JP2002251055A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic image forming device where abnormal electrification is prevented by electrifying an image carrier so that potential by electrification may be uniform. SOLUTION: This image forming device 1 is provided with a means for preventing a foreign matter from adhering to the surface of a spacer member 302 or a foreign matter from infiltrating in a spacer part H in an electrifying method by which an image carrier is electrified by means of discharge by arranging an electrifying roller 402a in non-contact with the image carrier by using the spacer member 302 and applying voltage to the roller 402a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copy machine, a printer, a facsimile machine, and the like, in which a charging roller using an electric discharge of an electrophotographic system process, which is an image recording apparatus, is arranged. The present invention relates to an image forming apparatus in which the distance between the image bearing member and the surface of the image carrier is kept constant in a non-contact manner, and charging is stably performed over a long period.

[0002]

2. Description of the Related Art In an electrophotographic process, a corona discharge is often used in each section such as a charging section for uniformly charging a photosensitive member, and a discharge product is generated by the corona discharge. Examples include ozone and nitrogen oxides. For example, as described in "Development of Corona Charger for Reducing Photoconductor Deterioration by Ozone" by Toshifumi Mingjin et al., Journal of the Electrophotographic Society, Vol. It is known that if the toner stays in the apparatus, it oxidizes the surface of the photoreceptor, lowers the photosensitivity of the photoreceptor and deteriorates the charging ability, thereby deteriorating the formed image. Also,
Deterioration of members other than the photoreceptor is promoted, and there is also a problem that the life of components is shortened.

[0003] Nitrogen oxides have the following disadvantages. It is known that nitrogen oxides are generated by discharge. Nitrogen oxides react with moisture in the air to produce nitric acid, and react with metals and the like to produce metal nitrates.
These products have a high resistance in a low humidity environment, but react with water in the air in a high humidity environment to have a low resistance. Therefore, when a thin film made of nitric acid or nitrate is formed on the surface of the photoreceptor, an abnormal image appears as if the image had flowed. This is because nitric acid or nitrate absorbs moisture to lower the resistance, thereby destroying the electrostatic latent image on the surface of the photoreceptor. further,
Since the nitrogen oxides remain in the air without being decomposed in the air even after the discharge, the compound formed from the nitrogen oxides adheres to the surface of the photoreceptor when charging is not performed, that is, during the process, It also occurs during periods of rest. Then, this compound permeates from the surface of the photoreceptor to the inside over time. Therefore, this contributes to the deterioration of the electrostatic latent image.

[0004] A method has been adopted in which deposits on the surface of the photoreceptor are removed by scraping the photoreceptor little by little during cleaning. However, the problem of deterioration due to cost increase and aging occurs, and is not an essential solution. By the way, a contact charging device for charging a photosensitive member by bringing a charging member into contact with (approaching) a photosensitive member has been proposed and put into practical use. For example, there has been known a roller-shaped charging member that is driven to contact a photosensitive member to charge the photosensitive member. The contact charging method has advantages such as a very small amount of ozone generated, a low power supply cost due to a low applied voltage, and easy electrical insulation design, as compared with the conventionally used corona charging method. are doing. Of course, the above-mentioned ozone, also a problem due to NO _x is reduced.

For example, as disclosed in Japanese Patent Application Laid-Open No. 63-7380, a roller-shaped charging member is contacted and driven on a photosensitive member to charge the photosensitive member. However, since the charging member is a rubber material, when the copying machine is stopped for a long time, the roller in contact with the photoconductor may be deformed. Further, since rubber is a material that easily absorbs water, the electric resistance greatly varies with environmental changes. Further, rubber requires several types of plasticizers and activators to exhibit its elasticity and prevent deterioration, and a dispersion aid is often used to disperse the conductive pigment. That is, since the surface of the photoreceptor is made of an amorphous resin such as polycarbonate or acrylic, it is very weak against the above-mentioned plasticizer, activator and dispersion aid.

Further, in the contact charging system, foreign matter is entangled between the charging member and the photosensitive member, and the charging member is contaminated, resulting in poor charging. The photoconductor is contaminated, which may cause image defects such as horizontal stripes. Therefore, a method has been proposed in which the charging roller is disposed in non-contact with the photoconductor so as to solve the above-mentioned problems such as contamination of the photoconductor and deformation of the roller. It is known that when DC charging of a non-contact charging roller is performed, the charging potential depends not only on the applied bias but also on the gap distance between the charging roller and the photoconductor. The charging potential changes due to the change in the gap distance,
To solve the problem of abnormal images,
Japanese Patent Application Laid-Open No. 7-287433 proposes a technique for performing stable discharge by providing minute irregularities on a discharge surface of a charger. As a result, even when the gap fluctuates, uniform charging without generating an abnormal image is enabled.
However, Japanese Unexamined Patent Publication No. Hei 7-287433 requires minute irregularities for the stability of discharge. These irregularities may change over time, such as being exposed to the harsh conditions of discharge. If the irregularities disappear, the desired effect cannot be obtained and uniform charging cannot be performed. That is, it may be difficult to perform uniform charging over a long period of time. Further, since the range of the fine unevenness that can be uniformly charged is limited, the production process becomes difficult, and the cost may increase.

[0007] The applied bias method includes a DC voltage and an AC superposition type. In the damage to the photoconductor,
It is known that the AC voltage is higher. The photoconductor is
A discharge product is generated by the discharge at the charging unit, similarly to the corona charger. The amount of this product is larger in the AC charging type roller charging. This is considered to be because the AC superposition type generates a reverse discharge between the charging roller and the photoconductor, and the number of discharges is much larger than that of the DC discharge. The method of applying a DC voltage is based on problems such as variations in charging potential due to gap fluctuations and stability of discharge.
Difficult for practical use. For this reason, it is considered that the AC superimposition type is a suitable method in the case of non-contact. But,
The AC superposition method is also strong in terms of the stability of the charging potential and the stability of the discharge with respect to the gap fluctuation compared to the DC voltage method, but if the fluctuation is too large, the stability is lost.
This causes an abnormal image.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide an electrophotographic image forming apparatus in which an image carrier is charged uniformly. An object of the present invention is to provide an image forming apparatus free from abnormal charging. It is still another object of the present invention to provide an image forming apparatus capable of maintaining a constant gap with an image carrier for a long period of time by a non-contact charging method and uniformly charging.

[0009]

In order to achieve the above-mentioned object, the present invention provides a charging roller arranged in a non-contact manner with an image carrier using a spacer member, and applying a voltage to the charging roller. In a charging method for charging an image carrier by discharging, an image forming apparatus is provided with means for preventing foreign matter from adhering to the surface of a spacer member or invading foreign matter into a spacer portion. The present invention also provides a charging method in which a charging roller is disposed in non-contact with an image carrier using a spacer member, a voltage is applied to the charging roller, and the image carrier is charged by discharging. An image forming apparatus provided with a means for cleaning the surface. The present invention also provides a charging method in which a charging roller is disposed in non-contact with an image carrier using a spacer member, a voltage is applied to the charging roller, and the image carrier is charged by discharging. An image forming apparatus is provided with means for removing foreign matter adhered to the surface.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an example of an image forming apparatus 1 to which the present invention is applied. FIG. 1A is an example of a single-color image forming apparatus, and FIG. 1B is a so-called full-color image forming apparatus that forms an image by superimposing four color toners. As shown in FIG. 1, the image forming apparatus 1 includes a photoconductor 2 that is driven to rotate clockwise in FIG. 1 in a main body housing (not shown). A writing unit 4, a development unit 5, a transfer unit 6, a paper separation unit 14, a cleaning unit 7, a photoconductor charge removal unit 8, and the like are provided.

The image forming apparatus 1 includes a paper feed cassette (not shown) for accommodating a plurality of recording papers, and the recording paper in the paper feed cassette is registered one by one by a paper feed roller (not shown). After the timing is adjusted in pairs, it is sent out between the transfer unit 6 and the photoconductor 2. The image forming apparatus 1 drives the photoconductor 2 to rotate clockwise in FIG.
After the photoconductor 2 is uniformly charged by the charging unit 3, the writing unit 4
Irradiates a laser modulated with image data to form an electrostatic latent image on the photoconductor 2, and forms the electrostatic latent image on the photoconductor 2.
The toner is adhered to the developing unit 5 by the developing unit 5 and is developed. The image forming apparatus 1 transfers the photoreceptor 2 on which a toner has been formed by forming a toner image by the developing unit 5 to a recording sheet conveyed between the photoreceptor 2 and the transfer unit 6 by the transfer unit 6, The recording paper on which the toner image has been transferred is conveyed to the fixing unit 10. The fixing unit 10
A fixing roller 11 is heated to a predetermined fixing temperature by a built-in heater, and a pressure roller 12 is pressed against the fixing roller 11 at a predetermined pressure. The recording paper conveyed from the transfer unit 6 is heated and pressed. After the toner image on the recording paper is fixed on the recording paper, the toner image is discharged onto a discharge tray (not shown).

On the other hand, the image forming apparatus 1 further rotates the photoreceptor 2 on which the toner image has been transferred to the recording paper by the transfer unit 6, and
After the toner remaining on the surface of the photoreceptor is scraped off by the cleaning unit 7 by the blade 13, the charge is removed by the photoreceptor discharging unit 8. The image forming apparatus 1 uniformly charges the photoreceptor 2 discharged by the photoreceptor discharging unit 8 by the charging unit 3 and then forms the next image in the same manner as described above. The cleaning unit 7
The method is not limited to a method in which the residual toner on the photoconductor 2 is scraped off by the blade 13, but may be a method in which the residual toner on the photoconductor 2 is scraped off by a fur brush, for example.

FIG. 2 shows an example of the configuration of the charging roller.
The charging roller 3 includes a conductive substrate 201 and a resistance layer 202 around the conductive substrate 201. The conductive substrate 201 has a diameter of 8 to
20 mm SUS cylinder. Also, the resistance layer 202
Comprises an epichlorohydrin rubber layer and a resin surface layer covering the surface thereof. Or a tetrafluoroethylene copolymer,
It has a thickness of 30 to 700 μm and a surface roughness Rz of about 0.1 μm, mainly containing a fluororesin such as polyvinylidene fluoride and tetrafluoroethylene perfluoroalkyl vinyl ether copolymer.
A resin tube of about 2 to 2 μm may be used. Other materials capable of performing uniform charging may be used.

The surface of the charging roller 3 is the photosensitive drum 1.
Move in the same direction as the surface. The length of the charging roller 3 in the longitudinal direction (axial direction) is the maximum image width A4 width (about 290).
mm). Charging roller 3
Are provided with spacers at both ends in the longitudinal direction thereof, and these spacers are brought into contact with the non-image forming areas at both ends of the photosensitive drum 2 so that the charged surface of the surface of the photosensitive drum 2 and the charged surface of the surface of the charging roller 3 are charged. Is maintained so that the distance at the nearest part is 5 to 100 μm. The closest distance is more preferably set to 10 to 70 μm. In this example, the thickness was set to 60 μm. A power supply for charging is connected to the charging roller 3. As a result, the charged surface is uniformly charged by the discharge in the gap H between the charged surface of the photosensitive drum 2 and the charged surface of the charging roller 3. As the applied bias, a DC voltage controlled by a constant current is used. AC when DC voltage is applied
Since the amount of generated discharge products is smaller than that of the superposition type, it is preferable to apply DC voltage to perform charging. of course,
As the applied bias, an AC superposition type may be used as necessary. The hardness of the charging roller is JIS-A in this embodiment.
Is about 30 to 80 degrees, but it is not necessary to contact the photosensitive drum.
Degree or higher hardness may be used.

FIGS. 3 to 7 show examples in which the spacer cleaning member of the present invention is arranged on a non-contact charging roller. FIG.
5 shows the case where the fixed spacer cleaning member 301a is arranged. As the spacer member, the film 302a was wound around both ends of the charging roller. This spacer 302a
Is designed to contact the photosensitive surface of the photoreceptor to obtain a certain gap between the charging roller and the image area of the photoreceptor. As the applied bias, a DC or AC superimposed type voltage is applied, and the photoconductor is charged by discharge generated in a gap between the charging roller and the photoconductor. Spacer 302a
Is pressed against a spacer cleaning member 301a. The spacer cleaning member 301a is made of a material, such as felt, which easily wipes and holds fine powder such as toner.

FIG. 4 shows a spacer cleaning member 401.
This is an example where a is rotatable. The spacer cleaning member winds a felt 403a that actually performs cleaning around the SUS metal rod 402a. And it is made rotatable like the charging roller. Thus, the spacer is cleaned. Incidentally, it is preferable that the peripheral lengths of the spacer cleaning member and the charging roller do not become integral multiples. If it is an integral multiple, the same positions of the spacer cleaning member and the charging roller come into contact with each other, so that the deterioration is concentrated on a specific surface, and the cleaning property of the spacer is reduced.

FIG. 5 shows a case where the spacer cleaning member and the charging roller cleaning member 501a are integrated. As in the case of FIG. 4, the spacer cleaning member winds a felt 503a or the like that actually performs cleaning around a SUS metal rod 502a. And it is made rotatable like the charging roller. This allows
At the same time as cleaning the charging roller, the spacer is cleaned.

FIG. 6 shows a spacer cleaning member 601.
This is an example of a case where a mechanism for reciprocating a in the axial direction of the charging roller 3 is provided. The cleaning device of the charging roller and the cleaning member of the spacer shown in FIG. 5 are further improved. For this purpose, for example, the arm 603a fixed 604a to the gear 602a is connected to the spacer cleaning member 601a. By rotating the gear, the spacer cleaning member 601a reciprocates in the axial direction. As a result, the cleaning performance of the spacer cleaning member is only partially reduced in performance,
It is possible to prevent the toner from remaining on the spacer and to change the gap.

FIG. 7 shows an optimal positional relationship between the charging roller 3, the developing device 72, and the image carrier cleaning member 73 in the longitudinal direction. FIG. 7 shows the position of the spacer member 74 of the charging roller. The effective developing width of the developing device 5 is set inside the spacer member 74 of the charging roller. The effective cleaning width of the image carrier cleaning member 73 extends outside the spacer member of the charging roller.
First, since the spacer member is outside the effective development width, the development area is only inside the spacer member. Therefore, the developed toner does not adhere to the image carrier in contact with the spacer portion.

Since the effective cleaning width of the image carrier is longer than that of the spacer member, the cleaning of the image carrier is performed up to the contact portion of the spacer member. That is, even if foreign matter such as toner or paper dust adheres to the contact portion of the spacer member on the image carrier, it is removed by the cleaning unit of the image carrier. Therefore, foreign matter does not adhere to the surface of the spacer member of the charging roller. Thus, the charging roller 3, the developing device 72, the image carrier cleaning member 73
By disposing the toner, toner, paper dust and the like do not enter the spacer member and adhere to the surface of the spacer member.

(Comparative Experiment 1) The following experiment was conducted to find out what kind of inconvenience occurs when foreign matter adheres to the spacer of the charging roller. The specification equipment is as follows. Copy machine: imageio 4570 remodeling machine Spacer member: Teflon (registered trademark) sheet Gap between roller and photoconductor: 70 μm (at rest) Applied bias: DC bias of constant voltage system (about -1.8)
(Set to kV) First, it was confirmed that toner and the like did not adhere to the Teflon sheet. Then, a copy image was output under the above conditions. The image at this time was not different from a normal image.

Next, a situation was created in which the toner easily adhered to the Teflon sheet, and a copy image was output in the same manner as above. As a result, a small amount of toner adhered to the background portion of the copy image. Further, in the halftone portion of the image, image unevenness due to non-uniform charging occurred. The state of the charging roller at this time was observed. Of course, the toner was thinly adhered to the Teflon sheet.
Then, when the gap between the roller and the photosensitive member was measured, the gap at rest was wider by 10 to 25 μm than when no toner was attached. That is, since the surface potential at the time of charging was lowered due to the widening of the gap, toner adhered to the background portion of the copy image.
Also, the widening of the gap caused abnormal discharge between the roller and the photoconductor, resulting in non-uniform charging and image unevenness in the halftone portion of the image.

The relationship between the gap and the charging potential can be explained by Paschen's law. In particular, when the gap is in a certain range, the discharge start voltage Vth (V) and the gap d (μm) are expressed by the empirical formula (1). Vth = 6.2 × d + 312: 40 ≦ d ≦ 120 (μm) Expression (1) From Expression (1), the discharge start voltage varies due to the variation of the gap. From the formula, the fluctuation width is as follows:
It can be seen that the discharge start voltage Vth changes by 6.2 V due to the fluctuation. Further, the charging potential V, when the applied voltage _{V 0,} represented as _V = _V 0 -Vth ...... formula (2). From the equations (1) and (2), when the gap changes, the charging potential changes, and the range of the change is 6.2V.
/ Μm. Applying this to the present results, if the gap fluctuates by 20 μm, the charging potential fluctuates by 20 × 6.2 = 124 (V). Actually, when the charging potential was measured based on the presence or absence of toner contamination on the spacer, the charging potential was lower by about 100 V when the gap was widened by contamination with toner.

(Comparative Experiment 2) Using the same apparatus as in Comparative Experiment 1, a cleaning pad made of felt was pressed against the spacer member of the charging roller. Then, a situation was created in which the toner easily adhered to the Teflon sheet, and a copy image was output in the same manner as before. This time, unlike Comparative Experiment 1, no abnormality was observed in the output image. That is,
By cleaning the spacer of the charging roller,
The gap does not fluctuate, and uniform charging can be performed.

FIGS. 8 to 12 show examples in which a member for polishing the spacer surface of the present invention is disposed on a non-contact charging roller. FIG. 8 shows a case where a member 301b for polishing the surface of a fixed spacer is arranged. Spacer member 302
As for b, a film was wound around both ends of the charging roller to form a spacer. The spacer 302b is brought into contact with the photosensitive surface of the photoconductor so as to obtain a certain gap between the charging roller and the image area of the photoconductor. As the applied bias, a DC or AC superimposed type voltage is applied, and the photoconductor is charged by discharge generated in a gap between the charging roller and the photoconductor. A member 301b for polishing the spacer surface is pressed against the spacer 302b. As a member 301b for polishing the spacer surface, a member having a roughened metal surface or a member to which a polishing tape is attached is used. Further, the member 301b for polishing the spacer surface is detachable and can be replaced. Thereby, the member 3 for polishing the spacer surface
Even if 01b deteriorates, the toner does not always adhere to the spacer surface by using the member 301b for polishing a new spacer surface.

FIG. 9 shows a case where a belt-shaped polishing tape is arranged. Polishing tape 4 for polishing spacer 302b
01b has a band shape and is wound around the roller 402b. The end is wound around another roller 403b. The polishing tape 401b is a portion where the spacer of the charging roller is polished.
Is pressed against the spacer by the roller 404b. The polishing tape 401 is formed by the roller 404b.
Since b has good adhesion to the surface of the spacer and a certain amount of force is applied, the surface of the spacer can be polished. The polishing tape is wound around two rollers, and can be wound from one roller to the other roller. For this reason, if the polishing surface of the polishing tape is deteriorated, the spacer can be polished on the surface that has not always deteriorated by winding up the polishing tape, and the toner does not adhere to the spacer surface. Further, a member for polishing the surface of the spacer with the roller may be replaceable.

FIG. 10 shows an example in which a member 20 for polishing the surface of the spacer is rotatable. The spacer cleaning member has a roughened surface 503b on a part of the surface of the SUS metal bar 502b (the surface that comes into contact with the spacer surface). And it is made rotatable like the charging roller. Thereby, the spacer is polished. The circumference of each of the member for polishing the spacer surface and the charging roller should preferably not be an integral multiple. If it is an integer multiple,
Since the same position of the member for polishing the spacer surface and the same position of the charging roller are in contact with each other, the deterioration is concentrated on a specific surface, and the polishing performance of the spacer is reduced.

FIG. 11 shows an example in which a mechanism for reciprocating the member 601b for polishing the spacer surface in the axial direction of the charging roller 3 is provided. For this purpose, for example, an arm 603b fixed 604b to a gear 602b
Is connected to a member 601b for polishing the spacer surface. By rotating the gear, the member 601b for polishing the spacer surface reciprocates in the axial direction. As a result, the polishing performance of the member for polishing the surface of the spacer is partially deteriorated, so that it is possible to prevent the toner from sticking on the spacer and changing the gap.

FIG. 12 shows an example in which a mechanism for bringing a member 20 for polishing the spacer surface into and out of contact with the charging roller is provided. The member 20 for polishing the spacer surface is connected to the arm 701b, and the tip of the arm can press the 705b vibration preventing member 20 against the charging roller. The arm 701b is movable so that the vibration preventing member can be separated from the state in which the charging roller is in contact with the charging roller. For this purpose, for example, the side opposite to the side connected to the member 20 for polishing the spacer surface at the end of the arm is fixed 704b to the gear 702b. And this gear 70
By rotating 2b, the position of arm 701b moves about fulcrum 703b. FIG. 12A shows a state in which the member 702b for polishing the spacer surface is stopped in a state where the member 20 for polishing the spacer surface is in contact with the charging roller 3, and FIG. This is a case where the gear 702b is stopped while being separated from the charging roller 3. Gear 7
By rotating 02b, both states can be changed. By the way, the operation timing of this contact / separation mechanism
This can be determined by detecting the current flowing through the charging roller.

FIG. 13 shows the result of detecting the current flowing through the charging roller with an oscilloscope. FIG. 13A shows a waveform when there is no abnormality in the output image, that is, when uniform charging is performed. FIG. 13B shows a waveform when an abnormality occurs in an output image due to charging, that is, when an abnormal discharge occurs. Observing the surface of the spacer member of the charging roller when abnormal discharge occurs, toner and the like are fixed on the surface, and the gap is widened. In the waveform of FIG. 13A, only noise 801 in measurement is observed, but when the abnormal discharge of FIG. 13B appears, a pulse-like current 802 is observed. That is, by detecting this current pulse, it is possible to know a sign that an abnormality occurs in the output image. Although this current pulse is generated, when it starts to be generated, almost no abnormality is seen in the output image, and it does not mean that much toner adheres to the surface of the spacer. Then, in order to clearly recognize the image as an abnormal image, a pulsed current is generated and a certain time has elapsed.

Therefore, as shown in FIG. 14, for example, an ammeter 901 may be arranged as a current detecting device between the charging roller and the power supply, and the contact / separation mechanism may be operated according to the output value 902. That is, when a certain or more current pulse is detected, the contacting / separating mechanism is operated by the programmable controller 903, and a member for polishing the spacer surface is pressed against the spacer, thereby polishing the spacer surface (FIG. 12).
(a)). Thus, the surface of the spacer can be polished only when the toner adheres to the surface of the spacer of the charging roller, so that the problem of scraping off the surface of the spacer does not occur. Further, when the charging process is being performed, that is, when the charging roller 3 is rotating, the member 20 for polishing the spacer surface is in the state shown in FIG. Is set to the state shown in FIG. Thus, the member 2 for polishing the spacer surface
By performing the contact and separation of 0, copying is paused for a long time in a state where the member 20 for polishing the spacer surface and the charging roller 3 are in contact with each other, and the vibration preventing member or the charging roller is not deformed. If the charging roller is deformed, charging unevenness may occur. by the way,
Since the fixed toner is polished, the polished toner becomes fine powder and scatters around. Therefore, as shown in FIG. 15, it is preferable to provide a fan 1000 so that the fine toner can be sucked. The fan is preferably provided with a guide 1002 to facilitate suction of fine powder. It is preferable that the suction location sucks fine toner from the downstream side of the charging so as not to adversely affect the writing process and the developing process.

(Comparative Experiment 3) The following experiment was conducted in the same manner as in Comparative Experiment 1 to determine what kind of inconvenience occurs when toner adheres to the spacer of the charging roller.
The equipment used is as follows. Copier: imageio 4570 modified machine Spacer member: Teflon sheet Gap between roller and photoreceptor: 70 μm (at rest) Applied bias: DC bias of constant voltage system (about -1.8)
(Set to kV) First, it was confirmed that the toner was not fixed to the Teflon sheet. Then, a copy image was output under the above conditions. The image at this time was not different from a normal image. Next, the photoconductor cleaning step of the copying machine was disabled. Then, copy output was continuously performed. After a while, a small amount of toner adhered to the background portion of the copy image. In addition, in the halftone portion of the image, image unevenness which was considered to be caused by charging non-uniformity occurred. At this time, the charging roller and the Teflon sheet as the spacer member were observed.

The toner adhered to the Teflon sheet. Then, when the gap between the roller and the photosensitive member was measured, the gap at rest was wider by 10 to 25 μm than when no toner was attached. That is, since the surface potential at the time of charging was lowered due to the widening of the gap, toner adhered to the background portion of the copy image. Also, the widening of the gap caused abnormal discharge between the roller and the photoconductor, resulting in non-uniform charging and image unevenness in the halftone portion of the image. As described above, the relationship between the gap and the charging potential is
This can be explained by Paschen's law. Therefore, when this is applied to this result, if the gap fluctuates by 20 μm, the charging potential becomes 20 × 6.2.
= 124 (V). Actually, when each charging potential is measured based on the presence or absence of toner contamination on the spacer, it is better when the gap is widened due to contamination with toner.
The charging potential was as low as about 100V.

(Comparative Experiment 4) Next, the current flowing through the charging roller was observed with an oscilloscope. In a state where the toner was not fixed on the Teflon sheet, the current waveform of FIG. 12A was observed. On the other hand, in the state where the toner was fixed, the pulse-like current of FIG. 12B was observed on the oscilloscope. The current pulse had a magnitude of as large as 0.7 mA in this measurement system. Therefore, it can be seen that by detecting the current flowing through the charging roller, it is possible to determine whether or not the toner has adhered to the Teflon tape as the spacer member.

(Comparative Experiment 5) In order to polish the toner adhered to the surface of the spacer of the charging roller, a SUS block whose surface was roughened was arranged as shown in FIG. At this time, the roughened surface was made to be able to contact the spacer. Under the same experimental conditions as in Comparative Experiment 3, the toner was fixed on the spacer surface. Then, the SUS subjected to the rough surface treatment was pressed against the spacer surface. A copying operation was performed in this state, and then the spacer surface was observed. As a result, there was no fixed toner on the spacer surface. That is, it was found that the surface of the spacer to which the toner was fixed was polished by the member for polishing the spacer surface. As a result, the gap between the charging roller and the photoconductor can always be kept constant.

(Comparative Experiment 6) Next, the member for polishing the spacer surface used in Comparative Experiment 5 was strongly pressed against the charging roller, and a copying operation was continuously performed. The photoreceptor cleaning process was particularly careful to work properly. After 20 minutes, the copying operation was stopped. At this time, when observing the spacer of the charging roller, the surface of the spacer was shaved. From this, it can be seen that if a member for polishing the surface of the spacer is kept pressed, the surface of the spacer is shaved particularly when pressed strongly. That is, it can be said that there is a possibility that the gap between the charging roller and the photosensitive member cannot be kept constant with time. This indicates that the problem described in claim 5 occurs. That is, it is understood that it is necessary to provide the contact / separation mechanism and perform the spacer polishing at appropriate intervals in order to stabilize for a long period of time.

[0037]

As described above, in the image forming apparatus according to the first aspect, toner does not adhere to the surface of the spacer. Therefore, the gap can be kept constant. As a result, the gap between the charging roller and the photoconductor is kept constant, and the discharge is stabilized. Further, the charging potential of the photoconductor changes with the gap between the charging roller and the photoconductor, but since the gap is constant, uniform charging is possible even with a non-contact roller, especially when a DC bias is applied. Also, no abnormal discharge occurs. In the image forming apparatus according to the second aspect, even if the toner adheres to the surface of the spacer, the toner can be removed by the spacer cleaning member. Therefore, the gap can be kept constant. As a result, the gap between the charging roller and the photoconductor is kept constant, and the discharge is stabilized. Further, the charging potential of the photoconductor changes with the gap between the charging roller and the photoconductor, but since the gap is constant, uniform charging is possible even with a non-contact roller, especially when a DC bias is applied. Also, no abnormal discharge occurs. In the image forming apparatus according to the third aspect, foreign matters such as toner can be efficiently removed by rotating the image forming apparatus. In addition, there is no deterioration of only a portion where the spacer cleaning is performed. Therefore, the gap can be kept constant for a long time, and uniform charging without image unevenness can be performed. As a result, the gap between the charging roller and the photoconductor is kept constant, and the discharge is stabilized. Also, the charging potential of the photoconductor changes with the gap between the charging roller and the photoconductor, but since the gap is constant,
Even with a non-contact roller, especially when a DC bias is applied, uniform charging is possible. Also, no abnormal discharge occurs.

In the image forming apparatus according to the fourth aspect, toner does not adhere to the surface of the spacer. Therefore,
The gap can be kept constant, and uniform charging without image unevenness can be performed. In particular, by swinging the spacer cleaning member in the axial direction of the charging roller, streak-like toner traces are not generated on the spacer surface, and gap fluctuation due to streak-like toner traces is eliminated. As a result, the gap between the charging roller and the photoconductor is kept constant, and the discharge is stabilized. Further, the charging potential of the photoconductor changes with the gap between the charging roller and the photoconductor, but since the gap is constant, uniform charging is possible even with a non-contact roller, especially when a DC bias is applied. Also, no abnormal discharge occurs. In the image forming apparatus according to the fifth aspect, by exchanging the spacer cleaning member, it is possible to constantly clean the spacer and prevent foreign matter from adhering to its surface for a long time. The gap can be kept constant, and uniform charging without image unevenness can be performed. In the image forming apparatus according to the sixth aspect, since the spacer member is disposed outside the effective development width, the toner adhered to the image carrier at the time of development comes to the spacer contact portion on the image carrier. Disappears. Therefore, the gap can be kept constant, and uniform charging without image unevenness can be performed. In the image forming apparatus according to the seventh aspect, it is located inside the effective width of the image carrier cleaning. For this reason,
Even if foreign matter such as toner adheres to the position of the spacer of the image carrier, the foreign matter is cleaned by the image carrier cleaning unit, so that the toner does not come to the spacer unit. Therefore, the gap can be kept constant, and uniform charging without image unevenness can be performed. By the way, since the spacer portion is outside the image area, even if the image carrier is slightly deteriorated by the cleaning member, the image is not affected. In the image forming apparatus according to the eighth aspect, toner does not come to the spacer portion. Therefore, the gap can be kept constant, and uniform charging without image unevenness can be performed.

In the image forming apparatus according to the ninth aspect, the foreign matter does not adhere to the spacer surface, so that the gap between the charging roller and the photosensitive member is kept constant, and the discharge is stabilized. Further, the charging potential of the photoconductor changes with the gap between the charging roller and the photoconductor, but since the gap is constant, uniform charging is possible even with a non-contact roller, especially when a DC bias is applied. Also, no abnormal discharge occurs. In the image forming apparatus according to the tenth aspect, by polishing the surface of the spacer, the toner fixed on the surface of the spacer can be removed, the gap can be kept constant, and uniform charging can be performed. In the image forming apparatus according to the eleventh aspect, deterioration of only a portion of the member for polishing the surface of the spacer does not occur. Therefore, the life of the member for polishing the surface of the spacer can be extended. In the image forming apparatus according to the twelfth aspect, the toner can be prevented from being fixed to the surface of the spacer for a long period of time by replacing the member for polishing the surface of the spacer with the minimum necessary parts.

In the image forming apparatus according to the thirteenth aspect, there is provided a contact / separation mechanism for preventing a member for polishing the surface of the spacer from coming into contact with the spacer, and the polishing operation does not act on the spacer unless necessary. To do. This allows
The spacer itself is scraped, the gap is narrowed, and the charging roller does not come into contact with the photoconductor, so that the photoconductor can be charged to a predetermined voltage. In the image forming apparatus according to the present invention, when the gap is widened and an abnormal discharge occurs, a current pulse having a wave height of several tens times or more of the current generated in the charging roller is generated. This current pulse is also generated when an abnormal discharge that does not appear in the image occurs. Therefore, the spacer can be polished at appropriate intervals by detecting the current pulse and using this detection as a signal to polish the spacer with a member for polishing the surface of the spacer. In the image forming apparatus according to the present invention, the adhesion of the toner to the surface of the spacer does not occur immediately after the image forming process is performed, but gradually grows. Therefore, by detecting the current flowing through the charging roller once for every 20 image forming processes, the performance does not deteriorate. In the image forming apparatus according to the present invention, after a paper jam occurs, a means for forcibly polishing the spacer surface is operated to polish the spacer surface, thereby preventing a gap from widening. be able to.

In the image forming apparatus according to the present invention, an air current is generated, and the toner fine particles generated by the polishing are sucked, so that the toner image and the photosensitive member are not adversely affected. In the image forming apparatus according to the eighteenth aspect, by polishing the spacer with a member for polishing the spacer surface, the toner can be prevented from sticking to the spacer surface, and the gap becomes constant. Therefore, the photoconductor can be charged uniformly and always at a stable charging potential. Because of this, reverse transfer does not occur in the transfer unit, so in a color image forming apparatus that requires multicolor development,
High-quality images can be formed.

[Brief description of the drawings]

FIG. 1A is an example of an image forming apparatus to which the present invention is applied, FIG. 1A is an example of a monochromatic image forming apparatus, and FIG.
This is a so-called full-color image forming apparatus that forms an image by overlapping color toners.

FIG. 2 is an example of a configuration of a charging roller.

FIG. 3 is an example in which a spacer cleaning member of the present invention is disposed on a non-contact charging roller, in which a fixed spacer cleaning member is disposed.

FIG. 4 is an example in which the spacer cleaning member of the present invention is arranged on a non-contact charging roller, and is an example in which the spacer cleaning member is rotatable.

FIG. 5 is an example in which the spacer cleaning member of the present invention is arranged on a non-contact charging roller, in which the spacer cleaning member and the cleaning member of the charging roller are integrated.

FIG. 6 is an example in which the spacer cleaning member of the present invention is disposed on a non-contact charging roller, and is an example in which a mechanism for reciprocating the spacer cleaning member in the axial direction of the charging roller is provided.

FIG. 7 shows an optimal positional relationship between a charging roller, a developing device, and an image carrier cleaning member in the longitudinal direction.

FIG. 8 is an example in which a member for polishing a spacer surface of the present invention is disposed on a non-contact charging roller, in which a member for polishing a fixed spacer surface is disposed.

FIG. 9 is an example in which a member for polishing the surface of the spacer of the present invention is disposed on a non-contact charging roller, in which a band-shaped polishing tape is disposed.

FIG. 10 is an example in which a member for polishing the spacer surface of the present invention is arranged on a non-contact charging roller, and is an example in which the member for polishing the spacer surface is rotatable.

FIG. 11 shows an example in which a member for polishing the spacer surface of the present invention is arranged on a non-contact charging roller, and a mechanism for reciprocating the member for polishing the spacer surface in the axial direction of the charging roller. This is an example of a case in which the device is provided.

FIG. 12 shows an example in which a member for polishing a spacer surface according to the present invention is arranged on a non-contact charging roller, and a mechanism for bringing a member for polishing the spacer surface into and out of the charging roller is provided. This is an example.

FIG. 13 shows the result of detecting the current flowing through the charging roller with an oscilloscope.

FIG. 14 is an example of a current detection device between a charging roller and a power supply.

FIG. 15 is an example in which a fan is provided in the image forming apparatus of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image forming apparatus 2 photoreceptor 3 charging unit (charging roller) 4 writing unit 5 developing unit 6 transfer unit 7 cleaning unit 8 photoreceptor static elimination unit 10 fixing unit 11 fixing roller 12 pressure roller 13 blade 14 paper separation unit 20 spacer Member for polishing surface 72 Developing device 73 Image carrier cleaning member 74 Space cleaning member 201 Conductive substrate 202 Resistive layer 301a, 401a, 501a, 601a Space cleaning member 302a Film 402a Metal rod 403a Felt 602a Gear 603a Arm 604a Fixed 301b, 601b Member for polishing the spacer surface 302b Spacer member 401b Polishing tape 402b, 403b, 404b Roller 602b Gear 603b Arm 604b Fixed 701b Arm 702 Metal 702b antivibration material 703b fulcrum 704b fixed 801 noise 802 current 901 ammeter 902 output value

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA06 ED03 EE01 EK09 HB19 2H030 AB02 AD02 BB23 BB63 2H200 FA02 GA12 GA23 GA47 GB01 GB12 HA12 HA14 HA29 HA30 HB03 HB12 HB22 HB26 HB45 HB47 JB06 JB16 LB07 LA07 LA07 LA07 LB27 LB33 LB35 LB39 MA01 PA06 PA10 PA30 PB05

Claims (18)

[Claims] 1. A charging method in which a charging roller is disposed in non-contact with an image carrier using a spacer member, a voltage is applied to the charging roller, and the image carrier is charged by discharging. An image forming apparatus provided with means for preventing foreign matter from adhering to the space or invading the spacer portion. 2. A charging method in which a charging roller is disposed in non-contact with an image carrier using a spacer member, a voltage is applied to the charging roller, and the image carrier is charged by discharging. An image forming apparatus, comprising: means for cleaning the image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the means for cleaning the surface of the spacer member is rotatable. 4. The image forming apparatus according to claim 2, wherein the means for cleaning the surface of the spacer member is movable in an axial direction of a charging roller. 5. The image forming apparatus according to claim 2, wherein the means for cleaning the surface of the spacer member is replaceable. 6. The image forming apparatus according to claim 1, wherein the spacer member is provided outside a developing effective width of a developing unit. 7. The image forming apparatus according to claim 1, wherein the spacer member is provided inside a cleaning effective width of the image carrier cleaning unit. apparatus. 8. The image forming apparatus according to claim 1, wherein the spacer member is outside the effective developing width of the developing unit and is wider than the effective cleaning width of the image carrier cleaning unit. An image forming apparatus provided inside. 9. A charging method in which a charging roller is disposed in non-contact with an image carrier using a spacer member, a voltage is applied to the charging roller, and the image carrier is charged by discharging. An image forming apparatus, comprising: means for removing foreign matter stuck to the image forming apparatus. 10. The image forming apparatus according to claim 9, wherein the means for removing the foreign matter fixed on the surface of the spacer member polishes the surface of the spacer member. 11. The image forming apparatus according to claim 10, wherein a contact surface between the means for polishing the surface of the spacer member and the spacer member is not a specific place. 12. The image forming apparatus according to claim 11, wherein the means for polishing the surface of the spacer member is replaceable. 13. The image forming apparatus according to claim 10, wherein the means for polishing the surface of the spacer member is capable of coming into contact with and separating from the spacer member. . 14. The image forming apparatus according to claim 10, wherein the power supply connected to the charging roller includes a unit for detecting a current flowing through the charging roller. An operation of a means for polishing the surface of the spacer member. 15. The image forming apparatus according to claim 10, wherein the current detection is performed at regular time intervals. 16. The image forming apparatus according to claim 10, wherein a means for polishing the surface of the spacer member is always operated after the paper jam is detected. 17. The image forming apparatus according to claim 10, wherein an air flow is forcibly generated to suck atmospheric air near the spacer member. 18. The image forming apparatus according to claim 9, wherein the image forming apparatus forms an image by overlapping toner a plurality of times.