Sheet conveying apparatus

Abstract: The present invention provides a sheet conveying apparatus comprising a convey roller (36) for conveying a sheet (p); a plurality of pinch rollers (37) arranged along the convey roller (36) and adapted to urge the sheet against the convey roller; a pinch roller holder (39) formed as one piece for supporting the plurality of pinch rollers (37), the rigidity of the pinch roller holder (39) in a sheet conveying direction being greater than the rigidity of the pinch roller holder (39) in a direction perpendicular to the sheet conveying direction; and a biasing means (40) for acting on the pinch roller holder (39) to urge the pinch rollers against the convey roller (36).

Description: The present invention relates to a sheet conveying apparatus according to the preamble of claim 1. Such an apparatus is used for conveying a recording sheet in a printer, typewriter, copying machine and the like and a conveying apparatus for conveying an original to be read in a facsimile system, copying machine, image reader, OCR and the like, and is useful for systems wherein a sheet being conveyed should not be floating at a desired position From the document "IBM Technical Disclosure Bulletin", Vol. 13, No. 11, April 1971, page 3539 a generic sheet conveying apparatus is known. This sheet conveying apparatus comprises ball pinch rollers which are urged against a convey roller. Between two pairs of ball pinch rollers there is a cut-out which reduces the rigidity of the ball pinch roller holder in a direction perpendicular to the sheet conveying direction. In the past, sheet conveying apparatuses used with a printer, scanner and the like are mainly of the type wherein pinch rollers are urged against a convey roller comprising a high friction surface member so that a sheet pinched between the convey roller and the pinch rollers is conveyed by friction forces generated between the rollers. According to one aspect, each pinch roller is mounted on a corresponding pinch roller holder made of plastic material and is biased toward a convey roller by a spring and the like. In the conventional sheet conveying apparatuses, it is necessary to provide one pinch roller holder for each pinch roller, and, since any gap must be maintained between the adjacent pinch roller holders, it is very difficult to urge the whole sheet against the convey roller uniformly. Thus, in an apparatus wherein a sheet being conveyed should not be floating at a desired position, there arises a problem if the sheet cannot be uniformly urged against the convey roller. Particularly, in an ink jet printer, since the sheet gets wet due to the ink discharged from a recording head, a recording surface of the sheet is floating, thereby deteriorating the recording quality. To avoid this, a plurality of pinch rollers may be mounted on a single pinch roller holder. In this case, however, if the single pinch roller holder is distorted or twisted, there arises the dispersion in the urging forces of the pinch rollers, thus causing a problem that gaps are created between some pinch rollers and the convey roller. The recording apparatuses can be grouped into ink jet type, wire dot type, thermal type, electrophotographic type or the like on the basis of the recording modes. The recording apparatus of ink jet type has many advantages that it has low noise, low running cost, low apparatus cost, high speed recording ability and compact body. Further, generally, since the recording head is not contacted with the recording sheet, by maintaining a small and constant gap between the recording head and the recording sheet, it is possible to obtain the high image quality. To this end, the recording sheet is held down by pinch rollers arranged near the recording head. In this case, since the recording sheet is held down in the proximity of the recording head, diameters of the pinch rollers are made smaller. However, when the conveyance of the recording sheet and the registration of the recording sheet are effected by using the small pinch rollers and the convey roller, since a nip between each pinch roller and the convey roller is small, if a thick sheet such as a post card is handled, the sheet cannot be adequately pinched between the nips, thereby causing the poor protruded amount and the poor registration. An object of the present invention is to provide a sheet conveying apparatus which can prevent the floating of a sheet to avoid the deterioration of the recording quality. The above object is achieved by the combination of features of claim 1. Preferred embodiments of the subject-matter of claim 1 are set forth in the dependent claims. According to an aspect of the invention there is provided a sheet conveying apparatus comprising a convey roller, a plurality of pinch rollers, and an urging means for urging the pinch rollers against the convey roller, and wherein the urging means serves to afford an urging force to a pinch roller holder which is formed from one-piece and to which the plurality of pinch rollers are attached. The rigidity of the pinch roller holder in a sheet conveying direction is considerably greater than the rigidity of the holder in a direction perpendicular to the sheet conveying direction. That is, the sheet is supported by the convey roller and the pinch roller holder and is conveyed by the pinch rollers urged against the convey roller. The rigidity of the pinch roller holder in the sheet conveying direction is considerably greater than the rigidity of the holder in the direction perpendicular to the sheet conveying direction. Thus, the lateral camber and torsion generated in the manufacture of the pinch roller holder is removed by the urging force acting on the pinch roller holder, thereby preventing the floating of the sheet. In the following, an embodiment of the present invention is described in detail with reference to the accompanied figures. Fig. 1 is a perspective view of a recording apparatus in which a sheet conveying apparatus according to an embodiment of the present invention is used; Fig. 2 is a side sectional view of a sheet conveying mechanism of the recording apparatus; Fig. 3 is a plan view of the sheet conveying mechanism; Fig. 4 is a side sectional view of a pinch roller holder; Fig. 5 is a perspective view showing an alteration of the pinch roller holder; Fig. 6 is a side sectional view showing another alteration of the pinch roller holder; The embodiment of the present invention will be explained with reference to Figs. 1 to 4. This embodiment shows a recording apparatus integrally incorporating an automatic sheet supplying device and comprising a sheet supply portion, a sheet conveying portion, a sheet discharge portion, a carriage portion, and a cleaning portion. First of all, constructions and operations of these portions will be briefly described. Fig. 1 is a perspective view showing a whole construction of the recording apparatus, and Fig. 2 is a sectional view showing the whole construction of the recording apparatus. The sheet supply portion 11 is attached to a body of the recording apparatus at an angle of 30 - 60 degrees. A recording sheet P fed from the sheet supply portion is recorded, and then is discharged horizontally. The sheet supply portion 11 comprises a sheet supply roller 5, separating claws (not shown), a movable side guide 19, a base 20, a pressure plate 21, a compression spring, a release lever 33, and a release cam 35. The recording sheets P are picked up by the rotation of the sheet supply roller 5 and then are separated one by one by the separating claws (not shown). The separated recording sheet P is sent to the sheet conveying portion. The sheet conveying portion 12 comprises a convey roller 36, pinch rollers 37, a pinch roller guide 39, pinch roller springs 40, an upper guide 45 and a platen 46. The recording sheet P sent to the sheet conveying portion 12 is conveyed to a nip between the convey roller 36 and the pinch rollers 37 while being guided by the platen 46, pinch roller guide 39 and upper guide 45. A PE sensor lever (not shown) serves to detect a tip end (leading end) of the recording sheet P, thereby determining a printing position on the recording sheet P. The pinch rollers 37 are urged against the convey roller 36 by biasing the pinch roller guide 39 by the pinch roller springs 40, thereby generating a conveying force for the recording sheet P. The recording sheet P conveyed by the paired rollers 36, 37 is advanced on and along the platen 46 by rotating the paired rollers 36, 37 by an LF motor 47; meanwhile, an image is recorded on the recording sheet by a recording head 49 on the basis of desired image information. The recording head 49 is integrally formed with an ink tank to provide an easily exchangeable ink jet recording head unit. The recording head 49 includes electrothermal converters so that the ink is discharged from an ink discharge opening by utilizing the change in pressure due to growth and contraction of a bubble caused by the film boiling generated when thermal energy is applied to the selected converter. The carriage portion 15 comprises a carriage 50 to which the recording head 49 is attached, a guide shaft 51 for reciprocally guiding the carriage in a direction perpendicular to a sheet conveying direction, a guide 52 for holding a rear end of the carriage and for maintaining a gap between the recording head and the recording sheet, a timing belt 55 for transmitting a driving force of a carriage motor 53 to the carriage 50, idle pulleys 56 for supporting the timing belt 55, and a flexible cable 57 for transmitting a head drive signal from an electric substrate to the recording head 49. The image is recorded on the recording sheet P being conveyed on the platen 46 by scanning the recording head 49 mounted on the carriage 50. The sheet discharge portion comprises a sheet discharge roller 59, a transmission roller 60 for transmitting a driving force of the convey roller 36 to the sheet discharge roller 59, spurs 61 for aiding the sheet discharge, and a discharge tray 62. The recording sheet P can be discharged onto the discharge tray 62 by the discharge roller 59 and the spurs 61 without deteriorating the image recorded on the recording sheet. The cleaning portion 16 comprises a pump 63 for cleaning the recording head 49, a cap 65 for preventing the drying of the recording head 49, and a drive switching arm 66 for switching the driving force from the convey roller 36 between the sheet supply portion 11 and the pump 63. Other than the sheet supplying operation and the cleaning operation, the drive switching arm 66 is positioned as shown in Fig. 1. In this case, since a planetary gear (not shown) which can be rotated around a roller shaft of the convey roller 36 is fixed at a predetermined position, the driving force from the convey roller 36 is not transmitted to both the sheet supply portion 11 and the pump 63. When the drive switching arm 66 is shifted to a direction shown by the arrow A by shifting the carriage 50, the planetary gear is shifted in response to the normal or reverse rotation of the convey roller 36. When the convey roller is rotated normally, the driving force is transmitted to the sheet supply portion, and when the convey roller is rotated reversely, the driving force is transmitted to the pump 63. Further, the LF motor 47 for driving the convey roller 36 and the carriage motor 53 for driving the carriage 50 may be stepping motors which can be rotated by a predetermined angle in response to signals sent from drivers (not shown). Next, a sheet conveying apparatus in this recording apparatus will be explained with reference to Figs. 2 to 4. In the illustrated embodiment, each pinch roller 37 has a length of 50 mm, and five pinch rollers are used so that an urging force can be applied to substantially the whole maximum width (of about 270 mm) of the recording sheet. The pinch rollers 37 are mounted on the pinch roller holder 39 so that they can smoothly rotated. The pinch roller springs 40 are positioned at corresponding portions 39b of pinch roller supporting portions 39a disposed at both ends of the pinch rollers 37, and each spring applies a force of about 400 gf to the pinch roller holder 39. The convey roller 36 has a metal shaft portion 36a, and an EPDM rubber portion (high friction member) 36b fitted around the shaft. A gear 70 for transmitting the driving force from the convey motor 47 to the convey roller 36 and a gear 71 for transmitting the driving force to the planetary gear mounted on the drive switching arm 66 are press-fitted on the shaft portion 36a of the convey roller 36. The pinch roller holder 39 is rotatably received in holes (not shown) formed in the upper guide 45 via a chassis 3. The other end of each pinch roller spring is supported by a corresponding spring receiving portion of the upper guide 45. In this condition, on the basis of the urging forces of the pinch roller springs 40, the ends of each pinch roller are biased by the pinch roller supporting portions 39a, with the result that the pinch rollers 37 are abutted against the rubber portion 36b of the convey roller 36 so that the recording sheet P pinched between the convey roller 36 and the pinch rollers 37 can be conveyed by the high friction conveying force. As shown in Figs. 3 and 4, the rigidity of the pinch holder 39 in the sheet conveying direction is increased and the rigidity of the holder in a direction perpendicular to the sheet conveying direction is positively decreased, by providing longitudinal ribs 39c on the holder. As a result, the lateral camber and torsion generated in the manufacture of the pinch roller holder 39 can be removed very easily by applying the above-mentioned urging forces. In the illustrated embodiment, although the camber amount of the pinch roller holder before assembling is about 20 mm at the most, only by applying the force of about 40 gf to each spring acting point 39b, all of five pinch rollers 37 can be abutted against the rubber portion 36b of the convey roller. That is, only about 10% of the spring force is used to correct the camber, and the other spring force (90% or more) can be used to urge the recording sheet. An alteration of the pinch rollers will be explained with reference to Fig. 5. In this alteration, the pinch roller holder 39 is formnd from a spring metal plate. A plurality of slits 39d are formed in the holder along the sheet conveying direction to decrease the rigidity of the holder in the direction perpendicular to the sheet conveying direction, thereby achieving the effect same as the aforementioned one. The reference numeral 39a denotes a pinch roller supporting portion, and 39d denotes a fitting hole for receiving the pinch roller. Incidentally, in this alteration, the slits 39c may be protruded as shown in Fig. 6 (by drawing) so that the longitudinal rigidity and the widthwise rigidity of the holder can be changed. Further, without ribs, slits or drawing, the longitudinal rigidity and the widthwise rigidity of the holder may be changed by forming the holder with anisotropy material. As mentioned above, according to the illustrated embodiment, since substantially the whole width of the sheet can be urged by the pinch rollers, the floating of the sheet can easily be prevented. Particularly, in an ink jet printer, it is possible to prevent the floating of the recording surface of the recording sheet due to the wetting of the sheet by the discharged ink, thereby preventing the deterioration of the recording quality. Further, since the rigidity of the pinch roller holder in the sheet conveying direction is increased and the rigidity of the holder in the direciton perpendicular to the sheet conveying direction is decreased, the camber and torsion of the holder can be corrected by the small force, and the pinch rollers can be uniformly urged against the convey roller by substantially net of the spring forces. Consequently, the uniform conveying force can be applied to the sheet, thereby conveying the sheet with high accuracy. Further, since the pinch roller holder is formed as one piece, it is possible to reduce the part cost and assembling cost. In addition, by reducing the number of parts, since the increase in reliability can be expected, it is possible to provide a sheet conveying apparatus which is cheap and reliable.

Claims: A sheet conveying apparatus comprising: a convey roller (36) extended in a direction perpendicular to a convey direction for conveying a sheet (P); a plurality of pinch rollers (37) arranged parallel to a longitudinal direction of said convey roller (36) and adapted to urge said sheet (P) against said convey roller (36); an elongate-shape pinch roller holder (39) of an integral construction for supporting said plurality of pinch rollers (37); and a biasing means (40) acting on said pinch roller holder (39) for urging said pinch rollers (37) against said convey roller (36), wherein said pinch roller holder (39) is elongated in the direction perpendicular to the convey direction, characterized in that each of said plurality of pinch rollers has a cylindrical shape extended in the direction perpendicular to the convey direction, and in that at least between the two supporting ends of each of said pinch rollers the rigidity of said pinch roller holder (39) in a sheet conveying direction is greater than the rigidity of said pinch roller holder (39) in a direction perpendicular to the sheet conveying direction. A sheet conveying apparatus according to claim 1, wherein the position where the biasing means (40) applies an urge force onto said pinch roller holder (39) is offset from the position where the pinch rollers (37) are supported in the longitudinal direction of the convey roller (36). A sheet conveying apparatus according to claim 1, wherein said pinch rollers (37), said pinch roller holder (39), and said biasing means (40) are arranged so that the position where said biasing means (40) applies an urge force onto said pinch roller holder (39) and the position of said pinch roller (37) supported by said pinch roller holder (39) are aligned with each other. A sheet conveying apparatus according to claim 1, wherein said pinch roller holder (39) has bearing portions (39a) for rotatably supporting both ends of said pinch rollers (37). A sheet conveying apparatus according to claim 4, wherein said pinch roller holder (39) is pivotably supported at its upstream end in the sheet conveying direction and rotably supports said pinch rollers (37) at its downstream end in the sheet conveying direction. A sheet conveying apparatus according to claim 5, wherein said biasing means (40) creates a biasing force on said pinch roller holder (39) at a position in the proximity of a plane passing through said bearing portions (39a) and extending in parallel with the sheet conveying direction and extending perpendicular to the rotary shaft of said pinch rollers (37). A sheet conveying apparatus according to claim 1, further comprising at least one rib (39c) formed in a single body on said pinch roller holder (39) and extending in the sheet conveying direction. A sheet conveying apparatus according to claim 1, wherein said pinch roller holder (39) is formed from a plate-shaped member in which a slit extending in the sheet conveying direction is formed. A sheet conveying apparatus according to claim 1, wherein positions where said biasing means (40) applies an urge force onto said pinch roller holder (39) correspond to the positions where said pinch rollers (37) are supported by said pinch roller holder (39).

Inventors: HIRAMATSU SOICHI, KAWAKAMI HIDEAKI, KINOSHITA HIROYUKI, NOJIMA TAKASHI, SAIKAWA SATOSHI, SAITO HIROYUKI, SUZUKI TETSUO, TANIGURO MASAHIRO, YANAGI HARUYUKI, HIRAMATSU, SOICHI, KAWAKAMI, HIDEAKI, KINOSHITA, HIROYUKI, NOJIMA, TAKASHI, SAIKAWA, SATOSHI, SAITO, HIROYUKI, SUZUKI, TETSUO, TANIGURO, MASAHIRO, YANAGI, HARUYUKI, HIRAMATSU, SOICHI, C/O CANON KABUSHIKI KAISHA, KAWAKAMI, HIDEAKI, C/O CANON KABUSHIKI KAISHA, KINOSHITA, HIROYUKI, C/O CANON KABUSHIKI KAISHA, NOJIMA, TAKASHI, C/O CANON KABUSHIKI KAISHA, SAIKAWA, SATOSHI, C/O CANON KABUSHIKI KAISHA, SAITO, HIROYUKI, C/O CANON KABUSHIKI KAISHA, SUZUKI, TETSUO, C/O CANON KABUSHIKI KAISHA, TANIGURO, MASAHIRO, C/O CANON KABUSHIKI KAISHA, YANAGI, HARUYUKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: B41J13
IPC codes: B41J13, B41J11