JP2012088421A - Charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging device which is simply configured and capable of cleaning up a whole surface of a grid electrode opposed to the photosensitive drum.SOLUTION: A representative configuration of a charging device according to the present invention is characterized in that a charging device 2 is provided with a grid electrode 13 which is opposed to a photosensitive drum 1 and a cleaning member (a grid electrode cleaning portion 14, a discharging wire cleaning portion 15, and a holder 16), having a brush 22 contacting with the grid electrode 13, for cleaning up the grid electrode 13 while it is moving, and fill materials of the brush 22 include an erectile bristle portion 23b extending further to the photosensitive drum 1 side than to the grid back surface of the grid electrode 13 at the photosensitive drum 1 side, and a bent portion 23a bent at an acute angle with respect to the erectile bristle 23b, while the tips of the fill materials of the brush 22 contact with the grid back surface 13a of the grid electrode 13 which is opposed to the photosensitive drum 1.

Description

  The present invention relates to a charging device used in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer.

  In a conventional image forming apparatus, dust or toner floating inside and outside the apparatus adheres to the discharge electrode, shield electrode, and grid electrode of a charging device that performs corona discharge. And the amount of adhesion increases as the discharge time of the corona discharge electrode becomes longer. For this reason, when a certain amount of image formation is performed, contamination of each electrode may cause a decrease in discharge efficiency and uneven discharge current to the charged body, which may cause deterioration in image quality of the output image. In addition, the life of the charging device is reduced. Accordingly, a cleaning device that automatically cleans the grid electrodes has been proposed (Patent Documents 1 to 3).

JP 09-297457 JP 2005-338797 A JP 09-54482

  However, Patent Documents 1 to 3 have a common problem that it is difficult to clean the surface of the grid electrode facing the photosensitive drum. That is, the grid electrode must be close to the photosensitive drum at 1 to 1.5 mm in order to suppress charging unevenness of the photosensitive drum. In order to provide the cleaning member in such a very narrow space, the cleaning device has a complicated configuration and requires a mechanism with very high accuracy.

  Patent Document 3 describes a configuration for cleaning both surfaces of such a grid electrode. However, in this configuration, since the sheet-like members are alternately placed on the wire grid, only half of the entire wire grid can be cleaned on the side of the grid electrode facing the photosensitive drum. Further, this configuration can be applied only to the wire grid, and the configuration is complicated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a charging device capable of cleaning the entire surface of a grid electrode facing a photosensitive drum with a simple configuration.

  In order to solve the above problems, a typical configuration of a charging device according to the present invention includes a grid electrode facing a charged body and a brush in contact with the grid electrode, and cleaning the grid electrode while moving. A brush device, wherein the fibers of the brush are bent at an acute angle with respect to the straight hair portion extending from the grid back surface of the grid electrode to the charged body side with respect to the grid back surface of the grid electrode. The tip of the fiber of the brush comes into contact with the back surface of the grid facing the body to be charged of the grid electrode as the cleaning member moves.

  According to the present invention, the entire surface of the grid electrode facing the photosensitive drum can be cleaned with a simple configuration.

1 is a configuration diagram of an image forming apparatus equipped with a charging device according to a first embodiment. (A) It is a side view of the charging device which concerns on 1st embodiment. (B) It is a front view of the charging device which concerns on 1st embodiment. (A) It is a top view of the grid electrode which concerns on 1st embodiment. (B) It is composition explanatory drawing of the cleaning member concerning a first embodiment. (A) It is explanatory drawing of the fiber which comprises the cleaning member which concerns on 1st embodiment. (B) It is the schematic of the injection molding apparatus which produces the fiber of the brush which concerns on 1st embodiment. It is the schematic of the metal mold | die of the fiber of the brush which concerns on 1st embodiment. It is explanatory drawing of the grid back surface cleaning process of the cleaning member which concerns on 1st embodiment. (A) It is explanatory drawing of the protrusion amount (DELTA) of the fiber of the brush which concerns on 1st embodiment, and penetration | invasion length l. (B) It is the figure explaining the penetration | invasion process to the grid back surface of the fiber which concerns on 1st embodiment. (A) It is explanatory drawing of the behavior of a fiber when (DELTA) is large. (B) It is explanatory drawing of the behavior of a fiber when (kappa) is large. It is explanatory drawing of the result of having observed the penetration | invasion process to the grid back surface of the fiber which concerns on 1st embodiment. (A) (b) It is the figure explaining the difference in the grid back surface contact area by the protrusion amount (DELTA). (C) It is the figure explaining a mode that a fiber contacts the next grid before returning. It is explanatory drawing of the result of having observed the separation process from the grid back surface of the fiber which concerns on 1st embodiment. It is a figure explaining a mode that a fiber returns to the original after contacting a grid surface. It is explanatory drawing of the result of having observed a mode that a fiber contact | abuts on the grid surface, and returns. (A) It is a figure showing the combination of a and b with the high cleaning effect in the case of E = 250 mg / cm < ² > and (theta) = 45 degree. (B) A diagram showing a combination of a and b that has a high cleaning effect when θ = 45 ° of a fiber having a Young's modulus of E = 250 mg / cm ² , E = 300 mg / cm ² , and E = 150 mg / cm ² . is there. (A) It is a figure showing the combination of a and b with a high cleaning effect in the case of (theta) = 30 degrees, 45 degrees, and 60 degrees of the fiber which has a Young's modulus of E = 250 mg / cm < ² >. (B) It is a graph showing the change of the coverage ratio of the toner of the grid back surface which concerns on 1st embodiment. (A) It is a graph showing the change of the removal rate of the mark on the grid back surface which concerns on 1st embodiment. (B) It is a graph showing the number of image outputs until the appearance of the white stripe when using the charging device according to the first embodiment. (A) It is composition explanatory drawing of the cleaning member which concerns on 2nd embodiment. (B) It is explanatory drawing of the force which acts on the fiber which concerns on 2nd embodiment. (A) It is a figure showing the combination of a and b with a high cleaning effect in the case of E = 250 mg / cm < ² >, (theta) = 60 degrees and (alpha) = 30 degrees. (B) It is composition explanatory drawing of the cleaning member concerning a third embodiment. (A) It is explanatory drawing of the advancing direction of the brush of the cleaning member which concerns on 1st embodiment. (B) It is a graph showing the change of the coverage ratio of the toner of the grid back surface which concerns on 3rd embodiment. (A) It is a graph showing the change of the removal rate of the mark on the grid back surface concerning 3rd embodiment. (B) It is a graph showing the number of image outputs until the appearance of the white stripe when using the charging device according to the third embodiment. (A)-(c) It is explanatory drawing of the structure of the bending direction of the fiber which has the same effect as 3rd embodiment. (D) It is explanatory drawing of a structure of the cleaning member of 4th embodiment.

[First embodiment]
A first embodiment of a charging device according to the present invention will be described with reference to the drawings.

[Description of charging device and image forming apparatus equipped with charging device]
FIG. 1 is a configuration diagram of an image forming apparatus equipped with a corona charging device 2 of the present embodiment. As shown in FIG. 1, a photosensitive drum 1 as a member to be charged is uniformly charged to a negative polarity by a corona charging device 2. By irradiating the photosensitive drum 1 with laser light L emitted from the scanner 7 corresponding to the image signal, the potential of the photosensitive drum 1 is attenuated, and an electrostatic latent image is formed. The formed electrostatic latent image is developed as a toner image by the two-component developing device 3 and transferred to the transfer material P by the transfer roller 4. The transfer residual toner remaining on the photosensitive drum 1 is scraped off by the cleaner 5. The transfer residual toner scraped off in the cleaner 5 is conveyed to a waste toner container (not shown) and collected. Thereafter, the history of the latent image potential is erased by the charge eliminating lamp 6, and then charged again by the corona charging device 2, and a series of image forming steps are repeated.

  FIG. 2A is a side view of the charging device 2. FIG. 2B is a front view of the charging device 2. As shown in FIGS. 2A and 2B, the corona charging device 2 includes a shield case 10, an insulating support 11, a discharge wire 12, a grid electrode 13, a grid electrode cleaning unit 14, and a discharge wire cleaning unit. 15 and holder 16. The insulating support portions 11 are provided at both ends of the shield case 10. The discharge wire 12 is provided in the inner longitudinal direction of the shield case 10 as a discharge electrode. The grid electrode 13 is provided on the side of the shield case 10 facing the photosensitive drum 1 (on the charged body side).

The grid electrode cleaning unit 14, the discharge wire cleaning unit 15, and the holder 16 are cleaning members that clean the discharge wire 12 and the grid electrode 13. In the present embodiment, no cleaning member is provided between the grid electrode 13 and the photosensitive drum 1. The holder 16 holds the grid electrode cleaning unit 14 and the discharge wire cleaning unit 15. The holder 16 is engaged with a rotatable screw shaft 17 disposed on the opposite side of the photosensitive drum 1 opposite side. The screw shaft 17 is held by a bearing 18 included in the insulating support portion 11, and is rotated by a motor M1 that can freely rotate. As the screw shaft 17 rotates, the holder 16 moves in the direction of arrow c.

  The grid electrode cleaning unit 14 and the discharge wire cleaning unit 15 move from the home position A to the grid end B as the holder 16 moves, and then move from the grid end B to the original home position A. This process is defined as a single cleaning process, and the grid electrode cleaning unit 14 and the discharge wire cleaning unit 15 clean the grid electrode 13 and the discharge wire 12.

  The discharge wire 12 is a φ60 μm tungsten wire, and is stretched through a spring (not shown) provided on the insulating support 11 and a spring. The discharge wire cleaning unit 15 is disposed such that the sponge pads 15a and 15b press the discharge wire 12 from both sides. Polishing paper or the like may be attached to the contact surfaces of the sponge pads 15a, 15b with the discharge wire 12.

  The charging range of the corona charging device 2 is Γ, and the opening is provided in a range corresponding to the region. Further, the surface of the grid electrode is subjected to a nickel plating treatment with a thickness of 1 μm as a rust prevention treatment. The distance Λ at the closest position between the grid electrode 13 and the photosensitive drum 1 is 1 mm.

FIG. 3A is a top view of the grid electrode 13. As shown in FIG. 3A, the grid electrode 13 uses SUS304, which is a planar plate member having a thickness of 0.1 mm, and has an inclination of φ with respect to the longitudinal direction of the grid in the etching process. forming a plurality of openings having a width of W _1. Further, the line width of the grid line to W _2. In the present embodiment, a grid having a combination of φ = 45 °, W ₁ = 1.4 mm, and W ₂ = 0.14 mm is used.

  FIG. 3B is a configuration diagram of the grid electrode cleaning unit 14. As shown in FIG. 3B, the grid electrode cleaning unit 14 includes a brush 22 and a brush holding member 19 that holds the brush 22. The distance L between the brush holding member 19 and the grid electrode 13 is 1 mm.

[Configuration of Brush 22]
FIG. 4A is a configuration diagram of the brush 22. As shown in FIG. 4A, the fibers 23 constituting the brush 22 are produced by injection molding described later. The fiber 23 has a straight hair portion 23b and a bent portion 23a. The straight hair portion 23b is orthogonal to the plane on which the grid electrode 13 is located. The straight hair portion 23 b passes between the grid electrodes 13 from the grid surface 13 c on the opposite side of the grid electrode 13 to the photosensitive drum 1 to the grid back surface 13 a side of the grid electrode 13 facing the photosensitive drum 1. It is growing towards. The bent portion 23a is bent at a predetermined angle θ with respect to the straight hair portion 23b and extends toward the back surface of the grid. Moreover, nylon resin or acrylic resin was used as a material of the fiber 23 which comprises the brush 22 of this embodiment.

  As parameters of the shape of the fiber 23 of the brush 22, the length of the bent portion 23a is defined as a, and the length of the fiber 23 of the straight hair portion 23b up to the bent point 23d is defined as b. Further, the direction of the tip 23c of the bent portion 23a of the fiber 23 is parallel to the moving direction of the brush 22, and all the fibers 23 are implanted so as to face the same direction.

[Manufacturing method of brush 22]
FIG. 4B is a configuration diagram of the injection molding machine 20 that manufactures the fibers 23 of the brush 22. As shown in FIG. 4B, the injection molding machine 20 is an injection molding machine having a screw with a mold clamping force of 850 t and a compression ratio of 1.8. FIG. 5A is a side view of a mold 21 for producing the fibers 23 of the brush 22. FIG. 5B is an elevation view of the mold 21 and an enlarged view of a brush molding portion. Nylon resin or acrylic resin, which is a raw material for the fibers 23 of the brush 22, is melted at a temperature of 250 ° C. and injected into the mold 21 heated to 80 ° C. by the injection molding machine 20, thereby producing the fibers 23 of the brush 22. It was.

[Behavior of brush 22 in cleaning process]
FIG. 6 is a diagram showing a process in which the fibers 23 of the brush 22 clean the surface of the grid electrode 13 facing the photosensitive drum. The grid electrode cleaning part 14 moves in the longitudinal direction of the grid electrode 13 with the rotation of the motor M1, and the tip 23c of the bent part 23a of the fiber 23 of the brush 22 passes through the state shown in FIGS. The grid back surface 13a is cleaned.

  The states 1 to 7 shown in FIG. 6 will be described in order. First, in the state 1, the tip 23c of the bent portion 23a of the fiber 23 comes into contact with the grid side surface 13b as the brush 22 moves. In the state 2, the tip 23 c of the bent portion 23 a of the fiber 23 enters the grid back surface 13 a as the brush 22 moves. In the state 3, the tip 23c of the bent portion 23a of the fiber 23 is in contact with the grid back surface 13a and removes foreign matters such as toner adhering to the grid back surface 13a. 4, a part from the point where the fiber 23 engages with the brush holding member 19 to the bending point 23 d comes into contact with the grid side surface 13 b, and the fiber 23 bends, whereby the tip 23 c of the bending part 23 a of the fiber 23. Moves away from the grid. In the state 5, the bent portion 23a of the fiber 23 comes into contact with the grid side surface 13b, and the fiber 23 as a whole moves in a direction of coming out of the grid back surface 13a while being largely bent. In the state 6, the fiber 23 comes off from the grid back surface 13a, and the entire fiber 23 is brought into contact with the grid surface 13c while being largely bent. In the state 7, the fiber 23 is detached from the grid surface 13c with the movement of the brush 22 and returns to the original state.

[Conditions for brush 22 to clean grid back surface 13a]
The conditions required for the fibers 23 of the brush 22 to clean the grid back surface 13a through such a state are the following three conditions.

[First Condition] Conditions under which the tip 23c of the fiber 23 enters the grid back surface 13a [Second Condition] Conditions under which the tip 23c of the fiber 23 comes into contact with the grid back surface 13a to wipe off foreign matters such as toner [Third Condition] A condition in which the fiber 23 returns to the original state without being caught by the grid electrode 13 as the brush 22 moves after the tip 23c abuts on the grid back surface 13a.

  Next, the relationship of the parameters of the fiber 23 necessary to satisfy these three conditions will be described.

[Consideration and observation results for the first condition]
First, discussion and observation results regarding the first condition where the tip 23c of the fiber 23 enters the grid back surface 13a will be described. As shown in FIG. 7A, the amount of protrusion Δ and the penetration length l are defined as quantities characterizing the penetration and contact of the tip 23c with the grid back surface 13a. When the protrusion amount Δ and the penetration length l are expressed by the parameters a, b, θ of the fiber 23 and the distance L between the grid electrode 13 and the brush holding member 19, Δ = a cos θ−b + L and l = b−L. Then, fiber parameter combinations that satisfy Δ <0 are excluded from the condition for the contact of the fibers 23 with the grid back surface 13a.

  If Δ = 0, the tip of the fiber 23 can geometrically penetrate into the grid back surface 13a, but considering the stress accompanying the bending of the fiber 23, the tip of the fiber 23 can be used only when Δ> 0. 23c can enter the grid back surface 13a.

  FIG. 7B is a diagram showing a state of the fiber 23 entering under the condition of Δ> 0. As shown in FIG. 7B, when Δ> 0, the tip 23c of the fiber 23 is caught by the grid side surface 13b, and the entire fiber is bent. The downward force acts on the tip 23c of the fiber 23 by the stress F1 accompanying the bending of the fiber 23, and the resultant force F2 of the frictional force with the grit side surface and the drag force from the grid side surface 13b acts on the tip 23c of the fiber 23. If F1 is larger than F2, the fibers 23 can pass through the grid side surface 13b and enter the grid back surface 13a.

  If the friction coefficient of the grid side surface 13b and the surface of the fiber 23 is ignored, the Young's modulus E of the fiber 23, the size of the protrusion amount Δ, and the ratio of the protrusion amount Δ and the penetration length l are the parameters of the fiber 23 that define F1 and F2. Two cases of κ = Δ / l are conceivable. Regarding the Young's modulus E of the fiber 23, the greater the Young's modulus E, the greater the stress F1 associated with the bending of the fiber 23, so that it does not enter the grit back surface.

  FIG. 8A shows the behavior of the fiber 23 when Δ is too large. As shown in FIG. 8A, when Δ is too large, the resultant force F2 of the frictional force and the effect from the end surface is larger than F1, and does not enter the grid back surface 13a.

  FIGS. 8B and 8A are diagrams showing how the behavior of the fiber 23 changes due to κ when Δ is too large compared to l. FIGS. 8B and 8B are diagrams showing how the behavior of the fiber 23 changes due to κ when l is too small compared to Δ. As shown in FIGS. 8B and 8A, when Δ is too large as compared with l, the resultant force F2 of the frictional force of the fiber 23 and the effect from the end face becomes larger than F1 and enters the grid back surface 13a. It is predicted that it will be difficult. As shown in FIGS. 8B and 8B, even when l is too small compared to Δ, the frictional force F2 of the fiber 23 becomes larger than F1 and does not enter the grid back surface 13a. Specifically, as shown in Tables 1 and 2 described later, good results were obtained for both cleanability and penetration when 0.1 mm <Δ <0.4 mm.

FIGS. 9A to 9D are views showing the result of capturing the state in which the tip 23c of the bent portion 23a of the fiber 23 penetrates the brush 22 into the grid back surface 13a by the CCD camera. As the brush 22, a fiber 23 having a bending angle of θ = 45 °, in which Young's modulus E and a and b are appropriately changed, was used. As a material of the fiber 23, nylon (E = 150 mg / cm ² , E = 250 mg / cm ² ) was used.

FIG. 9A shows the results when E = 250 mg / cm ² (nylon), Δ = 0.22 mm, and l = 0.2 mm. In this case, the fibers 23 can penetrate.

FIG. 9B shows the results when E = 150 mg / cm ² (nylon), Δ = 0.22 mm, and l = 0.2 mm. In this case, since the Young's modulus E was small, the fiber 23 could not enter the back surface.

FIG. 9C shows the results when E = 250 mg / cm ² (nylon), Δ = 0.37 mm, and l = 0.2 mm. In this case, since Δ was large, it was not possible to enter the back surface.

FIG. 9D shows the results when E = 250 mg / cm ² (nylon), Δ = 0.32 mm, and l = 0.1 mm. In this case, since κ was large, it could not enter the back surface.

[Consideration and observation results for the second condition]
Next, discussion will be made on the second condition in which the tip 23c of the fiber 23 comes into contact with the grid back surface 13a to wipe off foreign matters such as toner, and the result of observing the actual behavior of the fiber 23 with a CCD camera. As long as the first condition is satisfied, the tip 23c of the fiber 23 can be brought into contact with the grid back surface 13a. Therefore, a condition for wiping off foreign matters such as toner may be considered. Since foreign matters such as toner can be removed by slightly touching the tip 23c of the fiber 23, the contact area between the tip 23c of the fiber 23 and the grid back surface 13a is large in order to remove it more efficiently. Is more advantageous. For this purpose, the larger Δ is better.

10 (a) and 10 (b) show the length a of the bent portion 23a and the length of the straight hair portion 23b with respect to the fiber 23 having a Young's modulus of E = 250 mg / cm ² (nylon). It is a figure which shows the result of having changed b and seeing the behavior of the front-end | tip of the fiber. FIG. 10A shows the result when E = 250 mg / cm ² (nylon) Δ = 0.22 mm. FIG. 10B shows the result when E = 250 mg / cm ² (nylon) Δ = 0.12 mm. In the case of FIG. 10A in which Δ is large, the contact area between the tip 23c of the fiber 23 and the grid back surface 13a is larger than in FIG. 10B in which Δ is small.

[Consideration and observation results for the third condition]
Next, the third condition, the condition in which the fiber 23 returns to its original state without being caught by the grid electrode 13 as the brush 22 moves after the tip 23c of the fiber 23 abuts against the grid back surface 13a, and CCD The observation result by the camera is described. The following two conditions 3A and 3B exist in the third condition.

[Condition 3A] A condition in which the fiber 23 is not caught by the frictional force with the grid electrode 13 when the fiber 23 comes out of the grid electrode 13 [Condition 3B] When the fiber 23 comes out of the grid electrode 13 and returns to the original state, the next grid Conditions that do not contact the electrode 13.

  The reason why the condition 3A is necessary is as follows. That is, when the fiber 23 comes out of the grid electrode 13, the fiber 23 must pass while contacting the grid side surface 13 b in a greatly bent state as in the state of 5 in FIG. 6. At that time, a large frictional force is applied to each of the fibers 23 constituting the brush 22, and the sum of the forces is applied to the brush 22. When this force is larger than the driving force of the brush 22, the brush 22 is caught by the grid electrode 13, and the brush 22 does not move. For this reason, a large load is applied to the motor that drives the brush 22, which causes problems such as wear or disconnection of the fibers 23 constituting the brush 22.

  The reason why the condition 3B is necessary is as follows. That is, when the fiber 23 comes off from the grid electrode 13, the fiber 23 bends greatly as in the process 6 in FIG. 6, and the root portion of the fiber 23 precedes the tip 23c in the moving direction of the brush 22. FIG. 10C is a diagram showing prediction when the distance that the root portion of the fiber 23 precedes the distance between the grid electrodes 13 is large. As shown in FIG. 10C, at this time, the fibers 23 come into contact with the next grid electrode 13 before returning to the original state, and cannot come into contact with the grid back surface 13a.

[Consideration for Condition 3A]
As the parameters of the fiber 23 that characterizes the condition 3A, the length λ = a + b of the entire fiber and the Young's modulus E of the fiber 23 can be considered. The larger the λ is, the greater the deflection of the fiber 23 when the fiber 23 comes out of the grid electrode 13 and the greater the stress, so the frictional force applied to the fiber 23 also increases. It is also predicted that the greater the Young's modulus E, the greater the stress when the fiber 23 comes out, and the greater the frictional force applied to the fiber 23. Specifically, good results were obtained when 1 mm <λ <3 mm and 150 mg / cm <E <300 mg / cm as shown in Tables 1 and 2 described later.

[Observation results for Condition 3A]
FIG. 11A to FIG. 11C are diagrams showing the results of observation with a CCD camera while changing the Young's modulus E and λ. Nylon (E = 250 mg / cm ² ) and acrylic (E = 300 mg / cm ² ) were used as the material of the fiber 23.

FIG. 11A shows the case where E = 250 mg / cm ² (nylon) and λ = 2.2 mm. At this time, the fiber 23 can come out of the grid electrode 13.

This is a case where Young's modulus E = 300 mg / cm ² (acrylic) and λ = 2.2 mm in FIG. In the case of FIG. 11B, since the Young's modulus E is large, the fiber 23 is caught by the grid electrode 13 and the brush 22 is stopped.

FIG. 11C shows the case where Young's modulus E = 300 mg / cm ² (acrylic) and λ = 2.3 mm. In this case, since λ is large, the fiber 23 is caught by the grid electrode 13 and the brush 22 is stopped.

[Consideration for Condition 3B]
The parameter of the fiber 23 that characterizes the condition 3B is the distance that the intersection A between the bent portion 23a of the fiber 23 and the plane on which the grid electrode 13 moves until the fiber 23 returns to its original state from the assumption that the fiber 23 has been fully extended. δ can be raised. FIG. 12A shows δ.

When δ is expressed by the parameters a, b, θ of the fiber 23 and the distance L between the grid electrode and the brush holding member, δ = √ (λ ² −L ² ) + asin θ−Δtan θ. If it is assumed that the fiber 23 does not come off the grid electrode 13 until the fiber 23 is completely extended, the condition of the fiber 23 satisfying the condition 3B with respect to the grid interval D is δ <D.

  However, as shown in FIG. 12 (b), the fiber 23 is actually pulled out of the grid surface 13c in a bent state, so that the bent portion 23a of the fiber 23 and the grid electrode are required before the actual fiber 23 returns to the original state. The distance δ ′ traveled by the intersection A with a certain plane 13 is smaller than δ. Further, it is considered that the fiber 23 slips out on the grid surface due to the stress caused by the bending of the fiber 23, and the fiber 23 can come out of the grid electrode 13 even when δ is larger than D. In the present embodiment, the lower limit of δ is l tan θ, and if it is less than this, the fiber is not restored. Therefore, it is preferable that ltanθ <δ <D. In the case of the second embodiment described later, the lower limit of δ is bsin α + lcos α tan (θ−α).

[Observation results for Condition 3B]
FIG. 13A to FIG. 13C are diagrams showing the results of observation with a CCD camera while changing the Young's modulus E, a, and b. Nylon (E = 150 mg / cm ² , 250 mg / cm ² ) was used as the material of the fiber 23.

FIG. 13A shows the result when E = 250 mg / cm ² (nylon) and δ = 2.57 mm. At this time, the fiber 23 can return to the original state.

FIG. 13B shows the case where E = 150 mg / cm ² (nylon) and δ = 2.57 mm. At this time, the fiber 23 abuts on the next grid electrode 13 before returning to the original state, and cannot contact the grid back surface 13a.

  This is because the greater the stress of the fiber 23, that is, the greater the Young's modulus E, the easier the slip on the grid surface, and the greater the Young's modulus E, the easier the fiber 23 returns to its original state even if δ is large.

FIG. 13C shows the case where E = 250 mg / cm ² (nylon) and δ = 3 mm. In this case, since δ is large, the fiber 23 comes into contact with the next grid electrode 13 before returning to the original state and cannot come into contact with the grid back surface 13a.

[Verification of parameters of fiber 23 optimal for cleaning]
In order to satisfy the first condition to the third condition and to check the conditions under which the grid back surface 13a can be actually cleaned, the length a of the bent portion 23a and the length b of the straight hair portion 23b are each changed by 0.1 mm as parameters. A brush 22 was prepared. As the material of the fiber 23, nylon (E = 150 mg / cm ² , 250 mg / cm ² ) and acrylic (E = 300 mg / cm ² ) were used.

  Whether the brush 22 satisfies the first condition to the third condition is observed with a CCD camera, and the brush 22 having each parameter is mounted on the Canon imagePRESSSC1 remodeling machine manufactured by Canon, which is an actual image forming apparatus. The cleaning effect of 13a was measured.

  The evaluation of the cleaning effect was performed using a complex imagePRESSC1 modified machine manufactured by Canon Inc. using a charging device equipped with a brush having parameters of each fiber 23. An image is output by this multifunction device, and the number of image outputs until white streaks appear in the image due to uneven charging on the photosensitive drum 1 due to adhesion of foreign matters such as toner and blemishes to the grid electrode 13 was measured. .

  The grid back surface 13a is cleaned once every time 5000 images are output. The grid electrode cleaning unit 14 moves from the home position A in FIG. 2A to the grid end B, and thereafter moves from the grid end B to the original home position A as one cleaning process.

  In addition, as a criterion for evaluating the cleaning member, “good” was given when the number of image output sheets before white streaks appeared was 30,000 or more. In the case of 15,000 to 30,000 sheets, it was set as Δ (acceptable). In the case of less than 15,000 sheets, which is the same level as that of a straight-hair brush, it was evaluated as x (bad).

The case of E = 250 mg / cm ² (nylon) and θ = 45 ° is shown in Table 1 (all units are mm). FIG. 14A is a graph showing, as a region, combinations of the length a of the bent portion 23a and the length b of the straight hair portion 23b that satisfy the first condition to the third condition and have a high cleaning effect from Table 1. is there. In FIG. 14A, the vertical axis represents the length b of the straight hair portion of the fiber 23, and the horizontal axis represents the length a of the bent portion 23 a of the fiber 23.

Due to the manufacturing conditions of the brush 22, there is an error of about ± 0.1 mm in the length a of the bent portion 23a and the length b of the straight hair portion 23b. Considering this, when E = 250 mg / cm ² (nylon) and θ = 45 °, a combination of a = 0.7 mm, b = 1.3 mm or a = 0.6 mm, b = 1.3 mm It was most suitable for cleaning the grid back surface 13a.

同様にＥが１５０ｍｇ／ｃｍ^２（ナイロン）、３００ｍｇ／ｃｍ^２（アクリル）である２種類のブラシ２２を用いた場合でも表１と同様の表を作成し、清掃効果が良かったａ、ｂの組み合わせを領域として示したグラフを図１４（ｂ）に示す。図１４（ｂ）において縦軸は繊維２３の直毛部２３ｂの長さｂを、横軸は繊維２３の屈曲部２３ａの長さａを表す。

Similarly, even when two types of brushes 22 having E of 150 mg / cm ² (nylon) and 300 mg / cm ² (acrylic) were used, a table similar to Table 1 was created, and the cleaning effects of a and b were good. A graph showing combinations as regions is shown in FIG. 14B, the vertical axis represents the length b of the straight hair portion 23b of the fiber 23, and the horizontal axis represents the length a of the bent portion 23a of the fiber 23.

When E is increased from E = 250 mg / cm ² (nylon) to E = 300 mg / cm ² (acrylic), the region having a high cleaning effect decreases. This is an influence that the fiber 23 is caught on the grid side surface 13b because the Young's modulus E is large as described in the condition 3A of the third condition.

Moreover, even if E is reduced from E = 250 mg / cm ² (nylon) to E = 150 mg / cm ² (nylon), the region having a high cleaning effect decreases. This is because the Young's modulus is small as described in the condition 3B of the third condition, so that the fiber 23 comes into contact with the next grid electrode 13 before returning to the original state, and cannot come into contact with the grid back surface 13a. It is an influence.

Considering that there is an error of about ± 0.1 mm in the length a of the bent portion 23a and the length b of the straight hair portion 23b from the manufacturing conditions of the brush, the Young's modulus E is as good as possible with respect to a and b. Ideally, E = 250 mg / cm ² (nylon) or so.

Next, under the condition of Young's modulus E = 250 mg / cm ² (nylon), a brush with the bending angle θ changed to 30 ° and 60 ° was manufactured, and a table similar to Table 1 was prepared. FIG. 15A shows a graph showing a combination of a and b that is high as a region. In FIG. 15A, the vertical axis represents the length b of the straight hair portion 23b of the fiber 23, and the horizontal axis represents the length a of the bent portion 23a of the fiber 23.

  As the bending angle θ increases, the region having a high cleaning effect shifts to the side where the length b of the straight hair portion 23b is smaller. This is because the straight line representing the boundary condition Δ = 0 in which the fiber 23 cannot abut on the grid back surface 13a is represented by b = acos θ + 1, and in the region where Δ> 0 with the decrease in θ, the length b of the straight hair portion 23b is small. This is to shift the direction. As shown in FIG. 15A, the bend angle with good redundancy is preferably about θ = 45 °.

Based on the above observation and measurement results, the combination of E = 250 mg / cm ² (nylon), θ = 45 °, a = 0.7 mm, and b = 1.3 mm is optimal as the parameters of the fiber 23. Alternatively, a combination of E = 250 mg / cm ² (nylon), θ = 45 °, a = 0.6 mm, and b = 1.3 mm is optimal.

[Cleaning effect of this embodiment]
In particular, using a brush 22 having a combination of fiber parameters of E = 250 mg / cm ² (nylon), θ = 45 °, a = 0.7 mm, and b = 1.3 mm, the coverage ratio of the toner on the grid back surface 13a is examined. The result is shown in FIG. A Canon multifunction printer imagePRESSC1 modified machine was used. In FIG. 15B, the vertical axis represents the toner coverage on the grid back surface 13a, and the horizontal axis represents the number of output images. FIG. 15 (b) also shows the result of the toner coverage rate on the grid back surface 13a by a straight hair brush whose end is not bent. The grid back surface 13a was cleaned in the same manner as described above.

  The method for measuring the toner coverage on the grid back surface 13a is as follows. The corona charging device 2 is taken out for each image output number, and an image observed by the microscope on the grid back surface 13a is taken in. The toner adhesion portion was determined from the RGB ratio of the image, and was calculated by taking the quotient of the integrated value of the area of the toner adhesion portion and the area of the grid back surface 13a measured before image output.

  As shown in FIG. 15 (b), when cleaning with a straight-hair brush whose front end is not bent, the toner coverage on the back surface increases with the number of output images, and is 50% when outputting 40,000 sheets. Reach above. On the other hand, cleaning with the brush 22 that has been subjected to the bending process having the optimum parameters results in a toner coverage rate of only about 10% even when 40,000 sheets are output, and the grid back surface 13a is cleaned with the brush 22 that has been subjected to the bending process. There is an effect to.

  Next, assuming that foreign matters other than the toner, particularly dust and markings, were attached to the grid electrode 13, 100 markings were artificially attached to the grid back surface 13a. As the brush 22 subjected to the bending process and the straight hair brush not subjected to the bending process reciprocate between the home position A and the grid end B in FIG. The degree to which the mark on the back surface 13a was removed was measured. The result is shown in FIG. In FIG. 16A, the vertical axis represents the removal rate of the mark on the grid back surface 13a, and the horizontal axis represents the number of output images.

  As shown in FIG. 16 (a), in the cleaning with a straight brush whose tip is not subjected to bending treatment, the removal rate of the back-surface mark is 5% or less even after 20 cleanings, and the mark is hardly removed. On the other hand, in the cleaning with the brush 22 that has been subjected to the bending process having the above parameters, about 80% of the chipping can be removed by cleaning 20 times, and the bending process is also applied to dust such as chipping other than the toner. The brush is effective.

Further, by using a brush 22 having a combination of the following fiber parameters, the number of image outputs until white streaks appear in the image due to non-uniform charging on the photosensitive drum 1 due to foreign matters such as toner adhering to the grid. I investigated. The fiber parameters were E = 250 mg / cm ² (nylon), θ = 45 °, a = 0.7 mm, and b = 1.3 mm, which are the optimum parameters. A Canon multifunction printer imagePRESSC1 modified machine was used.

  Further, the grid back surface 13a is cleaned once every time 5000 images are output. As in the case described above, the grid electrode cleaning unit 14 moves from the home position A in FIG. 2A to the grid end B, and then moves from the grid end B to the original home position A. The cleaning process was performed once. The result is shown in FIG. As shown in FIG. 16 (b), when a straight brush that has not been bent is used, white lines appear due to uneven charging on about 10,000 sheets, whereas a brush that has been bent is used. In 22, no white streak appears up to nearly 50,000 sheets. By using the brush 22 subjected to the bending process, charging unevenness can be suppressed.

  The optimum values of E, θ, a, and b shown above are the shape of the grid electrode 13 shown in FIG. 3A and the distance between the grid electrode 13 and the brush holding member 19 shown in FIG. It changes with L. By selecting an optimal combination of E, θ, a, and b with respect to the shape of each grid electrode 13 and the distance L between the grid electrode 13 and the brush holding member 19, the same effect as described above can be expected.

  In the present embodiment, acrylic or nylon is selected as the material for the fibers 23 constituting the brush 22. However, it is only necessary to have an optimal Young's modulus E with respect to the shape of each grid electrode 13 of the charging device 2 and the distance L between the grid electrode 13 and the brush holding member 19. Various things can be considered and is not particularly limited.

  According to the present embodiment, the entire surface of the grid electrode 13 facing the photosensitive drum 1 can be cleaned with a simple configuration.

[Second Embodiment]
Next, a second embodiment of the charging device according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. FIG. 17A is a configuration diagram of the brush of the present embodiment. As shown to Fig.17 (a), the brush 32 of this embodiment makes the angle | corner (beta) which makes the fiber 23 which comprises the brush 22 of said 1st embodiment the moving direction of the brush 22, and the flocking direction of the fiber 23 into. The bent portion 23a is bent in a direction in which the tip 23c approaches the grid back surface 13a. The angle between the normal of the grid plane and the fiber 23 is α. The shape of the bending process for the fibers 23 is the same as that of the first embodiment.

[Consideration on Cleaning Process of Brush 32 of this Embodiment]
By providing the fibers 23 with an angle with respect to a plane on which the grid electrode 13 is provided, when the tip 23c comes into contact with the grid electrode 13, a force Fh from the brush holding member 19 acts as shown in FIG. The resultant force of the component Fv in the direction perpendicular to the grid plane of Fh and the stress F1 due to the bending of the fiber 23 acts on the portion of the fiber 23 that is in contact with the grid side surface 13b. For this reason, the fiber 23 can penetrate | invade more easily with respect to the grid back surface 13a. Therefore, it is possible to enter the grid back surface 13a even when the amount of protrusion Δ is larger than that in the first embodiment.

  However, since the fiber 23 has an angle, among the third conditions described in the first embodiment, the condition for the length λ of the entire fiber in the condition 3A becomes stricter. Because the fibers 23 have an angle, when the fibers 23 come out of the grid back surface 13a while abutting against the grid side surface 13b, the fibers 23 are bent more greatly, and the stress of the fiber is large, so that the fibers 23 receive from the grid side surface 13b. This is because the frictional force also increases.

[Verification of optimum fiber parameters for cleaning]

When E = 250 mg / cm ² (nylon), θ = 60 °, α = 30 °, the length a of the bent portion 23a and the length b of the straight hair portion 23b are each changed by 0.1 mm as parameters. A brush was made. Then, a table similar to Table 1 was created from the results of observation with a CCD camera as in the first embodiment and the results of evaluating the cleaning effect by mounting a brush produced on a Canon multifunction PRESSC1 modified machine manufactured by Canon Inc. In addition, the brush used was a fiber that was subjected to bending treatment by injection molding as in the first embodiment. The results are shown in Table 2 (all units are mm).

表２より清掃効果が高かった屈曲部２３ａの長さａ、直毛部２３ｂの長さｂの組み合わせを領域として示したグラフを図１８（ａ）に示す。図１８（ａ）において縦軸は繊維２３の直毛部２３ｂの長さｂを、横軸は繊維２３の屈曲部２３ａの長さａを表す。図１８（ａ）に示すように、Ｅ＝２５０ｍｇ／ｃｍ^２（ナイロン）、θ＝６０°、α＝３０°の場合には冗長性のよいａ＝０．４ｍｍ、ｂ＝１．５ｍｍの組み合わせが最適であった。

FIG. 18A shows a graph showing, as a region, a combination of the length a of the bent portion 23a and the length b of the straight hair portion 23b, which has a higher cleaning effect than Table 2. In FIG. 18A, the vertical axis represents the length b of the straight hair portion 23b of the fiber 23, and the horizontal axis represents the length a of the bent portion 23a of the fiber 23. As shown in FIG. 18A, when E = 250 mg / cm ² (nylon), θ = 60 °, α = 30 °, a combination of a = 0.4 mm and b = 1.5 mm with good redundancy. Was the best.

  As described above, the brush 32 having an appropriate combination of the length a of the bent portion 23a and the length b of the straight hair portion 23b is used even when the fiber 23 is angled with respect to the plane on which the grid electrode 13 is provided. Thus, the same effect as in the first embodiment can be obtained.

  In the present embodiment, nylon is selected as the material for the fibers 23 constituting the brush 32. However, it is only necessary to have an optimal Young's modulus E with respect to the shape of each grid electrode 13 of the charging device 2 and the distance L between the grid electrode 13 and the brush holding member 19. Various things can be considered and is not particularly limited.

[Third embodiment]
Next, a third embodiment of the charging device according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. FIG. 18B is a configuration diagram of the brush 42 of the present embodiment. As shown in FIG. 18B, the brush 42 of the present embodiment is configured such that the fibers 23 of the brush 22 of the first embodiment are directed in opposite directions between adjacent fibers in the bending direction. It is a thing. The shape of the bending process for the fibers 23 is the same as that of the first embodiment.

[Comparison of Cleaning Process of Brush 42 of this Embodiment and Brush 22 of First Embodiment]
FIG. 19A shows how the brush 22 moves when the bending direction of the fiber 23 is only one direction as in the first embodiment. When the brush 22 moves in the direction of arrow f in FIG. 19A, the bending direction of the fibers 23 and the moving direction of the brush 22 are aligned, and the grid back surface 13a can be cleaned. However, when the brush 22 moves in the direction of arrow g in FIG. 19A, the bending direction of the fiber 23 and the moving direction of the brush 22 are reversed, and the fiber 23 cannot clean the grid back surface 13a. Since the brush 22 reciprocates with respect to the grid electrode 13 by the rotation of the motor M1, as shown in FIG. 19A, the grid back surface 13a and the center line in the grid plane direction (brush moving direction) of the grid electrode 13 are used as a boundary. Define the A side and the B side. At this time, as can be seen from the processes 1 to 3 in FIG. 6, the contact force and the contact area with respect to the grid back surface 13a are different between the A side and the B side of the grid back surface 13a. Further, the tip 23c of the bent portion 23a of the brush 22 cannot come into contact with the grid side surface 13b on the B side. For this reason, the cleaning is different between the A side and the B side of the grid back surface 13a, and there is a possibility that the toner, flakes, etc. remain only on the B side.

  Therefore, by configuring the bending directions of the fibers to be opposite to each other as shown in FIG. 18B, the grid back surface 13a can be evenly cleaned in the forward path and the return path of the brush 42, and the cleaning efficiency is increased. Prevention of uneven cleaning can be expected.

[Cleaning effect of this embodiment]
Actually, as in the case of the first embodiment, FIG. 19B and FIG. 19B show the measurement results of the toner coverage rate on the grid back surface 13a and the mark removal rate on the grid back surface 13a using a brush 42 having the following fiber parameters. 20 (a). The fiber parameters were E = 250 mg / cm ² (nylon), which is the optimum parameter, θ = 45 °, a = 0.7 mm, and b = 1.3 mm. In FIG. 19B, the vertical axis represents the toner coverage on the grid back surface 13a, and the horizontal axis represents the number of output images. In FIG. 20A, the vertical axis represents the removal rate of the mark on the grid back surface 13a, and the horizontal axis represents the number of output images.

  The method for cleaning the grid back surface 13a is the same as in the first embodiment. As shown in FIG. 19B and FIG. 20A, the brush 42 in which the bending directions of the fibers are opposite to each other has better cleaning efficiency than the brush 22 whose bending direction is one direction.

  Further, as in the case of the first embodiment, FIG. 20B shows the result of examining the number of images output until a white streak appears in the image by outputting an image using the Canon imagePRESSSC1 modified machine manufactured by Canon. The method for cleaning the grid back surface 13a is the same as described above.

  Also in this experiment, when the brush 42 is used, the number of image outputs until the white streaks appear is higher and the cleaning effect is higher than the brush 22 in the first embodiment in which the bending direction is unidirectional.

  In the present embodiment, the fibers 23 constituting the brush 42 have been described using fibers in which the bending directions of the fibers are opposite to each other between adjacent fibers. In addition to this, the brush 42 may be mixed with fibers 23 in which the bending directions of the fibers 23 are opposite to each other with respect to the moving direction of the brush 42 as shown in FIGS. 21 (a) to 21 (c). The number of the fibers 23 having the bending direction with respect to the forward direction of the movement direction of the brush 42 and the number of the fibers 23 having the bending direction with respect to the backward direction needs to be equal. Also with this brush 42, the grid back surface 13a can be evenly cleaned in the forward path and the return path of the brush 42, and the same effect as in this embodiment can be expected.

[Fourth embodiment]
Next, a fourth embodiment of the charging device according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. FIG. 21D is a diagram showing a cleaning process by the brush 52 of the present embodiment. As shown in FIG. 21 (d), the brush 52 of the present embodiment is a mixture of the brush 22 of the first embodiment in which the tip portion of the fiber 23 is bent and the tip portion of the brush 22 having straight hair. It is a thing. The shape of the bending process for the fibers 23 is the same as that of the first embodiment.

  When the brush 22 is composed of only the bent fiber 23 as in the first embodiment, as described in the condition 3A of the first embodiment, the Young's modulus E of the fiber 23 is large or the length λ of the entire fiber is When it is large, the frictional force exerted on the fiber 23 from the grid side surface 13b becomes large. If the sum of the frictional force for all the fibers 23 exceeds the driving force of the motor, the brush 22 may be caught by the grid electrode 13 and not move. Therefore, a motor having a driving force larger than the sum of the frictional forces is used.

  However, in order to save cost and space, there is a case where a small motor having a small driving force has to be used. In that case, in order to reduce the torque applied to the motor by the frictional force exerted on the fibers 23, it is conceivable to reduce the number of the fibers 23 that are subjected to the bending treatment and constitute the brush 22. In this case, although the cleaning efficiency of the grid back surface 13a falls, it also becomes a subject that the cleaning efficiency of the grid surface 13c falls simultaneously.

  Therefore, as shown in FIG. 21 (d), the brush 52 has a configuration in which the tip of the fiber 23 is bent and the one having a straight hair is mixed so that the number of fibers is not changed. Yes. Accordingly, the straight hair fibers clean the grid surface 13c, and only the bent fibers whose number is reduced clean the grid back surface 13a. For this reason, the torque concerning a motor can be reduced, maintaining the cleaning efficiency of the grid surface 13c. Further, as in the first embodiment, the entire surface of the grid electrode 13 facing the photosensitive drum 1 can be cleaned with a simple configuration.

A ... Home position B ... Grid edge L ... Laser beam M1 ... Motor P ... Transfer material 1 ... Photosensitive drum 2 ... Corona charging device 3 ... Two-component developer 4 ... Transfer roller 5 ... Cleaner 6 ... Static elimination lamp 7 ... Scanner 10 Shield case 11 Insulating support 12 Discharge wire 13 Grid electrode 13a Grid back surface 13b Grid side surface 13c Grid surface 14 Grid electrode cleaning unit 15 Discharge wire cleaning units 15a and 15b Sponge pad 16 Holder DESCRIPTION OF SYMBOLS 17 ... Screw shaft 18 ... Bearing 19 ... Brush holding member 20 ... Injection molding machine 21 ... Die 22, 32, 42, 52 ... Brush 23 ... Fiber 23a ... Bending part 23b ... Straight hair part 23c ... Tip 23d ... Bending point

Claims (5)

A grid electrode facing the object to be charged;
A charging device comprising a brush that contacts the grid electrode, and a cleaning member that cleans the grid electrode while moving,
The fiber of the brush has a straight hair portion extending toward the charged body side from the grid back surface of the grid electrode on the charged body side, and a bent portion bent at an acute angle with respect to the straight hair portion, In accordance with the movement of the cleaning member, the tip of the brush fiber comes into contact with the back surface of the grid facing the charged body of the grid electrode.
The brush has an acute angle between the moving direction of the brush and the direction of flocking of the fibers of the brush, and the bent portion is bent in a direction in which the tip of the fiber of the brush approaches the back surface of the grid. The charging device according to claim 1.
The brush comprises a mixture of a bent portion bent in the moving direction of the brush and a bent portion bent in a direction opposite to the moving direction of the brush. Item 2. The charging device according to Item 1.
The charging device according to claim 1, wherein the brush includes a fiber having the bent portion and a fiber having only a straight hair portion not having the bent portion.
  The charging device according to claim 1, wherein the grid electrode has a plurality of openings formed in a flat plate-like member.

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