Paper conveying roller for image forming apparatus

Abstract: Disclosed is a paper conveying roller for image forming apparatus composed of a lower unit and an upper unit which is rotatably pivoted on said lower unit, having a paper conveying passage formed on the boundary surface of these upper and lower units, with one of a pair of paper conveying rollers disposed on the upper unit and the other one on the lower unit, wherein one of said paper conveying rollers (12) is supported by a spring (13).

Description: This invention relates to an image forming apparatus which has mutually separable body members comprising upper and lower units, with the upper unit rotatably supported on the lower unit. In such an apparatus, the units are separable to reveal a sheet conveying path formed where they meet, with one of a pair of sheet conveying roller means disposed on the upper unit and the other one on the lower unit. A sheet conveying apparatus used in an image forming apparatus such as a copying machine comprises a pair of sheet conveying rollers, conveying guide, etc. The sheet conveying path including these sheet conveying rollers and conveying guides leads from the sheet feed part to the sheet discharge part of the image forming apparatus, and an image forming process is performed on the sheet during its passage along the path. In a copying machine, for example, a photosensitive drum is disposed within the sheet conveying path, and the sheet being conveyed is caused to contact with the surface of the photosensitive drum in the transfer process during copying process, and the electrostatic toner image formed on the photoreceptor is transferred onto the sheet. In such a composed copying machine, in order to transfer the electrostatic toner image formed on the surface of photosensitive drum onto a correct position on the sheet, the conveying of the sheet must be synchronised accurately with the rotation of the photosensitive drum. On the other hand, it is known, for the ease of removal of a jammed sheet, for example, in an image forming apparatus, to divide the apparatus into upper and lower units, the upper unit being rotatably pivoted on the lower unit while a sheet conveying passage is formed at the boundary between the upper and lower units. In such image forming apparatus, one of a pair of paper conveying rollers in the paper conveying passage is disposed on the upper unit and the other one is on the lower unit. Generally, in the conventional image forming apparatus having such constitution, since the mounting positions of the shafts of the upper and lower rollers of the paper conveying rollers are completely fixed on the upper unit and lower unit, the relative positions of these rollers and the roller contacting pressures vary depending on the opening or closing state of the upper and lower units, and the capacity of the paper conveying passage is not stable. As a result, jamming tends to occur and/or the transfer position of the electrostatic toner image is not constant. DE-A-3 041 971 discloses an apparatus according to the preamble of claim 1. The rollers in the upper body member are spring-biased against the rollers in the lower body member. A problem of such an apparatus can be seen in the rigid mounting structure of the rollers on their axes. This problem is solved by the features in the characterizing portion of claim 1. US-A-1 897 054 discloses an apparatus having counter pressure members for sheet feeding and comprising a coil spring on which a roller is rotatably mounted, allowing movement of said roller in a direction perpendicular to the axis of the coil spring so as to compensate for variation in sheet thickness. A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, wherein : Fig. 1 is a perspective view of a lower sheet feed roller means of a sheet conveying apparatus in accordance with this invention ; Fig. 2 is a schematic sectional view of a copying machine to which the apparatus of Fig. 1 is applicable, shown in the open state ; and Fig. 3 shows the copying machine of Fig. 2 in the closed state. The copying machine shown in Figs. 2 and 3 comprises a lower unit A and an upper unit B. The upper unit B is supported on and pivoted to the lower unit A at fulcrum P, about which such upper unit B can rotate. The upper unit B includes a replacement unit 5 which integrally comprises a photosensitive drum 1, a primary charger 2, a cleaner unit 3, and a separation roller 4. This replacement unit can be freely attached to or detached from the upper unit B by means of a suitable detaching mechanism (not shown). Above this replacement unit 5 is disposed an optical system 6 consisting of a light source 60 and a focusing light transmitter 61. A developing device 7 comprising first developing part 70 and second developing part 71 is rotatably provided to the right of the photosensitive drum, as shown in the figures. The first developing part 70 and second developing part 71 are filled with toners of different colours, and a selected one of these developing parts may be brought into a position facing the photosensitive drum 1 by rotating the developing device. Ahead of the photosensitive drum 1, there is a paper sheet conveying guide 8, and a timing roller (PS roller) 9 and a sheet feed roller 11 are mounted on this guide, while a hand feed paper sheet detection switch 10 is provided at the right end of the upper unit B. In the upper right part of the lower unit A, there is a sheet conveying guide 15, and on this sheet conveying guide 15 are mounted a lower PS roller 16 opposite to the PS roller 9 of the upper unit B, and a lower sheet feed roller 12 opposite to said sheet feed roller 11. To the left of the PS roller 16 there is a transfer device 17 which faces the photosensitive drum 1 when the upper and lower units A, B are closed relative to each other, and to its left, a conveying guide 18 for conveying the transfer sheet is provided. A fixing roller 19 is disposed to the left of this conveying guide 18, and a discharge sheet detection switch 20 is disposed to the left of the fixing roller 19 for detecting the sheet discharged from the fixing roller. Furthermore, a sheet feed cassette 21 is detachably mounted at the bottom of this lower unit and at its sheet feed part there is provided a sheet feed roller 22. The paper sheet supplied from the sheet feed cassette 21 to the sheet feed roller 22, is conveyed up to the transfer part of the photosensitive drum 1 by way of said sheet feed rollers 11, 12, sheet conveying guides 8, 15 and PS rollers 9, 16. Said sheet conveying guides 8, 15, 18 are provided at the boundary between the upper and lower units A, B as shown in the drawing, and a sheet conveying path is formed thereby. Of the sheet feed rollers and PS rollers, the upper side rollers 11, 9 are mounted on the upper unit B and the lower side rollers 12, 16 are mounted on the lower unit A. Fig. 1 shows the mounting of the lower sheet feed roller 12 on the lower unit A. The lower sheet feed roller 12 is in fact constituted in this embodiment by four rollers 12a to 12d mounted parallel to the rotary shaft of the photosensitive drum 1. Coil springs 13a, 13b extend axially through the rollers 12a, 12b, respectively, each said spring being anchored at its opposite ends to respective pairs of support parts 14a, 14b, and 14c, 14d formed on the paper conveying guide 15. In this structure, the rollers 12a, 12b can rotate about the respective springs 13a, 13b, and are also displaceable by the action of the springs. The rollers 12c, 12d are supported by a common spring 13c. These rollers 12c, 12d are also rotatable about the spring 13c, and are also displaceable by the action of the spring. In this embodiment, thus, the lower sheet feed roller means 12 of a pair of paper feed roller means 11, 12 is supported by spring means 13 (13a to 13c). Therefore, when the upper and lower units A, B are dosed onto each other, if the position of the upper sheet feed roller 11 is deviated for any reason, this deviation is absorbed by the spring 13. That is, the contact position and contact pressure of the upper and lower sheet feed rollers 11, 12 are always constant. Accordingly, fluctuations of conveying force by the sheet feed rollers may be reduced, and stable paper conveyance may be achieved. Incidentally, rollers other than the driving roller of PS rollers 9, 16 may also be spring mounted in a manner as shown in Fig. 1. As described above, therefore, by spring-mounting one of the sheet conveying rollers according to the invention, if the position of the other roller opposite to this roller should be deviated, this deviation will be absorbed by the spring, and the contact position and contact pressure of the two rollers can be kept constant. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the present invention as claimed.

Claims: An image recording apparatus having a lower body member (A), an upper body member (B) hingedly connected to the lower body member for movement between a lowered, body closed position, and a raised body open position, and a sheet conveying device (8, 15, 11, 12) for conveying a sheet along a sheet feed path in said apparatus, said sheet conveying device comprising first and second roller means (11, 12) constituting drive means for advancing the sheet and mounted respectively on said upper and lower body members, said first and second roller means forming a nip for the sheet in said body closed position and being separated in said body open position, wherein one of said roller means (12) is spring biassed against the other (11) in said body closed position for regulation of the pinch pressure applied to the sheet, characterised in that said first and second roller means (11, 12) are mounted on respective sheet conveying guides (8, 15) which are provided on respective ones of said upper and lower body members and which form said sheet feed path in said body closed position, in that said one of said roller means comprises a plurality of axially aligned rollers (12a, 12b, 12c, 12d), and in that said spring means is constituted by a plurality of aligned elongate coil springs (13a, 13b, 13c) each extending axially through at least one of said rollers (12a, 12b, 12c, 12d) rotatably mounted thereon and each anchored at its opposite ends to a respective pair of support parts on the associated sheet conveying guide (15). An image recording apparatus according to claim 1, characterised in that said one of said roller means includes two rollers (12c, 12d) with a common said elongate coil spring (13c) extending axially through them.

Inventors: MASARU TSUJI, MASARU, TSUJI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1987
Main classification: G03G15
IPC codes: G03G15, B65H20, B65H5, G03G21