voltage to the charging member, a material detecting section for detecting a material of the charging member, and a detecting signal from the material detecting section. A control unit for controlling an applied voltage to the charging member, wherein the control unit is input in advance with a gradient of a surface potential of the member to be charged with respect to an applied voltage corresponding to a material of the charging member, The control unit applies a constant voltage to the charging member, measures a current flowing thereby, calculates a discharge start voltage using the current and the constant voltage, and outputs the discharge start voltage and a detection signal of the material detection unit. The applied voltage calculated by the slope of the corresponding surface potential is
A charging device characterized by applying a voltage from a power supply member to a charging member. 3. A rotating image carrier, a charging member for charging the image carrier by discharging, a power supply member for applying a charging voltage to the charging member, and a speed detecting unit for detecting a speed of a peripheral surface of the image carrier. A control unit that controls a voltage applied to the charging member in accordance with a detection signal of the speed detection unit. The gradient of the surface potential of the body is input in advance, the control unit applies a constant current to the charging member, measures the current flowing thereby, calculates a discharge starting voltage using the current and the constant voltage, An image forming apparatus, wherein an applied voltage calculated from the discharge start voltage and a gradient of a surface potential according to a detection signal of a speed detection unit is applied from a power supply member to a charging member. 4. A rotating image carrier, a charging member for charging the image carrier by discharge, a power supply member for applying a charging voltage to the charging member, a material detecting section for detecting a material of the charging member, and a material detecting section. A control unit that controls a voltage applied to the charging member in accordance with the detection signal, wherein the control unit includes an image carrier for an applied voltage corresponding to a material of the charging member. The control unit applies a constant current to the charging member, measures a current flowing thereby, calculates a discharge starting voltage using the current and the constant voltage, The applied voltage calculated by the discharge starting voltage and the slope of the surface potential according to the detection signal of the material detection unit,
An image forming apparatus, wherein a voltage is applied from a power supply member to a charging member.