Sheet feeding apparatus and image forming apparatus

A sheet feeding apparatus includes a sheet loader, a rear end holder, an air blower, a front end holder, a sender and an air controller. The sheet loader stores stacked sheets. The rear end holder holds a rear end of a topmost sheet on the sheet loader. The air blower blows air to the loaded sheets to raise a sheet. The front end holder holds a front end of the raised topmost sheet. The sender sends the sheet in the sheet feeding direction. The air controller controls the air blower to start blowing a raising air to raise the sheet after the rear end holder holds the rear end of a next sheet that is stacked under the topmost sheet before a rear end of the topmost sheet sent in the sheet feeding direction by the sender passes through the front end holder.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-000939 and Japanese Patent Application No. 2018-000938, both filed on Jan. 9, 2018, the entirety of both of which are hereby incorporated by reference herein and forms a part of the specification.

BACKGROUND

1. Field of the Invention

The present invention relates to a sheet feeding apparatus and an image forming apparatus.

2. Description of the Related Art

In image forming apparatuses that form an image on a sheet, air-suctioning sheet feeding apparatuses have been known in the art which store stacked sheets and feed them to an image formation unit (see JP 2016-117589A).

Such an air-suctioning sheet feeding apparatus includes:

a side end air blower that blows air to an upper sheet of stacked sheets on a sheet loader from the both sides (side ends) in the direction perpendicular to the sheet conveyance direction so as to raise the upper sheet;

a front end air blower that blows air to the topmost sheet from the front end thereof so as to raise the upper sheet and to separate the topmost sheet from the other sheets; and

a vacuum conveyer that holds and conveys a sheet in the conveyance direction with a conveyance belt disposed above the sheet stack.

This mechanism can send sheets one by one to a sheet conveyance path by holding only the topmost sheet and reliably separating it from the other sheets.

However, this sheet feeding apparatus only holds the topmost sheet and does not fix the other sheets below the topmost sheet while sending the topmost sheet. In this condition, since the second and other sheets may sometimes stick to the topmost sheet to cause double feeding, it is necessary not to raise and feed the next sheet until the topmost sheet has passed through the suction conveyer. This prevents an improvement of the productivity.

In this regard, JP 2012-046278A discloses providing a presser between a rear end regulator plate and a vacuum conveyer to press a sheet. When a sheet is moved in the direction opposite to the sheet feeding direction by separating air, the presser regulates the movement of the sheet in the direction opposite to the sheet feeding direction. That is, the presser fixes the sheet to prevent the second and other sheets from moving in the opposite direction.

In air-suctioning sheet feeding apparatuses, when a sheet is long in the sheet feeding direction, e.g. a long sheet, it is necessary that the separating air reaches the rear end of the sheet in order to completely separate the sheet from the other sheets thereunder. Too weak separating air results in insufficient separation of sheets, and the contact between the sheets increases the risk of double feeding. In contrast, too strong separating air may move a sheet backward or cause bucking of a sheet.

To cope with the problems, JP 2012-046278A discloses providing a presser that is disposed above the midway between the rear end regulator plate for regulating the rear end position of a sheet and the vacuum conveyer. When the sheet is moved in the direction opposite to the sheet feeding direction by the separating air, the presser regulates movement of a sheet in the direction opposite to the sheet feeding direction. This configuration can solve the above-described problem that occurs when the separating air is too strong.

However, pressing a sheet from above as in the method of JP 2012-046278A increases the friction between the topmost sheet and the other sheets thereunder and eventually increases the risk of double feeding.

SUMMARY

The present invention has been made in view of the above-described problems, and an object thereof is to provide a sheet feeding apparatus and an image forming apparatus that can reliably separate sheets to reduce the occurrence of double feeding.

To achieve at least one of the abovementioned objects, according to an aspect of the present invention, a sheet feeding apparatus includes:

a sheet loader which stores stacked sheets;

a rear end holder which holds a rear end in a sheet feeding direction of a topmost sheet on the sheet loader;

an air blower which blows air to the loaded sheets to raise a sheet;

a front end holder which holds a front end of the raised topmost sheet;

a sender which sends the sheet in the sheet feeding direction; and

an air controller which controls blow of the air from the air blower,

wherein the air controller controls the air blower to start blowing a raising air to raise the sheet after the rear end holder holds the rear end of a next sheet that is stacked under the topmost sheet before a rear end of the topmost sheet sent in the sheet feeding direction by the sender passes through the front end holder.

DETAILED DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment of the present invention will be described with the drawings. While a variety of limitations that are favorable for carrying out the present invention are included in the following first embodiment, the scope of the present invention is not limited to the following embodiment and illustrated examples.

Summary of Image Forming Apparatus

FIG. 1is an overall configuration view of an image forming apparatus100according to the present invention, andFIG. 2is a block diagram of the functional configuration of the image forming apparatus100.

As illustrated inFIG. 1andFIG. 2, the image forming apparatus100mainly includes an image forming apparatus main body100a, an image scanner SC, an automatic document feeder DF, an image processor30, a sheet feeder500and a hardware processor400. The hardware processor400and the sheet feeder500constitute a sheet feeding apparatus.

The image forming apparatus main body100aincludes an image formation unit110, a fixation unit7and a sheet conveyance system120. The image formation unit110includes a photoreceptor1, a charger2, image exposer3, a developer4, a transferrer5, a cleaner6and the like.

The sheet conveyance system120includes two-tired sheet feeding cassettes10,10that store sheets, sheet feeding conveyers11,11that feed sheets from the respective sheet feeding cassettes10one by one, a first conveyer12that conveys a sheet from the sheet feeding conveyers11,11to a point just before the image formation unit110, a second conveyer13that conveys a sheet from the first conveyer12to the downstream of the fixation unit7, a sheet ejector14that conveys a sheet to an ejection tray (not shown), a circulating re-feeder15that branches off from the second conveyer13and rejoins to the first conveyer12, a conveyance path switcher16that switches the conveyance path between the sheet ejector14and the circulating re-feeder15, and a flipping sheet ejector17that branches off from the circulating re-feeder15to flip a sheet.

The sheet feeder500includes a first sheet feeder50a, a second sheet feeder50band a third sheet feeder50cthat are vertically aligned.

Automatic Document Feeder and Image Scanner

The automatic document feeder DF conveys an original d mounted on a platen to the image scanner SC. The image scanner SC reads an image on either or both sides of the conveyed original d with an image sensor CCD. The image processor30performs analog processing, A/D conversion, shading correction, image compression and the like on an analog signal that is obtained by photoelectric conversion of the image sensor CCD. The image processor30sends the image signal thus obtained to the image exposer3.

The hardware processor400, which can communicate with an external device (e.g. personal computer) connected to a communicator (not shown) through a communication network, may also send an image signal received from the external device to the image exposer3via the image processor30.

Image Formation Unit

In the image formation unit110, the charger2charges the photoreceptor1, the image exposer3irradiates the photoreceptor1with a laser beam to form an electrostatic latent image, and the developer4develops the electrostatic latent image to form a toner image.

While being conveyed, a sheet P fed from the sheet feeding cassettes10by the sheet feeding conveyers11is synchronized with a toner image by a resist roller12aof the first conveyer12. The transferrer5then transfers the toner image to the sheet P, and the fixation unit7fixes the toner image.

In addition to the sheets P stored in the sheet feeding cassettes10, a sheet P stored in the sheet feeder500is also fed to the image forming apparatus main body100awhere a toner image is transferred to the sheet P.

The second conveyer13ejects the sheet P with the fixed image out of the apparatus. The cleaner6removes untransferred residual toner on the photoreceptor1. In double-sided printing, the conveyance path switcher16sends the sheet P with the image on the first side to the circulating re-feeder15where the sheet P is flipped. The image formation unit110forms an image on the second side, and thereafter the second conveyer13ejects the sheet P. In flipping ejection, the sheet P is deviated from a normal ejecting path and switches back at the flipping sheet ejector17. The second conveyer13ejects the sheet P thus flipped out of the apparatus.

Summary of Sheet Feeding Apparatus

FIG. 3is a schematic perspective view of the first sheet feeder50aof the sheet feeder500. For example, the first sheet feeder50a, the second sheet feeder50band the third sheet feeder50c, which are vertically aligned in the sheet feeder500as described above, have the same configuration, and only the first sheet feeder50awill be described here.

The first sheet feeder50aincludes a sheet container51, a front end air blower52, side end air blowers53,54, a sender55, a front end holder56, a rear end holder57, a conveyer58and the like.

Configuration of Sheet Container and Surroundings Thereof

The sheet container51includes a sheet loading pallet511as a horizontal sheet loader in which stacked sheets P are loaded, a rear end regulating member512that is disposed behind the sheet loading pallet511, i.e. at the upstream side in the sheet feeding direction a, and a front end regulating member513that is disposed in front of the sheet loading pallet511, i.e. at the downstream side in the sheet feeding direction a.

In the following description of the sheet feeder50, the left hand direction with respect to the sheet feeding direction a, which is a horizontal direction perpendicular to the sheet feeding direction a, is referred to as “left”, and the right hand direction with respect to the sheet feeding direction a, which is a horizontal direction perpendicular to the sheet feeding direction a, is referred to as “right”.

The sheet loading pallet511is supported in the sheet feeder50in a vertically movable manner.

The upper end of the front end regulating member513is slightly lower than the upper end of the rear end regulating member512. The sheet loading pallet511moves up and down by an actuator (not shown), and the hardware processor400controls the actuator so that the top of the stacked sheets P on the sheet loading pallet511is always at a specific level that is slightly lower than the upper end of the front end regulating member513. This level control using the actuator is based on the level of the topmost sheet P that is detected by a sensor (not shown) disposed at the rear end regulating member512.

When sheets P are not fed, e.g. when a user fills the sheet feeder with sheets P, the sheet loading pallet511may be in a lower position.

The rear end regulating member512moves up and down by an actuator (not shown). As described later, the rear end regulating member512moves in the height direction along with the rear end holder57. When sheets P are not fed, e.g. when a user fills the sheet feeder with sheets P, the rear end regulating member512may be in a higher position while the sheet loading pallet511may be in a lower position.

The rear end regulating member512is movable also in the sheet feeding direction a by an actuator (not shown) according to the length in the sheet feeding direction of sheets P.

Front End Air Blower and Side End Air Blower

The front end air blower52is disposed adjacent to the front end regulating member513at the downstream in the sheet feeding direction a of the front end regulating member513. Further, the side end air blowers53,54are disposed respectively at the right and left sides of the sheet loading pallet511. The side end air blowers53,54include flat and vertical inner side walls that function as regulating members for regulating the lateral position of sheets.

The front end air blower52and the side end air blowers53,54, in which air blowing fans521,531,541are respectively provided, are configured to blow air through air outlets522(seeFIG. 4),532,542. The front end air blower52and the side end air blowers53,54function as air blowers.

FIG. 4is a cross-sectional view illustrating the structure around the front end in the sheet feeding direction a of the topmost sheet P on the sheet loading pallet511.

The front end air blower52includes a nozzle523for blowing air through the air outlet522in a direction slightly inclined upward with respect to the direction opposite to the sheet feeding direction a. The front end air blower52includes a switching valve (not shown) in the nozzle523that allows switching the blow direction between upward blow and downward blow. In the downward blow, air is blown to the edges of the stacked sheets P, which is effective to raise a sheet P. In the upward blow, air is blown to the front end of the raised sheet P, which is effective to separate the topmost sheet P from other sheets that are raised along with the topmost sheet P, i.e. to puff up the sheets.

As illustrated inFIG. 3, the side end air blowers53,54include nozzles533,543for blowing air from the left and right sides of the topmost sheet P at the specified level toward the sheet P in the horizontal direction or a direction slightly inclined upward from the horizontal direction. The air outlets532,542of the nozzles533,543are formed such that the upper edges are higher than the topmost sheet P disposed at the specified height while the lower edges are lower than the topmost sheet P. When air is blown through the air outlets532,542of the side end air blowers53,54, this configuration allows blowing air to the top sheet P of the stacked sheets to raise the top sheet P.

The downward blow of the front end air blower52and the blow of the side end air blowers53,54serve as raising air for raising a stacked sheet P. The raising air may be constituted by only one of the downward blow of the front end air blower52and the air blow of the side end air blowers53,54.

The upward blow by the front end air blower52serve as separating air for separating the raised topmost sheet P from the other sheets raised along with the topmost sheet P.

Sender and Holder

FIG. 5is a plan view of the sender55and the front end holder56. As illustrated inFIG. 3toFIG. 5, the sender55is disposed above the sheet loading pallet511. InFIG. 3, the sender55is illustrated in a deviated position as illustrated by the arrows so that the other surrounding components are shown in the figure. However, the actual sender55is disposed above the downstream end in the sheet feeding direction a of the sheet loading pallet511as illustrated inFIG. 4.

The sender55includes four belt mechanisms aligned in the horizontal direction perpendicular to the sheet feeding direction a, a motor551as a sheet feeding driver for driving the belt mechanisms and a transmission gear train552intervened between the belt mechanisms and the motor551.

Each of the belt mechanisms includes a large-diameter roller553disposed at the upstream in the sheet feeding direction a, two small-diameter rollers554,555disposed at the downstream in the sheet feeding direction a and a belt556disposed around the rollers553,554,555. The motor551applies a torque to the large-diameter rollers553of the belt mechanisms in the direction of moving the lower side of the belts556in the sheet feeding direction a. Instead of the rollers553,554,555, sprockets may be used.

The belts556have small through holes over the entire surface, and the front end holder56(described later) can provide a vacuum though the small holes to hold a sheet P on the lower side of the belts556.

At the upstream in the sheet feeding direction a of the belt mechanisms, hold detectors557are provided to detect attachment of a sheet on the belts556. Each of the hold detectors557includes a detector body557aand an optical sensor557b. The detector body557ahas an approximately bar shape and is supported in such a manner that it can swing.

One end of the detector body557aprotrudes downward from the bottoms of the belts556. When a sheet P is held on the belts556, the detector body557ais swung so that one end thereof is pushed back in the upward direction. The detector body557ais configured such that when one end is pushed back, the other end moves downward accordingly to interrupt the sensor557b. The sensor557binputs the resultant change in the amount of received light to the hardware processor400so that the hardware processor400recognizes attachment of the sheet P.

As illustrated inFIG. 3toFIG. 5, the front end holder56includes a first duct561with one end inserted in the belts556of the sender55and a first fan562that is disposed at the other end of the first duct561to create a negative pressure inside the first duct561.

One end of the first duct561, which is inserted in the belts556, is formed in an approximately rectangular box shape with a first opening561aat the bottom. The front end holder56can draw air through the first opening561aby creating a negative pressure in the first duct561with the first fan562.

The first opening561aof the first duct561is disposed over the lower sides of the four belts556, and the portions of the belts556that are opposed to the first opening561acorrespond to a first holding area B where a sheet is held.

FIG. 6AandFIG. 6Bis a partially cross-sectional perspective view of the rear end holder57. As illustrated inFIG. 6AandFIG. 6B, the rear end holder57is fixed at the upper end of the rear end regulating member512. The rear end holder57includes a movable portion571that is disposed in contact with the rear end of the topmost sheet P and is movable upward by negative pressure and downward by its own weight, a second duct572with one end coupled to the movable portion571, and a second fan573that is disposed at the other end of the second duct572to create a negative pressure in the second duct572.

The movable portion571is a bottomed rectangular pipe that has a circular second opening571bat the center of a bottom571athat comes in contact with the topmost sheet P. The second opening571bcorresponds to a second holding area C where a sheet is held. When the second fan573is turned on, it draws air through the second opening571bin the direction of the arrow D in the figure and discharges the air in the direction of the arrow E in the figure. That is, when a sheet P is held on the second opening571bafter the second fan573is turned on, a negative pressure is created in the second duct572.

On a wall of the movable portion571, one or more pins571care provided. The pins571care inserted in a window hole572aof the second duct572so that the window hole572adefines the movable range in the height direction. That is, the movable portion571is movable between the position as illustrated inFIG. 6Ain which the second opening571bis in contact with the topmost sheet P on sheet loading pallet511and the position as illustrated inFIG. 6Bin which the second opening571bis the furthest away from the stacked sheets on the sheet loading pallet511.

The operation of the sender55, the front end holder56and the rear end holder57in a sheet feeding process will be described.

When the front end air blower52and the side end air blower53,54blow the raising air to raise one or more sheets P on the top of the stacked sheets on the sheet loading pallet511, the sender55and the front end holder56hold the front end of the raised topmost sheet P on the lower side of the belts556by the suction force created at the first holding area B.

Meanwhile, the second opening571bof the movable portion571is in contact with the topmost sheet P, and the rear end holder57holds the rear end of the sheet P on the movable portion571by the suction force created at the second holding area C. When the force by the negative pressure in the second duct572surpasses the total weight of the movable portion571and the rear end portion of the topmost sheet P, the movable portion571moves up to pull up the rear end of the sheet.

In this state, the sender55can rotate the belts556to send the sheet P in the sheet feeding direction a.

As illustrated inFIG. 4, the conveyer58is disposed in proximity to the sender55at the downstream in the sheet feeding direction a. The conveyer58includes an insertion guide581to which a sheet P sent from the lower side of the belts556can be inserted, large and small conveyance rollers582,583that are disposed in the middle of the insertion guide581to nip and convey the sheet P to the downstream in the sheet feeding direction a, a motor (not shown) as a driver that rotates the conveyance rollers582,583, and a sheet detector584constituted by an optical or contact sensor that detects arrival of the front end of the sheet P and passage of the rear end of the sheet P at the insertion guide581.

The insertion guide581is widely open in the vertical direction at the end at the upstream in the sheet feeding direction a, and the vertical width is gradually decreased in the sheet feeding direction a. The end at the downstream in the sheet feeding direction a is connected to the conveyance path of the sheet P to the image forming apparatus main body100a.

The large-diameter conveyance roller582and the small-diameter conveyance roller583, which are in contact with each other, is disposed in the insertion guide581so that the sheet P that has entered the insertion guide581passes through between the large-diameter conveyance roller582and the small-diameter conveyance roller583.

The large-diameter conveyance roller582is driven by a motor (not shown) that is controlled by the hardware processor400. The small-diameter conveyance roller583, which is in contact with the large-diameter conveyance roller582, receives a rotational torque in the opposite direction from the large-diameter conveyance roller583and rotates accordingly.

The sheet detector584is disposed in proximity to the conveyance rollers582,583at the upstream in the sheet feeding direction a. The sheet detector584detects whether the sheet P is present at the sheet detector584and constantly inputs the detection result to the hardware processor400. That is, when the detected state of the sheet P changes from the absent to present, the hardware processor400recognizes that the front end of the sheet P has reached the sheet detector584. Similarly, when the detected state of the sheet P changes from present to absent, the hardware processor400recognizes that the rear end of the sheet P has passed through the sheet detector584.

As used herein, the front end of a sheet P refers to the end of the sheet P that is in the downstream in the sheet feeding direction a, and the rear end of a sheet P refers to the end of the sheet P that is in the upstream in the sheet feeding direction a.

Hardware Processor

The hardware processor400includes a CPU (Central Processing Unit)401, a ROM (Read Only Memory)402, a RAM (Random Access Memory)403and the like. The CPU401reads a program in the ROM402according to processing to be performed, develops it in the RAM403and integrally controls the operation of the components (the image scanner SC, the automatic document feeder DF, the image processor30, the image forming apparatus main body100a, the sheet feeder500and the like) of the image forming apparatus100in cooperation with the developed program. In this process, the CPU401also references a variety of data stored in the storage410. For example, the storage410is constituted by a non-volatile semiconductor memory (so-called flash memory), a hard disk drive or the like.

The hardware processor400serves as an air controller and a hold controller.

The hardware processor400, which also includes a communicator constituted by a communication control card (not shown) such as a LAN card, can send or receive various data to and from an external device (e.g. personal computer) connected through a communication network such as a LAN (local area network) or a WAN (wide area network).

Sheet Feeding Control of Sheet Feeding Apparatus: Puffing Control by Rear End Holder

Sheet feeding control of the first sheet feeder50aof the sheet feeder500by the hardware processor400will be described. The same sheet feeding control is performed on the second sheet feeder50band the third sheet feeder50c.

First, the relationship between the strength of the raising air and the accuracy of separation of sheets P in the sheet feeding process will be described based onFIG. 7AandFIG. 7B.

When the sheet feeding process is started, the sheet feeder50blows the raising air to raise a top sheet P by using the front end air blower52and the side end air blowers53,54, holds the raised sheet P on the lower side of the belts556and sends the sheet P toward the conveyer58.

When the strength of the raising air is insufficient, the air does not reach and raise the rear end of the topmost sheet P as illustrated inFIG. 7A, and the topmost sheet P remains in contact with the next sheet. This increases the risk of double feeding

When the blow of the raising air is too strong, the topmost P is raised and held on the lower side of the belts556as illustrated inFIG. 7B. However, the second and other sheets P may sometimes be buckled.

As described above, it is difficult to control levitation of the rear end of the sheet only by blowing air from the front end air blower52and the side end air blowers53,54. To assist separation of the rear end, the rear end holder57pulls up the rear end of the sheet P.

This process will be described in detail withFIG. 8AthroughFIG. 8E. In the following description, the topmost sheet and the next sheet thereunder are denoted respectively as P0and P1.

As illustrated inFIG. 8A, at the start of the sheet feeding process, the movable portion571of the rear end holder57is in the lower position and in contact with the topmost sheet P0. When the sheet feeding process is started, the second fan573is turned on by a control of the hardware processor400to create a negative pressure in the second duct572. Then, air is drawn through the second opening571b, and the movable portion571holds the sheet P0.

Once the sheet P0is held, the negative pressure in the second duct572is increased as illustrated inFIG. 8B. When the negative pressure surpasses the total weight of the movable portion571and the rear end of the topmost sheet P0, the movable portion571moves up along with the sheet P0held thereon so as to pull up the rear end of the topmost sheet P0. As a result, the rear end of the topmost sheet P0is separated from the rear end of the next sheet P1.

As illustrated inFIG. 8C, when the topmost sheet P0is conveyed so that the rear end is detached from the movable portion571, the second opening571bis opened. Once the sheet is released, the pressure in the second duct572is increased. The movable portion571moves down by its own weight and comes in contact with the upper surface of the rear end of the next sheet P1.

When the movable portion571moves down to come in contact with the upper surface of the next sheet P1as illustrated inFIG. 8D, the movable portion571holds the next sheet P1since air is drawn through the second opening571b. Since the movable portion571fixes the next sheet P1, it can prevent the next sheet P1from being fed along with the topmost sheet P0to cause double feeding.

After the movable portion571holds the next sheet P1, the negative pressure in the second duct572is increased, and the movable portion571moves up to pull up the rear end of the next sheet P1and keep it in the lifted position as illustrated inFIG. 8Ewhile the topmost sheet P0is being conveyed. That is, puffing of the next sheet P1is started before the topmost sheet P0has passed through the conveyer58. This can reduce the waiting time and increase the production efficiency.

In the embodiment, the hardware processor400serves as an air controller to determine the timing of blowing the raising air from the front end air blower52and the side end air blowers53,54after the rear end holder57holds the sheet P based on at least one of the paper type, the length in the sheet feeding direction, the basis weight and the environment of the loaded sheets P. The ease of separating sheets P differs depending on the paper type. For example, while it is easy to separate sheets P having a rough surface such as recycled paper, it is difficult to separate closely contacted sheets such as coated paper. Further, it is more difficult to separate sheets P as the length in the feeding direction is longer or the basis weight is lighter. In a humid environment in which sheets P absorb moisture to have closer contact between them, it is difficult to separate the sheets P. Accordingly, as the sheets becomes less separable, the hardware processor400delays the blow timing to extend the time for the rear end holder57to pull up and hold the sheet P so as to improve the separation. By changing the blow timing of the raising air according to the conditions, it is possible to improve the separation.

Further, the hardware processor400as the air controller determines whether to blow the raising air from the front end air blower52and the side end air blowers53,54and the strength of the raising air based on at least one of the paper type, the length in the sheet feeding direction, the basis weight and the environment of the loaded sheets. For example, the hardware processor400may determine not to blow the raising air to highly separable sheets P. This can reduce damage on the sheets as well as unnecessary power consumption

The side end air blowers53,54may blow the raising air from the start of the sheet feeding process until the hold detectors557detect attachment of the front end of the sheet P. That is, the side end air blowers53,54may stop blowing air after the detection. This can stabilize the flow of the separating air from the front end air blower52.

Flow of Operation Control of Successive Sheet Feeding in Sheet Feeding Apparatus

The flow of an operation control of successive sheet feeding in the sheet feeding apparatus will be described with the flowchart ofFIG. 9and the timing charts ofFIG. 10AandFIG. 10B.FIG. 10Ais a timing chart of a case in which the rear end holder57does not hold a sheet during blow of the raising air, andFIG. 10Bis a timing chart of a case in which the rear end holder57holds a sheet during blow of the raising air.

The topmost sheet P0, which is the first sheet in the successive sheet feeding process, does not have a precedent sheet that is held on the belts556. In response to a request to start the sheet feeding process, the hardware processor400immediately determines the blow timing and the blow strength of the raising air based on printing conditions (Step 1). As used herein, the printing conditions refer to the paper type, the length in the sheet feeding direction, the basis weight and the environment of sheets P, and the hardware processor400makes the determination based on at least one of them. The relationship of the printing conditions to the blow timing and the blow strength of the raising air are stored beforehand in the storage410in the form of a table. The printing conditions may be either manually input by a user or determined by the hardware processor400that references environment information detected by a humidity sensor and job information.

Subsequently, the hardware processor sets the blow direction of the front end air blower52to the downward blow and controls the front end air blower52and the side end air blowers53,54to start blowing the raising air. As a result, the topmost sheet P0on the sheet loading pallet511is raised and held on the first holding area B of the belts556. Further, the hardware processor400turns on the second fan573of the rear end holder57. Then, the rear end of the topmost sheet P0is held on the second holding area C, and when the negative pressure in the second duct572surpasses the total weight of the movable portion571and the rear end of the topmost sheet P0, the movable portion571starts to move up (Step S2, (t1) inFIG. 10AandFIG. 10B).

The hardware processor400makes a determination as to whether the status of the hold detectors557is “ON”, which represents a sheet being detected (Step S3). If it is determined that the status is not “ON” (Step S3, No), the hardware processor400repeats the determination in Step S3.

Then, if the hold detectors557detect the sheet P (Step S3, Yes), the hardware processor400switches the blow direction of the front end air blower52to the upward blow to start blowing the separating air while it controls the side end air blowers53,54to stop the blow (Step S4, (t2) inFIG. 10AandFIG. 10B). As a result, the separating air is blown to an end of the raised sheet P. This improves the puffing, and the sheet P is completely separated from the next sheet P1.

Then, the hardware processor400activates the sender55to send the topmost sheet P in the sheet feeding direction a (Step S5, (t3) inFIG. 10AandFIG. 10B).

When the rear end the topmost sheet P is detached from the rear end holder57as the sender55sends it, the second opening571bbecomes open. Then, the negative pressure in the second duct572is decreased, and the movable portion571starts to move down by its own weight (Step S6, (t4) inFIG. 10B).

When the movable portion571moves down and eventually holds the rear end of the next sheet P1on the second holding area C, the movable portion571starts to move up again since the negative pressure in the second duct572is increased (Step S7, (t5) inFIG. 10B). As a result, the rear end of the next sheet P1is pulled up and separated from the sheet thereunder.

Subsequently, the hardware processor400switches the blow direction of the front end air blower52to the downward blow and controls the front end air blower52and the side end air blowers53,54to blow the raising air (Step S8, (t6) inFIG. 10AandFIG. 10B). As a result, the front end of the next sheet P1is raised and held on the first holding area B of the belts556.

The hardware processor400makes a determination as to whether the status of the hold detector557is “OFF”, which represents the rear end of the sheet P having been passed through the sender (Step S9). If it is determined that the status is not “OFF” (Step S9, No), the hardware processor400repeats the determination in Step S9.

If it is determined that the status of the hold detector557is “OFF” (Step S9, Yes), the hardware processor400stops the sender55(Step S10, (t7) inFIG. 10AandFIG. 10B).

Subsequently, the hardware processor400makes a determination as to whether the topmost sheet P is the last page of the current sheet feeding process (Step S11). If it is determined that the topmost sheet P is not the last page (Step S11, No), the control returns to Step S2to continue feeding the next sheet P1. If it is determined that the topmost sheet P is the last page (Step S11, Yes), the sheet feeding control ends.

Technical Effects of Embodiment

The sheet feeder500of the image forming apparatus100according to the embodiment can improve the productivity.

This will be described with the timing charts inFIG. 10AandFIG. 10B. After the rear end of the topmost sheet P0is detached from the rear end holder57, the rear end holder57holds and fixes the rear end of the next sheet P1. This allows reducing the period ((T1) inFIG. 10AandFIG. 10B) from the point ((t3) inFIG. 10AandFIG. 10B) of starting conveyance of the topmost sheet P0until the point ((t6) inFIG. 10AandFIG. 10B) of raising the next sheet P1.

Further, since the next sheet P1is fixed while the rear end holder57holds the rear end thereof, it is possible to shift the point ((t6) inFIG. 10AandFIG. 10B) of starting blow of the raising air to the next sheet P1to an earlier timing at which the sender55is still sending the topmost sheet P0, and it is possible to start blowing the separating air at the point ((t7) inFIG. 10AandFIG. 10B) at which the topmost sheet P0has passed through the sender55. This is also applicable to the subsequent sheets P. In this regard, it is possible to start conveyance of the next sheet P at an earlier timing by setting the period ((T3) inFIG. 10AandFIG. 10B) to the same length as in the prior art. The period T3is from the point ((t7) inFIG. 10AandFIG. 10B) of switching the blow direction of the front end air blower52to the upward blow to blow the separating air so as to start puffing the sheet P to the point ((t8) inFIG. 10AandFIG. 10B) of starting conveyance of the next sheet P1. That is, starting conveyance of the sheet P at an earlier timing can reduce the waiting time and thereby improve the productivity.

In the sheet feeder500of the embodiment, the hardware processor400changes the timing of blowing the raising air from the front end air blower52and the side end air blowers53,54, which is performed after the rear end holder57holds the rear end of the sheet P, based on at least one of the paper type, the length in the sheet feeding direction, the basis weight and the environment of the loaded sheets P. The timing of the blow is delayed in a less-separable condition so that the rear end holder57holds the sheet P for a longer time. That is, the length of time the rear end holder57holds the sheet P is changed according to the ease of separating the sheets P. This can improve the separation.

In the sheet feeder500of the embodiment, the hardware processor400maintains the blow direction of the front end air blower52in the downward blow to blow the raising air so as to raise the front end of the sheet from the other loaded sheets thereunder for a predetermined time after the start of the blow. Thereafter, the hardware processor400switches the blow direction to the upward blow to blow the separating air so as to separate the raised sheet from the other sheets thereunder. That is, the sheet feeder500firstly blows the raising air to raise a sheet and then switches the blow direction to blow the separating air toward the rear end. This can reduce the time required to separate the sheet P and improve the efficiency.

In the sheet feeder500of the embodiment, the hardware processor400controls the on/off and the strength of the blow of the raising air from the front end air blower52and the side end air blowers53,54and the on/off and the strength of the blow of the separating air from the front end air blower52based on at least one of the paper type, the length in the sheet feeding direction, the basis weight and the environment of the loaded sheets. This can improve the separation according to the conditions.

In the sheet feeder500of the embodiment, the hardware processor400serves as a hold controller. At the start of the sheet feeding process, sheet feeder500controls the rear end holder52to start holding the topmost sheet P0after starting blow of the raising air before the sheet P0reaches the front end holder. That is, the rear end of the sheet P0is pulled up before the front end is completely raised. This can reduce the waiting time and thereby improve the production efficiency.

Others

In addition to the above-described configuration, the on/off and the strength of the separating air may be determined based on at least one of the paper type, the length in the sheet feeding direction, the basis weight and the environment of the sheets. When the sheets are long, the strength of the separating air may be increased so that the separating air can reach the rear end to puff the sheets better. When the sheets are short in the conveyance direction, the strength of the separating air may be decreased, or the separating air may not be blown so that the damage on the sheets can be reduced.

In the above-described embodiment, the blow direction of the front end air blower52is switched between the upward blow and the downward blow based on the sheet feeding state. However, depending on the sheet type or the like, the blow direction may remain in either upward or downward blow. For example, when the sheets are curled in a downward concave shape, the upward blow may press the second sheet against the topmost sheet, which produces an opposite effect to the puffing. In such cases, it is effective to always keep the blow direction in the downward blow, and the puffing is achieved only by the rear end holder57that pulls up the rear end.

In the above-described embodiment, whether to hold the rear end of a sheet and the holding force of the rear end holder57may be controlled based on the paper type, the basis weight, the size and the environment of the sheets and the like. That is, the suction force may be increased in a less-separable condition. This can improve the separation. In contrast, when the sheets to be fed are thin sheets that are easy to raise but is readily winkled, the suction force may be decreased or the rear end holder57may not hold a sheet. This can reduce damage on the sheets. To change the suction force, the hardware processor400may serve as a hold controller to change the rotation speed of the second fan573so as to change the negative pressure in the second duct572.

In the above-described embodiment, the movable portion571moves up by negative pressure. However, the mechanism is not limited thereto, and the movable portion571may move up by an actuator such as a solenoid.

In the above-described embodiment, the movable portion571moves down by its own weight. However, the mechanism is not limited thereto, and the movable portion may move down by a biasing member such as a spring.

In the above-described embodiment, negative pressure is utilized to create the suction force. However, mechanism is not limited thereto, and static electricity may also be utilized. Further, any other mechanisms that can hold a sheet on the movable portion571may be utilized.

Second Embodiment

Hereinafter, a second embodiment of the present invention will be described with the drawings. While a variety of limitations that are favorable for carrying out the present invention are included in the following second embodiment, the scope of the present invention is not limited to the following embodiment and illustrated examples.

The same reference signs are denoted to the same components as those of the first embodiment, and the detailed description is omitted.

Flow of Operation Control of Successive Sheet Feeding in Sheet Feeding Apparatus

In the second embodiment, the flow of the operation control of successive sheet feeding in the sheet feeding apparatus is identical to that of the first embodiment as illustrated in the flowchart ofFIG. 9. However, conveyance of the next sheet P1is started at the same timing as that in the prior art so as to improve the puffing.

Technical Effects of Embodiment

A sheet feeder500of an image forming apparatus100of the embodiment can puff up sheets P more effectively.

This will be described with the timing chart inFIG. 11AthroughFIG. 11B. After the rear end of the topmost sheet P0is detached from the rear end holder57, the rear end holder57holds the rear end of the next sheet P1to fix it. This allows reducing the period ((T1) inFIG. 11AandFIG. 11B) from the point ((t3) inFIG. 11AandFIG. 11B) of starting conveyance of the topmost sheet P0until the point ((t6) inFIG. 11AandFIG. 11B) of raising the next sheet P1.

Further, since the next sheet P1is fixed while a rear end holder57holds the rear end thereof, it is possible to shift the point ((t6) inFIG. 11AandFIG. 11B) of starting blow of the raising air to the next sheet P1to an earlier timing while a sender55is sending the topmost sheet P0, and it is possible to start blowing the separating air from the point ((t7) inFIG. 11AandFIG. 11B) at which the topmost sheet P0has passed through the sender55. This is also applicable to the subsequent sheets P.

In this regard, it is possible to extend the period ((T3) inFIG. 11AandFIG. 11B) of puffing up the sheet P relative to the period ((T2) inFIG. 11AandFIG. 11B) of raising the next sheet P1by setting the period (total period of (T1), (T2) and (T3) inFIG. 11AandFIG. 11B) from the point ((t3) inFIG. 11AandFIG. 11B) of starting conveyance of the topmost sheet P0until the point ((t8) inFIG. 11AandFIG. 11B) of starting conveyance of the next sheet P1to the same length as in the prior art. In the present invention, this can reduce the friction between the loaded sheets and separate them completely so as to reduce the occurrence of double feeding.

In the sheet feeder500of the embodiment, the movable portion571moves down by its own weight after the sheet P is detached from the rear end holder57. Since the movable portion571does not require a dedicated mechanism for the downward movement, the effects of the present invention can be obtained with the simple configuration.

In the sheet feeder500of the embodiment, when the movable portion571holds a sheet P, it moves up by the negative pressure that is generated by the second fan573. Since the movable portion571does not require a dedicated mechanism for the upward movement, the effects of the present invention can be obtained with the simple configuration.

In the sheet feeder500of the embodiment, the movable portion571has a second opening571bat the portion that contacts with a sheet P. A hardware processor400controls the negative pressure such that when the movable portion571holds a sheet P, the force by the negative pressure is greater than the weight of the movable portion571, and when the movable portion571does not hold a sheet P, the force by the negative pressure is less than the weight of the movable portion571. This allows suitably controlling the upward and downward movement of the movable portion571.

The sheet feeder500of the embodiment includes a rear end regulating member512that regulates the position of the rear end in the sheet feeding direction of the loaded sheets, and the rear end holder57is disposed integrally with the rear end regulating member512. Therefore, the rear end holder57does not require a large space.

In the sheet feeder500of the embodiment, the rear end regulating member512is movable in the sheet feeding direction a of the sheets P, and the rear end holder57moves along with the rear end regulating member512according to the length in the sheet feeding direction a of the loaded sheets P. This allows reliably holding the rear end of a sheet P regardless of the size of the sheet P.

Others

In addition to the above-described configuration, the strength of separating air and raising air may be changed according to the paper type, the basis weight and the size of the sheets and the like. That is, to feed sheets which are difficult to raise, such as board paper, the strength of the separating air and the raising air may be increased to increase the raising effect. In contrast, to feed thin sheets which are easy to raise but readily curled, the strength of the separating air and raising air may be decreased to reduce damage on the sheets.

In the above-described embodiment, the separating air is switched between the upward blow and the downward blow according to the sheet feeding state. However, depending on the paper type or the like, the blow direction may be always kept in either upward blow or downward blow. For example, when the sheets are curled in a downward concave shape, the upward blow of the separating air may press the second sheet against the topmost sheet, which produces an opposite effect to puffing. In such cases, it is effective to always keep the blow direction of the separating air in the downward blow, and the puffing is achieved only by the rear end holder57that pulls up the rear end.

In the above-described embodiment, the strength and the negative pressure of the second fan573may be changed according to the paper type, the basis weight, the size and the environment of the sheets and the like. That is, for example, to feed board paper that is difficult to raise, the negative pressure may be increased to enhance the raising assist at the rear end. In contrast, to feed thin sheets that are easy to raise but readily curled, the negative pressure may be decreased to reduce the damage on the sheets that is caused when the rear ends are held.

In the above-described embodiment, the highest position of the movable portion571where it stops upward movement is defined by a pin571aand a window hole572a, and the pin571aabuts an end of the window hole572aat the highest position. However, the mechanism is not limited thereto. The window hole572amay be configured to be able to change the height position of the pin571aso that the movable range in the height direction of the movable portion571is selectable from several ranges. This allows setting the highest position according to the sheet conditions. For example, when the sheets are long in the sheet feeding direction and the friction between the sheets are high, the highest position may be set at a higher level so that the topmost sheet is separated from the other sheets thereunder as far as possible.

Alternatively, the highest position of the movable portion571may be set according to the sheet conditions by selecting the movement in the height direction of the rear end regulating member512from several ranges.

Variation

Hereinafter, a variation of the rear end holder57will be described.

As illustrated inFIG. 12, the rear end holder57of the variation has an outlet opening572bat the second duct572opposed to the rear end of the loaded sheets P. The outlet opening572bserves as a blower that blows air from the second fan573to the rear end of the loaded sheets in the direction of the arrow F in the figure. That is, air is blown through the outlet opening573bwhile the rear end of a sheet P is pulled up by the movable portion571. This can enhance the puffing effect.

Other Embodiments

In the foregoing, the present invention is specifically described with some embodiments. However, the above-described embodiments are merely preferred examples of the present invention, and the present invention is not limited thereto.

For example, the above-described embodiments are examples of color image forming apparatuses that transfer an image on the photoreceptor drum to the intermediate transfer roller by primary transfer and further transfers the image on the intermediate transfer roller to a sheet by using the secondary transfer roller. However, the present invention is also applicable to black and white image forming apparatuses that directly transfer an image from a photoreceptor drum to a sheet by using a transfer roller.

The above-described embodiments are examples of electrophotographic image forming apparatuses. However, the sheet feeding apparatus of the present invention is also applicable to inkjet image forming apparatuses.

The first embodiment is an example of the sheet feeding apparatus that holds and conveys sheets by using air. However, the present invention is also applicable to sheet feeding apparatuses that separate sheets by the friction of a sheet feeding roller.

In the above description, non-volatile memories, hard disks and the like are illustrated as examples of computer-readable media storing a program according to the present invention. However, the computer-readable medium is not limited thereto. Other computer-readable media that are applicable include portable recording media such as CD-ROM. Carrier wave is also applicable as a medium for distributing data of the program according to the present invention through a communication line.

Suitable changes can be made in the detailed configurations and operations of the components of the image forming apparatuses without departing from the features of the present invention.