Patent Application
20190004455
The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system, and more particularly to an image forming apparatus which includes an optical detection portion.
Downsizing of the entire image forming apparatus has been a critical issue, and a known downsizing technique for a color image forming apparatus is that toner images of respective colors on an image bearing member are once transferred onto an intermediate transfer belt, and the toner images of a plurality of colors on the intermediate transfer belt are collectively transferred to a recording material.
Generally speaking, a toner image is transferred from the intermediate transfer belt to a transfer material by a transfer portion using an electrostatic transfer process, in which transfer bias (transfer voltage) is applied, and electrostatic attraction is generated so as to form an electric field having the reverse polarity of the charging polarity of the toner image. As a method of preventing transfer failure in such a transfer portion by leakage of the transfer bias, Japanese Laid-open Patent Publication No. 2009-128481 discloses a method of grounding using a static elimination circuit which can switch the resistance value of the transfer material transport guide.
This image forming apparatus also includes a color resist control portion. First a resist mark (toner mark) using the toner of each color is formed on the intermediate transfer belt as a reference image for resist detection, by forming the toner image on the photosensitive drum and transferring the toner image onto the intermediate transfer belt. Then the resist marks are detected by an optical sensor, which is installed on the downstream side of the black image (last color) forming portion of the intermediate transfer belt, and color resist control, such as correcting the image writing start position onto the photosensitive drum, is performed. The optical sensor is disposed to irradiate the light of the optical sensor to a position where the intermediate transfer belt is wound around the rollers, so that the intermediate transfer belt does not deviate in the surface direction causing a change in the distance between the optical sensor and the intermediate transfer belt. In such an optical sensor, Japanese Laid-open Patent Publication No. 2015-82065 discloses a method of disposing a conductive member, to attract the discharged current, near the optical sensor for grounding, to prevent an electrostatic breakdown caused by user access when the intermediate transfer belt is replaced or the transfer material is jammed.
The method of disposing the static elimination circuit in the grounding path of the transfer material transport guide, however, requires a connection with the control portion and a dedicated static elimination circuit, which increases the size of the apparatus main body, and increases cost.
Further, the method of disposing a conductive member near the optical sensor for grounding requires a dedicated conductive member and a grounding path, which also increases the size of the apparatus main body, and increases cost.
The transfer material transport guide requires the static elimination circuit, and the optical sensor must be grounded by the conductive member disposed near the optical sensor, and the demanded resistance values of the transfer material transport guide and the optical sensor are different from each other. Therefore separate grounding paths are required so that electricity does not leak from the transfer material transport guide to the conductive member near the optical sensor. In this way, the transfer material transport guide and the optical sensor cannot be disposed in close proximity, which makes downsizing of the product difficult.
Furthermore, as the position of the optical sensor is closer to the intermediate transfer belt, the optical sensor can receive stronger reflected light, and the resolution of the optical sensor can be increased by condensing the light of the spectroscopic sensor, which can receive large light quantities. However, as the optical sensor is closer to the intermediate transfer belt, there is higher possibility that the optical sensor may be contacted to the intermediate transfer belt and be scratched when the intermediate transfer belt is replaced.
With the foregoing in view, it is an aspect of the present invention to implement the static elimination of the transfer transport guide, the prevention of the electrostatic breakdown of the optical sensor, and the improvement of the resolution of the optical sensor, while enabling the downsizing of the apparatus. It is another aspect of the present invention to provide an image forming apparatus which allows acquiring high quality color images by performing high precision color resist control.
It is provided with a view to achieving one aspect as describe above an image forming apparatus, including:
an image bearing member configured to bear a toner image;
a guide member configured to guide a transfer material to a transfer portion for transferring the toner image from the image bearing member to the transfer material; and
an electric unit that includes a device configured to be activated by electric power supply, wherein
the electric unit is configured to move to a first position and to a second position that is more retracted from the image bearing member than the first position,
the guide member is grounded via a resistance member when the electric unit is positioned at the first position,
the guide member is grounded without the resistance member when the electric unit is positioned at the second position.
Therefore the present invention can implement the static elimination of the transfer transport guide, the prevention of the electrostatic breakdown of the optical sensor, and the improvement of the resolution of the optical sensor, while enabling the downsizing of the apparatus. Further, the present invention can provide an image forming apparatus which allows acquiring high quality color images by performing high precision color resist control.
Further features of the prevent invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments.
The image forming apparatus 1 includes a first, second, third and fourth process cartridges 3Y, 3M, 3C and 3K, which are disposed in a row as a plurality of image forming portions. These process cartridges, 3Y, 3M, 3C and 3K, form a yellow (Y), magenta (M), cyan (C), and black (K) toner images respectively. Below the process cartridges 3Y, 3M, 3C and 3K, a laser scanner 4 serving as an exposing portion is disposed. Above these process cartridges 3Y, 3M, 3C and 3K, an intermediate transfer unit 5 is disposed for transferring the toner images, formed by the process cartridges 3Y, 3M, 3C and 3K, onto a transfer material S.
A composing element of each process cartridge having substantially the same configuration and the function to form each color image is described in general, omitting Y, M, C or K attached to each reference sign to indicate the color of the composing element, unless necessary.
The process cartridge 3 includes a photosensitive drum 12, which is a rotatable drum type (cylindrical) electrophotographic photosensitive member serving as a primary image bearing member. The process cartridge 3 also includes, as a processing portion to operate a photosensitive drum 12: a charging roller 13 which is a roller type charging member serving as a charging portion; a developing apparatus 14 serving as a developing portion; and a drum cleaning apparatus 17 serving as a photosensitive member cleaning portion. The photosensitive drum 12, the charging roller 13, the developing apparatus 14 and the drum cleaning apparatus 17 are integrated, and can be detachably attached to the image forming apparatus 1.
The photosensitive drum 12 is rotatably driven in an arrow R1 direction indicated in
The intermediate transfer unit 5 includes an intermediate transfer belt 6 constituted by an endless belt, which functions as a secondary image bearing member and an intermediate transfer member, and is disposed to face the four photosensitive drums 12Y, 12M, 12C and 12K. Here, as a toner image having at least one color, a four-color toner image is bore on the intermediate transfer belt 6. The intermediate transfer belt 6 is an example of a movable member that is used in the image forming apparatus 1. The intermediate transfer belt 6 is wound around a drive roller 7, a tension roller 8 and a secondary transfer counter roller 9, which serve as a plurality of stretching rollers. The intermediate transfer belt 6 is wound around the plurality of stretching rollers in a state of receiving a predetermined tensile strength by the tension roller 8. The intermediate transfer belt 6 rotates (circulates) at a predetermined velocity (peripheral velocity) in the arrow R2 direction indicated in
The toner image formed on the photosensitive drum 12 is transferred onto the intermediate transfer belt 6 at each primary transfer portion T1, because of the function of the primary transfer roller 10 (primary transfer). At this time, a predetermined primary transfer voltage (primary transfer bias), which is a DC voltage having a reversed polarity of the charging polarity of the toner during development (normal charging polarity), is applied to the primary transfer roller 10. For example, when a full color image is formed, a toner image having each color formed on the four photosensitive drums 12Y, 12M, 12C and 12K respectively is sequentially transferred onto the intermediate transfer belt 6 so as to be superimposed, whereby multiple toner images for a full color image are formed on the intermediate transfer belt 6.
The toner image formed on the intermediate transfer belt 6 is transferred onto the transfer material S, which is held between the intermediate transfer belt 6 and the secondary transfer roller 11, and is transported in the secondary transfer portion T2, because of the function of the secondary transfer roller 11 (secondary transfer). At this time, a predetermined secondary transfer voltage (secondary transfer bias), which is a DC voltage having a reversed polarity of the normal charging polarity of the toner, is applied to the secondary transfer roller 11.
The transfer material S, such as a recording paper and a plastic sheet, is supplied to the secondary transfer portion T2 by a feeding apparatus 18. The feeding apparatus 18 includes a cassette feeding portion 19, which separates and feeds the stacked and stored transfer material S one by one, a manual feeding portion 20, and a resist roller pair 21 which transports the transfer material S to the secondary transfer portion T2 at a predetermined timing.
The transfer material S, on which the toner image is transferred, is held by a fusing nip, which is constituted by a fusing roller 23 and a pressure roller 24, and is transported in a fusing apparatus 22 serving as a fusing portion, and during this process, heat and pressure are applied to the transfer material S, whereby the toner image is fused (firmly fixed) thereon. Then the transfer material S is transported by a discharge roller pair 25 and the like, and is discharged to a tray 26, which is disposed on the top surface of the image forming apparatus 1.
On the downstream side of the black (last color) image forming portion on the intermediate transfer belt 6, an optical sensor unit 29 is disposed, and detects a resist mark 28 (toner mark) generated by each color toner, which is a reference image for detecting color resist formed on the intermediate transfer belt 6. Then, based on this detection result, a color resist correction, such as correcting the image writing start position onto the photosensitive drum 12, is performed.
An optical sensor unit 29 serving as an electric unit will be described with reference to
The biasing unit 40 will be described next. The biasing unit 40 is attached to the main body frame 2. The biasing unit 40 is constituted by: a biasing base 41 which is made of semiconductive material; a biasing link 42 which is rotatably disposed in the biasing base 41; a biasing cap 43 which is made of semiconductive material, and which biases the optical sensor support member 34; and a biasing spring 44 which is a compression spring to apply biasing force. The biasing base 41 made of semiconductive material includes polyethylene terephthalate (PET) as an injection molding material. Here PET has the volume resistance of 10̂12 to 4.9×10̂14 Ω·cm, for example.
The operation of the optical sensor unit 29 will be described next, with reference to
On the other hand, when the intermediate transfer unit replacement door 50 is open, and the inside of the image forming apparatus is exposed by the user access operation to replace the intermediate transfer unit 5 or to remove jammed transfer material, as illustrated in
Here the biasing unit 40 constitutes the displacement mechanism. In concrete terms, the displacement mechanism includes the biasing base 41, the biasing link 42 and the biasing cap 43.
As described above, Example 1 provides for a mechanism as a displacement mechanism to displace the position of the optical sensor unit 29 to the first position or the second position, interlocking with the opening/closing operation of an intermediate transfer unit replacement door 50. Therefore, the transfer material transport guide 35 can be grounded via the biasing base 41 made of semiconductive material at the first position. As a result, the grounding can be achieved at a level of resistance which does not cause transfer failure due to the leak of transfer bias. At the second position, the intermediate transfer unit replacement door 50 is open, and the transfer material transport guide 35 is directly grounded, so as to prevent an electrostatic breakdown caused by user access when the intermediate transfer unit 5 is replaced or jammed transfer material is removed. As a result, the grounding path can be shared, and the transfer material transport guide 35 can play both roles of the transfer bias leak prevention and the electrostatic breakdown prevention, which can downsize the apparatus. Furthermore, the optical sensor unit 29 moves away from the intermediate transfer unit 5, hence the intermediate transfer unit 5 can be prevented from contacting and scratching the optical sensor unit 29 when the intermediate transfer unit 5 is replaced. As a result, the space between the optical sensor unit 29 and the intermediate transfer unit 5, required for replacement, can be provided when the optical sensor unit 29 is at the second position. This means that when the optical sensor unit 29 is at the first position, it is unnecessary to provide a space for replacement, and the optical sensor unit 29 may be close to the intermediate transfer unit 5, which improves the resolution of the optical sensor.
Although the present invention has been described using a specific example, the present invention is not limited to the above example. The intermediate transfer system which uses the intermediate transfer belt as the image bearing member is described in Example 1. However, the image forming apparatus can use a photosensitive drum as the image bearing member, so that the toner image formed on the photosensitive drum is transferred to the transfer material (this is the same for Example 2).
The optical sensor unit 29 is the color resist sensor in Example 1. However, the optical sensor unit 29 can be used for other devices which require protection from electrostatic breakdown.
The biasing base 41 is constituted by the semiconductive member in Example 1. However, the present invention is not limited to this configuration. The same effect can be implemented for a configuration of disposing a sheet material made of a sheet type semiconductive material, on the main body frame 2, or a configuration of disposing an electric resistance component, such as a plate type resistor, and grounding the transfer material transport guide 35 at the first position using the sheet material or the electric resistance component.
Example 2 of the optical sensor unit 29 according to the present invention will be described with reference to
An operation of the optical sensor unit 29 of Example 2 will be described with reference to
On the other hand, as illustrated in
By creating the grounding path like this, the same effect as Example 1 can be implemented.
In Example 2, a member made of semiconductive material is disposed in the optical sensor unit 29. Therefore semiconductive material need not be used for the biasing base 41 of the biasing unit 40. Further, the biasing spring conducting portion 44a, disposed in the biasing spring 44 in Example 1, is not required, hence the biasing unit 40 can be downsized. and design flexibility improves. As a result, downsizing of the apparatus can also be achieved.
Furthermore in Example 2, the biasing link earth member conducting portion 63a located on the biasing link 42 contacts the first earth member 36 when the optical sensor unit 29 is at the second position. At this time, the biasing link earth member conducting portion 63a, as the third support portion, may support not only the biasing link 42, but also the optical sensor unit 29 located at the second position. The optical sensor unit 29 may be supported by a different member, and the biasing link earth member conducting portion 63a may only contact the first earth member 36 for electric connection.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2017-130433, filed on Jul. 3, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-130433 | Jul 2017 | JP | national |
