JPH0784436A - Image forming device and electrifier - Google Patents

Abstract

PURPOSE:To prevent the discharge between contact electrifying-members and a body which is electrified, to prevent ozone and noise and to efficiently carry out uniform electrification free of irregularities by means of a simple structure by applying to a plurality of contact electrifying-members a DC bias lower than a voltage at which discharge is initiated. CONSTITUTION:An electrifier 12 is arranged along the direction in which a photoreceptor 11 rotates, and has a plurality of blade-like contact electrifying- members 16-19 which are in contact with the photoreceptor 11. The same DC bias voltage is applied to each of the contact electrifying-members 16-19 from a power source 20. In the determination of the DC bias voltage for the application to the contact electrifying-members 16-19, the DC bias is determined based on the material of the electrifying-members 16-19 and the required electrification- potential of the body 11 which is electrified. Here, when the DC bias voltage is too high, with the result that the voltage of a gap between the contact members 16-19 and the body 11 exceeds the voltage at which the discharge is initiated, discharge is caused. Therefore, the DC bias lower than the voltage at which the discharge is initiated is applied.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, an image forming apparatus electrostatically responds to an image signal by performing uniform charging on an electrostatic latent image carrier made of a photoconductor or the like by a charging device and then exposing by an exposure device. A latent image pattern is formed, the electrostatic latent image pattern is visualized by a developing device, and the visualized image is transferred to a transfer material by a transfer device and fixed by a fixing device. In such an image forming apparatus, as a charging device, a corona charging method of charging an electrostatic latent image carrier by corona discharge has been conventionally used. The corona charging method is widely used because it has advantages such as non-contact charging of the electrostatic latent image carrier and a simple structure.

Further, a contact charging system has been proposed in which a contact charging member such as a charging roller is brought into contact with the electrostatic latent image carrier and a bias is applied to the contact charging member to charge the electrostatic latent image carrier. There is. This contact charging method is efficient because the contact charging member is brought into contact with the electrostatic latent image carrier. Further, Japanese Examined Patent Publication No. Sho 63-9234 has a plurality of contact band electrons that are in contact with a photoreceptor that moves relative to each other, and a bias in which direct current and alternating current are superimposed is applied to these contact band electrons,
There is described a charging device in which the absolute value of the DC component increases toward the downstream side in the rotation direction of the photoconductor.

[0004]

In the above corona charging method, ozone is generated during corona discharge and the electrostatic latent image bearing member is charged in a non-contact manner, so charging efficiency is poor and high voltage must be applied. There are problems such as having to do it. Further, in the contact charging method, since the electric field is concentrated at the contact point between the contact charging member and the electrostatic latent image carrier, it is difficult to obtain continuous and uniform charging of the electrostatic latent image carrier, and uneven charging occurs. There was a problem that it was likely to occur.

Further, in the charging device described in Japanese Patent Publication No. 63-9234, when the voltage of the gap between the contact band electrons and the photoconductor becomes high, discharge occurs near the contact part between the contact band electrons and the photoconductor. Ozone is generated and the maximum advantage of the contact charging method cannot be utilized. In addition, the use of a new AC causes a problem of complicated power supply configuration, noise depending on the AC cycle, and uneven charging.

The present invention solves the above-mentioned drawbacks, can prevent the discharge between the contact charging member and the member to be charged, can prevent the generation of ozone and noise, and is simple and efficient. An object is to provide an image forming apparatus and a charging device that can perform uniform charging without unevenness.

[0007]

In order to achieve the above object, the invention according to claim 1 provides a charging device for uniformly charging an electrostatic latent image carrier, and an electrostatic latent image carrier. An exposing means for forming an electrostatic latent image pattern according to an image signal on the uniformly charged surface by exposure, and an electrostatic latent image pattern on the electrostatic latent image carrier is visualized by attaching colored particles. In an image forming apparatus having a developing unit for forming an image and a transfer / fixing unit for transferring and fixing a visible image on the electrostatic latent image carrier to a transfer material, the charging device is the electrostatic latent image carrier. Bias applying means for applying a DC bias equal to or lower than the discharge start voltage to the plurality of contact charging members.

According to a second aspect of the present invention, a plurality of contact charging members for charging the body to be charged, a measuring device for measuring the potential of the body to be charged, and the plurality of contact charging devices based on the measurement values of the measuring device. The control means controls each applied voltage of the member so that the potential difference between the plurality of contact charging members and the member to be charged becomes equal to or lower than the discharge start voltage. According to a third aspect of the present invention, a plurality of contact charging members that are set to have a resistance value such that each resistance value becomes large on the upstream side in the rotation direction of the member to be charged to charge the member to be charged, and the plurality of contact charging members. And a bias applying means for applying a DC voltage at which the potential difference between the plurality of contact charging members and the body to be charged becomes equal to or lower than the discharge start voltage.

According to a fourth aspect of the present invention, a plurality of contacts for charging the charged body are formed of a dielectric material having a capacitance set such that each electrostatic capacity becomes smaller toward the upstream side in the rotation direction of the charged body. A charging member and a bias applying means for applying a DC voltage to the plurality of contact charging members such that the potential difference between the plurality of contact charging members and the body to be charged is equal to or lower than the discharge start voltage are provided. According to a fifth aspect of the present invention, there is provided a charging device having a plurality of contact charging members for charging an object to be charged, wherein the contact charging member on the most downstream side in the rotation direction of the object to be charged among the plurality of contact charging members. The surface roughness of the portion in contact with the charged body is smaller than the surface roughness of the portion of the other contact charging member in contact with the charged body.

According to a sixth aspect of the present invention, there is provided a charging device having a plurality of contact charging members for charging a member to be charged, wherein at least a portion of the plurality of contact charging members which is in contact with the member to be charged is made of an elastic body. However, among the plurality of contact charging members, the rubber hardness of the contact charging member on the most downstream side in the rotation direction of the member to be charged is set to be the smallest as compared with the rubber hardness of the other contact charging members. According to a seventh aspect of the present invention, there is provided a charging device having a plurality of contact charging members for charging a body to be charged, wherein at least a portion of the plurality of contact charging members that contacts the body to be charged is made of a dielectric material. Dielectric volume resistivity of 5 *
It is 10 ⁵ or more and 1 * 10 ⁹ or less.

[0011]

According to the first aspect of the invention, the plurality of contact charging members charge the electrostatic latent image carrier, and the bias applying means applies a DC bias equal to or lower than the discharge start voltage to the plurality of contact charging members. According to the second aspect of the present invention, the plurality of contact charging members charge the charged body, and the potential of the charged body is measured by the measuring device. The control means controls each applied voltage of the plurality of contact charging members based on the measurement value of the measuring device so that the potential difference between the plurality of contact charging members and the body to be charged becomes equal to or lower than the discharge start voltage.

According to the third aspect of the present invention, the plurality of contact charging members, each of which has a resistance value such that each resistance value increases on the upstream side in the rotation direction of the charged body, charges the charged body,
The bias applying means applies a DC voltage to the plurality of contact charging members such that the potential difference between the plurality of contact charging members and the body to be charged becomes equal to or lower than the discharge start voltage. In the invention according to claim 4, a plurality of contact charging members made of a dielectric material having a capacitance set such that each capacitance becomes smaller toward the upstream side in the rotation direction of the charged body charges the charged body. The bias applying unit applies a DC voltage to the plurality of contact charging members such that the potential difference between the plurality of contact charging members and the body to be charged is equal to or lower than the discharge start voltage.

According to another aspect of the invention, the plurality of contact charging members charge the member to be charged, and the plurality of contact charging members contact the member to be charged of the contact charging member on the most downstream side in the rotation direction of the member to be charged. The surface roughness of the portion to be charged is smaller than the surface roughness of the portion of the other contact charging member that contacts the charged body.

According to a sixth aspect of the present invention, the plurality of contact charging members charge the body to be charged, and at least the portions of the plurality of contact charging members that are in contact with the body to be charged are made of an elastic body. The rubber hardness of the contact charging member on the most downstream side in the rotation direction is the smallest as compared with the rubber hardness of the other contact charging members. According to a seventh aspect of the present invention, the plurality of contact charging members charge the body to be charged, and at least the portions of the plurality of contact charging members that are in contact with the body to be charged are made of a dielectric material. If the rate is 5 * 10 ⁵ or more, 1 *
It is set to 10 ⁹ or less.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a first image forming apparatus to which the present invention is applied.
An example is shown. The first embodiment is an example of an electrophotographic copying apparatus, which includes an electrostatic latent image carrier 11 made of a photoconductor.
It has an exposure unit, a charging device 12, a developing device 13, a transfer unit 14, and a cleaning unit 15, which are not shown. When the switch for starting copying on the operation unit is pressed, the photoconductor 11 and the developing device 13 are driven by the drive unit to start rotation,
A scanner unit (not shown) starts reading a document and outputs the image signal to the exposure unit via the image processing unit. When the image signal in the memory is imaged instead of the image signal from the scanner unit, the reading of the image signal from the memory is started and the image signal is output to the exposure unit.

The photoconductor 11 is uniformly charged by the charging device 12 as the photoconductor 11 rotates, and is exposed by an exposure unit according to an image signal to form an electrostatic latent image pattern. This electrostatic latent image pattern moves with the rotation of the photoconductor 11, and the developing device 13 attaches colored particles called toner to make it visible. The toner on the photoconductor 11 is transferred to the transfer paper fed from the paper supply unit (not shown) by the transfer unit 14, and the toner is fixed on the transfer paper by the fixing unit (not shown). After the toner transfer, the photoconductor 11 advances to the cleaning unit 15, the cleaning unit 15 removes the residual toner, and then advances to the charging device 12 again.

FIG. 1 shows the structure of the charging device 12 and its mechanism will be described below. The charging device 12 has a plurality of blade-shaped contact charging members 16 to 19 arranged along the rotation direction of the photoconductor 11 and contacting the photoconductor 11, and these contact charging members 16 to 19 are the same from the power source 20. DC bias voltage is applied. Each contact charging member 16-1
The DC bias applied to 9 does not necessarily have to be the same voltage, but if these DC biases are the same, the configuration of the power supply 20 is the simplest.

Regarding the determination of the DC bias voltage applied to the contact charging members 16-19, the contact charging members 16-19 are used.
The DC bias is determined by the material of the above and the desired charging potential of the portion to be charged 11. Here, if the DC bias voltage is too high and the voltage of the gap between the contact charging members 16 to 19 and the charged portion 11 becomes equal to or higher than the discharge start voltage, discharge occurs.
Regarding the discharge of the air gap, the Baschen's discharge curve is well known, in which the discharge voltage is uniquely determined as a function of the voltage of the air gap and the width of the air gap.

FIG. 8 shows a discharge curve a of Baschen and a voltage curve b of a gap when a voltage is applied to the charging member.
The Baschen's discharge curve a is approximated by a linear expression with V = 312 + 6.2z V: voltage, z: gap width (μm) where the gap width is about 8 μm and has an inflection point and the gap width is about 8 μm or more. To be done. In the air gap, it is shown that discharge occurs at a voltage higher than the Baschen's discharge curve a and cannot exist stably.

The curve b is the width of the gap between the contact charging member and the portion to be charged when a voltage is applied to the contact charging member,
The voltage of the air gap at that portion is shown. The curve b shown in the drawing is in contact with the Baschen's discharge curve a, and in this case, discharge occurs at the portion where the gap width between the contact charging member and the charged portion corresponding to the contact is z ₀ . The voltage at this time is considered as the discharge start voltage and is shown as V ₀ in FIG.

In the conventional charging device, since the charging efficiency is emphasized and a voltage exceeding the discharge limit is applied to the contact charging member, discharge occurs even in the contact charging system.
Further, when the charging device has the conventional structure and a voltage that does not cause discharge is applied to the contact charging member, a sufficient charging potential cannot be obtained. In this example, by adopting the following configuration, it is possible to avoid generation of ozone due to generation of discharge, charge can be performed by charge injection by contact of the contact charging members 16 to 19, and further, sufficient charging potential can be obtained. It is possible to obtain uniform charging.

The contact charging members 16 to 19 are composed of four, but are composed of an appropriate number depending on the desired charging potential and the charging ability of the contact charging members. Contact charging member 16-1
The configuration 9 is a configuration in which elastic layers 16b to 19b are attached on bases 16a to 19a made of a conductive material. Elastic layer 16b
The materials 19a to 19b are polyurethane elastomers, and have an electrical resistance of medium resistance. Elastic layers 16b-1
As the material of 9b, other silicone-based rubber materials,
The volume resistivity is 5 * 10 by dispersing metal or carbon black in NBR, chloroprene rubber, etc. to make it semi-conductive.
It is about ⁵ to 1 * 10 ⁹ Ωcm.

If the resistance of the elastic layers 16b to 19b is larger than the above value, the charging efficiency is deteriorated, and if the resistance is smaller than the above value, a large current may flow and short circuit may occur. Elastic layer 1
The hardness of 6b to 19b is 35 to 6 in JIS-A hardness.
About 0 degrees is suitable. In this example, the elastic layer 16
The hardness of b to 19b is 40 degrees, and the contact charging member 16 to
The width of the contact portion between 19 and the photoconductor 11 is about 0.5 mm. The same voltage 600 V is applied from the power source 20 to the contact charging members 16 to 19.

FIG. 5 shows the results of measuring the charge amounts of the contact charging members 16-19. In FIG. 5, the mark ◯ indicates the measurement result of each charge amount of the contact charging members 16 to 19, and the charge amount of about 500 V is obtained by the contact charging members 16 to 19. This is a sufficient charge amount for image formation. At this time, according to the measurement, ozone was not detected. Although the blade-shaped contact charging members 16 to 19 are used in this example, roller brushes or the like may be used as the contact charging members 16 to 19.

FIG. 3 shows a second embodiment of the charging device to which the present invention is applied. In this second example, in the charging device of the image forming apparatus shown in FIG.
No. 18 is used, and the surface potential measuring probes 21 to 23 are arranged on the upstream side in the rotation direction of the charged body 11 with respect to the contact portion between the contact charging members 16 to 18 and the charged body 11.

In a charging device for charging a contact charging member with a voltage from a power source, it is important that the voltage in the gap between the contact charging member and the charging member is not higher than the discharge start voltage. In this example, the potential immediately before being charged by the contact charging members 16 to 18 in the charged body 11 is measured by the surface potential measuring unit 24 via the surface potential measuring probes 21 to 23, so that the contact charging members 16 to 1
8 improves the reliability of the applied voltage setting.

The surface potential measuring unit 24 measures the potential just before being charged by the contact charging members 16 to 18 on the member to be charged 11 via the surface potential measuring probes 21 to 23, and changes the output signal according to the measured value. Send to section 25. The variable resistance section 25 is composed of variable resistances 26 to 28 inserted between the contact charging members 16 to 18 and the power source 20, and the variable resistances 26 to 28 are adjusted by being changed by the output signal of the surface potential measuring section 24. As a result, the resistance values of the variable resistors 26 to 28 are changed so that the contact charging members 16 to 18 of the charged body 11 are changed.
Is adjusted according to the potential immediately before being charged.

As described above, the charged state of the charged body 11 is confirmed every time by the surface potential measuring section 24, and the voltage applied from the power source 20 to the contact charging members 16 to 18 is determined next. Good charging is performed. Further, even when the charged body 11 is already charged at the entrance of the contact portion with the contact charging members 16 to 18, or when reverse charging is generated, stable charging is possible, and environmental fluctuations or Stable charging is possible even when the state of the photoconductor changes with time. In the second embodiment, the materials of the contact charging members 16-18 are the same as those in the first embodiment.

FIG. 4 shows a third embodiment of the charging device to which the present invention is applied. A plurality of roller-shaped contact charging members 29 to 32
Are arranged along the rotation direction of the electrostatic latent image carrier 11 made of a photoconductor and are in contact with the photoconductor 11 with a predetermined contact width. The photoconductor 11 is rotationally driven in the direction of the arrow shown in the figure by the drive unit, and the contact charging members 29 to 32 are rotated along with the photoconductor 11 in the direction of the arrow shown. Each of the contact charging members 29 to 32 has an axis a29 to 32 made of a conductive material.
a and dielectric layers 29b to 32b are formed on the a
The same DC bias voltage is applied from the power source 33 to the to 32a.

The dielectric layers 29b to 32b are elastic bodies and have a rubber hardness of about 40 degrees according to JIS. In this embodiment, the dielectric layers 29b to 32b are silicone rubbers in which carbon black is dispersed, and the resistances are set differently depending on the amount of carbon black dispersed.
The volume resistivities of the dielectric layers 29b to 32b are set to 5 * 10 ⁵ or more and 1 * 10 ⁹ or less. For example, 1 * 10 ⁸ , 1 * 1 so as to gradually decrease from the upstream side in the photoconductor rotation direction.
It is set to 0 ⁷ , 5 * 10 ⁶ , 5 * 10 ⁵ Ωcm.

FIG. 6 shows the result of charging the photoconductor 11 with the dielectric layers 29b to 32b alone. Dielectric layers 29b-3
The resistance value of 2b is R1, R2, R3, and R4 from the higher resistance value (from the upstream side in the photoconductor rotation direction). In the actual device,
Assuming that the time taken for the photoconductor 11 to pass through the respective contact portions with the contact charging members 29 to 32 is t, the voltages applied to the photoconductor 11 at this time are V1 to V4 shown in FIG. As described above, the charging voltage of the photoconductor 11 rises faster as the resistance value of the contact charging member is smaller, and the voltage applied to the contact part of the photoconductor 11 with the contact charging member becomes larger within the contact time with the contact charging member. I will end up.

In the case of charging by the contact charging method, there is a possibility that the photosensitive member may be damaged due to a rapid increase in voltage near the contact portion with the contact charging member. In particular, the contact charging member 2 at the most upstream position in the rotation direction of the photoconductor that first comes into contact with the photoconductor
In No. 9, the potential difference between the photosensitive member 11 and the photosensitive member 11 is the largest, and a large current may flow at this point to damage the photosensitive member 11.

In order to solve such a problem, in this embodiment, the resistance of the contact charging member 29 at the most upstream position in the photosensitive member rotation direction is set higher than the resistance of the other contact charging members 30-32. As a result, the photoconductor 11 is prevented from being damaged due to a sudden increase in voltage. Further, in order to perform charging with higher efficiency, the resistance of the contact charging members 29 to 32 is set so as to gradually decrease from the upstream side in the photoconductor rotating direction. Figure 7
Is each charging roller 29 of the photoconductor 11 when the photoconductor 11 is charged by using four charging rollers 29 to 32 having different resistances.
~ 32 shows the charging potential after charging, and it can be seen that efficient and sufficient charging can be performed.

The fourth embodiment of the present invention is a charging device for charging the photoconductor by a plurality of charging rollers arranged along the rotation direction of the photoconductor, and is used in the image forming apparatus shown in FIG. . The charging roller is a metal cored bar provided with an elastic layer, and a DC bias voltage is applied to the cored bar from a power source. As a result of studying the case where the electrostatic capacity of the elastic layer of the charging roller is different, it was found that the charging voltage was higher when the electrostatic capacity of the elastic layer of the charging roller was higher.

In order to avoid a sudden increase in the voltage of the photoconductor when the photoconductor is charged by the charging roller at the most upstream position in the photoconductor rotation direction, the electrostatic capacity of the elastic layer of each charge roller is upstream in the photoconductor rotation direction. It is configured to become smaller toward the side. For example, a plurality of charging rollers may be arranged in the
When the roller, the second roller and the third roller are used, the material of the elastic body layer of the first roller is urethane rubber, and the material of the elastic body layer of the second roller is chloroprene rubber coated with nylon on the surface, The material of the elastic layer of the third roller is silicone rubber. The elastic layer of each charging roller has the same thickness, and the relative permittivity is about 3, 6 and 7 from the upstream side in the photoconductor rotating direction.

Further, in the fourth embodiment, the electrostatic capacity is gradually reduced from the upstream side in the direction of rotation of the photosensitive member by changing the thickness of the elastic layer while keeping the same material for the elastic layer of each charging roller. Even when changed in this way, the same effect as the fourth embodiment was obtained. Thus, the electrostatic capacity of the charging roller is gradually reduced from the upstream side in the rotation direction of the photoconductor, whereby efficient charging can be performed without generating ozone.

The fifth embodiment of the present invention is a charging device in which a DC bias voltage is applied from a power source to a plurality of charging rollers arranged along the rotation direction of the photoconductor to charge the photoconductor with these charging rollers. The surface roughness of the charging roller at the most downstream position in the rotation direction of the photoconductor is reduced to make the charging uniform.

When the photoconductor is charged under the condition that the voltage of the gap between the charging roller and the photoconductor is equal to or lower than the discharge start voltage, no discharge occurs, so that the spread of the charge is reduced and The uneven charging due to the contact state with the photoconductor becomes very noticeable. Therefore, the surface roughness of the charging roller needs to be smooth so as not to affect the image formed on the photosensitive member after being charged. Specifically, the surface roughness of the charging roller is required to be not more than 5 μm as a ten-point average roughness so that noise does not appear in the final image.

Generally, a rubber roller is molded by using a mold and then polishing the surface thereof. Since the surface roughness that can be smoothed by this surface polishing is about 20 μm, if a higher surface roughness is required, a step of further providing a surface layer on the rubber roller is necessary. However, an increase in the number of steps leads to cost increase and is not desirable. Also,
Even if the surface roughness of the charging roller on the upstream side of the photoconductor is smooth, if the surface roughness of the charging roller on the downstream side of the photoconductor is not smooth, the charged state of the photoconductor will be rough.

In view of this, in this embodiment, only the surface roughness of the charging roller, which is the most downstream of the plurality of charging rollers in the photosensitive member rotation direction, is set to about 5 μm. The photosensitive member is charged by a charging roller other than the charging roller located at the most downstream side in the rotating direction of the photosensitive member, and then passes through the contact portion with the charging roller located at the most downstream side in the photosensitive member rotating direction. As a result, it is possible to absorb the charging unevenness due to the surface roughness of the charging rollers other than the charging roller at the most downstream side in the rotation direction of the photoconductor.

For the same reason, it is also possible to compensate the uneven charging by setting the rubber hardness of the charging roller at the most downstream side in the rotation direction of the photosensitive member to be low. In the sixth embodiment of the present invention, a DC bias voltage is applied from a power source to a contact charging member composed of four charging rollers arranged along the rotation direction of the photosensitive member to charge the photosensitive member with these four charging rollers. In the charging device, the charging roller, which is the most downstream of the four charging rollers in the rotation direction of the photosensitive member, is set to have a low rubber hardness to compensate for uneven charging and uniform charging. The image shown in FIG. Used in forming equipment.

The material of the charging roller is urethane. The charging rollers other than the charging roller located on the most downstream side in the direction of rotation of the photosensitive member have a surface roughness of only 10 μm and have a surface roughness of 15 μm.
The charging roller on the most downstream side in the rotation direction of the photosensitive member is coated with urethane to form a surface roughness of 5 μm. When the photosensitive member was charged by the four charging rollers, the charging with less charging unevenness was performed as in the case where the surface coating was applied to all of the four charging rollers to form the surface roughness of 5 μm.

Further, in a charging device having a plurality of charging rollers made of silicone, the rubber hardness of the charging roller at the most downstream side in the photosensitive member rotation direction is 35 degrees according to JISA, and the rubber hardness of other charging rollers is 45 degrees according to JIS A. When the photoconductor is charged as, the rubber hardness of all charging rollers is JI.
As in the case where SA was set to 35 degrees, uniform charging could be performed. In this way, by reducing the rubber hardness of the charging roller on the most downstream side in the photoconductor rotation direction, it is possible to absorb uneven charging by charging rollers other than the charging roller on the most downstream side in the photoconductor rotation direction and perform uniform charging. There is out.

[0044]

As described above, according to the invention described in claim 1, a charging device for uniformly charging the electrostatic latent image carrier,
Exposure means for forming an electrostatic latent image pattern according to an image signal on the uniformly charged surface of the electrostatic latent image carrier by exposure, and an electrostatic latent image on the electrostatic latent image carrier. In the image forming apparatus, there is provided an image forming apparatus including: a developing unit that visualizes a pattern by attaching colored particles, and a transfer / fixing unit that transfers and fixes the visualized image on the electrostatic latent image carrier onto a transfer material. Since the apparatus has a plurality of contact charging members for charging the electrostatic latent image carrier, and a bias applying means for applying a DC bias below the discharge start voltage to the plurality of contact charging members, the charging member and It is possible to prevent discharge between the charged body and ozone and noise, and it is possible to perform sufficient charging. Moreover, it is possible to simply configure without using alternating current.

According to the second aspect of the present invention, a plurality of contact charging members for charging the body to be charged, a measuring device for measuring the potential of the body to be charged, and a plurality of the plurality of contact charging members based on the measured values of the measuring device. Since the control means is provided so as to control each applied voltage of the contact charging member so that the potential difference between the plurality of contact charging members and the body to be charged becomes equal to or lower than the discharge start voltage, environmental changes and the state of the body to be charged with time. Stable charging can be performed against changes.

According to the third aspect of the present invention, a plurality of contact charging members for charging the charged body are set such that the respective resistance values become large on the upstream side in the rotational direction of the charged body, and a plurality of contact charging members. Since the plurality of contact charging members are provided with the bias applying means for applying the DC voltage at which the potential difference between the plurality of contact charging members and the member to be charged is equal to or lower than the discharge start voltage, abrupt voltage is applied to the member to be charged. It is possible to prevent the above and perform stable charging.

According to the fourth aspect of the present invention, a plurality of electrostatic charges are formed, each of which is made of a dielectric material having a capacitance set such that each electrostatic capacitance becomes smaller toward the upstream side in the rotation direction of the charged body. The contact charging member and the bias applying means for applying a DC voltage to the plurality of contact charging members such that the potential difference between the plurality of contact charging members and the member to be charged is equal to or lower than the discharge start voltage. It is possible to prevent a sudden voltage from being applied to the device and perform stable charging.

According to a fifth aspect of the present invention, there is provided a charging device having a plurality of contact charging members for charging a member to be charged, wherein the charging device is located on the most downstream side in the rotation direction of the member to be charged among the plurality of contact charging members. Since the surface roughness of the portion of the contact charging member that contacts the charged body is smaller than the surface roughness of the portion of the other contact charging member that contacts the charged body, the uneven charging is efficiently compensated for and uniform. It can be charged.

According to a sixth aspect of the present invention, there is provided a charging device having a plurality of contact charging members for charging a member to be charged, wherein at least a portion of the plurality of contact charging members which is in contact with the member to be charged is an elastic body. In the plurality of contact charging members, the rubber hardness of the contact charging member on the most downstream side in the rotating direction of the body to be charged is set to be the smallest as compared with the rubber hardness of the other contact charging members, so that the charging unevenness can be efficiently achieved. Can be compensated for and uniform charging can be performed.

According to the seventh aspect of the present invention, therefore, it is possible to avoid a short circuit caused by a large current flowing through the contact portion between the charging member and the member to be charged, and at the same time, efficient charging can be performed. it can.

[Brief description of drawings]

FIG. 1 is a schematic view showing a charging device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the outline of the first embodiment.

FIG. 3 is a schematic view showing a second embodiment of the present invention.

FIG. 4 is a schematic view showing a third embodiment of the present invention.

FIG. 5 is a diagram showing a result of measuring a charge amount of the contact charging member of the first embodiment.

FIG. 6 is a diagram showing a result of charging a photoconductor with each contact charging member alone of the third embodiment.

FIG. 7 is a diagram showing a charging potential after charging by each contact charging member of the photoconductor when the photoconductor is charged by using four contact charging members having different resistances in the third embodiment.

FIG. 8 is a diagram showing a Baschen's discharge curve a and a voltage curve b of a void when a voltage is applied to the charging member.

[Explanation of symbols]

 11 Photoreceptor 12 Charging Device 16-19, 29-32 Contact Charging Member 20, 33 Power Supply 21-23 Surface Potential Measuring Probe 24 Surface Potential Measuring Section 25 Variable Resistance Section

Claims (7)

[Claims] 1. A charging device for uniformly charging an electrostatic latent image bearing member, and an electrostatic latent image corresponding to an image signal by exposure on a uniformly charged surface of the electrostatic latent image bearing member. An exposing means for forming an image pattern; a developing means for making the electrostatic latent image pattern on the electrostatic latent image carrier visible by adhering colored particles; and a developing image on the electrostatic latent image carrier. In an image forming apparatus having a transfer / fixing means for transferring and fixing to a transfer material, the charging device has a plurality of contact charging members for charging the electrostatic latent image carrier, and the plurality of contact charging members are provided. An image forming apparatus comprising: a bias applying unit that applies a DC bias equal to or lower than a discharge start voltage. 2. A plurality of contact charging members for charging a body to be charged, a measuring device for measuring the potential of the body to be charged, and a voltage applied to each of the plurality of contact charging members on the basis of a measurement value of the measuring device. A charging device comprising: a control unit that controls the potential difference between the plurality of contact charging members and the body to be charged to be equal to or lower than a discharge start voltage. 3. A plurality of contact charging members which are set to have a resistance value such that each resistance value increases on the upstream side in the rotation direction of the charged body, and which charge the charged body, and a plurality of the contact charging members. And a bias applying means for applying a DC voltage at which the potential difference between the contact charging member and the body to be charged is equal to or lower than the discharge start voltage. 4. A plurality of contact charging members, each of which is made of a dielectric material having a capacitance set such that each electrostatic capacitance becomes smaller toward the upstream side in the rotation direction of the charged body, and which charges the charged body. The contact charging member is provided with bias applying means for applying a DC voltage at which the potential difference between the plurality of contact charging members and the body to be charged is equal to or lower than the discharge start voltage. 5. A charging device having a plurality of contact charging members for charging a member to be charged, wherein the member to be charged is the contact charging member on the most downstream side in the rotation direction of the member to be charged among the plurality of contact charging members. A charging device, wherein a surface roughness of a contacting portion is smaller than a surface roughness of a contacting portion of another contact charging member. 6. A charging device having a plurality of contact charging members for charging a body to be charged, wherein at least a portion of the plurality of contact charging members that comes into contact with the body to be charged is made of an elastic body.
A charging device characterized in that, of the plurality of contact charging members, the rubber hardness of the contact charging member on the most downstream side in the rotation direction of the body to be charged is set to be the smallest as compared with the rubber hardness of the other contact charging members. 7. A charging device having a plurality of contact charging members for charging a member to be charged, wherein at least a portion of the plurality of contact charging members that contacts the member to be charged is made of a dielectric material.
A charging device characterized in that the volume resistivity of this dielectric is 5 * 10 ⁵ or more and 1 * 10 ⁹ or less.