Abstract:
The present-invention has as its object to provide a sheet conveying apparatus which can improve the correction accuracy of a sheet and can prevent the skew feeding of the sheet, and for this purpose, it provides a sheet conveying apparatus for conveying a sheet by sheet conveying means disposed along a sheet conveying path, including: skew detecting means for detecting the skew of the sheet being conveyed with respect to a sheet conveying direction; skew correcting means rotatable in a direction to correct the skew of the sheet in a state nipping the sheet in its skew state, on the basis of a detection signal from the skew detecting means; position correcting means for moving the skew correcting means in a direction intersecting with a sheet conveying direction; and control means for controlling so as to move the skew correcting means in the direction intersecting with the sheet conveying direction by the position correcting means while conveying the sheet by the skew correcting means, in order to convey the sheet in a state coincident with the sheet conveying direction when the skew correcting means is rotated to correct the skew of the sheet, and conveys the sheet in the rotated state.

Description:
[0001]     This application claims priority from Japanese Patent Application No. 2003-200734 filed Jul. 23, 2003, which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a sheet conveying apparatus for conveying a sheet to the image forming portion of an image forming apparatus, and particularly to a construction for correcting the skew of a sheet such as recording paper or an original.  
         [0004]     2. Description of the Related Art  
         [0005]     Heretofore, image forming apparatus and image reading apparatuses such as a copying machine, a printer, a facsimile apparatus and a scanner have been provided with sheet conveying apparatuses for conveying a sheet such as recording paper or an original to an image forming portion or an image reading portion. Some of such sheet conveying apparatus are provided with correcting means for effecting the skew conveying correction of the sheet or the positional deviation correction of the sheet to adjust the posture and position of the sheet before the sheet is conveyed to the image forming portion or the image reading portion.  
         [0006]     A correcting method by such correcting means uses a pair of registration rollers, and for example, in the case of an image forming apparatus, the so-called loop registration method of ramming the leading edge of a sheet against the nip between the pair of registration rollers being at a halt to thereby form a flexure in the sheet, causing the leading edge of the sheet to be along the nip by the elasticity of the sheet to thereby effect the correction of skew conveying, thereafter rotating the pair of registration rollers at predetermined timing, and synchronize the sheet with an image has become a mainstream.  
         [0007]     In such a loop registration method, however, a loop space for forming a loop becomes always necessary, and this has made the apparatus bulky. Also, when the loop space cannot be sufficiently secured, there is the problem that jam due to buckling occurs particularly to a sheet such as thin paper of weak rigidity, or a sound (so-called loop sound) is produced when the sheet is caused to abut against the pair of registration rollers.  
         [0008]     Further, there is the problem that the skew conveying correcting capability is changed by the degree of rigidity of the sheet. Specifically, in the case of thin paper low in rigidity, the abutting pressure when the leading edge of the sheet abuts against the registration roller nip is deficient and the leading edge of the sheet may sometimes not sufficiently abut against the pair of registration rollers, and in such case, skew conveying correction cannot be completely effected.  
         [0009]     Also, in the case of thick paper or the like high in rigidity, there is the inconvenience that by the shock with which the sheet abuts against the nip between the pair of registration rollers, the sheet goes through the nip between the pair of registration rollers, and if in order to prevent this, an attempt is made to give a load or the like to the pair of registration rollers, for example, by a brake member, it will result in an increase in the cost of the product.  
         [0010]     Furthermore, when the leading edge of the sheet is curled or broken, the leading edge of the sheet cannot be accurately along the nip portion of the pair of registration rollers, and this also results in the problem that skew conveying correction cannot be accurately effected and printing accuracy lowers.  
         [0011]     On the hand in recent years, the image forming apparatuses and the image reading apparatuses are adapted, by digitizing, to once be capable of reading an original, and thereafter electrically encoding the image information thereof and storing it in a memory. During image forming, they have been designed to read out the information in the memory, and form an image corresponding to the image formation of the original on a photosensitive member by a laser beam or an exposing apparatus such as an LED array and therefore, even in the copying of a plurality of sheets, the mechanical movement of an optical apparatus or the like becomes unnecessary.  
         [0012]     Thereby, the inter-sheet spacing which is the interval between a sheet and a sheet can be shortened, and it has become possible to treat many sheets within a short time. As a result, for example, in the case of the image forming apparatus, it has become possible to achieve a substantial improvement in the image forming speed without increasing the process speed during image forming.  
         [0013]     However, when as the sheet conveying apparatus, use is made of one adopting the already described loop registration method, design is made such that a sheet is once stopped to form a loop and therefore, the inter-sheet spacing is necessarily determined, and this comes to greatly affect an improvement in the image forming speed (productivity).  
         [0014]     So, in order to overcome such an inconvenience, Japanese Patent Application Laid-Open No. Hei 10-067448 proposes a sheet conveying apparatus adopting a registration method adapted to be capable of automatically correct the skew conveying of a sheet.  
         [0015]     This sheet conveying apparatus is provided with a pair of conveying rollers (registration rollers) for nipping and conveying a sheet therebetween, a sensor for detecting the skew amount of the sheet provided downstream of the conveying rollers with respect to the conveying direction thereof, and conveying roller inclination correcting means for displacing the conveying rollers so as to be inclined in a direction intersecting with a sheet conveying direction, and when the skew conveying of the sheet is to be corrected, it is adapted to displace the conveying rollers in accordance with the skew of the sheet on the basis of the information from the skew amount detecting sensor to thereby correct the skew conveying of the sheet.  
         [0016]     However, in such a conventional-sheet conveying apparatus for displacing the conveying rollers to thereby correct the skew conveying of the sheet, the conveying rollers (registration rollers) are in a posture inclined with respect to the original sheet conveying direction at a point of time whereat the skew conveying correction of the sheet has been effected and therefore, if in that state, the sheet is conveyed, the sheet will be fed in a skew direction with respect to the original sheet conveying direction.  
         [0017]     When so-called skew feeding in which the sheet S is thus fed in the skew direction occurs, there is the inconvenience that if this sheet conveying apparatus is applied, for example, to an image forming apparatus, an image will be obliquely transferred to the sheet and printing accuracy will become remarkably inferior.  
         [0018]     Against such inconvenience, design is made such that 
        (1) the pressure contact (nip) between the pair of conveying rollers is released at a point of time whereat the sheet has reached a post-step and the sheet has been held, or     (2) the rotational speed of the pair of conveying rollers is increased at the point of time whereat the sheet has reached the post-step and the sheet has been held, and the loop (flexure) of the sheet is formed between the post-step and the pair of conveying rollers to thereby absorb the skew feeding by the loop.        
 
         [0021]     In the case of item ( 1 ) above, however, there is the problem that a mechanism for releasing the nip between the pair of conveying rollers becomes necessary and the cost of the product is greatly increased, or the vibration when the nip is released adversely affects the post-step. Also, there is left the problem that if the sheet is held at the post-step, the nip must be released in a moment and it is very difficult to take the timing therefor.  
         [0022]     Also, in the case of item ( 2 ) above, there is the problem that when the distance from the conveying roller portion to the post-step portion is short, the absorption of the skew feeding by the loop is very difficult and the sheet becomes wrinkled. Also, when the rigidity of the sheet is high like thick paper or the like, the loop is not formed and the absorption of the skew feeding by the loop is impossible.  
       SUMMARY OF THE INVENTION  
       [0023]     So, the present invention has been made in view of such a situation, and an object thereof is to provide a sheet conveying apparatus, an image forming apparatus and an image reading apparatus which can improve the correction accuracy of a sheet, and also can prevent the skew feeding of the sheet.  
         [0024]     The present invention provides a sheet conveying apparatus for conveying a sheet by sheet conveying means disposed along a sheet conveying path, having: 
        skew detecting means for detecting the skew of the sheet being conveyed with respect to a sheet conveying direction;     skew correcting means rotatable in a direction to correct the skew of the sheet in a state nipping the sheet in its skew state, on the basis of a detection signal from the skew detecting means;     position correction means for moving the skew correcting means in a direction intersecting with the sheet conveying direction; and     control means for controlling so as to move the skew correcting means in the direction intersecting with the sheet conveying direction by the position correcting means while correcting the skew of the sheet by the skew correcting means.        
 
         [0029]     Also, the present invention provides a sheet conveying apparatus for conveying a sheet by sheet conveying means disposed along a sheet conveying path, having: 
        position detecting means for detecting the position of a side edge of the sheet conveyed along the sheet conveying path in a direction orthogonal to a sheet conveying direction;     calculating means for calculating the skew of the sheet on the basis of side edge position information from the position detecting means;     skew correcting means rotatable in a direction to correct the skew of the sheet in a state nipping the sheet in its skew state on the basis of the result of calculation from the calculating means;     position correcting means for moving the skew correcting means in a direction intersecting with the sheet conveying direction; and     control means for controlling so as to move the skew correcting means in the direction intersecting with the sheet conveying direction by the position correcting means while correcting the skew of the sheet by the skew correcting means.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIG. 1  is a cross-sectional view of the printer which is an example of an image forming apparatus provided with a sheet conveying apparatus according to a first embodiment of the present invention.  
         [0036]      FIG. 2  is a side view of the skew correction roller portion of the sheet conveying apparatus.  
         [0037]      FIG. 3  is a plan view of the skew correction roller portion of the sheet conveying apparatus.  
         [0038]      FIG. 4  is a control block diagram of the printer.  
         [0039]      FIG. 5  is a flow chart illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0040]      FIGS. 6A, 6B ,  6 C and  6 D are first views illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0041]      FIGS. 7A, 7B  and  7 C are second views illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0042]      FIG. 8  is a plan view of the skew correction roller portion of a sheet conveying apparatus according to a second embodiment of the present invention.  
         [0043]      FIG. 9  is a control block diagram of a printer provided with the sheet conveying apparatus.  
         [0044]      FIG. 10  is a part of a flow chart illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0045]      FIG. 11  is another part of the flow chart illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0046]      FIGS. 12A and 12B  are first views illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0047]      FIGS. 13A and 13B  are second views illustrating the skew conveying correcting operation of the sheet conveying apparatus.  
         [0048]      FIGS. 14A, 14B  and  14 C are plan views of the skew correction roller portion of a sheet conveying apparatus according to a third embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]     Some embodiments of the present invention will hereinafter be described in detail with reference to the drawings.  
         [0050]      FIG. 1  is a cross-sectional view of a printer which is an example of an image forming apparatus provided with a sheet conveying apparatus according to a first embodiment of the present invention.  
         [0051]     In  FIG. 1 , the reference numeral  1000  designates the printer, and this printer  1000  is provided with a printer main body  1001  and a scanner  2000  disposed on the upper surface of the printer main body  1001 .  
         [0052]     The scanner  2000  for reading an original is provided with a scanning optical system light source  201 , platen glass  202 , an openable and closable original pressure plate  203 , a lens  204 , a light receiving element (photoelectric conversion)  205 , an image processing portion  206 , a memory portion  208  for storing therein an image processing signal processed by the image processing portion  206 , etc.  
         [0053]     Design is made such that when the original is to be read light is applied to the original, not shown, placed on the platen glass  202  by the scanning optical system light source  201  to thereby read the original. The image of the read original is processed by the image processing portion  206 , and thereafter is converted into an electrically encoded electrical signal  207 , which is then transmitted to a laser scanner  111   a  which is image forming means. The image information processed and encoded by the image processing portion  206  can also be once stored in the memory portion  208  and be transmitted to the laser scanner  111   a  as required, by a signal from a controller  120 .  
         [0054]     The printer main body  1001  is provided with a sheet feeding apparatus  1002  for feeding a sheet S, a sheet conveying apparatus for conveying the sheet S fed by the sheet feeding apparatus  1002  to an image forming portion  1003 , the controller  120  which is control means for controlling the printer  1000 , etc.  
         [0055]     The sheet feeding apparatus  1002  is provided with a cassette  100 , a pickup roller  101 , and a separating portion comprising a feed roller  102  and a retard roller  103 , and design is made such that the sheets S in the cassette  100  are separated and fed one by one by the action of the pickup roller  101  moved up and down rotated at predetermined timing, and the separating portion.  
         [0056]     The sheet conveying apparatus  1004  is provided with a pair of conveying rollers  105 , and a skew correction roller portion  1  having a pair of ante-skew correction rollers  130  and a pair of skew correction rollers  2 , and is designed such that the sheet S fed from the sheet feeding apparatus  1002  is passed through a sheet conveying path  108  comprised of guide plates  106  and  107  by the pair of conveying rollers  105 , and thereafter is delivered to a sheet conveying path  110  comprised of guide plates  106  and  107 , and then is directed to the skew correction roller portion  1 . In this skew correction roller portion  1 , as will be described later, the sheet S has its skew conveying and positional deviation corrected, and thereafter is conveyed to the image forming portion  1003 .  
         [0057]     The image forming portion  1003  is provided with a photosensitive drum  112 , a laser scanner  111   a , a developing device  114 , a transfer charging device  115 , a separation charging device  116 , etc, and is designed such that during image forming, a laser beam from the laser scanner  111   a  is turned back by a mirror  113  and is applied to an exposure position  112   a  on the photosensitive drum being rotated in a clockwise direction, whereby a latent image is formed on the photosensitive drum and further, the latent image thus formed on the photosensitive drum is thereafter visualized as a toner image by the developing device  114 .  
         [0058]     Thereafter, the toner image on the photosensitive drum is transferred to the sheet S by a transfer charging device  115  in a transferring portion  112   b . Further, the sheet S to which the toner image has been thus transferred is electrostatically separated from the photosensitive drum  112  by the separation charging device  116 , and thereafter is conveyed to a fixing apparatus  118  by a conveying belt  117  and is subjected to the fixing of the toner image, and thereafter is discharged by discharge rollers  119 .  
         [0059]     In  FIG. 1 , the reference numeral  131  designates an exposing start sensor for detecting the sheet S passed between the pair of skew correction rollers  2 , and when this exposing start sensor  131  detects the sheet S passed between the pair of skew correction rollers  2 , the application of a laser beam by the laser scanner  111   a  is started.  
         [0060]     The distance  11  from the exposing start sensor  131  to the transferring portion  112   b  is equal to the distance from the laser beam application position  112   a  of the photosensitive drum  112  to the transferring portion  112   b , whereby it is possible to synchronize the sheet S and the leading edge position of the image on the photosensitive drum  112 .  
         [0061]     In the present embodiment, the printer main body  1001  and the scanner  2000  are discrete from each other, but in some cases, the printer main body  1001  and the scanner  2000  are integral with each other. Also, irrespective of whether the printer main body  1001  is discrete or integral with the scanner  2000 , if the processing signal of the scanner  2000  is inputted to the laser scanner  111   a , the printer main body  1001  functions as a copying machine, and if the transmitted signal of a facsimile apparatus is inputted to the laser scanner  111   a , the printer main body  1001  functions as a facsimile apparatus. Further, if the output signal of a personal computer is inputted to the laser scanner  111   a , the printer main body functions also as a printer.  
         [0062]     If conversely, the processing signal of the image processing portion  206  of the scanner  2000  is transmitted to other facsimile apparatus, the printer main body functions as a facsimile apparatus. Also, if in the scanner  2000 , an automatic original feeding apparatus  250  as indicated by dots-and-dash line is mounted in place of the pressure plate  203 , an original can also be automatically read.  
         [0063]      FIG. 2  is a side view of the skew correction roller portion  1 , and  FIG. 3  is a plan view thereof.  
         [0064]     As shown in  FIGS. 2 and 3 , the pair of skew correction rollers  2  which are skew correcting means are comprised of two skew correction rollers  2   a  and  2   b , and these skew correction rollers  2   a  and  2   b  are rotatably journalled by bearings  11   a ,  11   b  and  12   a ,  12   b , respectively, fixed to side plates  10   a  and  10   b  vertically provided on a frame  10 .  
         [0065]     The upper skew correction roller  2   a  is pressed against the lower skew correction roller  2   b  by a pressure spring, not shown.  
         [0066]     Also, the skew correction rollers  2   a  and  2   b  have gears  15  and  16 , respectively, mounted on one side thereof, and the pair of skew correction rollers  2   a  and  2   b  are designed to be rotated in synchronism with each other by these gears  15  and  16 .  
         [0067]     Further, a drive input gear  27  is fixed to the shaft end of the lower skew correction roller  2   b , and a gear  28  fixed to the output shaft of a skew correction motor  17  is in mesh engagement with the drive input gear  27 , whereby when the skew correction motor  17  is driven, the pair of skew correction rollers  2  are rotated.  
         [0068]     Further, on the skew correction motor side which is one end side of the pair of skew correction rollers  2 , there is provided a connecting member  18  for connecting the skew correction rollers  2   a  and  2   b  together and regulating the axial movement of the skew correction rollers  2   a  and  2   b . This connecting member  18  rotatably journals the respective skew correction rollers  2   a  and  2   b , and has a rack gear portion  18   b  provided on the bottom surface thereof, and a pinion gear  19  fixed to the output shaft of a lateral moving motor  20  is in mesh engagement with the rack gear portion  18   b.    
         [0069]     Thus, when for example, the pinion gear  19  is rotated in a clockwise direction, the connecting member  18  is moved rightwardly as viewed in  FIG. 2 , and therewith, the pair of skew correction rollers  2  are moved in a thrust direction, i.e., a direction intersecting with a conveying direction. That is, design is made such that by the lateral moving motor  20  which is position correcting means being driven, the pair of skew correction rollers  2  can be moved in the thrust direction (the axial direction of the pair of skew correction rollers).  
         [0070]     In  FIG. 2 , the reference numeral  21  denotes a first home position sensor, and design is made such that a first home position of the pair of skew correction rollers  2  in the thrust direction can be detected by this first home position sensor  21 .  
         [0071]     On the other hand, the frame  10  is mounted for pivotal movement about a pivot shaft  14  provided on a stay  13  fixed between the front side plate  1001   a  and rear side plate  1002   b  of the printer main body  1001 . This pivot shaft  14  becomes the center of pivotal movement during the correction of the inclination of the pair of skew correction rollers  2  which will be described later, and also becomes the reference position of the pair of skew correction rollers  2  on the axis thereof.  
         [0072]     Also, a gear  22  is fixed to the front side plate of the frame  10 , and the gear  22  is in mesh engagement with a rack gear  23  fixed to the output shaft of a rotating motor  24  mounted on the stay  13 .  
         [0073]     When this rotating motor  24  is rotated and for example in  FIG. 3 , the rack gear  23  is rotated in the clockwise direction, all of the frame  10  and members mounted on the frame  10  including the pair of skew correction rollers  2 , the skew correction motor  17 , etc. provided on the frame  10  may be pivotally moved (rotated) in a counter-clockwise direction about the pivot shaft  14 .  
         [0074]     That is, design is made such that by the rotation of the rotating motor  24 , the pair of skew correction rollers  2  can be displaced (rotated) so as to be inclined with respect to the thrust direction. In  FIG. 3 , the reference numeral  25  designates a second home position sensor provided on the stay  13 , and design is made such that a second position in a rotating (pivotal movement) direction in which the nip line of the pair of skew correction rollers  2  becomes parallel to the rotation center axis  112   c  of the photosensitive drum  112  is detected by this second home position sensor  25 .  
         [0075]     In  FIG. 3 , the reference characters  3   a  and  3   b  denote skew conveying detection sensors which are skew detecting means for detecting the skew of the leading edge of the sheet S, and these skew conveying detection sensors  3   a  and  3   b  are disposed downstream of the pair of skew correction rollers  2  with respect to the conveying direction and at a predetermined interval L in a direction orthogonal to the sheet conveying direction. The center line  3   c  linking the skew conveying detection sensors  3   a  and  3   b  together is disposed so as to be parallel to the axis  112   c  of the photosensitive drum provided on the downstream side with respect to the conveying direction.  
         [0076]      FIG. 4  is a control block diagram of the printer  1000  provided with such a sheet conveying apparatus  1004 , etc., and as shown in  FIG. 4 , the aforedescribed photosensitive drum  112 , conveying belt  117 , fixing device  118  and sheet discharging rollers  119  are directly connected to a main motor M, and are rotatable in synchronism with the main motor M. Also, the aforedescribed pickup roller  101 , feed roller  102 , retard roller  103 , conveying rollers  105  and the pair of ante-skew correction rollers  130  are designed to receive a driving force from the main motor M and be drive-controlled by clutches  102   b ,  105   b  and  130   b  ON/OFF controlled by a signal from a controller  120  through respective driving circuits  102   a ,  105   a  and  130   a.    
         [0077]     Also, design is made such that sheet size detection signals from sheet size detection sensors  100   b  and  100   b  installed in the sheet feeding cassette  100 , detection signals from the skew conveying detection sensors  3   a  and  3   b , or signals from the first home position sensor  21  and the second home position sensor  25  are inputted to the controller  120  which is control means. In the controller  120 , the skew amount of the sheet S is calculated by a calculating circuit  160  on the basis, for example, of the detection signals from the skew conveying detecting sensors  3   a  and  3   b.    
         [0078]     Further, the controller  120  is adapted to output a necessary control signal based on the result of detection to driving circuits  19   a ,  20   a ,  24   a  and  111   a , and drive the skew correction motor  17 , the lateral moving motor  20 , the rotating motor  24  and the laser scanner  111   a  by a predetermined amount or for a predetermined amount through these driving circuits  17   a ,  20   a ,  24   a  and  111   a.    
         [0079]     The skew conveying correcting operation of the printer  1000  (sheet conveying apparatus  1004 ) of such a construction will now be described with reference the flow chart of  FIG. 5  and  FIGS. 6A  to  6 C and  7 .  
         [0080]     First, when the first button, not shown, of the printer  1000  is depressed, the lateral moving motor  20  and the rotating motor  24  are driven and the operation of initializing the position of the pair of skew correction rollers  2  in the rotating direction and the thrust direction thereof is performed by the first home position sensor  21  and the second home position sensor  25  (step  1 ).  
         [0081]     After this initializing operation, the skew correction motor  17  is driven (ON) and the pair of skew correction rollers  2  start to be rotated (step  2 ). Here, when a sheet S skew-conveyed at an angle θ with respect to the sheet conveying direction P as shown in  FIG. 6A  is conveyed to the pair of skew correction rollers  2  which have thus started to be rotated, this sheet S will soon come into and be nipped by the nip portion of the pair of skew correction rollers  2 .  
         [0082]     Further, thereafter, the sheet S nipped between the pair of skew correction rollers  2  is conveyed forward along the sheet conveying direction P while remaining skew, whereby it is detected by the skew conveying detection sensors  3   a  and  3   b  disposed downstream of the pair of skew correction rollers  2  (step  3 ).  
         [0083]     Here, detection signals from these skew conveying detection sensors  3   a  and  3   b  are inputted to the controller  120 , whereafter the point of time at which the leading edge of the sheet passes and the skew amount of the sheet S nipped between the pair of skew correction rollers  2  are calculated by the calculating circuit  160  (step  4 ).  
         [0084]     Next, the controller  120  judges the presence or absence of the skew conveying of the sheet S from the result of this calculation (step  5 ), and if the skew conveying of the sheet S is absent (N at the step  5 ), the controller does not perform a correcting operation, but if the skew conveying of the sheet S is present (Y at the step  5 ), the controller calculates a skew conveying correction amount therefor, i.e., the drive amount of the rotating motor  24  (step  6 ).  
         [0085]     Here, when for example, the difference between the detection timing of the skew conveying detection sensor  3   a  and the detection timing of the skew conveying detection sensor  3   b  is Δt as shown in  FIG. 6C , assuming that the conveying speed of the sheet S is V 1  and the pitch (inter-sensor distance) of the skew conveying detection sensor  3   a  and  3   b  is L, the skew amount of the sheet S can be calculated by the following expression 1 as is apparent from  FIG. 6D . 
 
θ=tan −1  (Δt×V 1 /L)  (expression 1) 
 
         [0086]     Then, the rotating motor  24  is driven (ON) for a predetermined time in conformity with the skew amount θ of the sheet S calculated in the above expression 1 (step  7 ). By the rotating motor  24  being thus driven for the predetermined time in conformity with the skew amount of the sheet S, the pair of skew correction rollers  2  are pivotally moved (turned) by θ in the direction of arrow F, i.e., a direction intersecting with the conveying direction, about the pivot shaft  14  until as shown in  FIG. 7A , the leading edge of the sheet S nipped between the pair of skew correction rollers  2  becomes parallel to the axial direction of the transferring portion  112   b  (the axial direction of the photosensitive drum).  
         [0087]     When the pair of skew correction rollers  2  are thus pivotally moved, the conveying direction of the sheet S conveyed by the pair of skew correction rollers  2  is also inclined by an angle θ as compared with the original direction. As the result, the entire sheet is fed in an oblique direction indicated by dot-and-dash line at the angle of inclination (hereinafter referred to as “skew feeding”).  
         [0088]     So, in the present embodiment, as already described, the pair of skew correction rollers  2  are rotatively moved by θ, whereafter the rotating motor  24  is rendered OFF (step  8 ), and thereafter the lateral moving motor  20  is driven so as to move the pair of skew correction rollers  2  in the direction of arrow G indicated in  FIG. 7B .  
         [0089]     In this case, the sheet S is skew-fed by the pair of skew correction rollers  2  in a state skew by θ with respect to the transferring portion  112   b  and at the conveying speed V 1  and therefore, in order that this skew-fed sheet S may be conveyed in the original sheet conveying direction, the movement speed V 2  of the pair of skew correction rollers  2  in the thrust direction by the lateral moving motor  20  is, as shown in  FIG. 7C , 
 
V 2 =V 1 ×tan θ  (expression 2) 
 
         [0090]     The speed of the lateral moving motor  20  for skew feeding correction is determined by this expression 2 (step  9 ), whereafter the lateral moving motor  20  is driven (ON) (step  10 ). Thereby, the skew feeding of the sheet S can be corrected and the sheet S can be conveyed in a direction coincident with the original sheet conveying direction.  
         [0091]     Thereby, the skew conveying correction and skew feeding correction of the sheet S can be effected. If thereafter, the trailing edge of the sheet S has passed the pair of skew correction rollers  2  (Y at step  11 ), the lateral moving motor is stopped (OFF) (step  12 ).  
         [0092]     By the correcting operation as described above being performed, the sheet S is fed out in an accurate conveying posture without being skew with respect to the transferring portion  112   b , whereafter the toner image is transferred thereto. Thereafter, the operation of initializing the pair of skew correction rollers  2  is performed (step  13 ), and the pair of skew correction rollers  2  become ready for the correction of the skew conveying and skew feeding of the next sheet S. This initializing operation, as previously described, is performed on the basis of the signals from the first home position sensor  21  and the second home position sensor  25 .  
         [0093]     As described above, the skew of the sheet S is detected by the skew conveying detection sensors  3   a  and  3   b , and in conformity with the skew amount, the pair of skew correction rollers  2  are pivotally moved, whereby and whereafter the pair of skew correction rollers  2  are moved in the thrust direction by the lateral moving motor  20  while the sheet S is conveyed, whereby it is possible to effect very smooth and accurate skew conveying correction and skew feeding correction without once stopping the sheet S.  
         [0094]     That is, when as in the present embodiment, the pair of skew correction rollers  2  are pivotally moved (moved) in a direction to correct the skew of the sheet S, the lateral moving motor  20  is controlled so as to move the pair of skew correction rollers  2  at such a speed that the direction of the sheet S conveyed by the pair of skew correction rollers  2  coincides with the sheet conveying direction, whereby more accurate skew conveying correction and skew feeding correction can be accomplished.  
         [0095]     A second embodiment of the present invention will now be described.  
         [0096]      FIG. 8  is a plan view of the skew correction roller portion of a sheet conveying apparatus according to the second embodiment. In  FIG. 8 , the same reference characters as those in  FIG. 6  designate the same or corresponding portions.  
         [0097]     In  FIG. 8 , the reference numeral  4  designates a sheet side edge position detection sensor which is position detecting means comprised of a CCD sensor or the like for detecting the position of the side edge of the sheet S in the thrust direction, and this sheet side edge position detection sensor  4  is disposed between the pair of skew correction rollers  2  and skew conveying detection sensors  3   a ,  3   b  for detecting the skew of the leading edge of the sheet S.  
         [0098]      FIG. 9  is a control block diagram of a printer  1000  provided with such a sheet conveying apparatus  1004 , etc., and as shown in  FIG. 9 , the sheet side edge position detection sensor  4  is connected to a controller  120 .  
         [0099]     The skew amount of the sheet S is calculated by a calculating circuit  160  on the basis of detection signals from the skew conveying detection sensors  3   a  and  3   b  inputted to the controller  120 , and the positional deviation amount of the sheet S in the thrust direction (hereinafter referred to as the lateral reference deviation amount) is calculated on the basis of the detection signal of the sheet side edge position detection sensor  4 .  
         [0100]     The skew conveying correcting operation of the printer  1000  (sheet conveying apparatus  1004 ) of such a construction will now be described with reference to the flow charts of  FIGS. 10 and 11 , and  FIGS. 12A ,  12 B and  13 .  
         [0101]     When the start button, not shown, of the printer  1000  is first depressed, the lateral moving motor  20  and the rotating motor  24  are driven, and the operation of initializing the pair of skew correction rollers  2  is performed by the first home position sensor  21  and the second home position sensor  25  (step  1 ).  
         [0102]     After this initializing operation, the skew correction motor  17  is driven (ON) and the pair of skew correction rollers  2  start to be rotated (step  2 ). Thereafter, the sheet S skew by θ with respect to the sheet conveying direction P is fed to the pair of skew correction rollers  2  which have started to be rotated (see  FIG. 8 ), and this sheet S will soon come into and nipped by the nip portion of the pair of skew correction rollers  2  while remaining skew.  
         [0103]     Thereafter, the sheet S nipped between the pair of skew correction rollers  2  is fed forward along the sheet conveying direction P, as shown in  FIG. 12A , whereby the point of time at which the leading edge of the sheet passes is detected by the skew conveying detection sensors  3   a  and  3   b  disposed downstream of the pair of skew correction rollers  2  and the lateral reference deviation of the sheet S is detected by the sheet side edge position detection sensor  4  (step  3 ).  
         [0104]     Detection signals from the skew conveying detection sensors  3   a ,  3   b  and the sheet side edge position detection sensor  4  are inputted to the controller  120 , whereafter the skew amount of the sheet S nipped between the pair of skew correction rollers  2  and the lateral reference deviation amount of the sheet S are calculated by the calculating circuit  160  (step  4 ).  
         [0105]     Next, the controller  120  first judges the presence or absence of the skew conveying of the sheet S from the result of this calculation (step  5 ), and if the skew conveying of the sheet S is absent (when θ=0)(N at the step  5 ), and next judges whether lateral reference deviation is present (step  17 ). If the lateral reference deviation is present (Y at step  17 ), the lateral moving motor  20  is driven (ON)(step  18 ). When thereafter, it is detected by the detection signal from the sheet side edge position detection sensor  4  that the lateral position has been corrected (Y at step  19 ), the lateral moving motor  20  is stopped (OFF)(step  20 ).  
         [0106]     On the other hand, if the skew conveying of the sheet S is present (Y at step  5 ), a skew conveying correction amount therefor, i.e., the drive amount of the rotating motor  24 , is calculated by the already mentioned expression 1 (step  6 ).  
         [0107]     Thereafter, in conformity with the calculated skew amount θ of the sheet S, the rotating motor  24  is driven (ON) for a predetermined time (step  7 ). By the rotating motor  24  being thus driven for the predetermined time in conformity with the skew amount of the sheet S, the pair of skew correction rollers  2  are pivotally moved by θ in the direction of arrow F about the pivot shaft  14  until as shown in  FIG. 12B , the leading edge of the sheet S nipped between the pair of skew correction rollers  2  becomes parallel to the axial direction of the transferring portion  112  (the axial direction of the photosensitive drum).  
         [0108]     Next, after the rotating motor  24  has been driven for the predetermined time, it is stopped (OFF)(step  8 ), whereafter whether lateral reference deviation is present is judged (step  9 ). If the lateral reference deviation is absent (N at step  9 ), the correcting operation is not particularly performed, but if the lateral reference deviation is present (Y at step  9 ), the lateral moving motor  20  is driven (step  10 ).  
         [0109]     By the lateral moving motor  20  being thus driven, as shown in  FIG. 13A , the position of the side edge (end) of the sheet is moved to a predetermined position and the lateral position is corrected, and when this is detected by the detection signal from the sheet side edge position detection sensor  4  (Y at step  11 ), the lateral moving motor  20  is stopped (OFF).  
         [0110]     At this time, the leading edge of the sheet S nipped between the pair of skew correction rollers  2  is parallel to the axial direction of the transferring portion  112   b  (the axial direction of the photosensitive drum in the transferring portion), and the lateral position of the sheet S is also at a proper position, but as already described, when the pair of skew correction rollers  2  are pivotally moved, the conveying direction of the sheet S conveyed by the pair of skew correction rollers  2  is also inclined by the same angle θ as compared with the original direction, as shown in  FIG. 12B  already described, or  FIG. 13A . As the result, the entire sheet is skew-fed at the angle θ of inclination in a direction indicated by dot-and-dash line.  
         [0111]     So, next, after the pair of skew correction rollers  2  are thus pivotally moved by θ, the speed of the lateral moving motor  20  for skew feeding correction is determined by the already mentioned expression 2 (step  12 ), whereafter the lateral moving motor  20  is driven (ON)(step  13 ), to thereby move the pair of skew correction rollers  2  in the direction of arrow G as shown in  FIG. 13B . By the pair of skew correction rollers  2  being thus moved in the direction of arrow G, the skew feeding of the sheet can be corrected to thereby convey the sheet S in a direction coincident with the original sheet conveying direction. Thereby, the skew conveying correction and skew feeding correction of the sheet S can be accomplished.  
         [0112]     Next, when the trailing edge of the sheet S passes the pair of skew correction rollers  2  (Y at step  14 ), the lateral moving motor  20  is stopped (OFF)(step  15 ).  
         [0113]     By the correcting operation as described above being performed, the sheet S is fed out in an accurate conveying posture without being skew with respect to the transferring portion  112   b , whereafter a toner image is transferred thereto. Thereafter, the operation of initializing the pair of skew correction rollers  2  is performed (step  16 ), and the pair of skew correction rollers  2  become ready for the correction of the skew conveying and skew feeding of the next sheet S. This initializing operation is performed on the basis of signals from the first home position sensor  21  and the second home position sensor  25 , as previously described.  
         [0114]     As described above, the skew of the sheet S is detected by the skew conveying detection sensors  3   a  and  3   b , and in conformity with the skew amount, the pair of skew correction rollers  2  are inclined to thereby effect the skew feeding correction of the sheet S, whereafter the lateral reference deviation of the sheet S is corrected by the sheet side edge position detection sensor  4  and thereafter, the lateral moving motor  20  is controlled on the basis of information obtained by the skew conveying detection sensors  3 , whereby skew feeding correction can also be accomplished.  
         [0115]     By adopting such a construction, not only it is possible to effect very accurate skew conveying correction and skew feeding correction without once stopping the sheet S, but also the correction of the lateral reference deviation of the sheet becomes possible.  
         [0116]     Now, in the present embodiment, as in the first embodiment, the lateral moving motor  20  is rotated during sheet conveyance on the basis of the detection signals from the skew conveying detection sensors  3   a  and  3   b  to thereby effect skew feeding correction, but skew feeding correction can be effected even if design is made such that without the use of the skew conveying detection sensors  3   a  and  3   b , for example, the sheet side edge position detection sensor  4  is normally monitored, and the lateral moving motor  20  is rotated when the positional deviation or a change in the positional deviation amount of the sheet side edge is detected by the sheet side edge position detection means  4 .  
         [0117]      FIGS. 14A, 14B  and  14 C are plan views of the skew correction roller portion of a sheet conveying apparatus according to such a third embodiment of the present invention. In these figures, the same reference characters as those in  FIG. 8  designate the same or corresponding portions.  
         [0118]     In the present embodiment, the controller  120  is designed to find a change in the side edge position of the sheet S by a position detection signal from the sheet side edge position detection sensor  4 , and a position detection signal inputted after a predetermined time t1 has elapsed after this position detection signal has been inputted, and detect the skew of the sheet, i.e., the skew feeding of the sheet S, from this change in the sheet side edge position, and perform a skew feeding correcting operation on the basis of this detected information.  
         [0119]     Description will now be made of the skew feeding correcting operation in the present embodiment.  
         [0120]     When as shown in  FIG. 14A , a sheet S skew by θ with respect to the sheet conveying direction is fed, and the sheet S comes into and is nipped by the nip portion of the pair of skew correction rollers  2 , this sheet is thereafter fed forward along the sheet conveying direction P. The point of time at which the leading edge of the sheet passes the nip portion is detected by the sheet side edge position detection sensor  4  disposed downstream of the pair of skew correction rollers  2  and the first positional deviation in the thrust direction is detected by the sheet side edge position detection sensor  4 .  
         [0121]     Then, as shown in  FIG. 14B , a predetermined time after, the value of the sheet side edge position detection sensor  4  is again read, and when the difference between these two (plural) position detection signals from the sheet side edge position detection sensor  4  is ΔL, assuming that the sheet conveying speed is V 1 , the skew amount θ of the sheet can be calculated by the following expression 3 as is apparent from  FIG. 14C . 
 
θ=tan −1 (ΔL/(V 1 1×t1))  (expression 3) 
 
         [0122]     Not only the positional deviation amount of the sheet S, but also the skew amount θ of the sheet can be thus detected by the sheet side edge detection sensor  4  and therefore, if thereafter, control similar to that in the already described second embodiment is effected, it becomes possible to effect skew conveying correction, lateral position correction and skew feeding correction by the sheet side edge position detection sensor  4  alone.  
         [0123]     That is, by adopting a construction like that of the present embodiment, it is possible to detect both of the skew amount of the sheet S and the thrust position deviation of the sheet S by the sheet side edge position detection sensor  4  alone, whereby it is possible to effect skew conveying correction, lateral position correction and skew feeding correction accurately by a very simple construction.  
         [0124]     Further, in the hitherto described first and second embodiments, it never happens that as in the loop registration method, the sheet is once stopped at the skew correction roller portion to thereby form a loop and therefore, not only it is possible to minimize the inter-sheet spacing and an apparatus of high productivity can be provided, but also there is no production of a loop sound and the problem of buckling during the formation of a loop of thin paper can also be solved.  
         [0125]     Also, of course, the loop space becomes unnecessary and the downsizing of the apparatus is possible. Further, even if due to the deformation of the leading edge portion of the sheet S such as the curl or breakage of the leading edge portion, the sheet S comes to be nipped between the pair of skew correction rollers  2  in a posture differing from that before it is nipped, the skew conveying and skew feeding of the sheet S can be accurately corrected without being affected by it.  
         [0126]     Now, while in the description hitherto made, a case where as already described, the sheet conveying means is used in an image forming apparatus so as to be capable of accurately feeding out the sheet S to the image forming portion  1003  without skew or positional deviation has been described, the present invention is not restricted thereto, but can also be applied, for example, to an image reading apparatus so as to be capable of accurately feeding out the sheet S to an image reading portion for reading a sheet (original) which is a post-step, without skew or positional deviation.