Abstract:
A sheet feeding apparatus which includes a sheet loading tray for stacking sheets; a suction and conveyance section which is placed above stacked sheets on the sheet loading tray and sucks and conveys a sheet in the sheet conveying direction; an air blowing section which blows air at the stacked sheets on the sheet loading tray and causes the sheet to float up; and a skew correction section which corrects a skew of the sheet conveyed by the suction and conveyance section.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional application of U.S. patent application Ser. No. 12/762,838, filed on Apr. 19, 2010, the entire contents of which are incorporated herein by reference. The 12/762,838 application claimed the benefit of the date of the earlier filed Japanese Patent Application No. 2009-101733 filed Apr. 20, 2009, the benefit of which is also claimed herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a sheet feeding apparatus that separates and feeds one sheet at a time from a stack of sheets placed on a table for sheets, and to image forming apparatuses. 
         [0004]    2. Background Technology 
         [0005]    In recent years, air sheet feeding apparatuses that can feed a large quantity of sheets are being used in image forming apparatuses such as copying machines, printers, etc. An air sheet feeding apparatus is one in which a sheet is made to float up by blowing air on to the side surface of a stack of sheets, a sheet is made to get sucked on to the suction surface of a belt, etc., in which are formed air suction holes that suck in air, and the sheet is conveyed by driving the belt in a rotating manner. 
         [0006]    Conventionally, this kind of sheet feeding apparatus was one that fed large quantities of sheets of the same size or of the same type. However, in recent years, due to the progress in digital information technology, a printing method called print on demand has come into widespread use in which the data prepared by a computer, etc., is printed out directly without going through an intermediate step of preparing offset printing films or plates, and sheet feeding apparatuses have become necessary that can feed sheets of various types and sizes that are being used in the printing industry. 
         [0007]    In Examined Japanese Patent Application Publication No. 3855512 (Patent Document 1), an air sheet feeding apparatus has been disclosed wherein, nozzles (sheet raising means) that jet out air on the front surface of a stack of sheets for causing a sheet to float up, and nozzles (sheet separating means) for blowing air for separating other sheets from a single sheet that is made to be sucked and attached to the conveying belt are provided on the front side of the stack of sheets in the direction of feeding the sheet. 
         [0008]    According to Patent Document 1, sheet feeding is made possible without feeding several sheets simultaneously by selectively switching the air from the sheet raising means and the sheet separating means according to the timing of sheet feeding by the conveying belt. 
         [0009]    In Examined Japanese Patent Application Publication No. 3891405 (Patent Document 2), an air sheet feeding apparatus has been disclosed wherein, a sheet at the topmost surface of a stack of sheets is fed while being sucked by a suction and conveyance means because the sheet is floated up by a first air blowing means that blows air on the front surface of a stack of sheets from the front side of the direction of sheet feeding, and a second air blowing means that blows air on the side surface of the stack of sheets. 
         [0010]    According to Patent Document 2, a positioning member is provided that restricts the height on the side surface of a sheet or in its neighborhood, a constant sheet separation is obtained at all times by selecting the air blow from a second air blowing means in accordance with the size of the sheet. 
         [0011]    However, in an air sheet feeding apparatus described in Patent Document 1 or Patent Document 2, in order to separate definitely the topmost sheet that is sucked by the sucking and conveying section from the other sheets, a certain amount of space is required in the up-down direction between the topmost surface of the stack of sheets and the suction and conveyance section. 
         [0012]    In this kind of configuration, in the floating process of transiting from the stacked state to the state of getting sucked by the sucking and conveying section, since the raised sheet can take various types of postures (such as flexure or distortion) depending on the condition of the air getting into the stack of sheets, conditions can arise in which the leading edge of the sheet is sucked by the suction and conveyance section at an angle to the conveying direction. If a sheet is sucked and conveyed in this condition, the suction area moves towards the trailing edge so as to maintain the position of the leading edge of the sheet that is inclined. In other words, the sheet gets skewed. 
         [0013]    As described above, an air sheet feeding apparatus has the problem that the fluctuations in the sheet skewing are large, and improvement of sheet skewing is desired. In particular, the demand is very strict about the positional accuracy of the image formed on a sheet and the sheet (image registration) in the field of print on demand, and improvement of sheet skewing is strongly desired in the case of air sheet feeding apparatuses used in this field. 
         [0014]    In an image forming apparatus, although a skewing correction mechanism (paper registration mechanism) is provided at a position just before image transfer, particularly in the case of sheets of large sizes, since the part of the sheet on the upstream side is nipped by a plurality of conveying rollers, even if an attempt is made to correct a large skewing at this point of time, due to the pulling of the sheet between the registration mechanism and the conveying rollers, a large stress is applied on the sheet, problems occur such as buckling or wrinkling, etc. 
         [0015]    An object of the present invention is to solve the problem that the fluctuations in sheet skewing are large, and to provide an air sheet feeding apparatus having excellent sheet feeding performance that is demanded in the print on demand field. 
       SUMMARY OF THE INVENTION 
       [0016]    A sheet feeding apparatus and a system reflecting the aspects of the present invention for solving the above problems are the following: 
         [0000]    1. A sheet feeding apparatus including a sheet loading tray for stacking sheets; a suction and conveyance section which is placed above stacked sheets on the sheet loading tray and sucks and conveys a sheet in the sheet conveying direction; an air blowing section which blows air at the stacked sheets on the sheet loading tray and causes the sheet to float up; and a skew correction section which corrects a skew of the sheet conveyed by the suction and conveyance section.
 
2. The sheet feeding apparatus of above item 1, further including a pair of conveying rollers provided on a downstream side in the sheet conveying direction relative to the suction and conveyance section and along the width direction perpendicular to the sheet conveying direction, to convey the sheet conveyed from the suction and conveyance section towards the downstream side in the sheet conveying direction,
 
         [0017]    wherein the skew correction section is a section which controls the pair of conveyance rollers to stop, and during the period when the pair of conveyance rollers is stopped, controls at least the pair of conveyance rollers so that a leading edge of the sheet is made to abut against the pair of conveyance rollers. 
         [0000]    3. The sheet feeding apparatus of above item 1, further including a skew detection section which detects a skew amount of the sheet conveyed by the suction and conveyance section, 
         [0018]    wherein the suction and conveyance section comprises a plurality of sheet conveying sections, each of the plurality of sheet conveying sections being arranged along the width direction and being capable of conveying the sheet with independent conveying speed to each other, 
         [0019]    wherein the skew correction section is configured to control the conveying speeds of the plurality of sheet conveying sections respectively, according to the skew amount of the sheet detected by the skew detection section. 
         [0000]    4. The sheet feeding apparatus of above item 1, further including a skew detection section which detects a skew amount of the sheet conveyed by the suction and conveyance section; and a displacing section which displaces the suction and conveyance section with respect to the sheet conveying direction, 
         [0020]    wherein the skew correction section is configured to control the displacing section to change an angle of the suction and conveyance section with respect to the sheet conveying direction according to the skew amount of the sheet detected by the skew detection section. 
         [0000]    5. The sheet feeding apparatus of above item 3 or 4, further including a sheet detection sensor which detects a leading edge of the sheet fed out by the suction and conveyance section; and a pair of conveying rollers provided on a downstream side in the sheet conveying direction relative to the sheet detection sensor and along the width direction perpendicular to the sheet conveying direction, to convey the sheet conveyed from the suction and conveyance section towards the downstream side in the sheet conveying direction, 
         [0021]    wherein the skew correction section completes a skew correction before the leading edge of the sheet conveyed by the suction and conveyance section arrives at the pair of conveying rollers. 
         [0000]    6. The sheet feeding apparatus of above item 3 or 4, further including a sheet detection sensor which detects a leading edge of the sheet fed out by the suction and conveyance section; and a sheet separation section which blows air to separate sheets conveyed by the suction and conveyance section, the sheet separation section being provided on an upstream side relative to the sheet detection sensor, 
         [0022]    wherein, the skew detection section detects the skew amount of the sheet based on a signal from the sheet detection sensor, and the skew correction section stops the operation of the sheet separating section at least when the sheet detecting section is detecting the leading edge of the sheet. 
         [0000]    7. An image forming system including a sheet feeding apparatus of any one of above items 1 to 6, and an image forming apparatus which forms an image on a sheet conveyed by the sheet feeding apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings in which: 
           [0024]      FIG. 1  is an overall configuration diagram of an image forming apparatus having an image forming apparatus, an image reading apparatus, an automatic document feeding apparatus, and a large quantity sheet feeding apparatus; 
           [0025]      FIG. 2  is a perspective view of the important parts of a large quantity sheet feeding apparatus according to the present invention; 
           [0026]      FIG. 3  is a front middle cross-sectional view diagram showing the main unit of a sheet feeding apparatus; 
           [0027]      FIG. 4  is a side view diagram showing the main unit of a sheet feeding apparatus; 
           [0028]      FIG. 5  is a plan view diagram showing the main unit of a sheet feeding apparatus; 
           [0029]      FIG. 6  is a block diagram showing the control system related to the control section  100  that also functions as a skew correction section that corrects the skew of a sheet according to the present invention; 
           [0030]      FIGS. 7   a - 7   c  are schematic diagrams showing the operation of the conveying roller pair and the process of sheet correction; 
           [0031]      FIG. 8  is an operation timing chart showing the sheet conveying control related to a first preferred embodiment; 
           [0032]      FIG. 9  is a time chart showing the sheet conveying control carried out by the control section  100  as a skew correction section according to a second preferred embodiment of the present invention; 
           [0033]      FIG. 10  is schematic diagram showing an angle varying section  69  that varies the angle of the suction and conveyance section  60 . 
           [0034]      FIG. 11  is a schematic cross-sectional diagram in which the angle varying section  69  has been cut horizontally at the top surface of the top supporting member  81 ; and 
           [0035]      FIG. 12  is a flow chart showing the sheet conveying control carried out by the control section  100  functioning as a skew correction section according to a third preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]    While some preferred embodiments of the present invention are described below with reference to the drawings, the present invention shall not be construed to be limited to the preferred embodiments described below. 
         [0037]    Some preferred embodiments of the present invention are described below with reference to the drawings. 
         [0038]    Image Forming Apparatus: 
         [0039]      FIG. 1  is an overall configuration diagram of an image forming apparatus having an image forming apparatus A, an image reading apparatus SC, an automatic document feeding apparatus DF, and a large quantity sheet feeding apparatus LT. 
         [0040]    The image forming apparatus A shown in the figure is configured from an image forming section having a photoreceptor (image carrier)  1 , a charging unit  2 , an image exposure unit  3 , a developing unit  4 , a transfer unit  5 , and a cleaning unit  6 , etc., a fixing unit  7 , and a sheet conveying system. 
         [0041]    The sheet conveying system is configured to have a sheet feeding cassette  10 , a first sheet feeding section  11 , a second sheet feeding section  12 , a sheet discharging section  14 , a conveying path switching section  15 , a reentrant sheet re-feeding section  16 , and an inverting sheet discharging section  17 . 
         [0042]    A document d placed on the document table of the automatic document feeding apparatus DF is conveyed by a sheet feeding section, the images on one side or both sides of the document are read out by the optical system of the image reading apparatus SC, and read by an image sensor CCD. After the analog signal obtained by photoelectric conversion by the image sensor CCD is subjected to, in the image processing section  20 , analog processing, A/D conversion, shading correction, image compression processing, etc., the image signal is sent to the image exposure unit  3 . 
         [0043]    In the image forming section, the processes of charging, exposure, developing, transfer, separation, cleaning, etc., are carried out. 
         [0044]    In the image forming section, electric charge (negative electric charge in the present preferred embodiment) is put by the charging unit  2  on the photoreceptor  1 , an electrostatic latent image is formed by laser light emission from the image exposure unit  3 , and the electrostatic latent image is converted into an apparent image by the developing unit  4  and becomes a toner image (the toner image has negative electric charge in the present preferred embodiment). Next, a sheet P stored in the sheet feeding cassette  10  is conveyed from a first sheet feeding section  1 . On the other hand, the toner remaining on the photoreceptor  1  after transferring is cleaned by the cleaning unit  6 . 
         [0045]    The sheet P is conveyed in synchronization with the toner image by the second sheet feeding section  12  made of a registration roller. At this time, the skew during conveying is corrected by the sheet P abutting against the second sheet feeding section. In other words, the second sheet feeding section  12  is not only a registration section that synchronizes the toner image and the sheet P, but also a skew correction section that corrects the skew of the sheet during conveying. After that, the sheet P has the toner image transferred onto it by the transfer section after which it is fixed by the fixing unit  7 . The sheet P after fixing is discharged to outside the apparatus by the sheet discharging section  14 . 
         [0046]    Further, in the case of double sided copying, the sheet P with image formed on its first surface is fed to the reentrant sheet re-feeding section  16  and is turned upside down, and, after image formation is made on its second surface again in the image forming section, it is discharged to outside the apparatus by the sheet discharging section  14 . In the case of inverting sheet discharge, after the sheet P that has been branched from the normal sheet discharge path is turned upside down by being switched back in the inverting sheet discharging section  17 , it is discharged to outside the apparatus by the sheet discharging section  14 . 
         [0047]    Further, in the present preferred embodiment, the sheet feeding cassette  10  inside the image forming apparatus A can also have a sheet feeding apparatus according to the present invention to be described later, that is, it can have a suction and conveyance section, an air blowing section, and a skew correction section. 
         [0048]    Sheet Feeding Apparatus: 
         [0049]    The large quantity sheet feeding apparatus LT according to the present invention and connected to the image forming apparatus A has a sheet feeding apparatus main unit  30 , a first air blowing section  40  and a second air blowing section  50  as air blowing sections, a suction and conveyance section  60 , etc., stores a large quantity of sheets P, and feeds one sheet P at a time to the image forming apparatus A. 
         [0050]    The sheet feeding apparatus main unit  30  has sheet loading trays  31 , a sheet leading edge restricting member  32 , a sheet trailing edge restricting member  33 , and guide rails  34 . There are three sheet loading trays  31 , and the construction is such that each sheet loading tray  31  can be drawn out from the large quantity sheet feeding apparatus LT due to the guide rails  34 . For example, in the large quantity sheet feeding apparatus LT, 1300 sheets can be loaded in the first tray, and 1850 sheets each can be stored in the second and third trays, so that in total it is possible to store about 6000 sheets. 
         [0051]      FIG. 2  is a perspective view of the important parts of the sheet feeding apparatus main unit  30  according to the present invention,  FIG. 3  is a front cross-sectional view diagram of the sheet feeding apparatus main unit  30 ,  FIG. 4  is a side view diagram of the sheet feeding apparatus main unit  30 , and  FIG. 5  is a plan view diagram of the sheet feeding apparatus main unit  30 . 
         [0052]    The suction and conveyance section  60  of  FIG. 2  has been shown in an assumed position that has been shifted horizontally towards the downstream side of the sheet conveying direction by the extent indicated by the arrow b from its actual position when installed in the sheet feeding apparatus main unit  30 . 
         [0053]    As is shown in  FIG. 2 , a sheet stack Ps and the topmost sheet P 1  are placed on the sheet loading tray  31 , and are stored so that they can be raised or lowered along with the sheet loading tray by a mechanism not shown in the figure. 
         [0054]    A pair of sheet side edge restricting sections  70  restrict the sheet stack Ps in the width direction that is at right angles to the sheet conveying direction, and have on the inside the sheet side edge restricting members  71  in close contact with the side edges of the sheet stack Ps. The relative distance along the width direction of the sheets of the sheet side edge restricting section  70  can be changed freely, and restricts the position of the sheet stack Ps along the width direction according to the size of the sheet. 
         [0055]    The sheet side edge restricting section  70  has a box type structure with a large strength of rigidity and is sufficiently long in the sheet feeding direction, and it has been made possible to maintain the gap between the sheet side edge restricting member  71  and the side edge of the sheet stack Ps even at the topmost part of the sheet stack Ps to within the prescribed values for a wide range of sheet sizes. 
         [0056]    The sheet leading edge restricting member  32  restricts the leading edge of the sheet stack Ps in the sheet loading tray  31 , and is fixed to the sheet feeding apparatus main unit  30 . 
         [0057]    The sheet trailing edge restricting member  33  can be moved freely along the length direction of the sheet P, restricts the position of the trailing edge of the sheet Pin the sheet feeding direction, and is being supported by the sheet feeding apparatus main unit  30  so that it can be displaced along the sheet feeding direction. The sheet side edge restricting members  71  and the sheet trailing edge restricting member  33  are provided with a height and shape so that the sheet P can be restricted at all times even when the sheet P is made to float up by blowing air as described later. 
         [0058]    Further, as is shown in  FIG. 3 , in the sheet trailing edge restricting member  33  is placed a height sensor PS 3  that detects the height of the topmost part of the sheet stack loaded in the sheet loading tray. 
         [0059]    The topmost position of the of the sheet stack Ps loaded in the sheet loading tray  31  is maintained by a control section to be described later, based on the signal of the height sensor PS 3 , so as to be at the most optimum height for receiving the air blow. In other words, based on the result of detection by the height sensor PS 3  shown in  FIG. 3 , the bottom plate  34  of the sheet loading tray  31  is raised by driving a raising and lowering motor not shown in the figure, and control is carried out so that the topmost part of the stack of sheets Ps is at all times maintained to be at the prescribed height. 
         [0060]    Mechanism of Sheet Separation Using Air Blow: 
         [0061]    As is shown in  FIG. 2 , air is being blown from the sheet conveying direction and from the sheet width directions on the topmost part of the sheet stack Ps. The air blow in the sheet width direction is along the two directions of the arrows A 2  and A 2 , and even in the sheet conveying direction, the air blow is as indicated by the arrows B 1  and B 2 . 
         [0062]    First Air Blowing Sections: 
         [0063]    As is shown in  FIG. 2  and  FIG. 3 , the first air blowing sections  40  that blow air on to the top of the sheet stack Ps from the width directions are placed on both sides of the sheet loading tray  31 . The first air blowing sections  40  are provided in the sheet side edge restricting section  70 . A first air blowing section  40  is made of an air blowing fan  41 , guide plates  42 , etc. The air blow indicated by the arrows A 1  and A 2  is blowing air above the top part of the sheet stack Ps from the first air blow outlet  72  placed in the sheet side edge restricting member  71  of the sheet side edge restricting section  70 . As is shown in  FIG. 4 , the air blowing fan  41  has been installed on the sheet side edge restricting section  70  with its air outlet facing upward. The air that is discharged upwards has its direction changed by 90° by the guide plate  42  and is blown horizontally from the first air blow outlet  72  of the sheet side edge restricting member  71 . 
         [0064]    Further, the first air blow outlet  72  and the first air blow section  40  are provided in the sheet side edge restricting section  70 , can be moved integrally with the sheet side edge restricting member  71 , and it has been made possible to have a constant positional relationship with the sheet stack Ps at all times while corresponding to changes in the sheet size. 
         [0065]    As is shown in  FIG. 3 , relative to the first air blow outlet  72 , there are several air exhaust outlets  73  provided on the side surface of the sheet side edge restricting member  71  positioned on the upstream side in the direction of sheet conveying, and it has been ensured that there is no large distortion in the shape of the sheet that has floated up. 
         [0066]    Second Air Blowing Section: 
         [0067]    Next, the second air blowing section  50  placed on the downstream side of the sheet loading tray  31  in the sheet conveying direction and acting as a sheet separation section and as a sheet floating up section is described based on  FIG. 2  and  FIG. 3 . 
         [0068]    The second air blowing section  50  is constituted from an electric fan  51  and an air flow guide  52  connected to the electric fan  51 . The second air blowing section  50  blows air towards the leading edge and topmost part of the sheet stack loaded in the sheet loading tray from the second air blow outlet  53 A of the air flow guide  52 . The electric fan  51  has been installed inside the air flow guide  52 . In the top part of the air flow guide  52 , there is a second air blow outlet  53 A facing towards the downstream side of the sheet conveying direction. The air ejected from the second air blow outlet  53 A is facing horizontally towards the downstream side of the sheet conveying direction as shown by the arrow B 1  in  FIG. 2 . 
         [0069]    The air blow from the second air blow outlet  53 A is the air blow for making the sheet P at the topmost part of the sheet stack Ps separate and float up, and is being blown at the top part of the leading edge of the sheet stack Ps. At this time, the second air blowing section  50  operates as a floating up section that makes the sheet float up. 
         [0070]    Further, in the top part of the air flow guide  52 , there is a third air blow outlet  53 B on the downstream side of the second air blow outlet  53 A, and the third air blow outlet  53 B has been cut open so as to face upwards. The air flow from the third air blow outlet  53 B, as is shown in the arrow B 2  in  FIG. 2 , is pointing towards an obliquely upward direction at a sheet that is conveyed towards the upstream side relative to the detection position of the two sheet detecting sensors PS 2 A (PS 2 B) which are explained in detail later. 
         [0071]    The air blown in the direction B 2  from the third air blow outlet  53 B is the air blow for making only one sheet get sucked and conveyed by the suction and conveyance section  60 , and is being blown in the direction of the suction belt  63  of the suction and conveyance section  60 . 
         [0072]    The air flow guide  52 , as is shown in  FIG. 3 , links the second air blow outlet  53 A and the electric fan  51 , or is formed to have a duct structure that links the third air blow outlet  53 B and the electric fan  51 . The duct is branched into a first duct  54 A and a second duct  54 B. Further, there is a shutter  55  at the branching point, and this shutter  55  makes it possible to switch the air flow rate through the first duct  54 A and the second duct  54 B. 
         [0073]    The second air blowing section  50 , according to the selection by the shutter  55 , functions as a sheet flowing up section that ejects air from the second air blow outlet  53 A which is at the end of the first duct  54 A, or as the sheet separation section that ejects air from the third air blow outlet  53 B which is a the end of the second duct  54 B. 
         [0074]    By making the shutter  55  operate as an air flow switching section as shown in  FIG. 3  by a solenoid not shown in the figure, the function as a sheet separation section is put in the operating state or the stopped state, or else, the function as a sheet floating up section is put in the stopped state or the operating state. In other words, the second air blowing section  50  has two switchable functions. It is both the sheet floating up section that makes a sheet P float up and the sheet separation section that separates the sheet P. As is shown in  FIG. 3 , when the shutter is in the state indicated by continuous lines, the sheet separation section is in the operating state, and when it is in the state indicated by broken lines, the sheet separation section is in the stopped state. 
         [0075]    Suction and Conveyance Section: 
         [0076]    As is shown in  FIG. 3 , the suction and conveyance section  60  is positioned above the sheet stack Ps loaded in the sheet loading tray and is placed on the downstream side of the sheet conveying direction, and is fixed to the top supporting member of the large quantity sheet feeding apparatus LT. 
         [0077]    As is shown in  FIG. 2  and  FIG. 4 , the suction and conveyance section  60  has the first sheet conveying section  60 A and the second sheet conveying section  60 B along the width direction at right angles to the sheet conveying direction. Each sheet conveying section has a supporting member  68 , a large diameter roller  61 , two small diameter rollers  62 , and a suction belt  63  that is wound around and rotates over the large diameter roller  61  and the small diameter rollers  62 . 
         [0078]    Each supporting member  68  is fixed to the top supporting member  81 , and respectively supports one large diameter roller  61  and two small diameter rollers  62  in a free to rotate manner. 
         [0079]    The axes of the two large diameter rollers  61  are respectively coupled to two suction and conveyance motors (having a first suction and conveyance motor M 2 A and a second suction and conveyance motor M 2 B) which are fixed to each of the supporting members  68 . Further, two suction belts  63  can be rotated independently of each other by the two suction and conveyance motors. 
         [0080]    The suction belts  63  have a plurality of penetrating holes of small diameter pierced in them as is shown in the figure. On the inside of each suction belt  63  is a suction duct  64 A of the suction section  64  and are fixed to the supporting member  68 . 
         [0081]    The suction section  64  is made of a suction duct  64 A and a suction fan  64 B coupled thereto. At the bottom of the suction duct, there are openings  64 C ( FIG. 3 ) opposing respectively the suction belt  63 . The openings  64 C determine the air suction position of the suction and conveyance section  60 . The sucked air is exhausted to the back of the large quantity sheet feeding apparatus LT via the suction duct  64 A. 
         [0082]    Further, it is also possible to have a configuration in which a suction fan  64 B is provided in a fixed manner at the deep end of the sheet feeding apparatus main unit  30 , and connect it to the suction and conveyance section  60  by a suction duct. 
         [0083]    The suction fan  64 B is operating all the time, and the suction and conveyance section  60  adheres by sucking to the suction belt  63  the topmost sheet P that has floated up due to air blowing by the sheet separation mechanism which is described later. Next, due to the operation of the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B, the suction belt  63  rotates whereby the sheet P is conveyed in the sheet conveying direction (arrow a), and fed to the image forming apparatus A. It is possible to carry out control of varying independently the speeds of the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B, and these two operate under operating conditions that have been adjusted in advance so that the sheet P is conveyed in the sheet conveying direction. 
         [0084]    As is shown in  FIG. 3 , in the neighborhood of the opening  64 C of the suction duct  64 A, a sheet suction and adhesion sensor PS 1  has been placed that detects whether or not the topmost sheet P has been sucked by and adhered to the suction belt. 
         [0085]    Further, on the outlet side of the large quantity sheet feeding apparatus LT is placed a conveying roller pair  39  made of a master and a slave conveying rollers that definitely convey the sheet P conveyed by the suction belt to the image forming apparatus A. 
         [0086]    Sheet Detection Sensor: 
         [0087]    In addition, between the suction and conveyance section  60  and the conveying roller pair  39  in the sheet conveying direction, and also in the neighborhood of the suction belt  63 , a first sheet detection sensor PS 2 A and a second sheet detecting section PS 2 B that detect the leading edge of the sheet P that is passing through are placed along the width direction. 
         [0088]      FIG. 5  is a plan view diagram of the sheet feeding apparatus main unit, and shows that a first sheet detection sensor PS 2 A and a second sheet detecting section PS 2 B are placed on the downstream side in the sheet conveying direction (the direction of the arrow a) from the suction and conveyance section  60  while being separated by W (mm) along the width direction. In addition, a conveying roller pair  39  has been placed on the downstream side at a separation of D (mm) from the detection positions of the two sheet detection sensors. A clutch CL 1  is present between the shaft of the conveying roller pair  39  and the driving shaft  38  that rotates because of being coupled to conveying roller driving motor M 1 . 
         [0089]    The clutch CL 1  is a drive transmission selection section that switches the transmission of drive to the shaft of the conveying roller pair  39  from the driving shaft  38 . 
         [0090]    Control Section: 
         [0091]      FIG. 6  is a block diagram of the control system related to the control section  100  that also functions as a skew correction section that corrects the skew of sheets according to the present invention. 
         [0092]    The control section  100  has a computation and control section  101  made of a CPU and that rules the sheet conveying control and the main part of the skew correction section, a ROM  102  that stores the programs, a RAM  103  that is used in the calculation control carried out by the computation and control section  101 , drive circuits  104  that drive the motors and solenoids, etc., based on the instructions (signals) from the control section  100 , and a bus  105 . 
         [0093]    The sheet suction sensor PS 1 , the first sheet detection sensor PS 2 A, and the second sheet detecting section PS 2 B are connected to the control section  100  via an input interface that is not shown in the figure. 
         [0094]    The drive circuits  104  are the circuits that drive the solenoid SL 1  that actuates the shutter  55  of  FIG. 3 , the clutch CL 1  of  FIG. 5 , and the motors M 1 , M 2 A, and M 2 B shown in  FIG. 2 ,  FIG. 4 , and  FIG. 5 , and the motor M 3  to be described later. 
         [0095]    The computation and control section  101 , based on the signals from the first sheet detection sensor PS 2 A and the second sheet detecting section PS 2 B, and according to the control program, appropriately outputs to the drive circuits  104  the commands (signals) for driving the conveying roller driving motor M 1 , the first suction and conveyance motor M 2 A, and the second suction and conveyance motor M 2 B, so that sheets are conveyed one at a time to the image forming apparatus A. 
         [0096]    Sheet Skew Detection Section: 
         [0097]    The first sheet detection sensor PS 2 A and the second sheet detecting section PS 2 B detect the presence or absence of a passing sheet P, the timing th of the passing of the leading edge of a sheet is detected based on the timing at which the detection signal changes from the sheet absent level to the sheet present level. Also, the timing tr of the passing of the trailing edge of a sheet is detected based on the timing at which the detection signal changes from the sheet present level to the sheet absent level. Further, the sheet present or absent signal, the sheet leading edge detection signal, and the sheet trailing edge detection signal are output to the computation and control section  101 . 
         [0098]    The computation and control section  101  detects the time tha of the leading edge detection signal of the first sheet detection sensor PS 2 A and the time thb of the leading edge detection signal of the second sheet detection sensor PS 2 B, and based on their time difference (tha−thb), computes the amount (angle) and direction of skew of the sheet P. 
         [0099]    If the linear speed of the suction and conveyance belt  63  that is driven rotationally by the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B is taken as Vb (mm/sec), and the skew angle of the sheet P is taken as S, then the relationship of Equation 1 will be satisfied. 
         [0000]      θ=arc tan { Vb ( tha−thb )/ W}   Eqn. 1
 
         [0100]    As is shown in  FIG. 5 , θ is the skew angle of the leading edge of the sheet P, W is the distance between the detection position of the first sheet detection sensor PS 2 A and the detection position of the second sheet detection sensor PS 2 B. 
         [0101]    The computation and control section  101  is calculating the sheet skew angle θ (°) based on Eqn. 1. In addition, the direction of the skew is being judged depending on whether the difference (tha−thb) is negative or positive. When this difference is negative, the sheet P is judged to be skewed to the right, and to the left if the difference is positive. 
         [0102]    Further, the amount of skew of the sheet P can also be the time difference (tha−thb) of leading edge detection, or it can also be the distance d indicated in  FIG. 5 . 
         [0103]    The present invention shall not be limited to the sheet detection sensors shown here, but can also be on that detects the trailing edge of the sheet P. 
         [0104]    The sheet skew detection section can also be one that detects the above time difference (tha−thb) itself as the amount of skew. Further, it is also possible to store in advance a correspondence table between the time difference (tha−thb) and the skew angle θ, and to detect the skew angle θ by referring to this table. 
         [0105]    Skew Correction Section of the First Preferred Embodiment: 
         [0106]      FIG. 5  is an outline diagram showing the conveying roller pair used in the skew correction section of the first preferred embodiment of the present invention. 
         [0107]    The skew correction section of the first preferred embodiment is one that controls at least the rotational drive of the conveying roller pair  39 , by temporarily stopping the rotating conveying roller pair  39 , so that the leading edge of the sheet P abuts against the conveying roller pair  39  during the period that the conveying roller pair  39  has stopped. The operation of the clutch CL 1  is controlled so that the rotation of the conveying roller pair  39  is started again when a prescribed time period has elapsed after the leading edge of a sheet P is detected from the signal of a sheet detection sensor (PS 2 A or PS 2 B). Therefore, correcting sheet skew has been made possible using a paper registration mechanism of carrying out control so that the conveying roller pair  39  that was conventionally being rotated continuously is made to stop temporarily at a prescribed timing, and again made to start rotating again at another prescribed timing. The role undertaken by the loop forming roller in a conventional paper registration mechanism is being played by the suction belt  63 . 
         [0108]      FIGS. 7   a - 7   c  are schematic diagrams showing the operation of the conveying roller pair and the process of sheet correction. 
         [0109]      FIG. 7   a  shows a sheet P at the point of time when a sheet P skewed to the right has arrived at the nip of the left side conveying roller pair  39 . The broken line indicates the leading edge of the sheet P at the point of time when the leading edge of sheet P is passing through the first sheet detection sensor PS 2 A. At this point of time, the clutch CL 1  has stopped transmitting drive power, and the conveying roller pair  39  has stopped. It is very important that the clutch CL 1  should have stopped before the leading edge of the sheet P has arrived at the nip. 
         [0110]    The angle θ shown in the figure is the angle of skew of the sheet P. 
         [0111]      FIG. 7   b  shows the condition in which the leading edge of a sheet P has penetrated into the entire area of the nip of the conveying roller pair  39  by the conveying force of the suction and conveyance section  60 . The skew of the leading edge of the sheet P has been eliminated. The single dot and dash line at the left of the sheet P indicates the area in which the curling of the sheet P has become large. Corresponding to the sheet skew angle θ shown in  FIG. 4 , the looping of the left part of the leading edge of the sheet P is larger than the right part of the leading edge. At this point, the state of the clutch CL 1  is continuing to be the off state of power transmission. Of course, an appropriate amount of looping is formed even at the right part of the leading edge of the sheet (the area D in  FIG. 5 ). 
         [0112]      FIG. 7   c  is the point of time after the state of  FIG. 7   b  has been passed, the state of the clutch CL 1  has switched to the ON state of power transmission, and a certain additional time period has elapsed. As is shown in the figure, the skew of the sheet P has been corrected from the leading edge side due to the conveying force of the conveying roller pair  39  and sheet P is being conveyed normally in the sheet conveying direction. 
         [0113]    The loop formed in the sheet P in  FIG. 7   b , gradually moves toward the rear part of the sheet while maintaining its size, and gets eliminated when sheet P progresses and its trailing edge side is near the position where it is released from the suction and conveyance section  60 . 
         [0114]    The leading edge of the sheet P, which is floated up by the flow of air and is conveyed while being sucked by the suction belt  63  of the suction and conveyance section  60  with a skew angle of θ, has its progress stopped at the nip of the conveying roller pair  39  in the stopped condition. On the other hand, since the sheet next to the sheet P is conveyed at a prescribed interval by the suction and conveyance section  60  in the leading edge prevented condition, a loop with a prescribed range is formed in the sheet in the region D shown in  FIG. 5 . 
         [0115]    However, formation of a loop is only in the case of sheets which are easily buckled such as thin sheets, etc., and in the case of sheets which are not easily buckled such as thick sheets, etc., when the leading edge of the sheet arrives at the nip of the conveying roller  39  that is in the stopped state, because slipping occurs between the suction belt  63  and the sheet, the leading edge of the sheet abuts uniformly. 
         [0116]    After a prescribed period has elapsed, the state of the clutch CL 1  is switched to the ON state of power transmission, the conveying roller pair  39  starts rotating, and the sheet P is discharged towards the image forming apparatus A after its skew is corrected. 
         [0117]    As has been shown above, the sheet P, has no problems of sheet folding or wrinkling, and is conveyed to the downstream side with its skew corrected from the leading edge part. 
         [0118]      FIG. 8  is a timing chart of the operations of the sheet conveying control related to the first preferred embodiment. 
         [0119]      FIG. 8  shows the operation timings related to the sheet suction section PS 1  and the first sheet detection sensor PS 2 A (the second sheet detection sensor PS 2 B), the clutch CL 1  that carries out drive power transmission to the conveying roller pair  39 , the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B that rotate the suction belt  63 , and the solenoid SL 1  that actuates the shutter of the second air blowing section. 
         [0120]    The operation timings of the conveying roller drive motor M 1  and the air blowing fan  41  of the first air blowing section that floats up the sheet P, and of the motor fan  51  of the second air blowing section are the period from the start of sheet feeding until end of sheet feeding, during which period these are operating, which has been omitted from the descriptions. 
         [0121]      FIG. 8  shows the timing chart for the period from the beginning of sheet feeding in continuous sheet feeding to near the starting feeding the third sheet. The timing of sheet conveying is broadly divided into the first sheet suction Ta and first sheet feeding Tb, second sheet feeding Tc, and third sheet feeding Td. The operation timings of the different sections are determined by t 3  to t 7  set in advance for the sheet feeding starting timings Tb, Tc, and Td of the different sheets, the sheet leading edge detection timings, and for the sheet trailing edge detection timings. 
         [0122]    The timings of the sheet leading edge detection and the sheet trailing edge detection are judged based on the detection signals of the sheet detection sensors PS 2 A and PS 2 B, and differ for each sheet feeding. 
         [0123]    The operation of the clutch CL 1  that switches the drive of the conveying roller pair  39  that is carried out by the skew correction section of the first preferred embodiment according to the present invention is described below according to  FIG. 8 . 
         [0124]    The computation and control section  101  puts the clutch CL 1  in the power transmission OFF state when a sheet feeding is started. Next, a timer is started when the leading edge of a first sheet P is detected from the detection signal of the sheet detection sensor, and the clutch CL 1  is switched to the power transmission ON state after a prescribed time duration t 3  has elapsed. 
         [0125]    The prescribed time period t 3  is selected within a range so that it satisfies the following Eqn. 2, and also so that sheet folding, wrinkling, etc., due to excessive looping of the sheet P does not occur. D in Eqn. 2 is the distance (in mm) shown in  FIG. 4 , and Vb is the conveying speed of the sheet P by the suction belt  63 . Further, tm is the looping time determined for forming loops of less than a prescribed range. 
         [0000]        t 3 =D/Vb+tm   Eqn. 2
 
         [0126]    The control section  100  starts a timer when the trailing edge of the first sheet P is detected from the detection signal of the sheet detection sensor, and the clutch CL 1  is switched to the power transmission OFF state after a prescribed time duration t 5  has elapsed, and stops the conveying roller pair  39  in advance in order to correct the skew of the second sheet. 
         [0127]    The control section  100  carries out controls such as the above even for the second and succeeding sheets, and the skew of the sheet that occurs at the time that a sheet is sucked by the suction and conveyance section is corrected. 
         [0128]    However, although the looping time has been set here as tm, it is also possible to use a loop detection section that detects the amount of loop of the sheet. 
         [0129]    Skew Correction Section of a Second Preferred Embodiment: 
         [0130]      FIG. 9  is a time chart showing the operations of the different parts of the sheet feeding apparatus main unit  30  related to the sheet conveying control carried out by the control section  100  as a skew correction section according to the second preferred embodiment of the present invention. 
         [0131]    The computation and control section  101  according to the second preferred embodiment of the present invention calculates the difference (tha−fhb) between the sheet left and right leading edge timings based on the signals of the first sheet detection sensor PS 2 A and the second sheet detection sensor PS 2 B, and in addition, calculates the skew angle θ of the sheet and the skew direction data SD according to the above Eqn. 1. Next, the speed profile corresponding to the skew angle θ is determined by referring to a table that is not shown in the figure but that is stored in the ROM  102 , and outputs the determined speed profile to the drive circuit  104  of  FIG. 6 . The drive circuit  104  drives the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B in accordance with the received profile. 
         [0132]    These two suction and conveyance motors are both stepping motors, and drive the large diameter roller  61  in a rotating manner by a prescribed angle per each unit pulse signal. In addition, the sheet P can be conveyed at mutually independent conveying speeds, and the orientation of the sheet conveyed by the suction and conveyance section  60  can be changed freely by the speed profiles of the first suction and conveyance motor M 2 A and the second suction and conveyance motor M 2 B. 
         [0133]    In the time chart of  FIG. 9 , the speed profiles of the two suction and conveyance motors are shown as VPn, VPr+, and VPl+. 
         [0134]    VPn is the reference speed profile. VPr+ is the speed profile for correcting right skew with respect to the reference speed profile. VPl+ is the speed profile for correcting left skew with respect to the reference speed profile. 
         [0135]      FIG. 9  is only an example, and the amount of skew of the first sheet P is within the prescribed range, and is the case in which sheet skew correction is judged to be not required. The computation and control section  101  determines the speed profiles of both the suction and conveyance motors to be the reference speed profile VPn. 
         [0136]    On the other hand, the amount of sheet skew of the second sheet P is more than the prescribed range, and also the skew is towards the right, and this is the case in which sheet skew correction is judged to be required. The computation and control section  101  determines the speed profile of the first suction and conveyance motor M 2 A as the speed profile VPr+ according to the detected amount of skew in this case and determines the speed profile of the second suction and conveyance motor M 2 B as the reference speed profile VPn. 
         [0137]    Further, the amount of sheet skew of the third sheet P is more than the prescribed range, and also the skew is towards the left, and this is the case in which sheet skew correction is judged to be required. The computation and control section  101  determines the speed profile of the second suction and conveyance motor M 2 B as the speed profile VPl+ according to the detected amount of skew in this case and determines the speed profile of the first suction and conveyance motor M 2 A as the reference speed profile VPn. 
         [0138]    Further, the integrated area (speed×time) of the speed profile corresponds to the distance that the leading edge of the sheet P has progressed beyond leading edge detection. In the example shown in the second sheet in  FIG. 9 , the integrated area of the VPr+ speed profile is larger by the area of the projection shape H in the figure relative to the integrated area of the speed profile VPn. Therefore, the right part of the sheet progresses well in the sheet conveying direction by the distance corresponding to this area, and the sheet P rotates to the left relatively. As a result, the right part of the sheet progresses corresponding to the amount of skew d towards the right shown in  FIG. 4  and the skew of the sheet is completely corrected. 
         [0139]    Further, as a condition of making the correction of the sheet P complete, it is necessary to complete the correction of the skew of the sheet before the leading edge of the sheet arrives at the nip of the conveying roller pair  39 . 
         [0140]    As is shown in the timing chart of  FIG. 9 , the projection shape H has been set to within the time period t 9  (t 9 =t 8 −α) shown in the figure considering the fluctuations in the conveying speed, etc., of the suction belt  63 . Here, t 8  is the time period from the detection of the leading edge until the leading edge of the sheet arrives at the nip of the conveying roller pair  39 , and α is a constant considering the above fluctuations. 
         [0141]    Further, the computation and control section  101  determines the above speed profile VPr+ or VPl+ by referring to the table not shown in the figure so that the area of the projection shape H shown in  FIG. 9  changes according to the amount of skew or the skew angle, and outputs the speed profile VPn and the determined VPr+ or VPl+ to the drive circuit  104 . 
         [0142]    The drive circuit  104  drives the first suction and conveyance motor M 2 A or the second suction and conveyance motor M 2 B in accordance with the speed profile VPn or VPr+ or VPl+ input by the computation and control section  101 . 
         [0143]    In the above manner, in the skew correction section of the second preferred embodiment, the amount of skew of the sheet P is detected, after the orientation of the sheet P sucked by the suction and conveyance section  60  is changed with respect to the suction and conveyance section  60  according to the detected amount of skew thereby correcting the skew of the entire sheet including the leading edge, the sheet is sheet is conveyed to the nip of the conveying roller  39  with the same speeds at left and right at all times during the period from t 9  to t 8  shown in  FIG. 9 , this is a method that does not require the formation of a loop as in the first preferred embodiment, this method is superior in stable conveying of the sheet, and can convey smoothly. However, since this is a method in which high performance is required in the time resolution of the sheet skew detection section as the conveying speed of the apparatus becomes faster, it is necessary to take care such as selecting the sensors considering sufficiently the conveying speed at the time of design, etc. 
         [0144]    Skew Correction Section of a Third Preferred Embodiment: 
         [0145]    The skew correction section of a third preferred embodiment of the present invention is a control section  100  that controls the angle varying section as a displacement section described below so that the angle of the suction and conveyance section  60  with respect to the sheet conveying direction is changed according to the skew angle of the leading edge of the sheet P. 
         [0146]      FIG. 10  shows an angle varying section  69  that varies the angle of the suction and conveyance section  60 . As is shown in the figure, the two conveying belts  63  are rotated together by driving the first suction and conveyance motor M 2 A. 
         [0147]    The supporting member  68  of the suction and conveyance section  60  is supported below the top supporting member  81  of the sheet feeding apparatus main unit  30  by one reference supporting shaft  693  and tow sliding supporting shafts  694 . 
         [0148]    On the right end of the supporting member  68  is provided a flat gear wheel  695  drawing and ellipse with a radius R 1  centering on the reference supporting shaft  693 . On the other hand, above the top supporting member  81  of the sheet feeding main unit  30  is fixed a motor supporting member  691  that supports the angle varying motor M 3 , and a gear wheel  692  fixed to the shaft of the angle varying motor M 3  engages with the flat gear wheel  693 . 
         [0149]      FIG. 11  is a cross-sectional view schematic diagram cutting the angle varying section  69  horizontally at the top surface of the tops supporting member  81 , and shows the relationship between the top supporting member  81  and the supporting member  68  that is displaced with respect to the top supporting member  81 . 
         [0150]    The supporting member  68  that determines the orientation of the suction and conveyance section  60  can rotate horizontally with the reference hole  81 C opened in the top supporting member  81  as the pivot. The top supporting member  81  has two holes  81 B forming an inside ellipse R 2 , so that the sliding supporting shaft  694  can slide. In addition, a hole  81 A is provided at the position of the radius R 1  in which the gear wheel  692  fixed to the shaft of the angle varying motor M 3  passes through. 
         [0151]    The angle varying section  69  is one in which, when the gear wheel  692  of the angle varying motor M 3  is rotated by an angle φ in the direction of the arrow b, the flat gear wheel  695  moves in the direction of the arrow c, the suction and conveyance section  60  moves in the direction of the arrow d, and rotates by an angle θ with respect to the sheet conveying direction. 
         [0152]    The angle varying motor M 3  is one that can accurately rotate the gear wheel  692  in the desired direction by the desired angle, and although a stepping motor is suitable and is used, it is not necessary to restrict to this. 
         [0153]      FIG. 12  is a flow chart related to the sheet conveying control carried out by the control section  100  as a sheet skew correction section of the third preferred embodiment according to the present invention. 
         [0154]    The Steps S 01  to S 05  are controlled by the computation and control section  101 , and the Step S 06  is controlled by the drive circuit  104 . 
         [0155]    The Step S 01  is a step of judging whether or not the leading edge of the sheet P is detected by the first sheet detection section PS 2 A and the second sheet detection sensor PS 2 B. The operation progresses to Step S 02  when the judgment is YES in this step. 
         [0156]    The Step S 02  is a step of detecting the timings th 1  and th 2  of the leading edge of the sheet P from the signals of the first sheet detection sensor PS 2 A and the second sheet detection sensor PS 2 B, and the operation proceeds to Step S 03 . 
         [0157]    The Step S 03  is a step of calculating the direction of skew of the sheet P based on the timings th 1  and th 2  of the leading edge of the sheet P and calculating the sheet skew angle θ based on Eqn. 1. The operation proceeds next to Step S 04 . 
         [0158]    The Step S 04  is a step of referring to the table corresponding to the direction of skew and the angle θ of the sheet skew obtained in Step S 03  and obtaining the operating conditions of the angle varying motor (number of pulse steps and direction of rotation). 
         [0159]    The Step S 05  is a step of outputting the operation conditions obtained in Step S 04  to the drive circuit  104 . 
         [0160]    The Step S 06  is controlled by the drive circuit  104 , and is a step in which the drive of the angle varying section  69  is controlled according to the operation conditions obtained from the computation and control section  101 . For example, as is shown in  FIG. 11 , the motor shaft M 3  is rotated in the counterclockwise direction by an angle φ, and the suction and conveyance section  60  rotates (in the direction of the arrow a) by an angle θ with respect to the sheet conveying direction. As a result, the sheet skew is corrected by an angle θ in the direction of left skew. 
         [0161]    Further, the skew correction section  60  of the third preferred embodiment is, similar to the second preferred embodiment, one that carries out control so that the operation of the drive circuit  104  for correcting the skew of the sheet P is completed before the sheet P arrives at the nip of the conveying roller pair  39 . 
         [0162]    Further, in the skew correction sections of the second and third preferred embodiments, there are cases in which it is demanded that the timing of the leading edge of the sheet is detected accurately and that the amount of skew of the sheet P is detected with a high accuracy. In such situations, control is carried out so that air flow for separation by blowing air from the second air blowing section  50  shown in  FIG. 3  is stopped before detecting the timing of the leading edge of the sheet, thereby increasing the sheet skew detection accuracy, and making it possible to prevent wrong detection of sheet skew. Explanation is given based on the timing chart of  FIG. 10 . 
         [0163]    The time period t 6  shows the time period from the timing of the start of feeding of each sheet P to the timing of switching the state of the solenoid SL 1  from the separation state to the floating up state by operating the shutter of the second air blowing section. The time period tx is the time period from starting the sheet feeding until the time when the leading edge of the sheet is expected to be detected. As is shown in the figure, t 6  is set to be sufficiently smaller than tx so that the second air blowing section as a sheet separation section stops with sufficient margin before the timing at which the leading edge of the sheet P is detected. As a consequence, the second air blowing section as a sheet separation section is being controlled by the control section  100  as a skew correction section so that there is no problem caused to skew detection. 
         [0164]    According to a sheet feeding apparatus of the present invention, by providing a skew correction section that corrects the skew of a sheet conveyed by the suction and conveyance section, it is possible to solve the problem of the skew of a sheet before it is sent to the conveying path on the downstream side from the air sheet feeding apparatus.