Recording medium conveying mechanism and image forming apparatus using the same

Abstract: In a recording medium conveying mechanism for an image forming apparatus of the present invention, a first and a second rotary body rotate in contact with each other for conveying a paper sheet to which a toner image is to be transferred. The first and second rotary bodies are respectively mounted on the apparatus body and an openable cover mounted on the apparatus body. The second rotary body moves into or out of contact with the first rotary body in interlocked relation to the closing or the opening, respectively, of the cover. The conveying mechanism includes a first support member rotatably supporting the first rotary body on the apparatus body and including a first engaging portion. A second support member rotatably supports the second rotary body on the cover and includes a second engaging portion. The first and second engaging portions mate with each other when the cover is closed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a mechanism arranged in an image forming apparatus for conveying a paper sheet or similar recording medium and an image forming apparatus using the same. Description of the Background Art A copier, facsimile apparatus, printer or similar image forming apparatus includes a mechanism for conveying a paper sheet or similar recording medium with a pair of rotary bodies. The rotary bodies rotate in contact with each other to thereby nip the paper sheet therebetween. The paper sheet sometimes jams a sheet path arranged in the mechanism. In light of this, the mechanism should preferably be so arranged as to facilitate the removal of the jamming sheet. There has been proposed an image forming apparatus in which two rotary bodies rotatable in contact with each other are respectively mounted on the apparatus body and an openable cover or door mounted on the apparatus body. This type of apparatus allows the operator of the apparatus to easily remove a jamming sheet by opening the cover and thereby moving the rotary body mounted thereon away from the other rotary body. The prerequisite with the two rotary bodies is that their axes of rotation be accurately parallel to each other; otherwise, the mechanism is apt to fail to convey a paper sheet straight and often brings about a jam. However, parallelism between the two rotary bodies is difficult to achieve because not only the position of the rotary body on the cover but also the position of the cover relative to the apparatus body and opening and closing operations thereof need certain accuracy. Moreover, even if parallelism is set up between the rotary bodies, the relative position of the rotary bodies varies when the door becomes unstable due to repeated opening and closing. It is therefore extremely difficult to maintain the rotary bodies parallel over a long period of time. To prevent the cover from becoming unstable, a mechanism for opening and closing the cover may be formed of a highly rigid material or use may be made of a mechanism for preventing screws from being loosened. This kind of scheme, however, increases the cost of the apparatus. Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-156798 and 2000-214718. The Japanese patent application JP-A-04-007240 discloses a sheet conveyor. If purpose is to always properly bring a driven roller into press contact with a drive roller by providing a positioning member which positions the driven roller when an openable/closable sheet guide is closed to a side of the drive roller of the paired conveying rollers. Therefore the positioning member comprises a bearing that fits into a fork guide piece. SUMMARY OF THE INVENTION It is an object of the present invention to provide a recording medium conveying mechanism capable of insuring parallelism between two rotary bodies over a long period of time without resorting to any special measure against the instability of an openable cover, and an image forming apparatus using the same. The object is solved by the subject matter of independent claims 1 and 7. The dependent claims are directed to embodiments of advantage. In accordance with the present invention, in a recording medium conveying mechanism for an image forming apparatus, a first and a second rotary body rotate in contact with each other for conveying a paper sheet to which a toner image is to be transferred. The first and second rotary bodies are respectively mounted on the apparatus body and an openable cover mounted on the apparatus body. The second rotary body moves into or out of contact with the first rotary body in interlocked relation to the closing or the opening, respectively, of the cover. The conveying mechanism includes a first support member rotatably supporting the first rotary body on the apparatus body and including a first engaging portion. A second support member rotatably supports the second rotary body on the cover and includes a second engaging portion. The first and second engaging portions mate with each other when the cover is closed. An image forming apparatus including the above mechanism is also disclosed. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which: FIG 1 is a view showing an image forming apparatus embodying the present invention; FIG. 2 is a view showing an openable cover included in the illustrative embodiment in an open position; FIG. 3 is a fragmentary enlarged view of an image forming unit included in the illustrative embodiment; FIG. 4 is a fragmentary enlarged view showing the image forming unit with the cover being opened; FIG. 5 shows part of a side wall included in the image forming unit; FIG. 6 is an isometric view showing one end portion of an image transfer roller and a support member included in the illustrative embodiment; FIG. 7 shows how a recess and a rod portion included in the side wall and support member, respectively, mate with each other; and FIG. 8 demonstrates how the image transfer roller tends to move when rotated in contact with a photoconductive drum and how the roller moves when the cover is opened. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawings, an image forming apparatus embodying the present invention is shown and implemented as an electrophotographic laser printer by way of example. As shown, the printer, generally 200, includes an image forming unit 100 removably mounted to the printer body. The image forming unit 100 includes a photoconductive drum or image carrier 1, a charge roller 2, a developing unit 3, and a cleaning unit 4 for cleaning the drum 1. In the illustrative embodiment, the drum plays the role of a first rotary body. An optical writing unit 6 is positioned at one side of the image forming unit 100 for writing a latent image on the drum 1. The writing unit 6 may be of the conventional type using a semiconductor laser as a light source. In this type of writing unit 6, the semiconductor laser emits a laser beam in accordance with image data representative of a document image, which is read by a scanner. The laser beam, labeled 6a, is routed through a polygonal mirror, which is in rotation, a lens and a mirror to the drum 1, writing a latent image corresponding to the document image. The developing unit 3 develops the latent image with a toner or developer to thereby produce a corresponding toner image. A sheet cassette 7 is positioned below the image forming unit 100 and loaded with a stack of paper sheets or recording media 8. A pickup roller 9 pays out the paper sheets 8 from the sheet cassette 7 one by one toward a registration roller 11. The registration roller 11 once stops the paper sheet 8 and then drives it toward a nip between the drum 1 and an image transfer roller 10 such that the leading edge of the paper sheet 8 meets the leading edge of the toner image formed on the drum 1. In the illustrative embodiment, the image transfer roller 10 plays the role of a second rotary body. A fixing device 16 is positioned above the image forming unit 100 and includes a heat roller 14 and a press roller 15. The heat roller 14 and press roller 15 are pressed against each other at opposite sides of a sheet path 12. The heat roller 14 accommodates a heater 13 therein. An outlet roller 18 is positioned downstream of the fixing device 16 in the direction of sheet conveyance. The top of part of a casing 200a forms a stacker portion 17. The outlet roller 18 drives the paper sheet 8 coming out of a nip between the heat roller 14 and the press roller 15 out of the printer body to the stacker portion 17. A control unit 20 is disposed in the casing 200a for controlling various image forming means joining in the image forming process of the printer 200 as well as print data. The control unit 20 includes a control board loaded with various switches and control circuitry although not shown specifically. The control unit 200 is accommodated in a metallic casing 21, which extends downward from one side of the writing unit 6. In operation, while the drum 1 is in rotation, the charge roller 2 uniformly charges the surface of the drum 1. The writing unit 6 scans the charged surface of the drum 1 with a laser beam in accordance with image data, forming a latent image on the drum 1. The developing unit 3 includes a developing roller 3a on which toner or developer is deposited. The toner deposits on the latent image to thereby form a corresponding toner image. In parallel with the formation of the toner image on the drum 1, the pickup roller 9 pays out one paper sheet 8 from the sheet cassette 7 toward the registration roller 11. The registration roller 11 once stops the paper sheet 8 and then drives it toward the nip between the drum 1 and the image transfer roller 10 (image transfer nip hereinafter) at the previously stated timing. At the above nip, the toner image is transferred from the drum 1 to the paper sheet 8. Subsequently, the paper sheet 8 is brought into contact with a discharge brush 22 and discharged thereby. A peeler is held in contact with the drum 1 at a position slightly downstream of the image transfer nip in the direction of rotation of the drum 1. The peeler contacts the paper sheet 8 and physically peels it off the drum 1. The paper sheet 8 is then conveyed to the fixing unit 16. In the fixing unit 16, the heat roller 14 and press roller 15 nip the paper sheet 8 therebetween and fixes the toner image on the sheet 8 with heat and pressure. The outlet roller 18 conveys the paper sheet with the fixed toner image to the stacker portion 17. After the transfer of the toner image from the drum 1 to the paper sheet 8, the cleaning unit 4 removes the toner left on the drum 1 with a blade 4a. The toner removed by the blade 4a is collected in a case 4b. The casing 200a of the printer 200 supports an openable cover 201 and a manual sheet feed unit 23 via a single shaft 204, which is parallel to the axis of the image transfer roller 10. The openable cover 201 forms one side wall of the casing 200a adjoining the sheet path 12. The manual sheet feed unit 23 allows the operator of the printer to feed a thick sheet, OHP (OverHead Projector) sheet or similar special sheet by hand. The manual sheet feed unit 23 is rotatable about the shaft 204 between an open position indicated by a solid line in FIG. 1 and a closed position indicated by a phantom line. In the closed position, the manual sheet feed unit 23 is received in a space 201c formed in the casing 200a. A pickup roller 24 also feeds the sheet from the manual sheet feed unit 23 toward the registration roller 11. Assume that the operator opens the cover 201 about the shaft 204 clockwise, as viewed in FIG. 1. Then, as shown in FIG. 2, the image transfer roller 10 and discharge brush 22 and a sheet guide 201a, which are mounted on the cover 201, are moved away from the sheet path 12, exposing the sheet path 12 to the outside of the casing 200a. In this condition, the operator can easily mount or dismount the image forming unit 100 to or from the casing 200a, replace the fixing unit 16 or remove the paper sheet 8 jamming the sheet path 12. FIG. 3 is an enlarged view showing the image forming unit 100 together with arrangements around the unit 100. As shown, a protection shutter 101 is journalled to opposite side walls of the image forming unit 100 via a shaft 102. When the cover 201 is closed, the protection shutter 101 intervenes between the fixing device 16 and the drum 1 in order to prevent heat from being transferred from the heat roller 14 to the drum 1. As shown in FIG. 4, when the cover 201 is opened about the shaft 204, the protection shutter 101 automatically rotates about the shaft 102 to a position where it conceals the drum 1 from the outside of the image forming unit 100. Arrangements unique to the illustrative embodiment will be described hereinafter. FIG. 5 shows one side wall 70 of the image forming unit 100. As shown, a notch 70a is formed in one side of the side wall 70 and serves as an engaging portion. The side wall 70 not only forms part of the casing of the image forming unit 100, but also plays the role of a first support member for rotatably supporting the drum 1. FIG. 6 shows one end portion of the image transfer roller 10 and a member supporting it. As shown, a support member or second support member 104 rotatably supports the roller 10 and includes two annular bearing portions 104a and 104b. More specifically, a shaft 10a protruding form the end of the roller 10 is passed through the bearing portions 104a and 104b, so that the roller 10 is rotatably supported. A gear member 103 is positioned between the bearing portions 104a and 104b and formed with a through bore. The shaft 10a is passed through the bore of the gear member 104 as well, as illustrated. The gear member 103 includes a gear portion 103a and a roller portion 103b having a greater diameter than the gear portion 103a. The gear member 103 is affixed to the shaft 10a by a screw or similar fastening means. A gear is also mounted on each end of the drum 1 although not shown specifically. When this gear is brought into mesh with the gear portion 103a of the gear member 103, the rotation of the drum 1 can be transmitted to the image transfer roller 10. When the cover 201 is closed, the roller portion 103b of the gear member 103 abuts against the circumference of the drum 1 to thereby limit the bite of the image transfer roller 10 into the drum 1. It is to be noted that the roller portion of the roller 10 is formed of an elastic material, so that it can bite into the drum 1. The support member 104 additionally includes a cylindrical rod portion 104d and a tie portion 104c. The rod portion 104d extends in the axial direction of the shaft 10a of the image transfer roller 10. The tie portion 104c connects the rod portion 104d and two bearing portions 104a and 104b. As shown in FIG. 7, when the cover 201 is closed, the rod portion, or engaging portion, 104d is brought into engagement with the notch 70a of the side wall 70 under the action of a spring 105. Therefore, even when the cover 201 becomes unstable due to repeated opening and closing, the rod portion 104d and notch 70a cooperate to maintain the image transfer roller 10 parallel to the drum 1 over a long period of time. This obviates the need for a special measure against the instability of the cover 201. The spring 105 biases the image transfer roller 10 against the drum 1. The force of the spring 105 and the arrangement for the spring 105 to bias the support member 104 should preferably be selected in accordance with a force with which the image transfer roller 10 should press the drum 1, a pressure expected to act on the side wall 70, a layout around the support member 104 and so forth. Assume that the gears of the image transfer roller 10 are brought into mesh with, e.g., flange gears mounted on the drum or that the roller portion of the roller 10 is brought into contact with the drum 1 being rotated. Then, rotation transferred from the drum 1 to the roller 10 causes a force tending to move the roller 10 in a direction indicated by an arrow in FIG. 8 to act on the roller 10. As a result, the roller 10 is apt to move away from a preselected position out of parallelism with respect to the drum 1. In the illustrative embodiment, when the roller 10 tends to move in the direction shown in FIG. 8, the edge of the notch 70a of the side wall 70 catches the rod portion 104d of the support member 104 and thereby prevents the roller 10 from moving in the above direction. Therefore, parallelism between the drum 1 and the roller 10 is prevented from being disturbed by the instability of the cover 201 or the dislocation of the roller 10. When the cover 201 is opened, the image transfer roller 10 tends to revolve around the axis of rotation of the cover 201, as indicated by a dashed arrow in FIG. 8. Therefore, the notch 70a and rod portion 104d mating with each other prevent the cover 201 from being opened. This makes an exclusive locking mechanism for the cover 201 needless. The direction in which the image transfer roller 10 revolves at the beginning of opening of the cover 201 and the direction in which the roller 10 tends to move on contacting the drum 1 are coincident only when the cover 201 is held in the closed position. Therefore, the cover 201 does not open when subjected to a relatively weak force ascribable to the contact of the roller 10 with the drum 1 being rotated. However, the operator can easily open the cover 201 after slightly moving it away from the closed position with a relatively strong force. The illustrative embodiment has concentrated on a printer including a first rotary body implemented as the drum 1. However, the present invention is, of course, applicable even to an image forming apparatus in which the first rotary body is implemented as, e.g., an intermediate image transfer drum. In summary, it will be seen that the present invention provides an image forming apparatus having various unprecedented advantages, as enumerated below. (1) When an openable cover is closed, the engaging portion of a first support member mounted on the apparatus body and that of a second support member mounted on the cover mate with each other. Therefore, even when the cover becomes unstable, a second rotary body is surely positioned relative to a first rotary body and maintained parallel to the first rotary body without resorting to a special measure against instability, which would increase the cost of the apparatus. (2) Even when the second rotary body tends to move away from a preselected position due to drive transmitted via gears or contact with the first rotary body being rotated, the engaging portions of the first and second support members mating with each other prevent the second rotary body from moving. This is also successful to maintain the second rotary body parallel to the first rotary body. (3) When the cover tends to open by accident, the engaging portions mating with each other prevent the second rotary body from starting moving together with the cover and thereby prevent the cover from opening. In this sense, the engaging portions constitute a locking mechanism and therefore obviate the need for an exclusive locking mechanism. (4) When the cover is in its closed position, a photoconductive drum and an image transfer drum are maintained parallel to each other and insure straight conveyance of a recording medium over a long period of time. Moreover, straight conveyance protects images from deformation ascribable to the skew of a recording medium. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope of the claims. The present invention relates to an image forming apparatus like a printer, in particular to a toner printer but also to an inkjet printer, a copier, a facsimile device and so on. The first part of the image forming apparatus mentioned in the claims is in particular the apparatus body of the image forming apparatus or a moveable or a removable unit (releasably) linked with the apparatus body. In particular, the first part is stationary while only the second part is moved during the relative movement of the first and second part. In particular, the first and/or the second part is linked or connected or in contact with the apparatus body during this relative movement. The second part of the image forming apparatus mentioned in the claims is in particular a cover or door or moveable tray and so on. The relative movement between the first and second part may be a shifting movement but is preferably a pivoting movement. Preferably, a mechanism links the relative movement of the first and second part with the relative movement of the first and second rotary body. The relative movement of the first and second part is in particular a closing and opening movement, in particular a reciprocating movement. Preferably, the first part and second part are in contact with each other during the relative movement between the first and second position. Preferably, the first and second positions represent the two end positions of the relative movement. Preferably, the first position corresponds to a position where a cover or door is closed. Preferably, the second position corresponds to a position where a door or cover is open. This applies at least, when the first part is the apparatus body. The rotary bodies may comprise drums or rollers for transporting papers like conveying rollers or registration rollers. According to another embodiment, the rotary bodies may comprise fixing rollers, like heating rollers and pressing rollers. According to another embodiment the first and second rotary body may comprise a photoconductive drum and an image transfer roller, respectively. Preferably, the first and/or second support members link or connect the first and/or second rotary bodies with the apparatus body. Preferably, the first and second engagement portion (releasably) block or hinder the relative movement of the first and second part away from the first position into the direction of the second position, when the first and second part is in first position. Preferably, this blocking or hindering is performed by a releasable lock or by providing a certain resistance or frictional force. The term "releasable" means in particular, that an operator may perform the relative movement to release the first and second part by his own force, if the first and second engaging portions are mating with each other. Preferably, the first and second engaging portion define an engagement axis which is parallel to the rotation axis of the rotary bodies. Preferably, this is performed by constituting the engagement portions such that they may easily slide with respect to each other in a rotary direction. Preferably, this rotary direction is at least approximately perpendicular to the relative movement of the first and second engaging portion which results when the first and second part are moved away from the first position. In this way, an easy rotation around the engagement axis is possible while still a (releasable) hindering or blocking of the movement of the first and second part away from the first position is ensured. Preferably, at least one of the first and second support members is constituted such that a pivoting movement is allowed which results in a relative movement of the first and second rotary body towards each other or away from each other. Preferably, the axis of the afore-mentioned pivoting movement corresponds to the afore-mentioned engagement axis of the first and second engaging portion. The direction of relative movement between the first rotary body and the second rotary body has a certain angle to the direction of relative movement of the first part and the second part. This angle is between 45° and 135°, preferably between 80° and 100°, even more preferably around 90° or exactly 90°. This applies at least, when the first and second part are in the first position or are leaving the first position. In this way, the pressing of the first and second roller towards each other is not or nearly not influenced by any relative movement of the first and second part. This results in a stable contact force between the first and second roller. This again results in a reliable transport of the recording medium by the first and second rotary body. Generally, the image forming apparatus is constituted such that the relative movement of the first and second rotary body is in the afore-mentioned ranges of angle (preferably perpendicular) towards the direction of relative movement of the first and second part when the first and second part leaves the first position (towards the second position). Preferably, at least one of the support members is constituted such that it transforms a direction of pressure acting on the support member (e.g. by a spring) in another direction which results in that the afore-mentioned angle is closer or equal to 90° in comparison to the angle between direction of pressure and direction of relative movement of first and second part (when leaving the first position) e.g. by means of a lever arrangement.

Claims: A recording medium conveying mechanism for an image forming apparatus (200) wherein a first (1) and a second (10) rotary body rotate in contact with each other for conveying a recording medium to which an image is to be transferred or has been transferred, said first rotary body (1) and said second rotary body (10) are respectively mountable on or connectable with a first (200a) and second (201) part of said image forming apparatus, said first and second part being moveable relative to each other between a first and second position, said first and second rotary body being constituted to move into or out of contact with each other in interlocked relation to the relative movement of the first and second part into the first position or second position, respectively, said recording medium conveying mechanism comprising: a first support member (70, 100) rotatably supporting said first rotary body (1) on said first part (200a) and including a first engaging portion (70a); and a second support member (104) rotatably supporting said second rotary body (10) on said second part (201) and including a second engaging portion (104d); said first engaging portion (70a) and said second engaging portion (104d) mating with each other when said first and second part are in the first position; characterized in that a movement in order to separate the first (1) and second rotary body (10) is at an angle relative to the movement of the first part (200a) and second part (201) away from the first position towards the second position, wherein said angle is between 45° and 135°, preferably between 80° and 100°, even more preferably around 90°, at least when the first (1) and second rotary body (10) is in a region where both are in contact with each other or are nearly in contact with each other. The mechanism as claimed in claim 1, wherein said first rotary body comprises a photoconductive drum, which is an image carrier on which a toner image is to be formed, and said second rotary body comprises an image transfer roller for transferring said toner image from said photoconductive drum to the recording medium. The mechanism as claimed in claim 1 or 2, wherein said first engaging portion and said second engaging portion are so configured as to prevent, when mating with each other, said second rotary body from moving away from a preselected position due to rotation transmitted to said second rotary body. The mechanism as claimed in any of claims 1 to 3, wherein the first and second engaging portions are constituted to releasably block or hinder a movement of the first and second part away from the first position towards the second position, when the first and second engaging portion mate with each other. The mechanism as claimed in any of claims 1 to 4, wherein the first and second engaging portions are constituted to define an axis of engagement which is at least approximately parallel to both the axis of rotation of the first rotary body and the axis of rotation of the second rotary body, when the first and second engaging portion mate with each other. The mechanism as claimed in claim 5, wherein the first and second engaging portions are constituted such that the first and second rotary body are pivotable relative to each other and wherein the axis of engagement is the axis of the pivoting movement of the first and second rotary body. An image forming apparatus comprising the mechanism of any of claims 1 to 6 and comprising the first and second part which are moveable relative to each other between the first and second position, and wherein the first and second rotary body are mounted to or connected with the first and second part, respectively. The image forming apparatus of claim 7, comprising an apparatus body which is the first part; an image carrier on which a toner image is to be formed; a toner image forming means for forming the toner image on said image carrier; and an openable cover which is the second part and which is mounted on the apparatus body. The image forming apparatus of claim 7 or 8, wherein the first part and/or the second part comprises a pressing member (105) which presses the first rotary body (1) and/or the second rotary body (10) towards each other, respectively and wherein the first support member (70, 100) and/or the second support member (104) transforms the direction of pressure of the pressing member (105) into a relative movement between the first (1) and second rotary body (10) which is at an angle to the movement of the first (200a) and second part (201) away from the first position towards the second position, said angle being closer to 90° than the angle between the direction of pressure of the pressing member (105) and the direction of relative movement of the first part (200a) and the second part (201) when leaving the first position.

Inventors: TANAKA AKIYOSHI, TANAKA, AKIYOSHI
Applicants: RICOH KK, RICOH COMPANY, LTD.
Application year: 2001
Main classification: G03G21
IPC codes: G03G15, G03G21, B65H5