Title:
MEDIUM DISCHARGING MECHANISM AND IMAGE FORMING APPARATUS THAT EMPLOYS THE MEDIUM DISCHARGING MECHANISM
Kind Code:
A1


Abstract:
A medium discharging mechanism includes a first roller, a second roller, and a resiliently deformable member. The second roller is in pressure contact with the first roller to form a nip between the first roller and the second roller. The resiliently deformable member is formed of a resiliently deformable material and is rotatable about a rotating shaft of one of the second roller. The resilient member has a larger diameter than the second roller. The resilient member deforms at the nip such that a surface of the resilient ring is flush with the nip.



Inventors:
Numao, Hiroyuki (Tokyo, JP)
Application Number:
12/539214
Publication Date:
12/03/2009
Filing Date:
08/11/2009
Assignee:
OKI DATA CORPORATION (Tokyo, JP)
Primary Class:
International Classes:
B65H29/20
View Patent Images:



Primary Examiner:
MORRISON, THOMAS A
Attorney, Agent or Firm:
PANITCH SCHWARZE BELISARIO & NADEL LLP (PHILADELPHIA, PA, US)
Claims:
I claim:

1. A medium discharging mechanism, comprising: a first roller; a second roller in contact with said first roller; and a resiliently deformable member mounted to said second roller and including a large diameter than said second roller, said deformable member facing said first roller, wherein said resiliently deformable member includes a diameter that varies along its circumference.

2. The medium discharging mechanism according to claim 1, wherein said first roller is formed of a resilient body and said second roller is formed of a resin material being driven by said first roller to rotate together with said first roller when said first roller rotates.

3. The medium discharging mechanism according to claim 1, wherein said second roller includes an annular groove that is formed in a circumferential surface of said second roller and receives said resilient deformable body therein, the groove being formed at substantially a longitudinally middle portion of said second roller; wherein said resiliently deformable member includes an inner diameter; wherein said the groove includes a bottom surface having a diameter larger than the inner diameter.

4. The medium discharging mechanism according to claim 3, further comprising an urging member by which said second roller is urged against said first roller.

5. The medium discharging mechanism according to claim 1, wherein said second roller is positioned downstream of said first roller with respect to a transport path of the medium and forms a nip between said first roller and said second roller, the nip lying in a plane at an angle with the transport path in which the medium advances toward the nip.

6. The medium discharging mechanism according to claim 1, wherein the diameter varies at a plurality of locations along the circumference of said resiliently deformable member.

7. The medium discharging mechanism according to claim 1, wherein said second roller includes an annular groove formed in a circumferential surface of said second roller and said resiliently deformable member is in the shape of a ring fitted in the annular groove.

8. The medium discharging mechanism according to claim 7, wherein said resiliently deformable member deforms at a nip formed between said first roller and said second roller.

9. The medium discharging mechanism according to claim 8, wherein said resiliently deformable member deforms such that a surface of the resiliently deformable member is flush with the nip.

10. The medium discharging mechanism according to claim 1, wherein said resiliently deformable member is made of urethane foam.

11. The medium discharging mechanism according to claim 1, wherein said medium discharging mechanism is incorporated in an image forming apparatus.

12. The medium discharging mechanism according to claim 1, wherein said resiliently deformable member includes projections and recesses aligned alternately on a circumferential surface of said resiliently deformable member.

13. The medium discharging mechanism according to claim 1, wherein said resiliently deformable member has projections and recesses on its circumferential outer surface such that the projections and recesses form a wavy surface.

14. The medium discharging mechanism according to claim 1, wherein said resiliently deformable member is mounted outside of an area in which said first roller and said second roller are in contact with each other.

15. The medium discharging mechanism according to claim 1, wherein said resiliently deformable member is one of at least two resiliently deformable members mounted on longitudinal end portions of said second roller.

16. The medium discharging mechanism according to claim 1, wherein said second roller is one of a plurality of second rollers that rotate about the rotating shaft, wherein said resiliently deformable member is disposed such that said resiliently deformable member is sandwiched between adjacent second rollers.

17. The medium discharging mechanism according to claim 16, further comprising a weight member that is freely rotatable on the rotating shaft and hangs down from the rotating shaft, wherein when the medium is pulled in between said first roller and said second roller, the leading end of the medium pushes the weight member out of the way so that the weight member presses a surface of the medium until a trailing end of the medium leaves the nip.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser. No. 11/302,691, filed Dec. 14, 2005, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a medium-discharging mechanism and an image-forming apparatus that employs the medium-discharging mechanism.

A conventional image-forming apparatus such as a printer, copying machine, facsimile machine, and plotter is provided with a medium-discharging mechanism for discharging a printed medium. The medium-discharging mechanism includes a discharge roller and a pressure roller in pressure contact with the discharge roller. When the discharge roller is rotated in one direction, the pressure roller is driven to rotate in an opposite direction to the discharge roller such that the printed medium is pulled in therebetween. The printed medium is held between the discharge roller and pressure roller in a sandwiched relation, and is advanced to a stacker.

Once a rear end of the medium has passed through a nip formed between the discharge roller and pressure roller, the discharge roller and pressure roller no longer cause the medium to advance. Thus, the rear end of the medium tends to remain on the pressure roller, blocking the discharging path of the medium. When the rear end of the medium blocks the discharging path, the preceding page of the medium is pushed by the following page to drop from the stacker or resulting in a paper jam.

In order to solve this problem, a vane-like member is disposed at both longitudinal ends of the pressure roller. The vane-like member is formed of a soft material such as rubber or sponge. The vane-like member rotates together with the pressure roller to advance the medium toward stacker.

The vane-like member rotates continuously to hit the medium periodically irrespective of the position of the medium relative to the pressure roller. This gives rise to not only annoying noise but also wear-out of and damage to the vane-like member, thereby decreasing durability of the medium-discharging mechanism.

One conventional medium-discharging mechanism is constructed as follows: A driven gear is provided to a shaft that supports the vane-like member. A drive gear is provided which rotates in mesh with the driven gear on the shaft to drive the vane-like member in rotation. When the medium is being transported through the nip between the pressure roller and the discharge roller, the drive gear is not in mesh with the driven gear. After the rear end of the medium has passed the nip, the drive gear moves into a meshing engagement with the driven gear to drive the vane-like member into rotation. In other words, the drive gear is in mesh with the driven gear only after the medium has passed the nip.

With the aforementioned conventional medium-discharging mechanism, the vane-like member is rotated intermittently. This requires gears to have special shapes, increasing the number of components and complexity of the medium-discharging mechanism. The resulting image-forming apparatus is of large overall size and highly costly.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to solve the aforementioned drawbacks.

Another object of the invention is to provide a medium-discharging mechanism and image-forming apparatus that do not emit annoying noise, improves durability of the medium-discharging mechanism, and is suitable for miniaturizing the device, and reducing the manufacturing cost.

A medium discharging mechanism includes a first roller, a second roller, and a resilient member. The second roller is in pressure contact with the first roller to form a nip between the first roller and the second roller. The resilient member is formed of a resiliently deformable material and is rotatable about a rotating shaft of one of the second roller. The resilient member has a larger diameter than the second roller.

The resiliently deformable member deforms is in the shape of a ring fitted in an annular groove formed in a circumferential surface of the second roller.

The resiliently deformable member deforms at a nip formed between the first roller and the second roller.

The resiliently deformable member deforms at the nip such that a surface of the resilient ring is flush with the nip.

The resiliently deformable member is made of a high friction material.

The resiliently deformable member includes projections and recesses aligned alternately on a circumferential surface of the resiliently deformable member.

The resiliently deformable member has projections and recesses on its circumferential outer surface such that the projections and recesses form a wavy surface.

The resiliently deformable member is mounted outside of an area in which the first roller and the second roller are in contact with each other.

The resiliently deformable member is one of at least two resiliently deformable members mounted on longitudinal end portions of the second roller.

The second roller is one of a plurality of second rollers that rotate about the rotating shaft, wherein the resiliently deformable member is disposed such that the resiliently deformable member is sandwiched between adjacent second rollers.

The medium discharging mechanism further includes a weight that is freely rotatable on the rotating shaft and hangs down from the rotating shaft. When the medium is pulled in between the first roller and the second roller, the leading end of the medium pushes the weight out of the way so that the weight presses on a surface of the medium until a trailing end of the medium leaves the nip.

The first roller and second roller form a nip between them such that the nip lies in a plane at an angle with a transport path in which the medium advances toward the nip.

The first roller and the second roller are positioned so that the first roller is on one side of the transport path and the second roller is on the other side of the transport path, the first roller being upstream of the second roller.

An image forming apparatus incorporates the aforementioned medium discharging mechanism.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a schematic view of a printer according to a first embodiment;

FIG. 2 is a perspective view of a medium discharging mechanism according to the first embodiment;

FIG. 3 is a front view of a pertinent portion of the medium discharging mechanism according to the first embodiment;

FIG. 4A is a perspective view of the medium discharging mechanism;

FIG. 4B is a side view of a pertinent portion of the medium discharging mechanism;

FIG. 5 is an exploded perspective view of a pressure roller;

FIG. 6 illustrates the operation of the medium discharging mechanism;

FIG. 7 illustrates the operation of a medium discharging mechanism according to a second embodiment;

FIG. 8 is an exploded perspective view of a pressure roller according to a third embodiment;

FIG. 9 is a front view illustrating a medium discharging mechanism according to the third embodiment;

FIG. 10 is an exploded perspective view of a pressure roller according to a fourth embodiment; and

FIG. 11 is a front view of a pertinent portion of a medium discharging mechanism according to the fourth embodiment;

FIG. 12 is a perspective view illustrating a medium-discharging mechanism according to a fifth embodiment;

FIG. 13 is a side view of a medium-discharging mechanism according to the fifth embodiment before the paper is pulled in between the discharge roller and the pressure roller;

FIG. 14 is a side view illustrating the positional relation between paper and a weight member; and

FIG. 15 is a perspective view illustrating the positional relation between the paper and the weight member.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail with reference to the accompanying drawings. The image forming apparatus according to the invention will be described in terms of a printer.

First Embodiment

FIG. 1 is a schematic view of a printer according to a first embodiment.

FIG. 2 is a perspective view of a medium-discharging mechanism according to the first embodiment.

Referring to FIG. 1, a printer 11 includes image forming sections 12BK, 12Y, 12M, and 12C for black, yellow, magenta, and cyan images, respectively. Each of the image-forming sections includes a photoconductive drum 13 that bears an image on it. The image-forming section further includes a charging roller 14 that charges the surface of the photoconductive drum 13, a developing unit 16, and a cleaning unit 18, which are disposed to surround the photoconductive drum 13.

An LED head 15 is disposed over the photoconductive drum 13. A transfer unit is disposed under the photoconductive drum 13. The transfer unit includes a transport belt 19 that runs in a direction in which the image-forming sections are aligned, a drive roller 21 that drives the transport belt 19 to run, a driven roller 22 that is driven in rotation when a drive roller 21, and a transfer roller 17 that opposes the photoconductive drum 13 with the medium sandwiched between the transfer roller 17 and photoconductive drum 13.

The charging roller 14 uniformly charges the surface of the photoconductive drum 13. The LED head 15 illuminates the charged surface of the photoconductive drum 13 to form an electrostatic latent image in accordance with printed data. The developing unit holds toner therein and supplies the toner to the electrostatic latent image formed on the photoconductive drum 13, thereby developing the electrostatic latent image into a toner image. Paper 20 is fed from a paper-feeding mechanism 23 and is then attracted to the transport belt 19. The transport belt 19 attracts the paper 20, and advances through the image-forming sections 12BK, 12Y, 12M, and 12C such that toner images of the respective colors are transferred onto the paper 20 in registration, thereby forming a full color toner image.

A paper-feeding mechanism 23 is located at an upstream end in a direction of travel of the paper 20 (i.e., to the right of the driven roller 22). A paper cassette 24 holds a stack of the paper 20. A feed roller 25 separates the top page of the stack of the paper 20 and feeds the top page onto a transport path for the paper 20. A sensor 26 detects the passage of the paper 20. A transport roller 27 opposes the driven roller 22 such that the transport belt 19 is sandwiched between the transport roller 27 and the driven roller 22.

A fixing unit 28 is disposed to the left of the drive roller 21 (i.e., downstream side in a direction of travel of the paper 20). The fixing unit 28 includes a heat roller 29, and a pressure roller 30 in pressure contact with the heat roller 29, and fuses the toner image into a permanent color image.

Referring to FIG. 2, a medium-discharging mechanism is disposed at a downstream of the fixing unit 28. The medium-discharging mechanism includes a frame 37, three discharge rollers 31, three pressure rollers 32, a resilient ring 36A, and a stacker 50. The discharge roller 31 is rotatably supported on the frame 37. The pressure roller 32 is also rotatably supported on the frame 37, and is in pressure contact with the discharge roller 31. The resilient ring 36A is resiliently deformable and is mounted to the pressure roller 32 and pushes the paper 20 toward the stacker 50.

The shaft 31a of the discharge rollers 31 is rotatably supported on the frame 37, and extends through three discharge rollers 31 so that the discharge rollers rotate at three separate locations on the shaft 31a. A discharge guide 38 is formed at a downstream end portion of the frame 37. The three pressure rollers 32 are rotatably supported on the discharge guide 38 and are disposed to oppose the three discharge rollers 31.

The shaft 31a has a gear 40 mounted at its one end portion. The gear 40 is coupled to a motor gear, not shown, mounted on an output shaft of a motor 49 through idle gears 41-47. When the motor 49 rotates, the shaft 31a is rotated.

The discharge rollers 31 and pressure rollers 32 of the medium-discharging mechanism will be described.

FIG. 3 is a front view of a pertinent portion of the medium-discharging mechanism according to the first embodiment. FIG. 5 is an exploded perspective view of the pressure roller 32.

FIG. 6 illustrates the operation of the medium-discharging mechanism.

Referring to FIG. 3, the discharge roller 31 is formed of a resilient material such as silicone rubber, or EPDM rubber. The pressure roller 32 is molded from a resin and has a cylindrical inner space. The discharge roller 31 and pressure roller 32 are in pressure contact with each other to form a nip therebetween. The shaft 33 is supported on the discharge guide 38 and extends through the pressure rollers 32 so that the pressure rollers 32 are free to rotate on the shaft 33.

FIG. 4A is a perspective view of the medium-discharging mechanism. FIG. 4B is a side view of a pertinent portion of the medium-discharging mechanism.

The discharge guide 38 includes a spring assembly 35 mounted to a supporting member, not shown. The spring assembly 35 includes supports 35a and 35b that support the shaft 33, and flat springs 35c and 35d that urge the pressure rollers 32 against the discharge rollers 31.

Referring to FIG. 5, the pressure roller 32 is formed with a circumferential groove 32a at a laterally centered position. The resilient ring 36A is detachably received in the groove 32a, so that the resilient ring 36A is in coaxial alignment with a shaft of the pressure roller 32. The resilient ring 36A is generally ring-shaped and is made of a soft resiliently deformable material such as urethane foam. The resilient ring 36A has an inner diameter smaller than the diameter of the bottom of the groove 32a and has a larger outer diameter than the pressure roller 32. The resilient ring 36A is assembled to fit into the groove 32a of the pressure roller 32, so that the outer surface of the resilient ring 36A projects radially outwardly from the groove 32a. Shortly after the paper 20 leaves the nip formed between the discharge roller 31 and pressure roller 32, the outer surface of the resilient ring 36A pushes the rear end of the paper 20 to advance the paper 20 toward the stacker 50.

The discharge roller 31 and pressure roller 32 are in pressure contact with each other to form a nip between them. The outwardly projecting portion of the resilient ring 36A is pushed back or collapsed so that the outer surface of the resilient ring 36A is flush with the nip area. Therefore, the resilient ring 36A is not obstacle in advancing the paper 20 through the nip.

Referring to FIG. 6, in order to ensure that the paper 20 enters a nip formed between the discharge roller 31 and the resilient ring 36A without difficulty, the paper 20 is fed in a direction B tangent to a circumferential surface of the discharge roller 31 at which the nip is formed. The discharge roller 31 and pressure roller 32 oppose to each other so that the discharge roller 31 is on one side of the transport path 37 of the paper 20 and the pressure roller 32 is on the other side of the transport path 37 and the discharge roller 31 is slightly upstream of the pressure roller 32. Thus, the nip lies in a plane at an angle with a direction B in which the paper 20 is advanced.

The operation of the medium-discharge mechanism of the aforementioned configuration will be described.

When the printer 11 (FIG. 1) receives print data from a host apparatus such as a host computer or a controller, not shown, extracts image data for the respective colors, and feeds the image data to the corresponding image-forming sections. For example, image data for black is sent to the LED head 15 of the image-forming section 12BK. The LED head 15 illuminates the surface of the photoconductive drum 13, charged by the charging roller 14, thereby forming an electrostatic latent image for black on the photoconductive drum 13. Then, the developing unit 16 develops the electrostatic latent image for black into a black toner image.

The paper 20 is fed by the feed roller 25 and is detected by the sensor 26. The transport belt 19 transports the paper 20 in timed relation with the image formation performed at the image forming section 12BK. The transfer roller 17 transfers the black toner image from the photoconductive drum 13 onto the paper 20.

The transport belt 19 further advances, with the paper 20 attracted to it, to the image forming section 12Y for yellow image. The LED head 15 illuminates the surface of the photoconductive drum 13Y charged by the charging roller 14, thereby forming an electrostatic latent image for yellow on the photoconductive drum 13Y. Then, the developing unit 16 develops the electrostatic latent image for yellow into a yellow toner image. The transfer roller 17 transfers the yellow toner image from the photoconductive drum 13Y onto the paper 20.

Likewise, toner images of magenta and cyan are formed in the image forming sections 12M and 12C, respectively. Then, the developing units 16 develop the electrostatic latent images for magenta and cyan into magenta and cyan toner images, respectively. Then, the transfer rollers 17 transfer the magenta and cyan toner images from the photoconductive drums 13M and 13C, respectively, onto the paper 20 in sequence.

When a printing operation is initiated, the motor 49 (FIG. 2) drives the discharge roller 31 in a forward direction and the pressure roller 32 in the opposite direction to the discharge roller 31. At the same time, the resilient ring 36A is driven to rotate in the same direction as the pressure roller 32.

At this moment, as shown in FIG. 6, the resilient ring 36A is pushed back at all times by the discharge roller 31 to ensure that the paper 20 enters the nip between the discharge roller and the pressure roller 32. The resilient ring 36A regains its original shape after it has passed through the nip.

Thus, when the rear end of the paper 20 advances past the nip by the discharge roller 31 and the pressure roller 32, the resilient ring 36A moves into contact engagement with the rear end portion of the paper 20, and then pushes the rear end of the paper 20 onto the stacker 50. This completes a medium discharging operation. The resilient ring 36A is a resiliently, deformable body and has a high friction resistance on its surface. The high friction resistance is advantageous in pushing the rear end of the paper 20.

In the embodiment, the combination of the resilient ring 36A with the pressure roller 32 prevents the paper 20 from being hit periodically by a surrounding mechanical member so that no annoying noise is produced. The resilient ring 36A is in contact with the discharge roller 31 at all times, so that the resilient ring 36A will not wear out or be damaged. This ensures the durability of the discharge roller 31.

The resilient ring 36A is rotated continuously during the medium discharging operation. The continuous rotation of the resilient ring 31 eliminates the need for a gear(s) of a special shape, and therefore reduces the number of components, implements the small overall size of the printer 11, and reduces the manufacturing cost of the printer.

The resilient ring 36A has an inner diameter smaller than the diameter of the groove 32a, which allows the resilient ring 36A to be securely mounted on and dismounted from the pressure roller 32. This facilitates replacement of the resilient ring 36A.

Because the resilient ring 36A is pushed back at the nip between the resilient ring 36A and discharge roller 31, even when the paper 20 has a small thickness, no load is exerted on the paper 20 so that the paper 20 may be advanced smoothly.

Second Embodiment

FIG. 7 illustrates the operation of a medium-discharging mechanism according to a second embodiment.

FIG. 8 is an exploded perspective view of a pressure roller of the medium-discharging mechanism.

A resilient ring 36B according to the second embodiment has projections and recesses on its circumferential outer surface such that the projections and recesses form a wavy surface. The elements similar to those of the first embodiment have been given the same reference numerals and their description is omitted.

Referring to FIG. 7, the resilient ring 36B is formed of a resiliently deformable material such as urethane foam and has projections alternating with recesses to form a wave-shaped outer surface in a circumferential direction of the resilient ring 36B. When the outer surface of the resilient ring 36B enters the nip between the discharge roller 31 and the resilient ring 36B, the resilient ring 36B is resiliently pushed back or collapsed, and then regains its original shape when it appears at the exit side of the nip, i.e., a downstream side of the nip with respect to the direction in which the paper 20 is transported.

The projections and recesses that form a wave along the outer surface of the resilient ring 36B improve the ability of the resilient ring 36B to push the rear end of the paper 20.

Third Embodiment

In the first and second embodiments, the pressure roller 32 is formed with a groove 32a (FIG. 5) therein to which the resilient ring 36A or 36B is fitted. A third embodiment differs from the first and second embodiments in that the pressure roller 32 is divided into two roller segments and a resilient disc 36C is assembled between the roller segments. Elements similar to those in the first and second embodiments have been given the same reference numerals and the description is omitted.

FIG. 9 is a front view illustrating a medium-discharging mechanism according to the third embodiment.

Referring to FIG. 9, a pressure roller 32 includes a roller segment 32a and a roller segment 32b. The resilient disc 36C is resiliently deformable and is sandwiched between the roller segments 32a and 32b. A shaft 33 extends through the roller segments 32a and 32b. The third embodiment eliminates the need for making a groove in the shaft 33, and thus provides an easy-to-make mechanism.

The discharge roller 31 and pressure roller 32 are in pressure contact with each other to form a nip between them. The outwardly projecting portion of the resilient disc 36C is pushed back or collapsed so that the outer surface of the resilient disc 36C is flush with the nip area. Therefore, the resilient disc 36C is not obstacle in advancing the paper 20 through the nip.

Fourth Embodiment

FIG. 10 is an exploded perspective view of a pressure roller according to a fourth embodiment. FIG. 11 is a front view of a pertinent portion of a medium discharging mechanism according to the fourth embodiment. Elements similar to those in the first and second embodiments have been given the same reference numerals and their description is omitted.

Referring to FIG. 10, a pressure roller 52 has a larger length than a discharge roller 31, and laterally centered with respect to the discharge roller 31 such that the longitudinal end portions of the pressure roller 52 extend further than the discharge roller 31. The pressure roller 52 is formed with grooves 52a and 52b such that the discharge roller 31 is between the grooves 52a and 52b. Resilient rings 53a and 53b fit into the grooves 52a and 52b, respectively. The resilient rings 53a and 53b are generally ring-shaped and are made of a soft resilient material such as urethane foam. The resilient rings 53a and 53b have an inner diameter larger than that of the bottoms of the grooves 52a and 52b, and an outer diameter than that of the pressure roller 52.

Because the resilient rings 53a and 53b are not in contact with the discharge roller 31, the resilient rings 53a and 53b are not pushed back at all times and therefore maintains their original shape.

The paper 20 is pulled in between the discharge roller 31 and the pressure roller 32, and is advanced to a stacker. Shortly after the rear end of the paper 20 leaves the nip between the discharge roller 31 and the pressure roller 32, the resilient rings 53a and 53b push the rear end of the paper 20 to the stacker. This completes a medium discharging operation.

The resilient rings 53a and 53b project radially outwardly of the circumferential surface of the pressure roller 52, and causes the paper 20 to flex slightly. This makes the paper 20 slightly rigid in its entirety and is advantageous in transporting the paper 20 in a stable manner.

While the first to fourth embodiments have been described in terms of the resilient rings 36A-36C, 53a, 53b assembled to the pressure rollers 32 and 52, the resilient rings 36A-36C, 53a, 53b may also be assembled to the discharge roller 31 or to both discharge roller 31 and pressure roller 32.

Fifth Embodiment

When the trailing end of paper 20 leaves a medium discharging mechanism, the trailing end tends to be raised from the resilient rings of the first to fourth embodiments. If the paper 20 is soft, then the paper is attracted to a stacker 50 by the Coulomb force. Therefore, the resilient rings alone cannot apply a force to the paper 20 to push the paper 20 away from a medium-discharging mechanism.

FIG. 12 is a perspective view illustrating a medium-discharging mechanism according to a fifth embodiment. Referring to FIG. 12, three discharge rollers 31 are mounted at three separated locations on a shaft 31a. Three pressure rollers 32 are in pressure contact with corresponding discharge rollers 31. A weight member 39 is rotatably mounted on the shaft 31a between adjacent discharge rollers 31, and hangs downward due to its own weight, and rests on a shaft 32c of the pressure rollers 32 (FIG. 13). The paper 20 advances in a direction shown by arrow A.

FIG. 13 is a side view of a medium-discharging mechanism according to a fifth embodiment before the paper 20 is pulled in between the discharge roller 31 and the pressure roller 32.

When the paper 20 advances in the A direction, the leading end of the paper 20 pushes the weight member 39 and causes the weight member 39 to pivot in a direction shown by arrow B against the weight of the weight member 39.

FIG. 14 is a side view illustrating the positional relation between the paper 20 and the weight member 39.

FIG. 15 is a perspective view illustrating the positional relation between the paper 20 and the weight member 39 when the trailing end of the paper 20 leaves the medium discharging mechanism.

When the trailing end of the paper 20 leaves the medium discharging mechanism, the weight 39 is resting on the surface of the paper 20 such that the weight 39 exerts its own weight on the paper 20 in a direction shown by arrow C. The weight 39 presses the trailing end portion of the paper 20 on the resilient rings, allowing the resilient ring 36A to push reliably without idle rotation.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.