Patent Application
20170052496
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-160927 filed Aug. 18, 2015.
(i) Technical Field
The present invention relates to a sheet transport apparatus and an image forming apparatus.
(ii) Related Art
In related-art image forming apparatuses, a recording medium is transported from a transfer unit, which transfers a toner image from a photosensitive drum or an intermediate transfer body to the recording medium, to a fixing device or the like.
According to an aspect of the present invention, a sheet transport apparatus includes a first transport device, a second transport device, a first guide member, and a second guide member. The first transport device transports in a transport direction a sheet having one end portion and another end portion in a direction intersecting the transport direction and having a length of a preset value or more in the direction intersecting the transport direction. The second transport device is disposed downstream of the first transport device in the transport direction and transports the sheet. The first guide member has a flat plate shape, has a surface, is disposed between the first transport device and the second transport device such that the second transport device is closer to the first guide member than the first transport device, and guides the sheet to the second transport device. The second guide member is disposed between the first transport device and the second transport device such that the first transport device is closer to the second guide member than the second transport device and guides the sheet to the first guide member while curving the sheet such that the one end portion of the sheet and the other end portion of the sheet are separated from the surface of the first guide member.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Exemplary embodiments of the present invention will be described below with reference to the drawings.
An image forming apparatus 1 according to a first exemplary embodiment is structured as, for example, a color printer. The image forming apparatus 1 includes plural image forming devices 10, an intermediate transfer device 20, a sheet feed device 50, a fixing device 40, and so forth. The image forming devices 10 forms toner images developed by toner included in developer 4. The intermediate transfer device 20 holds the toner images formed by the image forming devices 10 and transports the toner images to a second transfer position where the toner images are transferred onto recording sheets 5 at last through second transfer. The recording sheets 5 each serve as an example of a recording medium. The sheet feed device 50 contains and transports each of the required recording sheets 5 to be supplied to the second transfer position of the intermediate transfer device 20. The fixing device 40 fixes the toner images having been transferred onto the recording sheet 5 through the second transfer performed by the intermediate transfer device 20. Reference numeral 1a of, for example,
The image forming devices 10 include four image forming devices 10Y, 10M, 10C, and 10K that each dedicatedly form a toner image of corresponding one of four colors, that is, yellow (Y), magenta (M), cyan (C), and black (K). These four image forming devices 10 (Y, M, C, and K) are inclined and arranged along a line in an inner space of the body 1a.
Each of the image forming devices 10 (Y, M, C, and K) includes a corresponding one of rotating photosensitive drums 11 as illustrated in
Each of the photosensitive drums 11 includes a grounded cylindrical or columnar base member. The image holding surface having a photoconductive layer (photosensitive layer) made of a photosensitive material is formed on the circumferential surface of the base member. This photosensitive drum 11 is supported such that the photosensitive drum 11 is rotated in a direction indicated by an arrow A by motive power transmitted from a rotational drive device (not illustrated).
The charger 12 includes a contact-type charging roller disposed so as to be in contact with the photosensitive drum 11. A charging voltage is supplied to the charger 12. In the case where the developing device 14 performs reversal development, a voltage or a current the polarity of which is the same as that of the toner supplied from this developing device 14 is supplied as the charging voltage. The charger 12 may be a contactless-type charging device such as a scorotron disposed on the surface of the photosensitive drum 11 in a state in which the charger 12 is not in contact with the photosensitive drum 11.
The light exposure device 13 forms the electrostatic latent image by radiating the light formed in accordance with the image information input to the image forming apparatus 1 to the circumferential surface of the charged photosensitive drum 11. The image information (signal) having been input to the image forming apparatus 1 by an arbitrary device is transmitted to the light exposure device 13 at a time when the latent image is formed.
The light exposure device 13 includes a light-emitting-diode (LED) print head. The LED print head includes plural LEDs as light emitting elements arranged in the axial direction of the photosensitive drum 11 so as to radiate the light in accordance with the image information to the photosensitive drum 11, thereby forming the electrostatic latent image. Alternatively, the light exposure device 13 may use a laser light formed in accordance with the image information to perform deflection scanning in the axial direction of the photosensitive drum 11.
As illustrated in
Each of the first transfer devices 15 (Y, M, C, and K) is a contact-type transfer device that includes a first transfer roller that is in contact with a circumference of the photosensitive drum 11 through an intermediate transfer belt 21 so as to be rotated. A first transfer voltage is supplied to the first transfer roller. As the first transfer voltage, a direct-current voltage the polarity of which is opposite to the polarity to which the toner is charged is supplied from a power unit (not illustrated).
As illustrated in
As illustrated in
The intermediate transfer belt 21 is an endless belt formed of a material including, for example, synthetic resin such as polyimide resin or polyamide resin in which a resistance adjuster or the like such as carbon black is dispersed. The belt support roller 22 serves as a tension applying roller that applies tension to the intermediate transfer belt 21 and also serves as a meandering correction roller that corrects meandering of the intermediate transfer belt 21. The belt support rollers 23 and 24 serve as driven rollers that hold a running position of the intermediate transfer belt 21. The belt support roller 25 serves as a drive roller that is rotated by a drive device (not illustrated) and also serves as a backup roller included in the second transfer unit. The belt support roller 26 serves as a support roller that supports a rear surface of the intermediate transfer belt 21 at a position where the intermediate transfer belt 21 is cleaned by the belt cleaner 27.
As illustrated in
As illustrated in
The fixing device 40 includes components such as a heating rotating body 41 and a pressure rotating body 42. The heating rotating body 41 is in the form of a drum or a belt and is heated by a heating unit so that a surface temperature of the heating rotating body 41 is maintained at a required temperature. The pressure rotating body 42 is in the form of a drum or a belt (in the form of a belt in an example illustrated in, for example,
The sheet feed device 50 is disposed below the image forming devices 10 (Y, M, C, and K) for yellow (Y), magenta (M), cyan (C), and black (K). The sheet feed device 50 includes one or more sheet containers 51 and feed devices 52 and 53. The sheet container 51 or the sheet containers 51 contain the stacked recording sheets 5 of, for example, the size or sizes and the type or types a user wishes to use. The feed devices 52 and 53 feed one sheet after another from the recording sheets 5 in the sheet container 51 or each of the sheet containers 51. The sheet container 51 or the sheet containers 51 are attached so as to allow the sheet container 51 or the sheet containers 51 to be drawn toward, for example, a front surface side (side facing the user who operates the sheet container 51 or the sheet containers 51) of the body 1a which is the left side surface side in an example illustrated in
Examples of the recording sheets 5 include plain paper used for electrophotographic copiers, printers, and so forth, overhead projector (OHP) transparencies, and thin paper such as tracing paper. In order to further improve smoothness of image surfaces after fixing, smoothness of the front side of the recording sheets 5 may be increased as much as possible. For example, coated paper made by coating the upper side of plain paper by resin or the like, so-called cardboard such as art paper for printing having a comparative large basis weight, and the like may also be used. According to classification of paper other than that based on the quality of paper, examples of the recording sheets 5 include paper such as envelopes and postcards having different forms from ordinary recording sheets.
There are various sizes of envelopes. The sizes of envelops are roughly classified into the standard sizes and the non-standard sizes. The sizes of the rectangular type envelopes are, for example, as follows: rectangular type No. 1 (142×332 mm), rectangular type No. 2 (119×277 mm), rectangular type No. 3 (120×235 mm), rectangular type No. 4 (90×205 mm), rectangular type No. 5 (90×185 mm), and so forth. The sizes of postcards are as follows: post office printed postcards (100×148 mm), privately made postcards (short side: 90 to 107 mm×long side: 140 to 154 mm), large-sized postcards having a maximum size (120×235 mm) of the standard-sized sealed letter, and so forth.
A sheet feed transport path 56 is provided between the sheet feed device 50 and the second transfer device 30. The sheet feed transport path 56 includes one or more sheet transport roller pairs 54, a transport guide 55, and so forth. The sheet transport roller pair 54 or the sheet transport roller pairs 54 transport each of the recording sheets 5 fed from the sheet feed device 50 to the second transfer position. The sheet transport roller pair 54 serves as, for example, rollers that adjust timing at which the recording sheet 5 is transported (registration rollers). Furthermore, a first transport guide 58 that serves as an example of a first guide member and a second transport guide 57 that serves as an example of a second guide member are provided between the second transfer device 30 and the fixing device 40. The recording sheet 5 having undergone the second transfer and fed from the second transfer roller 31 of the second transfer device 30 is transported to the fixing device 40 through the first transport guide 58 and the second transport guide 57. Furthermore, a sheet output roller pair 61 is disposed near a sheet output opening formed in the image forming apparatus body 1a. The sheet output roller pair 61 is used for outputting the recording sheet 5 having undergone fixing and fed from the fixing device 40 to a sheet output unit 60 provided in an upper portion of the body 1a along a transport guide 59. The detailed structures of the first and second transport guides 58 and 57 will be described later.
A switching gate 62 is provided between the fixing device 40 and the sheet output roller pair 61. The switching gate 62 switches the sheet transport path. The rotational direction of the sheet output roller pair 61 is switchable between a forward direction (output direction) and a reverse direction. In order to form images on both sides of the recording sheet 5, the rotational direction of the sheet output roller pair 61 is switched from the forward direction (output direction) to the reverse direction after a trailing end of the recording sheet 5 on one side of which an image had been formed has been passed through the switching gate 62. The transport path of the recording sheet 5 to be transported in the reverse direction by the sheet output roller pair 61 is switched by the switching gate 62, so that this recording sheet 5 is transported to a duplex transport path 63 extending in the substantially vertical direction along the side surface of the body 1a. The duplex transport path 63 includes a sheet transport roller pair 64, transport guides 65 to 68, and so forth. The sheet transport roller pair 64 transports the recording sheet 5 in an inverted state to the sheet transport roller pair 54.
Reference numeral 70 of
Furthermore, reference numerals 145 (Y, M, C, and K) of
Furthermore, reference numeral 100 of
Basic image forming operation performed by the image forming apparatus 1 are described below.
Here, an operation in which a full-color image is formed by combining the toner images of four colors (Y, M, C, and K) performed by four image forming devices 10 (Y, M, C, and K) is described.
Upon reception of instruction information requesting the image forming operation (printing), the image forming apparatus 1 starts four image forming devices 10 (Y, M, C, and K), the intermediate transfer device 20, the second transfer device 30, the fixing device 40, and so forth.
Consequently, in the image forming devices 10 (Y, M, C, and K), the photosensitive drums 11 are initially rotated in the arrow A direction, and the chargers 12 charge the surfaces of the respective photosensitive drums 11 to the required polarity (negative polarity according to the first exemplary embodiment) and the required potentials. Next, the light exposure devices 13 radiate the light emitted in accordance with image signals obtained by converting image information input to the image forming apparatus 1 into color components (Y, M, C, and K) to the surfaces of the charged photosensitive drums 11. Thus, the electrostatic latent images for the respective color components having the required potentials are formed on the surfaces of the photosensitive drums 11.
Next, the image forming devices 10 (Y, M, C, and K) each supply the toner of a corresponding one of the colors (Y, M, C, and K) charged to the required polarity (negative polarity) from the developing roller 141 to the electrostatic latent image for the corresponding one of the color components formed on the photosensitive drum 11. Thus, the electrostatic latent image is developed by causing the toner to electrostatically adhere to the photosensitive drum 11. Through this development, the electrostatic latent image for the corresponding one of the color components formed on the photosensitive drum 11 is developed with the toner of the corresponding one of four colors (Y, M, C, and K) and becomes a visual toner image of the color.
Next, when the toner images of the colors formed on the photosensitive drums 11 of the image forming devices 10 (Y, M, C, and K) are transported to the first transfer positions, the first transfer devices 15 transfer the toner images of the colors through the first transfer onto the intermediate transfer belt 21 of the intermediate transfer device 20 rotated in the arrow B direction such that the toner images are sequentially superposed on one another.
The drum cleaners 16 clean the surfaces of the photosensitive drums 11 by removing the adhering matter such that the adhering matter is scraped off from the surfaces of the photosensitive drums 11 in the image forming devices 10 where the first transfer has been performed. Thus, the image forming devices 10 are ready to perform the next image forming operation.
Next, the toner images having been transferred onto the intermediate transfer belt 21 through the first transfer are held and transported to the second transfer position by rotating the intermediate transfer belt 21 in the intermediate transfer device 20. Meanwhile, the sheet feed device 50 feeds the required recording sheet 5 to the sheet feed transport path 56 in accordance with the image forming operation. The recording sheet 5 is fed and supplied to the second transfer position by the sheet transport roller pair 54 or the sheet transport roller pairs 54 serving as the registration rollers at timing adjusted to timing of the transfer in the sheet feed transport path 56.
The second transfer roller 31 of the second transfer device 30 collectively transfers the toner images on the intermediate transfer belt 21 onto the recording sheet 5 through the second transfer at the second transfer position. Furthermore, the belt cleaner 27 cleans the surface of the intermediate transfer belt 21 by removing the adhering matter such as the toner remaining on the surface of the intermediate transfer belt 21 after the second transfer has been performed in the intermediate transfer device 20 having undergone the second transfer.
Next, the recording sheet 5 onto which the toner images have been transferred through the second transfer is removed from the intermediate transfer belt 21 and the second transfer roller 31 and then transported to the fixing device 40 through the first transport guide 58 and the second transport guide 57. The recording sheet 5 having undergone the second transfer is introduced into and passes through the contact portion between the heating rotating body 41 being rotated and the pressure rotating body 42 being rotated so as to be subjected to required fixing processes (heating and application of pressure) in the fixing device 40. Thus, the unfixed toner images are fixed onto the recording sheet 5. At last, in the case of the image forming operation where image formation is performed on only one of the sides of the recording sheet 5, the recording sheet 5 having undergone the fixing is output to the sheet output unit 60 provided in the upper portion of the body 1a by the sheet output roller pair 61.
Furthermore, in the case where images are formed on both sides of the recording sheet 5, the recording sheet 5 on one side of which an image has been formed is not output to the sheet output unit 60 by the sheet output roller pair 61. Instead, the rotational direction of the sheet output roller pair 61 is switched to the reverse direction while the trailing end of the recording sheet 5 is held by the sheet output roller pair 61. The recording sheet 5 transported in the reverse direction by the sheet output roller pair 61 passes through the upper side of the switching gate 62. Then, the recording sheet 5 is inverted while passing through the duplex transport path 63 including the sheet transport roller pair 64, the transport guides 65 to 68, and so forth and transported to the sheet transport roller pair 54 or the sheet transport roller pairs 54. The sheet transport roller pair 54 or the sheet transport roller pairs 54 feed and supply the recording sheet 5 to the second transfer position at timing adjusted to timing of the transfer, so that an image is formed on the back side of the recording sheet 5, and the recording sheet 5 is output to the sheet output unit 60 provided in the upper portion of the body 1a by the sheet output roller pair 61.
Through the above-described operation, the recording sheet 5 is output on which the full-color image made by combining the toner images of four colors has been formed. Of course, the image forming apparatus 1 may also form a monochrome image on the recording sheet 5 by using only the image forming device 10K for black (K).
As illustrated in
The length of the transport path of the recording sheet 5 from the second transfer device 30 to the fixing device 40 is set to be shorter than the length of a minimum-sized recording sheet 5 having a length in the transport direction which is the shortest for the image forming apparatus 1 to be able to form an image. That is, the recording sheet 5 is transported to the fixing device 40 through the first transport guide 58 and the second transport guide 57 by a transport force of the second transfer device 30.
The transport direction of the recording sheet 5 transported by the second transfer device 30 is the same as or substantially the same as a tangent direction at a pressure contact portion between the second transfer roller 31 and the backup roller 25. Furthermore, the transport direction of the recording sheet 5 on the entrance side of the fixing device 40 is the same as or substantially the same as a tangent direction at a pressure contact portion between the heating rotating body 41 and the pressure rotating body 42. According to the present exemplary embodiment, the transport direction of the recording sheet 5 transported by the second transfer device 30 and the transport direction of the recording sheet 5 transported by the fixing device 40 are not linear but form an obtuse angle α which is a required angle. A direction in which the second transport guide 57 guides the recording sheet 5 is set to be coincident with or substantially coincident with the transport direction of the recording sheet 5 transported by the second transfer device 30. Furthermore, a direction in which the first transport guide 58 guides the recording sheet 5 is set to be coincident with or substantially coincident with the transport direction of the recording sheet 5 transported by the fixing device 40.
The recording sheet 5 is transported in a direction along the second transport guide 57 and then brought into contact with the first transport guide 58. This contact with the first transport guide 58 changes the transport direction of the recording sheet 5 to a direction along the first transport guide 58 so as to transport the recording sheet 5 to the fixing device 40. The transport speed of the recording sheet 5 transported by the second transfer device 30 and that transported by the fixing device 40 are set to be the same or set such that the transportation speed of the recording sheet 5 transported by the fixing device 40 is slightly slower than that transported by the second transfer device 30. The recording sheet 5 is curved in the direction along the second transport guide 57 and the first transport guide 58 while being transported between the second transfer device 30 and the fixing device 40.
How the recording sheet 5 is curved while being transported between the second transfer device 30 and the fixing device 40 varies in accordance with arrangement of the second transport guide 57 and the first transport guide 58 and physical properties such as the width and the stiffness (basis weight) of the recording sheet 5. The recording sheet 5 transported by the second transfer device 30 is guided in the direction along the second transport guide 57 and brought into contact with the surface of the first transport guide 58 after the direction of a leading end of the recording sheet 5 is changed to the direction along the first transport guide 58.
The first transport guide 58 has a flat plate shape as illustrated in
The second transport guide 57 is integrally formed of synthetic resin or the like by injection molding. Alternatively, the second transport guide 57 may be partially separately formed. The second transport guide 57 extends from a position separated from the pressure contact portion between the second transfer roller 31 and the backup roller 25 of the second transfer device 30 by a required distance L on the downstream side in the transport direction of the recording sheet 5 to the first transport guide 58.
As illustrated in
As illustrated in
The second guide plates 5712 and 57110 are formed such that, as indicated by two-dot chain lines of
As a result, as illustrated in
The third guide plates 5711 and 57111 are, as illustrated in
As a result, as illustrated in
According to the present exemplary embodiment, as illustrated in
That is, the recording sheet 5 on which the toner images on the intermediate transfer belt 21 have been transferred through the second transfer by the second transfer device 30 is, as illustrated in
How the recording sheet 5 is transported through the second transport guide 57 varies in accordance with the width of the recording sheet 5. When a width W1 of the recording sheet 5 is less than the first threshold w1 (W1<w1), as illustrated in
As illustrated in
Next, when a width W2 of the recording sheet 5 is the first threshold w1 or more and less than the second threshold (w1≦W2<w2), as illustrated in
Thus, the recording sheet 5 having been guided to the first transport guide 58 is guided to the nip of the fixing device 40 as illustrated in
Furthermore, when a width W3 of the recording sheet 5 is the second threshold w2 or more, as illustrated in
Thus, the recording sheet 5 having been guided to the first transport guide 58 is guided to the nip of the fixing device 40 as illustrated in
Thus, even when the recording sheet 5 is thin paper having a comparatively small basis weight, the recording sheet 5 is set in the flat state by the initial contact of the central portion in the width direction of the edge of the leading end of the recording sheet 5 with the surface of the first transport guide 58 having a flat plate shape and the succeeding contact with the surface of the first transport guide 58 having a flat plate shape occurring gradually toward both the end portions of the recording sheet 5 in the width direction.
In contrast, in the case of a related-art sheet transport apparatus, the recording sheet 5 is transported through the first transport guide 58 in such a manner that the printing side of the recording sheet 5 is convex as illustrated in
As has been described, according to the above-described exemplary embodiment, the wrinkling of the recording sheet 5 may be suppressed compared to the case where both the end portions of the recording sheet 5 in the direction intersecting the transport direction is initially brought into contact with the guide member.
As illustrated in
According to the second exemplary embodiment, the transport guide may be easily formed, and accordingly, the production cost may be reduced.
The foregoing description of the exemplary embodiments 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 embodiments were 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 |
|---|---|---|---|
| 2015-160927 | Aug 2015 | JP | national |
