BACKGROUND

[0001] In some imaging apparatuses that include a fixing device to fix an image onto a print medium, the fixing device may cause a curl in the print medium,

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Fig. 1 is a schematic block diagram of an example image forming apparatus.

Fig. 2 is a schematic diagram of an example fixing device of an image forming apparatus.

Fig. 3 is a schematic diagram of an example fixing device of an image forming apparatus.

Fig. 4A is a schematic diagram of an example a fixing device of an image forming apparatus.

Fig. 4B is a schematic diagram illustrating a conveyance path for a print medium in the example fixing device shown in Fig. 4A.

Fig. 5 is a schematic diagram of an example curl reduction device.

DETAILED DESCRIPTION

[0003] In some image forming apparatuses, a fixing device may form a curl in a print medium, for example, for example due to toner image contraction caused by cooling or paper sheet expansion caused by moisture absorption. For example, a high-gloss fixing device may operate to heat and subsequently cool a toner image on a sheet of paper, thereby forming a curl in the sheet of paper, which may be difficult to correct after the sheet passes through the high-gloss fixing device.

[0004] In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. [0005] With reference to Fig. 1, an example image forming apparatus 100 includes a paper feeding tray 102, an exposure-developing device 104, a transfer device 108, a fixing device 108 and a paper output tray 110.

[0008] The paper feeding tray 102 includes a tray to store a stack of print media. The exposure-developing device 104 generates a toner image on a photosensitive drum. The exposure-developing device 104 includes, for example, a photosensitive drum, an exposure device to generate an electrostatic latent image on the photosensitive drum, and a developing device to develop the electrostatic latent image on the photosensitive drum with a developer so as to generate a toner image. The transfer device 108 receives a print medium from the paper feeding tray 102 and transfers the toner image on the photosensitive drum to the print medium. The transfer device 106 includes, for example, a transfer roller to transfer a toner image from the photosensitive drum to the print medium. The fixing device 108 receives the print medium having the toner image from the transfer device 106 and applies heat and pressure to the toner image, thereby fixing the toner image on the print medium. An example configuration of the fixing device 108 will be described with reference to Figs. 2 to 4. The paper output tray 110 includes a tray to receive the print medium discharged from the fixing device 108.

[0007] Fig. 2 is illustrates an example fixing device 200 for an image forming apparatus. The example fixing device 200 includes a primary fixing device 210, a curl reduction device 220, and a high-gloss fixing device 230. The primary fixing device 210 receives a print medium P having a toner image T, from the transfer device (cf. Fig. 1) and applies heat and pressure to the toner image T to fix the toner image T on a front face of the print medium P. The curl reduction device 220 receives the print medium P from the primary fixing device 210. The curl reduction device 220 applies a convex curl to the print medium P so that the front face of the print medium P (side with the toner image T) becomes convex, in order to reduce a curl that would be formed in the print medium P subsequently at the high-gloss fixing device 230. The high-gloss fixing device 230 receives the print medium P from the curl reduction device 220 and heats and then cools the fixed toner image T, to impart gloss to the toner image T. [0008] The primary fixing device 210 includes a primary heating roller 212 and a primary pressure roller 214. A primary fixing nip region 218 is defined between the primary heating roller 212 and the primary pressure roller 214. A heater 216 is included inside the primary heating roller 212. The primary pressure roller 214 is disposed in contact with the primary heating roller 212 and Is pressed toward the primary heating roller 212. In order to enhance a heating effect, a heater may be disposed inside the primary pressure roller 214. In some examples, the primary pressure roller 214 is a driving roller that is rotated in an arrow direction by a driving device and the primary heating roller 212 is rotated in conformity with the rotation of the primary pressure roller 214. In other examples, the primary heating roller 212 may be a driving roller that is rotated in an arrow direction by a driving device (not illustrated) and the primary pressure roller 214 may be rotated in conformity with the rotation of the primary heating roller 212. In the primary fixing nip region 218, the toner image T is fixed on the front face of the print medium P by heat and pressure. The print medium P having the fixed toner image T is subsequently sent out toward the curl reduction device 220.

[0009] The curl reduction device 220 includes a conveyance roller 224 to convey the print medium P, and a pair of driven rollers 228, 228. The curl reduction device 220 receives the print medium P having the fixed toner image T from the primary fixing device 210. The conveyance roller 224 is a driving roller that is rotated in an arrow direction by a driving device (not illustrated). The conveyance roller 224 rotates in an arrow direction while the print medium P is held between the conveyance roller 224 and the pair of driven rollers 226, 228 in such a manner that the conveyance roller 224 is in contact with a back face of the print medium P. The pair of driven rollers 228, 228 are rotated in conformity with the rotation of the conveyance roller 224. This allows the curl reduction device 220 to form a convex curl in the print medium P so that the front face of the print medium P becomes convex. Application of the convex curl to the print medium P can reduce a concave curl, which would be subsequently generated at the high-gloss fixing device 230. In addition, since the curl reduction device 220 receives the print medium P with the fixed toner T from the primary fixing device 210, the toner image T is prevented from being damaged at the time when the print medium P is passed through the curl reduction device 220. The print medium P, to which the convex curl has been applied, is subsequently sent out toward the high-gloss fixing device 230.

[0010] The conveyance roller 224 may be hollow inside and the curl reduction device 220 may include, inside the conveyance roller 224, a cooling device 225 to cool the toner image T The cooling device 225 may include for example, a cooling fan, a heat sink or a cooling duct. Cooling of the toner image T increases the tendency of the applied curl to remain on the toner image T, thereby increasing the tendency of the curl to be firmly applied to the print medium P. Alternatively, the fixing device 200 may include a cooling device 225, such as a cooling fan or a cooling duct, disposed outside the curl reduction device 220. In addition, when sufficient cooling is provided in the curl reduction device 220, the cooling device 225 may be omitted.

[0011] The high-gloss fixing device 230 includes an endless belt 231 that is stretched around a secondary heating roller 232, a first tension roller 237 and a second tension roller 238 to move circularly; and a secondary pressure roller 234 to press the print medium P towards the secondary heating roller 232 via the endless belt 231. The second tension roller 238 prevents the endless belt 231 from contacting a cooling device 239. In some examples, the second tension roller 238 may be omitted depending on the size or shape of the cooling device 239. A secondary fixing nip region 233 is defined between the secondary heating roller 232 and the secondary pressure roller 234. The secondary heating roller 232 has a heater 236 located inside the secondary heating roller 232. In order to enhance a heating effect, a heater (not illustrated) may also be disposed inside the secondary pressure roller 234. In one example, the secondary pressure roller 234 is a driving roller that is rotated in an arrow direction by a driving device (not illustrated), and the secondary heating roller 232 is rotated in conformity with the rotation of the secondary pressure roller 234. In this case, the endless belt 231 circularly moves according to the rotation of the secondary pressure roller 234. !n another example, the secondary heating roller 232 may be a driving roller that is rotated in an arrow direction by a driving device (not illustrated) and the secondary pressure roller 234 may be rotated in conformity with the rotation of the secondary heating roller 232. In this case, the endless belt 231 circularly moves according to the rotation of the secondary heating roller 232.

[0012] The first tension roller 237 is disposed at a predetermined distance from the secondary heating roller 232. In the secondary fixing nip region 233, the toner image T is melted by heat from the secondary heating roller 232 and pressed onto an outer peripheral surface of the endless belt 231 by the secondary pressure roller 234. Subsequently, the print medium P is conveyed from the secondary fixing nip region 233 to the first tension roller 237 in a state where the toner image T is affixed onto the outer peripheral surface of the endless belt 231. During the conveyance, the toner image T on the print medium P is cooled and solidified. When going beyond the first tension roller 237, the print medium P is released from the endless belt 231 due to the flexural rigidity of the print medium P and the curve of an outer peripheral surface of the first tension roller 237, and discharged toward a paper output tray.

[0013] In order to impart gloss to the toner image T, the outer peripheral surface of the endless belt 231 may be formed of a high reieasability material such as a fluorine resin, and processed so as to have a mirror surface. In addition, the high-gloss fixing device 230 may include the cooling device 239 to enhance a cooling efficiency. The cooling device 239 may include a cooling duct, a heat sink or a cooling fan, which is disposed inside the endless belt 231. However, when sufficient cooiing is provided in the high-gloss fixing device 230, the cooling device 239 may be omitted.

[0014] The fixing device 200 includes a first conveyance path 240 to convey the print medium P from the primary fixing device 210 to the curl reduction device 220, and a second conveyance path 242 to convey the print medium P from the curi reduction device 220 to the high-gloss fixing device 230. Each of the first and second conveyance paths 240, 242 may be substantially flat (planar) or linear. Providing a flat conveyance path for the print medium P can prevent a curl from being applied to the print medium P during conveyance.

[0015] The fixing device 200 may include a pair of guide plates 250 disposed at an inlet of the primary fixing device 210 to guide the print medium P to the primary fixing device 210, a pair of guide plates 254 disposed at an inlet of the curl reduction device 220 to guide the print medium P to the curl reduction device 220, and a pair of guide plates 252 disposed an inlet of the high-gloss fixing device 230 to guide the print medium P to the high-gloss fixing device 230. The guide plates 250 may be disposed to define therebetween a space that is tapered toward the primary fixing device 210. The guide plates 254 may be disposed to define therebetween a space that is tapered toward the curl reduction device 220. The guide plates 252 may be disposed to define therebetween a space that is tapered toward the high-gloss fixing device 230. A minimum distance D ₂ between the guide plates 252 can be less than a minimum distance D ₁ between the guide plates 250. This is because the toner image T is already fixed onto the print medium P at the inlet of the high-gloss fixing device 230 and the toner image T is less likely to be damaged even when the guide plates 252 contact the image. The narrower distance Da of the guide plates 252 may be set to guide the print medium P to the secondary fixing nip region 233 in a suitable shape, as the print medium P may have an unstable behavior because of a given convex curl.

[0016] Fig. 3 is a view showing a fixing device 300 of an image forming apparatus according to another example. The fixing device 300 is similar to the fixing device 200 shown in Fig. 2, with some differences, including that a first conveyance path 340 extends along a first tangent between a conveyance roller 324 and a first driven roller 326 in a curl reduction device 320, and that a second conveyance path 342 extends along a second tangent between a conveyance roller 324 and a second driven roller 328 in the curl reduction device 320. This can prevent an unnecessary curl from being applied to a print medium P when the print medium P goes into and out of the curl reduction device 320. The first driven roller 326 is a driven roller 326 disposed upstream in a rotational direction of the conveyance roller 324, and the second driven roller 328 is a driven roller 328 disposed downstream in the rotational direction of the conveyance roller 324. Components of the fixing device 300 that are similar to those of the fixing device 200, are each identified with a reference numeral obtained by adding "100" to the reference numeral of the similar component of the fixing device 200, and overlapping description is omitted.

[0017] Fig. 4A is a view showing a fixing device 400 of an image forming apparatus according to another example. The fixing device 400 is similar to the fixing device 200 shown in Fig. 2, with some differences, including that the fixing device 400 is configured so as to receive the print medium P from a lower part of the fixing device 400 and discharge the print medium P in a substantially lateral direction toward a paper output tray, and that each of first and second conveyance paths 440 and 442 has a curve that can apply a concave curl to the print medium P so that a front face of the print medium (side with the toner image T) becomes concave. The fixing device 400 allows a paper output tray to be provided, for example, at an upper portion of the image forming apparatus, thus enabling a size reduction of the image forming apparatus.

[0018] Fig. 4B is a schematic view showing the conveyance path for the print medium P in the fixing device 400, in which some of the components illustrated in Fig. 4A are omitted. The first conveyance path 440 has a curve to apply a concave curl to the print medium P so that the front face of the print medium P becomes concave, and a minimum curvature radius r1 of the curve may be greater than a curvature radius r3 of an outer peripheral surface of a conveyance roller 424 of a curl reduction device 420. Similarly, the second conveyance path 442 has a curve to apply a concave cur! to the print medium P so that the front face of the print medium P becomes concave and a minimum curvature radius r2 of the curve may be greater than a curvature radius r3 of the outer peripheral surface of the conveyance roller 424 of the curl reduction device 420. The curve of the first and second conveyance paths 440, 442 may be sized accordingly, so as to reduce an influence of a concave curl that decreases an effect of the curl reduction device 420, which occurs during conveyance of the print medium P.

[0019] In addition, the minimum curvature radius r2 of the curve in the second conveyance path 442 may be greater than the minimum curvature radius r1 of the curve in the first conveyance path 440. Forming a sharper curve upstream of the curl reduction device 420 if possible, can further reduce an influence of a concave curl that decreases an effect of the curl reduction device 420.

[0020] Components of the fixing device 400 that are similar to those of the fixing device 200, are each identified with a reference numeral obtained by adding "200” to a reference numeral of the similar component of the fixing device 200, and overlapping description is omitted.

[0021] Fig. 5 is a view showing a curl reduction device 500 according to one example. The curl reduction device 500 includes a conveyance roller 502 to convey the print medium P, a pair of driven rollers 504, 506 disposed to contact an outer peripheral surface of the conveyance roller 502, and a guide member 508 to guide the conveyance of the print medium P between the driven rollers 504, 506. The guide member 508 has a guide face 510 disposed between the first and second driven rollers 504, 506 to face an outer peripheral surface of the conveyance roller 502. The curl reduction device 500 receives the print medium P having the fixed toner image T from the primary fixing device (not illustrated). The conveyance roller 502 is a driving roller that is rotated in an arrow direction by a driving device (not illustrated).

[0022] The conveyance roller 502 rotates while holding the print medium P between the conveyance roller 502 and the pair of driven rollers 504 and 506 in a manner that the conveyance roller 502 makes contact with a back face of the print medium P (a face opposite to that of the toner image T). The driven rollers 504 and 506 are rotated in accordance with the rotation of the conveyance roller 502. This allows the curl reduction device 500 to apply a convex curl to the print medium P so that a front face of the print medium P becomes convex. At this time, the print medium P held between and by the conveyance roller 502 and the first driven roller 504 is guided by the guide face 510 toward and between the conveyance roller 502 and the second driven roller 506. The print medium P, to which the convex curl has been applied, is subsequently sent out toward the high-gloss fixing device (not illustrated).

[0023] The guide face 510 may have an inclination from a vertical plane relative to the radial direction of the conveyance roller 502 to more smoothly guide the print medium P. For example, a first inclination angle Q1 is a smaller angle among angles formed at the point where a first tangent L31 between outer peripheral surfaces of the conveyance roller 502 and the first driven roller 504 intersects a line L35 along the guide face 510. Namely, the first tangent L31 and the line 135 intersect to form substantially two pair of equal angles, among which the smaller angle corresponds to the first inclination angle 01. According to examples, the first inclination angle Q1 may be set between 30 and 50 degrees. In addition, a second inclination angle 02 is a smaller angle among angles formed at the point where a second tangent L32 between outer peripheral surfaces of the conveyance roller 502 and the second driven roller 506 intersects the line L35 along the guide face 510. Namely, the second tangent L32 and the line L35 intersect to form substantially two pair of equal angles, among which the smaller angle corresponds to the second inclination angle Q2. According to examples, the second inclination angle 02 may be set between 10 and 30 degrees.

[0024] The size of a curl that is applied by the curl reduction device 500 can be adjusted by varying a distance between the first driven roller 504 and the second driven roller 506. An increase of the distance between the first driven roller 504 and the second driven roller 506 enlarges a curl to be formed in the print medium P by the curl reduction device 500 while a reduction of the distance therebetween diminishes the curl to be formed in the print medium P. The size of a curl to be applied by the curl reduction device 500 may be determined based on the size of a curl generated at the high-gloss fixing device. For example, the size of a curl to be applied by the curl reduction device 500 may be set to such a size that substantially cancels (or prevents) the formation of a concave curl at the high-gloss fixing device. Additionally, in some examples, guide member 508 may be omitted depending on the distance between the first driven roller 504 and the second driven roller 506.

[0025] The conveyance roller 502 may be hollow inside and the curl reduction device 500 may include, inside the conveyance roller 502, a cooling device (not illustrated), such as a cooling fan, a heat sink or a cooling duct, to cool the toner image T. Cooling of the toner image T increases the tendency of the applied curl to remain on the toner image T, thereby increasing the tendency of the curl to be firmly applied to the print medium P.

[0026] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.