JP2010156920A - Electrifying roller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying roller and an image forming apparatus for obtaining excellent images by suppressing resonance. <P>SOLUTION: The electrifying roller 3 includes a sidewall 31a and a sidewall 31b, which are provided on both ends of a cylindrical body 31 and a cylindrical body 31 and mutually facing in an axial center direction, and charges a photoreceptor when at least an alternating current voltage is applied. An opening part 36a penetrating the sidewall 31a and an opening part 36b penetrating the sidewall 31b are formed in the sidewall 31a and the sidewall 31b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging roller and an image forming apparatus.

  An image forming apparatus such as a copying machine or a printer that employs an electrophotographic method uses an image formed of toner on a recording medium such as paper by a series of image forming processes such as a charging process, an exposure process, a development process, and a transfer process. Form. In the charging process, for example, a charging roller is disposed in the vicinity of the image carrier to uniformly charge the surface of the image carrier.

  As a charging roller for charging an image carrier, a charging roller described in Patent Document 1 below is known. This charging roller is arranged so that a gap member is wound around both ends and a predetermined charging gap is maintained between the image carrier and the image carrier is made non-conductive by applying a charging bias in which a DC voltage and an AC voltage are superimposed. It is configured to be contact charged.

JP 2007-121480 A

By the way, in order to reduce the weight, the charging roller adopts a pipe-type roller having a hollow inside (a cylindrical body having side walls provided at both ends in the axial direction).
However, when an AC voltage is applied to the pipe-type charging roller to drive the pipe-type charging roller, the air inside the charging roller may vibrate due to the pipe length and a resonance sound may be generated. This resonance sound is not only perceived as an unpleasant noise, but also causes the charging roller itself to vibrate to fluctuate the gap with the image carrier, resulting in poor charging of the image carrier that contributes to poor image formation. It will also cause.

  This resonance sound is one of the causes of the occurrence of mutual interference when the frequency of the AC voltage is close to the resonance frequency caused by the pipe length of the charging roller. Normally, the frequency of the AC voltage is designed to a value that does not generate resonance noise. However, when the rotation speed (printing speed) of the image carrier is variable, the speed is set to prevent charging failure of the image carrier. Accordingly, since the frequency of the AC voltage must be adjusted, resonance may occur as a result of this adjustment.

  SUMMARY An advantage of some aspects of the invention is that it provides a charging roller and an image forming apparatus capable of suppressing a resonance sound and obtaining a good image.

In order to solve the above problems, the present invention has a cylindrical body and side walls provided at both ends of the cylindrical body and facing each other in the axial direction, and at least an alternating voltage is applied to charge the image carrier. The charging roller employs a configuration in which an opening penetrating the side wall is formed in at least one of the side walls.
By adopting such a configuration, in the present invention, since the opening is formed in the side wall, it is possible to let the internal air that vibrates with the side wall as a fixed end escape from the opening to the outside. Further, since the area of the side wall is reduced, it is possible to reduce the internal air reflected by the side wall and vibrating in the axial direction.

In the present invention, a configuration is adopted in which the openings are provided on both of the side walls, and the provided positions are not coincident with each other in the opposing direction.
By adopting such a configuration, in the present invention, since the openings do not coincide with each other in the direction in which the openings face each other, the internal air is reduced from being reflected and vibrated at the same position on the side wall in the axial direction. The

Moreover, in this invention, the structure that the said opening part is provided with two or more by the surroundings of an axial center is employ | adopted.
By adopting such a configuration, in the present invention, since a plurality of openings are provided at regular intervals around the axis, the axis of the charging roller coincides with the center of gravity. The rotation drive is performed smoothly.

  In the present invention, an image forming apparatus including an image carrier and a charging roller for charging the image carrier, and the image forming apparatus including the above-described charging roller as the charging roller is obtained. .

1 is a schematic configuration diagram illustrating a printer according to an embodiment of the present invention. It is a figure which shows typically the photoreceptor and the charging roller in the printer in FIG. It is sectional drawing in the axial center direction of the charging roller in embodiment of this invention. It is a perspective view which shows the charging roller in embodiment of this invention. It is an arrow A figure and arrow B figure of the charging roller in FIG. It is a figure explaining the generation | occurrence | production mechanism of the resonance sound which generate | occur | produces in the charging roller in embodiment of this invention. It is a figure which shows the opening part in 2nd Embodiment of this invention. It is a figure which shows the opening part in 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a laser beam printer (hereinafter referred to as a printer) is exemplified as an image forming apparatus including the charging roller according to the present invention.

(First embodiment)
FIG. 1 is a schematic configuration diagram illustrating a printer 1 according to an embodiment of the present invention.
FIG. 2 is a diagram schematically showing the photoreceptor 2 and the charging roller 3 in the printer 1 in FIG.
As shown in FIG. 1, the printer 1 has a photoconductor (image carrier) 2 that carries an electrostatic latent image and a toner image. The photoconductor 2 is charged around the photoconductor 2. A charging roller 3; an exposure device 4 that forms an electrostatic latent image on the photoconductor 2; a developing device 5 that develops the electrostatic latent image on the photoconductor 2 with toner; and a transfer device that transfers the toner image on the photoconductor 2 6 and a cleaning device 7 for cleaning the photosensitive member 2 are disposed. The printer 1 also includes a control device 8 having a computer system that controls each component device in an integrated manner.

  The photoreceptor 2 has a cylindrical conductive substrate and a photosensitive layer formed on the peripheral surface (outer peripheral surface) thereof. For example, a conductive tube made of aluminum or the like is used as the conductive base material in the photosensitive member 2, and a conventionally known organic photosensitive member is used as the photosensitive layer. The photoconductor 2 is a rotary drive device having a rotary shaft 2a and a rotary shaft 2b projecting from both side surfaces in the axial direction so as to be rotatably supported via a bearing (not shown) and having a drive source such as a motor. 2c is configured to rotate at a predetermined speed around the axis (in this embodiment, in the direction of the arrow in FIG. 1 (clockwise)).

  The exposure device 4 writes an electrostatic latent image on the charged photoconductor 2 with, for example, a laser beam. The developing device 5 includes a developing roller 5a, a toner supply roller 5b, and a toner layer thickness regulating member 5c. Then, toner as a developer is supplied onto the developing roller 5a by the toner supply roller 5b, and the thickness of the toner on the developing roller 5a is regulated by the toner layer thickness regulating member 5c toward the photoreceptor 2. The electrostatic latent image on the photosensitive member 2 is developed with the conveyed toner, and a toner image is formed on the photosensitive member 2.

  The transfer device 6 includes a transfer roller 6a, and the transfer roller 6a transfers the toner image onto the photoreceptor 2 onto a transfer medium 13 such as transfer paper or an intermediate transfer medium. When the toner image is transferred to the transfer paper as the transfer medium 13, the toner image on the transfer paper is fixed by a fixing device (not shown) to form an image on the transfer paper, and the toner image is transferred to the transfer medium 13. When the toner image is transferred to the intermediate transfer medium, the toner image on the intermediate transfer medium is further transferred to the transfer paper, and then the toner image on the transfer paper is fixed by a fixing device (not shown) to form an image on the transfer paper. Is done.

  The cleaning device 7 has a cleaning member 7a such as a cleaning blade, for example, and the photosensitive member 2 is cleaned by the cleaning member 7a, and the transfer residual toner on the photosensitive member 2 is removed and collected.

Next, the configuration of the charging roller 3 according to the present invention will be described in detail with reference to FIGS.
FIG. 3 is a cross-sectional view in the axial direction of the charging roller 3 in the embodiment of the present invention.
FIG. 4 is a perspective view showing the charging roller 3 in the embodiment of the present invention.
5 is an arrow A view and an arrow B view of the charging roller 3 in FIG.
The charging roller 3 is a pipe-type charging roller having a hollow portion 30a therein, and includes a cylindrical body 31 having side walls 31a and 31b provided at both ends in the axial center direction. Further, the charging roller 3 includes a bias power source 32 that applies a voltage obtained by superimposing a DC voltage and an AC voltage.

  The charging roller 3 is formed from a conductive metal material (for example, a surface of the SUM 22 plated with Ni), and a conductive coating material is applied to the peripheral surface (outer peripheral surface) by, for example, spray coating. A resistance layer 31c is formed. Gap members 33 for restricting the charging gap G with the photosensitive member 2 to a predetermined distance (for example, about 10 to 50 μm) are provided on the peripheral surfaces of both ends of the cylindrical body 31. The gap member 33 is formed by winding a film member having a constant film thickness around the cylindrical body 31.

  The charging roller 3 is provided with a rotating shaft 31a1 and a rotating shaft 31b1 protruding from the side wall 31a and the side wall 31b so as to coincide with the axis. As shown in FIG. 2, the rotating shaft 31a1 and the rotating shaft 31b1 are rotatably supported by a bearing 34a and a bearing 34b, respectively. An urging device 35a and an urging device 35b are connected to the bearing 34a and the bearing 34b, respectively. The charging roller 3 is urged toward the photosensitive member 2 by the urging device 35a and the urging device 35b, and presses the gap member 33 and the peripheral surface of the photosensitive member 2 to form a charging gap G. The charging roller 3 to which a voltage obtained by superimposing a DC voltage and an AC voltage is applied from the bias power source 32 is configured to charge the photoconductor 2 in a non-contact manner with a charging gap G.

4 and 5, the side wall 31a and the side wall 31b facing each other in the axial direction of the cylindrical body 31 have an opening 36a and an opening 36b penetrating the side wall 31a and the side wall 31b in the axial direction, respectively. Is formed. The opening 36a and the opening 36b are configured to communicate the hollow portion 30a with the outside.
As shown in FIG. 5A, the opening 36a has a substantially arc shape formed around the rotation shaft 31a1. On the other hand, as shown in FIG. 5 (b), the opening 36b has a substantially arc shape formed around the rotation shaft 31b1, but the provided position does not coincide with the opening 36a in the opposite direction. ing. In the present embodiment, the opening 36a and the opening 36b are provided at positions that are symmetric with respect to the rotation shaft 31a1 and the rotation shaft 31b1, respectively.

Next, the operation of the printer 1 having the above-described configuration and the generation mechanism of resonance sound in the charging roller 3 will be described with reference to FIG. 6, and then the operation of the charging roller 3 having the above-described configuration will be described.
FIG. 6 is a diagram for explaining a generation mechanism of resonance generated in the charging roller 3 according to the embodiment of the present invention.

The printer 1 drives a charging roller 3 arranged with a charging gap G, and charges the surface of the photoreceptor 2 to a predetermined charging amount (uniformly). Specifically, the bias power supply 32 that has received a drive command from the control device 8 applies a voltage (Vcr) in which the AC voltage (Vac) is superimposed on the DC voltage (Vdc) to the charging roller 3, thereby causing the photoconductor. 2 is charged. The voltage (Vcr) applied by the bias power supply 32 is expressed by the following expression (1).
Vcr = Vdc + Vac (1)

The DC voltage (Vdc) is a parameter that determines the surface potential of the photosensitive member. For example, when the DC voltage is set to −600 (V), the surface potential of the photosensitive member 2 is slightly 0 (−600 (V)). V) is a value close to (for example, -590 (V)).
The AC voltage (Vac) superimposed on this DC voltage is expressed by the following equation (2).
Vac = 1 / 2Vpp · sin (2π · f · t) (2)
Here, Vpp, f, and t indicate the peak voltage of the AC voltage, the frequency of the AC voltage, and the time, respectively. Note that one half (1/2 Vpp) of the peak voltage (Vpp) is an amplitude voltage.

  The value of the peak voltage (Vpp) or the amplitude voltage (1/2 Vpp) is a value determined by the proximity distance between the surface of the charging roller 3 and the photosensitive member 2, the film thickness of the photosensitive member 2, the temperature and humidity in the apparatus, and the like. It is a requirement that the amplitude voltage is larger than a so-called discharge start voltage. This is because charging is performed by discharging. Specifically, when the distance (charging gap G) between the surface of the charging roller 3 and the surface of the photosensitive member 2 is 20 (μm) and the film thickness of the photosensitive member 2 is 20 (μm), the amplitude voltage is 800 to 900. It can be made to discharge by setting to (V). Note that the upper limit (900 (V) in the above example) is set because, if the applied voltage is too high, spark discharge (dielectric breakdown phenomenon) occurs beyond the discharge region that causes so-called discharge (corona discharge). This is because charging cannot be performed. Further, if the applied voltage is too high, ozone is generated too much when corona discharge occurs (ozone also serves as an oxidizing agent, so it is preferable not to generate ozone as much as possible from the viewpoint of influence on the human body).

  f (Hz) is the frequency of the AC voltage. f is determined by the peripheral speed of the photoreceptor 2 (the rotational speed of the photoreceptor 2). Specifically, if the peripheral speed of the photosensitive member 2 is about 100 (mm / s), A4 size paper is transported in the lateral feed and is about 10 ppm (printing speed of about 10 sheets per minute). Can be printed. In this case, if f is set to about 600 (Hz), human vision can be deceived with respect to charging spots in the so-called paper conveyance direction, that is, printing spots appearing during development, and good image formation can be performed. Can do.

  On the other hand, when the control device 8 gives a drive command to the rotational drive device 2c to increase the printing speed and changes the peripheral speed of the photosensitive member 2 from about 100 (mm / s) to about 200 (mm / s), A4 size paper can be transported horizontally and printing can be performed at about 20 ppm. However, if f remains at 600 (Hz), human vision cannot be deceived, and print spots caused by f can be printed. Is conspicuous, resulting in poor image formation. Therefore, in this case, the control device 8 gives a drive command for adjusting the frequency of the AC voltage to the bias power source 32 and adjusts it to about f = 1200 (Hz), whereby the problem of printing unevenness can be solved.

  However, if f is increased too much to prevent image formation defects as described above, there is a disadvantage that the current flowing during the discharge increases and the surface of the photoreceptor 2 is damaged by the discharge, and the amount of ozone generated There is a disadvantage that increases. Therefore, f is a value determined by the relationship with the rotation speed of the photosensitive member 2, but is appropriate in consideration of image formation characteristics that prevent printing spots from being visually recognized and discharge characteristics that prevent overdischarge. Will be adjusted to the value.

  The resonance noise is determined due to the length (axial direction) of the charging roller 3 and the frequency f of the AC voltage applied to the charging roller 3. More specifically, this resonance noise is one of the causes of occurrence of mutual interference when the resonance frequency caused by the pipe length of the charging roller 3 is close to the frequency of the AC voltage. The resonance sound is also determined by the amplitude (Vpp) of the AC voltage, but this is determined by the sound pressure (sound intensity) at each frequency. For example, as shown in a thin line in FIG. 6, the resonance sound is generated when air shakes in the axial direction in the hollow portion 30 a of the charging roller 3 with the side wall 31 a and the side wall 31 b as fixed ends.

Hereinafter, the resonance frequency will be specifically described with numerical values. Here, it is assumed that the length L of the discharge region of the charging roller 3 is 340 (mm) and the voltage Vcr = Vdc + Vac = −600 + 800 sin (2π · f · t) applied to the charging roller 3 is assumed.
Here, the moving speed (v) of air at room temperature is about 340 (m / s).
Then, the resonance frequency f ′ can be expressed by the equation f ′ = v / λ in the case shown in FIG. 6 from v = f′λ. Therefore, in the case of the above conditions, f ′ = 1000 (Hz) is obtained. That is, when f becomes f ′, a resonance sound is generated.

  According to the charging roller 3 of the present embodiment, the opening 36a and the opening 36b are formed in the side wall 31a and the side wall 31b as described above. Therefore, when the rotation speed of the photoconductor 2 is varied as described above. Even when the frequency of the AC voltage and the resonance frequency are close to each other and a resonance sound is generated, the resonance sound is reduced. That is, as shown in FIG. 6, since the opening 36a is formed in the side wall 31a serving as the fixed end, and the opening 36b is formed in the side wall 31b serving as the fixed end on the opposite side, air that vibrates in the axial direction. Can be released from the hollow portion 30a to the outside through the opening 36a or the opening 36b. Therefore, the degree of vibration of air in the hollow portion 30a is reduced, and as a result, the generation of resonance noise is suppressed. Further, since the positions where the opening 36a and the opening 36b are provided do not coincide with each other in the facing direction, even if the oscillating air cannot escape from the opening 36a to the outside, for example, Since the opening 36b provided symmetrically on the side can be released to the outside, the resonance sound can be more effectively suppressed.

Therefore, in the above-described embodiment, the cylindrical body 31 and the side wall 31a and the side wall 31b that are provided at both ends of the cylindrical body 31 and face each other in the axial direction and at least an alternating voltage is applied to charge the photoreceptor 2. The side wall 31a and the side wall 31b are formed by adopting the configuration in which the side wall 31a and the side wall 31b are formed with an opening 36a that penetrates the side wall 31a and an opening 36b that penetrates the side wall 31b. As a result, the air in the hollow portion 30a that vibrates can be released to the outside through the opening 36a and the opening 36b. Moreover, since the area of the side wall 31a and the side wall 31b becomes small, it is reduced that internal air reflects in the side wall 31a and the side wall 31b, and vibrates in an axial direction.
Therefore, in this embodiment, since the vibration of the charging roller 3 due to the resonance sound is suppressed by suppressing the resonance sound, there is an effect that a good image can be obtained.

  In the present embodiment, the printer 1 includes the photosensitive member 2 and a charging roller that charges the photosensitive member 2, and the configuration includes the charging roller 3 described above as the charging roller. Thus, there is an effect of obtaining the printer 1 that can suppress the generation of resonance sound that is perceived as unpleasant noise to the hearing and can form a good image.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, description of the part which has the same structure as the said embodiment shall be omitted.
FIG. 7 is a diagram showing the configuration of the opening 36a and the opening 36b in the second embodiment of the present invention.
FIG. 8 is a diagram showing the configuration of the opening 36a and the opening 36b in the second embodiment of the present invention.
As shown in FIGS. 7 and 8, in the second embodiment, the side wall 31a and the side wall 31b are provided with a plurality of openings 36a and openings 36b at regular intervals around the axis. Different.

  In the embodiment shown in FIG. 7, the opening 36a opens in a circular shape when viewed from the axial direction, as shown in FIG. 7 (a). A plurality (three in this embodiment) of openings 36a are provided, and are provided at equal intervals around the rotation shaft 31a1. On the other hand, as shown in FIG. 7B, the openings 36b open in a circular shape when viewed from the axial direction, and are provided in a plurality (three in this embodiment), and are equidistant from each other around the rotation shaft 31b1. However, the positions provided are not coincident with each other in the direction facing the opening 36a.

  On the other hand, in the embodiment shown in FIG. 8, the opening 36a has a substantially arc shape gradually approaching the rotating shaft 31a1 from the outer edge of the side wall 31a as it goes in the clockwise rotation direction, as shown in FIG. 8A. It is open. A plurality (three in this embodiment) of openings 36a are provided, and are provided at equal intervals around the rotation shaft 31a1. On the other hand, as shown in FIG. 8 (b), the opening 36b opens in a substantially arc shape gradually approaching the rotating shaft 31b1 from the outer edge of the side wall 31b as it goes counterclockwise. In the embodiment, three are provided, and are provided at equal intervals around the rotation shaft 31b1, but the provided positions are not coincident with each other in the direction facing the opening 36a.

  According to the charging roller 3 configured as described above, since a plurality of openings 36a and 36b are provided at regular intervals around the axis, the axis of the charging roller 3 coincides with the center of gravity, and the axis of the charging roller is aligned. The surrounding rotational drive is performed smoothly. Therefore, vibration of the charging roller 3 due to rotation is suppressed, and there is an effect that good charging can be performed in a state where the charging gap G is regulated to be constant.

  As mentioned above, although preferred embodiment of this invention was described referring drawings, this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  For example, in the above-described embodiment, it has been described that the opening is provided on both of the opposing side walls, but the present invention is not limited to the above configuration, and is provided on either one of the opposing side walls. But it has the effect of suppressing resonance. However, as in the above-described configuration, the resonance sound is more effectively suppressed by providing openings on both of the opposing side walls and making the positions provided in the opposing directions non-matching.

DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 2 ... Photoconductor (image carrier), 3 ... Charging roller, 31 ... Cylindrical body, 31a ... Side wall, 31b ... Side wall, 36a ... Opening, 36b ... Opening

Claims (4)

A charging roller provided on both ends of the cylindrical body and side walls opposed to each other in the axial direction and charging at least an alternating voltage to charge the image carrier;
The charging roller according to claim 1, wherein an opening penetrating the side wall is formed in at least one of the side walls.   2. The charging roller according to claim 1, wherein the openings are provided on both of the side walls, and the positions where the openings are provided do not coincide with each other in the facing direction.   The charging roller according to claim 1, wherein a plurality of the openings are provided at regular intervals around the axis. An image forming apparatus comprising an image carrier and a charging roller for charging the image carrier,
An image forming apparatus comprising the charging roller according to claim 1 as the charging roller.

Images