Patent Application
20080080907
The present application is directed to second transfer areas and methods of transferring toner images from an intermediate member to a media sheet. The second transfer area comprises a second transfer nip formed between a second transfer roller and a back-up roller. The media path moves through this nip with the media sheets moving along the path and receiving the toner image from the intermediate member. The amount of force applied by the second transfer roller may affect the transferability of the toner images to the media sheet. Further, the intermediate member may contact the second transfer roller at soft nip and hard nip locations. The lengths of these nips may also affect the transferability of the toner images.
The image forming device may include a laser printer (mono or color), facsimile, copier, or combination of two or more of these devices which is often referred to as an all-in-one device. The device may be sized to fit on a workspace, such as a desktop. The device may further include accessible work areas for the user to insert and remove media sheets, replace components within the device, and clear media jams from within the device.
A first toner transfer area 30 includes one or more imaging units 31 that are aligned horizontally extending from the front 13 to a back 15 of the body 12. Each imaging unit 31 includes a charging roll 32, a developer roll 33, and a rotating photoconductive (PC) drum 34. The charging roll 32 forms a nip with the PC drum 34, and charges the surface of the PC drum 34 to a specified voltage such as −1000 volts, for example. A laser beam from a printhead 36 contacts the surface of the PC drum 34 and discharges those areas it contacts to form a latent image. In one embodiment, areas on the PC drum 34 illuminated by the laser beam are discharged to approximately −300 volts. The developer roll 33, which also forms a nip with the PC drum 34, then transfers toner particles from a toner reservoir 37 to the PC drum 34 to form a toner image. The toner particles are attracted to the areas of the PC drum 34 surface discharged by the laser beam 35.
The toner reservoir 37 is operatively connected to each of the imaging units 31. The toner reservoirs 37 are sized to contain toner that is transferred to the imaging units 31 for image formation. The toner reservoirs 37 may be mounted and removed from the device 10 independently from the imaging units 31. In one embodiment, the toner reservoirs 37 each contain one of black, magenta, cyan, or yellow toner. Each of toner reservoirs 37 may be substantially the same, or one or more of the toner reservoirs 37 may hold different toner capacities. In one specific embodiment, the black toner reservoir has a higher capacity than the others. The toner reservoirs 37 may mount from a top 16 of the device 10, and may detach during removal with the imaging units 31 remaining within the device 10.
An intermediate transfer mechanism (ITM) 60 is disposed adjacent to each of the imaging units 31. In this embodiment, the ITM 60 is formed as an endless belt trained about support roller 29, tension roller 21 and back-up roller 22. The belt may be constructed from a variety of materials including polyimide, Ethylene TetrafluoroEthylene (ETFE), nylon, thermoplastic elastomers (TPE), polyamide-imid, and polycarbonate alloy. During image forming operations, the ITM 60 moves past the imaging units 31 in a clockwise direction as viewed in
The ITM 60 rotates and collects the one or more toner images from the imaging units 31 and then conveys the toner images to a media sheet at a second transfer area. The second transfer area includes a second transfer nip 40 formed between the back-up roller 22 and a second transfer roller 41.
A media path 44 extends through the device 10 for moving the media sheets through the imaging process. Media sheets are initially stored in the input tray 68 or introduced into the body 12 through a manual feed 48. The sheets in the input tray 68 are picked by a pick mechanism 67 and moved into the media path 44. In this embodiment, the pick mechanism 67 includes a roller positioned at the end of a pivoting arm. The roller rotates to move the media sheets from input tray 68 towards the second transfer area. In one embodiment, the pick mechanism 67 is positioned in proximity (i.e., less than a length of a media sheet) to the second transfer area with the pick mechanism 67 moving the media sheets directly from the input tray 68 into the second transfer nip 40. For sheets entering through the manual feed 48, one or more rollers are positioned to move the sheet into the second transfer nip 40.
The media sheet receives the toner image from the ITM 60 as it moves through the second transfer nip 40. The media sheets with toner images are then moved along the media path 44 and into a fuser area 70. Fuser area 70 includes fusing rollers or belts 71 that form a nip to adhere the toner image to the media sheet. The fused media sheets then pass through exit rollers 45 that are located downstream from the fuser area 70. Exit rollers 45 may be rotated in either forward or reverse directions. In a forward direction, the exit rollers 45 move the media sheet from the media path 44 to an output area 47. In a reverse direction, the exit rollers 45 move the media sheet into a duplex path 46 for image formation on a second side of the media sheet.
The ITM 60 first contacts the second transfer roller 41 before contacting the back-up roller 22. The first contact area, referred to as the soft nip 23a, is where the ITM 60 begins to wrap onto the second transfer roller 41 prior to contacting the back-up roller 22. A second contact area, referred to as the hard nip 23b, is where the ITM 60 is also supported by the back-up roller 22. The ITM 60 is in contact with both rollers 22, 41 in the hard nip 23b. As the media sheets move along the media path 44, the sheets first contact the soft nip 23a of the second transfer roller 41 and then proceed to the hard nip 23b. It has been determined that a greater soft nip 23a and hard nip 23b produce higher quality printed images.
The soft nip 23a may have a variety of lengths ranging from about 1.0 mm to about 4.8 mm. In one embodiment, the soft nip 23a has a length of about 1.7 mm. Other embodiments include a soft nip 23a of about 1.25 mm and about 2.6 mm. The hard nip 23b may also have a variety of lengths. In one embodiment, the hard nip 23b is about 4.0 mm.
The tension roller 21 is mounted on the end of the arm 24 and pivots about point 25. As illustrated in
As illustrated in
The size and positioning of the second transfer roller 41 within the main body 12 accommodates a larger roller than with previous devices. In one embodiment, the second transfer roller 41 has a diameter of about 25 mm.
The amount of force applied by the second transfer roller 41 further affects the transfer of the toner image to the media sheet at the second transfer area 40. In one embodiment, the amount of force applied by the second transfer roller 41 is greater than about 9 g/mm. Specific embodiments include the amount of force applied by the second transfer roller 41 to be about 15 g/mm, and about 25 g/mm. In yet another embodiment, the force is about 35 g/mm. This force causes a transfer nip pressure to transfer the toner image from the ITM 60 to the media sheet. In one embodiment, the transfer nip pressure is about 0.045 N/mm2.
The combination of the length of the soft nip 23a and the force at the second transfer nip 40 greatly affects the transfer of the toner image from the ITM 60 to the media sheet. In one embodiment, a soft nip of about 1.25 mm and a second transfer force of greater than about 15 g/mm results in good image transfer. In one embodiment, the force was about 15 g/mm. In another embodiment, the force was about 25 g/mm. In yet another embodiment, the force was about 35 g/mm.
In one embodiment, an ITM unit 80 is a replaceable component that may be removed from the body 12 and replaced with a new component. The ITM unit 80 includes the ITM 60, interior rollers 21, 22, and 29, and the second transfer roller 41. Removal and replacement of the second transfer roller 41 with the back-up roller 22 ensures that the pressure at the second transfer nip 40 is accurate upon replacement of the ITM unit.
In the embodiment described above, a force is applied to the second transfer roller 41 to form the pressure in the second transfer nip 40. In another embodiment, the force is applied through the back-up roller 22 with the second transfer roller 41 remaining relatively stationary. In another embodiment, a force is applied through both rollers to obtain the necessary nip pressure.
Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.
The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. In one embodiment, the back-up roller 22 is deformed due to contact with the second transfer roller 41. In another embodiment, neither of the rollers 22, 41 deform. In yet another embodiment, both rollers 22, 41 deform. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
