Image forming apparatus

An image forming apparatus includes a discharge rollers pair, a sheet pressing member and a discharge tray. The sheet pressing member includes a first rotational shaft, a detection piece and a corrugation piece. The corrugation piece protrudes in a radial direction different from a protruding direction of the detection piece from the first rotational shaft. When the detection piece is turned at a first angle into a first posture, the corrugation piece is changed into a contact posture where the corrugation piece comes into contact with the sheet to apply stiffness on the sheet. When the detection piece is turned at a second angle into a second posture, the corrugation piece is changed into a retracting posture where the corrugation piece separates from the sheet.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese patent application No. 2018-139443 filed on Jul. 25, 2018, which is incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to an image forming apparatus including a sheet discharging device configured to discharge a sheet on which an image is formed.

A sheet discharging device of an image forming apparatus is frequently provided with a corrugation piece which applies stiffness on a sheet during the sheet discharging in order to prevent the discharged sheet from being displaced. On the other hand, in a case where the sheet is switched back for duplex printing, if the sheet is applied with stiffness by the corrugation piece, an abnormal sound sometimes occurs when the sheet is conveyed along an inversion path.

Then, the corrugation piece is sometimes configured to be switchable into a corrugation applicable state and a corrugation non-applicable state. Alternatively, a sheet detecting device for detecting a height of sheets stacked on a discharge tray is sometimes provided with a corrugation part (the corrugation piece).

However, the former case requires a drive source (for example, a solenoid) for switching the corrugation piece into the corrugation applicable state and the corrugation non-applicable state. The later case has no measure for the abnormal sound when the sheet is switched back.

SUMMARY

In accordance with an aspect of the present disclosure, an image forming apparatus includes a discharge rollers pair, a sheet pressing member and a discharge tray. The discharge rollers pair is configured to discharge and switch back a sheet at a discharge port. The sheet pressing member is configured to press an upper face of the sheet discharged by the discharge rollers pair. On the discharge tray, the sheet discharged through the discharge port is stacked. The sheet pressing member includes a first rotational shaft, a detection piece and a corrugation applying piece. The first rotational shaft is supported above the discharge port along a width direction perpendicular to a discharge direction. The detection piece protrudes in a radial direction from the first rotational shaft and supported in an initial posture where the detection piece protrudes toward the discharge tray across the discharge port. The detection piece is turnable into a first posture where the detection piece is pushed up by the sheet discharged at a predetermined discharge angle and then turned at a first angle with respect to the initial state and into a second posture where the detection piece is pushed up by the sheet switched back at a predetermined inversion angle and then turned at a second angle different from the first angle with respect to the initial state. The corrugation applying piece protrudes in a radial direction different from a protruding direction of the detection piece from the first rotational shaft, is rotatable together with the detection piece and is configured to come into contact with the discharged sheet from an upper side to apply stiffness to the sheet. When the detection piece is turned at the first posture, the corrugation applying piece is changed into a contact posture where the corrugation applying piece comes into contact with the sheet to apply stiffness on the sheet. When the detection piece is turned at the second posture, the corrugation piece is changed into a retracting posture where the corrugation piece separates from the sheet.

DETAILED DESCRIPTION

Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

First, with reference toFIG. 1, an entire structure of a color printer1as an image forming apparatus will be described.FIG. 1is a front view schematically showing the color printer1. In the following description, a near side (a front side) of a paper surface ofFIG. 1is defined to be a front side of the color printer1, and a left-and-right direction is defined based on a direction in which the color printer1is viewed from the front side. In each figure, Fr and Rr respectively show a front side and a rear side of the color printer1.

An apparatus main body2of the color printer1is provided with a sheet feeding cassette5in which a sheet is stored, a sheet feeding device7configured to feed the sheet from the sheet feeding cassette5, an image forming part9configured to form a full color toner image on the fed sheet, a fixing device11configured to fix the toner image on the sheet, a sheet discharging device13configured to discharge the sheet on which the toner image is fixed and an discharge tray15on which the discharged sheet is stacked.

In the apparatus main body2, a one-side printing path17, a double-side printing path19and a common path21are formed. The one-side printing path17is formed so as to extend from the sheet feeding device7through the image forming part9to a branch part B at the downstream side of the fixing device11. The double-side printing path19is formed so as to branch from the one-side printing path17at the branch part B and join to the one-side printing path17between the sheet feeding device7and the image forming part9. The common path21is formed between the branch part B and the sheet discharging device13.

At the branch part B, an intermediate roller23and a branch guide25are provided. The branch guide25is supported by a rotational shaft of the intermediate roller23in a turnable manner. With the intermediate roller23, a one-side side conveyance roller27comes into contact from the side of the one-side printing path17to form a nip between the rollers. Furthermore, with the intermediate roller23, a double-side side conveyance roller29comes into contact from the side of the double-side printing path19to form a nip between the rollers. When the branch guide25is turned upward, the one-side printing path17is communicated with the common path21. When the branch guide25is turned downward, the double-side printing path19is communicated with the common path21.

Next, an image forming operation will be described. In a case of a one-side printing operation, the branch guide25is turned upward, and the one-side printing path17is communicated with the common path21. The sheet is fed from the sheet feeding cassette5by the sheet feeding device7to the one-side printing path17. After the toner image is transferred on the sheet at the image forming part9, the toner image is fixed on the sheet by the fixing device9. Then, the sheet is conveyed along the common path21, discharged by the sheet discharging device13and then stacked on the discharge tray15.

In a case of a double-side printing operation, the branch guide25is turned upward, and the one-side printing path17is communicated with the common path21. The sheet is fed from the sheet feeding cassette5by the sheet feeding device7to the one-side printing path17. After the toner image is transferred on one face of the sheet at the image forming part9, the toner image is fixed on the sheet by the fixing device9. Then, the sheet is conveyed along the common path21and then discharged above the discharge tray15. After the rear end of the sheet is passed through the nip between the intermediate roller23and the one-side side conveyance roller27, the branch guide25is turned downward, and the common path21is communicated with the double-side printing path19. The sheet is switched back by the sheet discharging device13, and conveyed to the double-side printing path19through the common path21. Then, the sheet is conveyed along the double-side printing path19and then the one-side printing path17. At the image forming part9, the toner image is transferred on the other face of the sheet and then fixed on the sheet by the fixing device11. After that, the branch guide25is turned upward, the one-side printing path17is communicated with the common path21. Then, the sheet is conveyed along the common path21and then discharged by the sheet discharging device13. The discharged sheet is stacked on the discharge tray15.

Next, with reference toFIG. 2andFIG. 3, the sheet discharging device13and its periphery will be described.FIG. 2is a cross sectional view showing the sheet discharging device and its periphery andFIG. 3is a disassembled view showing the sheet discharging device.

As shown inFIG. 2, on an upper face of the apparatus main body3, a rear wall3ainclined at a slightly obtuse angle with respect to a horizontal plane is formed. At an upper end portion of the rear wall3a, an opening3bis formed along a sheet width direction W perpendicular to the sheet discharge direction. The discharge tray15is integrally formed with a lower end of the rear wall3aso as to extend in the sheet discharge direction.

As shown inFIG. 2andFIG. 3, the sheet discharging device13includes a casing31, a discharge rollers pair33and a sheet pressing member35and an upper limit detection sensor37(refer toFIG. 3) which are stored in the casing31.

The casing31is formed by a pair of upper frame41and a lower frame43, and fixed to the rear wall3aso as to close the opening3b. Between the upper frame41and the lower frame43, the common path21is formed. The common path21is formed such that its height is gradually lowered from the side of the branch part B toward the side of a discharge port45.

As shown inFIG. 3, the discharge rollers pair33includes a drive roller51and a driven roller53. The drive roller51has a second rotational shaft51aand a plurality of roller bodies51b(two roller bodies in the embodiment) fixed to the second rotational shat51aat predetermined intervals. The second rotational shaft51ais disposed along an upper edge of the discharge port45and the two roller bodies51bare disposed at both sides of a center in the sheet width direction W. Both end portions of the second rotational shaft51aare supported by the upper frame41in a rotatable manner. To the one end portion of the second rotational shaft51a, a drive source (not shown) is connected. The second rotational shaft51ais driven by the drive source to be rotated in both directions.

The driven roller53has a third rotational shaft53aand two roller bodies53bfixed to the third rotational shat53aat predetermined intervals. The third rotational shaft53ais disposed along a lower edge of the discharge port45and the two roller bodies53bare disposed so as to come into contact with the two roller bodies51bof the drive roller51obliquely from the front lower side at a predetermined pressure. As a result, a discharge nip N2formed between the roller bodies51bof the drive roller51and the roller bodies53bof the driven roller53is inclined in an oblique upper direction toward the downstream side in the sheet discharge direction. Both end portions of the third rotational shaft53aare supported by the lower frame43in a rotatable manner. The driven roller53is driven by the drive roller51to be rotated in a counter direction of the rotation direction of the drive roller51.

When the drive roller51is rotated in one direction (the clockwise direction inFIG. 2), the sheet is discharged through the discharge port45from the common path21into a space above the discharge tray15. After that, when the drive roller51is rotated in the other direction (the counterclockwise direction inFIG. 2), the sheet is switched back from the space above the discharge tray15through the discharge port45to the common path21. As shown inFIG. 2, of the common path21, a lower path21A from the one-side side nip N1between the intermediate roller23and the one-side side conveyance roller27to the discharge nip N2of the discharge rollers pair33is inclined upward. On the other hand, of the common path21, an upper path21B from the discharge nip N2of the discharge rollers pair33to the double-side side nip N3between the intermediate roller23and the double-side side conveyance roller29is almost horizontal.

Next, the sheet pressing member35will be described with reference toFIG. 3andFIG. 4.FIG. 4is a side view showing the sheet pressing member when viewed from the front side of the color printer1. The sheet pressing member35includes a first rotational shaft61, a detection piece63and a corrugation piece67and a light shielding piece (a detected piece)69which are fixed to the first rotational shaft61. The first rotational shaft61, the detection piece63, the corrugation piece67and the light shielding piece69are formed integrally. However, the detection piece63, the corrugation piece67and the light shielding piece69may be formed separately from the first rotational shaft61, and they may be attached to the first rotational shaft61.

The detection piece63contains a center detection piece63A and a pair of end detection pieces63B. The center detection piece63A protrudes from a center portion of the first rotational shaft61in a radial direction of the first rotational shaft61. The end detection pieces63B protrude from end portions of the first rotational shaft61in the same radial direction as the center detection piece63A. The detection piece63is formed in a longitudinally long plate shape, and has a fixed portion63a, a base portion63b, a bent portion63cand a contact portion63din the order from the first rotational shaft61, as shown inFIG. 4. The fixed portion63ais fixed to the first rotational shaft61. The base portion63bprotrudes from the fixed portion63ain the radial direction of the first rotational shaft61. The bent portion63cis bent from the base portion63bin a direction crossing to the radial direction. The contact portion63dprotrudes from the bent portion63calmost parallel to the base portion63b. The end detection piece63B has a width wider than that of the center detection piece63A.

The corrugation piece67protrudes from the fixed portion63aof the center detection piece63A in an almost opposite direction to the protruding direction of the center detection piece63A with respect to the first rotational shaft61. The corrugation piece67has a base part71and a tip part73in the order from the fixed portion63a. The base part71protrudes from the fixed portion63ain the radial direction of the first rotational shaft61. The tip part73is bent from a tip end portion of the base part71in a direction crossing to the radial direction. A tip side portion of the base part71is formed into a semicircular curved portion71awhen viewed from in the axial direction of the first rotational shaft61. The curved portion71ais curved in a semicircular shape toward the upstream side in the rotational direction (the clockwise direction inFIG. 4) of the sheet pressing member35when the detection piece63is pushed up. On an outer face of the base part71, a rib75is formed along the longitudinal direction of the base part71(the radial direction of the first rotation shaft61). The tip part73has an extended portion77and a pressing portion79which are crossed each other at almost right angles. The extended portion77extends from a tip end of the base part71to the downstream side in the rotational direction (the clockwise direction inFIG. 4) of the sheet pressing member35when the detection piece63is pushed up. The pressing portion79is bent from a tip end of the extended portion77in a direction close to the first rotational shaft61. On an inner face of the tip part73, a rib81is formed along the longitudinal direction of the tip part73.

The light shielding piece69protrudes from one end portion of the first rotational shaft61(the end portion outside the pair of end detection pieces63B) in almost the same radial direction of the protruding direction of the detection piece63.

As shown inFIG. 2andFIG. 3, the sheet pressing member35is arranged above the discharge rollers pair33and closer to the discharge port45than the discharge rollers pair33with the detection piece63and the light shielding piece69at the side of the discharge tray15and the corrugation piece67at the side on the inside of the apparatus main body3. Both the end portions of the first rotational shaft61are supported by the upper frame41in a rotatable manner. At this time, as shown inFIG. 3, the center detection piece63A and the corrugation piece67are arranged between the two roller bodies51bof the drive roller51and between the two roller bodies53bof the driven roller53of the discharge rollers pair33.

As shown inFIG. 2, the sheet pressing member35is turned such that the detection piece63and the light shielding piece69are suspended in the oblique lower direction by their own weight above the discharge tray15across the discharge port45while the corrugation piece67is lifted in the oblique upper direction. The posture of the sheet pressing member35is called an initial posture. At the initial posture, the sheet discharged through the discharge port45by the discharge rollers pair33comes into contact with the detection piece63. And, when an amount of the sheets stacked on the discharge tray15is increased, the detection piece63comes into contact with the uppermost sheet of the sacked sheets and then pushed up gradually. Then, when the height of the stacked sheet becomes a predetermined height, a full stack of the sheet is detected (described later in detail).

The upper limit detection sensor37is a light sensor having a light emitting part and a light receiving part facing each other via a predetermined gap. When a light path between the light emitting part and the light receiving part is blocked or opened, an ON state and an Off state are switched. The upper limit detection sensor37is attached to the upper frame41so as to be positioned such that the light shielding piece69blocks the optical path when the detection piece63is pushed up to a predetermined height by the uppermost sheet of the stacked sheets on the discharge tray15.

A sheet discharging operation of the color printer1having the above described configuration will be described with reference toFIGS. 5A, 5B, 5C and 6.FIGS. 5A, 5B, 5C and 6are side views showing the sheet pressing member. In the following description, a leading edge of the sheet S in the sheet discharge direction is called a first edge E1and a tail edge of the sheet S in the sheet discharge direction is called a second edge E2. That is, when the sheet S is switched back in the opposite direction to the discharge direction, the lead edge of the sheet S is changed in the second edge E2and the tail edge of the sheet S is changed in the first edge E1.

As shown inFIG. 5A, before the sheet is discharged, the sheet pressing member35stands still in the initial posture. At the one-side printing operation, when the sheet S is conveyed along the one-side printing path17and then passed through the fixing device11, because the lower path21A from the one-side side nip N1to the discharge nip N2is inclined upwardly as described above, the sheet S is conveyed in the upper oblique direction. Additionally, because the discharge nip N2is inclined in the oblique upper direction toward the downstream side in the sheet discharge direction, the sheet S is discharged through the discharge port45from the discharge nip N2in a first direction along the oblique upper direction at a predetermined discharge angle. Then, the first edge E1of the sheet S comes into contact with the detection piece63of the sheet pressing member35, and the detection piece63is pushed up and the sheet pressing member35is turned in the clockwise direction inFIG. 5A. Then, as shown inFIG. 5B, the detection piece63is displaced into a first posture turned upwardly by a first angle α with respect to the initial posture.

On the other hand, the corrugation piece67is turned downwardly with resect to the initial posture to be displaced into a contact posture. In the contact posture, the corrugation piece67comes into contact with an upper face of the sheet S between the two roller bodies51bof the drive roller51and between the two roller bodies53bof the driven roller53of the discharge rollers pair33, and then pushes the sheet S downward. In detail, an outer face (a pressing face) of the pressing portion79of the tip part73of the corrugation piece67comes into contact with the sheet S. At this time, when viewed from the axial direction of the first rotational shaft61, the pressing portion79comes into contact with the sheet S below the discharge nip N2on a line T passing through the centers of the second rotational shaft51aof the drive roller51and the third rotational shaft53aof the driven roller53of the discharge rollers pair33. That is, the sheet S is put between the two roller bodies51bof the drive roller51and the two roller bodies53bof the driven roller53of the discharge rollers pair33, and the center portion of the sheet S is pushed downwardly so that the center portion of the sheet S is curved downwardly to be applied with stiffness. When the sheet pressing member35is turned in the above manner, the second rotational shaft51aof the drive roller51of the discharge rollers pair33enters the curved portion71aof the base part71of the corrugation piece67so that the second rotational shaft51aof the drive roller51does not interfere with the turning of the corrugation piece67.

Because the center portion of the sheet S is pushed downwardly by the corrugation piece67, the sheet S is discharged through the discharge port45while being curved and then stacked on the discharge tray15. After the second edge E2of the sheet S is passed through the discharge rollers pair33, the sheet pressing member35is turned into the initial posture (refer toFIG. 5A) by its own weight.

On the other hand, when the sheet S is conveyed in the sheet discharge direction at the double-side printing operation, until the second edge E2of the sheet S is passed through the one-side side nip N1, the corrugation piece67comes into contact with the sheet S in the same manner as the one-side printing operation. However, during a period where the second edge E2of the sheet S is passed through the one-side side nip N1and is passing through the common path21, the sheet S is put between the discharge rollers pair33only. Then, after the sheet S is discharged through the discharge port45for a predetermined length, the discharge rollers pair33is inverted. The sheet S is switched back and then conveyed in an almost horizontal second direction at a predetermined inversion angle until the second edge E2of the sheet S is conveyed through the upper path21B and caught by the double-side side nip N3. Because the inversion angle with respect to the horizontal direction is smaller than the discharge angle with respect to the horizontal direction, the sheet pressing member35is turned in the counter clockwise direction inFIG. 5Bby its own weight. Then, as shown inFIG. 5C, the detection piece63is turned into a second posture turned upward with respect to the initial posture by a second angle β smaller than the first angle α. On the other hand, the corrugation piece67is displaced into a retracting posture turned downward with respect to the initial posture. In the retracting posture, the corrugation piece67is separated from the sheet S upwardly. That is, when the sheet is switched back, the sheet S is not applied with stiffness. When the switched back sheet S is separated from the detection piece63, the sheet pressing member35is turned into the initial posture (refer toFIG. 5A) and then stands still.

When an amount of the sheets stacked on the discharge tray15is increased, the detection piece63is pushed up by the uppermost sheet gradually to turn the sheet pressing member35gradually. Then, as shown inFIG. 6, when the uppermost sheet S reaches a predetermine height and the discharge tray15is filled with the sheets, the light shielding piece69blocks the optical path of the upper limit detection sensor37and the ON state continues for a predetermined period. Then, it is detected that the discharge tray15is filled with the sheets. The angles α and β of the detection piece63when the detection piece63is pushed up by the discharged sheet and the switched back sheet are larger than an angle γ of the detection piece63when the detection piece63is pushed by the fully stacked sheets.

As described above, according to the color printer1of the present disclosure, when the sheet S is discharged, the corrugation piece67comes into contact with the sheet S to apply stiffness to the sheet S while when the sheet S is switched back, the corrugation piece67does not come into contact with the sheet S and apply the corrugation on the sheet S. Accordingly, it becomes possible to prevent the occurrence of abnormal sound when the sheet S is switched back and to apply the corrugation on the sheet S when the sheet S is discharged.

Additionally, by a difference of the turning angles of the detection piece63owing to a difference of the sheet discharge angles when the sheet is switched back and when the sheet is discharged, it is determined whether the corrugation piece comes into contact with the sheet S or not. Then, a member to operate the corrugation piece67individually is not required so that it becomes possible to make the structure of the sheet discharge device13simple.

Additionally, the center portion of the sheet S put between the discharge rollers pair33is pushed downward along the line T passing through the centers of the second rotational shaft51aof the drive roller51and the third rotational shaft53aof the driven roller53of the discharge rollers pair33. Accordingly, it becomes possible to apply stiffness on the sheet S effectively.

Additionally, the tangent line passing through the discharge nip N2of the discharge rollers pair33is inclined upwardly in the sheet discharge direction, and the sheet S is discharged from the discharge nip N in the oblique upper direction. Accordingly, when discharged, the sheet S easily comes into contact with the detection piece63of the sheet pressing member35so that it becomes possible to turn the sheet pressing member35surely.

In the present embodiment, the corrugation piece67is provided integrally with the center detection piece63A; however, the corrugation piece67may be directly fixed to the first rotational shaft61separately from the center detection piece63A.

Next, with reference toFIG. 7, a first modified example of the sheet pressing member of the present embodiment will be described.FIG. 7is a perspective view showing the first modified example of the sheet pressing member.

In the first modified example, the tip part73of the corrugation piece67of the sheet pressing member35is connected to the fixed portion63aof the center detection piece63A by a plate spring91as an elastic member. The plate spring91is curved in a semicircular shape toward the upstream side in the rotational direction (the clockwise direction inFIG. 7) of the sheet pressing member35when the detection piece63is pushed up.

By providing the plate spring91, when the pressing portion79of the tip part73of the corrugation piece68comes into contact with the sheet S at the sheet discharging, the corrugation piece67is elastically deformed in an opposite direction to the contact direction (the clockwise direction inFIG. 7). Accordingly, if the sheet has high stiffness, it becomes possible to prevent applying corrugation to the sheet excessively.

Next, with reference toFIG. 8, a second modified example of the sheet pressing member of the present embodiment will be described.FIG. 8is a perspective view showing the second modified example of the sheet pressing member.

In the second modified example, the sheet pressing member35includes three of the corrugation pieces67. The center corrugation piece67is provided integrally with the center detection piece63A. Both the two end corrugation pieces67are directly fixed to the first rotational shaft61inside the end detection pieces63B.

By providing the plurality of corrugation pieces67, the portions to be applied with stiffness are distributed in the sheet width direction W so that the sheet S is corrugated to be stiffened.

Although the present disclosure described the specific embodiment, the present disclosure is not limited to the embodiment. It is to be noted that one skilled in the art can modify the embodiment without departing from the scope and spirit of the present disclosure.