Patent Grant
7751763
This application is based on and claims the benefit of priority from the prior Japanese Patent Application No. 2006-42770, filed on Feb. 20, 2006, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer or a MFP (Multi-Function Peripheral) which is also called a digital composite apparatus.
2. Description of the Related Art
A tandem type image forming apparatus has been known as an image forming apparatus such as a copier or printer. In a tandem type image forming apparatus, plural photosensitive drums are arranged in parallel. Toner images respectively formed on the photosensitive drums are transferred to a paper sheet, multi-layered on the paper sheet, to obtain a color image. An image forming apparatus of this tandem type has an intermediate transfer belt unit.
Jpn. Pat. Appln. Laid-Open Publication No. 10-293514 describes an example of an image forming apparatus having such an intermediate transfer belt unit.
The image forming apparatus in this example has a unit casing, a conveyor mechanism, and an elevation mechanism. The conveyor mechanism has a conveyor belt suspended between first and second rollers provided in the unit casing. The elevation mechanism moves up and down the conveyor mechanism in relation to the unit casing. When replacing the conveyor belt or the like, the conveyor belt is moved away from a photosensitive drum. The elevation mechanism has a cam and a lever, and rotates the cam in accordance with rotation of the lever, thereby moving up and down the conveyor mechanism.
The conveyor belt and the photosensitive drum need to be apart from each other during maintenance services and in contact with each other during use. When the belt and drum are brought into contact with and moved apart from each other by the cam mechanism, peripheral units and members receive impact in some cases. For example, when plural gears are engaged together through such contact, tooth tips of the gears collide with each other to scratch or leave an impact scar on tooth surfaces of the gears. In this case, driving of the mechanism becomes stiff for each cycle, and causes color drifting or jitters in a formed image.
Jpn. Pat. Appln. Laid-Open Publication No. 2005-91725 describes an image forming apparatus implemented with a measure for relaxing impact as described above. In an example of this apparatus, a distant state of a transfer roller in which the roller is apart from an intermediate transfer belt transits to a contact state. Timing of such transition is adjusted so that an end of the transfer roller in the lengthwise direction is brought into contact with the intermediate transfer belt prior to the other end of the transfer roller.
However, the above measure for relaxing impact requires delicate adjustment for transition timing from a distant state to a contact state, and gives rise to a drawback of complex structure.
The present invention provides an image forming apparatus of a tandem type, which includes a mechanism for moving a transfer unit and a photosensitive drum apart from each other and reduces impact generated when a state of the unit and drum being apart from each other transits to a contact state.
Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus of the present invention.
An embodiment of the invention will now be described in detail with reference to the drawings.
In
The automatic document feeder 4 feeds a document to the image reader section 3, which reads the document and generates image data.
The image forming section 2 is constituted by, for example, a tandem type color laser printer, and scans a photosensitive member with a laser beam from a laser exposure device 20, to form an image.
The image forming section 2 includes image forming sections 2Y, 2M, 2C, and 2K for colors of yellow (Y), magenta (m), cyan (c), and black (K), respectively. The image forming sections 2Y, 2M, 2C, and 2K are arranged in parallel from the upstream side to the downstream side, below an intermediate transfer belt 11 as an intermediate transfer medium.
In the following description, components forming the image forming sections 2Y, 2M, 2C, and 2K will be denoted at reference numerals added with Y, M, C and K, respectively. In some cases, the components will be described omitting the reference numerals Y, M, C and K.
Since the image forming sections 2Y, 2M, 2C and 2K have the same structure, only the image forming section 2Y will be described below as a representative examples of the image forming sections. The image forming section 2Y has a photosensitive drum 12Y. An electric charger 13Y, a developing device 14Y, a transfer roller 15Y, a cleaner 16Y, a blade 17Y, and the like are located around the photosensitive drum 12Y. Details of the structure of the image forming section 2Y is shown enlarged in
The intermediate transfer belt 11 circularly moves, and semiconductive polyimide is used for the belt in view of heat resistance and abrasion resistance. The intermediate transfer belt 11 is suspended over a driving roller 22 and driven rollers 23 and 24. The intermediate transfer belt 11 can have contact with photosensitive drums 12Y to 12K. To a position of the intermediate transfer belt 11 where the belt faces the photosensitive drum 12Y, a primary transfer voltage of +1,000 V or so is applied from a primary transfer roller 15Y so that a toner image on the photosensitive drum 12Y is primarily transferred to the intermediate transfer belt 11.
A secondary transfer roller 25 is located so as to face the driving roller 22 suspending the intermediate transfer belt 11. When a paper sheet P passes between the driving roller 22 and the secondary transfer roller 25, a secondary transfer voltage of +1,000 V or so is applied from the secondary transfer roller 25, so that toner images on the intermediate transfer belt 11 are secondarily transferred to the paper sheet P. A belt cleaner 26 is provided near the driven roller 24 for the intermediate transfer belt 11.
In each of the image forming sections 2Y to 2K, the electric charger 13 electrically charges uniformly the whole surface of the photosensitive drum 12 to, for example, −700 V or so. The developing device 14 supplies the photosensitive drum 12 with a two-component developer by a developing roller 14a which is applied with a developing bias of −500 V or so. The two-component developer contains toner of one corresponding color and a carrier. The cleaner 16 removes residual toner on the surface of the photosensitive drum 12 by use of the blade 17.
Meanwhile, the laser exposure device 20 scans the photosensitive drum 12 in an axial direction of the drum with a laser beam emitted from a semiconductor laser element. The laser exposure device 20 includes a polygon mirror 20a, an imaging lens system 20b, a mirror 20c, and the like.
The sheet feeder section 6 has plural sheet feeder cassettes 6a and 6b to contain paper sheets of various sizes. The image forming apparatus 1 further has a manual feed tray 30 for manually feeding paper sheets.
Between the sheet feeder cassettes 6a and 6b and the secondary transfer roller 25, there are provided pickup rollers 31a and 32a, separation rollers 31b and 32b, conveyor rollers 33 and 34, and a resist roller 35. The pickup rollers 31a and 32a pick out paper sheets from inside the sheet feeder cassettes 6a and 6b. Between the manual feed tray 30 and the resist roller 35, there are provided a pickup roller 36a for picking up paper sheets P, and a manual sheet feed roller 37.
Further, a fixing device 39 is provided in the downstream side of the secondary transfer roller 25 along a vertical path 38 for vertically conveying paper sheets P fed from the sheet feeder cassettes 6a and 6b or the manual feed tray 30.
Between the fixing device 39 and the sheet output section 5, there are provided a sheet output conveyor path 40 and a reverse conveyor path 41. A gate 42 is provided on the reverse conveyor path 41 to distribute paper sheets P to the sheet output section 5 or to the reverse conveyor path 41. The reverse conveyor path 41 reverses and guides paper sheets P in a direction toward the secondary transfer roller 25. The reverse conveyor path 41 is used when carrying out double-sided printing.
Operation of the image forming apparatus shown in
Referring to the image forming section 2Y as an example, the photosensitive drum 12Y is irradiated with a laser beam in accordance with image information for yellow (Y), thereby forming an electrostatic latent image. From the electrostatic latent image, a toner image for yellow (Y) is formed by the developing device 14Y. Subsequently, the photosensitive drum 12Y makes contact with the intermediate transfer belt 11 being rotated, thereby primarily transferring the toner image for yellow (Y) to the intermediate transfer belt 11 by the primary transfer roller 15Y.
In a similar manner to the toner image forming process for yellow (Y), toner images for magenta (M), cyan (C), and black (K) are formed by the image forming section 2M, 2C, and 2K, and are sequentially transferred to the same position on the intermediate transfer belt 11 as the toner image for yellow (Y) has been formed. Thus, toner images for yellow (Y), magenta (M), cyan (C), and black (K) are transferred to the intermediate transfer belt 11, multi-layered on one another, so that a full color toner image is obtained.
Further, the intermediate transfer belt 11 secondarily transfers the full color toner image all at once to a paper sheet P by a transfer bias of the secondary transfer roller 25. The paper sheet P is fed to the position of the secondary transfer roller 25 from the sheet feeder cassettes 6a or 6b or the manual feed tray 30, synchronized with timing when the full color toner image on the intermediate transfer belt 11 reaches the secondary transfer roller 25. The paper sheet P to which the toner image has been secondarily transferred reaches a fixing roller 39, and the toner image is fixed.
In case of printing an image only on one side (single-sided printing), the paper sheet P is distributed to the sheet output section 5 by the gate 42. Otherwise, in case of double-sided printing or multi-layered printing, the paper sheet P is distributed to the reverse conveyor path 41 and conveyed again to the secondary transfer roller 25.
After completion of the secondary transfer, residual toner is cleaned from the intermediate transfer belt 11 by the belt cleaner 26. From each photosensitive drum 12, residual toner is cleaned by the cleaner 16 and blade 17 after primary transfer of a toner image to the intermediate transfer belt 11, to become ready for next image forming.
The blade 17 is in contact with the photosensitive drum 12. As the photosensitive drum 12 rotates, the blade 17 finely scrapes away a coating on the photosensitive drum 12 and an edge of the blade 17 itself is abraded. The process as described above is repeated so that an amount of abrasion of the photosensitive drum 12 or blade 17 exceeds a certain amount, and desired performance cannot be achieved. In other words, lifecycle of the photosensitive drum 12 or blade 17 depends on total operation period.
Therefore, the photosensitive drum 12 and primary transfer roller 15 are located away from each other (for example, at color image forming sections during monochrome character printing) in order to extend lifecycle except for some unavoidable part.
The same process as described above is carried out to form a toner image by each of the image forming sections 2Y to 2K for respective colors. Toner images for respective colors are layered on one another to form a color image. After forming the image, residual toner on the transfer belt 11 is cleaned by the belt cleaner 26.
When no color image is formed, e.g., when monochrome text information is formed, toner consumption can be reduced by developing only a latent image for black (K) In this case, the other color image forming sections 2Y, 2M, and 2C than the image forming section 2K should desirably not operated because lifecycle of each image forming section 2 depends on a total operation period.
If the transfer belt 11 is rotated in contact with the photosensitive drums 12 under pressure applied by primary transfer, the photosensitive drums 12 and the transfer belt 11 are abraded or damaged. Therefore, a mechanism for moving the transfer belt 11 apart from the photosensitive drums 12 is required.
A cam 44 and lifters 45Y, 45M, 45C, and 45K lift up the primary transfer rollers 15Y to 15K upon necessity, respectively, so as to leave the transfer belt 11.
Meanwhile, during a maintenance service for inspecting, repairing, or replacing a component, the whole transfer unit 21 needs to be moved apart from the photosensitive drums 12. Therefore, the invention employs a separation mechanism for moving the whole transfer unit 21 apart from the photosensitive drums 12 and bringing the unit 21 into contact with the drums 12.
In
The transfer unit 21 has support pins 212 which are attached to a frame 211 and protrude outward from the frame 211, as schematically illustrated within a circle A in
Although the fixed rails 53 are hidden behind frames 54 in
The unit holder mechanism 51 includes frames 54, a handle 52, an elevation links 55, link rods 56, and cams 57. The frames 54 are attached to the body of the image forming apparatus. The elevation links 55 are attached respectively to two sides of the handle shaft 52a which rotates as the handle 52 rotates. The link rods 56 move in lateral directions of the drawings as the elevation links 55 rotate. The cams 57 rotate as the link rods 56 move.
The fixed rails 53 each have a recessed cross-section in order to engage the support pins 212. A container section 58 for receiving a cam 57 is formed at a ceiling section of each recessed section. More specifically, as illustrated enlarged in a circle B in
The cams 57 each have a rotating shaft fixed to the body of the image forming apparatus 1. The cams 57 each lift up the ceiling section of the container section 58 or push down a bottom section of the container section 58, thereby to move up or down the whole fixed rails 53.
A spring 59 is attached to the ceiling section of each container section 58. The spring 59 makes contact with a protrusion 60 provided on the body of the image forming apparatus 1 when the fixed rails 53 move down. When the fixed rails 53 are going to move down, tip ends of the springs 59 are brought into contact with the protrusions 60. The fixed rails 53 are thereby energized by the springs 59 so as to lift up in an upward direction. Therefore, the cams 57 push down the fixed rails 53 against the biasing force of the springs 59.
Described next will be elevation operation of the transfer unit 21 by the unit holder mechanism 51. When the transfer unit 21 is set down, the transfer unit 21 is in contact with the photosensitive drums 12. When the transfer unit 21 is set up, the transfer unit 21 is apart from the photosensitive drums 12.
The cams 57 are eccentric cams which have rotating points located on the body of the image forming apparatus as illustrated in
When to lift up the fixed rails 53, the cams 57 lift up the fixed rails 53 against the dead weight of the fixed rails 53 (i.e., against gravity). When to move down the fixed rails 53, the cams 57 push down the fixed rails 53 against the biasing force of the springs 59.
Therefore, the fixed rails 53 move up and down continuously kept in contact with the cams 57. Accordingly, a cushioning effect is generated when the fixed rails 53 move up or down, and prevents the transfer unit 21 from abruptly moving apart from or into contact with the fixed rails 53. That is, the springs 59 and the gravity of the fixed rails 53 constitute a load means which continuously applies a load to the cams in a direction opposite to an upward or downward moving direction of the fixed rails 53 when the fixed rails 53 are moved up or down by rotation of the cams 57.
When the transfer unit 21 is brought into contact with the fixed rails 53 after once moving apart from the fixed rails 53, the gears 61 and 62 are engaged with each other. If impact occurs when the transfer unit 21 is brought into contact, tooth tips of the gears collide with each other and leave impact scars on tooth surfaces. If an impact scar is left, irregular rotation is caused and results in a defect such as a jitter in a formed image. However, the present invention is capable of relaxing impact caused by moving the transfer unit 21 apart from or into contact with the fixed rails 53 by means of the cams 57 and springs 59 When the fixed rails 53 are set down completely, the cams 57 position the fixed rails 53 in the lower side of the cams 57. Therefore, the transfer unit 21 can form images without receiving influence such as vibration.
Thus, the image forming apparatus according to the present invention relaxes impact which is caused when moving the transfer unit. Accordingly, malfunctions and defective images can be prevented.
Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-042770 | Feb 2006 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5765082 | Numazu et al. | Jun 1998 | A |
| 6061542 | Minami et al. | May 2000 | A |
| 6201944 | Onuki et al. | Mar 2001 | B1 |
| 6889027 | Tachiki et al. | May 2005 | B2 |
| 20030161667 | Park et al. | Aug 2003 | A1 |
| 20050141930 | Murakami et al. | Jun 2005 | A1 |
| 20060067745 | Yamada et al. | Mar 2006 | A1 |
| 20070059054 | Furukawa | Mar 2007 | A1 |
| 20070116496 | Morimoto et al. | May 2007 | A1 |
| 20070134028 | Funabashi | Jun 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 10-293514 | Nov 1998 | JP |
| 2005-091725 | Apr 2005 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070196142 A1 | Aug 2007 | US |
