JP4395007B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer or a copying machine.

Electrophotographic printer, an image forming apparatus such as a copying machine, on the member to be charged, called photosensitive member which rotates in one direction, a charging device for charging to a predetermined potential V ₀ which the corona discharge is widely used. This charging by corona discharge has an excellent characteristic of uniformly charging the surface of the photoconductor, but a high voltage of about 4 to 6 kV DC is used, so a large amount of ozone is generated at the time of corona generation. There are still challenges.

  As a countermeasure, there is a known configuration in which an AC voltage is applied to a contact-type charging device in which a desired charging potential is obtained at a relatively low voltage and a brush or roller that generates a very small amount of ozone is in contact with the photosensitive member. It has been. (For example, Patent Document 1) In the present technology, uniform charging can be realized by generating very little ozone (approximately 1/10 to 1/100 of the charging device by corona discharge), and the potential history of the photoreceptor can be removed. Therefore, there is no need for a static elimination process before the charging process, and there is an advantage that the entire image forming apparatus can be downsized. On the other hand, there are problems such as an increase in the size of the AC voltage source and generation of vibration noise generated in the nip portion due to the AC electric field.

There is also known a charging method that can apply a uniform surface potential to the photoreceptor and has a large ability to remove the potential history of the photoreceptor without using an AC voltage source. (For example, Patent Document 2) In this technique, a primary charger and a secondary static eliminator are combined with a contact-type charger and a discharge device using needle-like electrodes, and the surface of the photosensitive member is set to a predetermined potential V ₀ by the primary charger. After charging to a higher V ₁ , the voltage is set to a predetermined potential V ₀ by the secondary static eliminator.

However, a cleaning blade is provided to clean the surface of the photoconductor. However, the cleaning blade does not completely remove the surface of the photoconductor, and the remaining toner passes through the cleaning blade to the position of the charging device. When the charging device is a contact type, a phenomenon occurs that contaminates the surface in contact with the photoreceptor. When the charging member is contaminated, the contaminated material becomes a nucleus, and a strong electric discharge occurs due to local electric field concentration, and the charging is likely to be uneven. Here, in the case of the charging device in which the primary charger and the secondary static eliminator are combined, the non-uniform charging due to the contamination is relatively difficult to occur. However, the non-uniform charging due to the contamination is the secondary static eliminator. If the control limit is exceeded, the charging potential V ₀ before the exposure apparatus becomes non-uniform and the image is disturbed. For this reason, in a contact-type charging device, a technique is also known in which an applied voltage having a polarity opposite to that in a normal image forming operation is applied, and a cleaning operation is performed to return contaminants attached to the surface to the photoreceptor. However, for example, a charging device that combines a primary charger and a secondary static eliminator cannot obtain a sufficient cleaning effect by a simple cleaning control operation.

Japanese Examined Patent Publication No. 3-52058

JP-A-6-289688 Japanese Patent No. 1640214

  In a charging device that combines a primary charger and a secondary static eliminator, the effect of cleaning contaminants on the secondary static eliminator, which is the main part of charge control, is enhanced, the surface potential of the photoreceptor is stabilized, and the image is not disturbed. A forming apparatus is provided.

The present invention is in contact with the surface of the photoreceptor moves in a predetermined direction, wherein a primary charger for charging the photosensitive member surface to a potential V _1, in contact with the photosensitive member, and features to the primary charger located downstream of the photosensitive member movement direction, the photosensitive member the surface potential potential V ₁ and the secondary static eliminator polarity to neutralize so that potential V ₀ which has a smaller absolute value than the same as and the potential V ₁ In an image forming apparatus including a charging device having the following characteristics, an absolute value V _th1 of the potential difference between the primary charger and the photoconductor when the primary charger starts to charge the photoconductor during image formation is absolute. The secondary charge remover and the photoreceptor when a voltage having a high value and charging the photoreceptor surface potential to V ₁ is applied to the primary charger and the secondary charge remover begins to remove the photoreceptor. _Applied to the secondary static eliminator with V _{th2 as} the absolute value of the potential difference A voltage when the _{V 2 |} V 1 -V ₂ | voltage _{V 2} which satisfies ≧ _{V th2} is applied to the secondary static eliminator, a voltage _{V 2} which is and applied to the secondary static eliminator, The polarity is opposite to the voltage applied to the primary charger, and the voltage applied to the primary charger by the primary charger at the time of image formation is at least partly during non-image formation. A voltage having the same polarity and a lower absolute value than _Vth1 is applied, and the secondary neutralizer has a voltage opposite to the voltage applied to the secondary neutralizer during image formation and having a lower absolute value than _Vth2. The image forming apparatus is provided with an applied operation section.

According to the present invention, the cleaning effect of contaminants adhering to the secondary static eliminator is particularly enhanced, and the controllability capable of setting the photoreceptor surface potential to the predetermined potential V ₀ is stabilized over a long period of time, thereby preventing image disturbance. Image forming apparatus can be provided.

  In the cleaning operation of the charging device, a voltage application sequence is formed in the cleaning operation mainly by the operation of discharging contaminants from the secondary static eliminator onto the photosensitive member, and the contamination discharged from the primary charger to the photosensitive member. The cleaning effect of the secondary static eliminator was improved by setting the voltage application so that the secondary static eliminator was not re-incorporated when the object passed near the secondary static eliminator.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram of an image forming apparatus according to the present invention. The charging device 2, the exposure device 3, the developing device 4, and the transfer device are arranged along the rotation direction of the photosensitive member 1 (indicated by an arrow A in the figure). 5 and the cleaning device 6 are sequentially arranged. In this embodiment, although not shown, an erasing device is arranged between the transfer device 5 and the cleaning device 6, and the surface potential of the photoreceptor immediately before the charging device 2 is initialized to near zero potential.

  In the charging device 2, a primary charger 20 is disposed on the upstream side in the rotation direction of the photosensitive member 1, and a secondary static eliminator 21 is disposed on the downstream side.

During normal image formation, the absolute value is higher than the absolute value V _th1 (= 450 V) of the potential difference between the primary charger 20 and the photoconductor 1 when the primary charger 20 starts to charge the photoconductor 1. A voltage (−1050 V) for charging the body surface potential to V ₁ is applied from the power source 30 to the primary charger 20. Further, the absolute value V _th2 (= 550 V) of the potential difference between the secondary static eliminator 21 and the photoconductor 1 when the secondary static eliminator 21 starts to neutralize the photoconductor 1, and the voltage applied to the secondary static eliminator 21 as V ₂ . Then, a voltage V ₂ (= 150 V) satisfying | V ₁ −V ₂ | ≧ V _th2 is applied from the power supply 31 to the secondary static eliminator 21. Thus, the photoreceptor surface potential V ₀ after passing through the charging device 2 is made uniform to a desired potential V ₀ . In this embodiment, the surface potential of each photoconductor is set to V ₀ = −400V and V ₁ = −550V.

  Subsequently, the exposure device 3 exposes the surface of the photoreceptor 1, and an electrostatic latent image is formed on the surface of the photoreceptor 1. Next, in the developing device 4, toner is supplied onto the electrostatic latent image on the photoreceptor 1 to make a visible image. Next, in the transfer device 5, the visible image of the photoreceptor 1 is transferred from the paper hopper 8 through the transport path 9 to the paper 10 transported in the direction of arrow B. The toner image transferred onto the paper is then conveyed to the fixing device 7 where it is fixed on the paper. On the other hand, there is toner remaining on the photoreceptor 1 without being transferred to the paper 10 by the transfer operation. This is because the toner is charged opposite to a predetermined polarity (here, negative) due to the discharge during the transfer operation. The toner remaining on the surface of the photoreceptor 1 is cleaned from the surface of the photoreceptor 1 by the next cleaning device 6.

  However, the remaining toner that has not been completely removed from the photoreceptor 1 by the cleaning device 6 passes through the cleaning device 6 and reaches the position of the charging device 2, and comes into contact with the photoreceptor. There is a possibility of contaminating the surface of the secondary static eliminator 21. When the charging device 2 is contaminated, the contaminants become nuclei, and strong charging occurs due to local electric field concentration, and the surface of the photoconductor 1 is likely to be unevenly charged.

  In this embodiment, a primary charger 20 using a brush is employed as a contact charging method that is relatively resistant to contamination, and is rotated in the opposite direction to the rotation direction of the photoreceptor 1. In this case, the contaminants tend to sink into the gap between the brush hairs, and the surface of the charger is reduced by the contaminants.

  In this embodiment, since the secondary static eliminator 21 needs to make the surface potential of the photoreceptor 1 uniform, a rubber roller type contact static eliminator having a smaller surface irregularity than a brush is used. The body 1 is rotated following the rotation of the body 1.

  In this embodiment, in addition to the above method, as a means for removing contaminants attached to the charging device 2, the voltage applied to the charging device 2 is adjusted to adjust the primary charger 20 or the secondary charge remover 21. The operation of discharging contaminants from the surface of the photosensitive member 1 to the photoreceptor 1 is performed during non-image formation. Here, at the time of image formation, it has a time length including at least the printable length in the transport direction of the paper 10 to be printed.

  Next, the control method of the present embodiment will be described with reference to FIGS. 2 and 3, CHV represents a voltage waveform applied to the primary charger, and DCV represents a voltage waveform applied to the secondary static eliminator.

  FIG. 2 is a voltage sequence applied to the charging device 2 between sheets in a continuous operation mode in which the sheet 10 is continuously supplied, that is, in a non-image forming section between image formation and image formation.

In the non-image forming section, the primary charger 20 has the same polarity as the voltage (−1050 V) applied to the primary charger 20 during image formation and a voltage (−−) lower than V _th1 (= 450 V). 400 V) is applied to the secondary static eliminator 21, and has a polarity opposite to that of the voltage (150 V) applied to the secondary static eliminator 21 during image formation and has a lower absolute value than V _th2 (= 550 V) ( -500V) is applied.

During image formation, positively charged contaminants mainly adhere to the surface of the primary charger 20 to which a voltage of −1050 V is applied, and the surface of the secondary charger 21 to which a voltage of 150 V is applied. The negatively charged contaminants are mainly attached, and the positively charged contaminants of the primary charger 20 remain as they are, and the secondary static eliminator 21 is negatively charged by the operation in the non-image forming section. Contaminants are emitted to the photoreceptor 1. At this time, since the absolute value of the voltage of the primary charger 20 is lower than _Vth1 , the surface potential of the photoreceptor 1 is not negatively charged, and the negatively charged contaminants from the secondary static eliminator 21 are not charged. It can be effectively discharged to the photoreceptor 1. P shown in the figure is a time delay represented by P = L / v as the distance L between the primary charger 20 and the secondary static eliminator 21 and the peripheral speed v of the photoreceptor 1.

  In this operation, the contaminants of the primary charger 20 are not removed. This is because even if the characteristics of the charging device 2 of the present invention, that is, the charging in the primary charger 20 becomes somewhat unstable. The characteristic that can be stabilized by the secondary static eliminator 21 is used. Further, in this embodiment, as described above, the brush charging member having a relatively large tolerance against dirt is used, and the surface potential is further stabilized.

  In this embodiment, in addition to the above operation, the following control operation is performed in the non-image forming section at the end of the continuous operation mode.

  FIG. 3 shows a voltage sequence applied to the charging device 2 in the non-image forming section provided at the end of the continuous operation mode.

In the non-image forming section, first, (1) the primary charger 20 has the same polarity as that at the time of image formation, an absolute value higher than V _th1 (= 450 V), and from the photoreceptor surface potential V ₁ (= −550 V). When a voltage (−700 V) for charging to a potential V ₃ (= −250 V) having a low absolute value is applied, and the voltage applied to the secondary static eliminator 21 is V ₄ , In addition, an operation interval is provided in which the voltage V ₄ (= 150 V) is applied, which has the same polarity as the image formation and satisfies | V ₃ −V ₄ | <V _th2 (= 550 V). Following this, the (2) the primary charger 20, in the time of image formation and opposite _polarity, the absolute value of a voltage lower than _{V th1} (300 V) is applied, the secondary static eliminator 21, the image forming An operation section is provided which is applied with a voltage (150 V) which has the same polarity as that of the time and does not charge or charge the photosensitive member. (3) The primary charger 20 is applied with a voltage (−400V) having the same polarity as the voltage applied to the primary charger 20 during image formation and lower in absolute value than the V _th1. The secondary static eliminator 21 is provided with an operation period in which a voltage (−500 V) having a polarity opposite to that applied to the secondary static eliminator 21 at the time of image formation and having an absolute value lower than the V _th2 is applied.

  In these series of operations, in the section (1), the positively charged surface contaminants of the primary charger 20 remain as they are, and the positively charged contaminants slightly adhered to the surface of the secondary static eliminator 21 are exposed to light. Released to the body 1. At this time, since the surface potential of the photosensitive member 1 after passing through the primary charger 20 is −250 V, contaminants that are positively charged with respect to the positive voltage applied to the secondary static eliminator 21. However, an electric field that is more strongly returned to the photoreceptor 1 is formed. In the section (2), the main positively charged surface contaminants in the primary charger 20 are returned to the photoreceptor 1. At this time, the contaminant returned to the photoreceptor 1 passes through this region as it is because the secondary charger 21 is also applied with a positive voltage. Further, in the section (3), negatively charged contaminants slightly attached to the primary charger 20 and negatively charged contaminants mainly attached to the secondary charger are returned to the photoreceptor 1. At this time, as in the section (2), the contaminant returned to the photoreceptor 1 passes through this region as it is because the secondary charger 21 is also applied with a negative voltage.

  In the figure, the non-printing section is described with respect to the voltage waveform (CHV) applied to the primary charger 20, and the non-printing section with respect to the voltage waveform (DCV) applied to the secondary charge remover is shifted by time P. It will be.

  Although the above description has been given of the non-image forming section provided at the end of the continuous operation mode, this may be a non-image forming section at the end of the single printing mode in which only one sheet is conveyed.

  In the present embodiment, the primary charger 20 is a brush and the secondary static eliminator 21 is a roller as the charging device 2. For example, the primary charger is a roller, or other contact charging member (fixed brush). Or a fixed blade). The secondary static eliminator may be another contact charging member (fixed blade or the like) having a relatively uniform surface property.

As a result of the above operation, contaminants accumulated in the primary charger 20 and the secondary static eliminator 21 are released, and the cleaning effect of the contaminants adhering to the secondary static eliminator 21 is particularly enhanced and unstable due to the contaminants. Do charge is eliminated, the controllability of the surface potential of the photosensitive member 1 can be a predetermined potential V _0, long term stabilized over, it is possible to provide an image forming apparatus without the image distortion.

  In this embodiment, the contaminants discharged from the charging device 2 to the photoconductor 1 are arranged at positions where they are not in contact with the photoconductor 1 so that they are not collected by the developing device 4 and the transfer device 5. The apparatus 6 employs a configuration in which it is collected, but this is a voltage sequence that prevents collection at each part by using a voltage sequence for the developing device 4 and the transfer device 5 or collects it by the developing device 4. May be added.

  In this embodiment, the drum-shaped substrate of the photosensitive member 1 is grounded to zero potential. For example, a voltage may be applied to the substrate of the photosensitive member 1. In this case, a value obtained by superimposing the voltage applied to the base of the photoreceptor 1 on the control voltage value of the charging device 2 is applied.

  The present invention is an apparatus that stably charges an object to be charged and can be applied to an application that needs to prevent the charging apparatus from being contaminated for a long period of time.

1 is a schematic diagram of an image forming apparatus of the present invention. It is a figure of the charging device application voltage sequence in the non-image forming section during image formation. It is a figure of the charging device application voltage sequence in the non-image formation section at the time of the end of continuous operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charging device, 3 ... Exposure device, 4 ... Developing device, 5 ... Transfer device, 6 ... Cleaning device, 7 ... Fixing device, 8 ... Paper hopper, 9 ... Conveyance path, 10 ... Paper, 20 ... primary charger, 21 ... secondary static eliminator, 30 ... power source, 31 ... power source.

Claims (6)

Contacts the surface of the photoreceptor moves in a predetermined direction, wherein a primary charger for charging the photosensitive member surface to a potential V _1, the contact with the photosensitive member, a photosensitive member movement direction in parallel in the primary charger And a secondary static eliminator that neutralizes the surface potential of the photosensitive member so that the surface potential of the photosensitive member is equal to the potential V ₁ and has a polarity V ₀ that is smaller in absolute value than the potential V _1. In an image forming apparatus including the apparatus,
At the time of image formation, the photosensitive member surface potential is charged to V ₁ having an absolute value higher than the absolute value V _th1 of the potential difference between the primary charger and the photosensitive member when the primary charger starts to charge the photosensitive member. A voltage is applied to the primary charger, and an absolute value of a potential difference between the secondary static eliminator and the photoconductor when the secondary static eliminator starts to neutralize the photoconductor is set to V _th2 and the secondary neutralization is performed. the voltage applied to the collector when the V ₂ | V 1 _-V 2 _| voltage V ₂ which satisfies ≧ V _th2 is applied to the secondary static eliminator, and the voltage V applied to the secondary static eliminator ₂ is a polarity opposite to the voltage applied to the primary charger,
A voltage having the same polarity as the voltage applied to the primary charger at the time of image formation and an absolute value lower than _Vth1 is applied to the primary charger in at least a part of the section during non-image formation. 2. An image forming apparatus according to claim 1, wherein said secondary static eliminator is provided with an operation section in which a voltage having a polarity opposite to a voltage applied to said secondary static eliminator during image formation and having an absolute value lower than _Vth2 is applied. Contacts the surface of the photoreceptor moves in a predetermined direction, wherein a primary charger for charging the photosensitive member surface to a potential V _1, the contact with the photosensitive member, a photosensitive member movement direction in parallel in the primary charger And a secondary static eliminator that neutralizes the surface potential of the photosensitive member so that the surface potential of the photosensitive member is equal to the potential V ₁ and has a polarity V ₀ that is smaller in absolute value than the potential V _1. An image forming apparatus including the apparatus,
At the time of image formation, the photosensitive member surface potential is charged to V ₁ having an absolute value higher than the absolute value V _th1 of the potential difference between the primary charger and the photosensitive member when the primary charger starts to charge the photosensitive member. A voltage is applied to the primary charger, and an absolute value of a potential difference between the secondary static eliminator and the photoconductor when the secondary static eliminator starts to neutralize the photoconductor is set to V _th2 and the secondary neutralization is performed. the voltage applied to the collector when the V ₂ | V 1 _-V 2 _| voltage V ₂ which satisfies ≧ V _th2 is applied to the secondary static eliminator, and the voltage V applied to the secondary static eliminator ₂ is a polarity opposite to the voltage applied to the primary charger,
In at least some sections during non-image formation, the primary charger has the same polarity as that during image formation, and has a potential V _{3 having an} absolute value higher than V _{th1 and} lower than the photoreceptor surface potential V _1. When the voltage applied to the secondary static eliminator is V ₄ , the secondary static eliminator has the same polarity as that during image formation, and | V ₃ −V ₄ | < An operation interval in which a voltage V ₄ that satisfies V _th2 is applied is provided, and the voltage V ₄ applied to the secondary static eliminator has a polarity opposite to that of the voltage V ₃ applied to the primary charger. ,
Subsequently, a voltage having a polarity opposite to that at the time of image formation and an absolute value lower than _Vth1 is applied to the primary charger, and a photoconductor with the same polarity as that at the time of image formation is applied to the secondary charger. The voltage V ₄ applied to the secondary static eliminator has the same polarity as the voltage V ₃ applied to the primary charger.
Subsequently, a voltage having the same polarity as the voltage applied to the primary charger at the time of image formation and an absolute value lower than _Vth1 is applied to the primary charger. secondary static eliminator low voltage absolute value than V _th2 in voltage and reverse polarity applied at the time of image formation is applied operation period provided, the voltage V ₄ that is and applied to the secondary static eliminator, the 1 image forming apparatus, characterized in that the same polarity as the voltage V ₃ applied to the next charger.   3. The image forming apparatus according to claim 2, wherein the non-image forming section is a non-image forming section at the end of the continuous operation mode in which sheets are continuously supplied.   3. The image forming apparatus according to claim 2, wherein the non-image forming section is a non-image forming section at the end of the single print mode in which only one sheet is conveyed.   In the image forming apparatus configured to apply a predetermined voltage to the substrate of the photoreceptor, the polarity of the voltage applied to the charging device is based on the voltage applied to the substrate of the photoreceptor and the primary charger or the 5. The image formation according to claim 1, wherein the polarity is a positive or negative polarity generated by a difference between a voltage applied to a secondary static eliminator and a voltage applied to a substrate of the photosensitive member. apparatus.   In the image forming apparatus configured to ground the photosensitive substrate, the polarity of the voltage applied to the charging device may be applied to the primary charger or the secondary charge remover based on the grounded photosensitive substrate. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus has positive and negative polarities caused by a difference between an applied voltage and the grounded photoconductor substrate. 6.

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