JP2022064152A - Electrification device, image forming unit, and image forming apparatus - Google Patents

Abstract

To bring a cleaning member into contact with an electrifying member with an appropriate contact pressure.SOLUTION: An electrifying device 16 comprises: an electrifying roller 32 that is rotatable and in contact with a surface of a photoconductor drum 14 to electrify the photoconductor drum; a cleaning roller 34 that is rotatable and cleans a surface of the electrifying roller 32; a pulling spring 44 that brings the cleaning roller 34 and the electrifying roller 32 into contact with each other and can extend and contract in a longitudinal direction; and a bearing arm 40a that holds one end and the other end in the longitudinal direction of the pulling spring 44 in a bent state, and brings an outer peripheral part of the pulling spring 44 into contact with the cleaning roller 34. When the natural length of the pulling spring 44 is a spring natural length L1, and the length inside the pulling spring 44 in the bent state is a spring inside length in use L4, the spring natural length L1 and the spring inside length in use L4 are adjusted to be equal to each other.SELECTED DRAWING: Figure 4

Description

The present invention relates to a charging device, an image forming unit and an image forming device, and is suitable for application to, for example, an electrophotographic printer.

Conventionally, in an image forming apparatus using an electrophotographic process such as a printer, a copying machine, a facsimile machine or a multifunction device, a charging roller as a charging member comes into contact with the surface of the photosensitive drum to uniformly charge the surface of the photosensitive drum. A charging method is often used.

In the contact charging type image forming apparatus, since the charging roller is in direct contact with the photosensitive drum, the charging roller winds up dirt such as an external additive adhering to the surface of the photosensitive drum. Therefore, in such an image forming apparatus, a cleaning member as a cleaning member for cleaning the surface of the charged roller is provided, and as the cleaning member, a cleaning roller having a foam surface is often used (for example, Patent Document 1). reference).

Japanese Unexamined Patent Publication No. 2017-83643

However, in order to clean the surface of the charging member that applies voltage to the photosensitive drum, the cleaning member may be urged by an elastic member, but the cleaning member may not be in contact with the charging member with an appropriate pressure contact force. rice field.

The present invention has been made in consideration of the above points, and an object of the present invention is to propose a charging device, an image forming unit, and an image forming device capable of bringing a cleaning member into contact with a charging member with an appropriate pressure contact force.

In order to solve such a problem, in the charging device of the present invention, a charging member that is rotatable and contacts and charges the surface of the charged member, a cleaning member that is rotatable and cleans the surface of the charging member, and a cleaning member. The elastic member that can be expanded and contracted in the longitudinal direction and the one end side and the other end side in the longitudinal direction of the elastic member are held in a bent state, and the outer peripheral portion of the elastic member is in contact with the cleaning member. When the natural length of the elastic member is L1 and the inner length of the elastic member in the bent state is L4, L1 = L4.

Further, the image forming unit of the present invention is provided with the above-mentioned charging device.

Further, the image forming apparatus of the present invention is provided with the above-mentioned image forming unit.

In the present invention, when the cleaning member is momentarily separated from the charged member, the entire elastic member is stretched and the urging force is momentarily strengthened, and the elastic member immediately urges the cleaning member toward the charged member to perform cleaning performance. On the other hand, if the cleaning member is momentarily strongly pressed against the charged member, the entire elastic member cannot shrink any more and the urging force drops sharply, so that dust adhering to the cleaning member is deposited. Adhesion to the charged member can be suppressed, and the occurrence of printing defects can be suppressed.

According to the present invention, the cleaning member can be brought into contact with the charged member with an appropriate pressure contact force.

It is a left side view which shows the structure of an image forming apparatus. It is a front view which shows the structure of the charging apparatus by 1st Embodiment. It is sectional drawing which shows the structure of the charging device. It is a left side view which shows the structure of a bearing part. It is a front view which shows the structure of a cleaning roller. FIG. 5 is a cross-sectional view taken along the line BB of FIG. 5 showing a configuration of a cleaning roller according to the first embodiment. It is a figure which shows the structure of a tension spring. It is a left side view which shows the winding angle. It is a left side view which shows the nip amount. It is a block diagram which shows the control composition of an image forming apparatus. It is a table which shows the list of tension springs. It is a table which shows the evaluation result. It is a graph which shows the relationship between the shaft-to-axis distance and a bearing load. It is a graph which shows the relationship (1) between a nip amount and a bearing load. It is a graph which shows the relationship (2) between a nip amount and a bearing load. It is a front view which shows the structure of the charging apparatus by 2nd Embodiment. It is sectional drawing which shows the structure of the cleaning roller by 2nd Embodiment.

Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[1. First Embodiment]
[1-1. Configuration of image forming apparatus]
As shown in FIG. 1, the image forming apparatus 1 is, for example, a printer using an electrophotographic method, and by performing an image forming operation using a developer such as toner, a black-and-white image is printed on a medium P such as paper or film. Or to form a color image. Hereinafter, the position close to the cassette 7 or the direction toward the cassette 7 when viewed from an arbitrary position on the transport path on which the medium P is conveyed is referred to as upstream. Further, the position close to the stacker from which the medium P is discharged and loaded, or the direction toward the stacker, when viewed from an arbitrary position on the transport path, is referred to as a downstream direction. Furthermore, the direction from upstream to downstream is called the transport direction. The image forming apparatus 1 has a medium supply unit 2, a transport unit 3, an image forming unit 4, a transfer unit 5, and a fixing unit 6 inside the box-shaped housing from upstream to downstream.

[1-2. Configuration of medium supply unit]
The medium supply unit 2 has a cassette 7 and a hopping roller 8. The cassette 7 is detachably attached to the lower part of the housing of the image forming apparatus 1, and the media P are stored in a laminated state. The hopping roller 8 separates and takes out the medium P stored in the cassette 7 one by one from the uppermost portion thereof, and feeds the medium P toward the transport roller pair 10 located downstream thereof.

[1-3. Configuration of transport unit]
The transport unit 3 has transport roller pairs 10 and 11 arranged in order from upstream to downstream. The transport roller pairs 10 and 11 sandwich and transport the medium P unwound from the hopping roller 8, and at that time, correct the skew of the medium P and transport the medium P toward the transfer belt 26 along the transport direction.

[1-4. Composition of image forming part]
The image forming unit 4 has, for example, four developing units 12 (12K, 12C, 12M and 12Y). The developing units 12K, 12C, 12M and 12Y are arranged in order from the upstream side to the downstream side along the transport direction, and the developing agent image is displayed on the medium P by using toners (developing agents) having different colors. Form (toner image). Specifically, the developing units 12K, 12C, 12M and 12Y form black, cyan, magenta and yellow toner images using black, cyan, magenta and yellow toners, respectively.

Each of such toners of each color is composed of, for example, a predetermined colorant, a mold release agent, a charge control agent, a treatment agent, and the like, and each of these components is appropriately mixed or surface-treated. Manufactured by Of these, the colorant, the mold release agent, and the charge control agent each function as an internal additive. As the external additive, for example, silica, titanium oxide or the like is used, and as the binder resin, for example, a polyester resin or the like is used. Further, as the colorant, dyes, pigments and the like can be used alone or in combination of two or more. As the toner, for example, a toner having a circularity of about 0.94 to 0.98 and an average particle size of about 7 [μm] is used. As the external additive, for example, one having about 50 to 200 [nm] is used.

[1-4-1. Structure of developing unit]
The developing units 12K, 12C, 12M and 12Y have the same configuration except that toner images having different colors are used to form a toner image. Hereinafter, the developing units 12K, 12C, 12M and 12Y are collectively referred to as a developing unit 12. Each developing unit 12 has, for example, a photosensitive drum 14, a charging device 16, an exposure device 18, a developing roller 20, a toner supply unit 22, and a cleaning blade 24.

[1-4-1-1. Photosensitive drum configuration]
The photosensitive drum 14 is a member that supports an electrostatic latent image on a surface (surface layer portion), and is configured by using a photosensitive member (for example, an organic photosensitive member). Specifically, the photosensitive drum 14 has a conductive support and a photoconducting layer that covers the outer periphery (surface) thereof. The conductive support is made of, for example, a metal pipe made of aluminum or stainless steel. The photoconducting layer has, for example, a structure in which a charge generation layer and a charge transport layer are laminated in order. The photosensitive drum 14 rotates at a predetermined peripheral speed.

The charge generating layer contains a charge generating substance and a binder resin as main components. Various organic pigments and organic dyes can be used as the charge generating substance. Among them, metal-free phthalocyanine, copper indium chloride, gallium chloride, tin, oxytitanium, zinc, vanadium and other metals or their oxides, chloride-coordinated phthalocyanines, or monoazo, hisazo, trisazo or polyazo and other azos. Pigments and the like are preferable. The charge generating layer comprises fine particles of these charge generating substances, for example, polyester resin, polyvinyl acetate, polyacrylic acid ester, polymethacrylic acid ester, polyester, polycarbonate, polyvinylacet acetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy. It is used as a dispersion layer bonded with various binder resins such as resin, urethane resin, cellulose ester or cellulose ether.

The charge transport layer contains a charge transport substance and a binder resin as main components. The charge transporting substance includes, for example, heterocyclic compounds such as carbazole, indol, imidazole, oxazole, pyrazole, oxadiazol, pyrazoline and thiazazole, aniline derivatives, hydrazone compounds, aromatic amine derivatives, stylben derivatives, or compounds thereof. An electron donating substance such as a polymer having a group in the main chain or the side chain is used. The binder resin in the charge transport layer includes vinyl polymers such as polycarbonate, polymethylmethacrylate, polystyrene, and polyvinyl chloride, polyester, polyester carbonate, polysulfone, polyimide, phenoxy, epoxy, silicone resin, or polymers or portions thereof. Examples thereof include a cross-linked cured product, and polycarbonate is particularly preferable. Further, the binder resin in the charge transport layer may contain various additives such as an antioxidant and a sensitizer, if necessary.

[1-4-1-2. Configuration of charging device]
As shown in FIGS. 2, 3 and 4, the charging device 16 is a device for charging the surface of the photosensitive drum 14, and is mainly composed of a charging roller 32 and a cleaning roller 34. The charging roller 32 is arranged so that the rotation axis is oriented in the left-right direction so as to be in contact with the surface of the photosensitive drum 14. In the charging roller 32, the charging roller core metal 32a is rotatably supported by the outer charging roller bearings 36 provided near the left and right ends. The outer charged roller bearing 36 is urged toward the photosensitive drum 14 by a compression spring 38. Therefore, the charging roller 32 is urged toward the photosensitive drum 14. Further, on the left and right inner sides of the left and right outer charging roller bearings 36, inner charging roller bearings 40 that rotatably support the charging roller core metal 32a are provided. The inner charged roller bearing 40 has a substantially cylindrical and linear bearing arm 40a projecting from slightly above the central portion in the vertical direction on both front and rear surfaces toward the front-up direction and the rear-up direction, respectively.

The cleaning roller 34 is arranged with its rotation axis oriented in the left-right direction so as to be in sliding contact with the charging roller 32. In the cleaning roller 34, the cleaning roller core 34a is rotatably supported by cleaning roller bearings 42 provided near both left and right ends. The tension spring arm portion 44a of the tension spring 44 is engaged with the bearing arm 40a of the inner charged roller bearing 40. The tension spring 44 is bent so as to have a shape as if the capital letter "U" is rotated 180 degrees as a whole, and the inside of the bent shape of the tension spring coil portion 44b in the bent state is a cleaning roller bearing. It is wound around the outer peripheral surface of the peripheral side surface of 42, which is opposite to the charging roller 32. In this way, the charging device 16 bends the tension spring 44 locked to the inner charging roller bearing 40 and brings the inside of the bent shape into contact with the cleaning roller bearing 42, whereby the tension spring 44 and the charging roller 32 The bearing arm 40a of the coaxial inner charged roller bearing 40 was pulled. Therefore, the charging device 16 urges the cleaning roller bearing 42 toward the inner charging roller bearing 40 by the tension spring 44, so that the cleaning roller 34 is brought into contact with the charging roller 32 toward the charging roller 32. You can do it. In the present embodiment, the case where the outer charging roller bearing 36 and the inner charging roller bearing 40 are separate and separate parts has been described, but the outer charging roller bearing 36 and the inner charging roller bearing 40 may be integrated. good.

The bearing portion including the inner charged roller bearing 40, the cleaning roller bearing 42, and the tension spring 44 allows the charging device 16 to nip the cleaning roller 34 to the charging roller 32 by a load, so that the cleaning roller 34 is worn out. It is possible to cope with changes and fluctuations in the wall thickness of the cleaning roller elastic layer 34b. The cleaning roller 34 in the first embodiment is driven by the frictional force between the surface of the charging roller 32 and the surface of the cleaning roller 34 along with the rotation of the charging roller 32.

[1-4-1-2-1. Configuration of charging roller]
The charging roller 32 has a charging roller core metal 32a made of a conductive material, and a conductive charging roller elastic layer 32b is formed on the outer peripheral surface of the charging roller core metal 32a. For the charged roller core metal 32a, for example, an electroless nickel-plated SUM or a metal shaft body such as SUS is often used. In order to obtain an appropriate discharge with the photosensitive drum 14, rubber, a thermoplastic elastomer, a resin, or the like is often used for the charged roller elastic layer 32b so that the charged roller elastic layer 32b can be niped with the photosensitive drum 14. The charged roller elastic layer 32b is not limited to a single layer, and has a multi-layer structure of two or more layers as needed.

Examples of the material composed of the charged roller elastic layer 32b include epichlorohydrin rubber (CO, ECO, GECO), ethylene propylene rubber (EPM, EPDM), acrylonitrile-butadiene rubber (NBR), and hydride acrylonitrile-butadiene rubber (H-). NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), urethane rubber, silicone rubber, etc. A rubber composition can be used. In particular, rubber containing epichlorohydrin rubber (ECO) as a main component or rubber containing a mixture of epichlorohydrin rubber (ECO) and acrylonitrile-butadiene rubber (NBR) as a main component is often used. In this embodiment, a rubber containing epichlorohydrin rubber (ECO) as a main component was used.

As a conductive property of the charged roller elastic layer 32b, generally, if the resistance is too large, image defects due to uneven charging on the surface of the photosensitive drum 14 and poor charging occur. On the contrary, if the resistance is too small, a leak occurs due to scratches on the surface of the photosensitive drum 14, and the image becomes defective. Therefore, there is an appropriate resistance region in the conductive characteristics of the charged roller elastic layer 32b. In order to obtain an appropriate resistance region, an ionic conductive material, an ionic conductive agent, carbon black, a metallic oxide, or the like is used for the charged roller elastic layer 32b to give a predetermined conductivity. The charged roller elastic layer 32b can be either electronically conductive or ionic conductive as conductivity, but partial resistance unevenness may easily affect the charging unevenness of the photosensitive drum 14, resulting in resistance unevenness. In order to suppress the above, ionic conductivity is often used rather than electron conductivity.

The charged roller elastic layer 32b is preferably a resistance layer having a volume resistance value of ¹⁰⁶ to ¹⁰⁹ [Ω]. In the case of ionic conductivity, the resistance value of the charging roller 32 shows a value different depending on the temperature / humidity and the measured voltage, but here, the value measured in an environment of a temperature of 20 [° C.] and a humidity of 50 [% RH] is shown. ..

The hardness of the charged roller elastic layer 32b needs to form a minute gap between the surface of the charged roller 32 and the surface of the photosensitive drum 14 to secure a region that contributes to discharge based on Paschen's law. The hardness of the charged roller elastic layer 32b is adjusted in order to obtain an appropriate nip. At this time, a micro rubber hardness tester MD-1capa (TypeA) (manufactured by Polymer Meter Co., Ltd.) is used for the hardness of the charged roller elastic layer 32b, and peak measurement is performed. At this time, the measured value is preferably in the range of 35 to 80 degrees, but this hardness range also includes the purpose of absorbing the cylindrical runout and shape variation of the charging roller 32 and the photosensitive drum 14. If proper nips can be obtained for the charging roller 32 and the photosensitive drum 14, it is not necessary to stick to this value.

The outer surface shape of the charged roller elastic layer 32b is formed with a predetermined polishing grain and surface roughness by cutting, polishing step or mold molding. At this time, the surface roughness of the charging roller 32 varies slightly depending on the applied voltage and the usage environment, but according to Paschen's law, the maximum height Ry (compliance: JIS B 0601: 1994) is 1 [μm] to 40 [. A range of about [μm] is preferable.

The outer surface of the charged roller elastic layer 32b can be surface-treated or coated. The charging roller 32 can prevent substances contained in the charging roller elastic layer 32b from contaminating the photosensitive drum 14 by surface treatment or coating, adjust the surface resistance of the charging roller elastic layer 32b, and can also adjust the surface resistance of the charging roller elastic layer 32b. It is possible to provide the charging roller 32 with an appropriate roughness so that the toner or the toner external agent adhering on the surface of the 14 is less likely to adhere to the surface. As the surface treatment, for example, surface treatment such as ultraviolet irradiation or electron beam irradiation may be performed on the outer surface of the charged roller elastic layer 32b.

As a coating, there are a method of applying by dipping, spray, coater or the like. As the material to be applied, for example, acrylic resin, urethane resin, fluororesin, polyamide resin, polycarbonate resin, polyester resin, isocyanate resin and the like can be used, and one or a combination of two or more of these can be used. Further, as the material to be applied by the coating, a conductive agent or the like may be added as needed in addition to the above. Further, particles can be further mixed with these coating materials. As the particles to be mixed, for example, acrylic resin, urethane resin, fluororesin, polyamide resin, polycarbonate resin, polyester resin, isocyanate resin and the like can be used, and one or a combination of two or more of these can be used.

In the present embodiment, the charging roller 32 uses a metal shaft body in which free-cutting steel (SUM) is plated with non-electrolytic nickel as the charging roller core metal 32a, and epichlorohydrin rubber (epichlorohydrin rubber) is used as the charging roller elastic layer 32b. A rubber containing a mixture of ECO) and acrylonitrile-butadiene rubber (NBR) as a main component was used. The diameter of the charged roller core metal 32a was φ6 [mm], and the outer diameter of the charged roller elastic layer 32b was 9.5 [mm].

The surface of the charged roller elastic layer 32b is formed by shaping. A water / alcohol mixed solvent is used as a solvent for coating the charged roller elastic layer 32b, and a solution in which a polyamide (nylon) -based polymer and urethane resin particles are mixed is applied to vaporize the solvent to form a solution. Hardens. At this time, urethane resin particles having diameters of 20 [μm] and 10 [μm] were contained.

[1-4-1-2-2. Cleaning roller configuration]
As shown in FIG. 5, the cleaning roller 34 has a cleaning roller core body 34a, and has a cleaning roller elastic layer 34b on the outer peripheral surface of the cleaning roller core body 34a. For the cleaning roller core 34a, for example, an electroless nickel-plated SUM, a metal shaft such as SUS, a resin such as polyacetal (POM), or the like can be used. The structure of the cleaning roller elastic layer 34b may be one layer or a laminated structure of two or more layers. The cleaning roller elastic layer 34b may be configured to include a foam, or may be composed of two layers, a solid layer and a foam layer. The cleaning roller elastic layer 34b is arranged so as to spirally wind the entire surface of the cleaning roller core body 34a except for both ends. As shown in FIG. 6, in the present embodiment, the cleaning roller elastic layer 34b is wound around the surface of the cleaning roller core 34a at intervals in the longitudinal direction of the cleaning roller 34.

As the material constituting the cleaning roller elastic layer 34b, foamable resin such as polyurethane, polyethylene, polyamide or polypropylene, or silicone rubber, fluororubber, urethane rubber, ethylene propylene rubber (EPM, EPDM), ethylene propylene rubber ( EPM, EPDM), acrylonitrile-butadiene rubber (NBR), hydride acrylonitrile-butadiene rubber (H-NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR) or chloroprene rubber (CR) You may use a material made by mixing one kind or two or more kinds of rubber materials such as the above. If necessary, an auxiliary agent such as a foaming aid, a foam stabilizer, a catalyst, a curing agent, a plasticizer, or a vulcanization accelerator may be added to these.

The cleaning roller elastic layer 34b and the cleaning roller core 34a are adhered to each other by an adhesive 34c. As the adhesive 34c, for example, an adhesive made of an adhesive tape such as a double-sided tape is used. As the pressure-sensitive adhesive of the pressure-sensitive adhesive tape, an acrylic pressure-sensitive adhesive, a rubber-based adhesive, a silicone-based adhesive, or the like, which is used in combination with one or more kinds of pressure-sensitive adhesives can be used. Further, the adhesive tape can be used regardless of the presence or absence of the base material. As the cleaning roller 34 used in the present embodiment, an electroless nickel-plated shaft body made of free-cutting steel was used as the material of the cleaning roller core body 34a. A polyurethane foam, specifically Moltoprene SM-55 manufactured by Inoac Corporation, was used for the cleaning roller elastic layer 34b. As the pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive, specifically, a double-sided tape 5000NS manufactured by Nitto Denko Corporation was used. The cleaning roller elastic layer 34b is formed by attaching double-sided tape to the back surface of a urethane foam having a width of 8 [mm] and spirally winding a gap of 0.5 [mm] or less around the cleaning roller core 34a. rice field. The cleaning roller core 34a used had a diameter of 4 [mm], and the cleaning roller elastic layer 34b had a diameter of 6.0 [mm].

[1-4-1-2-3. Configuration of tension spring]
As shown in FIG. 7, the tension spring 44 is composed of a tension spring coil portion 44b and a tension spring arm portion 44a. The tension spring coil portion 44b is provided in the central portion of the tension spring 44 in the longitudinal direction, occupies most of the longitudinal direction, and has a coil shape. The tension spring arm portions 44a are provided on both outer sides of the tension spring coil portion 44b in the longitudinal direction and have a hook shape. As shown in FIG. 4, the tension spring arm portion 44a of the tension spring 44 is hooked on the bearing arm 40a of the inner charged roller bearing 40.

This tension spring 44 is a so-called tension spring, and even in a no-load state where no load is applied from the outside, the lines of the coils adjacent to each other in the longitudinal direction in the tension spring coil portion 44b are narrowed and closely adhered to form a close contact coil. There is. Therefore, even in a no-load state, the tension spring 44 has an initial tension, which is a force that causes the coils in the tension spring coil portion 44b to come into close contact with each other.

Further, the length in the longitudinal direction of the entire tension spring 44 (that is, the expansion / contraction direction in which the tension spring coil portion 44b expands / contracts) in the natural state in which the tension spring 44 is not pulled is defined as the spring natural length L1. The spring natural length L1 is specifically, from the inside of the bending of the hook-shaped end of one tension spring arm 44a to the inside of the bending of the hook-shaped end of the other tension spring arm 44a. The length is along the longitudinal direction. Further, the length of the tension spring coil portion 44b in the expansion / contraction direction in the natural state is defined as the natural length L0 of the coil portion. Further, the length of the tension spring arm portion 44a in the expansion / contraction direction is defined as the arm portion length La. Specifically, the arm length La is a length along the longitudinal direction from the end of the tension spring coil portion 44b to the inside of the bending of the hook-shaped end of the tension spring arm portion 44a. The arm length La is a constant value regardless of the expansion / contraction state of the tension spring coil portion 44b. Further, the outer diameter of the tension spring coil portion 44b is defined as the outer diameter R. This outer diameter R has a constant value regardless of the expansion / contraction state of the tension spring coil portion 44b.

Further, the length in the expansion / contraction direction of the center of the entire tension spring 44 in the use state in which the tension spring 44 is bent and stretched is defined as the spring center length L2 (FIG. 4) at the time of use. Specifically, the spring center length L2 at the time of use passes through the center of the entire tension spring 44 from the inside of the bending of the hook-shaped end portion of one tension spring arm portion 44a in the use state, and the other tension spring arm portion. The length is along the longitudinal direction to the inside of the bend at the end of the hook shape of 44a. Further, the length in the expansion / contraction direction of the bending inner portion of the entire tension spring 44 in the used state of the tension spring 44 is defined as the spring inner length L4 (FIG. 4). Here, the bending inner portion is the side of the tension spring 44 that is in contact with the cleaning roller bearing 42 in the outer peripheral portion of the tension spring coil portion 44b. That is, the spring inner length L4 at the time of use has both ends of the curve along the inner peripheral portion of the bending of the tensile spring coil portion 44b toward the bearing arm 40a, which is opposite to the tensile spring coil portion 44b at the outer peripheral portion of the bearing arm 40a. The length of the line extending to the end of the side. Therefore, in the used state, the length of the inner portion of the bend in the tension spring 44 is shorter than the length of the outer portion of the bend. The curve showing the spring center length L2 at the time of use and the curve showing the spring inner length L4 at the time of use are in a parallel state. The spring center length L2 during use is an image of the distance between the axes measured using a non-contact coordinate measuring device described later and the component shapes of the inner charged roller bearing 40 and the cleaning roller bearing 42 using a projector. It can be calculated by analysis.

Further, as shown in FIG. 8, an angle indicating the degree of bending of the tension spring 44, which indicates how much the tension spring 44 is wound around the cleaning roller bearing 42, is defined as a winding angle θ. Here, a straight line orthogonal to the virtual end face of the circular portion on one end side of the tension spring coil portion 44b is referred to as an extension line LN1 on one end side of the coil portion. Further, a straight line orthogonal to the virtual end face of the circular portion on the other end side of the tension spring coil portion 44b is defined as the extension line LN2 on the other end side of the coil portion. The winding angle θ is the angle on the side separated from the cleaning roller bearing 42 of the two angles formed by the coil portion extending wire LN1 on one end side and the coil portion extending wire LN2 on the other end side. Therefore, the winding angle θ becomes smaller as the tension spring 44 loosely winds around the cleaning roller bearing 42 so that one end and the other end of the tension spring arm 44a are separated from each other, while the winding angle θ becomes smaller. The tension spring 44 is strongly wound around the cleaning roller bearing 42 so that the portion and the other end portion are close to each other, and becomes larger.

When this winding angle θ is used, the spring inner length L4 at the time of use can be obtained by the following equation (1).

L4 = L2-0.5π × R × (θ / 180) …… (1)

Here, when the winding angle θ is 180 degrees, the spring inner length L4 at the time of use can be obtained by the following equation (2).

L4 = L2-0.5π × R …… (2)

In the present embodiment, the winding angle θ is 160 degrees, the outer diameter of the cleaning roller bearing 42 is 3.0 [mm], the central shaft of the charging roller core metal 32a in the charging roller 32, and the cleaning roller core in the cleaning roller 34. When the distance between the axes of 34a and the central axis is 7.4 [mm], the position of the bearing arm 40a is installed so that the central length of the tension spring 44 is 20.0 [mm].

Table TB1 of FIG. 11 shows the characteristics of the seven types of tension springs 44 used in this embodiment. For these tension springs 44, the material is SUS304-WPB, the wire diameter d is 0.26 [mm], the outer diameter R is 1.9 [mm], and the arm length La is 3.45 [mm]. , Each tension spring 44 was created. The spring constant k is calculated from the material, wire diameter d, number of turns Na, and outer diameter R of the tension spring 44. The natural length L0 of the coil portion is calculated by the wire diameter d × the number of turns Na. The spring natural length L1 is calculated by the coil portion natural length L0 + the arm portion length La × 2.

[1-4-1-2-4. Relationship between shaft distance and bearing load]
In this measurement, a tensile test is performed in which the cleaning roller bearing 42 around which the tension spring 44 is wound is pulled so as to be gradually separated from the bearing arm 40a by using the image forming apparatus 1 and the charging device 16 having the above-described configurations. The relationship between the distance between the axes of the charging roller 32 and the cleaning roller 34 and the bearing load, which is the load due to the tension spring 44 applied to the cleaning roller bearing 42, was measured.

The distance between the axes was measured using a non-contact three-dimensional measuring device NH-5Ns (manufactured by Mitaka Kohki Co., Ltd., objective lens × 50). Specifically, in this measurement, the central axis of the charging roller core metal 32a in the charging roller 32 and the cleaning roller core 34a in the cleaning roller 34 are obtained from the arc shape of the outer circumferences of the charging roller 32 and the cleaning roller 34 at a rotation angle of 30 degrees. The distance between the central axis of the charging roller 32 and the central axis of the cleaning roller 34 (that is, the tensile distance) was measured by determining the central axis of the charging roller 32.

The bearing load was measured by using a low-load universal material testing machine 5543A (manufactured by Instron Japan Company Limited), which is the load due to the tension spring 44 applied to the cleaning roller bearing 42.

The measured inter-axis distance and bearing load are shown in the inter-axis distance bearing load measurement result line ML1 of the graph GR1 in FIG. 13, with the X-axis as the inter-axis distance and the Y-axis as the bearing load.

When the distance between the shafts of the tension spring 44 in the bent state is short and is within the range A, the spring inner length L4 at the time of use is shorter than the spring natural length L1. Within this range A, the outside of the bending of the tension spring 44 is stretched as compared with the natural state, but the inside of the bending of the tension spring 44 is the same as the natural state and is not stretched. In other words, in the range A, the inside of the bending of the tension spring 44 is in a state where it does not shrink any more. In this way, the tension spring 44 in the bent state stretches on the outside of the bend as compared with the natural state until it is pulled by a force exceeding the initial tension, but the inside of the bend of the tension spring 44 is the same as in the natural state. It is not stretched.

When the distance between the shafts becomes long, in the range A, the elongation of the tension spring 44 is small until the point where the range B is entered, that is, until the initial tension is applied, even if the bearing load is applied. Further, when the distance between the shafts becomes long, the bearing load also changes relatively greatly according to the amount of change in the distance between the shafts in the range A in which the initial tension is not exceeded.

On the other hand, in the tension spring 44 in the bent state, when the cleaning roller bearing 42 is pulled from the range A beyond the initial tension and enters the range B, the spring inner length L4 becomes longer than the spring natural length L1 during use. Within this range B, both the outside and the inside of the bending of the tension spring 44 are in a stretched state as compared with the natural state. In the case of the range B, the tension spring 44 exhibits the behavior according to the spring constant. If the tension spring 44 is not used in the bent state but is used in a state of expanding and contracting along a straight line, the tension spring 44 is usually used so as to utilize the characteristics within the range B. Further, in the case of the range B, the amount of change in the bearing load according to the amount of change in the distance between the shafts is smaller than in the case of the range A.

Further, in the tension spring 44 in the bent state, in the case of the boundary between the range A and the range B, the inner length L4 of the spring and the natural length L1 of the spring are equal to each other at the time of use. The boundary between the range A and the range B is the position of the inflection point Pi, which is a point where the inclination of the inter-axis distance bearing load measurement result line ML1 changes significantly (details will be described later).

In this way, the tension spring 44 is used by bending the tension spring 44, and when the object is urged inside the bend, the change amount of the bearing load with respect to the change amount of the distance between the shafts is where the inside of the bend starts to stretch. It has a characteristic that a turning point Pi in which the inclination (that is, the inclination of the inter-axis distance bearing load measurement result line ML1) changes significantly appears.

[1-4-1-3. Exposure device configuration]
The exposure device 18 (FIG. 1) is a device that forms an electrostatic latent image on the surface (surface layer portion) of the photosensitive drum 14 by irradiating the surface of the photosensitive drum 14 with irradiation light to expose the surface. The exposure apparatus 18 is supported, for example, by the housing of the image forming apparatus 1. The exposure apparatus 18 includes, for example, a plurality of light sources that emit irradiation light and a lens array that forms an image of the irradiation light on the surface of the photosensitive drum 14. Examples of each of these light sources include a light emitting diode (LED: Light Emitting Diode), a laser element, and the like.

[1-4-1-4. Development roller configuration]
The developing roller 20 is a member that supports the toner for developing the electrostatic latent image on the surface, and is arranged so as to be in contact with the surface (peripheral surface) of the photosensitive drum 14. The developing roller 20 has, for example, a metal shaft and a semi-conductive urethane rubber layer that covers the outer periphery (surface) thereof. The developing roller 20 rotates at a predetermined peripheral speed in the direction opposite to that of the photosensitive drum 14, for example. The toner stored in the toner supply unit 22 is supplied to the developing roller 20 by a supply roller or the like.

[1-4-1-5. Configuration of toner supply unit]
The toner supply unit 22 is a container in which the above-mentioned toners of each color are stored. That is, black toner, cyan toner, magenta toner, and yellow toner are housed in the toner supply units 22 of each of the developing units 12K, 12C, 12M, and 12Y.

[1-4-1-6. Cleaning blade configuration]
One end of the cleaning blade 24 is in contact with the surface of the photosensitive drum 14, and the toner that is not transferred to the transfer belt 26 and remains on the surface of the photosensitive drum 14 is scraped off. The cleaning blade 24 is made of, for example, a flexible rubber material or a plastic material.

[1-5. Composition of transfer part]
The transfer unit 5 includes a transfer belt 26, a driven roller 27, a drive roller 28, a transfer roller 29, and a cleaning blade 30. The image forming unit 4 and the transfer unit 5 form an image forming unit 13 that forms a developer image (toner image) on the medium P while conveying the medium P.

One transfer roller 29 is provided for each of the developing units 12K, 12C, 12M and 12Y, and toner images of each color formed in the developing units 12K, 12C, 12M and 12Y are displayed on the medium P. Transfer electrostatically. A plurality of transfer rollers 29 are arranged so as to face each of the photosensitive drums 14 of the developing units 12K, 12C, 12M and 12Y so as to sandwich the transfer belt 26, and the plurality of transfer rollers 29 are substantially the same. Has a configuration. Further, each transfer roller 29 arranged to face the developing units 12C, 12M and 12Y is separated from the photosensitive drum 14 at a certain distance during monochrome printing.

The transfer belt 26 conveys the medium P conveyed by the transfer unit 3 to the fixing unit 6. The transfer belt 26 is stretched by a drive roller 28 and a driven roller 27, and rotates counterclockwise in FIG. 1. The drive roller 28 and the driven roller 27 each convey the transfer belt 26. The cleaning blade 30 scrapes off the toner adhering to the transfer belt 26.

[1-6. Configuration of fixing part]
The fixing unit 6 applies heat and pressure to the toner image on the medium P conveyed from the transfer belt 26, and fixes the toner image on the medium P. The fixing portion 6 has, for example, a heating roller 46 and a pressure roller 48 arranged to face each other with a transport path through which the medium P is conveyed. The heating roller 46 has a heater inside thereof. The pressure roller 48 is urged against the heating roller 46 to form a nip portion during the fixing process.

[1-7. Control mechanism configuration]
Here, the control mechanism of the image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 is provided with a control unit 50, a reception memory 52, an image data editing memory 54, an operation unit 56, a sensor group 58, and a power supply circuit 60 as control mechanisms. The image forming apparatus 1 is further provided with a drive motor 62. The drive motor 62 drives the photosensitive drum 14 (FIG. 1).

The control unit 50 includes an interface (I / F) control unit 64, a main control unit 66, an exposure device control unit 18S, a fixing control unit 6S, a transfer motor control unit 3S, and a drive control unit 62S. The main control unit 66 is composed of a microprocessor, a ROM, a RAM, an input / output port, and the like, and controls the entire processing operation in the image forming apparatus 1 by executing a predetermined program, for example. Specifically, the main control unit 66 receives print data and control commands from the I / F control unit 64, and of the exposure device control unit 18S, the fixing control unit 6S, the transfer motor control unit 3S, and the drive control unit 62S. The printing operation is performed by controlling the control. The I / F control unit 64 receives print data and control commands from an external device such as a personal computer (PC), or transmits a signal regarding the state of the image forming device 1.

The reception memory 52 temporarily stores print data from an external device such as a PC via the I / F control unit 64. The image data editing memory 54 receives the print data stored in the reception memory 52, and stores the image data in which the print data is edited. The operation unit 56 has, for example, an LED lamp for displaying information such as the state of the image forming apparatus 1 and an input unit (button or touch panel) for the user to give an instruction to the image forming apparatus 1. The sensor group 58 includes various sensors for monitoring the operating state of the image forming apparatus 1, for example, a position detection sensor for the medium P, a temperature / humidity sensor, a print density sensor, a toner remaining amount detection sensor, and the like.

The exposure apparatus control unit 18S sends the image data recorded in the image data editing memory 54 to the exposure apparatus 18, and controls the drive of the exposure apparatus 18. The fixing control unit 6S controls the voltage applied to the fixing unit 6 when the toner image transferred to the medium P is fixed to the medium P. When the transport unit 3 (hopping roller 8, transport roller pair 10 and 11) transports the medium P, the transport motor control unit 3S controls the operation of the transport unit 3. The drive control unit 62S controls the operation of the drive motor 62.

The power supply circuit 60 has a charging roller power supply 32V, a developing roller power supply 20V, a toner supply unit power supply 22V, and a transfer roller power supply 29V. Here, the charging roller power supply 32V, the developing roller power supply 20V, the toner supply unit power supply 22V, and the transfer roller power supply 29V apply voltages based on the instructions of the main control unit 66 to the charging roller 32 and the developing roller 20, respectively. It is applied to the toner supply unit 22 and the transfer roller 29. When a voltage is applied to the developing roller 20 by the developing roller power supply 20V, the toner carried by the developing roller 20 is developed on the electrostatic latent image formed on the surface of the photosensitive drum 14. Further, when a voltage is applied to the toner supply unit 22 by the toner supply unit power supply 22V, the toner is supplied from the toner supply unit 22 to the developing roller 20. Further, the surface of the photosensitive drum 14 is charged by applying a voltage to the charging roller 32 by the charging roller power supply 32V. Further, when a voltage is applied to the transfer roller 29 by the transfer roller power supply 29V, the toner image developed on the surface of the photosensitive drum 14 is transferred to the medium P.

[1-8. Evaluation of tension spring]
The tension spring 44 was examined using the image forming apparatus 1 and the charging apparatus 16 having the above-described configurations. In this study, as shown in FIG. 11, seven types of Nos. 1, No. 2. No. 3, No. 4, No. 5, No. 6 and No. The tension spring 44 of No. 7 was prepared, and each of them was evaluated at the time of continuous test, the nip amount of the cleaning roller 34 was measured, and the load applied to the cleaning roller bearing 42 was measured.

[1-8-1. Continuous test]
In this evaluation, the printed image was evaluated. The printed image was evaluated by evaluating the presence or absence of black spots (color spots) and density unevenness in 32 cycles of the charging roller, and the evaluation results are shown in Table TB2 of FIG. The measurement conditions are as follows.

・ 1 [%] Duty (print image density), 3 pages / Job continuous printing ・ Temperature 23 [° C], humidity 55 [%] printing 10,000 sheets,
・ After that, 10,000 sheets were printed in an environment with a temperature of 28 [° C] and a humidity of 80 [%].
・ After that, 10000 sheets were printed in an environment with a temperature of 10 [° C] and a humidity of 20 [%].
-Print a total of 30,000 sheets-After continuous printing, check the image quality under an environment of temperature 10 [° C] and humidity 20 [%]-Image confirmation pattern: Blank paper (0 [%] Duty (printed image density)), 2by2 (600 dpi) ), Solid

Here, the print image density is a value representing the ratio of the number of pixels in which the developer is transferred to the medium P to the total number of pixels when the image is decomposed in pixel units. For example, printing with an area ratio of 100 [%] when performing solid printing on the entire surface in a printable range of a predetermined area (one round of the photosensitive drum 14, one page of a printing medium, etc.) is printed with an image density of 100 [%]. The print corresponding to the area of 1 [%] with respect to the print image density of 100 [%] is called the print image density of 1 [%]. When the print image density DPD is expressed by a mathematical formula using the number of dots used Cm, the number of rotations Cd, and the total number of dots CO, it can be expressed as the following equation (3).

DPD [%] = Cm / (Cd × CO) × 100 …… (3)

However, the number of dots used Cm is the number of dots actually used to form an image while the photosensitive drum 14 rotates Cd, and the dots exposed by the exposure apparatus 18 during the formation of the image. Is the total number of. Further, the total number of dots CO is the total number of dots per rotation of the photosensitive drum 14, that is, it is not limited to the presence or absence of exposure, and is potentially used in forming an image that can be used during one rotation of the photosensitive drum 14. The total number of dots that can be used. In other words, the total number of dots CO is the total number of dots used when forming a solid image (solid image) in which the developer is transferred to all the pixels. Therefore, the value (Cd × CO) represents the total number of dots that can potentially be used to form the image while the photosensitive drum 14 rotates Cd.

In Table TB2, the presence / absence of black spots (color spots) is indicated by a symbol “◯” when no black spots are generated and a symbol “×” when black spots are generated. The presence or absence of density unevenness is marked with a symbol "○" when no density unevenness has occurred, and marked with a symbol "x" when density unevenness has occurred. This black spot (black dust) means that when the nip force from the cleaning roller 34 to the charging roller 32 is too strong, dust of the adhesive 34c, which is an insulator in the cleaning roller 34, adheres to the charging roller 32 and the photosensitive drum 14 It is generated in the medium P in the rotation cycle of the charging roller 32 because the charging of the charging roller 32 becomes impossible. Concentration unevenness is a rotation cycle of the charging roller 32 because the cleaning roller 34 cannot completely remove the external additive peeled off from the charging roller 32 when the nip force from the cleaning roller 34 to the charging roller 32 is insufficient. It occurs in the medium P.

Although not shown in Table TB2, when the nip force from the cleaning roller 34 to the charging roller 32 is too strong, dust of the adhesive 34c of the cleaning roller 34 adheres to the charging roller 32 and black spots are generated. Black spots may be stretched by the charging roller 32 by the nip pressure, and vertical band streaks may occur.

[1-8-2. Measurement of the nip amount of the cleaning roller]
In this measurement, a non-contact coordinate measuring device NH-5Ns (manufactured by Mitaka Kohki Co., Ltd., objective lens × 50) was used to measure how much the cleaning roller 34 was niped into the charging roller 32. Specifically, in this measurement, the central axis of the charging roller core metal 32a in the charging roller 32 and the cleaning roller core 34a in the cleaning roller 34 are obtained from the arc shape of the outer circumferences of the charging roller 32 and the cleaning roller 34 at a rotation angle of 30 degrees. The distance between the axes of the central axis of the charging roller 32 and the central axis of the cleaning roller 34 is measured by obtaining the central axis of the charging roller 32, and the shortened inter-axis distance is shown in FIG. 9 for the cleaning roller 34. The crushing amount B of the cleaning roller 34 is calculated on the assumption that it is equivalent to the crushing amount B which is the crushing amount of.

At this time, since the hardness of the charging roller elastic layer 32b of the charging roller 32 is sufficiently harder than that of the cleaning roller elastic layer 34b of the cleaning roller 34, it is considered that only the cleaning roller 34 is recessed, and the charging roller of the charging roller 32 is charged. The amount of crushing of the elastic layer 32b is ignored.

Further, when the wall thickness of the cleaning roller elastic layer 34b of the cleaning roller 34 is set to the wall thickness A, the nip amount of the cleaning roller 34 is calculated by the crushing amount B / wall thickness A, and the crushing amount B and the nip amount B / A are calculated. The evaluation results are shown in Table TB2 of FIG.

[1-8-3. Measurement of load applied to cleaning roller bearings]
In this measurement, a low-load universal material tester 5543A (manufactured by Instron Japan Company Limited) was used to measure the bearing load, which is the load due to the tension spring 44 applied to the cleaning roller bearing 42.

[1-8-4. Relationship between nip amount and bearing load]
In this evaluation, the calculated nip amount (crushing amount B / wall thickness A) and the measured bearing load are shown in Graph GR2 of FIG. 14, with the X-axis as the nip amount and the Y-axis as the bearing load. In Graph GR2, No. 2. No. 3, No. 6 and No. The nip amount and the bearing load in the tension spring 44 of No. 7 are shown. 1, No. 4 and No. The tension spring 44 of 5 is omitted. In addition, No. Only the nip amount and the bearing load in the tension spring 44 of No. 3 are shown in the nip amount bearing load measurement result line ML2 of the graph GR3 of FIG. 15 as a representative.

As shown in the graph GR3, in the range X where the nip amount B / A is 0 to 0.53, the slope of the change amount of the bearing load with respect to the change amount of the nip amount B / A (that is, the nip amount bearing load measurement result line ML2). The slope) is relatively gentle. Further, in the range Y where the nip amount B / A is in the range of 0.53 to 0.83, the slope of the change amount of the bearing load with respect to the change amount of the nip amount B / A (that is, the slope of the nip amount bearing load measurement result line ML2). However, it becomes larger than the range X. Further, in the range Z where the nip amount B / A is 0.83 to 1.0, the bearing load hardly changes with respect to the change amount of the nip amount B / A.

This is because, in the range Z, the distance between the axes of the charging roller 32 and the cleaning roller 34 is narrow, so that the tension spring coil portion 44b is loosened and the cleaning roller bearing 42 is not loaded with the bearing load. .. On the other hand, when the nip amount B / A becomes smaller and shifts from the range Z to the range Y, the bearing load starts to be applied to the cleaning roller bearing 42, but the inside of the bending of the tension spring coil portion 44b is slightly slackened and has not yet stretched. It is a state. Further, when the nip amount B / A becomes smaller and shifts from the range Y to the range X, the inside of the bending of the tension spring coil portion 44b begins to extend at the boundary between the range X and the range Y, and the load of the tension spring 44 is applied to the cleaning roller bearing 42. It hangs.

The approximate line ALx in the range X and the approximate line ALy in the range Y in the nip amount bearing load measurement result line ML2 intersect each other at the inflection point Pi. In other words, the slope of the approximate line ALx and the approximate line ALy changes at the point where the value of the X axis is the inflection point Pi. In this way, in the tension spring 44, the inflection point of inclination to the nip amount bearing load measurement result line ML2 at the point where the inside of the bend starts to extend at the boundary portion between the range X and the range Y, which shifts from the range Y to the range X. Pi can be seen. Such an inflection point Pi is found in each tension spring 44. The positions of the inflection points Pi in each tension spring 44 are shown in Table TB2 of FIG.

In this way, the tension spring 44 is used when the tension spring 44 is bent and is used to urge an object inside the bend. It has the characteristic that a variable point Pi appears in which the inclination of the amount (that is, the inclination of the nip amount bearing load measurement result line ML2) changes significantly.

[1-8-5. judgment result]
As shown in FIG. 12, No. 1 and No. In the tension spring 44 of 2, the position of the inflection point Pi is larger than the nip amount of 0.51. Therefore, No. 1 and No. The tension spring 44 of 2 has a strong nip pressure between the charging roller 32 and the cleaning roller 34, and the cleaning roller elastic layer 34b of the cleaning roller 34 repeatedly contracts and returns due to the rotation of the charging roller 32, whereby the cleaning roller elastic layer A part of the adhesive 34c used for adhering the 34b and the cleaning roller core 34a came up to the surface of the cleaning roller elastic layer 34b and adhered to the surface of the charging roller 32, and black spots of the charging roller 32 cycles were generated. ..

No. 3, No. 4, No. 5 and No. In the tension spring 44 of No. 6, the position of the inflection point Pi is within 0.07 ≦ nip amount ≦ 0.51. Therefore, No. 3, No. 4, No. 5 and No. In the tension spring 44 of No. 6, when the distance between the shafts is shortened and the nip amount shifts from the range Y to the range X beyond the inflection point Pi, the load load increases with respect to how the distance between the shafts shrinks (that is, how the nip amount decreases). Will drop sharply. Therefore, No. 3, No. 4, No. 5 and No. The tension spring 44 of 6 can prevent the cleaning roller 34 from being pushed into the charging roller 32 more than a certain amount even if the distance between the shafts is shortened and the nip amount is increased. As a result, No. 3, No. 4, No. 5 and No. The tension spring 44 of 6 can prevent a part of the adhesive 34c from rising to the surface of the cleaning roller elastic layer 34b and prevent the adhesive 34c from adhering to the surface of the charging roller 32. Thus, No. 3, No. 4, No. 5 and No. The tension spring 44 of 6 can suppress the generation of black spots and the occurrence of density unevenness in the charging roller 32 cycles. In addition, No. 3, No. 4, No. 5 and No. Since the tension spring 44 of No. 6 can suppress the generation of black spots, the generation of the vertical band streaks described above can also be suppressed.

No. Since the inflection point Pi of the tension spring 44 of 7 is 0 or less, the nip pressure between the charging roller 32 and the cleaning roller 34 is weak, and the tension spring 44 is strong even if the distance between the shafts becomes large when the charging roller 32 is rotationally driven. No load is obtained. Therefore, No. In the tension spring 44 of 7, the nip pressure of the charging roller 32 and the cleaning roller 34 cannot be sufficiently obtained, and the cleaning property of the surface of the charging roller 32 cannot be sufficiently obtained. As a result, No. In the tension spring 44 of No. 7, the surface of the charging roller 32 was contaminated with an external additive, so that the concentration of the charging roller 32 was uneven.

As described above, in the charging device 16, when the position of the inflection point Pi is within the range of 0.07 ≤ nip amount ≤ 0.51 by using the tension spring 44 having the inflection point Pi having a nip amount of 0.07 or more. , The occurrence of image defects can be suppressed. In this way, the charging device 16 is provided with the bearing load inflection point Pi in an appropriate range with respect to the nip amount.

[1-9. Effect, etc.]
In the above configuration, the charging device 16 attaches the cleaning roller 34 toward the charging roller 32 by winding the inside of the bending of the tension spring 44, which is a bent tension coil spring, around the cleaning roller bearing 42 coaxial with the cleaning roller 34. I tried to give a force and a nip force. Here, if the nip force is too strong, agglomerates of the cleaned toner external agent and the adhesive 34c generated during manufacturing when the sponge is adhered to the cleaning roller core 34a exude from the cleaning roller elastic layer 34b. Dust from the cleaning roller 34, such as dust, adheres to the charging roller 32. On the other hand, if the nip force is too weak, the cleaning roller 34 is separated from the charging roller 32, an appropriate nip amount cannot be obtained, and unevenness in the charging roller 32 cycle occurs. As described above, if the cleaning roller 34 is not in contact with the charging roller 32 with an appropriate pressure contact force, the cleaning performance may be deteriorated or printing defects may occur.

On the other hand, in the charging device 16, when the natural length of the tension spring 44 is the natural length L1 of the spring and the inner length of the tension spring 44 in the state of being wound around the cleaning roller bearing 42 in the bent state is the inner length of the spring L4 at the time of use. , Spring natural length L1 = spring inner length L4 at the time of use.

Therefore, in the charging device 16, even if the cleaning roller 34 momentarily separates from the charging roller 32 during the rotation of the charging roller 32 and the natural spring length L1 <the spring inner length L4 during use, the entire tension spring 44 Since the urging force is momentarily strengthened by the extension, the cleaning roller 34 can be immediately urged toward the charging roller 32 by the tension spring 44, and the deterioration of the cleaning performance can be suppressed.

On the other hand, in the charging device 16, even if the cleaning roller 34 momentarily strongly presses against the charging roller 32 during the rotation of the charging roller 32 and the natural spring length L1> the spring inner length L4 when used, the approximate line ALx. As the approximate line ALY has a larger inclination than the approximate line ALY (FIG. 15), the urging force (bearing load) drops sharply because the entire tension spring 44 cannot be contracted any more, so that it adheres to the cleaning roller 34. It is possible to suppress the adhesion of dust to the charging roller 32 and suppress the occurrence of printing defects.

As a result, the charging device 16 can bring the cleaning roller 34 into contact with the charging roller 32 with an appropriate pressure contact force, and can suppress deterioration of cleaning performance and printing defects.

Here, in recent years, miniaturization of the image forming apparatus 1 is an important item, and miniaturization of the charging apparatus 16 including the charging roller 32 and the cleaning roller 34 is also desired. The charging device 16 can be miniaturized by reducing the diameter of the cleaning roller 34, but by reducing the wall thickness of the charging roller elastic layer 32b in order to reduce the diameter, the charging roller elastic layer 32b and the charging roller core metal can be reduced. There is a problem that the adhesive 34c used for adhering to 32a is transferred to the surface of the charging roller 32, causing image defects in the charging roller 32 cycle.

On the other hand, in the charging device 16, when the cleaning roller 34 momentarily strongly presses against the charging roller 32 during the rotation of the charging roller 32, the entire tension spring 44 cannot be further contracted, so that the urging force suddenly increases. I tried to reduce it. Therefore, the charging device 16 can prevent the adhesive 34c from being transferred to the surface of the charging roller 32. As a result, the image forming apparatus 1 can reduce the size of the cleaning roller 34 while suppressing the occurrence of printing defects, and can reduce the size of the charging device 16 including the cleaning roller 34.

Here, even if the nip amount bearing load measurement result line ML2 shown in FIG. 15 falls into a range larger than the turning point Pi, the slope of the approximate line ALx remains instead of the approximate line ALy. Even though the distance between the shafts is small due to the large nip amount, the bearing load does not decrease easily even if the force is smaller than the initial tension. In this case, the nip force becomes too strong, and dust on the cleaning roller 34 adheres to the charging roller 32.

On the other hand, in the charging device 16, when the tension spring 44 is used in the bent state, when the inflection point Pi is exceeded, the bearing load decreases with respect to the increase in the nip amount with respect to the approximate line ALx, as in the approximate line ALy. I tried to increase the amount sharply. Therefore, even if the cleaning roller 34 momentarily strongly presses against the charging roller 32 during the rotation of the charging roller 32, the charging device 16 momentarily reduces the bearing load and adheres to the cleaning roller 34. It is possible to suppress the adhesion of dust to the charging roller 32 and suppress the occurrence of printing defects.

Further, the charging device 16 uses a tension spring 44 having an inflection point Pi having a nip amount of 0.07 or more so that the position of the inflection point Pi is within the range of 0.07 ≤ nip amount ≤ 0.51. .. Therefore, the charging device 16 can appropriately adjust the nip amount, and can suppress deterioration of cleaning performance and printing failure.

According to the above configuration, the charging device 16 has a charging roller 32 that is rotatable and contacts and charges the surface of the photosensitive drum 14 as a charged member, and a cleaning roller that is rotatable and cleans the surface of the charging roller 32. A tension spring 44 that is in contact with the cleaning roller 34 and the charging roller 32, and a tension spring 44 that can be expanded and contracted in the longitudinal direction, and one end side and the other end side of the tension spring 44 in the longitudinal direction are held in a bent state to be a tension spring. A bearing arm 40a that brings the outer peripheral portion of 44 into contact with the cleaning roller 34 is provided, and the natural length of the tension spring 44 is the natural length of the spring L1, and the inner length of the tension spring 44 in the bent state is the inner length of the spring L4. When this is done, the natural length of the spring L1 = the inner length of the spring at the time of use L4.

As a result, when the cleaning roller 34 is momentarily separated from the charging roller 32, the charging device 16 extends the entire tension spring 44 and momentarily strengthens the urging force to move the cleaning roller 34 to the charging roller 32 by the tension spring 44. Immediately urges the driver to aim and suppress the deterioration of cleaning performance. On the other hand, when the cleaning roller 34 momentarily strongly presses against the charging roller 32, the charging device 16 applies the cleaning roller 34 because the urging force drops sharply because the entire tension spring 44 cannot be further contracted. It is possible to prevent the adhering dust from adhering to the charging roller 32, and it is possible to suppress the occurrence of printing defects.

Thus, the charging device 16 can bring the cleaning roller 34 into contact with the charging roller 32 with an appropriate pressure contact force, and can suppress deterioration of cleaning performance and printing defects.

[2. Second Embodiment]
[2-1. Configuration of image forming apparatus]
The image forming apparatus 101 (FIG. 1) according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in that it has a charging device 116 instead of the charging device 16. The points of are similarly configured.

[2-2. Configuration of charging device]
As shown in FIG. 16 in which the member corresponding to FIG. 2 is designated by the same reference numeral, the charging device 116 has a gear 34 g added and a cleaning roller as compared with the charging device 16 according to the first embodiment. Although it differs in that it has a cleaning roller 134 instead of 34, it is similarly configured in other respects.

The gear 34g is fixed to one end side of the cleaning roller core 34a, and the driving force is transmitted from a motor (not shown) to rotate the cleaning roller core 34a. Therefore, the charging device 116 causes a peripheral speed difference between the surface of the charging roller 32 and the surface of the cleaning roller 134. As a result, the charging device 116 can have a stronger cleaning property than the charging device 16 by rubbing the surface of the charging roller 32 with the surface of the cleaning roller 134.

The cleaning roller 134 (FIG. 5) differs from the cleaning roller 34 according to the first embodiment in that it has a cleaning roller elastic layer 134b instead of the cleaning roller elastic layer 34b, but is the same in other respects. It is configured in. As shown in FIG. 17 in which the members corresponding to those in FIG. 6 are designated by the same reference numerals, in the second embodiment, the cleaning roller elastic layer 134b is wound around the surface of the cleaning roller core 34a at intervals in the longitudinal direction. ing.

The charging device 116 according to the second embodiment can have the same effect as the charging device 16 according to the first embodiment.

[3. Other embodiments]
In the first embodiment described above, the cleaning roller elastic layer 34b is wound around the surface of the cleaning roller core 34a at intervals in the longitudinal direction, and in the second embodiment, the surface of the cleaning roller core 34a is wound. The case where the cleaning roller elastic layer 134b is wound at intervals in the longitudinal direction has been described. The present invention is not limited to this, and the point is that the function as the cleaning roller 34 or 134 may be obtained by forming the cleaning roller elastic layer 34b or 134b so that the surface of the charging roller 32 is cleaned.

Further, in the above-described embodiment, the case where the cleaning roller 34 or 134 and the charging roller 32 perform a circular motion in only one direction about the axis of rotation, that is, rotate, has been described. The present invention is not limited to this, and the cleaning roller 34 or 134 and the charging roller 32 may at least rotate about a predetermined axis.

Further, in the above-described embodiment, the case where the present invention is applied to the so-called direct transfer type image forming apparatus 1 or 101 in which the toner image is directly transferred from the photosensitive drum 14 to the medium P has been described. The present invention is not limited to this, and is a so-called intermediate transfer method (or secondary transfer method) in which toner images of each color are sequentially transferred from the photosensitive drum 14 onto an intermediate transfer belt, and the toner images are transferred from the intermediate transfer belt to the medium P. The present invention may be applied to an image forming apparatus of (transfer method).

Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 or 101 using the developer used in the one-component developing method has been described. The present invention is not limited to this, and uses a two-component developing method developer which is a method of mixing a carrier and a toner and applying an appropriate charge amount to the toner by utilizing the friction between the carrier and the toner. The present invention may be applied to an image forming apparatus.

Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 or 101 having four developing units 12 and forming a color image using four colors of toner has been described. The present invention is not limited to this, and the present invention may be applied to an image forming apparatus having three or less or five or more developing units 12 and forming an image using toner having a predetermined number of colors.

Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 or 101 which is a single-function printer has been described. The present invention is not limited to this, and the present invention may be applied to an image forming apparatus having various other functions such as an MFP (Multi Function Peripheral) having a function of a copying machine or a facsimile apparatus. Further, the present invention may be applied to various electronic devices that form an image on a medium P such as paper by using a developer by an electrophotographic method.

Furthermore, the present invention is not limited to the above-described embodiment and other embodiments. That is, the present invention has an applicable scope to an embodiment in which a part or all of the above-mentioned embodiment and the above-mentioned other embodiment are arbitrarily combined, and an embodiment in which a part is extracted. be.

Further, in the above-described embodiment, the charging device is provided with a charging roller 32 as a charging member, a cleaning roller 34 or 134 as a cleaning member, a tension spring 44 as an elastic member, and a bearing arm 40a as a holding member. The case where the charging device 16 or 116 is configured is described. The present invention is not limited to this, and the charging device may be configured by a charging member having various other configurations, a cleaning member, an elastic member, and a holding member.

The present invention can be used when printing an image on a medium using an electrophotographic image forming apparatus.

1 ... image forming device, 2 ... medium supply unit, 3 ... transport unit, 4 ... image forming unit, 5 ... transfer unit, 6 ... fixing unit, 7 ... cassette, 8 ... hopping roller, 10, 11 ... Conveyor roller pair, 12 ... Development unit, 13 ... Image forming unit, 14 ... Photosensitive drum, 16, 116 ... Charging device, 18 ... Exposure device, 20 ... Development roller, 22 ... ... Toner supply unit, 24 ... Cleaning blade, 26 ... Transfer belt, 27 ... Driven roller, 28 ... Drive roller, 29 ... Transfer roller, 30 ... Cleaning blade, 32 ... Charging roller, 32a ... Charging roller core metal, 32b ... Charging roller elastic layer, 34, 134 ... Cleaning roller, 34a ... Cleaning roller core, 34b, 134b ... Cleaning roller elastic layer, 34c ... Adhesive, 34g ... Gear, 36 ... outer charged roller bearing, 38 ... compression spring, 40 ... inner charged roller bearing, 40a ... bearing arm, 42 ... cleaning roller bearing, 44 ... tension spring, 44a ... tension spring arm, 44b …… Tension spring coil part, 46 …… Heating roller, 48 …… Pressurizing roller, 50 …… Control unit, 52 …… Receiving memory, 54 …… Image data editing memory, 56 …… Operation unit, 58 …… Sensor group , 60 ... power supply circuit, 62 ... drive motor, 64 ... I / F control unit, 66 ... main control unit, 18S ... exposure device control unit, 6S ... fixing control unit, 3S ... transfer motor control Unit, 62S ... Drive control unit, 32V ... Charging roller power supply, 20V ... Development roller power supply, 22V ... Toner supply unit power supply, 29V ... Transfer roller power supply, La ... Arm length, L0 …… Coil part natural length, L1 …… Spring natural length, L2 …… Spring center length when used, L4 …… Spring inner length when used, θ …… Winding angle, P …… Medium.

Claims (10)

A charged member that is rotatable and comes into contact with the surface of the charged member to be charged.
A cleaning member that is rotatable and cleans the surface of the charged member,
An elastic member that can be expanded and contracted in the longitudinal direction to bring the cleaning member into contact with the charging member,
A holding member that holds one end side and the other end side of the elastic member in the longitudinal direction in a bent state and brings the outer peripheral portion of the elastic member into contact with the cleaning member is provided.
A charging device characterized in that L1 = L4 when the natural length of the elastic member is L1 and the inner length of the elastic member in a bent state is L4. When the layer thickness of the cleaning member is A, the deformation amount of the cleaning member deformed by applying the nip force by the elastic member is B, and the nip amount is B / A, the cleaning member with respect to the change amount of the nip amount. The charging device according to claim 1, wherein the inflection point at which the inclination of the change amount of the load on the load changes is in the range of 0.07 or more of the nip amount. The charging device according to claim 1 or 2, wherein the inflection point is within the range of 0.07 ≦ B / A ≦ 0.51. The elastic member is
When used to abut on the cleaning member in a bent state, it is characterized by having a non-linear characteristic in the slope of the amount of change in the load on the cleaning member with respect to the amount of change in the nip amount between the cleaning member and the charging member. The charging device according to any one of claims 1 to 3. The elastic member is
The claim is characterized in that the slope of the amount of change in the load on the cleaning member with respect to the amount of change in the nip amount changes around the inflection point when used to abut on the cleaning member in a bent state. 4. The charging device according to 4. When the length of the center of the elastic member in the bent state is L2 and the outer diameter of the coil portion of the elastic member is R, the inner length L4 of the elastic member in the bent state is calculated by the following equation (1). Required L4 = L2-0.5π × R …… (1)
The charging device according to any one of claims 1 to 5. When the winding angle indicating the degree of bending of the elastic member is θ, the length L4 inside the elastic member in the bent state is L4 = L2-0.5π × R obtained by the following equation (2). × (θ / 180) …… (2)
The charging device according to any one of claims 1 to 6, wherein the charging device is characterized by the above. The winding angle is
The claim is characterized in that the angle is formed by a straight line orthogonal to a virtual end face on one end side of the coil portion of the elastic member and a straight line orthogonal to a virtual end face on the other end side of the coil portion. 7. The charging device according to 7. An image forming unit including the charging device according to any one of claims 1 to 8. An image forming apparatus comprising the image forming unit according to claim 9.

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