JP2016142909A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of suppressing generation of leak current from a sheet metal member to an image carrier when applying transfer bias voltage.SOLUTION: An image formation device 1 comprises a sheet metal member 9 having a folding ridge line L almost parallel to an axial direction of a base substrate 51 of an image carrier 5. A first portion P1 including a center portion of the folding ridge line L presses the inner peripheral surface of an intermediate transfer belt 3, second portions P2 on both sides of the center portion in the folding ridge line L press a casing 53 of the image carrier 5, and a third portion P3 positioned between the first portion P1 and the second portion P2 in the axial direction faces the end part of the image carrier 5 in the sheet metal member 9. The third portion P3 has a configuration such that an impedance between the third portion P3 and the image carrier 5 is higher than an impedance at least between the first portion P1 and the image carrier 5.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus in which a toner image carried on an image carrier is transferred to an intermediate transfer belt by applying a transfer bias voltage to a primary transfer member.

  In the conventional image forming apparatus, as exemplified in Patent Document 1, each sheet metal member is pressed against the inner peripheral surface of the intermediate transfer belt by a pressure spring, and the intermediate transfer belt comes into contact with each image carrier. To form a primary transfer nip. Here, each sheet metal member is disposed so as to abut against the protrusions on both ends of the casing of the corresponding image carrier. Thus, each sheet metal member is accurately positioned with respect to the corresponding image carrier. When the intermediate transfer belt is rotationally driven, the inner peripheral surface of the intermediate transfer belt slides while being in contact with each sheet metal member.

JP 2002-139927 A

  The inventor of the present invention studied using the sheet metal member as described above as an electrode to which a transfer bias voltage is applied (that is, a primary transfer member) in order to reduce the cost of the image forming apparatus. Since a current flows through the intermediate transfer belt by applying the transfer bias voltage, if the image carrier is separated from the sheet metal member, a path through which the current flows in the intermediate transfer belt becomes long. In this case, the influence of the electrical resistance of the intermediate transfer belt becomes relatively large, and it is necessary to apply a relatively large transfer bias voltage. This causes an increase in the cost of the power supply circuit that generates the bias voltage. In order to solve such a problem, if the electric resistance of the intermediate transfer belt is simply lowered while the image carrier is separated from the sheet metal member, the current is easily diffused in the intermediate transfer belt. Deteriorating. From the above, it is preferable to make the sheet metal member as close as possible to the image carrier in order to serve as the primary transfer member.

  However, the sheet metal member needs to be longer than the image carrier in order to abut the end of the sheet metal member against the casing of the image carrier for accurate positioning while placing the sheet metal member close to the image carrier. There is. Therefore, the end of the sheet metal member is close to the end of the image carrier. At the end of the image carrier, for example, a grounded element tube is exposed, so that current easily leaks from the end of the sheet metal member to the end of the image carrier when a transfer bias voltage is applied. There was a problem.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of a leakage current from a sheet metal member to an image carrier when a transfer bias voltage is applied.

  One aspect of the present invention is an image forming apparatus, which is an image carrier in which a photosensitive layer is formed on the outer peripheral surface of a cylindrical substrate having conductivity, and an image carrier that carries a toner image; A casing for rotatably accommodating the image carrier, an intermediate transfer belt on which a toner image on the image carrier is transferred to an outer peripheral surface, and a transfer bias voltage for transferring the toner image to the intermediate transfer belt And a sheet metal member having a bending ridge line substantially parallel to the axial direction of the base body.

  A first portion including a central portion of the bent ridge line presses an inner peripheral surface of the intermediate transfer belt to form a primary transfer nip between the intermediate transfer belt and the image carrier. The second parts on both outer sides press the casing, the sheet metal member is positioned with respect to the image carrier, and the position in the axial direction is between the first part and the second part. When the third portion is a third portion facing the end of the image carrier in the sheet metal member, the impedance between the third portion and the image carrier is at least the first portion and the image The third portion is provided with a configuration that is higher than the impedance with the carrier.

  According to the above aspect, it is possible to provide an image forming apparatus capable of suppressing the occurrence of leakage current from the sheet metal member to the image carrier when a bias voltage is applied.

1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus. FIG. 2 is a schematic diagram illustrating a power supply circuit provided in the image forming apparatus of FIG. 1. FIG. 2 is a perspective view illustrating a main part of the image forming apparatus in FIG. 1. FIG. 4 is a view when a cross section of the image forming apparatus taken along line I-I ′ in FIG. 3 is viewed from the direction of arrow II. It is a schematic diagram which shows the 1st modification of an image forming apparatus. It is a schematic diagram which shows the 2nd modification of an image forming apparatus. It is a schematic diagram which shows the 1st example of the 3rd modification of an image forming apparatus. It is a schematic diagram which shows the 2nd example of the 3rd modification of an image forming apparatus. It is a schematic diagram which shows the 4th modification of an image forming apparatus.

  Hereinafter, an embodiment of the image forming apparatus will be described in detail with reference to the drawings.

<< First column: Definition >>
Some figures show an x-axis, a y-axis and a z-axis that are orthogonal to each other. The x axis and the z axis indicate the left and right direction and the up and down direction of the image forming apparatus 1. The y-axis indicates the front-rear direction of the image forming apparatus 1. In addition, the y axis indicates the axial direction of the image carrier 5.

  In addition, in the text and each figure, alphabetic small letters a, b, c, and d may be added as subscripts of reference numerals. a, b, c, and d represent yellow (Y), magenta (M), cyan (C), and black (K). For example, the image carrier 5a means a Y-color image carrier. In addition, although a subscript can be added but a subscript is not added to the reference symbol, it means four colors or each color. For example, the image carrier 5 means YMCK all colors or each color image carrier.

<< Third column: Overall configuration and printing operation of image forming apparatus >>
In FIG. 1, an image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. Various types of images (typically, a typical electrophotographic system and a tandem system are used. A full-color image or a monochrome image) is printed on the paper M. For this purpose, the image forming apparatus 1 includes an image forming unit 2 for each color, an intermediate transfer belt 3, and a secondary transfer roller 4.

For example, the image forming units 2 for four colors are juxtaposed in the x-axis direction and include image carriers 5 of corresponding colors. Each image forming unit 2 may be juxtaposed in the z-axis direction.
Each image carrier 5 is a so-called photosensitive drum, has a cylindrical shape extending in the y-axis direction, and rotates about its own axis, for example, in the direction of arrow α. Around each image carrier 5, at least a charger 6, a developing device 8, and a sheet metal member 9 that also serves as a primary transfer member are arranged from the upstream side to the downstream side in the rotation direction α.

Each charger 6 uniformly charges the peripheral surface of the rotating image carrier 5.
An exposure device 7 is provided below each image carrier 5. Each exposure device 7 irradiates a light beam B based on the image data to an exposure area immediately downstream of the charging area of the image carrier 5, thereby forming an electrostatic latent image of a corresponding color.

  Each developing device 8 supplies a corresponding color developer to the developing area immediately downstream of the exposure area of the corresponding color image carrier 5 to form a corresponding color toner image.

The intermediate transfer belt 3 is a so-called endless belt, and has a volume resistivity of about 10 ⁸ Ω · cm, for example. It spans the outer peripheral surface of at least two rollers arranged in the x-axis direction, and rotates in the direction indicated by the arrow β, for example. In the present embodiment, the outer peripheral surface of the intermediate transfer belt 3 is in contact with the upper end of each image carrier 5. However, the present invention is not limited to this, and the intermediate transfer belt 3 may be arranged such that its outer peripheral surface comes into contact with the lower end of each image carrier 5. Further, when the image forming units 2 are juxtaposed in the z-axis direction, the intermediate transfer belt 3 may be arranged such that its outer peripheral surface is in contact with one end in the left-right direction of each image carrier 5. good.

  Each sheet metal member 9 faces the image carrier 5 of the corresponding color with the intermediate transfer belt 3 interposed therebetween, and presses the inner peripheral surface 31 (see FIG. 4) of the intermediate transfer belt 3 from above, so that the image carrier 5 A primary transfer nip 91 is formed between the intermediate transfer belt 3 and the intermediate transfer belt 3. As shown in FIG. 2, the transfer bias voltage V generated by the power supply circuit 92 is applied to each sheet metal member 9 during the printing operation. The transfer bias voltage V has a polarity opposite to the polarity of the charging potential of the image carrier 5. As a result, the toner image carried on the image carrier 5 is transferred to the rotating intermediate transfer belt 3 at the corresponding primary transfer nip 91.

  Reference is again made to FIG. The secondary transfer roller 4 presses the outer peripheral surface of the intermediate transfer belt 3 in the vicinity of the right end of the intermediate transfer belt 3 to form a secondary transfer nip at a contact portion between the secondary transfer roller 4 and the intermediate transfer belt 3. Form. In the secondary transfer nip, the image carried on the intermediate transfer belt 3 is transferred onto the paper M. The sheet M passes through a known fixing device and is then discharged to a tray as a printed matter.

<< Fourth column: Detailed configuration of main part of image forming apparatus >>
Next, the main part of the image forming apparatus 1 will be described in detail with reference to FIGS.
First, each color image carrier 5 includes a cylindrical substrate 51 made of a conductive material and a photosensitive layer 52 formed on the peripheral surface of the substrate 51. Each base 51 is typically a base tube made of aluminum. Each photosensitive layer 52 is formed, for example, on the peripheral surface of the substrate 51 except for the end portion of the substrate 51 in the central axis direction, and generates an electric charge when irradiated with the light beam B. In other words, the base 51 is exposed at the end of the image carrier 5. The withstand voltage of each photosensitive layer 52 is about 1000 V in absolute value. The base 51 is connected to the ground via a frame or the like (not shown) of the image forming apparatus 1.

  Each image carrier 5 is accommodated in a casing 53 so as to be rotatable around its own axis. Each casing 53 is fixed to a frame or the like of the image forming apparatus 1, and supports the shafts at both ends of the image carrier 5 with both side walls facing in the front-rear direction. Moreover, the front and rear ends of each casing 53 protrude upward as compared with the central portion thereof. The intermediate transfer belt 3 is disposed such that it passes through the central portion of each casing 53 and its outer peripheral surface is in contact with the upper end of each image carrier 5. Further, upper end surfaces 531 at both front and rear ends of each casing 53 are substantially flat and parallel to the inner peripheral surface 31 of the intermediate transfer belt 3.

  Each sheet metal member 9 is manufactured as follows. First, a rectangular metal thin plate is prepared. The length of the thin plate is approximately the same as the length of the casing 53 in the front-rear direction, and the thickness is preferably 1 mm or more. A rectangular through hole serving as a concave portion H (see FIGS. 3 and 4) is formed in a predetermined portion (details will be described later) of the thin plate after bending. Then, the width direction edge part of a thin plate is bend | folded so that an acute angle may be made parallel to the length direction of a thin plate, and the curved surface 93 which has the bending ridgeline L by this is formed. Here, in FIG. 3, the bending ridge line L is virtually indicated by a two-dot chain line. Further, the end of the thin plate on the opposite side in the width direction is bent so as to form an angle of about 90 °. Both ends of the curved surface 93 are abutted against both upper end surfaces 531 of the casing 53 with the bending ridge line L extending in the front-rear direction. In this state, the sheet metal member 9 is biased downward by a biasing member 94 such as a spring, for example, and is positioned with high accuracy with respect to the image carrier 5.

  Further, due to the urging force of the urging member 94, the central portion of the curved surface 93 extending in the front-rear direction presses the inner peripheral surface 31 toward the axial direction of the image carrier 5. As a result, the intermediate transfer belt 3 is pressed against the image carrier 5, and a primary transfer nip is formed between them.

  Here, as shown in FIG. 4, in the bending ridgeline L, the center part which contact | abuts to the internal peripheral surface 31 is made into the 1st part P1. In addition, in the bending ridge line L, a portion that is on both outer sides of the central portion P1 and is in contact with both upper end surfaces 531 is defined as a second portion P2. Further, the position of the image carrier 5 in the axial direction (that is, the front-rear direction) is between both portions P1 and P2, and the intermediate transfer belt 3 is not interposed between the image carrier 5 and the sheet metal member 9. A portion facing the end is referred to as a third portion P3.

  In the present embodiment, by forming a through-hole in the sheet metal member 9, as shown in FIGS. 3 and 4, the third portion P3 is recessed upward from at least the first portion P1 in a plan view from the left-right direction. A recess H is formed. In the present embodiment, the recess H is recessed upward with respect to the second portion P2. Here, since the bending of the sheet metal member 9 is performed after the formation of the through hole, the curved surface 93 can be formed by a single bending process, and the accuracy such as the linearity of the bending ridge line L can be maintained at a low cost. Become. As a result, the positioning accuracy of the sheet metal member 9 with respect to the image carrier 5 can be maintained.

<< 5th column: Operation and effect of image forming apparatus >>
As described above, since the concave portion H is formed in the curved surface 93, the distance from the upper end (that is, the third portion P3) of the concave portion H to the peripheral surface of the image carrier 5 is at least the first portion P1 and the image carrier. It becomes larger than the distance to 5. Therefore, since the impedance between the upper end of the concave portion H and the end of the image carrier 5 can be made larger than at least the impedance between the first portion P1 and the central portion of the image carrier 5, the transfer bias voltage V can be applied. Sometimes, leakage current can be suppressed from flowing from the upper end of the recess H to the end of the image carrier 5.

  Further, since leakage current can be suppressed, the sheet metal member 9 can be abutted against the front and rear ends of the casing 53 in order to accurately position the sheet metal member 9 with respect to the image carrier 5. In other words, the sheet metal member 9 is suitable for serving as a primary transfer member. As a result, unlike the conventional case, it is not necessary to provide an electrode for applying a transfer bias voltage. Etc. can be reduced.

  Here, the possibility of occurrence of leakage current from the sheet metal member 9 to the image carrier 5 will be examined in more detail. First, when the transfer bias voltage V is applied to the sheet metal member 9, the substrate 51 is grounded between the sheet metal member 9 and the substrate 51 of the image carrier 5, so that a potential difference corresponding to the transfer bias voltage V is generated. . Further, a potential difference equal to or higher than the transfer bias voltage V is generated between the sheet metal member 9 and the portion where the electrostatic latent image is formed by the charging / exposure process on the photosensitive layer 52 of the image carrier 5. On the other hand, there is a portion where the intermediate transfer belt 5 having a high resistance value is interposed between the sheet metal member 9 and the image carrier 5, and a leak current hardly occurs in this portion. Even if the intermediate transfer belt 5 is not interposed, the portion where the electrostatic latent image is not formed in the region where the photosensitive layer 52 is formed has a sufficient withstand voltage in the photosensitive layer 52 itself. . The above is summarized as shown in Table 1 below.

From the above, the third portion P3 is the following portions (1) and (2) where leakage current is highly likely to occur.
(1) A portion of the sheet metal member 9 that is an end of the image carrier 5 and faces a non-formed portion of the photosensitive layer 52 (that is, an exposed portion of the substrate 5). (2) In the sheet metal member 9, the image carrier 5. Of the photosensitive layer 52 facing the non-contact portion with the intermediate transfer belt 3

《Sixth column: Other actions and effects》
Further, the concave portion H has an advantage that the change with time is very small, and as a result, the possibility that the impedance between the third portion P3 and the image carrier 5 is reduced is small. Furthermore, since only the step of forming the through hole is added, there is little concern about an increase in cost.

<Seventh column: first variation>
In the embodiment described above, the sheet metal member 9 is formed with the recess H that is recessed with respect to the third portion P3. However, the present invention is not limited to this, and as shown in FIG. 5, a sheet-like member 94 made of an insulating material is formed so as to cover the third portion P3 on the bending ridge line L without forming the recess H in the sheet metal member 9. May be affixed. Also by this, as described in the fifth column, since the impedance between the third portion P3 and the end portion of the image carrier 5 can be increased, the leakage current can be suppressed. In this case, the member 94 is configured to increase the impedance.

<< Eighth column: second modification >>
In addition to the first modified example, as shown in FIG. 6, a sheet-like first slidable member 95 having a predetermined thickness so as to cover the first portion P <b> 1, and from the surface of the sheet metal member 9 Alternatively, the first slidable member 95 having a surface with a low friction coefficient may be attached. Also by this, the distance between the third portion P3 and the end of the image carrier 5 can be made larger than the distance between the first portion P1 and the image carrier 5. As a result, as described in the fifth column, since the impedance between the third portion P3 and the end portion of the image carrier 5 can be increased, it is possible to suppress the leakage current from flowing. In this case, the first slidable member 95 is configured to increase the impedance. In addition, according to this modification, the intermediate transfer belt 3 can be slid well on the sheet metal member 9.

<< 9th column: 3rd modification >>
In the above embodiment, as shown in FIG. 7A, when the edge portion of the recess H reaches a position where it contacts the intermediate transfer belt 3, the sheet-like protection member 96 is preferably provided so as to cover the portion. The protective member 96 having a surface with a lower friction coefficient than the surface of the sheet metal member 9 may be attached. Thereby, it is possible to prevent the intermediate transfer belt 3 from being damaged at the edge portion of the recess H.

  In addition, this protection member 96 may be affixed so that the whole region of the 1st part P1 may be covered, as shown to FIG. 7B. Thereby, it becomes possible to cover the edge part of both the recessed parts H by affixing the protection member 96 once. Thereby, the assembly efficiency of the image forming apparatus 1 is improved.

<< Column 10: Fourth Modification >>
Further, in the above-described embodiment or each modified example, as shown on the left side in FIG. 8, the bending ridge line L is arranged on the line connecting the axis of the image carrier 5 and the center in the width direction of the primary transfer nip 91. As shown, the sheet metal member 9 was arranged (non-offset arrangement). Further, as shown on the right side of FIG. 8, from the line connecting the axis of the image carrier 5 and the center of the primary transfer nip 91 in the width direction, in the rotation direction β of the intermediate transfer belt 3 (or in the reverse direction of the rotation direction β). The sheet metal member 9 may be arranged so that the bending ridge line L is offset.

  Here, the position of the sheet metal member 9 is determined by abutting the bending ridge line L against the casing 53 of the image carrier 5. Therefore, the positional relationship in the vertical direction between the sheet metal member 9 and the image carrier 5 can vary due to the processing tolerance of the parts related to the abutment. In addition, the positional relationship in the vertical direction between the sheet metal member 9 and the image carrier 5 may vary during rotation of the image carrier 5 due to the eccentricity of the axis of the image carrier 5.

  The nip pressure of the primary transfer nip 91 may vary due to the variation in the vertical positional relationship between the sheet metal member 9 and the image carrier 5. Here, the fluctuation in the positional relationship in the vertical direction at the time of offset arrangement on the right side of FIG. 8 does not affect the fluctuation of the nip pressure as compared with the arrangement on the left side of FIG. As described above, the offset arrangement on the right side of FIG. 8 can reduce the fluctuation of the nip pressure, and can suppress the deterioration of the image quality, such as the lack of characters to be printed.

  Further, in the non-offset arrangement, if the nip pressure is increased, the outer peripheral surface of the image carrier 5 may be damaged. If the nip pressure is reduced, the tension of the intermediate transfer belt 3 causes the intermediate transfer belt 3 to move from the image carrier 5 to the intermediate transfer belt 3. May leave. That is, in the non-offset arrangement, a severe adjustment is required regarding the force with which the sheet metal member 9 is abutted against the casing 53. On the other hand, in the offset arrangement, even if the force for abutting the sheet metal member 9 against the casing 53 is increased, the abutting force is offset by the reaction force from the casing 53 and is the minimum that does not lose the tension of the intermediate transfer belt 3. The position of the sheet metal member 9 can be determined to a desired position by force.

  The image forming apparatus according to the present invention can suppress the occurrence of a leakage current from the sheet metal member to the image carrier when a bias voltage is applied, and is suitable for a facsimile machine, a copier, a printer, and a multifunction machine having these functions. is there.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Intermediate transfer belt 5 Image carrier 51 Base 52 Photosensitive layer 53 Casing 9 Sheet metal member 91 Primary transfer nip L Bending ridge line P1 First part P2 Second part P3 Third part

Claims (8)

An image carrier having a photosensitive layer formed on the outer peripheral surface of a cylindrical substrate having conductivity, and an image carrier that carries a toner image;
A casing for rotatably accommodating the image carrier;
An intermediate transfer belt on which the toner image on the image carrier is transferred to the outer peripheral surface;
A sheet metal member having a bending ridge line substantially parallel to the axial direction of the substrate, to which a transfer bias voltage is applied for transferring the toner image to the intermediate transfer belt,
A first portion including a central portion of the bent ridge line presses an inner peripheral surface of the intermediate transfer belt to form a primary transfer nip between the intermediate transfer belt and the image carrier;
Second portions on both outer sides of the central portion in the bending ridge line press the casing, and the sheet metal member is positioned with respect to the image carrier,
When the axial position is a third part between the first part and the second part, the third part facing the end of the image carrier in the sheet metal member, the third part An image forming apparatus, wherein the third portion has a configuration in which an impedance between the portion and the image carrier is at least higher than an impedance between the first portion and the image carrier.   The third portion is a portion of the sheet metal member that faces the non-formed portion of the photosensitive layer at the end of the base and / or a portion that faces the non-contact portion of the intermediate transfer belt in the photosensitive layer. The image forming apparatus according to claim 1, wherein   The image forming apparatus according to claim 1, wherein the configuration is a recess provided in the sheet metal member and is a recess recessed with respect to the first part and the second part.   The image forming apparatus according to claim 1, wherein the configuration is an insulating member provided in the third portion.   The first part is provided with a slidable member having a predetermined thickness, and the distance from the third part to the image carrier is at least larger than the distance from the first part to the image carrier. The image forming apparatus according to claim 1, wherein the third portion has the configuration.   The image forming apparatus according to claim 3, wherein a sheet-like protective member is provided at least in a portion of the concave portion that contacts the intermediate transfer belt when the concave portion extends to a position where the concave portion contacts the intermediate transfer belt. .   The image forming apparatus according to claim 6, wherein the protection member covers the entire area of the first portion.   8. The image forming apparatus according to claim 1, wherein the bent ridge line is separated from the primary transfer nip in a plan view when the widthwise center of the primary transfer nip is viewed from the axis of the base. 9. .

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