JP4810079B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a charging roller that is disposed in the vicinity of a photosensitive member and performs a charging process on the photosensitive member.

  2. Description of the Related Art Conventionally, in an image forming apparatus, a charging roller is pressed against or brought close to the surface of a photoconductor provided in an image forming unit, and a voltage (DC voltage or a superimposed voltage of DC voltage and AC voltage is applied to the charging roller. Etc.) is generally applied to charge the surface of the photoreceptor to a predetermined polarity and potential.

For example, there has been proposed an image forming apparatus having a charging roller suitable for high durability, which does not affect the charging characteristics of the charging roller, and is less likely to occur due to deterioration of the photoreceptor due to end discharge of the charging roller. (For example, refer to Patent Document 1). In such an image forming apparatus, an insulating layer is provided at both ends of the charging roller (corresponding to the non-image area corresponding to the non-image area of the photosensitive member), and the both ends of the charging roller are located at the ends of the charging roller. The electrical resistance value is increased to suppress the discharge amount at both ends.
JP-A-7-199599

  However, in the image forming apparatus described above, an insulating layer is formed on both ends of the charging roller, so that a step is likely to occur on the surface of the charging roller, and it is difficult to make the charging roller uniformly contact with the photoreceptor. At the same time, there is a problem that the cost required for the construction of the charging roller itself increases.

  The present invention has been made in view of such problems, and can reduce the abrasion generated at the end of the photosensitive member due to the end discharge of the charging roller without adding a special configuration to the charging roller. It is an object of the present invention to provide an image forming apparatus that can be used.

The present invention is formed by exposing a charged surface of a photosensitive member, a charging unit that is pressed against the photosensitive member and uniformly charges a contact surface thereof, a neutralizing unit that neutralizes the surface of the photosensitive member prior to charging, and a charged surface of the photosensitive member. a developing unit that by adhering toner to form a toner image with respect to the electrostatic latent image, in an image forming apparatus comprising a transfer unit that transfers the toner image to the transfer material, and the photosensitive body shaft of said discharging means The length in the direction is set to a length that does not reach the surface of the photoreceptor facing both ends of the charging unit, and the potential of the surface of the photoreceptor facing both ends of the charging unit is maintained. Is.

  According to the image forming apparatus of the present invention, it is possible to reduce the abrasion generated at the end of the photosensitive member due to the end discharge of the charging roller without adding a special configuration to the charging roller.

An image forming apparatus according to a first aspect of the present invention includes a charging unit that is pressed against a photoconductor to uniformly charge a contact surface thereof, a neutralizing unit that neutralizes the surface of the photoconductor prior to charging, and a charging unit. An image forming apparatus comprising: a developing unit that forms a toner image by attaching toner to an electrostatic latent image formed by exposing the surface of a photoreceptor; and a transfer unit that transfers the toner image to a transfer material. The length of the static eliminating unit in the axial direction of the photosensitive member is set to a length that does not reach the surface of the photosensitive member facing both ends of the charging unit, and the photosensitive member facing both ends of the charging unit is set. The structure which maintains the electric potential of a body surface is taken.

  According to this configuration, the potential of the surface of the photosensitive member facing both ends of the charging unit is maintained by controlling the neutralization region by the neutralizing unit. As a result, discharge to both ends on the surface of the photosensitive member is suppressed as compared with the central region. Therefore, scraping generated at the end of the photosensitive member due to end discharge of the charging roller without adding a special configuration to the charging roller. Can be reduced. As a result, the original life of the photoreceptor can be achieved.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the charging width by the charging unit is Lroll, the discharging width by the discharging unit is Ler, and the developing width by the developing unit is Ldev. A configuration is adopted in which the charging width, the static elimination width, and the development width are set to have a relationship of Lroll> Ler ≧ Ldev.

  According to this configuration, since the charging width, the static elimination width, and the development width are set to have a relationship of Lroll> Ler ≧ Ldev, the development area is made to correspond to the central portion in the static elimination area, and the static elimination area is set in the charging area. By making it correspond to the central portion, a stable surface potential can be obtained in the developing region corresponding to the image width, and discharge to both end portions on the photoreceptor surface can be surely suppressed as compared with the central region.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, a two-component development method is adopted as a development method by the developing unit.

  According to this configuration, the toner can be attached to the electrostatic latent image formed on the surface of the photoreceptor using the two-component development method. In this case, since the charge width, the charge removal width, and the development width are set to satisfy the relationship of Lroll> Ler ≧ Ldev, it is possible to reliably avoid the situation where the carrier adheres to the development area.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the charging unit is a charging roller to which a constant current type AC superimposed voltage is applied.

  According to this configuration, charging is performed with a constant current type AC superimposed voltage, so that the total sum of currents output from the entire charging roller is constant. In this case, if there is a distribution in the ease of discharge in the axial direction of the charging roller, the current output is given priority to the part where the current easily flows, while the current output is suppressed to the part where the current does not easily flow. For this reason, by controlling the charge removal region and setting the ease of discharging the current, the current can be efficiently distributed only to the necessary image region, and the required amount of current can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration around an image forming unit in an image forming apparatus according to an embodiment of the present invention.

  In the image forming unit shown in the figure, a charging roller 102 as a charging unit, an exposure device 103 and a developing roller 104 as components of the developing unit, a transfer roller 105 as a transfer unit, and a discharging unit are provided in the vicinity of the photosensitive member 101. A neutralizing LED 106 and a cleaning blade 107 are arranged.

  The photosensitive member 101 is rotated in the direction of the arrow in the drawing by a driving mechanism (not shown). The charging roller 102 is pressed against the surface of the photoconductor 101 and receives a voltage to uniformly charge the surface of the photoconductor 101. The charging roller 102 is connected to an AC power source (Vc-ac) driven by a constant current method (−1000 uA) and a DC power source (Vc-dc) driven by a constant voltage method (−700 V). A superimposed high voltage is applied. The exposure device 103 exposes the surface of the charged photoconductor 101 by irradiating a laser beam to form an electrostatic latent image on the surface of the photoconductor 101. The developing roller 104 attaches a certain amount of toner to the electrostatic latent image formed on the surface of the photoreceptor 101. In the present embodiment, the developing means having the developing roller 104 employs a two-component developing system. The developing roller 104 is connected to a DC power source (Vd-dc) driven by a constant voltage method as a developing bias. The transfer roller 105 transfers the toner attached to the electrostatic latent image to the recording paper P being conveyed. The neutralization LED 106 neutralizes the potential remaining on the surface of the photoconductor 101 prior to the charging process of the charging roller 102. The cleaning blade 107 directly contacts and removes toner remaining on the surface of the photoconductor 101 after transfer onto the recording paper P.

  In this embodiment, the case where the transfer unit is the transfer roller 105 has been described. However, the present invention is not limited to this, and any configuration may be employed as long as it has a similar function. Moreover, although the case where a static elimination means is static elimination LED106 is demonstrated, it is not limited to this, What kind of structure may be taken if it has the same function. Further, the power source connected to the developing roller 104 is not limited to a DC power source, and may be an AC superimposed power source.

  FIG. 2 is a diagram for explaining the positional relationship of components around the photoconductor 101 of the image forming apparatus according to the present embodiment.

  In the drawing, the positional relationship among the photosensitive member 101, the charging roller 102, the developing roller 104, and the charge eliminating LED 106 is shown. In particular, the width of the charging area (hereinafter referred to as “charging width”) of the photosensitive member 101 by the charging roller 102 is indicated by “Lroll”, and the width of the developing area of the photosensitive member 101 by the developing roller 104 (hereinafter referred to as “developing width”). ) Is indicated as “Ldev”, and the width of the static elimination region (hereinafter referred to as “static elimination width”) of the photosensitive member 101 by the static elimination LED 106 is indicated as “Ler”.

As shown in the figure, the charging width Lroll corresponds to a certain region in the central portion of the peripheral surface of the photoreceptor 101. The development width Ldev corresponds to a certain area in the central portion of the charging width Lroll on the peripheral surface of the photoconductor 101. The static elimination width Ler corresponds to a certain region in the central portion of the development width Ldev on the peripheral surface of the photoreceptor 101. That is, the charging width Lroll is set longer than the developing width Ldev, and the developing width Ldev is set shorter than the static elimination width Ler. That is, the charging width Lroll, the development width Ldev, and the static elimination width Ler are:
Lroll>Ler> Ldev
The relationship holds.

  According to the charging roller 102, the developing roller 104, and the static elimination LED 106 set to such a length, the static elimination LED 106 performs static elimination processing on a certain range of the charging area of the charging roller 102, and the development roller 104 Development processing is performed on a certain range of the charge removal area of the LED 106. Therefore, by making the development region correspond to the central portion in the charge removal region and making the charge removal region correspond to the central portion in the charging region, discharge to both ends of the surface of the photoconductor 101 is surely suppressed as compared with the central region. be able to.

  In particular, in the present embodiment, as described above, the two-component development method is adopted in the developing unit having the developing roller 104, but the relationship in which the charging width, the static elimination width, and the developing width satisfy Lroll> Ler> Ldev. Therefore, the potential difference between the surface potential of the photoconductor and the developing bias does not increase, and it is possible to reliably avoid a situation where carriers adhere to the developing region.

In the present embodiment, the case where the development width Ldev is set shorter than the static elimination width Ler is described. However, the present invention is not limited to this, and the development width Ldev is set to the same length as the static elimination width Ler. May be. That is, the charge width Lroll, the development width Ldev, and the charge removal width Ler are set to Lroll> Ler ≧ Ldev
The relationship may be established. Even in such a change, it is possible to obtain the same effect as that of the image forming apparatus of the present embodiment described later.

  FIG. 3 is a diagram for explaining a discharge state of the charging roller 102 with respect to the photosensitive member 101 of the image forming apparatus according to the present embodiment.

  In the figure, the amount of discharge from the charging roller 102 is indicated by the size of the arrow with respect to the photoconductor 101. As shown in the figure, the amount of discharge from the end of the charging roller 102 is smaller than the amount of discharge from the central portion of the charging roller 102. More specifically, in the charging roller 102, the amount of discharge from the portion of the photoconductor 101 that does not correspond to the static elimination width Ler is smaller than the amount of discharge from the portion of the photoconductor 101 that corresponds to the static elimination width Ler. . This is based on the fact that, on the peripheral surface of the photoconductor 101, it is easy to discharge the region where the neutralization process is performed by the neutralization LED 106, but it is difficult to discharge the region where the neutralization process is not performed. is there.

  Hereinafter, the ease of discharge on the surface of the photoreceptor 101 after the charge removal process in the charging roller 102 (difficulty of discharge) will be described with reference to FIGS. 4 and 5. FIG.

  4 and 5 are diagrams for explaining the difference between the surface potential of the photoconductor 101 immediately before the charging process (after the charge removal process) and the DC voltage of the charging roller 102. FIG. 4 and 5, the charging roller 102 (the charging roller 102 and the neutralizing LED 106 in FIG. 4) is shown below, and the surface potential of the photosensitive member 101 and the charging roller 102 are set in correspondence with the positions on the charging roller 102. The difference from the DC voltage is shown. In addition, an arrow indicating the degree of ease of discharge is shown corresponding to the position on the charging roller 102 shown below. The larger the arrow, the easier the discharge.

  FIG. 4 shows the difference between the surface potential of the photoreceptor 101 and the DC voltage of the charging roller 102 in the image forming apparatus according to the present embodiment. FIG. 5 shows the difference between the surface potential of the photoreceptor 101 and the DC voltage of the charging roller 102 in the image forming apparatus for comparison with the image forming apparatus according to the present embodiment. FIG. 5A shows a case where the static elimination LED 106 is provided corresponding to the entire area of the charging roller 102, and FIG. 5B shows a case where the static elimination LED 106 is not provided. In FIG. 5 as well, for convenience of explanation, the same reference numerals as those in the present embodiment are used.

  As shown in FIG. 4, the surface potential (−50 V) of the portion of the photoconductor 101 where the neutralizing LED 106 is arranged has a difference of −650 V compared to the DC voltage (−700 V) of the charging roller 102. On the other hand, the surface potential (−680 V) of the portion of the photoconductor 101 where the neutralizing LED 106 is not disposed has a difference of −20 V compared to the DC voltage (−700 V) of the charging roller 102. That is, the potential difference in the portion where the static elimination LED 106 is arranged is larger than the potential difference in the portion where the static elimination LED 106 is not arranged. For this reason, the portion where the neutralization LED 106 is disposed is more easily discharged, and the discharge amount of the charging roller 102 is also increased. On the other hand, the portion where the neutralization LED 106 is not disposed is less likely to be discharged than the portion where the neutralization LED 106 is disposed, and the discharge amount of the charging roller 102 is also reduced.

  On the other hand, in FIG. 5A, since the neutralizing LED 106 is provided corresponding to the entire area of the charging roller 102, the surface potential (-50V) of the photosensitive member 101 is the DC voltage of the charging roller 102 over the entire area. The difference is -650V compared to (-700V). Accordingly, there is no portion where the difference between the surface potential of the photosensitive member 101 and the DC voltage of the charging roller 102 exists, so that the current supplied to the charging roller 102 is used for discharging almost uniformly in the axial direction. For this reason, the discharge roller 102 is easily discharged by the amount of discharge area larger than that of the central region, that is, the dischargeable time is longer.

  In FIG. 5B, since the neutralization LED 106 is not provided, the surface potential (−680 V) of the photoconductor 101 is different from the DC voltage (−700 V) of the charging roller 102 over the entire area. -20V. Accordingly, there is no portion where the difference between the surface potential of the photosensitive member 101 and the DC voltage of the charging roller 102 exists, so that the current supplied to the charging roller 102 is used for discharging almost uniformly in the axial direction. For this reason, as in the case of FIG. 5A, the end of the charging roller 102 is slightly more easily discharged than the central region. In addition, although the potential difference is reduced over the entire shaft of the charging roller 102, the charging efficiency is lowered even in an image area that requires charging stability, which is counterproductive.

  6A and 6B illustrate the film abrasion (a) that occurs on the photoconductor 101 in the image forming apparatus described with reference to FIGS. 4 and 5 and the number of printing sheets that can be printed until the end of the photoconductor 101 is scratched (b). FIG. In FIG. 6, the image forming apparatus according to FIG. 5A is referred to as “Comparative Example 1”, and the image forming apparatus according to FIG. 5B is referred to as “Comparative Example 2”.

  As shown in FIG. 6A, when the film scraping at the center of the photoconductor 101 of the image forming apparatus according to the present embodiment reaches 10.5 μm, the film scraping of 11.0 μm occurs at the end. is doing. On the other hand, when film scraping at the center of the photoreceptor 101 of the image forming apparatus of Comparative Example 1 reaches 10.5 μm, film scraping of 16.5 μm occurs at the end. Further, when the film scraping at the central portion of the photoreceptor 101 of the image forming apparatus of Comparative Example 2 reaches 10.5 μm, the film scraping of 18.0 μm occurs at the end portion. As described above, according to the image forming apparatus of the present embodiment, film scraping at the end of the photoreceptor 101 can be reduced.

  Further, as shown in FIG. 6B, in the image forming apparatus according to the present embodiment, the number of printing durability until the end of the photoreceptor 101 is damaged is 65,000. On the other hand, the edge of the image forming apparatus of Comparative Example 1 was damaged at 37000 sheets, and the edge of the image forming apparatus of Comparative Example 2 was damaged at 36000 sheets. ing. As described above, according to the image forming apparatus of the present embodiment, it is possible to greatly increase the number of printing durability until the end of the photoreceptor 101 is damaged.

  FIG. 7 is a diagram showing the relationship between the charging current amount for the charging roller 102 and the film scraping on the photoreceptor 101. In the figure, the vertical axis indicates film scraping on the photosensitive member 101, and the horizontal axis indicates the amount of charging AC current per unit length of the charging roller 102.

  As shown in the figure, in the photosensitive member 101, when 1 μm of the charging roller 102 is charged by 1.5 μA, film abrasion of 5 μm occurs. Similarly, when 1 μm of the charging roller 102 is charged with 3.0 μA, the film scraping of 10 μm occurs. Since film scraping occurs on the photosensitive member 101 at such a ratio, the amount of charging current in the charging roller 102 is reduced in the image forming apparatus according to the present embodiment.

  As described above, according to the image forming apparatus according to the present embodiment, the potential of the surface of the photoconductor 101 facing both ends of the charging roller 102 is maintained by controlling the neutralization region by the neutralization LED 106. As a result, discharge to both end portions on the surface of the photoconductor 101 is suppressed as compared with the central region. It is possible to reduce the shaving that occurs in the part. As a result, the original lifetime of the photoreceptor 101 can be achieved.

  In particular, in the image forming apparatus according to the present embodiment, the length of the neutralizing LED 106 in the axial direction is set to a length that does not reach the surface of the photoreceptor 101 facing both ends of the charging roller 102. Without adding a special configuration to the charging roller 102, it is possible to maintain the electric potential of the surface of the photoconductor 101 facing both ends of the charging roller 102 by controlling the discharging region by the discharging LED 106.

  Further, in the image forming apparatus according to the present embodiment, the charging roller 102 to which a constant current type AC superimposed voltage is applied charges the photosensitive member 101, so that the image is output from the entire charging roller 102. The total current is constant. In this case, if there is a distribution in the ease of discharge in the axial direction of the charging roller 102, the current output is given priority to the portion where the current easily flows, while the current output is suppressed to the portion where the current does not easily flow. . For this reason, by controlling the charge removal region and setting the ease of discharging the current, the current can be efficiently distributed only to the necessary image region, and the required amount of current can be reduced.

  According to the image forming apparatus of the present invention, without adding a special configuration to the charging roller, the control on the image forming apparatus main body side reduces the abrasion generated at the end of the photosensitive member due to the discharge at the end of the charging roller. This is useful in that the life of the photoreceptor can be extended.

1 is a diagram illustrating a configuration around an image forming unit in an image forming apparatus according to an embodiment of the present invention. The figure for demonstrating the positional relationship of the component of the periphery of a photoconductor of the image forming apparatus which concerns on the said embodiment. The figure for demonstrating the discharge state of the charging roller with respect to the photoconductor of the image forming apparatus which concerns on the said embodiment. The figure for demonstrating the difference of the surface potential of the photoconductor immediately before the charging process in the image forming apparatus which concerns on the said embodiment, and DC voltage of a charging roller. (A) A diagram for explaining the difference between the surface potential of the photoreceptor immediately before the charging process and the DC voltage of the charging roller in the image forming apparatus for comparison with the image forming apparatus according to the above embodiment. FIG. 6 is a diagram for explaining the difference between the surface potential of the photoreceptor immediately before the charging process and the DC voltage of the charging roller in the image forming apparatus for comparison with the image forming apparatus according to the embodiment. (A) A diagram for explaining film scraping that occurs on the photoconductor in the image forming apparatus described in FIGS. 4 and 5. (b) A scratch on the end of the photoconductor in the image forming apparatus described in FIGS. Diagram for explaining the number of printing durability until The figure which shows the relationship between the charging current amount with respect to the charging roller of the image forming apparatus which concerns on the said embodiment, and the film scraping in a photoreceptor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Photoconductor 102 Charging roller 104 Developing roller 105 Transfer roller 106 Static elimination LED

Claims (4)

A charging unit that is pressed against the photoconductor to uniformly charge the contact surface thereof, a neutralizing unit that neutralizes the surface of the photoconductor prior to charging, and an electrostatic latent image formed by exposing the charged photoconductor surface. by adhering toner to an image forming apparatus comprising a developing means for forming a toner image, a transfer unit that transfers the toner image to the transfer material, and at the photoreceptor axial direction of said discharging means with respect to Is set to a length that does not reach the surface of the photoreceptor facing both ends of the charging means, and the potential of the surface of the photoreceptor facing both ends of the charging means is maintained. Image forming apparatus.   When the charge width by the charging means is Lroll, the charge removal width by the charge removal means is Ler, and the development width by the development means is Ldev, the charge width, the charge removal width, and the development width satisfy Lroll> Ler ≧ Ldev. The image forming apparatus according to claim 1, wherein 3. The image forming apparatus according to claim 2, wherein a two-component developing method is adopted as a developing method by the developing means.   The image forming apparatus according to claim 1, wherein the charging unit is a charging roller to which a constant current type AC superimposed voltage is applied.

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