JP3397339B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a contact charging system.
Regarding the image forming apparatus, especially when an alternating current is superposed on the contact charging member.
The present invention relates to an image forming apparatus for charging by applying direct current . More specifically, the feeling as an object to be charged (image bearing member)
Apply a direct current to the photoconductor and the charging member in contact with the photoconductor.
Charging means for charging and a photoconductor charged by the charging means
And an exposure means for exposing the image to form an electrostatic image.
The present invention relates to an image forming apparatus. In addition, the electrostatic image on the photoconductor
Image development means and transfer the developed image on the photoconductor to the transfer material
Transfer means and fixing means for heating and fixing the transfer material after transfer
And an image forming apparatus having:

[0002]

[0003]

[0004]

2. Description of the Related Art In the image forming apparatus as described above, a corona discharge device has been widely used as a device for charging the surface of an image bearing member as a member to be charged.

The corona discharge device is effective as a means for uniformly charging the surface of a member to be charged such as an image carrier to a predetermined potential. However, there is a problem that a high voltage power source is required and undesirable ozone is generated due to corona discharge.

In contrast to such a corona discharge device, the contact type charging device for charging the surface of the body to be charged by bringing the charging member to which a voltage is applied into contact with the surface of the body to be charged as described above can reduce the power supply voltage. In addition, since it has advantages such as a small amount of ozone generated, for example, in an image forming apparatus, instead of a corona discharge device, an image carrier such as a photoconductor or a dielectric is charged, and other charging surfaces of an object to be charged are charged. It has attracted attention as a means, and research for its practical application is underway.

For example, the applicant of the present invention first proposed (Japanese Patent Application No. 62-5
No. 1492 and No. 62-230334), an oscillating electric field having a peak-to-peak voltage that is more than twice the charging start voltage of the member to be charged when a DC voltage is applied to the charging member in the contact type charging device. By forming (alternating electric field, electric field (voltage) whose voltage value periodically changes with time) between the charging member and the body to be charged, and further by using a charging member having a high resistance layer on the surface layer. It is possible to achieve uniform charging of the charged body and prevention of leakage due to pinholes, scratches, etc. on the surface of the charged body such as the photoconductor.

Further, a conductive member (conductive potential maintaining member) such as a conductive fiber bristle brush or a conductive elastic roller as a charging member is brought into contact with the member to be charged, and a DC voltage is applied from the outside to the member to be charged. There is also one in which electric charge is directly injected into the surface to charge the surface of the body to be charged to a predetermined potential.

FIG. 20 is a cross-sectional view of a schematic structure of an example of the contact type charging device.

Reference numeral 1 is a body to be charged. In this example, it is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive member). The photoreceptor 1 of this example includes a conductive base layer 1b such as aluminum,
The photoconductive layer 1a formed on the outer surface is used as a basic constituent layer.

Reference numeral 2 is a charging member. This example is a roller type (hereinafter referred to as a charging roller). The charging roller 2 is composed of a central cored bar 2c, a conductive layer 2b formed on the outer periphery thereof, and a resistance layer 2a formed on the outer periphery thereof.

In the charging roller 2, both ends of the core metal 2c are rotatably supported by bearing members (not shown), and the charging roller 2 is disposed in parallel with the drum type photosensitive member 1 and is pressed on the surface of the photosensitive member 1 by pressing means (not shown). The photoconductor 1 is pressed against it with a predetermined pressing force, and is driven to rotate as the photoconductor 1 is rotationally driven. It is also possible to attach a gear or the like and transmit the driving force from the motor for forced rotation driving.

Reference numeral 3 denotes a bias applying power source for the charging roller 2. The power source 3 and the core metal 2c of the charging roller 2 are electrically connected, and a predetermined bias is applied to the charging roller 2 by the power source 3. Although only a DC voltage may be applied as the bias, it is preferable to apply an oscillating voltage in which the DC voltage is superimposed on the AC voltage as described above.

When the photosensitive member 1 as the member to be charged is rotationally driven, the photosensitive member 1 is pressed by the photosensitive member 1 and is charged by the charging roller 2 as a charging member to which a bias voltage is applied.
The outer peripheral surface is charged with a predetermined polarity and potential.

As shown in FIG. 1, which will be described later, in addition to the charging roller 2 as the charging means, an exposing means, a developing means, a transferring means, a cleaning means, an image fixing means and the like are required around and around the photosensitive member 1. The image forming process equipment is provided and the image forming mechanism is configured to execute image formation, but these process equipments are omitted in this figure.

[0016]

In the image forming apparatus as described above, the outer peripheral surface of the photoconductor is scraped by the cleaning blade of the cleaning means or the developer as the number of times of image formation increases. Then, the charging characteristic changes due to a change in equivalent capacitance due to a decrease in the thickness (layer thickness, film thickness) of the photoconductor.

In particular, when the charging means applies a contact type DC voltage, it is greatly affected by the change in the capacity of the photoconductor.
That is, when the number of times image formation is used increases and the film thickness of the photoconductor decreases, the direct current flowing through the charging roller increases and the surface potential of the outer peripheral surface of the photoconductor rises. Also, when the film thickness of the photoconductor is reduced and the surface potential is increased, the development contrast is increased and the development image density is increased, and at the same time, sufficient reverse contrast cannot be obtained for the potential of the white image. There was a problem in that it was thinly developed to give a "fog" image.

That is, when the film thickness of the photoconductor is decreased, the surface potential is increased and the bright portion potential of the surface potential is also increased accordingly. Further, since the sensitivity of the photoconductor decreases as the film thickness decreases, the surface potential corresponding to the white original, that is, the light portion potential does not drop sufficiently. Due to the above-mentioned two phenomena, the potential of the bright part is greatly increased, and the surface potential contrast between the black original and the white original is narrowed. The contrast was not obtained, and there was a problem that the light potential portion was thinly developed with the developer to form a “fog” image.

Even when it is adjusted so as not to be covered by the developing bias or the exposure lamp voltage (= the exposure amount of the light image irradiation), it is necessary to secure a wide adjustment range, so that the adjustment range is wide. Therefore, it was a factor of increasing the cost of power supplies.

Further, in an image forming apparatus having a structure in which an appropriate image forming condition is calculated by automatic control, it is difficult to optimize and adjust the appropriate image forming condition because the surface potential of the photoconductor changes, and the number of image forming times is increased. After a certain number of times, the fog image tended to be gradually generated.

In order to avoid this phenomenon, a surface potential sensor or the like for detecting the surface potential of the photoconductor is required, which greatly increases the cost, complicates and enlarges the apparatus, and is small and low in size. This has been a major obstacle in developing a high-priced image forming apparatus.

The resistance value of the resistance layer 2a of the charging member 2 is likely to change due to factors such as environmental humidity and progress of durability. Therefore, the surface potential of the photoconductor fluctuates, which is one of the factors that hinder stable formation of image density and image quality.

In addition, in order to deal with the uneven density of the photoconductor with respect to the pinhole, a method of detecting the voltage when a constant current is applied and correcting the voltage due to the resistance variation of the charging member is suitable. , The detection range of voltage is too wide for the change in the thickness of the photoconductor due to durability, and the detection device is expensive and large in size. And it was an obstacle to low prices.

The present invention is an image forming apparatus using a contact charging system.
In regard to the arrangement, no alternating current is superposed on the contact charging member.
An image forming apparatus that applies a direct current to charge an image forming apparatus eliminates the above-mentioned problems , that is, a photoconductor due to durability.
Film thickness change, charging member durability change, charging member resistance layer
Regardless of environmental changes, there is no shortage of charge and there is always sufficient image density.
The purpose is to maintain the degree and image quality .

[0025]

The present invention is an image forming apparatus having the following configuration.

(1) Charging the surface of the body to be charged
Image information is included on the surface of the charged body
Applying an image formation process that includes the step of irradiating a dark image
An image forming apparatus for performing image formation, wherein a belt of the charged body
The electric treatment means is a charging member to which only a DC voltage is applied.
Contact-type charging device that charges the surface of the body to be charged by contacting it with an electric body
And the charging member corresponds to the non-image forming area of the body to be charged.
The charging member is controlled at a constant DC voltage while
The amount of direct current is detected, and the charging member displays an image of the body to be charged.
DC current detected above when it corresponds to the formation area
Therefore, even if the thickness of the layer to be charged decreases, it is almost constant.
In order to secure the surface potential of the charged body of
As the amount of flowing current increases, the DC voltage output decreases
Corrected DC voltage is applied to the charging member to regulate the DC constant voltage.
An image forming apparatus characterized by being controlled .

(2) The temperature of the fixing roller of the image fixing device is special.
When the image forming device is ready for operation below a certain temperature
Only the charging member corresponds to the non-image forming area of the body to be charged
The charging member is controlled at a constant DC voltage while
The amount of direct current is detected, and the charging member displays an image of the body to be charged.
If it corresponds to the formation area,
The image forming apparatus described in (1) is characterized in that the charging member is controlled by a constant DC voltage .

(3) The charging member has a high resistance layer on its surface.
The image forming apparatus according to (1) or (2), which is a conductive charging member .

(4) The charging member is the image forming area of the body to be charged.
When it is compatible with the
The image forming apparatus according to any one of (1) to (3), which also performs control for correcting an exposure amount of light image irradiation .

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[Function] As described above, when contact charging is performed, the charged
When the film thickness of the photosensitive layer, which is the body, changes, the charging start voltage also changes. When charging with direct current, the difference between the applied voltage and the charging start voltage is the charging potential, and therefore the difference in the film thickness of the photosensitive layer greatly affects the charging potential. Therefore, in the present invention, as described above, the charging member corresponds to the non-image forming area of the member to be charged.
DC voltage control of the charging member during
The amount of DC current in the
When it corresponds to the area, it corresponds to the detected DC current amount.
On the other hand, even if the thickness of the layer to be charged is reduced, it is almost constant.
In order to secure the surface potential of the charged body,
Corrected to decrease the DC voltage output as the flow rate increases
The charging member is configured to control the DC constant voltage with the corrected DC voltage . As a result, the difference between the applied voltage and the charging start voltage can be kept substantially constant. More specifically, even if there is a change in the capacity of the photoconductor due to a decrease in the thickness of the photoconductor that is a charged body of the image forming apparatus due to an increase in the number of times of image formation, the photoconductor is changed in each case. By detecting the voltage-current characteristic according to the capacitance with respect to the body thickness, the optimum correction applied voltage at that time can be applied to the charging member. In addition, optimum correction exposure can be performed on the photoconductor.

According to this, as the thickness of the photosensitive member decreases, the amount of detected current when the non-image area constant voltage is applied increases, and the voltage decrease correction is applied to the image area applied voltage value according to the increase amount, and the exposure is performed. Since the increase correction of the lamp voltage for use is added, the charging process and the image formation in the optimum state are always executed.

When the resistance value of the resistance layer of the charging member increases due to environmental humidity fluctuations and durability fluctuations, the amount of detected current decreases, voltage increase correction is applied to the image area applied voltage value, and the exposure lamp is used. Since the voltage drop is corrected or the voltage is set to a constant voltage, sufficient charge density and image quality can always be obtained without insufficient charging.

[0039]

【Example】

<Embodiment 1> (FIGS. 1 to 10) (1) Example of image forming apparatus FIG. 1 shows a schematic configuration of an example of an image forming apparatus according to the present invention.

Reference numeral 1 denotes an image bearing member as a member to be charged, and this embodiment is of a drum type having a conductive base layer 1b such as aluminum and a photoconductive layer 1a formed on the outer peripheral surface thereof as a basic constituent layer. It is an electrophotographic photoreceptor. It is rotationally driven around the support shaft 1d at a predetermined peripheral speed (process speed) in the clockwise direction in the drawing.

Numeral 2 is a contact charging member which is in contact with the surface of the photosensitive member 1 to uniformly perform a primary charging process on the surface of the photosensitive member to a predetermined polarity and potential. In this example, a contact type charging member is a roller type (charging roller). The charging roller 2 is composed of a central core metal 2c, a conductive layer 2b formed on the outer periphery thereof, and two resistance layers 2a ₂ and 2a ₁ sequentially formed on the outer periphery thereof, and both ends of the core metal 2c are not shown. The bearing member is rotatably rotatably arranged in parallel with the drum type photoconductor 1 and is pressed against the surface of the photoconductor 1 by a pressing means (not shown) with a predetermined pressing force to rotate the photoconductor 1. Along with the rotation.

Then, a predetermined direct current (DC) bias is applied from the power source 3 to the cored bar 2c through the sliding contact 3a so that the peripheral surface of the rotary photosensitive member 1 is contact-charged to a predetermined polarity and potential. (Primary charging).

The surface of the photosensitive member 1 which has been uniformly charged by the charging member 2 is then subjected to the exposure L of the target image information (exposure slit exposure of the original image, laser beam scanning exposure, etc.) by the exposure means 10. An electrostatic latent image corresponding to the target image information is formed on the peripheral surface.

The exposing means 10 in the apparatus of this embodiment is a known original table fixed-optical system moving type original image forming slit exposing means. In the exposure means 10, 20 is a fixed original platen glass, O is an original document placed and set on the original platen glass with the image surface facing downward, 21 is an original pressing plate, 22 is an original illumination lamp (exposure lamp), 23 is a slit plate, 24 to
26 is a movable first to third mirror, 27 is an imaging lens, 28
Is a fixed mirror. The lamp 22, the slit plate 23, and the moving first mirror 24 move the lower surface of the original platen glass 20 from one end to the other end at a predetermined speed V, and the moving second and third mirrors 25 and 26 have a speed V / 2. Is moved and driven, and the downward document surface on the document table glass 20 is scanned from one end side to the other end side, and a document image is imaged on the surface of the rotary photoconductor 1 by slit exposure L.
To be done.

The latent image formed on the surface of the photosensitive member 1 is then developed by the developing means 1.
By 1, the toner images are sequentially visualized.
The toner image is then conveyed from the sheet feeding section (not shown) by the transfer section 12 to the transfer section between the photoreceptor 1 and the transfer section 12 at an appropriate timing in synchronization with the rotation of the photosensitive body 1. The images are sequentially transferred onto the surface of the transfer material 14. The transfer unit 12 in this example is a transfer roller, and the toner image on the surface of the photosensitive member 1 is transferred to the surface of the transfer material 14 by charging the transfer material 14 from the back with a polarity opposite to that of the toner.

The transfer material 14 to which the toner image has been transferred is separated from the surface of the photosensitive member 1 and conveyed to an image fixing means (not shown) to be subjected to image fixing and output as an image formed product. Alternatively, when the image is formed on the back side, the image is conveyed to the re-conveying unit to the transfer unit.

After the image transfer, the surface of the photosensitive member 1 is cleaned by the cleaning means 13 to remove adhering contaminants such as toner remaining after transfer, and is further discharged by the discharging exposure device 15.
It is repeatedly used for image formation.

(2) Various Examples of Charging Member 2 The roller-type charging member 2 may be driven to rotate according to the photosensitive member 1 as a charged member to be surface-moved and may be non-rotating. Alternatively, the photosensitive member 1 may be positively rotationally driven in the forward or reverse direction of the surface moving direction at a predetermined peripheral speed.

Besides the roller type, the charging member 2 can be constructed in a blade type, a block type, a rod type, a belt type or the like.

FIG. 2A shows a schematic cross-sectional view of an example of the blade type. In this case, the direction of the blade-shaped charging member 2 contacting the surface of the photoconductor 1 may be either forward or reverse to the surface movement direction of the surface of the photoconductor 1.

FIG. 2B shows a schematic cross-sectional view of an example of a block or rod shape.

In each type of charging member 2, 2c is a conductive core metal member, 2b is a conductive layer, and 2a is a resistance layer.

The block-shaped or rod-shaped roller is a rotatable roller type, and the core metal is provided without the power supply sliding contact 3a necessary for applying a bias voltage to the core metal member 2c. The lead wire leading to the power source 3 can be directly connected to the member 2c, and the electric noise that may be generated from the power feeding sliding contact 3a can be eliminated, and the space can be saved. It is also possible to adopt a configuration in which the cleaning blade of 1 is also used.

(3) Sequence FIG. 3 shows an example of the operation sequence of the apparatus shown in FIG. This example is 2
The case of continuous printing on one sheet is shown.

.. Based on the print (copy) start signal, the rotation drive of the photosensitive member 1 (hereinafter, referred to as a drum) of the apparatus which has been in the standby state until then is started to start the pre-rotation period. At the same time when the rotation of the drum 1 is started, the static elimination exposure 15 is turned on, and static electricity is discharged from one peripheral surface or more of the drum 1 in the section A1.

.. Next, the charging roller 2 which is a contact charging member
The DC bias, which is the primary charging bias for, turns on.

.. This primary charging bias begins with section B
1, constant voltage control is performed, DC current is detected during that period, and then charging roller DC corresponding to the detected DC current is detected.
Constant voltage control is performed.

The period before the image formation starts is the pre-rotation period of the drum 1, and the surface of the drum 1 during that period is the surface of the non-image forming area. Therefore, the charging roller 2 corresponds to the surface of the non-image forming area of the drum 1. The charging roller DC constant voltage control is performed in the section B1 of the pre-rotation period, and the DC current at this time is detected and the primary voltage correction (primary charging bias correction for the charging roller 2) is performed.

.. When the charging roller DC constant voltage control is started with the primary correction voltage, the first image is formed by image exposure (image forming slit exposure of the original image). The charging roller 2 corresponds to the image forming area surface of the drum 1, and the surface of the drum 1 is charged under the DC constant voltage control state.

.. A so-called drum surface between sheets until the image formation for the first print is completed and the image formation for the next second print is started is a non-image formation area surface. Then, the DC constant voltage control, the DC current detection, and the DC constant voltage control of the charging roller 2 are executed again during this sheet interval.

That is, when the printing of the first sheet is completed, the primary charging bias is set to the charging roller DC constant voltage control again in the section B2 between the sheets, the DC current is detected, and then the charging roller corresponding to the detected DC current is used. The constant voltage control is executed and the image formation for the second print is executed.

Even when three or more sheets are continuously printed, the sequence of the charging roller DC constant voltage control, DC current detection, and DC constant voltage control is similarly performed between each sheet.

.. When the image formation of the final print is completed, the drum 1 enters the post-rotation period, and in the section A2 of the post-rotation period, the static elimination exposure 15 on one circumferential surface or more of the drum 1 is performed.
Is removed and the charge is removed, and the rotation of the drum 1 and the charge removal exposure are OF
The status becomes F, and the apparatus enters the standby state until the next print start signal is input.

In the above structure, when the surface of the drum is scraped due to the durability and the film thickness of the photoconductor becomes thin, the DC constant which is made when the charging roller 2 corresponds to the surface of the non-image forming area of the drum 1 is determined. Detection D of voltage control period B1 or B2
The C current becomes high, and the charging roller 2 performs a charging process on the image forming area surface of the drum 1 under the constant voltage control of the charging roller DC with a decrease correction voltage according to the detected DC current, and image formation is executed. It

Further, especially in a low humidity environment, the resistance of the charging roller 2 rises , and the detected DC current of the charging roller DC constant voltage control in the above periods B1 and B2 becomes low. Since the charging roller 2 performs the charging process on the image forming area surface of the drum 1 under the constant voltage control of the charging roller DC with the increased correction voltage according to the detected DC current, the charging roller 2 performs the image formation. The charging potential of the drum 1 is made constant regardless of the resistance fluctuation in the environment.

(4) Voltage Correction Method Next, a method of performing optimal charging using the DC power supply 3 will be described.

First, the charging mechanism when a DC voltage is applied to the charging roller 2 by a DC power source will be described.

As the photosensitive member 1, a negative polarity OPC photosensitive drum was used. Specifically, an azo pigment is used as a CG for the photoconductor layer.
A negative polarity organic semiconductor layer (OPC) in which an L layer (carrier generation layer) and a mixture of hydrazone and a resin thereon are laminated as a CTL layer (carrier transport layer) to a thickness of 24 μm
Layer), the OPC photosensitive drum 1 is rotationally driven, the charging roller 2 is brought into contact with the surface of the OPC photosensitive drum 1, and a DC voltage V _DC is applied to the charging roller 2 to bring the OPC photosensitive drum 1 into contact with the charging roller 2 in a dark place for charging. The relationship between the surface potential V _D of the charged OPC photosensitive drum 1 after passing through the charging roller 2 and the DC voltage V _DC applied to the charging roller 2 was measured.

The line graph of 24 μm in FIG. 4A shows the measurement result. For the applied DC voltage V _DC , the charging has a threshold value for each drum film thickness as shown in FIG. 4A, the charging starts from a specific voltage, and the absolute value equal to or higher than the charging start voltage is applied. The obtained surface potential V
_{For D,} a linear relationship with a slope of 1 was obtained on the graph.

Here, the charging start voltage is defined as follows. That is, when only a DC voltage is applied to the charging member to the image carrier having a potential of 0 and the voltage is gradually increased, a graph of the surface potential of the photoreceptor as an image carrier with respect to the applied DC voltage is shown. I will write it. At this time, set the DC potential to 1
It is taken every 00V, but when the surface potential appears with respect to the surface potential 0, the first point is set to 10 points every 100V. A straight line is drawn from these 10 points by the least-squares method in statistics, and the value of the applied DC voltage when the surface potential is 0 on this straight line is the charging start voltage. The straight line in the graph of FIG. 4 is created by the above least square method.

That is, the DC voltage applied to the charging roller 2 is V
And _DC, a relationship of the surface potential V _D obtained OPC photosensitive drum 1 surface and the charge starting voltage is _{V TH, V D = V DC} -V HT ‥‥‥ (1).

The above equation (1) can be derived by using Paschen's law.

FIG. 5 shows an equivalent circuit formed by the charging roller 2 and the OPC photosensitive layer and the microscopic space Z at the contact portion between them. When the total resistance R _r of the charging roller 2 is small, the voltage drop I _D Rr caused by the current I _D flowing in the photoconductor layer 1a
Is sufficiently smaller than V _DC and can be ignored. First, R
Ignoring _r , the voltage Vg applied to the space Z is expressed by the following equation.

Vg = V _DC · Z / (L _S / K _S + Z) (2) V _DC : Applied voltage Z: Void L _S : Photoconductor layer thickness K _S : Photoconductor layer relative permittivity On the other hand, According to Paschen's law, the discharge phenomenon in the air gap Z can be approximated by the following linear expressions (3) and (4) when Z = 8 μ or more.

Vb = 312 + 6.2Z (when Vb> 0) (3) Vb = − (312 + 6.2Z) (when Vb <0) (4) Since Vb <0, (2) ) ・ (4) is written in the graph as shown in Fig.6. The horizontal axis represents the air gap distance Z, and the vertical axis represents the air gap breakdown voltage. The downward convex curve represents the Paschen's curve, and the upward convex curve represents the characteristics of the void voltage Vg with Z as a parameter.

Discharge occurs when the Paschen's curve and the curve ~ intersect, and the discriminant of the quadratic equation relating to Z obtained as Vg = Vb becomes 0 at the point where the discharge starts. Since this time is the discharge start limit, V _DC = V _TH .

Although Paschen's law relates to the discharge phenomenon in the air gap, even in the charging process using the charging roller 2, a slight amount of ozone is generated in the immediate vicinity of the charging portion (10 ^-2 as compared with corona discharge). -10 ^-3 ) is recognized,
It is considered that the charging by the charging roller is related to the discharge phenomenon. In order to control the V _D by V _DC is _{therefore, V DC = V R + V} TH ‥‥‥ (5) V R: using the target surface potential, V by set the potential target value V _R (5) formula _TH
V _D can be brought close to V _R by adding and seeking.

As can be seen from the equation (5), the threshold voltage V _TH is determined by D = L _S / K _S (6). At this time, the relative dielectric constant of the photosensitive layer is determined. The rate K _S changes under the influence of the temperature and humidity around the photoconductor, and the thickness L _S of the photoconductor layer changes in the direction of decreasing due to durability.

Therefore, the surface potential V
_D changes with the change of the threshold voltage V _TH .
In other words, if the values of K _S and L _S are known, the DC voltage value V _DC for making the surface potential V _{D an} appropriate value can be obtained.

Here, the electrostatic capacity C _P formed by the photosensitive drum 1 and the charging roller 2 is formed by the nip n between the contact portions of the both 1 and 2 as shown in FIGS. 7 (a) and 7 (b). Assuming that the contact area at the nip portion is S _P , C _P = S _P × K _S / L _S = S / D (7) from the equivalent circuit of FIG.

That is, C _P ∝1 / D. Therefore, if C _P is obtained, an appropriate DC voltage V _DC can be obtained by the equation (5).

In this embodiment, instead of specifying C _P of the drum (photoreceptor), the thickness (L _s ) of the charge transport layer (CT layer) of the drum is simply used as shown in FIG. The method of measuring the change of the charging characteristic due to the change of the discharge impedance, estimating the change of the photoconductor C _P , and correcting the applied voltage is adopted.

FIG. 7A shows the relationship between the voltage applied to the charging roller 2 and the drum surface potential measured for each drum CT layer thickness. Similarly, the amount of direct current at that time is shown in FIG. As can be seen from this figure, it can be read that the charging characteristics, the voltage-current characteristics, and the discharge starting voltage change depending on the drum CT layer thickness.

FIGS. 8A and 8B show this characteristic as the drum surface potential and the DC current with respect to the drum CT layer thickness when a constant voltage of an arbitrary voltage is applied. The relationship between the drum surface potential and the direct current depending on the CT layer thickness can be read.
As the CT layer becomes thinner, the drum surface potential (black potential V
_It can be seen that _D and the white potential V _L ) and the amount of direct current increase. That is, it is understood that the surface potential corresponding to the drum C _P can be estimated by measuring the amount of direct current when a specific constant voltage is applied.

From the above relationship, FIG. 9 is a diagram relating to the detected current amount for controlling the drum surface potential and the correction voltage output at that time even if the C _P changes due to the drum CT layer thickness change. Correction is performed so that the voltage output decreases as the detected current amount increases. The experimental results with this correction are shown in (a) and (b) of FIG.

The horizontal axis represents the number of durable images as the number of times of image formation, and shows the change of the drum surface potential at each time.
The surface potential transition in the case of applying only a specific constant voltage in the related art is represented by L, but the amount of direct current at the time of applying the constant voltage of the present invention is detected, and the applied voltage is corrected according to the amount of the current to apply the constant voltage. Then, as indicated by M, a constant drum surface potential can always be secured even if the number of durable sheets increases.

The above-mentioned OPC photosensitive drum was used in this experiment. A durability test was conducted on the image forming apparatus shown in FIG.

As shown in the layer structure model in FIG. 1, the charging roller 2 has 10 ⁴ to 10 ^{5 made} of EPDM or the like on the core metal 2c.
The conductive rubber layer 2b of the [Omega] cm is provided, the resistance layer 2a ₂ in the order of 10 ⁷ to 10 ⁹ [Omega] cm made of hydrin or the like thereon
Is provided, and 10 ⁷ to 10 ¹⁰ Ωcm made of nylon-based material such as resin (Note: trademark of Teikoku Kagaku Co., Ltd.)
With a blocking layer 2a ₁ as a surface layer having a hardness of A
The one having a sker-C measurement of about 50 ° to 70 ° was used. The charging roller 2 is applied to the photosensitive drum 1 with a total pressure of 16
It was contacted at 00 g and was driven to rotate for charging.

When the resistance value rises due to environmental humidity fluctuations and durability fluctuations of the resistance layer of the charging member, the detected current amount decreases,
Since the voltage increase correction is applied to the image portion applied voltage value, sufficient charge density and image quality can always be obtained without insufficient charging.

[0091]

<Embodiment 2> (FIG. 11) In comparison with the sequence of FIG. 3, the sequence of FIG. 11 is DC constant voltage control / DC current detection of the charging roller 2 only in the section B1 of the pre-rotation period of the drum 1. DC constant voltage control between sheets in continuous printing
In this example, C current detection is not performed.

The charging roller constant voltage control according to the DC current detected in the section B1 is performed at the time of forming each image in continuous printing.

However, the detected DC current and the correction voltage are updated in the section B1 of the pre-drum rotation period at the start of the next printing.

<Embodiment 3> (FIG. 12) The sequence of FIG. 12 is a multi-rotation period before the drum for increasing the temperature of the image fixing device (device warm-up period) which is executed when the image forming apparatus is powered on. ) To the charging roller 2
DC constant voltage control and DC current detection are performed.

After the warm-up is completed, the apparatus is in a standby state until the drum rotation / charge elimination exposure is turned off and a print start signal is input.

The primary charging bias of the charging roller in each image forming cycle after the print start signal is input is a DC constant voltage which is a correction voltage corresponding to the DC current detected by the DC constant voltage control in the pre-drum multi-rotation period. Image formation is performed under control.

The detected DC current and correction voltage are held until the image forming apparatus is powered off.

It is also effective to stabilize the image density that the detection is performed almost once a day, only in the morning. For example, if the power of the image forming apparatus is turned off for a short time in order to deal with a paper jam of the image forming apparatus, the current is detected again and the correction voltage is updated when the power is turned on again. That is, the correction voltage value may differ before and after the power is turned off depending on the detection accuracy of the detection current. If the correction voltage changes even a little in a short time, the user of the apparatus will feel a lot of discomfort, and the density adjustment value will be reset when the image is formed.

On the other hand, in order to improve the operation performance of the image forming apparatus, the charging roller constant voltage application, the current detection, and the correction constant voltage control are performed only when the apparatus is brought into a usable state in the morning. , The corrected constant voltage is maintained on the day of use.

As a method of determining the first morning, when the result of the practical test is effective, the first case when the fixing roller detection temperature of the image fixing device is equal to or lower than the specific temperature when the power of the image forming device is turned on is the first morning. Is the way. It was most effective to set the specific temperature here between 30 ° C and 130 ° C, especially about 100 ° C.

<Embodiment 4> (FIG. 13) When the DC current detection in the DC constant voltage control of the charging roller 2 is performed only once, the charging roller 2 as the charging member moves in the circumferential direction at the moment when the DC current is detected. There are the following obstacles when there is uneven resistance. That is, when a current is detected by a portion having a low resistance, a high current is detected, so that the constant voltage value after correction becomes low, and the charging potential at the time of image formation decreases. In the case of regular development, the image density decreases, and in the case of reversal development, the image density increases and an image defect such as a fog phenomenon occurs.

In order to solve the difference in image density due to the difference in detection current in the circumferential direction of the charging roller, in this embodiment, as shown in FIG.
As in the sequence shown in 3, the DC current detection is performed a plurality of times within the DC constant voltage control time of the charging roller 2, and the detected DC current values of the plurality of times are added or integrated, and the average value thereof is calculated. During image formation, constant voltage control of the charging roller 2 is performed with a correction voltage according to the average detected current value. In addition to this method, a method of removing the maximum value and the minimum value from the detected DC current values of a plurality of times may be used.

By the above method, stable current detection and correction voltage value can be obtained even with respect to the resistance irregularity of the charging roller 2 in the circumferential direction, and stable image formation can be always performed.

As described in Examples 1 to 4 above, even if there is a change in the photosensitive member capacity due to an increase in the number of image formations and a decrease in the photosensitive member thickness, the capacity with respect to the photosensitive member thickness is changed each time. By detecting the voltage-current characteristics according to the above, it is possible to apply the optimum correction applied voltage at that time to the charging member.

As a method thereof, the charging member is subjected to DC constant voltage control during non-image formation, and voltage correction is applied to the applied voltage value during image formation according to the detected current amount to perform constant voltage control.

According to this, as the thickness of the photosensitive member decreases, the amount of detected current when the non-image area constant voltage is applied increases, and the voltage decrease correction is applied to the image area applied voltage value in accordance with the increase amount, so that the voltage decrease correction is always performed. The charging process and the image formation in the optimum state are executed.

Further, when the resistance value rises due to environmental humidity fluctuations and durability fluctuations of the resistance layer of the charging member, the detected current amount decreases, and the voltage increase correction is added to the image portion applied voltage value.
It is possible to always obtain sufficient image density and image quality without insufficient charging.

[0109]

<Embodiment 5> (FIGS. 14 to 16) The mechanical structure of the image forming apparatus is the same as that shown in FIG.

FIG. 14 shows an operation sequence of the apparatus in this embodiment, and the outline is the same as the operation sequence of FIG. In the present embodiment, DC current detection, primary voltage correction, and voltage correction of the image exposure lamp 22 are performed during charging roller DC constant voltage control in the section B1 of the drum pre-rotation period.

When the charging roller DC constant voltage control is started with the primary correction voltage, 1 is set by the image exposure L with the correction lamp voltage.
The first image is formed.

Further, the DC constant voltage control of the charging roller 2, the DC current detection, the DC constant voltage control, and the lamp voltage control are executed again between the sheets between the first and second sheets of printing. That is, when the printing of the first sheet is completed, the primary charging bias is set to the charging roller DC constant voltage control again in the interval B2 between the sheets, the DC current detection is executed, and then the primary constant voltage control according to the detected DC current. Also, the lamp voltage control is executed, and the image formation for the second print is executed.

In continuous printing of three or more sheets, the sequence of charging roller DC constant voltage control, DC current detection, DC constant voltage control, and lamp voltage control is similarly performed between each sheet.

When the surface of the drum is scraped due to durability and the film thickness of the photoconductor becomes thin, the DC constant voltage control period B1 which is performed when the charging roller 2 corresponds to the surface of the non-image forming area of the drum 1 or The detection DC current of B2 becomes high, the charging process is performed on the image forming area surface of the drum 1 by the charging roller 2 under the DC constant voltage control with the reduced correction voltage according to the detection DC current, and the lamp voltage is also increased. The exposure amount is corrected by the control, and the image formation is executed.

Further, the resistance of the charging roller 2 is increased particularly in a low humidity environment, and the charging roller DC during the period B1 or B2 is increased.
The detection DC current of the constant voltage control becomes low. The charging roller 2 performs a charging process on the surface of the image forming area of the drum 1 under the control of the charging roller DC constant voltage with the increased correction voltage according to the detected DC current, and the image is formed by exposure with the correction lamp voltage. As the formation is performed, the charging roller 2
The charging potential of the drum 1 is made constant regardless of the resistance fluctuation in the environment.

FIG. 15 is a correlation diagram of the detected current, the corrected lamp voltage output value, and the increased exposure amount of the drum surface.

Experimental results with this correction are shown in FIGS. 16 (a) and 16 (b). The horizontal axis represents the number of durable images as the number of times of image formation, and shows the change of the drum surface potential at that time. In the conventional case where the surface potential changes only when a specific constant voltage is applied, the black potential V _D is represented by L and the white potential _VL is represented by O, but as in the present invention, the amount of DC current when the charging roller constant voltage is applied is detected. However, if the voltage applied to the charging roller is corrected according to the amount of the current and constant voltage control is performed, the drum surface potential is constantly controlled to decrease constantly as the number of durable sheets increases, as indicated by M and P, respectively. it can.

Further, the image exposure lamp voltage rises in accordance with the detected current amount, and the exposure amount increases, so that the white potential becomes Q.
As a result, the black potential V _D is M and the white potential V _L is Q.
The electric potential of Here, by controlling the black potential V _{D so as} to decrease, the rate of increase of the white potential V _L can be suppressed, and the change amount of the exposure amount can be suppressed small.

The photoconductor 1 and the charging roller 2 used in this experiment are the same as those used in the first embodiment.

<Sixth Embodiment> (FIG. 17) In contrast to the sequence of FIG. 14, the sequence of FIG. 17 executes charging roller DC constant voltage control and DC current detection only in the section B1 of the pre-rotation period of the drum 1. This is an example in which the charging roller DC constant voltage control and the DC current detection are not performed between the sheets in continuous printing.

The charging roller constant voltage control according to the DC current detected in the section B1, the voltage correction of the exposure lamp 22 and the correction voltage application are performed at the time of forming each image in continuous printing.

However, the detected DC current, the corrected primary voltage,
The correction lamp voltage is updated in the section B1 of the drum pre-rotation period at the start of the next printing.

<Embodiment 7> (FIG. 18) The sequence of FIG. 18 is a multi-rotation period before the drum (apparatus warm-up period) for raising the temperature of the image fixing apparatus, which is executed when the image forming apparatus is powered on. ) To the charging roller 2
DC constant current control and DC voltage detection are performed.

After the warm-up is completed, the apparatus is in a standby state until the rotation / charge elimination exposure of the drum is turned off and the print start signal is input.

The primary charging bias of the charging roller 2 in each image forming cycle after the print start signal is input is the DC of the primary correction voltage corresponding to the DC current detected by the DC constant voltage control in the pre-drum multi-rotation period. Image formation is performed by performing constant voltage control and correcting the voltage of the exposure lamp 22.

The detected DC current and the primary correction voltage and the lamp correction voltage are held until the power of the printer is turned off.

Further, as described in the third embodiment, it is effective for stabilizing the image density that the detection is performed almost once a day and only in the morning. For example, if the power of the image forming apparatus is turned off for a short time in order to deal with a paper jam of the image forming apparatus, the current is detected again and the correction voltage is updated when the power is turned on again. That is, the correction voltage value (primary correction voltage and lamp correction voltage) may differ before and after the power is turned off depending on the detection accuracy of the detection current. If the correction voltage changes even a little in a short time, the user of the apparatus will feel a lot of discomfort, and the density adjustment value will be reset when the image is formed.

On the other hand, in order to improve the operation performance of the image forming apparatus, the charging roller constant voltage is applied, the current is detected, the correction constant voltage is controlled, and the exposure lamp is used only when the apparatus is started up in the morning. The voltage correction of No. 22 is performed, and the corrected constant voltage and the corrected lamp voltage are maintained on the day of use.

As a method for determining the first morning, the result of the practical test was effective. The first method in the morning is when the fixing roller detection temperature of the fixing device is equal to or lower than a specific temperature when the power of the image forming apparatus is turned on. Is. The specific temperature here is 3
It was most effective to set the temperature between 0 ° C and 130 ° C, especially about 100 ° C.

<Embodiment 8> (FIG. 19) When the DC current is detected only once, when the charging roller 2 as the charging member has uneven resistance in the circumferential direction at the moment of detecting the DC current, There are the following obstacles. If you happen to detect a current in a low resistance area, a high current will be detected, so the constant voltage value after correction will be low, and the lamp voltage after correction will be high, and the charging potential during image formation will decrease. Will be done. In the case of regular development, the image density decreases, and in the case of reversal development, the image density increases and an image defect such as a fog phenomenon occurs.

In order to solve the image density difference due to the difference in the detection current in the roller circumferential direction, in this embodiment, the DC current detection is performed a plurality of times within the charging roller DC constant voltage control time as in the sequence shown in FIG. , Its multiple detection DC
The current values are added or integrated, and the average value is calculated.
During image formation, the charging roller constant voltage control is performed with a correction voltage according to the average detected current value, and the voltage of the exposure lamp 22 is corrected.

In addition to this method, detection DC may be performed a plurality of times.
A method of removing the maximum value and the minimum value from the current value may be used.

With the above method, stable current detection and correction voltage values (primary correction voltage and lamp correction voltage) can be obtained even with respect to resistance unevenness in the circumferential direction of the charging roller 2, and stable image formation is always performed. You can

As described in Examples 5 to 8 above, even when there is a change in the photosensitive member capacity due to an increase in the number of image formations and a decrease in the photosensitive member thickness, the capacity with respect to the photosensitive member thickness is changed each time. By detecting the voltage-current characteristic according to the above, the optimum correction applied voltage at that time can be applied to the charging member, and the optimum exposure can be performed by the optimum correction lamp voltage at that time.

As a method, constant voltage control is performed on the charging member during non-image formation, and voltage correction is applied to the applied voltage value during image formation according to the detected current amount to correct the constant voltage control and the image exposure lamp voltage. Then, the exposure amount supplementary control is performed.

According to this, as the thickness of the photosensitive member decreases, the amount of detected current when the non-image area constant voltage is applied increases, and the voltage applied to the image area is corrected by the voltage decrease and the lamp voltage is increased according to the increase amount. Since the exposure amount increase correction is added, the charging process and the image formation in the optimum state are always executed.

Further, when the resistance value rises due to environmental humidity fluctuations and durability fluctuations of the resistance layer of the charging member, the detected current amount decreases, and the lamp voltage decrease correction is performed by adding the voltage increase correction to the image part applied voltage value. Alternatively, since the lamp voltage is constant, there is no insufficient charging or fog, and a sufficient image density and image quality can always be obtained.

[0139]

As described above, according to the present invention, contact charging
AC is applied to the image forming apparatus using the method, especially the contact charging member.
Regarding an image forming apparatus that applies a non-overlapping direct current to charge an image forming apparatus , directly connect the photosensitive member and the charging member that is in contact with the photosensitive member.
A charging means for applying a flow to charge the battery and a charging means
Exposure means for forming an electrostatic image by exposing the charged photoreceptor to an image
When the image forming apparatus having, furthermore, electrostatic on the photoreceptor
Developing means for developing the image and the developed image on the photoconductor as the transfer material
A transfer means for transferring and a fixed method for heating and fixing the transfer material after transfer.
The image forming apparatus having
Regardless of changes in the film thickness of the photoreceptor, changes in the durability of the charging member, and environmental changes in the resistance layer of the charging member, sufficient image density and image quality can always be maintained without insufficient charging.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

2A and 2B are schematic cross-sectional views of a contact charging member of a form other than a roller type.

FIG. 3 is an operation sequence diagram of the device.

FIG. 4A and FIG. 4B are charging characteristic graphs, respectively.

FIG. 5 is an equivalent circuit diagram in which a microscopic space is formed between a photosensitive layer, a charging roller, and a contact portion between them.

FIG. 6 is a graph showing the relationship between the void gap and the void breakdown voltage.

7A is a diagram showing a contact nip portion between a photoconductor and a charging roller, and FIG. 7B is an equivalent circuit diagram.

8 (a) and (b) are graphs showing chargeability and film thickness dependence.

FIG. 9 is a graph showing the relationship between the detection voltage and the correction voltage output value.

10 (a) and (b) are explanatory diagrams of effects.

FIG. 11 is a sequence diagram of the apparatus according to the second embodiment.

FIG. 12 is a sequence diagram of the third embodiment device.

FIG. 13 is a sequence diagram of an apparatus according to the fourth embodiment.

FIG. 14 is a sequence diagram of the device of the fifth embodiment.

FIG. 15 is a relationship diagram of the detection current, the correction lamp voltage output value, and the increased exposure amount of the drum surface.

16 (a) and (b) are graphs of the experimental results with correction applied.

FIG. 17 is a sequence diagram of an apparatus according to the sixth embodiment.

FIG. 18 is a sequence diagram of the seventh embodiment device.

FIG. 19 is a sequence diagram of an eighth embodiment device.

FIG. 20 is a schematic view of an example of a contact charging device.

[Explanation of symbols]

1 Charged object (photoreceptor) 2 charging roller 3 Charging bias application power supply 10 Image exposure means 11 Developing means 12 Transfer means 13 Cleaning means 14 Transfer material

─────────────────────────────────────────────────── ─── Continued Front Page (72) Masanori Muramatsu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Isamu Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Makoto Yanagida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Fumihiro Arahira 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Takeshi Watanabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-4-9883 (JP, A) JP-A-4-57068 (JP, A) Special Kaihei 1-321448 (JP, A) JP 4-116673 (JP, A) JP 4-107478 (JP, A) JP 1-204081 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) G0 3G 15/02

Claims (4)

(57) [Claims] 1. A surface of an object to be charged is charged.
Light that contains image information on the surface of the charged body that has been subjected to the process and charging
Applying an imaging process that includes the step of irradiating an image
In the image forming apparatus for performing the image formation, the charging means of the member to be charged applies only a DC voltage.
The surface of the body to be charged is charged by bringing the charging member into contact with the body to be charged.
It is a contact type charging device, and the charging member corresponds to the non-image forming area of the member to be charged.
Sometimes the charging member is controlled to a constant DC voltage, and the direct current at that time is controlled.
The amount of electric current is detected, and the charging member is an image forming area of the body to be charged.
When it corresponds to, it depends on the amount of DC current detected above.
Therefore, even if there is a decrease in the thickness of the layer to be charged,
Direct current detected above in order to secure the surface potential of the electric body
Correct so that the DC voltage output decreases as the amount increases.
DC constant voltage control of the charging member with the applied corrected DC voltage
An image forming apparatus characterized by the above . 2. A fixing roller temperature of an image fixing device is a specific temperature.
When the image forming device is ready for operation below
However, the charging member corresponds to the non-image forming area of the member to be charged.
DC voltage control of the charging member during
The amount of DC current of the
When it corresponds to the range,
The image forming apparatus according to claim 1, wherein the charging member is controlled to have a constant DC voltage . 3. A conductive member having a high resistance layer on the surface of the charging member.
3. A charging member according to claim 1, which is a positive charging member.
The image forming apparatus according to item 1. 4. The charging member is opposed to the image forming area of the body to be charged.
In response, the optical image is changed according to the detected DC current amount.
The image forming apparatus according to claim 1, further comprising a control for correcting an exposure amount of irradiation .