JPH04358175A - Electrifier - Google Patents

Abstract

PURPOSE:To always execute the electrifying processing of a stable electrifying potential without disposing a dedicated equipment for destaticizing before electrifying such as an exposing lamp device for destaticizing and a discharger and further, being influenced by environmental humidity, on an electrifier on which an electrifying member provide with a resistant layer is arranged to be opposite to a body to be electrified without contacting, via a gap, and an oscillating voltage is applied to the electrifying member to execute the electrification of the body to be electrified. CONSTITUTION:In an electrifying device electrifying the surface of the body to be electrified 1 in such a manner that a voltage is applied to an electrifying member 2 disposed to be opposite to the surface of the body to be electrified 1 via the gap Z and provided with the resistant layer 2b on the part opposite to the body to be electrified 1, the voltage applied to the electrifying member 2 is the oscillating voltage (VDC+VAC), and when the body to be electrified is electrified from a state where it is destaticized, an oscillation center voltage component (VDDC) is controlled by a constant current. Simultaneously, a DC voltage is detected at this time, and then, controlled by a constant voltage.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to, for example, electronic copying machines and
Uniform charging treatment (
The present invention relates to a charging device that is effective as a means for performing (including static elimination processing).

0002

[Background Art] Conventionally, wire electrodes and shield electrodes such as corotrons and scorotrons, which have good uniform charging properties, have been used to uniformly charge the surface of a charged object such as an image carrier to a predetermined potential and polarity. Non-contact type corona dischargers are widely used.

[0003] However, corona dischargers often generate corona products such as ozone, and require additional means and mechanisms to deal with them, which are factors that increase the size and cost of the device. There are some problems such as:

[0004]Recently, therefore, the use of contact charging type charging means/devices is being considered in place of the corona discharger, which has many problems.

Contact charging is a method in which a charging member to which a voltage is applied is brought into contact with the surface of an object to be charged, such as an image carrier, with a predetermined pressing force to charge the surface of the object to be charged to a predetermined potential. The present applicant also discussed this contact charging in Japanese Patent Application Laid-Open No. 63-14966.
No. 9 and other publications propose means for uniformly charging a charged object by applying an oscillating voltage to a charging member to form an oscillating electric field between the charging member and the charged object.

However, the above-mentioned oscillating voltage application type contact charging device is used for image formation, for example, in which image information is written by line scanning on the charging surface of a photoreceptor as an image carrier to form an electrostatic latent image. When employed as a charging means for a photoreceptor in a device such as a laser beam printer, the following problems arise.

[0007] When outputting an image pattern in which laser irradiation and non-irradiation are repeated at high density and at equal intervals in the sub-scanning direction,
If the frequency of the alternating current (AC) component of the oscillating voltage applied to the charging member becomes close to the spatial frequency of the image pattern, interference fringes may occur on the image plane. This problem can be solved by making the frequency of the alternating current component sufficiently high, but since contact charging is used, the oscillating electric field formed between the charging member and the photoreceptor causes them to vibrate, causing the charging to occur. Vibration noise called sound is more likely to occur. This generation of charging noise is extremely inconvenient for reducing noise during printer operation in an office environment or the like.

Furthermore, if the charging member is left in contact with the photoreceptor, the charging member may be deformed, and especially if rubber is used as the charging member, the photoreceptor may deteriorate due to the plasticizer seeping out from the rubber and adhering to the photoreceptor. In some cases, images may become blurred.

[0009] Therefore, a charging device has been devised that solves the above problem by charging a charging member in a form in which the charging member is placed floating in close proximity to the photoreceptor with a small gap (void) in a non-contact manner. However, there is a problem that sufficient charging uniformity cannot be obtained.

0010

SUMMARY OF THE INVENTION To address this problem, the present applicant has proposed providing a resistive layer on the surface layer of the charging member to improve uniform charging performance. However, this case also has the following problems. That is, the resistive layer is made of rubber, plastic, etc. mixed with conductive fine powder, and as the environmental humidity decreases, the resistance of these materials increases, making them difficult to charge.

FIG. 5 shows the relationship between the direct current (DC) voltage applied to the charging member and the charging potential of the image bearing member as the charged member of the image forming apparatus under high humidity and low humidity. Under high humidity, an applied voltage VA is required to charge the image carrier to the potential VD, but under low humidity, a higher applied voltage VB is required. Therefore, in order to keep the potential constant, it is necessary to switch the applied voltage depending on the environmental humidity.

FIG. 6 shows D when constant current control is applied to the DC component.
The relationship between C current value and charging potential is shown. In this case the DC current I
If controlled at A, the charging potential is almost constant regardless of humidity. However, in order to carry out constant current control, it is necessary to perform a process of neutralizing the image carrier before the image carrier is charged. That is, if DC constant current control is performed without the static elimination process before the charging process, as shown by the broken line F in FIG. It is not possible to obtain a constant charging potential VD. A broken line F in FIG. 7 shows a temporal change in the charging potential of the image carrier when the DC component is controlled at a constant current in an image forming apparatus that does not have a pre-charging static elimination process. The solid line E is the one when constant voltage control is performed.

[0013] In the present invention, a charging member provided with a resistance layer is disposed opposite to an object to be charged in a non-contact manner with a gap therebetween, and an oscillating voltage is applied to the charging member to charge the object to be charged. With regard to objects, there is no need to install special equipment for static elimination before charging, such as an exposure lamp device for static elimination or a discharger.
Moreover, it is an object of the present invention to always carry out charging processing with a stable charging potential without being affected by environmental humidity.

[0014]

[Means for Solving the Problems] The present invention is a charging device characterized by the following configuration.

(1) In a charging device that charges the surface of the object to be charged by applying a voltage to a charging member which is disposed opposite to the surface of the object to be charged with a gap therebetween and has a resistance layer on the portion facing the object to be charged, the charging device charges the object to be charged. The voltage applied to the member is an oscillating voltage, and when the object to be charged is charged from a neutralized state, the oscillating center voltage component is controlled at a constant current, and the DC voltage at this time is detected and then the voltage is controlled at a constant voltage. A charging device that

(2) The charging device according to (1), wherein the facing gap distance between the charging member and the charged member is 1 mm or less.

(3) The charging device according to (1), wherein the oscillating voltage is a superimposed voltage of an AC component and a DC component.

(4) The oscillating voltage is a superimposed voltage of an alternating current component and a direct current component, and the peak-to-peak voltage value of the alternating current component is determined when the charging member is opposed to the surface of the charged object with a predetermined gap therebetween. When a DC voltage is applied between the charging member and the charged member starts to be charged, the applied DC voltage value is at least twice the charging start voltage value. (1) The charging device as described. A charging device characterized by constant current control based on the total amount of current.

[0019]

[Function] (a) Even if the charging member is disposed facing the surface of the charged object with a gap therebetween in a non-contact manner, when an oscillating electric field is applied to the charging member, the opposing gap between the charging member and the image carrier By forming an oscillating electric field in the area, the surface of the object to be charged is charged in the same manner as when the charging member is brought into contact with the surface of the object to be charged.

(b) Since the charging member faces the surface of the object to be charged with a gap therebetween and is not in contact with it, no vibration noise is generated even when a high frequency oscillating voltage is applied to the charging member. Therefore, a sufficient high frequency oscillating voltage can be applied to the charging member.
It is possible to uniformly charge the surface of the object to be charged, to prevent interference fringes from occurring on the image surface, and to respond to increased process speeds of image forming apparatuses and the like. Contamination of the surface of the image carrier due to direct contact with the charging member and the occurrence of image defects due to the contamination are prevented.

(c) In the first constant current control, the oscillating center voltage (DC component) of the oscillating voltage applied to the charging member changes as the environmental humidity decreases and the resistance of the resistance layer of the charging member increases, the constant current control is performed. Therefore, the output voltage of the power supply will automatically increase, and conversely, if the environmental humidity increases, the output voltage will decrease due to constant current control and change to a voltage that corresponds to the current environmental humidity. Then, the voltage is detected, and thereafter the DC component of the applied oscillating voltage is converted to constant voltage control so as to maintain the detected voltage. As a result, the charging potential of the charged object can be kept constant from the start to the end of charging, regardless of the environmental humidity.

[0022] The neutralized state (uncharged state) of the object to be charged before the start of charging is a state in which the DC component of the applied oscillating voltage is turned off and only the AC component is applied to the surface of the object to be charged at the end of the previous charging. or, in the case of an image forming apparatus, by exposing the entire surface of the object to be charged using an image information exposure means, using special equipment for static elimination before charging, such as an exposure lamp device for static elimination or a discharger. It can be easily created without deployment. Therefore, even if the object to be charged is repeatedly subjected to charging processing, such as an image bearing member of an image forming apparatus, the load remains constant without being affected by load fluctuations due to the rotations. That is, the charging potential of the charged object does not increase as the charged object rotates, but remains constant.

[0023]

【Example】

<Embodiment 1> (FIGS. 1 to 3) (1) Example of image forming apparatus FIG. 1 is a schematic diagram of an example of an image forming apparatus using a charging device according to the present invention as a charging means for an image carrier. The image forming apparatus of this example is a laser beam printer using an electrophotographic process.

Reference numeral 1 denotes an electrophotographic photosensitive drum as an image carrier (charged member), which is composed of an OPC photosensitive layer 1b formed on the outer peripheral surface of a conductive drum base 1a made of aluminum or the like.
Specified process speed (peripheral speed) in the clockwise direction of arrow a
It is rotationally driven with.

The peripheral surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 as a charging member, which will be described later.

One surface of the photosensitive drum, which has been uniformly charged, receives scanning exposure L of a laser beam output from a laser beam scanner (not shown) and modulated in accordance with time-series electric digital pixel signals of target image information. As a result, an electrostatic latent image corresponding to the desired image information is formed on the drum surface. The formed latent image is developed as a toner image by a developing device 4. The toner image is then transferred onto a transfer material S that is timing-fed from a paper feeding section (not shown) between the photosensitive drum 1 and a transfer roller 5 serving as a transfer means. A transfer voltage is applied to the transfer roller 5 from a power source (not shown) during transfer.

The transfer material S to which the toner image has been transferred is separated from the surface of the photosensitive drum, and the image is fixed by a fixing device 7. Further, the surface of the photosensitive drum 1 after the transfer is cleaned by removing residual toner and the like by a cleaning device 6, and is repeatedly used for image formation.

The image forming apparatus of this embodiment has a photosensitive drum 1
, a charging roller 2, a developing device 4, and a cleaning device 6 are collectively provided as a process unit (process cartridge) 8 that can be attached and detached from the main body of the image forming apparatus. This is done by sliding along the guide 9 of the forming device main body. The developing device 4 may be separate from the process unit 8. Further, the process unit 8 only needs to include at least the photosensitive drum 1 as an image carrier and the charging roller 2 as a charging member.

(2) Charging device The charging roller 2 as a charging member includes a conductive core metal 2a made of iron or stainless steel, a resistance device 2b formed concentrically and integrally coated on the core metal, and a resistor device 2b formed in the axial direction of the core metal 2a. In the resistance layer 2b
It consists of a spacer ring 2c made of an insulating material and integrally provided on both end sides of the spacer ring 2c.

The spacer ring 2c is concentric with the resistance layer 2b, and the radius of the spacer ring 2c is larger than the radius of the resistance layer 2b, so that the opposing gap formed between the surface of the photosensitive drum 1 as an object to be charged and the resistance layer 2b is larger than the radius of the resistance layer 2b. It is set larger by distance Z.

The resistance layer 2b is made of rubber/plastic or rubber/plastic mixed with conductive fine powder to adjust the resistance value, and the resistance value is generally 1 MΩ/cm2.
~500MΩ/cm2.

The above-mentioned charging roller 2 has both ends of a core bar 2a supported by bearings (not shown), and is held substantially parallel to the generatrix direction of the photosensitive drum 1, and both ends are pressed against the photosensitive drum 1 by biasing means such as pressing springs. The spacer rings 2c at both ends are kept in contact with the surface of the photosensitive drum 1 with a predetermined pressing force. Therefore, the charging roller 2 has a spacer ring 2c.
A portion of the resistive layer 2b in between is maintained in a non-contact facing state with a gap Z with respect to the surface of the photosensitive drum 1, and rotates as the photosensitive drum 1 rotates. The gap Z is preferably set to, for example, 1 mm or less, preferably 300 μm or less.

The charging roller 2 is connected to the photosensitive drum 1 as described above.
It may be driven to rotate in accordance with the rotation of the photosensitive drum 1, it may be actively rotated in the forward direction of the rotation direction of the photosensitive drum 1, it may be rotationally driven in the opposite direction, or it may be rotated in a non-rotating direction. It may also be in a stopped state.

Reference numeral 3 denotes a voltage applying power supply unit for the charging roller 2, which supplies an oscillating voltage (VDC+VAC) obtained by superimposing a DC voltage VDC and an AC voltage VAC to the core metal 2a of the charging roller 2. By applying this oscillating voltage to the charging roller 2, the circumferential surface of the rotating photosensitive drum 1, which is a charged object, is charged to the oscillating center voltage (=DC voltage VDC) of the oscillating voltage.

It is desirable that the alternating current component of the oscillating voltage be controlled by constant current. Further, it is desirable that the oscillating voltage has a peak-to-peak voltage that is at least twice the charging start voltage of the photosensitive drum 1 as the object to be charged when only DC voltage is applied to the charging roller 2, for example, 500 Vpp to 10 kVpp, frequency 1
The frequency is set between 00Hz and 10KHz.

The charging start voltage is the voltage applied at which the photosensitive drum 1 (photosensitive layer 1b), which is the object to be charged, whose potential was 0 in advance, starts to be charged when only a DC voltage is applied to the charging roller 2, which is the charging member. There is a DC voltage value. This charging start voltage varies depending on the material and layer thickness of the photoreceptor layer 1b, the type of the object to be charged, and the gap Z between the object to be charged and the charging member. By applying a voltage having a peak-to-peak voltage that is at least twice the charging start voltage between the charged body and the charged body, a good oscillating electric field is formed between the two,
It was found that charging uniformity could be obtained. This is because an oscillating electric field is formed between the charging member and the object to be charged, that is, charge transfer and reverse transfer occur. Furthermore, even if a peak-to-peak voltage smaller than twice the charging start voltage is applied between the charging member and the object to be charged, spot-like charging unevenness is likely to occur on the object to be charged.

The above-mentioned oscillating voltage (or AC component voltage)
is a voltage whose voltage value changes periodically, and its waveform may be a triangular wave, a rectangular wave, a sawtooth wave, etc. in addition to a sine wave, and is formed by periodically turning on and off a DC power supply. A square wave voltage may also be used.

(3) Control FIG. 2 shows the charging roller 2 of the image forming apparatus shown in FIG.
3 shows a timing chart of applied voltage control.

In the case of this embodiment, an oscillating voltage in which the AC component VAC and the DC component VDC described above are superimposed is applied from the power supply 3 to the charging roller 2 based on the charging start signal of the image forming execution sequence. to start charging the rotating photosensitive drum.

In this case, constant current control is performed on the DC component VDC of the oscillating voltage within one rotation of the photosensitive drum from the start of charging, and the DC voltage at this time is detected. Next, before the rotation of the photosensitive drum 1 enters the second rotation, the DC component VDC of the applied oscillating voltage is converted to constant voltage control so as to maintain the detected DC voltage.

The formation of a latent image by the exposure L may be started either during the above constant current control or after starting the constant voltage control.

After image formation is completed, for the next charging control, the AC component VAC of the oscillating voltage is left ON and the DC component VDC is turned OFF (=OV) to complete one or more revolutions of the photosensitive drum 1. After the static electricity is removed, the rotational drive of the photosensitive drum 1 and the application of the alternating current component VAC are stopped to enter a standby state.

In this way, during the first rotation of the drum when charging of the photosensitive drum 1 is started, the P voltage is applied to the charging roller 2 under constant current control with respect to the DC component VDC, as described above, so that the applied DC voltage is is the voltage VA in Figure 5 in the case of a high humidity environment, and the voltage VB in the case of a low humidity environment.
The charging potential of the photosensitive drum 1 becomes constant potential VD as shown in FIGS. 3, 4, and 5 regardless of the environmental humidity.

From the second revolution of the drum rotation after the photosensitive drum 1 starts to be charged, the DC component VDC is switched to constant voltage control, so that the charging potential of the photosensitive drum 1 thereafter is maintained constant as shown by the solid line graph E in FIG. be done.

To eliminate static electricity from the photosensitive drum 1 after image formation is completed, by turning off the DC component VDC of the oscillating voltage applied to the charging roller 1, the AC component VAC is used to remove static electricity from the photosensitive drum 1 (uncharged state). ) to prepare for the next charging control, and there is no need to provide dedicated static elimination equipment such as a static elimination exposure lamp device or a discharger for static elimination before charging.

Note that the DC voltage detection during constant current control may be performed when the power of the image forming apparatus is turned on or when the process unit 8 is installed, during the process of performing multiple rotations in front of the photosensitive drum.

The DC voltage of constant voltage control is not limited to maintaining the detected DC voltage during constant current control by constant voltage control, but can also be, for example, a value obtained by multiplying the detected DC voltage during constant current control by a coefficient or adding a constant value. But that's fine. At this time, constant current control is performed during non-image formation.

In the process of removing electricity from the photosensitive drum 1 in preparation for the next charging control after image formation is completed, as shown in FIG. It is also possible to carry out the process by scanning and exposing the entire surface of the rotary photosensitive drum for one or more revolutions using a laser beam scanner that writes image information and scans and exposes the entire surface of the rotary photosensitive drum. After this exposure and neutralization, the drive of the photosensitive drum 1 is stopped and placed in a standby state.

<Embodiment 2> (FIG. 4) This embodiment is an example in which a blade-type charging member is used. FIG. 4(a) is a cross-sectional side view, and FIG. 4(b) is a front view with the middle part omitted.

Reference numeral 11 denotes a charging blade as a charging member, which consists of a blade base 11a made of metal and a resistance layer 11b covering the outer surface of the blade base 11a. Both longitudinal ends of this charging blade 11 are connected to spacer members 12 with screws 13, respectively.
・It is fixed and installed with 13. Spacer member 12/1
2 is supported by a stationary member (not shown). A gap Z between the charging blade 11 and the photosensitive drum 1 is formed by a spacer member 12.1.
2. Since the charging blade 11 does not move, it is possible to suppress the generation of noise at the electrical contact portion. Further, compared to the charging roller 2, there is an advantage that the installation space can be omitted.

[0051] The charging member may be of any shape or form other than the roller type or blade type, such as a rod type, block type, wire type, or sheet type.

[0052]

As described above, in the present invention, a charging member provided with a resistance layer is disposed opposite to a charged object without contact with a gap therebetween, and an oscillating voltage is applied to the charging member to de-charge it. Regarding the charging device that charges the body, it is possible to maintain a stable charging potential at all times without having to install special equipment for static elimination before charging, such as an exposure lamp device for static elimination or a discharger, and without being affected by environmental humidity. The charging process can be carried out, and the intended purpose is well achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus using a charging device according to the present invention as a charging means for an image carrier.

[Figure 2] Example of timing chart for voltage application to the charging roller

[Figure 3] Other timing chart examples

[Figure 4] (
a) and (b) are a cross-sectional side view of a charging device in which the charging member is a charging blade, and a front view with the middle part omitted.

[Figure 5] Diagram showing the relationship between the DC voltage applied to the charging member and the charging potential

[Figure 6] Diagram showing the relationship between the DC current applied to the charging member and the charging potential

[Figure 7] Diagram showing the rotation of the photosensitive drum and changes in charging potential

[Explanation of symbols]

1 Photosensitive drums 2 and 11 as charged objects
Charging roller or charging blade 3 as a charging member Power source 2c/12 Spacer roller or spacer Z
gap

Claims (4)

[Claims] 1. A charging device that charges the surface of the object to be charged by applying a voltage to a charging member that is disposed opposite to the surface of the object to be charged with a gap therebetween and has a resistance layer on a portion facing the object to be charged,
The voltage applied to the charging member is an oscillating voltage, and when the object to be charged is charged from a neutralized state, the oscillating center voltage component is controlled at a constant current, and after the DC voltage at this time is detected, the voltage is controlled at a constant voltage. Characteristic charging device. 2. The charging device according to claim 1, wherein the facing gap distance between the charging member and the charged member is 1 mm or less. 3. The charging device according to claim 1, wherein the oscillating voltage is a superimposed voltage of an alternating current component and a direct current component. 4. The oscillating voltage is a superimposed voltage of an alternating current component and a direct current component. A claim characterized in that the applied DC voltage value when charging of the charged member starts by applying a DC voltage between the charged member and the member is at least twice the charging start voltage value when the charging start voltage value is taken as the charging start voltage value. Item 1. The charging device according to item 1.