Patent Application
20130223895
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-037707 filed Feb. 23, 2012.
The present invention relates to an image forming apparatus.
An image forming apparatus according to an aspect of the present invention includes an image carrier, a surface of which is charged while the image carrier is rotating, an exposing device that faces the image carrier at an exposure position and emits light toward the image carrier to form an electrostatic latent image on the charged surface of the image carrier, a developing member that develops the electrostatic latent image formed on the surface of the image carrier into a toner image, a transfer member that, while rotating, transports a recording medium to a transfer position, at which the transfer member faces the image carrier, and that transfers the toner image formed on the surface of the image carrier to the recording medium, the recording medium being wrapped around an outer peripheral surface of the transfer member, and a gripping member that is disposed on the transfer member, the gripping member gripping a leading end portion of the recording medium having been transported to the rotating transfer member at a gripping position. In the image forming apparatus, the following inequalities (1) and (2) are satisfied:
(L1−L3)×(V2/V1)<L2 (1)
L2 <(L1−L3+L4)×(V2/V1) (2)
Here, L1 denotes a peripheral length of the image carrier from the exposure position to the transfer position in a rotating direction of the image carrier. L2 denotes a peripheral length of the transfer member from the gripping position to the transfer position in the rotating direction of the transfer member. L3 denotes a length of a margin on a leading-end side of the recording medium in which no toner image is formed. L4 denotes a peripheral length of the transfer member, when a first recording medium and a second recording medium having a maximum size transportable by the transfer member are wrapped around the transfer member, between a trailing end of an image region of the first recording medium and a leading end of an image region of the second recording medium, the image regions of the recording media each being a region over the entire area of which an image is formable, the first recording medium being positioned on a side that is further upstream than the second recording medium in the rotating direction of the transfer member. V1 denotes a peripheral velocity of the image carrier. V2 denotes a peripheral velocity of the transfer member.
An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein:
An image forming apparatus 10 according to an exemplary embodiment of the present invention will be described referring to
As illustrated in
The image forming unit 12 that forms a toner image will be described first.
The image forming unit 12 includes an image carrier 22, on whose surface toner images are sequentially formed while the image carrier 22 is rotating. The image forming unit 12 also includes a charging device 24, an exposing device 26, a rotary developing device 28, and a cleaning device 46. The charging device 24 charges the surface of the image carrier 22. The exposing device 26 exposes the charged surface of the image carrier 22 to light to form an electrostatic latent image. The rotary developing device 28 develops the electrostatic latent image, having been formed on the surface of the image carrier 22, by using a developer into a toner image. The cleaning device 46 cleans remnants remaining on the image carrier 22.
The image carrier 22 is disposed so as to rotate in the arrow A direction and includes a negatively charged photosensitive layer 22A on the surface. The outer diameter of the image carrier 22 is 30 mm, for example. The charging device 24, the exposing device 26, the rotary developing device 28, and the cleaning device 46 are arranged around the image carrier 22 in this order in the arrow A direction. A driving source (not illustrated) that drives the image carrier 22 to rotate at a peripheral velocity V1 is also provided.
The charging device 24 is a roller-type charging device that is arranged so as to face the image carrier 22. While the charging device 24 is driven to rotate by the rotating image carrier 22, the charging device 24 charges the surface of the image carrier 22 by applying a charging bias to the surface from a charging-bias power source, which is not illustrated.
The exposing device 26 irradiates the surface of the image carrier 22 having been charged by the charging device 24 with light to form an electrostatic latent image. In this exemplary embodiment, the exposing device 26 includes, for example, multiple light emitting diodes (LEDs, which are not illustrated).
The rotary developing device 28 includes a rotation shaft 28A and developing members 28Y, 28M, 28C, and 28K for yellow (Y), magenta (M), cyan (C), and black (K) arranged around the rotation shaft 28A. The rotary developing device 28 rotates in the arrow C direction around the rotation shaft 28A.
In the rotary developing device 28, each of the developing members 28Y, 28M, 28C, and 28K is positioned at a position opposite the image carrier 22. The rotary developing device 28 then applies a developing bias from a developing bias power source, which is not illustrated, to each electrostatic latent image on the image carrier 22 having been formed by the exposing device 26 in order to sequentially develop the electrostatic latent images into toner images of the different colors.
These developing members 28Y, 28M, 28C, and 28K contain developers of corresponding colors.
The cleaning device 46 recovers toner remaining on the surface of the image carrier 22 without being transferred to the sheet medium P by the transfer device 14, which will be described below, or other extraneous matters from the surface of the image carrier 22. The cleaning device 46 according to the exemplary embodiment is a blade-type cleaner.
Transfer device
Now, description will be given on the transfer device 14 around which a sheet medium P is wrapped and that transfers a toner image having been formed thereon by the image forming unit 12 to the wrapped sheet medium P.
The transfer device 14 includes a transfer drum 30, a leading-end gripper 32, and a trailing-end gripper 34. The transfer drum 30 is taken as an example of a transfer member around which a sheet medium P, to which a toner image on the image carrier 22 is transferred, is wrapped. The leading-end gripper 32 is taken as an example of a leading-end gripping member that grips a leading end portion of the sheet medium P that is wrapped around the transfer drum 30. The trailing-end gripper 34 is taken as an example of a trailing-end controlling member that controls the position of a trailing end portion of the sheet medium P.
The transfer device 14 also includes a sheet sensor 36 that detects a sheet medium P passing thereby, a driving motor M1 (see
The transfer drum 30 arranged so as to face the image carrier 22 includes a rotation shaft 30A, a drum-shaped base portion 30B, and an elastically deformable elastic layer 30C that is formed around the outer peripheral surface of the base portion 30B. The outer diameter of the transfer drum is 119.4 mm, for example.
The elastic layer 30C, from a leading end to a trailing end of the elastic layer 30C in a direction in which the sheet medium P is transported, contiguously lies on the outer periphery of the drum-shaped base portion 30B. A portion of the transfer drum 30, around which even a maximum-size sheet medium P is not wrapped, is a cutout region 30D in which the elastic layer 30C is absent such that a part of the periphery of the elastic layer 30C is cut out.
The dimensions of the components and the positional relationships between the components are determined such that the transfer drum 30 and the image carrier 22 do not contact each other when the cutout region 30D of the transfer drum 30 faces the image carrier 22. A dielectric substance, such as a dielectric sheet, is not attached to the outer peripheral surface of the elastic layer 30C, and thus wrapping of a sheet medium P around the transfer drum 30 does not involve the use of electrostatic attraction.
As illustrated in
At the transfer position Tr, transporting of the sheet medium P that is nipped by the transfer drum 30 and the image carrier 22 is performed dominantly by using electrostatic attraction of the image carrier 22.
As illustrated in
As illustrated in
The sheet sensor 36 is disposed on a side that is further upstream, in the direction in which the sheet medium P is transported, than a stand-by position of the trailing-end gripper 34 (the position of the trailing-end gripper 34 illustrated in
As illustrated in
As illustrated in
The pressing plate 32A extends in a direction of a rotation axis of the transfer drum 30 (or may simply be referred to as a “drum axis direction”, below). For example, the pressing plate 32A is formed by bending a stainless steel plate, and has a single bent portion when viewed in the drum axis direction.
An axis direction of the shaft member 32B is along the drum axis direction. The shaft member 32B, which is cylindrical, is secured to a first end portion of the pressing plate 32A. Accordingly, when the shaft member 32B is rotated, the leading-end gripper 32 moves so as to switch between a gripping state, in which a second end portion of the pressing plate 32A grips the leading end portion of the sheet medium P (see
As illustrated in
As illustrated in
As illustrated in
The sheet controlling portion 34A is made of a film-formed resin material and is elastically deformable. Examples of the resin material include polyethylene terephthalate (PET), polyimide, and fluorocarbon resins.
The holding portions 34B extend in the radial direction of the transfer drum 30 (also simply referred to as a “drum radial direction”, below). The trailing-end gripper 34 also includes wedge-shaped shifting members 34C, whose movement in the drum axis direction causes the sheet controlling portion 34A to move in the drum radial direction via the holding portions 34B.
As illustrated in
In this configuration, when the controlling unit 20 controls a solenoid, which is not illustrated, to move the wedge-shaped shifting members 34C in the drum axis direction and insert each of the wedge-shaped shifting members 34C between one of the holding portions 34B and a corresponding stopper portion 34J, the holding portions 34B are moved in a radially outward direction. With this operation, the sheet controlling portion 34A switches to the releasing state, in which the sheet controlling portion 34A becomes separated from the elastic layer 30C to release the trailing end portion of the sheet medium P (see
On the other hand, when the controlling unit 20 controls a solenoid, which is not illustrated, to move the wedge-shaped shifting members 34C in the drum axis direction and pull out each of the wedge-shaped shifting members 34C from between one of the holding portions 34B and a corresponding stopper portion 34J, the holding portions 34B are moved in a radially inward direction. With this operation, the sheet controlling portion 34A switches to the controlling state in which the sheet controlling portion 34A brings the sheet medium P into contact with the elastic layer 30C such that the sheet medium P contiguously lies on the elastic layer 30C (see
As illustrated in
As described above, since the trailing-end gripper 34 is disposed as a body that is separate from the transfer drum 30, the position of the trailing-end gripper 34 is changeable with respect to the transfer drum 30.
When the leading-end gripper 32 grips the leading end portion of the sheet medium P, the leading-end gripper 32 does not allow the sheet medium P to move in the transporting direction and stops the sheet medium P from being separated from the transfer drum 30. On the other hand, when the trailing-end gripper 34 controls the trailing end portion of the sheet medium P, the trailing-end gripper 34 allows the sheet medium P to move in the transporting direction but stops the sheet medium P from being separated from the transfer drum 30.
The fixing device 16 that fixes a toner image formed on a sheet medium P onto the sheet medium P will be described now.
As illustrated in
When a sheet medium P holding a toner image is nipped between and transported by the heating roller 16A and the pressurizing roller 16B, the toner image is melted and pressurized and is thus fixed onto the sheet medium P.
Discharging rollers 44 are disposed on a side that is further downstream than the fixing device 16 in the direction in which the sheet medium P is transported. The discharging rollers 44 discharge the sheet medium P, having a toner image fixed thereon, to a discharge portion 42 formed on an upper surface of an apparatus body 10A.
Now, the sheet feeding unit 18 that feeds a sheet medium P to the transfer device 14 will be described.
The sheet feeding unit 18 is disposed at a lower portion in the apparatus body 10A of the image forming apparatus 10 and includes a sheet containing member 18A, a pick-up roller 18B, separation rollers 18C, and a leading-end sensor 18D. The sheet containing member 18A contains sheet media P. The pick-up roller 18B picks up the sheet media P from the sheet containing member 18A. The separation rollers 18C separate closely attached sheet media P from each other. The leading-end sensor 18D detects the leading end portion of a sheet medium P passing thereby.
The sheet feeding unit 18 also includes multiple transporting rollers 18E. Each sheet medium P is transported by the transporting rollers 18E along a transport path 40.
In this manner, each sheet medium P is transported along the transport path 40 from the sheet containing member 18A to the feeding-sheet position Pa, which is positioned on a side that is further upstream than the transfer position Tr in the direction of rotation of the transfer drum 30.
Now, operations of the entire configuration will be described.
Firstly, color image data that has been formed by a personal computer or the like, which is not illustrated, is input to an image signal processor (not illustrated) as red (R), green (G), and blue (B) data, for example, and is then subjected to image processing. The image data that has been subjected to image processing is converted into four-color gradation data for yellow (Y), magenta (M), cyan (C), and black (K), which is output to the exposing device 26, so that an image forming operation is started.
With the start of the image forming operation, the image carrier 22 and the transfer drum 30 start rotating together. Here, the peripheral velocity V1 of the image carrier 22 is higher than the peripheral velocity V2 of the transfer drum 30. For example, the peripheral velocity V1 of the image carrier 22 is approximately 0.5% to 1% higher than the peripheral velocity V2 of the transfer drum 30.
At this time, the leading-end gripper 32 and the trailing-end gripper 34 are in the releasing state.
While the leading-end gripper 32 rotates together with the transfer drum 30, the trailing-end gripper 34 remains stationary at the stand-by position without rotating together with the transfer drum 30.
The photosensitive layer 22A of the rotating image carrier 22 is charged by the charging device 24. The exposing device 26 then irradiates the image carrier 22 with light so that an electrostatic latent image for a first color (yellow, for example) based on the image information is formed on the image carrier 22.
Meanwhile, the rotary developing device 28 rotates so that a developing member containing a toner of the color corresponding to the electrostatic latent image to be formed on the image carrier 22 (the yellow developing member 28Y, if the corresponding color is yellow) is positioned at a position opposite the image carrier 22.
Thereafter, the developing member 28Y develops the electrostatic latent image on the image carrier 22 to form a toner image on the image carrier 22. This toner image is transported toward the transfer position Tr, at which the toner image faces the transfer drum 30, with the rotation of the image carrier 22.
With the start of the image forming operation, feeding of a sheet medium P is also started. Specifically, sheet media P that are picked up from the sheet containing member 18A by the pick-up roller 18B are separated by the separation rollers 18C. The separated sheet media P are forwarded to the transport path 40 by the transporting rollers 18E. The leading-end sensor 18D then detects the leading end portion of each sheet medium P passing thereby and transmits a detection signal to the controlling unit 20.
The controlling unit 20 that has received the detection signal controls transportation of the sheet medium P on the basis of the detection signal such that the sheet medium P arrives at the feeding-sheet position Pa at the same time as when the leading-end gripper 32 arrives at the feeding-sheet position Pa (see
Here, at the time of feeding the sheet medium P, information on the size of the sheet medium P that has been detected by a sheet-size sensor (not illustrated) is transmitted to the controlling unit 20.
As illustrated in
The leading-end gripper 32 gripping the sheet medium P then passes a position opposite the stationary trailing-end gripper 34. The leading-end gripper 32 having passed the trailing-end gripper 34 then moves toward the transfer position Tr while gripping the sheet medium P.
The sheet medium P that has passed the transfer position Tr while being gripped by the leading-end gripper 32 is consequently wrapped around the transfer drum 30 while being gripped by the leading-end gripper 32, as illustrated in
The toner image of the first color (yellow, for example) formed on the image carrier 22 is transferred to the sheet medium P on the transfer drum 30 at the transfer position Tr at which the image carrier 22 and the transfer drum 30 face each other. Part of toner remaining on the image carrier 22 after the transfer is recovered from the image carrier 22 by the cleaning device 46 (see
Thereafter, the sheet sensor 36 detects the trailing end portion of the sheet medium P passing thereby. The controlling unit 20 that has received a signal from the sheet sensor 36 sends an instruction to the trailing-end gripper 34.
The trailing-end gripper 34 having received the instruction switches from the releasing state to the controlling state to control the trailing end portion of the sheet medium P. The trailing-end gripper 34 that has switched to the controlling state starts rotating together with the transfer drum 30. In other words, the sheet controlling portion 34A of the trailing-end gripper 34 moves at the same velocity as the peripheral velocity V2 of the transfer drum 30.
As illustrated in
Likewise, forming and developing of latent images for a second and subsequent colors (magenta and cyan, for example), which precede a final color (black, for example), and transferring of toner images corresponding to the latent images is repeated in accordance with the above-described procedure.
As illustrated in
As illustrated in
The sheet medium P whose leading end portion is separated from the transfer drum 30 is transported toward the fixing device 16 illustrated in
As the sheet medium P is transported further, the trailing-end gripper 34 that controls the trailing end portion of the sheet medium P arrives at the stand-by position. At the stand-by position, the trailing-end gripper 34 switches from the controlling state to the releasing state to release the trailing end portion of the sheet medium P. The trailing-end gripper 34 that has switched to the releasing state stops at the stand-by position.
The toner images on the sheet medium P having been transported to the fixing device 16 are fixed onto the sheet medium P by the fixing device 16. As the sheet medium P is transported further, the sheet medium P becomes separated from the transfer drum 30. The sheet medium P is finally discharged to the discharge portion 42 by the discharging rollers 44.
Now, a relationship between L1 and the length of each component will be described, where L1 denotes the peripheral length of the image carrier 22 from an exposure position Ro to the transfer position Tr.
For easy understanding of the relationship between the lengths of components,
In
In
In
Each of the sheet media P1 and P2 is of a maximum size transportable by the transfer drum 30 (legal size, for example, in the exemplary embodiment).
The peripheral length of the transfer drum 30 from the gripping position Pa to the transfer position Tr is denoted by L2. The length of a leading-end margin on a leading-end side of the sheet medium P in which no toner image is formed is denoted by L3. The peripheral length of the transfer drum 30 from a limit position, up to which a toner image is formable, on the trailing-end side of the sheet medium P1 to a limit position, up to which a toner image is formable, on a leading-end side of the sheet medium P2 (this peripheral length is also referred to as an inter-image distance) is denoted by L4 (the distance between the sheet media+the leading-end margin+the trailing-end margin). The peripheral velocity of the image carrier 22 is denoted by the peripheral velocity V1, and the peripheral velocity of the transfer drum 30 is denoted by the peripheral velocity V2. Under the above conditions, the dimensions of components are determined such that the following inequalities (1) and (2) are satisfied:
(L1−L3)×(V2/V1)<L2 (1)
L2 <(L1−L3+L4)×(V2/V1) (2)
The length of the leading-end margin on the leading-end side of the sheet medium P in which a toner image is not formed is a length between the limit position, up to which a toner image is formable, on the leading-end side of the sheet medium P and the leading end of the sheet medium P.
As illustrated in
As illustrated in
As described above, when the configuration satisfies the inequalities (1) and (2), the exposure is started after the leading end portion of a first (preceding) sheet medium P1 is gripped, and the exposure is complete before the leading end portion of a second (subsequent) sheet medium P2 is gripped. In other words, while the exposure is performed, gripping of the leading end portion of the sheet medium P is not performed. This suppresses image defects due to vibration, which occurs through the gripping of the leading end portion of the sheet medium P, being transmitted to the exposure position Ro of the image carrier 22.
In the above case, a sheet medium P of a maximum size is taken into consideration. Accordingly, image defects due to vibration, which occurs through the gripping of the leading end portion of the sheet medium P, being transmitted to the exposure position Ro of the image carrier 22 are also prevented from occurring in sheet media P of any size.
Although the present invention has been described in detail on the basis of a specific exemplary embodiment, it is obvious to those skilled in the art that the present invention is not limited to the exemplary embodiment and that various other exemplary embodiments may be made within the scope of the invention. Although the positional relationships are described by taking the inequalities (1) and (2) as examples in the above exemplary embodiment, other configurations which are based on other formulae are also acceptable if the configurations consequently satisfy these inequalities (1) and (2).
The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-037707 | Feb 2012 | JP | national |
