JP2008116724A - Corona charger and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress a wire vibration due to interaction between discharge wires, regarding a corona charger having a plurality of discharge wires. <P>SOLUTION: The corona charger for charging an object with corona discharge includes: two discharge wires; supporting members that support both ends of each discharge wire by respective supporting points to stretch the two discharge wires in parallel to each other; and a power supply terminal for supplying the power to each discharge wire. A distance between the supporting points of one discharge wire is different from a distance between that of the other discharge wire. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a corona charging device having two or more discharge wires and an image forming apparatus including the corona charging device.

  As a charging device for an electrophotographic image forming apparatus, there is known a corona charging device that applies a high voltage to a stretched discharge wire to cause corona discharge to charge or charge a photoreceptor or paper. Among them, a high-speed machine in which a plurality of discharge wires are arranged along the moving direction of the photosensitive member may be used. This is to form a charged region having a sufficient width in the moving direction in order to stably charge the surface of the photosensitive member moving at high speed.

  However, it is known that when the discharge wire is subjected to corona discharge, the discharge wire vibrates in a direction orthogonal to the stretching direction of the discharge wire. When the discharge wire vibrates, the discharge is not stabilized and may cause disconnection. Therefore, in order to suppress vibration of the discharge wire, a discharge wire provided with a vibration isolation ring is known (for example, see Patent Document 1). Or what makes a vibration prevention member (vibration-proof member) adjoin or contact a discharge wire is known (for example, refer to patent documents 2).

The reason why the discharge wire vibrates with corona discharge is described in, for example, Patent Document 1. According to this, the Coulomb force acts on the discharge wire to which the voltage is applied between the electrode and the shield plate having different polarities. This Coulomb force is not constant and changes according to the fluctuation of the voltage applied to the discharge wire. Further, since the corona discharge itself is intermittently generated at very short time intervals, the Coulomb force also fluctuates accordingly. As the Coulomb force acting on the discharge wire varies, the discharge wire vibrates. The vibration develops into a larger vibration at a natural vibration frequency determined by the mass, tension, and length of the discharge wire. FIG. 5 is an explanatory view showing the structure of a conventional corona charger 101. In the corona charger 101, a voltage is applied to the discharge wires 111 and 113 through the power supply terminal 129 from an external high voltage power source. Due to the applied voltage, the discharge wires 111 and 113 undergo corona discharge, and charge an object (not shown) disposed opposite thereto. The voltage is applied using the grounded shield case 123 as a reference potential. When a positive voltage is applied, the discharge current flows from the discharge wires 111 and 113 to the shield case 123. The shield case 123 is grounded to a frame (not shown) via the ground terminal 131. FIG. 6 is an explanatory view showing a state in which a discharge wire vibrates during corona discharge, which is conventionally known. Similar vibrations occur in the discharge wires 111 and 113. As shown in FIG. 6, the discharge wire 111 vibrates between support points 115 and 117 at both ends. 6A is an example of the primary mode, FIG. 6B is an example of the secondary mode, and FIG. 6C is an example of the tertiary mode, but there may be vibrations of higher order modes.
Japanese Patent Laid-Open No. 51-16037 JP-A-5-64792

  In a corona charging device having a plurality of discharge wires, a Coulomb force acts particularly between two parallel wires, and mutual vibration is promoted. It is empirically known that breakage of the discharge wire is likely to occur as compared to that of a single discharge wire. Since the high-speed machine is used by customers with a high operation rate of the image forming apparatus, it is strongly required to make the maintenance cycle longer than that of the medium- and low-speed machine. In addition, downtime due to disconnection of the discharge wire or the like decreases the work efficiency of the customer, and thus reduction of downtime is strongly required.

  Of course, vibration suppression measures using a vibration isolating member or the like are taken, but this is also applied to a single discharge wire. In a corona charging device for a high-speed machine, a method for effectively suppressing vibration of a discharge wire is required.

  The present invention has been made in consideration of the above-described circumstances, and provides a method for effectively suppressing vibration of a wire due to the interaction of discharge wires in a corona charging device having a plurality of discharge wires. It is.

  The present invention is an apparatus for charging an object by corona discharge, and supports two discharge wires and both ends of each discharge wire at respective support points, and stretches the two discharge wires in parallel. A corona charging device comprising a support member and a power supply terminal for supplying power to each discharge wire, wherein a distance between support points of one discharge wire and a distance between support points of the other discharge wire are different from each other. provide.

  Furthermore, the present invention provides an electrophotographic image forming apparatus provided with the corona charging device.

  In the corona charging device according to the present invention, since the distance between the support points of one discharge wire and the distance between the support points of the other discharge wire are different from each other, each discharge wire has a different natural vibration frequency. Therefore, the mutual vibration is hardly promoted by the action between the discharge wires, and the vibration is effectively suppressed.

When the interval between the support points in the discharge wire having the wider support point interval is Lw and the interval between the support points in the narrow discharge wire is Ln, the ratio between the two is
Ln / Lw ≦ 0.97
It may be. In this way, a sufficient difference is secured in the natural vibration frequency of each discharge wire.

In addition, each support member may be arranged such that the position of the midpoint between the support point on one end side and the support point on the other end side in the wire stretching direction is different among the discharge wires. In this way, since the portion of the maximum amplitude is shifted when the discharge wire vibrates, the mutual vibration is hardly promoted by the action between the discharge wires, and the vibration is effectively suppressed.
Furthermore, the amount of deviation of the midpoint in the wire stretching direction may be 4 millimeters or more.

  The support member may be a positioning member that defines the shortest distance between the discharge wire and the object. Here, the positioning member may directly define the shortest distance between the discharge wire and the object. In this way, since the stretch length of each discharge wire can be defined using the positioning member, vibration of the discharge wire can be suppressed with a simple structure.

  Alternatively, the support member may be a vibration preventing member that suppresses vibration of the discharge wire that occurs during corona discharge. In this way, since the stretch length of each discharge wire can be defined using the vibration preventing member, the vibration of the discharge wire can be suppressed with a simple structure.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. The following description will provide a better understanding of the present invention. In addition, the following description is an illustration in all the points, Comprising: It should be understood that it is not restrictive.

(Corona charger structure)
FIG. 1 is an explanatory view showing an example of the structure of the corona charger of the present invention. Fig.1 (a) is a front view, FIG.1 (b) is AA 'sectional drawing of Fig.1 (a). Two discharge wires 11 and 13 are stretched in parallel on the corona charger 1. The distance between the support points 15 and 17 of the positioning part of the discharge wire 11 is L1, and the distance between the support points 19 and 21 of the positioning part of the discharge wire 13 is L2. The corona charger 1 in FIG. 1 is particularly different from the conventional corona charger 101 shown in FIG. 5 in that L1 and L2 are not equal, that is, L2> L1. In the conventional corona charging wire 101 shown in FIG. 5, the distance between the support points 115 and 117 of the positioning portion of the discharge wire 111 is L0. The distance between the support points 119 and 121 of the positioning portion of the discharge wire 113 is also L0. That is, the distance between the support points of the discharge wires 111 and 113 is equal and is L0. In the corona charger 101 according to the present invention, since L2 and L1 are not equal, the vibration of the discharge wire is less likely to be promoted by the interaction of the discharge wire as compared with the conventional one.

  Further, in the corona charger 1 of FIG. 1, the support points 15 and 19 on the side where the fixing screws 33 and 35 for fixing one end of the discharge wires 11 and 13 are arranged coincide with each other in the direction along the discharge wire. Yes. However, the other support points 17 and 21 are different from each other in the position along the discharge wire. Accordingly, the positions of the intermediate point P1 between the support points 15 and 17 of the discharge wire 11 and the intermediate point P2 between the support points 19 and 21 of the discharge wire 13 in the direction along the discharge wire are different from each other. Point P1 is a point where the maximum amplitude exists when the discharge wire 11 vibrates in the primary mode. Similarly, the point P2 is a point where the maximum amplitude exists when the discharge wire 13 vibrates in the primary mode. By arranging the support points so that the positions of P1 and P2 are shifted from each other, the shortest distance when the discharge wires 11 and 13 vibrate becomes longer. For this reason, vibration due to the interaction between the discharge wires 11 and 13 is hardly promoted.

  FIG. 2 is an explanatory view showing an example of a different structure of the corona charger of the present invention. The corona charger 1 in FIG. 2 has a position in the wire stretching direction between a point P3 between the support points 15 and 17 of the discharge wire 11 and a point P2 between the support points 19 and 21 of the discharge wire 13. Match. However, the distance L3 between the support points 15 and 17 of the positioning part of the discharge wire 11 is smaller than the distance L4 between the support points 19 and 21 of the positioning part of the discharge wire 13. That is, L3 and L4 are different. Therefore, the natural frequencies of the discharge wires 11 and 13 are different from each other, and the vibration is not easily promoted by the interaction between them.

  FIG. 3 is an explanatory view showing another example of the structure of the corona charger of the present invention. In the corona charger 1 of FIG. 3, both ends of the discharge wire 11 are supported by support points 15b and 17b of the vibration isolating member. Since the support points 15a and 17a by the positioning member are at the end of the wire rather than the support points 15b and 17b of the vibration isolating member, the discharge wire 11 vibrates with the support points 15b and 17b as nodes.

(Configuration of the electrophotographic process department)
FIG. 4 is an explanatory view schematically showing each station of the electrophotographic process included in the electrophotographic image forming apparatus of the present invention. In FIG. 4, each station of the electrophotographic process is arranged around the photosensitive drum 41. A portion above the photosensitive drum 41 and surrounded by a chain line is a laser optical system. The laser optical system 40 deflects and scans a laser beam emitted from a semiconductor laser element (not shown), which is a laser emission source, by the peripheral surface of the polygon mirror 44, and scans and exposes the surface of the photosensitive drum 41. . The polygon mirror 44 is rotationally driven by a polygon mirror drive motor 43. The laser beam reflected on the polyhedral peripheral surface of the rotating polygon mirror 44 is deflected in a direction perpendicular to the paper surface, and the surface of the photosensitive drum 41 is exposed through the fΘ lenses 45a and 45b and the cylindrical mirror 47. The laser beam exposes the surface in a direction parallel to the rotation axis of the photosensitive drum 41.

  A charging station comprising a corona charger 1 according to the present invention and a high voltage power source 12 for applying a voltage to the discharge wires 11 and 13 of the corona charger 1 is disposed around the photosensitive drum 41. The charging station charges the surface of the photosensitive drum 41 uniformly. In FIG. 4, the photosensitive drum 41 rotates in the arrow R direction. On the downstream side of the charging station along the rotation direction of the photoconductive drum 41, an exposure station is arranged in which the surface of the photoconductive drum 41 is irradiated with the laser beam and an electrostatic latent image is formed.

  Further, a developing station is disposed on the downstream side. The developing station includes a developing tank 49, a developing roller 49a disposed in the developing tank 49, and a developing bias power source 49b that applies a bias potential to the developing roller 49a. The developing roller 49a attaches toner to the surface according to the potential in each image area of the electrostatic latent image formed on the surface of the photosensitive drum 41. As a result, shades corresponding to the potential are formed on the surface of the photosensitive drum 41. This is development processing.

  On the downstream side of the developing station, a transfer station for transferring the toner to the transfer sheet 51 fed in synchronization with the toner image formed by the development is disposed. The transfer station includes a transfer charger 53 that charges the transfer sheet 51 in contact with the photosensitive drum 41 from the back side thereof, and a transfer power source 53b that applies a transfer voltage to the discharge wire of the transfer charger 53.

  Further, on the downstream side of the transfer station, there is disposed a peeling station that neutralizes the transferred transfer sheet 51 and peels the transfer sheet from the photosensitive drum 41 by the stiffness. The peeling station includes a peeling charger 57 that performs AC corona discharge, and a peeling power source 57b that applies a corona discharge voltage to the discharge wire of the peeling charger 57. The peeling charger 57 neutralizes the electrostatic transfer force to the photosensitive drum 41 by removing the charge from the transfer sheet 51 after the transfer. The corona charger of the present invention may be applied to each of the transfer charger 53 and the peeling charger 57.

  On the downstream side of the peeling station, there is disposed a static eliminating station that irradiates the surface of the photosensitive drum 41 after transfer with light. The static elimination station is constituted by a static elimination lamp 59. Further, a cleaning station that physically cleans the surface of the photosensitive drum 41 is disposed downstream of the static elimination station. The cleaning station includes a cleaner 61 that physically removes the toner remaining on the surface by bringing the edge of the elastic blade into contact with the surface of the photosensitive drum 41.

  The transfer sheet 51 peeled from the photosensitive drum 41 at the peeling station is guided to the fixing unit 63. The fixing unit 63 heats and melts the toner transferred onto the transfer sheet, and fixes the toner onto the transfer sheet 51.

(Experimental example)
Table 1 shows the results when aging was performed for about 1 million sheets in a high-temperature and high-humidity environment with a temperature of 30 ° C. and a humidity of 80% using the electrophotographic image forming apparatus equipped with the corona charger of FIG. It is a table | surface which shows the comparison result of the magnitude of vibration of a discharge wire, the presence or absence of a disconnection, the presence or absence of a charging failure, and the discharge wire. The applied voltage to the discharge wire is about -5.5 kV, the moving speed of the photoreceptor surface is 400 mm / second, and the value of L2 is 340 mm. The material of the discharge wire is tungsten, its diameter is 30 μm, and the tension of the discharge wire is about 150 kg / mm ² .

  In Table 1, the leftmost column is the value of the ratio between the distances L1 and L2 between the support points of each discharge wire. Those having a ratio value of 1.00 are conventional corona chargers. The presence or absence of disconnection is a result of whether or not the discharge wire is disconnected during live-action aging. The charging failure is a result of visual evaluation of periodic shading unevenness in the conveyance direction appearing in the image of the photographed sample. The density unevenness evaluation method is a method in which unevenness exceeding a predetermined allowable standard is observed in the solid portion of the image or unevenness exceeding the allowable standard is observed in the thin line portion of the image. Bad) “Yes”.

  From the result of actual image aging, when L1 / L2 is in the range of 0.99 or less, there is no disconnection of the discharge wire, and in the range of L1 / L2 of 0.97 or less, there is no density unevenness due to charging failure. Therefore, it is preferable that the distance between the support points of each discharge wire satisfies the relationship L1 / L2 ≦ 0.97.

  In Table 1, the magnitude of the vibration indicates a result of visually confirming the magnitude of the vibration in the case of L1 / L2 = 0.97 which is the above-described boundary value. It can be seen that the smaller the value of L1 / L2, the smaller the vibration of the discharge wire.

  Table 2 shows the amount of misalignment at the midpoint in the wire stretching direction, that is, the distance between the points P1 and P2 in FIG. Is shown. The conditions for live-action aging are the same as those for Table 1.

  In Table 2, the leftmost column is the amount of misalignment of the midpoint. A device having a displacement of 0 mm is a conventional corona charger. Similar to Table 1, the presence or absence of disconnection is a result of whether or not a breakage of the discharge wire occurred during live-action aging. The charging failure is a result of visual evaluation of periodic shading unevenness of a live-action sample.

  From the results of actual image aging, when the deviation amount is 2 mm or more, there is no disconnection of the discharge wire, and when the deviation amount is 4 mm or more, there is no density unevenness due to charging failure. Therefore, it is preferable that the gap between the support points of each discharge wire satisfies the relationship that the deviation amount is 4 mm or more.

In Table 1, the magnitude of the vibration indicates a result of visually confirming the magnitude of the vibration when the deviation amount is 4 mm, which is the above-described boundary value. It can be seen that the larger the deviation, the smaller the vibration of the discharge wire.
Although the above experimental example shows an example of the present invention, the present invention can also be applied to different conditions. For example, the diameter of the discharge wire is generally 30 μm or more and less than 80 μm. The moving speed of the photoreceptor surface is generally 300 mm / second or more. As a material for the discharge wire, in addition to tungsten, stainless steel or a tungsten-based alloy such as W or W-Mo alloy is used. In addition, molybdenum, titanium, a titanium-based alloy, or the like is used. The applied voltage to the discharge wire is generally -5 to 6 kV. As a result, the surface of the photoreceptor is charged to 600 to 800V. For example, the present invention can be applied to these.

  Finally, it is apparent that there can be various modifications of the present invention in addition to the above-described embodiment. Such variations should not be construed as not belonging to the features and scope of the invention. The scope of the present invention is intended to include all modifications within the meaning and range equivalent to the scope of the claims.

It is explanatory drawing which shows an example of the structure of the corona charger of this invention. It is explanatory drawing which shows an example from which the structure of the corona charger of this invention differs. It is explanatory drawing which shows another example of the structure of the corona charger of this invention. It is explanatory drawing which shows typically each station of the electrophotographic process using the corona charger of this invention. It is explanatory drawing which shows the structure of the conventional corona charger. It is explanatory drawing which shows a mode that a discharge wire vibrates at the time of corona discharge known conventionally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Corona charger 12 High voltage power supply 11, 13, 111, 113 Discharge wire 15, 17, 19, 21, 115, 117, 119, 121 Support point 15a, 17a, 19a, 21a Support point 15a, 17a of positioning part , 19a, 21a Anti-vibration member support point 23, 123 Shield case 25, 27, 125, 127 Holder 29, 129 Feed terminal 31, 131 Ground terminal 33, 35, 133, 135 Fixed screw 37, 39, 137, 139 Tension Spring 40 Laser optical system 41 Photosensitive drum 43 Polygon mirror drive motor 44 Polygon mirror 45a, 45b fΘ lens 47 Cylindrical mirror 49 Developer tank 51 Transfer sheet 53 Transfer charger 53b Transfer power supply 57 Peeling charger 57b Peeling power supply 59 Static elimination lamp 61 Cleaner 63 Fixing part 103 Object

Claims (7)

A device for charging an object by corona discharge,
Two discharge wires;
A support member that supports both ends of each discharge wire at respective support points, and stretches the two discharge wires in parallel;
A power supply terminal for supplying power to each discharge wire;
A corona charging device characterized in that an interval between support points of one discharge wire and an interval between support points of the other discharge wire are different from each other. When the interval between the support points in the discharge wire having the wider support point interval is Lw and the interval between the support points in the narrow discharge wire is Ln, the ratio between the two is
Ln / Lw ≦ 0.97
The corona charging device according to claim 1.   2. The corona charging device according to claim 1, wherein each support member is disposed such that a position of a midpoint between a support point on one end side and a support point on the other end side in a wire stretching direction is different between the discharge wires. .   4. The corona charging device according to claim 3, wherein the amount of misalignment of the midpoint in the wire stretching direction is 4 millimeters or more.   The corona charging device according to claim 1, wherein the support member is a positioning member that defines a shortest distance between the discharge wire and the object.   The corona charging device according to claim 1, wherein the support member is a vibration preventing member that suppresses vibration of a discharge wire generated during corona discharge.   An electrophotographic image forming apparatus comprising the corona charging device according to claim 1.

Images