JP4827472B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus provided with means for detecting a leakage current of a charging roller.

  In recent years, there has been a demand for lower ozone in image forming apparatuses, and contact-type charging apparatuses and non-contact-type charging apparatuses that are excellent in charging efficiency and generate less discharge products have been put into practical use. The contact-type charging device is a device in which a charging roller is brought into contact with a photosensitive member, and a voltage is applied to the charging roller to discharge the photosensitive member to charge the surface of the photosensitive member to a predetermined potential. The non-contact type charging device does not bring the charging roller into contact with the photosensitive member, but provides a small gap between the charging roller and the photosensitive member so that a discharge phenomenon can occur, and is arranged in a non-contact manner so that a voltage is applied to the charging roller. Is applied to discharge the photoconductor to charge the surface of the photoconductor to a predetermined potential.

However, even in contact-type charging devices and non-contact-type charging devices, if damage such as pinholes occurs on the photoreceptor due to discharge breakdown, current flows concentrated on that part, and other parts are not charged. When an image is output as an image, there is a problem that an abnormal image such as a horizontal black line appears. On the other hand, this problem does not occur in all charging rollers, and there are charging rollers in which current tends to concentrate on scratches on the photoreceptor and charging rollers that do not.
Also, abnormal images such as horizontal black streaks may occur as described above due to deterioration of parts of the charging roller, surface layer wear of the charging roller, deterioration with time due to adhesion of low-resistance substances, and the like. In this case, the charging roller on which the horizontal streak image appears is a defective product, but the user cannot determine the charging roller on which the abnormal image is generated until the abnormal image is actually output. This causes the user to wastely use supplies such as toner and paper.

  As a conventional technique that has been improved in order to solve the above-described problem of the charging roller, for example, one piece is provided on each of the upstream side and the downstream side of the photosensitive member moving across the perpendicular line from the rotation center of the charging roller to the photosensitive member. Auxiliary rollers are provided, and the auxiliary roller is in contact with both the charging roller and the photosensitive member, and the frictional resistance at the contact portion between the charging roller and the auxiliary roller is set larger than the frictional resistance between the charging roller and the photosensitive member. A charging device (for example, see Patent Document 1) in which the moving direction of the charging roller and the photosensitive member is reversed in the region is disclosed. Further, in the charging roller having an elastic layer and a surface layer covering the elastic layer, the elastic layer is made of epichlorohydrin rubber, and the surface layer is made of nylon 6 in which non-doped tin oxide is dispersed. , Nylon 6-6, Nylon 6-10, Nylon 11 and Nylon 12 and consisting of an alcohol-soluble copolymer nylon resin containing as polymerization units, the amount of non-doped tin oxide in the surface layer is 40 A charging roller (for example, see Patent Document 2) in which the material of the charging roller is adjusted such that the surface resistance of the charging roller is increased by setting the weight percent to 70% by weight or more is disclosed. And charging means for charging an object to be charged by applying an AC voltage; current measuring means for measuring a current flowing between the charging means and the object to be charged when an AC voltage is applied to the charging means; A charging device (for example, refer to Patent Document 3) having specific current extracting means for extracting a specific current having a specific frequency from the current is disclosed.

JP-A-6-069151 Japanese Patent Application Laid-Open No. 10-069151 JP 2005-017869 A

  The present invention has been made in view of the above problems, and provides an image forming apparatus equipped with means for detecting a defect of the charging roller as described above and notifying the user of the timing for replacing the charging roller. Also, if the detection means is in contact with the charging roller during image formation, current flows through both the image carrier and the detection means, and the charging efficiency of the image carrier is reduced and the image carrier is charged. An object of the present invention is to provide an image forming apparatus that can cope with this problem.

To solve the above problems, the present invention is that had the following characteristics.
The image forming apparatus of the present invention leaks from an image carrier, a charging roller for charging the image carrier by superimposing an AC bias on a DC bias, a leakage current detection member having a low resistance portion and a high resistance portion, and the charging roller. An image forming apparatus comprising: a current detection unit configured to detect a leakage current of a charging roller including a current detection unit configured to detect a value of a current flowing through the current detection member, wherein the leakage current detection member extends along a longitudinal direction of the charging roller. The length is the same as the length in the longitudinal direction of the charging roller, and the high resistance portion is disposed on the surface of the low resistance portion with a spiral gap, and the leakage current detection member is connected to the charging roller. On the other hand, the leakage current of the charging roller is detected in a non-contact state.
As described above, the leakage current detection members arranged in a non-contact manner are arranged in a plurality of locations or in a spiral shape, or by rotating the leakage current detection members arranged in this way, a partial area of the entire charging roller is rotated. Degradation can also be detected.

  By means for solving the above-mentioned problems, the image forming apparatus of the present invention can detect deterioration of the charging roller by means for detecting leakage current of the charging roller, so that the user is notified of the abnormality without outputting an abnormal image. As a result, there is an effect that the user does not have to waste supplies such as toner and paper. Further, the image forming apparatus of the present invention is equipped with a contact / separation mechanism that allows the leakage current detection member to contact and separate from the charging roller, so that the current flowing from the charging roller flows only to the image carrier during image formation. it can. Also, by electrically floating the leakage current detection member during image formation, the current flowing from the charging roller can flow only to the image carrier during image formation, and the image carrier can be charged. It is possible to prevent a reduction in efficiency and non-uniform charging of the image carrier.

  In the image forming apparatus of the present invention, the leakage current detection member is disposed in a non-contact manner with respect to the charging roller, thereby preventing an increase in torque of the charging roller and contamination of the leakage current detection member. Further, since the leakage current detection member arranged in a non-contact scans or rotates from end to end on the charging roller, partial deterioration of the entire charging roller can also be detected. In addition, the image forming apparatus of the present invention prevents the leak current detecting member disposed in contact with the charging roller from rotating the charging roller so that the position where the leak current is detected is the same every time. Contamination can be prevented and the lifetime of the leakage current detection member can be extended.

Embodiments according to the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a main cross-sectional view around the image carrier of the image forming apparatus of the present invention. In FIG. 1, 1 is an image carrier, 2 is a charging roller, 3 is a PET (high resistance member) having a thickness of about 30 [μm], 4 is SUS (low resistance member), and 5 is a plate-like leak. The current detection member is shown. SUS (low resistance member) 4 is connected to the current detection unit.
FIG. 2 is a view of the periphery of the image carrier of the image forming apparatus of the present invention as seen from the longitudinal direction. 2 in FIG. 2 is a gap of PET (high resistance member) having a width of about 100 [μm], and a part of SUS (low resistance member) is exposed. As can be seen from FIGS. 1 and 2, the SUS (low resistance member) 4 of the leakage current detection member 5 is electrically connected to the current detection unit.
Further, the leakage current detection member 5 is arranged in non-contact with the charging roller 2. At this time, the shortest distance between the charging roller 2 and the leakage current detection member 5 was about 30 [μm]. By disposing the charging roller and the leakage current detection member in a non-contact manner, an increase in torque of the charging roller 2 and contamination of the leakage current detection member 5 can be prevented.

  FIG. 3 is a graph showing the relationship between the current value I when no abnormal image occurs and the AC bias (Vpp) applied at that time. When the charging roller is mounted on the image forming apparatus of the present invention, the current value I displayed by the current detection unit is plotted against Vpp, which is the peak-to-peak voltage of the AC bias applied at that time. Referring to FIG. 3, when Vpp is varied from 600 to 2500 [V], the plot remains linear and the current value I is within 1.5 [mA] at the maximum. As shown in FIG. 4, when Vpp is in the range of 600 to 2500 [V], current does not flow concentrating only on SUS (low resistance member) in the gap 6 portion of PET (high resistance member). It is shown that. Here, the arrow in FIG. 4 represents an image of the current flowing from the charging roller to the leakage current detection member.

  FIG. 5 is a graph showing the relationship between the current value I when an abnormal image occurs and the AC bias (Vpp) applied at that time. When the charging roller is mounted on the image forming apparatus, the current value I displayed by the current detection unit is plotted against the AC bias (Vpp) applied at that time. Referring to FIG. 5, when Vpp is 2000 [V], the current value I deviates from the linearity and shows a value exceeding 2 [mA]. As shown in FIG. 6, when Vpp is 2000 [V], a large current flows from the charging roller to the gap 6 where the SUS (low resistance member) of the leakage current detection member is exposed. ing. Here, the arrow in FIG. 6 represents the image of the current flowing from the charging roller to the leakage current detection member. This is the same as the phenomenon that current concentrates on the scratches (pinholes) of the photoreceptor.

  The high-voltage power supply of the image forming apparatus according to the first embodiment is of a type that can stably output up to 2500 [V] and current of 2 [mA] when the AC bias frequency is 900 [Hz]. From the results of FIG. 5 and FIG. 5, if the current value detected by the current detection unit when applying Vpp of 2500 [V] is within 2 [mA], the charging roller does not generate an abnormal image (horizontal black streak). If it exceeds 2 [mA], it can be said that the charging roller generates an abnormal image (horizontal black streaks).

Table 1 below shows the presence or absence of current values and abnormal images (horizontal black streaks) after running tests. A running test is performed with the image forming apparatus of the present invention, and the current value detected by the current detection unit when Vpp is applied 2500 [V] every 1000 [sheets] (1K [sheets]), and the charging roller at that time Evaluation was made to output an image using a photoconductor with scratches. At the time of running 40,000 [sheets] (40K [sheets]) from the beginning, the current value is within 2 [mA], and an abnormal image (horizontal black streak) is generated even if the image is output with a scratched photoconductor. Did not appear. At the time of running 48000 [sheets] (48K [sheets]), the current value was 2.88 [mA] and exceeded 2 [mA]. At that time, when an image was output with a photoconductor having scratches, an abnormal image (horizontal black streaks) was generated. From this, it was found that the deterioration of the charging roller over time can be detected by the image forming apparatus having the above-described mechanism.

FIG. 7 is a main cross-sectional view of the periphery of the image carrier in which the contact / separation mechanism is provided in the image forming apparatus of the present invention. In FIG. 7, reference numeral 1 denotes an image carrier, 2 denotes a charging roller, and 8 denotes a roller-shaped leakage current detection member. The leak current detection member 8 is arranged in a dotted line portion by an approach / separation mechanism at the time of image formation.
If the leakage current detection member 8 is in contact with or close to the charging roller 2 at the time of image formation, current flows not only to the image carrier 1 but also to the leakage current detection member 5, so that the image carrier 1 is charged. The image became uneven and image distortion occurred. Therefore, when a contact / separation mechanism for separating the leakage current detection member 3 from the charging roller 2 at the time of image formation is mounted, it is possible to prevent the charging efficiency of the image carrier 1 from being lowered and the image carrier 1 from being unevenly charged. It was possible to prevent image disturbance.
Further, the non-contact leakage current detection member 8 in FIG. 7 has a roller shape, but the leakage current detection member may have a plate shape as shown in FIG.

FIG. 8 is a main cross-sectional view of the periphery of an image carrier provided with a float switch in the image forming apparatus of the present invention. A float switch 15 in FIG. 8 is a switch for electrically floating the leakage current detection member 8 and is installed between the leakage current detection member 8 and the current detection unit.
If the leakage current detection member 8 is not in an electrically floating insulated state during image formation, current flows not only to the image carrier 1 but also to the leakage current detection member 8, so that the image carrier 1 is charged. The image became uneven and image distortion occurred. Therefore, the float switch 15 is activated at the time of non-image formation to connect the leakage current detection member 8 to the current detection unit, the float switch 15 is opened at the time of image formation, and the leak current detection member 8 is electrically connected at the time of image formation. It was set as the structure which made the floated insulation state. Thereby, the current flowing from the charging roller 2 flows only to the image carrier 1 at the time of image formation, thereby preventing the charging efficiency of the image carrier 1 from being lowered and the image carrier 1 from being non-uniformly charged. Image disturbances could be prevented.

  FIG. 9 is a diagram illustrating an example in which the leakage current detection member arranged in a non-contact manner scans the charging roller. As shown in FIG. 9, the leakage current detection member 5 is moved from end to end of the charging roller 2 so that the leakage current of the entire charging roller can be detected. In this way, partial defects of the charging roller can be detected.

FIG. 10 is a diagram illustrating an example in which a plurality of low resistance portions of the leakage current detection member arranged in a non-contact manner are arranged in the longitudinal direction of the charging roller. A plate-like leakage current detection member was arranged so as to cover the entire charging roller as indicated by 7 in FIG. 10, and a plurality of PET (high resistance member) gaps 6 were provided. By doing so, the charging roller 2 may be partially deteriorated due to uneven contact of the charging roller cleaner, etc., but partial deterioration of the entire charging roller can also be detected.
Further, the non-contact leakage current detection member 7 in FIG. 10 is an example in which a plate-like, low resistance portion is arranged at a plurality of locations in the longitudinal direction of the charging roller. However, as shown in FIG. It may be arranged in a non-contact manner and rotated.

FIG. 11 is a diagram illustrating an example in which the leakage current detection member is arranged in contact with the charging roller. Reference numeral 8 in FIG. 11 denotes a roller-shaped leakage current detection member, which is arranged in contact with the charging roller and rotates.
12 is a cross-sectional view of the leakage current detection member of FIG. As can be seen from FIG. 12, the SUS (low resistance member) 10 in FIG. 11 is electrically connected to the current detection unit. If the leak current detection member and the charging roller are detected at the same location each time, a defect such as toner clogging occurs in the gap portion.
Therefore, the leakage current detection member is formed in a roller shape and rotated around the charging roller so that the detection portions of the charging roller 2 and the leakage current detection member 8 are not concentrated in one place. By doing so, it was possible to prevent the leakage current detection member 8 from being contaminated and to extend its life. Further, by setting the surface roughness of the PET (high resistance member) of the leakage current detection member 8 to 10 [μm] or more, the leakage current detection member 8 and the charging roller 2 can be rotated together.

  FIG. 13 is a diagram illustrating an example in which a plurality of low resistance portions of the leakage current detection member arranged in contact with each other are arranged in the longitudinal direction of the charging roller. A roller-shaped leakage current detection member was disposed so as to cover the entire charging roller as indicated by 9 in FIG. 13, and a plurality of PET (high resistance member) gaps 10 were provided. The leakage current detection member 9 is arranged in contact with the charging roller and rotates. By doing so, partial deterioration of the entire charging roller can be detected, and the same effect as in FIG. 10 was obtained.

FIG. 14 is a diagram illustrating an example in which the low resistance portions of the leakage current detection member arranged in contact are arranged in a spiral shape in the longitudinal direction of the charging roller. As shown at 11 in FIG. 14, the gap 10 of the PET (high resistance member) of the leakage current detection member is arranged in a spiral shape and is configured to rotate. By rotating with the charging roller 2, partial defects in the entire charging roller can be detected.
14 is an example in which the non-contact leakage current detection member 11 is disposed in contact with the charging roller. However, the leakage current detection member 11 may be disposed in a non-contact manner and rotated.

FIG. 3 is a cross-sectional view of the periphery of the image carrier of the image forming apparatus of the present invention. FIG. 3 is a view of the periphery of the image carrier of the image forming apparatus of the present invention as viewed from the longitudinal direction. It is a graph which shows the relationship between the electric current value I when an abnormal image does not generate | occur | produce, and the AC bias (Vpp) applied at that time. It is a figure which shows that the electric current does not flow only in the gap where the low resistance member of the leakage current detection member is exposed from the charging roller. It is a graph which shows the relationship between the electric current value I in case an abnormal image generate | occur | produces, and the AC bias (Vpp) applied at that time. It is a figure which shows a mode that the large electric current flowed into the clearance gap where the low resistance member of the leakage current detection member was exposed from the charging roller. 3 is a cross-sectional view of the periphery of an image carrier in which an image forming apparatus of the present invention is provided with a contact / separation mechanism. FIG. 3 is a cross-sectional view of the periphery of an image carrier in which a float switch is provided in the image forming apparatus of the present invention. It is a figure which shows the example which the leakage current detection member arrange | positioned non-contact scans on the charging roller. It is a figure which shows the example by which the low resistance site | part of the leakage current detection member arrange | positioned non-contactingly was arrange | positioned in multiple places in the longitudinal direction of the charging roller. It is a figure which shows the example which has arrange | positioned the leakage current detection member in contact with the charging roller. It is sectional drawing of the leakage current detection member of FIG. It is a figure which shows the example in which the low resistance site | part of the leakage current detection member arrange | positioned in contact is arrange | positioned in multiple places in the longitudinal direction of a charging roller. It is a figure which shows the example by which the low resistance site | part of the leakage current detection member arrange | positioned in contact is arrange | positioned helically in the longitudinal direction of a charging roller.

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging roller 3 PET (high resistance member)
4 SUS (low resistance member)
5 Leakage current detection member (plate)
6, 10 Clearance 7 Leakage current detection member (non-contact, multiple low resistance parts are arranged)
8 Leakage current detection member (roller shape)
9 Leakage current detection member (one with multiple low resistance parts in contact)
11 Leakage current detection member (spiral)
15 Float switch

Claims (1)

An image carrier;
A charging roller for charging the image carrier by superimposing an AC bias on a DC bias;
An image forming apparatus comprising: a leakage current detection member having a low resistance portion and a high resistance portion; and a means for detecting a leakage current of the charging roller comprising a current detection portion for detecting a current value flowing from the charging roller to the leakage current detection member. And
The leakage current detection member is
The length along the longitudinal direction of the charging roller is the same as the length in the longitudinal direction of the charging roller,
The high resistance portion is disposed on the surface of the low resistance portion with a spiral gap,
The image forming apparatus, wherein the leakage current detection member detects a leakage current of the charging roller in a non-contact state with respect to the charging roller .

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