JPH04328589A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an oscillation sound(electrostatic charging sound) and interference fringe on an image surface when high frequency oscillating voltage is impressed on an electrostatic charging member, to prevent the contamination of the surface of an image carrier caused by the direct contact of the electrostatic charging member and the occurrence of a faulty image caused by the contamination, and to facilitate the uniform electrostatic charging processing and the uniform destaticizing processing on the surface of the image carrier in an image forming device where an image producing process including stages where the surface of the image carrier is electrostatically charged and destaticized by the electrostatic charging member is applied. CONSTITUTION:The electrostatic charging member 21 is opposed to the surface of the image carrier 1 by interposing a gap Z. At the electrostatic charging stage of the surface of the carrier 1, the surface of the carrier 1 is electrostatically charged by impressing the first oscillating voltage (Vac+Vdc1) between the member 21 and the surface of the carrier 1. At the destaticizing stage of the surface of the carrier 1, the surface of the carrier 1 is destaticized by impressing the second oscillating voltage (Vac+Vdc2) whose oscillating center voltage is smaller than the first oscillating voltage between the member 21 and the surface of the carrier 1.

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 that forms an image by applying an image forming process that includes a step of charging the surface of an image carrier with a charging member and a step of removing the charge.

0002

2. Description of the Related Art Conventionally, in image forming apparatuses such as laser printers and copying machines that utilize an electrophotographic process or an electrostatic recording process, the surface of an image carrier such as an electrophotographic photoreceptor or an electrostatic recording dielectric material is polarized to a predetermined polarity.・Corona dischargers such as corotrons and scorotrons, which have good uniform charging properties, are widely used as means for uniformly charging or eliminating static electricity.

However, corona dischargers require an expensive high-voltage power source, require space for themselves and the shield space for the high-voltage power source, and often generate corona products such as ozone, which require additional equipment to deal with them. It has problems such as requiring means and mechanisms, which make the device larger and more expensive.

[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. In contact charging, a charging member to which a voltage (for example, a DC voltage of about 1 to 2 KV or a superimposed voltage of a DC voltage and an AC voltage, etc.) 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. This device charges the surface of a charged body to a predetermined potential, and the present applicant also reported in Japanese Patent Application Laid-Open No. 63-149669, etc. A method has been proposed for uniformly charging a charged object by forming an oscillating electric field having a peak-to-peak voltage between a charging member and a charged object. Furthermore, Japanese Patent Application Laid-Open No. 64-73364 proposes a means for preventing electrical leakage due to pinholes, scratches, etc. on the surface of a charged object such as a photoreceptor by providing a resistive layer on the surface of a charging member. .

[0005]

[Problems to be Solved by the Invention] However, the contact charging device as described above cannot be used with an image forming device that forms an electrostatic latent image by writing image information on the charging surface of an image carrier by line scanning, such as a laser beam. When used as a charging means for printers, the following problems arise. That is, when outputting a high-density, evenly spaced image pattern in the sub-scanning direction, interference fringes may occur on the image surface if the frequency of the AC voltage applied to the contact charging member and the spatial frequency of the image pattern become close. be. Although this problem can be solved by increasing the frequency of the AC voltage to a sufficiently high frequency, vibration noise (charging noise) due to the AC electric field is likely to occur due to contact charging.

Furthermore, in the above-mentioned contact charging device, since the charging member slides directly on the surface of the image carrier, the surface of the image carrier is likely to be contaminated, which may cause image defects.

An object of the present invention is to provide an image forming apparatus that solves the above-mentioned problems.

[0008]

[Means for Solving the Problems] The present invention is an image forming apparatus characterized by the following configuration. (1) In an image forming apparatus that performs image formation by applying an image forming process that includes a step of charging the surface of an image carrier with a charging member and a step of removing the charge, the charging member is placed opposite to the surface of the image carrier with a gap. In the step of charging the surface of the image carrier, the surface of the image carrier is charged by applying a first oscillating voltage between the charging member and the surface of the image carrier; An image forming apparatus characterized in that static electricity is removed from a surface of an image carrier by applying a second oscillating voltage having a center oscillating voltage smaller than the first oscillating voltage.

(2) The image forming apparatus according to (1), wherein the facing gap distance between the charging member and the surface of the image carrier is 1 mm or less.

(3) The image forming apparatus according to (1), wherein the first and second oscillating voltages are a superimposed voltage of an AC component voltage and a DC component voltage.

(4) The first and second oscillating voltages are superimposed voltages of an AC component voltage and a DC component voltage, and the second oscillating voltage is an OV of the DC component voltage, or a DC voltage of the first oscillating voltage. The image forming apparatus according to (1), wherein the voltage is set to a lower level than the component voltages.

(5) The first and second oscillating voltages are superimposed voltages of an AC component voltage and a DC component voltage, and the AC component voltage is the peak-to-peak voltage value, or the charging member is placed at a predetermined gap on the surface of the image carrier. When a DC voltage is applied between a charging member and an image carrier facing each other with the same angle and the applied DC voltage value when charging of the image carrier starts is taken as a charging start voltage value, the charging start voltage value is the charging start voltage value. The image forming apparatus according to (1), wherein the image forming apparatus is twice or more as large as .

[0013]

[Operation] Even if the charging member is disposed facing the image carrier surface with a gap (gap) in a non-contact manner, when the first or second oscillating electric field is applied to the charging member, the charging member and the image By forming an oscillating electric field in the gap (charging part) facing the carrier, it is possible to carry out charging or neutralization of the surface of the image carrier in the same way as when a charging member is brought into contact with the surface of the image carrier. .

[0014] Since the charging member faces the image carrier surface 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, which enables uniform charging and neutralization of the image bearing surface, prevents interference fringes from occurring on the image surface, and directs the charging member directly to the charging member. Contamination of the surface of the image carrier due to contact and the occurrence of image defects due to the contamination are prevented.

[0015] Furthermore, by switching the voltage applied to the charging member between the first oscillating voltage and the second oscillating voltage during the charging process of the image carrier and during the neutralizing process as described above, one charging member can be charged. It can be used as both a charger and a static eliminator, and there is no need to provide special exposure means for static electricity removal, making this type of image forming apparatus as compact, simple, and low cost as possible. etc. can be achieved.

[0016]

【Example】

<Embodiment 1> (FIGS. 1 to 5) FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment, and FIG. 2 is a front view of a charging device portion.

Reference numeral 1 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 of this embodiment is composed of a grounded aluminum drum base 1b and an organic photoconductor (OPC) layer formed on the outer peripheral surface of the drum base, and has an outer diameter of 30 mm, as shown by the arrow. is rotated clockwise at a predetermined circumferential speed (process speed).

The circumferential surface of the rotary photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging device 2, which will be described later, and then subjected to exposure L (scanning exposure using a laser scanner or the like) by an image information exposure means (not shown). By subjecting the document image to imaging slit exposure, etc.), an electrostatic latent image corresponding to target image information is formed. The formed latent image is developed as a toner image by a developing device 3. The toner image is then transferred to a transfer material P that is timing-fed from a paper feeding section (not shown) between the photosensitive drum 1 and a transfer roller 4 serving as a transfer means, and the transfer material P that has received the toner image transfer is The image is transported to a fixing device (not shown), where the image is fixed and output as an image formed product.

In the charging device 2, 21 is a charging roller as a charging member. The charging roller 21 includes a conductive core part 21a, a conductive roller part 21b made of iron, aluminum, etc. concentric with the core part 21a, and a dielectric breakdown prevention device that covers the circumferential surface of the conductive roller part 21b. It consists of a surface layer 21c made of a resistance material such as cellulose or nylon, and spacer ring layers 21d provided along the circumference at both ends of the roller, respectively.

The charging roller 21 has both ends of a core metal portion 21a supported by bearings (not shown), and is placed substantially parallel to the generatrix of the photosensitive drum 1, and biasing means 21e, such as a spring, presses both ends of the charging roller 21. Press with 21e and spacer ring layer 2c
- At portion 2c, the charging roller 2 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force.

Therefore, in the charging roller 21, the portion of the charging roller between the spacer ring layers 21d and 21d corresponds approximately to the thickness of the spacer ring layers 21d and 2d on both ends of the photosensitive drum 1.
They are held in a non-contact state where they face each other with a gap Z between them. The gap Z is, for example, 1 mm or less, preferably 300 mm.
A setting of μm or less is desirable.

The charging roller 21 may be driven to rotate in accordance with the rotation of the photosensitive drum 1, may be actively rotated in the forward direction of the rotation direction of the drum 1, or may be rotationally driven in the opposite direction. It may be in a non-rotating stopped state.

Reference numeral 6 denotes a power source for applying voltage to the charging roller 21, and the voltage of this power source 6 is applied via a sliding contact electrode 21f brought into contact with the end of the core metal 21a of the charging roller 2. Ru. In this embodiment, the power source 6 includes an AC power source 6a that generates an AC component voltage and a DC power source 6b that generates a DC component voltage.

Reference numeral 7 denotes a control circuit unit (CPU) that controls the output voltage level of the DC power supply 6b. This control circuit section 7 is connected to a DC power source 6b when the image forming process is a photosensitive drum charging step.
A first level DC component voltage Vdc1 is generated from , and a second level DC component voltage Vd is generated during the photosensitive drum static elimination process.
The DC power supply 6b is controlled to generate c2. Second
The level DC component voltage Vdc2 is set to OV or a voltage lower than the first level DC component voltage Vdc1.

Therefore, during the charging process, as shown in FIG. 3, the charging roller 21 receives the output AC component V from the AC power source 6a from the power source 6.
ac and the first level DC component voltage Vdc of the DC power supply 6b
A first oscillating voltage A (voltage whose voltage value changes periodically with time) consisting of a superimposition (Vac+Vdc1) of 1 and 1 is applied, and during the static elimination process, the output AC component Vac of the AC power source 6a and the second oscillating voltage A of the DC power source 6b are applied. The DC component voltage V at the level of
A second oscillating voltage B consisting of a superimposition with dc2 (Vac+Vdc2) is applied. The oscillating center voltage of the first oscillating voltage A is Vdc1, the oscillating center voltage of the second oscillating voltage B is Vdc2, and the oscillating center voltage V of the second oscillating voltage B
dc2 is smaller than the vibration center voltage Vdc1 of the first vibration voltage A.

The peak-to-peak voltage value of each of the first and second oscillating voltages A and B, that is, the output AC component voltage V from the AC power supply 6a
The peak-to-peak voltage value Vpp of ac is determined by applying a DC voltage to the charging roller 21, which is a charging member, by facing the surface of the photosensitive drum 1, which is an image bearing member, with a predetermined gap Z therebetween. When the applied DC voltage value when charging starts is taken as the charging start voltage value Vt, the charging start voltage value Vt is twice or more.

FIG. 4 shows the charging potential Vs of the photosensitive drum 1 when changing the peak-to-peak voltage Vpp (frequency f=1000 Hz) of the sinusoidal AC voltage Vac, which is the oscillating voltage applied to the charging roller 21, and the charging roller 21 and the photosensitive drum 1. The gap with the drum 1 is shown for Z=80 μm and Z=150 μm (DC component voltage −650 V). Gap Z=80μm
Then, when the AC component voltage Vac is Vpp=1800 V or more, the peak-to-peak voltage Vpp is more than twice the charging start voltage value when DC voltage is applied, and the process of charging and reverse charging is repeated in the gap between the charging roller 21 and the photosensitive drum 1. JP-A No. 63-14966 discloses that the photosensitive drum 1 is uniformly charged.
This can be understood from Publication No. 9. On the other hand, it can be seen that uniform charging is achieved when the AC component voltage is Vpp=2600 V or higher in the gap Z=150 μm.

Next, FIG. 5 shows the charging potential Vs of the photosensitive drum 1 when the DC component voltage Vdc in FIG. 4 is used as a parameter. From this, when Z = 80 μm, Vpp = 1800 V or more, and when Z = 150 μm, Vpp =
In the area where uniform charging of 2600V or more is performed,
It can be seen that the charging potential Vs of the photosensitive drum 1 is determined by the DC component voltage Vdc applied to the charging roller 21.

In this embodiment, when performing image formation (charging During the process), the DC component voltage Vdc1 applied to the charging roller 21 is -550V. As a result, the charging roller 21 receives the first oscillating voltage A.
(=Vac+Vdc1) is applied, and the photosensitive drum 1 is uniformly charged to approximately -550V, and a uniform image is obtained.

[0030]Next, a static elimination process is started in which the image forming process on the photosensitive drum is completed, and a signal indicating the completion of the image forming process on the photosensitive drum is sent from the control circuit section 7 to the DC power supply 6b, and the charging roller 21 is charged. The DC component voltage Vdc2 to be applied is set to OV. As a result, the charging roller 21 receives a second oscillating voltage B (=
Vac) is applied, the charging roller 21 operates as a static eliminator, and can uniformly remove static electricity from the photosensitive drum 1. Thereafter, all voltages applied to the charging roller 21 are turned off, the rotational drive of the photosensitive drum 1 is stopped, and the photosensitive drum 1 is put into a standby state.

As a result, since the charging roller 21 is not in contact with the photoreceptor 1, sufficient alternating current component V is generated without producing vibration noise.
Since AC voltage can be applied to the charging roller 21 both during the charging process of the photosensitive drum 1 and during the static electricity removal process,
The charging process) uniformly charges the photosensitive drum, and after image formation is completed (
In the static electricity removal step), image formation can be completed by uniformly removing static electricity from the photosensitive drum. Therefore, there is no need to provide special static elimination equipment, exposure equipment, etc. for static elimination.

In this embodiment, the DC applied voltage V during static elimination
Although dc2 is set to OV, this voltage may be set to a value substantially equal to or lower than the potential at which the photoreceptor is neutralized, and is not limited to OV.

<Embodiment 2> (FIGS. 6 and 7) FIGS. 6 and 7 show an example in which a blade-type charging member is used. FIG. 6 is a front view of the main parts, and FIG. 7 is a side view.

Reference numeral 21A is a charging blade made of a conductive or semiconductive material as a charging member, and a resistance layer may be provided on the surface thereof. Both ends of this charging blade 21A are fixed and attached to spacer members 12, 12, respectively, with screws 13, 13. The spacer members 12 are supported by a stationary member (not shown). A gap Z between the charging blade 21A and the photosensitive drum 1 is defined by the spacer members 12. Voltage is applied directly to the blade 21A by the power source 6 through the lead wire 6c.

[0035] Since the charging member 21A is constructed in such a way that it does not move, it is possible to suppress the generation of noise at the electrical contact portion. Furthermore, the charging roller 21
There is also the advantage that space can be omitted compared to .

The charging member is the roller body 21 or the blade body 21.
Not limited to A, brush-shaped ones, belt-shaped ones, etc. can also be used as appropriate. Further, the present invention is not limited to a drum-shaped photoreceptor, and the present invention can also be implemented using a belt photoreceptor. The present invention can also be implemented in a structure in which the charging member and the photoreceptor are integrated into a process cartridge.

[0037] Furthermore, the charging polarity may be either positive or negative,
The voltage waveform of the alternating current component is not limited to a sine wave, but may also be a rectangular wave, a triangular wave, or the like, or a rectangular wave voltage formed by turning on and off a direct current voltage.

Second level DC voltage Vdc after image formation
2 does not necessarily have to be OV, and this value should be set to a potential value that will not cause any change in the characteristics even if the photoreceptor used is left as it is, and if the photoreceptor is substantially neutralized. good. Normally, if you keep it below 50V, there will be no problem.

[0039]

[Effects of the Invention] As described above, according to the present invention, it has all the same advantages as the contact charging method, and since it is a non-contact charging method, it charges with sufficient vibration voltage without producing vibration noise (charging noise). Since it can be applied to the member, it is possible to uniformly charge and eliminate static electricity, it can prevent interference fringes from occurring on the image surface, it can prevent contamination of the image carrier surface due to direct contact with the charging member, and the occurrence of image defects due to this. Prevented. In addition, by switching the oscillating voltage applied to the charging member, one charging member can be operated as a charger during image formation (charging process) and as a static eliminator after image formation (static elimination process). There is no need to provide special exposure means or the like for this purpose, and this type of image forming apparatus can be made as compact, simple, and low cost as possible.

[Brief explanation of drawings]

[Figure 1] Schematic configuration diagram of an image forming apparatus according to an embodiment

[2
Figure] Front view of charging device part

[Figure 3] Diagram explaining the relationship between the first and second oscillating voltages

[Figure 4] Graph showing the relationship between the peak-to-peak voltage of the AC component voltage applied to the charging member and the surface potential of the photosensitive drum

[Figure 5]
Ditto graph

[Figure 6] Front view of the main parts of an example using a blade-type charging member

[Figure 7] Its side view

[Explanation of symbols]

1 Photosensitive drum 2 as an image carrier Charging devices 21 and 21A Charging roller or charging blade 6 as a charging member Voltage application power source 6a AC power source 6b DC power source Z Gap

Claims (5)

[Claims] 1. An image forming apparatus that performs image formation by applying an image forming process that includes a step of charging the surface of an image carrier with a charging member and a step of removing the charge, the charging member being connected to the surface of the image carrier with a gap between the charging member and the surface of the image carrier. The image carrier surface is charged by applying a first oscillating voltage between the charging member and the image carrier surface, and the image carrier surface is charged by applying a first oscillating voltage between the charging member and the image carrier surface. An image forming apparatus characterized in that static electricity is removed from the image carrier surface by applying a second oscillating voltage having a vibration center voltage smaller than the first oscillating voltage between the image carrier surface and the image carrier surface. 2. The image forming apparatus according to claim 1, wherein the facing gap distance between the charging member and the surface of the image carrier is 1 mm or less. 3. The image forming apparatus according to claim 1, wherein the first and second oscillating voltages are superimposed voltages of an AC component voltage and a DC component voltage. 4. The first and second oscillating voltages are superimposed voltages of an AC component voltage and a DC component voltage, and the second oscillating voltage is a superimposed voltage of the DC component voltage, or the DC component of the first oscillating voltage. The image forming apparatus according to claim 1, wherein the voltage is set to a level lower than the voltage. 5. The first and second oscillating voltages are superimposed voltages of an alternating current component voltage and a direct current component voltage, and the alternating current component voltage has a peak-to-peak voltage value that allows the charging member to maintain a predetermined gap from the image carrier surface. When a DC voltage is applied between a charging member and an image carrier facing each other and the applied DC voltage value when charging of the image carrier starts is taken as a charging start voltage value, the charging start voltage value is The image forming apparatus according to claim 1, wherein the image forming apparatus is twice or more.