Sheet feeding apparatus and image forming apparatus

A sheet feeding apparatus 80 includes a lifter plate 23 that is disposed in a sheet storage case 4 and stacks a sheet 7a, an air heater 14 and a fan 11 that blow heated air to the sheet 7a stacked on the lifter plate 23, and a control device 16 that changes a control condition of the heated air blown by the air heater 14 and the fan 11 based on a storage period of time of the sheet 7a on the lifter plate 23.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus that includes a sheet stacking portion, which stacks sheets disposed in a sheet feeding apparatus body, and a heated air blowing portion, which blows heated air to the sheets stacked to the sheet stacking portion.

2. Description of the Related Art

In an image forming apparatus, such as a copying machine or a printer, continuously feedable sheets are generally limited to high quality paper or plain paper designated by a copying machine maker. In these sheets, since smoothness of a surface is low and air permeability is high (air can easily pass through the sheets), the air easily flows between the sheets. Accordingly, when each sheet is extracted from the stacked sheets, absorption between the sheets is rarely generated. As a result, overlapping sheet feeding is rarely generated.

Meanwhile, in recent years, with diversification of a recording medium, an image may be formed on thick paper, an OHP sheet, and tracing paper. Further, in order to give a white degree or luster in accordance with a market request for coloring, even in sheets having a smooth surface, such as coat paper and art paper where a surface of a sheet is subjected to coating processing, an image formation request has been increased. In addition, in the OHP sheet, the tracing paper, the art paper, and the coat paper, since smoothness is high and air permeability is low (air rarely passes through them), the air is not easily flown between the sheets. Accordingly, when the sheets are stacked in a high-humidity environment in particular, the sheets can be easily absorbed there between. In a friction separation system that is generally used in a copying machine or a printer according to the related art, separation is not sufficiently made. As a result, overlapping sheet feeding or erroneous feeding is frequently generated.

In regards to the sheets that have the high smoothness and the low air permeability, techniques for suppressing absorption between the sheets and reducing overlapping sheet feeding or erroneous feeding are disclosed in Japanese Patent Application Laid-Open Nos. 6-32473 and 2001-048366.

Specifically, Japanese Patent Application Laid-Open No. 6-32473 discloses a sheet feeding apparatus including an air exhaust portion that blows air heated by a dehumidifying heater provided at the lower side of a housing frame to a top surface or a side surface of a sheet stacked on a stack tray. According to this apparatus, it is possible to resolve a problem of absorption between the sheets by blowing the heated air to the sheets and removing humidity.

Japanese Patent Application Laid-Open No. 2001-048366 discloses a sheet feeding apparatus including an air blowing portion that blows air heated by an air heating portion to sheets stored in a sheet storage portion. According to this apparatus, it is possible to resolve a problem of absorption between the sheets by controlling the air heating portion and blowing air having proper humidity.

Meanwhile, according to the techniques that are related to sheet feeding disclosed in Japanese Patent Application Laid-Open Nos. 6-32473 and 2001-048366, if a sheet bundle is additionally stacked in a state where the sheets are stored in the sheet feeding apparatus, the sheets that are stored in the sheet feeding apparatus are located below the added sheet bundle. The sheets that are located at the bottom portion continuously are stored in the sheet feeding apparatus until there is no sheet that is stored in the sheet feeding apparatus. As such, if a long period of time passes in a state where the sheets are not used, moisture that is contained in the sheets may be continuously evaporated by the heated air blown to the sheets. In addition, if proper moisture is not contained in the sheets, warping is generated in the sheets. As a result, a sheet conveyance defect may be easily generated, or a surface property of the sheet or an electrostatic resistance value varies to cause a defective image to be easily formed. Accordingly, between the sheets that are stored in the sheet feeding apparatus for a long period of time and sheets that are newly stacked, image qualities may be different from each other, even though the same printed material is formed. In order to avoid this problem, a method is considered in which the amount of moisture contained in sheets having various surface properties is measured at the time of feeding the sheets and an image formation condition is changed. However, it is difficult to carry out the method, because the amount of contained moisture should be instantaneously measured at the time of feeding the sheets. Further, a method is also considered in which provided is a measuring apparatus that measures the amount of moisture of the sheets stored in the sheet feeding apparatus. However, if the measuring apparatus is provided, this causes enormous costs.

Accordingly, the present invention provides a sheet feeding apparatus that can properly maintain the amount of moisture contained in a sheet even though a storing period of time of the sheet is increased, prevent a sheet conveyance defect and an image formation defect on the sheet from being generated due to a decrease in the amount of moisture contained in the sheet, and stably output a high-quality printed material.

SUMMARY OF THE INVENTION

A sheet feeding apparatus according to an embodiment of the present invention includes a sheet stacking portion that stores sheets; a heated air blowing portion that blows heated air to the sheets stacked on the sheet stacking portion; and an air condition changing portion that changes a control condition of the heated air blown by the heated air blowing portion based on a storage period of time where each of the sheets is stored on the sheet stacking portion.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a cross-sectional view illustrating the main configuration of a copying machine1according to an embodiment of the present invention. As illustrated inFIG. 1, the copying machine1that serves as an image forming apparatus includes an image reader200that reads out an original image, a printer300, and a feeding portion400. The feeding portion400includes sheet storage cases401and451that include a common feeding mechanism. Each of the sheet storage cases401and451stores a bundle of sheets7a, that is, a sheet bundle7. The sheet storage case401can store the sheet bundle7that includes 1000 sheets. The sheet storage case451can store the sheet bundle7that includes 1500 sheets.

The sheet storage cases401and451may include an air heater or a fan serving as a “heated air blowing portion” that adjusts the temperature of air blown to the sheets7abased on a condition of the internal temperature or humidity of the sheet storage cases401and451. Further, the sheet storage cases401and451may include a dehumidifying heater that constantly maintains a condition of the temperature or humidity of the internal air of the sheet storage cases401and451.

The image reader200is mounted with an original feeding apparatus100. The original feeding apparatus100feeds each of the original sheets as the sheets upwardly set to an original tray113in a leftward direction sequentially from a head sheet. The original feeding apparatus100conveys the original sheet from a left side on a platen glass102via a moving original image reading position to a right side along a curved path, and discharges the original sheet to an external discharge tray112. When the original sheet passes through the moving original image reading position on the platen glass102from the left side to the right side, the original image is read out by a scanner unit104that is held at a position corresponding to the moving original image reading position. The reading method is generally called a moving original reading method. Specifically, when the original sheet passes through the moving original image reading position, a lamp103of the scanner unit104irradiates light onto a reading surface of the original sheet, and the light reflected from the original sheet is guided to a lens108through mirrors105,106, and107. The light that has passed through the lens108forms an image on an imaging surface of an image sensor109.

As such, if the original sheet is conveyed such that the original sheet passes through the moving original image reading position from the left side to the right side, original reading scanning where a direction orthogonal to a conveying direction of the original sheet is used as a main scanning direction and the conveying direction is used as a sub-scanning direction is performed. That is, when the original sheet passes though the moving original image reading position, the original sheet is conveyed in the sub-scanning direction while the original image is read out by the image sensor109for each line in a main scanning direction, such that the entire original image is read out. In addition, the optically read image is converted into image data by the image sensor109and is then output. The image data that is output from the image sensor109is subjected to a predetermined process in an image signal controlling portion (not illustrated) and is then input to an exposure controlling portion110of the printer300as a video signal.

Further, the original feeding apparatus100conveys the original base to the platen glass102and stops the original base at a predetermined position. In this state, the scanner unit104scans the original base from a left side to a right side. As a result, the original sheet can be read out. This reading method is called a so-called fixed original reading method. When the original base is read out without using the original feeding apparatus100, first, a user lifts the original feeding apparatus100and places the original sheet on the platen glass102. In addition, the original sheet is read out by allowing the scanner unit104to scan the original sheet from a left side to a right side. That is, when the original sheet is read out without using the original feeding apparatus100, fixed original reading is performed.

Based on the input video signal, the exposure controlling portion110of the printer300modulates a laser beam and outputs the modulated laser beam. The laser beam is irradiated onto a photosensitive drum111while being scanned by a polygon mirror. An electrostatic latent image according to the scanned laser beam is formed on the photosensitive drum111. Here, as described in detail below, when the fixed original reading is performed, the exposure controlling portion110outputs a laser beam such that a correct image (image that is not a mirror image) is formed.

The electrostatic latent image on the photosensitive drum111is converted into a visible image as a developer image by a developer that is supplied from a development device (not illustrated). Further, at timing that is synchronized with a point of time when the laser beam starts to be irradiated, the sheet is fed from each of the sheet storage cases401and451or a duplex conveying path. This sheet is conveyed between the photosensitive drum111and a transfer portion116. The developer image that is formed on the photosensitive drum111is transferred to the sheet that is fed by the transfer portion116.

The sheet where the developer image is transferred is conveyed to a fixing portion117, and the fixing portion117thermally pressurizes the sheet7aand fixes the developer image on the sheet7a. By switching a flapper (not illustrated), the sheet7athat has passed through the fixing portion117is discharged to a first discharge tray119through a first discharge roller118or a second discharge tray121through a second discharge roller120.

FIG. 2is a schematic diagram illustrating the configuration of a sheet feeding apparatus80that is mounted in a copying machine1. The sheet feeding apparatus80may be provided separately from the copying machine1as illustrated inFIG. 2or provided in the copying machine1. As described above, the sheet feeding apparatus80includes an air loosening mechanism, an air heater, and a dehumidifying heater (not illustrated), which are installed in a sheet storage case4that is a “sheet feeding apparatus body”.

As illustrated inFIG. 2, the copying machine1is supplied with the sheet7afrom the sheet storage case4through a conveying roller2and a conveyance path3, and forms an image on the sheet7a. A pick-up roller5starts to rotate at the same time as when sheet feeding starts, and the uppermost sheet6that is placed at the highest position is transmitted to the conveying roller2and the conveyance path3. In this case, the sheet7amay be fed using the pick-up roller5, but may be fed by air feeding through an air sucking belt (not illustrated).

A sheet detecting sensor8serving as a “sheet surface position detecting portion” that is a “sheet bundle position detecting portion” detects “sheet information”, for example, the thickness, density, and size of the sheet7a, and transmits the sheet information to a “control portion” serving as an “air condition changing portion”, that is, a control device16. The control device16functions as a “warm air control condition changing portion” that changes a control condition of warm air. Further, the “sheet information” may be input from an operation screen30by the user. Further, the sheet detecting sensor8detects that the uppermost sheet6of the sheet bundle7is moved up to the highest position of an inner portion of the sheet storage case4.

A temperature detecting sensor9that is a “temperature detecting portion” detects the internal temperature of the sheet storage case4and transmits information to the control device16. A humidity detecting sensor10that is a “humidity detecting portion” detects the internal humidity of the sheet storage case4and transmits information to the control device16.

A lifter plate23serving as a “sheet stacking portion” where the sheets7acan be stacked is disposed in the sheet storage case4that is the “sheet feeding apparatus body”. The lifter plate23is configured to be lifted and lowered in the sheet storage case4. A duct13is disposed on the side of the lifter plate23. A fan11that is a portion of the “heated air blowing portion” is disposed on an opening side of an outlet of the duct13. The fan11blows “heated air” to a peripheral portion of the uppermost sheet6that is disposed at the uppermost position of the sheet7aso as to loosen the sheet7a, thereby preventing coat sheets from overlapping each other. A swing shutter19reciprocally moves in a “sheet loading direction”, for example, an up-to-down direction, and blocks or passes a portion of the heated air blown from the fan11and loosens the sheet7a. The swing shutter19is driven by a swing motor (not illustrated).

The sheet7ais stacked on the lifter plate23. The lifter plate23is lifted up to a position where the uppermost sheet6can always be detected by the sheet detecting sensor8serving as the “sheet bundle position detecting portion”, by means of a lifter motor512(refer toFIG. 3) (which will be described in detail below) in a state where the sheet storage case4is closed.

Further, the lifter plate23includes a sheet existence/non-existence detecting sensor21and a lifter plate lower limit detecting sensor22. The sheet existence/non-existence detecting sensor21detects whether or not the sheet7aexists on the lifter plate23. The sheet existence/non-existence detecting sensor21is used in order to detect when the sheet7ais replaced in a state where the sheet storage case4is opened. However, when the sheet7ais extracted from the sheet storage case4, all of “storage periods of time” are cleared. The sheet existence/non-existence detecting sensor21can detect whether the sheet exists or not, regardless of a state where the sheet storage case4is closed or a state where the sheet storage case4is opened.

The lifter plate lower limit detecting sensor22detects a movement amount by which the lifter plate23is moved to a floor face of the sheet storage case4. As will be described in detail below, the lift-up amount of the lifter plate23is detected by the sheet detecting sensor8and the lifter plate lower limit detecting sensor22, and an addition amount of the sheet bundle7is calculated based on the lift-up amounts before and after supplying the sheet7a. Further, the sheet existence/non-existence detecting sensor21can detect whether the sheet exists or not, even though the sheet storage case4is opened.

The duct13is disposed on the side of the lifter plate23. An air heater14is mounted in the duct13. The air is sucked from the lower side of the duct13, heated by the air heater14, and discharged by the fan11. The air heater14is set such that the heated air is blown to the sheet7abefore starting to feed the sheet7aand during the feeding operation of the sheet7a. Further, the air heater14may be set such that the heated air is blown to the sheet7a, only before starting to feed the sheet7aor the feeding operation of the sheet7a. If an SSR17that is connected to an AC voltage18is controlled by the control device16, the air heater14makes heat generated from an internal resistor and heats the air sucked from the lower side.

An air heater temperature detecting sensor15that is the “air heater temperature detecting portion” comes into contact with the air heater14and transmits information related to the temperature of the air heater14to the control device16. The control device16performs an ON/OFF control operation on the AC voltage18and the SSR17based on the information transmitted from the air heater temperature detecting sensor15. A control condition of the control device16is a temperature condition. The control device16performs temperature control based on a temperature table (refer toFIGS. 6A and 6B) and a temperature correction table (refer toFIG. 7), which will be described in detail below, such that the temperature of the air heater14has a constant value. The detailed control will be described below. Further, in regards to an error detecting method of the air heater14, a control operation is performed such that the air heater temperature detecting sensor15is used to output a high temperature error, when the temperature reaches the predetermined temperature or more. Further, when the temperature does not reach the predetermined temperature even though a predetermined time passes after a driving signal of the air heater14is output from the control device16, the air heater temperature detecting sensor15is used to output a low temperature error. However, in regards to the low temperature error of the air heater14, a control operation is performed such that the low temperature error is displayed on the operation screen30only when the low temperature error of a cassette heater40(which will be described in detail below) is also simultaneously generated.

A cassette heater temperature detecting sensor41that is a “cassette heater temperature detecting portion” comes into contact with the cassette heater40and transmits temperature information related to the cassette heater40to the control device16. Similar to the air heater14, the control device16performs an ON/OFF control operation on the AC voltage18and the SSR17based on the information transmitted from the cassette heater temperature detecting sensor41. However, in regards to the cassette heater40, supplying of power to the cassette heater40may be controlled based on the values that are calculated by the temperature detecting sensor9and the humidity detecting sensor10.

FIG. 3is a block diagram illustrating a control device16. A CPU501executes a program that is used to perform each driving control operation on the sheet storage case4. As illustrated at the lower side ofFIG. 3, the CPU501is connected to a RAM503and a ROM502. The detailed contents of the ROM502will be described below with reference toFIG. 4and the detailed contents of the RAM will be described below with reference toFIG. 5. Further, the CPU501is connected to the sheet existence/non-existence detecting sensor21that is the “sheet existence/non-existence detecting portion” and the lifter plate lower limit detecting sensor22serving as the “sheet surface position detecting portion” that is the “sheet bundle position detecting portion”.

As illustrated at the upper side ofFIG. 3, the CPU501is connected to an A/D converter504, and the A/D converter504is connected to a sheet detecting sensor8, a temperature detecting sensor9, a humidity detecting sensor10, a cassette heater temperature detecting sensor41, and an air heater temperature detecting sensor15. Analog values that are input from the various sensors8,9,10,41, and15are converted into digital values that enable analog levels to be determined by the CPU501. A PWM generating circuit505can generate an ON/OFF pulse with respect to the SSR17that has been described with reference toFIG. 2.

As illustrated at the left side ofFIG. 3, the CPU501is connected to a motor driver506and a pulse encoder507. The motor driver506and the pulse encoder507are connected to the lifter motor512serving as a “sheet surface lifting mechanism”. The lifter motor512lifts a sheet surface of the uppermost sheet6up to the predetermined position, after the sheet bundle7is supplied. Further, the pulse encoder507measures the number of driving pulses when the lifter motor512is driven. Information of the number of driving pulses is received by the CPU501, and the CPU501measures the position of the lifter plate23of the sheet storage case4based on the number of driving pulses. Further, the motor driver506drives the lifter motor512that drives the lifter plate23as described above. In addition, the motor driver506is connected to a conveyance motor510that drives the conveying roller and a swing shutter driving motor511that drives the swing shutter, and drives the conveyance motor510and the swing shutter driving motor511.

As illustrated at the right side ofFIG. 3, the CPU501can operate a solenoid to open the sheet storage case4by operating an opening solenoid switch20. Further, the CPU501operates a fan driving driver508, thereby operating the fan11. Further, the CPU501can communicate with the copying machine1through a serial communication driver509. In particular, although not illustrated in the drawings, the CPU501has a clock that is provided in the CPU501and can recognize an arbitrary time. Although not illustrated in the drawings, even in the configuration where the CPU501obtains temporal information from the copying machine1through the serial communication driver509, it is obvious that the same effect can be obtained.

FIG. 4is a diagram illustrating an address map of a ROM502. The ROM502stores a program area601, a motor driving setting table602, and a heater control temperature table603. The program area601stores a control program body and data. The motor driving setting table602stores driving parameters, such as a driving speed or an acceleration rate, which are needed to drive the conveyance motor510, the swing shutter driving motor511, and the lifter motor512. The heater control temperature table603stores a temperature table (refer toFIGS. 6A and 6B) for heater control (which will be described in detail below) or a temperature correction table (refer toFIG. 7) for heater control (which will be described in detail below).

FIG. 5is a diagram illustrating an address map of a RAM503. The RAM503stores a work and stack area701and a sheet bundle management memory702. The work and stack area701is a work and stack area that is needed to execute a program. The sheet bundle management memory702stores information (refer toFIGS. 8A to 8D) that is related to the sheet bundle7, which will be described in detail below.

In the above configuration, the operation until the air heater14starts to adjust the temperature and loosens the sheet7aand the pick-up roller5starts to feed the sheet will be described. First, the control device16determines an optimal air heater target temperature based on the “temperature and humidity information” transmitted from the temperature detecting sensor9and the humidity detecting sensor10to the control device16and the “sheet information” transmitted from the sheet detecting sensor8to the control device16. Specifically, the “sheet information” includes information that is related to the thickness, density, and size of the sheet.

FIGS. 6A and 6Billustrate temperature tables for heater control. As illustrated inFIGS. 6A and 6B, the target temperature of the air heater14that serves as the “heated air blowing portion” is set. First, as illustrated inFIG. 6A, it is assumed that the sheet detecting sensor8determines a sheet P stored in the sheet storage case4as a coat sheet.

As illustrated by a dot J, it is assumed that the temperature detecting sensor9detects the internal temperature of the sheet storage case4as 25° C. and the humidity detecting sensor10detects the internal humidity of the sheet storage case4as 70%. In this case, the target temperature of the air heater14is set to 90° C. Here, an environment where the temperature is adjusted to 90° C. is called an E2 environment. The E2 environment is a target environment that is set when the humidity is H2(=60%) or more. If the control device16determines that the internal temperature of the sheet storage case4is 90° C. or less based on the information transmitted from the air heater temperature detecting sensor15, the control device16turns on a power supply device of the SSR17such that power is supplied to the air heater14, thereby increasing the temperature. In contrast, if the control device16determines that the internal temperature of the sheet storage case4is higher than 90° C., the control device16turns off the power supply device of the SSR17such that supplying of power to the air heater14is stopped.

Next, as illustrated by a dot K, it is assumed that the temperature detecting sensor9detects the internal temperature of the sheet storage case4as 35° C. and the humidity detecting sensor10detects the internal humidity of the sheet storage case4as 50%. In this case, the target temperature of the air heater14is set to 60° C. Here, an environment where the temperature is adjusted to 60° C. is called an E1 environment. The E1 environment is a target environment that is set when the temperature is T1(=50° C.) or less in the case where the humidity is H2(=40 to 60%). If the control device16determines that the internal temperature of the sheet storage case4is 60° C. or less based on the information transmitted from the air heater temperature detecting sensor15, the control device16turns on the power supply device of the SSR17such that power is supplied to the air heater14, thereby increasing the temperature. In contrast, if the control device16determines that the internal temperature of the sheet storage case4is higher than 60° C., the control device16turns off the power supply device of the SSR17such that supplying of power to the air heater14is stopped.

Next, as illustrated by a dot L, it is assumed that the temperature detecting sensor9detects the internal temperature of the sheet storage case4as 55° C. and the humidity detecting sensor10detects the internal humidity of the sheet storage case4as 40%. In this case, the air heater14is turned off (this case is described as “OFF” in the drawings, which is applicable to the following description). As such, the case where the air heater14is turned off corresponds to the case where the internal humidity of the sheet storage case4is lower than H2(=60%) and the temperature thereof is higher than T1(=50° C.). Further, the case where the air heater14is turned off corresponds to the case where the internal humidity of the sheet storage case4is lower than H1(=40%) and the temperature thereof is lower than T1(=50° C.). However, the chart that is illustrated inFIG. 6Ais exemplary. Although the temperature table needs to be more minutely divided as an optimal temperature adjustment specification, the temperature table is simply illustrated herein.

Next, as illustrated inFIG. 6B, it is assumed that the sheet detecting sensor8determines the sheet P stored in the sheet storage case4as a non-coat sheet. In this case, power is not supplied to the air heater14. That is, the control device16continuously maintains a state where the SSR17is turned off. However, the chart ofFIG. 6Bis exemplary. Although the temperature table needs to be more minutely divided as an optimal temperature adjustment specification, the temperature table is simply illustrated herein.

FIG. 7illustrates a temperature correction table for heater control. As illustrated inFIG. 7, when the control device16determines that the sheet P is a coat sheet and an internal environment of the sheet storage case4is an E1 environment, a correction temperature is different depending on a waiting time that is a “storage period of time” of the sheet P in the sheet storage case4. For example, if the waiting time is within the “predetermined period of time”, for example, 2 hours, the correction temperature is set as 0° C. as the “temperature where correction is not made”, which is the “first target temperature”.

If the waiting time passes the “predetermined period of time” and is not less than 2 hours and less than 24 hours, the correction temperature is set as −10° C. as the “temperature where correction is made”, which is the “second target temperature”. If the waiting time passes the “predetermined period of time” and is not less than 24 hours, the correction temperature is set as −15° C. as the “temperature where correction is made”, which is the “second target temperature”.

When the control device16determines that the sheet P is a coat sheet and an internal environment of the sheet storage case4is an E2 environment, a correction temperature is different depending on a waiting time that is the “storage period of time” of the sheet P in the sheet storage case4, in the same way as the above. For example, if the waiting time is within the “predetermined period of time”, for example, 2 hours, the correction temperature is set as 0° C. as the “temperature where correction is not made”, which is the “first target temperature”.

If the waiting time passes the predetermined period of time and is not less than 2 hours and less than 24 hours, the correction temperature is set as −15° C. as the “temperature where correction is made”, which is the “second target temperature”. If the waiting time passes the predetermined period of time and is not less than 24 hours, the correction temperature is set as −30° C. as the “temperature where correction is made”, which is the “second target temperature”.

As such, the “second target temperature” is set to be lower than the “first target temperature”. When the sheet P is a non-coat sheet, the correction temperature is set as 0° C., regardless of whether the internal environment is the E1 environment or the E2 environment. When the correction temperature is set as 0° C., the air heater14is not controlled.

Accordingly, the target temperature of the air heater14is corrected in accordance with the storage period of time of the sheet7astarting from a point of time when the sheet bundle7is stored in the sheet storage case4. For example, as illustrated by the dot K inFIG. 6A, it is assumed that the sheet bundle7is a coat sheet bundle, the internal temperature of the sheet storage case body4ais 35° C., and the humidity thereof is 50%. In this case, the controlled target temperature is 60° C. In addition, it is assumed that the sheet bundle7of the coat sheets is stored for 5 hours under the E1 environment. In this case, the temperature of 10° C. is subtracted from the target temperature of 60° C. As a result, the target temperature after the correction becomes 50° C. Further, when the sheet7ais a non-coat sheet, the air heater14is not operated. Therefore, the correction temperature is 0° C. and the target temperature stays 60° C.

FIG. 8Ais a schematic diagram illustrating a format of a data structure that is related to a sheet bundle7. A data structure800of the sheet bundle management memory includes a sheet bundle ID801, a sheet bundle top surface position802, a sheet bundle bottom surface position803, a sheet bundle supply time804, a lift-up amount805at the time of supplying sheets, and a sheet bundle ID806of a bottom surface. The data structure800of the sheet bundle management memory stores a “sheet bundle position” detected by the sheet detecting sensor8and the lifter plate lower limit detecting sensor22, that is, a sheet bundle top surface position802and a sheet bundle bottom surface position803as “position information”, for “every sheet bundle”, that is, every sheet bundle7. The data structure800functions as a “position storage portion”. Further, the data structure800of the sheet bundle management memory702functions as a “supply time storage portion” that stores a sheet bundle supply time804recognized by a clock as “supply time information”, for every sheet bundle7. The sheet bundle ID (ID)801is an ID that is used to identify each sheet bundle. An area of the ID801is assigned with a number of 1, 2, . . . , in the order of sheet bundles disposed at lower positions.

The sheet bundle top surface position (Lup)802is a top surface position of the sheet bundle7that is supplied to the lifter plate23. The number of driving pulses of the lifter motor512is stored in an area of the Lup802. In this case, uppermost surface position information such as the sheet bundle top surface position802that is detected whenever the sheet bundle7is stacked on the lifter plate23is stored for every sheet bundle7. In the case where no sheet7aexists on the lifter plate23, the Lup802becomes 0, when the lifter plate23is disposed at the lowest position.

The sheet bundle bottom surface position (Ldwn)803is a bottom surface position of the sheet bundle7that is supplied to the lifter plate23. The number of driving pulses of the lifter motor512is stored in the area of the Ldwn803. In this case, lowermost surface position information such as the sheet bundle bottom surface position803that is detected whenever the sheet bundle7is stacked on the lifter plate23is stored for every sheet bundle7. Regardless of whether or not the sheet7aexists on the lifter plate23, the Ldwn803becomes 0, when the lifter plate23is disposed at the lowest position.

The sheet bundle top surface position (Lup)802and the sheet bundle bottom surface position (Ldwn)803will be described in detail below with reference toFIGS. 10A to 10F.

The sheet bundle supply time (TsupN)804is a time when the sheet bundle7is supplied and the sheet storage case4is closed. The supply time information that is related to a supply time of the sheet bundle7that is detected whenever the sheet bundle7is stacked on the lifter plate23is stored for every sheet bundle7. The lift-up amount (LiftN)805at the time of supplying the sheet bundle is a movement amount by which the lifter plate23is lifted when the sheet bundle7is supplied and the sheet storage case4is closed, that is, a displacement. The number of driving pulses of the lifter motor512is stored in the area of the LiftN804.

In the sheet bundle ID (IDp)806of the bottom surface, the sheet bundle ID (ID)801of the sheet bundle7that is previously stacked below the newly stacked sheet bundle7is stored.

Further, the sheet bundle top surface position (Lup)802, the sheet bundle bottom surface position (Ldwn)803, and the lift-up amount (LiftN)805at the time of supplying the sheet bundle are used as “position information”.

FIGS. 8B to 8Dare schematic diagrams illustrating utilization embodiments of a data structure that is related to a sheet bundle7. When the lifter plate23where the sheet bundle7is not placed is lifted up, the number of driving pulses of the lifter motor512is set as 1000. In this case, it is assumed that the sheet bundles7are supplementally stacked.

A data structure807of the sheet bundle management memory indicates a data structure that is related to the sheet bundle7stored in a lowermost portion of the lifter plate23. As illustrated inFIG. 8B, since the sheet bundle7is first placed on the lifter plate23, the data structure that is related to ID=1 is assigned. Since the sheet bundle7is disposed in the lowermost portion of the lifter plate23, Ldwn becomes 0. If the lift-up amount LiftN at the time of supplying the sheet bundle7is set to 850, the sheet bundle top surface position Lup becomes 150. In this case, 07.07.10.16:40 is recorded as the sheet bundle supply time TsupN. Since another sheet bundle7does not exist below the sheet bundle7, IDp=0 is assigned.

Next, a data structure808of the sheet bundle management memory indicates a data structure that is related to the sheet bundle7stored on the sheet bundle7stacked on the lifter plate23. As illustrated inFIG. 8C, since the sheet bundle7is secondly placed on the lifter plate23, ID=2 is assigned. Since the sheet bundle7is disposed on the sheet bundle7that is stacked on the lifter plate23, Ldwn becomes 150. If the lift-up amount LiftN at the time of supplying the sheet bundle7is set to 530, the sheet bundle top surface position Lup becomes 470. In this case, 07.07.10.21:12 is recorded as the sheet bundle supply time TsupN. Since another sheet bundle7exists below the sheet bundle7, IDp=1 is assigned.

Next, a data structure809of the sheet bundle management memory indicates a data structure that is related to the sheet bundle7disposed on the sheet bundle7stacked on the lifter plate23. As illustrated inFIG. 8D, since the sheet bundle7is thirdly placed on the lifter plate23, ID=3 is assigned. Since the sheet bundle7is placed on the sheet bundles7that are stacked on the lifter plate23, Ldwn becomes 470. If the lift-up amount LiftN at the time of supplying the sheet bundle7is set to 170, the sheet bundle top surface position Lup becomes 830. In this case, 07.07.10.23:37 is recorded as the sheet bundle supply time TsupN. Since another sheet bundle7exists below the sheet bundle7, IDp=2 is assigned.

As such, if the new sheet bundle7is additionally disposed on the sheet bundle7that is stored on the lifter plate23, a new sheet bundle management memory is added to in RAM503. In particular, although not illustrated in the drawings, when the sheet storage case4is opened and all of the sheet bundles7in the sheet storage case4are extracted, all of the sheet bundle management memories are cleared. Although not illustrated in the drawings, the sheet bundle management memory is cleared in regard to the sheet bundle7where all of the sheets7aare fed.

FIG. 9is a flowchart illustrating a process of supplying a sheet bundle7to a lifter plate23by opening and closing a sheet storage case4. The control device16starts an algorithm at the time of opening and closing the sheet storage case4(Step901, hereinafter, a “Step” is simply referred to as “S”). The control device16determines whether the sheet storage case4is opened or not (S902). At this time, in the case of YES, in accordance with an instruction from the control device16, the lifter plate23is lifted down up to a position where the lifter plate lower limit detecting sensor22is turned on (S903). In this state, an operator supplements the sheets7ain the sheet storage case4. In the case of NO, the control device16determines again whether the sheet storage case4is opened or not (S902).

Next, if the lifter plate23is lifted down (S903), the sheet bundle7is placed on the lifter plate23. Then, the control device16determines whether the sheet storage case4is closed or not (S904). At this time, in the case of YES, the control device16starts to lift up the lifter plate23(S905). The control device16monitors whether the sheet detecting sensor8is turned on or not (S906). In the case of YES, the control device16generates a new sheet bundle management memory (S907). When the new sheet bundle management memory is generated, a sheet bundle ID is added, a sheet bundle bottom surface position is calculated, a sheet bundle supply time is stored, the lift-up amount as a “movement distance” is stored, and a sheet bundle ID of a bottom surface is added (S907).

In the case of NO, the control device16monitors whether a predetermined time passes, that is, a time-out is made (S908). In the case of YES, the control device16displays a message, which indicates that the sheet bundle7does not exist in the sheet storage case4, on a display portion (not illustrated) (S909). In the case of NO, the control device16monitors again whether the sheet detecting sensor8is turned on or not (S906). If a new sheet bundle management memory is generated, the algorithm is returned (S910). The algorithm of when the sheet storage case4is opened and closed starts (S901).

FIGS. 10A to 10Fare schematic diagrams illustrating a positional relationship between a lifter plate23and a sheet bundle7when a sheet bundle is supplied. As illustrated inFIGS. 10A,10C, and10E, when the sheet storage case4is closed, the lifter plate23is lifted up until the uppermost sheet6of the sheet bundle7comes into contact with the sheet detecting sensor8and the sheet detecting sensor8is turned on. As illustrated inFIGS. 10B,10D, and10F, when the sheet storage case4is opened, the lifter plate23is lifted down up to the bottom surface of the sheet storage case4, and the sheet bundle7is supplemented again.

At this time, the driving pulses of the lifter motor512are counted, and the counted number is stored in the sheet bundle management memory in a form of ID=N. If the height from the bottom portion of the sheet storage case4to the sheet detecting sensor8corresponds to the pulse number of K, the sheet bundle top surface position Lup (N) of the supplemented sheet bundle is represented by the following Equation.

[Equation 1]
Lup(N)=K−LiftN(1)
In the same way, the sheet bundle bottom surface position Ldwn (N) of the supplemented sheet bundle is represented by the following Equation.
[Equation 2]
Ldwn(N)=Lup(N−1)  (2)
In this way, the boundary of the sheet bundle7is recognized. Further, the control device16calculates the position information of the supplied sheet bundle7based on the lift-up amounts of the lifter plate23before and after supplying the sheet7a, which are stored in a sheet bundle management memory702.

Hereinafter, the case where the height from the bottom portion of the sheet storage case4to the sheet existence/non-existence detecting sensor21corresponds to the number of pulses of K=1000 is exemplified.

As illustrated inFIG. 10A, when the sheet bundle7at the (N−2)-th stage is stacked on the lifter plate23, the lifter plate23is lifted up to a position where the uppermost sheet6of the sheet bundle7at the (N−2)-th stage comes into contact with the sheet detecting sensor8. In this case, the lifter plate23is lifted up from the bottom surface of the sheet storage case4, and moves up to the position where the uppermost sheet6comes into contact with the sheet detecting sensor8. The lifter plate lower limit detecting sensor22detects LiftN=850 pulse number. In addition, as illustrated inFIG. 10B, if the lifter plate23moves to the bottom surface of the sheet storage case4, the CPU501determines that the sheet bundle7at the (N−2)-th stage corresponds to Lup=150 pulse number and Ldwn=0 pulse number.

Next, as illustrated inFIG. 10C, when the sheet bundle7at the (N−1)-th stage is stacked on the sheet bundle7at the (N−2)-th stage, the lifter plate23is lifted up to a position where the uppermost sheet6of the sheet bundle7at the (N−1)-th stage comes into contact with the sheet detecting sensor8. In this case, the lifter plate23is lifted up from the bottom surface of the sheet storage case4, and moves up to the position where the uppermost sheet6comes into contact with the sheet detecting sensor8. The lifter plate lower limit detecting sensor22detects LiftN=530 pulse number. In addition, as illustrated inFIG. 10D, if the lifter plate23moves to the bottom surface of the sheet storage case4, the CPU501determines that the sheet bundle7at the (N−1)-th stage corresponds to Lup=470 pulse number and Ldwn=150 pulse number.

Next, as illustrated inFIG. 10E, when the sheet bundle7at the N-th stage is stacked on the sheet bundle7at the (N−1)-th stage, the lifter plate23is lifted up to a position where the uppermost sheet6of the sheet bundle7at the N-th stage comes into contact with the sheet detecting sensor8. In this case, the lifter plate23is lifted up from the bottom surface of the sheet storage case4, and moves up to the position where the uppermost sheet6comes into contact with the sheet detecting sensor8. The lifter plate lower limit detecting sensor22detects LiftN=170 pulse number. In addition, as illustrated inFIG. 10F, if the lifter plate23moves to the bottom surface of the sheet storage case4, the CPU501determines that the sheet bundle7at the N-th stage corresponds to Lup=830 pulse number and Ldwn=470 pulse number.

When the sheet bundles7at the (N−2)-th to N-th stages are stacked on the lifter plate23at different points of time, the “storage period of time” of the sheet bundle7that has the “largest thickness” is included as a reference and the target temperature of the heated air is set. In accordance with the “thickness”, “storage period of time”, and “disposition environment” of the sheet bundle7, the control temperature of the air heater14is changed. As a result, optimal control is enabled.

When the sheet bundles7at the (N−2)-th to N-th stages are stacked on the lifter plate23at different points of time, the “storage period of time” of the sheet bundle7at the (N−2)-th stage as the lowest stage is included as a reference and the target temperature of the heated air may be set. Alternatively, the target temperature of the heated air may be set based on the “storage period of time” and the “thickness” of the sheet bundle7at the (N−2)-th stage as the lowest stage.

Based on a combination of parameters such as the “storage period of times” and the “thicknesses” of the individual sheet bundles7until the sheet bundle7at the N-th stage as the uppermost stage from the sheet bundle7at the (N−2)-th stage as the lowest stage, the target temperature can be more minutely set.

Further, the sheet bundle7that previously is stored on the lifter plate23corresponds to the “previously stored sheets”, and the sheet bundle7that is added to the “previously stored sheets” corresponds to the “added sheets”.

FIG. 11is a flowchart illustrating a feeding operation of when a sheet bundle7is fed from a sheet storage case4. The control device16starts the operation of the feeding portion (S1101). When the sheet bundle7is fed, first, the control device16acquires the current time Tnow (S1102). Next, the control device16acquires the current temperature and humidity by the temperature detecting sensor9and the humidity detecting sensor10, and determines an environmental compartment ENVnow (S1103). The control device16calculates the height of the shift surface (Lup(N)now=K−LiftN) from the current lifter plate23(S1104). In particular, although not illustrated in the drawings, the CPU501always detects the height of the sheet surface using the driving pulses of the lifter motor512.

Since the sheet bundle7is the sheet bundle7whose sheet bundle ID has the largest value, a difference Tstaynow between the current time Tnow and the time when the sheet bundle7is supplemented in the sheet storage case4is operated (S1105).

Next, based on ENVnow and Tstaynow, the control temperature of the air heater14is determined from the temperature table for heater control illustrated inFIGS. 6A and 6Band the temperature correction table for heater control illustrated inFIG. 7. The control temperature of the heated air is changed and the feeding operation starts (S1107). The process is returned to the feeding operation (S1108).

According to the embodiment of the present invention, the control device16changes a control condition of the heated air based on the storage period of time of the sheet7athat is stored in the sheet storage case4. Accordingly, the amount of moisture that is contained in the sheet7ais varied depending on the storage period of time of the sheet7ain the sheet storage case4. When the storage period of time is decreased, the amount of moisture that is contained in the sheet7ais increased. When the storage period of time is increased, the amount of moisture that is contained in the sheet7ais decreased. The control device16changes the control condition of the heated air based on the storage period of time of the sheet7aand a state of the heated air is adjusted in accordance with the amount of moisture that is contained in the sheet7a. In this case, the amount of moisture that is contained in the sheet7ais always maintained at a constant level. As a result, the amount of moisture contained in the sheet7acan be prevented from being excessively increased and decreased, a conveyance defect of the sheet7aor an image formation defect on the sheet7ais suppressed, and a high-quality printed material is stably output. Further, an expensive measuring apparatus that measures a contained moisture amount does not need to be provided in order to estimate the amount of moisture contained in the sheet7a.

Further, the control device16changes the temperature condition of the heated air and the amount of moisture contained in the sheet7ais varied depending on a degree of evaporation.

Further, when the storage period of time of the sheet7ais short, the temperature is set to a relatively high first target temperature. When the storage period of time of the sheet7ais long, the temperature is set to a relatively low second target temperature. Accordingly, the sheet7awhere the storage period of time is long is not heated at the unnecessarily high temperature. As a result, the sheet7awhere the storage period of time is long can maintain the contained moisture amount more properly than the related art.

Further, if the storage period of time of the sheet7a, the internal temperature and humidity of the sheet storage case4, and the types of the sheets7aare combined and the control condition is changed, the control condition of the heated air is precisely set.

Further, the sheet detecting sensor8detects the position of the sheet bundle7whenever the sheet bundle7is newly stacked on the lifter plate23. Based on the position information that is related to the plurality of sheet bundles7, the control condition of the sheet7ais step-wisely changed. In actuality, the control condition of the sheet7ais changed based on the sheet bundle7that is stored on the lifer plate23for a longest period of time.

Further, the control condition of the sheet7ais step-wisely changed based on the supply time information that is related to the supply times of the plurality of sheet bundles7. In actuality, the control condition of the sheet7ais changed based on the sheet bundle7that is stored on the lifer plate23for a longest period of time.

Further, as described above, the image forming apparatus may be configured using the image forming portion, such as the sheet feeding apparatus80and the photosensitive drum111.

This application claims the benefits of Japanese Patent Application No. 2008-151280, filed Jun. 10, 2008, which is hereby incorporated by reference herein in its entirety.